Accessible Amino Research Articles

Revealing the correlation between the performance of silica-based DAC adsorbents and their pore natures

Direct air capture (DAC) technology is a potential carbon negative process, which can effectively reduce the emission of carbon dioxide (CO2) in the atmosphere. Amine-functionalized porous materials are promising because of their high ratio of accessible amino groups and fast adsorption/desorption kinetics. This work reveals the correlation between the specific surface area, pore radius, and pore volume of the silica-based DAC adsorbents and their CO2 adsorption capacity and adsorption rate. Four typical silica-based DAC adsorbent materials loaded with polyethylenimine (PEI) were studied, including hydrophilic fumed silica (HFS), Santa Barbara Amorphous-15 (SBA-15), Mobil Crystalline Materials-41 (MCM-41), and silica gel (SG). It is observed that when the PEI loading is constant, adsorbent materials with larger specific surface area, larger pore radius, and larger pore volume tend to show the higher adsorption capacity and faster adsorption-desorption rate. Humidity is beneficial for the CO2 capture capacity, but it slows down the CO2 uptake rate at the same time. The capacity of 50%PEI@SBA-15 adsorbent can reach to 3.24 mmol/g under 90% relative humidity (RH). Supports with small pore radius tend to have unfavorable performance at dry conditions. After the inlet gas is humidified, the CO2 capacity of the MCM-41 material is enhanced greatly, from 0.91 mmol/g to 2.92 mmol/g. This work provides guiding principle for synthesizing appropriate adsorbents with higher DAC capacity, higher adsorption and desorption rate at ambient conditions.

Antimicrobial Active Chitosan-Based Cotton Yarns: Effect of Chitosan Solution Concentration

Using the exhaustion-pad-dry-rinse method, chitosan was applied to alkaline-scoured and bleached cotton yarns in a solution with concentrations ranging from 0.2–1% to achieve good antimicrobial activity against the bacteria Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive). Studied samples were also assessed by measuring the amount of introduced chitosan, amount of accessible amino groups, mechanical properties, whiteness index and the b* colour coordinate. Alkaline-scoured and bleached cotton yarns treated with all concentrations of the chitosan solution showed good antimicrobial activity against Escherichia coli and Staphylococcus aureus. Better antimicrobial activity was achieved against Escherichia coli. Increasing the concentration of chitosan solution deteriorated the mechanical properties of chitosan-treated cotton yarns. The optimal concentration of chitosan solution incorporated in the exhaustion phase to obtain chitosan-treated yarns with good antimicrobial activity and mechanical properties was 0.6%. The best antimicrobial treatment should minimise potential economic costs while providing functionality.

Amino group functionalized pitch-based carbocatalyst for the Henry reaction of furfural

BackgroundTo transform the commodity wastes into high performance materials such as catalyst supports can facilitate the circular economy. Therefore, pitch-based carbon (MPC) which is mainly regarded as a premium carbon byproduct from the petroleum refinery was used to synthesize the supported amino catalyst for the Henry reaction of furfural. MethodsThe amino functionalized pitch-based carbon was prepared by the facile chemical nitration and reduction. The surface textures of the functionalized carbon materials were carefully scrutinized by various characterization techniques, including PXRD, XPS, FT-IR, 13C SSNMR, and Raman spectroscopy. Meanwhile, the amount of surface accessible amino groups was quantified by the colorimetric method using 2-iminothiolane hydrochloride (ITL) as molecular probe. Significant findingThe results reveal that the surface amino groups were immobilized and quantified as 0.391 mmol/g at the periphery of MPC. Moreover, this amino functionalized carbon denoted NRE-MPC could catalyze the Henry reaction of furfural with nitromethane in isopropanol at 90 °C for 6 h to yield 2-(2-nitrovinyl)furan (NVF) as the major product in 65% with 87% furfural conversion. NRE-MPC can be also easily recycled at least four times and the peripheral amino groups alongside the graphitic domains of MPC were still chemically active with perceptible reactivity reduction.

Comprehensive Discovery of the Accessible Primary Amino Group-Containing Segments from Cell Surface Proteins by Fine-Tuning a High-Throughput Biotinylation Method

Cell surface proteins, including transmembrane and other surface-anchored proteins, play a key role in several critical cellular processes and have a strong diagnostic value. The development of quick and robust experimental methods remains vital for the accurate and comprehensive characterization of the cell surface subproteome of individual cells. Here we present a high-throughput technique which relies on the biotinylation of the accessible primary amino groups in the extracellular segments of the proteins, using HL60 as a model cell line. Several steps of the method have been thoroughly optimized to capture labeled surface proteins selectively and in larger quantities. These include the following: improving the efficiency of the cell surface biotinylation; reducing the endogen protease activity; applying an optimal amount of affinity column and elution steps for labeled peptide enrichment; and examining the effect of various solid-phase extraction methods, different HPLC gradients, and various tandem mass spectrometry settings. Using the optimized workflow, we identified at least 1700 surface-associated individual labeled peptides (~6000-7000 redundant peptides) from the model cell surface in a single nanoHPLC-MS/MS run. The presented method can provide a comprehensive and specific list of the cell surface available protein segments that could be potential targets in various bioinformatics and molecular biology research.

Automated prediction of site and sequence of protein modification with ATRP initiators.

One of the most straightforward and commonly used chemical modifications of proteins is to react surface amino groups (lysine residues) with activated esters. This chemistry has been used to generate protein-polymer conjugates, many of which are now approved therapeutics. Similar conjugates have also been generated by reacting activated ester atom transfer polymerization initiators with lysine residues to create biomacromolecular initiators for polymerization reactions. The reaction between activated esters and lysine amino groups is rapid and has been consistently described in almost every publication on the topic as a “random reaction”. A random reaction implies that every accessible lysine amino group on a protein molecule is equally reactive, and as a result, that the reaction is indiscriminate. Nonetheless, the literature contradicts itself by also suggesting that some lysine amino groups are more reactive than others (as a function of pKa, surface accessibility, temperature, and local environment). If the latter assumption is correct, then the outcome of these reactions cannot be random at all, and we should be able to predict the outcome from the structure of the protein. Predicting the non-random outcome of a reaction between surface lysines and reactive esters could transform the speed at which active bioconjugates can be developed and engineered. Herein, we describe a robust integrated tool that predicts the activated ester reactivity of every lysine in a protein, thereby allowing us to calculate the non-random sequence of reaction as a function of reaction conditions. Specifically, we have predicted the intrinsic reactivity of each lysine in multiple proteins with a bromine-functionalised N-hydroxysuccinimide initiator molecule. We have also shown that the model applied to PEGylation. The rules-based analysis has been coupled together in a single Python program that can bypass tedious trial and error experiments usually needed in protein-polymer conjugate design and synthesis.

Assessment of chemically and enzymatically modified chitosan with eugenol as a coating for viscose functionalization for potential medical use

The present work deals with the preparation of chemically and enzymatically eugenol-modified chitosan and its application as a green coating on viscose for the potential production of medical textiles. The elemental composition of chemically and enzymatically eugenol-modified chitosan was determined by attenuated total reflection Fourier transform infrared (ATR FT-IR) and proton nuclear magnetic resonance (1H NMR) spectroscopy. Moreover, potentiometric titration was used to estimate the number of accessible amino groups. The chitosan–eugenol formulation possesses a high antioxidant capacity level, as shown by the high content of phenolic compounds analyzed by the following methods: (a) Folin–Ciocalteu; (b) reduction of Fe3+ ions; and (c) α, α-diphenyl-β-picrylhydrazyl (DPPH•). Viscose coated with chitosan–eugenol formulations was evaluated by ATR FT-IR spectroscopy and Acid Orange VII spectrophotometric methods, the results of which demonstrated the successful deposition of these formulations on the fibers. Scanning electron microscopy showed the presence of the functional coating on the viscose. Finally, antimicrobial testing was performed to determine inhibition of selected pathogenic micro-organisms using the ASTM E 2149-01 standard. The antioxidant activity of the functionalized viscose was investigated spectrophotometrically by the DPPH• method. It was found that the coatings of eugenol-modified chitosan impart antimicrobial activity to the viscose against Gram-positive and Gram-negative bacteria as well as fungi, and cause inhibition of free radicals by introducing an antioxidant character. The chemical and enzymatic modification of chitosan offers many opportunities for the incorporation of many natural active ingredients into the chitosan system, which provides a good basis for further work related to the functionalization of chitosan for sanitary and medical use.

Synthesis of a Novel Curcumin Derivative as a Potential Imaging Probe in Alzheimer's Disease Imaging.

Curcumin has been of interest in the field of Alzheimer's disease. Early studies on transgenic mice showed promising results in the reduction of amyloid plaques.However, curcumin is very poorly soluble in aqueous solutions and not easily accessible to coupling as it contains only phenolic groups as potential coupling sites. For these reasons only few imaging studies using curcumin bound as an ester were performed and curcumin is mainly used as nutritional supplement. In the present study we produced an aminoethyl ether derivative of curcumin using a nucleophilic substitution reaction. This is a small modification and should not impact the properties of curcumin while introducing an easily accessible reactive amino group. This novel compound could be used to couple curcumin to other molecules using the standard methods of peptide synthesis. We studied the aminoethyl-curcumin compound and a tripeptide carrying this aminoethyl-curcumin and the fluorescent dye fluorescein (FITC-curcumin) in vitro on cell culture using confocal laser scanning microscopy and flow cytometry. Then these two substances were tested ex vivo on brain sections prepared from transgenic mice depicting Alzheimer-like β-amyloid plaques. In the in vitro CLSM microscopy and flow cytometry experiments we found dot-like unspecific uptake and only slight cytotoxicity correlating with this uptake. As these measurements were optimized for the use of fluorescein as dye we found that the curcumin at 488nm fluorescence excitation was not strong enough to use it as a fluorescence marker in these applications. In the ex vivo sections CLSM experiments both the aminoethyl-curcumin and the FITC-curcumin peptide bound specifically to β- amyloid plaques. In conclusion we successfully produced a novel curcumin derivative which could easily be coupled to other imaging or therapeutic molecules as a sensor for amyloid plaques.

Enhanced cyclic CO2/N2 separation performance stability on chemically modified N-doped ordered mesoporous carbon

The modification of ordered mesoporous carbon (OMC) via NH3 heat treatment and subsequent amine refluxing at increased temperature was investigated to improve their performances for cyclic CO2/N2 separation stability and kinetics. Characterizations conducted with nitrogen adsorption/desorption isotherm, Fourier transform infrared spectroscopy, elemental analysis, and X-ray photoelectron spectroscopy demonstrated that the porosity and surface chemistry of the OMCs were tuned by modification. Adsorption evaluation with volumetric and gravimetric methods under various conditions indicated that the resulting amine-introduced N-doped OMC presented a high CO2 adsorption capacity with fast kinetics, outstanding selectivity at 50 °C and maintained superior separation performance after 20 cycles. The presence of accessible amino groups in considerable amounts renders the modified mesoporous carbon a promising candidate for CO2 capture from flue gas by using the temperature swing adsorption.

Multimodal Cleavable Reporters versus Conventional Labels for Optical Quantification of Accessible Amino and Carboxy Groups on Nano- and Microparticles.

Many applications of nanometer- and micrometer-sized particles include their surface functionalization with linkers, sensor molecules, and analyte recognition moieties like (bio)ligands. This requires knowledge of the chemical nature and number of surface groups accessible for subsequent coupling reactions. Particularly attractive for the quantification of these groups are spectrophotometric and fluorometric assays, which can be read out with simple instrumentation. In this respect, we present here a novel family of cleavable spectrophotometric and multimodal reporters for conjugatable amino and carboxyl surface groups on nano- and microparticles. This allows determination of particle-bound labels, unbound reporters in the supernatant, and reporters cleaved off from the particle surface, as well as the remaining thiol groups on particle, by spectrophotometry and inductively coupled optical emission spectrometry (32S ICP-OES). Comparison of the performance of these cleavable reporters with conductometry and conventional labels, utilizing changes in intensity or color of absorption or emission, underlines the analytical potential of this versatile concept which elegantly circumvents signal distortions by scattering and encoding dyes and enables straightforward validation by method comparison.

Development of Chitosan Membranes as a Potential PEMFC Electrolyte

Commercial chitosan and chitosan extracted from shrimp shells are being used to design membranes to be tested as low cost electrolyte in PEM fuel cells. This study investigated the influence of the deacetylation degree (DD) and molar mass (M V ) of the chitosans used in the composition of membranes on its performance regarding to proton conductivity and other properties. Preliminary results indicate that the chitosan extracted from shrimp shells generated membranes with promising properties such as proton conductivity, which demonstrated to be even a 100 times higher than those shown by commercial chitosan membranes. The significant increase in proton conductivity can be associated with the higher number and availability of amino groups (–NH2) in the chitosan produced in the laboratory, which presents higher DD and lower M V . It is believed that the properties of chitosan can be manipulated in such a way that it would be possible to obtain proton conductivity values closer to that presented by Nafion®.

Characterisation of heat-induced protein aggregation in whey protein isolate and the influence of aggregation on the availability of amino groups as measured by the ortho-phthaldialdehyde (OPA) and trinitrobenzenesulfonic acid (TNBS) methods.

Whey protein isolate (WPI) solutions, with different levels of aggregated protein, were prepared by heating (5% protein, pH 7, 90°C for 30min) WPI solutions with either 20mM added NaCl (WPI+NaCl), 5mM N-ethylmaleimide (WPI+NEM) or 20mM added NaCl and 5mM NEM (WPI+NaCl+NEM). Gel electrophoresis demonstrated that the heated WPI and WPI+NaCl solutions had higher levels of aggregated protein, due to more covalent interactions between proteins, than the heated WPI+NEM and WPI+NaCl+NEM solutions. There were marked differences in the levels of amino groups between all heated WPI solutions when measured by the OPA and TNBS methods, with lower levels being measured by the TNBS method than by the OPA method. These results demonstrate that the measurement of available amino groups by the OPA method is less impacted than by the TNBS method after heat-induced structural changes, arising from disulfide or sulfhydryl-disulfide bond-mediated aggregation of whey protein molecules.

Determination of amino groups on functionalized graphene oxide for polyurethane nanomaterials: XPS quantitation vs. functional speciation

Simple spectrophotometric method for the estimation of accessible amino groups and preparation of polyurethane nanocomposites.

The modification of cotton substrate using chitosan for improving its dyeability towards anionic microencapsulated nano-pigment particles

The cotton samples were treated by chitosan solution at acidic condition to modify their dyeing properties to anionic coloring materials. By fluorescence spectrum together with FTIR, XRD and TGA analysis, it was concluded that the chitosan molecules could spontaneous transfer from solution onto cotton surface yet would not influence its internal structure. In order to color the chitosan-treated cotton, an anionic polystyrene-encapsulated copper phthalocyanine (CuPc) pigment was prepared in a miniemulsion process. The full encapsulation of nano-pigment could be directly observed by TEM. The encapsulation would not alter the crystal structure and color properties of CuPc while could make the nano-pigment more stable against centrifuge and temperature variation. Finally, the dyeing properties of this encapsulated nano-pigment on chitosan-treated cotton samples were studied. It was indicated the chitosan molecules on cotton had great capability to improve the uptake of encapsulated nano-pigment mainly due to the accessible amino groups introduced.

Surface modification of titanium oxide nanoparticles with chelating molecules: New recognition devices for controlling the selectivity towards lanthanides ionic separation

A series of hybrid TiO2 nanoparticles containing chelating molecules based on diethylenetriaminepentaacetic acid (DTPA) moiety have been synthesized and thoroughly characterized by TEM, SEM, powder XRD, FT-IR, 13C solid-state MAS NMR, CHN elemental analysis, and BET. The surface modification of these nano-materials was established by coupling accessible amino group functions of TiO2/PABA supports (para-amino benzoic acid, PABA) with either modified-monoanhydride or -carboxylic acid compounds. The extraction percentages, distribution coefficients (KdGd), capacities (CGd) and ionic selectivities (SGd/La) of these surface-functionalized nano-structured materials between lanthanum and gadolinium in acidic range of pH were investigated.

Organization of Subunits in the Membrane Domain of the Bovine F-ATPase Revealed by Covalent Cross-linking

The F-ATPase in bovine mitochondria is a membrane-bound complex of about 30 subunits of 18 different kinds. Currently, ∼85% of its structure is known. The enzyme has a membrane extrinsic catalytic domain, and a membrane intrinsic domain where the turning of the enzyme's rotor is generated from the transmembrane proton-motive force. The domains are linked by central and peripheral stalks. The central stalk and a hydrophobic ring of c-subunits in the membrane domain constitute the enzyme's rotor. The external surface of the catalytic domain and membrane subunit a are linked by the peripheral stalk, holding them static relative to the rotor. The membrane domain contains six additional subunits named ATP8, e, f, g, DAPIT (diabetes-associated protein in insulin-sensitive tissues), and 6.8PL (6.8-kDa proteolipid), each with a single predicted transmembrane α-helix, but their orientation and topography are unknown. Mutations in ATP8 uncouple the enzyme and interfere with its assembly, but its roles and the roles of the other five subunits are largely unknown. We have reacted accessible amino groups in the enzyme with bifunctional cross-linking agents and identified the linked residues. Cross-links involving the supernumerary subunits, where the structures are not known, show that the C terminus of ATP8 extends ∼70 Å from the membrane into the peripheral stalk and that the N termini of the other supernumerary subunits are on the same side of the membrane, probably in the mitochondrial matrix. These experiments contribute significantly toward building up a complete structural picture of the F-ATPase.

Temporary Conversion of Protein Amino Groups to Azides: A Synthetic Strategy for Glycoconjugate Vaccines.

Conjugation of synthetic oligosaccharides and native polysaccharides to proteins is an important tool in glycobiology to create vaccines and antigens to screen lectins, toxins, and antibodies. A novel approach to potentiate and profile the immune response to vaccines involves targeting antigens directly to dendritic cells (DCs), the key cells engaged in the immunization process. Inclusion of a carbohydrate ligand recognized by C-type lectins expressed on their cell surface ensures targeting of vaccines to DCs and improved immunological responses. Here we describe a strategy that permits three sequential orthogonal conjugation reactions to prepare glycoconjugates and apply them to the synthesis of a conjugate vaccine that is targeted for uptake by DCs. The carrier protein is treated with an azo-transfer reagent to convert accessible amino groups to azide and then amide bond formation via reaction with carboxylic acid side chains is used to attach amino tether groups of a ligand to the protein. Azide-alkyne Huisgen cycloaddition conjugation, "click chemistry" is used to attach a second ligand equipped with a propargyl group or an analogous terminal alkyne, and following reduction of protein azide groups back to amine, these amino acid side chains can be subjected to amide formation such as reaction with succinimide esters or homobifunctional coupling reagents such as dialkyl squarate.

Interaction of β-Lactoglobulin with Small Hydrophobic Ligands - Influence of Covalent AITC Modification on β-LG Tryptic Cleavage

Covalent modification of proteins with bioactive organosulfur compounds is suggested to reduce the smell and increase the stability of the compound. Aside from these effects the covalent modification may also alter the physiochemical properties of the protein. In this study, the whey protein β-lactoglobulin (β-LG) was covalently modified with bioactive organosulfur compound allyl isothiocyanate (AITC), originating from cabbage. Native and AITC modified β-LG were subjected to tryptic and chymotryptic digestion to assess the influence of the covalent modification on peptide formation. AITC was shown to modify at least 13 different amino acid residues, containing thiol- or amino groups, in a concentration dependent manner. Therefore, AITC modification can be controlled to some extent. Besides cysteine thiols, the most accessible amino groups for AITC modification were found at the N-terminal end of the protein (residues L1 and K8) along with lysine residues K91, K77 and K83. Higher amount of AITC addition resulted in a significant blocking of several tryptic cleavage sites of β-LG (for example residue K14) resulting in longer peptides, influencing the concentration of certain bioactive peptides following tryptic cleavage.

Sulfonyl Fluorides as Alternative to Sulfonyl Chlorides in Parallel Synthesis of Aliphatic Sulfonamides

Two types of aliphatic sulfonyl halides (Cl versus F) were compared in parallel synthesis of sulfonamides derived from aliphatic amines. Aliphatic sulfonyl fluorides showed good results with amines bearing an additional functionality, while the corresponding chlorides failed. Both sulfonyl halides were effective in the reactions with amines having an easily accessible amino group. Aliphatic sulfonyl chlorides reacted efficiently with amines bearing sterically hindered amino group while the corresponding fluorides showed low activity.

Different plasma-based strategies to improve the interaction of anionic dyes with polyester fabrics surface

Low-pressure plasma treatments with subsequent immobilization of functional macromolecules from aqueous solution have gained an increasing popularity for its applications in new industrial processes. In this work, two different strategies to endow polyester fabrics (PET) with accessible primary amino groups are compared.(a) NH2 groups were produced directly using low-pressure ammonia plasma. (b) Negatively charged groups were introduced by low-pressure oxygen plasma to hydrophilize the fabric surfaces and used as anchor groups for the immobilization of water-borne polyelectrolyte copolymers poly(vinyl amine-co-vinyl amide) (PVAm).To study the effects of these surface modifications, a combination of various surface-sensitive characterization techniques such as X-ray photoelectron spectroscopy (XPS), streaming potential measurements and time-dependent contact angle measurements were used. Furthermore, the influence of the pre-treatments on the interaction of PET fabrics with water-soluble dyes was evaluated. For that purpose, color strength and fastness tests were carried out to prove the effectiveness of pre-treatments.

Characterization of regenerated cellulose fibers antimicrobial functionalized by chitosan

Despite numerous investigations during recent decades in the field of antimicrobially treating textile fibers using chitosan, many obscurities remain regarding the adsorption/desorption behavior of chitosan and the influences of the accessible amino group content on the antimicrobial effectiveness of chitosan-treated fibers. Accordingly, the principal aim of the presented research was to evaluate different regenerated cellulose fibers regarding their abilities to provide highest antimicrobial effectiveness after chitosan treatments. Regenerated cellulose fibers such as viscose, modal and lyocell were antimicrobial functionalized by chitosan from solutions. The adsorption and desorption of the chitosan were analyzed using potentiometric titration, the spectrophotometric method with C.I. Acid orange VII, the Kjeldahl technique and polyelectrolyte titration. Mechanical properties of functionalized fibers were also checked. The antimicrobial activities of chitosan-functionalized cellulose fibers were examined, with regard to pathogen bacteria and fungi. The highest amino group content as a consequence of more intensive chitosan adsorption was found in viscose followed by modal and, finally, by lyocell. It was confirmed that those fibers with higher content of amino groups demonstrated a better reduction in pathogenic bacteria as well as pathogenic fungi. The functionalized cellulose fibers displayed potential utility in different fields of application, as exemplified by medical textiles for single use.