A statistical thermodynamic supermolecule-continuum study of ion hydration: Cell and shell methods

A theoretical study of ion hydration using the statistical thermodynamic supermolecule-continuum method is described. The cell and shell methods are used for configurational averaging. Enthalpies, free energies and entropies are calculated for Li⁺, Na⁺, K⁺, F^– and Cl^– each four coordinated with water. The results are in reasonable accord with experiment. A comparison of the site method, cell method and shell method results is presented. The supermolecule-continuum approach to solvent effects seems to be capable of accommodating essential features for the calculation of solvation energy and solvent effects on structure and properties.     

Microbiological transformations of 19-oxygenated ent-kauranes

The microbiological transformations of three 19-oxygenated ent-kauranes with Rhizopus nigricans, Aspergillus ochraceous and Calonectria decora have been investigated. The most common transformation observed is hydroxylation at the C-1 and C-7 positions. For ent-kaur-16-en-19-oic acid allylic hydroxylation and hydration of the double bond also occur.     

Special features in the chemical structure of phosphorus isocyanates

The UV and IR absorption spectra and the NMR and NQR spectra of certain isocyanates of three- and four-coordinated phosphorus have been investigated. The reciprocal effect of the phosphorus atom and the NCO group is discussed on the basis of spectral analysis, quantum chemical calculations of the electron systems, and calculations of the normal vibrational forms. Comparison of the (PO) frequencies in the IR spectra of the phosphorus isocyanates with the Taft gives a linear relationship which testifies to the predominant inductive effect of the NCO group on the P(O)R₁R₂ grouping. A similar relationship is observed between the resonance frequency _res in the NMR spectra and for C1P(O)R₁R₂ compounds. The effect of the phosphorus atom on the electronic system in the NCO group is shown by the hypsochromic shift of the absorption band in the210-m region and an appreciable increase in its intensity, compared with alkyl isocyanates. This fact, which agrees with the NMR spectral data and the quantum chemical calculations, indicates the presence of conjugation in the P-N bond. We found the order of the P-N bond to be approximately 1.2. This partial double-bond nature of the P-N bond results from the interaction of the p electrons of nitrogen in the NCO group with the d orbitals of the phosphorus atom.We are grateful to our colleagues at the Kazan Physicotechnical Institute AS USSR A. I. Rivkind, S. G. Salikhov, and I. A. Safin for recording the spectra.     

Kinetic modelling of the thermal oxidation of polyisoprene elastomers. Part 1: Unvulcanized unstabilized polyisoprene

The thermal oxidation of an unvulcanized, unstabilized polyisoprene rubber (IR) has been studied in the 40-140 °C temperature range. Ageing was monitored by FTIR determination of double bonds and carbonyl groups, mass uptake measurement, and weight average molar mass determination. A mechanistic scheme based on the standard scheme for radical chain oxidation, but taking into account the diversity of initiation processes and the existence of inter- and intramolecular radical additions to double bonds, was built. The kinetic model derived from this scheme is composed of seven differential equations to be solved in discrete thickness layers to take into account the kinetic control by oxygen diffusion. This system was numerically solved using a Matlab program dedicated to stiff systems of differential equations. The elementary rate constants and other kinetic parameters were then determined from experimental data, using an inverse approach. A set of physically reasonable parameter values was obtained, thus allowing us to envisage lifetime predictions at low temperature (long term). The results led to observations difficult to make from classical analytical studies, for instance the predominance of bimolecular hydroperoxide decomposition among other initiation modes or the competition between intermolecular hydrogen abstraction and intramolecular addition of peroxy radicals to double bonds.     

Extraction of californium/III/ from aqueous pyrophosphate and tripolyphosphate solutions with D2EHPA

Extraction of californium/III/ with di-/–2-ethylhexyl/ phosphoric acid /D2EHPA/ in heptane from pyrophosphate media is almost quantitative between pH 4 and 5. From tripolyphosphate media, however, two to three extractions are needed in the pH range of 3–5 to isolate Cf³⁺ completely. Reextraction experiments show that 1M H₂SO₄ can back-extract Cf³⁺ completely while two to three reextractions with 5M HNO₃ can only separate californium/III/. Reverse phase partition chromatography experiments were performed to recover 300 g of californium/III/. From slope analysis of the extraction data the composition of the extracted species has been found to be Cf/H₂P₂O₇/A.HA and Cf/H₄P₃O₁₀/.A₂.2HA from pyrophosphate and tripolyphosphate solutions, respectively, where D2EHPA is abbreviated as /HA/₂.     

Electron impact mass spectrometry of the acetates of zinc,magnesium, cobalt and manganese

The electron impact mass spectra of the acetates of zinc, magnesium, cobalt and manganese have been investigated using a direct inlet probe. Volatile tetrahedral complexes are produced on heating, and ions of the form [M₄(OCOCH₃)₆O]^+˙ (M = Co and Mn) and [N₄(OCOCH₃)₅O]⁺ (N = Zn or Mg) are observed. A mixture of magnesium and cobalt acetates produces ions of the form [Mg_nCo_4–n(OCOCH₃)₆O]^+˙.     

Azo coupling and aminomethylation of 2,5-diphenylpyrrole and its derivatives

The azo coupling of 2,5-diphenylpyrrole with arenediazonium chlorides has given previously unknown 3-arylazopyrroles and 4-phenylazo-3-phenylhydrazono-3H-pyrrole. The methylation and reductive acetylation of the anylazo derivatives have led to N-methylarylazo and acetylamino derivatives of 2,5-diphenylpyrrole. 3-Amino-2, 5-diphenylpyrrole has been obtained by the reduction of 3-p-chlorophenylazo-2,5-diphenylpyrrole. The aminomethylation of 2,5-diphenylpyrrole and its derivatives with bis(dialkylamino)methanes had led to aminomethyl derivatives.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5. pp. 612–615, May, 1986.     

3'-nitrophenylpropyloxycarbonyl (NPPOC) protecting groups for high-fidelity automated 5' --> 3' photochemical DNA synthesis

[structure: see text]. The most powerful DNA microarrays would be prepared by photolithography with free 3'-ends that could be processed enzymatically. A photoremovable group that could be removed in quantitative yield would ensure high purity of the synthesized probes. We have developed new pyrimidine building blocks for 5' --> 3' DNA synthesis with high cycle yields using the NPPOC (3'-nitrophenylpropyloxycarbonyl) protecting group. These phosphoramidites were proved in automated photochemical DNA synthesis on a modified synthesizer.