Nanoparticles (which have sizes ranging between 3–500 nm), and sub-nanoclusters (which are around 1 nm in diameter) are utilized in many fields, including medicine, robotics, materials science, and engineering. Their small size and large surface-area-to-volume ratios give them unique properties, rendering them valuable in a variety of applications, ranging from pollution control to chemical synthesis.
Recently, quasi-sub-nanomaterials, which are about 1–3 nm in scale have attracted attention because they have a dual nature–they can be regarded as nanoparticles, as well as inorganic molecules. Understandably, controlling the number of atoms in a quasi-sub-nanomaterial could be of much value. However, synthesizing such precise molecular structures is technically challenging, but scientists at Tokyo Tech were certainly up for this challenge.
Dendrons—highly branched molecular structures consisting of basic imines—have been suggested as precursors for the precise synthesis of quasi-sub-nanomaterials with the desired number of atoms. The imines in the dendrons function as a scaffold that can form complexes with certain acidic metallic salts, accumulating metals on the dendron structure. These, in turn, can be reduced to metal sub-nanoclusters with the desired number of atoms. However, synthesizing dendrons with a high proportion of imines is an expensive process with low yield.
Now, in a study published in Angewandte Chemie, the researchers explain how they have combined multiple dendrimer structures to form a supramolecular capsule composed of more than 60 imines. "The synthesis of dendron-assembled supramolecules was accomplished by connecting internal core units and external dendron units—which determine the central structure and terminal branches, respectively," explains Assistant Professor Takamasa Tsukamoto, who was involved in the study. The internal structure of this supramolecule contained a six-pronged core with acidic tritylium, while each outer unit contained dendrons with imines. The interaction between the acidic core and the basic outer structure resulted in a self-assembling organo-complex.
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