scholarly journals Free energy changes in ribonuclease A denaturation. Effect of urea, guanidine hydrochloride, and lithium salts.

1983 ◽  
Vol 258 (18) ◽  
pp. 11143-11146 ◽  
Author(s):  
F Ahmad
Keyword(s):  
Free Energy ◽  
Guanidine Hydrochloride ◽  
Ribonuclease A ◽  
Lithium Salts

Denaturation of proteins. IV. N.M.R. studies of ribonuclease-A

1972 ◽  
Vol 25 (1) ◽  
pp. 209 ◽  
Author(s):  
JH Bradbury ◽  
NLR King
Keyword(s):  
Formic Acid ◽  
Deuterium Oxide ◽  
Guanidine Hydrochloride ◽  
Difference Spectrum ◽  
Potassium Thiocyanate ◽  
Ribonuclease A ◽  
Relative Increase ◽  
Intermediate Form ◽  
State Process ◽  
Major Transition

The denaturation of ribonuclease-A by the addition of urea, guanidine hydrochloride, formic acid, and potassium thiocyanate to solutions in water or D2O at 33� has been followed by nuclear magnetic resonance (N.M.R.) spectroscopy. ��The complex N.M.R. spectra at low field can be simplified greatly by a difference spectrum obtained by subtracting the spectrum obtained in deuterium oxide from the corresponding spectrum in water, whence the resonances of protons attached to nitrogen are isolated. Binding of urea and guanidine hydrochloride at concentrations well below that needed for unfolding is shown by modification of the C2 histidine resonances due to the histidines located at positions 12 and 119. This confirms that these denaturants inactivate the enzyme by binding at its active site as proposed by Barnard.The unfolding of ribonuclease by urea and guanidine hydrochloride at acid pH is shown to be a two-state process in which the fraction of unfolded molecules (cross-linked random coils) is calculated directly from the relative increase in heights of the various n.m.r, resonances. The unfolding in [D2]formic acid is characterized by the first (major) transition with a midpoint at 8% [D2] formic acid (v/v) and a second (minor) transition centred at 58% [D2]formic acid. In pure formic acid there is evidence of aggregate formation. An intermediate form characterized by a double methionine SCH3 resonance occurs during the first transition. There are therefore a minimum of five different states present during this unfolding. The major unfolding process produced by potassium thiocyanate is followed by a refolding to a non-native ordered form. This unfolding process is incomplete and three different

scholarly journals Thermodynamic Hydricity of Small Borane Clusters and Polyhedral closo-Boranes

Molecules ◽  
2020 ◽  
Vol 25 (12) ◽  
pp. 2920 ◽  
Author(s):  
Igor E. Golub ◽  
Oleg A. Filippov ◽  
Vasilisa A. Kulikova ◽  
Natalia V. Belkova ◽  
Lina M. Epstein ◽  
...  
Keyword(s):  
Free Energy ◽  
Proton Transfer ◽  
Solvent Effect ◽  
Coordination Number ◽  
Gibbs Free Energy ◽  
Boron Atom ◽  
Hydride Transfer ◽  
Dft Method ◽  
Lithium Salts

Thermodynamic hydricity (HDAMeCN) determined as Gibbs free energy (ΔG°[H]−) of the H− detachment reaction in acetonitrile (MeCN) was assessed for 144 small borane clusters (up to 5 boron atoms), polyhedral closo-boranes dianions [BnHn]2−, and their lithium salts Li2[BnHn] (n = 5–17) by DFT method [M06/6-311++G(d,p)] taking into account non-specific solvent effect (SMD model). Thermodynamic hydricity values of diborane B2H6 (HDAMeCN = 82.1 kcal/mol) and its dianion [B2H6]2− (HDAMeCN = 40.9 kcal/mol for Li2[B2H6]) can be selected as border points for the range of borane clusters’ reactivity. Borane clusters with HDAMeCN below 41 kcal/mol are strong hydride donors capable of reducing CO2 (HDAMeCN = 44 kcal/mol for HCO2−), whereas those with HDAMeCN over 82 kcal/mol, predominately neutral boranes, are weak hydride donors and less prone to hydride transfer than to proton transfer (e.g., B2H6, B4H10, B5H11, etc.). The HDAMeCN values of closo-boranes are found to directly depend on the coordination number of the boron atom from which hydride detachment and stabilization of quasi-borinium cation takes place. In general, the larger the coordination number (CN) of a boron atom, the lower the value of HDAMeCN.

Thermodynamic characterization of the partially denatured states of ribonuclease A in calcium chloride and lithium chloride

1985 ◽  
Vol 63 (10) ◽  
pp. 1058-1063 ◽  
Author(s):  
Faizan Ahmad
Keyword(s):  
Calcium Chloride ◽  
Lithium Chloride ◽  
Guanidine Hydrochloride ◽  
Thermodynamic Quantity ◽  
Ribonuclease A ◽  
Ultraviolet Region ◽  
Conformational Properties ◽  
Far Ultraviolet ◽  
Denatured States

The denaturations of ribonuclease A by calcium chloride and lithium chloride were studied by circular dichroism measurements in the far-ultraviolet region. The temperature dependence of the equilibrium constant for the unfolding of the protein by calcium chloride and lithium chloride gave values of 46 and 52 kcal mol−1 (1 cal = 4.1868 J) for the enthalpy of denaturation at 25 °C and pH 7.0, respectively. Thermodynamic parameters for the denaturation by calcium chloride and lithium chloride are compared with those for the heat and guanidine hydrochloride denaturation. It has been observed that the thermodynamic quantity, be it free energy, entropy, or enthalpy, cannot be related quantitatively to the extent of unfolding measured by various conformational properties of the protein.

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