title: Positive homotropic allosteric receptors for neutral guests: annulated tetrathiafulvalene-calix[4]pyrroles as colorimetric chemosensors for nitroaromatic explosives.
abstract: The study of positive homotropic allosterism in supramolecular receptors is important for elucidating design strategies that can lead to increased sensitivity in various molecular recognition applications. In this work, the cooperative relationship between tetrathiafulvalene (TTF)-calix[4]pyrroles and several nitroaromatic guests is examined. The design and synthesis of new annulated TTF-calix[4]pyrrole receptors with the goal of rigidifying the system to accommodate better nitroaromatic guests is outlined. These new derivatives, which display significant improvement in terms of binding constants, also display a positive homotropic allosteric relationship, as borne out from the sigmoidal nature of the binding isotherms and analysis by using the Hill equation, Adair equation, and Scatchard plots. The host-guest complexes themselves have been characterized by single-crystal X-ray diffraction analyses and studied by means of UV-spectroscopic titrations. Investigations into the electronic nature of the receptors were made by using cyclic voltammetry; this revealed that the binding efficiency was not strictly related to the redox potential of the receptor. On the other hand, this work serves to illustrate how cooperative effects may be used to enhance the recognition ability of TTF-calix[4]pyrrole receptors. It has led to new allosteric systems that function as rudimentary colorimetric chemosensors for common nitroaromatic-based explosives, and which are effective even in the presence of potentially interfering anions.
authors.affiliation: Department of Chemistry and Biochemistry, The University of Texas at Austin, 1 University Station, A5300, Austin, TX 78712, USA.
authors.forename: Jung Su
authors.initials: JS
authors.lastname: Park
authors.forename: Franck
authors.initials: F
authors.lastname: Le Derf
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Bejger
authors.forename: Vincent M
authors.initials: VM
authors.lastname: Lynch
authors.forename: Jonathan L
authors.initials: JL
authors.lastname: Sessler
authors.forename: Kent A
authors.initials: KA
authors.lastname: Nielsen
authors.forename: Carsten
authors.initials: C
authors.lastname: Johnsen
authors.forename: Jan O
authors.initials: JO
authors.lastname: Jeppesen
mesh_terms: D047250:Calixarenes / Q000138:chemical synthesis / Q000737:chemistry*; D003124:Colorimetry; D018360:Crystallography, X-Ray; D003500:Cyclization; D053834:Explosive Agents / Q000737:chemistry*; D006571:Heterocyclic Compounds / Q000737:chemistry*; D008968:Molecular Conformation; D011166:Porphyrins / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D053834:Explosive Agents; D006571:Heterocyclic Compounds; D011166:Porphyrins; C469811:calix(4)pyrrole; D047250:Calixarenes; C063887:tetrathiafulvalene