Speciation of chitosan-phosphate and chitosan-nucleotide systems in an NaCl aqueous solution

The speciation of chitosan (310 kDa) with organic (adenosine 5′-monophosphate, AMP, and adenosine 5′-triphosphate, ATP), and inorganic phosphorus containing ligands (phosphate and pyrophosphate) was investigated in NaCl aqueous solutions at I = 0.1 mol L−1 and T = 25°C. For all the systems, the investigated results obtained gave evidence for the formation of (chitosan)LHi complex species (L = nucleotides, phosphate and pyrophosphate; i = 1 to 4, but for AMP, i = 1 to 3). The stability data of complex species were used to calculate the sequestering ability of chitosan towards phosphorus compounds considered here, expressed as pL50 i.e., −log(total chitosan concentration) necessary to bind 50% of ligand. The pL50 values, calculated at different pH values, show quite a good sequestering ability of chitosan towards phosphorus compounds, in particular for the ones having higher negative charge, such as pyrophosphate and ATP.