Lorentzian stationary surfaces and null curves in {R^4_2}

We discuss a property of the Gaussian curvature and the normal curvature of Lorentzian stationary surfaces in \({R^4_2}\) , from the view point of null curves in \({R^4_2}\) . We also discuss some examples.     

A DFT study on proton transfers in hydrolysis reactions of phosphate dianion and sulfate monoanion

B3LYP calculations were carried out on hydrolysis reactions of monosubstituted(R) phosphate dianion and sulfate monoanion. In the reacting system, water clusters (H₂O)₂₂ and (H₂O)₃₅ are included to trace reaction paths. For both P and S substrates with R = methyl group, elementary processes were calculated. While the phosphate undergoes the substitution at the phosphorus, the sulfate does at the methyl carbon. For the S substrate with R = neopentyl group, the product tert‐amyl alcohol was found to be formed via a dyotropic rearrangement from the neopentyl alcohol intermediate. For R = aryl groups, transition‐state geometries were calculated to be similar between P and S substrates. Calculated activation energies are in good agreement with experimental values. After the rate‐determining transition state of the substitution, the hydronium ion H₃O⁺ is formed at the third water molecule. It was suggested that alkyl and aryl substrates are of the different reactivity of the hydrolysis. © 2014 Wiley Periodicals, Inc.     

Clarification of the role of protein in carbonmonoxy myoglobin by investigating electronic states

This article reports the proton tautomerization effects of distal histidine residues in carbonmonoxy myoglobin according to the density functional calculations of the whole protein. The electron eigenstates and electrostatic potential (ESP) distributed around heme and its pocket vary significantly depending on the protonation positions of the distal histidine residues. To investigate the range over which the electronic structures are affected by the proton tautomerization, the quantum mechanics/molecular mechanics (QM/MM) method is applied to probe the QM size to reproduce the atomic partial charges and ESP around the active center. Consequently, we show that these properties converged for the 300 pm QM/MM system in this study. During the analysis, we also find that amino residues such as Phe43, Val68, and Phe138 interact strongly with heme through orbital mixing, indicating that the protein is a medium not only interacting with the reaction center, but also buffering on electrons. © 2013 Wiley Periodicals, Inc.     

A short-step synthesis of naphtho[2,3-b]furan-4,9-dione

Phthalic anhydride in THF was added to 3-lithiofuran 2 in THF to give 3,3-di-(3-furyl)-1,3-dihy-droisobenzofuran-1-one 4 . On the other hand, 2 in THF was added to phthalic anhydride in THF to give 2-(3-furanoyl)benzoic acid 3 by the inverse addition method. Further, the parent naphtho[2,3-b]furan-4,9-dione 1 was obtained from the reaction of 3 with two equimolar amounts of LDA.     

Magnetotransport properties of untwinned YBa2Cu3Oy single crystals: novel 60-K-phase anomalies in the charge transport

We present the result of our accurate measurements of the a- and b-axis resistivity (ρ_a and ρ_b), magnetoconductivity Δσ/σ, Hall coefficient R_H, and the a-axis thermopower S_a in untwinned YBa₂Cu₃O_y single crystals in a wide range of doping (6.45≤y≤7.0). The systematics of our data reveals a number of novel 60-K-phase anomalies in the charge transport: (i) temperature dependences of ρ_a show anomalous overlap below ∼130 K for 6.65≤y≤6.80, (ii) Hall mobility μ_H shows an enhancement near y?6.65, which is reflected in an anomalous y dependence of σ_xy, (iii) with decreasing temperature R_H shows a marked drop upon approaching T_c only in samples with 6.70≤y≤6.85, (iv) superconducting fluctuation magnetoconductivity is anomalously enhanced near y?6.7, and (v) H_c2 is anomalously reduced near y?6.70. We discuss that the fluctuating charge stripes might be responsible for these anomalies in the charge transport.     

Sb/As intermixing in self-assembled GaSb/GaAs type II quantum dot systems and control of their photoluminescence spectra

The intermixing of Sb and As atoms induced by rapid thermal annealing (RTA) was investigated for type II GaSb/GaAs self-assembled quantum dots (QD) formed by molecular beam epitaxy growth. Just as in InAs/GaAs QD systems, the intermixing induces a remarkable blueshift of the photoluminescence (PL) peak of QDs and reduces the inhomogeneous broadening of PL peaks for both QD ensemble and wetting layer (WL) as consequences of the weakening of quantum confinement. Contrary to InAs/GaAs QDs systems, however, the intermixing has led to a pronounced exponential increase in PL intensity for GaSb QDs with annealing temperature up to 875 °C. By analyzing the temperature dependence of PL for QDs annealed at 700, 750 and 800 °C, activation energies of PL quenching from QDs at high temperatures are 176.4, 146 and 73.9 meV. The decrease of QD activation energy with annealing temperatures indicates the reduction of hole localization energy in type II QDs due to the Sb/As intermixing. The activation energy for the WL PL was found to drastically decrease when annealed at 800 °C where the QD PL intensity surpassed WL.     

Regioselective beta-metalation of meso-phosphanylporphyrins. Structure and optical properties of porphyrin dimers linked by peripherally fused phosphametallacycles

meso-Diphenylphosphanylporphyrins were successfully prepared via Pd-catalyzed C-P cross-coupling reaction of the corresponding meso-iodoporphyrins with diphenylphosphane. The meso- phosphanylporphyrins underwent regioselective metalation at the beta carbon to produce novel classes of porphyrin dimers linked by peripherally fused phosphametallacycles. A Pd-mononucler complex was structurally characterized by X-ray crystallography, which revealed a flat structure of the Pd-linked porphyrin pi systems. Both experimental and theoretical results demonstrate that the orbital interaction between the pyrrolic ppi orbitals and the metal dpi orbital affects optical and electrochemical properties of the metal-linked coplanar porphyrin dimers.     

Construction of an Artificial Ferrimagnetic Lattice by Lithium Ion Insertion into a Neutral Donor/Acceptor Metal–Organic Framework

Construction of a molecular system in which the magnetic lattice exhibits long‐range order is one of the fundamental goals in materials science. In this study, we demonstrate the artificial construction of a ferrimagnetic lattice by doping electrons into acceptor sites of a neutral donor/acceptor metal–organic framework (D/A‐MOF). This doping was achieved by the insertion of Li‐ions into the D/A‐MOF, which was used as the cathode of a Li‐ion battery cell. The neutral D/A‐MOF is a layered system composed of a carboxylate‐bridged paddlewheel‐type diruthenium(II,II) complex as the donor and a TCNQ derivative as the acceptor. The ground state of the neutral form was a magnetically disordered paramagnetic state. Upon discharge of the cell, spontaneous magnetization was induced; the transition temperature was variable. The stability of the magnetically ordered lattice depended on the equilibrium electric potential of the D/A‐MOF cathode, which reflected the electron‐filling level.     

Theoretical study of C-H and N-H sigma-bond activation reactions by titinium(IV)-imido complex. Good understanding based on orbital interaction and theoretical proposal for N-H sigma-bond activation of ammonia

The C-H sigma-bond activation of methane and the N-H sigma-bond activation of ammonia by (Me3SiO)2Ti(=NSiMe3) 1 were theoretically investigated with DFT, MP2 to MP4(SDQ), and CCSD(T) methods. The C-H sigma-bond activation of methane takes place with an activation barrier (Ea) of 14.6 (21.5) kcal/mol and a reaction energy (DeltaE) of -22.7 (-16.5) kcal/mol to afford (Me3SiO)2Ti(Me)[NH(SiMe3)], where DFT- and MP4(SDQ)-calculated values are given without and in parentheses, respectively, hereafter. The electron population of the CH3 group increases, but the H atomic population decreases upon going to the transition state from the precursor complex, which indicates that the C-H sigma-bond activation occurs in heterolytic manner unlike the oxidative addition. The Ti atomic population considerably increases upon going to the transition state from the precursor complex, which indicates that the charge transfer (CT) occurs from methane to Ti. These population changes are induced by the orbital interactions among the d(pi)-p(pi) bonding orbital of the Ti=NSiMe3 moiety, the Ti d(z2) orbital and the C-H sigma-bonding and sigma*-antibonding orbitals of methane. The reverse regioselective C-H sigma-bond activation which leads to formation of (Me3SiO)2Ti(H)[NMe(SiMe3)] takes place with a larger Ea value and smaller exothermicity. The reasons are discussed in terms of Ti-H, Ti-CH3, Ti-NH3, N-H, and N-CH3 bond energies and orbital interactions in the transition state. The N-H sigma-bond activation of ammonia takes place in a heterolytic manner with a larger Ea value of 19.0 (27.9) kcal/mol and considerably larger exothermicity of -45.0 (-39.4) kcal/mol than those of the C-H sigma-bond activation. The N-H sigma-bond activation of ammonia by a Ti-alkylidyne complex, [(PNP)Ti(CSiMe3)] 3 (PNP = N-[2-(PH2)2-phenyl]2-]) ,was also investigated. This reaction takes place with a smaller E(a) value of 7.5 (15.3) kcal/mol and larger exothermicity of -60.2 (-56.1) kcal/mol. These results lead us to predict that the N-H sigma-bond activation of ammonia can be achieved by these complexes.     

Diastereomer-specific effects of double-stranded peptides conjugated with -L-Tyr-L-Phe- or -L-Tyr-D-Phe- residues on tyrosine phosphorylation and inhibition of src(ts)NRK, A431, MCF-7, and DU145 cell growth

The interaction between growth inhibition and chirality, especially of diastereomers, has an important modifying effect on cancer cell proliferation. Previously, we have reported on the design, synthesis, and chemical properties of a series of novel, double-stranded peptides, (y-AA-x-AA)(2)-(CH(2))(12), with -y-AA-x-AA- and -z-AA-y-AA-x-AA- sequences conjugated to the spacer. Here, we extend those results by showing that (D-, L-) and (L-, D-) diastereomers are more potent inhibitors of tyrosine phosphorylation than (L-, L-). Although the replacement of the L-Phe-L-Phe sequence with L-Tyr-L-Phe produces a less active inhibitor, the double-stranded peptide conjugated with L-Tyr-D-Phe is more active than that conjugated with L-Tyr-L-Phe. In addition, we show that SDS-PAGE gel profiles of tyrosine phosphorylation following treatment with bis(y-Tyr-x-Phe)-N,N-dodecane-1,12-diamine appear very similar to profiles of tyrosine phosphorylation following treatment with an analog of the tyrosine kinase inhibitor, erbstatin. Moreover, the level of autophosphorylation of the epidermal growth factor receptor kinase domain (EGFRKD) treated with bis(L-Tyr-D-Phe)-N,N-dodecane-1,12-diamine was lower than that seen following treatment with bis(L-Phe-D-Phe)-N,N-dodecane-1,12-diamine. These data provide new insights for the control of cancer cell proliferation through drug designs which replace the less active -L-Phe-L-Phe- (and -D-Phe-L-Phe-) with the more active -L-Tyr-L-Phe- (and -L-Tyr-D-Phe-) sequence.