Synthesis of 1-(pyridylalkyl)-1-aza-3,6-diphosphacycloheptanes

Reactions of 1,2-bis[(hydroxymethyl)(phenyl)phosphino]ethane with primary pyridylalkylamines gave earlier unknown 1-aza-3,6-diphosphacycloheptanes containing the pyridyl group in the exocyclic substituent. The reactions were found to be stereoselective, preferentially yielding the racemate with the RR/SS-configuration of the P atoms. A mixture of diastereomers of 3,6-diphenyl-1-[2-(2-pyridyl)ethyl]-1-aza-3,6-diphosphacycloheptane reacted with dichloro(cycloocta-1,5-diene)platinum(II) to give cis-P,P-chelate complexes from the meso-isomer and bridged oligomeric complexes from the racemate.     

Synthesis of functionalized tetrahydro-1,3-diazepin-2-ones and 1-carbamoyl-1H-pyrroles via ring expansion and ring expansion/ring contraction of tetrahydropyrimidines

A general approach to 6-phenylthio-substituted 2,3,4,5-tetrahydro-1H-1,3-diazepin-2-ones based on the ring expansion reaction of 1,2,3,4-tetrahydropyrimidin-2-ones under the action of nucleophiles has been developed. The first step of the synthesis was preparation of N-[(2-benzoyloxy-1-tosyl)ethyl]urea by three-component condensation of 2-benzoyloxyethanal, urea and p-toluenesulfinic acid. Nucleophilic substitution of the tosyl group in the obtained sulfone with sodium enolates of α-phenylthioketones followed by cyclization-dehydration, and debenzoylation gave 4-hydroxymethyl-5-phenylthio-1,2,3,4-tetrahydropyrimidin-2-ones which were transformed into the 4-mesyloxymethyl-derivatives. Treatment of the latter with nucleophilic reagents, such as NaCN, sodium diethyl malonate, PhSNa, MeONa, NaBH(4), sodium succinimide, or potassium phthalimide, afforded the target multi-functionalized diazepinones. The obtained 6-phenylthio-diazepinones and their 6-tosyl-substituted analogues were converted into 3-substituted 1-carbamoyl-1H-pyrroles under acidic conditions as a result of ring contraction. Effective one-pot synthesis of the latter from 4-mesyloxymethyl-pyrimidines was realized using a ring expansion/ring contraction sequence.     

Conformation analysis of nucleic acids and proteins adsorbed on single-shell carbon nanotubes

This paper presents a concise review of the experimental and calculated data reported in the literature on the noncovalent interactions of DNA and proteins with the nonfunctionalized carbon nanotubes. Our Raman scattering and electron microscopy data on carbon nanotubes and SEIRA spectral data on changes in the conformational state of the main biological polymers (DNA, Poly, BSA, and RNase) in reactions with single-shell carbon nanotubes allowed us to define the character of noncovalent interactions in the tube biomolecule system. An analysis of the data showed that reactions of DNA with nanotubes lead to the binding on the surface of the nanotube and form stable complexes with van der Waals interactions, in which stacking plays the major role and which changes the hydrogen bonds in the biological molecule with structure rearrangements. Albumin and RNase are presumably adsorbed at the conventional binding sites of these proteins on the nanotube with participation of hydrophobic interaction and π stacking, as indicated by structure rearrangements in proteins.     

General approach to 6-tosyl-2,3,4,5-tetrahydro-1H-1,3-diazepin-2-ones via nucleophile-mediated ring expansion of tetrahydropyrimidines

A general six-step approach to 6-tosyl-2,3,4,5-tetrahydro-1H-1,3-diazepin-2-ones has been developed. The key step involves a ring expansion reaction of 4-mesyloxymethyl- or 4-tosyloxymethyl-5-tosyl-1,2,3,4-tetrahydropyrimidin-2-one mediated by nucleophilic reagents.     

Nonlinear optical properties of poly(N-vinylcarbazole)-C60 nanocomposites

Physics of the Solid State - The influence of the fullerene content and temperature on the IR absorption and luminescence spectra of poly(N-vinylcarbazole) (PVK)-C60 composites prepared by vacuum...     

On the Choice of a Distributed Basis Set in Calculations of Transition-Dipole Moments in the One-Determinant Approximation

The so-called “asymptotic projection technique” developed in previous papers of the authors is applied to the calculation of electronic transition-dipole moments (TDMs) in the one-determinant approximation between states of the same spin and spatial symmetry. The basic equations of the method and specific features of their application to a TDM calculation are briefly discussed. The attention focusses on the choice of a finite one-particle basis set. For this purpose, two possible algorithms for constructing distributed basis sets are proposed. In the first of them, the construction is based on minimization of the Hartree–Fock energy (E_HF) with respect to nonlinear basis set parameters. In the second case, the parameters are determined by minimizing the functional E = E_HF + E_MP2, which includes the electron correlation through the second order of Møller–Plesset perturbation theory (Е_МР2). On the whole, the results of calculations in both basis sets are in agreement with high-accuracy calculations performed by configuration interaction methods. The basis set adapted for E = E_HF + E_MP2 significantly improves the accuracy as compared to the basis set of the first type.     

Mesodroplet Heterogeneity of Low-Concentration Aqueous Solutions of Polar Organic Compounds

It is found experimentally that a mesoscopic droplet phase is formed in low-concentration aqueous solutions of various polar organic compounds, which are considered in the chemical literature as infinitely soluble in water. The content of dissolved organic molecules in droplets is much higher than in the ambient solution. The droplet size increases with temperature. Theory can explain the mesodroplet formation by the phase separation of a binary mixture affected by the dichotomous noise of twinkling hydrogen bonds between molecules of organic compound and water. The Snyder polarity index, which is used by chemists as a miscibility criterion for molecular compounds, depends in the model on the dipole moments of mixed molecules and the energy and number of hydrogen bonds. With this refinement, it can be used as an estimation criterion for the existence and intensity (i.e., the number of droplets per unit volume of organic aqueous solution) of mesodroplet separation.

     

Electron spin resonance on enantiomorphic centers in PbZrO3:Gd3+ crystals

The Gd³⁺ ESR spectrum of the antiferroelectric phase of a PbZrO₃ single crystal contains at least one pair of magnetically equivalent components. The angular dependences of the resonance magnetic field that were constructed for them transform into one another by mirror reflection in a plane perpendicular to the antipolarization axis of the crystal. The constants in the spin Hamiltonians for the corresponding pair of paramagnetic centers are determined assuming monoclinic symmetry. Fiz. Tverd. Tela (St. Petersburg) 41, 1279–1281 (July 1999)     

2,3-Dihydro-1H-1,3-diazepin-2-ones: synthesis and novel rearrangements into pyrrole derivatives

A novel synthesis of 2,3-dihydro-1H-1,3-diazepin-2-ones based on thermal elimination of methanol from 4-methoxy-2,3,4,5-tetrahydro-1H-1,3-diazepin-2-ones has been developed. The prepared dihydrodiazepinones underwent two new rearrangements under basic or acidic conditions to give the pyrrole derivatives, 3-(aminomethylene)-2,3-dihydro-1H-pyrrol-2-ones and 1-carbamoyl-1H-pyrroles, respectively. Plausible mechanisms for the rearrangements are proposed.