Fe (III) - Galactomannan Solid and Aqueous Complexes: Potentiometric, EPR Spectroscopy and Thermal Data

Abstract

Galactomananas podem ser empregadas como aditivos na indústria alimentícea para modificar a viscosidade do produto final. Como não são absorvidas pelo organismo humano, sua adição a alimentos dietéticos é muito promissora. Os equilíbrios entre Fe(III) e galactomananas e arabinogalactana de várias leguminosas foram caracterizadas por titulações potenciométricas e espectroscopia de EPR. Os logaritmos das constantes de equilíbrio para a formação dos complexos ML (M = Fe(III) e L = unidade monomérica dos biopolímeros) foram iguais a 15,4, 14,1 e 18,5 para as galactomananas de C. fastuosa, L. leucocephala e S. macranthera, respectivamente. Os valores de log K para a formação das espécies protonadas (MHL) foram 3,1, 3,3 para as galactomananas de C. fastuosa, L. leucocephala e não foi detectado no caso da galactomanana de S. macranthera. Os valores de log de K para a formação de ML 2 foram 14,1, 13,3 e 15,2, respectivamente. Não foi possível obter dados relativos ao equilíbrio entre arabinogalactana e Fe(III) devido à formação de produtos insolúveis logo no início das titulações. Os ensaios no estado sólido mostraram não somente uma grande interação dipolar entre dois íons Fe(III) na estrutura polimérica complexada, tanto maior quanto menos substituída é a galactomanana, mas também a estabilidade térmica resultante desta complexação. Os produtos complexados podem conferir uma abrangência maior na utilização em produtos dietéticos, pois a presença de um metal essencial no complexo, quando de sua descomplexação nos vários processos fisiológicos dos organismos, faculta a absorção desse íon metálico.Galactomannans can be employed in food industries to modify the final rheological properties of the products. Since they are not absorbed by the living organisms they can also be used in dietary foods. The equilibria involving the interactions of Fe(III) and galactomannans and arabinogalactan of several leguminous plants were characterized by potentiometric titrations and EPR spectroscopy. The log of the equilibrium constants for the formation of ML species, where M is the metal ion and L is the monomeric unit of the biopolymers, were 15.4, 14.1 and 18.5, for the galactomannans of C. fastuosa, L. leucocephala and S. macranthera, respectively. Log K values for protonated species (MHL) were 3.1, 3.3, and were not detected for the galactomannan of S. macranthera. The log K values for the formation of ML 2 were 14.1, 13.3 and 15.2, respectively. Early formation of insoluble products in the equilibrium with arabinogalactan and Fe(III) prevented acquisition of reliable data. The solid complexes assays showed a great dipolar interaction between two Fe(III) ions in the inner structure of the biopolymer which increased as the degree of substitution of the galactomannan decreased, and also showed the resulting thermal stability. The complexes impart a new possibility of providing essential metal ions in dietary foods since decomplexation of the complexes can occur at different pH values existing in the human body.

Chemical equilibrium in the complexation of first transition series divalent cations Cu2+, Mn2+ and Zn2+ with chitosan

“…The potentiometric titrations were carried out in duplicate, according to the methodology developed in the Chemical Equilibrium Laboratory-LEQ-UFPR [24][25][26] for biopolymers, in a Micronal pH meter (Brazil, model B-374) with a glass electrode H 3 O + sensitive (AnalyserBrazil, model SM01), and a saturated calomel reference electrode (Analyser-Brazil, model SR 02). The potentiometric apparatus was calibrated with standard HCl and KOH (Merck, Brazil) solutions in order to read -log [H + ] directly.…”

“…19 Studies in the literature involved absorption of metal ions in chitosan, [20][21][22] but complete equilibrium investigations with determination of binding constants, as well as pH speciation, have only recently been addressed in the literature. [23][24][25][26] Also, the reported studies presented different experimental conditions from this present work.…”

Two galactomannan preparations from seeds from Mimosa scabrella (bracatinga): Complexation with oxovanadium(IV/V) and cytotoxicity on HeLa cells

“…The protonation is due to the HO-6 group, which is the only one acidic enough to release or uptake a proton in the aqueous equilibrium and its value is very close to that for primary alcohols [61][62][63]. A previous study about mannan and galactomannan showed that the protonation constant of C-6-O À can vary from K = 1.17 ± 0.04 Â 10 9 to K = 3.39 ± 0.05 Â 10 9 , respectively [12,18].…”

Characterization of the Complex of Human-like Collagen with Calcium

“…The thermal behavior of the calcium complex was completely different from that of HLC with respect to the loss of mass and the temperature intervals in which it took place, indicating the formation of a new chemical compound with more stable thermodynamic properties [33]. The first dehydration range of the HLC-Ca complex lies between 35°C and 238°C.…”