STUDIES ON THE INTERRELATIONSHIP AMONG THE INTENSITY OF A RAMAN MARKER BAND OF CAROTENOIDS, POLYENE CHAIN STRUCTURE, AND EFFICIENCY OF THE ENERGY TRANSFER FROM CAROTENOIDS TO BACTERIOCHLOROPHYLL IN PHOTOSYNTHETIC BACTERIA

Abstract Resonance Raman spectroscopy was used to study the polyene-chain structure of carotenoids in light-harvesting pigment-protein complexes from purple photosynthetic bacteria. When major carotenoids of Rhodobacter sphaeroides were incorporated into the light-harvesting complexes of Chromatium vinosum , they showed a relatively intense Raman band at 965 cm^-1 arising from the CH out-of-plane wagging modes of the polyene chain. This result was almost the same as that for the intrinsic carotenoids in Chromatium vinosum , but completely different from that for the intrinsic carotenoids in Rhodobacter sphaeroides . On the other hand, the intrinsic carotenoids of Chromatium vinosum lost the intensity of the 965 cm^-1 Raman band upon protein denaturation. These results support the view that the intensity of the 965 cm^-1 Raman band reflects distortion of the polyene chain, independent of its chemical structure. The polyene-chain distortion is affected by the apoprotein to which carotenoids are bound. The distortion of the polyene chain is correlated with a decrease in the efficiency of the energy transfer from carotenoids to bacteriochlorophyll.     

Molecular dynamics study of the spectroscopic properties of liquid benzene

A molecular dynamics (MD) simulation, which includes all degrees of freedom of atomic motion, has been performed to investigate several spectroscopic properties such as infrared and Raman spectra, permittivity, and refractive index of liquid benzene. Infrared and Raman spectra of liquid benzene were measured at room temperature, and these experimental results were compared with our MD simulated spectra. The simulated infrared spectra reproduced the four fundamental v ₁₁, v ₁₈, v ₁₉, and v ₂₀ bands, and the simulated Raman spectra reproduced the seven fundamental v ₁, v ₂, v ₆, v ₇ v ₈, v ₉, and v ₁₀ bands as expected from the selection rule. These simulated spectra were in good agreement with the observed ones in the frequency and relative intensity of fundamental vibrations of benzene. The v ₁₆ and v ₄ bands appeared in the simulated Raman spectra. These bands are exceptions to the selection rule, and these facts indicate that the breakdown of the symmetry of D_6h of a benzene molecule occurs in a liquid state. The simulated permittivity, and refractive index were also in good agreement with other experimental values.     

A quantitative analysis of recombination data in high magnetic fields

Magnetic field effects on the hydrogen abstraction reaction of 4-methoxybenzophenone with thiophenol in several solvents of different viscosity have been reported, and the observed magnetic field dependence was explained as caused by the Δg and a polarized initial triplet radical pair state. The present work reports a quantitative analysis of the data based on a recently derived general analytical formula. It is found that the observed magnetic field dependence can be explained as originating from an unpolarized triplet state, if both the coherent mixing caused by different g values of the two radicals and the incoherent mixing due to spin relaxation are included. Several different expressions for the magnetic field dependence of the longitudinal and transverse relaxation rates were applied. Rather surprisingly, the different models gave almost identical fits. However, the values obtained of the microscopic parameters depended significantly on the model. Physically sensible parameter values were obtained only when the complete magnetic field dependence of the two relaxation times were used. For this model it was found that both the anisotropy factor of the g tensors and the diffusion coefficient agreed with expectations.     

Biphotonic photochemistry of benzophenones in dimethylsulphoxide: a flash photolysis EPR study

Benzophenone and its derivatives in dimethylsulphoxide (DMSO) exhibit biphotonic photochemistry under 355 nm laser photolysis. Flash photolysis electron paramagnetic resonance experiments demonstrate that a single laser pulse is capable of producing and exciting benzophenone triplets, which can sensitize dimethylsulphoxide and subsequently lead to photodecomposition. In decafluorobenzophenone, electron transfer is the dominant process of the highly excited triplet state. Despite the rapid radiationless decay of 2-hydroxybenzophenone (2OHbenzophenone) in non-polar solvents, radical signals are observed from the photoexcitation of 2OHbenzophenone in DMSO. This is attributed to the sufficiently rapid excitation of the triplet state, which competes with the radiationless decay process, aided by the unique solvent properties of DMSO. It is concluded, in contrast to literature data, that the excited triplet state of DMSO is reactive, and can produce methyl radicals that show triplet mechanism polarization via the biphotonic photoexcitation of benzophenone.     

Magnetic field effects on electron transfer reactions involving sextet-spin (S = 5/2) intermediates generated on photoexcitation of a Cr(III)-porphyrin complex

The excited trip-sextet (⁶T₁) state of chloro-(3-methylimidazol)-(meso-tetraphenylporphyrinato) chromium(III) (Cr^IIIP) is quenched by 1,1′-dibenzyl-4,4′-bipyridinium (BV²⁺) in acetonitrile through electron transfer to give ⁵(Cr^IIIP^·+) and ²BV^·+. The intermediate is a geminate ion pair in the sextet (Sx) state ⁶[⁵(Cr^IIIP^·+) ²BV^·+], which decays through either the escape from a solvent cage to give the free ions or the spin conversion to the quartet (Qa) state followed by back electron transfer. The free ion yield (Φ_FI) increased with increasing magnetic field from 0 to 4 T and then slightly decreased from 4 T to 10 T. These magnetic field effects are explained as follows. Under low fields where the Zeeman splitting of the spin sublevels is lower than or comparable with the electron spin dipole—dipole interaction within ⁵(Cr^IIIP^·+), this interaction effectively induces the Sx → Qa conversion of [⁵(Cr^IIIP^·+)²BV⁺] to result in low Φ_FI values. Under high fields where the Zeeman splitting is larger than the dipole—dipole interaction, the Sx → Qa conversion is decreased with increasing field to cause higher Φ_FI values. The slight decrease in Φ_FI above 4 T may be due to the Δg mechanism.     

N-myristoylated proteins,key components in intracellular signal transduction systems enabling rapid and flexible cell responses

N-myristoylation, one of the co- or post-translational modifications of proteins, has so far been regarded as necessary for anchoring of proteins to membranes. Recently, we have revealed that N^α-myristoylation of several brain proteins unambiguously regulates certain protein–protein interactions that may affect signaling pathways in brain. Comparison of the amino acid sequences of myristoylated proteins including those in other organs suggests that this regulation is involved in signaling pathways not only in brain but also in other organs. Thus, it has been shown that myristoylated proteins in cells regulate the signal transduction between membranes and cytoplasmic fractions. An algorithm we have developed to identify myristoylated proteins in cells predicts the presence of hundreds of myristoylated proteins. Interestingly, a large portion of the myristoylated proteins thought to take part in signal transduction between membranes and cytoplasmic fractions are included in the predicted myristoylated proteins. If the proteins functionally regulated by myristoylation, a posttranslational protein modification, were understood as cross-talk points within the intracellular signal transduction system, known signaling pathways could thus be linked to each other, and a novel map of this intracellular network could be constructed. On the basis of our recent results, this review will highlight the multifunctional aspects of protein N-myristoylation in brain.     

Pyrochemical treatment of spent nitride fuels for MA transmutation

Nitride fuels have several advantages including high thermal conductivity and high metal density(like metallic fuels) and high melting point and isotropic crystal structure(like oxide fuels). Since the late 1990 s, the partitioning and transmutation of minor actinides(MA) has been studied to decrease the long-term radio-toxicity of high-level waste and to mitigate the burden of final disposal. Japan Atomic Energy Agency(JAEA) has proposed a dedicated transmutation cycle using an accelerator-driven system(ADS) with nitride fuels containing MA. The nitride fuel cycle we have developed includes a pyrochemical process. Our focus is on the electrolysis of nitride fuels and their refabrication from the recovered actinides; other processes are similar to the technology for metal fuel treatment and have been studied elsewhere. Here, we summarize our activity on the development of the pyrochemical treatment of spent nitride fuels.     

NMR Study of Pore Surface and Size in a Mesoporous Material FSM-16

Surface structure, pore size distribution and pore wall thickness of a mesoporous material FSM-16 have been studied by X-ray powder diffraction (XRD), ^lH and ²⁹Si MAS NMR and ¹H liquid-state NMR, and by applying surface silylation as a probe. Concentrations of surface hydroxyl groups for FSM-16 are estimated from ²⁹Si and ¹H MAS NMR, which are about 3×l0²¹ g^-1, corresponding to approximately 3 nm^-2. O₂ molecules contribute to ²⁹Si spin-lattice relaxation of Q² and Q³ as well as Q⁴, suggesting thin wall thickness. ¹H MAS NMR spectra indicate the presence of isolated and hydrogen-bonded hydroxyl groups. Both hydroxyl groups are silylated, where the silylated fraction is about 50%. The spatial distribution of surface hydroxyl groups is estimated from the line width in ¹H static spectra. A rather homogeneous distribution is demonstrated in one of the samples. The sample with less homogeneous distribution has a larger affinity for moisture. Pore size and pore wall thickness were determined by ¹H NMR measurements on water saturated FSM-16 samples, which are in good agreement with literature values obtained by N₂ adsorption isotherms and transmission electron micrographs on a similar sample. In benzene saturated samples, a non-freezing surface layer of benzene is much thicker than that of water, which indicates a stronger interaction between benzene and the FSM-16 surface.     

Solar diurnal anisotropy measured using muons in GRAPES-3 experiment in 2006

The GRAPES-3 experiment at Ooty contains a large-area (560 m²) tracking muon detector. This detector consists of 16 modules, each 35 m² in area, that are grouped into four supermodules of 140 m² each. The threshold energy of muons is sec(θ) GeV along a direction with zenith angle θ and the angular resolution of the muon detector is 6°. Typically, it records ~4×10⁹ muons every day. The muon detector has been operating uninterruptedly since 2001, thus providing a high statistics record of the cosmic ray flux as a function of time over one decade. However, prior to using these data, the muon rate has to be corrected for two important atmospheric effects, namely, variations in atmospheric pressure and temperature. Because of the near equatorial location of Ooty (11.4°N), the seasonal variations in the atmospheric temperature are relatively small and shall be ignored here. Due to proximity to the equator, the pressure changes at Ooty display a dominant 12 h periodic behaviour in addition to other seasonal changes. Here, we discuss various aspects of a novel method for accurate pressure measurement and subsequent corrections applied to the GRAPES-3 muon data to correct these pressure-induced variations. The pressure-corrected muon data are used to measure the profile of the solar diurnal anisotropy during 2006. The data, when divided into four segments, display significant variation both in the amplitude (~45%) and phase (~42 m) of the solar diurnal anisotropy during 2006, which was a period of relatively low solar activity.