Interaction of amino acids with gold and silver clusters

Binding of gold and silver clusters with amino acids (glycine and cysteine) was studied using density functional theory (DFT). Geometries of neutral, anionic, and cationic amino acids with Au3 and Ag3 clusters were optimized using the DFT-B3LYP approach. The mixed basis set used here was denoted by 6-31+G** (union or logical sum)LANL2DZ. This work demonstrated that the interaction of amino acids with gold and silver clusters is governed by two major bonding factors: (a) the anchoring N-Au(Ag), O-Au(Ag), and S-Au(Ag) bonds and (b) the nonconventional N-H...Au(Ag) and O-H...Au(Ag) hydrogen bonds. Among the three forms of amino acids, anionic ones exhibited the most tendency to interact with the Au and Ag clusters. Natural bond orbital analysis was performed to calculate charge transfer, natural population analysis, and Wiberg bond indices of the complexes. Atoms-in-molecules theory was also applied to determine the nature of interactions. It was shown that these bonds are partially electrostatic and partially covalent.     

Formation of long-lived clusters and silver nucleation in the γ-irradiation of aqueous silver perchlorate solutions containing polyphosphate

It was found that long-lived positively charged and neutral silver clusters were formed by the radiation-chemical reduction of Ag⁺ ions in aqueous solutions containing sodium polyphosphate. The nuclearity of the clusters increased with absorbed dose; then, quasi-metal particles were formed. The process culminated in the formation of silver nanoparticles.Translated from Khimiya Vysokikh Energii, Vol. 39, No. 2, 2005, pp. 83–87.Original Russian Text Copyright © 2005 by Ershov, Abkhalimov, Sukhov.This revised version was published online in April 2005 with a corrected cover date.     

High chemical reactivity of silver nanoparticles toward hydrochloric acid

High chemical reactivity of Ag nanoparticles was observed in the reaction with hydrochloric acid: Ag (nanoparticles)+ HCl-->AgCl + H2; the reaction product silver chloride was characterized by X-ray powder diffraction to give a direct evidence for the reaction which has been proved impossible for the bulk Ag.     

The influence of Ag+ ions on transformations of silver clusters in polyacrylate aqueous solutions

It is shown that transformations of unstable clusters, intermediates of the borohydride reduction of silver cations, in weakly alkaline polyacrylate aqueous solutions are governed by the competition between the processes of their oxidation, coalescence into larger particles, and reduction of silver cations. Moreover, these processes depend on the loading of a polyanion with cations and can be controlled by the addition of Ag⁺ ions.     

Synthesis of amino polycarboxylic acids of the adamantane series

The Ritter reaction of dibasic carboxylic acids of the adamantane series with carboxy and carboxymethyl groups attached to bridgehead carbon atoms afforded a number of amino polycarboxylic acids.     

The aromatic amino acid behaviour in aqueous amide solutions

The enthalpies of solution of L-phenylalanine in the mixtures of water with the protein denaturant urea have been measured in the temperature range of 288.15–318.15 K. Using the results of the present research and literature data of free energies, the standard thermodynamic functions of the solute transfer from water to aqueous urea solutions have been estimated in a wide temperature range. The enthalpic, heat capacity, entropic and free energy parameters of the solute-urea pair and triplet interactions have been computed. The amino acid — amide pair interaction was found to be attractive in the temperature range studied due to the favourable enthalpic term. The triplet interaction being slightly repulsive reveals the enthalpic origin also. The examination of the Savage and Wood additivity-of-groups approach does indicate the inapplicability of this scheme to enthalpies and entropies of interaction. It has been found for the first time that the heat capacity of interaction changes its sign at 303 K, i.e. the temperature dependence of enthalpic and entropic parameters passes through the pronounced extrema near the temperature of the minimum of the heat capacity of pure water.     

Development kinetics of silver clusters on silver halides

Silver nuclei are produced by pulse radiolysis at the surface of AgCl nanocrystallites in the presence of an electron donor, the methyl viologen, which induces the growth of silver nuclei. The experimental results observed on the increase of the silver atom concentration and on the decay of the donor concentration during this process, which is similar to the photographic development by an electron donor, are compared with the kinetics obtained from numerical simulation. The model assumes that the formation of silver clusters with a supercritical nuclearity is required before the start of an electron transfer reaction from the two reduced forms of the donor methyl viologen to the silver clusters. The reaction is controlled by the access of the donor to the surface sites of the AgCl crystallite. The rate constant values of the successive steps of the mechanism are derived from the adjustment of calculated kinetics to experimental signals under various conditions, using a single set of parameters which are fairly suitable under all conditions studied.     

Ligand dynamics and reactivity in trimetallic clusters

The general relationships between trinuclear cluster reactivity and the ligand dynamical processes in these systems are explored. Three specific mechanistic studies are presented: (1) the rate and stereochemistry of ligand addition to ₃-imidoyl complexes, (2) the factors influencing the rate of carbon-hydrogen bond activation in ₃-alkyne complexes, and (3) the origin of anomalously large kinetic deuterium isotope effect in metal to ligand and ligand to metal hydrogen transfer in trinuclear and binuclear complexes. In all three cases, the current state of the mechanistic studies are summarized and the possible rate of specific ligand dynamical processes in controlling the mechanism are put forth.     

Formation and stability of charged amino acid clusters and the role of chirality

Amino acid clusters have been studied by several groups and most notably magic number clusters and chiral recognition have been reported. In this work, we have studied the formation of amino acid clusters by electrospray ionization (ESI) and their stability by high-energy collision-induced dissociation (CID). Appearance sizes were determined for multiply charged clusters where the charge is either due to protons or to sodium ions. Finally, we conclude that chiral selectivity plays an important role in cluster formation but seems to be of minor importance for the fragmentation of mixed clusters.     

Photoelectron spectroscopy of silver clusters

A comparison of x-ray photoemission from Ag clusters deposited on polygraphite and highly oriented pyrolitic graphite shows the influence of the support both on the valence band and on the core 3d level of the metal. Positive shifts have been obtained with respect to the bulk for the Fermi edge and the 3d peaks depending on the number of silver atoms deposited on the substrates. When the deposition is very small (cluster regime) the positive shifts of the binding energies are quite different for different substrates and cannot have a common origin. In contrast with recent work, we show that several effects contribute to these shifts: initial state effects like charge redistribution as well as final state effects like the hole-electron interaction.     

Effect of amino acid sorption on formation of water clusters in ion-exchange membranes

The average size and number of water clusters inside ion-exchange membranes are calculated from experimental isotherms of water vapor sorption as a result of considering the sorption in terms of the clusterization theory. It is established that, in MK-40 heterogeneous cation-exchange membrane, water clusters are not formed, while, inside MF-4SK perfluorinated homogeneous membrane, intense cluster formation takes place. The effect of amino acid sorption on cluster water is considered. An increase in the membrane hydrophobicity as a result of the incorporation of amino acid ions leads to prevailing interaction of water molecules with one another rather than with the polymer phase, which is evident from an enlargement of water clusters.     

Nucleation of silver upon the reduction by hydrogen in aqueous polyphosphate-containing solutions: Formation of clusters and nanoparticles

In the reduction of Ag⁺ ions by hydrogen in aqueous polyphosphate-containing solutions, the formation of metal nanoparticles is preceded by the emergence of clusters comprising a few silver atoms and ions. In the process of cluster aggregation, their nuclearity increases and quasi-metallic particles followed by metal nanoparticles are formed. The efficiency of nanoparticle formation rises with the increasing concentration of polymer stabilizer. The mechanism of the formation of hydrosol is discussed.     

Formation of silver clusters in nozzle expansions

The first successful experiments to generate continuum silver cluster beams from nozzle expansions are described. A mixture Ar/Ag expands out of a conical nozzle (0.35 mm dia., 10° cone angle, length 17 mm). At 2150 K, total pressure 300 kPa, silver partial pressure 8 kPa the silver intensity measured with a rate meter 479mm away from the source is 1.8 nm/s, or 0.02 g m^?2s^?1. The data for the onset of clustering confirm the predictions of the scaling laws developed to compare condensation in nozzle expansions of metal vapors with that of rare gases.     

Nanofiltration of amino acid and peptide solutions: mechanisms of separation

This is a study of the nanofiltration of various charged amino acids and peptides, in solutions of increasing complexity, through an inorganic membrane. Whatever the solution studied, charge effects, repulsion of coions and attraction of the counterions, more than size effects, prevail in the behavior of the solute. The extent of the transmission of a given solute, and hence the selectivity of the separation, were strongly affected by solute environment, mainly because of competitive solute/solute and solute/membrane interactions. However, despite the complexity, the experimental data were always in accordance with the following principles: (i) whatever solution, the electric neutrality was always recovered and (ii) the number of charges, rather than global net charge, should be considered in order to account for amino acid and peptide transmissions. On the basis of these principles, a general mechanism for amino acid and peptide separation in nanofiltration is proposed.     

Optical and ESR studies of silver clusters

The optical and ESR spectra of Ag(O), Ag₂⁺ and Ag₄³⁺ centres formed in γ-irradiated aqueous and ethanol glasses have been monitored under identical conditions. The ESR spectra of the Ag(O) centres sugest that they initially retain the solvation of the parent Ag⁺ ions but that solvent molecules are gradually lost on annealing. This loss is reflected in marked high-frequency shifts in the electronic transitions. An intense band observed in the range 265–290 nm grew in simultaneously. This is assigned to Ag₂³⁺ ions. These have a well characterised ESR spectrum, but have not previously been studied optically.     

The electron transfer reactivity of kaempferol and its interaction with amino acid residues

In this work, the electron transfer reactivity of kaempferol was studied and the interaction in vivo between kaempferol and protein was simulated. Dimethylsulfoxide (DMSO) as an aprotic solvent was employed to simulate the specific environment. Various residues of amino acids were used to study the effect of the amino acids in the active site of protein on the electron transfer reactivity of kaempferol. Experimental results revealed that the redox activity of kaempferol was different in aprotic medium DMSO from that in water, and a new redox process was further found. Of all the residues tested, nitrogenous nucleophile, for example, imidazole, was observed to be able to facilitate the electron transfer of kaempferol, and the mechanism was also proposed. This work might provide a simple model to study the electron transfer reactivity of some small active organic molecules, especially medicines, in specific environment, which might approach a more accurate understanding of the activity of some medicines in vivo.     

Density,viscosity, and N2O solubility of aqueous amino acid salt and amine amino acid salt solutions

Physicochemical properties of aqueous amino acid salt (AAS), potassium salt of sarcosine (KSAR) and aqueous amine amino acid salt (AAAS), 3-(methylamino)propylamine/sarcosine (SARMAPA) have been studied. Densities of KSAR were measured for sarcosine mole fraction 0.02 to 0.25 for temperature range 298.15 K to 353.15 K, the viscosities were measured for 0.02 to 0.10 mole fraction sarcosine (293.15 K to 343.15 K) while the N₂O solubilities were measured from 0.02 to 0.10 mole fraction sarcosine solutions (298.15 K to 363.15 K). Densities of SARMAPA were measured for sarcosine mole fraction 0.02 to 0.23 for temperature range (298.15 K to 353.15 K), viscosities were measured for 0.02 to 0.16 mole fraction sarcosine (293.15 K to 343.15 K) while the N₂O solubilities were measured from 0.02 to 0.16 mole fraction sarcosine solutions (298.15 K to 343.15 K). Experimental results were correlated well with empirical correlations and N₂O solubility results for KSAR were predicted adequately by a Schumpe model. The solubilities of N₂O in AAS and AAAS are significantly lower than values for amines. The solubilities vary as: amine > AAAS > AAS.