73 research outputs found
Metal Ion Dependence of the Asymmetric Transamination of Phenylpyruvic Acid by Pyridoxamine in the Presence of β-Cyclodextrin
Transamination reactions of phenylpyruvic acid and pyridoxamine
in the presence of metal ions and B-cyclodextrin as a chiral
auxiliary have been investigated in neutral aqueous solution.
The rate and extent of the transamination, and the asymmetric
induction observed in the reaction depend upon the nature of the
metal ion. In particular, while Zn2+and C02+yield preferentially
the aldimine complex of L-phenylalanine, Cu2\u27 yields preferentially
the complex of D-phenylalanine and Ni2+only the racemic
product. It is proposed that the ketimine complexes are bound to
B-cyclodextrin through the phenyl group of the keto acid residue
and that the stereoselectivity of the reaction is originated by some
direct interaction of the hydroxyl groups of the cyclodextrin
moiety and the metal ions. Although the extent of asymmetric
induction is modest in these simple systems (10-20°/0 optical
purities), the present results show that transition metal complexes
can play a prominent role in determining the steric course of the
asymmetric reaction
Comparison of Newly Diagnosed Ocular Hypertension and Open-Angle Glaucoma: Ocular Variables, Risk Factors, and Disease Severity
Purpose. To describe the distribution of ocular variables, risk factors, and disease severity in newly diagnosed ocular hypertension (OH) or open-angle glaucoma (OAG).
Methods. Eligible subjects underwent a complete history and examination. Adjusted odds ratios (ORs) and 95% confidence intervals (CIs) obtained from multiple logistic regression models were used to compare OAG to OH and advanced to early/moderate OAG.
Results. 405 subjects were enrolled: 292 (72.1%) with OAG and 113 (27.9%) with OH. 51.7% had early, 27.1% moderate, and 20.9% advanced OAG. The OR for OAG versus OH was 8.19 (P < 0.0001) for disc notch, 5.36 (P < 0.0001) for abnormal visual field, 1.45 (P = 0.001) for worsening mean deviation, 1.91 (P < 0.0001) for increased cupping, 1.03 for increased age (P = 0.030), and 0.36 (P = 0.010) for smoking.
Conclusions. Increased age was a risk for OAG, and smoking decreased the risk of OAG compared to OH. Almost half of the OAG subjects had moderate/advanced disease at diagnosis
KEY ELEMENTS IN THE STRUCTURE AND FUNCTION RELATIONSHIP OF THE MGCL2/TICL4/LEWIS BASE ZIEGLER-NATTA CATALYTIC SYSTEM
A new generation of polyolefin elastomers from single centre catalysis: towards natural rubber?
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