for 1 h equipped with a nalorac indirect detection probe 1 h chemical shifts were referenced to external sodium 3 trimethylsilyl propionate 2 2 3 3 d 4 in d 2 o prior to nmr analysis the sample of n sup u03b1 acetyl n sup u03b5 pha lysine was acidified with dcl cambridge isotopes inc until inhibition of amide proton exchange was observed for proton and total correlation spectroscopy tocsy experiments the intense water signal was attenuated by transmitter pre irradiation the proton nmr spectrum of n sup u03b1 acetyl n sup u03b5 pha lysine was recorded at 25 u00b0 c from 64 transients under the following conditions pre acquisition delay 2 s acquisition time 1 89 s 37 760 complex data points pulse width 7 u03bcs 80 u00b0 flip angle and spectral width 10 000 hz the free induction decay was processed with a line broadening apodization of 1 0 hz for tocsy eight transients were collected for each of 200 t 1 domain increments a 10 ms mixing period was employed resulting in cross peaks for only the strongest scalar couplings geminal and vicinal the acquisition time was 0 256 s in t 2 2048 complex data points and 0 050 s in t 1 200 data points tocsy data was processed by the hypercomplex method with gausian weighting in both t 1 and t 2 dimensions digital signal processing was employed.