Biomimetic Approach to the Design of Selective Oxoanion Receptors for Use in Membrane-Based Potentiometric Sensors

The need to selectively recognize and complex ions and molecules is common in many areas of science and industry. Nature’s ability to selectively detect or sense specific compounds in a variety of ways and under many different conditions has long been the source of inspiration in the application and development of recognition-based chemistry. Biofunctional membranes present one such example where polymeric membranes can be designed with a desired function by using or mimicking natural chemical recognition systems. The components found in living organisms that have selective recognition features (i.e., proteins, enzymes, membrane systems, sensory neurons, etc.) have been the subject of much intense study. The rapid, selective, and sensitive response of natural sensory systems that employ recognition chemistry can serve as a model in the development of biosensors. This includes mimicking natural receptors,1 antibiotics,2,3 and even olfactory membranes4 to accomplish desired tasks. One group has successfully immobilized double-helical DNA directly onto an electrode surface and obtained a biosensor that responded selectively to DNA-binding substances (via intercalation) as well as to magnesium ion.5 The applications which await the development of novel biosensors cover a wide range of disciplines, including environmental, medical, industrial, and other venues of research

Calix[n] imidazolium as a new class of positively charged homo-calix compounds

Macrocycles based on neutral calixarenes and calixpyrroles have been extensively explored for ion binding, molecular assembly and related applications. Given that only these two types of calix compounds and their analogs are available, the introduction of new forms of widely usable calix macrocycles is an outstanding challenge. Here we report the quadruply/quintuply charged imidazole-based homo-calix compounds, calix[4/5] imidazolium. The noncovalent (C-H)(+)/pi(+) -anion interactions of the imidazolium rings with anions inside and outside the cone are the stabilizing factors for crystal packing, resulting in self-assembled arrays of cone-shaped calix-imidazolium molecules. Calix[4] imidazolium senses fluoride selectively even in aqueous solutions. Calix[5] imidazolium recognizes neutral fullerenes through pi(+) -pi interactions and makes them soluble in water, which could be useful in fullerene chemistry. Not only derivatization and ring expansion of calix[n] imidazolium, but also their utilization in ionic liquids, carbene chemistry and nanographite/graphene exfoliation could be exploited.close10