Oxidizing species in the mechanism of cytochrome P450

This review discusses the mechanisms of oxygen activation by cytochrome P450 enzymes, the possible catalytic roles of the various iron--oxygen species formed in the catalytic cycle, and progress in understanding the mechanisms of hydrocarbon hydroxylation, heteroatom oxidation, and olefin epoxidation. The focus of the review is on recent results, but earlier work is discussed as appropriate. The literature through to February 2002 is surveyed, and 175 referenced are cited.     

Time-stepping algorithms for semidiscretized linear parabolic PDEs based on rational approximants with distinct real poles

Time dependent problems in Partial Differential Equations (PDEs) are often solved by the Method Of Lines (MOL). For linear parabolic PDEs, the exact solution of the resulting system of first order Ordinary Differential Equations (ODEs) satisfies a recurrence relation involving the matrix exponential function. In this paper, we consider the development of a fourth order rational approximant to the matrix exponential function possessing real and distinct poles which, consequently, readily admits a partial fraction expansion, thereby allowing the distribution of the work in solving the corresponding linear algebraic systems in essentially Backward Euler-like solves on concurrent processors. The resulting parallel algorithm possesses appropriate stability properties, and is implemented on various parabolic PDEs from the literature including the forced heat equation and the advection-diffusion equation.Dedicated to Professor J. Crank on the occasion of his 80th birthday     

Electric and magnetic hyperfinestructure investigations in the 5s 25p 3 and 5s 25p 26s Configurations of121, 123Sb

Optical hyperfinestructure investigations in several spectral lines were carried out in the Sb-I spectrum from which for the first time accurate values of the hfs-splitting constantsA andB of the ground configuration 5p ³ and also for five of the eight levels of the first excited configuration 5p ²6s were obtained. With these parameters the influence of core polarization effects is calculated to bea _c= ?6.6(4) mK, (equivalent to a magnetic field of ?283(20) kG perp-electron spin). The quadrupole momentQ ₁₂₁= ?0.36(4) b (including Sternheimer correction) was obtained with the experimental valuesb _3/2= ?14.3(1.0) mK and 〈r ^?3〉 =11.2(3) a.u. andQ ₁₂₃= ?0.49(5) b withb _3/2= ?19.9(1.0) mK resp. This evaluation also yields the relativistic correction factor η= ?(C″/C′) · S _r/R′ _r=1.13(2). —For the first time, too, isotope shift investigations in Sb-I lines were possible which permit to determine the isotope shift constant βC _exp= 40(10) mK, and a value δ〈r ²〉^{121, 123}=0.12(4) fm² for the change in the mean square nuclear charge radius between¹²¹Sb and¹²³Sb which is about 50 percent of the prediction of the unified nuclear model.     

Optical-fiber source of polarization-entangled photons in the 1550 nm telecom band

We present a fiber-based source of polarization-entangled photons that is well suited for quantum communication applications in the 1550 nm band of standard fiber-optic telecommunications. Polarization entanglement is created by pumping a nonlinear-fiber Sagnac interferometer with two time-delayed orthogonally polarized pump pulses and subsequently removing the time distinguishability by passing the parametrically scattered signal and idler photon pairs through a piece of birefringent fiber. Coincidence detection of the signal and idler photons yields biphoton interference with visibility greater than 90%, while no interference is observed in direct detection of either signal or idler photons. All four Bell states can be prepared with our setup and we demonstrate violations of the Clauser-Horne-Shimony-Holt form of Bell's inequality by up to 10 standard deviations of measurement uncertainty.     

Carbon-carbon bond cleavage by cytochrome p450(BioI)(CYP107H1)

Cytochrome p450(BioI)(CYP107H1) is believed to supply pimelic acid equivalents for biotin biosynthesis in Bacillus subtilis: we report here that the mechanistic pathway adopted by this multifunctional p450 for the in-chain cleavage of fatty acids is via consecutive formation of alcohol and threo-diol intermediates, with the likely absolute configuration of the intermediates also reported.     

Routes to control of H2 Coulomb explosion in few-cycle laser pulses

We have measured coincident ion pairs produced in the Coulomb explosion of H2 by 8-30 fs laser pulses at different laser intensities. We show how the Coulomb explosion of H2 can be experimentally controlled by tuning the appropriate pulse duration and laser intensity. For laser pulses less than 15 fs, we found that the rescattering-induced Coulomb explosion is dominated by first-return recollisions, while for longer pulses and at the proper laser intensity, the third return can be made to be the major one. Additionally, by choosing suitable pulse duration and laser intensity, we show H2 Coulomb explosion proceeding through three distinct processes that are simultaneously observable, each exhibiting different characteristics and revealing distinctive time information about the H2 evolution in the laser pulse.     

Electro-responsive asymmetric nanopores in polyimide with stable ion-current signal

For the preparation of a single asymmetrically shaped nanopore in a polyimide membrane, Kapton foils were irradiated with single heavy ions and subsequently etched from one side in sodium hypochlorite (NaOCl). The other side of the membrane was protected from etching by a stopping medium containing a reducing agent for hypochlorite ions (OCl^-). The resulting conical nanopore rectified ion current and exhibited a stable ion-current flow. Received: 23 May 2002 / Accepted: 2 September 2002 / Published online: 15 January 2003 RID="*" ID="*"Corresponding author. Fax: +49-6159/712-179, E-mail: Z.Siwy@gsi.de