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21.
22.
Fadila Balegroune Pierre Braunstein Laurent Douce Yves Dusausoy Daniel Grandjean Michael Knorr Martin Strampfer 《Journal of Cluster Science》1992,3(3):275-296
The reactions of K[Fe{Si(OMe)3}(CO)3(PY)][PY=Ph2PCH2C(O)Ph, Ph2PCH2C(O)[(-C5H4)FeCp] (Cp=5-C5H5), Ph2P(CH2)2CN] with CdCl2·2.5H2O, ZnX
2 (X=Cl, I) or InCl3 afforded Fe-Cd-Fe or Fe-M(-X)2
M-Fe (M=Cd, Zn, In;X=Cl, I) and Fe-InCl2 complexes. Some of them contain an unusual and labile -2-SiO alkoxysilyl bridge which may be associated with a bridging mode for the ketophosphine ligand (first such example structurally established), thus providing original results in bimetallic chemistry on the intramolecular coordination of oxygendonor functions ofchemically different hemilabile ligands firmly attached to a neighboring metal center. The structures of the trinuclear complex (3), of the chlorobenzene solvate of the tetranuclear complex (4a·C6H5Cl) and of [mer-(OC)3{(EtO)3Si} (4e) have been determined by X-ray diffraction. Crystals of 3 are orthorhombic, space groupPbcn, witha=19.010(4),b=11.766(5),c=26.998(7)Å, andZ=4. Crystals of4a·C6H5Cl are monoclinic, space groupC2/c witha=22.455(3),b=17.680(2),c=16.627(4)Å, =90.80(4)°, andZ=4. Crystals of4e are monoclinic, space groupC2/c witha=25.392(5),b=18.554(6),c=16.28(1)Å, =120.73(3)°, andZ=4. The structures were solved using direct methods and Fourier difference techniques and refined by blocked full-matrix least squares toR=0.035 (R
w
=0.049) for 2719 observed reflections, toR=0.042 (R
w
=0.056) for 3082 observed reflections, and toR=0.057 (R
w
=0.075) for 1850 observed reflections for3, 4a·C6H5Cl and4e, respectively. The Fe-Zn complexes (9a), (9b) and (9c) were prepared and characterized by spectroscopic methods.Part 21 in the Series: Complexes with Functional Phosphines. Part 20: P. Braunstein, S. Coco Cea, A. DeCian, and J. Fischer (1992).Inorg. Chem.
31, 4203. 相似文献
23.
The kinetics of peptide release during in vitro digestion of 4 protein sources (casein, cod protein, soy protein, and gluten) were investigated. Samples were sequentially hydrolyzed with pepsin (30 min) and pancreatin (2, 4, or 6 h) in a dialysis cell with continuous removal of digestion products. Nondialyzed digests were fractionated by ion-exchange chromatography and ultrafiltration. Animal proteins were digested at a greater rate than plant proteins. Target amino acids of specific enzymes appeared more rapidly in the dialyzed fractions when compared to other amino acids. Throughout the hydrolysis, nondialyzed digests contained a higher proportion of peptide mixtures with basic-neutral properties. Except for gluten, peptide fractions with molecular weights that exceeded 10 kDa (basic-neutral, BN > 10) were rapidly hydrolyzed during the first 2 h of pancreatin digestion. The kinetics of release and the composition of peptide fractions were different when the protein sources were compared. The analysis of amino acids revealed that threonine and proline proportions were relatively high in BN > 10 and in peptide fractions with molecular weight between 10-1 kDa (BN 10-1), while tyrosine, phenylalanine, lysine, and arginine predominated in the low molecular weight (<1 kDa) fractions. More resistant peptides were generally rich in proline and glutamic acid. The role of in vitro digestion assays in dietary protein quality evaluation is discussed. 相似文献
24.
A quantitative 1H and 11B NMR study of the redistribution equilibria between the NMe2 group and the Cl, SMe,OMe and F substituents on the mono and difunctional boron centers (R2B- and RB<) is reported. The preferential affinity of the amino group towards dialkylated boron centers is shown by the examination of the “intersystem” constant sets. A relative affinity scale is proposed. 相似文献
25.
K. Yuvaraj Iskander Douair Dafydd D. L. Jones Laurent Maron Cameron Jones 《Chemical science》2020,11(13):3516
An extremely bulky, symmetrical three-coordinate magnesium(i) complex, [{(TCHPNacnac)Mg}2] (TCHPNacnac = [{(TCHP)NCMe}2CH]−, TCHP = 2,4,6-tricyclohexylphenyl) has been prepared and shown to have an extremely long Mg–Mg bond (3.021(1) Å) for such a complex. It was shown not to react with either DMAP (4-dimethylaminopyridine) or CO. Three unsymmetrical 1 : 1 DMAP adducts of less bulky Mg–Mg bonded species have been prepared, viz. [(ArNacnac)Mg–Mg(DMAP)(ArNacnac)] (ArNacnac = [(ArNCMe)2CH]− Ar = 2,6-xylyl (Xyl), mesityl (Mes) or 2,6-diethylphenyl (Dep)), and their reactivity toward CO explored. Like the previously reported bulkier complex, [(DipNacnac)Mg–Mg(DMAP)(DipNacnac)] (Dip = 2,6-diisopropylphenyl), [(DepNacnac)Mg–Mg(DMAP)(DepNacnac)] reductively trimerises CO to give a rare example of a deltate complex, [{(DepNacnac)Mg(μ-C3O3)Mg(DMAP)(DepNacnac)}2]. In contrast, the two smaller adduct complexes react with only two CO molecules, ultimately giving unusual ethenediolate complexes [{(ArNacnac)Mg{μ-OC(H) C(DMAP−H)O}Mg(ArNacnac)}2] (Ar = Xyl or Mes). DFT calculations show the latter reactions to proceed via reductive dimerizations of CO, and subsequent intramolecular C–H activation of Mg-ligated DMAP by “zig–zag” [C2O2]2− fragments of reaction intermediates. Calculations also suggest that magnesium deltate complexes are kinetic products in these reactions, while the magnesium ethenediolates are thermodynamic products. This study shows that subtle changes to the bulk of the reacting 1 : 1 DMAP–magnesium(i) adduct complexes can lead to fine steric control over the products arising from their CO reductive oligomerisations. Furthermore, it is found that the more activated nature of the adduct complexes, relative to their symmetrical, three-coordinate counterparts, [{(ArNacnac)Mg}2], likely derives more from the polarisation of the Mg–Mg bonds of the former, than the elongated nature of those bonds.Subtle changes to the bulk of 1 : 1 adducts of DMAP with magnesium(i) complexes leads to steric control over the products arising from their reductive oligomerisations of carbon monoxide. 相似文献
26.
The binding of a chiral quaternary ammonium ion to a cyclopeptide containing aromatic amino acid subunits is affected not only by the configuration of the cation but also by the configuration of the chiral counterion. Analysis of the binding equilibria shows that complex formation involves interaction of the whole ion pair with the host indicating that steric requirements of the anion influence complex geometry and stability. 相似文献
27.
Dieter Seebach Laurent Schaeffer Franois Gessier Pascal Bindschdler Corinna Jger Delphine Josien Sascha Kopp Grald Lelais YogeshR. Mahajan Peter Micuch Radovan Sebesta BerndW. Schweizer 《Helvetica chimica acta》2003,86(6):1852-1861
Multigram amounts of suitably protected β2‐amino acids with 17 of the 20 proteinogenic side chains are prepared by diastereoselective reactions of Li, B, or Ti enolates of the corresponding 3‐acyl‐4‐isopropyl‐5,5‐diphenyloxazolidin‐2‐ones (acyl‐DIOZ; 1 ) with appropriate electrophiles (amidomethylation, hydroxyalkylation, (benzyloxycarbonyl)methylation) in yields of 55–90% and with diastereoselectivities of 80 to >97% (Scheme). The primary products 2 – 8 thus obtained are converted to protected β2‐amino acids by standard procedures (Table 1). Many of the DIOZ derivatives are highly crystalline compounds (31 X‐ray crystal structures in Table 2). The chiral auxiliary DIOZ, readily prepared in either enantiomeric form, is recovered with high yield. 相似文献
28.
Laurent Chaloin Nicole Van Mau Frédéric Heitz Laurent Chiche Jean-Claude Talbot 《Colloids and surfaces. B, Biointerfaces》1998,10(6):389R-412
In order to elucidate the influence on the lipidic environment on the recognition process of its membrane associated receptor, the interactions of the vasoconstrictor peptide endothelin 1 with various phospholipids have been investigated using different lipidic model membranes: monolayers at constant surface pressure, vesicles and micelles. A monolayer study of ET1 adsorbed onto the water surface has shown that the C-terminus of the peptide points towards the aqueous phase. Penetration measurements into lipidic monolayers indicate that ET1 adsorbs to phospholipids with an orientation similar to that of the air–water interface and fluorescence measurements are in agreement with such an orientation of the peptide. This adsorption is selective for neutral phospholipids and indicates that the nature of the phospholipid headgroups is of major importance for the approach of the membrane associated receptor. 相似文献
29.
Simple calculations can help to predict which derivatives in a series of organic compounds are potential lasing material. In conjugated systems, a necessary condition for lasing is that there is not less than a specific minimum energy difference between a first excited allowed and a second excited forbidden transition. This order of transition and energy spacing can be obtained by judicious substitutions even in molecules that do not meet these conditions. Lasing action in the near UV has been observed in five new compounds. 相似文献
30.