Revealing the Relationship between Electric Fields and the Conformation of Oxytocin Using Quasi-Static Amide-I Two-Dimensional Infrared Spectra

Abstract

It is reported that the cis/trans conformation change of the peptide hormone oxytocin plays an important role in its receptors and activation and the cis conformation does not lead to antagonistic activity. Motivated by recent experiments and theories, the quasi-static amide-I 2D IR spectra of oxytocin are investigated using DFT/B3LYP (D3)/6-31G (d, p) in combination with the isotope labeling method under different electric fields. The theoretical amide-I IR spectra and bond length of the disulfide bond are consistent with the experimental values, which indicates that the theoretical modes are reasonable. Our theoretical results demonstrate that the oxytocin conformation is transformed from the cis conformation to the trans conformation with the change of the direction of the electric field, which is confirmed by the distance of the backbone carbonyl oxygen of Cys6 and Pro7, the Ramachandran plot of Cys6 and Pro7, the dihedral angle of C β -S-S-C β , and the rmsd of the oxytocin backbone. Moreover, the trans conformation as the result of the turn in the vicinity of Pro7 has a tighter secondary spatial structure than the cis conformation, including stronger hydrogen bonds, longer γ-turn geometry involving five amino acids, and a more stable disulfide bond. Our work provides new insights into the relationship between the conformation, the activation of the peptide hormone oxytocin, and the electric fields.

Intermolecular Vibration Energy Transfer Process in Two CL-20-Based Cocrystals Theoretically Revealed by Two-Dimensional Infrared Spectra

“…As mentioned above, the impact sensitivity of cocrystal energetic materials depends on the rate of mechanical energy transfer, [ 25 , 26 , 27 ] and the 2D IR spectra have an advantage in detecting the intramolecular and intermolecular vibrational energy transfer due to the unique cross-peak mechanism, that is, the intensity of cross-peaks is proportional to the vibrational energy transfer in the 2D IR spectra [ 35 , 36 , 37 , 38 , 39 , 40 , 41 ]. The normalized and simulated 2D IR spectra and the corresponding IR spectra, which show the fundamental frequency and relative intensity of the NO 2 asymmetric stretching, are presented in Figure 3 .…”

“…The normalized and simulated 2D IR spectra and the corresponding IR spectra, which show the fundamental frequency and relative intensity of the NO 2 asymmetric stretching, are presented in Figure 3 . The diagonal peaks are a pair of positives (blue in color) and negatives (yellow in color), which represent the ν = 0→1 transition and ν = 1→2 absorptions, [ 35 , 36 , 37 , 38 , 39 , 40 ] respectively. In the 2D IR spectra of the TNT/CL-20 ( Figure 3 , left), four positive–negative couplets appear along the diagonal, with their ω τ peak positions corresponding to those in the IR spectrum, and the diagonal peak at ω m = ω τ = 1596.3 overlaps with the diagonal peak at ω m = ω τ = 1588.6.…”

“…These works demonstrated that the 2D IR method possessed both high structural sensitivity and high time resolution, and it could simultaneously excite and probe many vibrational chromophores with varying frequencies [ 34 , 35 ]. Recently, the 2D IR method has attracted extensive attention in the field of the dynamics and structures of interfaces and surfaces as well as condensed-phase molecular systems [ 36 , 37 , 38 , 39 , 40 , 41 ].…”