Probing a Hydrogen-π Interaction Involving a Trapped Water Molecule in the Solid State

Area of Science:

• Solid-state chemistry
• Biomacromolecular analysis
• Advanced spectroscopy

Background:

• Detecting and characterizing trapped water molecules in solid materials, including biomacromolecules, presents significant challenges.
• Understanding water's role in molecular recognition is crucial for chemistry and biology.

Purpose of the Study:

• To develop and demonstrate a method for detecting single water molecules within solid chemical entities.
• To investigate the non-covalent interactions binding water molecules in complex structures.
• To establish proton-detected solid-state NMR as a key technique for probing weak interactions.

Main Methods:

• Proton-detected solid-state Nuclear Magnetic Resonance (NMR) experiments.
• High magnetic field strengths (28.2 T) and magic-angle spinning (100 kHz).
• Quantum-chemical calculations, including Density Functional Theory (DFT).

Main Results:

• Successfully detected a single water molecule within a calix[4]arene cavity of a lanthanide complex.
• Observed water proton resonances near 0 ppm, confirmed by DFT calculations.
• DFT calculations revealed the sensitivity of proton chemical shifts to hydrogen-π interactions.

Conclusions:

• Proton-detected solid-state NMR is effective for detecting single water molecules in solid-state systems.
• The technique can probe weak non-covalent interactions, such as hydrogen-π interactions.
• This method is becoming essential for studying molecular recognition in chemistry and biology.