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Cooperative Binding of Fluoride Anions to a Flexible Cystine‐Based Receptor Containing Two 3,5‐Dinitrobenzamide Motifs
Author(s) -
Deka Barnali,
Sarma Rupam J
Publication year - 2018
Publication title -
chemistryselect
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.437
H-Index - 34
ISSN - 2365-6549
DOI - 10.1002/slct.201800956
Subject(s) - chemistry , hydrogen bond , fluoride , crystallography , receptor , stereochemistry , binding constant , binding site , molecule , inorganic chemistry , organic chemistry , biochemistry
Abstract The binding of fluoride (F̄) anions to cystine‐based ligands containing two 3,5‐dinitrobenzamide motifs (receptors L1 , L2 ) were monitored using UV/vis and 1 H NMR spectroscopy. Detailed UV/vis studies revealed that interactions of L1 and L2 with F̄ anions were cooperative, characterised by sigmoidal binding isotherms. The binding isotherms for L1 /F̄ and L2 /F̄ were analysed using the Hill equation, and the results fitted to a cooperative two‐site binding model (Hill coefficient, n H ≈ 1.89, 2.06). In both cases, the association constant, K 2 > K 1 , indicating that the interactions between L1 (or L2 ) and F̄ anion in the completely bound state were more favourable than the partially bound intermediate state. However, such cooperative binding behaviour was not observed for the methionine‐derived 3,5‐dinitrobenzamide receptor, L3 . 1 H NMR studies provided further insights into the nature of receptor/F̄ interactions, particularly the role of hydrogen bonding and anion‐π interactions. The binding geometries of the 1:1 complex of L1 with F̄ anions were optimised using density functional theoretical (DFT) calculations, which suggested the formation of anion‐assisted ‘sandwich‘ complex. In case of the 1:2 complex, the DFT optimised structure for L1 /F̄ system was consistent with ‘open‘ conformation for the receptor.