We have developed an ethanol-free formulation method of [(18) F]florbetapir ([(1) (8) F]AV-45) using a commercially available automated JFE multi-purpose synthesizer. We have also evaluated the radiochemical stability in an ethanol-free solution of [(18) F]AV-45 under visible light irradiation and dark conditions by comparison with a conventional 10% ethanol solution of [(18) F]AV-45. [(18) F]AV-45 was obtained with a radiochemical yield of 55.1 ± 2.2% (decay-corrected to end of bombardment), specific activity of 591.6 ± 90.3 GBq/µmol and radiochemical purity of >99% within a total synthesis time of about 73 min. The radiochemical purity of [(18) F]AV-45 formulated by dissolving the ethanol-free solution was found to decrease as a function of the period of exposure to visible light. In contrast, the visible light photolysis could be suppressed by adding 10% ethanol to the formulation or by avoiding exposure to visible light. In the radiosynthesis of [(18) F]AV-45 formulated by dissolving the ethanol-free solution, [(18) F]AV-45 could be obtained with high radiochemical purity and high stability by avoiding exposure to visible light.

Rubrivivax gelatinosus having both the spheroidene and spirilloxanthin biosynthetic pathways produces carotenoids (Cars) with a variety of conjugated chains, which consist of different numbers of conjugated double bonds (n), including the C=C (m) and C=O (o) bonds. When grown under anaerobic conditions, the wild type produces Cars for which n = m = 9-13, whereas under semiaerobic conditions, it additionally produces Cars for which n = m + o = 10 + 1, 13 + 1, and 13 + 2. On the other hand, a mutant, in which the latter pathway is genetically blocked, produces only Cars for which n = 9 and 10 under anaerobic conditions and n = 9, 10, and 10 + 1 under semianaerobic conditions. Those Cars that were extracted from the LH2 complex (LH2) and the reaction center (RC), isolated from the wild-type and the mutant Rvi. gelatinosus, were analyzed by HPLC, and their structures were determined by mass spectrometry and 1H NMR spectroscopy. The selective binding of Cars to those pigment-protein complexes has been characterized as follows. (1) Cars with a shorter conjugated chain are selectively bound to LH2 whereas Cars with a longer conjugated chain to the RC. (2) Shorter chain Cars with a hydroxyl group are bound to LH2 almost exclusively. This rule holds either in the absence or in the presence of the keto group. The natural selection of shorter chain Cars by LH2 and longer chain Cars by the RC is discussed, on the basis of the results now available, in relation to the light-harvesting and photoprotective functions of Cars.

The reaction mechanism of trypsin was studied by applying DFT and ab initio molecular orbital (MO) calculations to complexes of trypsin with a congeneric series of eight para-substituted hippuric acid phenyl esters, for which a previous quantitative structureactivity relationship (QSAR) study revealed nice linearity of Hammett substitution constant σ(-) with logarithmic values of the MichaelisMenten and catalytic rate constants. Based on the LERE procedure, we performed QSAR analyses on each elementary reaction step during the acylation process. The present calculations showed that the rate-determining step during the acylation process is the transition state (TS) between the enzymesubstrate complex (ES) and tetrahedral intermediate (TET), and that the proton transfer occurs from Ser195 to His57, not between His57 and Asp102. The LERE-QSAR analysis statistically suggested that the variation of overall free-energy changes leading to formation of TS is governed mostly by that of activation energies required to form TS from ES. In spite of a very limited number of congeneric ligands in the current work, it is critically essential to clarify and verify physicochemical meanings of a typical QSAR/Chemoinformatics parameter, Hammett σ(-) based on quantum chemical calculations on the proteinligand kinetics; how Hammett σ(-) behaves in terms of proteinligand interaction energies.

No abstract