Optical resolution methods

Despite the large number of elaborate enantioselective syntheses for the preparation of a single enantiomer to achieve industrial and scientific goals, the separation and purification of enantiomers (components of racemic compounds) is also necessary. Hence, we present the most often used thought-provoking modern methods based on momentous recognitions (e.g. spontaneous resolution, induced crystallization, resolution by formation of diastereomers, resolution by formation of non-covalent diastereomers, resolution by diastereomeric salt formation, resolution by diastereomeric complex formation, "half equivalent" methods of resolution, separation by crystallization, separation by distillation, separation by supercritical fluid extraction, resolution with mixtures of resolving agents, resolution with a derivative of the target compound, enantioselective chromatography, resolution by formation of covalent diastereomers, resolution by substrate selective reaction, kinetic resolution without enzymes, kinetic resolution by enzyme catalysis, hydrolytic and redox enzymes, kinetic and thermodynamic control, resolutions combined with 2nd order asymmetric transformations, enrichment of partially resolved mixtures, role of the solvent and methods of optimization in the separation of diastereoisomers, non-linear effects and selected examples of resolution on an industrial scale).     

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. During damped oscillations, or steady-state conditions, however, chiral amplification from a very small initial enantiomeric excess to more than 99% occurs in a semibatch configuration. Calculations indicated spontaneous enantiomeric product enrichment (i.e., accumulation of one of the enantiomers at the cost of the other one) from strictly achiral starting conditions in a semibatch configuration due to the inherent numerical error of the integrator method, which can be regarded as a model of the statistical fluctuation in the numbers of enantiomeric molecules.     

Thermal behavior of oligo[(ε-caprolactone)-co-δ-gluconolactone] enzymatically synthesized in reaction conditions optimized by experimental design

Journal of Thermal Analysis and Calorimetry - The thermal behavior of co-oligomers of ε-caprolactone (ECL) with gluconolactone, compared to the ε-caprolactone oligomer, has been assessed...     

Solvation/desolvation during the redox transformation of poly(3-methylthiophene)

Solvation/desolvation effects were studied during the redox transformation of poly(3-methylthiophene) by electrochemical quartz crystal microbalance technique. The effect was demonstrated by studying the phenomenon in different solvents, and comparing the results after a solution change. From the data obtained with the same film transferred between nitrobenzene and acetonitrile in both directions, the solvation effect was directly evidenced, and the virtual molar mass of the moving species in and from the same film was determined to illustrate semi-quantitatively the effect of the solvation.This paper is dedicated to Professor G. Horányi on the occasion of his 70th birthday and in recognition of his outstanding contribution of electrochemistryCsaba Visy, Emese Kriván are ISE members     

Hydroformylation – amidocarbonylation of androstene and pregnene derivatives

Androstene and pregnene derivatives were functionalized by amides with rhodium or binary rhodium–cobalt catalysts. Whereas the Rh–PPh₃ catalyzed reaction results in the unsaturated amido‐methylidene derivatives, the rapid hydrogenation of these compounds takes place in the presence of a basic PR₃ ligand. Using a binary rhodium–cobalt system, amidocarbonylation of the steroids occurs with high chemo‐ and regio‐selectivity. Our experiments did not support literature reports claiming the essential role of a bimetallic cluster as the active catalyst. Copyright © 2002 John Wiley & Sons, Ltd.     

Glassy carbon electrode modified with hemin and new melamine compounds for H<Subscript>2</Subscript>O<Subscript>2</Subscript> amperometric detection

In an attempt to increase the stability and efficiency of hemin-modified electrodes, the present work reports the preparation of a new modified glassy carbon electrode obtained by immobilization of hemin (Hm) on the electrode surface together with a new N-substituted melamine (2,4,6-triamino-1,3,5-triazine) based G-2 dendrimer comprising p-aminophenol as peripheral unit (Den) or with one of its analogues, a melamine G-0 dimer (Dim). Basic structural features, able to determine intimate relationships between Hm and Dim (or Den) at room temperature in solid state, were evidenced with the use of vibrational analysis carried out by FT-IR. This method revealed contacts between Hm and Dim or Den respectively as H-bond interactions, proton-interchange, and π-π stacking interactions. The new modified electrodes were characterized by cyclic voltammetry and electrochemical impedance spectroscopy and tested for amperometric detection of H₂O₂. In this purpose, GC/Hm-Dim electrode exhibited better catalytic properties than GC/Hm-Den electrode, but lower stability.     

Application of simultaneous monitoring of the in situ impedance and optical changes on the redox transformation of two polythiophenes: Direct evidence for their non-identical conductance–charge carrier correlation

The redox transformation of poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3-octylthiophene) (POT) has been studied and compared by combining simultaneous in situ UV–Vis–NIR spectroelectrochemical and ac impedance techniques. Simultaneous changes of the conductance and the rate of the absorbance increase/decrease of the optically different charge carriers in the selfsame film gave direct and unquestionable evidence for that in PEDOT synthesised in aqueous solution the mono-cationic, while in POT the di-cationic segments are primarily responsible for the development of the name-giving property of conducting polymers. This difference in the role of the charge carriers could be partially observed between PEDOTs prepared in aqueous and acetonitrile (AN) solutions.     

Combination of in situ UV–Vis-NIR spectro-electrochemical and a.c. impedance measurements: A new, effective technique for studying the redox transformation of conducting electroactive materials

Simultaneous in situ UV–Vis-NIR spectro-electrochemical and a.c. impedance techniques have been realized for the first time. Combination of the data obtained by these parallel, independent methods can be exploited in the future in the elucidation of the redox mechanism of various transparent electroactive layers.     

Single-Step Traveling-Wave Quantum State Engineering in the Coherent State Representation

We describe a recently introduced single-step traveling-wave quantum state engineering scheme using the one-dimensional coherent-state representation introduced by Janszky. In this representation, the photon number expansion of the output state is derived in a compact formula that is advantageous for numerical optimization. Using this formula, we determine several sets of physically controllable parameters of the scheme yielding various nonclassical target states.