Infrared signature of micro-hydration in the organophosphate Sarin: an ab initio study

Abstract

The infrared (IR) spectra of micro-hydrated Sarin•(H2O)n clusters containing between one and four explicit waters have been studied using ab initio density functional theory (DFT) methods. The phosphate group P=O bond vibration region (∼1270 to 1290 cm(-1)) revealed the largest frequency variation with hydration, with a frequency red shift reflecting the direct hydrogen bond formation between the P=O of Sarin and water. Small variations to the P-F stretch (∼810 to 815 cm(-1)) and the C-O-P vibrational modes (∼995 to 1004 cm(-1)) showed that the water interactions with these functional groups were minor, and that the structures of Sarin were not extensively perturbed in the hydrated complexes. Increasing the number of explicit hydration waters produced only small vibrational changes in the lowest free energy complexes. These minor changes were consistent with a single water-phosphate hydrogen bond being the dominant structure, though a second water-phosphate hydrogen bond was observed in some complexes and was identified by an additional red shift of the P=O bond vibration. The H2O•H2O vibrational modes (∼3450 to 3660 cm(-1)) increased in complexity with higher hydration levels and reflect the extended hydrogen bonding networks formed between the explicit waters in the hydrated Sarin clusters. Graphical Abstract Ab initio studies of the infrared signature for micro-hydrated Sarin.

Spectroscopic and inclusion properties of G-series chemical warfare agents and their simulants: a DFT study

“…All calculations were in the gas phase and correlated well with experiment for the P-O-R asymmetric stretch, however, the P=O stretches were shifted to significantly lower frequencies for GB, GD and GF. Consideration of explicit microsolvation in the current study (Table 5) has given more accurate results, in agreement with data from Alam and Pearce for GB (33), and represents a better protocol for the G-series of CWAs. Indeed, it may be that microsolvation is a more appropriate method to model other CWAs and their simulants, however, due to the extended computational time required, it was not considered in this study.…”

Insights into the binding of arginine to adenosine phosphate from mimetic complexes

“…the experimental spectra, typically around 1.00-1.05, apparently to compensate for anharmonic effects. [38][39][40][41][42][43][44][45] In line with those findings, in our study a fair agreement in the position of part of the IRMPD bands is already observed in the IR spectra predicted computationally without scaling. Nevertheless, the best agreement between the experiment and the oB97X-D, CAM-B3LYP and MP2 computations is obtained if the vibrational modes with participation of the phosphate group are singled out and their frequencies are left unscaled, while a scaling factor of 0.97 is applied to the frequencies of the vibrational modes with a marginal participation of the phosphate group, namely those of the backbones of the ribose and guanine moieties and of the guanidinium guest cation (e.g., C-C, C-N or C-O stretching vibrations, CH n bending vibrations, see Table 1).…”

Theoretical Study of the Microhydration the Chemical Warfare Agent Sulfur Mustard

“…Hydrated microclusters formed by the nerve agent sarin have been probed to understand the impact of adding discrete water molecules to its binding energies and the vibrational wavenumber of the phosphate-water hydrogen bond (H-bond). Different nerve agents and their simulants have been microhydrated to determine the extent to which the simulants mimic the properties of the original CWAs in solution .…”