Evidence for two different active oxygen species in cytochrome P450 BM3 mediated sulfoxidation and N-dealkylation reactions

Herein, we report the results from two experiments that are consistent with sulfoxidation and N-dealkylation involving two different enzyme substrate complexes and thus two different active oxygen species that do not interchange. The first experiment involves the use of a mutant that may increase the amount of the hydroperoxy-iron species (FeIIIO2H).1 This mutant increases the amount of sulfoxidation relative to the amount of N-dealkylation by 4-fold. In a second experiment, deuterium substitution on the N-methyl groups of substrate does not result in an increase in sulfoxidation. This later result is consistent with N-dealkylation and sulfoxidation being mediated by two different active oxygen species. While the data indicate two active oxygen species, they do not distinguish between the different possibilities for the active oxygen species.     

Golden opportunities in natural product synthesis: first total synthesis of (-)-isocyclocapitelline and (-)-isochrysotricine by gold-catalyzed allene cycloisomerization

The first enantioselective total syntheses of the beta-carboline alkaloids (-)-isochrysotricine (1) and (-)-isocyclocapitelline (2) are reported which confirm the absolute configuration of these natural products. Key steps are the copper-mediated S(N)2'-substitution of propargyl oxiranes 13/14 and the gold-catalyzed cycloisomerization of alpha-hydroxyallene 15, resulting in a highly efficient center-to-axis-to-center chirality transfer.     

Highly Luminescent,Water‐Soluble Lanthanide Fluorobenzoates: Syntheses,Structures and Photophysics,Part I: Lanthanide Pentafluorobenzoates

Highly luminescent, photostable, and soluble lanthanide pentafluorobenzoates have been synthesized and thoroughly characterized, with a focus on Eu^III and Tb^III complexes as visible emitters and Nd^III, Er^III, and Yb^III complexes as infrared emitters. Investigation of the crystal structures of the complexes in powder form and as single crystals by using X‐ray diffraction revealed five different structural types, including monomeric, dimeric, and polymeric. The local structure in different solutions was studied by using X‐ray absorption spectroscopy. The photoluminescence quantum yields (PLQYs) of terbium and europium complexes were 39 and 15 %, respectively; the latter value was increased almost twice by using the heterometallic complex [Tb_0.5Eu_0.5(pfb)₃(H₂O)] (Hpfb=pentafluorobenzoic acid). Due to the effectively utilized sensitization strategy (pfb)^?→Tb→Eu, a pure europium luminescence with a PLQY of 29 % was achieved.     

Half-lives of platinum isotopes from photoactivation

The half-lives of the platinum isotopes ^189,191,197Pt and of the 4-day isomer in ^195mPt have been measured with high precision using the photoactivation technique. The γ-ray activity was counted over several half-lives with a high-purity germanium detector. The measured half-lives are: T_1/2(¹⁸⁹Pt) = 12.1 ± 1.5 h; T_1/2(¹⁹¹Pt) = 2.862 ± 0.007 d; T_1/2(¹⁹⁷Pt) = 19.96 ± 0.05 h; T_1/2(^195mPt) = 4.0104 ± 0.0047 d. Received: 13 September 1999     

Investigation of carrier dynamics in Zn1−xMgxO by time-resolved photoluminescence

The influence of the Mg concentration and lattice temperature on the carrier recombination dynamics in Zn_1−xMg_xO alloys has been studied by time-resolved photoluminescence for different emission and excitation energies. Carrier localization effects are found to play a significant role, becoming increasingly important for lower temperatures and higher Mg concentrations. Emission energy dependent dynamics were analyzed by the application of the theoretical model, yielding a characteristic localization energy of 60±15 meV for the sample with the highest Mg concentration of x=0.21.