Mechanistic Insights into NO Releasing by Functionalized Carbon Quantum Dots: A DFT Study

Area of Science:

• Nanomaterials Science
• Computational Chemistry
• Biomedical Engineering

Background:

• Carbon quantum dots (CQDs) are explored for photoresponsive nitric oxide (NO) delivery.
• Understanding the photolytic mechanism and functionalization effects is crucial for rational design.

Purpose of the Study:

• To elucidate the atomistic mechanism of NO release from functionalized CQDs under visible light.
• To investigate the role of CQD functionalization and physiological pH on NO release.

Main Methods:

• Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) calculations were employed.
• A model system (CQD_CA ^CYS+TPP···NO) was systematically investigated.
• Ground-state reactivity, protonation effects, and excited-state properties were probed.

Main Results:

• Cysteine deprotonation is essential for S-NO bond formation.
• A low-energy, SNO-localized excited state with n → π* character drives photoinduced electron transfer.
• The system remains stable under physiological pH but is destabilized in very acidic conditions.

Conclusions:

• A mechanistic framework for light-induced NO release from functionalized CQDs was established.
• Findings clarify the synergistic roles of CQD, cysteine, TPP, and NO moieties.
• Provides principles for engineering advanced CQD platforms for biomedical applications.