N-ACETYL-L-ASPARTATE AND ACETATE H-1-NMR SIGNAL OVERLAPPING UNDER MILD ACIDIC PH CONDITIONS

The pH dependence of methyl proton chemical shifts of acetate, acetoac etate, N-acetyl-L-aspartate (NAA), and N-acetyl-L-aspartyl-L-glutamate (NAAG) were studied from pH 3 to pH 9. Only slight shifts of acetoace tate, NAA, and NAAG methyl signals were observed, whereas the acetate signal was largely shifted as a result of the titration of its acidic function. At pH 4.7, acetate and NAA methyl signals overlapped, wherea s at more acidic pH, the acetate signal appeared downfield when compar ed to that of NAA. Results are discussed in terms of spectra misinterp retation risks linked to uncontrolled sample pH, on the one hand, and in terms of pH control and contamination by exogenous acetate during p erchloric acid cell extract preparation, on the other.