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Variable-temperature (31)P{(1)H} NMR spectroscopy of the agostic complexes M(CO)(3)(PCy(3))(2) (M = Mo, W) indicates dynamic behavior as evidenced by collapse below -20 degrees C of a singlet to an AB signal plus a shifted singlet. The inequivalency of the phosphines is possibly due to the presence of conformational isomers resulting from hindered rotation of the M-P bond or, less likely, a geometric isomer with pseudo-cis PCy(3) ligands. Further studies on the coordination chemistry of W(CO)(3)(PR(3))(2) (R = iPr, Cy) were performed. The bridging dinitrogen complex [W(CO)(3)(PiPr(3))(2)](2)(&mgr;-N(2)) (1) was cleanly formed in the reaction of W(CO)(3)(PiPr(3))(2) with N(2). Complex 1 was structurally characterized and compared with other bridging dinitrogen compounds of tungsten. The ethylene complex W(CO)(3)(PCy(3))(2)(eta(2)-C(2)H(4)) (2) was synthesized and characterized by X-ray crystallography in order to compare the binding mode of ethylene with that of H(2). Phenylsilane reacted with W(CO)(3)(PR(3))(2) (R = iPr, Cy) to form the thermally unstable oxidative addition (OA) products WH(SiH(2)Ph)(CO)(3)(PR(3))(2) (3, R = Cy; 4, R = iPr). Diphenylsilane reacted with W(CO)(3)(PiPr(3))(2) at 60 degrees C to form the bridging silyl species [W(CO)(3)(PiPr(3))(&mgr;-SiHPh(2))](2) (5), which was confirmed by spectroscopic techniques and X-ray crystallography to have two 3-center 2-electron W.H.Si interactions. Detailed comparisons of the binding and activation of silanes versus H(2) on various 16e metal centers suggest a high degree of similarity, but relative ease of OA depends on the electrophilicity of the metal-ligand fragment and other factors such as bond energetics. Increasing the electrophilicity of the metal center (e.g., adding positive charge) may aid in stabilizing alkane coordination.
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PMID:Comparison of H-H versus Si-H sigma-Bond Coordination and Activation on 16e Metal Fragments. Organosilane, N(2), and Ethylene Addition to the Agostic Complex W(CO)(3)(PR(3))(2) and Dynamic NMR Behavior of the Latter. 1167 1

Binary brush structures consisting of poly(cysteine methacrylate) (PCysMA) "corrals" enclosed within poly(oligoethylene glycol methyl ether methacrylate) (POEGMA) "walls" are fabricated simply and efficiently using a two-step photochemical process. First, the C-Cl bonds of 4-(chloromethyl)phenylsilane monolayers are selectively converted into carboxylic acid groups by patterned exposure to UV light through a mask and POEGMA is grown from unmodified chlorinated regions by surface-initiated atom-transfer radical polymerisation (ATRP). Incorporation of a ratiometric fluorescent pH indicator, Nile Blue 2-(methacryloyloxy)ethyl carbamate (NBC), into the polymer brushes facilitates assessment of local changes in pH using a confocal laser scanning microscope with spectral resolution capability. Moreover, the dye label acts as a radical spin trap, enabling removal of halogen end-groups from the brushes via in situ dye addition during the polymerisation process. Second, an initiator is attached to the carboxylic acid-functionalised regions formed by UV photolysis in the patterning step, enabling growth of PCysMA brushes by ATRP. Transfer of the system to THF, a poor solvent for PCysMA, causes collapse of the PCysMA brushes. At the interface between the collapsed brush and solvent, selective derivatisation of amine groups is achieved by reaction with excess glutaraldehyde, facilitating attachment of aminobutyl(nitrile triacetic acid) (NTA). The PCysMA brush collapse is reversed on transfer to water, leaving it fully expanded but only functionalized at the brush-water interface. Following complexation of NTA with Ni2+, attachment of histidine-tagged proteorhodopsin and lipid deposition, light-activated transport of protons into the brush structure is demonstrated by measuring the ratiometric response of NBC in the POEGMA walls.
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PMID:Fabrication of microstructured binary polymer brush "corrals" with integral pH sensing for studies of proton transport in model membrane systems. 2971 97