**1. Introduction**

104 Biomedicine

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However, apart from external magnetic fields, another variety of natural magnetism is around, namely, magnetic fields of atomic nuclei of magnetic isotopes. Some of them produce intramolecular magnetic fields which are 10-100 times greater than terrestrial (Grant & Harris, 1996). This raises the question of whether living cells can perceive the difference between magnetic and non-magnetic isotopes of the same chemical element. There is also a practical issue of whether the cell can take advantage of the magnetic isotopes.

The present article is a mini-review of the works of our group in this direction. The premises for our research have been the findings of magnetic-isotope effect (MIE) in chemical and biochemical physics within recent years (Brocklenhurst, 2002; Buchachenko, 2009). Following the concept of "nuclear spin catalysis in biopolymer nanoreactors" (Koltover, 2007, 2008), in experiments with bacteria *Escherichia coli*, the commonly accepted microbial model, we have revealed that the cells enriched with magnetic 25Mg demonstrate essentially higher viability by comparison to the cells enriched with the nonmagnetic isotopes of magnesium (Bogatyrenko et al., 2009a, 2009b; Koltover et al., 2012). Furthermore, in experiments with *Saccharomyces cerevisiae*, another standard cell model, we have revealed that the magnetic isotope of 25Mg, by comparison to nonmagnetic isotope 24Mg, is essentially more effective stimulator of the recovery processes in the yeast cells after short-wave UV irradiation. The rate of post-radiation recovery was found to be twice as good for the cells enriched with 25Mg as compared to the cells enriched with nonmagnetic isotope (Grodzinsky et al, 2011). Thus, the magnetic-isotope effects have been revealed, for the first time, *in viv*o. It opens up a new way in biomedicine, based on the stable magnetic isotopes, namely, the novel preventive medicine including new, 25Mg-based, anti-stress drugs as well as anti-aging and anti-radiation protectors.

(Fig. 1c).

2002; Buchachenko, 2009):

Stable Magnetic Isotopes as a New Trend in Biomedicine 107

reactants. Four quartet "channels" are forbidden by the law of the spin conservation

To lift the ban on reactions forced by the law of spin conservation, spins of the reactants must be changed. Inasmuch as spin-orbital coupling is negligibly small in organic free radicals, magnetic fields are the only means which are able to change the spin states and, thereby, switch the reaction over spin-forbidden and spin-allowed channels. The probability of chemical reaction is a function of the parameters of magnetic interactions (Brocklenhurst,

*; H1; J; a; I; mI;* 

and amplitude of microwave magnetic fields. Correspondingly, acceleration of the freeradical reaction can be achieved through changes in the total electron spin of reactants by interaction with an applied external magnetic field. The parameter *J* is energy of the exchange interaction. Correspondingly, the reactions of organic free radicals or ion-radicals can be catalyzed via interaction of partners of the radical pair with a foreign, third spin

The above mentioned equation also contains parameters of hyperfine coupling *a*, nuclear

interactions of electron spins with magnetic nuclei which are known as the cause of the hyperfine splitting in EPR spectra of free radicals. Correspondingly, acceleration of the freeradical reactions can be achieved through changes in the total electron spin of reactants by interaction with magnetic fields of magnetic nuclei. This is known as "magnetic-isotope effect" (MIE): the reaction shows different reaction rates and different yields of products according to whether the reagents contain magnetic or nonmagnetic isotopes (Brocklenhurst, 2002; Buchachenko, 2009). While classical isotope mass effect selects isotopic nuclei in accordance with their masses, MIE selects isotopes by spin and magnetic moment. In action, MIE is a purely kinetic phenomenon and manifests itself as the dependence of the reaction rate on the nuclear spins of the reactants. Within recent years, MIE in chemistry has been discovered for a number of magnetic isotopes, among them H–D, 13C, 17O, 29Si, 33S, 73Ge, 117,119Sn, 199,201Hg, and 235U (Buchachenko, 2009). By analogy with "electron spin catalysis", the enhancement of the reaction rate by the nuclear spins of the reactants can be

In biochemistry, MIE has been recently discovered for magnetic isotope of magnesium, 25Mg, by A.L. Buchachenko and his group. It is generally known that energetic demands of every operation in living systems are met by molecules of ATP, be it eukaryotic cells of animals and plants or prokaryotic cells of bacteria. In aerobic organisms, most of ATP is produced in the so-called "oxidative phosphorylation". There are specific enzymes, "biomolecular nanoreactors", organized in the respiratory electron transport chains (ETC). Normal function of the ETC enzymes, be it mitochondrial nanoreactors in eukaryotic cells of animals or similar nanoreactors of bacteria cells, is in the transport of electrons, one by one, from the electron donor molecules to the end enzyme, cytochrome oxidase, from which the electrons are transferred to molecules of oxygen with two electron reduction of oxygen into water. Free energy released during the electron transport is used by the specific enzyme,

*n)* 

and *H*1 are frequency

n, i.e., the parameters of

*P=f(H;* 

In this equation *H* is external magnetic field (Zeeman interaction),

carrier, like nitroxide radical. It is called "electron spin catalysis".

spin *I*, nuclear spin projection *m*I, and nuclear magnetic moment

denoted as the "nuclear spin catalysis" (Koltover, 2007, 2008).
