Investigation of the Composition and Formation Constant of Molecular Complexes

Abstract

It has been the purpose of the present paper to investigate and explore the There has been an upsurge of research interest in molecular complexes of the donor-acceptor type during the last two decades (1). Despite the large number of papers dealing with molecular complexes, only a small percentage of these studies use nuclear magnetic resonance (NMR) spectroscopy as a means of determining complex formation equilibria, their compositions, and thermodynamic data. More recent papers include the work of Kuntz (2, 3), Foster (4, 5), Hanna (6, 7), and their coworkers. In particular, Hanna and Ashbaugh (6), observing the basic assumption of Huggins and Pimentel (8) for the correlation of the NMR measurements to the equilibrium, noted that equilibrium constants in hydrogen-bonding systems can successfully be determined by NMR spectroscopy (9), and that complex formation equilibria between donors and acceptors are similar to those found in hydrogenbonding systems. According to Hanna and Foster, if the concentration of acceptor is kept considerably lower than that of the donor, then the plot of the ratio of the observed chemical shift relative to however, be investigated in a later paper. Since in most NMR measurements, we keep CAO constant and vary CDO, it is convenient to define a set of dimensionless quantities as follows: K1* = K1 CAO; CDO* = CD0/CA0; CAD* = CAD/CA0M In terms of these dimensionless quantities, Eq. 3 becomes,

Water‐soluble calix[4]resorcinarenes as chiral NMR solvating agents for bicyclic aromatic compounds

“…Stoichiometries of complexes were determined using Job's method. [57][58][59] The concentration of calixresorcinarene and substrate were continuously varied throughout the series while maintaining a total concentration of calixresorcinarene and substrate of 40 mM for each sample. Association constants were determined using the Scatchard method (Foster-Fyfe) of infinite dilutions of host while maintaining the concentration of substrate at 2 mM.…”

Carboxymethylated cyclodextrins and their complexes with Pr(III) and Yb(III) as water‐soluble chiral NMR solvating agents for cationic compounds

“…[36][37][38] The concentration of the cyclodextrin and substrate were continuously varied throughout the series, while maintaining a total concentration of 20 mM.…”

Polycations. IX. Polyammonium derivatives of cyclodextrins: syntheses and binding to organic oxyanions

“…First, the association constants noted for the phosphorus oxyanion species, while greater than unity, are generally less than 10 3 (4.8-460, with only one observed to be greater than 10 3 : 1,200). Significantly stronger interactions are observed with the amino acid series (8)(9)(10)(11)(12)(13)(14) for which the general range is 10 3 -10 4 , with one instance (4biv interacting with 9) more than 10 5 . The cyclodextrin derivative most effective at serving as host for all of the amino acid series guests is 4biv, that bearing the 8-hydroxyoctyl substituent on each of the DABCO rings.…”

“…The variation of this change in chemical shift with changing of the relative concentrations of host and guest species can be used to determine association constants [10][11][12], but is not amenable to the direct determination of the stoichiometry of the association using continuous variation of mole concentration methods [13][14]. In the present instance, a 1:1 association of host with guest is deduced by the fit of the data with the Benesi-Hildebrand equation for such an association [9][10] and by calculations of host cavity and guest sizes using Chem 3D‫.ם‬ For measurement of the association constants, to measured neutral solutions (D 2 O, pD ‫ס‬ 7) of the polycationic cyclodextrin hosts were added varying amounts of measured solutions of the three series of biologically derived oxyanion guests, volumes being adjusted for standardization.…”