Some realistic calculations on the migration process of hydrogen isotopes in bcc metals

By adopting the empirical interaction potential between hydrogen and metal atoms determined in our previous paper, calculations have been performed of the 2T configuration, in which two neighboring tetrahedral (T) sites are equally shared by a hydrogen (H) atom. The tunneling matrix element J and the activation energy are estimated by calculating the excitation energy of the H atom for the 2T state and the energy difference between the 2T and 1T state, respectively.From these calculations, it is suggested that H atoms in V and Fe migrate between the ground states of neighboring T sites by adiabatic transitions, whereas in the lower temperature region in Ta by non-adiabatic tunneling process.     

A new experimental limit for the decay K+ → π+γγ

A search for K⁺ → π⁺γ, π⁺γγ, π⁺γγγ was made detecting pions from stopped kaons in the kinetic energy region between 117 MeV and 127 MeV. New Limits of 1.4 ×10^?6, 8.4 × 10^?6 and 1.0 × 10^?4 for the branching ratio were obtained assuming a phase-space spectrum on the pion energy. The first limit also aplies to another process K⁺ → π⁺ + a, where a is a light meson with mass smaller than 100 MeV/c² and decays into nγ's with lifetime less than 10^?9 s.     

Photoinduced electron transfer processes in 1,8-naphthalimide-linker-phenothiazine dyads

Photoinduced electron transfer (PET) processes of 1,8-naphthalimide-linker-phenothiazine (NI-L-PTZ) dyads have been investigated using the nanosecond- and picosecond-transient absorption measurements. Two kinds of linker were introduced, i.e., polymethylene-linked dyad (NI-C8-PTZ and NI-C11-PTZ) and a poly(ethyl ether)-linked one (NI-O-PTZ). The 355 nm pulsed laser excitation of NI-C8-PTZ, NI-C11-PTZ, and NI-O-PTZ in acetonitrile produced NI radical anion (NI*-) and PTZ radical cation (PTZ*+) with the absorption bands around 420 and 520 nm, respectively, through charge transfer from PTZ to NI in the singlet excited state (NI(S1)) as well as in the triplet excited states (NI(T1)) in acetonitrile. On the other hand, the charge transfer process occurred only from NI(S1) in nonpolar solvents. The rates of charge transfer and charge recombination processes largely depended on the solvent polarity and they are affected by the length of linkers and electronic coupling through polyether linker. The PET mechanism is discussed in terms of the free energy change for the charge transfer.     

Molecular biology of histidine decarboxylase and prostaglandin receptors

Histamine and prostaglandins (PGs) play a variety of physiological roles as autacoids, which function in the vicinity of their sources and maintain local homeostasis in the body. They stimulate target cells by acting on their specific receptors, which are coupled to trimeric G proteins. For the precise understanding of the physiological roles of histamine and PGs, it is necessary to clarify the molecular mechanisms involved in their synthesis as well as their receptor-mediated responses. We cloned the cDNAs for mouse L-histidine decarboxylase (HDC) and 6 mouse prostanoid receptors (4 PGE(2) receptors, PGF receptor, and PGI receptor). We then characterized the expression patterns and functions of these genes. Furthermore, we established gene-targeted mouse strains for HDC and PG receptors to explore the novel pathophysiological roles of histamine and PGs. We have here summarized our research, which should contribute to progress in the molecular biology of HDC and PG receptors.     

Intrinsic versus extrinsic anomalous Hall effect in ferromagnets

A unified theory of the anomalous Hall effect (AHE) is presented for multiband ferromagnetic metals with dilute impurities. In the clean limit, the AHE is mostly due to extrinsic skew scattering. When the Fermi level is located around anticrossing of band dispersions split by spin-orbit interaction, the intrinsic AHE to be calculated ab initio is resonantly enhanced by its nonperturbative nature, revealing the extrinsic-to-intrinsic crossover which occurs when the relaxation rate is comparable to the spin-orbit coupling.     

Multicomponent QM study on the reaction of HOSO + NO2 with H2O: Nuclear quantum effect on structure and reaction energy profile

The hydrogen transfer reaction in the reaction of HOSO + NO₂ with and without H₂O have been investigated using multicomponent quantum-mechanics method, which can directly take nuclear quantum effect (NQE) of light nuclei into account. For the case of the reaction without H₂O, our calculation reveals that the reaction leading to trans-HONO is preferred. For the reaction with H₂O, water-non-mediated and water-mediated (hydrogen-relay) hydrogen transfer mechanism are investigated. The NQE of hydrogen nucleus lowers the relative energy of the stationary point structures and reduces the activation barrier of the reactions. The largest stabilization is found in the transition state structure of the hydrogen-relay type reaction. H/D isotope effects for the reactions are also analyzed. In particular, H/D isotope effect on the activation barrier is analyzed in detail with the aid of the active strain model.