In-Situ Investigation of Discolouration Processes Between Historic Oil Paint Pigments

Discolouring interactions between paint pigments have been observed since the mid 19^th century. The source of some of these discolourations is the production of copper sulfides from an interaction between cadmium sulfide pigments and copper containing pigments. In this work, the discolouring interaction between cadmium yellow and malachite pigments was observed dynamically using the environmental scanning electron microscope (ESEM).     

Dielectric spectroscopy on aqueous solutions of pyridine and its derivatives

The complex (dielectric) permittivity has been measured as a function of frequency between 1 MHz and 40 GHz for aqueous solutions of pyridine, 2- and 3-methylpyridine, as well as 2,4- and 2,6-dimethylpyridine at various temperatures and solute concentrations. Different relaxation spectral functions are used to analytically represent the data, in particular the Cole-Cole function. The solute contribution to the extrapolated static permittivity has been calculated to show that, in correspondence with other aqueous solutions of organic molecules and ions, the permittivity of the solvent seems to be enhanced with respect to the pure water value. Also in accordance with other aqueous systems it is found that the principal dielectric relaxation time for equimolar solutions of stereo isomers at the same temperature may significantly differ from one another. A further result is the finding of an unusually strong temperature dependence in the relaxation time of the 1 molar solution of 2,6-dimethylpyridine.     

Quantum chemical studies on molecular structural conformations and hydrated forms of salicylamide and O‐hydroxybenzoyl cyanide

Ab initio and density functional theory (DFT) methods have been employed to study the molecular structural conformations and hydrated forms of both salicylamide (SAM) and O‐hydroxybenzoyl cyanide (OHBC). Molecular geometries and energetics have been obtained in the gaseous phase by employing the Møller–Plesset type 2 MP2/6‐311G(2d,2p) and B3LYP/6‐311G(2d,2p) levels of theory. The presence of an electron‐releasing group (SAM) leads to an increase in the energy of the molecular system, while the presence of an electron‐withdrawing group (OHBC) drastically decreases the energy. Chemical reactivity parameters (η and μ) have been calculated using the energy values of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) obtained at the Hartree–Fock (HF)/6‐311G(2d,2p) level of theory for all the conformers and the principle of maximum hardness (MHP) has been tested. The condensed Fukui functions have been calculated using the atomic charges obtained through the natural bond orbital (NBO) analysis scheme for all the optimized structures at the B3LYP/6‐311G(2d,2p) level of theory, and the most reactive sites of the molecules have been identified. Nuclear magnetic resonance (NMR) studies have been carried out at the B3LYP/6‐311G(2d,2p) level of theory for all the conformers in the gaseous phase on the basis of the method of Cheeseman and coworkers. The calculated chemical shift values have been used to discuss the delocalization activity of the electron clouds. The dimeric structures of the most stable conformers of both SAM and OHBC in the gaseous phase have been optimized at the B3LYP/6‐311G(2d,2p) level of theory, and the interaction energies have been calculated. The most stable conformers of both compounds bear an intramolecular hydrogen bond, which gives rise to the formation of a pseudo‐aromatic ring. These conformers have been allowed to interact with the water molecule. Special emphasis has been given to analysis of the intermolecular hydrogen bonds of the hydrated conformers. Self‐consistent reaction field (SCRF) theory has been employed to optimize all the conformers in the aqueous phase (ε = 78.39) at the B3LYP/6‐311G(2d,2p) level of theory, and the solvent effect has been studied. Vibrational frequency analysis has been performed for all the optimized structures at MP2/6‐311G(2d,2p) level of theory, and the stationary points corresponding to local minima without imaginary frequencies have been obtained for all the molecular structures. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Quantum chemical calculation of cation interaction with water molecules and ethylene glycol

A computer modeling is carried out for the structure and IR spectra of ethylene glycol-9 water molecules and ethylene glycol-9 water molecules-M⁺ systems, where M⁺ = Na⁺, K⁺. The presence of cations changes the structure of the glycol hydrate shell, which leads to a decrease in the activation energy of glycol self-diffusion in the solution with the addition of salts in comparison with its value in the water-glycol solution.     

Quantum chemical study of the effects of interaction of polyhydrated Hg(II) with methylcobalamin — A derivative of vitamin B<Subscript>12</Subscript>

Quantum chemical methods were used to investigate the mechanism of interaction of polyhydrated Hg(II) with methylcobalamin — a derivative of vitamin B₁₂. Migration of the methyl group in the B₁₂·Hg(II) nH₂O cluster, initiating the formation of methylmercury, is considered. The reaction of substitution of methylmercury for the cobalt atom in the corrin fragment of B₁₂ has been studied. The thermodynamic and activation characteristics of these processes have been obtained. The mercury analog of vitamin B₁₂ is shown to exist in two radically different conformations.     

Quantitative chemical composition of thin films with infrared spectroscopic ellipsometry: application to hydrated oxide films on aluminium

A method to quantify the composition of thin films using infrared spectroscopic ellipsometry (IRSE), supplemented by visible spectroscopic ellipsometry (VISSE), is proposed. Because ellipsometry measures the thickness and optical constants of a surface layer simultaneously, the absorption coefficient of the film as a function of wavelength can be obtained. Using values of the absorption coefficients for the pure components of the film, the percentages (mol.% or wt.%) of each component in the film can be calculated. The method is demonstrated in a study of the hydration of oxide films on electropolished aluminium and the anodically formed barrier oxide film. The IRSE technique shows that hydration of the films by immersion in boiling water results in the conversion of aluminium oxide to pseudoboehmite. Copyright © 2003 John Wiley & Sons, Ltd.     

Hydration of Cement Slurry in The Presence of Spent Cracking Catalyst

The physicochemical properties of spent fluidized bed cracking catalyst and its influence on hydration process of cement slurry were studied. The samples were cement slurries prepared with water/solid=0.5 and additions of used catalyst amounted to 0, 5, 10, 15, 20 and 25%with resp. to the solid. After definite time they were subjected to thermogravimetric analysis (TG, DTG, DTA) and, in order to determine the progress of reaction with water, the heat of hydration was measured by means of isotherm calorimetry. The studies disclosed that the spent cracking catalyst is not merely an inactive filler in cement slurries, but it modifies the course of the hydration process. The spent catalyst is a pozzolana additive and its presence leads to a decrease of calcium hydroxide contents in the system. The spent catalyst affect on the heat of cement hydration. Small amounts additive accelerate the process of binding. This revised version was published online in August 2006 with corrections to the Cover Date.     

Hydration of shrinkage-compensating binders with different compositions and water-binder ratios

The calorimetric data of blended shrinkage-compensating binders with different compositions were measured at 25°C at different water-binder ratios using an isothermal calorimeter. The hydration characteristics of shrinkage-compensating binders were evaluated and their influence on the expansive properties of blended shrinkage-compensating binders was determined. Composition and w/b ratio significantly affect the hydration rate and degree of shrinkage-compensating binders, as well as their expansive and mechanical properties. The total heat of hydration of binders decreases with w/c ratios. Its final hydration degree also decreases with w/c ratio. The ternary binders composed with Portland cement, mineral admixture and expansive agent show low hydration heat and rate of heat evolution, but their total heat of hydration increases continuously and surpasses that of binary binder in later period at low w/b ratio. This revised version was published online in August 2006 with corrections to the Cover Date.     

Investigation of hydration of α-amino acids by means of absorption millimeter spectroscopy

The hydration indexes for 19 protein -amino acids are measured by means of absorption millimeter spectroscopy (AMS) at 31.42 GHz. The plot of the hydration indexes on the area of surface of aliphatic amino acid molecules accessible for water is a straight line located above the points corresponding to aromatic or polar amino acids. The contribution of nonpolar groups in the hydration index is greater than that of polar groups provided that their accessible surface areas are equal. The contribution to hydration of -OH and-CONH₂ groups in Ser. Gin, and Asn coincides in sign with that of pure hydrophobic hydration but the value of the contribution is significantly smaller. The change in mobility of water molecules, which is the basis of the AMS method, may serve as the physicochemical foundation for the construction of a new hydrophobicity scale for amino acids comparable with the already existing scales.Deceased September 2, 1995.Translated fromIzvestiya Akodemii Nauk. Seriya Khimicheskaya, No. 3, pp. 618–622, March, 1996.     

Aqueous solutions of azoniaspiroalkane halides. VI. Apparent molal volumes and apparent molal heat capacities of chlorides and iodides

Densities and heat capacities of aqueous solutions of azoniaspiroalkane halides, (CH₂) _n N⁺ (CH₂) _n X^– (where X=Cl, I andn=5,6), have been measured at 25°C using a flow densimeter and a flow microcalorimeter. The limiting apparent molal volumes (ø _v ) and apparent molal heat capacities (ø _cp ) obtained from these data are compared with those of the azoniaspiroalkane bromides and the corresponding tetraalkylammonium halides. The concentration dependence of ø _v and ø_cp are examined for clues on the influence of solute hydration, structure, and conformational flexibility on the excess functions of quaternary ammonium halides.