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High-level quantum chemical computations have provided significant insight into the fundamental physical nature of non-covalent interactions. These studies have focused primarily on gas-phase computations of small van der Waals dimers; however, these interactions frequently take place in complex chemical environments, such as proteins, solutions, or solids. To better understand how the chemical environment affects non-covalent interactions, we have undertaken a quantum chemical study of π– π interactions in an aqueous solution, as exemplified by T-shaped benzene dimers surrounded by 28 or 50 explicit water molecules. We report interaction energies (IEs) using second-order Møller–Plesset perturbation theory, and we apply the intramolecular and functional-group partitioning extensions of symmetry-adapted perturbation theory (ISAPT and F-SAPT, respectively) to analyze how the solvent molecules tune the π– π interactions of the solute. For complexes containing neutral monomers, even 50 explicit waters (constituting a first and partial second solvation shell) change total SAPT IEs between the two solute molecules by only tenths of a kcal mol −1 , while significant changes of up to 3 kcal mol −1 of the electrostatic component are seen for the cationic pyridinium–benzene dimer. This difference between charged and neutral solutes is attributed to large non-additive three-body interactions within solvated ion-containing complexes. Overall, except for charged solutes, our quantum computations indicate that nearby solvent molecules cause very little “tuning” of the direct solute–solute interactions. This indicates that differences in binding energies between the gas phase and solution phase are primarily indirect effects of the competition between solute–solute and solute–solvent interactions.
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Towards and understanding of CO2 microsolvation: Microwave spectroscopy of CO2 complexes with fluoroethylenes
The need for a deep understanding of CO2 interactions with other mols. is significant given the importance of supercrit. CO2 (s.c.-CO2) as a green solvent, and interest in design of novel materials for CO2 capture and storage. Soly. of fluorinated compds. in s.c.-CO2 is generally higher than their hydrocarbon analogs and fluorination of hydrocarbon compds. improves "CO2-philicity". Although dissoln. of a compd. in s.c.-CO2 (or any solvent) is a complex process, much can be learned by systematic examn. of solute-solvent interactions as a function of solute mol. properties in dimers and other small clusters. In the present study, Fourier-transform microwave spectroscopy and Symmetry Adapted Perturbation Theory (SAPT) calcns. have been used to examine intermol. interactions between CO2 and a series of fluorinated ethylene mols. with varying degree and position of fluorination (1-3 F atoms). While 1-fluoro-, 1,1-difluoro- and 1,1,2-trifluoroethylene...CO2 complexes are planar (with two isomers obsd. for 1-fluoroethylene), cis-1,2-difluoroethylene...CO2 is nonplanar. Although lowest energy structures predicted by MP2/6-311++G(2d,2p) calcns. are not always in agreement with obsd. configurations, SAPT calcns. provide binding energies consistent with the obsd. structures. We are now extending these studies to trimers contg. one fluorinated ethylene with two CO2 "solvent" mols. in order to gain further insight into structural and energetic changes as a solvation shell is formed.
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- Award ID(s):
- 1664900
- PAR ID:
- 10060586
- Date Published:
- Journal Name:
- 254th American Chemical Society National Meeting
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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