[First posted: 2.01.17/most recent edits & additions: 2.28.17]

Preamble: this conjecture relates foremost to Topic III. Gravitational Cycles & Induced Torque Into the Cell, but is also relevant to Topics I: Isotopes in the Cell, and IV: Asymmetry in the Cell Nucleus as a Means for Driving Torque. But it also relates to arguments addressing the possible cause for the shared circadian rhythm found in all plants, insects and animals.

Hypothesis: All the amino acids in the body except one share the same odd left-handed chirality. And, if even a tiny fraction of these molecules possess the wrong chirality, it can be fatal to the cell. Since the ability of the cell to manage chirality is essential to life, it warrants conjecture about whether there might be a more fundamental means for discerning chirality - that is, a more fundamental means than that defined by the chemical bonding configuration. In looking for possible underlying connections, we note a result from particle physics where the observation of beta-decay has shown that nature has a similar but deeper level of preference for left-handed configurations. The conjecture in this section will explore a possible shared reason for this.

To explore this notion, let us first review the defintion of chirality. Chirality is a property that an object possesses when its configuration is fundamentally different from the configuration of its reflection. Thus, the letter 'Q' is chiral, but the letter 'O' is not; O is achiral. The asymmetry that establishes the chirality, such as the tick-mark in the letter Q above, is typically referred to as either having a left-handed (L) or a right-handed (R) configuration. The L or R sense of chirality, such as seen in the two Q's above, may seem equivalent and without a fundamental reason for preferring one configuration over the other, but for some unknown reason, life has established a preference in our biology for one configuration over the other. The functional proteins in organelles are comprised of right-handed sugars and left-handed amino acids.

We want to consider whether the biological prejudice that exists for of a particular chiral handedness extends to details smaller than the realm normally defined by chemical bonding structure. In particular, we may ask: does the presence of isotopes in an otherwise achiral molecule make it chiral? By example, consider the four molecules shown below. The two on the left are conventionally achiral, while the third from the left is chiral due to the introduction of the off-axis oxygen atom. The pertinent question is: if we build a molecule such as the one on the right, comprised of 5 atoms of 12C and 1 atom of 13C, is the molecule chiral? More importantly, does the cell treat it as chiral?

From the journal Nature Chemistry:
(9 April 2009|doi;10.1038nchem.209):

"Molecules that are apparently achiral may in fact be chiral by virtue of the distribution of 12C and 13C between enantiotropic groups. Unfortunately, it is difficult to determine experimentally whether this is the case because of the similarity of the isotopes and the minute enantiomeric excess that are likely to be involved."

And, more recently from the journal Angewandte Chemie:
(18 October 2016|doi;10.1002/anie.201608955):

"Chirality arising from isotopic substitution, especially with atoms heavier than hydrogen isotopes, is usually not considered a source of chirality in a chemical reaction. An 2N,2N,3N,3n-tetramethyl-2,3-butanediamine containing nitrogen (14N/15N) isotope chirality was synthesized and it was revealed that this istopically chiral diamine compound acts as a chiral initiator for symmetric autocatalysis."

Electron orbital configuration has provided chemists with a convenient scale for delineating chirality. However, if chirality is fundamental to cell function, then perhaps in biological environments, the notion must be extended to smaller scales. If an evolutionary advantage could have been gained by monitoring, selecting, or manipulating chirality at the nuclear level, then it likely would have been incorporated into cell functions. Thus, let us consider other another aspect of nuclear structure than can be used for chiral distinction - nuclear spin.

Nuclear spin and magnetic moments can be thought of as fine-scale, decimal point adjustments to the spin and angular momentum assigned to the electronic structure of an atom. The energy associated with nuclear spin orientation is also tiny. It too can be thought of as a decimal point correction to the energy configuration of a molecule. Because the difference in energy between nuclear spin states is usually tiny, it is typically swamped by the thermal activity within the cell. However, to understand how the spin orientation of one molecule can have an effect on the larger distributions of energy within its environment we can borrow the explanation for how a cloud chamber works. A cloud chamber is a sealed environment housing super-saturated water vapor. When a single charged particle comes flying through the chamber, it ionizes the vapor and condenses it onto condensation nuclei leaving the trail behind for us to see. The system environment is so pre-charged that the smallest difference in ion density produces the dramatic trail so familiar to particle physicists.

Nuclear spin offers intriguing modeling options because - in an external magnetic field such as the earths - the spin possesses a magnetic moment that gives the host atom slightly different energy values depending on its orientation. Flipping the spin orientation of the nucleus is much easier than flipping the entire molecule because the nucleus is so much more compact than the electron structure ~ roughly 700 times easier for a hydrogen atom (1H). Thus, if the cell can be selective about the nuclear spin orientation of the molecules it builds with, it can give the cell a finer scale energy currency than chemical changes provide. Further, the speed at which the energy can be manipulated is potentially thousands of times faster. When looking to balance energy and torque around the cell, having pico-second control over a decimal point energy currency can be a big advantage.

Still further is the opportunity for nuclear magnetic moments to drive local torque in the cell. When a host atom possessing a nuclear magnetic moment is placed in a magnetic field it will have a preference to align with that field. However, if that host atom or molecule were constrained from rotating - as would be expected from its electronic bonding structure - then the tendency to align with the external field results in a torque that produces an internal stress in the molecule. This stress can produce a precession such as that discussed in Topic VI, which, of course can be seen as a potential mechanism for regulating cell rhythms. (See too, the topic about Larmor Frequency/Precession.)

With this in mind, let us revisit the comment above that all the amino acids in the body except for one share the same odd left-handed chirality. That exception is glycine, pictured below as achiral.

What happens if we can bring the conditions for chirality down to the nuclear level and include the spin of the two hydrogen atoms flanking the center carbon? If we treat the hydrogen as 1H, with a nucleus comprised of a lone proton, then we obtain the four possible structures shown below:

The first two on the left produce identical enantiomers at the nuclear level; I have labeled them .achiral (“dot-achiral”) since we are evaluating the level of chirality or achirality now to second order; a decimal point increase in accuracy. The two isomers at the right though produce different enantiomers. When we apply this higher order requirement for chirality, we see that glycine too is chiral - but it is ‘dot-chiral’. Further, if we referred to the handedness of the chirality, the molecules become either dot-chiral-left, or dot-chiral-right.

Applying this finer level for evaluating chirality shows that glycine too can be treated as a chiral molecule.

If we apply the same level of accuracy to glycine when it is built using 2H rather than 1H - a less common but frequently found isotopic version - we expose another method for establishing decimal-point chirality. This is shown in the diagram below using singly deuterated glycine.


What gives this extension even more fascinating modeling potential is that the isomers of hydrogen when comprised of a single proton must involve spin states in multiples of ½ since the proton is a fermion. But deuterium - with that extra neutron - has integer nuclear spin and when joined with oxygen as D2O requires spin states of either 0 or 2.

Rationalizing such conjecture requires very sophisticated experiments - many of which must be within in vivo environments. However, because chirality is so critical to life, it is worth extending this conjecture a little further...

Isomeric Tunneling?
(See also, Topic II). Bound neutron decay and the transport of nuclear spin or chirality can provide an attractive mechanism for DNA to fine-tune the energy distribution within the cell. Significantly, we find theories emerging at the most fundamental levels that postulate the possible transport or tunneling of spin-states and chirality between particles.
(see, for example: Chen et al, Nonlinear Chiral Transport Phenomena, arXiv:1603.03620v1 11 Mar 2016; or J. Rusnak and B. Serot; The Nuclear Spin-Orbit Force in Chiral Effective Field Theories, arXiv:nucl-th/9709064v1 28 Sep 1997; or Alexander, Marcian & Smolin, Gravitational origin of the weak interaction’s Chirality arXiv:1212.5246v2 7 Jan 2013).

The possible tunneling of the isomeric spin state of hydrogen - right through the chiral carbon of glycine - is shown schematically below.

It can be argued that the resolution of such nuclear-scaled chirality is possible between coupled systems that have been in resonant proximity to each other for any extended time periods. But, as noted above, there is also the likelihood that such a small chiral signature would be swamped by thermal activity. For one molecule to recognize the difference in spin orientation in a second molecule, the coupled pair must maintain quantum coherence, or at least, a time-averaged definition of quantum coherence that can apply to pico-second time intervals. Preferably, the environment enveloping the coupled molecules would be calm and thermally stable for the duration over which an event occurs. Where in the cell might we find such a calm sheltered environment? There is perhaps no more balanced place to begin looking than the interior of the DNA molecule.

Chirality in DNA. DNA is a helical molecule - as are all helical structures. The opposite handed strands of DNA are bound together by a chain of hydrogen-bonds that run the length of the molecule; exemplified below in the A-T & G-C pairings.

If chirality is established by the electron bonding structure, then the N-H---N bond is achiral. However, as shown below, if we build our bonding structure from atoms found in their most common isotopic form, (14N-1H---14N), and allow chirality to be established at the nuclear level, then N-H---N suddenly becomes chiral.

[Important to many of the discussions on this website (see Topics I, II, III, IV & VIII) is the observation that this sense of chirality can disappear when the atoms are constructed from their less common isotopic flavors. If, for example, 1H is replaced by 2H, then the spin of the deuterium core can take the state of '0', and chirality is lost. If, evidence can be found to show that chiral tunneling is possible, then such 0-spin locations become nodes thack block the tunneling process.]

[This discussion will continue in the coming months after the introductory arguments listed on the home page of this site have been built. Please visit us again in the spring for conjecture on the following chiral-related topics. Posted 2.02.17]

Chirality in Acceleration when Driven by Multiple Gravitating Bodies?

Chirality of the Sun-Earth-Moon Orbital Configuration?

The Treatment of Groups in the Interpretation of Chirality?

Beta-Decay and the Chirality of our Local Acceleration Background?

Isotropy and the Dynamic Character of Molecules?

Chiral Tunnelling and the Cell Cycle?

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[NOTE: It is quite possible that, as commonly conjectured, the handedness expressed in cell manipulations and in particle decay is simply a result of random historical events that expressed a preference for L over R and this subsequently became embedded into the preference file of all future cells. Support for this position may be given by analogy: a wood screw can be seen to function equally well if the threads are cut in either a left-handed or right-handed spiral. Thus, it might be argued that screws should be found in both configurations with equal frequency. Yet, if we go into a hardware store to buy wood screws we find that they are all right-handed, 'turn-to-the-right-to-tighten' screws. And the logical explanation for this is that while either configuration may have been an option, only one orientation could become the standard for early screw manufacturers, and that just happened to be right-handed screws. But it may also be considered whether there was a small functional reason for the initial choices - both in wood screws and molecular configurations. Pertaining to screws, perhaps it can be argued that the 'turn-to-the-right-to-tighten' choice was due to the prevalence of right-handed people and the manner in which the right hand more easily rotates to the right than the left. Pertaining to biological chirality, might there also be a small functional advantage in L-chirality over R-chirality? But because chirality is so critical to the cell, we believe it justifies the above conjecture.]

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