Finding a relationship on how a three-dimensional protein folds from its linear amino acid chain gets more complex with increasing chain length, so working on a smaller peptide conformational problem can provide initial ideas on what are the main molecular forces and how these influence the folding process. Following the study of conformations of amino acid units entering the proteins to understand the secondary structure of small peptides, this paper proposes mathematical models for the several two-rotor cross-sections of the five-dimensional N-acetyl-glycyl-glycine-N′-methylamide potential energy hypersurface (PEHS). These cross-sections are extracted along the first glycine subunit, with its coordinates fixed at the five energy minima of the glycine diamide. The resulting mathematical models yield an average RMSE of 1.36 kJ mol−1 and an average R2 of 0.9923 with respect to energy values obtained from DFT calculations. The minima geometries obtained from these models are also in good agreement with DFT-optimized energy minima conformers. An important aspect of this study also tackles the relationship between the PEHS of the glycyl-glycine diamide and its glycine subunits. It has been observed that there are deviations up to 28.35 kJ mol−1 and 29.52 kJ mol−1 between the PEHS cross-sections along γL and γD conformations, respectively, in the first glycine subunit. This may suggest that there are significant backbone–backbone intermolecular forces acting on the dipeptide. The abovementioned findings can help in developing more complex mathematical models for polypeptide folding from amino acid subunits.
