¹H NMR Chemical Shifts and J-Coupling Constants Dependence on Temperature and pH: Implications for the Quantification...

¹H MRS enables the non-invasive measurement of various compounds in biological systems, both in vitro and in vivo. It thus offers the possibility of investigating characteristic metabolic processes and identifying biomarkers under both normal and pathological conditions. Therefore, a reliable quantification of important compounds is essential. Many quantification methods established for this purpose use model spectra based on prior knowledge of chemical shifts and J-coupling constants. The broad application range of ¹H MRS also allows its use at different temperatures and pH values based on the physiological conditions of the model organism. Against this background, this work aimed to investigate 15 important metabolic compounds in terms of their temperature and pH dependence of chemical shifts and J-coupling constants. The results indicate that the majority of the compounds exhibit significant changes in their spectra in response to temperature changes. Additionally, the pH can significantly influence the spectra. Therefore, model functions were calculated to predict the chemical shift and the J-coupling constants in the investigated range for each combination of temperature and pH. In addition, the influence of incorrect prior knowledge in quantifying the metabolite concentration was analysed. For the higher concentrated metabolites (> 2 mM), only minor errors in the quantification result from the use of incorrect prior knowledge regarding the chemical shifts and the J-coupling constants, except for Cr and PCr. As the concentration of the metabolite decreases, the percentage error in the estimated concentration increases. Thus, the model functions can be applied to quantifying spectra for various organisms and their specific physiological properties. This optimisation is essential to avoid or minimise errors in quantifying ¹H MRS data.