**5. Conclusions and outlook**

118 Biomedicine

phosphorylation has been shown to result in the decreased production of О2●─ (see, e.g., Mailloux et al., 2011). Hence, the higher rate of oxidative phosphorylation with magnetic 25Mg, in comparison with nonmagnetic 24Mg, through the reduction of the H+-gradient "backpressure" should decrease the false electron leakage onto oxygen, thereby reducing

●─ as by-products of the electron transport.

●─ as the by-

From the point of view of chemical kinetics, with decrease in the rate of oxidative phosphorylation, there is the retardation of electron transport in the sites of the electrontransport chains which are coupled with phosphorylation of ADP. Inasmuch as the input of electron-transport nanoreactors becomes overflowed with electrons ("electron-transport jam"), the probability of electron leakage on oxygen increases. The more is acceleration of

products of electron transport is bound to be much lower with 25Mg-ADP by comparison

Thus, with magnetic 25Mg, the biopolymer nanoreactors of oxidative phosphorylation operate not only more effective but more reliable too, in comparison with their operation on non-magnetic isotopes 24Mg and 26Mg. Downgrading production of О2●─, the magnetic isotope of magnesium produces, actually, a beneficial preventive antioxidant effect. This antioxidant effect of the nuclear spin, that 25Mg favors the less production of reactive oxygen species, should obviously increase longevity of the electron-transport nanoreactors. Therefore, it can reveal itself in nature as the kinetic nuclear-spin selection of the favorable isotope, namely, the kinetic isotope enrichment with magnetic 25Mg in the processes of recycling and regeneration of the electron-transport nanoreactors. For example, one can expect for the enrichment with the favorable magnetic 25Mg in recycling and regeneration of

Contrary, in the case of photosynthetic nanoreactors, one can predict undesirable prooxidant effect of the magnetic nucleus of 25Mg. Indeed, it is known that the function of the vast majority of chlorophyll molecules (Chl), as the derivatives of the magnesiumprotoporphyrin complexes, is to absorb light energy and transfer it to the specific energy sinks, the so-called reaction centers of the photosynthetic nanoreactors (Nelson & Cox, 2008). While performing this energy-transfer function, the light-exited Chl molecules are in the singlet state (1Chl\*, electron spin *S*=0). However, there is probability of the radiationless relaxation into the triplet state (3Chl, *S*=1) followed by formation of singlet oxygen, 1O2, the molecules of which are substantially more reactive by comparison with usual triplet O2 molecules and, thereafter, produce oxidative damages. As nuclear spin of 25Mg can catalyze the conversion of 1Chl\* into the triplet 3Chl, one can expect for the higher yield of 1O2 and, thereafter, more photodynamic damages in the cells with the chlorophyll molecules containing 25Mg instead of the spinless 24Mg or 26Mg. Correspondingly, it is beyond reason to hope for selection of the magnetic 25Mg, in the case of algae or green plants. Besides, the functional disadvantage of 25Mg should be followed by increased synthesis of carotenoids and other natural antioxidants. Indeed, measurements of magnesium isotopic composition of the chlorophylls extracted from cyanobacteria and similar analysis of the chlorophyll forms in the leaves of English Ivy (*Hedera helix L*.) have revealed the isotope distribution following usual classical mass-isotope effect with no evidence for depletion or enrichment of

the ATP synthesis, the less is probability of the "jam". Hence, the yield of О<sup>2</sup>

cell mitochondria with aging of the cells (Koltover, 2007, 2010b).

the yield of free radicals О<sup>2</sup>

with 24Mg-ADP or 26Mg-ADP.

25Mg (Black et al., 2007).

Factual evidence of magnetic isotope effect, on its own, indicates that the "bottle-neck" of the process under investigation is a free-radical or ion-radical reaction. Within the scope of free radical research, MIE can serve as the unique indicator to elucidate if the reaction under study proceeds through a free-radical or ion-radical pair as the key operand of the reaction.

Up to date, however, there have been no efforts to detect magnetic-isotope effects for other elements, except magnesium, in biopolymer nanoreactors.

Our experimental data have documented, for the first time, the beneficial magnetic-isotope effects of 25Mg *in vivo*. Although the detailed mechanisms of the ability of the living cell to perceive magnetic properties of the atomic nuclei require further investigations, the "nuclear spin catalysis", as such, always and unambiguously indicates that the reaction under study is a spin-selective process with participation of paramagnetic intermediates, such as free radical pair, ion-radical pair or triplet state that undergo the spin conversion. Along this line the general principles of spin chemistry, amongst them – control of biochemical reactivity in living cells by the selective modification with stable magnetic isotopes, hold considerable promise. In part, the preventive antioxidant effect of 25Mg opens the ways toward the novel biomedicine of anti-stress anti-aging drugs enriched with the magnetic-isotopes. The discovery of the magnetic-isotope effect in radiation biology opens up the way to the development of novel radio-protectors, based on the magnetic isotopy. Furthermore, inasmuch as the electron and nuclear spin moments can be changed by external magnetic fields, it makes possible to exert control over efficiency and reliability of biomolecular nanoreactors with the help of relevant magnetic and electromagnetic fields.
