Interaction and Dynamics in a Fully Biodegradable Glucose-Containing Naturally Abundant Deep Eutectic Solvent: Temperature-Dependent Time-Resolved Fluorescence Measurements

A new room-temperature deep eutectic solvent (DES) composed of glucose, urea, and water has been prepared and its relaxation dynamics explored via temperature-dependent time-resolved fluorescence measurements employing hydrophilic and hydrophobic solute probes. Differential scanning calorimetry measurements indicate a glass transition temperature (T-g) of similar to 236 K. Measured viscosity coefficients (eta) vary from similar to 600 to similar to 100 cP in the temperature range 318 <= T/K <= 343 and exhibit Arrhenius-type temperature dependence with an activation energy of similar to 65 kJ mol(-1). Interestingly, this DES forms a stable liquid at similar to 300 K but is too viscous to be accurately measured by us below 318 K. Temperature-dependent dynamic fluorescence anisotropy measurements using hydrophobic and hydrophilic solutes of similar sizes reveal bi-exponential kinetics and Arrhenius-type temperature dependence for solute rotation times ((tau(r))) but with significantly decreased activation energies, similar to 31 kJ mol(-1) (hydrophobic) and similar to 21 kJ mol(-1) (hydrophilic). Deviation from hydrodynamics is further reflected in the strong fractional viscosity dependence