Inclusion Complexation of Carbethopendecinium Bromide with Some α- and β-Cyclodextrins Studied by Potentiometry with Membrane Electrodes

Abstract

Inclusion complexation of an antimicrobial quaternary ammonium salt, carbethopendecinium bromide (SBr, Septonex), with five cyclodextrins was investigated potentiometrically using the prepared membrane electrodes selective to the surface-active carbethopendecinium cations (S+). Relatively strong complexation of the S+ cations with native α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), and their random-substituted derivatives, namely hydroxypropyl-α-cyclodextrin (HP-α-CD), methyl-β-cyclodextrin (M-β-CD), and hydroxypropyl-β-cyclodextrin (HP-β-CD), was evidenced in dilute aqueous solution. In the region where the potentiometrically determined concentration of the free S+ cations remained lower than the critical micelle concentration (cmc) of SBr by a factor of ca ten, formation of the 1:1 complexes with the complexation constants K11 ≈ 104-105 was evaluated by two respective methods, based on a modified linear and a non-linear regression. Deviations from the 1:1 complexation were observed when concentration of the free S+ cations approached cmc of SBr more closely and also in solutions with large excess of α-CD. Comparison of K11 values corroborated the inclusion of the n-C14H29 alkyl chain of the carbethopendecinium cation as the mechanism of its complexation with cyclodextrins. The well-soluble native α-CD with good complex-forming capability towards S+ cations may be especially suitable for possible blocking the undesirable residues of carbethopendecinium bromide.

Determination of carbethopendecinium bromide in eye drops by capillary electrophoresis with capacitively coupled contactless conductivity detection

“…The addition of CDs to the BGEs was tested as a prospective way of suppressing the interaction between the analyte and the CE capillary wall. In accordance with the previous information concerning fundamental studies of the complex formation between CDs and septonex 14, 15, suggesting that the long alkyl chain of septonex enters the hydrophobic CD cavity to form relatively stable inclusion complex, the addition of different CDs (α‐CD, β‐CD, γ‐CD, HP‐α‐CD, HP‐β‐CD, HP‐γ‐CD, 2,6‐DM‐β‐CD) to our BGEs (based on phosphate, acetate, MES, HEPES, TAPSO, MOPSO, or BES) resulted in more or less usable resolution of the peak of septonex from the EOF. Although septonex is a chiral compound possessing one asymmetric centre, no chiral recognition was observed with all CDs tested.…”

“…The formation of inclusion complexes between long alkyl moiety and hydrophobic cavity of CD seems to be a possible mechanism of interaction here. Analogous complex formation of septonex with different natural and modified CDs was studied and confirmed by potentiometry with ion‐selective electrodes 15. MEKC with deoxycholate pseudostationary phase 16 and CEC 17 was also proposed as an effective method for the separation of quaternary ammonium compounds.…”

The formation of host–guest complexes between surfactants and cyclodextrins

“…by using a surfactant concentration range between 0.01 and 0.1 mM [165]. Other studies using potentiometric techniques to investigate the surfactant-cyclodextrin hostguest formation can be found [123,124,[166][167][168][169][170][171].…”

Electrochemistry of Cyclodextrin Inclusion Complexes of Pharmaceutical Compounds

“…Binding constants in solution are usually determined from potentiometric titrations or plots of cyclic voltammetry peak potentials vs CD concentration after assessing the guest/host ratio in the complex [33,34]. Potentiometric measurements are more frequently used in studying the inclusion complexes of pharmaceutical compounds with cyclodextrins [35][36][37][38][39][40][41][42][43][44][45][46][47][48], and ion-selective electrodes are employed, for the direct measurement of the guest activity in the solution [49][50][51][52]. Decreased peak currents in cyclic voltammetry and shifts in the oxidation and reduction potentials are observed on complexation, owing to the smaller diffusion coefficients of the complexes than that of the guest alone, and to the relatively high stability of these complexes.…”