The enthalpy of formation of selenocysteine: A G3 and G4 quantum chemical study

• The gas phase ΔHf of selenocysteine has been calculated.
• The two divergent values for the gas phase ΔHf of diethyl selenide have been disentangled and a value assigned.
• The lowest energy conformers for selenocysteine have been identified.

The gas phase enthalpy of formation of the amino acid containing selenium, selenocysteine, has been calculated using G3 and G4 calculations, the values being (−347.7 and −345.2) kJ · mol−1, respectively. The enthalpies of formation of the counterpart amino acids containing oxygen and sulfur, serine and cysteine, have also been calculated. The enthalpies of formation of compounds H2Z, C2H5ZH and (C2H5)2Z (ZO, S, Se) have been calculated and compared with their available experimental values. The agreement between calculated and experimental values gives us confidence in our calculated values for the gas phase enthalpy of formation of selenocysteine.

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