engleski

Solvation effect on the complexation of alkali-metal cations with calix[4]arene ketone derivate

The solvation effect on the complexation of alkali-metal cations with calix[4]arene ketone derivative (L) was systematically explored. The complexation reactions were studied by means of UV-Vis spectrophotometric and microcalorimetric titrations in ethanol (EtOH), methanol (MeOH), N-methylformamide (NMF), N, N-dimethylformamide (DMF) and dimethy sulfoxide (DMSO). The stability constants of the corresponding complexes were determined, as were the enthalpies and entropies of the complexation reactions. On the basis of ligand solubilities and the literature data regarding cation solvation, the Gibbs energies for transfer of reactants and product among solvents were obtained. The investigated calix[4]arene L binds Na+ cation rather efficiently in all examined solvents, whereas the complexation of K+ cation was observed only in methanol. The complexation of other alkali-metal cations was either not observed or the stability constants of the complexes were to low to be reliably determined. The sodium binding affinity of L in the investigated solvents reduces as follows: EtOH  MeOH  NMF  DMF  DMSO. The notable influence of the solvent on the NaL+ complex stability can be mainly attributed to differences in the entropic contributions to standard reaction Gibbs energies. The higher stability of NaL+ in comparison to KL+ in methanol is predominantly the consequence of more favourable rH°. All studied complexation reactions are enthalpically controlled. On the contrary, the ligand dissolution was found to be endothermic in all cases. The solubilities of L in studied solvents were rather similar, except in N, N-dimethylformamide, in which the most favourable solvation of the macrocycle was noticed. As a consequence, the differences in complex stabilities in the investigated solvents can be explained by taking into account solely the cation and the complex solvation.

solvation ; complexation ; thermodynamics ; calixarenes

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