Atomic structure of a thin silica film on a Mo(112) substrate: a two-dimensional network of SiO4 tetrahedra

The structure of a thin single crystalline SiO(2) film grown on Mo(112) has been studied by scanning tunneling microscopy, infrared reflection absorption spectroscopy, and x-ray photoelectron spectroscopy. In excellent agreement with the experimental results, density functional theory calculations show that the film consists of a two-dimensional network of corner sharing [SiO(4)] tetrahedra, with one oxygen of each tetrahedron binding to the protruding Mo atoms of the Mo(112) surface.     

Cooperative Formation of Long‐Range Ordering in Water Ad‐layers on Fe3O4(111) Surfaces

The initial stages of water adsorption on magnetite Fe₃O₄(111) surface and the atomic structure of the water/oxide interface remain controversial. Herein, we provide experimental results obtained by infrared reflection–absorption spectroscopy (IRAS) and temperature‐programmed desorption (TPD), corroborated by density functional theory (DFT) calculations showing that water readily dissociates on Fe_tet sites to form two hydroxo species. These act as an anchor for water molecules to form a dimer complex which self‐assembles into an ordered (2×2) structure. Water ad‐layer ordering is rationalized in terms of a cooperative effect induced by a hydrogen‐bonding network.     

Initiation of explosion-induced transformations in energy-saturated materials with nanoadmixtures by a high-voltage electric discharge

We have reported on the results of an experimental investigation of the effect of inert admixtures on the threshold characteristics of the breakdown (initiation) voltage in energy-saturated materials. A physicomathematical model that describes the experimental results has been proposed.     

Geometric Structure of 2-Phenyl-1,3-dithia-5,6-benzocycloheptene 1-Oxide

Two-dimensional nuclear Overhauser effect spectroscopy (2D NOESY) was used to determine proton-proton distances for the chair conformer of 2-phenyl-1,3-dithia-5,6-benzocycloheptene 1-oxide in CD₂Cl₂ in the system CS₂-CDCl₃. Changing the solvent by a more polar changes the molecular conformation. As a result, the dipole moment may also be affected, and this should be taken into account in analysis of solvent effects on thermodynamic parameters of the conformational equilibrium.     

Reversible intramolecular Dieckmann-type condensation of 2-(2-hydroxymethyl-5,5,6-trimethoxytetrahydropyran-3-ylcarbonyl)-cyclopentanone: an alternative access to medium-sized lactones

1. Download high-res image (100KB)
2. Download full-size image

     

Guest controlled aggregation of amphiphilic sulfonatomethylated calix[4]resorcinarenes in aqueous solutions

Supramolecular nanoaggregates formed through the association of amphiphilic sulfonatomethylated calix[4]resorcinarenes with different substituents on the lower rim (methyl, pentyl, heptyl) and number of aromatic, aliphatic, and cationic guests differing in their shapes and sizes were investigated in aqueous solution by various NMR techniques ((1)H, 2D NOESY, FT-PGSE). It was shown that slight variations of the alkyl chain length on the lower rim of calixresorcinarenes dramatically change their aggregation behavior. Unlike the other calixresorcinarenes studied, the "head-to-tail" packing mode is observed for calixresorcinarene with pentyl moieties on the lower rim, which is unusual for amphiphilic calixarene aggregates. This calixresorcinarene demonstrates the stronger binding capacity toward the guest molecules due to their encapsulation into the capsule-like aggregate subunits. The guest-host complexation modifies the properties of both components, with the size of the resulted colloid particles being controlled by the guest nature.     

An efficient method for the synthesis of imidazo[1,5-a]quinoxalines from 3-acylquinoxalinones and benzylamines via a novel imidazoannulation

The reaction of 3-aroylquinoxalin-2(1H)-ones and their N-alkyl analogues with benzylamines in DMSO proceeds through an intermediate formation of N-(α-quinoxalinylbenzylydene)benzylamine, which when subjected to oxidative cyclocondensation gives imidazo[1,5-a]quinoxalines. Applying this new approach of imidazoannullation to the bis-3-aroylquinoxalines makes it possible to develop fundamentally new methods of the synthesis of bis-imidazo[1,5-a]quinoxalines with the use of different benzylamines and heteromacrocycles with the 1,3-bis(3-arylimidazo[1,5-a]quinoxalin-1-yl)benzene structural fragment when m-xylylenediamine is used.