Detection of picramic acid and picramate in henné products by NMR Spectroscopy

Painting and body art are increasing their utilisation as well as their cultural impact, since piercing and tattoos are expanding social phenomena, involving many young people. However, the utilised materials often enter the market with insufficient control and several cases of skin damages are reported. Safety of the utilised products must be ensured by adequate quality controls which must be easily made, rapid, low cost, clear and persuasive. The method here reported, regards the analysis on the possible presence of picramic acid in the ethyl acetate extracts of commercial henné powders by NMR Spectroscopy. In the proton spectrum, three sets of peaks could be detected, corresponding to the three classes of makers resonances: hennosides, typical markers of Lawsonia inermis, the henné plant; picramic acid or picramate; fatty acids. In particular, the set of signals corresponding to hennosides can be used as markers of the utilisation of the correct raw material of henné.     

Pyrene-1-Carboxylate in Water and Glycerol Solutions: Origin of the Change of p<Emphasis Type="Italic">K</Emphasis> Upon Excitation

Pyrene-1-carboxy acid has a pK of 4 in the ground state, and a pK of 8 in the excited state. Fluorescence spectra of the acid and base forms are presented as a function of solvent and temperature. Ab initio quantum calculations indicate that the bond between the ring system and the carboxyl group has aromatic character that becomes stronger upon excitation. This stabilization helps to account for the increase in pK upon excitation.     

Onset of diffusive behavior in confined transport systems

We investigate the onset of diffusive behavior in polygonal channels for disks of finite size, modeling simple microporous membranes. It is well established that the point-particle case displays anomalous transport, because of slow correlation decay in the absence of defocusing collisions. We investigate which features of point-particle transport survive in the case of finite-sized particles (which undergo defocusing collisions). A similar question was investigated by Lansel, Porter, and Bunimovich [Chaos 16, 013129 (2006)], who found that certain integrals of motion and multiple ergodic components, characteristic of the point-particle case, remain in "mushroom"-like systems with few finite-sized particles. We quantify the time scales over which the transport of disks shows features typical of the point particles, or is driven toward diffusive behavior. In particular, we find that interparticle collisions drive the system toward diffusive behavior more strongly than defocusing boundary collisions. We illustrate how, and at what stage, typical thermodynamic behavior (consistent with kinetic theory) is observed, as particle numbers grow and mean free paths diminish. These results have both applied (e.g., nanotechnological) and theoretical interest.     

The nonequilibrium Lorentz gas

We study the conductivity of a Lorentz gas system, composed of a regular array of fixed scatterers and a point-like moving particle, as a function of the strength of an applied external field. In order to obtain a nonequilibrium stationary state, the speed of the point particle is fixed by the action of a Gaussian thermostat. For small fields the system is ergodic and the diffusion coefficient is well defined. We show that in this range the Periodic Orbit Expansion can be successfully applied to compute the values of the thermodynamic variables. At larger values of the field we observe a variety of possible dynamics, including the breakdown of ergodic behavior, and later the existence of a single stable trajectory for the largest fields. We also study the behavior of the system as a function of the orientation of the array of scatterers with respect to the external field. Finally, we present a detailed dynamical study of the transitions in the bifurcation sequence in both the elementary cell and the fundamental domain. The consequences of this behavior for the ergodicity of the system are explored. (c) 1995 American Institute of Physics.     

Bromazepam determination in human plasma by high-performance liquid chromatography coupled to tandem mass spectrometry: a highly sensitive and specific tool for bioequivalence studies

A rapid, sensitive and specific method to quantify bromazepam in human plasma using diazepam as the internal standard (IS) is described. The analyte and the IS were extracted from plasma by liquid-liquid extraction using diethyl ether-hexane (80 : 20, v/v). The extracts were analyzed by high-performance liquid chromatography (HPLC) coupled to electrospray tandem mass spectrometry (MS/MS). Chromatography was performed isocratically on a Genesis C(18) analytical column (100 x 2.1 mm i.d., film thickness 4 microm). The method had a chromatographic run time of 5.0 min and a linear calibration curve over the range 5.0-150 ng ml(-1) (r(2) > 0.9952). The limit of quantification was 5 ng ml(-1). This HPLC/MS/MS procedure was used to assess the bioequivalence of two bromazepam 6 mg tablet formulations (bromazepam from Medley SA Indústria Farmacêutica as the test formulation and Lexotan from Produtos Roche Químico e Farmacêutico SA as the reference formulation). A single 6 mg dose of each formulation was administered to 24 healthy volunteers (12 males and 12 females). The study was conducted using an open, randomized, two-period crossover design with a 3 week washout interval. Since the 90% CI for C(max), AUC(last), AUC(0-240 h) (linear) and AUC((0- infinity )) ratios were all inside the 80-125% interval proposed by the US Food and Drug Administration, it was concluded that the bromazepam formulation from Medley is bioequivalent to the Lexotan formulation for both the rate and the extent of absorption.     

Mechanism of electrohydrodimerization of acrylonitrile on mercury from aqueous solutions

The electrohydrodimerization (EHD) of acrylonitrile (AN) on mercury from aqueous solutions was examined by a polarographic technique with positive feedback for IR compensation as well as by differential-capacity measurements, with the aim of determining optimal experimental conditions under which the formation of the hydrodimer adiponitrile (ADN) is decidedly favoured over that of the saturated monomer propionitrile (PN). Several tetraalkylammonium cations at low concentrations (≈10^?3M) and several supporting electrolytes were employed for this purpose. The best conditions for EHD were attained in aqueous solutions of 1.3 to 1.5 M Na⁺ or Li⁺ citrate containing 10^?3M dodecylethyldimethylammonium (DEDMA) bromide. Under these conditions a gradual increase in the AN bulk concentration from 10^?2M to 0.2 M causes a progressive splitting of the single two-electron wave due to PN formation into two consecutive one-electron waves, the first of which is due to ADN formation. Differential-capacity measurements indicate that such a progressive passage from the formation of the saturated monomer to that of the hydrodimer is accompanied by a gradual coadsorption of AN and DEDMA on the electrode surface, which demonstrates that the coupling reaction yielding ADN takes place in the adsorbed state.Mechanisms for PN formation at AN concentrations <10^?2M and for ADN formation at the higher AN concentrations at which EHD takes place have been proposed.     

Free‐electron laser multiplex driven by a superconducting linear accelerator

Free‐electron lasers (FELs) generate femtosecond XUV and X‐ray pulses at peak powers in the gigawatt range. The FEL user facility FLASH at DESY (Hamburg, Germany) is driven by a superconducting linear accelerator with up to 8000 pulses per second. Since 2014, two parallel undulator beamlines, FLASH1 and FLASH2, have been in operation. In addition to the main undulator, the FLASH1 beamline is equipped with an undulator section, sFLASH, dedicated to research and development of fully coherent extreme ultraviolet photon pulses using external seed lasers. In this contribution, the first simultaneous lasing of the three FELs at 13.4 nm, 20 nm and 38.8 nm is presented.     

Temporal asymmetry of fluctuations in nonequilibrium steady states: links with correlation functions and nonlinear response

The presence of temporal asymmetries in fluctuation paths of nonequilibrium systems has recently been confirmed numerically in nonequilibrium molecular dynamics simulations of particular deterministic systems. Here we show that this is a common feature of homogeneously driven and thermostatted, reversible, deterministic, chaotic, nonequilibrium systems of interacting particles. This is done by expressing fluctuation paths as correlation functions. The theoretical arguments look rather general, and we expect them to easily extend to other forms of driving and thermostats. The emergence of asymmetry is also justified using the transient time correlation function expression of nonlinear response theory. Numerical simulations are used to verify our arguments.     

Changes in water structure induced by the guanidinium cation and implications for protein denaturation

The effect of the guanidinium cation on the hydrogen bonding strength of water was analyzed using temperature-excursion Fourier transform infrared spectra of the OH stretching vibration in 5% H 2O/95% D 2O solutions containing a range of different guanidine-HCl and guanidine-HBr concentrations. Our findings indicate that the guanidinium cation causes the water H-bonds in solution to become more linear than those found in bulk water, and that it also inhibits the response of the H-bond network to increased temperature. Quantum chemical calculations also reveal that guanidinium affects both the charge distribution on water molecules directly H-bonded to it as well as the OH stretch frequency of H-bonds in which that water molecule is the donor. The implications of our findings to hydrophobic solvation and protein denaturation are discussed.