Unraveling Hydration Shell Dynamics and Viscosity Effects Around Cyanamide Probes via 2D IR Spectroscopy

Area of Science:

• Biophysics
• Physical Chemistry
• Molecular Biology

Background:

• Hydration dynamics and solvent viscosity are crucial for biomolecular structure and function.
• Protein and membrane fluctuations are strongly linked to solvent fluctuations.
• Vibrational probes are used to study local interactions and solvent dynamics, but their response to bulk viscosity is less understood.

Purpose of the Study:

• To investigate ultrafast hydration dynamics around a cyanamide (NCN) probe attached to deoxycytidine in aqueous solutions with varying glycerol content.
• To explore the impact of bulk viscosity on the behavior of vibrational probes in biological systems.
• To understand the relationship between local hydration dynamics and bulk solvent properties.

Main Methods:

• Two-dimensional infrared spectroscopy (2D IR) was used to probe hydration dynamics.
• A cyanamide (NCN) vibrational probe was attached to deoxycytidine.
• Molecular dynamics (MD) simulations were performed to model local hydration and probe dynamics.

Main Results:

• Frequency correlation decay times increased linearly with bulk viscosity (0.9–11.4 ps over 0.96–49.1 cP).
• Glycerol addition did not significantly alter the hydration of deoxycytidine.
• MD simulations indicated NCN probe frequency fluctuations are mainly influenced by water dynamics in the second solvation shell.

Conclusions:

• The study provides insights into how solvent viscosity affects hydration dynamics at the molecular level.
• Findings suggest that the NCN probe's response is sensitive to the dynamics of water molecules in the second solvation shell.
• The research highlights the utility of vibrational probes for studying localized hydration dynamics in complex biological environments.