Hexacoordinate triphenylantimony(V) complex with tridentate bis-(3,5-di-tert-butyl-phenolate-2-yl)-amine ligand: Synthesis,NMR and X-ray study

The oxidative addition reaction of 4,6-di-tert-butyl-N-(2-hydroxy-3,5-di-tert-butyl-phenyl)-o-iminobenzoquinone (IBQ) to triphenylantimony(III) proceeds with the migration of hydroxyl-proton to a nitrogen atom to form tridentate O,N,O′-coordinated bis-(3,5-di-tert-butyl-phenolate-2-yl)-amine ligand. In accordance with ¹H, ¹³C, DEPT NMR data, the new hexacoordinate complex [bis-(3,5-di-tert-butyl-phenolate-2-yl)-amine]triphenylantimony(V), [(AP-AP)H]SbPh₃ (1) in solution has a C_s symmetry plane leading to the equivalence of two O,N-chelate o-aminophenolato moieties. The molecular structure of 1 · acetone was studied by a single-crystal X-ray. Compound 1 was found to be air-stable both in solid and in solution. Its oxidation by PbO₂ leads to paramagnetic [4,6-di-tert-butyl-N-(3,5-di-tert-butyl-phenolate-2-yl)-o-iminobenzosemiquinolato]triphenylantimony(V), [(AP-ISQ)]SbPh₃ (2).     

Characterization of platinum anticancer drug protein-binding sites using a top-down mass spectrometric approach

A proof-of-principle study on the application of a top-down electrospray ionization Fourier transform ion cyclotron resonance mass spectrometric approach for characterization of the primary binding sites of the platinum anticancer agents cisplatin, transplatin, and oxaliplatin on ubiquitin is presented. Through employment of different fragmentation techniques, the binding sites of cisplatin and oxaliplatin were found at N-terminal methionine-containing ubiquitin fragments, while transplatin was observed to be attached to 19Pro-Ser-Asp-Thr-Ile-Glu24. The binding to proteins is of particular relevance for the mode of action of metallodrugs with regard to (de)activation, transport, excretion, etc. To the best of our knowledge, this is the first top-down mass spectrometric study on the protein binding site characterization of transition-metal anticancer agents and demonstrates the potential of the applied technique for investigating metal drug-protein interactions.     

Monte Carlo simulation of polymer analogous reaction in confined conditions: effects of ordering

The influence of energetic parameters of the interchain homo- and heterocontacts on a local ordering of Bernoullian copolymers has been studied using Monte Carlo simulations and probabilistic analysis. The results of both methods are in a good agreement. Then simple Monte Carlo procedure was employed to study the ordering in products of a polymeranalogous reaction with accelerating effect of neighboring groups. When the reaction with intra- and interchain acceleration and local ordering proceed simultaneously in confined conditions, the ordering might affect the process so that the formation of certain nano-structures (in particular, not trivial strip-like ones) is possible.     

Submanifolds Of Maximal Nullity In Symmetric Spaces

A non-totally-geodesic submanifold of relative nullity n — 1 in a symmetric space M is a cylinder over one of the following submanifolds: a surface F ² of nullity 1 in a totally geodesic submanifold N³ ? M locally isometric to S ²(c) × ? or H ²(c) × ?; a submanifold F ^k+1 spanned by a totally geodesic submanifold F ^k(c) of constant curvature moving by a special curve in the isometry group of M; a submanifold F ^k+l of nullity k in a flat totally geodesic submanifold of M; a curve.     

Influence of Environmental Parameters on the Stability of the DNA Molecule

Fluctuations in viscosity within the cell nucleus have wide limits. When a DNA molecule passes from the region of high viscosity values to the region of low values, open states, denaturation bubbles, and unweaving of DNA strands can occur. Stabilization of the molecule is provided by energy dissipation—dissipation due to interaction with the environment. Separate sections of a DNA molecule in a twisted state can experience supercoiling stress, which, among other things, is due to complex entropic effects caused by interaction with a solvent. In this work, based on the numerical solution of a mechanical mathematical model for the interferon alpha 17 gene and a fragment of the Drosophila gene, an analysis of the external environment viscosity influence on the dynamics of the DNA molecule and its stability was carried out. It has been shown that an increase in viscosity leads to a rapid stabilization of the angular vibrations of nitrogenous bases, while a decrease in viscosity changes the dynamics of DNA: the rate of change in the angular deviations of nitrogenous bases increases and the angular deformations of the DNA strands increase at each moment of time. These processes lead to DNA instability, which increases with time. Thus, the paper considers the influence of the external environment viscosity on the dissipation of the DNA nitrogenous bases’ vibrational motion energy. Additionally, the study on the basis of the described model of the molecular dynamics of physiological processes at different indicators of the rheological behavior of nucleoplasm will allow a deeper understanding of the processes of nonequilibrium physics of an active substance in a living cell to be obtained.     

Nitrogen modified carbide-derived carbons as adsorbents of hydrogen sulfide

Carbide-derived carbons produced from titanium carbide at temperatures from 600 degrees C to 1000 degrees C and exhibiting different porosities were treated with urea in order to introduce nitrogen containing species to their surface. Adsorption of hydrogen sulfide in the dynamic conditions in the presence of moisture was studied on initial and modified samples. The samples, before and after exposure to hydrogen sulfide, were characterized using adsorption of nitrogen, potentiometric titration, elemental analysis, and thermal analysis. The results showed that the introduction of nitrogen significantly enhances the performance of carbons in the process of hydrogen sulfide removal. The amount adsorbed and the degree of oxidation depended on the porosity. On the samples with very small pores, the adsorption was limited, probably owing to the sterical hindrances. With an increase in the size and volume of micropores, in which water and hydrogen sulfide can be accommodated, the efficiency of H(2)S removal by CDC increased.     

Kinetic approach for evaluation of total antioxidant activity

We propose a novel approach for assessment of total antioxidant activity by monitoring kinetics of hydrogen peroxide (H₂O₂) scavenging after its injection into liquid sample under study. H₂O₂ is known to be the strongest oxidant, really presented in human body in contrast to the majority of the model oxidative systems used for evaluation of antioxidant activity. In addition, kinetic approach, being more informative than the commonly used determination of the final product, obviously provides better discrimination of potential antioxidants. Prussian Blue based sensor due to its high sensitivity and operational stability allowed to monitor kinetics of hydrogen peroxide consumption in turbid and colored samples. The pseudo-first order kinetic constants of hydrogen peroxide scavenging in the presence of different food additives correlated with total antioxidant activity of these samples evaluated via standard procedure based on lipid peroxidation. However, in contrast to the standard method, the proposed kinetic approach is expressed and does not require fresh biological tissues.     

Combined asymptotic and direct approach to the nonlinear plane problem of dynamics of a thin curved strip

On the example problem of large elastic oscillations of a thin curved strip we present a combined modeling approach: the non-reduced continuous problem splits asymptotically into a system of linear equations of the rod model and a problem over the thickness; direct approach to a material line provides nonlinear equations; after the numerical solution of the reduced problem we restore the distributions of stresses, strains and displacements over the thickness. Convergence to the solution for the non-reduced continuum as the thickness tends to zero justifies the analytical conclusion that the curvature and variation of the material properties over the thickness do not require special treatment for classical Kirchhoff's rods. Further terms of the asymptotic expansion lead to a model with shear and extension, in which curvature appears in a non-trivial way. The results of the study are illustrated by a numerical example and provide better understanding of the relation between the solutions of the original and dimensionally reduced problems for spatial rods and shells. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Control of sp2/sp3 carbon ratio and surface chemistry of nanodiamond powders by selective oxidation in air

The presence of large amounts of nondiamond carbon in detonation-synthesized nanodiamond (ND) severely limits applications of this exciting nanomaterial. We report on a simple and environmentally friendly route involving oxidation in air to selectively remove sp(2)-bonded carbon from ND. Thermogravimetric analysis and in situ Raman spectroscopy shows that sp(2) and sp(3) carbon species oxidize with different rates at 375-450 degrees C and reveals a narrow temperature range of 400-430 degrees C in which the oxidation of sp(2)-bonded carbon occurs with no or minimal loss of diamond. X-ray absorption near-edge structure spectroscopy detects an increase of up to 2 orders of magnitude in the sp(3)/sp(2) ratio after oxidation. The content of up to 96% of sp(3)-bonded carbon in the oxidized samples is comparable to that found in microcrystalline diamond and is unprecedented for ND powders. Transmission electron microscopy and Fourier transform infrared spectroscopy studies show high purity 5-nm ND particles covered by oxygen-containing surface functional groups. The surface functionalization can be controlled by subsequent treatments (e.g., hydrogenization). In contrast to current purification techniques, the air oxidation process does not require the use of toxic or aggressive chemicals, catalysts, or inhibitors and opens avenues for numerous new applications of nanodiamond.     

Competing interactions in two dimensional Coulomb systems: surface charge heterogeneities in coassembled cationic-anionic incompatible mixtures

A binary mixture of oppositely charged components confined to a plane such as cationic and anionic lipid bilayers may exhibit local segregation. The relative strengths of the net short range interactions, which favors macroscopic segregation, and the long range electrostatic interactions, which favors mixing, determine the length scale of the finite size or microphase segregation. The free energy of the system can be examined analytically in two separate regimes, when considering small density fluctuations at high temperatures and when considering the periodic ordering of the system at low temperatures [F. J. Solis, S. I. Stupp, and M. Olvera de la Cruz, J. Chem. Phys. 122, 054905 (2005)]. A simple molecular dynamics simulation of oppositely charged monomers, interacting with a short range Lennard-Jones potential and confined to a two dimensional plane, is examined at different strengths of short and long range interactions. The system exhibits well-defined domains that can be characterized by their periodic length scale as well as the orientational ordering of their interfaces. By adding salt, the ordering of the domains disappears and the mixture macroscopically phase segregates in agreement with analytical predictions.