Autoxidation of drying oils adsorbed on porous solids

Oxidation of benzaldehyde in some multiphase betaine-benzaldehyde-water systems

The results of oxidation studies in ternary multiphase betaine-benzaldehyde-water systems show that the maximum rate of oxidation depends primarily on the benzaldehyde content and composition of the phase with the shortest induction period in the system under examination. The effects of chain length and concentration of the S-amphiphile (betaine) are important only in so far as they influence the phase equilibria of the ternary systems.

Oxidation of benzaldehyde in some single phase betaine-benzaldehyde-water systems

The oxidation rates of increasing concentrations of benzaldehyde in ternary systems of the L1 type have been measured in aqueous solutions of four betaine homologues. On applying corrections for extra-micellar material, the rate becomes independent of the betaine concentration and is related to the micellar ratio of benzaldehyde to betaine when this ratio exceeds 1. The rate of oxidation in an LC system has been determined and compared with that in L1 systems. The site and mechanism of the oxidation reaction in these systems is postulated.

Lipid oxidation: biologic effects and antioxidants--a review

The detection and measurement of lipid oxidation in biological systems and some biologic effects of this oxidation are reviewed. The role of lipid oxidation in the process of photocarcinogenesis and the protective effect of antioxidants against this process also are discussed. The mechanism of such protection is unknown and studies directed at elucidating the mechanism of antioxidant effect in photocarcinogenesis and in some other pathological conditons believed to involve lipid oxidation are needed. In addition to this, epoxidation of lipids observed in monolayer studies requires further investigation, particularly in the presence of some other unsaturated molecules. The possible significance of such a study--particularly in the presence of polycyclic aromatic hydrocarbon carcinogens, where formation of epoxides is generally accepted as active intermediates--is also discussed. In addition, present knowledge on the role of lipid peroxides in the destruction of proteins and biomembranes, in chemically induced toxicity and in generation of singlet oxygen is presented.

Autoxidation and effects of pro- and antioxidants in lyophilized red blood cell membranes

Oxygen uptake and effects of pro- and antioxidants have been compared at 80 C in lyophilized red blood cell (RBC) bilayer membranes (ghosts). In this dry and relatively immobile system, catalytic metals have pronounced effects. When ghosts are prepared in the usual manner, in phosphate buffer, hypotonic saline, or deionized water (DI), oxygen uptake is extremely slow and limited unless: (a) catalytic metal, e.g. cobaltous ion, is supplied in the absence of metal-complexing buffers and (b) residual phosphate buffer is removed by repeated deionized water or hypotonic saline washes. Ghosts adsorb d-alpha-tocopherol strongly from 1% alcohol emulsion in buffer in amounts far above normal RBC concentrations, whereas synthetic antioxidant uptake seldom exceeds the normal tocopherol level. Uptake and effectiveness of antioxidants introduced by either perfusion or in the vapor phase, and resistance of ghosts to autoxidation introduced by either perfusion or in the vapor phase, and resistance of ghosts to autoxidation are discussed as they relate to protection of lyophilized membranes and freeze-dried foods.

Autoxidation of fatty acid monolayers adsorbed on silica gel: I. Nature of adsorption sites

An unsaturated fatty acid monolayer deposited on a silica gel surface has been chosen as a model for studying non-enzymatic autoxidation of membrane lipids. Studies to determine the suitability of this system as a model for biomembranes were conducted to define the nature of the monolayers, particularly with respect to the factors determining the concentration of the fatty acid molecule on unit area of the surface. The results from adsorption isotherm, high temperature dehydroxylation, and infrared spectra studies show that adsorption of a monomolecular layer of fatty acids occurs and that the number of molecules absorbed corresponds to the number of isolated, non-hydrogen-bonded silanol groups. It is presumed the binding is by hydrogen bonding of the carboxyl groups to silanol groups. The packing density of the fatty acid molecules is 1.25 molecule/100 A2 which is similar to the density of the isolated silanol sites on the surface.

Autoxidation of fatty acid monolayers adsorbed on silica gel: II. Rates and products

Unsaturated fatty acid monolayers on silica gel have been autoxidized, and the rate of fatty acid disappearance and products obtained from those membrane-like assemblies have been studied. Fatty acid monolayers consisting of pure linoleic acid, linolelaidic acid, and oleic acid were autoxidized at 60 C. The rates of autoxidation of linoleic acid and linolelaidic acid monolayers followed by the disappearance of substrates are considerably faster than that in bulk phase, and the rates conform to apparent first order kinetics. Autoxidation of linoleic and linolelaidic acid monolayers, unlike bulk phase, produced only a small amount of diene conjugation, and the major products formed were identified as 9,10-epoxy and 12,13-epoxyoctadecenoic acid in roughly equal quantities. The epoxidation is stereospecific, with cis and trans olefins giving cis and trans epoxides, respectively. Oleic acid was autoxidized to only a small extent during 27 hr and produced no detectable amount of epoxide.