Synthesis, structure, and reactions of (acylimino)triaryl-lambda(5)-bismuthanes: first comparative study of the (acylimino)pnictorane series.

The synthesis, structure, and reactions of (acylimino)triaryl-lambda(5)-bismuthanes and a comparative study of the structure and reactivity of a series of (acylimino)pnictoranes are reported. Treatment of ortho-substituted triarylbismuth dichlorides 1 (Ar(3)BiCl(2); Ar = 2-MeC(6)H(4), 2-MeOC(6)H(4), 2,4,6-Me(3)C(6)H(2)) with amides 2 (H(2)NCOR; R = CF(3), CCl(3), 3,5-(CF(3))(2)C(6)H(3)) in the presence of 2.2 equiv of KO-t-Bu in dichloromethane afforded (acylimino)triaryl-lambda(5)-bismuthanes 3 (Ar(3)Bi=NCOR) in yields of 77-96%. The ortho-substituted aryl ligands and the electron-withdrawing N-substituents afford kinetic and thermodynamic stabilization, respectively, to the reactive Bi=N bond. The structures and properties of a series of (acylimino)pnictoranes (Ar(3)M=NCOR and H(3)M=NCOCF(3); M = P, As, Sb, Bi) are compared by IR and (13)C and (15)N NMR, X-ray crystallography, and ab initio molecular orbital calculations. It was found that the contribution of the M(+)-N=C-O(-) canonical form becomes more prominent and the single-bond character of the M=N bond increases progressively as the pnictogen atom becomes heavier. The Bi=N bond of (acylimino)-lambda(5)-bismuthanes 3 possesses a highly polarized single-bond character, probably due to the differences in orbital size and electronegativity between the bismuth and nitrogen atoms. Thermal decomposition of (aroylimino)triaryl-lambda(5)-bismuthane 3f (o-Tol(3)Bi=NCOAr; Ar = 3,5-(CF(3))(2)C(6)H(3)) produces a gel in dry conditions or aniline 12 (ArNH(2)) in slightly wet conditions with a good recovery of tris(2-methylphenyl)bismuthane (4a). It is likely that the aryl isocyanate 13 (ArNCO) is produced during the thermolysis via a concerted C --> N migration of the Ar group with an elimination of the triarylbismuthonio group as bismuthane 4a. (Acylimino)triaryl-lambda(5)-bismuthanes 3 oxidize 1,1,2,2-tetraphenylethanediol, benzenethiol, methanol, and ethanol to benzophenone, diphenyl disulfide, methyl formate, and acetaldehyde, respectively, in two different reaction pathways depending on the structure of the substrates. Compound 3d (o-Tol(3)Bi=NCOCCl(3)) transfers the nitrenoid moiety to triphenylphosphane, triphenylarsane, and tris(2-methylphenyl)stibane to give the corresponding (acylimino)pnictoranes (Ar(3)M=NCOCl(3); M = P, As, Sb) and 4a, suggesting that 3d is thermodynamically much less stable than their lighter pnictogen counterparts. The copper-catalyzed decomposition of 3 (o-Tol(3)Bi=NCOR) afforded N-acyl-o-toluidines 18 (o-TolNHCOR) via a Bi --> N migration of the tolyl group. The observed reactivities of (acylimino)triaryl-lambda(5)-bismuthanes 3 demonstrate a good leaving ability of the bismuthonio group.

Quantitative determination of amygdalin epimers by cyclodextrin-modified micellar electrokinetic chromatography.

A new capillary electrophoresis method was developed for the quantitative determination of the amygdalin epimers, amygdalin and neoamygdalin, which are biologically significant constituents in the crude drugs, namely Persicae Semen and Armeniacae Semen. The effects of surfactants, additives and other analytical parameters were studied. As a result, the resolution of two epimers was performed by cyclodextrin-modified micellar electrokinetic chromatography with a buffer containing alpha-cyclodextrin and sodium deoxycholate. By the application of this method, a simple, fast and simultaneous quantitative determinations of amygdalin epimers in the crude drugs (Persicae Semen and Armeniacae Semen) and the Chinese herbal prescriptions (Keishi-bukuryo-gan and Mao-to) were achieved.

Cohesin-dockerin interactions of cellulosomal subunits of Clostridium cellulovorans.

The cellulosome of Clostridium cellulovorans consists of three major subunits: CbpA, EngE, and ExgS. The C. cellulovorans scaffolding protein (CbpA) contains nine hydrophobic repeated domains (cohesins) for the binding of enzymatic subunits. Cohesin domains are quite homologous, but there are some questions regarding their binding specificity because some of the domains have regions of low-level sequence similarity. Two cohesins which exhibit 60% sequence similarity were investigated for their ability to bind cellulosomal enzymes. Cohesin 1 (Coh1) was found to contain amino acid residues corresponding to amino acids 312 to 453 of CbpA, which contains a total of 1,848 amino acid residues. Coh6 was determined to contain amino acid residues corresponding to residues 1113 to 1254 of CbpA. By genetic construction, these two cohesins were each fused to MalE, producing MalE-Coh1 and MalE-Coh6. The abilities of two fusion proteins to bind to EngE, ExgS, and CbpA were compared. Although MalE-Coh6 could bind EngE and ExgS, little or no binding of the enzymatic subunits was observed with MalE-Coh1. Significantly, the abilities of the two fusion proteins to bind CbpA were similar. The binding of dockerin-containing enzymes to cohesin-containing proteins was suggested as a model for assembly of cellulosomes. In our examination of the role of dockerins, it was also shown that the binding of endoglucanase B (EngB) to CbpA was dependent on the presence of EngB's dockerin. These results suggest that different cohesins may function with differing efficiency and specificity, that cohesins may play some role in the formation of polycellulosomes through Coh-CbpA interactions, and that dockerins play an important role during the interaction of cellulosomal enzymes and cohesins present in CbpA.

Molecular mechanisms in the reversible regulation of morphology, proliferation and collagen metabolism in hepatic stellate cells by the three-dimensional structure of the extracellular matrix.

Hepatic stellate cells (vitamin A-storing cells, lipocytes, interstitial cells, fat-storing cells, Ito cells) exist in the perisinusoidal space of the hepatic lobule and store 80% of the body's retinoids as retinyl palmitate in lipid droplets in the cytoplasm. Under physiological conditions, these cells play pivotal roles in the regulation of retinoid homeostasis; they express specific receptors for retinol-binding protein (RBP), a binding protein specific for retinol, on their cell surface, and take up the complex of retinol and RBP by receptor-mediated endocytosis. However, in pathological conditions such as liver fibrosis, these cells lose retinoids and synthesize a large amount of extracellular matrix (ECM) components including collagen, proteoglycan and adhesive glycoproteins. The morphology of these cells also changes from star-shaped stellate cells to that of fibroblasts or myofibroblasts. The three-dimensional structure of ECM components was found to regulate reversibly the morphology, proliferation and functions of hepatic stellate cells. Molecular mechanisms in the reversible regulation of stellate cells by ECM imply cell surface integrin binding to ECM components followed by signal transduction processes and then cytoskeleton assembly.

Hepatic stellate cells (vitamin A-storing cells) change their cytoskeleton structure by extracellular matrix components through a signal transduction system.

When cultured on a polystyrene surface or aminoalkylsilane-coated cover glasses, rat and human hepatic stellate cells exhibit a flattened, fibroblast-like shape with well-developed stress fibers. However, culturing the cells on type I collagen gel results in the elongation of long, multipolar cellular processes, whereas cells cultured on Matrigel maintain their round shapes. Dual fluorescence staining of microtubules and fibrillar actin indicated that the processes extend together with collagen fibers and contained microtubules as the core, whereas the periphery contained fibrillar actin. Immunofluorescence staining of vinculin showed that the focal adhesions were distributed mainly in lamellipodia when cultured on aminoalkylsilane-coated cover glasses, whereas in the cells cultured on type I collagen gel they were localized to the tips of the processes and along their bottom surface contacting collagen fibers. Wortmannin, as well as staurosporin and herbimycin A, inhibited the elongation process and induced the retraction of elongated processes. The wortmannin treatment also resulted in an alteration in focal adhesion distribution from the processes to cell bodies. These results indicate that the cell surface integrin binding to interstitial collagen fibers induces the elongation of processes through signaling events and the subsequent cytoskeleton assembly in hepatic stellate cells.

Cellulose promotes extracellular assembly of Clostridium cellulovorans cellulosomes.

Cellulosome synthesis by Clostridium cellulovorans was investigated by growing the cells in media containing different carbon sources. Supernatant from cells grown with cellobiose contained no cellulosomes and only the free forms of cellulosomal major subunits CbpA, P100, and P70 and the minor subunits with enzymatic activity. Supernatant from cells grown on pebble-milled cellulose and Avicel contained cellulosomes capable of degrading crystalline cellulose. Supernatants from cells grown with cellobiose, pebble-milled cellulose, and Avicel contained about the same amount of carboxymethyl cellulase activity. Although the supernatant from the medium containing cellobiose did not initially contain active cellulosomes, the addition of crystalline cellulose to the cell-free supernatant fraction converted the free major forms to cellulosomes with the ability to degrade crystalline cellulose. The binding of P100 and P70 to crystalline cellulose was dependent on their attachment to the endoglucanase-binding domains of CbpA. These data strongly indicate that crystalline cellulose promotes cellulosome assembly.

Evidence that dipicolinic acid is covalently bound to specific macromolecules in spores of Bacillus subtilis.

Two dipicolinic acid (DPA)-binding macromolecules with molecular masses of about 440 kDa and 230 kDa were detected in the soluble fractions of dormant and germinated spores of Bacillus subtilis using native PAGE and an immunological technique. In SDS-PAGE, only one band with the molecular mass of about 50 kDa was found. Proteinase K partially digested the 440-kDa macromolecule of dormant spores to convert it into a 230-kDa one, and completely digested both the 440-kDa and 230-kDa bands of germinated spores. DNase I did not affect either DPA-binding macromolecules. This suggests that the two DPA-binding macromolecules are of similar origin, their main component is protein and a conformational change may occur during germination. DPA was not dissociated from the DPA-binding macromolecules by extensive dialysis and SDS treatment, suggesting the presence of a covalent bonding.