Naslov
Influence of Response Factors on Determining Equilibrium Association Constants of Noncovalent Complexes by Electrospray Ionization Mass Spectrometry

Autori
Gabelica, Valerie ; Galić, Nives ; Rosu, Frederic ; Houssier, Claude ; De Pauw, Edwin

Izvornik
Journal of Mass Spectrometry (1076-5174) 38 (2003), 1; 491-501

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
Electrospray mass spectrometry; Non-covalent complexes; Binding constants; Oligonucleotides; Cyclodextrins

Sažetak
A method for determining the equilibrium association constant of a complexation reaction A + B AB by electrospray ionization mass spectrometry is described. The method consists in measuring the relative intensities of the peaks corresponding to A and to AB in equimolar A:B solutions at different concentrations C0. The results are fitted by a non-linear least squares procedure, with the two variable parameters being the equilibrium association constant Ka, and a factor R, defined by: I(AB)/I(A) = R [AB]/[A]. The factor R is the ratio between the response factors of AB and A, and corrects for the relative electrospray responses of the complex and the free substrate A, mass discrimination of instrumental origin, and/or moderate in-source dissociation. The method is illustrated with the following two systems: complexes between a double-stranded 12-base pair oligonucleotide and minor groove binders, and cyclodextrin complexes with  ,  -dicarboxylic acids. For the oligonucleotide complexes, it is found that the response of the complex is not dramatically different than the response of the freeoligonucleotide duplex, as the double helix conformation is disturbed by the drug only to a minor extent. In the case of cyclodextrin complexes, these complexes were found to have a much higher response than free cyclodextrin. This can be due to the fact that cyclodextrin is neutral in solution, while the complex is charged, but it can also stem from the fact that a significant proportion of the complex is in a non-inclusion geometry. The present method requires the exact determination of the concentrations of the reactants and is applicable to 1:1 complexes.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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