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SDS-PAGE under non-reducing conditions is one of the most commonly used techniques for recombinant monoclonal antibody purity and stability indicating assay. On non-reducing SDS-PAGE, bands with a lower molecular weight than the intact antibody are routinely observed and is a common feature of IgG molecules. These fragments were analyzed by in-gel digestion followed by matrix-assisted-laser-desorption-ionization time-of-flight (MALDI-TOF) mass spectrometry, Western blot and by comparing the banding pattern of sample prepared in the presence of a reducing reagent. The fragments bands were identified as antibody lacking one light chain, two heavy chains, one light chain and one heavy chain, free heavy chain and free light chain. Sensitivity of fragmentation to sample buffer pH, incubation time, reducing reagent and alkylation reagents indicated that fragments were formed during sample preparation, but not present in the samples analyzed. Disulfide bond scrambling and β-elimination are the two major mechanisms of the formation antibody fragments. Mass spectrometry analysis suggested that disulfide bond scrambling can be prevented by specifically modifying free sulhydryl using alkylation and thus reduced the amount of artifacts on non-reducing SDS-PAGE. Breakage of disulfide bonds by β-elimination was evidenced by the detection of dehydroalanine using mass spectrometry. [ABSTRACT FROM AUTHOR]

The synergistic effect of the mixture of hexadecyl trimethyl ammonium bromide (HTAB) and various concentrations of NaBr on the corrosion of cold rolled steel in 0.5 M sulfuric acid has been investigated using weight loss method and polarization method. The results reveal that the corrosion of cold rolled steel has been efficiently inhibited by HTAB in the presence of NaBr in sulfuric acid, and inhibition efficiency increases with increasing concentration of NaBr at the same temperature. A synergistic effect has been observed for HTAB with NaBr at every experimental temperature. The polarization curves show that the complex of HTAB and NaBr is a mixed-type inhibitor. The experimental results suggest that the presence of bromide ion in the solution stabilizes the adsorption of HTAB molecules on the metal surface and improves the inhibition efficiency of HTAB. Langmuir adsorption isotherm equation was obeyed at all the temperatures studied. The synergism parameters have been calculated and discussed. The results obtained from weight loss method and polarization method are in good agreement. [ABSTRACT FROM AUTHOR]

The inhibition of NaBr on the corrosion of cold rolled steel in 1.0 M phosphoric acid was studied by using weight loss method and polarization method. It was found that the adsorption of bromide ion can prevent steel from corrosion and the adsorption follows the Langmuir adsorption isotherm. Polarization studies showed that NaBr is a mixed-type inhibitor for steel corrosion in 1.0 M phosphoric acid. Thermodynamic parameters such as adsorption heat, adsorption entropy and adsorption free energy were obtained from the experimental data of temperature studies for the inhibition process at four temperatures ranging from 30 to 45°C. The kinetic data such as apparent activation energies and pre-exponential factors at different concentrations of the inhibitor were calculated, and the effects of the apparent activation energy and pre-exponential factor on the corrosion rate of cold rolled steel were discussed. The inhibitive action was satisfactorily explained by using thermodynamic and kinetic models. The results obtained from polarization experiment were in good agreement with those obtained from weight loss measurement. [ABSTRACT FROM AUTHOR]