Science & Technology

from elementary particles to biomolecules — ScienceDay by day

If we examine the appropriate to the left hand, we are able to see these are specular photos — that’s, like symmetrical shapes mirrored in a mirror — and so they can’t superimpose on one another. This property is chirality, a characteristic of the matter that performs with the symmetry of organic buildings at completely different scales, from the DNA molecule to the tissues of the center muscle.

Now, a brand new article revealed within the journal Nature Communications reveals a brand new mechanism to switch the chirality between molecules within the nanoscale area, in line with a examine led by the UB lecturer Josep Puigmartí-Luis, from the Faculty of Chemistry and the Institute of Theoretical and Computational Chemistry (IQTC) of the University of Barcelona.

Chirality: from elementary particles to biomolecules

Chirality is an intrinsic property of matter that determines the organic exercise of biomolecules. “Nature is asymmetric, it has a left and a right and can tell the difference between them. The biomolecules that build up the living matter — amino acids, sugars and lipids — are chiral: they are formed by chemically identical molecules that are the specular images to each other (enantiomers), a feature that provides different properties as active compounds (optical activity, pharmacological action, etc.),” notes Josep Puigmartí-Luis, ICREA researcher and member of the Department of Materials Science and Physical Chemistry.

“Enantiomers are chemically identical until they are placed in a chiral environment that can differentiate them (like the right shoe ‘recognizes’ the right foot). Living systems, made of homochiral molecules, are chiral environments (with the same enantiomer), are chiral environments so they can ‘recognize’ and respond in a different way to enantiomeric species. In addition, they can control easily the chiral sign in biochemical processes giving stereospecific transformations.”

How to acquire chiral molecules by means of chemical reactions

Chirality management is decisive within the manufacturing of medicine, pesticides, aroma, flavours and different chemical compounds. Each enantiomer (molecule with a sure symmetry) has a sure exercise which is completely different from the opposite chemically similar compound (its specular picture). In many circumstances, the pharmacological exercise of an enantiomer may be scarce, and within the worst situation, it may be very poisonous. “Therefore, chemists need to be able to make compounds as single enantiomers, which is called asymmetric synthesis,” says Puigmartí-Luis.

There are a number of methods to manage the signal of chirality in chemical processes. For occasion, utilizing pure enantiopure compounds generally known as the chiral pool (as an illustration, amino acids, hydroxy acids, sugars) as precursors or reactants that may turn into a compound of curiosity after a sequence of chemical modifications. The chiral decision is an alternative choice that permits separating enantiomers by means of the usage of an enantiomerically pure resolving agent, and get well the compounds of curiosity as pure enantiomers. The use of chiral auxiliaries that assist a substrate react in a diastereoselective manner is one other environment friendly methodology to acquire an enantiomerically pure product. Last, the uneven catalysis — based mostly on the usage of asymmetrical catalysers — is the highest process to achieve the asymmetrical synthesis.

“Every method described above has its own pros and cons,” notes Alessandro Sorrenti, member of the Section of Organic Chemistry of the University of Barcelona and collaborator within the examine. “For instance, chiral resolution — the most widespread method for the industrial production of enantiomerically pure products — is intrinsically limited to 50% yield. The chiral pool is the most abundant source of enantiopure compounds but usually, there is only one enantiomer available. The chiral auxiliary method can offer high enantiomeric excesses but it requires additional synthetic phases to add and remove the auxiliary compound, as well as purification steps. Finally, chiral catalysers can be efficient and are only used in small amounts but they only work well for a relatively small number of reactions.”

“All the mentioned methods make use of enantiomerically pure compounds — in the form of resolving agents, auxiliaries or ligands for metal catalysers — , which ultimately derive direct or indirectly from natural sources. In other words, nature is the ultimate form of asymmetry.”

Controling the chirality signal by means of fluid dynamics

The new article describes how the modulation of the geometry of a helical reactor at a macroscopic degree permits controlling the signal of chirality of a course of at a nanometric scale, an unprecedented discovery so far within the scientific literature.

Also, the chirality is transferred top-down, with the manipulation of the helical tube to the molecular degree, by means of the interplay of the hydrodynamics of uneven secondary flows and the spatiotemporal management of reagent focus gradients.

“For this to work, we need to understand and characterize the transport phenomena occurring within the reactor, namely, the fluid dynamics and the mass transport, which determine the formation of reagent concentration fronts and the positioning of the reaction zone in regions of specific chirality,” notes Puigmartí-Luis.

In a helical channel, the circulate is extra advanced than in a straight channel, for the reason that curved partitions generate centrifugal forces which outcome within the formation of secondary flows within the aircraft perpendicular to the route the fluid (principal circulate). These secondary flows (vortices) have a twin operate: they’re opposed-chirality areas and construct the required chiral setting for enantioselection. In addition, by advection inside the system and for the event of reagent focus gradients.

By modulating the geometry of the helical reactor on the macroscopic degree, “it is possible to control the asymmetry of the secondary flows in such a way that the reaction zone, — the region where reagents meet at a suitable concentration for reacting — is exposed exclusively to one of the two vortices, and thus to a specific chirality. This mechanism of chirality transfer, based on the rational control of fluid flow and mass transport, enables ultimately to control enantioselection depending on the macroscopic chirality of the helical reactor, where the handedness of the helix determines the sense of the enantioselection,” says Puigmartí-Luis.

The findings make clear new frontiers to realize the enantioselection at a molecular degree — with out the usage of enantiopure compounds — solely by combining geometry and the working circumstances of the fluid reactors. “Also, our study provides a new fundamental insight of the mechanisms underlying the chirality transfer, demonstrating that this intrinsic property of living matter is based on the interaction of physical and chemical restrictions acting synergistically across multiple length-scales,” concludes the lecturer Josep Puigmartí-Luis.

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