New mechanism to transfer chirality between molecules in the nanoscale
field
Chirality: from fundamental particles to biomolecules

Date:
April 27, 2022
Source:
University of Barcelona
Summary:
New research describes how the modulation of the geometry of a
helical reactor at a macroscopic level enables controlling the sign
of chirality of a process at a nanometric scale, an unprecedented
discovery to date in the scientific literature.



FULL STORY ==========================================================================
If we compare the right to the left hand, we can see these are specular
images -- that is, like symmetrical shapes reflected in a mirror --
and they cannot superimpose on each other. This property is chirality,
a feature of the matter that plays with the symmetry of biological
structures at different scales, from the DNA molecule to the tissues of
the heart muscle.


==========================================================================
Now, a new article published in the journal Nature Communications
reveals a new mechanism to transfer the chirality between molecules
in the nanoscale field, according to a study led by the UB lecturer
Josep Puigmarti'-Luis, from the Faculty of Chemistry and the Institute
of Theoretical and Computational Chemistry (IQTC) of the University
of Barcelona.

Chirality: from fundamental particles to biomolecules Chirality is an
intrinsic property of matter that determines the biological activity 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 Puigmarti'-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 obtain chiral molecules
through chemical reactions Chirality control is decisive in the production
of drugs, pesticides, aroma, flavours and other chemical compounds. Each enantiomer (molecule with a certain symmetry) has a certain activity which
is different from the other chemically identical compound (its specular
image). In many cases, the pharmacological activity of an enantiomer can
be scarce, and in the worst scenario, it can be very toxic. "Therefore, chemists need to be able to make compounds as single enantiomers, which
is called asymmetric synthesis," says Puigmarti'-Luis.



========================================================================== There are several strategies to control the sign of chirality in chemical processes. For instance, using natural enantiopure compounds known as
the chiral pool (for instance, amino acids, hydroxy acids, sugars) as precursors or reactants that can become a compound of interest after a
series of chemical modifications. The chiral resolution is another option
that enables separating enantiomers through the use of an enantiomerically
pure resolving agent, and recover the compounds of interest as pure enantiomers. The use of chiral auxiliaries that help a substrate react
in a diastereoselective way is another efficient methodology to obtain
an enantiomerically pure product. Last, the asymmetric catalysis --
based on the use of asymmetrical catalysers -- is the top procedure to
reach 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 in the study. "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 sign through fluid dynamics The new article describes how the modulation of the geometry of a helical reactor at a macroscopic level
enables controlling the sign of chirality of a process at a nanometric
scale, an unprecedented discovery to date in the scientific literature.



========================================================================== Also, the chirality is transferred top-down, with the manipulation of
the helical tube to the molecular level, through the interaction of
the hydrodynamics of asymmetric secondary flows and the spatiotemporal
control of reagent concentration 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 Puigmarti'-Luis.

In a helical channel, the flow is more complex than in a straight channel, since the curved walls generate centrifugal forces which result in the formation of secondary flows in the plane perpendicular to the direction
the fluid (main flow). These secondary flows (vortices) have a dual
function: they are opposed-chirality regions and build the necessary
chiral environment for enantioselection. In addition, by advection within
the device and for the development of reagent concentration gradients.

By modulating the geometry of the helical reactor at the macroscopic
level, "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 Puigmarti'-Luis.

The findings shed light on new frontiers to achieve the enantioselection
at a molecular level -- without the use of enantiopure compounds --
only by combining geometry and the working conditions 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 Puigmarti'-Luis.


========================================================================== Story Source: Materials provided by University_of_Barcelona. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Semih Sevim, Alessandro Sorrenti, Joa~o Pedro Vale, Zoubir
El-Hachemi,
Salvador Pane', Andreas D. Flouris, Tiago Sotto Mayor, Josep
Puigmarti'- Luis. Chirality transfer from a 3D macro shape to the
molecular level by controlling asymmetric secondary flows. Nature
Communications, 2022; 13 (1) DOI: 10.1038/s41467-022-29425-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220427100457.htm

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