Protonation Equilibria of Carminic Acid and Stability Constants of Its Complexes with Some Divalent Metal Ions in Aqueous Solution

Abstract

The dissociation constants of carminic acid (7-D-glucopyronosyl-3,5,6,8-tetrahydroxy-1-methyl-9,10-dioxo-anthracene-2-carboxylic acid) (CA), together with the stability constants of its Cu(II), Zn(II), Ni(II), Co(II) and Hg(II) complexes, were studied potentiometrically in aqueous medium at 25.0 (1)°C, and at the ionic background of 0.1 mol·dm −3 of NaCl, and determined with the SUPERQUAD computer program. It has been observed that carminic acid has five dissociation constants, and for H 5 L their values are 3.39 (7), 5.78 (7), 8.35 (7), 10.27 (7), and 11.51 (7). This ligand behaves as a bi-dentate ligand, and the carboxyl and the ortho hydroxy groups of the ligand coordinate to the metal ions. Various metal complexes were produced in solution under the experimental conditions, for each metal ion used, including hydrolyzed species. The species distribution curves of the complexes formed in the solution were calculated and reviewed. The stability of the complexes was found to follow the order: Cu(II) > Zn(II) > Ni(II) > Co(II) > Hg(II).

Characterization of Dye Extracts from Historical Cultural-Heritage Objects Using State-of-the-Art Comprehensive Two-Dimensional Liquid Chromatography and Mass Spectrometry with Active Modulation and Optimized Shifting Gradients

“…Compounds that are highly and variably charged at the 1 D mobile-phase pH of 7.5 elute as very broad peaks from the mixed-mode ion-exchange separation. A case in point is carminic acid (analyte #2), with p K a values of 3.39, 5.78, 8.35, 10.27, and 11.51, 19 and a resulting charge close to −3 at the 1 D conditions. In the vicinity of a p K a value, different analyte ions will be differently charged.…”

Study of the leaching potential in a soil and its depuration capacity: perspectives in a landfill selection

“…Additionally, the surface area and the high molecular weight may be related to adsorption due to the thin pore size in soil. Likewise, the molecular structure shows a bi-dentate ligand (carboxyl and the orthohydroxy groups) which may ligand and coordinate metal ions [18]. This may be the explanation why the conductivity was reduced, because hypothetically the absorbed carminic acid may interact with ions which pass through the soil column [18].…”

“…Likewise, the molecular structure shows a bi-dentate ligand (carboxyl and the orthohydroxy groups) which may ligand and coordinate metal ions [18]. This may be the explanation why the conductivity was reduced, because hypothetically the absorbed carminic acid may interact with ions which pass through the soil column [18]. Even more, in pH experiment (see Figure 6), this parameter was the most relevant condition for transport of pollutants, which is the reason why although, the percentage of water infiltrated (PWI) was higher than 15% in all layers the carminic acid was not detected in leaching water even in L2 which presented the highest PWI (Table 2).…”

Change is permanent: thoughts on the fading of cochineal-based watercolor pigments

“…This is possible, but there is less advantage from electron delocalization in this configuration. For carminic acid, formation of M(CA) complexes, where M = Cu(II), Zn(II), Co(II), or Hg(II), has a large log 10 β and occurs over a wide pH range [38]. A tin complex of CA recrystallized from organic solvents was found to have seven-coordinate tin [39].…”