Tetrabutylammonium anion salts, titration

The conversion of squaraine 19a to the rotaxane 18 D 19a causes a modest red-shift only in both absorption (10 nm) and emission (7 nm) but an approximately threefold decrease in quantum yield. The addition of two triazole rings (dye 19b) did not significantly alter the quantum yield of 17b (Table 4). A macrocycle-induced quenching effect was verified by fluorescence titration experiments adding aliquots of 18 to a solution of squaraine 17b in methylene chloride [58]. Treatment of the 18 d 17b psuedorotaxane system with the tetrabutylammonium salts of chloride, acetate, or benzoate leads to the displacement of squaraine 17b from the macrocyclic cavity and the nearly complete restoration of its fluorescence intensity. The 18-induced quenching of 17b does not support the utility of this system as a bioimaging probe however, the pseudorotaxane system 18 Z> 17b acts as an effective and selective anion sensor with NIR fluorescence. 

As proven by H NMR titration experiments in DMSO-d6, the upper rim bridged derivative 3 exhibits very good binding abilities towards many selected anions (in the form of tetrabutylammonium salts). On the other hand, recep-... 

Proton NMR titrations in DMSO-de at 298 K were conducted in order to determine the stability constants of receptors 12a, 12b and 12c with a range of anions, added as their tetrabutylammonium salts. The strongest association constants were obtained for the 20-membered macrocycle 12b with the most significant increase in affinity between the macrocycles being observed in the binding of chloride. Enlargement from the 18-membered macrocycle... 

Fluorescent titration experiments with receptors 21b and 22b were carried out in DMSO with a variety of anions, added as the tetrabutylammonium salts, in order to compare the stabihty constants of the mono- and bis-functionalized receptors. The strongest anion binding was observed with the bis-functionalized receptor (22b) with stability constants of 108000, 9700... 

Jurczak and co-workers have described l,8-diamino-3,6-dichlorocarbazole as a building block for anion receptor construction. Stability constants for receptors 52a and 52b with various anions, added as tetrabutylammonium salts, were calculated by NMR titration experiments in DMSO-d6/0.5% water and it was foimd that compoimd 52b boimd anions more strongly with constants of 115 and 8340 M for chloride and benzoate, respectively, compared to 13 M and 1230 M with compoimd 52a with chloride and acetate, respectively [70]. 

Ferrocenyl-modified dendrimers were found to be able to recognize small inorganic anions [105, 106]. From shifts of the ferrocene-based peak potentials in cyclic voltammetry in CH2CI2 solution and shifts of 5nh in NMR, resulting from the titration of the dendrimers with the tetrabutylammonium salts of anions such as H2P04 , HS04 , C1 , and NO3 , changes in the apparent association constant of the anion with the ferrocenyl dendrimer were monitored. 

Determined by UV-vis spectroscopic titrations in CH4a2 (anions are studied as their tetrabutylammonium salts with 1 1 binding stoichiometries). 

The binding behavior of these receptors at 25 °C was investigated first by proton NMR spectroscopy in CD3CN/DMSO-t/e (9 1 v/v), as well as by UV-vis spectroscopy and isothermal titration calorimetry in MeCN/DMSO (97 3, v/v). The receptors displayed a selective colorimetric response when exposed to the fluoride, dihydrogen phosphate, and acetate anions (studied in the form of the corresponding tetrabutylammonium salts) and an enhanced affinity as compared to a comparable calix[4]pyrrole system lacking the dipyrrolylquinoxaline-containing strap. 

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