Cytochromec−Crown Ether Complexes as Supramolecular Catalysts: Cold-Active Synzymes for Asymmetric Sulfoxide Oxidation in Methanol

A series of supramolecular complexes of various cytochrome c proteins with 18-crown-6 derivatives behave as cold-active synzymes in the H_2O_2 oxidation of racemic sulfoxides. This interesting behavior contrasts with native functionality, where the employed proteins act as electron transfer carriers. ESI-MS, UV, CD, and Raman spectroscopic characterizations reveal that four or five 18-crown-6 molecules strongly bind to the surface of the cytochrome c and also that nonnatural low-spin hexacoordinate heme structures are induced in methanol. Significantly, crown ether complexation can convert catalytically inactive biological forms to catalytically active artificial forms. Horse heart, pigeon breast, and yeast cytochromes c all stereoselectively oxidize (S)-isomers of methyl tolyl sulfoxide and related sulfoxides upon crown ether complexation. These supramolecular catalysts show the highest efficiency and enantiomer selectivity at −40 °C in the H_2O_2-dependent sulfoxide oxidation, while oxidative decomposition of the heme moieties predominantly occurs at room temperature. The oxidation reactivity of the employed sulfoxides is apparently related to steric constraints and electrochemical oxidation potentials of their S O bonds. Among the cytochrome c complexes, yeast cytochrome c demonstrates the lowest catalytic activity and degradation reactivity. It has a significantly different protein sequence, suggesting that crown ether complexation effectively activates heme coordination but may additionally alter the native backbone structure. The proper combination of cytochrome c proteins, 18-crown-6 receptors, and external circumstances can be used to successfully generate “protein-based supramolecular catalysts” exhibiting nonbiological reactivities

Polarized Raman spectra of oriented films of Α-helical poly( L -alanine) and its N -deuterated analogue

Polarized Raman spectra were obtained on well oriented films of Α-helical poly( L -alanine) (Α-PLA) and its N -deuterated analogue in order to obtain definitive assignments of the E 2 -species modes. Such assignments were aided by an analysis of factors that can lead to ‘cross-talk’ between A , E 1 and E 2 spectra, viz. reflection of the incident beam and non-perfect lateral and axial chain orientation in the sample. The convincing assignment of at least eleven significant E 2 modes in Α-PLA has led to the refinement of a new empirical force field and a more detailed normal mode analysis. © 1998 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34894/1/210_ftp.pd