Calibration of the EVB potential

0 for phenol and 8.3 for cysteine. From these pK s and those of water (15.7), PhOPOjH (5.7) and CH3CH2SPO3H (5.9) the barriers for reaction of OH with Ph0P03H and RSPO3H can be estimated as 19.2 and 13.5 kcal/mol, respectively. Also the barriers for PhO and RS attack on phosphate monoanion (reverse reactions) are obtained as 32.0 and 29.2 kcal/mol, respectively. The barrier for OH reaction with methyl phosphate monoanion is estimated to be 

These results can now be combined to give two free energy profiles each having two TSs separated by a high-energy minimum for the uncatalyzed reaction in water. 

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