| Jul 02, 2024 |
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(Nanowerk News) Versatile molecular frameworks called discrete supramolecular structures act like microscopic building blocks customizable for a wide variety of applications. The structures can serve in drug delivery, provide unique environments for catalytic reactions or plug into a molecular machine.
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In their paper published in the Journal of the American Chemical Society (“Social Self-Sorting of Quasi-Racemates: A Unique Approach for Dual-Pore Molecular Crystals”), researchers from Yokohama National University presented a new methodology to advance self-assembly of dual-functional supramolecular materials.
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| The illustration depicts alcohol and water molecules being adsorbed only into one of the two types of pores. (Image: Yokohama National University)
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Self-assembly involves the spontaneous generation of a well-defined, discrete supramolecular architecture from a given set of components under thermodynamic equilibration. Typically, a binary combination of precursors, each bearing complementary functional groups, is assembled into a stable product. Multicomponent systems, which include at least two precursors having identical functional groups, remain relatively unexplored.
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Scientists are investigating methods to shepherd different precursors with the same functional groups into a unified supramolecular structure through “social self-sorting.” In social self-sorting, the transitions between complex self-sorted systems mimic the regulatory function found in nature, which are capable of selective but adaptive recognition behavior.
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To achieve this goal, researchers have been developing strategic approaches to prevent random incorporation and “narcissistic self-sorting,” where each type of precursor assembles into independent structures.
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One approach is through a technique called chiral self-sorting, which relies on the complementarity of chirality (right or left-handedness). When a racemic precursor (mixture of two chiral molecules called enantiomers) is used, both enantiomers are frequently incorporated into a single structure.
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Right-handed and left-handed molecules tend to align alternately when they crystallize, and it is possible to arrange “quasi-racemates” that have slight structural differences between the right-handed and left-handed forms.
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“Previous research has focused mainly on achieving the alignment of these molecules, and applying this phenomenon to the development of functional materials has been a challenge,” said corresponding author Suguru Ito, associate professor of engineering at Yokohama National University.
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In their study, Ito’s team explored arranging “quasi-racemates” with slight structural differences between right-handed and left-handed forms to create crystalline materials with pores of varying sizes. The social self-sorting of two pairs of quasi-racemates was achieved by forming a ring-shaped molecule with four connecting molecules. This stable ring is obtained through a reversible reaction between the aldehyde groups of the quasi-racemates and the amine groups of the connecting molecules. As a result, the ring-shaped molecules can crystallize into porous molecular crystals featuring two types of tube-like pores.
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“This represents a milestone achievement in applying the arrangement techniques of right-handed and left-handed molecules to the creation of functional materials,” Ito said.
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Designing porous materials with dual-pore systems presents a complex task, yet such materials are highly valuable due to their advanced functionalities. Because each pore can be functionalized distinctly, dual-pore materials enable simultaneous multiple functions or specific designs for complex applications.
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Experimental evidence confirmed that these dual pores exhibit different adsorption properties.
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This study emphasizes the utility of quasi-racemates in constructing socially self-sorted supramolecular structures with two distinct functionalities. Furthermore, the methodology sets the stage for the generation of a novel class of dual-pore molecular crystals.
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“To the best of our knowledge, this is the first dual-pore molecular crystal formed by socially self-sorted macrocycles,” Ito said.
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Future investigations will aim to develop various multi-functional crystalline materials by applying the technique of arranging quasi-racemates.
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“My ultimate goal is to establish a method for precisely arranging organic molecules and to develop functional crystalline materials that are beneficial to society,” Ito said.
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