Understanding the Solid-State Structure of Riboflavin through a Multitechnique Approach.

Area of Science:

• Biophysics
• Crystallography
• Materials Science

Background:

• Riboflavin (vitamin B2) acts as an optically functional material in the tapetum lucidum, enhancing vision in low-light conditions.
• The solid-state structure of biogenic riboflavin is not well-understood, limiting the rationalization of its biological function.

Purpose of the Study:

• To determine the solid-state structure of synthetic riboflavin.
• To elucidate the intermolecular hydrogen-bonding arrangement in crystalline riboflavin.
• To investigate the optical properties of riboflavin for its biological role.

Main Methods:

• Multitechnique approach including microcrystal X-ray diffraction (XRD), powder XRD, and 3D electron diffraction (3D-ED).
• High-resolution solid-state 13C Nuclear Magnetic Resonance (NMR) spectroscopy.
• Dispersion-augmented density functional theory (DFT-D) calculations and refractive index measurements.

Main Results:

• A novel solid-state structure of riboflavin was determined, differing in hydrogen bonding from previous reports.
• Experimental and computational methods consistently supported the proposed structure and hydrogen-bonding network.
• Refractive index values for riboflavin were experimentally and computationally determined.

Conclusions:

• The determined solid-state structure provides insights into riboflavin's optical function in the tapetum lucidum.
• The study highlights potential challenges in using DFT-D for hydrogen-bonded material structure determination.
• Understanding riboflavin's structure is vital for its role in vision and potentially other optical applications.