Researchers unlock mystery of how 'handedness' arises

May 08, 2012
Colored patches represent parallelogram outlines around pairs of triangles that have formed chiral super-structures. Parallelograms having different "handedness" and orientations are color-coded and superimposed over each other. Credit: Thomas G. Mason and Kun Zhao

The overwhelming majority of proteins and other functional molecules in our bodies display a striking molecular characteristic: They can exist in two distinct forms that are mirror images of each other, like your right hand and left hand. Surprisingly, each of our bodies prefers only one of these molecular forms.

This mirror-image phenomenon -- known as chirality or "handedness" -- has captured the imagination of a UCLA research group led by Thomas G. Mason, a professor of chemistry and physics and a member of the California NanoSystems Institute at UCLA.

Mason has been exploring how and why chirality arises, and his newest findings on the physical origins of the phenomenon were published May 1 in the journal Nature Communications.

"Objects like our hands are chiral, while objects like regular triangles are achiral, meaning they don't have a handedness to them," said Mason, the senior author of the study. "Achiral objects can be easily superimposed on top of one another."

Why many of the important in our bodies almost always occur in just one chiral form when they could potentially exist in either is a mystery that has confounded researchers for years.

"Our bodies contain important molecules like proteins that overwhelmingly have one type of chirality," Mason said. "The other chiral form is essentially not found. I find that fascinating. We asked, 'Could this biological preference of a particular chirality possibly have a physical origin?'"

In addressing this question, Mason and his team sought to discover how chirality occurs in the first place. Their findings offer new insights into how the phenomenon can arise spontaneously, even with achiral building-blocks.

Mason and his colleagues used a manufacturing technique called , which is the basis for making , to make millions of microscale particles in the shape of achiral triangles. In the past, Mason has used this technique to "print" particles in a wide variety of shapes, and even in the form of letters of the alphabet.

Using optical microscopy, the researchers then studied very dense systems of these lithographic triangular particles. To their surprise, they discovered that the achiral triangles spontaneously arranged themselves to form two-triangle "super-structures," with each super-structure exhibiting a particular chirality.

In the image that accompanies this article, the colored outlines in the field of triangles indicate chiral super-structures having particular orientations.

So what is causing this phenomenon to occur? Entropy, says Mason. His group has shown for the first time that chiral structures can originate from physical entropic forces acting on uniform achiral particles.

"It's quite bizarre," Mason said. "You're starting with achiral components — triangles — which undergo Brownian motion and you end up with the spontaneous formation of super-structures that have a or chirality. I would never have anticipated that in a million years."

Entropy is usually thought of as a disordering force, but that doesn't capture its subtler aspects. In this case, when the triangular particles are diffusing and interacting at very high densities on a flat surface, each particle can actually maximize its "wiggle room" by becoming partially ordered into a liquid crystal (a phase of matter between a liquid and a solid) made out of chiral super-structures of triangles.

"We discovered that just two physical ingredients — and particle shape — are enough to cause chirality to appear spontaneously in dense systems," Mason said. "In my 25 years of doing research, I never thought that I would see chirality occur in a system of achiral objects driven by entropic forces."

As for the future of this research, "We are very interested to see what happens with other shapes and if we can eventually control the chiral formations that we see occurring here spontaneously," he said.

"To me, it's intriguing, because I think about the chiral preference in biology," Mason added. "How did this chiral preference happen? What are the minimum ingredients for that to occur? We're learning some new physical rules, but the story in biology is far from complete. We have added another chapter to the story, and I'm amazed by these findings."

To learn more, a message board accompanies the publication in Nature Communications, an online journal, as a forum for interactive discussion.

This research was funded by the University of California. Kun Zhao, a postdoctoral researcher in Mason's laboratory, made many key contributions, including fabricating the triangle particles, creating the two-dimensional system of particles, performing the optical microscopy experiments, carrying out extensive particle-tracking analysis and interpreting the results.

Along with Mason, co-author Robijn Bruinsma, a UCLA professor of theoretical physics and a member of the California NanoSystems Institute at UCLA, contributed to the understanding of the chiral symmetry breaking and the liquid crystal phases.

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User comments : 10

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MrVibrating
not rated yet May 08, 2012
Entropic gradients fuel negentropic ones, fuel more entropic ones and so on, at every scale everywhere... was this really so surprising? I'd be more surprised if Stuart Kauffman hasn't suggested it already but still, cool resolution to a long-standing mystery.

thingumbobesquire
1 / 5 (1) May 08, 2012
If it were simply entropy, how and by why what circumstance did the close packing occur? Entropy again?

So what we have here is a recursive reductio ad adsurdum species of mathematical supposition which takes entropy as a given that somehow miraculously always leads to less and less disorder. Cannot we see the fallacy of composition in the premises of reasoning here?

In fact, the quality of step function increases in the living processes in the biosphere to both capture and organize energy in increasing density of throughput to ever higher states of evolution is evidence not of entropy but the very opposite.

This evolution culminates in the human species ability to consciously change its mode of capture and organization of energy via creative problem solving expressed in technology. Once again, further devastating evidence that negative entropy is the subsuming potential latent in the universal process of development, not stochasticity or for that matter irrationality...
Terriva
1 / 5 (3) May 09, 2012
In dense aether model the origin of chirality is way simpler and it's based on the fact, the living cells are tiny curved "bubbles" and the chiral molecules adsorb differently on the curved surfaces. Those who know about lotus leaf effect maybe remember, these concave surfaces are hydrophobic for hydrophilic molecules (like the sugars) and vice-versa: negatively curved convex surfaces attract these less polar ones, like the proteins. With connection to different adsorption coefficients of L- and D-chiral molecules it would lead into separation of these molecules inside and outside of curved surface. Which could be verified experimentally, if we would prepare a mayonnaise from liposomes and mixture of chiral molecules: both hydrophilic, both hydrophobic ones. The lipid droplets of mayonnaise should accumulate the L-hydrophobic and D-hydrophobic molecules into itself preferentially.
Terriva
1 / 5 (2) May 09, 2012
The above experiment is interesting, but I don't see straightforward connection to the chirality of life there. The chiral molecules don't need any triangles to form itself and vice-versa: the formation of chiral structures from these triangles doesn't explain, why living cells tend to accumulate L-proteins and D-sugars into itself.

What's worse, for triangles it's not difficult to form a chiral structures simply because the formation of achiral ones is way less probable - it would require the spontaneous formation of symmetric clusters and/or straight chains, which is improbable with respect to probability. IMO this explanation could be verified simply with computer simulation, which would glue triangles into larger clusters randomly. I'd guess, at the end of simulation the chiral structures would prevail in this mixture over symmetrical ones. Every large molecule tends to be chiral, because the probability of symmetrical bonding is the less probable, the larger such a molecule is.
jaditod
not rated yet May 09, 2012
we have concerns with this article that we found very similar to writing for us on PLOS ONE in 2007. READERS PLEASE confront OUR FINDINGS WITH THIS ARTICLE PLEASE. AND WE WAIT YOUR OPINION THANKS THIS IS THE LINK PLEASE REAS IT AT Geometric Triangular Chiral Hexagon Crystal-Like Complexes Organization in Pathological Tissues Biological Collision Order
Jairo A. Díaz, Natalia A. Jaramillo, Mauricio F. Murillo
Jairo A Díaz ... Biological Order Jairo A. Díaz * Natalia A. Jaramillo ... . 2007 12 12 2007 2 12 e1282 9 12 2006 9 11 2007 Diaz
PLoS ONE: Research Article, published 12 Dec 2007
PLEASE HELP US TO CLARIFY
THANKS VERY MUCH FOR YOUR OPINION
REPRESENT THIS ARTICLE A PLAGIARISM OR NOT ?

JAIRO DIAZ AUTHOR.
Macksb
1 / 5 (1) May 09, 2012
Consider the Brazil Nut Effect by way of analogy. When a jar of mixed nuts is shaken, the brazil nuts will self-organize in their own section of the jar. There's good literature on the web.

How would that analogy apply to the above article? Well, suppose we consider not the triangle itself, but rather the hypotenuse of the triangle as our brazil nut. Hypotenuses self-organize together--like to like. Brownian motion is akin to shaking the jar.

Once a parallelogram is formed, that introduces a new apparent "unit" that can in fact be broken down into its external parts (long side, short side, corners). Again, like may self-organize with like. The odd shape of a parallelogram, as opposed to a rectangle, may "drive" the chirality.

The analogy to the Brazil Nut Effect is not perfect--no chirality there--but it is a fun comparison in light of the entropy arguments, at least. It offers a perspective on self-organization, and perhaps on the chirality of such organization as well.
jaditod
not rated yet May 09, 2012
THANKS VERY MUCH FOR YOUR OPINION

JAIRO DIAZ AUTHOR
Terriva
1 / 5 (2) May 09, 2012
PLEASE HELP US TO CLARIFY THANKS VERY MUCH FOR YOUR OPINION
REPRESENT THIS ARTICLE A PLAGIARISM OR NOT ?
If the newer article doesn't contain a citation of your work, then it's definitely sloppy with respect to review of existing research. The omitting of relevant citation can be classified as a scientific fraud in some cases, but I don't think, the later work is example of it, because whole the experimental subject of both articles is completely different.
jaditod
not rated yet May 09, 2012
"So what is causing this phenomenon to occur? Entropy, says Mason. His group has shown for the first time that chiral structures can originate from physical entropic forces acting on uniform achiral particles".this statement is not entirely true 5 years ago in our article published in PLoSOne document in Cancer Tissues that molecular crystals represented by triangular chiral hexagons derived from a collision-attraction event against collagen type I fibrils emerge at microscopic and macroscopic scales presenting a lateral assembly of each side of hypertrophy helicoid fibers, that represent energy flow in cooperative hierarchically chiral electromagnetic interaction in pathological tissues and arises as a geometry of the equilibrium in perturbed biological systems

in disorder systems, the intrinsic collisions generate order in terms of triangular chiral self assembly complexes
Tachyon8491
not rated yet May 13, 2012
The conclusion that chirality is the result of entropy appears much too off-pat to me: it's too simplistic a model of any dynamics involved. I feel strongly that the origin of chirality should be traceable to further depths of the quantal microdomain - e.g. asymmetry in weak interactions and particle decays could well be supplying the required bias. It's obviously not an indeterministic, random effect and caused by more fundamental asymmetry or "primary chirality" that has to arise at very fundamental levels of ontogeny. It cannot arise by spontaneous "emergence" at more complex levels in the ontological hierarchy without a more primary cause, e.g. perhaps at planck dimensional level.

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