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Towards processive allosteric catalysts for molecular encoding – PRALLOCAT

Towards processive allosteric catalysts for molecular encoding

Data-storage is undoubtedly a major concern of our modern societies<br />and molecular encryption is probably one of the most promising way to tackle this problem.In this proposal, we intend to set the foundations for a molecular encoding system able to write on a polymer substrate in a sequential and controlled fashion Such system, lies on the design of a new class of catalysts, namely processive allosteric catalysts,<br />that could further contribute to the elaboration of molecular computing machines.

Processivity and sequentiality

This project would take advantage of a pseudo-rotaxane catalyst-polymer assembly to achieve the processivity while sequentiality would be ensured by an original ratchet mechanism allowing unidirectional slippage of the catalyst along the polymer chain; the writing control will be achieved by allosteric communication. The design of the targeted processive allosteric catalysts combine a cavity to a bimetallic complex in order to bring a threaded polymer chain in close proximity with two metallic sites featuring two distinct functions: “writing” (active site = Mwrite) and “reading/ratcheting” (regulatory site = Mread/ratchet). In practice, our design associates a hexaphyrin subunit (H) to one or two cyclodextrin hosts (CD) to yield 1:1 (HCD) or 1:2 (CDHCD) hybrid compounds. Having these molecules in hands, three major objectives can be delineated to achieve a proof-of-concept for a molecular encoding system:<br />- allosterically controlled writing;<br />- sequential writing from ratcheting;<br />- controlled and sequential writing from allosteric communication and ratcheting.

The scientific program will be divided into 5 distinct tasks.
Task 1 is the global coordination task of the project.
The second task (Task 2) is related to the synthesis and characterization of the ligands constituted of a regular hexaphyrin cap coupled to a single or two protected cyclodextrins. All new organic compounds will be characterized by standard techniques (structural characterization, conformational analysis, electronic and chiroptical properties).
The third task (Task 3) will focus on the coordination and host-guest properties (including the polymer threading) of the hexaphyrin-cyclodextrin ligands prepared in Task 2.
In the fourth task (Task 4), we will investigate the catalytic activity of metal complexes towards the controlled and sequential writing on a polymer tape.
The last task (Task 5) concerning the dissemination of the project’s results will be achieved through communication in high impact factor journals and international congress.

During this first part, many advances were obtained. We finalized two key studies, one on hexaphyrins capped by cryptants, the other on hexaphyrins doubly capped by cyclodextrins. These studies published in prestigious international journals support us in the interest of this type of structures for the targeted applications. Following this, we have developed a whole range of new hybrid hexaphyrin-cyclodextrin compounds. In particular, those whose subunits are connected by two covalent bridges are accessible on a large scale, and their coordination properties are much greater than their triply bridged analogs. In order to develop a host-guest chemistry, we have on the one hand enlarged the cavity of the cyclodextrin, and on the other hand «uncluttered« their opening. Also, in order to develop a catalytic activity, a structural modification of the hexaphyrin subunit was carried out. These results are very encouraging, and we are actively pursuing the study of these hybrid compounds.

We are now focusing on the coordination properties of both the doubly-bridged hybrids and the enlarged ones. For the latters, a large scale synthesis will be done in order to investigate their host-guest properties as well. Reactivity studies will also start soon with the structurally modified hexaphyrins.

“Tren-Capped Hexaphyrin Zinc Complexes : Interplaying Molecular Recognition, Möbius Aromaticity, and Chirality”
Ruffin, H.; Nyame Mendendy Boussambe, G.; Roisnel, T.; Dorcet, V.; Boitrel, B.; Le Gac, S. J. Am. Chem. Soc. 2017, 139, 13847-13857.

“Cyclodextrin-Sandwiched Hexaphyrin Hybrids. Side-to-Side Cavity Coupling Switched by a Temperature and Redox Responsive Central Device”
Ménand, M.; Sollogoub, M.; Boitrel, B.; Le Gac, S. Chem. Eur. J. 2018, 24, 5804-5812.

Cover Feature: Cyclodextrin-Sandwiched Hexaphyrin Hybrids: Side-to-Side Cavity Coupling Switched by a Temperature- and Redox-Responsive Central Device (Chem. Eur. J. 22/2018)

Some life essential processes such as DNA replication involve processive enzymes able to bind and slide along a single substrate (generally a biopolymer) achieving a series of transformations without dissociation. The development of artificial counterparts is still at an early stage, though man-made processive catalysts could become the cornerstone for molecular information processing. Indeed, the controlled writing/reading on a polymer tape would set the basis of computing at the molecular level.
This proposal intends to set the foundations for a molecular encoding system able to write on a polymer substrate in a sequential and controlled fashion. Such system, which is still undescribed, lies on the design of a new class of catalysts, namely processive allosteric catalysts, that could further contribute to the elaboration of molecular computing machines. This project would take advantage of a pseudo-rotaxane catalyst-polymer assembly to achieve the processivity while sequentiality would be ensured by an original ratchet mechanism allowing unidirectional slippage of the catalyst along the polymer chain; the writing control will be achieved by allosteric communication. The design of the targeted processive allosteric catalysts combine a cavity to a bimetallic complex in order to bring a threaded polymer chain in close proximity with two metallic sites featuring two distinct functions: “writing” (active site) and “reading/ratcheting” (regulatory site). In practice, our design associates a hexaphyrin subunit (H) to one or two cyclodextrin hosts (CD) to yield 1:1 (HCD) or 1:2 (CDHCD) hybrid compounds. These sophisticated ligands fulfill all the prerequisites defined for a processive allosteric catalyst working in a sequential manner: (i) a confined space between the hexaphyrin and the cyclodextrin able to thread a polymer ensuring the processivity and (ii) two differentiated coordination sites allowing to assign different roles to a couple of metal ions (writing and reading/ratcheting).
Our working program includes: (i) the synthesis and characterization of hexaphyrin-cyclodextrin ligands, with structural variations concerning the hexaphyrin cap and the cyclodextrin rims. This will allow to tune the coordination properties as well as the pseudo-rotaxane catalyst-polymer assembly; (ii) assessment of the coordination and host-guest properties of the HCD hybrids, together with polymer threading studies; (iii) investigations of the catalytic activity of HCDs metal complexes, focusing on the catalytic epoxidation of alkenes. Optimized oxidation conditions will be defined with model hexaphyrin compounds, and these will be applied to the HCD metal complexes with a threaded polybutadiene chain. More particularly, we will focus on the two following points, an allosteric control of the writing event and a sequential writing from either an inherent or a coordination ratchet.
The achievement of this project would constitute a real breakthrough in the field of processive catalysis. It would open the way to even more complex processes, such as the reading and replication of an encoded polymer.




Project coordination

Stéphane Le Gac (Institut des Sciences Chimiques de Rennes)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

CNRS-Université de Rennes 1 Institut des Sciences Chimiques de Rennes

Help of the ANR 206,550 euros
Beginning and duration of the scientific project: September 2016 - 36 Months

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