Adsorption Behavior Of Amino Acid Research Articles

Cation exchange to montmorillonite induces selective adsorption of amino acids

Concentrating simple organic molecules, such as amino acids, in the adsorbed phase could have been an early step in prebiotic evolution towards more complex bio-macromolecules on the early Earth. Smectite clay minerals represent potential selective sorbents for prebiotic molecules because of their negative structural charge and high surface area. This study evaluated the adsorption behavior of amino acids to montmorillonite, a well-characterized smectite, at varying pH and fluid compositions. At both pH 5 and 7 in a sodium chloride fluid, amino acids with basic sidechains (L-arginine and L-lysine), which are primarily cationic under these conditions, were selectively adsorbed to montmorillonite with Langmuir constants much greater than amino acids that were predominantly zwitterionic or anionic in solution. On average, the Langmuir constants for the cationic amino acids were 30 (pH 5) and 50 (pH 7) times greater than the constants for zwitterionic amino acids and 120 (pH 5) and 80 (pH 7) times greater than the constants for L-glutamic acid. Under the same pH conditions in a magnesium chloride solution, the adsorption of L-arginine and L-lysine was substantially inhibited with Langmuir constants ∼ 10 times smaller. These observations suggest that cation exchange is the dominant adsorption mechanism for amino acids on montmorillonite. X-ray diffraction and infrared spectroscopy indicate that L-arginine and L-lysine enter the smectite interlayer where the protonated amino sidechain has the strongest interactions with the mineral surface, further supporting adsorption driven primarily through electrostatic interactions. Therefore, smectites on the early Earth may have selectively concentrated cationic amino acids, providing a potential template for the polymerization of α-amine linked peptides.

Theoretical elucidation of the amino acid interaction with graphene and functionalized graphene nanosheets: insights from DFT calculation and MD simulation.

Graphene-amino acid interaction is gaining significance mainly based on its possible biomedicine applications. The density functional theory (DFT) calculation and molecular dynamics simulation (MD) are applied to obtain a comprehensive understanding of the adsorption mechanism of three kinds of amino acids, namely, alanine (Ala), glycine (Gly), and valine (Val) over the surface of graphene and functionalized graphene nanosheets. In this study, several analyses such as solvation energy, adsorption energy, intermolecular distances, and charge properties are used to explore the adsorption behavior of amino acid on the nanosheets. The calculated adsorption energies show that the interaction of amino acids with functionalized graphene is greater than the pristine graphene. Regarding DFT computations, the adsorption of Val on the graphene about -10kJ/mol is stronger than Gly and Ala. Meanwhile, it is found that the geometrical parameters and electronic properties of graphene change drastically upon functionalization, and the formation of hydrogen bonds between -COOH functional group and amino acids enhances the adsorption energy about 12-30%. To obtain a deeper comprehension of the interaction nature, the atoms in molecules (AIM) and the natural bond orbital (NBO) studies have been performed. Furthermore, the MD simulations are employed to assess the dynamic properties of our designed systems. The results from the present study demonstrate that the movement of the amino acids into the carriers is spontaneous and forms stable complexes.

Mechanism of photocatalytic oxidation of amino acids: Hammett correlations

Amino acids are important constituents of microorganisms and organic matter in water and may contribute to generation of nitrogenous disinfection by-products (N-DBPs) during chlorination and chloramination. The photocatalytic oxidation of amino acids has thus been carried out to seek their mineralization and to understand their interactions with solid TiO2 surfaces, which have a wide range of applications in biological and environmental fields. In the present study, the photodecomposition of amino acids (R-CH(NH3+)COO−) onto TiO2 aqueous suspension was examined using Hammett correlations to enhance understanding the mechanism of the mineralization of amino acids to NH4+, NO3−, and CO2. Amino acids, except Ser, Asp, and Glu, had reasonable linear Hammett correlations. The deviation of alcoholic and dicarboxylic groups containing amino acids (Ser, Asp, and Glu) from the Hammett correlations suggests that not only steric and inductive factors, but also other processes such as adsorption behavior of amino acids onto solid surface also contributed to mineralization of amino acids to oxidized species. The rate constants for the release of NH4+ and CO2 were also correlated with the second-order rate constants for the reactions of hydrated electron and OH, respectively. Correlations had negative relationships, which indicate that the nature of reactive species, reaction pathways and intermediates, involved in mineralization of amino acids under illuminated aqueous TiO2 suspensions, differs from the redox species (e.g. eaq−, O2−, and OH) in homogeneous reactions. Mechanism in light of correlations was briefly discussed.

Adsorption Behavior of Amino Acids on a Stainless Steel Surface

The adsorption behavior of various amino acids on a stainless steel surface was investigated at 30°C and over a pH range of 3–10. Acidic and basic amino acids except histidine adsorbed remarkably at pH 3–4 and 7–10, respectively, and showed Langmuir-type adsorption isotherms. The effects of pH and ionic strength on the adsorption isotherms were investigated to analyze the interactions between amino acids and adsorption sites on the stainless steel. Hydrophobic amino acids and glycine showed only small adsorbed amounts at all pHs tested. For the acidic and basic amino acids, reversibility of the absorption and the influence of the ionic strength on the adsorption behavior were examined. The adsorption isotherms of the derivatives of aspartic acid were also measured in order to examine the contribution of the carboxylic groups of acidic amino acids to the adsorption. Furthermore, a Fourier-transform infrared spectroscopic analysis and semiempirical molecular orbital calculation were carried out to analyze the ionization states and the configuration of the amino acids adsorbed on a stainless steel surface. These investigations suggest that the acidic and basic amino acids adsorb through two electrostatic interactions of two ionized groups in the amino acid with a stainless steel surface.