IS WATER CHIRAL ?
Yosef Scolnik IYAR
Deviation from identity of
macroscopic properties of
enantiomers –via water
chiral preference
y
Right and left polypeptides alpha-helix
and a drawing by Darwing of a kudu, showing in it
horns alpha helix manifestation in nature
Presentation Outline
•
•
•
•
•
Historical Background
Introduction (PVED)
Experiment Description
Conclusions
Implications and Future work
• In collaboration with Meir Shinitzky
David Deamer ,Eshel Ben Jacob
• The current dogma is that chiral isomers
are perfect mirror images –identical in their
macroscopic properties.
Our work provides experimental proof of
macroscopic differences between
chiral isomers- in contrary to the
mentioned dogma, in water solutions.
Historical Background
• Notion that the physical world has handedness
properties from antiquity,
• Anthropic principle: humans, the microcosmos,
epitomize the universe, the macrocosmos.
• Louis Paster state that dissymmetric structures
prevail in the natural world, as the outcome of
the action of universal chiral forces.
• “Le ‘univers est dissym’etrique”
• The handedness of the universe
• From atoms to human beings, nature is
asymmetric with respect to chirality ,or left
and right – handedness.
• Most objects in nature are not identical with their
mirror images:
• Processes such as chemical reactions may
exhibit chirality.
• Certain atomic and nuclear interactions
• With no a priori reason, the real world usually
displays chirality.
• Examples: right hand people,
Molecules can also be
chiral.
• All the 20 amino acids but one,
glycine are chiral. Proteins are made
of L-aminoacids. Sugars are D.
• Reasons for the preference of life to
L-enantiomers are to be looked at the
subnuclear Scale.
Introduction
• All known elementary particles interact
through four types of forces:
• Gravity,
• Electromagnetic forces
ordinary chemical reactions
• The strong nuclear force
(holds atomic nuclei together)
• The weak nuclear force
radioactive decay - beta rays)
• Till 1957 – the assumption was that the four
forces are parity conserving = react the
•
same with a process and its mirror
image
Then it was found that the weak force is not
parity conserving.
The parity violation experiment (1957) result:
beta particles have chiral asymmetry : left
handed electrons far outnumbered right
handed ones.
• Only right handed antineutrino and left-handed
neutrino exists.
• The reasons for handedness at
fundamental level are unknown.
• It was believed the parity
nonconservation is confined to
nuclear reactions.
• Interaction of atoms and light or
chemical reactions seemed to
conserve parity.
• In the late 60’s, Weinberg,
Salam and
Glashow developed a unification of
the weak and electromagnetic forces.
A new “electroweak” force
between an atom’s electrons and the
protons and neutrons in its nucleus.
-
• The existence of this non conserving
parity force was confirmed in the
1970’
• Because the electroweak force
distinguishes between left and
right, atoms and molecules
must be chiral.
• Are chiral asymmetries at one
level linked to those at another?
• The electroweak force transfer the
chirality in the lower level of
elementary particles to the higher
level of atoms.
-
• On a slightly larger scale, the
electroweak force causes a chiral
molecule to exist in a lower or higher level
than its enantiomer.
This tiny effect was not observed,
theoretical calculations were done.
• PVED : 10-16 -10-17 ev
•
to
L –molecules in
mol racemic mixture.
5
10
6
10 more
• The tiny excess of one enantiomer in a
racemic mixture due to PVED can, in
principle, be amplified by an external
autocatalytic process to a level of
detectable macroscopic difference
• Our work is in the realm of the
linkage and transfer of parity
violation from level to level from
molecules to more complicated
systems, life itself ?
• It provides the experimental
proof and propose an
explanation to this linkage
-possibly –the chiral nature of
water –to be demostrated
Experimental approaches demostrations
of the chiral preference of water
• Peptide Transitions to alpha
Helix
• Stearoyl Serine “quasi-peptide
formation”
• Solubility and cluster formation
of Alanine
Transition to alpha Helix
• Poly glutamic acid and poly lysine are
water soluble poly peptides which
undergo structural changes related to
the degree of ionization of their side
chains.
• in ionized state- “random coil”.
• In the neutral state --helical structure
which has a distinctive circular dichroism
(CD) spectrum.
Glutamic acid
• Circular dichroism (CD)
spectroscopy measures
differences in the absorption
of left-handed polarized light
versus right-handed
polarized light which arise
due to structural asymmetry
Wavelength
250
248
245
243
240
238
-40
235
233
230
228
225
223
220
218
215
213
210
208
205
203
200
Millidegrees
80
60
40
poly (D-Glu)24
20
0
-20
poly (L-Glu)24
-60
-80
80
15
10
H 2 O mi n u s D2 O pol y (L-Gl u ) 24
0
-5
60
Millidegrees
5
40
H 2 O mi n u s D2 O pol y (D-Gl u ) 24
poly (L-Glu)24
-10
250
246
242
237
233
229
225
220
216
212
208
203
-15
20
Millidegrees
Wavelength
0
-20
poly (D-Glu)24
-40
-60
H2O
D2O
250
248
246
244
242
240
238
236
234
232
230
228
226
224
222
220
218
216
214
212
210
208
206
204
202
200
Wave le ngth
-80
•
In the random coil region the CD
spectra of the enantiomeric
couples were not identical
• net difference in the equilibrium
state of their random coil
conformations.
• D2O markedly affected the CD
spectrum of poly (L-Glu)24 but
had a significantly smaller effect
on the spectrum of poly (D-Glu)24
--
-
• In the random coil region, small
differences in energy of the fluctuating
conformations, which determine the
equilibrium, could cause the deviation
from mirror image spectra of poly (DGlu)24 and poly (L-Glu)24.
• In the -helix region energies the
intramolecular hydrogen bonding are
much larger and could mask small energy
differences
ITC
• Isothermal titration calorimetry (ITC)
profiles at increments of decreasing pH
were determined at 30º C, either in H2O or
in a 4:1 (v/v) mixture of D2O and H2O
-
• ITC profiles can be divided into three
distinct regions related to the degree
of ionization of the side chains:
• pH>6, random coiled structures,
pH~6-3, the range of transition to helix,
pH<3, where the polypeptides are at
their -helix conformation
-
the transition to -helix of poly (D-Glu)24
started at a point of higher proportion of
ionized side chains than in poly (L-Glu)24
(at pH 6.2 compared to 5.8, respectively),
indicating a stronger tendency of
poly D-glutamic acid to adopt an
- helix structure.
• The associated change in enthalpy of
the transition to -helix of poly (DGlu)24 was considerably higher than
that of poly (L-Glu)24
 DH poly (L-Glu)24 (H2O) = -1.31
 DH poly (D-Glu)24 (H2O) = -1.48
-
• The abolishment of the differences
between the enantiomeric poly
peptides in water by D2O, overrules
the possibility of an undetectable flaw
in their synthesis. In that case the
results in both solvents would be
identical.
• Synthesis of L-PGA with 1% D –glutamic
acid “impurity” added – same results
• Corrobation by another group
• The most plausible interpretation for
the above differences is that poly (DGlu)24 has a higher -helix stability
than poly (L-Glu)24
• 10 -helical turns of poly D-glutamic
acid would have an excess energy of
an additional hydrogen bond
compared to its poly L-glutamic acid
enantiomer
• a poly peptide of L- amino acids
in water might be solvated slightly
more than its mirror image
poly D- amino acids, so that the
latter adopts an apparently more
hydrophobic nature.
• In D2O-H2O 4:1, the above
differences were greatly
diminished due to an almost
selective effect on the ITC profile
of poly (L-Glu)24,
• key issue in our suggested
hypothesis which is presented
below.
• PVED seems the only physical effect which
can lead to chiral enhancement. As PVED is
extremely small, any expansion to the
macroscopic realm must be associated with
additional processes
• In our poly amino acid systems, amplification
of PVED could operate in two independent,
yet cooperating, processes. The first is
autocatalysis of helix formation or
breaking
The more important amplification is
due to
Water chiral preference
• bulk water is a mixture of ortho-H2O
and para-H2O in a 3:1 ratio (due to
the 3 degenerate states of orthoH2O).
-
• We propose that, since orthoH2O bears a magnetic dipole,
it has a slight preference to
react with L-enantiomers due
to PVED induced electronic
component difference from Denantiomersmagnetic interactions.
• If this hypothesis is correct, then the spin
isomers of H2O and their selective effect
on chiral isomers should be greatly
diminished in D2O (that does not have
spin isomers and magnetic dipole)
• Indeed, this is what we have
found.
• Furthermore, the main effect of this
mixture is on (L-Glu)24
Mirror Symmetry breaking in self
assembly micelles of N- stearoyl –serine
enantiomers
• Circular dichroism spectra were
recorded for micellar aggregates
of N-Stearoyl (L or D) Serine in
DDW or D2O. micelle formation
kinetics and final form were
different for L–Stearoyl serine and
D-Stearoyl serine in DDW.
• However, in D2O, both
racemates show spectra
similar to those of D-Stearic
serine in DDW
Circular Dichroism of L-NSS (L- Stearoyl serine
)(upper curves)
and D-NSS (D- Stearoyl serine )(lower curves in
DDW
two state water clue? Grander water research
Circular Dichroism of L-NSS (L- Stearoyl
serine )(upper curves)
and D-NSS (D- Stearoyl serine in D2O
CD of L-NSS in DDW + 10% methanol =upper graph violet
CD of L-NSS in DDW =upper graph red
CD of D-NSS in DDW+ 10% methanol =lower graph green
CD of D-NSS in DDW) =lower graph black
(the two CD spectra of D-NSS are indeed almost identical )
L and D Alanine optical activity in
DDW and D2O:
• As can be seen in graph 1 and graph 2 –
the CD spectra of, i.e.- the optical activity
• of L and D alanine is different in DDW(
double distilled water) and identical in
D2O
•
• An interesting point (worthwhile of
its own research) is the source of
the difference in optical activity
between water and heavy water –
irrespectively of the enantiomers
difference. The plausible
explanation is a different
tendency to form clusters.
Implications
The chiralic preference of water –
shown in this work – can be the
amplification mechanism of the PVED
that transfer the parity non
conservation to macroscopic levels –
and among other
things- may explain life preference to
L-enantiomers .
• Obvious implications on water
structure and properties:
• WATER IS CHIRAL !!!
Direct CD measurements of water