Malonaldehyde, a very reactive member of the homologous
series of dialdehydes, is associated with the autoxidative deterioration
of lipids. Its measurement, in autoxidized lipid systems is an
expression of the extent of oxidation, in lipids. Malonaldehyde lends
itself well to such determinations because of the sensitivity and
specificity of its quantification in complex lipid systems. Complete
knowledge of the formation of malonaldehyde in autoxidized lipids. is
lacking. Such knowledge would undoubtedly promote a better understanding
of lipid autoxidation mechanisms.
In this investigation, a method for detecting malonaldehyde
through the use of its reaction with p-aminobenzoic acid was developed.
This was adapted for use in measuring malonaldehyde in
lipids and in tissue samples. The reaction between p-aminobenzoic
acid and malonaldehyde was partially characterized, and a mechanism
for the formation of the reaction product was postulated.
The quantification of malonaldehyde in lipid systems by the use
of p-aminobenzoic acid involves the use of a mild reducing agent such
as stannous chloride to prevent interference from hyd roperoxides
present in the system. The p-aminobenzoic acid reaction is highly
specific for malonaldehyde and proceeds smoothly and rapidly at
room temperature in a non-aqueous chloroform-methanol solvent
system to yield a highly colored compound having a maximum
absorbance at 406 mμ. and with a molar absorptivity of 73,500. The
absorbance value may be converted directly to parts-per-million
malonaldehyde through the use of a conversion factor in a simple
equation. The limits of detectability of themethod are on the order
of one ppm malonaldehyde. The measurement of malonaldehyde in
the lipid fraction of tissue samples involves the prior extraction of
the lipid with a non-aqueous chloroform-methanol solvent, by an
extraction method which was developed for this purpose.
The reaction of malonaldehyde with p-aminobenzoic acid
involves the condensation of two molecules of p-aminobenzoic acid
with one molecule of malonaldehyde. The reaction exhibits a rate
maximum at a hydrogen ion concentrations of about 0.1 molar, and
also exhibits rate dependencies upon the concentrations of both
malonaldehyde and p-aminobenzoic acid. This strongly suggests that
the reaction proceeds according to an S [subscript N] 2 mechanism. A postulated
mechanism involves nucleophilic 1,4-addition of the amino nitrogen of p-aminobenzoic acid to the enol of malonaldehyde followed by-loss
of water to form the enamine. The reaction with a second molecule
of p-aminobenzoic acid involves nucleophilic substitution of the
amino nitrogen at the carbonyl function of malonaldehyde followed
by loss of water to form an imine linkage. / Graduation date: 1968
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/26808 |
| Date | 10 August 1967 |
| Creators | Follett, Mark Samuel |
| Contributors | Sinnhuber, Russell O. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
Page generated in 0.0023 seconds