Bucket chemosensors

Of the diverse supramolecule architectures considered for chemosensor design, we emphasize one—a miniature bucket. Supramolecular buckets maintain a cylindrical cavity with structurally and chemically well-defined upper and lower rims. By virtue of its molecular shape, the bucket is an intrinsic receptor site. A supramolecular bucket alone, however, is an inadequate chemosensor because a signal cannot be produced. In the simplest chemosensing constructs, the analyte generates a signal upon association with the bucket whereas in more elaborate designs, functionality at the rim of the bucket offers sites to attach a discrete reporter site. The thematic focus of this chapter is bucket chemosensors that operate by the 3R scheme shown in Fig. 2, namely, a measurable change in a... 

Rather, conformational effects are discussed as necessary for the specific bucket chemosensors of Sec. IV. 

The conformational flexibility of several bucket chemosensors is reduced upon analyte binding. In the rigidified state, the luminescence from the reporter site is enhanced. Scheme 11 pictorially represents the transduction process. The precise mechanism by which nonradiative decay is disrupted in chemosensors of this type is usually ill defined. 

A bucket-shaped cavity provides the consummate supramolecular architecture for analyte recognition. The most prominent buckets used in chemosensor design... 

The utilization of monosubstituted CDs in Scheme 7 presents the drawback that excimer formation depends not only on the concentration of analyte, but also on the bimolecular assembly of the reporter site. The overall signal response of chemosensors of this type therefore depends on the concentration of the analyte and receptor. To alleviate the complication of assembling the reporter site, Ueno and coworkers have appended two monomers to the rim of the CD bucket. The preferred design entails the inclusion of one monomer in the CD bucket. Analyte recognition frees the included monomer, enabling it to interact with its partner tethered to the external rim of the bucket. 

Calixarenes may also bear excimer reporter sites, although the details of signal transduction are inherently different from those of CD-based excimer chemosensors. First, unlike Schemes 7 and 8, the fluorescent monomer units are not included within the calixarene bucket. Rather, calixarene functions as only a scaffold, bearing monomer subunits. Second, analyte seldom enters the calixarene bucket. The most common design for this type of chemosensor is shown in Scheme 9. A preformed excimer is disrupted by analyte binding at the... 

The explosion of supramolecule architectures makes the elaboration of new receptors an obvious target of future investigation. Buckets are endpoints of a continuum of supramolecules based on rings and other cylindrical structures [413], These related macromolecules demonstrate bucket-type, lock-and-key interactions that are similar to those of CDs and calixarenes. The unique physical and chemical properties of the different supramolecule reporter sites enable the selectivity and sensitivity of analyte recognition to be exquisitely tuned. Depending on the analyte and the application, it is likely that new supramolecule architectures will be the cornerstones of many new chemosensor platforms. 

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