Goncharuk et al.

Chemistry Central Journal 2013, 7:103

http://journal.chemistrycentral.com/content/7/1/103

RESEARCH ARTICLE Open Access

Revealing water’s secrets: deuterium depleted

water
Vladyslav V Goncharuk, Alina A Kavitskaya, Iryna Yu Romanyukina and Oleksandr A Loboda*

Abstract
Background: The anomalous properties of water have been of great interest for generations of scientists. However
the impact of small amount of deuterium content which is always present in water has never been explored before.
For the first time the fundamental properties of deuterium depleted (light) water at 4°C and 20°C are here presented.
Results: The obtained results show the important role of the deuterium in the properties of bulk water. At 4°C the
lowest value of the kinematic viscosity (1.46 mm2 /s) has been found for 96.5 ppm D/H ratio. The significant deviation
in surface tension values has been observed in deuterium depleted water samples at the both temperature regimes.
The experimental data provides direct evidence that density, surface tension and viscosity anomalies of water are
caused by the presence of variable concentration of deuterium which leads to the formation of water clusters of
different size and quantity.
Conclusions: The investigated properties of light water reveal the origin of the water anomalies. The new theoretical
model of cluster formation with account of isotope effect is proposed.
Keywords: Deuterium depleted water, Surface tension, Viscosity, Water clusters

Introduction At zero°C the ice structure has all hydrogens in a

For over thousand years water kept its secrets. At the “bonded” state. With the gradual increase of temperature
first glance water seems to be one of the most simple the number of broken water hydrogen bonds increases
and abundant substances, however in addition to H2 O it too. This process is accompanied by a decrease in the
has also H3 O+ , OH− , HOD, and OD− moieties [1] which volume and an increase in the density. However, also
are in part responsible for the multifold of unusual prop- the “competitive” process of thermal expansion should be
erties. There have been numerous attempts to explain considered, which operates in an opposite way (reduces
the anomalies of water (Pauling’s, Robinson, Takahashi, the density). Below 4°C, at atmospheric pressure the ther-
Chaplin’s two states model etc.) [2-7]. The most intrigu- mal expansion coefficient (α=(δ ln υ / δ T)P ) is negative.
ing and discussed theory on the origin of water anomalies The magnitude of the α also reflects the correlations
is the water cluster model [5]. The density inhomo- between the entropy and volume fluctuations. These fluc-
geneities of ∼1nm length-scale have been reported from tuations are positively correlated at the temperature above
the small-angle X-ray scattering measurements [8]. Con- 4°C and anti-correlated below 4°C at which decrease in
versely, the existence of density inhomogeneities in liquid volume results in an corresponding increase in entropy
water has been called into question recently [9]. How- value. In fact, upon the formation of open hydrogen
ever the attempts to interpret the x-ray diffraction data to bonded network the orientational contribution to the
probe the molecular arrangement even in the first coordi- entropy is decreased which is instantly accompanied by
nation shell of liquid water can not provide unambiguous a volume expansion [13]. With increasing temperature
structural information [10-12]. from 0°C to 4°C, the effect of hydrogen bonds cleavage
prevails over the thermal expansion, so the total volume
decreases (large clusters break up into smaller clusters).
*Correspondence: o.a.loboda@iccwc.kiev.ua The decrease in volume leads to an increase of density,
A.V. Dumansky Institute of Colloid Chemistry and Chemistry of Water, National
Academy of Sciences, Kyiv, Ukraine
which goes to a maximum at 4°C. At this point the density
increment held due to the cleavage of hydrogen bonds is
© 2013 Goncharuk et al.; licensee Chemistry Central Ltd. This is an Open Access article distributed under the terms of the
Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use,
distribution, and reproduction in any medium, provided the original work is properly cited.
Goncharuk et al. Chemistry Central Journal 2013, 7:103 Page 2 of 5
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balanced by the effect of thermal expansion which causes It is interesting to note how the small variations of D2 O
a decrease in density. At temperatures above 4°C, the molecules (for example from 4 to 19 ppm) can affect
effect of thermal expansion prevails over the destruction the physical properties of the whole system. This effect
of hydrogen bonds, resulting in the loss of the density becomes more pronounced as the temperature lowers,
[6,7]. Thus, one may assume that at the temperature range but diminishes or masked by other collective processes at
0° - 4°C an increase of non-hydrogen bonded H atoms >150 ppm and under conditions of the higher tempera-
might occur due to the collapse of large supramolecular tures. With the increase of deuterated water molecules in
complexes into the small clusters. Reducing the size of the range of 19-97 ppm the kinematic viscosity decreases
the clusters would lead to the volume decrease which is from 1.5145 to 1.4627 mm2 /s, while the surface tension
inversely proportional to the density. is almost constant (77.58) at 4°C. The densities of the
However none of the proposed models take into account water samples with deuterium contents ranging from 2
isotope composition of water and therefore can not fully to 97 ppm do not deviate at both temperature values 4°C
unravel the complexity of water. The physical properties and 20°C. Substantial deviations of the surface tension
of heavy water, water enriched with the deuterium and and kinematic viscosity are observed in water probes with
heavy-oxygen isotopes, are well-known [14-17]. The boil- a D/H ratio of 146 ppm. At 4°C the kinematic viscos-
ing and freezing points of such water are shifted from the ity sharply increases and constitutes 1.5896 mm2 /s. The
relevant points of normal water. Heavy water is widely surface tension’s decrease pattern pertains to water at 4°
used in nuclear power reactors as a neutron moderator and 20°C as well, though it is more characteristic at 4°C.
[18]. It has also been reported to be harmful for living The deuterium concentration less than 2 ppm has not be
beings and toxic for cells [19]. Fortunately the amount of achieved experimentally to date.
deutereuted water molecules in normal water insignifi-
cantly small and is about 150 ppm. Discussion
The majority of science community neglects the con- As is expected the density of light water does not show
centration of heavy isotopes of protium in water and any appreciable change due to the very small quantity
assumes that it consists of solely H2 O. In this work we of deuteriated water at the 1 - 150 ppm level. Surface
investigate the effect of these small quantities of D2 O in tension (ST) on the other hand is the result of weak inter-
normal water by elaborating the extreme case of the deu- molecular interactions in liquid water. The decrease of ST
terium depleted water i.e. light water. The prime purpose with increasing temperature is usually associated with a
of the present research is to study the physical prop- decrease in density due to the increase of intermolecular
erties of light water. Experimental measurements in the distances. However, it should be noted, all experimental
absence of the deuterated water indirectly tell us how measurements indicate that the changes of ST far exceed
important is the content of D2 O for the magnitude of the corresponding change in density. For example, in the
physical constants. The list of published peer-reviewed temperature range from 0 to 100°C, the volume is changed
research papers on the topic of light water is scarce (less by 4% while ST is reduced by 22%. This significant change
than few dozens of papers) and almost limited to the effect of ST can not be explained only by the change in the
of deuterium-depletion on living cells [20-22]. However density or the interaction of individual molecules, but
to the best of our knowledge the fundamental physi- can be tackled on the basis of the cluster model. With
cal properties of pure light water (below 150 ppm) have increasing temperature, the average cluster size decreases.
never been investigated. Therefore the overall aim of the Also, the increase in temperature enlarges the interclus-
work is to generalize the obtained knowledge in order ter distances, which entails a reduction of unbound O-
to build up a comprehensive view on the organization of H groups in the surface layer, that causes a decrease
water. of ST.
At a constant isotopic content the size of the clusters
Results depends on the temperature. The gradual increase of the
The density, kinematic viscosity and surface tension of temperature also leads to an increase of intercluster dis-
water with varying amounts of deuterium obtained for the tances and the breaking of large clusters into the smaller
temperature regimes 4° and 20°C are shown in Table 1. ones which reflects an increase of free hydrogen bond O-
The dilution of light water (2 ppm) by heavy water content H groups. However at selected constant temperatures, the
up to 19 ppm elevates the kinematic viscosity and surface fraction of NHB H atoms varies as a function of the con-
tension, though the density does not change significantly. centration of deuterium, which is manifested in a change
This effect is observed at the both temperatures, but is in the characteristics of the viscosity and the surface ten-
more profound at 4°C. An increase in temperature leads to sion. This change in the physicochemical properties of
a significant reduction of the viscosity and surface tension water means that the deuterium introduced into the sys-
values. tem affect the distribution of the bound and unbound
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Table 1 Kinematic viscosity, surface tension and density of deuterium depleted (Superlight), Semilight, Normal,
Semiheavy and Heavy water samples studied at 4°C and 20°C
Water Deuterium Kinematic viscosity, mm2 /s Surface tension, mN/m Density, g/cm3
sample content 4°C 20°C 4°C 20°C 4°C 20°C
2 ppm 1.5458 ± 0.0017 0.9923 ± 0.0017 76.27 ± 0.01 73.93 ± 0.01 1.0001 ± 0.00015 0.9979 ± 0.00015
Superlight
4.2 ppm 1.5179 ± 0.0017 0.9626 ± 0.0017 76.39 ± 0.01 73.93 ± 0.01 0.99950 ± 0.00015 0.9982 ± 0.00015
18.9 ppm 1.5145 ± 0.0017 n/a 77.58 ± 0.01 n/a 0.99995 ± 0.00015 0.9999 ± 0.00015
37 ppm 1.4863 ± 0.0017 n/a 77.58 ± 0.01 n/a 0.99980 ± 0.00015 n/a
Semilight
41.3 ppm 1.4900 ± 0.0017 n/a 77.34 ± 0.01 n/a 0.99989 ± 0.00015 0.9999 ± 0.00015
96.5 ppm 1.4627 ± 0.0017 n/a 77.58 ± 0.01 n/a 1.00040 ± 0.00015 1.0004 ± 0.00015
144.7 ppm 1.5746 ± 0.0017 1.0075 ± 0.0017 75.49 ± 0.01 72.58 ± 0.01 1.00027 ± 0.00015 0.9975 ± 0.00015
Normal
145.6 ppm 1.5896 ± 0.0017 1.0057 ± 0.0017 74.87 ± 0.01 72.75 ± 0.01 1.00030 ± 0.00015 1.0001 ± 0.00015
52% 1.6502 ± 0.0017 1.0534 ± 0.0017 74.83 ± 0.01 70.39 ± 0.01 n/a n/a
Semiheavy
53% 1.6514 ± 0.0017 1.0862 ± 0.0017 74.87 ± 0.01 70.39 ± 0.01 1.05850 ± 0.00015 1.0532 ± 0.00015
90.98% 1.7813 ± 0.0017 1.1968 ± 0.0017 70.08 ± 0.01 67.08 ± 0.01 1.1052 ± 0.00015 1.1052 ± 0.00015
Heavy
99.96% 1.7500 ± 0.0017 1.274 ± 0.0017 69.93 ± 0.01 67.80 ± 0.01 1.1040 ± 0.00015 1.1042 ± 0.00015

OH groups. The question arises is how? From the data dodekahedra (b) with 20 water molecules composed from
conducted for experiments with a light water one sees 12 pentamers (a). Next to it is a cluster (c) consisting
that the surface tension has a maximum value for a con- of 100 water molecules on the surface of which there
tent of deuterium ≤ 96.5 ppm. The atoms of deuterium are 30 unbound hydrogen atoms. If 4 additional deuter-
having mass twice of the protium make more stronger ated active centers appear then the cluster can break
O-D bonds than O-H bonds. Our theoretical calcula- down into five basic dodecahedra, which together will
tions show stable spherical structures with encapsulated produce 50 unbound hydrogen atoms (NHB H atoms).
guest molecules [23]. We anticipate that the deuterium The next largest cluster (d) contains 280 water molecules
atoms form the core of the cluster, around which the light and only 60 NHB H atoms. The collapse of such a clus-
molecules are arranged symmetrically in a strictly defined ter into 14 elementary subclusters will make possible the
mosaic order. Upon reduced concentration of deuterium formation of 140 NHB H atoms. Thus an increase in
(≤155 ppm) the clusters can be expected of a larger size deuterium content leads to a decrease in the size of the
than in extreme cases of pure light and heavy water, which clusters, which in its turn leads to an increase of NHBs,
means fewer NHB H atoms and hence a greater surface and the last in our opinion, causes a decrease of sur-
tension. Because the larger clusters have a lower “mobil- face tension and viscosity under conditions of constant
ity” in comparison with small water clusters, then the temperature.
dynamic viscosity must also to increase with increasing When the ice melts at 0°C into the liquid water it absorbs
cluster size and the registered deviations of kinematic an energy of 80cal/g [24]. This energy 80cal/gm does not
viscosity values must be in consistency with the corre- lead to an increase in temperature. We may speculate that
sponding deviations of dynamic viscosity at the condition the major part of this energy is spent for cleavage of 13%
of constant density of water. of the hydrogen bonds in the structure of ice, while the
Dilution of the light water with the heavy water con- 87% of the bonds may remain intact. Therefore, the cluster
tent should lead to the increase of the cluster size. This sizes must be huge in order to accommodate 87% hydro-
trend reaches its maximum at D/H ∼150 ppm inherent to gen bonds “inherited” from the structure of ice. Small
the normal water. Then, however, the further deuterium clusters mean a large number of broken hydrogen bonds.
atoms compete with each other in the process of clus- The experimental data display the decrease in the size of
ter formation, which leads to a decrease of the clusters the clusters with the increase in temperature [25]. Also
size under the excess of the deuterium isotope. Let’s try to theoretical calculations [26,27] show the broadening of
answer the question what is really behind this mechanism? oxygen-oxygen radial distribution function upon temper-
In our earlier work [23] we investigated the homologous ature increase. Apparently the elongation of inter-cluster
series of icosahedral water clusters with various inclu- distance contributes to the water density decrease. The
sions (CO2 , CH4 , (H2 O)n ) (see Figure 1). Among these increase in inter-cluster distances with increasing temper-
series the smallest spherical cluster, which can accom- ature also leads to a decrease in the number of NHB H
modate, for instance a deuterated hydronium cation, is atoms per unit area and, consequently, ST reduction.
Goncharuk et al. Chemistry Central Journal 2013, 7:103 Page 4 of 5
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Figure 1 Pentamer coordinated water network: (a) cyclic pentamer, (b) 512 dodecahedral cluster (H2 O)20 , (c) homological icosahedral
(H2 O)100 and (d) (H2 O)280 clusters.

Finally, considering the role of isotope effect on physical Russia). The heavy water 90.98% has been produced by
properties of water one can not neglect the O18 /O16 ratio. “Cinta Crystal” Ltd. (Kyiv, Ukriane) in accordance with
Based on results obtained from our investigation we may the standard specification (TU) 95-1893-89; the 99.96%
conclude that the concentration of the heavy isotope of heavy water purchased from MERCK company (Darm-
oxygen is closely related with the concentration of deu- stadt Germany). The water samples with the 52% and
terium. The increase of deuterium connected with the 53% content of deuterium have been obtained by dilu-
increase of 18 O/16 O ratio: at 4 ppm of D/H the O18 /O16 tion of 90.8% heavy water using light water (4.2 ppm). The
is 910 ppm,; at 52,53% D/H the 18 O/16 O concentrations semiheavy water (52, 53% D/H ) has been studied due to
are 1479,1552 ppm correspondingly. This indirectly sig- the maximum content of HDO molecules formed in the
nifies the bound character of these two heavy isotopes. self exchange equilibrium reaction H2 O+D2 O ↔ 2HDO.
The simultaneous increase or decrease of 18 O and 2 H Analysis of the isotopic composition of water has been
quantities become possible during formation of covalent performed using modified mass-spectrometer (MI-1201)
bonds between them which give appearance to the D2 18 O, at the Institute of Geochemistry of the Environment,
HD18 O molecules. It should be noted that these molecules National Academy of Sciences.
make hydrogen bonding stronger than the 1 H2 16 O or The modified stalagmometric method is used for the
HD16 O species due to the lower energy of zero point measuring surface tension. The surface tension is calcu-
vibrational level. In our opinion the heavy isotopes of lated according to the formula:
oxygen when they participate in cluster formation play Vg ρ
a static role and make an additional contribution to the σ = ( ) (1)
2πR n
stability of the cluster while the deuterium atoms govern
the whole process of water structuring and hence causes where volume V corresponds to n drops, which are
the qualitative changes of physicochemical properties of released from the stalagmometer with the radius of stalag-
water. mometer tube R, ρ is the density of the liquid. In order to
For the first time the experimental studies have been exclude the factor of the stalagmometer dependence, the
conducted on deuterium depleted water. The anomalous drops number of standard (nx ) and investigated (no ) liq-
properties of water at 4°C are found to be due to the heavy uids is counted. If the liquid with known surface tension
isotope of protium, which is responsible for the water is used then the surface tension of the other liquid can be
cluster formation. The developed conception of determin- calculated from the equation:
ing factor of deuterium is in a good agreement with the no ρx
σx = σo (2)
experimental data obtained for the water samples with nx ρo
various deuterium content at the same conditions. The Methodology for the obtaining density, kinematic vis-
represented model provides a comprehensive assessment cosity parameters can be found elsewhere [28]. The mea-
of the “isotope composition - water structure” relations. surements are carried out in a sealed box, maintaining the
temperature of 4 ± 0.1°, 20 ± 0.05°at a relative humidity of
Materials and methods 60% and a pressure of 750 mmHg. All experiments are
Water samples with the D/H ratio 2.0; 4.2; 18.9; 37.0; carried out above the dew point.
96.5; 144.7; 145.615 ppm have been obtained by vacuum The relative mean errors are 0.11% (kinematic viscosity),
distillation and purchased from Clarte company (Moscow, 0.01% (surface tension) and 0.015% (density).
Goncharuk et al. Chemistry Central Journal 2013, 7:103 Page 5 of 5
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Competing interests 26. Lazaridis T, Karplus M: Orientational correlations and entropy in liquid
The authors declare no competing interests. water. J Chem Phys 1996, 105:4294–4316.
27. Shaik MS, Liem SY, Popelier LA: Properties of liquid water from a
Authors’ contributions systematic refinement of a high-rank multipolar electrostatic
VG designed and supervised the project; AK and IR carried out the potential. J Chem Phys 1996, 132:174504.
experiments; VG, AK and OL analyzed the data; OL simulated the model and 28. Goncharuk V, et al: Physicochemical properties and biological activity
wrote the manuscript. All authors discussed the results and commented on of the water depleted of heavy isotopes. J Wat Chem Tech 2011,
the manuscript. All authors read and approved the final manuscript. 33:8–13.

Received: 14 February 2013 Accepted: 28 May 2013 doi:10.1186/1752-153X-7-103

Published: 17 June 2013 Cite this article as: Goncharuk et al.: Revealing water’s secrets: deuterium
depleted water. Chemistry Central Journal 2013 7:103.
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