title: Nanoscale Catalysts for NMR Signal Enhancement by Reversible Exchange.
abstract: Two types of nanoscale catalysts were created to explore NMR signal enhancement via reversible exchange (SABRE) at the interface between heterogeneous and homogeneous conditions. Nanoparticle and polymer comb variants were synthesized by covalently tethering Ir-based organometallic catalysts to support materials comprised of TiO2/PMAA (poly methacrylic acid) and PVP (polyvinyl pyridine), respectively, and characterized by AAS, NMR, and DLS. Following parahydrogen (pH2) gas delivery to mixtures containing one type of "nano-SABRE" catalyst particles, a target substrate, and ethanol, up to ~(-)40-fold and ~(-)7-fold1H NMR signal enhancements were observed for pyridine substrates using the nanoparticle and polymer comb catalysts, respectively, following transfer to high field (9.4 T). These enhancements appear to result from intact particles and not from any catalyst molecules leaching from their supports; unlike the case with homogeneous SABRE catalysts, high-field (in situ) SABRE effects were generally not observed with the nanoscale catalysts. The potential for separation and reuse of such catalyst particles is also demonstrated. Taken together, these results support the potential utility of rational design at molecular, mesoscopic, and macroscopic/engineering levels for improving SABRE and HET-SABRE (heterogeneous-SABRE) for applications varying from fundamental studies of catalysis to biomedical imaging.
authors.affiliation: Department of Chemistry and Biochemistry, Southern Illinois University, Carbondale, Illinois 62901.
authors.forename: Fan
authors.initials: F
authors.lastname: Shi
authors.affiliation: Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee 37232-2310, United States ; Department of Radiology, Vanderbilt University, Nashville, Tennessee 37232-2310, United States.
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Coffey
authors.affiliation: Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee 37232-2310, United States ; Department of Radiology, Vanderbilt University, Nashville, Tennessee 37232-2310, United States ; Department of Physics, Vanderbilt University, Nashville, Tennessee 37232-2310, United States.
authors.forename: Kevin W
authors.initials: KW
authors.lastname: Waddell
authors.affiliation: Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee 37232-2310, United States ; Department of Radiology, Vanderbilt University, Nashville, Tennessee 37232-2310, United States ; Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee 37232-2310, United States ; Vanderbilt-Ingram Cancer Center (VICC), Vanderbilt University, Nashville, Tennessee 37232-2310, United States ; Department of Biochemistry, Vanderbilt University, Nashville, Tennessee 37232-2310, United States.
authors.forename: Eduard Y
authors.initials: EY
authors.lastname: Chekmenev
authors.affiliation: Department of Chemistry and Biochemistry, Southern Illinois University, Carbondale, Illinois 62901 ; Materials Technology Center, Southern Illinois University, Carbondale, Illinois 62901, United States.
authors.forename: Boyd M
authors.initials: BM
authors.lastname: Goodson
keywords: HET-SABRE; Iridium; PHIP; SABRE; hyperpolarization; parahydrogen