A time-resolved photoacoustic calorimetry study of the dynamics of enthalpy and volume changes produced in the photodissociation of carbon monoxide from sperm whale carboxymyoglobin.

The dynamics of the enthalpy and volume changes produced in the photodissociation of carbon monoxide from sperm whale myoglobin is investigated by time-resolved photoacoustic calorimetry. The enthalpy and volume changes for the formation of the geminate pair, which occurs within 50 ns of photolysis, are delta H = -2.2 +/- 2.8 kcal/mol and delta V = -10.0 +/- 1.0 mL/mol relative to carboxymyoglobin. The enthalpy and volume changes associated with formation of deoxymyoglobin and solvated carbon monoxide, formed with a half-life of 702 +/- 31 ns at 20 degrees C, are delta H = 14.6 +/- 3.4 kcal/mol and delta V = 5.8 +/- 1.0 mL/mol relative to carboxymyoglobin.