An Electron Spin Resonance Study on the Association of Nitroxide Spin Probes With Aggregates of Peptide-Surfactants

Abstract

The association of nitroxide spin probes with aggregates of peptide-surfactants was investigated in aqueous media. The spin-labeled fatty acid was completely incorporated into the peptide-surfactants with anisotropic immobilization, while the less hydrophobic nitroxide radical was distributed between the hydrophobic and electrostatic regions of the aggregates. The peptide-surfactants may form tighter aggregates than the ordinary micelles.

Artificial Enzymes

“…The enantioselectivity was also observed when the β-replacement reaction was mediated by the covesicle formed with 38a, 31 (n ) 16), and an additional peptide lipid having (S)-binaphthol and (S)-alanyl moieties (34) in the presence of Cu(II) ions. 126,127 The binaphthol moiety of the lipid acts as a chiral ligand toward the intermediate Schiff base chelate to control the enantioselectivity.…”

“…While micelles provide hydrophobic reaction sites effective for acceleration of various enzyme-mimetic reactions, those aggregates are generally soft and difficult to achieve conformational fixation of substrates for regio- and stereospecific reactions. Peptide surfactants bearing amino acid residue(s), such as 7 , developed by Murakami et al may improve such a weak aspect of micellar aggregates, since the amphiphiles tend to form tight aggregates relative to those formed with simple surfactants, originating from the intramicellar hydrogen-bonding interaction. − …”

“…Peptide surfactants bearing amino acid residue(s), such as 7, developed by Murakami et al may improve such a weak aspect of micellar aggregates, since the amphiphiles tend to form tight aggregates relative to those formed with simple surfactants, originating from the intramicellar hydrogen-bonding interaction. [34][35][36][37] It is well recognized that incorporation of substrate species into aqueous micelles proceeds through hydrophobic, electrostatic, and charge-transfer interactions. On the other hand, the hydrogen-bonding interaction between a substrate and a catalyst seems to be also effective for stereoselective catalysis in the hydrophobic micellar phases.…”

“…Murakami et al also examined enantioselectivity by the catalytic bilayer membranes in the transamination reaction. [118][119][120][121] The enantioselective formation of D-R-amino acids in the half-transamination reaction of R-keto acids with 36b was observed by employing the bilayer covesicle composed of 31 (n ) 16) having an L-alanine residue and a peptide lipid (34) bearing both a chiral (S)-binaphthol moiety as a bidentate ligand and an L-alanine residue in the presence of Cu(II) ions at pH 7.0 and 30.0 °C; the observed ee values were 40, 34, 24, and 15% for valine, leucine, phenylalanine, and alanine, respectively. 120 Since the racemic valine was obtained in the absence of 34, the chiral reaction site provided by the bilayer aggregate formed with 31 alone is insufficient for the enantioselective transamination.…”

Sodium Dodecyl Sulfate-Poly(ethylene oxide) Association by Spin Labeling

“…To our knowledge, few spin labeling experiments have been performed to investigate the polymer-surfactant interactions, the published studies refer to surfactant-protein interactions. [11][12][13][14] Experiments Both surfactant and polymer were purchased from Aldrich and used without further purification. Two polymer masses have been used: 4 X 106 and 8 X 106 Daltons.…”