Solvatochromic Polarity, Physicochemical Properties, and Spectral Analysis of New Triple NADES-Based on Urea-Glycerol

Imagine a solvent that can be tuned like a musical instrument—now, ten new green solvents show us how, with polarities ranging from gentle to water-like intensity.

Scientists have crafted ten new type-V natural deep eutectic solvents (NADES) using urea as a hydrogen-bond acceptor, paired with glycerol, organic acids, or carbohydrates. These aren't just mixtures—they're highly organized hydrogen-bonded networks, as revealed by their densities (1.243–1.361 g/cm³) and high molar refraction and polarizability values. The carboxyl and hydroxyl groups in the donors pack the structures tightly, making them compact and robust.

Surface tension measurements (46.9–80.3 mN/m) show a wide range, categorizing the solvents into low, medium, and high polarity groups. But the real star is solvatochromic analysis using Nile Red, betaine 30, and Kamlet–Taft parameters. All NADES exhibit high E_NR, ET(30), and E_TN values, placing them as highly polar media—comparable to water—yet each with a unique hydrogen-bond donating or accepting personality.

The normalized Kamlet–Taft parameters reveal a broad solvent spectrum, from strongly H-bond accepting to strongly donating or dipolar systems. This tunability is a game-changer for green chemistry, offering fine-tuned solvents for extracting and dissolving bioactive compounds. These NADES are not just eco-friendly alternatives; they're precision tools for future sustainable processes.

Key Points

• Ten type-V NADES synthesized with urea and three donor groups.
• High polarity comparable to water, tunable via third component.
• Green, versatile solvents for bioactive extraction and solvation.