Oxidation and N‐Alkylation at the C‐6 Position of Galactomannan Extracted from Caesalpinia ferrea var. ferrea Seeds

Abstract

Summary: Carboxyl (GMOX) and carboxyl-aminoalkylated derivatives (GMOXD) of galactomannan (GM), extracted from the seeds of Caesalpinia ferrea (Pau-ferro; Brazilian Ironwood), were synthesised by selective modification of the polysaccharide at the C-6 position in the presence of TEMPO reagent (2,2,6,6-tetramethylpiperidine-1-oxyl) and dodecylamine, with high yields (77 and 94% for GMOX and GMOXD, respectively). The chemical modifications were confirmed by Fourier-transform infrared (FTIR) and nuclear magnetic resonance ( 13 C-NMR) spectroscopy. Analysis by gel permeation chromatography (GPC) coupled to refractive index (RI), lightscattering (LS) and viscometer detectors revealed a decrease in molar-mass values and the intrinsic viscosity and an increase in polydispersity. Modification of galactomannan with a primary amine led to an interesting anionic water-soluble polymeric surfactant, as determined by interfacial tension values at 24 o C. The critical aggregation and micellar concentration values of amphiphilic GMOXD were determined to be 0.48 and 0.89% (w/v), respectively. The development of polyelectrolyte and amphiphilic derivatives of GM and their physicochemical characterisation can contribute to numerous product applications such as nano-structured films, cosmetics and pharmaceuticals.

Enzymatic and chemical oxidation of polygalactomannans from the seeds of a few species of leguminous plants and characterization of the oxidized products

“…This unexpected and not previously described phenomenon poses a technical difficulty in the accurate measurement of its extent with a Brookfield viscosimeter, so that the values reported in Table 3b after 10 min are to be taken as a good approximation of the actual viscosity reached in the first stage of chemical oxidation. Thereafter and in all cases, viscosity steadily decreased to values lower than at the beginning of the reaction and after 6 h all mixtures were solutions with a viscosity <200 mPa s. Furthermore, in all chemically oxidized PGM, a white insoluble, fluffy precipitate appeared, likely due to oxidative depolymerization/debranching caused by the TEMPO/NaBr system and aggregates formation, as described by others (Shibata and Isogai, 2003;De Souza et al, 2011). At 3 h, the concentration of reducing ends increased by about 3-fold with fenugreek, 4-fold with guar and locust bean, 2.6-fold with sesbania, and 5-fold with tara.…”

“…The reaction time course was further characterized and the end products of enzymatic oxidation were compared to the "classic" NaClO/NaBr/TEMPO chemical oxidation of polysaccharides described by several Authors (De Nooy et al, 1995;Sierakowski et al, 2000;Kato et al, 2003;Matsushiro et al, 2006;De Souza et al, 2011). In either cases a partial TEMPO-induced oxidative depolymerization and/or debranching of the polysaccharides was considered likely to occur, as also reported by others (Kato et al, 2003;Shibata and Isogai, 2003;De Souza et al, 2011).…”