The surface of ordered mesoporous benzene-silica hybrid material: an infrared and ab initio molecular modeling study

Joint IR and computational results allow a detailed characterization of the surface properties of a mesoporous benzene-silica hybrid material with crystal-like wall structure. After outgassing at 450 degrees C, hydroxyl species mainly consist of noninteracting silanols, with both O-H and Si-O stretching modes at lower frequencies than those of SiOH in silica. Interaction with several probe molecules, followed both by experiment and calculus, shows that the aryl group in the coordination sphere of Si imparts a lesser acidity with respect to the isolated silanol in silica. In contrast, adsorption isotherms indicate that the interaction with acetone is stronger with benzene-silica than with silica: this is interpreted in terms of secondary interactions taking place between the slightly acidic CH in acetone and the electronic cloud in benzene-like rings. This suggests that both the inorganic component and the organic one play a role in dictating the surface behavior.     

Association of model peptides and dehydropeptides: N-acetyl-l-alanine- and dehydroalanine N′,N′-dimethylamides

The comparative studies on the association of Ac-ΔAla-NMe₂ and Ac-l-Ala-NMe₂ in carbon tetrachloride were performed by the analysis of their average molecular weight, dipole moments and FTIR spectra. To aid spectroscopic interpretation and gain some deeper insight into the nature of associates, the geometries of the minimum energy of the dimers of Ac-ΔAla-NMe₂ and Ac-l-Ala-NMe₂ were calculated by the B3LYP/6-31+G** method. The average molecular weight in the studied concentration range, for the ΔAla and l-Ala peptide, as determined by the osmometric method, did not exceed 1.5 and 1.2 of the monomeric mass, respectively. Accordingly, the percentage of the monomeric form (α) decreased as concentration was increased more significantly for the ΔAla analogue than for its saturated counterpart. In the studied concentrations, the dipole moment of the unsaturated compound decreases and that of its counterpart is almost constant. We identified a wider range of dimeric forms of Ac-ΔAla-NMe₂ than those of Ac-l-Ala-NMe₂. While Ac-ΔAla-NMe₂ mainly forms cyclic dimers, built of open conformers H/F, specific for α,β-dehydroamino acids, Ac-l-Ala-NMe₂ forms cyclic and linear dimers, characteristic for the usual amino acids. Ac-ΔAla-NMe₂ has a greater tendency to associate than its saturated variant, which is the result of stronger hydrogen bonds.     

Molecular vibrations in a gradient extremal path

Summary The calculation of vibrational states using a gradient extremal path is discussed. Gradient extremal paths are defined by local criteria, which lead to stable solutions. This has certain advantages in comparison with a steepest-descent path, which is often difficult to determine accurately. For cases where a reaction path formalism is applicable, a path based on the gradient extremal concept gives results in close agreement with those obtained using traditional steepest-descent methods. We present algorithms for carrying out such calculations and also give some numerical results.     

Generalized inverse method for computation of molecular force field

The generalized inverse method is applied to the force constants calculation problem having a nearly singular Jacobian matrix, and by substituting it by one of lower rank which is near to it and well conditioned it is possible to eliminate the convergence difficulties of the least squares iteration process. A further significant advantage of the method is that certain matrix theoretical considerations give the possibility of deciding at the end of the iteration which force constants are determined by the available observations. Numerical results for the dimethylmercury molecule are given.     

Effect of the rhenium additive to VOx/TiO2 and MoOx/TiO2 catalysts on their properties in oxidative dehydrogenation of propane

VO_x/TiO₂ and MoO_x/TiO₂ catalysts with the addition of Re (Re/V or Mo = 0.5) were synthetized and tested in oxidative dehydrogenation of propane and in reduction by propane. XPS measurements showed depletion of the surface in Re. The Re additive does not affect the total conversion of propane, but increases the selectivity to propene. The effect is more pronounced for the MoO_x/TiO₂ catalyst. The increase in the selectivity to propene is accompanied with the increase in the reducibility of the catalysts.     

Asymmetry of electron transmission through monolayers of helical polyalanine adsorbed on gold surfaces

Polyalanine derivatives containing cysteamine linker R-(Ala)14NH-(CH2)2-SH, where R is ferrocenecarbonyl or hydrogen, were synthesized and then used to form self-assembled monolayers on gold. The tilt angles and the packing density of the molecules within monolayer assemblies were determined by FTIR spectroscopy and scanning tunneling microscopy, respectively. Electrochemical properties of monolayer-modified electrodes were studied using cyclic voltammetry and impedance spectroscopy. Measurements of electron-transfer rates using electrochemical techniques and scanning tunneling spectroscopy revealed asymmetry dependent on the applied voltage. It is suggested that the observed electron-transfer behavior is connected with the electric field generated by the molecular dipole of the polyalanine helix.     

Rejuvenating old computerized spectrometric instrumentation: discussion of two case histories

Computerized analytical instruments of late 70's and 80's are facing rapid technological obsolescence, although they are often retaining good analytical performances. Responsibility is to be attributed to the fast advance in computer technology, which is leaving little or no back-compatibility with old standards and data formats. Rejuvenation may be reached by simple hardware and software modifications, to allow data exchange with modern PC's and LIMS. Two typical case histories for spectrometric instrumentation of late 70's are then presented and discussed in a general fashion.     

IR study of heterogeneity of OH groups in zeolite HY-splitting of OH and OD bands

We have been studying the problem of heterogeneity of OH groups in zeolites HY for a long time. The heterogeneity was suggested by the shift of the IR band of OH groups restoring upon ammonia desorption and also by the fact that the band of OH groups forming hydrogen bonds was relatively broad (broader than for homogeneous acidic OH). In the present study we present another important argument for heterogeneity: the splitting of the IR band of free OH and OD groups in a zeolite of Si/Al=8.3 dealuminated by (NH₄)₂SiF₆ treatment. Such a splitting is the best seen in low temperature spectra of OD groups. We found less acidic 3640 cm⁻¹ (AlO)(SiO)₂SiO₁HAl(OSi)₃ and more acidic 3625 cm⁻¹ (SiO)₃SiO₁HAl(OSi)₃ groups. The presence of these two kinds of hydroxyls corresponds to the presence of Si(2Al) and Si(1Al), respectively, detected in ²⁹Si MAS NMR spectra. We also found a small amount of strongly acidic 3599 cm⁻¹ hydroxyls interacting with extraframework Al species.     

Determination of the proton affinity of carbon dioxide by photoionization mass spectrometry

The adiabatic ionization energies and COOH⁺ appearance energies for a series of carboxylic acids have been measured by dissociative photoionization mass Spectrometry. Using the stationary electron convention, a heat of formation of 143.5 ± 0.7 kcal mol^?1 (1 kcal = 4.184 kJ) at 298 K is derived for the carboxyl cation in the gas phase, which corresponds to an absolute proton affinity for carbon dioxide of 128.1 ± 0.7 kcal mol^?1.     

Targeting apoptosis via chemical design: inhibition of bid-induced cell death by small organic molecules

Bid is a key member of the Bcl-2 family proteins involved in the control of the apoptotic cascade in cells, leading to cell death. Uncontrolled cell death is associated with several human pathologies, such as neurodegenerative diseases and ischemic injuries. Therefore, Bid represents a potential yet unexplored and challenging target for strategies aimed at the development of therapeutic agents. Here we show that a multidisciplinary NMR-based approach that we named SAR by ILOEs (structure activity relationships by interligand nuclear Overhauser effect) allowed us to rationally design a series of 4-phenylsulfanyl-phenylamine derivatives that are capable of occupying a deep hydrophobic crevice on the surface of Bid. These compounds represent the first antiapoptotic small molecules targeting a Bcl-2 protein as shown by their ability to inhibit tBid-induced SMAC release, caspase-3 activation, and cell death.