Arthrichitin. A New Cell Wall Active Metabolite from Arthrinium phaeospermum

Arthrichitin (1), C(33)H(46)N(4)O(9), is a new cell wall active depsipeptide isolated from the fermentation broth of Arthrinium phaeospermum (HIL Y-903022). Its structure was elucidated on the basis of spectroscopic and chemical degradation studies. Arthrichitin consists of serine, beta-keto tryptophan, glutamic acid, and 2,4-dimethyl-3-hydroxydodecanoic acid units.     

A search for high energy neutrinos from SN 1987A,the Carb,Hercules X-1, and Cygnus X-3 with the Fréjus detector

With the Fréjus detector we studied four astrophysical point-like sources by using \(v_e (\bar v_e )\) and \(v_\mu (\bar v_\mu )\) interactions in the detector and \(v_\mu (\bar v_\mu )\) interactions in the surrounding rock. No excess of events was found. Therefore upper limits of neutrino fluxes and source luminositics are quoted. These limits confirm results from other experiments. In addition new limits are presented for spectral indices above 3.     

Gas phase 1,3-deoxystannylation reactions of γ-substituted organotin alcohols utilizing chemical ionization mass spectrometry

The gas phase 1,3-deoxystannylation reactions of γ-substituted organotin alcohols have been studied by methane and isobutane chemical ionization mass spectrometry. It was found that γ-hydroxybutyltributyltin and γ-hydroxybutyldibutyltin chloride undergo the 1,3-deoxystannylation reaction to a greater extent than the corresponding 1,4-deoxystannylation using the δ-substituted analogues of the above named compounds. This result substantiates the unusual reactivity of γ-substituted organotin alcohols under gas phase protonolysis conditions.The electronic factors affecting the stabilization of the transition state were ascertained with γ-phenyl-γ-hydroxypropyltrimethyltin derivatives, in which the γ-phenyl group was substituted with groups such as H, p-OMe, p-Me, p-Cl, p-F, m-OMe, m-Me, m-Cl and m-CF₃. We observed a reasonably linear Hammett relationship when plotting the log [P ? 17]_x⁺/[P ? 17]_H⁺ vs. σ⁺ with rho (ρ) equal to ?1.0.Thus electron-donating groups stabilize the [P ? 17]⁺ ion and carbon—tin sigma (σ) electrons can either, by a neighbouring group effect, attack the nucleofugic center, or the carbonium ion can attack the carbon—tin σ electrons to form the trimethyltin cation and a cyclopropane derivative. Consequently, we propose that a two-step mechanism for the 1,3-deoxystannylation reaction is operating in the gas-phase with this type of compound. The factors contributing to this gas phase reaction will be discussed.     

Identification of the adsorption sites of molecular oxygen on Si(111) using XPS

Most of the oxygen adsorb dissociatively on Si, however there is also a significant amount of metastable molecular oxygen chemisorbed on Si. The adsorption site/configuration of these molecular oxygen species is still a controversial subject. New XPS results for oxygen adsorption on Si(111) 7×7 (150K) are presented. They reveal four distinct oxygen components; one of the metastable components has never been reported before. We tentatively identify them as: i) stable oxide (Si-O-Si bridges)(˜532 eV), ii) diffusing oxygen atom (˜533 eV) in silicon oxide and iii) metastable molecular oxygen species (˜527.6 eV and ˜530.6 eV). The latter have been attributed to peroxy radical which is defined as a diatomic oxygen bonded to a single Si adatom. Our results allow us to distinguish the two main configurations of peroxy radical: paul-para and grif. Both of them possess a lifetime of ˜ 180 min.     

RESOLUTION OF SPECTRAL AND LIFETIME HETEROGENEITY OF TRYPTOPHAN FLUORESCENCE IN BACTERIORHODOPSIN

Abstract— The picosecond time-resolved fluorescence decay of bacteriorhodopsin (BR) was analyzed by the maximum entropy method. Results showed five distributions of lifetimes indicating at least five decay components. A wavelength-dependent study of emission decay of BR was carried out in the wavelength region from 310 to 390 nm. The decay at each wavelength was resolvable into four decay components by the discrete exponential analysis. The three short lifetime components (100 ± 20 ps, 400 ± 50 ps and 1.0 ± 0.1 ns) were independent of wavelength, whereas the longest lifetime component was wavelength dependent (varying from 4.1 ns at 310 nm to 5.7 ns at 390 nm). These results are inconsistent with the existing model of associating the fluorescence of bacteriorhodopsin with two or four lifetime components. An attempt is made to associate the five decay components with the emitting tryptophans of BR.     

Gas chromatographic quantitation of methoxyphenamine and three of its metabolites in plasma

Sensitive gas chromatographic procedures for the determination of methoxyphenamine and three of its metabolites in plasma have been developed. The metabolites were measured using an electron-capture detector. This simple procedure is based on the precipitation of protein from a 1-ml plasma sample with 10% trichloroacetic acid, followed by aqueous derivatization with pentafluorobenzoyl chloride at pH 9.2 and a single-step cyclohexane extraction. The lower limit of detection for the N-desmethyl, O-desmethyl and aromatic 5-hydroxy metabolites of methoxyphenamine were 1.6, 3.1 and 2.2 ng ml-1, respectively, with coefficients of variation less than 10%. The poor electron-capture response of fluorinated derivatives of methoxyphenamine necessitated the use of nitrogen-phosphorus detection. Extractive derivatization with pentafluorobenzoyl chloride, without the need for protein precipitation, enabled quantitation of methoxyphenamine down to 3.8 ng ml-1 from a 2-ml aliquot of plasma. In a pilot study involving healthy volunteers who received a single oral dose of methoxyphenamine hydrochloride plasma concentration could be followed in all three subjects for at least 24, 32, 12 and 4 h for methoxyphenamine and the O-desmethyl, 5-hydroxy and N-desmethyl metabolites, respectively.     

Oxidation – Reduction Reactions of Tetrachloroaurate(III) Anion with Triphenyl Derivatives of Group V Elements

The reduction of the tetrachloroaurate (III) anion by L (L = PPh₃, AsPh₃, SbPh₃) is quantitative in non-aqueous solution. The products are the gold(I)-complexes AuClL (L = AsPh₃, SbPh₃) and Au(PPh₃)⁺₂ together with the corresponding oxidation product LCl₂. Kinetic studies show that the reactions are first order in AuCl^?₁ and L. In addition a path independent of PPh₃ was found in dichloromethane. These data are interpreted in terms of mechanisms which involve reduction of AuCl^?₄ to AuCl^?₂ followed by equilibrium formation of AuClL for L = AsPh₃ and SbPh₃. For PPh₃, the data are consistent with a chloride replacement by PPh₃ to give AuCl₃ PPh₃, which is followed by a rapid reduction by a second mole of PPh₃. Equilibrium formation constants are reported for several Au(I) complexes.     

A water-mediated tautomerism mechanism in formamide and amidine. An ab initio study

Formamide, formamidic acid, and amidine water complexes were studied using 3-21G fully optimized structures and 6–31G energies. Hydrogen bonding and a water-mediated tautomerism mechanism were examined. The optimized complexes show that relaxation of the monomers has occurred. Hydrogen bond lengths and energies fall within the range of values found using other basis sets and other comparable systems.