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Abstract #1671

Determination of the PKa of a Hyperpolarized H13CO3- PH Probe

Thomas C. Booth1, 2, Mikko I. Kettunen1, 2, Ferdia A. Gallagher1, 2, Brett WC Kennedy1, 2, Tiago B. Rodrigues1, 2, Sarah E. Bohndiek1, 2, Kevin M. Brindle1, 2

1Biochemistry, University of Cambridge, Cambridge, United Kingdom; 2Cambridge Research Institute, Cancer Research UK, Cambridge, United Kingdom

Tissue pHe can be determined using 13C MRS and hyperpolarized 13C-labelled bicarbonate. Using an assumed pKa, the H13CO3- and 13CO2 signal intensities allow pH determination using the Henderson-Hasselbalch equation. We compared pH derived by DNP NMR with direct potentiometric measurement of H+ activity using a glass electrode. Using pKa = pH log ([H13CO3]/[ 13CO2]), we assigned the pH determined potentiometrically as the standard and determined whether the 13C MRS derived pKa diverges when there is alteration of ionic strength, pH, temperature and protein concentration within a clinically relevant range of values. Additionally, the pKa in human blood was determined.