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Published on: January 24, 2018
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Solvation of the Glycyl Radical
Bun Chan1,2, Jamie Rintelman3, Geoffrey P F Wood2
1Graduate School of Engineering , Nagasaki University , Bunkyo 1-14 , Nagasaki 852-8521 , Japan.
The Journal of Physical Chemistry. A
|August 31, 2018
Summary
Explicit water molecules stabilize the zwitterionic glycyl radical, but the neutral form remains energetically favored. This solvation impacts hydrogen abstraction pathways, potentially protecting amino acids from radical damage in biological systems.
Area of Science:
- Computational chemistry
- Biophysical chemistry
- Free radical chemistry
Background:
- Glycine exists as a zwitterion in aqueous solution, while the glycyl radical prefers a neutral form.
- Understanding the energetic landscape of these species is crucial for predicting their reactivity and biological implications.
Purpose of the Study:
- To investigate the effect of explicit water molecules on the stability of neutral (N) and zwitterionic (Z) glycyl radicals.
- To determine the solvation requirements for stabilizing the zwitterionic form and its energetic relationship with the neutral form.
- To analyze the implications of these solvation effects on the hydrogen abstraction reaction pathway.
Main Methods:
- Quantum chemical calculations were employed to model the glycyl radical in the presence of varying numbers of explicit water molecules.
- Energy differences between the neutral and zwitterionic forms were computed to assess stability.
- Transition structures for hydrogen abstraction by the hydroxyl radical were analyzed.
Main Results:
- A minimum of three water molecules are needed to stabilize the zwitterionic glycyl radical as a local minimum.
- Even with approximately 20 water molecules, the neutral form remains energetically favored over the zwitterionic form by about 50 kJ mol⁻¹.
- Energetic convergence is driven by the solvation of polar functional groups, not complete molecular solvation.
- The transition structure for α-hydrogen abstraction more closely resembles glycine than the glycyl radical.
- The barrier for hydrogen abstraction is higher from zwitterionic glycine compared to the neutral isomer.
Conclusions:
- Solvation by explicit water molecules influences the relative stability of neutral and zwitterionic glycyl radicals.
- The preference for the neutral form of the glycyl radical in aqueous environments is maintained even with significant solvation.
- The increased hydrogen abstraction barrier from zwitterionic glycine may offer a protective mechanism against radical damage to free amino acids in biological systems.
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