Abstract:
A bioadsorbent chitosan; a derivative of chitin polysaccharide composed of randomly distributed
β-(1-4)-linked D-glucosamine and N-acetyl-D-glucosamine (Cahyaningrum et al., 2004) was
reported by our group to be much effective as a drinking water purification agent as the percent
removal of Cd(II), Pb(II) and Cr(VI) from drinking water by chitosan were 94%, 64% and 70%
respectively under optimized conditions (De Silva et al., 2014). It is widely known that chitosan
can make complexes with certain metal ions as chitosan has different possible binding sites for
metals (figure 1). But little attempt has been made to understand the interaction mechanism of
chitosan and heavy metals. Hence the aim of this study was to simulate the IR spectrum of chitosan
by DFT calculations and to identify the vibrational bands associated with the possible metal
binding sites which can be used as a tool to investigate the interaction mechanism of chitosan and
heavy metals.
Methodology
All theoretical calculations reported in this study were carried out by use of the Gaussian 09
program package. Although chitosan is a polymer, a trimer shown in figure 01 was used to
represent chitosan in all theoretical studies. First the structural parameters of the optimized
structure of the chitosan have been obtained using electron density functional theory (DFT) with
the Becke–Lee–Yang–Parr functional (B3LYP) and 6-31G (d) basis set employing in a gas phase
model. Then the IR spectrum of the chitosan was simulated by using the computed frequencies of
the optimized geometrical configuration of the trimer in gas phase. The experimental FTIR
spectrum for chitosan was obtained from a Bruker Alpha-T spectrometer.
