Damodaran Krishnan Achary Explains Choosing NMR Techniques for Complex Systems

Damodaran Krishnan Achary, research professor and director of the Nuclear Magnetic Resonance (NMR) Facility at the University of Pittsburgh, discusses strategies for selecting NMR techniques to study complex chemical systems. Drawing on decades of experience managing one of the university’s most versatile NMR facilities, Achary highlights how different experiments provide unique insights into molecular structure, dynamics, and interactions that would be difficult or impossible to obtain using conventional methods.

Pulse field gradient (PFG) NMR, he explains, is particularly powerful for measuring diffusion coefficients and probing molecular connectivity. Achary provides examples from polymer and nanomaterials research: in one case, diffusion NMR confirmed the formation of a block copolymer by comparing the diffusion of the individual polymer blocks with the final molecule. Similarly, the technique can distinguish between free and bound ligands on nanoparticle surfaces based on differences in molecular mobility, a task that standard NMR cannot resolve.

Relaxation NMR experiments are ideal for investigating ultra-fast dynamics and small-scale molecular aggregations. They are also essential for quantitative NMR, where accurate knowledge of nuclear relaxation times ensures reliable measurements of concentrations or structural populations. Multinuclear NMR further expands the analytical toolkit, offering insights from nuclei beyond ^1H and ^13C. Achary notes that his facility has successfully examined more than two dozen different NMR-active nuclei, often using broad-band probes without additional hardware, providing complementary information on chemical environments and interactions.

Finally, ultra-high-resolution techniques, including reduced spectral width and pure shift NMR, enable the detailed characterization of complex small molecules when conventional 2D experiments lack sufficient resolution. These approaches enhance peak separation, clarify overlapping signals, and provide deeper structural insights.

Through these examples, Achary emphasizes the importance of matching NMR methodology to the scientific question at hand. By leveraging diffusion, relaxation, multinuclear, and ultra-high-resolution experiments, researchers can extract detailed structural and dynamic information from complex systems, illustrating the versatility and power of modern NMR spectroscopy.