Ab initio molecular orbital study of dications of 1,5‐dichalcogenacyclooctanes

The molecular and electronic structures of the dications of three homonuclear and three heteronuclear dichalcogenacyclooctanes (chalcogen = S, Se, or Te) were investigated by ab initio molecular orbital calculations. Four energy‐minimum structures were located for each dication. Three of those (chair‐chair, boat‐boat, and boat‐chair) have the cis configuration with respect to the chalcogen lone pairs, and the remaining one has the trans configuration. The cis isomers were found to be much more stable than the trans isomer. Among the three cis structures, the stability is in the order of boat‐chair > boat‐boat > chair‐chair for all dications. This order can be explained by considering the nonbonding H···H interactions. The chair‐chair structure (C_2v symmetry) of the 1,5‐dithiacyclooctane dication has a very low vibrational frequency of a₂ symmetry, and its LUMO energy is lower than those of boat‐boat and boat‐chair. These can rationalize the fact that in the crystalline state the dication adopts a distorted C₂ chair‐chair conformation. The transition states between the three conformers of the homonuclear dications were also located. The corresponding energy barriers are relatively low, which is consistent with their NMR spectra. The relative stabilities of the homonuclear and heteronuclear dications were elucidated on the basis of their energies and those of the corresponding neutral compounds. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:31–41, 2000     

The Bioassay-Guided Isolation of Growth Inhibitors of Adult T-Cell Leukemia (ATL), from the Jamaican Plant <em>Hyptis verticillata</em>, and NMR Characterization of Hyptoside

Through bioassay-guided isolation, five compounds with growth inhibitory activity on S1T, an adult T-cell leukemia (ATL) cell line, were isolated from the crude methanol extract of the aerial parts of Hyptis verticillata.     

LIGAND COUPLING AND PSEUDOROTATION IN THE REACTION OF ALKYL 2-PYRIDYL SULFOXIDE WITH GRIGNARD REAGENTS

Abstract

In the reaction of benzyl 2-pyridyl sulfoxide (1) with C₆H₅CH₂MgCl, the incoming Grignard reagent tends to couple preferentially with 2-pyridyl group at lower temperatures, whereas, at higher temperatures, coupling between benzyl and 2-pyridyl groups with 1 tends to increase due presumably to the relatively more facile pseudorotation² at higher temperatures.     

Frame-rate analysis of arterial blood flow in human and rat using laser speckle image sensing

In imaging of blood flow by means of a laser speckle technique, we have proposed so far an estimation parameter based on the spatial contrast of speckle patterns observed for the blood flow in skin tissue and a blood vessel. This parameter enable us to image a relative blood flow distribution from a single speckle pattern, thus, it analyzes the blood flow with a frame-rate of an imaging device used. In this study, we investigated availability of this parameter for detecting changes in arterial blood flow caused by medication and cold stimulation to the skin tissue. Experiments were conducted for an anesthetized rat and a human wrist to confirm the feasibility of the present parameter.     

SYNTHESES AND SOME PROPERTIES OF SULFOXIDES,SULFILIMINES, AMINOSULFONIUM SALTS AND SULFOXIMINES CONTAINING PYRIDINE NUCLEI

Abstract

Several 2-pyridyl sulfides (1) (e.g., methyl (1a), ethyl (1b), isopropyl (1c), benzyl (1d), 1-phenylethyl (1e), l-menthyl (If) 2-pyridyl sulfides; and bis(2-pyridylthio)methane (1g), and methyl 2-(N-oxy-pyridyl) sulfide (1h) were prepared by the usual method. Sulfoxides (2) were prepared by oxidation of the corresponding sulfides with m-chloroperbenzoic acid in good yields. A few sulfoxides were found to work as phase-transfer catalysts for some typical nucleophilic reactions in nonpolar solvents such as benzene, and in two-phase systems such as benzene-water. S-2-Pyridyl-N-(p-toluenesulfonyl) sulfilimines (3) were prepared upon treatment of sulfides with Chloramine-T. Hydrolysis of N-(p-toluenesulfonyl)-2-pyridyl-o-tolylsulfilimine (3i) with conc. sulfuric acid gave the corresponding free sulfilimine in a moderate yield. S-2-Pyridyl sulfoximines (4) were not obtained by the general method from the sulfoxides and hydrazoic acid. Alkyl-2-pyridyl sulfoximines, however, were obtained by oxidation of the free sulfilimines derived from the corresponding aminosulfonium salts (5) prepared by reaction of the sulfides with mesitylene-sulfonylhydroxylamine (MSH). These free sulfilimines and sulfoximines thus prepared were found to give adducts with a few copper salts.     

KINETICS OF THE REACTION OF SULFIMIDES WITH POTASSIUM HYDROXIDE IN METHANOL

Abstract

The reaction of sulfimides with hydroxide ion in methanol gave the corresponding sulfoxide (the solvolysis product) and/or the corresponding α-methoxysulfide (the Pummerer type product). The pseudo first order rates for the solvolysis reaction and the Pummerer type reaction were determined using a large excess of potassium hydroxide. The rates of the solvolyses are correlated with [sgrave] values and the values of ρ _X = +1.2 and ρ _Y = +0.8 were obtained for aryl methyl N-aryl-sulfonylsulfimides (p-XC₆H₄S(NSO₂C₆H₄Y-p)CH₃), and both the activation enthalpy and entropy calculated are δH≠ = 18.8 kcal mol^?1 and δS≠ = –23.9 e.u. (PhS(NSO₂C₆H₄CH₃-p)CH₃), respectively. Hammett correlation with [sgrave] values for the Pummerer type reaction gave ρz = +2.0 for N-aryl-sulfonyltetramethylenesulfimides ((CH₂)₄SNSO₂C₆H₄Z-p), and the activation enthalpy and entropy are δH≠ = 27.9 kcal mol^?1 and δS≠ = +13.3 eu ((CH₂)₄SNSO₂C₆H₄CH₃-p), respectively. All these observations suggest that the solvolysis reaction proceeds via the initial nucleophilic attack of hydroxide ion on the sulfur atom of the sulfimide namely via an S _N 2 process at the sulfur atom whereas the Pummerer type reaction proceeds by way of the E 1cb mechanism.     

STUDY OF THE MECHANISM FOR THE REARRANGEMENT OF THIOLSULFINATE WITH ACETIC ANHYDRIDE BY 13C AND 18O-TRACER EXPERIMENTS

Abstract

Recently, we found that benzyl phenylmethanethiolsulfinate (I) reacts with acetic anhydride at 60°C to afford the rearranged sulfoxide, i.e., an almost 1:1 mixture of both erythro and threo-1-(acetoxylthio)benzyl benzyl sulfoxides(II) in a substantial yield.     

Fabrication of χ{2) Grating in Poled Polymer Waveguide Based on Direct Laser Beam Writing

A simple method is described for fabricating high resolution χ⁽²⁾ grating in poled polymer waveguide. It is found that the second-order nonlinearity of corona-poled polymer thin film is erased after visible laser (450 nm) irradiation. The mechanism of the erasure of χ^{2) is discussed. High resolution χ⁽²⁾ grating structure in several poled polymer waveguides is demonstrated by direct writing with a cw He-Cd laser.On leave from the Department of Optical Instruments, Zhejiang University, Hangzhou, Zhejiang Province, 310027, P.R. of China.     

Quantum interference effect of resonant transport in nano-scale systems

We propose a new method of analyzing the quantum interference effect of the resonant transport in ballistic open systems. The new method is to obtain the resonant eigenvalues by computing the norm of the retarded and advanced Green's functions. Using the method, we illustrate for a fullerene and an AB-ring the relation between each resonant state and each asymmetric conductance peak, namely the Fano peak. We show that the combination of resonant states determines the symmetry of a conductance peak and that the Fano peak is caused by the asymmetry of the numerator of the conductance around a resonance. The Fano peak appears not only due to the quantum interference effect as often claimed, but more generally due to the resonant transport.