Adsorption and Separation of Aromatic Amino Acids from Aqueous Solutions Using Metal-Organic Frameworks

A Chiral COFs Membrane for Enantioselective Amino Acid Separation

Incorporating chiral molecules in the covalent organic frameworks (COFs) with uniformly ordered pores results in chiral COFs, which have been highly promising candidates for enantioseparation. Herein, a homochiral COF nanochannel membrane is reported by introducing chiral centers (L-phenylalanine methyl ester) into one of the organic ligands for the enantioseparation of chiral amino acids. The separation results show that the D-isomer is preferentially transported through the porous membrane channel. This composite membrane exhibits excellent selectivity for racemic phenylalanine with the highest enantiomeric excess value of up to 99.4 %. The adsorption and molecular modeling studies substantiate the experiment results by showing higher bonding affinity towards D-isomer over L-isomer. The excellent enantioselective gating performance unveils the porous COF skeleton with chiral selectors and the size-matching synergy for stereoselective interactions with chiral isomers.

Full-Color Emissive Zirconium-Organic Frameworks Constructed via in Situ "One-Pot" Single-Site Modification for Tryptophan Detection and Energy Transfer

Organic linker-based luminescent metal-organic frameworks (LMOFs) have received extensive studies due to the unlimited species of emissive organic linkers and tunable structure of MOFs. However, the multiple-step organic synthesis is always a great challenge for the development of LMOFs. As an alternative strategy, in situ "one-pot" strategy, in which the generation of emissive organic linkers and sequential construction of LMOFs happen in one reaction condition, can avoid time-consuming pre-synthesis of organic linkers. In the present work, we demonstrate the successful utilization of in situ "one-pot" strategy to construct a series of LMOFs via the single-site modification between the reaction of aldehydes and o-phenylenediamine-based tetratopic carboxylic acid. The resultant MOFs possess csq topology with emission covering blue to near-infrared. The nanosized LMOFs exhibit excellent sensitivity and selectivity for tryptophan detection. In addition, two component-based LMOFs can also be prepared via the in situ "one-pot" strategy and used to study energy transfer. This work not only reports the construction of LMOFs with full-color emissions, which can be utilized for various applications, but also indicates that in situ "one-pot" strategy indeed is a useful and powerful method to complement the traditional MOFs construction method for preparing porous materials with tunable functionalities and properties.

In Situ Preparation of Tannic Acid-Modified Poly(N-isopropylacrylamide) Hydrogel Coatings for Boosting Cell Response

The improvement of the capability of poly(N-isopropylacrylamide) (PNIPAAm) hydrogel coating in cell adhesion and detachment is critical to efficiently prepare cell sheets applied in cellular therapies and tissue engineering. To enhance cell response on the surface, the amine group-modified PNIPAAm (PNIPAAm-APTES) nanohydrogels were synthesized and deposited spontaneously on tannic acid (TA)-modified polyethylene (PE) plates. Subsequently, TA was introduced onto PNIPAAm-APTES nanohydrogels to fabricate coatings composed of TA-modified PNIPAAm-APTES (PNIPAAm-APTES-TA). Characterization techniques, including TEM, SEM, XPS, and UV-Vis spectroscopy, confirmed the effective deposition of hydrogels of PNIPAAm as well as the morphologies, content of chemical bonding-TA, and stability of various coatings. Importantly, the porous hydrogel coatings exhibited superhydrophilicity at 20 °C and thermo-responsive behavior. The fluorescence measurement demonstrated that the coating's stability effectively regulated protein behavior, influencing cell response. Notably, cell response tests revealed that even without precise control over the chain length/thickness of PNIPAAm during synthesis, the coatings enhanced cell adhesion and detachment, facilitating efficient cell culture. This work represented a novel and facile approach to preparing bioactive PNIPAAm for cell culture.

Enhancing Electrochemical Signal for Efficient Chiral Recognition by Encapsulating C60 Fullerene into Chiral Lanthanum-Based MOFs

Chiral metal-organic frameworks (MOFs) have attracted much attention due to their highly tunable regular microporous structures. However, chiral electrochemical recognition based on chiral MOFs is often limited by poor charge separation and slow charge transfer kinetics. In this case, C60 can be encapsulated into the cavity of [La(BTB)]n by virtue of host-guest interactions through π-π stacking to synthesize the chiral composite C60@[La(BTB)]n and amplify electrochemically controlled enantioselective interactions with the target enantiomers. A large electrostatic potential difference is generated in chiral C60@[La(BTB)]n due to the host-guest interaction and the inhomogeneity of the charge distribution, leading to the generation of a strong built-in electric field and thus an overall enhancement of the conductivity of the chiral material. Their enantioselective detection of tryptophan enantiomers was demonstrated by electrochemical measurement. The results showed that chiral MOF materials can be used for enantiomeric recognition. It is worth noting that this new material derived from the concept of host-guest interaction to enhance charge separation opens up unprecedented possibilities for future enantioselective recognition and separation.

Aqueous two-phase system based on pH-responsive polymeric deep eutectic solvent for efficient extraction of aromatic amino acids

Recently, more and more attention has been paid to the construction of stimulus-responsive aqueous two-phase systems (ATPSs) for the extraction and separation of various bioactive compounds. In this work, an ATPS based on a pH-responsive polymeric deep eutectic solvent (PDES) and phosphate salt was constructed for the first time. The pH-response properties of the PDES were studied through a series of experiments. Additionally, the phase formation mechanism was studied through experiments and simulations. This novel PDES-based ATPS was used to extract aromatic amino acids (AAAs). The extraction efficiencies for tyrosine (Tyr), phenylalanine (Phe), and tryptophan (Trp) reached 95.25%, 99.05%, and 99.10%, respectively. By adjusting pH, PDES was recycled and reused. This novel and recyclable PDES-based ATPS could be an efficient method for the extraction of AAAs, which could also be applied used as a versatile and sustainable method for the extraction of other bioactive compounds in the future.

Size- and Emission-Controlled Synthesis of Full-Color Luminescent Metal-Organic Frameworks for Tryptophan Detection

The development of nanoscaled luminescent metal-organic frameworks (nano-LMOFs) with organic linker-based emission to explore their applications in sensing, bioimaging and photocatalysis is of great interest as material size and emission wavelength both have remarkable influence on their performances. However, there is lack of platforms that can systematically tune the emission and size of nano-LMOFs with customized linker design. Herein two series of fcu- and csq-type nano-LMOFs, with precise size control in a broad range and emission colors from blue to near-infrared, were prepared using 2,1,3-benzothiadiazole and its derivative based ditopic- and tetratopic carboxylic acids as the emission sources. The modification of tetratopic carboxylic acids using OH and NH2 as the substituent groups not only induces significant emission bathochromic shift of the resultant MOFs, but also endows interesting features for their potential applications. As one example, we show that the non-substituted and NH2 -substituted nano-LMOFs exhibit turn-off and turn-on responses for highly selective and sensitive detection of tryptophan over other nineteen natural amino acids. This work sheds light on the rational construction of nano-LMOFs with specific emission behaviours and sizes, which will undoubtedly facilitate their applications in related areas.

Metal organic frameworks-in-nanochannels: A tailorable chromatography membrane for isolation of target protein

Metal-organic frameworks (MOFs) demonstrate strong potential in biosample separation. However, the obtained MOFs powders are unsuitable for recovery techniques in an aqueous solution, especially the challenges of withdrawing MOFs particles and expanding their functions for specific applications. Herein, a general strategy is designed utilizing metal oxide-nanochannel arrays as precursors and templates for in-situ selective growth of MOFs structures. The exemplary MOFs (Ni-bipy) with tailored composition are selectively grown in NiO/TiO₂ nanochannel membrane (NM) using NiO as the sacrificial precursor, which enables one to achieve a ∼262 times concentration of histidine-tagged proteins within 100 min. The significantly improved adsorption efficiency in a wide pH range and the effective enrichment from a complex matrix as a nanofilter illustrate the great potential of MOFs in nanochannels membranes for the high-efficiency recovery of essential proteins in complex biological samples. The porous self-aligned Ni-MOFs/TiO₂ NM exhibits biocompatibility and flexible functionalities, which is desirable for the generation of multifunctional nanofilter devices and developing biomacromolecule delivery vehicles.

A chiral metal-organic framework {(HQA)(ZnCl2)(2.5H2O)}n for the enantioseparation of chiral amino acids and drugs

Chiral metal-organic frameworks (CMOFs) with enantiomeric subunits have been employed in chiral chemistry. In this study, a CMOF formed from 6-methoxyl-(8S,9R)-cinchonan-9-ol-3-carboxylic acid (HQA) and ZnCl2, {(HQA)(ZnCl2)(2.5H2O)}n, was constructed as a chiral stationary phase (CSP) via an in situ fabrication approach and used for chiral amino acid and drug analyses for the first time. The {(HQA)(ZnCl2)(2.5H2O)}n nanocrystal and the corresponding chiral stationary phase were systematically characterised using a series of analytical techniques including scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, circular dichroism, X-ray photoelectron spectroscopy, thermogravimetric analysis, and Brunauer-Emmett-Teller surface area measurements. In open-tubular capillary electrochromatography (CEC), the novel chiral column exhibited strong and broad enantioselectivity toward a variety of chiral analytes, including 19 racemic dansyl amino acids and several model chiral drugs (both acidic and basic). The chiral CEC conditions were optimised, and the enantioseparation mechanisms are discussed. This study not only introduces a new high-efficiency member of the MOF-type CSP family but also demonstrates the potential of improving the enantioselectivities of traditional chiral recognition reagents by fully using the inherent characteristics of porous organic frameworks.

Two-Dimensional Metal-Organic Framework-Based Cellular Scaffolds with High Protein Adsorption, Retention, and Replenishment Capabilities

Metal-organic frameworks (MOFs) are porous materials with adsorption, storage, and separation capabilities due to their high specific surface areas and large pore volumes. MOFs are thus used in biomedical applications, and MOF nanoparticles have been widely studied as nanocarriers for drug delivery systems. Several research groups recently reported that specific MOF nanoparticles can adsorb and retain proteins, suggesting to us that MOF nanoparticles may have advantages as novel cell culture scaffolds. However, MOF nanoparticles cannot be used as two-dimensional scaffolds for cells. We therefore established a bottom-up technique to construct two-dimensional MOFs [MIL-53 (Al)] on polymer films. The developed two-dimensional MIL-53 (Al) film [fMIL-53 (Al)] exhibited high serum protein adsorption, retention, and replenishment capabilities as compared to conventional cell culture scaffolds. β-Galactosidase, used as a model protein, adsorbed on fMIL-53 (Al) exhibited original enzymatic activity, indicating that proteins are not denatured during the adsorption process. The viability of mouse myoblast cells (C2C12) cultured on fMIL-53 (Al) was 100%, indicating the cell compatibility of fMIL-53 (Al). Importantly, C2C12 cells cultured on serum protein-preadsorbed fMIL-53 (Al) exhibited excellent long-term adhesion, morphology, and proliferation even in a medium lacking serum proteins, demonstrating an important advantage of fMIL-53 (Al) as a cell culture scaffold, given that conventional cell culture scaffolds typically require a serum-containing medium to support stable cell adhesion and proliferation. To our knowledge, this is the first report regarding the application of MOFs as cell culture scaffolds and will serve as a starting point for studying two- and three-dimensional MOF-based cellular scaffolds for cell culture systems and for in vitro and in vivo tissue engineering.

[Advances in separation and analysis of aromatic amino acids in food]

Amino acids are important building blocks of proteins in the human body, which are involved in many metabolic pathways. Patients with metabolic diseases such as phenylketonuria, tyrosinemia, and hepatic encephalopathy are genetically defective and cannot metabolize aromatic amino acids (AAA) in food; hence, a regular diet may lead to permanent physiological damage. For this reason, it is necessary to restrict the intake of AAA in their daily diet by limiting natural protein intake, while ensuring normal intake of low protein foods and supplementation with low-AAA protein equivalents. Sources of low-AAA protein equivalents currently rely on free amino acid complex mixtures and low-AAA peptides (also known as high-Fischer-ratio peptides), which have better absorption availability and palatability. AAA separation and analysis techniques are essential for the preparation and detection of low-AAA peptides. Researchers in this field have explored a variety of efficient adsorption materials to selectively remove AAA from complex protein hydrolysates and thus prepare low-AAA peptide foods, or to establish analysis strategies for AAA. Covering more than 70 publications on AAA removal and separation in the last decade from Web of Science Core Collection and China National Knowledge Infrastructure, this review analyzes the structural characteristics and physicochemical properties of AAA, and summarizes the technological progress of AAA removal based on adsorbents such as activated carbon and resin. The applications of two-dimensional nanomaterials, molecular imprinting, cyclodextrins, and metal-organic frameworks in AAA adsorption and analysis from three dimensions, i. e., sample pretreatment, chiral separation and adsorption sensing, are also reviewed. The mainstream adsorbents for AAA removal, such as activated carbon, still suffer from poor specificity and cause environmental pollution during post-use treatment. Existing AAA separating materials show impressive selective adsorption capability in food samples and chiral mixtures as well as high sensitivity in adsorption sensing. The development of an efficient detection technology for AAA may help in detecting trace AAA in food and in evaluating chiral AAA adulteration in food samples. By exploring the advantages and disadvantages of each type of technology, we provide support for the advancement of the removal and analysis techniques for AAA.

Nanoarchitectonics of a MOF-in-Nanochannel (HKUST-1/TiO2) Membrane for Multitarget Selective Enrichment and Staged Recovery

Enrichment and separation of specific endogenous molecules are essential for disease diagnosis and the pharmaceutical industry. Although many solid sorbents have been developed for target molecule enrichment, simultaneous separation of multitargets is still a challenge for adsorbents. In this study, we develop a multitarget selective sorbent based on a nanochannel membrane prepared by the anodization of a Ti-Cu alloy. The in situ growth of a metal-organic framework (MOF, herein using Cu-based HKUST-1) in the nanochannels enables the resulting MOF-in-nanochannel membrane to act as a nanofilter. Benefitting from the size-exclusion effect of MOFs and the distinct surface characteristics of each component in the HKUST-1/TiO₂ nanochannels, the as-proposed membranes can be simply operated as a filter and exhibit satisfactory selectivities and enrichment capacities in the separation of aromatic amino acids, histidine-rich proteins, and phosphoproteins. More importantly, the adsorbed multitargets can be further controllably released from the membrane in a sequence via a staged recovery process. The use of this system is envisioned to provide an innovative and potential design for efficient sorption media for the selective enrichment and staged separation of specific biomolecules.

Type II porous ionic liquid based on metal-organic cages that enables L-tryptophan identification

Porous liquids with chemical separation properties are quite well-studied in general, but there is only a handful of reports in the context of identification and separation of non-gaseous molecules. Herein, we report a Type II porous ionic liquid composed of coordination cages that exhibits exceptional selectivity towards L-tryptophan (L-Trp) over other aromatic amino acids. A previously known class of anionic organic-inorganic hybrid doughnut-like cage (HD) is dissolved in trihexyltetradecylphosphonium chloride (THTP_Cl). The resulting liquid, HD/THTP_Cl, is thereby composed of common components, facile to prepare, and exhibit room temperature fluidity. The permanent porosity is manifested by the high-pressure isotherm for CH4 and modeling studies. With evidence from time-dependent amino acid uptake, competitive extraction studies and molecular dynamic simulations, HD/THTP_Cl exhibit better selectivity towards L-Trp than other solid state sorbents, and we attribute it to not only the intrinsic porosity of HD but also the host-guest interactions between HD and L-Trp. Specifically, each HD unit is filled with nearly 5 L-Trp molecules, which is higher than the L-Trp occupation in the structure unit of other benchmark metal-organic frameworks.

A novel approach for the preparation of core-shell MOF/polymer composites as mixed-mode stationary phase

The nickel organic framework capped with polyvinylpyrrolidone was prepared and synergistically immobilized onto porous silica surface as the mixed-mode stationary phase for high-performance liquid chromatography. Here, polyvinylpyrrolidone firstly was chosen as functional molecules to change morphology and size of the metal organic framework. The silica microspheres were then modified by them via a simple bonding method rather than in-situ growth method with the aid of electrostatic interaction commonly used before. The stationary phase showed flexible selectivity for separation of both hydrophilic and hydrophobic compounds, especially for hydrophilic compounds such as carbohydrates, alkaloids and sulfonamides etc. The chromatographic behaviors were evaluated by investigating various factors, and a typical mixed-mode retention feature of the column was observed. The composites could be prepared repetitively, and relative standard deviations of retention time of objective compounds among different batches were less than 1.75%. It also showed excellent chromatographic reproducibility, stability and potentiality for application in real samples. In short, the composites can be used for a feasible option for analysis of multiple compounds as the mixed-mode stationary phase and it provides a general approach for preparing MOFs-based composites by changing morphology and size of MOFs.

Anti-Tim4 Grafting Strongly Hydrophilic Metal-Organic Frameworks Immunoaffinity Flake for High-Efficiency Capture and Separation of Exosomes

Exosomes have become the most ideal analysis target for liquid biopsy since they carry a large amount of genetic materials. The study on exosomes has great significance for cancer diagnosis and prognosis. However, the extremely low concentration renders the development of a robust exosomes enrichment technique, with the merits of low nonspecific cell adhesion, high-capture efficiency, and easy nondestructive release of captured exosomes, of vital significance. We successfully designed and developed a novel Tim4@ILI-01 immunoaffinity flake material. First, a strongly hydrophilic ILI-01 MOFs matrix material was fabricated with cationic ionic liquid 1,3-bis(4-carboxybutyl)imidazolium bromide as the organic ligand. The nonspecific adsorption of the ILI-01 MOFs material was only 0.7% after two washings with a neutral buffer. Moreover, based on the inherent abundant carboxyl groups on the ILI-01 MOFs flake, they can be facilely functionalized with an anti-Tim4 antibody with the bonding efficiency of 82.4%. The capture efficiency of the developed Tim4@ILI-01 immunoaffinity material for exosomes reached 85.2%, which is 5.2 times higher than that via the gold standard ultracentrifugation method. Furthermore, based on the Ca²⁺-dependent characteristic of the binding between the Tim4@ILI-01 immunoaffinity material and phosphatidylserine (PS) on the surfaces of exosomes, the captured exosomes can be easily released with the addition of a chelating agent under neutral eluent conditions. Thus, the captured exosomes maintained good biological activity. The developed Tim4@ILI-01 immunoaffinity flake was successfully applied for enrichment of exosomes from serums of healthy persons and lung adenocarcinoma patients. The levels of the expressed CD44 gene significantly changed under different stages of lung adenocarcinoma cancer. All these results demonstrate that the Tim4@ILI-01 immunoaffinity flake is a robust enrichment material and has a good potential in practical clinical applications.

Polyethylenimine-functionalized polyacrylonitrile anion exchange fiber as a novel adsorbent for rapid removal of nitrate from wastewater

The development of an adsorbent with high adsorption ability and favorable cyclic regeneration performance for the removal of nitrate residues from wastewater is a task of vital importance. To this end, polyacrylonitrile fiber (PANF) was modified with polyethyleneimine (PEI), and alkyl groups were then introduced around the active amine groups to prepare three polymer-based anion exchange fibers (PAN-PEI-3C, PAN-PEI-5C, and PAN-PEI-8C). The novel fibers were characterized using techniques such as scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The adsorption isotherms of the fibers were best fitted by the Langmuir model, and PAN-PEI-5C exhibited a higher adsorption amount of nitrate (31.32 mg/g) than the other adsorbents. The equilibrium was reached expeditiously (within 10 min), and both pseudo-first-order and pseudo-second-order models could well describe the adsorption kinetics. More attractively, the saturated PAN-PEI-5C could be eluted using a low-concentration (0.3 M) NaCl solution, without any sharp loss of adsorption amount for five consecutive cycles in the presence of dissolved organic matter (DOM). Furthermore, PAN-PEI-5C could effectively adsorb low-concentration nitrate from real secondary effluents in a fixed-bed column experiment. Our work provides a promising and low-cost material for the removal of nitrate residues in practical applications.

Tailoring Activated Carbons for Efficient Downstream Processing: Selective Liquid-Phase Adsorption of Lysine

The essential amino acid lysine is of great importance in the nutrition and pharmaceutical industries and is mainly produced in biorefineries by the fermentation of glucose. In biorefineries, downstream processing is often the most energy-consuming step. Adsorption on hydrophobic adsorbents represents an energy, resource, and cost-saving alternative. The results reported herein provide insights into the selective separation of l-lysine from aqueous solution by liquid-phase adsorption using tailored activated carbons. A variety of commercial activated carbons with different textural properties and surface functionalities is investigated. Comprehensive adsorbent characterization establishes structure-adsorption relationships that define the major roles of the specific surface area and oxygen functionalities. A 13-fold increase of the separation of lysine and glucose is achieved through systematic modification of a selected activated carbon by oxidation, and lysine adsorption is enhanced by 30 %.

Hydrophobic Metal-Organic Frameworks: Assessment, Construction, and Diverse Applications

Tens of thousands of metal-organic frameworks (MOFs) have been developed in the past two decades, and only ≈100 of them have been demonstrated as porous and hydrophobic. These hydrophobic MOFs feature not only a rich structural variety, highly crystalline frameworks, and uniform micropores, but also a low affinity toward water and superior hydrolytic stability, which make them promising adsorbents for diverse applications, including humid CO2 capture, alcohol/water separation, pollutant removal from air or water, substrate-selective catalysis, energy storage, anticorrosion, and self-cleaning. Herein, the recent research advancements in hydrophobic MOFs are presented. The existing techniques for qualitatively or quantitatively assessing the hydrophobicity of MOFs are first introduced. The reported experimental methods for the preparation of hydrophobic MOFs are then categorized. The concept that hydrophobic MOFs normally synthesized from predesigned organic ligands can also be prepared by the postsynthetic modification of the internal pore surface and/or external crystal surface of hydrophilic or less hydrophobic MOFs is highlighted. Finally, an overview of the recent studies on hydrophobic MOFs for various applications is provided and suggests the high versatility of this unique class of materials for practical use as either adsorbents or nanomaterials.

Ligand Exchange in the Synthesis of Metal-Organic Frameworks Occurs Through Acid-Catalyzed Associative Substitution

The syntheses of metal-organic frameworks (MOFs) can be improved through modulated synthesis, synthesis employing precursors, and postsynthetic exchange (PSE) modifications, all of which share ligand exchange as a common and crucial reaction. To date, however, the mechanism of ligand exchange and the underlying principles governing it have remained elusive. Herein, we report energy landscapes for the ligand exchange processes of 1,4-benzenedicarboxylic acid and 2,3,5,6-tetrafluoro-1,4-benzenedicarboxylic acid with Zr₆O₄(OH)₄(OMc)₁₂ (OMc = methacrylate), as calculated using density functional theory (DFT). The rate-limiting step of ligand exchange follows an associative-substitution mechanism catalyzed by protons, consistent with previous kinetic data. Our calculations suggest that the acid catalysis is dependent on the relative basicities of the incoming and outgoing ligands coordinated in the complex, allowing molecular-level rationalization of many seminal MOF syntheses that had previously been interpreted macroscopically. Our results provide new insights for MOF synthesis and new clues for the rational de novo synthesis of MOFs.

Solid-phase extraction of phenoxyacetic acid herbicides in complex samples with a zirconium(IV)-based metal-organic framework

A zirconium(IV)-based metal-organic framework material (MOF-808) has been synthesized in a simple way and used for the extraction of phenoxyacetic acids in complex samples. The material has good thermal and chemical stability, large specific surface area (905.36 m²/g), and high pore size (22.18 Å). Besides, it contains a large amount of Zr-O groups, easy-to-form Zr-O-H bond with carboxyl groups of phenoxyacetic acids, and possesses biphenyl skeleton structure, easy to interact with compounds through π-π and hydrophobic interactions. These characteristics make the material very suitable for the extraction of certain compounds with a high extraction efficiency and excellent selectivity. The extraction conditions were optimized, and then an analytical method was successfully established and applied for analysis of actual samples. The solid-phase extraction method based on prepared material had a wide linear range of 0.2-250 μg/L and a low detection limit of 0.1-0.5 μg/L for four phenoxyacetic acid compounds including 2,4-dichlorophenoxyacetic acid, 2-(2,4-dichlorophenoxy) propionic acid, 4-chlorophenoxyacetic acid, and dicamba. The relative standard deviations of intra- and interday precision were 1.8-3.8 and 4.3-6.9%, and the recoveries after spiking were between 77.1 and 109.3%. The results showed that the material is a desired substituent for the extraction of compounds with benzene ring structure containing carboxyl groups.

Protein-Rich Biomass Waste as a Resource for Future Biorefineries: State of the Art, Challenges, and Opportunities

Protein-rich biomass provides a valuable feedstock for the chemical industry. This Review describes every process step in the value chain from protein waste to chemicals. The first part deals with the physicochemical extraction of proteins from biomass, hydrolytic degradation to peptides and amino acids, and separation of amino acid mixtures. The second part provides an overview of physical and (bio)chemical technologies for the production of polymers, commodity chemicals, pharmaceuticals, and other fine chemicals. This can be achieved by incorporation of oligopeptides into polymers, or by modification and defunctionalization of amino acids, for example, their reduction to amino alcohols, decarboxylation to amines, (cyclic) amides and nitriles, deamination to (di)carboxylic acids, and synthesis of fine chemicals and ionic liquids. Bio- and chemocatalytic approaches are compared in terms of scope, efficiency, and sustainability.

Core-Shell Metal-Organic Frameworks as the Mixed-Mode Stationary Phase for Hydrophilic Interaction/Reversed-Phase Chromatography

Stationary phases with mixed-mode mechanisms have emerged as a hot research topic. In the present research, monodisperse core-shell UiO-67@SiO₂ materials were prepared and further served as the packed column for mixed-mode hydrophilic interaction liquid chromatography/reversed-phase liquid chromatography. The developed UiO-67@SiO₂ materials were characterized via thermogravimetric analysis, scanning electron microscopy, X-ray Powder diffraction, and Fourier transform infrared techniques. The developed UiO-67@SiO₂ column shows flexible selectivity for separation of both hydrophobic (anilines, alkylbenzenes, and polycyclic aromatic hydrocarbons) and hydrophilic (thioureas) compounds. Furthermore, the UiO-67@SiO₂ column was also utilized to characterize potential pollutants in lake water samples. In summary, the UiO-67@SiO₂ column provided flexible selectivity and wide-range retention behaviors for both hydrophilic and hydrophobic analytes.

Improving the adsorption capacity for ovalbumin by functional modification of aminated mesoporous silica nanoparticles with tryptophan

Tryptophan (Trp) modified aminated mesoporous silica nanoparticles (AMSNs), shortened to Trp-AMSNs, are prepared via covalent binding. The obtained Trp-AMSNs exhibit a uniform size of ca. 83 nm, a mesopore diameter of ca. 2.6 nm, along with a pore volume of 0.439 cm³ g^-1. It is demonstrated that Trp-AMSNs selectively adsorb ovalbumin (Ova) from complex biological matrices. At pH 5.0, 1.0 mg of Trp-AMSNs produces an adsorption efficiency of 96% for 100 mg L^-1 Ova in 1.0 mL of solution. An adsorption capacity of 1240.3 mg g^-1 is derived for Ova, which is much improved with respect to that of the native AMSNs. The retained Ova could be readily recovered by a sodium dodecyl sulfate (SDS) solution (0.5%, m/v), providing a recovery of 71.2%. Trp-AMSNs are further applied for the isolation of Ova from a protein mixture (with a molar ratio of ovalbumin/lysozyme of 1 : 10) and an egg-white sample. High-purity Ova is obtained, as demonstrated by SDS-PAGE assay results.