2.1.8.2. Absorbency Under Load (AUL) - BADA

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RESULT AND DISCUSSION
The important part of present study is that through chemical modification of lysyl residues with
EDTAD by introducing a number of carboxyl groups into protein molecules. It should be
mentioned that EDTAD is a bifunctional reagent which is able to acylate of polypeptides either
inter or intramolecularly. Theoretically, one molecule of EDTAD reacts with one lysyl residue
which is shown in Figure 18. In this reaction three carboxyl groups can be incorporated for each
lysyl residue modified, into the protein molecule [15] . This completely improves the net anionic
charge of the protein with various sites for water binding, which causes in unfolding the protein
structure.
Crosslinking of EDTAD-modified protein with cross-linking agents such as glutaraldehyde should
be produced the chemically-crosslinked protein hydrogel with superabsorbent properties.
Moreover, crosslinking is rather performed in aqueous solution in order to develop both intera and
inter molecular bonding for immobilizing the modified protein in the aqueous solutions. The ideal
reaction pathway for the reaction of protein with EDTAD and GLA is shown in Figure 18.
In the present work, after crosslinking with GLA and before drying, the protein superabsorbent
hydrogels were treated with polar organic solvents. Organic solvents are able to remove any
residual GLA and breakdown undesirable bonds between GLA and hydroxyl groups of amino acid
chains, so the hydrophilic hydroxyl groups attend to absorb water molecules. In detail, the effect of
ethanol, isopropanol and acetone for increasing the swelling capacity of protein hydrogel was
investigated.
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