Colloidal copper and peculiarities of its reaction with silver ions in aqueous solution

Interactions between colloidal copper and silver ions lead to the formation of silver nanoparticles. The reaction proceeds through the intermediate stage of the formation of a copper-silver contact pair. The formation of bimetallic Ag_coreCu_shell nanoparticles is observed in the presence of the “seeding” silver nanoparticles and upon the simultaneous radiochemical reduction of Ag⁺ and Cu²⁺ ions.     

Transmetalation reaction between hydrophobic silver nanoparticles and aqueous chloroaurate ions at the air-water interface

The transmetalation reaction between a sacrificial nanoparticle and more noble metal ions in solution has emerged as a novel method for creating unique hollow and bimetallic nanostructures. In this report, we investigate the possibility of carrying out the transmetalation reaction between hydrophobic silver nanoparticles assembled and constrained at the air-water interface and subphase gold ions. We observe that facile reduction of the subphase gold ions by the sacrificial silver nanoparticles occurs resulting in the formation of elongated gold nanostructures that appear to cross-link the sacrificial silver particles. This transmetalation reaction may be modulated by the insertion of an electrostatic barrier in the form of an ionizable lipid monolayer between the silver nanoparticles and the aqueous gold ions that impacts the gold nanoparticle assembly. Transmetalation reactions between nanoparticles constrained into a close-packed structure and appropriate metal ions could lead to a new strategy for metallic cross-linking of nanoparticles and generation of coatings with promising optoelectonic behavior.     

Effect of silver ions on codischarge of copper and silver at a platinum electrode at the copper underpotentials

Codischarge of copper and silver ions at potentials more positive than the equilibrium potential of the Cu⁺²/Cu system is studied by the voltammetry technique. At the Ag⁺ concentrationc below 10^-7 M, silver ions make no noticeable impact on the formation of a Cu_ad monolayer but decelerate that of supermonolayers of Cu at almost equilibrium potentials. Atc ≥ 4 × 10^-5 M, voltammograms indicate the concurrent adsorption of Cu_ad and Ag_ad and the nucleation and deposition of phase Ag     

Electronic structure of copper phthalocyanine: an experimental and theoretical study of occupied and unoccupied levels

An experimental and theoretical study of the electronic structure of copper phthalocyanine (CuPc) molecule is presented. We performed x-ray photoemission spectroscopy (XPS) and photoabsorption [x-ray absorption near-edge structure (XANES)] gas phase experiments and we compared the results with self-consistent field, density functional theory (DFT), and static-exchange theoretical calculations. In addition, ultraviolet photoelectron spectra (UPS) allowed disentangling several outer molecular orbitals. A detailed study of the two highest occupied orbitals (having a(1u) and b(1g) symmetries) is presented: the high energy resolution available for UPS measurements allowed resolving an extra feature assigned to vibrational stretching in the pyrrole rings. This observation, together with the computed DFT electron density distributions of the outer valence orbitals, suggests that the a(1u) orbital (the highest occupied molecular orbital) is mainly localized on the carbon atoms of pyrrole rings and it is doubly occupied, while the b(1g) orbital, singly occupied, is mainly localized on the Cu atom. Ab initio calculations of XPS and XANES spectra at carbon K edge of CuPc are also presented. The comparison between experiment and theory revealed that, in spite of being formally not equivalent, carbon atoms of the benzene rings experience a similar electronic environment. Carbon K-edge absorption spectra were interpreted in terms of different contributions coming from chemically shifted C 1s orbitals of the nonequivalent carbon atoms on the inner ring of the molecule formed by the sequence of CN bonds and on the benzene rings, respectively, and also in terms of different electronic distributions of the excited lowest unoccupied molecular orbital (LUMO) and LUMO+1. In particular, the degenerate LUMO appears to be mostly localized on the inner pyrrole ring.     

Fluorescence response of TICT-active aminostilbenes to copper(II) ions: redox reaction vs ion recognition

Cu(II)-selective fluorescence enhancement (1, 2, and 4) or fluorescence quenching (3) was observed for aminostilbenes 1–4 in acetonitrile. The fluorescence responses result from efficient Cu(II)-mediated oxidation of 1–4 that forms new fluorescent species rather than from any specific noncovalent interactions. Evidence of redox reactions includes irreversible Cu(II) titration spectra, spectroscopic observation of the radical cations, and isolation of oxidized aminostilbene dimers. These results provide a new method for synthesis of tetrasubstituted tetrahydrofurans and suggest that aminostilbenes with twisted intramolecular charge-transfer activity are potential fluorescence-enhanced Cu(II) chemodosimeters. The role of Cu(II)-mediated redox reactions should be always taken into account in mechanisms for sensing of arylamine-based Cu(II)-selective fluoroionophores.     

Reduction and aggregation of silver,copper and cadmium ions in aqueous solutions of gelatin and carboxymethyl cellulose

Radiolytic reduction of silver, copper and cadmium ions and the subsequent formation of their clusters was studied in aqueous gelatin or carboxy methyl cellulose (CMC) solutions. Presence of gelatin or CMC in the solution affects the early processes. The rate of reduction by hydrated electron reduces due to complexation. However, when the ratio of silver ions to monomeric chains decreases over a certain limit the process of reduction inhibits completely. The effect of ionic strength or pH and the reducing radical on the rate of formation of colloidal Cu and Cd is also discussed.     

The effects of charge transfer on the aqueous solvation of ions

Ab initio-based charge partitioning of ionic systems results in ions with non-integer charges. This charge-transfer (CT) effect alters both short- and long-range interactions. Until recently, the effects of CT have been mostly neglected in molecular dynamics (MD) simulations. The method presented in this paper for including charge transfer between ions and water is consistent with ab initio charge partitioning and does not add significant time to the simulation. The ions of sodium, potassium, and chloride are parameterized to reproduce dimer properties and aqueous structures. The average charges of the ions from MD simulations (0.900, 0.919, and -0.775 for Na(+), K(+), and Cl(-), respectively) are consistent with quantum calculations. The hydration free energies calculated for these ions are in agreement with experimental estimates, which shows that the interactions are described accurately. The ions also have diffusion constants in good agreement with experiment. Inclusion of CT results in interesting properties for the waters in the first solvation shell of the ions. For all ions studied, the first shell waters acquire a partial negative charge, due to the difference between water-water and water-ion charge-transfer amounts. CT also reduces asymmetry in the solvation shell of the chloride anion, which could have important consequences for the behavior of chloride near the air-water interface.     

Absolute solvation free energy of Li+ and Na+ ions in dimethyl sulfoxide solution: a theoretical ab initio and cluster-continuum model study

The solvation of the lithium and sodium ions in dimethyl sulfoxide solution was theoretically investigated using ab initio calculations coupled with the hybrid cluster-continuum model, a quasichemical theory of solvation. We have investigated clusters of ions with up to five dimethyl sulfoxide (DMSO) molecules, and the bulk solvent was described by a dielectric continuum model. Our results show that the lithium and sodium ions have four and five DMSO molecules into the first coordination shell, and the calculated solvation free energies are -135.5 and -108.6 kcal mol(-1), respectively. These data suggest a solvation free energy value of -273.2 kcal mol(-1) for the proton in dimethyl sulfoxide solution, a value that is more negative than the present uncertain experimental value. This and previous studies on the solvation of ions in water solution indicate that the tetraphenylarsonium tetraphenylborate assumption is flawed and the absolute value of the free energy of transfer of ions from water to DMSO solution is higher than the present experimental values.     

The influence of solvation and finite temperatures on theWittig reaction: A theoretical study

The effects of the solvent and finite temperature (entropy) on the Wittig reaction are studied by using density functional theory in combination with molecular dynamics and a continuum solvation model. Standard gas-phase zero-temperature calculations are found to give similar results to previous studies. Gas-phase dynamics simulations allow the free energy profile of the reaction to be calculated through thermodynamic integration. The free energy profile is found to have a significant entropic barrier to the addition step of the reaction where only a small barrier was present in the potential energy curve. The introduction of the solvent dimethyl sulfoxide causes a change in the structure of the intermediate from the oxaphosphetane structure to the dipolar betaine structure. The overall reaction energy is changed only slightly. When the effects of both entropy and the solvent are included a significant entropic barrier to the addition reaction is obtained and the predicted intermediate again has the betaine structure.     

Electronic structure of polyphosphate ions

The electronic and stereochemical structure of the polyphosphate ions (PO₃) ₂ ^2– , P₂O₇ ^4–, and (PO₃)₃ ^3–, and also of model nucleoside polyphosphates, which play an important role in the accumulation and transport of energy in biosystems, were investigated by the MNDO quantum-chemical method. The electron density distribution in the systems is analyzed, and the centers most favorable for interaction with metal ions are identified. It is shown that the investigated ions are thermally stable systems, and this is largely due to the delocalization of the excess electron charge along the polyphosphate chain.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 6, pp. 673–679, November–December, 1987.     

ABSINTH: a new continuum solvation model for simulations of polypeptides in aqueous solutions

A new implicit solvation model for use in Monte Carlo simulations of polypeptides is introduced. The model is termed ABSINTH for self-Assembly of Biomolecules Studied by an Implicit, Novel, and Tunable Hamiltonian. It is designed primarily for simulating conformational equilibria and oligomerization reactions of intrinsically disordered proteins in aqueous solutions. The paradigm for ABSINTH is conceptually similar to the EEF1 model of Lazaridis and Karplus (Proteins 1999, 35, 133). In ABSINTH, the transfer of a polypeptide solute from the gas phase into a continuum solvent is the sum of a direct mean field interaction (DMFI), and a term to model the screening of polar interactions. Polypeptide solutes are decomposed into a set of distinct solvation groups. The DMFI is a sum of contributions from each of the solvation groups, which are analogs of model compounds. Continuum-mediated screening of electrostatic interactions is achieved using a framework similar to the one used for the DMFI. Promising results are shown for a set of test cases. These include the calculation of NMR coupling constants for short peptides, the assessment of the thermal stability of two small proteins, reversible folding of both an alpha-helix and a beta-hairpin forming peptide, and the polymeric properties of intrinsically disordered polyglutamine peptides of varying lengths. The tests reveal that the computational expense for simulations with the ABSINTH implicit solvation model increase by a factor that is in the range of 2.5-5.0 with respect to gas-phase calculations.     

The thermochemical characteristics of the solvation of amines and silver ions in methanol-dimethylformamide mixtures

The heat effects of solution of ethylenediamine, sodium perchlorate, and silver perchlorate in the nonaqueous methanol-dimethylformamide binary solvent were determined calorimetrically at 298.15 K. The suggestion of equal enthalpies of solvation of Ph₄P⁺ and PhB^? was used to calculate the enthalpies of transfer of the ClO ₄ ^? and Ag⁺ ions from methanol to dimethylformamide. The influence of the composition of methanol-dimethylformamide solvents on the energy characteristics of solvation of ethylenediamine, Ag⁺, and ClO ₄ ^? was considered.     

Quantum chemical model of solvation for calculation of electrode potentials of redox processes involving ferrocene,cobaltocene, and their ions

Quantum chemical calculations of solvation energy for ferrocene and cobaltocene molecules and their ionic forms in water, acetonitrile, methanol, and acetone are performed in terms of the B3LYP density functional method by taking into account solvation effects and using the polarized continuum model (PCM). Standard electrode potentials of the corresponding redox pairs, the effect of solvent on them, and the overall energy of the transfer of cobaltocene cation and anion between two solvents are calculated. The calculation results well agree with the available experimental data. The present study provides sufficiently reliable grounds for the application of an ion—metallocene molecule redox pair as a pilot system for the comparison of electrode potentials and solvation energies in different solvents.     

Electronic structure of aqueous borohydride: a potential hydrogen storage medium

Borohydride salts have been considered as good prospects for transportable hydrogen storage materials, with molecular hydrogen released via hydrolysis. We examine details of the hydration of sodium borohydride by the combination of X-ray absorption spectroscopy and first principles' theory. Compared to solid sodium borohydride, the aqueous sample exhibits an uncharacteristically narrow absorption feature that is shifted to lower energy, and ascribed to the formation of dihydrogen bonds between borohydride and water that weaken the boron-hydrogen covalent bonds. Water also acts to localize the highly excited molecular orbitals of borohydride, causing transitions to excited states with p character to become more intense and a sharp feature, uncharacteristic of tetrahedral molecules, to emerge. The simulations indicate that water preferentially associates with borohydride on the tetrahedral corners and edges.     

Electronic structure of long polyene ions

The ionization potentials, densities of the one-electron states, and distribution of the charge have been calculated in the -electronic approximation for linear polyene ions containing up to 100 carbon atoms. The role of the electrostatic interaction in these systems has been discussed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 4, pp. 393–398, July–August, 1989.     

Thermochemistry of copper(II) ion solvation in aqueous organic solvents

The integral heat effects of CuCl₂ dissolution in aqueous DMSO, aqueous ethanol and aqueous acetone solutions at 298. 15 K in the electrolyte concentration range 0.001–0.01M were measured by means of calorimetry. ΔH _sol ⁰ values were obtained by extrapolation to zero electrolyte concentration. Literature data were used to determine the thermodynamic characteristics of Cu²⁺ transfer from water to aqueous organic solvents.     

Electronic structure of crystalline copper phthalocyanine

The electronic structure of copper-phthalocyanine (CuPc) has been studied both experimentally and theoretically. Experiments have been performed on alpha and beta crystalline phases, using photoemission spectroscopy to probe core levels and valence band spectra. Different photon energies have been used, in order to probe different sample depths. Only minor differences have been observed in the experimental data on the two different phases, except for a small charge effect on the beta phase crystal. First-principles calculations have been performed using the density functional for molecular and three-dimensional periodic solids (Dmol(3)) code on both the single CuPc molecule and the beta phase, allowing the identification of the different atomic and angular contributions to the experimental density of states. In particular, the highest occupied molecular level is mainly due to Cu and N states. The comparison between theoretical data obtained for the CuPc in the beta phase and in the single molecule shows that the interchain interaction between the molecules is negligible, whereas slightly stronger intrachain interactions occur.     

Electronic structure of small copper clusters

An all-electron ab initio LCAO -MO SCF calculation has been carried out for the electronic structure of small copper clusters (Cu_n, n = 2–6). The basis set superposition error occurring in the calculation, the equilibrium configuration of Cu₃, the bond energy in the clusters, and the localized d-hole in excited and ionized states of Cu₂ are closely examined.     

Electronic structure of copper phthalocyanine: a comparative density functional theory study

We present a systematic density functional theory study of the electronic structure of copper phthalocyanine (CuPc) using several different (semi)local and hybrid functionals and compare the results to experimental photoemission data. We show that semilocal functionals fail qualitatively for CuPc primarily because of underbinding of localized orbitals due to self-interaction errors. We discuss an appropriate choice of functional for studies of CuPc/metal interfaces and suggest the Heyd-Scuseria-Ernzerhof screened hybrid functional as a suitable compromise functional.