Synthesis and application of cyclodextrin conjugates
Cyclodextrins, a family of compounds formed from a cyclic array of glucose monomers, contain a hydrophobic cavity which displays selective complexation of size specific guests. This selective molecular recognition is critical to the development of successful chemosensors. A selection of cyclodextrin-conjugates have been designed to report complexation of guests into the cyclodextrin cavity by optical and electrochemical means. Alkylated cyclodextrins containing a single linker group have been synthesised allowing the development of two cyclen-appended cyclodextrin conjugates and their lanthanide complexes. The tetraamide ligand (25) displayed a high rigidity, assessed by (^1)H NMR and luminescence methods. The Tb complex of the monoamide ligand [Tb.26] displayed long lived luminescence arising from energy transfer from cyclodextrin-complexed napthalene to the lanthanide. The association constant, K(_11), between naphthalene and the cyclodextrin [Tb.26], was calculated as 10,200 M(^-1). K(_11) between the Gd complex [Gd.26] and GdDOTAPh (40) was determined to be 1740M(^-1) by NMRD. These association constants are ca 14 and 7 times greater respectively than for the corresponding complexes with β-cyclodextrin (1). Bromonaphthalenes exhibit long lived phosphorescence when complexed within cyclodextrins. Four bromonaphthalene-appended cyclodextrins (57-60) were designed to form inframolecular self-complexes. Competitive complexation of optically transparent guests was expected to reduce the lifetime of phosphorescent emission. The four conjugates were successfully synthesised, although luminescence studies revealed no evidence for complex formation and no response upon competitive guest complexation was observed. The rotaxane (95) and corresponding thread (92) of a hydrophilic ferrocene- cyclodextrin conjugate were made and structurally assessed by CD, (^-1)H NMR and MALDI-TOF MS. The hydrophilic per-O-ethyl conjugates (93 & 100) were also synthesised. A lipophilic quinoline-cyclodextrin conjugate (94) was made, which, when incorporated into an optode membrane, allowed the detection of acetylcholine at micromolar concentrations.