Intramolecular electronic excitation energy transfer in dermorphine and its analogues

The fluorescence quantum yields of dermorphine and its analogues Ala¹-dermorphine and Ala⁵-dermorphine were measured at the two different excitation wavelengths λ₁ = 280 nm and λ₂ = 260 nm. Hence the efficiencies of the excitation energy transfer from phenylalanine to tyrosine in the above oligopeptides were determined. It has been found from the results obtained that the mean phenylalanine-tyrosine separation in Ala⁵-dermorphine is 10^ longer than that in Ala¹-dermorphine. Moreover, good agreement was found between the quantum efficiency of energy transfer for dermorphine and the value calculated from kinetic equations using the transfer efficiencies determined for Ala¹- and Ala⁵-dermorphine analogues.