Transient electrical response of K0.30MoO3: Effects of isoelectronic dopants

In this paper, we examine the variation of threshold fields and the transient response of tungsten- and rubidium- substituted K_0.30MoO₃. We find that the dc threshold electric field for the onset of nonlinear behavior scales linearly with tungsten concentration, but varies as the square of the rubidium concentration, indicating strong and weak pinning effects, respectively. In tungsten- substituted samples, the threshold field becomes a strong function of frequency in the range 0.01– 1000 Hz. Above a critical frequency which depends on the doping level, the threshold field is proportional to -log (frequency). We interpret these results as a further example of the spin glass- like response of the CDW. Nonlinear conductivity is observed only after the voltage has exceeded the threshold for a finite time interval.     

Resonant Raman scattering in a superconducting transition metal compoundTiN

Resonant Raman scattering has been observed in TiN. The resonance energy at 2.8 eV corresponds to the low-energy edge of interband transitions. The measured one-phonon Raman spectra which show a gap between the acoustic and optic modes are discussed.     

Hexafluoroacetone as a Protecting and Activating Reagent. <Emphasis Type="Italic">N</Emphasis>- and <Emphasis Type="Italic">O</Emphasis>-Glycosylation of Isoserine and Isocysteine

Summary. Starting from HFA-protected malic and thiomalic acid a series of O- and N-glycoconjugates suitable for peptide and depsipeptide modification has been synthesized.     

Initial velocity distributions of ions generated by in-flight laser desorption/ionization of individual polystyrene latex microparticles as studied by the delayed ion extraction method

The delayed ion extraction method has been used to study characteristics of the initial velocity distributions of positive and negative ions produced simultaneously by laser desorption/ionization (LDI) from non-impacted single aerosol polymeric particles, using a bipolar time-of-flight (TOF) instrument (LAMPAS 2). Due to the geometry of the setup and the characteristics of the ablation process, only the projections of the velocities on the axis of the mass spectrometer can be directly studied. Additionally, since the mean initial velocity under these conditions should be close to zero, it was necessary to extend the method by taking into account higher order contributions of the velocity distribution. Theoretical expressions for these higher order terms are presented and discussed. The bipolar characteristics of the instrument permit evaluation and treatment of a possible instrumental artifact caused by small inclinations of the ionizing laser with respect to the ideal incidence direction. Results of a number of experiments are presented and discussed in relation to the theoretical expressions presented, and to possible ablation scenarios. Evidence pointing out that, under our experimental conditions, only partial ablation of the latex particles occurs was obtained. The variance of the distribution of the projection of the initial velocities can be directly estimated from these results. By assuming that the total initial velocities of the ions are developed completely according to a single-temperature adiabatic expansion mechanism, temperatures of approximately 50 K/Da can be assigned to the ion clouds from the variance estimations. If a two-temperature model is used, a radial temperature of about 100 K/Da results. These values are in reasonable agreement with results for polymer ablation from the literature.     

Homologation of α-hydroxy acids to α-unsubstituted β-hydroxy carboxamides via Arndt-Eistert reaction

Here we studied the homologation of leucic and phenyl lactic acid via Wolff-rearrangement of their diazoketones to the corresponding β-hydroxy acids. This reaction requires distinct conditions to that of their amino acid analogues. The choice of the O^α-substituent can selectively direct the reaction to α-unsubstituted β-hydroxy carboxamides or (E)-α,β-unsaturated carboxamides and offers a new route from α-hydroxy acids to such compounds.     

Electrochemical crystal growth in the cesium molybdate-molybdenum trioxide system

A systematic investigation of crystal growth in the cesium molybdate/molybdenum trioxide system is described. A previously unknown blue cesium molybdenum bronze phase has been prepared as well as the known red bronze, Cs_0.33MoO₃, and high-quality crystals of the Magneli-phase compound, γ-Mo₄O₁₁. This new blue bronze, with empirical formula, Cs_0.19MoO_2.85, is monoclinic with cell constants, a = 19.198(4) Å, b = 5.519(2) Å, c = 12.213(2) Å, and β = 119.44(2)°. Measurements of the susceptibility and of the resistivity vs temperature are reported. As is the case for other alkali molybdenum bronzes, the product formed is determined by the molar ratio of alkali molybdate to molybdenum trioxide and the melt temperature.     

FLUORESCENCE ENERGY TRANSFER BETWEEN DIMETHYLDIAZAPEROPYRENIUM DICATION AND ETHIDIUM INTERCALATED IN POLY d(A-T)

Dimethyldiazaperopyrenium is one of the largest known DNA intercalators. Fluorescence energy transfer occurred between dimethyldiazaperopyrenium (donor) and ethidium (acceptor) when these dyes were bound to a double-stranded polynucleotide such as poly d(A-T). The addition of increasing amounts of ethidium bromide led to a marked shortening of the fluorescence lifetime of the donor, whereas the excited state of the acceptor was progressively populated via energy transfer from the donor. Critical Förster distance between these two chromophores was calculated to be 3.8 nm. The observed transfer efficiency was lower than that calculated on the basis of this critical distance and a statistical distribution of bound drugs. These results are discussed taking into account the conformational change induced by intercalation of dimethyldiazaperopyrenium in the double-stranded polynucleotide.