Fast excited-state intramolecular proton transfer and subnanosecond dynamic stokes shift of time-resolved fluorescence spectra of the 5-methoxysalicylic acid/diethyl ether complex

Excited-state intramolecular proton transfer (ESIPT) occurring in the salicylic acid (SA) derivative 5-methoxysalicylic acid (5-MeOSA) in an apolar solvent (cyclohexane) and in the presence of the hydrogen bond accepting agent diethyl ether (DEE) is investigated. Analysis of the directly measured subnanosecond time-resolved emission spectra (TRES) together with conventional steady-state fluorescence and time-correlated single-photon-counting (TCSPC) decays indicates that ESIPT in this system occurs much faster than fluorescence, and that the equilibrium between normal and tautomeric excited states is established before the emission from both states takes place. However, changes in time- and frequency-resolved fluorescence of the 5-MeOSA/DEE complex are observed due to structural relaxation within the complex, which is reflected in the dynamic Stokes shift of the tautomeric fluorescence band. The normal fluorescence band of 5-MeOSA/DEE does not exhibit marked changes within the investigated time range. A single-exponential relaxation time of 460 ps was determined for the dynamic Stokes shift of the tautomeric band, and it is attributed to a geometric change within the 5-MeOSA/DEE complex upon excitation. Since both tautomeric and normal emission bands are well resolved and exhibit different time-dependent behaviors, a double-well potential appears to be adequate to describe the excited state of the system studied.     

Inhibiting effect of beta-cyclodextrin on thymine dimerization photosensitized by para-aminobenzoic acid

Beta-cyclodextrin can act as an efficient inhibitor of the photosensitized dimerization of thymine by para-aminobenzoic acid (PABA) in aqueous solution. This can be explained by considering the formation of an inclusion complex between PABA and beta-cyclodextrin.     

Hypochlorous acid-induced oxidative damage of human red blood cells: effects of tert-butyl hydroperoxide and nitrite on the HOCl reaction with erythrocytes

Hypochlorous acid, one of the most powerful biological oxidants, is believed to be important in the pathogenesis of some diseases. The purpose of this study was to further characterise the membrane and intracellular events which resulted in HOCl-induced oxidative impairments and haemolysis of human erythrocytes and interaction of different oxidative agents, which accumulated during respiratory burst, in the process of RBS oxidation. The sequence of cellular events after red blood cell exposure to HOCl: cell morphological transformations, oxidation of cellular constituents, enzyme modifications, and haemolysis have been evaluated. It was shown that HOCl-treated cells underwent colloid-osmotic haemolysis, preceded by rapid morphological transformations and membrane structural transitions. The activation energy of the process of haemolysis (after removal of the excess of oxidative agent) was estimated to be 146+/-22 kJ/mol at temperatures above the break point of Arrhenius plot (31-32 degrees C). This value corresponds to the activation energy of the process of protein denaturation. Modification of erythrocytes by HOCl inhibited membrane acetylcholinesterase (uncompetitive type of inhibition), depleted intracellular glutathione, activated intracellular glutathione peroxidase, but did not induce membrane lipid peroxidation. The presence of other oxidants, nitrite or tert-butyl hydroperoxide (t-BHP), promoted the oxidative damage induced by HOCl and led to new oxidative reactions.     

Combustion process in a spark ignition engine: analysis of cyclic peak pressure and peak pressure angle oscillations

In this paper we analyze the cycle-to-cycle variations of peak pressure p _max and peak pressure angle α _pmax in a four-cylinder spark ignition engine. We examine the experimental time series of p _max and α _pmax for three different spark advance angles. Using standard statistical techniques such as return maps and histograms we show that depending on the spark advance angle, there are significant differences in the fluctuations of p _max and α _pmax . We also calculate the multiscale entropy of the various time series to estimate the effect of randomness in these fluctuations. Finally, we explain how the information on both p _max and α _pmax can be used to develop optimal strategies for controlling the combustion process and improving engine performance.     

Water-window microscopy using a compact, laser-plasma SXR source based on a double-stream gas-puff target

We report on a compact, desktop size, laboratory type microscopy setup, based on a short wavelength gas puff target soft X-ray source, which emits incoherent radiation in “water-window” spectral range. The microscope employs a Wolter type I reflective objective and allows capturing magnified images of objects with ~1-μm spatial resolution and exposure time as low as 5 s. A detailed characterization and optimization of both the source and the microscope setups are presented and discussed.     

Stochastic differential equations for the kinetic and hydrodynamic equations

A finite system of stochastic interacting particles is considered. The system approximates the solutions of the kinetic equations (the Boltzmann equation, the Boltzmann-Enskog equation) as well as the solutions describing the macroscopic evolution of fluids: the Euler and the Navier-Stokes hydrodynamic equations.     

Red and blue shifted hydridic bonds

By performing MP2/aug‐cc‐pVTZ ab initio calculations for a large set of dimer systems possessing a R? H hydridic bond involved in diverse types of intermolecular interactions (dihydrogen bonds, hydride halogen bonds, hydride hydrogen bonds, and charge‐assisted hydride hydrogen bonds), we show that this is rather an elongation than a shortening that a hydride bond undergoes on interaction. Contrary to what might have been expected on the basis of studies in uniform electric field, this elongation is accompanied by a blue instead of red shift of the R? H stretching vibration frequency. We propose that the “additional” elongation of the R? H hydridic bond results from the significant charge outflow from the sigma bonding orbital of R? H that weakens this bond. The more standard red shift obtained for stronger complexes is explained by means of the Hermansson's formula and the particularly strong electric field produced by the H‐acceptor molecule. © 2014 Wiley Periodicals, Inc.