[Ru(Me4phen)2dppz](2+), a Light Switch for DNA Mismatches

Area of Science:

• Coordination Chemistry
• Biophysical Chemistry
• Molecular Diagnostics

Background:

• DNA mismatches are critical in genetic stability and disease, including cancer.
• Detecting DNA mismatches efficiently is crucial for diagnostics and understanding DNA repair mechanisms.
• Ruthenium complexes have shown promise as luminescent probes for nucleic acids.

Purpose of the Study:

• To investigate the luminescent properties of the [Ru(Me4phen)2dppz](2+) complex for detecting single base mismatches in DNA.
• To elucidate the binding mode and affinity of the ruthenium complex to mismatched DNA.
• To assess the potential of this complex as an early diagnostic tool for cancer related to mismatch repair deficiencies.

Main Methods:

• Luminescence spectroscopy to measure emission enhancement upon binding to DNA mismatches.
• Binding affinity studies comparing matched and mismatched DNA sequences.
• Copper(II) phenanthroline quenching experiments to determine the binding site (minor groove).
• Correlation analysis between luminescence intensity and thermodynamic destabilization of mismatches.

Main Results:

• The [Ru(Me4phen)2dppz](2+) complex exhibits significantly enhanced luminescence in the presence of DNA single base mismatches.
• The complex shows a 26-fold higher binding affinity for mismatches than for matched base pairs.
• The excited state emission lifetime is longer for ruthenium bound to mismatches (160 ns) compared to matched sites (35 ns).
• Binding occurs via a metalloinsertion mode from the minor groove, confirmed by quenching experiments.
• Luminescence intensity correlates with the thermodynamic destabilization of the DNA mismatch.

Conclusions:

• The [Ru(Me4phen)2dppz](2+) complex acts as a sensitive luminescent "light switch" for single base DNA mismatches.
• The observed luminescence enhancement is attributed to higher binding affinity and longer excited state lifetime at mismatch sites.
• The metalloinsertion binding mode from the minor groove is key to the complex's selectivity.
• This ruthenium complex holds potential as a novel diagnostic tool for detecting deficiencies in DNA mismatch repair, relevant for early cancer detection.