Heteroassociation of the bromine-containing anions of sulfophthaleins in aqueous solution

Abstract

The ability of bromine containing anions of sulfophthalein dyes, such as bromophenol blue (BPB), bromocresol green (BCG), bromocresol purple (BCP), bromothymol blue (BTB), as well as non substituted phenol red (PhR), to form heteroassociates in aqueous solution was investigated. Singly and doubly charged anions BPB, BCG, BCP, BTB, and PhR (HAn -, An 2-) are capable of forming stable heteroassociates of composition Ct + •HAn -and (Ct + ) 2 •An 2-with cationic polymethine dyes (Ct + ), such as pinacyanol and quinaldine red. The enthalpies of formation of the dye ions and heteroassociates were calculated by semiempirical methods, and the most probable structure of heteroassociates was determined.Sulfophthalein dyes have long been effectively used as acid base and metallochromic indicators, and also as analytical reagents for photometric determination of many metal ions, surfactants, organic bases, etc. 1-4 The sulfo phthaleins possess a range of specific features, such as the possibility of the separate existence of anionic protolytic forms, their stability, weak dimerization, good resolution of absorption bands of singly and doubly charged ions in the electronic spectra and, as a result, the high color con trast of indicator transitions. 1,4-7 In this class of com pounds, bromo derivatives of sulfophthaneins (BDSP), such as bromophenol blue (BPB), bromocresol green (BCG), bromocresol purple (BCP), and bromothymol blue (BTB), have attracted attention. These BDSP are also used for the high precision in situ determination of pH of pure 8,9 and natural waters (a mixture of sulfophthaleins is used). 10,11 BDSP is the basis of sensitive elements of optical рН sensors, 12 fiber optic biosensors, and chips 13-16 (e.g., BTB and acetylcholine esterase doped with a sol gel film are sensitive to the content of organophosphate pesticide). 14 Indicators are effectively used for the study of serum albumin. 17-20 One of the most promising fields of application of BDSP as analytical reagents is the quanti tative determination of the range of components in bio agents and pharmaceuticals: antiviral (indinavir), 21 anti microbial (enoxacin), 22 antibacterial (gatifloxacin, 23 sparfloxacin, 24 ofloxacin 25 ), antihistaminic (oxomem azine), 26,27 and hypotensive (irbesartan, 28 nifedipine, 29 dilti azem 30 ) agents, antidepressants (tianeptine, 31 trazodone, 32 sertraline, fluoxetine, venlafaxine 33 ), antiulcer agents (raniti dine), 34 etc. 35,36 It is noteworthy that the high precision and rapid methods described above are based on the for mation of heteroassociates (ionic pairs) between the com ponent to be determined and the anionic forms of BDSP. Very often heteroassociates are extracted into an organic phase (tricloromethane, 21,22,25,27,29,30,32 dichlorometh ane 26,36 ). Let us note that solutions of BDSP are rather complex, since each of the dyes is subjected to many pro tolytic and tautomeric transformations (even in a thin film state BDSP can exist as an equilibrium mixture of associated lactone, quinoid, and zwitterionic form...

Cation–Anionic Interactions of Dyes in Aqueous Solutions: Bromocresol Purple in the Processes of Dissimilar Association

“…Data for K as were obtained at C Ct+ ≈ 6•10 -7 mol/L for several C An j− values and at three wavelengths (see Table 2). The obtained data on the logarithmic values of the association constant are in good agreement with the values of K as , which were defined earlier by us [59] (QB: 6.67 ± 0.05 (Ct + •HAn − ), 11.07 ± 0.10 ((Ct + ) 2 •An 2− ); QR: 4.78 ± 0.06 and 8.23 ± 0.04, respectively) for slightly different concentration ranges of Ct + and BP. This fact confirms the validity of considering the indicated stoichiometry of a dissimilar association from the position of an equilibrium model.…”

“…The method is integrated into the software packages "HyperChem 8.0", Hupercube, Inc., New York, NY, USA (evaluation version) and "MOPAC 2009", Stewart Computational Chemistry, Colorado Springs, CO, USA. The principles of calculations for the structures of dyes and their ionic associates have been described in more detail previously [3,56,59,60].…”

“…The linear regression equation has the form in the concentration range of 1.0•10 −6 -1.0•10 −4 mol/L for QR [59]:…”

“…Note that these cations have been used previously under the study of the processes of anionic dye association [57][58][59].…”

Association of 5,5′-Dibromo-o-Cresolsulfonphthalein Anions with Dye Cations in Aqueous Solution

“…Note, that these cations have been used previously under the study of the processes of anionic dye association. [44][45][46]…”