Synthesis and ligand-based mixed valency of cis- and trans-Cr(III)(X(4)SQ)(X(4)Cat)(L)(n) (X = Cl and Br,n = 1 or 2) complexes: effects of solvent media on intramolecular charge distribution and ligand dissociation of Cr(III)(X(4)SQ)(3)

The treatment of Cr(III)(X(4)SQ)(3) (SQ = o-semiquinonate; X = Cl and Br) with acetonitrile affords trans-Cr(III)(X(4)SQ)(X(4)Cat)(CH(3)CN)(2) (X = Cl (1) and Br (2)). In the presence of 2,2'-bipyridine (bpy) or 3,4,7,8-tetramethyl-1,10-phenanthrene (tmphen), the reaction affords Cr(III)(X(4)SQ)(X(4)Cat)(bpy).nCH(3)CN (X = Cl, n = 1 (3); X = Br, n = 0.5 (4)) or Cr(III)(X(4)SQ)(X(4)Cat)(tmphen) (X = Cl (5) and Br (6)), respectively. All of the complexes show a ligand-based mixed-valence (LBMV) state with SQ and Cat ligands. The LBMV state was confirmed by the presence of the interligand intervalence charge-transfer band. Spectroscopic studies in several solvent media demonstrate that the ligand dissociation included in the conversion of Cr(III)(X(4)SQ)(3) to 1-6 occurs only in solvents with relatively high polarity. On the basis of these results, the effects of solvent media were examined and an equilibrium, Cr(III)(X(4)SQ)(3) <--> Cr(III)(X(4)BQ)(X(4)SQ)(X(4)Cat) (BQ = o-benzoquinone), is proposed by assuming an interligand electron transfer induced by solvent polarity.     

Structural and substituent effects on [M]+. vs. [MH]+ formation in fast atom bombardment mass spectra of simple organic compounds

The peak intensity ratios of [M]^+. vs. [MH]⁺ were measured in the fast atom bombardment (FAB) mass spectra of readily available test compounds with 3-nitrobenzyl alcohol as the matrix. For simple aromatic amines, the ratio increases as the ionization energy of the substrate decreases. 4-Substituted benzophenones showed preferential formation of [MH]⁺ ions, regardless of the nature of the substituents. This is probably due to the fact that the benzophenoes have carbonyl groups which can form hydrogen bonds with the matrix molecule. The peak intensity ratio is roughly proportional to the Hammett σ^+. Among 4-substituted biphenyls, both bromo and chloro substituents afforded abnormally high peak intensity ratios. The effects of the substituents in these compounds are discussed semi-quantitatively in terms of the Hammett correlation and the hard and soft acids and bases principle. The mechanism of ion formation in FAB and chemical ionization (CI) ion sources appeared to be different because some of the compounds studied showed an intense [M]^+. peak with a relatively weak [MH]⁺ peak in FAB spectra but exhibited a strong [MH]⁺ peak in ordinary CI spectra.     

Regioselective Silylations of C-2 Hydroxyl Groups of Cyclodextrins Dependent on Reaction Temperature

Silylations of the C-2 hydroxyl group of cyclodextrins were carried out using t-butyldimethylsilyl imidazole in the presence of 4A molecular sieves in N,N-dimethylformamide. A unique aspect of this silylation method is the temperature dependence of the regioselectivity; silylation at 0 °C regioselectively favored the C-6 position to afford mono-6-O-t-butyldimehylsilyl-cyclodextrins, whereas silylation at 140 °C exhibited high regioselectivity on the C-2 hydroxyl group.     

Inverse problem for Sturm-Liouville and hill equations

Summary We discuss the inverse Sturm-Liouville problem on a finite interval by the method of transformation kernel. The -function, the Fredholm determinant of the transformation kernel, is explicitly written down in terms of the spectral data, from which a very explicit representation formula for the potential is deduced, and well-posedness of the inverse problem is established. The above method is also applicated to the inverse problem for Hill equations, in particular to the isospectral problem. We obtain an analog of FIT formula and a regularity theorem.     

Quantification of polychlorinated dibenzo-p-dioxins and dibenzofurans by direct injection of sample extract into the comprehensive multidimensional gas chromatograph/high-resolution time-of-flight mass spectrometer

Polychlorinated dibenzo-p-dioxins and dibenzofurans in crude extracts of fly ash and flue gas from municipal waste incinerators were quantified using a comprehensive multidimensional gas chromatograph (GC x GC) coupled to a high-resolution time-of-flight mass spectrometer (HR-TOFMS). For identification and quantification, we developed our own program to prepare 3D chromatograms of selected mass numbers from the data of the GC x GC/HR-TOFMS. Isolation of all congeners with a TCDD toxic equivalency factor from the other isomers by only one injection was confirmed. The instrumental detection limit of TCDD on the GC x GC/HR-TOFMS was 0.9 pg by the relative calibration method. Quantification of these substances in the crude extracts was achieved by direct injection to the GC x GC/HR-TOFMS. The results agree with the values obtained using a generic gas chromatography/high-resolution mass spectrometry (GC/HRMS) system. It was confirmed that measurement by high-resolution TOFMS and GC x GC effectively reduces interference from other chemicals.     

Pseudorotaxane-like supramolecular complex of coenzyme Q10 with gamma-cyclodextrin formed by solubility method

The purpose of this study is to reveal whether Coenzyme Q10 (CoQ10) forms pseudorotaxane-like supramolecular complex with gamma-cyclodextrin (gamma-CyD). The poorly soluble complex of CoQ10 with gamma-CyD in water was prepared by the solubility method. The X-ray diffraction pattern of the CoQ10/gamma-CyD complex was different from that of the physical mixture, but almost the same as that of polypropylene glycol (PPG)/gamma-CyD polypseudorotaxane. Also, the differential scanning calorimetrical study and FT-IR study demonstrated the interaction between CoQ10 and gamma-CyD in the solid state. The 1H-NMR study and the yield study of the supramolecular complex of CoQ10 with gamma-CyD demonstrated that the stoichiometry was 5 : 1 (gamma-CyD : CoQ10). The dispersion rate of CoQ10 was markedly increased by the formation of the supramolecular complex with gamma-CyD, possibly due to submicron-ordered particle formulation. In fact, CoQ10 was found to form submicron-sized supramolecular particles with gamma-CyD, when prepared by the solubility method. Consequently, the present study showed that CoQ10 forms the pseudorotaxane-like supramolecular complex with gamma-CyD in water.     

Efficient Regioselective Synthesis of Mono-2-O-Sulfonyl-cyclodextrins by the Combination of Sulfonyl Imidazole and Molecular Sieves

Abstract

Cyclodextrins are cyclic oligosaccharides consisting of six or more α-1,4-linked D-glucopyranose units, which possess primary hydroxyl groups at the C-6 positions and secondary hydroxyl groups at the C-2 and C-3 positions. Because cyclodextrins have a hydrophobic and optically active interior, they have been utilized as transporters of hydrophobic molecules and small molecular mimics of enzymes. The chemical modification of cyclodextrins has been investigated in order to improve these characteristics. Sulfonations of the primary or secondary hydroxyl groups of cyclodextrin have been applied for further functionalization of cyclodextrin, and several methods for regioselective sulfonations have been developed. Among these strategies, selective monotosylation of the C-6 hydroxyl group is done relatively easily by reaction of α or β-cyclodextrin and p-toluenesulfonyl chloride in pyridine^1,2 or in alkaline aqueous solution.^3,4 However, sulfonation of the secondary hydroxyl groups is more difficult and new sulfonation methods must be developed to provide precursors for cyclodextrin analogues such as amino and sulfide analogues. Several strategies for the sulfonation of one C-2 hydroxyl group have been reported. However, because reaction conditions can require specific sulfonation reagent,⁵ alkaline condition,^3-7 strict anhydrous conditions,^8,9 or use of protected C-6 hydroxyl groups,^10,11 the methodology is not convenient to employ.     

Structural studies of large nucleoprotein particles,vaults

Vault is the largest nonicosahedral cytosolic nucleoprotein particle ever described. The widespread presence and evolutionary conservation of vaults suggest important biologic roles, although their functions have not been fully elucidated. X-ray structure of vault from rat liver was determined at 3.5 Å resolution. It exhibits an ovoid shape with a size of 40 × 40 × 67 nm³. The cage structure of vault consists of a dimer of half-vaults, with each half-vault comprising 39 identical major vault protein (MVP) chains. Each MVP monomer folds into 12 domains: nine structural repeat domains, a shoulder domain, a cap-helix domain and a cap-ring domain. Interactions between the 42-turn-long cap-helix domains are key to stabilizing the particle. The other components of vaults, telomerase-associated proteins, poly(ADP-ribose) polymerases and small RNAs, are in location in the vault particle by electron microscopy.     

Efficient synthesis of 2,6,9-triazabicyclo[3.3.1]nonanes through amine-mediated formal [4+4] reaction of unsaturated imines

Formal [4+4] reaction of the unsaturated benzyl- or allylimines, which is efficiently mediated by primary amine, provides the 2,6,9-triazabicyclo[3.3.1]nonane derivatives. Variously substituted homo- and hetero-coupling products are obtained in good to excellent yields by quite a simple procedure under mild conditions: by mixing the unsaturated aldehydes with the amines at room temperature.