Electronic Excitations in G-quadruplexes Formed by the Human Telomeric Sequence: A Time-Resolved Fluorescence Study

Area of Science:

• Biophysics
• Molecular Biology
• Spectroscopy

Background:

• G-quadruplexes are crucial DNA structures, particularly in telomeres.
• Understanding their photophysical properties is key to their biological function.

Purpose of the Study:

• To investigate the photophysical properties of the human telomeric G-quadruplex (Tel21/K+).
• To elucidate the dynamics of electronic excitations and energy transfer within the G-quadruplex structure.

Main Methods:

• Femtosecond to nanosecond fluorescence decay and anisotropy measurements.
• Excitation at 267 nm using fluorescence upconversion and time-correlated single photon counting.
• Analysis in conjunction with theoretical studies.

Main Results:

• Efficient energy transfer among bases occurs on the femtosecond timescale via exciton states.
• Major fluorescence originates from bright excited states (1-100 ps) with weak charge transfer character.
• Charge transfer states involving guanines decay after 100 ps, emitting in the red spectrum.
• Tel21/K+ exhibits longer electronic excitation persistence and more pronounced charge transfer than tetramolecular G-quadruplexes.

Conclusions:

• The structural rigidity of the monomolecular Tel21/K+ G-quadruplex enhances electronic excitation persistence.
• Reduced nonradiative decay pathways and favored collective effects contribute to distinct photophysical properties.
• These findings offer insights into the photophysics of telomeric G-quadruplexes and their potential biological implications.