ANOMALOUS TEMPERATURE FLUORESCENCE QUENCHING OF N-TRP TERMINAL PEPTIDES

The photophysics of Trp-containing peptides is extremely affected by t he position of the indole ring with respect to the substituents. In th is work an unusual temperature fluorescence quenching behavior is pres ented. The N-tryptophan terminal peptides (N-Trp) show an increase of the static emission intensity as rising the temperature from 10 to abo ut 40 degrees C. The anomaly is typical of the N-Trp terminal peptides since neither tryptophan (Trp) nor glycyl-tryptophan (Gly-Trp) and al anyl-tryptophan (Ala-Tip) show the same trend, a similar behavior is n ot detected in the C-tryptophan terminals. The other important feature s are the wavelength and pH dependence of the effect. The anomaly is i n fact detected only at neutral pH and for excitation wavelength nea, the red edge of the UVB absorption band of indole. An interpretation o f the anomaly is suggested, though more sophisticated techniques are n eeded to better focus the problem; the model proposed involves the sup erimposition of a ground state effect (the temperature-induced equilib rium shift from the zwitterionic to the anionic form of the peptides) and an excited state mechanism. At present no unique interpretation ca n be provided about the excited state mechanism that favors the anomal y and some suggestions are discussed. (C) 1995 John Wiley, & Sons, Inc .