Influence of non-ionic polymers on solvent properties of water as detected by studies of acid–base equilibria of sulphonephthalein and fluorescein dyes

Abstract

Acid-base equilibria of sulphonephthalein dyes, fluorescein and eosin, in aqueous solutions of several non-ionic polymers containing 0.01 or 0.05 mot dm-3 buffers have been studied as functions of the polymer concentration and the initial pa: of the buffer. Spectrophotometric and potentiometric data show that the paH in the polymer solution depends on the initial pa: of the buffer and on the type and concentration of polymer present in the solution.The general trend observed in aqueous solutions containing 0.01 mol dm-3 universal buffer was that for pa: < 5.5 the polymers examined decrease the acidity of the aqueous medium with an intensity dependent on their chemical nature and concentration. The polymers studied did not affect the pa: of the aqueous medium in paH range 5.57.5. At pa: > 7.5 the polymers decrease the basicity of the aqueous medium. The effects may be viewed as a shift of paH of the aqueous medium towards 7.0, the effect increasing with distance from 7.0. The results of studying acid-base and tautomeric equilibria of fluorescein and eosin in polymer solutions show that the equilibrium constants for the dyes change in reference to pure water. The changes determined are similar to those observed for the dyes in water-organic solvent mixtures.The acid-base equilibria of the dyes in the aqueous polymer solutions examined appear to change owing to polymer effects on the structure and/or state of water, leading to changes in the hydration and thermodynamic activity of both H+ and OH-ions. This view is supported by the data obtained in the study of solvatochromic effects of sulphonephthalein dyes in polymer solutions. The results obtained support the earlier suggestion that aqueous polymer solutions behave as water-like liquids of varied solvent properties.

Spectroscopic and Kinetic Characterization of Eosin–5-Maleimide

“…The extinction coefficients for EM at 520 nm and EMA at 518 nm (our measured peak positions) in sodium phosphate buffer, pH 7.4, are identical, making the extinction coefficient for EM at 520 nm equal to 95,400 M Ϫ1 cm Ϫ1 . Under these conditions, EM is a dianion (23). This extinction value is very similar to the average of six values for the dianion of the parent chromophore, Eosin Y, in water (96,000 M Ϫ1 cm Ϫ1 ).…”

“…The temperature dependence of hydrolysis (at pH 7.8) gave a relatively large activation energy, 23.7 Ϯ 0.8 kcal/mol, which might reflect the fact that both reactants are negatively charged at this pH (23). The ionic strength dependence clearly reflects a reaction between like-charged reactants, with a positive slope from the Debeye-Huckel plot of 1.53 Ϯ 0.089 (22).…”

“…For a ⌸-⌸* transition such as the long wavelength band of EM (28), a shift to the blue with increasing solvent polarity, such as we see, would normally be taken to indicate that the ground state is more dipolar than the excited state (27,29). However EM is a dianion in buffer at pH 7.4 (23), and it is important to question whether it remains a dianion in nonaqueous solvents. A pH titration of Eosin Y in methanol found the absorbance maximum of the dianion to be 520 -522 nm (30), essentially identical to its position (518 nm) in aqueous media (11,12,26).…”

Application of integral‐equation theory to aqueous two‐phase partitioning systems

“…Most of these previous modeling efforts have focused on a description of nonelectrostatic forces, in particular excluded-volume forces, affecting phase diagrams and partition coefficients. For example, an 1974a; Reitherman et al, 1973;Bamberger et al, 1984;Brooks et al, 1984;Sharp et al, 1986;Zaslavsky et al, 1978Zaslavsky et al, -1983Zaslavsky et al, , 1986Zaslavsky et al, -1988Zaslavsky et al, , 1991. For realistic engineering applications, it is essential that electrostatic forces be included in any model for aqueous solutions containing proteins.…”

Protolytic properties of dyes embedded in gelatin films

“…In turn, the latter is always higher than pK a w for the second ionization step of eosin on going from water to micelles of non-ionic surfactants 54 and solutions of non-ionic polymers. 55 In another paper, 56 the character of the dependence of absorbance at 552 nm (eosin concentration of The pH-induced color changes of the films can be easily observed by the naked eye (Table 3).…”