What is a Radical Pair?
- A radical is a molecule with an unpaired electron spin and thus has spin s=1/2.
- When two single electron wave functions, one on each of two adjacent atoms, overlap they create a bonding orbital which then contains two electrons, one from each atom.
- A singlet state is when the spins of the two electrons are aligned oppositely.
- A triplet state is when the spins are aligned parallel.
- When a molecule is exposed to light of a certain wavelength (s), it can result in the sudden rupture of a covalent bond. The two resulting pieces are known as free-radicals.
An external field only influences radical pairs, generally by slowing down processes that require a change of spin. When a magnetic field is applied, less radicals can change their spin and more succeed in separating from their partner. The consequence of this is that, on average, radicals live longer and their overall concentration increases when a field is applied.
- To have an effect on the average lifetime of a radical pair a MF must alter the transition rate between the original S state and the T state.
- Some failings in the RPM at low MF values (~GMF) have been overcome in a new mechanism described by Timmel et al 1998 and Ritz et al 2000, that could change the lifetime of a radical pair in external magnetic fields much smaller than hyperfine fields.
- Essentially QM in nature, when a small MF is applied, pairs of electron spin energy levels that were degenerate in the absence of the applied field, split into resolved doublets.
- In theory this leads to an increase in the singlet to triplet conversion rate and thus increase the life of a radical pair formed in a singlet state, and that increasing the magnetic field further could lead to a decrease in the singlet to triplet conversion rate and hence a decrease in the RP lifetime as the applied field becomes comparable with the effective hyperfine fields.
Above Diagram - schematic representation of the radical pair interconversion process. Source: Ritz et al, 2000.
What are the Dangers Posed by Radical Pairs in the Human body?
- Free radicals can cause cellular and DNA damage.
- DNA damage can lead to the development of cancer.
Given the recognized importance of free radicals on a wide range of biological processes, from aging to cancer, there is little doubt that any external agent that can influence free-radical behaviour can have health consequences for the human body.