FLUORESCENCE OF CYSTEINE AND CYSTINE

We interpret the UV absorption and fluorescence of cysteine and cystin e from ab initio calculations of the ground states and lowest excited singlet states of the two molecules. We derive the optimized energies and geometry parameters from HF/6-31G computations on the ground state and CIS/6-31G computations of the excited state. We present vibration al frequencies of the ground and excited states and quantitative predi ctions for UV absorption and fluorescence. We also show experimental m easurements of cystine fluorescence. Cystine is shown to fluoresce at 700 nm.