Van t Hoff analysis

Binding of heme by isolated N-domain causes a change in sedimentation coefficient consistent with a more compact conformation and leads to the more avid association with the C-domain (125). Sedimentation equilibrium analysis showed that the Kd decreases from 55 pM to 0.8 pM (Fig. 5) (106). In addition, the calorimetric AH (-1-11 kcal/mol) and AS (-1-65 kcal/mol K) for the heme-N-domain-C-domain interaction and the AH (-3.6 kcal/mol) and AS (-1-8.1 kcal/mol K) derived from van t Hoff analysis of ultracentrifuge data for the interaction in the absence of heme indicate that hydrophobic interactions predominate in the presence of heme and a mix (e.g., hydrophobic and van der Waals forces) drives the interaction in the absence of heme. However, FTIR spectra (Fig. 6) indicate that little change in the secondary structure of domains or intact hemopexin occurs upon heme binding (104). 

By carrying out the chromatographic analysis at different temperatures a van t Hoff analysis is possible which demonstrates that enantiodifferentiation is enthalpic in nature with the all-5 enantiomer of the host binding more strongly by ca. 0.5 kcal mol-1 (2 kj mol-1)... 

T. L. Chester and J. W. Coym, Effect of phase ratio on van t Hoff analysis in reversed-phase liquid chromatography, and phase-ratio-independent estimation of transfer enthalpy,/. Chromatogr. A 1003 (2003), 101-111. 

It has been argued that EEC is a mere artifact (120). In an attempt to establish the existence of the EEC effect, a collection of thermodynamic data collected for the binding of 136 drugs to their receptors revealed strong correlation between enthalpy and entropy (116). Some have attributed these results to inaccuracies of the van t Hoff analysis that is used for the measurement of thermodynamic parameters (121). But isothermal titration calorimetry data (ITC) does not suffer from the same inaccuracies that plague the van t Hoff analysis. We have recently created a dataset that contains more than 400 entries containing structural and isothermal titration data (122). A plot of the enthalpy and entropy results in the following linear relationship ... 

Are the irreversible denaturation pathways truly irreversible Thomas and coworkers have demonstrated that the activity of (inactive) oxidized aFGF can be recovered by the addition of the reducing agent dithiothreitol (10). Furthermore, as previously mentioned, various formulation additives have minimized thermally induced aggregation of aFGF. In addition to the physiological implications, these irreversible denaturation pathways also complicate thermodynamic analyses of protein stability, particularly those which rely on van t Hoff analysis of denaturation profiles. 

Papalia GA, Giannetti AM, Arora N, Myszka DG (2008) Thermodynamic characterization of pyrazole and azaindole derivatives binding to p38 mitogen-activated protein kinase using Biacore T100 technology and van t Hoff analysis. Anal Biochem 383 255-264... 

The formation of quadruplex structures, whatever their type, is clearly enthalpy driven, with an enthalpy per quartet of —15 to —25 kcal moD For example, concerning intramolecular quadruplexes, the van t Hoff analysis of the melting process of unmodified DNA samples reveals a AH° of 19.8 and... 

Bi- and tetramolecular structures also give quite comparable enthalpies. However, the validity of the van t Hoff analysis for some of these quadruplexes is questionable, as the melting curve used to determine thermodynamic parameters rarely corresponds to a true equilibrium curve. We will address this point later in the manuscript. An enthalpy of formation of —21 to —26 kcal mol per quartet is found for the G2T2NT2G2 sequence in comparison to —22.5 kcal mol per quartet measured for the G4T4G4 sequence. Concerning parallel quadruplexes, analysis of the calorimetric or thermokinetic data gives a value of —72 kcal moD (ref. 27) and —76.5 kcal moD (ref. 28) for the TG4T sample... 

Infrared spectroscopic studies have shown that adsorbed carbon monoxide interacts with Brensted acid Si(OH)Al groups of the zeolite H-ZSM-5 forming hydrogen-bonded H-CO and H—OC species, which are characterized by C-0 stretching IR absorption bands at 2175 and 2112 cm", respectively. By means of variable-temperature FTIR spectroscopy, these C-bonded and O-bonded adducts were found to be in a temperature dependent equilibrium which can be described as ZH CO = ZH- OC, where Z stands for the zeolite framework. The corresponding enthalpy change was found to be AH° = 4.2 kJ mol", as derived from a van t Hoff analysis of the intensity of the corresponding IR absorption bands as a function of temperature. 

NMR, and 2D NMR (COSY, NOESY). Under kinetic control via formation of Fe complexes, the main cycHc product was the triangular 44. Under thermodynamic control, using more labile transition metal complexes, e.g., Zn , the ratio of cycHc species was found to be concentration and temperature dependent, and under an adequate entropic driving force, the cychc dimer 43 was formed exclusively. This system was probed via variable temperature NMR to reveal a dynamic equihbrium between the entropically favored dimer 43 and enthalpically favored trimer 44 (14DT9604). A van t Hoff analysis was performed to measure the thermodynamics of interconversion between structures (Figure 20). 

The simplest way to derive thermodynamic parameters from UV melting data is to apply a van t Hoff analysis of the data by assuming a two-state model (i.e. native and denatured states) and that the difference in heat capacities of the native and denatured states, ACp°, is zero (13-16) (more complex models are described in Section 5). At each temperature the absorbance can be used to calculate the fraction of strands in the native and denatured states, thereby allowing the calculation of an equilibrium constant (10). Thus, the absorbance versus temperature profile is used to determine the temperature dependence of... 

A van t Hoff analysis of UV melting data caimot be used to reliably measiure... 

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