Addition of aluminum and gallium species to aromatic and alkyl-substituted 1,4-diaza-1,3-butadiene ligands

In this report, we investigate the interactions of Me(x)MCl(3-x) (x = 0-3, M = Al, Ga) with various aromatic and alkyl-substituted 1,4-diaza-1,3-butadiene (R)DAB ligands (or α-diimine ligands) to give a variety of structures in solution and in the solid state. In combination with other previously reported structures, certain general trends of reactivity of these species can be deduced, although there are still some unexplained modes of reactivity. The methylated Al species react with aromatic-substituted (R)DAB ligands to provide final products that result from C═N insertion into the Al-CH(3) group followed by rearrangement reactions. The addition of methyl groups onto the backbone of the (R)DAB ligand is insufficient to stop the insertion and rearrangement processes from occurring. In the case of MeAlCl(2) with the bulky (DiPP)DAB ligand, the reaction could be followed spectroscopically from the monoadduct through the inserted/rearranged final product. Methylated Ga species, however, are much less predictable in their behavior with aromatic-substituted (R)DAB ligands. Depending on the exact species and ratios used, coordinated adducts can be formed and identified, or inserted/rearranged products similar to the aluminum reactions can be obtained. Quite interestingly, cation/anion pairs can also be formed in which GaCl(3) or MeGaCl(2) act as a chloride acceptors. This behavior was unique and substantially different from the analogous Al reactions which formed either a dicoordinated adduct or an inserted/rearranged complex. When the stronger-donating alkyl-substituted (R)DAB ligands were used with Me(2)GaCl, only cation/anion pairs were obtained. Surprisingly, when the same reactions were performed using Me(2)AlCl as a reagent, irreproducible results were obtained.     

New microsecond isomers in 189, 190Bi

The ¹³⁷I nucleus, populated in the spontaneous fission of ²⁴⁸Cm has been studied by means of prompt γ-ray spectroscopy using the EUROGAM2 array. Medium-spin yrast excitations in ¹³⁷I were observed for the first time. The experimental level scheme is compared to the shell model calculation with modified Kuo-Herling interaction. The theoretical predictions differ significantly from the experimental results, indicating that the excitation pattern in ¹³⁷I deviates significantly from the shell model scheme. Received: 6 June 2001 / Accepted: 4 October 2001     

低能大束斑射频离子源

一、引言 射频离子源素有结构简单。维护运行方便,质子比高等优点;并且造价低,在大规模工业应用上与其他源型相比,具有优越的竞争能力。 目前,仅限于单孔引出,射频离子源最大引出质子流强,均在5mA以下,且没有开发这种离子源型的应用。我们研制的毫安级射频离子源,其特点是低能、大束斑。它除了应用     

Determination of unlabeled and 13C6-labeled moricizine in human plasma using thermospray liquid chromatography-mass spectrometry

Moricizine hydrochloride is an orally effective antiarrhythmic agent currently marketed in the Soviet Union and undergoing clinical testing in the United States. To facilitate the simultaneous analysis of unlabeled and 13C6-labeled moricizine in human plasma, a specific and sensitive method employing liquid-liquid extraction followed by thermospray liquid chromatography-mass spectrometry (LC-MS) was developed. Plasma samples, after addition of [2H11]moricizine as an internal standard, were extracted into methylene chloride under alkaline conditions. Extracts were evaporated, reconstituted with mobile phase, and chromatographed on an ODS column. The LC mobile phase consisted of methanol-0.1 M ammonium acetate containing 0.2% triethylamine (65:35) and it was used at a flow-rate of 1.5 ml/min. Under these conditions, moricizine and [13C6]moricizine coeluted at 1.2 min, while [2H11]moricizine eluted slightly earlier. The MS system consisted of a Finnigan 4600 TSQ and a Vestec thermospray interface. Selected ions at m/z 428, 434, and 439 were scanned at 0.2 s per ion. Over a plasma concentration range of 10-800 ng/ml, intra-day precision (n = 3) ranged from 1.8 to 13.3% and intra-day accuracy ranged from 1.9 to 15.8%. This method was successfully used to assay human plasma samples from a pilot moricizine bioavailability study in which tablets and solution containing moricizine hydrochloride and [13C6]moricizine, respectively, were simultaneously administered.     

Can inflation explain the second law of thermodynamics?

The inflationary model of the universe can explain several of the cosmological conundra that are mysteries in the standard hot big bang model. Paul Davies has suggested that inflation can also explain the second law of thermodynamics, which describes the time asymmetry of the universe. Here I note several difficulties with this suggestion, showing how the present inflationary models must assume the arrow of time rather than explaining it. If the second law is formulated as a consequence of the hypothesis that there were no long-range spatial correlations in the initial state of the universe, it is shown how some of the cosmological conundra might be explained even without inflation. But if the ultimate explanation is to include inflation, three, essential elements remain to be demonstrated which I list.     

Kinetics and mechanisms of hydrolysis and aminolysis of thioxocephalosporins

The effect of replacing the beta-lactam carbonyl oxygen in cephalosporins by sulfur on their reactivity has been investigated. The second-order rate constant for alkaline hydrolysis of the sulfur analogue is 2-fold less than that for the natural cephalosporin. The thioxo derivative of cephalexin, with an amino group in the C7 side chain, undergoes beta-lactam ring opening with intramolecular aminolysis by a reaction similar to that for cephalexin itself. However, the rate of intramolecular aminolysis for the S-analogue is 3 orders of magnitude greater than that for cephalexin. Furthermore, unlike cephalexin, intramolecular aminolysis in the S-analogue occurs up to pH 14 with no competitive hydrolysis. The rate of intermolecular aminolysis of natural cephalosporins is dominated by a second-order dependence on amine concentration, whereas that for thioxocephalosporins shows only a first-order term in amine. The Bronsted beta(nuc) for the aminolysis of thioxo-cephalosporin is +0.39, indicative of rate-limiting formation of the tetrahedral intermediate with an early transition state with relatively little C-N bond formation.