Search results for "TYR"

Sulfated and Non-Sulfated Glycopeptide Recognition Domains of P-Selectin Glycoprotein Ligand 1 and their Binding to P- and E-Selectin

2009

Total synthesis through block glycosylation and selective chemical O-sulfation of tyrosine residues yielded the glycopeptide recognition domain A (X=SO(3) (-)) of the P-selectin glycoprotein ligand 1, in which the terminal sialic acid of the complex hexasaccharide side chain was replaced by (S)-cyclohexyl lactic acid. In binding assays the O-sulfated structure A showed high affinity towards P-selectin, the non-sulfated towards E-selectin.

Density functional theory study of the mechanism of the proline-catalyzed intermolecular aldol reaction

2002

Transition structures associated with the C-C bond-formation step of the proline-catalyzed intermolecular aldol reaction between acetone and isobutyraldehyde have been studies using density functional theory methods at the B3LYP/6-31G** computational level. A continuum model has been selected to represent solvent effects. For this step, which is the stereocontrolling and rate-determining step, four reactive channels corresponding to the syn and anti arrangement of the active methylene of the enamine relative to the carboxylic acid group of l-proline and the re and si attack modes to both faces of the aldehyde carbonyl group have been analyzed. The B3LYP/6-31G** energies are in good agreemen…

1979

The kinetics of the anionic polymerization of styrene were investigated under pressure (1≤p/bar < 1800) with Na+ as counter ion in tetrahydropyran (THP) as solvent and with Cs+ as counter ion in 1,2-dimethoxyethane (DME) as solvent. The results yielded the activation volume of the contact ion pair ΔV and the sum (ΔV + ΔVcs) of the activation volume of the solvent separated ion pair ΔV and the volume change upon formation of solvent separated ion pairs from contact ion pairs ΔVcs. The numerical values are negative. The activation volume of the solvent separated ion pairs could be estimated.

Direct potentiometric immunoelectrodes

1993

TK pencil fine mines type Faber Castell Super polymer from Staedtler are used as graphite based material for an atrazine-sensitive immunoelectrode. Eighteen procedures are tested to immobilize antibodies against atrazine but only one turned out to be useful for the preparation of a graphite based immunoelectrode. It incorporates binding of glutardialdehyde to active sites of the graphite surface and subsequent cross-linking of the antibodies with glutardialdehyde. The method has been carefully optimized with respect to selectivity and the cross-sensitivity is determined for such an electrode based on atrazine-rabbit and atrazine-sheep antibodies as well. Due to the structural difference of …

Novel prolinamide-supported polystyrene as highly stereoselective and recyclable organocatalyst for the aldol reaction

2008

A new prolinamide derivative anchored to a polystyrene support has been straightforwardly prepared and employed as heterogeneous catalyst in the direct asymmetric aldol reaction with good results in terms of yield and stereoselectivity. The optimal reaction conditions were found when a 1:2 (v/v) water/chloroform mixture was used. This mixture was the best compromise between the good swelling properties of chloroform and the formation of a concentrated organic phase due to the presence of water. Noticeably, the enantioselectivities obtained employing acetone as ketone were, to the best of our knowledge, the highest achieved with a supported proline derivative. This catalyst can be easily rec…

Polystyrene-supported proline as recyclable catalyst in the Baylis–Hillman reaction of arylaldehydes and methyl or ethyl vinyl ketone

2008

Abstract Polystyrene-supported proline has been used as co-organocatalyst (10 mol%) with imidazole (10 mol%) in the Baylis–Hillman reaction between methyl or ethyl vinyl ketone and arylaldehydes. Recycling studies showed that the proline resin can be used up to five cycles with high isolated yields. This study represents the first example of supported proline as heterogeneous catalyst in the above reaction and broaden the scope of this catalytic material.

Rare Earth Half-Sandwich Catalysts for the Homo- and Copolymerization of Ethylene and Styrene

2001

The synthesis of rare earth metal half-sandwich hydrido complexes [Ln(η5:η1-C5Me4SiMe2NCMe3)(THF)(μ-H)]2(Ln = Y, Lu, Yb, Er, Tb) through σ-bond metathesis of the alkyl complexes [Ln(η5:η1- C5Me4SiMe2NCMe3)(CH2SiMe3)(THF)], easily accessible by the reaction of the amino-cyclopentadiene with [Ln(CH2SiMe3)3(THF)2], was developed. The dimeric lanthanide hydrido complexes are highly fluxional involving THF dissociation and cis-trans isomerization of the linked amidocyclopentadienyl ligand. The presence of a monomer-dimer equilibrium is suggested by cross-over experiments. They were tested as single-site, single-component catalysts for the polymerization of ethylene, α-olefin, and styrene, as wel…

Single-Component Polymerization Catalysts for Ethylene and Styrene:  Synthesis, Characterization, and Reactivity of Alkyl and Hydrido Yttrium Complex…

1999

Yttrium alkyl complexes Y(η5:η1-C5Me4SiMe2NCMe2R)(CH2SiMe3)(THF) (R = Me, Et) and Y(η5:η1-C9H6SiMe2NCMe3)(CH2SiMe3)(THF) can be prepared in high yields by a σ-bond metathesis reaction between Y(CH2SiMe3)3(THF)2 and amino-functionalized cyclopentadienes or indene. The structure of Y(η5:η1-C5Me4SiMe2NCMe2Et)(CH2SiMe3)(THF) was shown by single-crystal X-ray diffraction to be that of a three-legged piano stool. Reaction of Y(CH2SiMe3)3(THF)2 with the tridentate linked amido−cyclopentadienyl ligands (C5Me4H)SiMe2NHR (R = CH2CH2OMe, CH2CH2NMe2, CH2CH2CH2OMe, CMe2CH2OMe), which contain an additional donor site, results in the cleavage of the silicon−cyclopentadienyl bond and the formation of the t…

The effect of free polymer on the interactions and the glass transition dynamics of microgel colloids.

2002

By studying the phase behaviour and the short range order of polystyrene microgel colloids in a good solvent we demonstrated that these particles can be considered as hard spheres or nearly hard spheres if the internal cross link density is made sufficiently high. A binary mixture of 1:50 crosslinked (1 crosslink per 50 monomers) particles with a size ratio R(small)/R(large) = 0.83 and a number ratio N(small)/N(large) = 2.7 was characterized with respect to the short range order and glass transition dynamics. We found that this mixture can be mapped onto a one-component hard sphere system with an effective polydispersity of 11%, even though for the particle interactions an inverse power pot…

The effect of free polymer on the glass transition dynamics of microgel colloids

2002

Abstract From the phase behavior we establish that 1:10 crosslinked polystyrene microgel colloids in a good solvent can be considered as hard spheres whereas 1:50 crosslinked particles are slightly softer. Nevertheless, the glass transition dynamics of 1:10 microgels and a binary mixtures of 1:50 microgels can be described in both cases within the mode coupling theory for hard spheres. The only difference is that the increase of the polydispersity from about 7% to about 13% when going from the one-component system to the mixture is accompanied by a shift of the glass transition from ϕ g ≈0.56 to ϕ g ≈0.595. On addition of linear polystyrene to the 1:50 binary mixture we find a tremendous ac…