RF Absorption Involving Biological Macromolecules

Definition:

There has been much attention paid to theoretical mechanisms by which radio frequency (RF) irradiation may affect biological processes. One area that has not been extensively studied is whether RF can subtly effect the action of individual enzymes. In many biological molecules, physical displacement of atoms from one conformation to another is intimately connected to their biological function. For example, the conformation of hemoglobin is altered after one heme group absorbs oxygen in such a way that the three remaining heme groups become much more likely to absorb oxygen. This greatly increases the efficiency of hemoglobin as an oxygen transporter. The change in oxygen affinity is driven by the conformation change of the molecule which involves very localized changes in the conformation of the heme group, as well as change over larger sections of the molecule.

The absorption of RF energy, in all cases discussed, is to modes of bulk matter rather than to intramolecular modes of a specific molecule. The question still remains as to whether that energy can be transmitted to other modes in a way that can athermaly alter biological function. It is known that at high enough temperature, biological function is altered. The question then is, can energy be transferred more efficiently to active modes in a way different from assumptions related to thermal heating. The question can be answered because there is a considerable amount of

knowledge about energy transfer between modes in bulk systems [Maradudin et al., 1963].

Since the intramolecular modes of the molecule have been shown to all be at higher frequencies than those of the bulk matter, the transfer to active modes must involve scattering to higher frequency. The leading scattering terms for lattice modes involve three phonons and the net rate of transfer involve the activation levels of the modes that are out of equilibrium. If there were resonant absorption, the absorbing mode would have the greatest level of activation. 

The leading upconversion process would then be frequency doubling, that is, that process in which the initial two phonons were of the RF absorbing mode leading to the third created phonon of twice the frequency. The largest transfers would then be to modes nearby in frequency. The high frequency active modes would then only have energy transferred to them when modes were populated out of equilibrium up to near the active mode frequency by pumping up all the modes at frequencies in between. This transfer of energy through a large number of modes is exactly the process of thermalization. For an athermal effect, there would have to be a transfer to the one mode greatly in excess of the transfer of energy to all other modes. This could only happen by a very unusual strong coupling between a bulk and an intramolecular active mode. Since they are so different in character, this is extremely
unlikely.

Individual protein molecules have a lower limit to the frequency intramolecular vibrational mode they can support resonantly. No resonant RF absorption could occur to a single protein molecule of this size below this frequency. Bulk intramolecular modes are present at lower frequency and i f any RF absorption occurred it would be to bulk modes.