title: Cosolvent Effects on Solute-Solvent Hydrogen-Bond Dynamics: Ultrafast 2D IR Investigations.
abstract: Cosolvents strongly influence the solute-solvent interactions of biomolecules in aqueous environments and have profound effects on the stability and activity of several proteins and enzymes. Experimental studies have previously reported on the hydrogen-bond dynamics of water molecules in the presence of a cosolvent, but understanding the effects from a solute's perspective could provide greater insight into protein stability. Because carbonyl groups are abundant in biomolecules, the current study used 2D IR spectroscopy and molecular dynamics simulations to compare the hydrogen-bond dynamics of the solute's carbonyl group in aqueous solution, with and without the presence of DMSO as a cosolvent. 2D IR spectroscopy was used to quantitatively estimate the time scales of the hydrogen-bond dynamics of the carbonyl group in neat water and 1:1 DMSO/water solution. The 2D IR results show spectral signatures of a chemical exchange process: The presence of the cosolvent was found to lower the hydrogen-bond exchange rate by a factor of 5. The measured exchange rates were 7.50 × 10(11) and 1.48 × 10(11) s(-1) in neat water and 1:1 DMSO/water, respectively. Molecular dynamics simulations predict a significantly shorter carbonyl hydrogen-bond lifetime in neat water than in 1:1 DMSO/water and provide molecular insights into the exchange mechanism. The binding of the cosolvent to the solute was found to be accompanied by the release of hydrogen-bonded water molecules to the bulk. The widely different hydrogen-bond lifetimes and exchange rates with and without DMSO indicate a significant change in the ultrafast hydrogen-bond dynamics in the presence of a cosolvent, which, in turn, might play an important role in the stability and activity of biomolecules.
authors.affiliation: Physical and Materials Chemistry Division-CSIR, National Chemical Laboratory , Dr. Homi Bhabha Road, Pashan, Pune 411008, India.
authors.forename: Somnath M
authors.initials: SM
authors.lastname: Kashid
authors.affiliation: Department of Chemistry, Ulsan National Institute of Science and Technology (UNIST) , 50 UNIST-gil, Ulsan 44919, Korea.
authors.forename: Geun Young
authors.initials: GY
authors.lastname: Jin
authors.affiliation: Physical and Materials Chemistry Division-CSIR, National Chemical Laboratory , Dr. Homi Bhabha Road, Pashan, Pune 411008, India.
authors.forename: Sayan
authors.initials: S
authors.lastname: Bagchi
authors.affiliation: Department of Chemistry, Ulsan National Institute of Science and Technology (UNIST) , 50 UNIST-gil, Ulsan 44919, Korea.
authors.forename: Yung Sam
authors.initials: YS
authors.lastname: Kim
mesh_terms: D006860:Hydrogen Bonding; D056004:Molecular Dynamics Simulation; D012997:Solvents / Q000737:chemistry*; D013055:Spectrophotometry, Infrared / Q000379:methods*
chemical_list: D012997:Solvents