Nuclear magnetic resonance (NMR) spectroscopy utilizes radio-waves to probe atomic-scale structure and dynamics in molecules and materials. NMR is widely applied in fundamental research as well as engineering, medicine and industry. One of the greatest challenges for applications of NMR is the inherently low sensitivity due to the weak alignment of the magnetic nuclei and low efficiency of radio wave (Faraday Law) detection. Hyperpolarization methods can help over overcome this limitation. Over the past few decades, an entire research community devoted to the development of hyperpolarization methods has emerged.
Among the most successful of them is parahydrogen derived polarization (PDP), also known as PHIP. In a 1986 PRL, Prof. Dan Weitekamp (Caltech) proposed that the singlet spin order inherent to parahydrogen could be transformed to NMR-observable hyperpolarization (enhanced, non-equilibrium nuclear spin polarization) by chemical hydrogenation reaction, which would result in high-field NMR signal enhancements exceeding four orders of magnitude. A year later, the prediction was confirmed in the lab by his student and reported in JACS. As of March 2020, the two papers have been cited over 700 times each (Google Scholar), and the research community working on variants of the original “PASADENA” effect continues to expand. A recent review of the many promising applications in biomedicine recently appeared in ACIE.
Bowers re-entered the field in 2015 and his lab has transitioned to parahydrogen enhanced polarization by heterogeneous catalysis as the main research topic. This was made possible by establishing partnerships with experts in catalysis science. One of the main objectives is to develop solid catalysts that deliver high-performance conversion of parahydrogen spin order into hyperpolarization in liquids and gases. In collaboration with Prof. Helena Hagelin-Weaver of UF Chemical Engineering, Pt, Ir, Rh, and Pd nanoparticles were prepared on various support materials (e.g. silica, alumina, titania, and ceria) and tested in a variety of parahydrogen NMR experiments, including the observation of parahydrogen signal enhancement by pairwise replacement catalysis. New insights into the molecular mechanisms and kinetics can be obtained from the spin-dynamics of parahydrogen during catalytic transformations.
Perhaps the most remarkable discovery in the Bowers lab was surface-mediated singlet to magnetization conversion over Pt3Sn intermetallic nanoparticles (iNPs). Referred to as the SWAMP effect (Surface Waters Are Magnetized by Parahydrogen), hyperpolarized water, methanol and ethanol were produced simply by bubbling parahydrogen gas through suspensions of the insoluble catalyst in the Earth’s field. Potential applications include sensitivity enhanced NMR of proteins, medical angiography, and low-field MRI. The. remarkable iNP materials were synthesized in the laboratory of Prof. Wenyu Huang (Iowa State Chemistry Department) using his novel ship-in-a-bottle protocol where the intermetallic phase is prepared within a protective mesoporous silica shell.
Other ongoing collaborative work involves the studies using atomically dispersed Pt stabilized on shaped cerium oxide nanocrystals which exhibit a remarkably high activity and pairwise selectivity. These ultra-low loading catalysts were prepared using a modified Atomic Layer Deposition technique in the laboratory of Prof. Hagelin-Weaver.
With new funding from the NHMFL User Collaborative Grants Program, the Bowers group is currently developing equipment for parahydrogen enhanced NMR that will be made available for external users of the NHMFL-AMRIS facility. This includes a recently completed parahydrogen enrichment system with a demonstrated enrichment of 98% over a wide range of operating conditions. Also under construction are a parahydrogen storage and dispensing system, a high-pressure NMR system for gas/liquid experiments with parahydrogen, and a parahydrogen spray-injection hydrogenation reactor system for solution phase parahydrogen enhanced polarization studies. The combination of state-of-the-art parahydrogen enhanced NMR capabilities and state-of-the-art NMR and imaging spectrometers will provide unparalleled capabilities for NHMFL users.
A unique aspect of the Bowers research program is its interdisciplinary approach. The research has developed a niche area where state-of-the-art catalysis science interfaces with advanced nuclear magnetic resonance techniques and spin dynamics. This also provides extraordinary education and training opportunities. The Bowers group regularly participates in several different NSF Research Experiences for Undergraduates programs as well as UF’s CPET-SSTP where high school students like Jason Katz, a senior at Boca-Raton High School, spend a summer month working in the lab. In addition to the promising applications that can impact society through improvements in health care and better utilization of energy resources, education and training of the next generation of scientists produces broader impacts of the NSF-supported research in the Bowers lab.
The Bowers Lab is committed to a diverse and inclusive multidisciplinary research culture that enables lab members to reach individual goals, advance knowledge in our field, and mentor and train the next generation of scientists. All members of the Bowers Lab contribute to an environment that values and respects all individuals and their unique abilities. A laboratory culture where everyone feels they belong is our priority and critical to our success.