Real-space finite-difference approach for multi-body systems: path-integral renormalization group method and direct energy minimization method

The path-integral renormalization group and direct energy minimization method of practical first-principles electronic structure calculations for multi-body systems within the framework of the real-space finite-difference scheme are introduced. These two methods can handle higher dimensional systems with consideration of the correlation effect. Furthermore, they can be easily extended to the multicomponent quantum systems which contain more than two kinds of quantum particles. The key to the present methods is employing linear combinations of nonorthogonal Slater determinants (SDs) as multi-body wavefunctions. As one of the noticeable results, the same accuracy as the variational Monte Carlo method is achieved with a few SDs. This enables us to study the entire ground state consisting of electrons and nuclei without the need to use the Born-Oppenheimer approximation. Recent activities on methodological developments aiming towards practical calculations such as the implementation of auxiliary field for Coulombic interaction, the treatment of the kinetic operator in imaginary-time evolutions, the time-saving double-grid technique for bare-Coulomb atomic potentials and the optimization scheme for minimizing the total-energy functional are also introduced. As test examples, the total energy of the hydrogen molecule, the atomic configuration of the methylene and the electronic structures of two-dimensional quantum dots are calculated, and the accuracy, availability and possibility of the present methods are demonstrated.     

Fabrication of a freestanding GaN layer by direct growth on a ZnO template using hydride vapor phase epitaxy

A new hydride vapor phase epitaxy (HVPE)-based approach for the fabrication of freestanding GaN (FS-GaN) substrates was investigated. For the direct formation of low-temperature GaN (LT-GaN) layers, the growth parameters were optimized: the polarity of ZnO, the growth temperature, and the V/III ratio. The FS-GaN layer was achieved by gas etching in an HVPE reactor. A fingerprint of Zn out-diffusion was detected in the photoluminescence measurements, especially for the thin (80 μm) FS-GaN film; however, a thicker film (400 μm) was effectively reduced by optimization of GaN growth.     

Phosgene‐free synthesis of polypeptides: Useful synthesis for hydrophobic polypeptides through polycondensation of activated urethane derivatives of α‐amino acids

We report a useful synthetic method of polypeptides using a series of urethane derivative of α‐amino acids (l ‐leucine, l ‐phenylalanine, l ‐valine, l ‐alanine, l ‐isoleucine, l ‐methionine), which are readily synthesized by N‐carbamoylation of tetrabutylammonium salts of α‐amino acids with diphenyl carbonate. Heating these urethane derivatives in N,N‐dimethylacetamide in the presence of n‐butylamine successfully gave the corresponding polypeptides with well‐defined structures through polycondensation with the elimination of phenol and CO₂. The matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry investigation showed that the resulting polypeptides had an n‐BuNH₂‐incorporated initiating end and an amino group at propagating end. These results strongly indicated that primary amines served as an initiator in this polycondensation system. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3726–3731     

Development and validation of a hydrophilic interaction chromatography–tandem mass spectrometry for quantification of nicotine and its metabolites in human maternal and cord sera

A selective and sensitive HILIC‐MS/MS method for the simultaneous quantification of nicotine and its metabolites in human maternal and cord sera was developed and validated. After solid‐phase extraction, LC separation was achieved on a hydrophilic interaction chromatography. The validated method is capable of selective identification as well as accurate and sensitive quantification. Analyte recovery ranged from 86.2 to 107.7% and intra‐ and inter‐day assay precision were less than 15% relative standard deviation. This sensitive HILIC‐MS/MS method can be used to determine nicotine and its metabolic profile in smokers. This validated method is useful for the determination of nicotine and its metabolites in human serum in future studies of the effects of nicotine exposure on neonatal outcome. Copyright © 2010 John Wiley & Sons, Ltd.     

Sub-micrometer patterns of molecular photo-switches using laser induced molecular implantation techniques (LIMIT)

Using laser induced molecular implantation techniques (LIMIT) in thin polymer films highly space selective patterning of photochromic molecules has been created of 800 nm dimensions. In this way diffraction gratings have been fabricated which operate as photo-switching devices. These transient gratings are permanent molecular implants in a polymer films that can be UV-irradiation activated or thermally deactivated. No further grating writing is required for this transient switching effect once the permanent implantation has been made.     

Structural Characterization of a Pentacoordinate Monohydrosilane with the Apical Si-H Bond

A pentacoordinate phenyldibenzosilazocine containing the apical Si-H bond has been prepared and characterized by ¹H and ²⁹Si NMR spectra and X-ray analysis.