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991.
The kinetics of the complex-formation reactions between monofunctional palladium(II) complexes [Pd(NNN)Cl]+, where NNN is 2,2′:6′,2″-terpyridine (terpy), diethylenetriamine (dien) or bis(2-pyridylmethyl)amine (bpma), with pyridine, 4-methylpyridine, 4-acetylpyridine, 4-cyanopyridine and 4-aminopyridine, have been studied in methanol at 25 °C using stopped-flow spectrophotometry. The highest reactivity was observed for the [Pd(terpy)Cl]+ complex, whereas 4-aminopyridine is the strongest nucleophile. The results, compared with those previously published on the [Pt(NNN)Cl]+ complexes, are discussed in terms of reactivity and discrimination ability of the reaction centre. The crystal structure of [Pd(terpy)(py)](ClO4)2 has been determined by X-ray diffraction. Crystals are triclinic, space group , and consist of distorted square planar [Pd(terpy)(py)]2+ cations and perchlorate anions. The Pd-N bond length to the central atom of terpy ligand is well below 2.0 Å and significantly shorter than any of the other M-N distances. The pyridine plane forms a dihedral angle of 61.9(2)° with the coordination N4 donors. 相似文献
992.
Hiroshi Sakiyama Yoshio Watanabe Rie Ito Yuzo Nishida 《Inorganica chimica acta》2004,357(14):4309-4312
The electronic spectra of dinuclear cobalt(II) complexes [Co2(bomp)(MeCO2)2]BPh4 (1) and [Co2(bomp)(PhCO2)2]BPh4 (2) were studied [H(bomp): 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-methylphenol]; the spectral components obtained by Gaussian curve analysis were well simulated based on the angular overlap model using the aomx program. The first transition band 4T1 → 4T2(4F) of an octahedral high-spin cobalt(II) complex was found to be sensitive to the distortion around the cobalt(II) ion. 相似文献
993.
Two novel phosphino-phosphaferrocenes [η5-C5H4(CH2)nPPh2]Fe(η5-PC4H2-2,5-Cy2) (PP1: n=1; PP2: n=2) have been designed and prepared in order to clarify weak chelate effect in the previously reported (η5-C5H4CH2PPh2)Fe[η5-PC4H2-2,5-((-)-menthyl)2] (1). 31P NMR studies of reactions of PP1 with PdCl2(cod) (6) revealed that PP1 showed stronger tendency to coordinate to the PdII center in bidentate fashion compared to 1. On the other hand, chelate effect in PP2 was negligibly weak and a reaction of PP2 with 6 in a PP2/6 = 2/1 molar ratio gave a complex PdCl2(PP2)2 (10) cleanly in which PP2 coordinated to the palladium center at the PPh2 moiety as a monodentate ligand. X-ray crystal structure studies of chelate complexes PdCl2(PP1) (7) and PdCl2(PP2) (9) showed that 9 had deviations from an idealized geometry in the square planar complex which could be attributed to a larger chelate ring of PP2, while PP1 in 7 constructed nearly ideal geometry for the square planar complex.From comparison of the coordination behavior between 1, PP1, and PP2, it is concluded that steric bulk of (-)-menthyl groups in 1 is the main factor of the weak chelate coordination of 1. 相似文献
994.
H. Hanika-Heidl 《Inorganica chimica acta》2004,357(6):1748-1760
Single crystals of three derivatives of the structurally still incompletely characterized coordination polymer [(Me3Sn)4Ru(CN)6] 1b have been prepared and subjected to crystallographic studies: [1b · 4H2O]=2b forms stacks of puckered ∞2[Ru{μ-CNSn(Me3)NC}2] sheets interlinked by hydrogen bonds in making use of two additional CNSn(Me3)OH2 ligands and quasi-zeolitic water. Mild drying of 2b leads to the “missing link” between 1b and 2b, [1b · 2H2O], 3b. The structure of [1b · 2tp] (tp=4-thiopyridone) consists of a three-dimensional, negatively charged host framework comprising (via Sn-S bonds) one “aromatic” thione linkage and a [Me3Sn · tp]+guest ion involving a more zwitterionic form of tp. Slow uptake of Me3SnCl from the gas phase by an aqueous solution of K4[Ru(CN)6] and tp afforded the novel assembly [1b · 2H2O · 0.8pms · 0.2pds] (pms/pds=4,4′-dipyridylmono-/disulfide), the supramolecular architecture of which resembles that of 2b. Bridging pms or pds molecules occupy equivalent interlayer sites, and the pms/pds ratio is likely to vary. At least three further assemblies containing again 1b and either tp or pds/pms have likewise been isolated, however, not as single crystals. 相似文献
995.
A potentially heptadentate ligand H3L (N,N′-bis(2-hydroxybenzyl)-1,3-bis[(2-aminoethyl)amino]-2-propanol) and its two Ni(II) complexes, [Ni(H2L)H2O](H2O)3ClO4 (1) and [Ni(H2L)(H2O)](H2O)Cl (2) were prepared and characterized. X-ray structural analyses indicate that complex 1 has a distorted octahedral coordination geometry, with four amine N atoms of H2L− defining the equatorial plane, one aqua O atom and one phenoxo O atom of the ligand occupying two axial positions, respectively. The Ni(II) center of 2 has coordination geometry similar to that of 1. IR and electronic spectra of 1 and 2 are in agreement with their crystal structural features. Approximately along the ab plane, 2D supramolecular structure of 1 is assembled through multiple hydrogen bonds between hydroxy groups of the ligands, coordinated and crystal lattice H2O and π-π stacking interactions between adjacent phenyl rings of the ligands, while for that of 2, probably along the a axis, 1D chain structure is also formed by multiple hydrogen bonds, but lack of π-π stacking interactions. 相似文献
996.
For a deeper insight into the structure of Bombyx mori silk fibroin, some model peptides containing tyrosine (Y), valine (V), and serine (S) in the basic (AG)n sequence were synthesized by the solid-phase method and analyzed by Raman spectroscopy in order to clarify their conformation and to evaluate the formation and/or disruption of the ordered structure typical of B. mori silk fibroin upon incorporation of Y, V, and S residues into the basic (AG)n sequence. The Raman results indicated that the silk I structure remains stable only when the Y residue is positioned near the chain terminus; otherwise, a silk I --> silk II conformational transition occurs. The peptides AGVGAGYGAGVGAGYGAGVGAGYG(AG)3 and (AG)3YG(AG)2VGYG(AG)3YG(AG)3 treated with LiBr revealed a prevalent silk II conformation; moreover, the former contained a higher amount of random coil than the latter. This result was explained in relation to the different degrees of interruption of the (AG)n sequence. The Raman analysis of the AGSGAG-containing samples confirmed that the AGSGAG hexapeptide is a good model for the silk II crystalline domain. As the number of AGSGAG repeating units decreased, the random coil content increased. The study of the Y domain (I850/I830 intensity ratio) allowed us to hypothesize that in the packing characteristic of Silk I and Silk II conformations the Y residues experience different environments and hydrogen-bonding arrangements; the packing typical of silk I structure traps the tyrosyl side chains in environments more unfavorable to phenoxyl hydrogen-bonding interactions. 相似文献
997.
The 26S proteasome complex, which consists of a 20S proteasome and a pair of 19S regulatory particles, plays important roles in the degradation of ubiquitinated proteins in eukaryotic cells. The alpha7 subunit of the budding yeast 20S proteasome is a major phosphorylatable subunit; serine residue(s) in its C-terminal region are phosphorylated in vitro by CKII. However, the exact in vivo phosphorylation sites have not been identified. In this study, using electrospray ionization quadrupole time-of-flight mass spectrometry analysis, we detected a mixture of singly, doubly, and triply phosphorylated C-terminal peptides isolated from a His-tagged construct of the alpha7 subunit by nickel-immobilized metal affinity chromatography. In addition, we identified three phosphorylation sites in the C-terminal region using MS/MS analysis and site-directed mutagenesis: Ser258, Ser263, and Ser264 residues. The MS/MS analysis of singly phosphorylated peptides showed that phosphorylation at these sites did not occur successively. 相似文献
998.
Duxbury MS Ashley SW Whang EE 《Biochemical and biophysical research communications》2004,313(4):992-997
Blebbistatin is a novel 1-phenyl-2-pyrrolidinone derivative capable of inhibiting non-muscle myosin II activity with a high degree of specificity. We examined the effects of blebbistatin on pancreatic adenocarcinoma cellular migration, invasion, adhesion, and spreading. Blebbistatin dose-dependently inhibited cellular migration and invasiveness, quantified by modified Boyden chamber assay. Matrix metalloproteinase 2 and 9 activities were unaffected by blebbistatin and cellular proliferation was inhibited only by concentrations of blebbistatin exceeding those required to inhibit myosin II activity and to interfere with migration and invasion. While blebbistatin treatment did not affect cell adhesion to the extracellular matrix component fibronectin, it markedly impaired cell spreading on this substrate. Cell surface expression of the archetypal fibronectin receptor (alpha(5)beta(1) integrin) was unaffected by blebbistatin. Our observations illustrate the critical role of non-muscle myosin II in pancreatic adenocarcinoma cellular invasiveness and extracellular matrix interaction and suggest that therapeutic strategies targeting myosin II warrant further investigation. 相似文献
999.
Cho YR Lee SJ Jeon HB Park ZY Chun JS Yoo YJ 《Biochemical and biophysical research communications》2004,323(3):769-775
Sulfation of proteoglycans is an important post-translational modification in chondrocytes. We previously found that 3'-phosphoadenosine 5'-phosphosulfate (PAPS) synthetase-2 levels increased more than 10-fold during mesenchymal cell chondrogenesis. Given that PAPS is the sole sulfur donor, and is produced only by PAPS synthetase in all cells, increased expression of PAPS synthetase-2 should be a prerequisite for increased sulfation activity of chondrocytes. We found that sodium chlorate, a specific inhibitor of PAPS synthetase, inhibited proteoglycan sulfation during chondrogenesis. In contrast, sodium chlorate unexpectedly induced early expression of type II collagen and increased the number of cartilage nodules during chondrogenesis. Inhibition of sulfation also accelerated the down-regulation of N-cadherin and fibronectin during chondrogenesis. These findings suggest that sulfation has an important regulatory role in coordinating the timely expression of extracellular matrix molecules during chondrogenesis, and that under-sulfation may cause the breakdown of this coordination, leading to premature chondrogenesis. 相似文献
1000.
Li SJ Nakagawa A Tsukihara T 《Biochemical and biophysical research communications》2004,324(2):529-533
We found that the maximum emission of the tryptophyl fluorescence of hen egg-white lysozyme is shifted from 337 to 323 nm and quenched to the extent of 55% with an increase in concentrations of NiCl2 from 0 to 2M in 50 mM Na acetate buffer (pH 4.7). In contrast, NaCl does not influence the fluorescence of lysozyme up to 2M. To elucidate the particular effects of Ni2+ on the tryptophyl fluorescence of lysozyme, we have measured the assembly behavior and secondary structure of lysozyme in various concentrations of NiCl2, and determined the structures of lysozyme crystals grown in 0.3, 0.5, and 1.0M NiCl2, respectively. The results of analytical centrifugation and circular dichroism experiments show that lysozyme keeps a monomer state and has an identical secondary structure, irrespective of NiCl2 concentrations. The crystal structures show that all crystals grown in different concentrations of NiCl2 have an identical main chain and side chain conformation. And one Ni2+ binding with Odelta atom of Asp52 in the active site and coordinating with five water molecules to form hexagonal coordination has been determined for each crystal structure. Based on these results, we have proposed that Ni2+ quenches the fluorescence of Trp62 and Trp108 due to the binding of Ni2+ to the active site of lysozyme. 相似文献