Numerical study of localization in Anderson model for disordered systems

The localization properties in the Anderson model of two dimensional square lattices are investigated numerically. Pretty large lattices composed of 10⁴ (= 100 × 100) sites are dealt with, and the overall behaviors of the eigenvectors near the band center are directly examined. Fairly sharp transition and the exponentially decaying localized states are visualized.     

A self-consistent cluster theory of amorphous materials

A cluster method for the electronic structure of amorphous materials is presented with an application to amorphous diamond. Eight-atom cluster model gives a pseudogap in the density of states.     

Control of a photoreaction by electron spin resonance (II): The effect of radical pair lifetime on the control efficiency

The magnetic-field and the microwave effects on the photoreactions of anthraquinone-2-sulfonate and anthraquinone-2-carboxylic acid with xanthene were observed in an SDS micellar solution. The reaction products were analyzed by high performance liquid chromatography. With increasing the magnetic-field strength from the residual value to 400 mT, the yield of dixanthenyl, which is an “escape product”, increased considerably. Upon irradiating the system with a microwave (9400 MHz, 1.0 kW), however, the yield decreased almost to the minimum value at around 334 mT, where the intermediate radical pair becomes resonant with the microwave field. Therefore, we can detect the ESR spectrum of the transient radical pair by the product yield (product-yield-detected ESR or PYESR). In the present study, we observed a clear reversed microwave effect at the center of the PYESR spectrum, whose cause was attributed to “spin locking” of the radical pair by an intense microwave field. The microwave effects for the two systems were, different from each other in several respects including the extent of this spin locking effect in the product yield. The PYESR spectra were calculated by using a quantum mechanical method to discuss the relation between the microwave effect and the radical pair dynamics, the latter of which was also observed in the present study by the “pulse-PYESR” method.     

Theoretical analysis of oxygen reduction reaction and H2O2 formation and the impact of CF3SO3H coverage on Pt (111)

Theoretical analysis of ORR on Pt (111) was carried out with the combined technique of DFT calculation and the UBI-QEP method in order to understand the overall ORR pathways, behavior of H₂O₂ formation, and the impact of trifluoromethane sulfonic acid (CF₃SO₃H and TfOH) coverage, the alternative material of Nafion^®, on the reactivity on the Pt surface. The ORR scheme consisting of elementary reactions was then modeled to determine the dominant path and the limiting step based on their activation energies. The results showed that the dominant ORR path included the H₂O₂ formation step and OOH formation step was limiting. When TfOH covered the Pt surface, it was revealed that the adsorption energy of an O₂ molecule on Pt (111) was decreased due to the lower Fermi level and the d-band center, resulting in decreasing the activation energy of the limiting step. TfOH, however, could suppress the O₂ adsorption on the Pt surface. In addition, with the TfOH coverage, it was indicated that the limiting step of ORR was shifted to H₂O-production step which was after the H₂O₂ production, resulting in the enhancement of the H₂O₂ formation.     

Molecular dynamics study of solubilization of cyclohexane,benzene, and phenol into mixed micelles composed of sodium dodecyl sulfate and octaethylene glycol monododecyl ether

Molecular dynamics calculations of a mixed micelle composed of sodium dodecyl sulfate (SDS) and octaethylene glycol monododecyl ether (C₁₂E₈) were performed for six compositions (SDS/C₁₂E₈ = 100/0, 80/20, 60/40, 40/60, 20/80, and 0/100) to investigate the composition dependence of the mixed micelle structure and solubilization of cyclohexane, benzene, and phenol molecules by the micelle. The radial density distribution of the hydrophilic polyoxyethylene (POE) group of C₁₂E₈ as a function of distance from the micelle center is very sharp for micelles with high SDS content because the POE group captures a Na⁺ ion in solution and wraps around it to form a compact crown-ether-like complex. The hydrophobic dodecyl groups of SDS and C₁₂E₈ were separately distributed in the mixed micelle core. ΔG(r) evaluated for each solute showed that despite the structural changes of the micelle the binding strength of the solute molecules to the micelle did not change significantly. © 2019 Wiley Periodicals, Inc.     

CH/pi hydrogen bonds determine the selectivity of the Src homology 2 domain to tyrosine phosphotyrosyl peptides: an ab initio fragment molecular orbital study

The CH/pi hydrogen bond is a weak molecular force occurring between CH groups (soft acids) and pi-systems (soft bases), and has been recognized to be important in the interaction of proteins with their specific ligands. For instance, it is well known that Src homology-2 protein (SH2) recognizes its specific pTyr peptide in two key regions, pTyr-binding region and specificity-determining region, by the use of attractive molecular forces, including the CH/pi hydrogen bond. We hypothesized that the CH/pi hydrogen bond plays a key role in determining the selectivity of SH2 proteins, and studied this issue by the ab initio fragment molecular orbital (FMO) method. The FMO calculations were carried out, at the HF/6-31G* and MP2/6-31G* level, for SH2 domains of Src, Grb2, P85alpha(N), Syk, and SAP, in complex with corresponding pTyr peptides. CH/pi hydrogen bonds have in fact been found to be important in stabilizing the structure of the complexes. We conclude that the CH/pi hydrogen bond plays an indispensable role in the recognition of SH2 domains with their specific pTyr peptides, thus playing a vital role in the signal transduction system.     

Stable ion and electrophilic chemistry of the sterically crowded stilbene 1,1'-Bi(benzocyclobutenylidene) and its derivatives

Generation and NMR studies of novel carbocations and carboxonium ions are reported from sterically hindered stilbene 1,1'-bi(benzocyclobutenylidene) 1, its dimethoxy derivative 5, and from their skeletally rearranged derivatives, namely, the spirocyclic ketone 6, diastereomeric alcohols 7 and isomeric diols 8. Quenching experiments on the carbocations under various conditions resulted in the formation/isolation of several novel covalent adducts. Acid-catalyzed isomerization of the diols 8 produced a remarkable dimeric molecule, whose structure was confirmed by X-ray analysis. Reactions of hindered stilbenes 1 and 5 with Br 2/CDCl 3 were examined via NMR experiments. The experimentally observed carbocations were also studied computationally by GIAO-DFT and by NICS.     

Analytical method for determination of disaccharides derived from keratan sulfates in human serum and plasma by high-performance liquid chromatography/turbo-ionspray ionization tandem mass spectrometry

We established a highly sensitive LC/MS/MS method for the analysis of the disaccharides produced from keratan sulfates (KS). It was revealed that the disaccharides produced by keratanase II enzymatic digestion of KS could be determined with high sensitivity by negative ion mode of multiple reaction monitoring. Furthermore, monosulfated and disulfated disaccharides can be separated using a Hypercarb (2.0 mm i.d. x 150 mm, 5 microm) with a gradient elution of acetonitrile-0.01 m ammonium bicarbonate (pH 10). This method was applied to the determination of KS in serum and plasma of control subjects. The intra-day precision expressed as %CV was within 6.8% for five replicate analyses with three different control serum. The inter-day (overall, n = 15) precision was within 7.3% for three days. This method is sensitive, reproducible and would be useful for clinical analysis.