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.     

Succinates and maleates of some cardenolides,and their potassium salts

The succinates of corotoxigenin, digitoxigenin, and oleandrigenin, and the maleate of strophanthidin, and their potassium salts, have been synthesized. In contrast to the initial cardenolides (1, 4, 7, and 10), the succinates (2, S, and 8) and the maleate (11) and their potassium salts (3, 6, 9, and 12) possess no cardiotonic activity.Ukrainian Pharmaceutical Academy, Kharkov-2, ul. Pushkinskaya, 53. State Scientific Center for Drugs, Kharkov-85 ul. Astronomicheskaya 33. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 568–571, July–August, 1996 Original article submitted February 7, 1996     

Atomic Absorption Assay of Noble Metals in Ores with the Use of Sample Decomposition by Ultrasound

An atomic absorption assay of gold, silver, and palladium in various types of ores is performed with the use of ultrasound at the fire assay stage. It is shown that ultrasound can reduce the temperature and duration of fusion and increase the recovery of noble metals into the lead button.     

Characteristic functions of almost solvable extensions of Hermitian operators

The characteristic operator-functions W() are studied of the almost solvable extensions of an Hermitian operator. The inverse problem is solved, a multiplication theorem is proved, and a formula is derived expressing W() in terms of the Weyl function and the boundary operator. Characteristic functions are computed of various differential and difference operators, with the help of which are proved theorems of the completeness of the systems of proper and adjoint vectors.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 44, No. 4, pp. 435–459, April, 1992.     

The rheology of hydrogels based on chitosan–gelatin (bio)polyelectrolyte complexes

Influence of the chitosan concentration in the low-concentrated acidic hydrogels formed by (bio)polyelectrolyte chitosan–gelatin complexes (at a constant gelatin concentration of 1%) was studied by shearing in steady flow and linear oscillations. These complexes, including native gelatin, demonstrate clearly expressed viscoelastic properties. Viscoelastic properties correlated well with the non-Newtonian behavior of hydrogels (according to the Cox–Merz rule). Increasing the chitosan concentration (from 0.1% to 0.6%) results in exponential growth of the apparent viscosity, yield stress, and storage modulus. However, a further increase in chitosan concentration to 0.8% leads to a reduction in these rheological parameters due to the electrostatic repulsion of similarly charged polyelectrolyte complexes under the high concentration of these complexes. The macro-rheological properties of chitosan–gelatin gels are mainly determined by the colloidal structure of sol-precursors in solutions. The yield stress dependence on the radius of the dispersed particles is of square type. Electron photomicrographs showed that the introduction of even small quantities of chitosan leads to radical changes in the supramolecular structure of the gelatin gel.