arginine sidechain spin systems:

reason for assigning:  peak patterns in HSQC, HNCO, and HNCACB as well as chemical shifts matching up well with BMRB statistics

 - assign amino acid type
 - assign atomtypes of peaks:  CA -> CD, CB -> CG, CO -> CZ, H -> HE, and N -> NE
 - identify folding of CZ and NE peaks
 - tag spin system as sidechain
 - retag peaks as sidechain