Reactions catalyzed by bacterial cytochromes P450

The cytochromes P450 are a large family of oxidative haemoproteins that are responsible for a wide variety of oxidative transformations in a variety of organisms. This review focuses upon the reactions catalyzed specifically by bacterial enzymes, which includes aliphatic hydroxylation, alkene epoxidation, aromatic hydroxylation, oxidative phenolic coupling, heteroatom oxidation and dealkylation, and multiple oxidations including C-C bond cleavage. The potential for the practical application of the oxidizing power of these enzymes is briefly discussed.

Products of Cytochrome P450BioI (CYP107H1)-Catalyzed Oxidation of Fatty Acids

[GRAPHICS] Oxidation of tetradecanoic and hexadecanoic acids by cytochrome P450(Biol) (CYP107H1) produces mainly the 11-, 12-, and 13-hydroxy C-14 fatty acids and the 11- to 15-hydroxy C-16 fatty acids, respectively. In contrast to previous reports, terminal hydroxylation is not observed. The enantiospecificity of fatty acid hydroxylation by P450(Biol) was also determined, and the enzyme was shown to be moderately selective for production of the (R)-alcohols.

Thermal characterization of polyester-melamine coating matrices prepared under nonisothermal conditions

Thermal analysis methods (differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical thermal analysis) were used to characterize the nature of polyester-melamine coating matrices prepared under nonisothermal, high-temperature, rapid-cure conditions. The results were interpreted in terms of the formation of two interpenetrating networks with different glass-transition temperatures (a cocondensed polyester-melamine network and a self-condensed melamine-melamine network), a phenomenon not generally seen in chemically similar, isothermally cured matrices. The self-condensed network manifested at high melamine levels, but the relative concentrations of the two networks were critically dependent on the cure conditions. The optimal cure (defined in terms of the attainment of a peak metal temperature) was achieved at different oven temperatures and different oven dwell times, and so the actual energy absorbed varied over a wide range. Careful control of the energy absorption, by the selection of appropriate cure conditions, controlled the relative concentrations of the two networks and, therefore, the flexibility and hardness of the resultant coatings. (C) 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Cbem 41: 1603-1621, 2003.

Chain scission and branching in irradiated poly(tetrafluoroethylene-co-hexafluoropropylene)

The radiation chemistry of poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) with a TFE mole fraction of 0.90 has been studied under vacuum using Co-60 gamma-radiation over a range of temperatures and absorbed doses. The radiolysis temperatures were 300, 363, 423, 523 and 543 K. New structure formation in the copolymers was analysed by solid-state F-19 NMR spectroscopy. The new structures formed in the copolymers have been identified and the G-values for the formation of new chemical structures have been investigated at 363 and 523 K. These two temperatures are just above and just below the polymer T-g and T-m, respectively. At the lower temperature, there was no evidence for any chain branching and an estimate of G(S) of 1.0 was obtained. A value of G(S) of 1.3 and a minimum value of G(X)(Y) of 1.3 were obtained at 523 K. (C) 2003 Society of Chemical Industry.

N-Substituent effect of maleimides on acrylate polymerization initiated by three-component systems

In this paper, the relative photopolymerization efficiency for polymerization of a difunctional acrylate initiated by various N-substituted maleimides in the presence of amine and benzophenone are compared on the basis of a photo-differential scanning calorimetry (photo-DSC) study. The trends in the polymerization rates were obtained from the photopolymerization profiles and expressed in terms of a photoinitiation index, I-p. An N-substituent index, I-s, which indicates whether each N-substituent plays either a positive (when I-s > 1) or a negative (when I-s < 1) role in the initiation process relative to MI (unsubstituted maleimide), was determined. (C) 2003 Society of Chemical Industry.

Non-ideal monitoring of a qubit state using a quantum tunnelling device

We propose a model for non-ideal monitoring of the state of a coupled quantum dot qubit by a quantum tunnelling device. The non-ideality is modelled using an equivalent measurement circuit. This allows realistically available measurement results to be related to the state of the quantum system (qubit). We present a quantum trajectory that describes the stochastic evolution of the qubit state conditioned by tunnelling events (i.e. current) through the device. We calculate and compare the noise power spectra of the current in an ideal and a non-ideal measurement. The results show that when the two qubit dots are strongly coupled the non-ideal measurement cannot detect the qubit state precisely. The limitation of the ideal model for describing a realistic system maybe estimated from the noise spectra.

Enhanced spin injection efficiency in ferromagnet/semiconductor tunnel junctions

Within the ballistic transport picture, we have investigated the spin-polarized transport properties of a ferromagnetic metal/two-dimensional semiconductor (FM/SM) hybrid junction and an FM/FM/SM structure using quantum tunnelling theory. Our calculations indicate explicitly that the low spin injection efficiency (SIE) from an FM into an SM, compared with a ferromagnet/normal metal junction, originates from the mismatch of electron densities in the FM and SM. To enhance the SIE from an FM into an SM, we introduce another FM film between them to form FM/FM/SM double tunnel junctions, in which the quantum interference effect will lead to the current polarization exhibiting periodically oscillating behaviour, with a variation according to the thickness of the middle FM film and/or its exchange energy strength. Our results show that, for some suitable values of these parameters, the SIE can reach a very high level, which can also be affected by the electron density in the SM electrode.

Difficult macrocyclizations: New strategies for synthesizing highly strained cyclic tetrapeptides

Cyclic tetrapeptides are an intriguing class of natural products. To synthesize highly strained cyclic tetrapeptides; we developed a macrocyclization strategy that involves the inclusion of 2-hydroxy-6-nitrobenzyl (HnB) group at the N-terminus and in the middle of the sequence. The N-terminal auxiliary performs a ring closure/ring contraction role, and the backbone auxiliary promotes cis amide bonds to facilitate the otherwise difficult ring contraction. Following this route, the all-L cyclic tetrapeptide cyclo-[Tyr-Arg-Phe-Ala] was successfully prepared.

Advanced precursors in marine biosynthetic study. Part 3: The biosynthesis of dichloroimines in the tropical marine sponge Stylotella aurantium

The biosynthetic origins of the dichloroimine group in the stylotellanes A and B 1,2 have been investigated by incorporation of [C-14]-labeled farnesyl isocyanide 7 and farnesyl isothiocyanate 3 into the sponge Stylotella aurantium. (C) 2002 Elsevier Science Ltd. All rights reserled.