Molecular Recognition Using Tetralactam Macrocycle and Development of Synthavidin Technology

Biotin/(strept)avidin binding is a remarkable molecular recognition process in nature with extraordinary high binding affinity (Ka ~ 10^15 M-1). Biotin/(strep)avidin self- assembly is a powerful platform for nanoscale fabrications with many different applications in science, medicine, and nanotechnology. However, there are several well recognized structural drawbacks of biotin/(strept)avidin self-assembly that limit performance in certain technical areas, and there is a great need for synthetic mimics that can either become superior replacement or operational partners with bio-orthogonal recognition properties. Our group is pursuing a synthetic mimic approach, called synthavidin technology, that is based on high affinity binding of tetralactam macrocycle and squaraine dye in water. This thesis presents different ways to manipulate the underlying molecular recognition process that produces this high affinity binding pair. A set of structurally related compounds was prepared and studied to reveal the factors that control the binding thermodynamics and kinetics. Also presented are synthetic methods to fine tune the photophysical properties using tetralactam macrocycle recognition in water while keeping the high affinity. As a new molecular recognition platform with high affinity in water, three practical applications of synthavidin technology are demonstrated. The first part demonstrates the concept of in situ capture for detection of neuraminidase, an indicator enzyme of flu infection. The second part uses the high affinity and rapid association between squaraine and tetralactam macrocycle for noncovalent functionalization of liposome surface. Part three illustrates the concept of pre-assembly and its application in fabricating fluorescent molecular probes for tumor targeting.