Determination of thiol content
The degree of thiolation was determined using Ellman’s
reagent reaction, as described elsewhere (Marschutz Michaela
& Bernkop-Schnurch, 2002). The 5,50-dithiobis(2-nitrobenzoic
acid) (DTNB) molecule reacts with the thiol chemical group to
release a 2-nitro-5-thiobenzoate (TNB) ion, which further
ionizes to TNB2. The latter ion has a yellow color that can be
detected by visible light at 412 nm.
In brief, 5 mg of modified polymer were hydrated in 1.75 ml
of DDW. Then, 500 ml of 0.5 M phosphate buffer pH 8.0 and 500 ml
0.03% (w/w) Ellman’s reagent dissolved in the same buffer was
added to the sample and the resulting solution was incubated
for 2 h. Finally, the absorbance at 412 nm was measured. The
concentration of the thiol groups was determined using a
standard calibration curve obtained by measuring a series of
solutions containing increasing amounts of L-cysteine.