Creationism in Crisis - Scientists Show How Large Molecules Self-Assemble - No Gods Required Again

Attraction between the dipoles of several macromolecules leads to their mesomorphic assemblies, in contrast with typical polyelectrolyte behavior.

Credit: Shibananda Das

Game-changing New Theory Upends What We Know About How Charged Macromolecules Self-assemble : UMass Amherst

The recent rum of bad news for Creationism just got worse, with the news that scientists from the University of Massachusetts Amherst have discovered how large molecules such as proteins and DNA can self-assemble with nothing more than the laws of chemistry and physics. As always when one of Creationism's favourite gaps is snapped shut by science, no gods were found and the 'mystery' required nothing more than the operation of the natural laws of chemistry and physics.

In the words of one of the researchers:

The significance of the discovery that dipoles drive the assembly of polymers is immense because it throws new light on one of the fundamental mysteries of life’s processes, [how biological materials know how to self-assemble into coherent, stable structures]. The theory changes the paradigm of how we think about these systems, and highlights the unacknowledged role that dipoles play in the self-assembly of biological materials.

Professor Murugappan Muthukumar, senior author
Department of Polymer Science and Engineering, University of Massachusetts, Amherst, MA, USA

What is a dipole? Dipole Definition in Chemistry and Physics

As the University of Massachusetts Amherst news release explains:

In a discovery with wide-ranging implications, researchers at the University of Massachusetts Amherst recently announced in the Proceedings of the National Academy of Sciences that uniformly charged macromolecules—or molecules, such as proteins or DNA, that contain a large number of atoms all with the same electrical charge—can self-assemble into very large structures. This finding upends our understanding of how some of life’s basic structures are built.

Traditionally, scientists have understood charged polymer chains as being composed of smaller, uniformly charged units. Such chains, called polyelectrolytes, display predictable behaviors of self-organization in water: they will repel each other because similarly charged objects don’t like to be close to each other. If you add salt to water containing polyelectrolytes, then molecules coil up, because the chains’ electrical repulsion is screened by the salt.

However, “the game is very different when you have dipoles," says Murugappan Muthukumar, the Wilmer D. Barrett Professor in Polymer Science and Engineering at UMass Amherst the study’s senior author.

While many molecules have either a positive or negative charge, dipoles have both. This means that polymers composed of dipoles behave very differently from the more familiar polyelectrolytes, which have either a positive or negative electrical charge: they expand in a salty solution and can form cross-links with other dipole polymer chains, which then leads to the formation of complex polymer structures.

Dipoles can make polyelectrolytes behave more like polyzwitterions, which exhibit an ‘anti-polyelectrolyte effect.’ This effect is also a feature of the traditional chemical polyzwitterions, whose dipoles are made of chemical bonds. Therefore, for physical polyzwitterion in dilute solutions, the polymer size increases with increasing ionic strength, exhibiting a globule-to-coil transition due to the intra-chain dipole interactions.

Dr Di Jia, co-author
Department of Polymer Science and Engineering, University of Massachusetts, Amherst, MA, USA

Dipolar polymers are capable of forming complex, self-regulating structures which could be employed in everything from drug-delivery systems to next-generation polymers.

We theorize that these dipolar forces in charged macromolecules play a significant role in almost all biological assembly processes, such as the spontaneous birth of membraneless organelles.

Professor Murugappan Muthukumar.

Furthermore, these dipole-composed polymers exhibit an “in-between” state, called “mesomorphism.” In the mesomorphic state, the polymers are neither widely dispersed nor tightly coiled, but congregated into large, stable, uniform structures that have the ability to “self-poison,” or dissolve.

The scientists give more detail in the statement of significance and the abstract to their open access paper in PNAS:

Significance

Control of self-assembled structures of charged macromolecules in aqueous solutions is vital in myriads of natural phenomena. In the simplest situation, uniformly charged polyelectrolyte chains in electrolyte solutions are homogeneously distributed due to their electrostatic repulsion. In stark contrast to this well-established result, we find that the same system exhibits rich phase behavior consisting of precipitation, an interlude of self-assembled mesomorphic structures that can self-poison, and homogeneous solution, in the presence of a small organic anion. Using conceptual arguments, our experiments reveal that this phenomenon originates from dipole–dipole interactions overwhelming charge–charge repulsion. The discovered principle of dipole-directed assembly is essential to understand and control macromolecular structures in the broader context of polyzwitterions, polyelectrolyte–surfactant complexation, coacervation, and membraneless organelles.

Abstract

Uniformly charged polyelectrolyte molecules disperse uniformly in aqueous electrolyte solutions, due to electrostatic repulsion between them. In stark contrast to this well-established result of homogeneous polyelectrolyte solutions, we report a phenomenon where an aqueous solution of positively charged poly(L-lysine) (PLL) exhibits precipitation of similarly charged macromolecules at low ionic strength and a homogeneous solution at very high ionic strength, with a stable mesomorphic state of spherical aggregates as an interlude between these two limits. The precipitation at lower ionic strengths that is orthogonal to the standard polyelectrolyte behavior and the emergence of the mesomorphic state are triggered by the presence of a monovalent small organic anion, acrylate, in the electrolyte solution. Using light scattering, we find that the hydrodynamic radius R_h of isolated PLL chains shrinks upon a decrease in electrolyte (NaBr) concentration, exhibiting the “anti-polyelectrolyte effect.” In addition, R_h of the aggregates in the mesomorphic state depends on PLL concentration c_p according to the scaling law, R_h~c_p^1/6. Furthermore, at higher PLL concentration, the mesomorphic aggregates disassemble by a self-poisoning mechanism. We conjecture that all these findings can be attributed to both intra- and interchain dipolar interactions arising from the transformation of polycationic PLL into a physical polyzwitterionic PLL at higher concentrations of acrylate. The reported phenomenon of PLL exhibiting dipole-directed assembly of mesomorphic states and the anti-polyelectrolyte effect are of vital importance toward understanding more complex situations such as coacervation and formation of biomolecular condensates.

Jia, Di; Muthukumar, Murugappan
Dipole-driven interlude of mesomorphism in polyelectrolyte solutions
Proceedings of the National Academy of Sciences; 119(40); e2204163119. DOI: 10.1073/pnas.2204163119

Copyright: © 2022 The authors.
Published by PNAS. Open access
Reprinted under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

So, another of that dwindling supply of gaps in which Creationists try to force fit their god is slammed shut and as always no gods were found to be necessary.

Mind you, the preposterous notion that every one of the countless trillions of protein and DNA molecules in each and every one of us, and every other living organism, required the services of a single magician doing magic to assemble, was only ever the sort of childish notion that a Creationist could believe. It was so ludicrous that it's almost sad to see it slammed shut, though no doubt there will be a concerted effort to prise it open again, by creationists whose ever-shrinking little god needs every gap going, even made-up ones.

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