Isotope chirality in long-armed multifunctional organosilicon ("Cephalopod") molecules.

Long-armed multifunctional organosilicon molecules display self-replicating and self-perfecting behavior in asymmetric autocatalysis (Soai reaction). Two representatives of this class were studied by statistical methods aiming at determination of probabilities of natural abundance chiral isotopomers. The results, reported here, show an astonishing richness of possibilities of the formation of chiral isotopically substituted derivatives.

Limits of the Classical Concept of Concentration.

Solutions of very low concentrations cannot be treated by the usual concept of concentration. Stochastic calculations are performed for the analysis of such solutions containing one or a few molecule(s). It is concluded that these systems escape the usual concentration parameters.

Stochastic and empirical models of the absolute asymmetric synthesis by the Soai-autocatalysis.

Absolute asymmetric synthesis (AAS) is the preparation of pure (or excess of one) enantiomer of a chiral compound from achiral precursor(s) by a chemical reaction, without enantiopure chiral additive and/or without applied asymmetric physical field. Only one well-characterized example of AAS is known today: the Soai-autocatalysis. In an attempt at clarification of the mechanism of this particular reaction we have undertaken empirical and stochastic analysis of several parallel AAS experiments.

First molecules, biological chirality, origin(s) of life.

Origin(s) of biological chirality appear(s) to be intimately connected to origin(s) of life. Prebiotic evolution toward these important turning points can be traced back to single chiral molecules. These can be small (monomeric) units as amino acids or monosaccharides or oligomers as oligo-RNA type molecules.

Amino acid ligand chirality for enantioselective syntheses.

Amino acids are attractive sources of chirality in stoichiometric or catalytic transition metal/organic chemistry. In spite of easy availability and other advantages, the application of these ligands is hindered by several problems. Now, at the dawn of emerging D-amino acid biochemistry, efforts in this direction are becoming increasingly important.

Aqueous-phase quantitative NMR determination of amino acid enantiomer ratio by 13C-NMR using chiral neodymium shift reagent.

A neodymium-(S)-PDTA (PDTA = N,N,N',N'-tetrakis[(hydroxycarbonyl)methyl]-1,2-diaminopropane) complex was found exceptionally useful in the quantitative determination of enantiomer ratios of water-soluble natural amino acids by (13)C-NMR. The method is demonstrated on mixtures of L- and D-enantiomers of various amino acids. The interactions of the chiral shift reagent with the amino acid molecules were rationalized by molecular orbital calculations.

Enantioselective synthesis utilizing enantiomorphous organic crystal of achiral benzils as a source of chirality in asymmetric autocatalysis.

Chiral crystals of achiral benzils act as efficient chiral initiators of asymmetric autocatalysis to afford highly enantioenriched pyrimidyl alkanols whose absolute configurations depend upon the enantiomorph of the crystal used in conjunction with asymmetric autocatalysis with amplification of enantiomeric excess.

Oscillatory symmetry breaking in the Soai reaction.

A kinetic model of spontaneous amplification of enantiomeric excess in the autocatalytic addition of diisopropylzinc to prochiral pyrimidine carbaldehydes is extended by a negative feedback process. Simulations based on the extended model result in large-amplitude oscillations both in a continuous-flow stirred tank reactor (CSTR) and in a semibatch configuration under optimized initial conditions. When sustained oscillations are maintained in a CSTR, no enantiomeric product distribution could be observed in the calculated series; the system keeps its initial enantiomeric ratio endlessly.

Isotope chirality and asymmetric autocatalysis: a possible entry to biological chirality.

Natural-abundance isotopic substitution in isotopically prochiral groups of otherwise achiral molecules can provide stochastically formed enantiomeric excesses which exceed the sensitivity threshold of sensitive asymmetric autocatalytic (Soai-type) reactions. This kind of induction of chirality should be taken into consideration in in vitro model experiments and offer a new kind of entry into primary prebiotic or early biotic enantioselection in the earliest stages of molecular evolution.

Violation of distribution symmetry in statistical evaluation of absolute enantioselective synthesis.

Enantiomeric excesses obtained in absolute enantioselective synthesis by chiral autocatalysis (Soai-reaction) were statistically analyzed. Two sets of parallel experiments, which were performed under chemically different conditions, are available. One group contains 37, while the other contains 84 preparative results.

Astrobiology and biological chirality.

The emerging discipline of astrobiology could gain valuable support from research dealing with the problems of biological chirality. The most profitable fields of common interest are: (a) living organisms under extraterrestrial conditions, (b) extraterrestrial signatures of life and (c) origin(s) of biological chirality. These areas of complementary and overlapping fields are analysed on the basis of selected references.

Empirical description of chiral autocatalysis.

The only known example of chiral autocatalysis is the alkylation of N-heterocyclic aldehydes with iPr(2)Zn (Soai reaction). The mechanism and some details of this reaction are not yet clear. An empirical formula is proposed here for the description of this chiral autocatalytic reaction.

Enantioselective reduction of C=N double bond by chromium(II) complexes of natural amino acids.

Asymmetric reduction of oximes was performed by chromium(II) complexes of natural amino acids in aqueous phase or in H(2)O/DMF (1:1) solvent. Medium-to-quantitative chemoselectivity (54% to >95%) and low-to-medium enantioselectivity (5-50% ee) were found.