Abstract
The Host-Guest complexation of octakis-(diphenoxyphosphoryloxy)tetramethylcalix[4]resorcinarene (CR) and 5,17-bis-(N-tolyliminomethyl)-25,27-dipropoxycalix[4]arene (CA) with 6 diterpenoid (resin) acids has been studied by the reversed phase high-performance liquid chromatography (RP HPLC). The chromatographic characteristics (retention time tR and retention factor k’) of resin acids have been determined. The lipophilicity values log P of the acids, binding constants KA (395-682 M-1 for CR and 844-1268 M-1 for CA), as well as Gibbs free energies ∆G (-14.79 – -16.14 kJ/mol for CR and -16.70 – -17.67 kJ/mol for CA) of the complexes with resin acids have been calculated. Molecular modelling of CA complexes has revealed the presence of hydrogen bonds between carboxylic groups of acids and nitrogen atoms of imino groups at the upper rim or oxygen atoms of the hydroxyl groups at the lower rim of the CA macrocycle. Molecular modelling of CR complexes has shown the presence of hydrogen bonds between carboxylic groups of acids and oxygen atoms of diphenoxyphosphoryloxy groups at the upper rim of the CR macrocycle. The effect of log P values on KA values of the CR/CA complexes has been assessed. The linear dependence of the binding constants on the acid lipophilicity indicates a significant role of solvophobic interactions on the complexation. The relationship between supramolecular (KA) and physicochemical (log P, pKa) characteristics of acids has been determined.
Highlights
Results and DiscussionThe CR/CA were registered on the chromatograms by sharp peaks with retention factors k’ 8.65 (CR) and 0.89 (CA)
The Host-Guest complexation of octakis-(diphenoxyphosphoryloxy)tetramethylcalix[4]resorcinarene (CR) and 5,17-bis-(N-tolyliminomethyl)-25,27-dipropoxycalix[4]arene (CA) with 6 diterpenoid acids has been studied by the reversed phase high-performance liquid chromatography (RP HPLC)
Chromatograms of the resin acids obtained before and after CR and CA addition in the mobile phase are presented in Fig. 2, 3
Summary
The CR/CA were registered on the chromatograms by sharp peaks with retention factors k’ 8.65 (CR) and 0.89 (CA). Chromatograms of the resin acids obtained before and after CR and CA addition in the mobile phase are presented, 3. A comparative estimation of the chromatograms presented, 3 shows that CR and CA addition to the mobile phase decreases the retention times and changes the elution order of acids. It should be noted CA addition allows separating abietic 5 and neoabietic 6 acids (Fig. 3). Retention factors k’ of resin acids 1-6 determined before and after CR/CA addition. The values of КА (М-1) and ΔG (kJ/mоl) of the calixarene complexes with resin acids 1-6
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