UV irradiation of polycyclic aromatic hydrocarbons in ices: production of alcohols, quinones, and ethers.
(1/2682)
Polycyclic aromatic hydrocarbons (PAHs) in water ice were exposed to ultraviolet (UV) radiation under astrophysical conditions, and the products were analyzed by infrared spectroscopy and mass spectrometry. Peripheral carbon atoms were oxidized, producing aromatic alcohols, ketones, and ethers, and reduced, producing partially hydrogenated aromatic hydrocarbons, molecules that account for the interstellar 3.4-micrometer emission feature. These classes of compounds are all present in carbonaceous meteorites. Hydrogen and deuterium atoms exchange readily between the PAHs and the ice, which may explain the deuterium enrichments found in certain meteoritic molecules. This work has important implications for extraterrestrial organics in biogenesis. (+info)
Conformational changes generated in GroEL during ATP hydrolysis as seen by time-resolved infrared spectroscopy.
(2/2682)
Changes in the vibrational spectrum of the chaperonin GroEL in the presence of ADP and ATP have been followed as a function of time using rapid scan Fourier transform infrared spectroscopy. The interaction of nucleotides with GroEL was triggered by the photochemical release of the ligands from their corresponding biologically inactive precursors (caged nucleotides; P3-1-(2-nitro)phenylethyl nucleotide). Binding of either ADP or ATP induced the appearance of small differential signals in the amide I band of the protein, sensitive to protein secondary structure, suggesting a subtle and localized change in protein conformation. Moreover, conformational changes associated with ATP hydrolysis were detected that differed markedly from those observed upon nucleotide binding. Both, high-amplitude absorbance changes and difference bands attributable to modifications in the interaction between oppositely charged residues were observed during ATP hydrolysis. Once this process had occurred, the protein relaxed to an ADP-like conformation. Our results suggest that the secondary structure as well as salt bridges of GroEL are modified during ATP hydrolysis, as compared with the ATP and ADP bound protein states. (+info)
A new bile acid conjugate, ciliatocholic acid, from bovine gall bladder bile.
(3/2682)
This study was carried out to investigate the occurrence of ciliatocholic acid in bovine gall bladder bile. Ciliatocholic acid was synthesized according to the method described by Bergstrom and Norman for the synthesis of taurocholic acid. Elemental analysis, melting point, and the infrared spectrum of this substance were determined. An isolation procedure for ciliatocholic acid was established by stepwise elution with an HCl-ethanol solvent system using a Dowex-1 anion exchange resin column chromatographic technique. Ciliatocholic acid amounting to 158 mug (as ciliatine) per 100 ml of gall bladder bile was found in the fraction eluted with 0.01 N HCl in 50% ethanol. This coumpound was purified by preparative thin-layer chromatography and confirmed to be ciliatocholic acid from the hydrolytic stability, phosphorus determination, and chromatographic behavior. Thus, bovine gall bladder bile contains a small amount of ciliatocholic acid. (+info)
Infrared dichroism of the DNA-caffeine complex. A new method for determination of the ligand orientation.
(4/2682)
Infrared linear dichroism (LD) measurements on films of the DNA-caffeine complex in terms of the relative humidity (r.h.) show two main effects. Firstly, there is an insertion of caffeine molecules into the DNA double helix (B form), as evidenced by a very strong parallel LD behaviour of the 745 cm-1 band due to the C-H out-of-plane deformation vibration of caffeine. Furthermore, a high r.h. values a modified B form occurs in the complex similar to the B form recently reported by BRAHMS and coworkers for DNA-polypeptide complexes. The reversible B-A transition of the DNA in dependence of the r.h. is not affected in general in the presence of caffeine. (+info)
The two-dimensional IR nonlinear spectroscopy of a cyclic penta-peptide in relation to its three-dimensional structure.
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A form of two-dimensional (2D) vibrational spectroscopy, which uses two ultrafast IR laser pulses, is used to examine the structure of a cyclic penta-peptide in solution. Spectrally resolved cross peaks occur in the off-diagonal region of the 2D IR spectrum of the amide I region, analogous to those in 2D NMR spectroscopy. These cross peaks measure the coupling between the different amide groups in the structure. Their intensities and polarizations relate directly to the three-dimensional structure of the peptide. With the help of a model coupling Hamiltonian, supplemented by density functional calculations, the spectra of this penta-peptide can be regenerated from the known solution phase structure. This 2D-IR measurement, with an intrinsic time resolution of less than 1 ps, could be used in all time regimes of interest in biology. (+info)
High base pair opening rates in tracts of GC base pairs.
(6/2682)
Sequence-dependent structural features of the DNA double helix have a strong influence on the base pair opening dynamics. Here we report a detailed study of the kinetics of base pair breathing in tracts of GC base pairs in DNA duplexes derived from 1H NMR measurements of the imino proton exchange rates upon titration with the exchange catalyst ammonia. In the limit of infinite exchange catalyst concentration, the exchange times of the guanine imino protons of the GC tracts extrapolate to much shorter base pair lifetimes than commonly observed for isolated GC base pairs. The base pair lifetimes in the GC tracts are below 5 ms for almost all of the base pairs. The unusually rapid base pair opening dynamics of GC tracts are in striking contrast to the behavior of AT tracts, where very long base pair lifetimes are observed. The implication of these findings for the structural principles governing spontaneous helix opening as well as the DNA-binding specificity of the cytosine-5-methyltransferases, where flipping of the cytosine base has been observed, are discussed. (+info)
2-mercapto N-(azolyl)benzenesulfonamides. VI. Synthesis and anti-HIV activity of some new 2-mercapto-N-(1,2,4-triazol-3-yl)benzenesulfonamide derivatives containing the 1,2,4-triazole moiety fused with a variety of heteroaromatic rings.
(7/2682)
A series of 2-mercapto-N-(1,2,4-triazol-3-yl)benzenesulfonamide derivatives containing the triazole moiety fused with a variety of heteroaromatic rings [XVI-XXVIII] was obtained by the reactions of 3-methylthio-1,4-2-benzodithiazine 1,1-dioxide derivatives [Ia-d] with 2-hydrazines [IIa-f]. Some of the intermediate 1,1-dioxide-1,4,2-benzodithiazin-3-ylhydrazines [III-XV] initially formed were also isolated. Preliminary screening data indicated that compounds [XVI-XIX and XXVII] were anti-HIV inactive, whereas other compounds showed a high [XXI and XXIII], fairly high [XXIII and XXVI] or moderate [XX, XXIV, XXV and XXVIII] activity. The compound [XXI] exhibited also high activity against ten selected HIV mutants. (+info)
Synthesis, anti-HIV and anticancer activities of new 4-(2-mercaptobenzenesulfonyl)perhydro-1,2,4-triazin-3-ones.
(8/2682)
Syntheses of N-(6-chloro-1,1-dioxo-7-R1-1,4,2-benzodithiazyn-3-yl)-N'-(2- hydroxyethyl)hydrazines (IIa-d], N-(6-chloro-1,1-dioxo-7-methyl-1,4,2-benzodithiazyn-3-yl)-N'-(2- chloroethyl)hydrazine [IV], 4-(4-chloro-5-R1-2-mercaptobenzenesulfonyl)perhydro-1,2,4-triaz in-3-ones [IIIa-d] and 5-chloro-4-methyl-2-(3-oxoperhydro-1,2,4-triazin-4- ylsulfonyl)phenylthioacetic acid [V] have been described. Preliminary screening data have indicated that compounds [IIIa-d] exhibit either a moderate or a high anti-HIV activity and a moderate anticancer activity in some human tumor cell lines. (+info)