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Complexation of Anions Including Nucleotide Anions by Open‐Chain Host Compounds with Amide, Urea, and Aryl Functions
Author(s) -
Werner Frank,
Schneider HansJörg
Publication year - 2000
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/(sici)1522-2675(20000216)83:2<465::aid-hlca465>3.0.co;2-f
Subject(s) - chemistry , denticity , carboxylate , amide , medicinal chemistry , stereochemistry , ethylenediamine , ligand (biochemistry) , aryl , urea , hydrogen bond , crystallography , inorganic chemistry , molecule , alkyl , organic chemistry , receptor , crystal structure , biochemistry
A systematical evaluation of association constants between halide, phosphate, and carboxylate anions with N ‐methylformamide ( 1 ) and the related bidentate receptors 2 – 6 (derived from, e.g. , phthalic acid or ethylenediamine) in CDCl 3 as solvent yielded increments of complexation free‐energy Δ Δ G for each single H‐bond, which varied like, e.g. , 5.1 kJ/mol (for Cl − ), 4.0 kJ/mol (for Br − ), 4.0 kJ/mol (for I − ) (with values taken from Tables 1 and 2 ), in line with expected H‐bond strength. The observed complexation induced NH‐NMR shift (CIS) values also showed a regular change, in the case of 1 , e.g. , from 5.0 to 2.8 to 2.1 ppm ( Table 1 ), with about half of these values with the bidentate ligands ( Tables 2 and 3 ). Tridentate hosts led to a substantial binding increase, if strain‐free convergence of all NH donor functions towards the anion was possible. The tris[urea] ligand 10 yielded, even in the polar solvent DMSO, with Cl − a Δ G of −21.5 kJ/mol and with Br − of −10⋅5 kJ/mol, whereas with I − , no association was detectable. The results demonstrated that small, inexpensive, and conformationally mobile host compounds can exhibit high affinities as well as descrimination with anions, as much as more preorganized receptors do which require multistep synthesis. The corresponding adamantyl derivative 13 allowed measurements also in CDCl 3 , with K =4.3⋅10 4 M −1 for chloride ( Table 7 ). Complexes with nucleotide anions were again particularly strong with the tridentate urea‐based ligands, the latter being optimal ligands for chloride complexation. For the association of 10 with AMP 2− and GMP 2− in (D 6 )DMSO, the association constants were 3⋅10 4 M −1 ( Table 8 ) and almost the same as with Cl − . In the case of the urea derivatives 17 , 18 , and 21 , containing only one phenyl or pyrenyl substituent, however, the Δ G values decreased in the order A>C>T>G ( e.g . −13.6, −11.6, −7.6, −10.5 kJ/mol in the case of 17 , resp.; Table 8 ). In H 2 O, the pyrenyl‐substituted urea derivatives allow measurements with fluorescence, and, unexpectedly, show only smaller nucleobase discrimination, with constants around 3⋅10 3 M −1 .