Systems chemistry is a young discipline that takes a look at the long-ignored dynamic processes occurring in complex chemical mixtures. As such, systems chemistry breaks with a long-held dogma of preparative chemistry: the focus no longer lies on isolated, pure compounds, but rather on dynamic mixtures of molecules.
Of particular interest are molecular networks that exhibit the ‘far-from-equilibrium’ phenomena ubiquitously found in macroscopic and (sub-)microscopic biological systems: self-replication, sustained (chemical) oscillations or non-linear responses to stimuli. Open questions in this area include: how can out-of-equilibrium systems best be created and what are suitable energy sources? What transformations comprise the toolbox of systems chemistry? What are possible applications? For a review article on supramolecular systems chemistry click here.
We have entered this field by introducing the acid-catalyzed exchange of O,O,O-orthoesters to the toolbox of dynamic covalent chemistry. We demonstrated that orthoesters readily exchange with a wide range of alcohols under mild conditions and we disclosed the first report of an orthoester metathesis reaction. We also showed that dynamic orthoester systems give rise to pronounced metal "template" effects, which can only be understood when considering the system as a whole: each compound is connected to others via agonistic or antagonistic relationships, which are best visualized in 3D (see Image).
Due to the tripodal architecture of orthoesters, we expect that this exchange process will find unique applications in dynamic polymers, porous materials and host–guest architectures.
We could apply orthoester exchange to the synthesis of new coronands and cryptands, a class of compounds that can accommodate metal ions in a preorganized two- or three-dimensional environment. The discovery of these molecules in the 1960s was a milestone in supramolecular chemistry, leading to countless applications from organic synthesis to metallurgy and medicine. Typically coronands and cryptands are prepared via multistep organic synthesis and one of their characteristic features is the high stability of their covalent framework.
We were able to use orthoester exchange for the one-pot template synthesis of a new class of coronates and cryptates, in which acid-labile O,O,O-orthoesters serve as bridgeheads (see Image). In contrast to their classic analogues, these new compounds are constitutionally dynamic in the presence of acid (giving rise to some fascinating systems chemistry effects) and can be induced to release their guest via irreversible deconstruction of the cage.
These unprecedented properties open up a wide range of application opportunities, from systems chemistry to molecular sensing and drug delivery.
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