Accurate Molecular Size Determination by Diffusion Ordered NMR Spectroscopy Based on an Improved Diffusion Model

Area of Science:

• Chemistry
• Physical Chemistry
• Chemical Physics

Background:

• Diffusion coefficients are crucial for understanding molecular behavior.
• Diffusion-ordered spectroscopy (DOSY) NMR is a key technique for measuring diffusion coefficients.
• Existing models for correlating diffusion coefficients with molecular descriptors have limitations across different substance classes.

Purpose of the Study:

• To develop a novel semiempirical model for interpreting diffusion coefficients.
• To establish a more universally applicable model for small molecule diffusion.
• To improve the correlation between diffusion coefficients and molecular descriptors.

Main Methods:

• Analysis of existing diffusion models using a dataset of 95 molecules.
• Development of a new semiempirical model based on molecular volume.
• Validation of the model across diverse compound classes including organic, organometallic, and coordination compounds.

Main Results:

• Previous models assuming spherical molecules introduce significant errors.
• The new model using molecular volume achieves a 2σ error range of 12% for diffusion coefficients.
• The model demonstrates accuracy for organic, organometallic, and coordination compounds, independent of molecular weight or density.

Conclusions:

• Molecular volume is a superior descriptor for diffusion compared to radius-based parameters.
• The developed model provides an accurate and broadly applicable method for interpreting DOSY NMR diffusion data.
• The model's utility is confirmed by its precise analysis of uranyl complexes.