Hydroxyl Radical-π Interaction in a Single Crystal.

Area of Science:

• Supramolecular Chemistry
• Organic Radical Chemistry
• Crystallography

Background:

• Organic radical stability is typically achieved through steric hindrance, spin-delocalization, and non-covalent interactions like π-π stacking and hydrogen bonding.
• Previously, no single crystals containing hydroxyl radicals (•OH) had been reported due to their high reactivity.

Purpose of the Study:

• To achieve the stabilization of hydroxyl radicals (•OH) within a single crystal.
• To elucidate the stabilizing interactions responsible for hydroxyl radical (•OH) persistence in the crystalline state.

Main Methods:

• Crystallization from a filtrate containing a chromenopyridine radical (DCP(2)•) and dissolved water.
• Analysis of crystal packing and computational studies to identify stabilizing interactions.
• Confirmation of •OH presence using mass spectrometry (TEMPO adduct), solid-state EPR, solution NBT assay, and DMPO spin trapping.

Main Results:

• Successfully stabilized hydroxyl radicals (•OH) in single crystals alongside DCPH(2).
• Identified π-•OH and •OH···N hydrogen bonding as key stabilizing interactions.
• Experimental and computational methods confirmed the presence and stability of •OH within the crystal structure.

Conclusions:

• This study reports the first instance of stabilizing hydroxyl radicals (•OH) in single crystals.
• Supramolecular interactions, specifically π-•OH and hydrogen bonding, are crucial for stabilizing these highly reactive species in the solid state.
• The findings open new avenues for studying reactive radical species in crystalline environments.