On the optical rotation of 1 (or 3)-stearoyl-sn-glycerol

Small specific rotation is one of the setbacks in the studies of 1 (or 3)-acyl-sn-glycerols, which makes assessment of the optical purity/establishment of the identity of new compounds difficult. Some unusually large data reported for 3-stearoyl-sn-glycerol in the literature suggested that use of low sample concentrations in recording optical rotations might alleviate the long-existing (though probably ‘hidden’ to those, who are not working in this area) problem. To verify the astonishing data and to explore the potential cause(s) for the unexplained phenomenon, a systematic study was performed. The results revealed that the ‘amplifying’ effect at low concentrations did not exist. And those seemingly ‘flawless’ literature data were proven to be artefacts. The sign of specific rotation for 3-stearoyl-sn-glycerol was shown to be changeable with dilution, providing a warning for the risk in assignment of absolute configurations of similar compounds on the basis of a single point optical rotation data.