Deviation from identity of macroscopic properties ofenantiomers –via water

chiral preference y

IS WATER CHIRAL ?Yosef Scolnik IYAR

Right and left polypeptides alpha-helixand 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 ShinitzkyDavid 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)

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• 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” forcebetween 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

• 105 to 106 more L –molecules in mol racemic mixture.

• 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 -a-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

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H 2 O m i n u s D 2 O p o l y ( L - G l u ) 2 4

H 2 O m i n u s D 2 O p o l y ( D - G l u ) 2 4

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• 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 (D-Glu)24 and poly (L-Glu)24.

• In the a-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 a-helix, pH<3, where the polypeptides are at their a-helix conformation

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the transition to a-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 a- helix structure.

• The associated change in enthalpy of the transition to a-helix of poly (D-Glu)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 –glutamicacid “impurity” added – same results

• Corrobation by another group

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• The most plausible interpretation for the above differences is that poly (D-Glu)24 has a higher a-helix stability than poly (L-Glu)24

• 10 a-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 ortho-H2O).

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• We propose that, since ortho-H2O bears a magnetic dipole, it has a slight preference to react with L-enantiomers due to PVED induced electronic component difference from D-enantiomers-magnetic 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

• 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.

Mirror Symmetry breaking in self assembly micelles of N- stearoyl –serine

enantiomers

• 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 greenCD 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

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• 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.

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ImplicationsThe chiralic preference of water –shown in this work – can be theamplification mechanism of the PVEDthat transfer the parity nonconservation to macroscopic levels –and among otherthings- may explain life preference toL-enantiomers .

• Obvious implications on water structure and properties:

• WATER IS CHIRAL !!!

Direct CD measurements of water