Frequency-dependent polarizabilities of amino acids as calculated by an electrostatic interaction model

The frequency-dependent polarizability of the 20 essential amino acids has been calculated by an electrostatic interaction model where an Unsöld-type of model has been adopted for the frequency dependence. The interaction model has previously been parametrized from Hartree-Fock calculations on a set of molecules, and the model is in this work extended by sulfur parameters by including a set of 18 small sulfur compounds. The results for the amino acids by using the interaction model compare well with Hartree-Fock calculations with deviations of around 5% for the isotropic polarizability. Furthermore, the intrinsic (or optical) dielectric constant related to the polarizability has been calculated for three small proteins, ribonuclease inhibitor, lysozyme, and green fluorescent protein, adopting the interaction model. The results are consistent with the intrinsic dielectric constants found for proteins in the literature.