Small-angle X-ray Diffraction Studies Research Articles

Small-angle X-ray diffraction study of the thermotropic and lyotropic phases of five alkyl cyclic and acyclic disaccharides: Influence of the linkage between the hydrophilic and hydrophobic moieties

We present a comparative study of the thermotropic and lyotropic phases of 5 surfactants with an aliphatic chain of 12 carbon atoms and a cyclic or acyclic sugar head with different linkages between the two moieties. These linkages can concern different chemical groups or different orientations between the head and the chain. The compounds included the α- and β-N dodecyl-D-maltosides, N-dodecylamino-1-deoxylactitol, N-dodecyl lactobionamide and N-acetyl N-dodecyl lactosylamine. The influence of the polar head (with closed- and opened-type sugars) and the linkage with the hydrocarbon chain on the phases obtained by the heating of the anhydrous compounds and after addition of water was studied by X-ray diffraction and optical microscopy. In the anhydrous state, the surfactants were either crystalline or amorphous. On heating, they went through a liquid crystal smectic phase which, in some cases, was preceded by solid-to-solid transitions. On addition of water, the sequence of phases from the micellar phase to the lamellar phase was accounted for in terms of the geometric model of Sadoc and Charvolin. However, with certain surfactants this sequence was not complete, and the domains of existence of phases were altered.

Small angle X-ray diffraction study of blends of nylon 6 and a liquid crystal copolyester

Small angle X-ray diffraction (SAXS) analysis of blends between nylon 6 and the liquid crystal copolyester Vectra has been performed as a function of composition and thermal treatment in order to make a correlation with the thermal and structural properties of these systems and to get information about their morphological characteristics. Simultaneous small and wide angle X-ray diffraction experiments using synchrotron radiation have been carried out in dynamic experiments to investigate in real time the polymorphic transformations that occur with increasing temperature and the structural changes observed during the melting process.

The overlap between the thin- and thick-filament reflections in the small-angle X-ray diffraction pattern from a molluscan smooth muscle

Small-angle X-ray diffraction studies of the living anterior byssus retractor muscle (ABRM) of Mytilus edulis have been carried out using a long (2.2 m) point-focusing camera to investigate the overlap between the thin- and thick-filament reflections. While the reflections due to the cross-bridge lattice on the thick filaments in the resting ABRM are distant in the axial direction from the thin-filament layer lines, the paramyosin cores of the thick filaments produce reflections very close to the thin-filament reflections at axial spacings of 387, 59 and 51 Å. Using such a long camera it becomes possible to separate these reflections due to an improvement in the angular resolution and increase in the difference between the widths of the thin- and thick-filament reflections, and it is shown that the intensities of the 387 and 59 Å thin-filament layer lines gradually drop to zero close to the meridian. It becomes relatively easy to observe the thin-filament-based X-ray pattern by use of the long camera, making it possible to show a partial resemblance of the small-angle X-ray pattern from the contracting ABRM with the pattern from the rigorized ABRM.

Physical effects of cholesterol on arterial smooth muscle membranes: evidence of immiscible cholesterol domains and alterations in bilayer width during atherogenesis

Small angle X-ray diffraction was used to examine arterial smooth muscle cell (SMC) plasma membranes isolated from control and cholesterol-fed (2%) atherosclerotic rabbits. A microsomal membrane enriched with plasma membrane obtained from animals fed cholesterol for up to 13 weeks showed a progressive elevation in the membrane unesterified (free) cholesterol:phospholipid (C/PL) mole ratio. Beyond 9 weeks of cholesterol feeding, X-ray diffraction patterns demonstrated a lateral immiscible cholesterol domain at 37 degrees C with a unit cell periodicity of 34 A coexisting within the liquid crystalline lipid bilayer. On warming, the immiscible cholesterol domain disappeared, and on cooling it reappeared, indicating that the immiscible cholesterol domain was fully reversible. These effects were reproduced in a model C/PL binary lipid system. In rabbits fed cholesterol for less than 9 weeks, lesser increases in membrane C/PL mole ratio were observed. X-ray diffraction analysis demonstrated an increase in membrane bilayer width that correlated with the C/PL mole ratio. This effect was also reproduced in a C/PL binary lipid system. Taken together, these findings demonstrate that in vivo, feeding of cholesterol causes cholesterol-phospholipid interactions in the membrane bilayer that alter bilayer structure and organization. This interaction results in an increase in bilayer width peaking at a saturating membrane cholesterol concentration, beyond which lateral phase separation occurs resulting in the formation of separate cholesterol bilayer domains. These alterations in structure and organization in SMC plasma membranes may have significance in phenotypic modulation or aortic SMC during early atherogenesis.

Phase behavior and lyotropic-liquid crystal structure of alkyltrimethylammonium bromide-water mixtures around freezing temperature of water

Freezing and melting behaviors of concentrated cationic surfactant-water binary systems were investigated by using differential scanning calorimetry and polarized light microscopy, and the phase diagrams around the freezing temperature of water were constructed. The surfactants studied were decyl- and octyl-trimethylammonium bromide (abbreviated as DeTAB and OTAB). The OTAB-water system forms a lyotropic-liquid crystal in highly concentrated region of ca. 80 wt% OTAB. The head groups of OTAB strongly interact with water molecules and reduce freezing point of water down to −33°C. To clarify the structure of the liquid-crystalline phase, small angle X-ray diffraction study was carried out on DeTAB-water system as a function of composition at various temperatures. The observed diffraction patterns indicate the formation of the hexagonal phase, H α , and suggests that the H α phase consists of finite cylinder micelles with length increasing with surfactant content.

Small angle x-ray diffraction studies of PET fibres

Small angle x-ray diffraction studies of PET fibres

Differential scanning calorimetry and small angle x-ray diffraction study of the interaction of (R)-PAF, (R)-ET-18-OMe and (R)-Lyso-PAF with model membranes

(R)-PAF, (R)-ET-18-OMe and (R)-Lyso-PAF are ether phospholipid analogs exhibiting different biological activities. All three molecules are highly lipophilic and interact with cell membranes. The manner in which their interactions occur is relevant to their biological activities and may provide information on their mechanism(s) of action at the molecular level. We have studied the interactions of (R)-PAF, (R)-ET-18-OMe and (R)-Lyso-PAF with model membranes using differential scanning calorimetry (DSC). A concentration-dependence study with DSC shows that all three analogs induce similar changes in the thermotropic behavior of model membranes. All produce a slight decrease in the main phase transition temperature of DPPC bilayers (ΔT c = 0.3 to 1.4 °C) but have a more substantial effect on the pretransition (ΔT c = 0.8 to 4.5 °C). All three disorder phosphatidylcholine (PC) membranes but impart order to PC/cholesterol membranes. We have used small angle x-ray diffraction experiments to supplement the DSC evidence on the topography of the ether lipid analogs in the bilayers. All three appear to insert themselves in the bilayer with their long chain parallel with the membrane bilayer chains.

Thermotropic liquid-crystalline properties of some novel hexuronic acid derivatives bearing a single or two alkyl chains

X. Auvray, B. Labulle, C. Petipas, J. Bertho, T. Benvegnu and D. Plusquellec, J. Mater. Chem., 1997, 7, 1373 DOI: 10.1039/A607305K

Small-Angle X-ray Diffraction of Muscle Using Undulator Radiation from the Tristan Main Ring at KEK

Time-resolved X-ray diffraction of muscle has demanded ever-increasing flux into small sample volumes with low beam divergence. Results are reported of static and time-resolved small-angle X-ray diffraction studies on muscle fibers using a hard X-ray undulator installed in the Tristan main ring at KEK, Tsukuba, Japan, as an innovative source of synchrotron radiation more intense and better collimated than that available with the Photon Factory bending-magnet beamline. Static studies used the low divergence of the source to obtain detailed high-quality diffraction patterns of stable muscle states. The diffraction patterns from live skeletal muscles showed the numerous (over 100) meridional reflections. The well collimated beam from the undulator made it possible to clearly resolve, with an angular resolution of ca 700 nm, the closely spaced diffraction peaks arising from the two halves of the thick filaments centred on the M lines in a sarcomere, in addition, the diffraction peaks from the thin filaments on opposite sides of the Z bands could be resolved with an angular resolution of ca 1000 nm. The detailed structure of the meridional pattern defines the nature of the molecular packing in the thick and thin filaments. Time-resolved experiments using a focusing mirror aimed to prove cross-bridge states in striated muscle fibers by collecting X-ray diffraction data at a 0.185 ms time resolution from sinusoidally oscillating chemically skinned rabbit muscle fibers during active contraction and in rigor. When sinusoidal length changes at 500 Hz with a peak-to-peak amplitude of 0.6% of the muscle length were applied to a small fiber bundle, the tension showed a simple elastic response during the length oscillation. In the active muscle the intensity of the 14.5 nm myosin-based meridional reflection changed out of phase with the tension change during the oscillating length change. In contrast, in the rigor muscle it occurred in phase with the tension change. The high time-resolved experiments provide an insight into the coupling between conformational changes and force generation of the actomyosin cross-bridges. These studies provide a preview of the expected gains for muscle studies from the more widespread use of undulator radiation at third-generation synchrotron sources.

Modes of action of terpene penetration enhancers in human skin; Differential scanning calorimetry, small-angle X-ray diffraction and enhancer uptake studies

The mechanisms through which the terpenes, d-limonene, 1–8-cineole and nerolidol, increase the permeability of human stratum corneum (s.c.) and the mechanisms underlying propylene glycol (PG)/terpene synergy were investigated using differential scanning calorimetry (DSC), small-angle X-ray diffraction (SAXD) and enhancer uptake studies. DSC experiments identified two major lipid transitions at 72° and 83°C. d-Limonene reduced the temperatures of both transitions by approx. 20°C without affecting their enthalpies ( ΔH). 1–8-Cineole also reduced the temperatures of both transitions by approx. 20°C but also reduced ΔH for the first major lipid transition; ΔH for the second was unaffected. d-Limonene increased the combined entropy change ( ΔS) associated with both lipid transitions by 11% whereas 1–8-cineole decreased ΔS by 32%. The decrease in ΔS produced by 1–8-cineole provides evidence that this enhancer is lipid disruptive at normal skin temperature. Nerolidol reduced the transition temperatures of both major lipid transitions by approx. 4°C and also decreased their cooperativity. Reduced bilayer cooperativity indicates that this enhancer also disrupts the intercellular lipids. Lack of a clear baseline prevented accurate measurement of ΔH and ΔS values following nerolidol treatment. SAXD experiments showed that d-limonene and 1–8-cineole act to reduce the intensity of lipid based reflections. Decreases in reflection intensities may be linked to a disruption of lipid packing within the bilayers and/or to a disturbance in the stacking of the bilayers. Treatment with nerolidol did not markedly reduce the intensities of the bilayer based reflections. Uptake studies revealed that large quantities of terpenes can be accommodated by the s.c. (mean uptake of d-limonene, 1–8-cineole and nerolidol was 8.90%, 26.2% and 39.6% w/w dry s.c.). The possibility that terpene enhancers pool in the s.c. is discussed. DSC and SAXD investigations provided fragmented evidence that PG/terpene synergy may produce enhanced lipid bilayer disruption. Enhancer uptake studies showed that PG does not significantly increase terpene delivery to the s.c. above that provided by application of neat terpenes.

Small-angle X-ray diffraction studies on interface sharpness of amorphous Se/CdSe superlattices

X-ray diffraction measurements have been performed to evaluate the interface sharpness of Se/CdSe amorphous multilayers as well as their thermal stability. A value of about 1.6 nm has been measured as the effective interface thickness, d i. It decreased to d i ≈ 1.3 nm after the samples were annealed at an optimum temperature, T a ≈ 360 K. A negative interdiffusion coefficient has been obtained in this case. More complicated temperature dependences of the X-ray diffraction peaks have been observed at higher annealing temperatures. Two different thermally dependent processes have been considered.

Conducting Langmuir-Blodgett films of heptadecylcarboxymethyl-BEDT-TTF

Abstract Surfactant compounds containing the bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) donor group appeared to be very promising for production of highly conducting Langmuir-Blodgett (LB) films. A new donor compound, i.e. heptadecylcarboxymethyl-BEDT-TTF, is used to increase interaction of the molecules with water. It possesses donor properties of hexadecyl-BEDT-TTF and contains a strong hydrophilic group which does not prevent close packing of BEDT-TTF fragments due to its small dimensions. As a result, uniform highly conducting LB films of heptadecylcarboxymethyl-BEDT-TTF are deposited from the water subphase containing FeCl 3 . Conductivity of the films reaches 4 ohm −1 cm −1 . Electron and small-angle X-ray diffraction studies are carried out. Some structure parameters are determined. Proceeding from these data possible structure models are proposed and peculiarities of the structure are discussed. The films are sensitive to the effect of electron beam and lose conductivity under irradiation. Thus, a desirable insulating pattern can be created in the conducting material which is important for technological applications.

Small angle X-ray diffraction and differential scanning calorimetric studies on O-methyl-(−)-Δ 8-tetrahydrocannabinol and its 5′ iodinated derivative in membrane bilayers

We have previously studied and compared the location of (−)- Δ 8-tetrahydrocannabinol (Δ 8-THC) with that of O-methyl-Δ 8-THC (Me-Δ 8-THC) in the membrane using partially hydrated dimyristoylphosphatidylcholine (DMPC) bilayers ((Mavromoustakos et al. (1990) Biophys. Acta 1024, 336–344; Yang et al. (1993) Life Sci. 53, 117–122). Δ 8-THC was found to be located near the membrane interface with its phenolic hydroxyl group anchored near the carbonyl groups of DMPC while the more lipophilic Me-Δ 8-THC is located deeper in the membrane bilayer. Parallel experiments using Me-Δ 8-THC and its 5′-iodo analog (5′-I-Me-Δ 8-THC allowed us to determine the topography of these two molecules in the bilayer. Our results from small angle X-ray diffraction and differential scanning calorimetry (DSC) combined with previous data on the orientation of Me-Δ 8-THC in model membranes, led us to the conclusion that these molecules intercalate between contiguous acyl chains in the lipophilic moiety of the membrane bilayer. The terminal iodo group in 5′-IMe-Δ 8-THC was found to reside in a region extending approx. ± 5 Å from the center of the bilayers. The location of Me-Δ 8-THC in the membranes as well as its orientation may explain its inability to effectively perturb the bilayer lipid chains.

Small Angle X-Ray Diffraction Studies of an Ester/Biphenyl Mixture (5CB/ME 50.5) Showing an Injected Smectic Phase

Abstract The molecular organisation in a binary mixture of a strongly polar mesogen (5CB) and a weakly-polar mesogen (ME50.5) is investigated using results of X-ray scattering and density studies. Analysis of the intensity distribution of X-ray scattering has yielded results for orientational order parameters in addition to smectic layer spacings and effective molecular lengths. The results are compared with a mean field theory of the smectic phase. Previously unexplained results for mixtures showing a minimum in the anisotropy of physical properties coincident with a maximum in the nematic/smectic A transition entropy are shown to be consistent with the theory. We conclude that favourable packing of molecules in the injected smectic A phase stabilises the layers but increases the orientational free volume, consistent with a lower orientational order parameter.

Enigmatic thermotropic phase behavior of highly asymmetric mixed-chain phosphatidylcholines that form mixed-interdigitated gel phases

Twelve saturated mixed-chain phosphatidylcholines have been identified for which the thermotropic phase behavior observed upon cooling from the L alpha phase is dependent upon the thermal history of the sample in the gel phase. If fully hydrated samples of these lipids are cooled and soon thereafter examined by differential scanning calorimetry, one observes a single highly cooperative endotherm (the chain-melting phase transition) upon heating, and on subsequent cooling, a single exotherm that may occur at temperatures as much as 4-6 degrees C below that of the single endotherm observed upon heating. In contrast, if the samples are incubated in the gel state at low temperatures for prolonged periods of time, one observes a single heating endotherm as before, but two sharp exotherms upon cooling. The latter transitions occur at temperatures close to that of the single endotherm observed upon heating and the single cooling exotherm observed prior to incubation in the gel state. The combined enthalpy of the two cooling exotherms is the same as that of the single heating endotherm or the single cooling exotherm initially observed. Infrared spectroscopic and X-ray diffraction studies indicate that the structural conversions characteristic of liquid-crystalline/gel phase transitions occur at both of those cooling exotherms. Of the 12 lipids that exhibit this unusual behavior, nine fulfill the previously defined structural requirements for the formation of the so-called mixed-interdigitated gel phase, and there is evidence in the literature that one of the three remaining lipids also forms such a structure. Infrared spectroscopic studies of the other two lipids indicate that their gel phases exhibit spectroscopic features that closely resemble those of lipids that meet the previously defined structural criteria for the formation of mixed-interdigitated gel phases and that differ markedly from those of both saturated symmetric-chain and saturated mixed-chain phosphatidylcholines that do not normally form mixed-interdigitated gel phases. Also, electron density reconstructions based on small-angle X-ray diffraction studies of the gel phases of those two lipids indicate that the thickness of their gel phase bilayers is consistent with their forming mixed-interdigitated gel phases. Thus the unusual thermotropic phase behavior described here may be a general characteristic of phosphatidylcholines that form mixed-interdigitated gel phases. This unusual behavior is not associated with any major change in any of several physical properties of these lipid bilayers but may arise from an alteration of the size and/or structure of microdomains present in the liquid-crystalline phase.

Disorder-order transitions in soft sphere polymer micelles.

Diblock copolymers in a selective solvent often assemble into spherical micelles. These micelles demonstrate long range order at moderate polymer concentrations. We explore the nature of the disorder-order transition in micellar suspensions through small angle x-ray diffraction studies. The phase behavior includes body-centered cubic (bcc) and face-centered cubic (fcc) lattices. We present the first phase diagram for block copolymer micelles to include both bcc and fcc structures and characterize the lattice selection by a ratio of coronal layer thickness to core radius.

Preparation and Properties of Ferroelectric Liquid-Crystalline Polysiloxanes Possessing (S)-(−)-4-(2-methylbutyloxycarbonyl)phenyl 4′-(5-hexyloxy)biphenyl-4-carboxylate as Side Chain Mesogen Unit

New ferroelectric liquid crystalline polysiloxanes 5 containing a side chain mesogenic group were prepared by the reaction between poly(methylsiloxane) 4 with various degrees of polymerization and the mesogenic compound possessing terminal olefin, (S)-(−)-4-(2-methylbutyloxycarbonyl)phenyl 4′-(5-hexenyloxy)biphenyl-4-carboxylate 3, in the presence of a platinum catalyst. The polarized microscopic observation indicated that both the olefinic precursor 3 and the resulting polysiloxanes 5 displayed enantiotropic smectic A (SA) and smectic C (SC*) mesophases. The polymers showed transitions from isotropic to SA phases and from SA to SC* phases in the range of 250–220°C and 215–188°C, respectively, where the SC* phase was exhibited even at room temperature. The phase transition temperature increased with increasing molecular weight of the polysiloxane backbone. The small angle X-ray diffraction study indicated that the layer spacing increased and the tilt angle of the mesogenic side chain unit decreased with increasing temperature, and they became constant after a particular temperature of SC*−SA transition. The observed layer spacing of 2.9 nm in SA phase agreed with the calculated value of 3.1 nm. The polymers are switchable by an electric field and the minimum response time was 175 ms.

Fabrication and Characterisation of Type-M Dispenser Cathodes for Microwave Tubes

The technology of high current density type-M dispenser cathodes for microwave tubes has been developed. This technology has been utilised to fabricate several batches of dispenser cathodes. These cathodes are capable of providing current densities better than 20 Amp/cm2 at the operating temperature of 1050* C. Their emission performance is studied in oxidising gases. Small angle X-ray diffraction study is carried out to examine changes in the emitting surface during fabrication of these cathodes.

Fabrication of an organic superlattice film by molecular beam deposition

A superlattice film of 5, 10, 15, 20 tetraphenylporphyrin (H2TPP; C44H30N4) and 5, 10, 15, 20 tetraphenylporphyrinato zinc (ZnTPP; C44H28N4Zn) was grown on a hydrogen terminated surface of Si (100) wafer which was kept at −25 °C. The organic molecular beam deposition technique was used for the fabrication under ultrahigh vacuum between 3×10−9 and 3×10−10 Torr. The small angle x-ray diffraction study has revealed that the period of the superlattice was 4.4 nm, which was also confirmed by the oscillation of the same period observed in a secondary ion mass spectrometry depth profile of Zn. The Fourier-transform infrared spectroscopy measurement indicated that the quasi-planar molecules of H2TPP and ZnTPP were inclined at an angle of 70° with respect to the substrate surface. The film surface was very flat and any roughness could not be detected by field emission secondary electron microscope observation. An atomic force microscope (AFM) therefore was used to investigate the surface. The root mean square roughness calculated from the AFM image was 0.37 nm.

Small angle X-ray diffraction studies of (−)- Δ8-tetrahydrocannabinol and its O-methyl analog in membranes

Small angle X-ray diffraction was used to study the topography of (−)- Δ 8-tetrahydrocannabinol( Δ 8-THC) and its pharmacologically inactive methoxy analog (−)-O-methyl- Δ 8-tetrahydrocannabinol(Me- Δ 8-THC) in a membrane. The membrane preparations were partially hydrated dimyristoylphosphatidylcholine (DMPC) bilayers. Comparisons between electron density profiles from the drug-containing and drug-free membranes showed that the amphipathic Δ 8-THC resides near the interface of the bilayer where the polar phenolic OH of the drug molecule is oriented towards the corresponding polar side of the phospholipid bilayer. Conversely, the highly hydrophobic Me- Δ 8-THC distributes deeper in the bilayer away from the interface. Our results point out that these two structurally-related, but pharmacologically very different, cannabinoids interact with membranes in strikingly different manners. This observation may, in part, explain the different pharmacological properties of the two cannabinoids.