FmR α analysis: Rapid and direct estimation of relaxation and kinetic parameters from dynamic nuclear polarization time courses

Purpose To introduce a direct method for estimating relaxation and kinetic parameter values from rapid dissolution dynamic nuclear polarization (RD‐DNP) NMR time courses. Theory and Methods The analysis relied on a kinetic model that is often used to analyze data in these studies—a unidirectional (bio)chemical reaction with rate constant k 1 , coupled to longitudinal relaxation of the magnetization of substrate and product that is characterized by the time constant T 1 . The latter value was estimated from the width of the product curve (peak) at the height α relative to the maximum height. We showed α ∼ 0.8 under most conditions, so we measured the interval between the falling and rising parts of the curve at the relative height 0.8. We called this the “fall‐minus‐rise time at height α ,” or FmR α , and found that FmR 0.8 ∼ T 1 . The ratio β = (product signal/substrate signal) when the product is maximal was shown to be equal to k 1 T 1 . Therefore, k 1  =  β/FmR 0.8 . Results FmR α analysis was demonstrated with 13 C NMR RD‐DNP data recorded from hemolysates and from previously published data. Conclusion FmR α analysis enables immediate estimates of kinetic and relaxation parameters from 13 C NMR RD‐DNP data. The values can be used as initial estimates in more extensive computer‐based data‐regression analysis. Magn Reson Med 73:2075–2080, 2015. © 2014 Wiley Periodicals, Inc.