Table 1.

Effect of the side chain of residue X on computed ¹³C′ shielding

Xa	Δb (ppm)
Thr	4.3
	1.9
	1.5
Asp	0.9
	1.1
	1.6
Val	0.6
	0.9
	2.7
Met	0.7
	0.3
	1.6
Trp	2.3
	0.6
	0.9
Tyr	1.2
	−0.4
	1.0
Gln	1.5
	0.5
	1.5
Ile	3.2
	1.5
	1.8

^aResults of the computed ¹³C′ shielding for residue X in the tripeptide: Ac-GXA-NMe, for X in column 1. All the listed results were obtained by assuming that the backbone torsional angles (φ,ψ) of residue A were fixed (as indicated in the Materials and Methods section) at an extended conformation, namely φ = −140° and ψ = +140°. However, among all the possible values of the backbone torsional angles (φ,ψ) of residue X, sampled every 10°, the set φ = −60° and ψ = −30° was chosen because a computed ¹³C′ shielding value exists for all the listed residues for this particular set of backbone torsional angles.

^bFor each residue X there are three Δ values (see Methods section); each of these values corresponds to a difference, Δ computed by using a given χ¹ side-chain rotamer of X, namely −180°, −60° or +60°. For all the listed residues there is, at least, one second-order difference, between Δ values, > 0.5 ppm, indicating the need to consider the side-chain effect for an accurate computation of the ¹³C′ shielding of residue X, as mentioned in the Materials and Methods section.