Solution NMR determination of the seating(s) of meso-nitro-etioheme-1 in myoglobin: implications for steric constraints to meso position access in heme degradation by coupled oxidation

The highly stereoselective cleavage of hemin in myoglobin by coupled oxidation has been attributed to steric barriers that leave more space near the alpha- than the other meso-positions. The steric barriers near meso positions in myoglobin have been investigated by establishing the thermodynamics and dynamics of possible seatings in the pocket of horse myoglobin of a four-fold symmetric etioheme I modified with a bulky nitro group at a single meso position. The cyanomet complex of this reconstituted myoglobin exhibits three sets of (1)H NMR resonances that are linked dynamically and occur in approximate populations ratios of 0.82:0.10:0.08. Two dimensional (1)H NMR has been used to assign the hemin and heme pocket resonances in the major isomer in solution and to determine that the hemin is oriented with the nitro group at the canonical gamma-meso position of native hemin. The dominance of this isomer is attributed to the solvent exposure of this portion of the hemin which stabilizes the highly polar nitro group. Using a combination of magnetization transfer among methyl groups of the three isomers due to "hopping" of the hemin about its normal, the assigned resonances of an isoelectronic, bis-cyano complex of meso-nitro-etioheme I, and the known essentially constant rhombic perturbation of heme pocket sites on the hyperfine shifts of heme methyl (Kolczak, U.; Hauksson, J. B.; Davis, N. L.; Pande, U.; de Ropp, J. S.; Langry, K. C.; Smith, K. M.; LaMar, G. N. J. Am. Chem. Soc. 1999, 121, 835-843); the two minor isomers are shown to place their bulky nitro group at the canonical delta-meso (8%) and alpha-meso positions (10%). The comparable population of the isomers with nitro groups at the hydrophobic alpha- and delta-meso positions dictates that, while the static crystal structure finds more room near the alpha-meso position, the deformation at minimal energetic expense near the alpha- and delta-meso positions is comparable. These results argue that factors other than simple steric influences control the selectivity of the ring cleavage in myoglobin.     

An Improved Procedure for the Synthesis of Prostaglandin Analogues

Hydrozirconation-iodination of a terminal acetylene followed by lithium-iodide exchange and finally dilithio cyanocuprate mediated conjugate addition to an appropriate cyclopentenone is reported as an efficient method for the synthesis of prostaglandin analogues.     

Surface plasmon-polariton waves in optically active media

A theory of surface plasmon-polariton wave propagation along an interface of an optically active medium and metal or metamaterial has been developed. It is shown that optical activity leads to changing of cross section and polarization of the surface modes, whereas the propagation constant in first approximation does not depend on the gyrotropy coefficient.     

Polarization properties of surface plasmon polaritons at the boundary of topological insulators with the axion effect

Properties of surface plasmon polariton waves are theoretically studied in structures containing topological insulators with the axion effect. The effect of axion properties on dispersion, localization, and polarization of plasmon polaritons is analyzed. A possibility of determining the axion effect from the variation in the plasmon-polariton polarization is shown, and conditions for enhancement of polarization effects are revealed in waveguide structures of the dielectric?metal?dielectric type.     

Radiation damage and annealing in Sb implanted diamond

The predicted, but as yet unobserved, intradonor absorption spectrum of the hydrogenic-like donors in CdF₂ crystals is presented. The role of phonon coupling in these spectra is discussed. From the data on the insulator-semiconductor transition in CdPbF₂ it is concluded that the dominant factor in convertibility of CdF₂ to a semiconducting state is its electron affinity, the largest among the fluorites (x≈4 eV).     

Inverse faraday effect in plasmonic films

It is shown that the inverse Faraday effect appears in the case of surface plasmon polariton propagation near a metal/paramagnetic interface. The inverse Faraday effect in nanostructured periodically perforated metal-dielectric films increases because of the excitation of surface plasmon polaritons. In this case, a stationary magnetic field is amplified by more than an order of magnitude compared to the case of a smooth paramagnetic film. The distribution of an electromagnetic field is sensitive to the wavelength and the angle of incidence, which allows one to effectively control the local magnetization that arises due to the inverse Faraday effect.     

The transient hyperfine field at Si,Pd and Pt ions traversing iron and nickel foils

A measurement of the hyperfine interactions on swift²⁸Si,¹¹⁰Pd, and¹⁹⁴Pt ions recoiling through magnetized iron and nickel foils indicates that for these ions the strength of the transient magnetic field scales with the net magnetization of the ferromagnet.Supported in part by the National Science Foundation.     

Reorientation precession measurements of quadrupole moments in103Rh

The quadrupole moments of the 3/2^? and 5/2^? states in¹⁰³Rh have been determined by measuring the precession of the gamma-ray angular distribution following Coulomb excitation;¹⁶O and³²S beams have been used. The structure of the negative-parity states in¹⁰³Rh is found to be in agreement with the model of Arima and Iachello.