Chloride binding studies

Kavanaugh JS, Rogers PH, Case DA, Arnone A. High resolution x-ray study of deoxyhemoglobin Rothschild 37b Trp to Arg a mutation that creates an intersubunit chloride-binding site. Biochemistry 1992 31 4111-4121. 

Receptor 16 was reported to form a 1 1 complex with chloride ions in chloroform (K = 500 M ), exhibiting fast exchange on the NMR time scale (73). Such hosts, containing four tin binding sites, were shown to be considerably more effective than mononuclear organotin compounds for chloride binding. In 1991, Newcomb and co-worker (74) published modeling studies for these tin based hosts as well as a crystal structure of 17. 

The trinuclear receptor 18 and its propyl linked analog 19 have been reported by Jurkschat et al. (75, 76). Receptor 18 was shown to transport chloride and bromide ions from water through dichloromethane, but the process was slow. Crystallography of 19a indicated chloride binding between a pair of tin atoms, while NMR studies indicated that 19b involved all three tin atoms in the binding process. No quantitative evaluation of binding affinities was attempted. 

Another structural motif effective in binding anions is that of two face-to-face 1,3,5-trisubstituted benzenes with bridges containing amines (12). These receptors were observed to bind small anions with some selectivity. In the majority of binding studies, monovalent species such as nitrate and chloride bind more weakly (log Kg2.5) compared to dianions such as sulfate (log Ks 6.0). This structural motif was expanded even further in the elegant azaparacyclophane (13). At pH 4, this cubane is tetraprotonated and binds anionic fluorescent molecules such as l-anilinonaphthalene-8-sulfonate (ANS). ... 

The studies of chloride binding to hemoglobin, discussed above, have indicated that the binding sites for anions may be well defined in structural terms. A similar approach will probably prove fruitful for the identification of ligand binding sites in other proteins. 

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