Analysis of NADES and its water tailoring effects constructed from inulin and L-proline based on structure, physicochemical and antifreeze properties.

ABSTRACT

The structure, physicochemical and anti-freeze properties of natural deep eutectic solvent (NADES) composed of inulin and L-proline (molar ratio of 111) were investigated. Proton nuclear magnetic resonance (1H NMR), Fourier infrared spectroscopy (FTIR), and Raman spectroscopy revealed extensive hydrogen bonding in the pure NADES system, and the addition of water weakens the hydrogen bonding interactions between the components. The smaller transverse relaxation time (T2) represents the stronger hydrogen bond strength, and NADES+40 % H2O exhibited a large T2 (71.68 ms). When 10 % water was added, the viscosity decreased from 3620 mPa·s to 1777 mPa·s, but the conductivity increased to approximately twice the original value. Furthermore, adding 10 % water lowered the glass transition temperature (Tg) of NADES by 5.6 °C. NADES+10 % H2O exhibited favorable thermal stability and freezing resistance, as evidenced by the fact that approximately 82.61 % of the ice crystals area <200 µm2 after 30 min of crystallization. The changes in the structure, physicochemical, and anti-freezing properties of water-tailored NADES are expected to enable the design of novel antifreeze agents.