ISIS Report 18/10/10
Water’s Quantum Jazz
Other reports in this series
Dancing with Macromolecules
Macromolecules need lots of water to
function effortlessly and acquire completely new talents when fully hydrated Dr. Mae-Wan Ho
referenced and illustrated version of this paper is posted on ISIS members’ website and can be downloaded here
Please circulate widely and repost, but you must give the URL of the original and preserve all the links back to articles on our website
Organisms have an enormous repertoire of
chemical reactions that enables them to transform energy and materials for
growth, development, and to do all that’s required of being alive. Perhaps most
remarkably, these chemical reactions are catalyzed by specific enzyme proteins that
accelerate the reaction rates by a factor of 1010 – 1023.
But the question of how enzymes work remains unanswered to this day .
One lead player
that has received far too little attention until relatively recently is water. It
is well known that enzymes and other macromolecules, DNA and RNA, need a
minimum amount of water in order to work at all, and much more to work
efficiently. That is why cells are loaded with water, some 70 percent by
weight. In terms of number of molecules, water far outnumbers all other
chemical species - ions, small organic molecules and macromolecules – added
Water is needed
for macromolecules to become flexible, so they can dance freely to water’s
quantum jazz, in order to accomplish their otherwise impossible tasks of making
sluggish chemical reactions happen spontaneously and effortlessly.
are indeed coming around to the view that proteins act quantum mechanically,
or, as some of us have proposed years ago, enzyme proteins are quantum
molecular machines that transform energy coherently (see  The Rainbow and the Worm, The
Physics of Organisms, ISIS publication). But we must backtrack to sketch
the whole picture.
Supercool hydration water
Within the past 20 years, water has gained
recognition as an active constituent of cell biochemistry and not just an inert
solvent . Water has a special relationship with proteins in the protein’s
‘hydration shell’. The hydration shell can be defined as water associated with
the protein at the hydration end point, when further addition of water produces
no change of its essential properties; in the case of an enzyme, this would be
its enzyme activity. This hydration shell is a single layer of water molecules covering
the protein surface. Water outside the monolayer is perturbed to a
significantly smaller extent, typically not detected by measurements of
properties such as heat capacity, volume or heat content (though it is
increasingly recognized by newer measurement techniques, see later). The
hydration shell is about 0.2g/g dry protein. The activity of lysozyme, for
example, closely parallels the development of surface motion as hydration
increases, which is thus responsible for the function of the protein.
In contrast to bulk water,
protein-hydration water does not freeze at 0 ˚C, but can be supercooled
right down to a glass transition  at Tg ~ 170 K (≡-103
˚C), and is reflected in discontinuities in the specific heat and thermal
expansion coefficient of the hydration water. Below that temperature, the
hydration water freezes into a glass, a non-crystalline solid that does not
have a defined molecular order. Near Tg, the movement of water is
The protein however, has its
own dynamic transition, an abrupt onset of atomic motions that can be detected
by neutron scattering, and occurs at TD ~225 + 5 K. This
is a generic property of hydrated proteins, and is absent in dehydrated
systems. It is therefore related to the dynamics of the hydration shell. Some
researchers regard the protein dynamic transition as the “microscopic
manifestation” of the glass transition of the hydration shell. Others, however,
interpret it as a liquid to liquid transition, from a fluid, high density
liquid (HDL) to the less fluid, low density liquid (LDL), or supercooled water
behaviour was found for confined water in various biological and non-biological
environments, and a range of 18 solutions including low molecular weight
organic glass formers, polymers, sugars as well as protein and DNA probed with
broad band dielectric spectroscopy (see Box) between 10-2 and 107
Hz . Universal features in the dynamics of water appeared both above and
below the glass transition, which were similar to supercooled water and
supercooled confined water respectively. However, the glass transition
temperature spans a rather broad range from 165 to 220 K.
dielectric is a molecule such as water that is polarized - with separated
positive and negative charges - or can be polarized by an applied electric
field. Dielectric spectroscopy measures the dielectric response of a sample to
an external electromagnetic field applied over a range of frequencies. The
dielectric property of a material is expressed in a complex number known as
permittivity. The real part of permittivity measures the energy stored, the
imaginary part measures the energy loss and is called the dielectric loss. When
the external field is applied, dipoles in the sample will orient with the
applied field. At low frequencies, they can follow the polarization of the
applied field perfectly, resulting in maximum permittivity and minimum
dielectric loss. As the frequency increases, the molecules can no longer keep
up with the changing electric field, this results in less energy stored and
higher losses. At even higher frequencies, the molecules no longer respond to
the applied field, and the molecules come apart. For example, water molecules
are ‘stretched’ at frequencies above 1011 Hz, and beyond that, they
relaxation time is a measure of the time it takes for separated charge in a
dielectric to become neutralised by conduction process.
More hydration shells revealed
Within the past several years, a new Terahertz
(1012 Hz) spectroscopy has created a stir in the protein hydration
community. Martina Havenith and colleagues at Ruhr University Bochum, Germany,
have been using this new ‘table-top’ technology to reveal global properties of
proteins and their hydration shells , prompting a number of water scientists
to rethink protein hydration.
sophisticated techniques have been used to probe the dynamics of proteins and
hydration water over a wide range of time and space. For example, NMR relaxation spectroscopy resolves water dynamics
from nanoseconds to seconds whereas X-ray crystallography reveals fixed protein
structures and bound water molecules in the protein interior and vicinity. Both
techniques provide information on the short range hydration up to 3 Å
(angstrom, 10-10 m) from the protein surface which corresponds to
one hydration layer. Traditional dielectric
spectroscopy probes dynamics from 100 seconds down to 100 ps (picoseconds, 10-12 s). Terahetz dielectric spectroscopy extends the time scale down to ps
range. Neutron scattering
resolves ps dynamics. On the fastest time scales, two-dimensional infrared
spectroscopy probes processes that take place in femtoseconds (1 fs =10-15
s). And the remarkable picture emerging is that protein and hydration dynamics
may be correlated over all time scales, as indeed they would be in quantum
coherent systems .
spectroscopy, made possible by powerful ‘table-top’ Terahertz electromagnetic
sources, opens up a new window between microwaves and infrared to peer into the
global interactions of water with proteins that are fully dissolved (in excess
The absorption of the solvated
protein increases linearly with frequency in a narrow
frequency range of 2.25-2.55 THz. Concentrating on measurements at a single
frequency, the researchers found that the absorption coefficient of the
solution relative to bulk water increases with protein concentration before
dropping and decreasing almost linearly at higher concentrations. The concentration
dependence of the THz absorption gives similar curves at three different
temperatures 15, 20 and 22 ˚C (see Fig.1, left).
Figure 1 Absorption coefficient vs
protein concentration (left) and it explanation (right)
At 0.5 to 1 mM
protein concentration, when the absorption coefficient peaks and begins to fall
again, the volume of water displaced by the protein molecules is negligible at
around 1 percent. Consequently, the hydration water around the protein must be
contributing substantially to the total THz absorption.
The researchers resorted to
molecular dynamic simulations to compute the absorbance of the protein and the
first hydration layer as a function of the distance between protein surfaces,
which would depend on the protein concentration. In agreement with experiment
observations at concentrations beyond the peak of absorbance, the distance
between the proteins significantly influences the absorbance of the protein and
its first hydration layer and layers beyond. The absorbance decreases as the
proteins are brought closer together from 24 to 18 A, then flattens for the
shortest distances, changing little with distance between proteins.
Further molecular dynamic
simulations revealed that the hydrogen bonds between water molecules in
hydration layers up to about 10 Å survive longer
than those in bulk water. The experimental data indicate an average separation
of >20 Å when absorbance peaked, spanning some 7 layers of water.
The initial findings were made in
a genetically engineered protein l*6–85, but similar results were obtained with natural lysozyme and myoglobin . At 23 g water per g protein of lysozyme, absorbance surged upwards with
increased structural flexibility of the protein. Myoglobin, similarly, exhibited
a maximum at 98 percent by weight of water (24g/g).
While bulk water
and its absorption decrease with increasing protein concentration, this is more
than offset by the absorption of hydration layers and the hydrated protein,
which becomes a dynamically coherent unit (Fig. 1, diagram on the right).
Ferroelectric hydration water
The unexpected findings in Terahertz
dielectric absorption spectroscopy [6, 7] have stimulated researchers to
examine the electrostatic properties of the hydration water. David leBard and
Dmetry Matyushov at Arizona State University, Tempe, USA, said that  to explain those observations
requires a very large “effective dipole moment of the protein and its hydration
shell, much exceeding the dipole moment of the protein itself.”
and Matyushov showed by means of numerical simulations that protein hydration
waters are polarized into a ferroelectric shell some 3-5 water molecules thick
with large average dipole moment. Moreover, the dipole moment of the hydration
shell fluctuates with large amplitude, much bigger than those in bulk water,
and far exceeding the magnitude prescribed by the usual linear response theory,
as also demonstrated in real measurements. These large fluctuations are
dominated by slow nanosecond dynamics probably associated with collective
conformational movements of the protein.
findings are just what is expected from the dynamic liquid
crystalline nature of living organisms discovered in my laboratory in 1992
implying that water associated with macromolecules are also polarized and
moving coherently with the macromolecules .
Is there any
evidence that the protein-hydration system is quantum coherent, as I have
suggested the organism is quantum coherent?
Quantum dance of proteins
The possibility of quantum tunnelling has
been invoked in enzyme catalysis. Quantum tunnelling is a quantum mechanical
effect in which particles go under an energy barrier to achieve a
chemical reaction that’s impossible in classical chemistry. Quantum tunnelling
is already well accepted in electron transfer and frequently observed for
proton transfer .
and experimental studies have clearly shown that the flexibility of the
proteins induced by water is important in reducing free energy barrier between
reactants and products. The flexing of proteins increases the probability of quantum
tunnelling between reactants and products by a transient compression of the energy
barrier. (Obviously, in the case of proton or electron transfer, quantum
tunnelling would only take place if the actions of donor and acceptor are also
correlated or coherent, so coherence must extend to the ensemble of donor and
acceptor proteins.) The same studies indicate that the dynamics of proteins are
closely tied to that of water. Some scientists would go as far as to say it is
mainly the mobility of water that determines the magnitude of protein
fluctuations, not only at the protein surface, but also in the protein core. But
then the collective, conformational movements of proteins would feedback to influence
the hydration water coherently (see above).
One sign of
quantum effect is the difference in behaviour observed when hydrogen (H) is
substituted with its heavy isotope deuterium (D), as already clearly indicated
for water itself (see  Cooperative and
Coherent Water, SiS 48).
Fabio Bruni and
colleagues at University Studi Rome Tre in Italy used dielectric spectroscopy
to compare the dielectric relaxation of lysozyme in ordinary water (H2O)
and in heavy water (D2O) in the frequency range of 10-2
to 107 Hz, and over the temperature range 210 K to 330 K .
If the effect is
classical, there should be no difference between the sample in H2O
or D2O. However, large differences were found. In particular, the
dielectric relaxation times of H2O were completely different from
those measured with D2O over the entire temperature range (see Fig. 2).
2 Dielectric relaxation time t vs temperature
T (a); natural logarithm of the reciprocal of relaxation times ratiotD/tH (≡wH/wD) vs reciprocal of temperature; the horizontal dotted line
marks the value 1.4, which should hold for all temperatures if there were no
These observations were in close agreement with
results of a sophisticated theoretical study using quantum mechanical methods
from first principles.
In addition, the researchers reanalysed data
from a deep inelastic neutron scattering experiment, which measured momentum
distribution of protons n(p) and mean kinetic energy for a lysozyme sample
prepared the same way as for the dielectric spectroscopy experiment.
Measurements were made both above and below the protein’s dynamic transition
temperature (see above) at 290 K and 180 K respectively. They computed the
minimum fraction of protons required to produce the observed difference in the
distribution of momentum between the two temperatures, assuming that the mean
kinetic energies of the proton is independent of temperature except for the
small kT (Boltzmann, background) contribution; and that the momentum
distribution at 290 K arises from a population of protons with the same n(p) as
that at 180 K plus a contribution due to an unknown fraction of protons showing
a characteristic quantum mechanical behaviour. This fraction of protons that
showed quantum behaviour turns out to be 0.29, precisely the fraction of
protons present in the sample that belong to the hydration water.
Water electrifies DNA
The fascinating story of DNA and water is
just beginning. Hydrating shells of DNA share many of the properties of
hydration shells of proteins. In addition, water turns DNA into a electrical conductor
and gives it magnetic properties; and many are looking into exploiting
synthetic DNA in new molecular electronic devices.
Hydration water of DNA appears
to have quite unusual dynamics as measured by time-resolved Stokes-shift (TRSS)
and confirmed by molecular dynamics simulation. In the TRSS experiments on a 17
base pair oligonucleotide, light excites the DNA and is re-emitted as
fluorescence, shifted to lower energy compared to the light absorbed (Stokes
shift). The mean fluorescence frequency is measured as a function of time
after excitation, covering six decades from 40 fs to 40 ns.
unexpectedly, the relaxation (decay of fluorescence) did not show distinctive
time scales that could be easily attributed to multiple, independent processes.
Rather it fits a single power law, suggesting a high degree of correlation over
all time scales.
by Mark Berg at South Carolina University in the United States used a
polarization model based on the idea that the coupling between components in
the system is due to polarization of one component by another, which not only
fit the experimental data well, but also enabled them to assign the TRSS
response to different components of the system: the water, the counter-ions of
DNA or the DNA molecule itself . The results showed that water is the
dominant contributor to the TRSS response at all times. Its relaxation spans
the entire measured time range and accounts for the power law behaviour.
Counter-ions have a secondary, but non-negligible contribution with a
well-defined relaxation time of about 200 ps. The DNA relaxation time is near
30 ps, but the amplitude is very small.
ability of DNA to conduct electricity has remained controversial for years. But
Christophe Yamahata and colleagues at Tokyo University and Kagawa University
Takamatsu in Japan have convincingly demonstrated that the ability of DNA to
transport electrical charge depends on water . DNA bundles suspended in air
between nano-tweezers (see Fig. 3) increased exponentially in electrical
conductivity up to 106 fold as the relative humidity of the air
increased. The increase was attributed to an increase in the concentration of
charge carriers as DNA hydration rose with relative humidity; the charge
carriers being H+ and OH-, suggesting that proton
(positive electricity) jump conduction could be involved (see  Positive Electricity Zaps Through
Water Chains, SiS 28) as well as electron conduction.
3 DNA suspended in air with nano-tweezers
finding is that the pathway for charge transfer (conduction) is through the
stacked bases in the core of the double helix where the p molecular
orbitals overlap. A molecular orbital is a waveform describing the distribution
and energy of a pair of electrons, and is most commonly represented as a linear
combination of atomic orbitals of atoms forming a covalent bond in the
molecule. A p orbital is the molecular orbital of a p bond where two lobes of
the atomic orbitals overlap and join up. The halves of a molecule joined by a p bond cannot rotate
about that bond without breaking it. Carbon and nitrogen compounds form p bonds when they
engage in multiple bonding, as in C=C and N=N. In ring compounds such as
benzene and bases in DNA, where double and single bonds alternate, the p bond electrons
are delocalized, or spread over the entire ring structure and stabilizes it.
Berashevich and Tapash Chakraborty at the University of Manitoba, Winnipeg,
Canada, used quantum chemical calculations to demonstrate that interaction of
the bases with water (see Fig. 4) breaks some of the p bonds in the ring
structure of the bases, giving rise to unbound p electrons. These unbound
electrons, together with the change in DNA conformation from A (dehydrated)
form to B (hydrated) form, could account for the exponential increase in
conductivity as relative humidity and hydration of the DNA molecule increases.
Figure 4 Water binding to DNA bases
low temperatures, the efficiency of charge transfer is determined by the spin
interaction of two unbound electrons located on neighbouring bases of the same
strand. Exchange is allowed only when the electron spins are antiparallel (in
opposite directions). Hence the conductance of DNA can be controlled by a
magnetic field. This gives the potential for developing nanoscale ‘spintronic’
devices based on the DNA molecule, where the efficiency of spin interaction
will be determined by the DNA sequence.
Regardless of the practical
applications, these findings have profound implications for the biological
functions of DNA, apart from serving as a linear code for the sequence of amino
acids in proteins. We are only touching the tip of a very large iceberg.