Concentration-Dependent Association of Flavylium Chloride with Differential Hydroxy Moieties in Ethanol

Flavylium ions (6a–6e) were synthesized using Aldol condensation to compare the spectroscopic properties caused by the different numbers and locations of hydroxy groups on the flavylium cations (AH+). Without the addition of acid, increasing the concentration of flavylium ions to 10 mM in ethanol led to the following observation. The flavylium ions with the least number of OH groups (6a and 6b) showed a change in peak at higher concentrations, whereas 6c and 6d did not show the same degree of change in their 1H-NMR signals. This suggests an equilibrium that shifts the isomers B, CE, and Cz more towards the flavylium ion with more OH groups even at low concentrations. One possibility for the cause of this shift is that the flavylium ions become more stable through aggregation. In addition to the NMR results, the UV measurements confirmed that isomers with fewer OH groups showed a more dramatic shift towards the flavylium ion at higher concentrations. Using modeling data at DFT//B3LYP/6311**G(d) level, the self-association was investigated to show that the hydrogen bonding of OH groups is the main player but cannot stabilize entirely without the presence of the chloride ion in the complex.

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

The interaction between single- or double-charged anions of bromocresol purple (BP) and cyanine cations (quinaldine blue, QB, or quinaldine red, QR) at concentrations of dyes 5.0·10−7–4.0·10−5 mol/L has been investigated by vis-spectroscopy. The thermodynamic constants of dissimilar associations (Kas) have been studied. Comparison of the values of lg Kas shows that QB− associates of BP− are more stable (6.61 ± 0.07) than QR associates (4.84 ± 0.06); a similar phenomenon is observed for associates of the BP2− anion. Semi-empirical calculations (PM3 method) are in agreement with the vis-spectroscopy data and indicate that the association of dye into an associate is possible. The standard enthalpies of formation of associates (ΔfHo) and energy diagrams have been determined. The ΔfHo data indicate that the formation of an associate between dye ions is an energetically favourable process. The gain in energy significantly exceeds the systematic error of semi-empirical calculations and increases from 157 kJ/mol (associate ”BP− + QB+”) to 729 kJ/mol (associate “BP2− + QR+”). The most probable structures of dissimilar associates are presented. The study of the dissimilar association develops the concept of intermolecular interactions in solutions.

Publisher’s Note to Launch Colorants—A Scientific Journal of Dyes, Pigments and Color Chemistry

On 11 May 2010, the code ISSN 2079-6447 was obtained for Colorants following an application to the ISSN Center in Paris [...]

Colorants: A New Journal Bringing Colour to Life

Colorant: A substance which is used to impart colour to another material! [...]