Heavy Water

HEAVY WATER, H|0, D₂0, water formed by the combination of oxygen with the heavy isotope (see) of hydrogen with atomic weight 2.0136 (symbol H² or D-deuterium, in contrast to hydrogen with atomic weight 1.00756-H¹-protium). H², and then heavy water, were first discovered in 1932 by Urey and colleagues. Heavy water is present as a constant impurity in ordinary water (in tap water approximately 2 parts heavy water to 6,500 parts ordinary water). During prolonged electrolysis of ordinary water, an increase in the content of heavy water is observed. This is the basis for the method of obtaining heavy water (Lewis, Mc Donald). Heavy water can also be obtained from H², separated from H¹ by the method of diffusion of gaseous hydrogen (Herz). An increase in the content of H² can also be achieved by fractional distillation of water, fractional adsorption of hydrogen on carbon. 99.9% pure heavy water has a freezing point of +3.8°, boiling point of 101.42°. The vapor pressure, dielectric constant, surface tension, polarity of heavy water are lower than those of ordinary water, the latent heat of evaporation, viscosity, density, pH(?) are higher. Temperature of maximum density +11.6°. On the physical properties of heavy water compared with the properties of ordinary water-see table (Selwood and Frost). With increasing temperature, the differences decrease.- Properties Ordinary water Heavy water 100% pure (calculated) Refractive index n_D . . Molecular refraction Viscosity η₂₀........ Surface tension σ at 20° (dyn/cm).... 0.9982 1.33283 3.711 10.87 72.75 1.1056 1.3281 3.677 14.2 67.8 Heavy water apparently has a toxic effect on animal and plant organisms when used in high concentrations. Seeds of Nicotiana tabacum var. purpurea did not germinate in heavy water (Lewis). Spirogyra, placed in heavy water, does not move, no breaking of threads or cell division occurs in it. According to studies by a number of authors, 92% heavy water is poisonous for freshwater organisms: tadpoles (Rana clamitans) died after 1 hour, fish (Lebistes reticulatus) after 2 hours, flatworms (Planaria maculata) and protozoa (Paramaecium caudatum) after 48 hours. Thus, lower animals appear to be less sensitive to heavy water than higher ones. All the animals mentioned above survived in 30% heavy water. Small concentrations of heavy water apparently in some cases may not only not have a harmful effect on the plant organism, but even have a beneficial effect. Thus, Lakemann and Leunig report that concentrations of heavy water not exceeding 0.54% have a protective effect against the disinfecting action of silver nitrate on Bacterium coli and Bacillus pyocyaneus. In addition to heavy water H₂O, the existence of heavy water H²H¹O is also possible, as well as other compounds containing H². It is possible that the mechanism of the biological action of heavy water should be sought in its effect on enzymatic processes. Even simple chemical reactions proceed differently in heavy water than in ordinary water: thus, the mutarotation of glucose is slowed down 3 times, while the inversion of sucrose, on the contrary, is accelerated 17-2 times. The effect of heavy water on enzymatic catalysis is even stronger: fermentation is slowed down 8 times, respiration is also inhibited, but to a lesser extent. Heavy water inactivates one of the important enzymes-catalase; in connection with the latter circumstance, there is apparently also the inhibitory effect of heavy water on the assimilation of CO₂ by algae. On the other hand, in organisms, a preferential accumulation of heavy water has been noted, both as part of the water contained in the tissues of the organism (very long-lived plants with vigorous water exchange were studied-for example, willows), and in water obtained by burning organic substances of tissues. This apparently indicates the ability of the organism to retain the heavy isotope of hydrogen in its tissues. At the same time, ordinary diffusion exchange when fish are placed in water with an increased content of heavy water leads to a rapid establishment of equilibrium between the organism and the environment. Apparently, the reason for the difference in the biological action of heavy water compared to ordinary water should be sought in the strong decrease in the rate of all physicochemical processes in the organism under the influence of the heavy isotope of hydrogen H² (G. N. Lewis).

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