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

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

Two Dimensional Crystallization of Three Solid Lipid A‑Diphosphate Phases

Surface-tension-induced liquid-crystal growth of monomeric lipid A-diphosphate in aqueous dispersions is reported as a function of concentration, (<i>c</i>), and temperature, (<i>T</i>), and at low ionic strength (10^–3 M). As the temperature was varied, a solid–liquid transition was revealed in the surface layer at a fixed lipid A-diphosphate bulk concentration. Here, the development of different two-dimensional (<i>2-d</i>) faceted crystal morphologies was observed and, as growth proceeded, these faceted <i>2-d</i> crystals became unstable. Selected area electron microscopy diffraction (SAED) and X-ray diffraction (XRD) measurements of the faceted <i>2-d</i> crystalline lipid A-diphosphate layers exhibited a pseudohexagonal molecular arrangement. The crystalline layer was a smectic F, <i>S</i>_F, phase below the critical temperature, <i>T</i>_C, and a smectic I, <i>S</i>_I, phase above <i>T</i>_C (15 °C). Both phases could be described in terms of the same C-centered monoclinic unit cell. The in-plane order extended for a limited distance although the layers were coupled. The analysis of the SAED patterns revealed short-range order in the <i>S</i>_F phase (5–15 °C), but long-range order in the <i>S</i>_I phase, for the temperature range 15–30 °C. The observed <i>2-d</i> solid hexatic phase and the <i>2-d</i> liquid hexatic phase had correlation lengths of 220 Å. This, the hexatic phase, displayed short-range in-plane positional order and quasi long-range, sixfold bond-orientational order. The <i>S</i>_I phase showed long-range order characteristics of a hexatic <i>2-d</i> crystal. The two-, four-, or six-layer crystalline lipid A-diphosphate films exhibited <i>2-d</i> hexatic order and 6<i>n</i>-fold bond-orientational order. These films did not evolve into the <i>S</i>_F phase, demonstrating that the two phases were thermodynamically distinct. A finite tilt angle of φ = 15° was calculated for the lipid A-diphosphate molecule; the tilt was toward the small side of the rectangular <i>2-d</i> lattice. The constraint of six close-packed acyl chains in two distinct phases with the same symmetry suggests that the <i>S</i>_F → <i>S</i>_I transition was first-order

14N and 81Br Quadrupolar Nuclei as Sensitive NMR Probes of n-Alkyltrimethylammonium Bromide Crystal Structures. An Experimental and Theoretical Study

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Antimicrobial nano-assemblies of tryptocidine C, a tryptophan-rich cyclic decapeptide, from ethanolic solutions

Tryptocidine C (TpcC), a Trp-rich cyclodecapeptide is a minor constituent in the antibiotic tyrothricin complex from Brevibacillus parabrevis. TpcC possesses a high tendency to oligomerise in aqueous solutions and dried TpcC forms distinct self-assembled nanoparticles. High-resolution scanning electron microscopy revealed the influence of different ethanol:water solvent systems on TpcC self-assembly, with the TpcC, dried from a high concentration in 15% ethanol, primarily assembling into small nanospheres with 24.3 nm diameter and 0.05 polydispersity. TpcC at 16 μM, near its CMC, formed a variety of structures such as small nanospheres, large dense nanospheroids and facetted 3-D-crystals, as well as sheets and coarse carpet-like structures which depended on ethanol concentration. Drying 16 μM TpcC from 75% ethanol resulted in highly facetted 3-D crystals, as well as small nanospheres, while those in 10% ethanol preparation had less defined facets. Drying from 20 to 50% ethanol led to polymorphic architectures with a few defined nanospheroids and various small nanoparticles, imbedded in carpet- and sheet-like structures. These polymorphic surface morphologies correlated with maintenance of fluorescence properties and the surface-derived antibacterial activity against Staphylococcus aureus over time, while there was a significant change in fluorescence and loss in activity in the 10% and 75% preparations where 3-D crystals were observed. This indicated that TpcC oligomerisation in solutions with 20–50% ethanol leads to metastable structures with a high propensity for release of antimicrobial moieties, while those leading to crystallisation limit active moieties release. TpcC nano-assemblies can find application in antimicrobial coatings, surface disinfectants, food packaging and wound healing materials