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Proteins in Solution and at Interfaces
Published in E. D. Goddard, K. P. Ananthapadmanabhan, Interactions of Surfactants with Polymers and Proteins, 2018
Various physical and chemical treatments lead to the denaturation of proteins in solution. Denaturation is the uncoiling or unfolding of the tertiary and secondary structure without rupture of the covalent links of the primary structure. Though it may be accompanied by protein aggregation and loss of solubility, denaturation is generally a reversible process unless accompanied by oxidation of cysteine or disulfide interchange. The Gibbs free energy of stabilization of the native structure relative to the unfolded state is typically much less than 1 kT per amino acid residue, which means that for purely thermodynamic reasons the structure is susceptible to change by altering the temperature or the local solution environment. The folding/unfolding transition is a cooperative process, since the disruption of any significant portion of the folded structure leads to an unfolding of the rest. Most proteins are unfolded by guanidinium chloride in 6-M solution (approaching the solubility limit). The presence of the salt has the effect of greatly reducing the hydrophobic interaction between nonpolar residues by disrupting the ordered hydrogen-bonded structure of water. Proteins may also be denatured by heating, by changes in pH, or by addition of a solvent such as ethanol. Extremes of pH can induce unfolding because the native state has groups buried in the unionized form that can only ionize after unfolding. Most notable in this connection are the residues His and Tyr, whose presence can induce protein unfolding at low and high pH values, respectively.
When size matters: exploring the potential of aminocyclopropenium cations as head groups in triphenylene-derived ionic liquid crystals in comparison with guanidinium and ammonium units
Published in Liquid Crystals, 2018
Juri Litterscheidt, Paul Judge, Andrea Bühlmeyer, Korinna Bader, Jeffrey S. Bandar, Tristan Lambert, Sabine Laschat
The guanidinium chloride 2 displayed only monotropic behaviour in the DSC. Upon 2nd heating, endothermal melting into the isotropic liquid was detected at 45°C, while the cooling cycle showed an exothermal isotropic to mesophase transition at 78°C and a crystallisation at 19°C, respectively (Figure 3, Table 1). Under the POM, focal conic were visible at 82°C upon cooling from the isotropic phase (Figure 4(b)).
Preparation, characterization and use of new lignocellulose-based bio nanocomposite as a heterogeneous catalyst for sustainable synthesis of pyrimido benzazoles
Published in Green Chemistry Letters and Reviews, 2018
Shiva Molaei, Shahrzad Javanshir
To further extended the scope of this new protocol and to explore the effectiveness of the catalyst PS/ZnO, the reaction between various aromatic aldehydes, C–H acidic compounds and 2-aminobenzazole derivatives, or guanidinium chloride in optimized conditions was realized and led to a series of pyrimidobenzazole with high in a short reaction time yields (Table 2).
On the impact of ethanol on the rejection and transfer mechanism during ultrafiltration of a charged macromolecule in water/ethanol
Published in Environmental Technology, 2020
H. Al Jawad, M. Rabiller-Baudry, P. Loulergue, C. Bejjani, A. Lejeune, H. Mawlawi, G. Nasser, S. Taha
The intrinsic viscosity of a fully unfolded protein can be estimated according to the empirical equation proposed by Tanford et al. [42] in the case of protein denaturation obtained by addition of at least 5 M guanidinium chloride