. 2022 Jul 26;7(31):27755–27768. doi: 10.1021/acsomega.2c03942

6-31+G(d) Level of Theory in the Gas Phase^a ^h.

conf.^b	H-bond type^c	β-bend^d	ΔE^e	ΔH^f	ΔG^g
ECEPP3-1	OH1 → 4, 4 → 3, OH5 → 1		10.64	10.61	9.46
ECEPP3-2	OH1 → 4, 4 → 3, OH5 → 1		10.50	10.93	8.85
ECEPP3-3	OH1 → 4, 4 → 3, OH5 → 1		11.94	11.86	11.31
ECEPP3-4	OH1 → 4, 2 → 5, 3 → 1, 5 → 2	βII′₃₄	10.32	10.72	11.25
ECEPP3-5	OH1 → 3, 4 → 1	βII′₂₃	17.75	17.47	15.62
ECEPP3-6	OH1 → 4, 2 → 5, 3 → 1, 4 → 2, 5 → 2	βII′₃₄	4.22	4.57	4.76
ECEPP3-7	OH1 → 4, 4 → 2, OH5 → 1		8.89	8.85	6.60
ECEPP3-8	4 → 1	βII′₂₃	20.59	19.97	17.65
ECEPP3-9	OH1 → 3, 2 → 5, 4 → 3		6.90	6.92	5.88
MM1	OH1 → 3, 2 → 5, 4 → 2, 5 → 2	βII′₃₄	7.24	7.44	5.11
MM2	OH1 → 3, 4 → 1	βII′₂₃	17.75	17.47	15.62
MM3	1 → 4, 3 → 1		17.69	17.45	13.78
MM4	1 → 4, 3 → 1		17.08	16.72	14.30
VG	2 → OH5, 5 → 2	βII′₃₄	11.50	11.32	7.42
J1	1 → 4, 4 → 1, 5 → 3, OH5 → 4	βI′₂₃	13.99	14.18	12.16
J2	1 → 4, 4 → 1, 5 → 3	βI′₂₃	13.70	13.62	10.73
J3	4 → 1, 5 → 3, OH5 → 4	βI′₂₃	11.59	11.22	9.39
WH1	OH1 → 3, 4 → 1	βI′₂₃	12.23	12.31	10.61
WH2	OH1 → 4, 4 → 1	βII′₂₃	11.60	11.41	9.26
WH3	OH1 → 3		18.08	17.58	13.52

Torsion angles (°) are listed in Table 3.

The definition of conformations is noted in footnotes b–e of Table 3.

Each H-bond type n → m stands for the H-bond between the H donor (e.g., the amide H atom for backbone) of the residue n and the H acceptor (e.g., the carbonyl O atom for backbone) of the residue m. In addition, OH1 and OH5 represent the hydroxyl H atom of the side chain of the Tyr1 residue and the carboxylic H atom of the Leu5 residue, respectively. 5OH represents the O atom of the carboxylic OH group of the Leu5 residue.

βII′₂₃ and βI′₂₃ stand for the type II′ and I′ β-bend at the Gly2–Gly3 sequence, which are stabilized by the 4 → 1 H-bond. βII′₃₄ stands for the type II′ β-bend at the Gly3–Phe4 sequence, which is stabilized by the 5 → 2 H-bond.

Relative electronic energies in kcal mol^–1.

Relative enthalpies in kcal mol^–1 at 25 °C.

Relative Gibbs free energies in kcal mol^–1 at 25 °C and 1 atm.

The population of each conformer was calculated by its ΔG at 25 °C.

Table 4. Type of H-Bond, β-Bend, and Thermodynamic Properties of Local Minima for the Neutral Leu-EnK Optimized from the Structures Obtained by the ECEPP Force Field and DFT Methods at the DSD-PBEP86-D3BJ/def2-TZVP//M06-2X/6-31+G(d) Level of Theory in the Gas Phaseah.

Table 4. Type of H-Bond, β-Bend, and Thermodynamic Properties of Local Minima for the Neutral Leu-EnK Optimized from the Structures Obtained by the ECEPP Force Field and DFT Methods at the DSD-PBEP86-D3BJ/def2-TZVP//M06-2X/6-31+G(d) Level of Theory in the Gas Phase^a ^h.