The biodegradable biopolymer chitosan had its linear structure chemically modified in a two-step reaction, first by exploring the amino reactivity with glycidylmethacrylate, whose intermediate product, containing an aldehyde group, was then reacted with 1,2-ethanedithiol. Chitosan and the synthesized biopolymers were characterized by elemental analyses, infrared spectroscopy, nuclear magnetic resonance of the carbon nucleus in the solid state, X-ray diffractometry, thermogravimetry and scanning electron microscopy, to give a degree of immobilization of 3.00 mmol g(-1). The available basic nitrogen, sulfur and oxygen Lewis centers attached to the enlarged pendant chains enriched the ability of the biopolymer for copper, lead and cadmium sorption from aqueous solution, to give maximum capacities of 2.05 +/- A 0.01; 2.53 +/- A 0.02 and 1.88 +/- A 0.01 mmol g(-1), when compared to chitosan with 1.54 +/- A 0.33; 1.22 +/- A 0.04 and 1.12 +/- A 0.08 mmol g(-1), respectively, using the Langmuir sorption isotherms. Based on the present results, the highest amount of these cation sorptions, especially with lead that is associated with sulfur-cation soft interactions, is dependent directly on not only the presence of long pendant chain attached, but also the availability of favorable Lewis base centers. The experimental data adjusted to the Langmuir, the Freundlich and the Temkin sorption isotherms using linear and non-linear regression methods and are in agreement with the best fit for Langmuir model type I.