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Isothermal microcalorimetry to investigate non specific interactions in biophysical chemistry.

Ball V, Maechling C - Int J Mol Sci (2009)

Bottom Line: We will emphasize that in most cases these "non specific" interactions, as their definition will indicate, are favoured or even driven by an increase in the entropy of the system.The origin of this entropy increase will be discussed for some particular systems.We will also show that in many cases entropy-enthalpy compensation phenomena occur.

View Article: PubMed Central - PubMed

Affiliation: Institut National de la Santé et de la Recherche Médicale, Strasbourg, France. vincent.ball@medecine.u-strasbg.fr <vincent.ball@medecine.u-strasbg.fr>

ABSTRACT
Isothermal titration microcalorimetry (ITC) is mostly used to investigate the thermodynamics of "specific" host-guest interactions in biology as well as in supramolecular chemistry. The aim of this review is to demonstrate that ITC can also provide useful information about non-specific interactions, like electrostatic or hydrophobic interactions. More attention will be given in the use of ITC to investigate polyelectrolyte-polyelectrolyte (in particular DNA-polycation), polyelectrolyte-protein as well as protein-lipid interactions. We will emphasize that in most cases these "non specific" interactions, as their definition will indicate, are favoured or even driven by an increase in the entropy of the system. The origin of this entropy increase will be discussed for some particular systems. We will also show that in many cases entropy-enthalpy compensation phenomena occur.

Show MeSH
Variation of the binding enthalpy between BSA and PAH as a function of the ionic strength, as obtained from ITC [113].
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f6-ijms-10-03283: Variation of the binding enthalpy between BSA and PAH as a function of the ionic strength, as obtained from ITC [113].

Mentions: These experimental data are in reasonable agreement with those obtained from a van’t Hoff analysis but not identical [111]. At low ionic strength, the interaction enthalpy is exothermic and decreases in absolute value when the ionic strength increases. The same trend has been observed for the interactions between bovine serum albumin (BSA) and poly(allylamine) (PAH) in conditions where the protein and the polycation are oppositely charged (10 mM Tris buffer, x M NaCl at pH 7.4) [113], Figure 6. In this case, the interaction enthalpy was endothermic, which clearly shows that the BSA-PAH complexation process is driven by an increase in entropy. Unfortunately, a whole titration curve could not be obtained by means of ITC because of phase separation phenomena occurring upon an increase in the BSA/PAH ratio. This seems to be a recurrent difficulty in the investigation of polyelectrolyte–polyelectrolyte complexation, even if some data are available [114–116]. It appears that the inter-polyelectrolyte complexation process is driven through an increase in entropy, as was already suggested very early in the literature [117]. In addition, the ITC binding curves have been interpreted with a very simple and unrealistic binding model: a one to one stoichiometry between anionic and cationic sites. This model totally neglects cooperative binding effects as well as a possible mismatch between the cationic and anionic sites. From this point of view it seems urgent to perform ITC titrations as well as measurement of the binding constant by an independent method (for instance fluorescence quenching) in the case of monodisperse polyelectrolytes of variable charge density. Charged homopolypeptides (cationic: (Lys)n, anionic (Glu)n or (Asp)n) as well as aliphatic n,n-ionenes [93] seem to be very promising candidates to achieve this aim.


Isothermal microcalorimetry to investigate non specific interactions in biophysical chemistry.

Ball V, Maechling C - Int J Mol Sci (2009)

Variation of the binding enthalpy between BSA and PAH as a function of the ionic strength, as obtained from ITC [113].
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2812836&req=5

f6-ijms-10-03283: Variation of the binding enthalpy between BSA and PAH as a function of the ionic strength, as obtained from ITC [113].
Mentions: These experimental data are in reasonable agreement with those obtained from a van’t Hoff analysis but not identical [111]. At low ionic strength, the interaction enthalpy is exothermic and decreases in absolute value when the ionic strength increases. The same trend has been observed for the interactions between bovine serum albumin (BSA) and poly(allylamine) (PAH) in conditions where the protein and the polycation are oppositely charged (10 mM Tris buffer, x M NaCl at pH 7.4) [113], Figure 6. In this case, the interaction enthalpy was endothermic, which clearly shows that the BSA-PAH complexation process is driven by an increase in entropy. Unfortunately, a whole titration curve could not be obtained by means of ITC because of phase separation phenomena occurring upon an increase in the BSA/PAH ratio. This seems to be a recurrent difficulty in the investigation of polyelectrolyte–polyelectrolyte complexation, even if some data are available [114–116]. It appears that the inter-polyelectrolyte complexation process is driven through an increase in entropy, as was already suggested very early in the literature [117]. In addition, the ITC binding curves have been interpreted with a very simple and unrealistic binding model: a one to one stoichiometry between anionic and cationic sites. This model totally neglects cooperative binding effects as well as a possible mismatch between the cationic and anionic sites. From this point of view it seems urgent to perform ITC titrations as well as measurement of the binding constant by an independent method (for instance fluorescence quenching) in the case of monodisperse polyelectrolytes of variable charge density. Charged homopolypeptides (cationic: (Lys)n, anionic (Glu)n or (Asp)n) as well as aliphatic n,n-ionenes [93] seem to be very promising candidates to achieve this aim.

Bottom Line: We will emphasize that in most cases these "non specific" interactions, as their definition will indicate, are favoured or even driven by an increase in the entropy of the system.The origin of this entropy increase will be discussed for some particular systems.We will also show that in many cases entropy-enthalpy compensation phenomena occur.

View Article: PubMed Central - PubMed

Affiliation: Institut National de la Santé et de la Recherche Médicale, Strasbourg, France. vincent.ball@medecine.u-strasbg.fr <vincent.ball@medecine.u-strasbg.fr>

ABSTRACT
Isothermal titration microcalorimetry (ITC) is mostly used to investigate the thermodynamics of "specific" host-guest interactions in biology as well as in supramolecular chemistry. The aim of this review is to demonstrate that ITC can also provide useful information about non-specific interactions, like electrostatic or hydrophobic interactions. More attention will be given in the use of ITC to investigate polyelectrolyte-polyelectrolyte (in particular DNA-polycation), polyelectrolyte-protein as well as protein-lipid interactions. We will emphasize that in most cases these "non specific" interactions, as their definition will indicate, are favoured or even driven by an increase in the entropy of the system. The origin of this entropy increase will be discussed for some particular systems. We will also show that in many cases entropy-enthalpy compensation phenomena occur.

Show MeSH