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Kinetics of the Base Vatalysed Hydrolysis of MethylParaben Revisited: Implications for Determination of the Effective Volume of Flowmicrocalorimeters Used to Study Cell Cultures


R.N. Bento, M.A. Rendas, C.E.S. Bernardes, M.S.C.S. Santos, F. Antunes, M.E. Minas da Piedade

Thermochim. Acta 2018, 659, 82-88.

DOI: 10.1016/j.tca.2017.11.008

Abstract

The kinetics of hydrolysis of methyl paraben (methyl 4-hydroxybenzoate, MP) by NaOH has been proposed as a reference system to calibrate the effective volume (Veff) of flow-calorimetry vessels that are often used in studies of living cells. This parameter is essential to relate the observed calorimetric signal with a specific cell number or biomass and its determination relies on a rate constant, k, obtained under the assumption of pseudo-first-order kinetics. The significant discrepancies noted between published k values led us to test the reliability of this approximation for different NaOH/MP concentration ratios and at temperatures in a range typically used for living cell studies (292–310 K). Kinetic experiments carried out by spectrophotometry, isothermal microcalorimetry, and flow microcalorimetry indicated that the 9/1 NaOH/MP molar ratio typically used for Veff determinations does not ensure the pseudo-first-order kinetic conditions assumed in the Veff calculation model. It is recommended that a NaOH excess of at least 20/1 be used to warrant a < 5% error in k, which translates into an identical error in Veff.

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