Mapping H⁺ in the Nanoscale (A₂C₄)₂-Ag₈ Fluorophore.

Area of Science:

• Supramolecular Chemistry
• Biophysical Chemistry
• Materials Science

Background:

• DNA-silver nanostructures can form supramolecular optical chromophores.
• Understanding the structure-spectrum relationship in these nanoscale materials is crucial but poorly understood.

Purpose of the Study:

• To elucidate the atomic-level structure and protonation patterns of the green-emitting fluorophore (A2C4)2-Ag8.
• To correlate the specific DNA structure with its observed optical spectrum.
• To investigate the role of silver ions in perturbing DNA's electronic properties.

Main Methods:

• Neutron diffraction was employed to map protonation sites within the (A2C4)2-Ag8 complex.
• Calorimetry studies were conducted to assess silver ion cross-linking.
• Spectroscopic analysis was inferred from the fluorophore's emission.

Main Results:

• The DNA host in (A2C4)2-Ag8 exhibits two distinct substructures with unique protonation patterns.
• Three cytosines per strand chelate a silver cluster, with Ag+ likely acting as cross-linkers.
• Adenines and adjacent cytosines anchor a second silver cluster via deprotonated nitrogen atoms, indicating silver-induced electronic perturbation.

Conclusions:

• The specific arrangement of silver ions and the resulting DNA protonation states are critical for the observed green fluorescence.
• Atomic-level structural insights provide a pathway to control and tune the electronic spectra of DNA-silver nanoclusters.
• This work highlights the potential for designing novel optical materials based on DNA-metal interactions.