Diffusional attenuation during soft pulses: A Zangger-Sterk pure shift iDOSY experiment

Area of Science:

• Nuclear Magnetic Resonance Spectroscopy
• Physical Chemistry

Background:

• Diffusion-ordered spectroscopy (DOSY) experiments are valuable for measuring diffusion coefficients.
• Zangger-Sterk pure shift DOSY experiments offer advantages in simplicity and sensitivity.
• Analytical calculation of diffusional attenuation in these experiments is challenging.

Purpose of the Study:

• To numerically investigate diffusional attenuation in Zangger-Sterk pure shift iDOSY experiments.
• To establish a model for predicting experimental outcomes.
• To enable accurate diffusion coefficient measurements for small molecules.

Main Methods:

• Numerical simulations of diffusional attenuation.
• Modeling the dependence of attenuation on diffusion-encoding gradient amplitude.
• Analytical calculation for a limiting case (hard 180° pulse).
• Comparison of numerical simulations with experimental data.

Main Results:

• Diffusional attenuation follows a shifted Gaussian function of gradient amplitude under typical conditions.
• A limiting gradient shift can be analytically determined.
• Selective pulse shapes introduce a scaling factor for the gradient shift.
• Experimental validation confirms simulation predictions.

Conclusions:

• The pure shift iDOSY method allows for accurate diffusion coefficient measurements in small molecules.
• Accounting for the effective diffusion-encoding gradient shift is crucial for precise results.
• Numerical modeling provides a robust approach to understanding and optimizing these experiments.