Effects of chirality during electrochemical oxidation of 2,3 butanediol stereoisomers

Microheterogeneous Electrocatalytic Chiral Recognition at Monoclinic Vanadium-Doped Zirconias: Enantioselective Detection of Glucose

Synthetic tetragonal and monoclinic vanadium-doped zirconias (t- and m-VxZr1-xO2, 0.005 < x < 0.150) exert an effective catalytic effect toward the electrochemical oxidation of glucose in aqueous alkaline media. The catalytic effect of monoclinic specimens attached to carbon and fluorine-doped tin oxide electrodes exhibits a remarkable enantioselectivity, so that catalytic currents for the oxidation of L-glucose at +0.92 V vs AgCl/Ag are considerably larger than those obtained for the oxidation of D-glucose. This enantioselectivity can be associated with the existence of a noncentrosymmetric coordination of vanadium centers in the monoclinic crystalline form of zirconia. From the electrochemical results, it can be suggested that the electrocatalytic mechanism includes the formation of glucose-vanadium surface adducts and electron transfer between catalytic centers and the substrate. The interference from chloride ions in the electrocatalytic process is significantly decreased by covering the zirconia particles with a layer of amorphous silica. These results propose that incorporation of catalytically active centers into nonsentrosymmetric sites of inorganic crystalline materials can be taken as a plausible strategy for chiral recognition via electrocatalysis.

Structure-selective recognition by voltammetry: enantiomeric determination of amines using azophenolic crowns in aprotic solvent

The enantiomeric recognition of amines by voltammetry using electroactive macrocyclic molecules, nitroazophenolic crown ethers, is reported. The oxidation potential of the nitroazophenol moiety in nitroazophenols with 18-crown-6 sensitively depends on the structure of alkyl amines. Based on this phenomenon, enantiomeric amines and even the quantitative assay of the R/S ratio in enantiomeric mixtures can be selectively recognized by using 18-crown-6 azophenol (3-H) with chiral centers. In the case of phenylglycinol, the association constants (K) of 3-H for the R and S forms have an R/S value of 3.5. The peak potential of the R form in square-wave voltammograms reproducibly differs from that of the S form by 32 mV, within which the peak potential linearly varies with the enantiomeric ratio. Free energy perturbation and molecular dynamics simulation provide deeper understanding of the enantiomeric recognition in this system. The theoretical analysis indicates that the free energy difference between diastereomeric complexes agrees well with the experimental results, and the pi-pi or charge-charge interaction plays a key role in enantiomeric recognition.