Influence of the anions on the N-cationic benzethonium salts in the solid state and solution: Chloride, bromide, hydroxide and citrate hydrates

Abstract

The crystal structures of the hydrated cationic surfactant benzethonium (Bzth) chloride, bromide, hydroxide, and citrate have been determined by X-ray diffraction analysis and compared with their structures in solution well above their critical micelle concentration. The differences in the nature of the various anions of the four Bzth-X materials lead to unique anion environments and 3-D molecular arrangements. The water molecule in the monoclinic Bzth-Cl or Bzth-Br forms is hydrogen bonded to the halides and particularly to the hydrogens of the methoxy groups of the Bzth moiety notwithstanding the weak Brønsted acidity of the methoxy hydrogens. The citrate strongly interacts with the hydrogens of the methoxy group forming an embedded anionic spherical cluster of a radius of 2.6 Å. The Bzth-OH crystallizes in a hexagonal lattice with two water molecules and reveals free water molecules forming hydrogen bonded channels through the Bzth-OH crystal along the c-axis. The distances between the cationic nitrogen and the halides are 4.04 Å and 4.20 Å, significantly longer than expected for typical van der Waals distances of 3.30 Å. The structures show weakly interacting, alternating apolar and polar layers, which run parallel to the crystallographic a-b planes or a-c planes. The Bzth-X salts were also examined in aqueous solution containing 20% (v/v) ethanol and 1.0 % (v/v) glycerol well above their critical micelle concentration by small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). The [1,1,1] planes for the Bzth Cl or Br, the [0,0,2] and [1,1,0] planes for the Bzth-citrate, the [2,-1,0] planes and the [0,0,1] planes for the Bzth-OH found in the crystalline phase were also present in the solution phase, accordingly, the preservation of these phases are a strong indication of periodicity in the solution phase.

Surface and interface properties of benzethonium chloride-montmorillonite

“…ity against head and neck cancer [1][2][3], BZT is used in numerous pharmaceutical formulations as: active ingredient for antiseptics e.g. topical anti-infective in veterinary medicine, [4][5][6][7], many fungi and lipid-containing viruses are susceptible to BZT [8] and was also found as efficient non-viral reagent gene vectors due to their safety and other inherent properties over viral delivery techniques to transfect outer DNA into animal cells in vitro [9,10].…”

The characteristic curvature (Cc) of ionic surfactants assessed via Small-Angle X-ray Scattering (SAXS)

“…The SAXS profile for the oil-free BCl control was not analyzed using the ellipsoidal model for two reasons, first that the signal was too noisy to have well-defined features, and second the uncertainty in assigning a well-defined headgroup. While we have highlighted the quaternary ammonium group for BCl in Figure 9, the only previous BCl-SAXS study found in the literature suggests that the phenyl group, the ethoxy groups, and bound water form a headgroup environment that has a different electron distribution from other well-defined quaternary cationic surfactants 34 . One other important feature in Figure 9 is that the right-side exponent of the transition fit is nR = -2, suggesting that the Teubner-Strey model is still relevant for these systems; however, as indicated in the fit summary in Table S9, the system prepared with 0.1% NaCl (ln(S)= -1.36) has an nR= -1.43.…”