Biomedical Engineering Reference
In-Depth Information
It has been shown that carboxyl groups present in the cell walls of nonliving biomaterials
contribute to metal-ion binding (Gardea-Torresdey, et al., 1999; 2001; Riddle, et al., 1997;
Kelley, et al., 1999). Our group has used a variety of methods(Lin, et al., 2002; Drake, et al.,
1996; Xia and Rayson, 1995; Drake, et al., 1996; 1997) to characterize the binding groups
present in the cell walls of
Datura innoxia.
This plant is a member of the
Solanaceae
plant
family and native to Mexico and the southwestern United States. To minimize variability of
cell types investigated, the cell-wall fragments used are cultured anther cells of the plant.
This plant was selected for study because it is a heavy metal resistant perennial that is both
tolerant of arid climates and resistant to herbivory (Drake et al., 1996).
Our group has concentrated primarily on nonviable biomaterials, specifically cell wall
fragments from the cultured anther cells of
Datura innoxia.
The present study used frontal
affinity chromatography with inductively coupled plasma optical emission spectroscopy
(ICP-OES) detection for simultaneous monitoring both uptake and release of metal ions to
both a chemically modified and native
D. innoxia
biomaterial (Williams and Rayson, 2003).
The objective of the present study was to further investigate such sites through sequential
exposure and subsequent stripping of three similar metal ions (Cd
2+
, Ni
2+
, and Zn
2+
) to both
a modified and the native biosorbents, thus to study the role of carboxylate furface
functionalities on passive metal ion binding of this material.
It has been demonstrated (Drake, et al., 1996) that carboxylate-containing binding sites can
be removed through the formation of the corresponding methyl esters by reaction with
acidic methanol for 72 hours (Drake, et al., 1996). Undertaking a similar series of
experiments with such a chemically modified sorbent enables the investigation of alternate
binding sites.
2. Materials and methods
2.1 Esterification of biomaterial
The cultured anther cells from
D. innoxia
were washed and prepared as described elsewhere
(Drake, et al,, 1996; 1997). Only cell fragment aggregates with a mesh size greater than 200 (<
127 μm) were used for esterification. Following a method described elsewhere (Drake, et al.,
1996), 10.0 grams of the biomaterial were suspended in 0.1 M HCl in methanol. The slurry
was continuously heated at 60C and stirred for 72 hours. The biomaterial was then
recovered through vacuum filtration, rinsed three times with 16.0-M water
(Barnstead,Millipore Ultrapure), freeze-dried, and set aside for later immobilization.
2.2 Immobilization of biomaterial
In their native state, biomaterials have poor mechanical strength, low density, and a small
particle size that can cause column clogging (Stark and Rayson, 2000). These characteristics
can yield poor candidates for column-based water treatment applications. For this study
native and modified
D. innoxia
biomaterials were each immobilized in a polysilicate matrix.
The 40-60-mesh size fraction of the ground, and sieved immobilized biosorbents was then
packed into columns. The process for immobilization has been described in detail elsewhere
(Stark and Rayson, 2000).
Briefly, a suspension of 20 grams of the 100-200 mesh fraction of the washed biomaterial was
generated with 300 mL of 5% v/v sulfuric acid adjusted to pH 2.0 by addition of a 6% (w/v)
solution of Na
2
SiO
3
5H
2
O. This suspension was stirred for 1 hour and the pH of the solution
