Raman spectroscopic approach to monitor the in vitro cyclization of creatine → creatinine

in: Chemical Physics Letters (2015)
Singh, Ranjan K.; Gangopadhyay, Debraj; Singh, Sachin Kumar; Singh, Pushkar; Tarcea, Nicolae; Deckert, Volker; Popp, Jürgen; Sharma, Poornima
The cyclisation of creatine → creatinine occurs naturally in body through an enzymatic pathway. It acts as a primary source of energy during muscular activity. Several experimental techniques have been used earlier to investigate the kinetics of this reaction in vitro. In the present work a novel approach to study the kinetics of this reaction at molecular level and step by step monitoring of the reaction intermediates (neutral, zwitterionic and protonated microspecies of creatine) has been applied with precision employing Raman spectroscopy. The time series Raman spectra of aqueous solution of creatine at pH ~3 have been analyzed to estimate the amount of each of the three microspecies at specific time intervals. The in vitro cyclisation mechanism has been correlated with the metabolic creatine → creatinine cyclisation. The protonated species of creatine has been found to be the precursor of cyclic creatinine and clear signature of creatinine formation is observed in the spectra after ~180 minutes. Rate constants calculated at three different pH values (~1, ~3 and ~5) from Raman spectral intensities clearly show that at room temperature the reaction has highest rate at pH ~3 and slows down at higher as well as lower pH values. Thus acidic environment in blood or acidosis will increase the rate of creatinine formation which is hazardous for renal patients.

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