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Steric Requirements (steric + requirement)

Distribution by Scientific Domains
Chemistry75%

Selected Abstracts

Characterization of an exosite binding inhibitor of matrix metalloproteinase 13

PROTEIN SCIENCE, Issue 1 2008
Lata T. Gooljarsingh
Abstract Matrix metalloproteinase 13 (MMP13) is a key enzyme implicated in the degradation of the extracellular matrix in osteoarthritis. Clinical administration of broad spectrum MMP inhibitors such as marimastat has been implicated in severe musculo-skeletal side effects. Consequently, research has been focused on designing inhibitors that selectively inhibit MMP13, thereby circumventing musculo-skeletal toxicities. A series of pyrimidine dicarboxamides were recently shown to be highly selective inhibitors of MMP13 with a novel binding mode. We have applied a molecular ruler to this exosite by dual inhibition studies involving a potent dicarboxamide in the presence of two metal chelators of different sizes. A larger hydroxamate mimic overlaps and antagonizes binding of the dicarboxamide to the exosite whereas the much smaller acetohydroxamate synergizes with the dicarboxamide. These studies elucidate the steric requirement for compounds that fit exclusively into the active site, a mandate for generating highly selective MMP13 inhibitors. [source]

Immobilisation of the BINAP Ligand on Dendrimers and Hyperbranched Polymers: Dependence of the Catalytic Properties on the Linker Unit

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2009
Jutta
Abstract A series of immobilised Carbo-BINAP ligands has been synthesised using poly(propylene imine) (PPI) dendrimers as soluble supports. They contain up to 64 BINAP ligands at their periphery without an additional linking unit. Despite the high steric requirements of the ligand, all dendrimers could be completely functionalised, resulting in the immobilised systems in good yields. Furthermore, the immobilisation strategy that worked out for the fixation of AMINAP ligands with additional linking units as well as of Carbo-BINAP ligands without additional linking units on dendrimers has thus been extended to less regularly hyperbranched poly(ethylene imines) (PEI) as soluble supports. In that way it has been possible to attach on average 9, 26, and 138 Glutaroyl-AMINAP or Carbo-BINAP ligands to PEIs of different molecular weights. The catalytic properties of these systems in the copper-catalysed hydrosilylation of acetophenone were investigated. The dendritic PPI-bound Carbo-BINAP ligands displayed a strong dependence of enantioselectivity and activity on the generation of the dendrimer. For the Carbo-BINAP and Glutaroyl-AMINAP ligands immobilised on the hyperbranched polymers, however, activities and enantioselectivities comparable to those of the mononuclear catalysts were found. The macromolecular, immobilised BINAP ligands could be recycled several times without any observable loss of activity or enantioselectivity. [source]

Reactive Blending of Polyamides with Different Carbonyl Containing Olefin Polymers

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 6 2003
David Sémeril
Abstract In this paper the blending of polyamides nylon 6 and nylon 12, with a perfectly alternating ethylene/CO copolymer containing 50 mol-% carbonyl groups (polyketone) is investigated in comparison to blends of the same polyamides with polyolefins containing varying degrees of carbonyl group incorporation. These include a poly[ethylene- co -(methyl acrylate)] copolymer containing 1.9 mol-% methyl ester groups and poly[ethylene- co -(ethyl undecylenate)] copolymers with between 0.20 and 1.25 mol-% ester incorporation. Blends were obtained of polyamides and the polyolefins in compositions between 20/80 and 80/20 in solution and in a Brabender mixer. SEM studies together with TGA, DSC and FTIR measurements show excellent compatibilization for both polyketone and poly[ethylene- co -(methyl acrylate)] copolymers with the nylons. The poly[ethylene- co -(ethyl undecylenate)] polymers displayed much less compatibilization although they still performed significantly better compared to pure polyethylene. The difference in compatibilization is discussed with respect to the importance of both the number of interactive groups present in the polyolefin and the steric requirements of hydrogen bond formation. SEM micrograph of the fracture surface of the blend nylon 6/polyethylene 70:30. [source]

A ferrocenyl-substituted pseudo­titanocene complex

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2000

The title compound, (,5 -cyclo­penta­dienyl)[(1,2,3,4,5-,)-4-ferro­cenyl-1,2,5,6-tetrakis­(tri­methyl­silyl)­cyclo­hexa-2,4-dien-1-yl]­titanium(II), [TiFe(C5H5)2(C23H42Si4)] or [Ti{,5 -C6H2{Fe­(,5 -C5H4)(,5 -C5H5)}{Si(CH3)3}4}(,5 -C5H5)], possesses two directly linked metallocene units that subtend an angle of 52.9,(1)° (defined by the least-squares planes of the directly connected ,-ligands) associated with the steric requirements of the bulky tri­methyl­silyl substituents. The cyclo­hexa­dienyl ligand adopts an envelope conformation; the perpendicular distance of its ,5 -plane to the Ti atom is 1.512,(1),Å. [source]