Intermolecular interactions and 3D structure in cellulose-NaOH-urea aqueous system

Area of Science:

• Cellulose science and technology
• Polymer chemistry
• Materials science

Background:

• Cellulose dissolution in NaOH/urea aqueous solution at low temperatures is a significant advancement.
• Understanding the molecular interactions is key to optimizing this process.

Purpose of the Study:

• To elucidate intermolecular interactions in cellulose/NaOH/urea aqueous solution.
• To characterize the structure of formed inclusion complexes.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy ((15)N and (23)Na) to probe molecular interactions.
• Cryogenic Transmission Electron Microscopy (Cryo-TEM) for structural observation.
• M06-2X/6-31+G(d) theoretical calculations for 3D structure modeling.

Main Results:

• Direct hydrogen bonding observed between hydroxyl ions (OH-) and urea, not directly with cellulose.
• Sodium ions (Na+) interact with both cellulose and urea.
• Formation of cellulose-NaOH-urea-H2O inclusion complexes (ICs) confirmed.
• Low temperature enhances hydrogen bonding and cluster stability, aiding cellulose binding.
• ICs exhibit extended conformation (3.6 nm diameter, 300 nm length).
• Intramolecular hydrogen bonds (O3H···O5) may persist within ICs.

Conclusions:

• The study clarifies the interaction mechanism in cellulose/NaOH/urea solutions.
• The 3D structure of cellulose chains within dilute solutions is elucidated.
• Findings provide insights into the formation and stability of cellulose inclusion complexes.