Methods were developed and optimized for the preparation of the 2,3-cis- and the 10,11-cis-isomers of silybin by the Lewis acid catalyzed (BF3∙OEt2) isomerization of silybins A (1a) and B (1b) (trans-isomers). The absolute configuration of all optically pure compounds was determined by using NMR and comparing their electronic circular dichroism data with model compounds of known absolute config...

Centre for Systems Chemistry, Strating Mathematics and Natural Sciences, Univers Groningen, The Netherlands. E-mail: b.l Fax: +31-50-3634279 Department of Radiology, University of Groningen, Hanzeplein 1, 9713 GZ, Groning † Electronic supplementary information ( 1–8 and NMR spectra. Isomerization Isomerization cycle of compound 1 (Fig. CD spectra for compound 1 and 8 (Fig compound 1 (Fig. S15) ...

Wavelength- and time-resolved fluorescence experiments have been performed on the photoactive yellow protein, the E46Q mutant, the hybrids of these proteins containing a nonisomerizing "locked" chromophore, and the native and locked chromophores in aqueous solution. The ultrafast dynamics of these six systems is compared and spectral signatures of isomerization and solvation are discussed. We f...

1,2-Pentadiene has been decomposed in single pulse shock tube experiments. There appear to be a large number of parallel decomposition and isomerization channels. The following rate expressions for isomerization in the temperature range 1100–1250 K and pressures between 200 and 300 kPa have been obtained k(1,2-pentadiene→ 1-pentyne) = 1.0× 10 exp(−32300± 900 K/T ) s−1 k(1,2-pentadiene→ cis/tran...

Mechanisms of thermal isomerization of allyl tetrazolyl ethers derived from the carbocyclic allylic alcohols cyclohex-2-enol and 3-methylcyclohex-2-enol and from the natural terpene alcohol nerol were investigated. In the process of the syntheses of the three 1-aryl-5-allyloxytetrazoles, their rapid isomerization to the corresponding 1-aryl-4-allyltetrazol-5-ones occurred. The experiments showe...

Polyunsaturated fatty acid (PUFA) oxidation by thiyl radicals (RS ) is believed to be responsible for some of the biological radiation damage. At the same time, RS can cause isomerization of PUFA double bonds with the formation of trans isomers. The aim of this study was to better understand the competition between lipid peroxidation and geometrical isomerization processes in biomimetic model s...

Articles you may be interested in Velocity dependence of friction and Kramers relaxation rates Is slow thermal isomerization in viscous solvents understandable with the idea of frequency dependent friction? We present new data on the ground state isomerization rate of DODeI and compare our results to previously obtained excited state data. We find that the one-dimensional Kramers expression doe...

l-Rhamnose isomerase (l-RhI) catalyzes the reversible isomerization of l-rhamnose to l-rhamnulose. Previously determined X-ray structures of l-RhI showed a hydride-shift mechanism for the isomerization of substrates in a linear form, but the mechanism for opening of the sugar-ring is still unclear. To elucidate this mechanism, we determined X-ray structures of a mutant l-RhI in complex with l-r...

Ultrafast deep-ultraviolet through near infrared (210-950 nm) transient absorption spectroscopy complemented by ab initio multiconfigurational calculations offers a global description of the photochemical reaction pathways of bromoform following 255-nm excitation in methylcyclohexane and acetonitrile solutions. Photoexcitation of CHBr3 leads to the ground-state iso-CHBr3 product in a large quan...

Density functional theory (DFT) is the only quantum-chemical avenue for calculating thermochemical/kinetic properties of large polycyclic aromatic hydrocarbons (PAHs) such as graphene nanoflakes. Using CCSD(T)/CBS PAH isomerization energies, we find that all generalized gradient approximation (GGA) and meta GGA DFT functionals have severe difficulties in describing isomerization energies in PAH...