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Single-crystal X-ray diffraction, FTIR and Raman spectroscopies and scanning electron microscopy are used to study a comprehensive structural characterization of the colorless and yellow forms of N-hydroxyphthalimide (NHP), the deuterated form (NDP), and the ethoxylated form (ethoxy-NHP). The study shows that the crystalline yellow form of NHP exhibits a strong absorption band at 575 nm whereas the colorless NHP form does not, however the various NHP forms decompose at temperatures considerably below the melting point.

Stable and regular shaped colloidal nanocrystals are seen in a dilute electrostatically stabilized aqueous solution of lipid A diphosphate. It is reported that they are fragile and easily damaged when exposed to the electron beam.

Single crystalline clusters of lipid A-monophosphate were grown from organic dispersions containing 5-15% (v/v) water at various volume fractions, [lowercase_phi_synonym], and temperatures. The morphology of the single lipid A-monophosphate crystals was either rhombohedral or hexagonal. The hexagonal crystals were needlelike or cylindrical in shape, with the long dimension parallel to the c axis of the unit cell. The crystalline clusters were studied using electron microscopy and x-ray powder diffraction. Employing molecular location methods following a Rietveld refinement and whole-pattern refinement revealed two monoclinic crystal structures in the space groups P21 and C2, both converged with RF = 0.179. The two monoclinic crystal structures were packing (hydrocarbon chains) and conformational (sugar) polymorphs. Neither of these two structures had been encountered previously. Only intramolecular hydrogen bonding was observed for the polymorphs, which were located between the amide and the carboxyl groups. Another crystalline structure was found in the volume-fraction range 2.00 × 10-3 ≤ [lowercase_phi_synonym] ≤ 2.50 × 10-3, which displayed hexagonal symmetry. The hexagonal symmetry of the self-assembled lipid A-monophosphate crystalline phase might be reconciled with the monoclinic symmetry found at low-volume-fractions. Therefore, lowering the symmetry from cubic, i.e., Ia [formula]d, to rhombohedral R [formula] m, and finally to the monoclinic space group C2 was acceptable if the lipid A-monophosphate anion was completely orientationally ordered. [ABSTRACT FROM AUTHOR]

A study of the structure of stable regular-shaped nanocrystals of hexa-acylated (C14) lipid A-monophosphate from Escherichia coli was carried out using dilute electrostatically stabilized aqueous dispersions at low ionic strength (I=1.0×10-5M NaCl). An order-to-order transition of colloidal clusters of lipid A-monophosphate was found at two volume fractions: [lowercase_phi_synonym]=5.9×10-4 and [lowercase_phi_synonym]=11.5×10-4. The clusters belonged to the cubic space groups Pm3n and Ia3d with unit-cell dimensions of a=4.55 nm and a=6.35 nm, respectively, as revealed by small-angle x-ray diffraction and electron-diffraction results of thin nanocrystals of lipid A-monophosphate... [ABSTRACT FROM AUTHOR]

A new structural form of charged lipid A diphosphate, with a molecular weight of 5.9×106 Da and a rodlike shape (L=800 nm), was found in aqueous solutions at pH 8.5. The experimental techniques used in the investigation were light scattering, small-angle x-ray scattering (SAXS), and electron microscopy. Measurements of the static-structure factor S(Q) as a function of the ionic strength are presented over the concentration regimes C≥C* and C≤C*, with C*=1 particle/length3. The position of the first maximum of the structure factor S(Q) was found to scale with C1/3 below and with C1/2 above, the critical concentration C* (2.5 μg/mL). SAXS results in the semidilute concentration range C>=C* show that strong interparticle correlations exist even at concentrations as high as 15C*, in contrast with results for hard-rod systems. The magnitude of the correlations depends on both the lipid A diphosphate concentration at pH 8.5 and the Debye screening length k-1. For a constant lipid A diphosphate concentration at pH 8.5, as the amount of salt was increased a decrease in structure was observed. There was also a shift in the peak of the first maximum position Qmax to larger scattering wave vectors. The observed phase behavior (C=15C*) exhibited an isotropic I-Sm transition and an I-N-Sm transition, which were recorded on electron microscope images. [ABSTRACT FROM AUTHOR]

In this investigation, a study of the self-assembly of electrostatically stabilized aqueous dispersions of nanometric lipid A-monophosphate clusters from Escherichia coli was carried out in three different volume-fraction regimes. The experimental techniques used in the investigation were osmotic pressure, static and quasielastic light scattering, scanning electron microscopy and transmission electron microscopy, and small-angle x-ray scattering. Experiments were carried out at low ionic strength (I=0.1–5.0 mM NaCl) at 25 °C. At volume fractions between 1.5×10-4<=[lowercase_phi_synonym]<=5.4×10-4, the lipid A-monophosphate clusters had an average rms hydrodynamic diameter of d=7.5 nm, and a weighted-average molecular weight of (1.78±0.23)×105 g mol-1. Quasielastic light scattering (LS) experiments yield similar values for the particle size and particle size distribution compared to electron microscopy, small-angle x-ray scattering, and LS experiments. When the volume fraction was increased to a higher regime 5.4×10-4≤=[lowercase_phi_synonym]≤=9.50×10-4, much larger clusters of lipid A monophosphate formed. The clusters detected in this volume-fraction range were assembled from between 8 and 52 of the d=7.5 nm clusters and the assemblies are densely packed in such a way that colloidal crystals composed of the monodisperse microspheres are in physical contact with their nearest neighbors. Clusters that formed in volume fractions between 10.0×10-4≤=[lowercase_phi_synonym]<=40.0×10-4 revealed a weighted-average molecular weight of (10.15±0.17)×106 g mol-1 and a hydrodynamic diameter of ∼d=70.6 nm. The crossover volume fraction between the small and the large clusters appeared at [lowercase_phi&#95... [ABSTRACT FROM AUTHOR]

The structural characterization of lipid A-diphosphate in aqueous solutions was carried out to understand the formation of calcium carbonate crystals which might cause direct direct resistance to viral and bacterial invasion and/or penetration with respect to cationic antimicrobial peptides (CAM) activity. The formation of the calcite and vaterite is found to be controlled by the nucleation, adsorption pH, and the shape-dependent template of lipid A-diphosphate.

The phase transitions of colloidal lipid A-diphosphate aqueous dispersions are examined by using small-angle X-ray-scattering, light-scattering, and electron microscope experiments. The different lipid A-diphosphate vitreous phases might play significant role in the preparation of pharmaceuticals, adjuvants, and vaccine formulations.

Three methods are used to investigate the thermodynamic and structural properties of the lipid A system. The methods used are light scattering, osmotic pressure measurements and small angle X-ray scattering.

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. [ABSTRACT FROM AUTHOR]

Surface-tension-induced liquid-crystalgrowth of monomeric lipidA-diphosphate in aqueous dispersions is reported as a function ofconcentration, (c), and temperature, (T), and at low ionic strength (10–3M). As the temperaturewas varied, a solid–liquid transition was revealed in the surfacelayer at a fixed lipid A-diphosphate bulk concentration. Here, thedevelopment of different two-dimensional (2-d) facetedcrystal morphologies was observed and, as growth proceeded, thesefaceted 2-dcrystals became unstable. Selected areaelectron microscopy diffraction (SAED) and X-ray diffraction (XRD)measurements of the faceted 2-dcrystalline lipidA-diphosphate layers exhibited a pseudohexagonal molecular arrangement.The crystalline layer was a smectic F, SF, phase below the critical temperature, TC, and a smectic I, SI, phase above TC(15 °C). Both phases could be describedin terms of the same C-centered monoclinic unit cell. The in-planeorder extended for a limited distance although the layers were coupled.The analysis of the SAED patterns revealed short-range order in the SFphase (5–15 °C), but long-rangeorder in the SIphase, for the temperaturerange 15–30 °C. The observed 2-dsolidhexatic phase and the 2-dliquid hexatic phase hadcorrelation lengths of 220 Å. This, the hexatic phase, displayedshort-range in-plane positional order and quasi long-range, sixfoldbond-orientational order. The SIphaseshowed long-range order characteristics of a hexatic 2-dcrystal. The two-, four-, or six-layer crystalline lipid A-diphosphatefilms exhibited 2-dhexatic order and 6n-fold bond-orientational order. These films did not evolve into the SFphase, demonstrating that the two phases werethermodynamically distinct. A finite tilt angle of φ = 15°was calculated for the lipid A-diphosphate molecule; the tilt wastoward the small side of the rectangular 2-dlattice.The constraint of six close-packed acyl chains in two distinct phaseswith the same symmetry suggests that the SF→ SItransition was first-order. [ABSTRACT FROM AUTHOR]

The nature of the fluid phase transitions of charged-stabilizedspherical lipid A–diphosphate clusters in aqueous dispersionswas explored using a combination of small-angle X-ray scattering (SAXS)and electron microscopy. In contrast to previous studies, rather thanremoving NaCl, NaOH was added to the dispersions to promote crystallization.The fluid phase experiments were carried out employing titrationswith mM·L–1NaOH (cS), along with variations in the particle-number density, n. When cSwas increased, anew fluid disordered phase of self-assembled lipid A–diphosphatewas encountered, followed by a crystalline bcc phase and then a newfluid phase containing 70 nm lipid A–diphosphate particles.The bcc crystal structure found in this regime had a lattice constantof 35.6 nm. By varying cS(mM L–1), it was possible to determine the effective charge, zeff, for various nvalues and the screening parameter, k, for theexcess electrolyte. For sufficiently large values of n, lipid A–diphosphate crystallized because of an increasein zeffat a constant cS. When the cSwasincreased, the crystals melted with little change in zeff. The existence of a bcc–fluidphase transition for different values of cSwas supported by applying the Debye correlation function to theobtained data. An increase in cSenhancedinterparticle interaction and attraction. The effective charge and kaccounted for counterion condensation and many-body effects.If the effective charge determined from scattering measurements wasused in the simulations, the equilibrium phase boundaries were consistentwith predicted universal melting-line simulations. At any particle-numberdensities, n, when the melting line was reached,70 nm clusters were formed. [ABSTRACT FROM AUTHOR]