Rotamer-specific fluorescence quenching in tyrosinamide: Dynamic and static interactions

Area of Science:

• Biophysical Chemistry
• Photochemistry
• Molecular Spectroscopy

Background:

• Tyrosinamide exhibits distinct phenol rotamer conformations around the C(α)-C(β) bond.
• Fluorescence quenching is a sensitive technique for probing molecular environments and interactions.
• Acrylamide is a common quencher used to study excited-state dynamics.

Purpose of the Study:

• To investigate the environments of tyrosinamide's three phenol rotamers using fluorescence quenching.
• To analyze the contributions of dynamic and static quenching to the observed nonlinear Stern-Volmer plots.
• To determine the fractional intensity and dynamic quenching constants for individual rotamers.

Main Methods:

• Steady-state fluorescence quenching with acrylamide.
• Time-resolved fluorescence quenching studies.
• Analysis of Stern-Volmer plots to differentiate quenching mechanisms.

Main Results:

• Steady-state acrylamide quenching of tyrosinamide produced nonlinear Stern-Volmer plots.
• Time-resolved studies allowed independent determination of fractional intensity and dynamic quenching constants for each rotamer.
• The nonlinearity was attributed to distinct dynamic quenching constants for each rotamer and the presence of static quenching.

Conclusions:

• The nonlinear Stern-Volmer plot for tyrosinamide is explained by the presence of multiple rotamers with unique dynamic quenching behaviors.
• Static quenching contributes to the observed nonlinearity, consistent with either the sphere-of-action or ground-state complex models.
• This study provides a detailed understanding of tyrosinamide's photophysical properties in solution.