The kinetics of the autoxidation of polyunsaturated fatty acids |
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Authors: | John P Cosgrove Daniel F Church William A Pryor |
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Affiliation: | (1) Department of Chemistry and Biochemistry, Louisiana State University, 70803 Baton Rouge, LA;(2) The Biodynamics Institute, Louisiana State University, 70803 Baton Rouge, LA |
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Abstract: | The kinetics of the autoxidation of a series of polyunsaturated fatty acids (PUFA) with increasing degrees of unsaturation
and the mono-, di-and triglycerides of linoleate have been studied in homogeneous chlorobenzene solution at 37 C under 760
torr of oxygen. The autoxidations were initiated by thermal decomposition of azo initiators and followed by measuring the
rate of oxygen uptake. The rate of chain initiation was determined by the induction period method using α-tocopherol as the
chainbreaking antioxidant. The measured oxidizabilities of the PUFA are linearly dependent on the number of doubly allylic
positions present in the molecule. Thus, the oxidizability of linoleate is 2.03×10−2 M−1/2 sec−1/2, and the value for docosahexaenoate is five times greater, 10.15×10−2 M−1/2 sec−1/2. The rate of autoxidation for all PUFA studied and for the mono- and diglyceride is proportional to the substrate concentration
and to the square root of the rate of chain initiation, implying that the autoxidation of these compounds follows the usual
kinetic rate law. The autoxidation of the triglyceride is more complex and does not appear to follow the same rate law at
all substrate concentrations. This deviation from the usual kinetic rate expression may be due to lipid aggregation at low
concentrations of the triglyceride. |
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