Interaction of Different Metal Ions with Carboxylic Acid Group: A Quantitative Study

Reversible Ligand Detachment from CdSe Quantum Dots Following Photoexcitation

The nanocrystal-ligand boundaries of colloidal quantum dots (QDs) mediate charge and energy transfer processes that underpin photochemical and photocatalytic transformations at their surfaces. We used time-resolved infrared spectroscopy combined with transient electronic spectroscopy to probe vibrational modes of the carboxylate anchoring groups of stearate ligands attached to cadmium selenide (CdSe) QDs that were optically excited in solid nanocrystal films. The vibrational frequencies of surface-bonded carboxylate groups revealed their interactions with surface-localized holes in the excited states of the QDs. We also observed transient and reversible photoinduced ligand detachment from CdSe nanocrystals within their excited state lifetime. By probing both surface charge distributions and ligand dynamics on QDs in their excited states, we open a pathway to explore how the nanocrystal-ligand boundary can be understood and controlled for the design of QD architectures that most effectively drive charge transfer processes in solar energy harvesting and photoredox catalysis applications.

Understanding the release, migration, and risk of heavy metals in coal gangue: An approach by combining experimental and computational investigations

The lack of understanding on the environmental fate and implications of heavy metals in coal gangue (CG) has restrained its utilization. Conventional extraction methods provide empirical measures of heavy metal speciation, lacking a detailed description of bound strength, which limits long-term risk assessment. In this study, the releasing and migrating behavior of six heavy metals (Cd, As, Pb, Ni, Cu, and Cr) were investigated through an approach by combining experimental and computational investigations. The corresponding mechanisms and risks were understood and discussed on a molecular level. The results suggested that CG is primarily a natural kaolinite α-quartz and anatase mineral. The sequence extraction results showed that heavy metals in CG are mainly distributed in stable silicate and iron manganese oxide-bound states. The toxicity characteristic leaching procedure test advised Cu, Cr, Ni, and Pb had a high toxic level and thus required long-term monitoring and controlling. A quantum chemical calculation demonstrated that the heavy metals were more likely to be embedded in silicate minerals with high binding energy than those binding on the anatase surface. The findings of this research provide a promising approach to comprehensively evaluate the stability mechanism and potential long-term risks of heavy metals in solid waste.

Correlation of Elemental Transfer, Bioactive Compounds and Antioxidant Activity on Lactuca sativa L. Grown in Soil with Functionalized CNT and HMs

While heavy metals (HM) have been considered in recent decades to be the most common and problematic pollutants, the expansion of the list of pollutants due to the active use of carbon nanotubes (CNT) raises new questions about the benefit and harm of HM released to nature individually or fixed on CNT walls. A pot experiment was conducted to compare the effect of two classes of potential pollutants-metal salts of Pb, Mn, Cu, Zn, Cd, and Ni; and functionalized CNTs with COOH, MnO2, Fe3O4, and MnO2-Fe3O4-applied in soil, on the elemental transfer, the bioactive compounds accumulation, and the antioxidant activity in lettuce. While CNTs mainly increased the elemental transfer from soil to leaves, HM salts strongly obstructed it. In the presence of CNTs, the antioxidant activity in lettuce leaves correlated with the transfer of elements from soil to root and from root to leaves. The excess of HMs in soil induced a greater variation of the polyphenols quantity and antioxidant activity than the excess of CNTs. It might be assumed that lettuce perceived HMs as a more aggressive stressor than CNTs and more strongly activated the defense mechanism, showing the reduction of the element transfer and enhancing of total polyphenol production and antioxidant activity.

Mussel-Inspired Nanocellulose Coating for Selective Neodymium Recovery

Neodymium (Nd) is one of the most in-demand rare earth elements (REEs) for developing the next generation of magnetic medical devices and clean energy. Eco-friendly and sustainable nanotechnology for REE recovery may be highly suitable to address the limited global supply while minimizing the environmental footprints of current practice, such as solvent extraction. Here, we present a novel one-step mussel-inspired nanocellulose coating (MINC) using bifunctional hairy cellulose nanocrystals (BHCNC), bearing dialdehyde and dicarboxylate groups. The dialdehyde groups enable dopamine-mediated orthogonal conjugation of BHCNC to substrates, such as microparticles, while the high content of dicarboxylate groups yields high-capacity and selective Nd removal against ferric, calcium, and sodium ions. To the best of our knowledge, the MINC-treated substrate provides the most rapid selective removal and recovery of Nd ions even at low Nd concentrations with a capacity that is among the highest reported values. We envision that the MINC will provide new opportunities in developing next-generation bio-based materials and interfaces for the sustainable recovery of REEs and other precious elements.

Open Linear Polymer Host-Guest Interactions Sensed by Luminescent Silver Nanodots

The selectivity of the linear polymer chain toward its binding moieties has been considered negligible; thus, a clear demonstration showing the best-fit binding of a linear polymer to its guest counterpart is still unknown. Luminescent poly(acrylic acid) (PAA)-stabilized silver nanodots (PAA-AgNDs) have been applied as a turn-on sensor to monitor the interaction between the PAA chain and its binding cations. The binding of cations ions to the PAA chain may cross-link the linear PAA chain via coordination with carboxylate, which increases the rigidity of the polymer chain, retards the nonradiative decay of PAA-AgNDs, and consequently enhances the emission of silver nanodots while inducing a blue-shift of its emission spectrum. For the first time, we have demonstrated that a linear polymer chain can act as an open host to selectively bind to its best-matching cations. Specifically, among Group 2 cations (Mg2+, Ca2+, Sr2+, Ba2+), calcium ions show the strongest bonding to the PAA polymer chain. Our research suggests that, with extra rigidity, the polymer improves its chemical stability as calcium ions cross-linked the linear polymer. Meanwhile, it has also been demonstrated that luminescent silver nanodots can be excellent probes for the detection of polymer activities with straightforward and simple visualization methods.

Natural organic matter flocculation behavior controls lead phosphate particle aggregation by mono- and divalent cations

Phosphate addition is commonly applied to remediate lead contaminated sites via the formation of lead phosphate particles with low solubility. However, the effects of natural organic matter (NOM) with different properties, as well as the contributions of specific interactions (particle-particle, particle-NOM, and NOM-NOM) in enhanced stabilization or flocculation of the particles, are not currently well understood. This study investigates the influence of two aquatic NOM and two soil or coal humic acid (HA) extracts on the aggregation behavior of lead phosphate particles and explores the controlling mechanisms. All types of NOM induced disaggregation and steric stabilization of the particles in the presence of Na⁺ (100 mM) or low (1 mM) Ca²⁺ concentrations, as well as at low NOM concentrations (1 mg_C/L). However, for the soil and coal HA, a threshold at NOM concentrations of 10 mg_C/L and high (3 mM) Ca²⁺ concentrations was observed where bridging flocculation (rather than steric stabilization) occurred. In situ attenuated total reflectance - Fourier transform infrared characterization confirmed adsorption of the soil and coal humic acid extracts (10 mg_C/L) onto the surface of the lead phosphate particles in 3 mM Ca²⁺, whereas dynamic and static light scattering demonstrated extensive HA flocculation that dominated the overall scattered light intensities. These results imply that the accelerated aggregation was induced by a combination of HA adsorption and bridging flocculation by Ca²⁺. Overall, this research demonstrates that the type of NOM is critical to predict the colloidal stability of lead phosphate particles. Aquatic NOM stabilized the particles under all conditions evaluated, but soil or coal HA with higher molecular weight and aromaticity showed highly variable stabilization or flocculation behavior depending on the HA and Ca²⁺ concentrations available to adsorb to the particles and participate in bridging. These results provide new mechanistic insights on particle stabilization or destabilization by NOM.

l-Lysine Stabilized FeNi Nanoparticles for the Catalytic Reduction of Biomass-Derived Substrates in Water Using Magnetic Induction

The reduction of biomass-derived compounds gives access to valuable chemicals from renewable sources, circumventing the use of fossil feedstocks. Herein, we describe the use of iron-nickel magnetic nanoparticles for the reduction of biomass model compounds in aqueous media under magnetic induction. Nanoparticles with a hydrophobic ligand (FeNi₃ -PA, PA=palmitic acid) have been employed successfully, and their catalytic performance is intended to improve by ligand exchange with lysine (FeNi₃ -Lys and FeNi₃ @Ni-Lys NPs) to enhance water dispersibility. All three catalysts have been used to hydrogenate 5-hydroxymethylfurfural into 2,5-bis(hydroxymethyl)furan with complete selectivity and almost quantitative yields, using 3 bar of H₂ and a magnetic field of 65 mT in water. These catalysts have been recycled up to 10 times maintaining high conversions. Under the same conditions, levulinic acid has been hydrogenated to γ-valerolactone, and 4'-hydroxyacetophenone hydrodeoxygenated to 4-ethylphenol, with conversions up to 70 % using FeNi₃ -Lys, and selectivities above 85 % in both cases. This promising catalytic system improves biomass reduction sustainability by avoiding noble metals and expensive ligands, increasing energy efficiency via magnetic induction heating, using low H₂ pressure, and proving good reusability while working in an aqueous medium.

Surface charge regulation using classical density functional theory: the effect of divalent potential determining ions

The charge regulation approach has been used to describe the charge of surfaces susceptible to the presence of protons and other ions. Conventionally, this model is used with the Poisson-Boltzmann equation, which generally neglects the finite size of the ions and the electrostatic correlations. Recently, progress has been made by coupling charge regulation with classical density functional theory (DFT), which explicitly includes these correlations. However, little is known about charge regulation at surfaces with both acid-base equilibria and complexation with multivalent ions. The main purpose of this work is to investigate the role divalent ions play in charge regulation. Using DFT, we show that the size of the divalent ion has significant consequences on the surface charge density and it should not be neglected. For the surface reactions investigated, the larger the size of the divalent cation, the greater the charge on the surface due to higher divalent concentration there. At low divalent concentration, the ion correlations play a second-order but non-negligible role; using Poisson-Boltzmann theory with point ions cannot recover the DFT surface charge. At high concentrations, ion correlations play a dominant role by creating charge inversion.

Potentiometric MIP-Modified Screen-Printed Cell for Phenoxy Herbicides Detection

In this study, a molecularly imprinted polymer (MIP)-based screen-printed cell is developed for detecting phenoxy herbicides using 2-methyl-4-chlorophenoxyacetic acid (MCPA) as the template. MCPA is a phenoxy herbicide widely used since 1945 to control broadleaf weeds via growth regulation, primarily in pasture and cereal crops. The potentiometric cell consists of a silver/silver chloride pseudo-reference electrode and a graphite working electrode coated with a MIP film. The polymeric layer is thermally formed after drop-coating of a pre-polymeric mixture composed of the reagents at the following molar ratio: 1 MCPA: 15 MAA (methacrylic acid): 7 EGDMA (ethylene glycol dimethacrylate). After template removal, the recognition cavities function as the ionophore of a classical ion selective electrode (ISE) membrane. The detected ion is the deprotonated MCPA specie, negatively charged, so the measurements were performed in phosphate buffer at pH 5.5. A linear decrease of the potential with MCPA concentration, ranging from 4 × 10^-8 to 1 × 10^-6 mol L^-1, was obtained. The detection limit and the limit of quantification were, respectively, 10 nmol L^-1 and 40 nmol L^-1. A Nernstian slope of about -59 mV/dec was achieved. The method has precision and LOD required for MCPA determination in contaminated environmental samples.

Application of biochar for minewater remediation: Effect of scaling up production on performance under laboratory and field conditions

Metals discharged from abandoned mines are a major source of pollution in many parts of the world. As a result, there is a growing need for suitable low-cost remediation methods. While a large literature base exists demonstrating the efficacy of biochar to remove metals from solution, most studies are confined to the laboratory. This study examines the effects on the biochar quality when scaling up production from laboratory to pilot scale. Pilot scale biochars were produced using a 600 kg batch pyrolysis reactor, these chars were then deployed in the field using a series of 100 mm × 1200 mm cylindrical treatment cells installed at the point of discharge from an abandoned mine site. Most biochars produced at a pilot removed more zinc under laboratory conditions, however all of the biochars showed a reduced performance when tested in the field, this ranged from a 14% to an 85% reduction depending on the biochar.

Short-Chain Acid Additives to Control PbI2 Crystallization in Hybrid Perovskite Films

The quality and the performance of hybrid perovskite (HP)’s films strongly depend on the complete conversion into MAPbI3 of a spin-coated solution of methylammonium iodide (MAI) and PbI2. Highly crystalline PbI2 on a substrate limits such a conversion and, consequently, the HP’s solar cell performances. We investigate for the first time the use of short-chain organic acids as additives in a non-complexing solvent like γ-butyrolactone (GBL), that can retard retard the crystallization of PbI2. Based on XRD analyses of the spin coated films, the acetic acid is the most effective additive in retarding the PbI2 crystallization, making Pb2+ available for a subsequent reaction with MAI. These results open a new experimental path for fabricating perovskite films by single or sequential step methods involving acid additives.

State-of-the-Art Development in Liquid Crystal Biochemical Sensors

As an emerging stimuli-responsive material, liquid crystal (LC) has attracted great attentions beyond display applications, especially in the area of biochemical sensors. Its high sensitivity and fast response to various biological or chemical analytes make it possible to fabricate a simple, real-time, label-free, and cost-effective LC-based detection platform. Advancements have been achieved in the development of LC-based sensors, both in fundamental research and practical applications. This paper briefly reviews the state-of-the-art research on LC sensors in the biochemical field, from basic properties of LC material to the detection mechanisms of LC sensors that are categorized into LC-solid, LC–aqueous, and LC droplet platforms. In addition, various analytes detected by LCs are presented as a proof of the application value, including metal ions, nucleic acids, proteins, glucose, and some toxic chemical substances. Furthermore, a machine-learning-assisted LC sensing platform is realized to provide a foundation for device intelligence and automatization. It is believed that a portable, convenient, and user-friendly LC-based biochemical sensing device will be achieved in the future.

Chemodiversity, Biological Activities and Molecular Docking Studies of Leptadenia pyrotechnica (Forssk.) Decne: A Comprehensive Approach to Validate Its Medicinal Use

Leptadenia pyrotechnica (Forssk.) Decne is growing in Cholistan desert, and is known for its laxative, analgesic, anabolic and astringent, antioxidant, anti-inflammatory, antibacterial, antitumor, hypolipidemic and antiatherosclerotic properties. The present study disclosed the metabolic picture of L. pyrotechnica and validates its folk uses. LP-H fraction constitute 25.79±0.11 mgGAE/g extract and 20.64±0.33 mgRE/g extract of phenolic and flavonoid content, respectively, followed by LP-E (23.15±0.33 mgGAE/g extract and 19.40±0.13 mgRE/g extract), however, LP-E exhibited the highest free radical scavenging (DPPH: 21.05±0.45mgTE/g and ABTS: 68.12±0.53 mgTE/g) and metal reducing (FRAP: 44.93±1.66, CUPRAC: 117.42±1.28 mgTE/g, respectively) activities. The total antioxidant capacity in Phosphomolybdenum assay (1.52±0.14 mmolTE/g) and ferrous ion chelating (11.57±0.29 mgEDTAE/g) activities were observed highest for LP-H extract. In cholinesterase's inhibitory assays, the LP-E and LP-W extracts exhibited inhibitory values as 2.43 and 2.40±0.07 mgGALAE/g extract, respectively against AChE, while against BChE the LP-H displayed the highest value as 5.98±0.44 mgGALAE/g extract. The LP-H fraction also showed the highest inhibition potential (7.72±0.14 mmol ACAE/g and 0.55±0.01 mmol ACAE/g, respectively) against α-glucosidase and α-amylase enzymes, while, in tyrosinase inhibitory assay, all the fractions exhibited significant activities in the range of 59.35±0.29 to 55.18±0.49 mgKAE/g extract. RP-UHPLC/MS analysis of LP-M disclosed the presence of 57 metabolites of various classes. A multivariate analysis and molecular docking study was also carried out to establish relationships between the metabolites and the biological activities, which finally validate the use of L. pyrotechnica as herbal medicine or component nutraceutical, food and cosmetic industry.

Mechanistic insight into selective adsorption and easy regeneration of carboxyl-functionalized MOFs towards heavy metals

The development of heavy metal adsorbents with high selectivity has become a research hotspot due to the interference of coexisting ions (e.g., Na⁺, Ca²⁺) in the actual wastewater, but the more difficult regeneration caused by high adsorption selectivity severely limits its practical applications. Herein, a carboxyl adsorbent, MIL-121, demonstrated high adsorption selectivity for heavy metals at 10,000 mg/L of Na⁺ (removal > 99% for Cu²⁺) as well as unexpected easy regeneration (desorption > 99%) at low H⁺ concentration (10^-3.5-10^-3.0 M), which is hundreds of times lower than that of ever reported selective adsorbents (> 10^-1 M H⁺). X-ray photoelectron spectrometry (XPS), extended X-ray absorption fine structure (EXAFS) coupled with Density functional theory (DFT) simulation unveil that the -COOH groups in MIL-121 for heavy metals adsorption is specific inner-sphere coordination with higher binding energy (1.31 eV for Cu), and less energy required for regeneration (0.26 eV for H). Similar high selectivity and easy regeneration were also satisfied with other heavy metals (e.g., Pb²⁺, Ni²⁺), and removal of heavy metals remained > 99% in 10 consecutive adsorption-desorption cycles. For actual copper electroplating wastewater treatment, MIL-121 could produce ~ 3600 mL clean water/g sample, outperforming 300 mL that of the benchmark commercial adsorbent D-113. This study shows the potential of MIL-121 for heavy metal wastewater treatment and provides mechanistic insight for developing adsorbents with high selective adsorption and easy regeneration.

How Polytetrafluoroethylene Lubricates Iron: An Atomistic View by Reactive Molecular Dynamics

The tribochemistry and transfer film formation at the metal/polymer interface plays an essential role in surface protection, wear reduction, and lubrication. Although the topic has been studied for decades, challenges persist in clarifying the nanoscale mechanism and dynamic evolution of tribochemical reactions. To investigate the tribochemistry between iron and polytetrafluoroethylene (PTFE) in ambient and cryogenic environments, we have trained and expanded a ReaxFF reactive force field to describe iron-oxygen-water-PTFE systems (C/H/O/F/Fe). Using ReaxFF molecular dynamics simulations, we find that mechanical shearing of single asperity induced the degradation of PTFE molecules and radicals, showing subsequent oxidation and hydroxylation reactions of the radicals initiated by C-C bond cleavage, in agreement with previous experimental observations. Furthermore, we studied mechanisms of interfacial tribochemical reactions and formation of transfer films. We found that tribochemical wear and Fe-C and Fe-F bonding networks are important mechanisms for anchoring molecular chains to form a transfer film on the iron countersurface. Hydroxyl groups can dehydrogenate to form short and strong chelation bonds with the Fe₂O₃ countersurface. A friction-induced oriented molecular layer plays a key role in reducing friction, which is responsible for the excellent lubrication property. By varying temperatures in the range of 10-300 K, we found a nonmonotonic change in friction with a maxima at 100 K. At cryogenic temperatures, the molecular mobility was obviously suppressed, while the chain rigidity was enhanced, resulting in the less oriented interface and brittle-like shear interface, which is responsible for nonmonotonic friction. This work elucidates mechanisms of tribochemical reactions and transfer film formation between iron and PTFE at the atomistic level, facilitating design and development of self-lubricating materials, especially under harsh conditions.

Natural Acidic Polysaccharide-Based Memristors for Transient Electronics: Highly Controllable Quantized Conductance for Integrated Memory and Nonvolatile Logic Applications

As a leading candidate for further memory and computing applications, memristors are being developed in an important direction of transient electronics. Herein, wafer-scale acidic polysaccharide thin films are reported as promising materials for memristors with remarkable transient characteristics. The memristor shows freestanding and lightweight features, and can be fully dissolved in deionized water within 3.5 s. More importantly, the ion-confinement capability of acidic polysaccharides where the cations can interact with the ionizable acid groups enables atomic manipulation of conductive filament. As a result, (i) a single device can produce 16 highly controllable and independent quantized conductance (QC) states with quasi-nonvolatile and nonvolatile characteristics and (ii) QC switching can be performed with ultrafast speed (2-5 ns) and low energy consumption (0.6-16 pJ). These remarkable features make the memristor promising for fast, low-power, and high-density memory and computing applications. Based on QC switching, the encoding/decoding and nonvolatile basic Boolean logic are designed and implemented. More importantly, "stateful" material implication logic which is promising for future in-memory computing is demonstrated with QC switching. These results significantly advance acidic polysaccharides to develop nanodevices with quantum effects.

Hydration and Charge-Transfer Effects of Alkaline Earth Metal Ions Binding to a Carboxylate Anion, Phosphate Anion, and Guanine Nucleobase

To investigate the ability of alkaline earth metal ions to tune ion-mediated DNA adsorption, hydrated Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ ions bound to a carboxylate anion, phosphate anion, and guanine nucleobase were modeled using density functional theory (DFT) and a combined explicit and continuum solvent model. The large first solvation shell of Ba²⁺ requires a larger solute cavity defined by a solvent-accessible surface, which is used to model all hydrated ions. Alkaline earth metal ions bind indirectly or directly to each binding site. DFT binding energies decrease with increasing ion size, which is likely due to ion size and hydration structure, rather than quantum effects such as charge transfer. However, charge transfer explains weaker ion binding to guanine compared to phosphate or carboxylate. Overall, carboxylate and phosphate anions are expected to compete equally for hydrated Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ ions and larger alkaline earth metal ions may induce weaker ion-mediated adsorption. The ion size and hydration structure of alkaline earth metal ions may effectively tune ion-mediated adsorption processes, such as DNA adsorption to functionalized surfaces.

Hierarchical Self-Assembly of Amphiphilic β-C-Glycosylbarbiturates into Multiresponsive Alginate-Like Supramolecular Hydrogel Fibers and Vesicle Hydrogel

Ordered molecular self-assembly of glycoamphiphiles has been regarded as an attractive, practical and bottom-up approach to obtain stable, structurally well-defined, and functional mimics of natural polysaccharides. This study describes a versatile and rational design of carbohydrate-based hydrogelators through N,N'-substituted barbituric acid-mediated Knoevenagel condensation onto unprotected carbohydrates in water. Amphiphilic N-substituted β-C-maltosylbarbiturates self-assembled into pH- and calcium-triggered alginate-like supramolecular hydrogel fibers with a multistimuli responsiveness to temperature, pH and competitive metal chelating agent. In addition, amphiphilic N,N'-disubstituted β-C-maltosylbarbiturates formed vesicle gels in pure water that were scarcely observed for glyco-hydrogelators. Finally, barbituric acid worked as a multitasking group allowing chemoselective ligation onto reducing-end carbohydrates, structural diversity, stimuli-sensitiveness, and supramolecular interactions by hydrogen bonding.

Relating natural organic matter conformation, metal complexation, and photophysics

We investigated the relationship between changes in fluorescence intensity and in fluorescence anisotropy for Suwannee River Natural Organic Matter (SRNOM) due to the formation of NOM-metal complexes with divalent and trivalent metals commonly present in both fresh water and sea water environments. We chose metal ions whose complexes give rise to both fluorescence quenching (Fe3+, Cu2+) and fluorescence enhancement (Al3+, Mg2+). Stern–Volmer type analyses quantified the changes in the SRNOM fluorescence as a function of metal concentration. All metals display strong complexation with SRNOM, associated with their effect on fluorescence. Experiments with Fe3+ further show strong effects due to NOM aggregation at all but the lowest metal concentrations studied here. There was little to no change in the conformation of SRNOM as inferred from fluorescence anisotropy caused by increasing metal concentration. These results suggest that there is no correlation between photophysical changes and conformational changes in NOM associated with complexation by the metal ions.

Tunable, conductive, self-healing, adhesive and injectable hydrogels for bioelectronics and tissue regeneration applications

Conductive hydrogels are attracting considerable interest in view of their potential in a wide range of applications that include healthcare and electronics. Such hydrogels are generally incorporated with conductive materials/polymers. Herein, we present a series of conductive hydrogels (Ch-CMC-PDA), prepared with no additional conductive material. The hydrogels were synthesized using a combination of chitosan, cellulose (CMC) and dopamine (DA). The conductivity (0.01-3.4 × 10^-3 S cm^-1) in these gels is attributed to ionic conductivity. Very few conductive hydrogels are endowed with additional properties like injectability, adhesiveness and self-healing, which would help to widen their scope for applications. While the dynamic Schiff base coupling in our hydrogels facilitated self-healing and injectable properties, polydopamine imparted tissue adhesiveness. The porosity, rheological, mechanical and conductive properties of the hydrogels are regulated by the CMC-dialdehyde-polydopamine (CMC-D-PDA) content. The hydrogel was evaluated in various bioelectronics applications like ECG monitoring and triboelectric nanogenerators (TENG). The ability of the hydrogel to support cell growth and serve as a template for tissue regeneration was confirmed using in vitro and in vivo studies. In summary, the integration of such remarkable features in the ionic-conductive hydrogel would enable its usage in bioelectronics and biomedical applications.

Stimuli-Responsive, Hydrolyzable Poly(Vinyl Laurate-co-vinyl Acetate) Nanoparticle Platform for In Situ Release of Surfactants

A stimuli-responsive, sub-100 nm nanoparticle (NP) platform with a hydrolyzable ester side chain for in situ generation of surfactants is demonstrated. The NPs were synthesized via copolymerization of vinyl-laurate and vinyl-acetate [p-(VL-co-VA), 3:1 molar ratio] and stabilized with a protective poly(ethylene-glycol) shell. The NPs are ∼55 nm in diameter with a zeta potential of -54 mV. Hydrolysis kinetics in an accelerated, base-catalyzed reaction show release of about 11 and 30% of the available surfactant at 25 and 80 °C, respectively. The corresponding values in seawater are 22 and 76%. The efficiency of the released surfactant in reducing the interfacial tension, altering wettability, and stabilizing oil-water emulsion was investigated through contact angle measurements and laser confocal scanning microscopy and benchmarked to sodium laurate, a commercially available surfactant. All these measurements demonstrate both the efficacy of the NP system for surfactant delivery and the ability of the released surfactant to alter wettability and stabilize an oil-water emulsion.

Role of surface functional groups of hydrogels in metal adsorption: From performance to mechanism

Hydrogels have been studied quite intensively in recent decades regarding whether their metal adsorption abilities may be modified or even enhanced via functionalization (i.e., functionalizing the surfaces of hydrogels with specific functional groups). Studies have found that functionalizing hydrogels can in fact give them higher adsorptive power. This enhanced adsorptive performance is articulated in this paper through critically reviewing more than 120 research articles in such terms as the various techniques of synthesizing functionalized hydrogels, the roles that specific functional groups play on adsorption performance, selectivity, reusability, as well as on adsorption mechanism. Moreover, this critical review offers insight into future designs of functionalized hydrogels with specific metal adsorption capabilities.

Designable Carboxymethylpachymaran/Metal Ion Architecture on Sunflower Sporopollenin Exine Capsules as Delivery Vehicles for Bioactive Macromolecules

There are multiple obstacles in the gastrointestinal tract (GIT) for oral administration of bioactive macromolecules. Here, we engineered an oral delivery vehicle (sporopollenin exine capsules with carboxymethylpachymaran (CMP)/metal ion modification) with targeted release based on food-grade ingredients and processing operations. Then, the interaction and binding mechanisms between CMP and metal ions in the vehicle were investigated. By using β-galactosidase (β-Gal) as a model protein, the systems were characterized for the surface morphology and monitored by the in vitro release profile of β-Gal. Notably, the CMP/metal ion systems not only markedly decreased the CMP dosage but also achieved a valid long-term release compared with the previously reported CMP system. Among all the systems, the CMP/3% AlCl₃ system showed the best ability to control the release with the maximum residual activity of β-Gal at nearly 72% after 24 h of treatment. Subsequently, the interaction mechanism between CMP and metal ions within the system was characterized by the perspectives of microstructure, rheological properties, and spectroscopy characteristics. The results indicated that the low pH conditions are conducive to the further cross-linking of CMP and metal ions, resulting in a high gel strength and thus a dense structure, which can impact the controlled release of β-Gal in the GIT. Overall, the system may be utilized in the administration of medical and functional foods, specifically for the delivery of bioactive proteins via the oral route.

Optical Multisensor Array with Functionalized Photonic Droplets by an Interpenetrating Polymer Network for Human Blood Analysis

Photonic solid-state cholesteric liquid crystal (CLC_solid) droplets intertwined with a poly(acrylic acid) (PAA) network that has an interpenetrating polymer network (IPN) structure (referred to as photonic IPN CLC_solid-PAA droplets) were used as individual sensors in the dots of a PAA-patterned array film after functionalization via immobilization of the receptors and a metal-ion treatment. The photonic IPN CLC_solid-PAA droplets in the PAA-patterned array film were pH-responsive and showed an observable change in the reflected central color. This "smart" property, coupled with the photonic color response, makes these devices ideal photonic sensors. The immobilization of urease and phenylboronic acid on the PAA network allowed for the application of several 10 μm photonic IPN CLC_solid-PAA droplets to the optical photonic biosensors through facilitated volumetric changes in the PAA network in response to urea and glucose analytes, with high selectivity for major components in human serum, acceptable sensitivity for use with human serum, and extreme stability due to a solid-state structure. The blueshift of the reflected color of the KOH-treated photonic IPN CLC_solid-PAA droplets could be used for divalent metal-ion detection. The compartmentalized photonic IPN CLC_solid-PAA droplets in the patterned array film could be used for multiple detection applications, as evidenced by the ability to conduct pH, divalent metal ion, urea, and glucose detections in one patterned array film. This new platform opens the door for many interesting applications with numerous combinations of responsive hydrogel matrices and receptors.

Collation Efficiency of Poly(Vinyl Alcohol) and Alginate Membranes with Iron-Based Magnetic Organic/Inorganic Fillers in Pervaporative Dehydration of Ethanol

Hybrid poly(vinyl alcohol) and alginate membranes were investigated in the process of ethanol dehydration by pervaporation. As a filler, three types of particles containing iron element, i.e., hematite, magnetite, and iron(III) acetyloacetonate were used. The parameters describing transport properties and effectiveness of investigated membranes were evaluated. Additionally, the physico-chemical properties of the resulting membranes were studied. The influence of polymer matrix, choice of iron particles and their content in terms of effectiveness of membranes in the process of ethanol dehydration were considered. The results showed that hybrid alginate membranes were characterized by a better separation factor, while poly(vinyl alcohol) membranes by a better flux. The best parameters were obtained for membranes filled with 7 wt% of iron(III) acetyloacetonate. The separation factor and pervaporative separation index were equal to 19.69 and 15,998 g⋅m⁻²⋅h⁻¹ for alginate membrane and 11.75 and 14,878 g⋅m⁻²⋅h⁻¹ for poly(vinyl alcohol) membrane, respectively.

Supramolecular Biocomposite Hydrogels Formed by Cellulose and Host-Guest Polymers Assisted by Calcium Ion Complexes

Hydrogels are biocompatible polymer networks; however, they have the disadvantage of having poor mechanical properties. Herein, the mechanical properties of host-guest hydrogels were increased by adding a filler and incorporating other noncovalent interactions. Cellulose was added as a filler to the hydrogels to afford a composite. Citric acid-modified cellulose (CAC) with many carboxyl groups was used instead of conventional cellulose. The preparation began with mixing an acrylamide-based αCD host polymer (p-αCD) and a dodecanoic acid guest polymer (p-AADA) to form supramolecular hydrogels (p-αCD/p-AADA). However, when CAC was directly added to p-αCD/p-AADA to form biocomposite hydrogels (p-αCD/p-AADA/CAC), it showed weaker mechanical properties than p-αCD/p-AADA itself. This was caused by the strong intramolecular hydrogen bonding (H-bonding) within the CAC, which prevented the CAC reinforcing p-αCD/p-AADA in p-αCD/p-AADA/CAC. Then, calcium chloride solution (CaCl₂) was used to form calcium ion (Ca²⁺) complexes between the CAC and p-αCD/p-AADA. This approach successfully created supramolecular biocomposite hydrogels assisted by Ca²⁺ complexes (p-αCD/p-AADA/CAC/Ca²⁺) with improved mechanical properties relative to p-αCD/p-AADA hydrogels; the toughness was increased 6-fold, from 1 to 6 MJ/m³. The mechanical properties were improved because of the disruption of the intramolecular H-bonding within the CAC by Ca²⁺ and subsequent complex formation between the carboxyl groups of CAC and p-AADA. This mechanism is a new approach for improving the mechanical properties of hydrogels that can be broadly applied as biomaterials.

Self-assembling two-dimensional nanophotonic arrays for reflectivity-based sensing

We propose a nanoplasmonic platform that can be used for sensing trace levels of heavy metals in solutions via simple optical reflectivity measurements. The considered example is a lead sensor, which relies on the lead-mediated assembly of glutathione-functionalized gold nanoparticles (NPs) at a self-healing water/DCE liquid | liquid interface (LLI). Capillary forces tend to trap each NP at the LLI while the negatively charged ligands prevent the NPs settling too close to each other. In the presence of lead, due to chelation between the lead ion and glutathione ligand, the NPs assemble into a dense quasi-2D interfacial array. Such a dense assembly of plasmonic NPs can generate a remarkable broad-band reflectance signal, which is absent when NPs are adsorbed at the interface far apart from each other. The condensing effect of the LLI and the plasmonic coupling effect among the NP array gives rise to a dramatic enhancement of the reflectivity signals. Importantly, we show that our theory of the optical reflectivity from such an array of NPs works in perfect harmony with the physics and chemistry of the system with the key parameter being the interparticle distance at the interface. As a lead sensor, the system is fast, stable, and can achieve detection limits down to 14 ppb. Future alternative recognizing ligands can be used to build sister platforms for detecting other heavy metals.

We propose a nanoplasmonic platform that can be used for sensing trace levels of heavy metals in solutions via simple optical reflectivity measurements at the liquid–liquid interface.

Programmed antibacterial and mineralization therapy for dental caries based on zinc-substituted hydroxyapatite/ alendronate-grafted polyacrylic acid hybrid material

The domination of cariogenic bacteria in dental plaque biofilms is the primary cause of dental caries. In view of this, for the purpose of an effective treatment of dental caries, it is of great importance to inhibit the activity of acidogenic bacteria and promote the remineralization of damaged teeth simultaneously. However, the expensive antibacterial agents and poor mineralization ability of materials limit the practical applications. Biomineralization regulated by non-collagenous proteins (NCPs) gives hints to combine the remineralization ability of NCPs with accessible antibacterial property effectively. In this work, we propose a programmed antibacterial and remineralization strategy for the therapy of dental caries based on zinc-substituted hydroxyapatite/ alendronate-grafted polyacrylic acid hybrid nanoneedles (ZHA@ALN-PAA). This hybrid material dissolves in the acidic caries environment and regulate the pH to nearly neutral (6.5). Abundant calcium/ phosphate ions are supplemented and the ALN-PAA embedded in it has also been released, which assists the biomineralization on tooth defect. It has been revealed that the inhibition ratio of ZHA@ALN-PAA against Streptococcus mutans is the highest (11.25 folds that of HA), which originates from the highest zinc ions released (132.9 mg/L). Besides, the interspace of etched enamel is fully filled with regenerated nanorods and the surface microhardness (SMH) is significantly improved (3.68 folds that of etched enamel) after only 3 days of mineralization in vitro. This strategy developed here is simple and cost-effective, which can be referred to design the effective anti-caries materials applied for clinic treatment and daily oral care.

Neurosporaxanthin Overproduction by Fusarium fujikuroi and Evaluation of Its Antioxidant Properties

Neurosporaxanthin (NX) is a carboxylic carotenoid produced by some filamentous fungi, including species of the genera Neurospora and Fusarium. NX biosynthetic genes and their regulation have been thoroughly investigated in Fusarium fujikuroi, an industrial fungus used for gibberellin production. In this species, carotenoid-overproducing mutants, affected in the regulatory gene carS, exhibit an upregulated expression of the NX pathway. Based on former data on a stimulatory effect of nitrogen starvation on carotenoid biosynthesis, we developed culture conditions with carS mutants allowing the production of deep-pigmented mycelia. With this method, we obtained samples with ca. 8 mg NX/g dry mass, in turn the highest concentration for this carotenoid described so far. NX-rich extracts obtained from these samples were used in parallel with carS-complemented NX-poor extracts obtained under the same conditions, to check the antioxidant properties of this carotenoid in in vitro assays. NX-rich extracts exhibited higher antioxidant capacity than NX-poor extracts, either when considering their quenching activity against [O2(1g)] in organic solvent (singlet oxygen absorption capacity (SOAC) assays) or their scavenging activity against different free radicals in aqueous solution and in liposomes. These results make NX a promising carotenoid as a possible feed or food additive, and encourage further studies on its chemical properties.

Recent Trends in Controlling the Enzymatic Browning of Fruit and Vegetable Products

Enzymatic browning because of polyphenol oxidases (PPOs) contributes to the color quality of fruit and vegetable (FV) products. Physical and chemical methods have been developed to inhibit the activity of PPOs, and several synthetic chemical compounds are commonly being used as PPO inhibitors in FV products. Recently, there has been an emphasis on consumer-oriented innovations in the food industry. Consumers tend to urge the use of natural and environment-friendly PPO inhibitors. The purpose of this review is to summarize the mechanisms underlying the anti-browning action of chemical PPO inhibitors and current trends in the research on these inhibitors. Based on their mechanisms of action, chemical inhibitors can be categorized as antioxidants, reducing agents, chelating agents, acidulants, and/or mixed-type PPO inhibitors. Here, we focused on the food ingredients, dietary components, food by-products, and waste associated with anti-browning activity.

In Situ Ni2+ Stain for Liposome Imaging by Liquid-Cell Transmission Electron Microscopy

Solvated soft matter, both biological and synthetic, can now be imaged in liquids using liquid-cell transmission electron microscopy (LCTEM). However, such systems are usually composed solely of organic molecules (low Z elements) producing low contrast in TEM, especially within thick liquid films. We aimed to visualize liposomes by LCTEM rather than requiring cryogenic TEM (cryoTEM). This is achieved here by imaging in the presence of aqueous metal salt solutions. The increase in scattering cross-section by the cation gives a staining effect that develops in situ, which could be captured by real space TEM and verified by in situ energy dispersive x-ray spectroscopy (EDS). We identified beam-induced staining as a time-dependent process that enhances contrast to otherwise low contrast materials. We describe the development of this imaging method and identify conditions leading to exceptionally low electron doses for morphology visualization of unilamellar vesicles before beam-induced damage propagates.

Nanocrystals of Lead Chalcohalides: A Series of Kinetically Trapped Metastable Nanostructures

We report the colloidal synthesis of a series of surfactant-stabilized lead chalcohalide nanocrystals. Our work is mainly focused on Pb4S3Br2, a chalcohalide phase unknown to date that does not belong to the ambient-pressure PbS-PbBr2 phase diagram. The Pb4S3Br2 nanocrystals herein feature a remarkably narrow size distribution (with a size dispersion as low as 5%), a good size tunability (from 7 to ∼30 nm), an indirect bandgap, photoconductivity (responsivity = 4 ± 1 mA/W), and stability for months in air. A crystal structure is proposed for this new material by combining the information from 3D electron diffraction and electron tomography of a single nanocrystal, X-ray powder diffraction, and density functional theory calculations. Such a structure is closely related to that of the recently discovered high-pressure chalcohalide Pb4S3I2 phase, and indeed we were able to extend our synthesis scheme to Pb4S3I2 colloidal nanocrystals, whose structure matches the one that has been published for the bulk. Finally, we could also prepare nanocrystals of Pb3S2Cl2, which proved to be a structural analogue of the recently reported bulk Pb3Se2Br2 phase. It is remarkable that one high-pressure structure (for Pb4S3I2) and two metastable structures that had not yet been reported (for Pb4S3Br2 and Pb3S2Cl2) can be prepared on the nanoscale by wet-chemical approaches. This highlights the important role of colloidal chemistry in the discovery of new materials and motivates further exploration into metal chalcohalide nanocrystals.

Co-functionalization with phosphate and carboxylate on polydiacetylene for colorimetric detection of calcium ions in serum

In this study, co-functionalization with phosphate and carboxylate on polydiacetylene (PDA) was proposed to detect calcium ions in serum, inspired by biologically abundant phosphate-calcium ion and carboxylate-calcium ion binding. The cooperative interaction of calcium ions with phosphate and carboxylate in PDA induced the change of electronic properties in the backbone without aggregation of liposomes, accompanied by blue-to-purple color transition. The cooperative effect through the introduction of mixed ligands facilitated the selective detection of calcium ions over magnesium ions, which was a source of major interference in many calcium ion probes, and in the presence of major serum metal ions. The sensor system exhibited highly sensitive detection of calcium ions with an estimated limit of detection of 0.97 μM. In addition, the detection method was employed to determine the concentration of calcium ions in various serums.

DBU-Catalyzed One-Pot Synthesis of Nearly Any Metal Salt of Fatty Acid (M-FA): A Library of Metal Precursors to Semiconductor Nanocrystal Synthesis

The metal salts of fatty acid (M-FA) are the most widely used metal precursors to colloidal semiconductor nanocrystals (NCs). They play a key role in controlling the composition, shape, and size of semiconductor NCs, and their purity is essential for attaining impeccable batch-to-batch reproducibility in the optical and electrical properties of the NCs. Herein, we report a novel, one-pot synthesis of a library of highly pure M-FAs at near-quantitative yields (up to 91%) using 1,8-diazabicyclo[5.4.0]undec-7-ene or the related nonionic/noncoordinating base as an inexpensive and ecofriendly catalyst in a green solvent medium. The method is highly general and scalable with vast academic and industrial potential. As a practical application, we also demonstrate the use of these high-quality M-FAs in the synthesis of the spectrum of colloidal semiconductor NCs (III-V, II-VI, IV-VI, I-VI, I-III-VI, and perovskite) having absorption/emission in visible to the near-infrared region.