Stereoselective aldol additions of titanium enolates of N-acetyl-4-isopropyl-thiazolidinethione

The addition of chlorotitanium enolates of N-acetyl isopropyl thiazolidine-2-thione to aldehydes was investigated. The stereoselectivity of the aldol products was controlled by the number of equivalents of base added. The syn aldol product was obtained preferentially when 2 equiv of Lewis acid and 1 equiv of base were employed. The anti aldol product was obtained preferentially when 1 equiv of Lewis acid and 2 equiv of base were employed for unsaturated aldehydes. Unexpected results were found with hindered aldehydes when 2 equiv of base were employed.     

Flame ionization detection after splitting the water effluent in subcritical water chromatography

The coupling of subcritical water separation with flame ionization detection (FID) in the split mode has been investigated in this study. In order to keep the FID system stable during subcritical water separation, a Tee union was connected between the separation column and the FID system to split the water flow. The ratio of the water flow to the FID system over the flow-rate to a waste bottle varied depending on the dimension of capillary tubings and the total water flow-rate used. Separations of several carbohydrates, carboxylic acids, and amino acids were performed on commercially available columns using a laboratory-made subcritical water chromatography-FID system. The FID system was very stable in this split mode even at total flow-rate as high as 1.24 ml/min. The linear dynamic range was up to three orders of magnitude and the limit of detection (LOD) ranged from 38 to 111 ng (306-925 ng/microl injected) with split ratios of approximately 1:10 to approximately 1:17 (FID/waste bottle) for several analytes studied. However, the LOD can be significantly lowered by adjusting the dimensions of the restrictors to allow a higher percentage of the total flow to the FID system.     

Combined Dynamic Model for the Kinetics of Electron Transfer from Cytochrome to a Bacteriochlorophill Dimer in Reaction Centers of Rps. Sulfoviridis

The electron transfer from the heme of cytochrome c to the bacteriochlorophill dimer in reaction centers of photosynthetic purple bacteria Rps. sulfoviridis is studied by laser flash photolysis at 40–296 K in conditions where one, two, or three cytochrome hemes are chemically reduced. In the model used for the electron transfer kinetics, the protein relaxation is described with a temperature-independent oscillatory coordinate and a temperature-dependent diffusion coordinate, with the protein dielectric relaxation times widely distributed along the diffusion coordinate. It is found that all the protein complexes can be divided into proteins with fast (k _et = 10⁷ to 10^–4 s^–1) and slow (k _et 100 s^–1) electron transfer. These populations presumably differ by the protonation state of the functional group. The contribution of the oscillatory and diffusion coordinates alters, which severely affects k _et. Parameters V _ab, G, , ₀, and for these reactions are determined.     

PHOTOTRANSFORMATION KINETICS OF UNDEGRADED OAT AND PEA PHYTOCHROME INITIATED BY LASER FLASH EXCITATION OF THE RED-ABSORBING FORM

Abstract— Phototransformation at 2°C of the red-absorbing form of phytochrome (Pr) to the far-redabsorbing form (Pfr) was studied with both undegraded oat ( Avena sativa L., cv. Garry) and undergraded pea Pisum sativum L., cv. Alaska) phytochrome. Phototransformation was initiated by a 15-ns laser pulse with maximum emission near 600 nm and output power of 30 mJ. The first resolvable transformation intermediate exhibited relative to Pr a maximum absorbance increase near 700 nm and was fully present at the earliest time measured, which was 60 ns after the flash. This intermediate absorbance decayed by two reactions for oat phytochrome (half-lives of 11 and 140 μs assuming parallel reactions) and by three for pea phytochrome (half-lives of 14, 280 and 1600 μs assuming parallel reactions). The kinetics of the slowest reaction for pea phytochrome, however, might be somewhat distorted by an instrument artifact. The appearance of the far-red-absorbing phytochrome, as monitored by absorbance increase at 720 nm, occurred by at least two reactions for both oat (half-lives of 47 and 250 ms assuming parallel reactions) and pea (half-lives of 170 and 770 ms assuming parallel reactions) phytochrome. The possibility of slower reactions was not tested. Assays for possible proteolysis of the phytochrome samples studied here indicated that the presence of degraded phytochrome could not account for the observed multiphasic kinetics except possibly for one phase of the triphasic intermediate decay seen with pea phytochrome.     

Infrared Applications at ANKA

ANKA is a relatively new synchrotron radiation facility at the Forschungszentrum Karlsruhe, a large government research center in the southwest of Germany. The acronym stands for Angstrom Source Karlsruhe. The electron storage ring is 110.4 m in circumference and stores a 2.5 GeV electron beam at a typical current of 200 mA. The facility has been open for users since March 2003.     

Origin and Use of Hydroxyl Group Tolerance in Cationic Molybdenum Imido Alkylidene N-Heterocyclic Carbene Catalysts

The origin of hydroxyl group tolerance in neutral and especially cationic molybdenum imido alkylidene N-heterocyclic carbene (NHC) complexes has been investigated. A wide range of catalysts was prepared and tested. Most cationic complexes can be handled in air without difficulty and display an unprecedented stability towards water and alcohols. NHC complexes were successfully used with substrates containing the hydroxyl functionality in acyclic diene metathesis polymerization, homo-, cross and ring-opening cross metathesis reactions. The catalysts remain active even in 2-PrOH and are applicable in ring-opening metathesis polymerization and alkene homometathesis using alcohols as solvent. The use of weakly basic bidentate, hemilabile anionic ligands such as triflate or pentafluorobenzoate and weakly basic aromatic imido ligands in combination with a sterically demanding 1,3-dimesitylimidazol-2-ylidene NHC ligand was found essential for reactive and yet robust catalysts.