Solvent effects on oxygen-17 chemical shifts in methyl formate: linear solvation shift relationships

A multiple linear regression analysis has been carried out using the Kamlet-Abboud-Taft solvatochromic parameters in order to quantify the solvent effects on the (17)O chemical shifts of methyl formate (MF). The influence of the solvents upon the carbonyl oxygen chemical shifts is smaller for MF than for N-methylformamide (NMF). The influence (in parts per million) of the solvent polarity-polarizability reduces from -21.9pi* in amides to -9.6pi* in MF. The influence of the solvent hydrogen-bond-donor acidities reduces from -42.0alpha in formamides to -16.9alpha in MF. The solvent effects upon the dicoordinated oxygen chemical shifts of MF are smaller in magnitude and opposite in direction, i.e., 4.8pi* and 2.6alpha, than those for the carbonyl oxygen. (17)O hydration shifts have been calculated for the NMF + (H(2)O)(6) and MF + (H(2)O)(5) complexes by the ab initio GIAO method at the 6-311 + G** level. The hydration shifts calculated for the carbonyl oxygens of NMF and MF and for the dicoordinated oxygen of MF, -102.4, -64.7, and 17.6 ppm, respectively, show the same trend as the corresponding empirical hydration shifts, -101.7, -42.0, and 14.2 ppm.     

Conformational changes in poly(vinyl alcohol)-graft-polyacrylamide in aqueous solutions vs graft content

Conformational changes have been studied in intramolecular polymer-polymer complexes (intraPC) of graft copolymers of poly(acrylamide) and poly(vinyl alcohol) (PVA-g-PAA) with various numbers of grafts (4-42) per molecule as a function of temperature and copolymer concentration. It is shown that the magnitude of conformational change depends on the grafts content while the temperature range over which the conformation changes occur is essentially determined by copolymer concentration. The conformational changes are reversible on heating and cooling.     

Growth Morphology and Structure Peculiarities of Superthin Titanium Films

Superthin titanium films of 0.3 to 2 nm thickness, prepared by radio-frequency sputtering, have been studied by modern X-ray methods, such as reflectometry, fluorescent analysis and grasing-beam structural analysis. Two simple models were used to describe early stages of film growth. It has been shown that the thinnest titanium films were the TiO₂ islands with an equal height. Thicker films could be described as bilayers Ti/TiO₂. The films became continuous already near 1.5 nm effective thickness.     

Crystal Structure and Growth Morphology of Nickel Superthin Films

Ni superthin films of t = 0.3–3.5 nm thickness prepared by radio-frequency sputtering have been studied by mordern X-ray methods, such as reflectometry, fluorescence analysis and grazing-beam structure analysis. The results have shown that the films were polycrystalline and their densities correspond to bulk values for nickel already at the early stage of growth. None oxides were found in Ni films. The model of earliest stage film growing have been suggested: film begins to grow by the island mechanism, but the crystallization front remains perfectly plane during the growth.