Design and synthesis of pyrene-based probes and their fluorescent detection of Sb(III)

A series of pyrene-based fluorescent (FL) probes for Sb(III) were designed and synthesized. All of them exhibited luminescence by pyrene excimers in the mixture of DMSO and water and showed enhanced emission with the addition of Sb(III). By comparing their FL response to Sb(III), the effects of intramolecular hydrogen bond, inductive effect, and steric effect were investigated. Meanwhile, the FL enhancement factor of the best performing probe reached 10.28 and the detection limit was calculated to be 0.0535 mg/L, indicating that it might be used as a potential candidate for the treatment of Sb(III) in printing and dyeing wastewater.

Synergistic synthesis of gold nanoflowers as upconversion near-infrared nanoprobe energy acceptor and recognition unit for improved hydrogen sulfide sensing

A highly sensitive and selective upconversion near-infrared (NIR) fluorescence and colorimetric dual readout hydrogen sulfide (H2S) nanoprobe was constructed based on the excellent NIR fluorescence emission performance of upconversion nanomaterials (UCNPs), the specific recognition effect of synergistically synthesized gold nanoflowers (trypsin-stabled AuNFs (Try-AuNFs)) and the effective NIR fluorescence quenching capability. In this assay, the sensing strategy included three processes. First of all, the synthesized UCNPs can emit 803 nm NIR fluorescence when they were excited by 980 nm excitation light. Secondly, as a result of the principle of fluorescence resonance energy transfer (FRET), Try-AuNFs can effectively quench the NIR fluorescence of UCNPs at 803 nm, which can effectively improve the signal-to-background ratio of nanoprobes, thereby improving the sensitivity of the probes. Thirdly, in the presence of H2S, the Try protective layer on the surface of Try-AuNFs was specifically penetrated, which will subsequently cleave Try-AuNFs via the strong S-Au bond. As such, the NIR fluorescence of UCNPs will be restored, achieving high selectivity and sensitivity detection of H2S. Under optimized conditions, the linear response range of H2S was 0.1-300 μM, and the detection limit was 53 nM. It is worth noting that the Try on the surface of Try-AuNFs via the synergistic effect can increase the steric hindrance of the probe, and this can effectively prevent the interaction between the probe with biothiols (cysteine (Cys), homocysteine (Hcy)) and other natural amino acids (non-thiol-containing) with resultant in the high selectivity regarding the detection of H2S in human serum, which is unlikely to be achieved by AuNFs synthesized by the gold seed method (Se-AuNFs). This work not only provided a new type of UCNPs fluorescence quencher and recognition unit, but also exemplified that the use of the physical properties (steric hindrance) of protein ligands on the surface of nanoflowers can improve the specificity of the probe. This will provide new ideas for the design of other nanoprobes.

Integration of Functional Groups to Enhance the Solubility and Stability of Viologen in Aqueous Organic Redox Flow Batteries

The chemical stability and energy density of redox couples are crucial factors in enhancing the durability and cost competitiveness of aqueous flow batteries. This study proposed integrating functional groups to viologen anolyte to increase its solubility and, consequently, energy density and stability for prolonged performance. Specifically, sulfonate and ester groups were selectively incorporated at the nitrogen sites of viologen to enhance solubility, leveraging their asymmetry and double hydrophilicity. Furthermore, an alpha-methyl group was introduced between the bipyridine and ester groups to enhance the chemical stability by preventing stacking and dimerization that can lead to irreversible degradation. The modified viologen demonstrated a remarkable solubility of 3.0 M in deionized water, corresponding to a volumetric capacity of 80.404 Ah L-1. Additionally, the designed viologen exhibits outstanding retention of 92.4% after 200 cycles with a minimal capacity fading rate of 0.055% per cycle in a 0.1 M flow cell test.

Branch-Chain-Rich Diisopropyl Ether with Steric Hindrance Facilitates Stable Cycling of Lithium Batteries at - 20 °C

Li metal batteries (LMBs) offer significant potential as high energy density alternatives; nevertheless, their performance is hindered by the slow desolvation process of electrolytes, particularly at low temperatures (LT), leading to low coulombic efficiency and limited cycle stability. Thus, it is essential to optimize the solvation structure thereby achieving a rapid desolvation process in LMBs at LT. Herein, we introduce branch chain-rich diisopropyl ether (DIPE) into a 2.5 M Li bis(fluorosulfonyl)imide dipropyl ether (DPE) electrolyte as a co-solvent for high-performance LMBs at - 20 °C. The incorporation of DIPE not only enhances the disorder within the electrolyte, but also induces a steric hindrance effect form DIPE's branch chain, excluding other solvent molecules from Li+ solvation sheath. Both of these factors contribute to the weak interactions between Li+ and solvent molecules, effectively reducing the desolvation energy of the electrolyte. Consequently, Li (50 μm)||LFP (mass loading ~ 10 mg cm-2) cells in DPE/DIPE based electrolyte demonstrate stable performance over 650 cycles at - 20 °C, delivering 87.2 mAh g-1, and over 255 cycles at 25 °C with 124.8 mAh g-1. DIPE broadens the electrolyte design from molecular structure considerations, offering a promising avenue for highly stable LMBs at LT.

Mechanical stress combines with planar polarised patterning during metaphase to orient embryonic epithelial cell divisions

The planar orientation of cell division (OCD) is important for epithelial morphogenesis and homeostasis. Here, we ask how mechanics and antero-posterior (AP) patterning combine to influence the first divisions after gastrulation in the Drosophila embryonic epithelium. We analyse hundreds of cell divisions and show that stress anisotropy, notably from compressive forces, can reorient division directly in metaphase. Stress anisotropy influences the OCD by imposing metaphase cell elongation, despite mitotic rounding, and overrides interphase cell elongation. In strongly elongated cells, the mitotic spindle adapts its length to, and hence its orientation is constrained by, the cell long axis. Alongside mechanical cues, we find a tissue-wide bias of the mitotic spindle orientation towards AP-patterned planar polarised Myosin-II. This spindle bias is lost in an AP-patterning mutant. Thus, a patterning-induced mitotic spindle orientation bias overrides mechanical cues in mildly elongated cells, whereas in strongly elongated cells the spindle is constrained close to the high stress axis.

Heteroaggregation kinetics of nanoplastics and soot nanoparticles in aquatic environments

Heteroaggregation between polystyrene nanoplastics (PSNPs) and soot nanoparticles (STNPs) in aquatic environments may affect their fate and transport. This study investigated the effects of particle concentration ratio, electrolytes, pH, and humic acid on their heteroaggregation kinetics. The critical coagulation concentration (CCC) ranked CCCPSNPs > CCCPSNPs-STNPs > CCCSTNPs, indicating that heteroaggregation rates fell between homoaggregation rates. In NaCl solution, as the PSNPs/STNPs ratio decreased from 9/1 to 3/7, heteroaggregation rate decreased and CCCPSNPs-STNPs increased from 200 to 220 mM due to enhanced electrostatic repulsion. Outlier was observed at PSNPs/STNPs= 1/9, where CCCPSNPs-STNPs= 170 mM and homoaggregation of STNPs dominated. However, in CaCl2 solution where calcium bridged with STNPs, heteroaggregation rate increased and CCCPSNPs-STNPs decreased from 26 to 5 mM as the PSNPs/STNPs ratio decreasing from 9/1 to 1/9. In composite water samples, heteroaggregation occurred only at estuarine and marine salinities. Acidic condition promoted heteroaggregation via charge screening. Humic acid retarded or promoted heteroaggregation in NaCl or CaCl2 solutions by steric hindrance or calcium bridging, respectively. Other than van der Waals attraction and electrostatic repulsion, heteroaggregation was affected by steric hindrance, hydrophobic interactions, π - π interactions, and calcium bridging. The results highlight the role of black carbon on colloidal stability of PSNPs in aquatic environments.

Inhibition of RNA Phosphodiester Backbone Cleavage in the Presence of Organic Cations of Different Sizes

Living cells contain various types of organic cations that may interact with nucleic acids. In order to understand the nucleic acid-binding properties of organic cations of different sizes, we investigated the ability of simple organic cations to inhibit the RNA phosphodiester bond cleavage promoted by Mg2+, Pb2+, and RNA-cleaving serum proteins. Kinetic analysis using chimeric DNA-RNA oligonucleotides showed that the cleavage at ribonucleotide sites was inhibited in the presence of monovalent cations comprising alkyl chains or benzene rings. The comparison of the cleavage rates in the presence of quaternary ammonium and phosphonium ions indicated that the steric hindrance effect of organic cations on their binding to the RNA backbone is significant when the cation size is larger than the phosphate-phosphate distance of a single-stranded nucleic acid. The cleavage inhibition was also observed for ribonucleotides located in long loops but not in short loops of oligonucleotide structures, indicating less efficient binding of bulky cations to structurally constrained regions. These results reveal the unique nucleic acid-binding properties of bulky cations distinct from those of metal ions.

Tunable schiff-based networks with different bonding sites for enhanced photocatalytic activity under visible-light irradiation: The effects of steric hindrance

Organic polymers hold great potential in photocatalysis considering their low cost, structural tailorability, and well-controlled degree of conjugation for efficient electron transfer. Among the polymers, Schiff base networks (SNWs) with high nitrogen content have been noticed. Herein, a series of SNWs is synthesized based on the melamine units and dialdehydes with different bonding sites. The chemical and structural variation caused by steric hindrance as well as the related photoelectric properties of the SNW samples are investigated, along with the application exploration on photocatalytic degradation and energy production. The results demonstrate that only SNW-o based on o-phthalaldehyde responds to visible light, which extends to over 550 nm. SNW-o shows the highest tetracycline degradation rate of 0.02516 min-1, under 60-min visible light irradiation. Moreover, the H2O2 production of SNW-o is 2.14 times higher than that of g-C3N4. The enhanced photocatalytic activity could be ascribed to the enlarged visible light adsorption and intramolecular electron transfer. This study indicates the possibility to regulate the optical and electrical properties of organic photocatalysts on a molecular level, providing an effective strategy for rational supramolecular engineering to the applications of organic materials in photocatalysis.

Discovery of ASP6918, a KRAS G12C inhibitor: Synthesis and structure-activity relationships of 1-{2,7-diazaspiro[3.5]non-2-yl}prop-2-en-1-one derivatives as covalent inhibitors with good potency and oral activity for the treatment of solid tumors

Although KRAS protein had been classified as an undruggable target, inhibitors of KRAS G12C mutant protein were recently reported to show clinical efficacy in solid tumors. In our previous report, we identified 1-{2,7-diazaspiro[3.5]non-2-yl}prop-2-en-1-one derivative (1) as a KRAS G12C inhibitor that covalently binds to Cys12 of KRAS G12C protein. Compound 1 exhibited potent cellular pERK inhibition and cell growth inhibition against a KRAS G12C mutation-positive cell line and showed an antitumor effect on subcutaneous administration in an NCI-H1373 (KRAS G12C mutation-positive cell line) xenograft mouse model in a dose-dependent manner. In this report, we further optimized the substituents on the quinazoline scaffold based on the structure-based drug design from the co-crystal structure analysis of compound 1 and KRAS G12C to enhance in vitro activity. As a result, ASP6918 was found to exhibit extremely potent in vitro activity and induce dose-dependent tumor regression in an NCI-H1373 xenograft mouse model after oral administration.

Toward a mechanistic understanding of Rhenium(VII) adsorption behavior onto aminated polymeric adsorbents: Batch experiments, spectroscopic analyses, and theoretical computations

Rhenium, a rare and critical metal, existing in the industrial wastewater has been aroused extensive interests recently, due to its environmental and resource issues. Chitosan, an easily available, low-cost and eco-friendly biopolymer, was prepared and modified by grafting primary, secondary, tertiary and quaternary amino groups, respectively. Adsorption behaviors and interactions between ReO4- and these four types of aminated adsorbents were investigated through batch experiments, spectroscopic analysis, and theoretical computations. Chitosan modified with secondary amines showed an extremely high uptake of ReO4- with 742.0 mg g-1, which was higher than any reported adsorbents so far. Furthermore, a relatively high adsorption selectivity for Re(VII), as well as the stable and facile regeneration of these aminated adsorbents revealed a promising approach for Re(VII) recovery in full-scale applications. The electrostatic attraction was illustrated to be the main adsorption mechanism by Fourier Transform Infrared Spectroscopy and X-ray Photoelectron Spectroscopy analyses. Significantly, the sub-steps of the adsorption process, encompassing the transformation of binding sites and the subsequent binding between these sites and the adsorbate, have been thoroughly investigated through the density functional theory (DFT) calculation method. This approach was firstly proposed to clearly demonstrate the differences in Re(VII) adsorption behavior onto four types of aminated adsorbents, resulting the importance of not only strong binding energy but also an appropriate binding spatial environmental for effective Re(VII) adsorption.

Combined effects of particle size and humic acid corona on the aggregation kinetics of nanoplastics in aquatic environments

Nanoplastics (NPs) contaminant in aquatic environments is one of the pressing environmental concerns globally. However, the combined effects of particle size and humic acid (HA) corona on the aggregation behavior of NPs have not been revealed yet. Therefore, this study explored the influence of HA corona on the aggregation kinetics of NPs with three different particle sizes under various water quality conditions. Results showed that in the absence of HA corona, the aggregation kinetic processes of all the three NPs were affected by the repulsive force originating from the hydration layer. Moreover, the smaller the particle size, the more obvious the effect. HA corona played a steric hindrance role for all the three NPs based on the extended-Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory in monovalent solutions, resulting in the impediment of aggregation. Whereas, in divalent solutions, the HA corona of 100 and 200 nm NPs experienced three stages: deformation, electrostatic-patch and bridging; while that of 40 nm NPs underwent electrostatic-patch and steric hindrance. The larger number of HA molecules distributed on 100 and 200 NPs surfaces led to more interactions with Ca2+ and NPs, which was the key factor for HA corona to play more diverse roles. According to the two dimension correlation spectroscopy analysis (2D-COS), the structural change in the interaction between HA and NPs was that the aromatic ring of NPs took precedence, followed by the carbonyl groups of HA. This study provided new insights into the combined effects of HA corona and particle size on the aggregation kinetics of NPs and established a theoretical foundation for predicting and assessing the transport and fate of NPs.

Colloidal stability and aggregation behavior of CdS colloids in aquatic systems: Effects of macromolecules, cations, and pH

Redox-dynamic environments such as river floodplains and paddy fields have been demonstrated to be important sources of CdS colloids. To date, the aggregation kinetics of CdS colloids had not yet been studied, and the structure and properties of macromolecules on the interaction between different macromolecules and CdS colloids, as well as the aggregation behavior of CdS colloids are unclear. This study investigated the colloidal stability of CdS colloids in model aqueous systems with various solution chemistry and representative of macromolecules. The results showed that increased electrolyte concentration destabilized CdS colloids by charge screening, with the cationic effect following Ca²⁺ > Mg²⁺ > K⁺ > Na⁺; Higher solution pH stabilized CdS colloids by raising the critical coagulation concentration from 33 to 56 mM NaCl. Electron microscopy and spectroscopy verified the strong interaction between macromolecules and CdS colloids, and macromolecule adsorbed on the surface of CdS to form a protective layer called "NOM corona". The interaction between macromolecules and CdS induced distinct aggregation behaviors in NaCl and CaCl₂ solutions. The steric repulsion generated by "NOM corona" significantly stabilized CdS colloids in NaCl solution, and the stabilizing order was consistent with the adsorbing capacity of macromolecules on CdS colloids, namely Bovine serum albumin (BSA) > sodium alginate (SA) > calf thymus DNA (DNA) > Suwannee River humic acid (HA). BSA and DNA also inhibited CdS colloids aggregation in the CaCl₂ solution due to the balance of steric hindrance, cation bridging, and electrostatic repulsion. For HA and SA, Ca²⁺ bridging and EDL compression contributed to their destabilization of CdS colloids in CaCl₂ solution. Macromolecules concentration affect corona formation that alter stability of CdS colloids. There results showed that the complex influences of solution chemistry and macromolecules on fate and transport of CdS colloids in environment. The findings will help to understand the potential risks of CdS colloids in environment.

Antibody Immobilization

In the ELISA format(s), the capture antibody is usually affixed to a solid phase, commonly referred to as the immunosorbent. How to tether the antibody most effectively will depend upon the physical properties of the support (plate well, latex bead, flow cell, etc.) as well as its chemical nature (hydrophobic, hydrophilic, the presence of reactive groups such as epoxide, etc.). Of course, it is ultimately the suitability of the antibody to withstand the linking process while preserving its antigen-binding efficiency that must be determined. In this chapter, the antibody immobilization processes and their consequences are described.

Aggregation kinetics of polystyrene nanoplastics in gastric environments: Effects of plastic properties, solution conditions, and gastric constituents

Nanoplastics are inevitably ingested into human gastric environment, wherein their aggregation kinetics and interactions with gastric constituents remain unclear. This study investigated the early-stage (20 min) and long-term (1-6 h) aggregation kinetics of four commonly-found polystyrene nanoplastics (PSNPs) including NP100 (100-nm), A-NP100 (100-nm, amino-modified), C-NP100 (100-nm, carboxyl-modified), and NP500 (500-nm) under gastric conditions. Five simulated human gastric fluids (SGFs) including SGF1-3 (0-3.2 g/L pepsin and 34.2 mM NaCl), SGF4 (400 mM glycine), and SGF5 (nine constituents), three pH (2, fasted state; 3.5, late-fed state; and 5, early-fed state), and 1-100 mg/L PSNPs were examined. Aggregation rates ranked NP100 > A-NP100 ≈ C-NP100 > NP500, SGF5 > SGF4 > SGF3 > SGF2 > SGF1, and pH 2 > 3.5 > 5. Increasing PSNP concentration enhanced aggregation rate up to 13.82 nm/s. Aggregation behavior generally followed the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Pepsin, glycine, and proteose-peptone strongly influenced PSNP stability via electrostatic interaction and steric hindrance imparted by protein corona. Freundlich isotherm suggested that PSNPs adsorbed organic constituents following lysozyme > porcine bile > proteose-peptone > pepsin > glycine > D-glucose, inducing changes in constituent structure and PSNP properties. These findings provide insights on the transport of nanoplastics in the gastric environments.

Redispersion of dried plant nanocellulose: A review

Nanocellulose has undergone substantial development as a high value-added cellulose product with broad applications. Dried products are advantageous to decrease transportation costs. However, dried nanocellulose has redispersion challenges when rewetting. In this work, drying techniques, factors affecting redispersibility, and strategies improving the nanocellulose redispersibility are comprehensively reviewed. Hydrogen bonds of nanocellulose are unavoidably developed during drying, leading to inferior redispersibility of dried nanocellulose, even hornification. Drying processes of nanocellulose are discussed first. Then, factors affecting redispersibility are discussed. Following that, strategies improving the nanocellulose redispersibility are analyzed and their advantages and disadvantages are highlighted. Surface charge modification and steric hindrance concept are two main pathways to overcome the redispersion challenge, which are mainly carried out by chemical modification, additive incorporation and non-cellulosic component preservation. Despite several advancements having been achieved, new approaches for enhancing the nanocellulose redispersibility are still required to promote the industrial-scale applications of nanocellulose in various domains.

Aromaticity effect on supramolecular aggregation. Aromatic vs. cyclic monohydroxy alcohols

In this paper, the steric hindrance effect related to the presence of either a cyclic or aromatic ring on the self-association process in the series of monohydroxy alcohols (MAs), from cyclohexanemethanol to 4-cyclohexyl-1-butanol and from benzyl alcohol to 4-phenyl-1-butanol, was studied using X-Ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FTIR) spectroscopy, Broadband Dielectric Spectroscopy (BDS) and the Pendant Drop (PD) methods. Based on FTIR results, it was shown that phenyl alcohol (PhA) and cyclohexyl alcohol (CA) derivatives reveal substantial differences in the association degree, the activation energy of dissociation, and the homogeneity of supramolecular nanoassociates suggesting that the phenyl ring exerts a stronger steric impact on the self-assembling of molecules than cyclohexyl one. Additionally, XRD data revealed that phenyl moiety introduces more heterogeneity in the organization of molecules compared to the cyclic one. The changes in the self-association process of alcohols were also reflected in differences in the molecular dynamics of the H-bonded aggregates, as well as in the Kirkwood factor, defining the long-range correlation between dipoles, which were slightly higher for CAs with respect to those determined for PhAs. Unexpectedly it was also found that the surface layers of PhAs were more organized than those formed by CAs. Thus, these findings provided insight into the impact of aromaticity on the self-assembly process, H-bonding pattern, supramolecular structure, and intermolecular dynamics of the studied alcohols.

Influence of protein configuration on aggregation kinetics of nanoplastics in aquatic environment

Aggregation kinetics of nanoplastics in aquatic environment are influenced by their interactions with proteins having different structures and properties. This study employed time-resolved dynamic light scattering (TR-DLS) to investigate the effects of 5 proteins (bovine hemoglobin (BHb), bovine (BSA) and human serum albumin (HSA), collagen type I (Col I), and bovine casein (CS)) on aggregation kinetics of polystyrene nanoplastics (PSNPs) under natural water conditions, which were simulated using various ionic strength (1-1000 mM NaCl and 0.01-100 mM CaCl₂), pH (3-9), and protein concentration (1-5 mg/L of total organic carbon). The results indicated that the interactions between proteins and PSNPs strongly depended on electrostatic properties, protein structures, and solution chemistries, which induced distinct aggregation behaviors in NaCl and CaCl₂ solutions. Electrostatic repulsion and steric hindrance dominated their interactions in NaCl solution by stabilizing PSNPs with the order of spherical BSA and disordered CS > heart-shaped HSA > fibrillar Col I; whereas positively charged BHb destabilized PSNPs with aggregation rate of 1.71 nm/s at 300 mM NaCl. In contrast, at CaCl₂ concentration below 20 mM, proteins destabilized PSNPs following the sequence of HSA > BHb > Col I > BSA depending on counterbalance among double layer compression, cation bridging, and steric hindrance; whereas CS stabilized PSNPs by precipitating Ca²⁺ that inhibited charge screening effect. Both protein concentration and solution pH affected protein corona formation, surface charge, and protein structure that altered stability of PSNPs. Characterizations using fluorescence spectroscopy, circular dichroism, and two-dimensional correlation analysis spectroscopy showed fluorescence quenching and ellipticity reduction of proteins, indicating strong adsorption affinity between PSNPs and proteins. The study provides insight to how protein configuration and water chemistry affect fate and transport of nanoplastics in aquatic environment.

DNA methylation detection and site analysis by using an electrochemical biosensor constructed based on toehold-mediated strand displacement reaction

DNA methylation has become a novel target for early diagnosis and prognosis of cancer as well as other related diseases. The accurate detection of the methylation sites of specific genes proved to be of great significance. However, the complex biological nature of clinical samples and the detection of low-abundance targets led to higher requirements for the testing technology. It has been found that by virtue of high sensitivity, rapid response, low cost, facile operation and applicability to microanalysis, electrochemical sensors have greatly contributed to the process of clinical diagnosis. In this study, a facile, rapid and highly sensitive electrochemical biosensor based on the peak current change was developed on the basis of high selectivity of toehold and greater efficiency of PNA strand displacement and used for the detection and site analysis of DNA methylation. Moreover, compared with non-methylated DNA sequences, methylated DNA sequences could be readily invaded by PNA probes, thereby resulting in the strand displacement and significant electrical signals. Therefore, methylation of cytosine sites was primarily analyzed based on electrical signals. Strand displacement by the target DNA sequences with different methylated sites can lead to substantial changes of strand displacement efficiency. As a result, the methylation sites can be analyzed on the basis of corresponding peak current response relation. This method has a detection limit of 0.075 pM and does not involve various complicated steps such as bisulfite treatment, enzyme digestion and PCR amplification. Indeed, one detection cycle can be completed in 60 min. The proposed technology might exhibit great potential in early clinical diagnosis and risk assessment of cancers and related diseases.

Steric hindrance effect on the excited-state proton transfer process: TDDFT study on the fluorescent sensing mechanism of a fluoride sensor

An understanding of the excited-state process and the sensing mechanism for specific anions can be helpful for the design and synthesis of fluorescent sensors in analytical chemistry and biotechnology. Here, we theoretically investigated the fluorescent response mechanism of a reported acylhydrazone-based fluorescent sensor (Soft Matter, 2019, 15, 6690) for fluoride recognition using the time-dependent density functional theory approach. At the M06/TZVP/SCM level, the vertical excitation energies, which were calculated based on the ground state and first singlet-state geometries of the sensor molecule, agreed well with the experimental ultraviolet-visible and fluorescence spectra. Therefore, the time-dependent density functional theory method was considered reasonable and effective. According to the frontier orbital analysis and an excited-state potential energy scan, we proposed an excited-state proton transfer mechanism for the sensor-fluorine complex, where the steric hindrance leads to a high potential barrier. The excited-state proton transfer process facilitates sensor molecule deprotonation, alleviates its steric hindrance effect and expands its conjugated system. As a result, the fluorescence emission band of the sensor molecule was red-shifted significantly with the addition of fluoride anion. Based on this fluorescence difference, the sensor could be used for fluoride anion identification. This work provides a strategy to study sensor-analyte interactions in the excited state and offers an approach to tune the fluorescence emission wavelength of sensor molecules in anionic environments.

Dimethylmonothioarsinic acid and dimethyldithioarsinic acid in the environment: Sorption characteristics on 2-line ferrihydrite and acute toxicity to Daphnia magna

Dimethylmonothioarsinic acid (DMMTA(V)) and dimethyldithioarsinic acid (DMDTA(V)), which are commonly found in landfill leachate and pore water of rice paddy soil, have attracted considerable attention for their high toxicity. This study aims to evaluate the behavior and potential risks of DMMTA(V) and DMDTA(V) in the environment by conducting an equilibrium sorption test using 2-line ferrihydrite and acute toxicity (immobilization) test using Daphnia magna. The overall maximum sorption capacity (q_m) derived by the Langmuir isotherm model showed an increase in the order of inorganic arsenate (As(V)) > dimethylarsinic acid (DMA(V)) > DMMTA(V) > DMDTA(V), which was likely due to steric hindrance due to the presence of methyl and thiol groups. Moreover, DMMTA(V) and DMDTA(V) showed no or negligible change in q_m with pH change, while q_m decreased rapidly with increasing pH in As(V) and DMA(V). The 50% inhibition concentrations (IC50) for As(V), DMA(V), DMMTA(V), and DMDTA(V), which were measured after 48 h exposure to D. magna, were 9.5, > 30, 1.7, and 6.5 mg/L, respectively. Overall, the results demonstrated that DMMTA(V) and DMDTA(V) have high mobility and eco-toxicity in the environment and that methylated thioarsenicals should be accurately monitored and controlled.

Structure-guided steric hindrance engineering of Bacillus badius phenylalanine dehydrogenase for efficient L-homophenylalanine synthesis

BACKGROUND

Direct reductive amination of prochiral 2-oxo-4-phenylbutyric acid (2-OPBA) catalyzed by phenylalanine dehydrogenase (PheDH) is highly attractive in the synthesis of the pharmaceutical chiral building block L-homophenylalanine (L-HPA) given that its sole expense is ammonia and that water is the only byproduct. Current issues in this field include a poor catalytic efficiency and a low substrate loading.

RESULTS

In this study, we report a structure-guided steric hindrance engineering of PheDH from Bacillus badius to create an enhanced biocatalyst for efficient L-HPA synthesis. Mutagenesis libraries based on molecular docking, double-proximity filtering, and a degenerate codon significantly increased catalytic efficiency. Seven superior mutants were acquired, and the optimal triple-site mutant, V309G/L306V/V144G, showed a 12.7-fold higher k_cat value, and accordingly a 12.9-fold higher k_cat/K_m value, than that of the wild type. A paired reaction system comprising V309G/L306V/V144G and glucose dehydrogenase converted 1.08 M 2-OPBA to L-HPA in 210 min, and the specific space-time conversion was 30.9 mmol g^-1 L^-1 h^-1. The substrate loading and specific space-time conversion are the highest values to date. Docking simulation revealed increases in substrate-binding volume and additional degrees of freedom of the substrate 2-OPBA in the pocket. Tunnel analysis suggested the formation of new enzyme tunnels and the expansion of existing ones.

CONCLUSIONS

Overall, the results show that the mutant V309G/L306V/V144G has the potential for the industrial synthesis of L-HPA. The modified steric hindrance engineering approach can be a valuable addition to the current enzyme engineering toolbox.

Colloidal stability of nanosized activated carbon in aquatic systems: Effects of pH, electrolytes, and macromolecules

Nanosized activated carbon (NAC) is a novel adsorbent with great potential for water reclamation. However, its transport and reactivity in aqueous environments may be greatly affected by its stability against aggregation. This study investigated the colloidal stability of NAC in model aqueous systems with broad background solution chemistries including 7 electrolytes (NaCl, NaNO₃, Na₂SO₄, KCl, CaCl₂, MgCl₂, and BaCl₂), pH 4-9, and 6 macromolecules (humic acid (HA), fulvic acid (FA), cellulose (CEL), bovine serum albumin (BSA), alginate (ALG), and extracellular polymeric substance (EPS)), along with natural water samples collected from pristine to polluted rivers. The results showed that higher solution pH stabilized NAC by raising the critical coagulation concentration from 28 to 590 mM NaCl. Increased cation concentration destabilized NAC by charge screening, with the cationic influence following Ba²⁺ > Ca²⁺ > Mg²⁺ >> Na⁺ > K⁺. Its aggregation behavior could be predicted with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory with a Hamaker constant (A_CWC) of 4.3 × 10^-20 J. The presence of macromolecules stabilized NAC in NaCl solution and most CaCl₂ solution following EPS > BSA > CEL > HA > FA > ALG, due largely to enhanced electrical repulsion and steric hindrance originated from adsorbed macromolecules. However, ALG and HA strongly destabilized NAC via cation bridging at high Ca²⁺ concentrations. Approximately half of NAC particles remained stably suspended for ∼10 d in neutral freshwater samples. The results demonstrated the complex effects of water chemistry on fate and transport of NAC in aquatic environments.

4,6-Di-O-Benzylidenyl group-directed preparation of 2-deoxy-2-azido-α-d-galactopyranosides promoted by 3-O-TBDPS

In this study, we designed a method to prepare 2-deoxy-2-azido-α-d-galactopyranosidic bonds using 4,6-di-O-benzylidenyl-3-O-t-butyldiphenylsilyl protected 2-deoxy-2-azido-1-thio-d-galactopyranoside 5 as donors. The donor 5 gives a good to excellent α-selectivity in the glycosylation with secondary alcohols, which was found to be associated with the benzylidenyl on 4,6-di-O and TBDPS on 3-O of the donor 5. Compared with results of the donor 6 and 7, the 3-O-TBDPS could increase the activity of the thioglycoside, and the lone pairs on 4,6-di-O-benzylidenyl group enhanced the gg-cofnormation, which plays a role in improving the stereoselectivity. Finally, this method was demonstrated through the synthesis of a α-galactosamine -containing pentasaccharide 26.

Photooxidation of 2,3-dihydroquinazolin-4(1H)-ones: retention or elimination of 2-substitution

A series of mono and disubstituted 2,3-dihydroquinazolin-4(1H)-ones (DHQZs) were synthesized and the electronic and steric effects of the C₂- and N₃-substitutions on the retention or elimination of the C₂-substitution by exposing them to the ultraviolet light were investigated. Electron transfer from photo-excited dihydroquinazolinones to chloroform solvent is proposed, in which both lone pairs on the N₁- and N₃-atoms can be involved in this process. The extent of the N₁- and N₃-atoms contributions in this electron-transfer process and also the retention or elimination of the C₂-substitutions are dependent on the nature and steric hindrance of both C₂- and N₃-substitutions. The experimental results are supported by the computational studies. Photoinduced electron-transfer reaction of a series of mono and disubstituted 2,3- dihydroquinazolin-4(1H)-ones was investigated.

Influence of environmental and biological macromolecules on aggregation kinetics of nanoplastics in aquatic systems

Nanoplastics derived from degradation of micro- or macroplastics are emerging contaminants in aquatic environments, where their fate and transport as well as toxicity are affected by aggregation. This study employed time-resolved dynamic light scattering to investigate the aggregation kinetics of polystyrene nanoplastics (PSNPs) in the presence of four macromolecules (sodium alginate (SA), bovine serum albumin (BSA), extracellular polymeric substance (EPS), and Suwannee River humic acid (HA)) in solutions containing monovalent (NaCl) and divalent (CaCl₂) salts at different pH. Our results showed that the macromolecules enhanced PSNP stability in NaCl solutions but destabilized PSNPs in CaCl₂ solutions at pH 6. In NaCl solutions, macromolecules inhibited PSNP aggregation due to steric hindrance originated from macromolecular layer adsorbed on PSNPs. The strongest stabilization effect was observed for BSA having the greatest hydrodynamic adsorption layer thickness of 21.9 nm, followed by HA, EPS, and SA. In CaCl₂ solutions, SA significantly destabilized PSNPs via alginate bridging with Ca²⁺, which enhanced with concentrations of SA and CaCl₂. The destabilization effects of other three macromolecules in CaCl₂ solutions were governed by the interplay among molecular bridging, charge screening, and steric hindrance. An increased pH in NaCl or CaCl₂ solutions containing macromolecules all stabilized PSNPs due to elevated electrostatic repulsion, except that SA destabilized PSNPs in CaCl₂ solutions via enhanced molecular bridging. The stabilization effect of macromolecules may also compete with the destabilization effect under seawater condition. This study suggested that PSNP aggregation in aquatic environments could be strongly affected by macromolecules and solution chemistry.

Modeling the transport of neutral disinfection byproducts in forward osmosis: Roles of reverse salt flux

The rejection of disinfection byproducts (DBPs) is an important consideration for the application of forward osmosis (FO) in wastewater recycling. However, the transport of organic compounds in FO is not well predicted by existing models, partially because these models have not incorporated the effect of reverse salt flux, a phenomenon previously shown to influence the transport of pharmaceutical compounds. In this study, we investigated the effects of reverse salt flux on DBP transport in FO and the corresponding mechanisms. We used a commercial Aquaporin membrane and tested sixteen DBPs relevant to wastewater recycling. Using draw solutions constituted by NaCl, MgSO₄, or glucose in a bench-scale FO system, we first confirmed that higher reverse salt flux resulted in lower DBP permeance. By integrating results from the bench-scale FO system and those from diffusion cell tests, we showed that two mechanisms contributed to the hindered DBP transport: the steric hindrance in the active layer caused by the presence of the draw solute and the retarded diffusion of DBPs in the support layer via a "salting-out" effect. Lastly, we developed a modified solution-diffusion model incorporating these two mechanisms by accounting for the free volume occupied by draw solute molecules in the active layer and by introducing the Setschenow constant, respectively. The modified model significantly improved the prediction of permeance for halogenated DBPs, and revealed the relative importance of steric hindrance (dominant for large DBPs) and retarded diffusion (dominant for hydrophobic DBPs). The modified model did not accurately predict the permeance of nitrosamines, attributable to their extremely high hydrophilicity or large size.

Rational design of the carbonyl reductase EbSDR8 for efficient biosynthesis of enantiopure (R)-3-chloro-1-phenyl-1-propanol

(R)-3-Chloro-1-phenyl-1-propanol ((R)-CPPO) is an important chiral intermediate for antidepressants. For its efficient biosynthesis, the carbonyl reductase EbSDR8 was engineered to asymmetrically reduce the unnatural substrate 3-chloro-1-phenyl-1-propanone (3-CPP) at high concentrations. Molecular docking and molecular dynamics simulations of the resulting mutants suggested enlarged substrate binding pocket and more reasonable interactions between the enzyme and the substrate or cofactor as the reasons for the enhanced catalytic activity and thus the remarkably improved conversion of high-concentration 3-CPP. Using the best mutant EbSDR8^{G94A/L153I/Y188A/Y202M} as the whole-cell biocatalyst, reduction of 3-CPP (1.0 M) was conducted using 100% isopropanol as both the solvent and co-substrate for NADH regeneration, delivering (R)-CPPO with ˃ 99% ee_p and 95.5% conversion. This result suggests EbSDR8^{G94A/L153I/Y188A/Y202M} as a potential biocatalyst for green production of (R)-CPPO at the industrial scale. KEY POINTS: • Rational design of EbSDR8 by modulating steric hindrance and molecular interactions; • Non-aqueous biocatalysis using isopropanol as both the solvent and co-substrate; • Whole-cell catalyzed production of 161 g/L enantiopure (R)-CPPO from 1.0 M of 3-CPP. Graphical Abstract.

Waste shrimp shell-derived hydrochar as an emergent material for methyl orange removal in aqueous solutions

Shrimp processing and consumption generate large amounts of waste shrimp shell (WSS) rich in chitin and protein. Herein, we successfully synthesized WSS-based hydrochar (WSH) adsorbent through deproteinization and deacetylation followed by hydrothermal carbonization (HTC) and acid washing. For comparison, another hydrochar (CCH) adsorbent was synthesized from HTC of commercial chitosan under identical conditions. Specifically, WSH contained rich nitrogen-containing functional groups with a long aliphatic chains structure. Acid etching of calcium carbonate in WSS led to a higher specific surface area of WSH (12.65 m²/g) which was nearly 6 times higher than that of CCH (2.13 m²/g). The lower deacetylation degree of WSH was responsible for higher amide I and amino groups retained therein. Under an optimal initial solution pH of 4.0, WSH could rapidly achieve a superb adsorption capacity of 755.08 mg/g for methyl orange molecule. Moreover, the adsorption process followed a pseudo-second-order kinetics model and was well described by a monolayer adsorption pattern based on the Langmuir isotherm model with correlation coefficients higher than 0.9989. Prominent adsorption performance of WSH for methyl orange was mainly attributed to electrostatic interactions, while steric hindrance effect had a detrimental impact on the adsorption capacity of CCH. Superb adsorption capacity and excellent regeneration performance suggest WSH could be a promising and affordable adsorbent candidate for anionic dye removal.

Removal of antimonite and antimonate from water using Fe-based metal-organic frameworks: The relationship between framework structure and adsorption performance

We investigated the adsorption performance of five Fe-based MOFs (Fe-BTC, MIL-100(Fe), MIL-101(Fe), MIL-53(Fe) and MIL-88C(Fe)) for removal of antimonite (Sb(III)) and antimonate (Sb(V)) from water. Among these MOFs, MIL-101(Fe) exhibited the best adsorption capacities for both Sb(III) and Sb(V) (151.8 and 472.8mg/g, respectively) which were higher than those of most adsorbents previously reported. The effect of steric hindrance was evident during Sb removal using the Fe-based MOFs, and the proper diameter of the smallest cage windows/channels should be considered an important parameter during the evaluation and selection of MOFs. Additionally, the adsorption capacities of MIL-101(Fe) for Sb(V) decreased with increasing initial pH values (from 3.0 to 8.0), while the opposite trend was observed for Sb(III). Chloride, nitrate and sulfate ions had a negligible influence on Sb(V) adsorption, while NO₃^- and SO₄^2- improved Sb(III) adsorption. This result implies that inner sphere complexes might form during both Sb(III) and Sb(V) adsorption.

An equation for biomimicking macromolecular crowding using Escherichia coli MG1655 strain

Macromolecules present in the intracellular environment of a cell are densely packed, resulting in a highly crowded cytosolic environment. This crowded milieu influences several biochemical equilibria such as diffusibility and association constant of biomolecules which impose a serious impact on cellular functions as well as its processes. A number of in silico and in vitro studies have been reported till date about using synthetic crowding agents for resembling such a crowding environment within the cell. Lately, it has been realized that synthetic crowders are not suitable for mimicking the intrinsic environment of the cell. In this study, proteins were assumed to be the major biological molecule which contributes to the crowding environment. We have semi-theoretically determined the total protein concentration within an individual E. coli MG1655 cell which changes notably as the growth curve proceeds from 0.2 to 1.0 OD₆₀₀. The average range of total cellular protein concentration throughout the batch culture was found to be in the range of 15.2 to 178 fg/fL of cytoplasmic volume. The fundamental knowledge gained through the study was translated to applied research in the form of an equation. We propose an equation that could help to mimic the OD₆₀₀ dependent crowding environment present within a single cell of E. coli in the desired volume of reaction solution. In a nutshell, the equation provides quantitative estimation of the volume of culture required to prepare the cell lysate for biomimicking the intracellular crowding environment in vitro. This finding provides a new insight into the cellular cytosolic environment that could be used as a platform to frame more cells like environment in cell-free protein synthesis (CFPS) system for synthetic biology applications.

Photoelectrochemical determination of malathion by using CuO modified with a metal-organic framework of type Cu-BTC

A photoelectrochemical (PEC) sensor was constructed for the detection of non-electroactive malathion. It is based on the use of a hierarchical CuO material derived from a Cu-BTC metal-organic framework (where BTC stands for benzene-1,3,5-tricarboxylic acid). The modified CuO was obtained by calcination of Cu-BTC at a high temperature (300 °C) and possesses a high photocurrent conversion efficiency. Under irradiation with visible light and in the presence of malathion, the formation of the CuO-malathion complex on the CuO gave rise to an increase in steric hindrance. This results in a decrease in photocurrent. This novel PEC detection method has a lower detection limit of 8.6 × 10^-11 mol L^-1 and a wide linear range (1.0 × 10^-10 ~ 1.0 × 10^-5 mol L^-1). Graphical abstract Schematic presentation of the Cu-BTC MOF derived photoelectrochemical sensor for non-electroactive malathion detection.

Formation of nanosuspensions in bottom-up approach: theories and optimization

BACKGROUND

Nanosuspensions, liquid dispersions with nanometer size distribution, are becoming trendy in pharmaceutical practice to formulate poorly water-soluble drugs and to enhance their bioavailability. Generally, nanosuspensions are produced in two main approaches; top-down or bottom-up. The former is based on size-reduction of large particles via milling or high pressure homogenization. The latter is focused on the mechanisms of nucleation and particle growth.

METHODS

In this review, the critical factors influencing the kinetics or dynamics of nucleation and growth are discussed. Subsequently, the mechanisms of nanosuspension instability as well as strategies for stabilization are elaborated. Furthermore, the effects of stabilizers on key parameters of instability as well as the process of choosing an appropriate stabilizer is discussed.

RESULTS

Steric and electrostatic stabilizations or combination of them is essential for nanosuspensions formulation to prevent coagulation. Accordingly, some characteristics of stabilizers play critical role on stability and optimization of nanosuspensions; i.e., HLB and concentration. Nevertheless, after reviewing various articles, it is ascertained that each formulation requires individual selection of surfactants according to the parameters of the particle surface and the medium.

CONCLUSIONS

Based on the results, application of excipients such as stabilizers requires proper optimization of type and concentration. This implies that each formulation requires its own optimization process. Graphical Abstract ᅟ.

A versatile fluorometric aptasensing scheme based on the use of a hybrid material composed of polypyrrole nanoparticles and DNA-silver nanoclusters: application to the determination of adenosine, thrombin, or interferon-gamma

The authors describe a versatile aptasensing scheme based on the use of polypyrrole nanoparticles (PPyNPs) and DNA-silver nanoclusters (DNA-AgNCs) for multiple target detection. The DNA-AgNCs consist of two functional domains, viz. (a) a nucleation domain for attaching the metal core of the nanoclusters, and (b) a recognition domain which consists of a single-stranded aptamer. In the absence of analytes, the single-strand recognition domain will be absorbed onto the surface of the PPyNPs through π stacking and hydrophobic interactions. As a result, the red fluorescence of the DNA-AgNCs (with excitation/emission peaks at 535/625 nm) is quenched by the PPyNPs. On introducing the analytes, the DNA-AgNCs will bind them. This leads to the desorption of DNA-AgNCs and the recovery of the red fluorescence. Based on the above strategy, a versatile, sensitive and selective aptasensor was established for detection of adenosine, thrombin and interferon-gamma. The method was applied to the detection of the above targets in (spiked) serum samples and gave satisfactory results, with detection limit of 0.58 nM for IFN-γ, 0.39 nM for adenosine, and 2.2 nM for thrombin. The use of PPyNPs results in uniquely low non-specific absorption and in improved analytical results in case of real-sample analysis when compared to previously reported methods. Graphical abstract Schematic illustration of DNA-silver nanoclusters and polypyrrole nanoparticles in an aptasensor for detection of multiple targets.

Use of (meth)acrylamides as alternative monomers in dental adhesive systems

OBJECTIVES

Methacrylamides are proposed as components for dental adhesive systems with enhanced resistance to hydrolytic and enzymatic degradation. The specific objective of this study was to evaluate the polymerization kinetics, water sorption and solubility, pH-derived degradation and microtensile bond strength of various monofunctional acrylamides and meth(acrylamides) when copolymerized with dimethacrylates.

METHODS

Base monomers were added at 60 wt%, and included either BisGMA or UDMA. Monofunctional monomers were added at 40 wt%, including one (meth)acrylate as the control, two secondary methacrylamides and two tertiary acrylamides. DMPA (0.2 wt%) and DPI-PF6 (0.4 wt%)/BHT (0.1 wt%) were added as initiators/inhibitor. Polymerization kinetics wwere followed with near-IR spectroscopy in real time. Water sorption (WS) and solubility (SL) were measured following ISO 4049. Monomer degradation at different pH levels was assessed with 1H NMR. Microtensile bond strength (MTBS) was assessed in caries-free human third molars 48 h and 3 weeks after restorations were placed using solvated BisGMA-based adhesives (40 vol% ethanol). Data were analyzed with one-way ANOVA/Tukey's test (α = 0.05).

RESULTS

As expected, rate of polymerization and final degree of conversion (DC) were higher for the acryl versions of each monomer, and decreased with increasing steric hindrance around the vinyl group for each molecule. In general, UDMA copolymerizations were more rapid and extensive than for BisGMA, but this was dependent upon the specific monofunctional monomer added. WS/SL were in general higher for the (meth)acrylamides compared to the (meth)acrylates, except for the tertiary acrylamide, which showed the lowest values. One of the secondary methacrylamides was significantly more stable than the methacrylate control, but the alpha substitutions decreased stability to degradation in acid pH. MTBS in general was higher for the (meth)acrylates. While for all materials the MTBS values at 3 weeks decreased in relation to the 24 h results, the tertiary acrylamide showed no reduction in bond strength.

SIGNIFICANCE

This study highlights the importance of considering steric and electronic factors when designing monomers for applications where rapid polymerizations are needed, especially when co-polymerizations with other base monomers are required to balance mechanical properties, as is the case with dental adhesives. The results of this investigation will be used to design fully formulated adhesives to be tested in clinically-relevant conditions.

An electrochemical DNA biosensor analytic technique for identifying DNA methylation specific sites and quantify DNA methylation level

We herein developed a novel electrochemical biosensor to detect DNA methylation level, and to quantitatively analyze multiple methylated sites. Graphene oxide was modified with anti-5-methylcytosine antibody to specifically bind CpG methylation sites, and horseradish peroxidase (HRP)-labeled IgG secondary antibody was bound to the former antibody. In buffer containing H₂O₂ and hydroquinone, HRP-IgG catalyzed the oxidation of hydroquinone into benzoquinone over H₂O₂, thereby generating electrochemical reduction signals. The number of 5-methylcytosine was directly proportional to current signal, thereby allowing accurate quantification of methylation level. We also analyzed monomethylated target sequences with different sites. After different methylated sites were captured by the probe, the steric hindrance differences between -CH₃ hydrophobic sphere and the electrode surface were induced. The peak current decreased with reducing distance from the electrode surface, so DNA methylation sites were identified by measuring corresponding peak current responses. With a low detection limit (1 fM), this DNA biosensor was suitable for ultrasensitive DNA methylation detection. The linear detection range was 10^-15 M to 10^-8 M. Meanwhile, this method had high specificity, stability and repeatability, thus being widely applicable to the clinical detection of DNA methylation.

Evaluation of protein-ligand interactions using the luminescent interaction assay FlimPIA with streptavidin-biotin linkage

Post-translational modifications, such as phosphorylation, are crucial in the regulation of protein-protein interactions and protein function in cell signaling. Here, we studied the interaction between the transactivation domain peptide of cancer suppressor protein p53 and its negative regulator Mdm2 using a novel protein-protein interaction assay, based on the modified FlimPIA using the streptavidin-biotin interaction to link the p53 peptide and the probe enzyme. We succeeded in detecting an attenuation in the affinity of p53 towards Mdm2 caused by the phosphorylation at Thr18. It showed that the targets, which are not easy to fuse with the FlimPIA probes, such as phosphorylated peptides can be used in this system. Also, the use of streptavidin nanobeads was found effective to get clearer signal, probably due to concentration of the detection system onto the bead surface. The system was further applied to the detection of FKBP-FRB interaction using biotinylated FKBP domain, which suggested another potential merit of this system that allows to avoid misfolding and steric hindrance often observed for the fusion protein approach.

Immunoassays for scarce tumour-antigens in exosomes: detection of the human NKG2D-Ligand, MICA, in tetraspanin-containing nanovesicles from melanoma

Background

Tumour-derived exosomes can be released to serum and provide information on the features of the malignancy, however, in order to perform systematic studies in biological samples, faster diagnostic techniques are needed, especially for detection of low abundance proteins. Most human cancer cells are positive for at least one ligand for the activating immune receptor NKG2D and the presence in plasma of NKG2D-ligands can be associated with prognosis.

Methods

Using MICA as example of a tumour-derived antigen, endogenously expressed in metastatic melanoma and recruited to exosomes, we have developed two immunocapture-based assays for detection of different epitopes in nanovesicles. Although both techniques, enzyme-linked immunosorbent assay (ELISA) and Lateral flow immunoassays (LFIA) have the same theoretical basis, that is, using capture and detection antibodies for a colorimetric read-out, analysis of exosome-bound proteins poses methodological problems that do not occur when these techniques are used for detection of soluble molecules, due to the presence of multiple epitopes on the vesicle.

Results

Here we demonstrate that, in ELISA, the signal obtained was directly proportional to the amount of epitopes per exosome. In LFIA, the amount of detection antibody immobilized in Au-nanoparticles needs to be low for efficient detection, otherwise steric hindrance results in lower signal. We describe the conditions for detection of MICA in exosomes and prove, for the first time using both techniques, the co-existence in one vesicle of exosomal markers (the tetraspanins CD9, CD63 and CD81) and an endogenously expressed tumour-derived antigen. The study also reveals that scarce proteins can be used as targets for detection antibody in LFIA with a better result than very abundant proteins and that the conditions can be optimized for detection of the protein in plasma.

Conclusions

These results open the possibility of analyzing biological samples for the presence of tumour-derived exosomes using high throughput techniques.

Electronic supplementary material

The online version of this article (10.1186/s12951-018-0372-z) contains supplementary material, which is available to authorized users.

Feasibility of reusing the black liquor for enzymatic hydrolysis and ethanol fermentation

The black liquor (BL) generated in the alkaline pretreatment process is usually thought as the environmental pollutant. This study found that the pure alkaline lignin hardly inhibited the enzymatic hydrolysis of cellulose (EHC), which led to the investigation on the feasibility of reusing BL as the buffer via pH adjustment for the subsequent enzymatic hydrolysis and fermentation. The pH value of BL was adjusted from 13.23 to 4.80 with acetic acid, and the alkaline lignin was partially precipitated. It deposited on the surface of cellulose and negatively influenced the EHC via blocking the access of cellulase to cellulose and adsorbing cellulase. The supernatant separated from the acidified BL scarcely affected the EHC, but inhibited the ethanol fermentation. The 4-times diluted supernatant and the last-time waste wash water of the alkali-treated sugarcane bagasse didn't inhibit the EHC and ethanol production. This work gives a clue of saving water for alkaline pretreatment.

Tuning self-assembled morphology of the Aβ(16-22) peptide by substitution of phenylalanine residues

The effects of the two phenylalanine (Phe) residues in the blocked Aβ(16-22) peptide on its self-assembly have been investigated by replacing both of them with two cyclohexylalanines (Chas) or two phenylglycines (Phgs). TEM and SANS studies revealed that the flat and wide nanoribbons of Aβ(16-22) were transformed into thin nanotubes when replaced with Chas, and thinner and twisted nanofibrils when replaced with Phgs. The red-shifting degree of characteristic CD peaks suggested an increased twisting in the self-assembly of the derivative peptides, especially in the case of Ac-KLV(Phg)(Phg)AE-NH2. Furthermore, molecular dynamics (MD) simulations also indicated the increasing trend in twisting when Chas or Phgs were substituted for Phes. These results demonstrated that the hydrophobic interactions and spatial conformation between Cha residues were sufficient to cause lateral association of β-sheets to twisted/helical nanoribbons, which finally developed into nanotubes, while for Phg residue, the loss of the rotational freedom of the aromatic ring induced much stronger steric hindrance for the lateral stacking of Ac-KLV(Phg)(Phg)AE-NH2 β-sheets, eventually leading to the nanofibril formation. This study thus demonstrates that both the aromatic structure and the steric conformation of Phe residues are crucial in Aβ(16-22) self-assembly, especially in the significant lateral association of β-sheets.

Steric hindrance regulated supramolecular assembly between β-cyclodextrin polymer and pyrene for alkaline phosphatase fluorescent sensing

We herein report a strategy for sensitive alkaline phosphatase (ALP) fluorescent sensing based on steric hindrance regulated supramolecular assembly between β-cyclodextrin polymer (polyβ-CD) and pyrene. The fluorescence of pyrene was enhanced more than 10 times through supramolecular assembly with polyβ-CD. The 5'-phosphorylated dsDNA probe with pyrene attached on the 3'-terminal could be cleaved by λ exonuclease (λ exo), yielding pyrene attached on mononucleotides. Pyrene attached on mononucleotides could easily enter the cavity of polyβ-CD, resulting in fluorescence enhancement. When ALP was introduced, it could remove 5'-phosphate groups from dsDNA and then prevented the cleavage of dsDNA. Pyrene attached on dsDNA was difficult to enter the cavity of polyβ-CD because of steric hindrance, resulting in an inconspicuous fluorescence enhancement. Owing to the excellent fluorescence enhancement during steric hindrance regulated supramolecular assembly, excellent performance of the assay method was achieved for ALP with a detection limit of 0.04 Um L(-1). The detection limit was superior or comparable with the reported methods. Besides, this method was simple in design, avoiding double-labeling of probe.

What factors influence the reactivity of C-H hydroxylation and C=C epoxidation by [Fe(IV)(L(ax))(1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane)(O)](n+)

Density functional theory is used to investigate geometric structures and mechanisms for hydroxylation and epoxidation from propene for four non-heme iron complexes, [Fe(IV)(L(ax))(TMC)(O)](n+), which are the inverted isomers of [Fe(IV)(O)(TMC)(Lax)](n+) (Lax = acetonitrile (AN), monoanionic trifluoroacetate (TF), azide (N3), thiolate (SR)). The Fe(IV)O unit is found to be sterically less hindered in [Fe(IV)(L(ax))(TMC)(O)](n+) than that in [Fe(IV)(O)(TMC)(L(ax))](n+). Becke, three-parameter, Lee-Yang-Parr (B3LYP) calculations show that hydroxylation and epoxidation proceed via a two-state-reactivity on competing triplet and quintet spin surfaces; and the reactions have been invariably mediated by the S = 2 state. The reaction pathways computed reveal that 2-AN is the most reactive in the four [Fe(IV)(L(ax))(TMC)(O)](n+) complexes; along the reaction pathway, the axial ligand moves away from the iron center, and thus, the energy of the LUMO decreases. The anionic axial ligand, which is more electron releasing than neutral AN, shows a strong overlap of iron orbitals. Thus, the anionic ligand does not move away from the iron center. The H-abstraction is affected by the tunneling contribution, the more electron donation power of the axial ligand, the more effect of the tunneling contribution. Adding the tunneling correction, the relative reactivity of the hydroxylation follows the trend: 2-AN > 2-SR ≈ 2-N3 > 2-TF. However, for the epoxidation, the reactivity is in the following order of 2-AN > 2-TF > 2-N3 > 2-SR. Except for 2-AN, 2-X (L(ax) = TF, N3, SR) complexes chemoselectively hydroxylate even in the presence of a C=C double bond.

Particulate structure of phytoglycogen studied using β-amylolysis

Phytoglycogen (PG), a dendrimer-like glucan particulate, has a much higher dispersed molecular density than amylopectin (AP). In this study, β-amylase was used to investigate the effect of high molecular density of PG on its susceptibility to enzymatic hydrolysis. AP and PG reached the limit of β-amylolysis at 20 and 480 min, respectively, suggesting a much higher resistance of PG to β-amylase. The majority of PG β-amylolysis occurred in the initial 2 min, followed by a slow progression that implied low accessibility of internal particulate portion to enzyme. The chain length profile of PG β-limit dextrin showed only one population of long chains, indicating the absence of branch clusters with PG. At the limit of β-amylolysis, a substantial decrease in the molar mass was observed for both PG and AP, whereas only a slight reduction in the Z-average root mean square radius was observed for PG (from 24.5 to 23.1 nm) compared to that of AP (from 91.1 to 69.6 nm).

Cytotoxicity profile of novel sterically hindered platinum(II) complexes with (1R,2R)-N(1),N(2)-dibutyl-1,2-diaminocyclohexane

Four Pt(II) complexes of (1R,2R)-N(1),N(2)-dibutyl-1,2-diaminocyclohexane with two alkyl branches as steric hindrance have been designed and synthesized. In vitro cytotoxicity of these compounds indicated complex 4 is a cytotoxic agent more potent than its parent molecule, oxaliplatin, against almost all the tested cell lines. Agarose gel electrophoresis study showed that the kinetic reactivity of complex 4 with DNA is slow down due to the sterically hindered effect, demonstrating that it may possess a different mechanism of action from cisplatin. Flow cytometry results revealed that complex 4 induced apoptosis of tumor cells by blocking the cell-cycle progression in the G2/M phase. Western blot analysis showed it had a similar apoptotic mechanism to cisplatin which could induce apoptosis via a mitochondrial-dependent pathway.

Signal loss due to oligomerization in ELISA analysis of amyloid-beta can be recovered by a novel sample pre-treatment method

According to the predominant theories, soluble amyloid-beta (Aβ) aggregates are the principal neurotoxic agents in Alzheimer’s disease pathology, making them a popular target for the development of therapeutics and diagnostic markers. One of the most commonly used methods for determining the concentration of Aβ is ELISA. However, ELISA was developed for monomeric proteins and may be ill-suited for detecting aggregates. Therefore, we investigated the effect of aggregation on the ELISA measurement and developed a novel chemical pre-treatment method, designed to disaggregate Aβ peptides, to improve the ELISA measurement of the total Aβ concentration.

Synthetic Aβ40 monomers, Aβ42 oligomers and biological samples from mice and humans were subjected to a chemical pre-treatment protocol with: trifluoroacetic acid (TFA), formic acid (FA) or hexafluoroisopropanol (HFIP) prior to ELISA analysis. In our study we have shown that:

•

Aβ oligomerization leads to epitope masking and steric hindrance and results in an underestimation of the total Aβ content with ELISA.

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Chemically pre-treating samples to disaggregate oligomers can (partially) recover the signal loss.

•

This novel sample pre-treatment method could provide a more accurate ELISA measurement of the total Aβ concentration in samples with a high oligomer content.

Effects of the steric hindrance of micropores in the hyper-cross-linked polymeric adsorbent on the adsorption of p-nitroaniline in aqueous solution

A hyper-cross-linked polymeric adsorbent with "--CH2--phenol--CH2--" as the cross-linked bridge (denoted GQ-05), and another hyper-cross-linked polymeric adsorbent with "--CH2--p-cresol--CH2--" as the cross-linked bridge (denoted GQ-03) were synthesized to reveal the effect of the steric hindrance of micropores in the hyper-cross-linked polymeric adsorbent on adsorption capacity and adsorption rate of p-nitroaniline (PNA) from aqueous solution. The results of adsorption kinetics indicated the order of the adsorption rate GQ-05>GQ-03. The pseudo-first-order rate equation could describe the entire adsorption process of PNA onto GQ-05 while the equation characterized the adsorption process of GQ-03 in two stages. The order of the adsorption capacity GQ-05>GQ-03 was demonstrated by thermodynamic analysis and dynamic adsorption. The steric hindrance of micropores in the hyper-cross-linked polymeric adsorbent was a crucial factor for the order of the adsorption capacity and adsorption rate.

Effect of silica fouling on the removal of pharmaceuticals and personal care products by nanofiltration and reverse osmosis membranes

In this study, one reverse osmosis (XLE) and two nanofiltration (NF90 and NF270) membranes were fouled by silica to evaluate its effect on the flux decline as well as the removal of six pharmaceuticals and personal care products (PPCPs) including carbamazapine (CBZ), triclosan (TRI), ibuprofen (IBU), sulfadiazine (DIA), sulfamethoxazole (SMX) and sulfamethazine (SMZ) from pH 3 to 10. The membranes were characterized by physicochemical properties including hydrophobicity, surface morphology and PPCPs adsorption with or without the presence of silica fouling to validate the rejection mechanisms of PPCPs. The fouling mechanisms were investigated using the modified Hermia model. It was found that all membranes with silica fouling showed more severe permeate flux decline at low pHs (3 and 5) than at high pHs (8 and 10) by the decomposition of nonionized silica particles to form a dense gel layer on membrane surfaces, which was hard to be removed by backwash. Silica fouling rendered the membrane surface considerably more hydrophilic, and only IBU, TRI and SMZ were adsorbed on membranes. Silica fouling on tight membranes (NF90 and XLE) can promote rejection of most PPCPs because the dense fouling layer could supply membrane with synergistic steric hindrance to reduce the transportation of PPCPs across membrane surface, implying that size exclusion is the dominating mechanism. While for loose NF270, electrostatic repulsion dominates by enhanced rejection of PPCPs as pH increased. Although fouling layer could provide extra steric hindrance for NF270, its effect was overwhelmed by the accompanied cake-enhanced concentration polarization phenomenon (CEOP). CEOP impeded back diffusion of PPCPs into the feed solution, trapped and accumulated PPCPs on membrane surface so as to increase their diffusion across membrane. At all pH levels, intermediate blocking and gel layer formation was the major fouling mechanism for tight and loose membrane, respectively.

Steric hindrance of 2,6-disubstituted benzoic acid derivatives on the uptake via monocarboxylic acid transporters from the apical membranes of Caco-2 cells

Benzoic acid is a typical substrate for monocarboxylic acid transporters (MCTs), and easily taken up from the apical membranes of Caco-2 cells by MCTs. However, some benzoic acid derivatives were sparingly taken up by Caco-2 cells. To elucidate the mechanism of lower uptake of the derivatives, we investigated the effect of substitution of benzene ring on the uptake by MCTs using Caco-2 cells. Among the benzoic acid derivatives tested, the uptake of 2,6-disubstituted benzoic acids was markedly lower than that of other benzoic acids. Co-incubation of the 2,6-disubstituted derivatives with benzoic acid did not decrease the uptake of benzoic acid, while co-incubation with other derivatives significantly decreased the uptake of benzoic acid. Kinetic analyses elucidated that the uptake of 2,6-dichlorobenzoic acid and 2,3,6-trichlorobenzoic acid did not involve the carrier-mediated process. The 2,6-disubstitution of benzoic acid may prevent the access of carboxylic acid group to MCTs expressed on the apical membranes of Caco-2 cells.

Synthesis and study on a series of phosphorescent Cu(I) complexes having sterically blocking ligands

In this paper, we report six phosphorescent Cu(I) complexes with 1,10-phenanthroline-derived ligands and phosphorous ligands, including their synthesis, crystal structures, photophysical properties, and electronic nature. The Cu(I) center has a distorted tetrahedral geometry within the Cu(I) complexes. Theoretical calculation reveals that all emissions originate from triplet metal-to-ligand-charge-transfer excited state. It is found that the introduction of alkyl moieties into 2,9-positions of 1,10-phenanthroline is highly effective on restricting the geometric relaxation that occurs in excited states, which greatly enhances the photoluminescence (PL) performances, including PL quantum yield improvement, PL decay lifetime increase, and emission blue shift.

Crystal structure analysis of EstA from Arthrobacter sp. Rue61a--an insight into catalytic promiscuity

In this article we analyze the reasons for catalytic promiscuity of a type VIII esterase with β-lactamase fold and the ability to cleave β-lactams. We compared the structure of this enzyme to those of an esterase of the same type without any lactamase ability, an esterase with moderate lactamase ability, and a class C β-lactamase with similar fold. Our results show that for these enzymes, the difference in the substrate specificity is sterically driven.