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Hydrogen Transfer-Driven Photocatalysis in a Hydrogen-Bonded Melamine-Barbiturate Assembly
Ivan V Moskalenko1, Eleonora Shliakhova1, Artur Abdullaev1
1Infochemistry Scientific Center, ITMO University, Saint-Petersburg 191002, Russia.
The Journal of Physical Chemistry. A
|March 19, 2026
Summary
Hydrogen-bonded supramolecular assemblies generate reactive oxygen species (ROS). This study reveals mechanisms of ROS and radical generation in melamine barbiturate crystals, offering a new detection strategy.
Area of Science:
- Supramolecular chemistry
- Photochemistry
- Materials science
Background:
- Metal-free photocatalysts are sought as alternatives to metal-based ones.
- Supramolecular assemblies offer a promising platform for photogeneration of reactive oxygen species (ROS).
- Melamine barbiturate (MB) crystals are investigated for their photophysical properties.
Purpose of the Study:
- To investigate the mechanisms of ROS and radical generation in melamine barbiturate (MB) crystals.
- To explore the potential of MB assemblies as metal-free photocatalysts.
- To develop a novel method for detecting short-lived radicals within crystal lattices.
Main Methods:
- Electron Paramagnetic Resonance (EPR) spectroscopy to detect singlet oxygen (1O2) and radicals.
- Quantum chemical modeling to elucidate reaction pathways.
- Synthesis of MB assemblies encapsulating a TEMPO-ol nitroxyl probe.
- X-ray diffraction for structural characterization.
- Kinetic experiments and thermodynamic parameter calculations.
Main Results:
- UV irradiation of MB crystals generated singlet oxygen (1O2) with a steady-state concentration of (1.2 ± 0.3) × 10-14 M.
- Quantum chemical modeling confirmed 1O2 reacts with barbituric acid to form hydroperoxyl (HOO·) and carbon-centered radicals.
- A novel supramolecular strategy successfully encapsulated a TEMPO-ol probe within MB crystals.
- The TEMPO-ol probe selectively captured mobile HOO· radicals in situ via exchange interaction, leading to radical termination.
Conclusions:
- Melamine barbiturate crystals are effective in photogenerating singlet oxygen.
- A new method for in situ detection of short-lived radicals in heterogeneous environments was developed using supramolecular assemblies.
- This work provides insights into ROS photogeneration mechanisms and offers a metal-free alternative for photocatalysis and radical detection.
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