Adsorption Of Amino Acids Research Articles

Molecular dynamics simulations of amino acid adsorption and transport at the acetonitrile-water-silica interface: the role of side chains.

The solvation and transport of amino acid residues at liquid–solid interfaces have great importance for understanding the mechanism of separation of biomolecules in liquid chromatography. This study uses umbrella sampling molecular dynamics simulations to study the adsorption and transport of three amino acid molecules with different side chains (phenylalanine (Phe), leucine (Leu) and glutamine (Gln)) at the silica–water–acetonitrile interface in liquid chromatography. Free energy analysis shows that the Gln molecule has stronger binding affinity than the other two molecules, indicating the side chain polarity may play a primary role in adsorption at the liquid–solid interface. The Phe molecule with a phenyl side chain exhibits stronger adsorption free energy than Leu with a non-polar side chain, which can be ascribed to the better solvated configuration of Phe. Further analysis of molecular orientations found that the amino acid molecules with apolar side chains (Phe and Leu) have ‘standing up’ configurations at their stable adsorption state, where the polar functional groups are close to the interface and the side chain is far from the interface, whereas the amino acid molecule with a polar side chain (Gln) chooses the ‘lying’ configuration, and undergoes a sharp orientation transition when the molecule moves away from the silica surface. Extending our simulation studies to systems with different solute concentrations reveals that there is a decrease in the adsorption free energy as well as surface diffusion as the solute concentration increases, which is related to the crowding in the interfacial layers. This simulation study gives a detailed microscopic description of amino acid molecule solvation and transport at the acetonitrile–water–silica interface in liquid chromatography and will be helpful for understanding the retention mechanism for amino acid separation.

Glutamate adsorption on the Au(111) surface at different pH values

Adsorbed amino acids can modulate the behavior of metal nanoparticles in advanced applications. Using a combination of electrochemical experiments, FTIR spectroscopy, and DFT calculations, glutamate species interacting with the Au(111) surface in solution are here investigated. Electrochemical results indicate that the adsorption behavior depends on the solution pH (which controls the glutamate ionization) and on the charge of the surface. Glutamate adsorption starts at potentials slightly negative to the potential of zero charge. The thermodynamic analysis of these results indicates that two electrons are exchanged per molecule, implying that both carboxylic groups become deprotonated upon adsorption. The FTIR spectra reveal that carboxylate groups are bonded to the surface in the bidentate configuration (with both oxygen atoms attached to the surface). Plausible adsorbed configurations, consistent with the whole of these insights, were found using DFT. -Additionally, it was observed that glutamate oxidation only takes place when the surface is oxidized, which suggests that this oxidation process involves the transfer of an oxygen group to the molecule, though, according to the FTIR spectra, the main chain remains intact.

Kinetika Adsorpsi Zat Warna Tartrazina Menggunakan Limbah Ampas Tahu sebagai Adsorben

It has been conducted a research about the utilization waste of tofu as adsorbent of tartrazine dye. Utilization waste of tofu as adsorption because tofu contains protein which has the power adsorption of amino acids that form a zwitter ion. The purpose of this study was to determine the adsorption process and adosrption kinetics model of tartrazine dye by waste of tofu as adsorbent. Making the adsorbent is done by making waste of tofu into powder with a size of 100 mesh. The method used in the analysis of tartrazine dye is using UV-Vis. Adsorption of of tartrazine dye using waste of tofu at concentrations of 50 ppm and a contact time of 80 minutes with weight adsorbent 0.3 g. The two isotherms were used that Langmuir isotherm and Freundlich isotherm, the adsorption studies of tartrazine dye adsorbent waste of tofu follow Freundlich adsorption isotherms with a correlation coefficient (R2) of 94.4%, KF is 0.0026 mg/g and n is 0.5621. Adsorption kinetics of of tartrazine dye adsorbent waste of tofu following the model of adsorption Ho pseudo-second order with a correlation coefficient (R2) of 100%, Xe is 1.7761 mg/g and k2,ads is -0.6550 g/mg minutes. The mechanism adsorption of of tartrazine dye with waste of tofu as adsorbent is chemisorpsi process.

Is the electrochemical or the “green chemistry” method the optimal method for the synthesis of ZnO nanoparticles for applications to biological material? Characterization and SERS on ZnO

This work developed ecological procedures for the synthesis of stable, uniform, and pure ZnO nanoparticles for biological and medical applications. Nanoparticles were synthesized on two synthesis pathways: (i.) electrochemical zinc dissolution in a solution free of surfactants (ZnONPs) and (ii.) from banana skin (ZnONPs-GS) by a green synthesis – a cheap method that allows efficient use of waste from plant products. ATR-FTIR, Raman, and UV-Vis confirmed the formation of ZnO nanoparticles. XRD showed a high crystalline hexagonal structure, whereas TEM and DLS confirmed that nanoparticles are pure, well dispersed, and have a rather uniform size and spherical shape. ZnO nanoparticles were evaluated for their ability to adsorb selected amino acids and to promote the SERS effect. SERS spectra on the surface of ZnO nanoparticles were compared with SERS spectra on the surface of Zn. The obtained data show that (i.) with the use of specific marker bands SERS allows us to distinguish between amino acids and to determine the state of zinc surfaces (distinguish between Zn and ZnONPS and ZnONPs-GS), (ii.) ZnONPs-GS obtained from “green chemistry” are more friendly to biological material than those obtained using the electrochemical method because their surface is free from hydroxyl groups, which easily form reactive oxygen species, and (iii.) considering the view in the literature that metal surface type and metal roughness/nanoparticle size influence adsorption, the obtained results supplement the current understanding of amino acid adsorption on various metal surfaces.

L-Lysine Amino Acid Adsorption on Zeolite L: a Combined Synchrotron, X-Ray and Neutron Diffraction Study.

Invited for this month's cover are the groups of Annalisa Martucci and Luisa Pasti at the University of Ferrara (Italy). The cover picture shows L-lysine amino acid adsorption on zeolite L. The role of zeolite channels in the stabilization of the lysine absorbed and the effect of water on protein structure are elucidated at atomistic level. The stabilization of the L α-helical conformation is related to strong H-bonds between the tail aminogroups of lysine molecules and the Brønsted acid site as well as to complex intermolecular H-bond system between water molecules, zeolite and amino acid. Read the full text of their Full Paper at 10.1002/open.202000183.

Investigating adsorption of model low-MW AOM components onto different types of activated carbon – influence of temperature and pH value

ABSTRACT Low molecular weight algal organic matter (AOM), as a frequent water contaminant with poor coagulation efficiency, adversely affects the quality of produced water and serves as a source of potentially carcinogenic disinfection by-products. AOM removal from water is inevitable to eliminate the negative health and environmental impacts. This research evaluates the removal of arginine, phenylalanine and aspartic acid, which are amino acids abundant in AOM. Adsorption experiments were performed at 10, 18 and 25 °C and pH 5, 7 and 9 using two different activated carbons (FTL, PIC). Amino acids showed endothermic adsorption behaviour, with a higher removal at higher temperature. Higher temperature increased the diffusion of amino acid molecules, reduced the solution viscosity, or enhanced the hydrophobic interactions contributing to adsorption. The effect of temperature manifested differently during experiments depending on the chemical nature of the amino acids, the pH value and the surface properties of the carbon. Phenylalanine isotherms showed specific waves (Langmuir type 4). pH had a greater effect on arginine adsorption than did temperature. Aspartic acid isotherms exhibited a decrease in adsorption at higher pH values and higher temperatures. The principal mechanisms involved in amino acid adsorption were hydrophobic interactions, electrostatic interactions or hydrogen bonds.

Adsorption and isomerization of amino acids within zeolites: Impacts of acidity, amine functionalization, pore topology and sidechains

Adsorption and isomerization of amino acids within zeolites are investigated by two-layer ONIOM theoretical methods, focusing on the impacts of acidity, amine functionalization, pore topology and sidechains. Meanwhile, relationships of zwitterionic stabilization and isomerization activities with zeolite acidity and basicity are established. Adsorption structures are strongly perturbed by all factors except acidity. Distribution of different glycine isomers is significantly altered by all zeolites and also depends on zeolite basicity. Zwitterionic isomers, the active form to conduct the biological and pharmaceutical functions, are non-existent in the isolated state while remain stable within all acidic zeolites or not very highly basic zeolites. Zwitterions always show stronger interactions with zeolites than canonical isomers and zeolites with moderate acidities or basicities are the most effective for zwitterionic stabilization. Larger porous zeolites favor zwitterionic stabilization, and distinct from the isolated state, sidechains disfavor zwitterionic stabilization within zeolites while degree of influences depends on identity of sidechains, causing relative stabilities with canonical isomers to rank as proline (Pro) > glycine (Gly) > valine (Val) > protonated arginine (ArgH) > arginine (Arg). Zeolites greatly stabilize zwitterions and enable the occurrence of catalytic isomerization reactions. Isomerization to zwitterionic isomers proceeds facilely within all zeolites. Acidity increase of M-ZSM-5 zeolites or basicity decrease of amine-functionalized zeolites facilitates zwitterion formation, and zwitterion formation is the most favorable for Pro while disfavored for Arg. Results also provide insights to other host-guest interactions and catalytic mechanisms.

Enantioselective Separation Using Chiral Amino Acid Functionalized Polyfluorene Coated on Mesoporous Anodic Aluminum Oxide Membranes.

Homochiral mesoporous anodic aluminum oxide membranes (AAO) were prepared by coating protected chiral D/L aspartic acid appended polyfluorene in the pores. These chiral AAO membranes successfully demonstrated enantioselective recognition and separation of a range of amino acids from their aqueous racemic mixture by simple filtration. Enantioselective separation was achieved by selective adsorption of one enantiomer from the aqueous racemic mixture into the chiral pores of the AAO membrane leaving the filtrate enriched with the other enantiomer. Extraction and quantification of the adsorbed amino acid (glutamic acid) demonstrated that 1 mg of homochiral polyfluorene could effectively extract about 3.5 mg of glutamic acid with 95% enantiomeric excess in 24 h. This is one of the highest enantiomeric excesses (ee %) and yields reported so far in the literature for a racemic mixture of glutamic acid. The pore size of the AAO membrane influenced the efficiency of separation with a reduction in pore size from 200 to 20 nm leading to reduced ee % (∼95% to ∼28%). These results raise the possibility for a facile method to carry out enantioselective separation.

Amino acid adsorption on tetraphenyl porphyrin films

In this work, metal free, zinc and copper tetraphenyl porphyrin thin films were employed as substrates to study their interaction with glycine, serine, glutamate, lysine and argynine amino acids in order to investigate the effect of the metallic center and the amino acid characteristics in the adsorption phenomena. The amount of amino acid adsorbed on the films was quantified by using the Ruhemann method. Adsorption isotherms were obtained and analyzed in order to predict the adsorption mechanism for each case. In addition, the morphology of the films was investigated before and after the amino acid immersion by using scanning electron and atomic force microscopies. On the other hand, dynamic contact angle measurements were performed to monitor the spreading phenomena and changes in the hydrophobic nature of the surfaces after the amino acid interaction. From the results, it was observed that the largest deposited amino acid on all three surfaces corresponded to the positively charged compounds, while serine was the lowest adsorbed amino acid in all cases. These results can be attributed to electronic interactions between the amino acids’ lateral chains and the electronic [Formula: see text] distribution of the porphyrin macrocycle ring, and they provide important information regarding the amino acid selectivity of adsorption on tetraphenyl porphyrin films.

Confirmation of Initial Stable Adsorption Structures of Leucine and Tyrosine Adsorbed on a Cu(110) Surface

The structures and stability levels of leucine (Leu) and tyrosine (Tyr) adsorbed on a Cu(110) surface, at initial levels of coverage (less than 0.25 monolayer), were investigated using reflection–absorption infrared spectroscopy and high-resolution photoemission spectroscopy (HRPES), as well as by performing density functional theory calculations. At an initial coverage, the O–H dissociation bonded structure was indicated from the spectral results to be the most favorable structure for Leu adsorbed on the Cu(110) surface, whereas the O–H dissociated-N dative bonded structure was most favorable for adsorbed Tyr. These models were further supported by the results of experiments, in which the systems were exposed to other molecules and HRPES was used to monitor whether the amine or carboxylic groups of the adsorbed amino acids became reactive.

Bonding and thermal stability of cysteine on single-crystalline iron oxide surfaces and Pt(111).

Model studies on the adsorption of simple amino acids on single-crystalline substrates provide the basis for understanding the interactions of more complex biomolecules with inorganic materials. In this study, the adsorption and thermal stability of cysteine on Pt(111) and on monolayer FeO(111)/Pt(111) and thick Fe3O4(111)/Pt(111) films have been investigated in ultrahigh vacuum by means of x-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, and temperature-programmed desorption. At low adsorption temperature (160 K), cysteine stays intact on all studied surfaces. However, the thermal stability differs dramatically. Decomposition via dehydrogenation, decarbonylation/decarboxylation, and deamination starts already below room temperature on Pt(111). By contrast, adsorbed cysteine is stable up to 500 K on Fe3O4(111) and then gets oxidized in a redox reaction involving the Fe3O4 substrate. FeO(111)/Pt(111) is a special case, where decarbonylation of cysteine occurs below room temperature, which is most likely initiated by a structural modification and concomitant charge transfer at the Pt-FeO interface induced by the carboxyl group of the adsorbed cysteine. The experimental results suggest that cysteine binds to the surfaces with the carboxyl group on the iron oxides and with the carboxyl and amino groups on Pt(111).

Toward the origin of life over feldspar surfaces: Adsorption of amino acids and catalysis of conformational interconversions

AbstractFeldspars are a group of tectosilicate minerals terminated with a full layer of hydroxyl groups and have been regarded as “hotbed” for birth of life. In this study, periodic density functional theory calculations are conducted to address two associated issues, as adsorption of amino acids and conformational interconversions over feldspar surfaces. Distribution of glycine isomers depends strongly on the number of interacted surface silanols (n), and canonical isomers exist exclusively for n ≤ 2 while zwitterions predominate for n = 3. Adsorption of amino acids is significantly affected by sidechains, especially those forming H‐bonds with surfaces; however, sidechain contacts with feldspar surfaces disfavor zwitterion stabilization, and zwitterions become preferred without sidechain contacts. For all amino acids, conformational interconversions undergo four elementary steps, and proton transfer between two carboxylic‐O atoms (step 2) is always rate‐decisive. Step 2 is greatly accelerated with catalysis of surface silanols and activation barriers depend significantly on sidechains. All amino acids have moderate activation barriers and conformational interconversions (in both forward and reverse directions) proceed favorably at ambient conditions. Sidechains of amino acids exhibit influences through sidechain contacts with surfaces rather than as substituent effect.

Theoretical study of glycine amino acid adsorption on graphene oxide.

The non-dissociative and dissociative adsorptions of zwitterionic Gly on graphene oxide (GO) was studied in the framework of DFT using a cluster model approach. In this work, the interaction with an epoxy group of GO basal plane was mainly considered. As a comparison, the non-dissociative and dissociative adsorptions of neutral Gly were also taken into account. The non-dissociative adsorption modes for zwitterionic and neutral Gly conformers show binding energies of 12.2 and 14.4kcalmol-1, respectively. These molecules are thought to remain over the GO surface due to attractive noncovalent interactions. Two dissociative adsorption modes, for Z-Gly and N-Gly, show smaller binding energies of 7.2 and 8.4kcalmol-1, where the deprotonated species links strongly through a C-O or C-N covalent bond to the GO surface. The results obtained in the present theoretical approach to the glycine/graphene oxide system support the fact that glycine can be attached to epoxy groups of graphene oxide basal planes in addition to the anchoring on edge oxidation groups. In summary, we conclude that glycine can be used as a reducing agent as well as a functionalizer of GO sheets.

Room-temperature preparation of a chiral covalent organic framework for the selective adsorption of amino acid enantiomers.

Herein, we have reported the facile room-temperature synthesis of a chiral covalent organic framework (CCOF) for the enantioselective adsorption of amino acids. The prepared CCOF provides various stereoscopic interactions with amino acids for highly selective adsorption of their enantiomers.

Theoretical investigation of amino-acid adsorption on hydroxylated quartz surfaces: dispersion can determine enantioselectivity

Chiral mineral surfaces, such as quartz, are attractive substrates for use in enantioselective separation and may have contributed to the origin of biological homochirality. In this work, we apply density-functional theory and the exchange-hole dipole moment (XDM) dispersion model to study the adsorption of 5 amino acids (glycine, serine, alanine, valine, and phenylalanine) on a hydroxylated α-quartz (0001) surface. It is demonstrated that London dispersion is responsible for 30-50% of the total adsorption energies and its inclusion or omission can reverse predictions of enantioselectivity. Differing dispersion stabilization, caused by the opposing side-chain placements relative to the quartz surface, lead to differences of 1.0 and 1.8 kcal mol-1 in the adsorption energies of the alanine and phenylalanine enantiomers, respectively. These results are consistent with a 3-point model, with the hydrogen-bonding sites conserved and variations in the dispersion interactions determining enantioselectivity.

Evaluating Adsorption of Proline Amino Acid on the Surface of Fullerene (C60) and Carbon Nanocone by Density Functional Theory

Determination of proline is of great importance and investigating the interaction of this amino acid with nanostructures play a key role in the construction of novel appropriate sensors for proline measurement. In this regard, proline adsorption on the surface of fullerene and carbon nanocone was studied by density functional theory. For this purpose, the structures of fullerene, nanocone, proline and proline-adsorbent complexes at two different configurations were optimized geometrically. Then, IR and Frontier molecular orbital calculations were done in the temperature range of 298.15-398.15 K at 10˚ intervals. The obtained adsorption energies, adsorption enthalpy changes, Gibbs free energy variations and thermodynamic equilibrium constants showed that the adsorption of proline on the surface of nanocone is exothermic, spontaneous, one sided and experimentally feasible. In this sense, proline adsorption on the fullerene is endothermic, non-spontaneous, balanced and experimentally impossible. The achieved specific heat capacity values reveal that carbon nanocone can be used in the development of thermal sensors for the determination of proline. The effect of temperature on the adsorption process was also checked out and the results indicate that 298.15 is the optimum temperature for the studied procedure. Some HOMO-LUMO parameters such as energy gap, electrophilicity, maximum charge capacity, chemical hardness and chemical potential were also evaluated. Accordingly, the findings demonstrate that carbon nanocone can be utilized in the electrochemical determination of proline.

Ultra-low concentration protein detection based on phenylalanine-Pd/SWCNT as a high sensitivity nanoreceptor.

Pd doped single-walled carbon nanotubes as an enhanced physical transducer with phenylalanine amino acid can be efficiently used as a biocompatible nanoreceptor to detect proteins. DFT/B3LYP was used to calculate the optimized geometries, energies and electron density parameters to determine the stability and reactivity of the nanoreceptor. Among different adsorbed configurations of phenylalanine, the amine and carboxylic acid sites have higher adsorption energies and more stable complexes. With direct strong chemical adsorption of phenylalanine amino acid onto the Pd doped single-walled carbon nanotube, the free active carboxylic acid group of the amino acid can react with free amine groups on the surface of the proteins. More over the π–π stacking interaction between the free aromatic ring of adsorbed phenylalanine amino acid onto the functionalized single-walled carbon nanotube and the aromatic rings of the proteins also contributes to the intelligent detection of proteins. Frontier molecular orbital and molecular electrostatic potential (MPE) surface studies have been employed to investigate the active sites of the nanoreceptor. The effects of different solvents on the structural and electronic properties were investigated. Finally, in order to investigate biological function of the biosensor, docking studies were performed.

Isolation of sugarcane amino acids from aqueous solution by ARHA

In this research work, adsorption of sugarcane amino acids on activated rice husk ash (ARHA) has been studied. The pore distribution of the ARHA falls between macroporous and mesoporous domains. The BET surface area of the ARHA was typically found as SBET = 16.48 m2/g. The adsorption properties of studied sugarcane amino acids depend on several factors such as pKa, functional group present, polarity, molecular weight, size and solution condition such as pH, ionic strength and adsorbed concentration. Adsorption was found to increase markedly with increase in ionic strength from 0.02 to 0.1 M suggesting a role for the hydrophobic force in this adsorption process. Adsorption was reduced substantially by the addition of urea; therefore, hydrogen bonding seems to play an important role in this adsorption process. ARHA was characterized by FT-IR, SEM and BET techniques for its use for selective adsorption for sugarcane amino acids from their aqueous solutions. Typical Langmuirian (L2) type adsorption isotherms were observed and adsorption mechanism has been proposed. Thermodynamics parameters of the adsorption process have also been evaluated. This study showed that the ARHA could be employed as low- cost and effective adsorbent for the removal of sugarcane amino acids.

Impact of Glutamate Carboxylation in the Adsorption of the α-1 Domain of Osteocalcin to Hydroxyapatite and Titania.

One proposed mechanism of implant fouling is attributed to the nonspecific adsorption of non-collagenous bone matrix proteins (NCPs) onto a newly implanted interface. With the goal of capturing the fundamental mechanistic and thermodynamic forces that govern changes in these NCP recognition domains as a function of γ-carboxyglutamic acid (Gla) post-translational modification and surface chemistry, we probe the adsorption process of the most commonly occurring NCP, osteocalcin, onto a mineral and metal oxide surface. Here, we apply two enhanced sampling methods to independently probe the effects of post-translational modification and peptide structure on adsorption. First, well-tempered metadynamics was used to capture the binding of acetyl and N-methylamide capped glutamic acid and Gla single amino acids onto crystalline hydroxyapatite and titania model surfaces at physiological pH. Following this, parallel tempering metadynamics in the well-tempered ensemble (PTMetaD-WTE) was used to study adsorption of the α-1 domain of osteocalcin onto hydroxyapatite and titania. Simulations were performed for the α-1 domain of osteocalcin in both its fully decarboxylated (dOC) and fully carboxylated (OC) form. Our simulations find that increased charge density due to carboxylation results in increased interactions at the interface, and stronger adsorption of the single amino acids to both surfaces. Interestingly, the role of Gla in promoting compact and helical structure in the α-1 domain resulted in disparate binding modes at the two surfaces, which is attributed to differences in interfacial water behavior. Overall, this work provides a benchmark for understanding the mechanisms that drive adsorption of Gla-containing mineralizing proteins onto different surface chemistries.

Influence of Biocorona Formation on the Transformation and Dissolution of Cobalt Nanoparticles under Physiological Conditions.

Cobalt (Co) nanoparticles (NPs) are produced in different applications and unintentionally generated at several occupational and traffic settings. Their diffuse dispersion may lead to interactions with humans and aquatic organisms via different exposure routes that include their transformation/dissolution in biological media. This paper has investigated the particle stability and reactivity of Co NPs (dispersed by sonication prior to exposure) interacting with selected individual biomolecules (amino acids, polypeptides, and proteins) in phosphate-buffered saline (PBS). No or minor adsorption of amino acids (glutamine, glutamic acid, lysine, and cysteine) was observed on the Co NPs, independent of the functional group and charge. Instead, phosphate adsorption resulted in the formation of a surface layer (a corona) of Co phosphate. The adsorption of larger biomolecules (polyglutamic acid, polylysine, lysozyme, and mucin) was evident in parallel with the formation of Co phosphate. The dissolution of the Co NPs was rapid as 35–55% of the particle mass was dissolved within the first hour of exposure. The larger biomolecules suppressed the dissolution initially compared to exposure in PBS only, whereas the dissolution was essentially unaffected by the presence of amino acids, with cysteine as an exception. The formation of Co phosphate on the NP surface reduced the protective properties of the surface oxide of the Co NPs, as seen from the increased levels of the released Co when compared with the nonphosphate-containing saline. The results underline the diversity of possible outcomes with respect to surface characteristics and dissolution of Co NPs in biological media and emphasize the importance of surface interactions with phosphate on the NP characteristics and reactivity.