Search results for "RAV"

I. Glass Transition. Theoretical concepts on the glass transition of polymers and their test by computer simulation

1996

Various organic molecules, in particular polymers, are extremely good glass formers and allow the study of supercooled melts near the glass transition in metastable equilibrium. Theories of the glass transition imply such an equilibrium (e.g. mode-coupling theory, or Gibbs-di Marzio theory) and can hence be tested in these systems. Simplified lattice models for polymer melts (e.g. the bond fluctuation model) have been developed that can very efficiently be studied by Monte-Carlo simulation, and although they fail to accurately describe the local structure, they describe many features of the experiments very well. In this model, the mechanism of the glass transition is a competition between …

Photoaffinity labeling of the coupling factor 1 from the thermophilic bacterum PS3 by 8-azido ATP

1984

AbstractTo localize the nucleotide binding sites of the F1ATPase (TF1) from the thermophilic bacterium PS3 we have used 14C-labeled 8-azido ATP (8-N3ATP) as photoaffmity label. 8-N3ATP is hydrolyzed by the F,ATPase in the absence of ultraviolet light. Irradiation by ultraviolet light of the enzyme in the presence of 8-N3ATP results in reduction of ATPase activity and in preferential nucleotide specific labeling of the α subunits (0.8–0.9 mol 8-N3ATP/TF1,α:β = 4:1). Inactivation and labeling do not depend on the presence of Mg2+. Both effects decrease upon addition of various nucleotide di- or triphosphates.

Innovative Combination of Three Alternating Current Relaxation Techniques: Electrical Charge, Mass, and Color Impedance Spectroscopy. Part I: The Tool

2009

Technical details concerning the simultaneous acquisition of three impedance functions (electrochemical impedance spectroscopy, alternating current electrogravimetry or mass impedance, and alternating current colorimetry or color impedance) are presented. The analysis of each type of impedance function gives interesting information about the species participating during the electrochemical processes. Furthermore, obtaining three impedance functions in situ allows the crossed impedance functions to be calculated. These functions are especially useful in detecting delays between the color, mass, and electrical charge response of the system to the same perturbation, and it allows species parti…

1997

On the basis of an extended series of monodisperse oligomers of the dialkoxy-substituted phenyleneethenylenes 1a–i the Eqs. (3) and (4) were conceived in order to determine the limiting values of the energies Ei and the wavelengths λi of the UV/vis absorption. The convergence of the Ei, and λi values with a growing number n of repeating units permits a precise prediction of the Ei,∞ and λi,∞ values of the corresponding polymer 1j as well as a statement about the overall effect of conjugation ΔEi and the effective conjugation length ECL. A great variety of different conjugated oligomers 2–14 can be evaluated by the same algorithm.

A Mixed-Ligand Approach for Spin-Crossover Modulation in a Linear FeII Coordination Polymer

2014

In this work, we present a family of Fe(II) coordination polymers of general formula [Fe(btzx)(3-3x)(btix)(3x)](ClO4)2 with interesting spin-crossover properties. These coordination polymers have been synthesized using chemical mixtures of two different but closely related ligands, 1,4-bis(tetrazol-1-ylmethyl)benzene (btzx) and 1,4-bis(triazol-1-ylmethyl)benzene (btix), and the effect of a gradual substitution of the ligand in the spin transition temperature has been investigated. Several chemical mixtures have been structurally characterized by X-ray powder diffraction indicating a clear critical amount in the composition of the mixture after which mixed phases rather than a single phase c…

Stilbene Content of MatureVitis viniferaBerries in Response to UV-C Elicitation

2001

A method using HPLC analysis has been used to compare the level of resveratrol and its derivatives, piceid, pterostilbene and epsilon-viniferin, in grapevine berries of three Vitis vinifera varieties. The concentration of these compounds has been evaluated in healthy and Botrytis cinerea infected grape clusters, both in natural vineyard conditions and in response to UV elicitation.

UV-B-Induced acute toxicity of pyrene to the waterflea Daphnia magna in natural freshwaters.

1999

Abstract The effects of various water characteristics in natural freshwaters on the acute toxicity of one polycyclic aromatic hydrocarbon (PAH), pyrene, to a pelagic invertebrate Daphnia magna was studied under ultraviolet B (UV-B) radiation and in the dark. Pyrene was photoactivated and was more toxic to D. magna in the presence of UV-B radiation. Dissolved organic material (DOM), measured as dissolved organic carbon (DOC), significantly reduced the photoenhanced toxicity of pyrene. Under UV-B radiation the EC50 values were lower and in relation to the amount of DOM, ranging from 3.0 to 30.0 μg/L pyrene, whereas in the dark they were between 29.2 and 54.8 μg/L and not related to the amount…

Biopartitioning micellar chromatography: An alternative high-throughput method for assessing the ecotoxicity of anilines and phenols

2007

An investigation of the use of the chromatographic retention (log k) as an in vitro approach for modelling the toxicity to Fathead Minnows of anilines and phenols is developed. A data set of 65 compounds with available experimental toxicity data was used. Log k data at three pH values were used for the compounds classification and two groups or 'MODEs' were identified. For one 'MODE' a quantitative retention-activity relationship (QRAR) model was calculated. Finally, it was used to estimate the toxicity to Fathead minnows of anilines and phenols for which experimental data are not available. These estimations were compared to those obtained from another toxicity (to Tetrahymena pyriformis) …

Influence of Several Effectors on the Structure-Activity Relationship of Spleen Phosphodiesterase

1993

The influence of Mg(II) and organic solvents on the structure-activity relationship of spleen phosphodiesterase II was analyzed using UV and fluorescence spectroscopies. An increase in the RNase activity found in the presence of Mg(II) was related to the enzyme-Mg(II) interaction detected by UV spectroscopy. In the fluorescence spectra of phosphodiesterase strong hypochromic and bathochromic effects were observed when RNA was present at a concentration (52 μg ml−1) of the same magnitude as the concentration that inhibits the activity (Ki = 40 μg ml−1). The strong quenching observed in the presence of RNA shows the importance of large dynamic and static quenching of the Trp residues of the e…

O-Ribosyl-phosphate purine as a constant modified nucleotide located at position 64 in cytoplasmic initiator tRNAsMetof yeasts

1991

The unknown modified nucleotide G*, isolated from both Schizosaccharomyces pombe and Torulopsis utilis initiator tRNAs(Met), has been identified as an O-ribosyl-(1"----2')-guanosine-5"-phosphate, called Gr(p), by means of HPLC, UV-absorption, mass spectrometry and periodate oxidation procedures. By comparison with the previously published structure of Ar(p) isolated from Saccharomyces cerevisiae initiator tRNA(Met), the (1"----2')-glycosidic bond in Gr(p) has been postulated to have a beta-spatial conformation. The modified nucleotide Gr(p) is located at position 64 in the tRNA(Met) molecules, i.e. at the same position as Ar(p). Since we have also characterized Gr(p) in Candida albicans ini…