Theozyme for antibody aldolases. Characterization of the transition-state analogue

A theozyme for antibody aldolases has been studied at the MP2/6-31G** computational level. Formation of two cooperative hydrogen-bonds between the acidic hydrogen atoms of the enamine and of a methanol molecule with the oxygen atom of the aldol acceptor markedly favors the C-C bond-formation associated with the aldol reaction. A comparative analysis of the geometry, the charge distribution and the shape of the molecular electrostatic potential of the transition structure (TS) with the covalent adduct, resulting from the reaction of methylamine and the beta-diketone used as a hapten allows us to characterize the transition-state analogue (TSA) generated at immunization. This finding allows us to propose a hapten based on a chiral beta-ketosulfoxide that could give the formation of a TSA that addresses the tetrahedral geometry of the TS.     

Stereocontrolled reactions mediated by a remote sulfoxide group: synthesis of optically pure anti-beta-amino alcohols

[reaction: see text] A one-step synthesis of enantiomerically pure anti-1,2-amino alcohol derivatives has been achieved by reaction of prochiral oxygenated 2-p-tolylsulfinylbenzyl carbanions with N-sulfinylimines bearing the same configuration at sulfur.     

Carbohydrate-derived spiroketals: stereoselective synthesis of di-D-fructose dianhydrides via intramolecular aglycon delivery

[reaction: see text] A one-pot synthesis of C(2)-symmetric di-d-fructose dianhydrides having the 1,6,9,13-tetraoxadispiro [4.2.4.2]tetradecane skeleton has been accomplished via intramolecular aglycon delivery from (6 --> 6) xylylene-tethered fructofuranose precursors. The stereochemical outcome of the glycosylation-spiroketalization process is governed by the geometrical constraints imposed by the rigid tetracyclic structure of the final compound.     

Simultaneous determination of "earthy-musty" odorous haloanisoles and their corresponding halophenols in water samples using solid-phase microextraction coupled to gas chromatography with electron-capture detection

Certain haloanisoles present at trace levels cause a large part of earthy-musty off-flavor problems in drinking water. These potent odorous chemicals come mainly through biomethylation of their corresponding halopenols. To enable the investigation of both families of compounds, a method involving solid-phase microextraction (SPME) was developed and the main parameters governing SPME were optimized. This method allows the simultaneous quantification of haloanisoles and halophenols at levels ranging from 1 to 100 or 250 ng/l, with detection limits of about 0.5 ng/l and could be applied to potable as well as raw surface waters.     

Editorial: Past,present and future of the combinatorial chemistry in Spain

Molecular Diversity -     

69,71Ga NMR studies of a superconducting Ga 84 cluster compound

We present ^69,71Ga-NMR experiments on microcrystalline samples of the recently discovered supramolecular compound Ga ₈₄ [ N ( SiMe ₃ ) ₂ ] ₂₀ Li ₆ Br ₂ ( thf ) ₂₀ ^. 2 toluene, which is composed of ligand-coordinated Ga₈₄ metal clusters, packed together in a fully ordered crystalline matrix. The compound is highly conducting and even shows superconductivity below T _c ~ 7.2 K. Our preliminary results between 10-300 K show a metallic-like behavior: the nuclear spin-lattice relaxation rate T ₁ ^-1 follows the Korringa law ⁶⁹ ( T ₁ T ) ^-1 = 0.36 s ^-1 K ^-1 , but with a relaxation rate approximately three times smaller than in bulk -Ga metal. No quantum-size effects are observed, the Korringa law being followed down to 10 K, whereas the quantum-gaps for individual clusters should amount to ~ 10 ³ K. These results therefore suggest a transport process based on intermolecular charge transfer, similar as in alkali-doped fullerenes and silicon-clathrates.     

Analytic surface germs with minimal Pythagoras number

We determine all complete intersection surface germs whose Pythagoras number is 2, and find that they are all embedded in ³ and have the property that every positive semidefinite analytic function germ is a sum of squares of analytic function germs. In addition, we discuss completely these properties for mixed surface germs in ³. Finally, we find in higher embedding dimension three different families with these same properties. Partially supported by DGICYT, BFM2002-04797 and HPRN-CT-2001-00271 Mathematical Subject Classification (2000): 11E25, 14P15.An erratum to this article can be found at     

An O(n 2) Active Set Algorithm for Solving Two Related Box Constrained Parametric Quadratic Programs

Recently, O(n ²) active set methods have been presented for minimizing the parametric quadratic functions (1/2)x Dx–a x+| x–c| and (1/2)x Dx–a x+(/2)( x–c)², respectively, subject to lxb, for all nonnegative values of the parameter . Here, D is a positive diagonal n×n matrix, and a are arbitrary n-vectors, c is an arbitrary scalar; l and b are arbitrary n-vectors such that lb. In this paper, we show that each one of these algorithms may be used to simultaneously solve both parametric programs withno additional computational cost.