Complexation of Charged Porphyrins by Charged and Metal‐Chelated EDTA‐Tethered β‐Cyclodextrin Dimers: A Thermodynamic Study on the Influence of Tether Charge and Flexibility on Binding Affinity

Abstract

Keywords: Cyclodextrins / Molecular recognition / Host-guest systems / PorphyrinoidsComplex formation between charged porphyrin guests and charged or neutral β-cyclodextrin (CD) host dimers linked by ethylenediamine-N,N,NЈ,NЈ-tetraacetate (EDTA) tethers was assessed by microcalorimetry. Two EDTA-tethered CD dimers (1 and 2) were employed to obtain a series of structurally similar CD dimers with different tether charges and flexibilities through either (partial) protonation or metal chelation (with Ca II or Eu III ) of the EDTA tether. Both the tether charge and the flexibility of the CD dimers strongly influenced the binding properties, giving rise to binding constants differing by factors of up to 22. The effect of tether charge was elucidated by the complexation of tetraanionic meso-tetrakis(4-sulfonatophenyl)porphyrin (TSPP) by the different forms of CD dimer 1. Tether charge-dependent complex (de)solvation gave rise to large systematic and counteracting changes in binding enthalpy and entropy, resulting in a binding affinity

Interaction of Cyclodextrins with Brooker's Merocyanine in Aqueous Solution

“…The formation of inclusion complexes involving 2 and the modified CyDs was possible, with the substitution of the hydroxyl groups by methyl or hydroxypropyl groups giving the b-CyD a higher flexibility. [31,32] This substitution also increases the solubility of CyDs in aqueous medium due to the breaking of the internal rigidity attributed normally to b-CyD in view of the formation of intramolecular hydrogen bonding. [33,34] As expected, the diminution in the preorganization of the b-CyD by structural modification makes difficult a tight and space-filling accommodation of dye 2, so that its mobility within the cavity is higher, reducing substantially its binding to the substrate.…”

Inclusion Complexes Containing Quaternary Azaaromatic Moieties

“…51 It was observed that 2 forms with the dimer (3) the 1:2 complex, i.e. 51 It was observed that 2 forms with the dimer (3) the 1:2 complex, i.e.…”

Secondary Face‐to‐Face 2–2′ β‐Cyclodextrin Dimers Linked with Fluorescent Rigid Spacer Arms: A Cyclodextrin‐Based Ratiometric Sensor for Bile Salts

“…[14,15] In addition to the cooperative binding through which the two adjacent CD cavities of these bridged bis(CD)s can encapsulate guest molecules, the linker can contribute to the stabilization of such complexes by providing additional binding interactions or contributing to extending the overall binding site. [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] Secondary-face-linked β-CD dimers often show higher complexing constants than those bridged by primary faces, [18][19][20][21]35] probably due to the fact that guest Scheme 1. CD units can be linked through their primary faces, i.e., 6-6Ј bis(CD), through a head-to-tail fashion, i.e., 6-2Ј or 6-3Ј bis(CD), and through their secondary faces, i.e., 2-2Ј or 3-3Ј bis(CD).…”