The synthesis of 6-trifluoroethyl-l-lysine: a method to introduce functionality at C-6 of l-lysine

Described is a method of introducing trifluoroalkyl groups at C-6 of lysine. This chemistry has the potential to introduce a variety of functionality at C-6 of lysine.     

Cation transport by a redox-active synthetic ion channel

The synthesis, cation binding and transmembrane conductive properties of a novel group of synthetic ion channels containing a redox-active centre are described. Experiments using a black lipid membrane preparation revealed that these compounds function effectively as ion channels. Subsequent 23Na NMR spectroscopy studies focused on a synthesized ion channel with a ferrocene centre. When incorporated in vesicular bilayers, this channel was demonstrated to support a Na+ flux that was at least six times faster than ion transport by monensin. Since oxidation of the ferrocene moiety completely inhibited the Na+ transport, the redox-active centre provides a potential mechanism for controlling ion flux.     

Do solid surface potential barriers retard convoy peak electrons?

Using a coaxial cylindric electron spectrometer and an electrostatic ion energy analyzer in tandem, a direct measurement of the difference of the energy of convoy peak electron and the electron equivalent ion energy of protons emerging from the downstream surface of C, Au and Al foils is performed in the proton energy range from 60 to 250 keV. This measurement is made possible using the accepted evidence that for a gas target these energies are equal. It is found that also for the beam foil convoy peak electrons, within an experimental average uncertainty of about ±0.1 eV, there is no difference between these energies. If one accepts that the origin of convoy electrons is from inside the solid, the conclusion is that no retardation by the solid surface potential barrier, which is of the order of a few eV, is observed. This is attributed to the strong electron-ion Coulomb interaction which almost completely overshadows the force exerted on the electron by the field of the surface barrier.     

Ethylene polymerization over supported MAO/(nBuCp)2ZrCl2 catalysts: Influence of support properties

The catalytic system methylaluminoxane (MAO) and bis(n-butylcyclopentadienyl)zirconium dichloride ((nBuCp)₂ZrCl₂) was immobilized on commercial silica, silica-alumina and aluminophosphate calcined at different temperatures. The properties of the supports were determined by using N₂ adsorption-desorption isotherms at 77 K, FT-IR spectroscopy and SEM. After aluminium and zirconium impregnation, the catalysts were analyzed by ICP-AES, FT-IR and UV-vis spectroscopy. Ethylene polymerizations were carried out in a Schlenk tube at 70 °C and 1.2 bar of ethylene pressure. The polyethylene obtained was characterized by GPC, DSC and SEM.Catalysts supported on silica-alumina exhibited higher polymerization activity than those supported on silica and aluminophosphate. Besides, the activity of MAO/(nBuCp)₂ZrCl₂ catalytic system supported on silica-alumina and aluminophosphate decreased strongly with support calcination temperature, while remained almost constant when silica was employed as support. All these experimental features suggest a role of the support acid properties and hydroxyl group population in the generation of active polymerization species.     

Study of the 1,4-dihydroxyanthraquinone-yttrium(III) complex in solution and in the solid state

The photometric and fluorometric characteristics of the complex formed by 1,4-dihydroxyanthraquinone with Y(III) in 20–80% water-ethanol solution are described by the study of several variables. The stoichiometry and stability constant of the complex in the solution are 1:1 and log K = 4.57, respectively. The 1,4-dihydroxyanthraquinone-Y(III) solid complex has been prepared and studied by infrared spectroscopy and thermal analysis. The thermal behavior of this compound has been studied using thermogravimetry and differential scanning calorimetry techniques and the residue verified by X-ray diffraction.     

Studies on alkaline protease produced by Bacillus sp. NG312

An alkalophilic hyperproducer of alkaline protease, Bacillus sp. NG312, was isolated, and the enzyme showed maximum activity at pH 11.0 and 60°C. The temperature optimum was increased by 10°C in presence of Ca²⁺. The crudeenzyme was found to have half-life of 11 d at 37°C and maximum stability at pH 9.0–10.0. It also exhibited very good stability in presence of detergent components and some locally available commericial detergent powders.     

Infrared-induced conformational isomerization and vibrational relaxation dynamics in melatonin and 5-methoxy-N-acetyl tryptophan methyl amide

The conformational isomerization dynamics of melatonin and 5-methoxy N-acetyltryptophan methyl amide (5-methoxy NATMA) have been studied using the methods of IR-UV hole-filling spectroscopy and IR-induced population transfer spectroscopy. Using these techniques, single conformers of melatonin were excited via a well-defined NH stretch fundamental with an IR pump laser. This excess energy was used to drive conformational isomerization. By carrying out the infrared excitation early in a supersonic expansion, the excited molecules were re-cooled into their zero-point levels, partially re-filling the hole created in the ground state population of the excited conformer, and creating gains in population of the other conformers. These changes in population were detected using laser-induced fluorescence downstream in the expansion via an UV probe laser. The isomerization quantum yields for melatonin show some conformation specificity but no hint of vibrational mode specificity. In 5-methoxy NATMA, no isomerization was observed out of the single conformational well populated in the expansion in the absence of the infrared excitation. In order to study the dependence of the isomerization on the cooling rate, the experimental arrangement was modified so that faster cooling conditions could be studied. In this arrangement, the pump and probe lasers were overlapped in space in the high density region of the expansion, and the time dependence of the zero-point level populations of the conformers was probed following selective excitation of a single conformation. The analysis needed to extract isomerization quantum yields from the timing scans was developed and applied to the melatonin timing scans. Comparison between the frequency and time domain isomerization quantum yields under identical experimental conditions produced similar results. Under fast cooling conditions, the product quantum yields were shifted from their values under standard conditions. The results for melatonin are compared with those for N-acetyl tryptophan methyl amide.     

Observation of defect clustering in Gd-doped calcium fluoride

Abstract

Solid solutions Ca_1-xGd_xF_2+x for 3 × 10^?7≤ x ≤10^?1 have been studied by electron paramagnetic resonance (EPR) and ionic thermal currents (ITC). The EPR experiments show the presence of two single-ion sites a cubic and a tetragonal Gd³⁺ center which co-exist with comparable abundances for intermediate impurity concentrations. The cubic center predominates at very low and high concentrations. Seven different relaxation processes have been identified from the ITC spectra and the variation of their intensity vs. x was measured. The absolute concentrations of the cubic and nn Gd³⁺ dipoles were calculated. The scavenging of interstitial fluorines by the neutral clusters explains both the abundance of cubic sites at high concentration and the variety of orientable clusters detected by ITC.