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

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 (¹³C-NMR) spectroscopy. Analysis by gel permeation chromatography (GPC) coupled to refractive index (RI), light-scattering (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 °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.