Stabilisation of eudesmane cation by tryptophan 334 during aristolochene synthase catalysis

Analysis of the hydrocarbons produced during catalysis by mutants of aristolochene synthase from Penicillium roqueforti indicated that Trp 334 had a pivotal function for the efficient production of aristolochene from farnesylpyrophosphate most likely by stabilising the intermediate, eudesmane cation.     

Reversed-phase HPLC of polymer additives with multiple on-line spectroscopic analysis (UV,IR, (1)H NMR and MS)

The reversed-phase chromatography of a number of polymer additives has been undertaken with on-line characterisation via a combination of diode array UV, (1)H NMR, IR spectroscopy and mass spectrometry. This combination of spectrometers enabled the on-flow collection of full UV, (1)H NMR, IR and mass spectra for a range of common polymer additives in amounts ranging from ca. 230 to 900 micro g on-column. The practical difficulties associated with multiple hyphenation and potential future developments are discussed.     

The International Measurement Evaluation Programme (IMEP):

 For the 6th measurement round of the International Measurement Evaluation Programme, "Trace Elements in Water", pictures are now available in electronic form displaying the results and answers from participating laboratories, against reference values for the amount content anchored in the SI system via Primary Methods of Measurement. Received: 30 May 1998 · Accepted: 2 June 1998     

Dynamical symmetries in relativistic kinetic theory

This paper is part of a program investigating symmetries that are defined at a physical or observational level rather than purely geometrically. Here we generalize previous work on dynamical matter symmetries of relativistic gases. If the matter symmetry vector is surface-forming with the dynamical Liouville vector, then Einstein's equations reduce it to a Killing symmetry of the metric. We show that this conclusion is unaltered if the gas particles are subject to a nongravitational force (including the electromagnetic force on charged particles) or if the gravitational field obeys higher-order field equations. In the Brans-Dicke theory, the matter symmetry reduces to a homothetic symmetry of the metric. This is also the case for a generalized conformal symmetry in Einstein's theory. We consider the problem of relaxing the surface-forming assumption in an attempt to determine whether there are dynamical symmetries that do not necessarily reduce to geometrical symmetries of the metric.     

Supercritical Fluid Chromatography of polyphenolic compounds in grape seed extract

Summary Supercritical Fluid Chromatography with a packed column on a mixture of eight polyphenols has been optimized. Carbon dioxide which was modified with methanol which contained less than 1% (w/w) citric acid as a secondary additive served as the mobile phase. Two tandem diol columns were used sequentially. The optimized method was applied to a supercritical fluid grape seed extract. Various components in the extract could be identified by retention time and ultraviolet spectral comparison with our synthetic mixture of polyphenols.     

Microwave spectrum,dipole moment,and a proposed structure for 1-cyanobicyclo[1.1.0]butane

The microwave spectra of the normal and the 2-¹³C isotopic species of 1-cyanobicyclo[1.1.0]butane have been observed and assigned, leading to the following rotational constants: (normal), A=8807.202 ± 0.004, B=2924.334 ± 0.002, C=2509.322 ± 0.002 and (isotope), A=8608.85 ± 0.85, B=2902.88 ± 0.02, and C=2478.56 ± 0.02 MHz. Measurements of the second-order Stark effect led to _T=4.08 ± 0.01 D. Based on the available microwave data coupled with geometryoptimizedab initio molecular orbital structures for cyanocyclopropane and 1-cyanobicyclo[1.1.0]-butane, a molecular structure for the latter molecule is proposed. Analysis of the dipole moments of these molecules and of bicyclo[1.1.0]butane has led to the conclusion that the bicyclobutyl group is a better electron donor than is cyclopropyl. In addition, a simple frontier molecular orbital model is not sufficient for explaining all of the structural changes that occur on substituting cyano at the bridgehead of bicyclo[1.1.0]butane.     

Efficient synthesis of 5-substituted-4,5-dihydro-1,2,4-triazin-6-ones and 5-substituted-1,2,4-triazin-6-ones

Treatment of methyl α-(dimethylarninomethyleneamino)carboxylates 1 (from α-amino acids and dimethylformamide dimethylacetal) with hydrazine gives 5-substituted-4,5-dihydro-1,2,4-triazin-6-ones 2 , which are smoothly dehydrogenated to 5-substituted-1,2,4-triazin-6-ones 3 with potassium permanganate in acetone/acetic acid.