Disulfide Chromophores Arise from Stereoelectronic Effects.

Bonds between sulfur atoms are prevalent in natural products, peptides, and proteins. Disulfide bonds have a distinct chromophore. The wavelength of their maximal absorbance varies widely, from 250 to 500 nm. Here, we demonstrate that this wavelength derives from stereoelectronic effects and is predictable using quantum chemistry. We also provide a sinusoidal equation, analogous to the Karplus equation, that relates the absorbance maximum and the C-S-S-C dihedral angle. These insights provide a facile means to characterize important attributes of disulfide bonds and to design disulfides with specified photophysical properties.