engleski

A new method for spectrophotometric determination of protonation constants

A new method for the determination of stoichiometric protonation constants by means of spectrophotometric titrations was developed and implemented in the commercial program Mathematica [1]. The method does not include the pH measurements. It was validated on the simulated spectra generated using the program Simulant [2] and thereafter used to determine protonation constants of the potassium hydrogen phthalate (KHPh) and 1-(p-toluenesulfonyl)cytosine (TsC) [3] in aqueous solutions. For comparison, the data obtained by simultaneous potentiometric and spectrophotometric titrations were analysed by the commercial program SPECFIT [4, 5]. The agreement between the pK values determined with different computational (and experimental) approaches was satisfactory. The protonation constant of TsC has not been previously determined. The obtained value (lg(K1/dm3 mol-1) = 2.34) is more than two units lower than the value for cytosine (lg(K1/dm3 mol-1) = 4.61) [6]. A detailed explanation of such a significant influence of tosyl group remains the subject of further research.

protonation constant ; spectrophotometric determination

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