Kinetic studies on stilbazulenyl-bis-nitrone (STAZN), a nonphenolic chain-breaking antioxidant in solution, micelles, and lipid membranes.
The rate constants, k(inh), for reaction of stilbazulenyl-bis-nitrone (STAZN, 1) with peroxyl radicals and the number of radicals trapped, n, are compared with those of phenolic antioxidants 2,2,5,7,8-pentamethyl-6-hydroxychroman (PMHC, 4a), 2,5,7,8-tetramethyl-6-hydroxychroman-2-carboxylic acid (Trolox, 4b), and 2,6-di-tert-butyl-4-methoxyphenol (DBHA, 5). The behavior of STAZN depended markedly on the media and type of initiator used, water-soluble or lipid-soluble. In styrene/chlorobenzene and initiation by azo-bis(isobutyronitrile) (AIBN), k(inh) (STAZN) = 0.64 k(inh) (5) = 0.02k(inh) (4a). On addition of methanol, the k(inh) of STAZN increased 6-fold to be four times that of 5 while that of 4a decreased 6-fold. In aqueous SDS-micelles containing methyl linoleate and initiation with water-soluble azo-bis(amidinopropane)2HCl, ABAP, the relative k(inh) values were 1 >or= 4b > 5. In dilinoleoylphosphatidyl choline (DLPC) bilayers and initiation with lipid-soluble azo-bis-2,4(dimethylvaleronitrile) (DMVN), the k(inh) order was 5 > 4b > 1. During initiation with ABAP in micelles and bilayers, the calculated values of k(inh) for STAZN changed during the induction period. The experimental results are interpreted in terms of the conformation of STAZN, which is transoid in homogeneous solution but cisoid in aqueous dispersions of lipids. In such dispersions, the STAZN lies at the lipid-water interface where it traps water-soluble peroxyl radicals by a single electron-transfer mechanism. The cisoid conformation at lipid-water interfaces is supported by theoretical calculations.
Mojumdar
Subhash C
SC
Contribution from the Departments of Chemistry, Mount Allison University, Sackville, NB, E4L 1G8 Canada.
Becker
David A
DA
DiLabio
Gino A
GA
Ley
James J
JJ
Barclay
L Ross C
LR
Ingold
K U
KU
D000975:Antioxidants / Q000737:chemistry*; D005609:Free Radicals; D007700:Kinetics; D008041:Linoleic Acids / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry; D008563:Membrane Lipids / Q000737:chemistry*; D008823:Micelles; D008968:Molecular Conformation; D009570:Nitriles / Q000737:chemistry; D009589:Nitrogen Oxides / Q000737:chemistry*; D010084:Oxidation-Reduction; D010713:Phosphatidylcholines / Q000737:chemistry; D012717:Sesquiterpenes; D012996:Solutions; D013053:Spectrophotometry; D013237:Stereoisomerism; D013997:Time Factors; D014867:Water / Q000737:chemistry
D000975:Antioxidants; D005609:Free Radicals; D008041:Linoleic Acids; D008051:Lipid Bilayers; D008563:Membrane Lipids; D008823:Micelles; D009570:Nitriles; D009589:Nitrogen Oxides; D010713:Phosphatidylcholines; D012717:Sesquiterpenes; D012996:Solutions; C459743:stilbazulenyl nitrone; D014867:Water; C005575:methyl linoleate; C022246:isobutyronitrile