Second-order perturbational treatment of normal coordinates in the string model for the hydration reaction of formaldehyde

A perturbation theory for normal coordinates of nonadiabatic solvation is presented by means of the “string model” of chemical reactions. The dynamic normal coordinate is introduced for the perturbational treatment of the “intrinsic” normal coordinates that are orthogonal to the reaction path. The reaction is defined as the intrinsic reaction coordinate (IRC ) that is treated as a string. The string is thrown in the external force field that acts as a nonadiabatic source of perturbation. As an application of the present treatment, the effect of a water molecule for hydration reaction of formaldehyde is calculated. A second-order perturbation effect for the enhancement of the reaction rate is found.     

Novel canonical coding method for representation of three-dimensional structures

A new canonical coding method for representation of three-dimensional structures, CAST (CAnonical representation of STereochemistry), is described. CAST canonically codes stereochemistry around an atom in a molecule. The same CAST notations are given for atoms of molecules in the same conformation. The CAST code is based on the dihedral angles of four atoms that are uniquely defined by a molecular tree structure. CAST has successfully represented similarities and differences between several conformers.     

Formation and stabilization model of the 42-mer Abeta radical: implications for the long-lasting oxidative stress in Alzheimer's disease

Amyloid fibrils mainly consist of 40-mer and 42-mer peptides (Abeta40, Abeta42). Abeta42 is believed to play a crucial role in the pathogenesis of Alzheimer's disease because its aggregative ability and neurotoxicity are considerably greater than those of Abeta40. The neurotoxicity of Abeta peptides involving the generation of free radicals is closely related to the S-oxidized radical cation of Met-35. However, the cation's origin and mechanism of stabilization remain unclear. Recently, structural models of fibrillar Abeta42 and Abeta40 based on systematic proline replacement have been proposed by our group [Morimoto, A.; et al. J. Biol. Chem. 2004, 279, 52781] and Wetzel's group [Williams, A. D.; et al. J. Mol. Biol. 2004, 335, 833], respectively. A major difference between these models is that our model of Abeta42 has a C-terminal beta-sheet region. Our biophysical study on Abeta42 using electron spin resonance (ESR) suggests that the S-oxidized radical cation of Met-35 could be generated by the reduction of the tyrosyl radical at Tyr-10 through a turn structure at positions 22 and 23, and stabilized by a C-terminal carboxylate anion through an intramolecular beta-sheet at positions 35-37 and 40-42 to form a C-terminal core that would lead to aggregation. A time-course analysis of the generation of radicals using ESR suggests that stabilization of the radicals by aggregation might be a main reason for the long-lasting oxidative stress of Abeta42. In contrast, the S-oxidized radical cation of Abeta40 is too short-lived to induce potent neurotoxicity because no such stabilization of radicals occurs in Abeta40.     

The discovery of polymer‐clay hybrids

The first successful example of a polymer‐clay hybrid was nylon‐clay hybrid (NCH), which is a nano‐meter‐sized composite of nylon‐6 and 1‐nm‐thick exfoliated aluminosilicate layers of the clay mineral. NCH was found and developed at Toyota Central Research and Development Laboratories over 17 years ago. The NCH containing a few weight percentages of clay exhibits superior properties such as high modulus, high strength, and good gas‐barrier properties. The key for the discovery of NCH was the polymerization of a nylon monomer in the interlayer space of the clay. This highlight presents the development of NCH from its discovery to its commercialization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 819–824, 2004     

Significant differences in site of protonation and extent of fragmentations in chemical ionization and fast atom bombardment mass spectrometry of simple bifunctional compounds. A mechanistic implication for formation of protonated molecules

Chemical ionization (CI) and fast atom bombardment (FAB) mass spectra of simple bifunctional aromatic compounds were compared. Some significant differences were revealed with respect to the site of protonation and extent of fragmentations. Unlike conventional CI ionization, the protonated molecule formation by FAB could not be accounted for by ordinary proton transfer reactions in the gas phase. The observed ions under FAB conditions appear to be regulated by proton exchange reactions through frequent collisions in some particular region between the matrix and the gas phase.     

Spatial distribution of YO molecules ejected from laser-ablated YBa2 Cu3 O7−x

One-dimensional imaging laser-induced fluorescence spectroscopy has been used for in-situ measurements of spatial distributions of YO molecules produced during the ArF-laser ablation of YBa₂ Cu₃ O _7–x in vacuum and oxygen gas environment. The time-integrated angular distribution of particles ejected in vacuum has a cos ⁿ form, where 11 <n < 13. When oxygen gas was introduced, YO molecules were confined in a smaller volume, and temporal changes of their spatial distribution were interpreted in terms of blast-wave formation.