Metachromatic behaviour of dyes in solution. Interpretation on the basis of interaction between dye ions and counter-ions

Abstract

Metachromatic behaviour has been induced in the visible spectra of solutions of ionic dyes by increasing the dye concentration, adding salts, and by lowering the dielectric constant of the solvent from medium to low values. The spectral changes are of the same general type, irrespective of the method used, and are exhibited only by those dyes in which the characteristic charge is an integral part of the chromophoric system. The H-bands which appear are attributed primarily to interaction between the dye ions and counter-ions, although in aqueous solution aggregation is important too, probably because counter-ions are included in the aggregates. A new band (L-band), at even shorter wavelengths than the H-band, was observed in solvents of very low dielectric constant and from which the dye soon precipitated. This L-band is attributed to strong interaction between dye ions and counter-ions to produce an undissociated species in which the ions are not separated by solvent molecules. Non-isosbestic spectral changes which occur in water at high dye concentrations are attributed to the presence of a small proportion of this species. The present hypothesis permits a simple explanation of metachromatic behaviour in accordance with the principles of colour and constitution.

Solvatochromic and Single Crystal Studies of Two Neutral Triarylmethane Dyes with a Quinone Methide Structure

“…However, the possibility of an equilibrium between two ground states has also been suggested [16,17,18,19]. On the other hand, it has been also argued that counter anions interacting with the dimethylamino groups of CV could be responsible for the changes in the UV-VIS spectra [20]. In our case, as 1 and 2 are neutral compounds no effect of counter anion can be observed and thus the presence of two bands in the UV-visible spectrum of 1 has to be related to the existence of an equilibrium between two ground states or the split of the excited state into two neighboring electronic levels.…”

The promiscuous protein binding ability of erythrosine B studied by metachromasy (metachromasia)

“…Because ErB is a member of the eosin series and is among the relatively few anionic dyes that exhibit color change (metachromasy) upon complex formation (McKay and Hillson, ; Prentø, ), we explored this property to study the affinity and stoichiometry of its protein binding using spectrophotometric methods with BSA and CD40L as representative targets. Increasing concentrations of added protein did indeed produce a progressive bathochromic (red) shift in the absorption spectra of ErB (Figures and ), and quantification of the corresponding data suggested binding affinities of 15–20 μM for both proteins, in excellent agreement with our previous observation that ErB acts as a promiscuous PPI inhibitor with a remarkably consistent IC 50 in exactly this range (Ganesan et al ., ).…”

The role of inorganic electrolyte (salt) in cellulosic fibre dyeing: Part 2 theories of how inorganic electrolyte promotes dye uptake

“…22 The extent of aggregation observed for various classes/ types of dye is known to depend on several factors, being influenced by various physical and chemical attributes of the surrounding environment, insofar as, aggregation increases with decreasing temperature, reduced liquor ratio (which is equivalent to increased dye concentration) and, of relevance to this paper, the presence of inorganic electrolyte. In the latter context, inorganic electrolyte has been observed to promote both the rate and extent of aggregation of various classes of dye in solution, [181][182][183][184][185][186][187] although as might be anticipated, different classes/types of dye (e.g. non-metallised acid dyes, pre-metallised acid dyes, basic dyes, direct dyes, etc.)…”