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SJ Lee

Publications and source records attributed to SJ Lee.

At least 19 recordsLinked to original sources
PubMed2001

Study of B Decays to Charmonium States: B-->eta(c)K and B --> chi(c0)K.

In a sample of 9.66x10(6)B&Bmacr; pairs collected with the CLEO detector we make the first observation of B decays to an eta(c) and a kaon. We measure branching fractions B(B+-->eta(c)K+) = (0.69(+0.26)(-0.21)+/-0.08+/-0.20)x10(-3) and B(B degrees -->eta(c)K degrees ) = (1.09(+0.55)(-0.42)+/-0.12+/-0.31)x10(-3), where the first error is statistical, the second is systematic, and the third is from the eta(c) branching fraction uncertainty. From these we extract the eta(c) decay constant in the factorization approximation, f(eta(c)) = 335+/-75 MeV. We also search for B decays to a chi(c0) and a kaon. No evidence for a signal is found and we set 90% C.L. upper limits: B(B+-->chi(c0)K+)<4.8x10(-4) and B(B degrees -->chi(c0)K degrees )<5.0x10(-4).

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PubMed2000

New hybrid ligands with a trans-1,2-diaminocyclohexane backbone: competing chelation modes in palladium-catalyzed enantioselective allylic alkylation

Three new hybrid ligands with trans-1,2-diaminocyclohexane backbone have been synthesized from (1R,2R)-2-aminocyclohexylcarbamic acid tert-butyl ester (4), which is prepared through an indirect monoprotection of the diamine. The ligands are (1R, 2R)-N-2-[2-(dimethylamino)benzoyl]aminocyclohexyl-2-(diphenylphosph anyl)benzamide and its di-n-butylamino- and diphenylamino-derivatives (3a-c), which belong to formal P,N-type chelates with possible wide bite angles in the metal chelation. To evaluate the new hybrid ligands against well-known P,N- and P, P-chelates (1 and 2), they were employed in the palladium-catalyzed allylic alkylations between two standard racemic allylic acetates, 2-acetoxy-1,3-diphenyl-2-propene (14a) and 2-acetoxy-1, 3-dimethyl-2-propene (14b), and dimethyl malonate under different reaction conditions. The catalytic system with the new ligands showed good reactivity toward both the substrates with moderate enantioselectivities (up to 78% ee toward 14a and 80% ee toward 14b). Of particular note, dramatic changes in the sense and in the degree of the enantioselectivity were observed depending on the ligands and reaction conditions, which suggested a different chelation mode was competing with the supposed P,N-chelation mode. An X-ray crystal structure of a chelated palladium complex [Pd(3c)(eta(3)-PhCHCHCHPh)]PF(6) was obtained, which showed a P, O-chelation mode in which a carboxamide oxygen acted as the O-ligand. This is the first example of the enantioselective palladium-catalyzed allylic alkylation in which a P,O-chelated complex of a carboxamide group participated as the ligand group.

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PubMed2000

The Effect of Fluid Shear Stress on Endothelial Cell Adhesiveness to Polymer Surfaces with Wettability Gradient.

In this study, the adhesive strength of endothelial cells (ECs) attached on polymer surfaces with different hydrophilicity was investigated using wettability gradient polyethylene (PE) surfaces prepared by corona discharge treatment from a knife-type electrode whose power increases gradually along the sample length. The EC-attached wettability gradient surfaces were mounted on parallel-plate flow chambers in a flow system prepared for cell adhesiveness test. Three different shear stresses (150, 200, and 250 dyne/cm(2)) were applied to the flow chambers and each shear stress was maintained for 120 min to investigate the effect of shear stress and surface hydrophilicity on the EC adhesion strength. It was observed that the ECs were adhered more onto the positions with moderate hydrophilicity of the wettability gradient surface than onto the more hydrophobic or hydrophilic positions. The maximum adhesion of the cells appeared at around water contact angles of 55 degrees. The EC adhesion strength was higher on the hydrophilic positions than on the hydrophobic ones. However, the maximum adhesion strength of the cells also appeared at around water contact angles of 55 degrees. More than 90% of the adhered cells remained on that position after applying the shear stress, 250 dyne/cm(2) for 2 h, whereas the cells were completely detached on the hydrophobic position (water contact angle, about 86 degrees ) within 10 min after applying the same shear stress. It seems that surface hydrophilicity plays a very important role for cell adhesion strength. Copyright 2000 Academic Press.

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PubMed2000

Type-Two intramolecular diels-alder reactions of pyrazolo-o-quinodimethanes

Two isomeric series of homologous N-(acryloyloxy)alkylated pyrazolo-3-sulfolenes 10a-c and 18a-c have been efficiently synthesized from a common starting material, 4,6-dihydro-1H-thieno[3, 4-c]pyrazole (5). Thermolysis of these fused 3-sulfolenes provides the corresponding o-quinodimethanes which simultaneously undergo "type-two" intramolecular Diels-Alder reactions to form two- and three-atom-bridged tricyclic pyrazoles which are otherwise difficult to prepare. It was also demostrated that, depending on the N-substitution position of the pyrazolo-fused 3-sulfolenes, the temperature required for the thermal extrusion of SO(2) and the regioselectivity of the T2-IMDA reactions were influenced substantially.

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