Conformational Complexity of Succinic Acid and Its Monoanion in the Gas Phase and in Solution: Ab Initio Calculations and Monte Carlo Simulations
Abstract
Optimized structures and relative energies for conformers of succinic acid and its monoanion in the gas phase were obtained using ab initio molecular orbital calculations at the MP2/6-311+G^(**)//HF/6-31G^* and MP2/6-311+G^(**)//HF/6-31+G^* levels, respectively. The lowest energy conformer for succinic acid, designated ZsgsZ, has a gauche conformation about the central C2−C3 bond; the lowest energy conformer with an E-acid group and an internal hydrogen bond is ca. 3 kcal/mol higher in energy. The lowest energy structure for the monoanion, Ecgs, does have the expected internal hydrogen bond and is 15 kcal/mol more stable than any alternative. The ab initio results were used to determine corresponding torsional-energy parameters in the OPLS all-atom force field. This allowed application of statistical perturbation theory in Monte Carlo simulations to explore the effect of hydration on the conformational equilibria. The diacid and monoanion were both computed to be ca. 80% gauche in water at 25 °C. These results are in excellent agreement with NMR data. Though the conformational results are consistent with the gauche effect, their true origin requires a detailed understanding of the potential internal hydrogen bonding and solvation. Thus, in contrast to the monoanion's striking gas-phase preference, neither the diacid nor monoanion are computed to populate E conformers in aqueous solution.
Additional Information
© 1998 American Chemical Society. ReceiVed April 13, 1998. Publication Date (Web): September 5, 1998. Gratitude is expressed to Julian Tirado-Rives for helpful discussions and to the National Science Foundation for financial support.Attached Files
Supplemental Material - ja9812397_s.pdf
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Additional details
- Eprint ID
- 60663
- DOI
- 10.1021/ja9812397
- Resolver ID
- CaltechAUTHORS:20151001-101405733
- NSF
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2015-10-01Created from EPrint's datestamp field
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2021-11-10Created from EPrint's last_modified field