“Calixarenes” is among the handful of names that immediately makes sense to many different molecular chemists communities.
This is not surprising if one considers the exceptionally broad applicative range of this family of compounds, from metallic cations and molecules recognition to sensors, including gas separation, drug delivery, etc.
Indeed, the pioneering work of C.D. Gutsche and collaborators during the 80’s made available a whole family of these macrocyclic compounds in the pure state, according to simple, easily scalable synthetic protocols. This allowed for these molecules to be extensively studied during the last 30 years. Nowadays, this is still a very active field of research, as witnessed by the hundreds of papers involving calixarenes that are still published per year. More than any other metrics, this sustained interest from many different communities, demonstrate the importance of these compounds.
One may thus consider that the synthesis of the starting calixarenic plateforms is a fully understood and closed chapter, but our work shows that this is far from being the case. Indeed, we reported a new family of calixarenes, left overlooked for 30 years: the giant calixarenes.
We serendipitously discovered that under specific conditions, some p-(alkyloxy)functionalised phenols are prone to produce very large calixarenic oligomers (including from 15 to 100 phenolic subunits) in high yields (up to 65%), on a very large scale (up to 400g yet). Since our early puzzling observations (2007), it took us more than 10 years to get a clear understanding of what was going on. We designed and conducted a research program allowing for the influence of all the parameters involved in calixarenes synthesis to be systematically investigated. This period was also necessary to gather together all the characterization tools needed to assemble all the pieces of the puzzle.
This discovery opens a completely new chapter in calixarenes history. This also raises more fundamental questions, as giant calixarenes syntheses are performed using very concentrated reagents solutions, far from the more conventional high dilutions conditions commonly used to get macrocycles of comparable sizes. In some cases, these syntheses can even be performed in the solid state, without any stirring/grinding mechanism, revealing a new solid-state chemistry.
Along with their intrinsic fundamental interest, these new macromolecular objects are also opening interesting applicative perspectives. Indeed, their size range (between 3 and 10 nm), their huge functionalization possibilities and their ease of synthesis on a large scale make them interesting for such applications as vectorization or nanometer-sized supports for metals.