Quasi-Static Two-Dimensional Infrared Spectra of the Carboxyhemoglobin Subsystem under Electric Fields: A Theoretical Study

Abstract

There is no doubt that electric fields of a specific frequency and intensity could excite certain vibrational modes of a macromolecule, which alters its mode coupling and conformation. Motivated by recent experiments and theories, we study the mode coupling between the Fe–CO mode and CO-stretch mode and vibration energy transfer among the active site and proteins in carboxyhemoglobin (HbCO) under different electric fields using the quasi-static two-dimensional infrared spectra. This study uses iron–porphyrin–imidazole–CO and two distal histidines in HbCO as the subsystem. The potential energy and dipole moment surfaces of the subsystem are calculated using an all-electron ab initio (B3LYP-D3­(BJ)) method with the basis set Lanl2dz for the Fe atom and 6-31G­(d,p) for C, H, O, and N atoms. Although the subsystem is reduced dimensionally, the anharmonic frequency and anharmonicity of the CO-stretch mode show excellent agreement with experimental values. We use the revealing noncovalent interaction method to confirm the hydrogen bond between the Hε atom of the His63 and the CO molecule. Our study confirms that the mode coupling between the Fe–CO mode and CO-stretch mode does not exist when the subsystem is free of electric field perturbation, which is coupled when the electric field is −0.5142 V/nm. In addition, with the increases of distance between the active site and the His92, there is no vibrational energy transfer between them when the electric field is 1.028 V/nm. We believe that our work could provide new ideas for increasing the dissociation efficiency of the Fe–CO bond and theoretical references for experimental research.

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.…”

“…The calculation of quasi-static 2D IR spectra has been described in detail elsewhere [ 35 , 38 ]. Briefly, based on the ground, two-exciton and combination band frequencies of NO 2 asymmetry stretching modes, two-exciton Hamiltons are diagonalized, and the anharmonicity, which is essential to creating the 2D IR spectra, is calculated with an anharmonic frequency [ 50 ].…”

“…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 ].…”

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

“…Structure–activity studies concern the structural features leading to agonism or antagonism of the OT effect on uterus prompted based on the cis/trans conformation, ,− and it is reported that electric fields of specific intensity and frequency can excite certain vibrational modes of proteins, which alters their conformations. − Therefore, in this paper, we theoretically study the response of the OT conformation to electric fields using quasi-static amide-I 2D IR spectra in combination with isotope labeling methods. On one hand, we aim to study hydrogen bonds among different residues because OT has an obvious β-turn geometry. − ,− ,, On the other hand, based on the Cys6-Pro7 isomer, the cis/trans conformations of OT are detected using 2D IR spectra under different electric fields. − …”