Thermogravimetric Study of Biomass Pyrolysis Kinetics. A Distributed Activation Energy Model with Prediction Tests

The pyrolysis of four biomasses (corn stalk, rice husk, sorghum straw, and wheat straw) was studied at different temperature-time functions in an inert gas flow by thermogravimetric analysis (TGA). Linear and stepwise heating programs were employed. A distributed activation energy model (DAEM) with three pools of reactants (three pseudocomponents) was used because of the complexity of the biomass samples of agricultural origin. Compensation effects were observed between the kinetic parameters as in the works of other investigators. The compensation effects result in ambiguous parameter values; hence, they were eliminated with a decrease in the number of unknown parameters. For this purpose, some of the kinetic parameters were assumed to be the same for the four biomasses. This approach also helps to express the similarities of the samples in the model. The 16 experiments were evaluated simultaneously by the method of least squares, yielding dependable kinetic parameters. The resulting models describe well the experimental data and are suitable for predicting experiments at higher heating rates. The checks on the prediction capabilities were considered to be an essential part of the model verification

Influence of acid-induced conformational variability on protein separation in reversed phase high performance liquid chromatography

Influence of acid concentration in the mobile phase on protein separation was studied in a wide concentration range of using trifluoroacetic acid (TFA) and formic acid (FA). At low, 0.001-0.01 v/v% TFA concentration and appropriate solvent strength proteins elute before the column's dead time. This is explained by the proteins having a structured, but relatively extended conformation in the eluent; and are excluded from the pores of the stationary phase. Above ca. 0.01-0.05 v/v% TFA concentration proteins undergo further conformational change, leading to a compact, molten globule-like structure, likely stabilized by ion pairing. Proteins in this conformation enter the pores and are retained on the column. The results suggest a pore exclusion induced separation related to protein conformation. This effect is influenced by the pH and type of acid used, and is likely to involve ion-pair formation. The TFA concentration needed to result in protein folding (and therefore to observe retention on the column) depends on the protein; and therefore can be utilized to improve chromatographic performance. Conformation change was monitored by circular dichroism spectroscopy and mass spectrometry; and it was shown that not only TFA, but FA can also induce molten globule formation

HPLC enrichment/isolation of proteins for post-translational modification studies from complex mixtures

The paper describes a macroporous RP-HPLC method for separation and isolation/enrichment of proteins from complex mixtures. The method is robust and efficient; using 2.1 or 4.6 mm diameter columns provides sufficient material for subsequent proteomic analysis. The main advantage of the method is that most protein variants are isolated in the same fraction, as separation is not based on differences in isoelectric point. This is highly advantageous for studying complex mixtures and post-translational modifications. Examples related to glycosylation analysis are discussed in detail