A STUDY OF THE OPTICAL ROTATION OF LIPIDS EXTRACTED FROM SOILS, SEDIMENTS, AND THE ORGUEIL CARBONACEOUS METEORITE

Abstract

During the past few years a considerable amount of information has been accumulated on the optical rotatory dispersion of biologically significant compounds. Optical rotatory dispersion data has, in several instances, been useful in elucidating structural details of molecules, such as those of certain proteins. The optical rotations of several lipid and hydrocarbon compounds are also known. On the other hand, there is very little information available on the optical rotation of lipids which occur in soils, marine sediments, and sedimentary rocks. There are some exceptions, such as petroleum and coal. The optical rotations of petroleum distillate fractions and of coal have been studied.'-4 It was found that most petroleum fractions are dextrorotatory but a few show levorotation.2 The chemical composition of lipids in soils and sediments has also been studied,-7 and fatty acids, saturated and aromatic hydrocarbons, and so on have been described. An investigation of the optical rotations of soil and sediment lipids may eventually be helpful to elucidate some of the transformation processes that the decayed biological matter is subjected to in the geological habitat. A study of the optical activity of soil and sediment lipids may also be of value in explaining the true nature of the optical activity reported in lipid fractions extracted from carbonaceous meteorites.8-11 The following three topics are discussed in this report: (1) control experiments performed in order to evaluate various factors that may cause false optical activity readings, (2) optical activity measurements made on soil and sediment, and (3) optical activity measurements on carbonaceous meteorite lipids. Necessary Precautions for the Measurement of the Optical Rotation of Soil, Sediment, and Meteorite Lipids.-The measurement of the optical rotation of soil, sediment, and meteorite lipids is a most difficult task which can be successfully accomplished only if utmost care is exercised. The lipids are usually extracted from the sediment samples with a solution of benzene and methanol in a Soxhlet apparatus. The extracts are usually yellow to dark brown in color. They may contain suspended particulate matter and they usually show only a few millidegrees of optical rotation. Investigators working on problems of optical rotatory dispersion will, of course, realize that such samples could easily give spurious readings in all commnercially available polarimeters unless the necessary precautions are taken. The major part of this study consisted of control experiments in order to define the factors that may lead to spurious rotations and to establish precisely the precautional procedures which one has to follow to avoid artifacts. In this study, a modified Bendix model 460-C Polarmatic Recording Spectropolarimeter was used. A series of control experiments were performed to evaluate the instrument in order to find out if it was indeed suitable for this study. The effects of the optical density of the solutions, suspended particulate matter, and the fluorescence of the solutions were studied in detail, together with such possible sources of