A new synthetic route towards the mono-O-protected anti-conformationally constrained pyrimidine acyclic nucleoside.
(1/17)
Novel synthetic approach to mono-O-protected anti-conformationally constrained pyrimidine acyclic nucleoside was attained from the coupling of lithiated 2,4-dimethoxy-6-methylpyrimidine with 1-benzyloxy-3-(tert-butyldiphenylsilyloxy)propan-2-one, followed by the sequential reactions of methylthiomethylation, cyclization, hydroxylation, and dealkylation. (+info)
Termolecular ion-molecule reactions in Titan's atmosphere. IV. A search made at up to 1 micron in pure hydrocarbons.
(2/17)
The results of a study of ion-molecule reactions occurring in pure methane, acetylene, ethylene, ethane, propyne, propene, propane, and diacetylene at pressures up to 40 microns of pressure are reported. A variety of experimental methods are used: The standard double resonance in an ICR, for determination of the precursor ions and the modulated double resonance ejection in an ICR, for the determination of the daughter ions. The FA-SIFT technique was used for validation and examination of termolecular reactions with rate coefficients that are less than 10(-26) cm(6) s(-1). An extensive database of reaction kinetics already exists for many of these reactions. The main point of this study was the determination of the accuracy of this database and to search for any missing reactions and reaction channels that may have been omitted from earlier investigations. A specific objective of this work was to extend the study to the highest pressures possible to find out if there were any important termolecular reaction channels occurring. A new approach was used here. In the pure hydrocarbon gases the mass spectra were followed as a function of the pressure changes of the gas. An initial guess was first made using the current literature as a source of the reaction kinetics that were expected. A model of the ion abundances was produced from the solution of the partial differential equations in terms of reaction rate coefficients and initial abundances. The experimental data was fitted to the model for all of the pressures by a least squares minimization to the reaction rate coefficients and initial abundances. The reaction rate coefficients obtained from the model were then compared to the literature values. Several new channels and reactions were discovered when the modeled fits were compared to the actual data. This is all explained in the text and the implications of these results are discussed for the Titan atmosphere. (+info)
Synthesis and biological evaluation of ebselen and its acyclic derivatives.
(3/17)
Five ebselen and three acyclic ebselen derivatives were synthesized. These compounds were screened for their glutathione peroxidase (GSH Px)-like activity and scavenging activity against 1,1-diphenyl-2-pycryl-hydrazyl (DPPH) and peroxynitrite radical. All tested compounds displayed similar significant GSH Px-like activity, which are slightly higher than that of ebselen. The peroxynitrite scavenging activity showed that the acyclic allylseleno 4c was five times more potent than ebselen. (+info)
In vitro assessment of alkylglycosides as permeability enhancers.
(4/17)
series of alkylglycosides has been evaluated on human cell lines to determine its ability to open cellular tight junctions. Alkylglycosides were applied to cell monolayers; the resulting change in resistance was determined by transepithelial electrical resistance measurements. Change in resistance across cell monolayers is an indication of tight junction activation, whereas subsequent increase in resistance signifies monolayer recovery. Of the 13 alkylglycosides tested, 4 caused irreversible solubilization of cell membranes, 5 allowed a partial recovery of the monolayer after a relatively rapid reduction in resistance, and 4 induced a decrease in resistance with more complete cell recovery. Alkylglycosides allowing extensive cell recovery after removal may indicate tight junctions' activity dominance over membrane fluidity. Repeated application of alkylglycosides for 6 hours lowered resistance across cells, which returned to near-normal values after a recovery period of 48 hours. A model dye was transported across the cell monolayer only in the presence of an alkylglycoside, although recovery of cells was incomplete. Activity of the alkylglycosides was unrelated to either the carbon chain length or to the carbohydrate moiety. A direct correlation was established between the concentration of applied alkylglycoside and reduction in resistance over a constant time period. Dodecylmaltoside and octylglucoside were found to be optimal in decreasing resistance at low concentrations and allowing significant recovery of cells. Therefore these 2 alkylglycosides may be useful in facilitating drug transport across biological membranes. (+info)
The Cassini UVIS stellar probe of the Titan atmosphere.
(5/17)
The Cassini Ultraviolet Imaging Spectrometer (UVIS) observed the extinction of photons from two stars by the atmosphere of Titan during the Titan flyby. Six species were identified and measured: methane, acetylene, ethylene, ethane, diacetylene, and hydrogen cyanide. The observations cover altitudes from 450 to 1600 kilometers above the surface. A mesopause is inferred from extraction of the temperature structure of methane, located at 615 km with a temperature minimum of 114 kelvin. The asymptotic kinetic temperature at the top of the atmosphere determined from this experiment is 151 kelvin. The higher order hydrocarbons and hydrogen cyanide peak sharply in abundance and are undetectable below altitudes ranging from 750 to 600 km, leaving methane as the only identifiable carbonaceous molecule in this experiment below 600 km. (+info)
Nestmate recognition cues in the honey bee: differential importance of cuticular alkanes and alkenes.
(6/17)
In social insects, recognition of nestmates from aliens is based on olfactory cues, and many studies have demonstrated that such cues are contained within the lipid layer covering the insect cuticle. These lipids are usually a complex mixture of tens of compounds in which aliphatic hydrocarbons are generally the major components. The experiments described here tested whether artificial changes in the cuticular profile through supplementation of naturally occurring alkanes and alkenes in honeybees affect the behaviour of nestmate guards. Compounds were applied to live foragers in microgram quantities and the bees returned to their hive entrance where the behaviour of the guard bees was observed. In this fashion we compared the effect of single alkenes with that of single alkanes; the effect of mixtures of alkenes versus that of mixtures of alkanes and the whole alkane fraction separated from the cuticular lipids versus the alkene fraction. With only one exception (the comparison between n-C(19) and (Z)9-C(19)), in all the experiments bees treated with alkenes were attacked more intensively than bees treated with alkanes. This leads us to conclude that modification of the natural chemical profile with the two different classes of compounds has a different effect on acceptance and suggests that this may correspond to a differential importance in the recognition signature. (+info)
Inhibition of class D beta-lactamases by acyl phosphates and phosphonates.
(7/17)
The susceptibility of typical class D beta-lactamases to inhibition by acyl phosph(on)ates has been determined. To a large degree, these class D enzymes behaved very similarly to the class A TEM beta-lactamase towards these reagents. Dibenzoyl phosphate stood out in both cases as a lead compound towards a new class of effective inhibitors. (+info)
Gas chromatography method for the characterization of ethanol steam reforming products.
(8/17)
Ethanol steam reforming is a promising reaction for producing fuel cell hydrogen. Depending on catalyst and reaction conditions, mixtures of condensable hydrocarbons and organic and inorganic gases are produced. This paper proposes an economic and effective solution for separating and detecting these compounds employing a gas chromatograph equipped with two columns, two 6-way valves, and two detectors. (+info)