Table 2. Type of H-bond, β-Bend, Thermodynamic Properties, and Population of 11 Local Minima for the Neutral Leu-EnK Calculated at the DSD-PBEP86-D3BJ/def2-TZVP//M06-2X/6-31+G(d) Level of Theory in the Gas Phase^a.

conf.	H-bond typeb	β-bendc	ΔEd	ΔHe	ΔGf	wg
n01	OH1 → 3, 4 → 2, OH5 → 1		0.00	0.00	0.00	63.6
n02	OH1 → 3, 4 → 2, 5 → 2, OH5 → 1	βII′34	2.48	2.55	1.18	8.6
n03	OH1 → 3, 4 → 2, OH5 → 1		1.95	2.07	1.23	7.9
n04	OH1 → 3, 4 → 2, OH5 → 1		2.06	2.09	1.25	7.7
n05	OH1 → 3, 4 → 2, OH5 → 1		2.79	3.03	1.83	2.9
n06	OH1 → 3, 4 → 2, OH5 → 1		1.86	1.97	1.85	2.8
n07	OH1 → 3, 4 → 2, OH5 → 1		0.47	0.70	2.19	1.6
n08	OH1 → 3, 4 → 2, OH5 → 1		3.74	3.93	2.25	1.4
n09	OH1 → 3, 4 → 2, OH5 → 1		4.20	3.95	2.44	1.0
n10	OH1 → 3, 4 → 2, OH5 → 1		1.47	1.80	2.74	0.6
n11	OH1 → 3, 4 → 2, OH5 → 1		2.96	3.02	2.90	0.5

^aTorsion angles (°) are listed in Table 1. Only 11 local minima with the relative Gibbs free energy (ΔG) < 3 kcal mol^–1 are listed.

^bEach 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.

^cβII′₃₄ stands for the type II′ β-bend at the Gly3–Phe4 sequence, which is stabilized by the 5 → 2 H-bond.

^dRelative electronic energies in kcal mol^–1.

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

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

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