Combined application of neutron and synchrotron radiation for investigation of the influence of dimethyl sulfoxide on the structure and properties of the dipalmitoylphosphatidylcholine membrane

The influence of dimethyl sulfoxide (DMSO) on the structure and properties of the dipalmitoylphosphatidylcholine membrane was studied at positive temperatures by a combination of X-ray diffraction and small-angle neutron scattering. Penetration of DMSO molecules into the lipid membrane was found to depend on the mole fraction of DMSO in an aqueous solution, X _DMSO. At X _DMSO > 0.08 the SO group penetrates into the bilayer polar region, thus resulting in structural alterations. At X _DMSO > 0.2 defects in the membrane surface are developed.     

Dimethyl sulfoxide-induced dehydration of the intermembrane space of dipalmitoylphosphatidylcholine multilamellar vesicles: Neutron and synchrotron diffraction study

Small-angle neutron scattering spectra of a polydispersed population of dipalmitoylphosphatidylcholine (DPPC) unilamellar vesicles in heavy water in the presence of dimethyl sulfoxide (DMSO) are analyzed by means of the separated form-factor method. An increase in the mole fraction of DMSO in water from 0 to 15% was shown to lead to an increase in the thickness of the bilayer to the characteristics repeat distances of DPPC multilamellar membranes. This fact is indicative of dehydration of the intermembrane space and a steric contact between adjacent DPPC bilayers at 15% mole fraction of DMSO.     

Influence of cholesterol and ceramide VI on the structure of multilamellar lipid membranes at water exchange

The structural changes in the multilamellar lipid membranes of dipalmitoylphosphatidylcholine (DPPC)/cholesterol and DPPC/ceramide VI binary systems during hydration and dehydration have been studied by neutron diffraction. The effect of cholesterol and ceramide on the kinetics of water exchange in DPPC membranes is characterized. Compared to pure DPPC, membranes of binary systems swell faster during hydration (with a characteristic time of ∼30 min). Both compounds, ceramide VI and cholesterol, similarly affect the hydration of DPPC membranes, increasing the repeat distance due to the bilayer growth. However, in contrast to cholesterol, ceramide significantly reduces the thickness of the membrane water layer. The introduction of cholesterol into a DPPC membrane slows down the change in the parameters of the bilayer internal structure during dehydration. In the DPPC/ceramide VI/cholesterol ternary system (with a molar cholesterol concentration of 40%), cholesterol is partially released from the lamellar membrane structure into the crystalline phase.     

Formation of the long-periodicity phase in model membranes of the outermost layer of skin (Stratum corneum)

Model SC membranes (lipid membranes fabricated from the main components of the lipid matrix of the outermost layer of mammalian skin (stratum corneum (SC)) are used to study the general regularities of the nanostructurization of SC lipid matrix. A model membrane from the outermost layer of skin SC with a composition ceramide 1/ceramide 6/cholesterol/palmitic acid/cholesterol sulfate and a component weight ratio of 30/30/20/15/5 has been investigated by X-ray diffraction. It is shown that the membrane structure at pH = 7.2 consists of two short-periodicity phases with repeat distances d = 47 and 35.7 Å and a long-periodicity phase with d = 127 Å. An increase in pH to 9.0 leads to destruction of the long-periodicity phase, while the short-periodicity phase is retained with d = 48.3 Å.     

Charge carrier transport in solid state crystallized poly-Si films on glass

The influence of the used substrate and the deposition temperature, T_d, of the amorphous starting material on the transport properties of solid state crystallized poly-Si is investigated. For poly-Si on a-SiN_X:H coated borofloat glass a very small free-carrier concentration that is independent of T_d is observed and charge transport is governed by intra-grain scattering mechanisms. For poly-Si on Corning glass the carrier concentration exhibits an inverted U shape as T_d increases. These samples exhibit activated behavior of the Hall mobility that is consistent with thermionic carrier emission over potential barriers.     

Size effects in [N(CH3)4]2Zn0.58Cu0.42Cl4 crystals

The temperature dependences of birefringence in thin [N(CH₃)₄]₂Zn_0.58Cu_0.42Cl₄ crystals in the thickness range 20 × 10^?6 ≤ d ≤ 500 ? 10^?6 m have been investigated. An increase in the temperatures of the parent phase-incommensurate phase and incommensurate phase-ferroelectric phase transitions has been found. The reasons for the shift in the phase transition temperatures with a decrease in the thickness of [N(CH₃)₄]₂Zn_0.58Cu_0.42Cl₄ crystal and the size effect in crystals with an incommensurate superstructure are discussed.     

Preparation and evaluation of some novel liquid crystals as antioxidants

Four liquid crystal compounds of the form 2-sec-butyl-4-[(4-X-phenyl) diazenyl) phenyl-4-(octadecyloxy] benzoate symbolized as I18_a, I18_b, I18_c, and I18_d were prepared in which the substituent (X) was taken CH₃O-, CH₃-, Br-, and -NO₂, respectively. Characterization of prepared compounds is done using FT-IR, ¹H-NMR, mass spectroscopy, and elemental analysis. Their mesophase was investigated by differential scanning calorimetry. Their antioxidant efficiency for Egyptian lubricating base oil was tested via monitoring the oxidation reaction through the change in total acid number. The obtained results showed that the efficiency of these compounds was ranked as follows I18_d > I18_c > I18_b > I18_a.     

Photocarrier diffusion lengths of high-growth-rate microcrystalline silicon

We report on photocarrier transport of high-growth-rate microcrystalline Si (μc-Si) in conjunction with the lateral size, σ_L, of crystallites’ conglomerate (grain) determined from the atomic force microscope (AFM) topographic images on the basis of fractal concepts. μc-Si films were prepared using very-high-frequency plasma-enhanced chemical vapor deposition at a high deposition rate of 6.8 ± 0.5 nm/s. μc-Si thicknesses, d, were varied from 0.53 μm to 5.6 μm. With an increase in d, σ_L increased from 70 nm to 590 nm. At the same time, the ambipolar diffusion lengths, L_amb, of photocarriers, observed using the steady-state photocarrier grating (SSPG) technique, increased from 50 nm to 420 nm. Log–log plots of L_amb versus d and σ_L versus d were both expressed as a power law with an exponent of 0.9, yielding a simple linear relation between L_amb and σ_L. Moreover, their ratio, L_amb/σ_L, was below unity, implying the intra-grain carrier diffusion. From these results, the role of the grain (column) boundaries for photocarrier diffusion in μc-Si is discussed.     

Analysis of the conformational polymorph crystal structures by means of molecular Voronoi-Dirichlet polyhedra

The nonvalent interactions in the crystal structures of 16 conformational polymorphs of the C _a H _b N _c O _d S _e composition (a, b, c, d, and e are stoichiometric indices), including 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (“ROY”) (which has seven different modifications), have been analyzed using the characteristics of molecular Voronoi-Dirichlet polyhedra. It is established that a unique combination of implementable types of intra- and intermolecular nonvalent contacts corresponds to each conformational polymorph.     

ESR and optical absorption of cupric ion in borate glasses

ESR and optical absorption of Cu²⁺ were measured in xNa₂O(100?x)B₂O₃ (1 ≤ x ≤ 75), x ZnO(100?x)B₂O₃ (46 ≤ x ≤ 64) and x Pb(100?x)b₂O₃ (20 ≤ x ≤ 75) glasses, where x is expressed in mol.%. Spin hamiltonian parameters and ligand field absorption energy changed abruptly in the regions of 15 ≤ x ≤ 23 and 37 ≤ x ≤ 55 in the soda system, while both parameters were hardly dependent upon the glass composition in zinc and lead systems. The magnitude of micro-environmental fluctuation of Cu²⁺-complexes in the glasses was estimated qualitatively and correlated with the distribution of the strength of π-bonding between cupric ion and oxygen in the glass. Typical network modifiers and intermediates behaved differently, especially in the composition region of invert glass; the large deformation of the coordination sphere of Cu²⁺ in lead glasses due to the stronger PbO bond resulted in the large distribution of $\text{g}{}_{\mathrm{}}$. The situation was reverse in the case of soda glasses.     

Observation of chemical reaction and liquid structure of SGe by Raman spectroscopy

The measurements of the Raman spectra on liquid Ge_XS_1?X (0≤X≤0.1) were carried out. The A₁ mode of $\text{GeS}{}_{\mathrm{<mtext>4</mtext><mtext>2</mtext>}}$ (ca. 340 cm^?1) was observed in the liquids. The comparison with the spectra of liquid S suggests that Ge reacts on the polymeric species. During the chemical reaction of solid Ge and liquid S below ca. 500°C, the L.T.GeS₂ crystal growth was observed. The spectral features of the L.T.GeS₂ surprisingly resemble those of GeS glasses. The glass forming region was extended to X = 0.03 by careful rapid quenching. The overall compositional dependence of the Raman spectra of Ge_XS_1?X (0.03≤×≤0.341) was analysed in comparison with the spectra of the L.T. and the H.T. crystal and can be explained by the model that with increase of X(>ca. 0.2) the H.T. GeS₂-like spectra emerge abruptly from the L.T.GeS₂-like spectra in lower X. Standing on the model, the glassy structures in this system are discussed.     

Kinetics of the exchanges at the solid–liquid interface during the dissolution process of gallium orthophosphate

Gallium orthophosphate is a piezoelectric material with an α-quartz structure. In order to manufacture bulk acoustic wave devices (BAW), controlled chemical dissolution is often used to reduce the thickness of the piezoelectric membranes. This paper presents the kinetics of the chemical exchanges, which occur at the solid–liquid interface during the chemical dissolution of GaPO₄ in phosphoric acid. Based on chemical composition of phosphoric acid solvent, the pure dissolution rate is determined. A strong anisotropy of chemical reactivity is formed. The dissolution rate is the lowest for the crystallographic z-plane (0 0 0 1) but this orientation is the most sensitive with respect to the proton concentration and the temperature. In accordance with the crystal growth rates, the nucleation at the interface for the (1 0 2 0) plane, named X-plane, is also the most rapidly dissolved. Assuming the activation energies corresponding to dissolution and to nucleation are like standard activation energies, the different values of the standard enthalpy variation are calculated. The most important variation is obtained for the z-plane (Δ_rH=−14.3 kJ/mol) and the lowest for the X-plane (Δ_rH=−5.4 kJ/mol).     

USAXS studies of monosaccharide gels. I. Dependence of the glucofuranose-based gel structure on the gelator concentration

Glucofuranose-derivative based gels with various gelator concentration were studied using ultra-small angle X-ray scattering (USAXS) in the scattering vector range 0.0028–0.25 nm⁻¹. A complex method of data processing was applied to extract the structural parameters of the gelator, such as the mass fractal and surface fractal dimensions, d_m and d_s, respectively, the radius of gyration, R_g, the distance distribution function, p(r), as well as the volume distribution function, D(R), of particles forming aggregates. The results of these analyses show that the aggregate structure changes with the gelator concentration: when it increases, the size of the aggregates decreases, rough aggregates of the fractal type evolve to better developed smooth ones, and their shape changes from disk-like to rod-like. These results suggest that only two different types of aggregates are formed depending on the gelator concentration, and a gradual change between them is observed.     

Spectroscopy,oxidation-reduction behaviour and DC conductivity of a vanadium-containing barium aluminoborate glass

The vanadium(IV)-vanadium(V) equilibrium in a 37.5BaO, 5.0Al₂O₃, 57.5B₂O3 mol% + X mol% V₂O₅ (where X = 0.25?32.5) glass system has been studied as functions of temperature, partial pressure of oxygen and total vanadium concentration of the melt. The vanadium(V)/vanadium(IV) ratio in the melt increased with increasing partial pressure of oxygen, lowering temperature of melting, and with increasing total vanadium content of the melt. With X ? 10, the vanadium(V)/vanadium(IV) ratio became almost independent of the total vanadium content of the melt.With this knowledge of oxidation-reduction behaviour, a series of glasses containing 2.8?32.5 mol% V₂O₅ (at about 4 mol% intervals) and having a constant vanadium(IV)/vanadium(V) ratio (0.17) were prepared. Density, electronic absorption spectrum (both d-d and charge transfer transitions), and ESR of these glasses were measured. Optical and ESR spectra of these glasses indicated the vanadium(IV) to be present as vanadyl ion, VO²⁺; g| decreased monotonically with increasing vanadium content of these glasses, whereas gβ remained unchanged. The charge transfer transition energy due to vanadium(V) decreased, and the extinction coefficient increased by orders of magnitude with increasing vanadium content of the glass; the most striking changes occurred at X ≈ 10 mol%. DC conductivity of these glasses was measured at different temperatures; a plot of log (?/T) versus 1/T produced straight lines. The slope of these lines remained almost constant (39 ± 1 kcal/mol) for the glasses containing up to about 10 mol% V₂O₅; with further increase of V₂O₅ the slope decreased sharply.It has been concluded that the abrupt changes in properties like partial molar volume of V₂O₅, charge transfer spectrum of vanadium(V), activation energy of polaron hopping — all of which occurred around X ≈ 10 mol% — is due to a major change in the nature of vanadate groups rather than vanadium(IV) in these glasses.     

The thermal stability and related properties of iron-base glasses

The crystallization temperature of Fe_80?XM_XP₁₃C₇ and Fe_80?XN_XP₁₃C₇ alloys has been investigated, where M is Zr, Nb, Mo, Ru, Rh or Pd, and N is B, C, Si, P, As, Sn or Sb. Zr and Mo effectively increase T_X and Pd decreases it. The increase in crystallization temperature T_X with the concentration of elements M, is larger for the second group of periodic elements, except for the case of Pd, compared with the first group of periodic elements. The crystallization temperature is related to the average electron concentration, the atomic size and the atomic cohesive energy of the additive metal.The metalloidal elements N, except for Sn and Sb, increase the T_X of Fe_80?XN_XP₁₃C₇ alloys. In particular, the addition of B, C, Si of P definitely increases T_X and small amounts of Sn or Sb markedly decrease it. Contrary to the effects of metallic elements, the effects of metalloidal elements do not show the general trend. However, in the same group of the periodic system T_X decrease with increasing the atomic size and decreasing cohesive energies for metalloidal elements.     

X-ray diffraction study of defects in zinc-diffusion-doped silicon

Samples of CZ n-Si〈Zn〉(111) are prepared by high-temperature zinc-diffusion annealing followed by quenching and are studied by X-ray diffraction. The silicon contains an initial phosphorus impurity and zinc-compensating admixture at concentrations N _P = 1.5 × 10¹⁴ cm^?3 and N _Zn = 1 × 10¹⁴ cm^?3; i.e., the relation N _P/2 < N _Zn < N _P is fulfilled. Microdefects are studied by double- and triple-crystal X-ray diffraction in the dispersion free modes (n, ?n) and (n, ?n, +n). The samples are found to contain microdefects with two characteristic sizes (average sizes of about 1 μm and 70 nm). The interplanar distance in the near-surface layer with a thickness of 0.1 μm is smaller than this parameter in the remaining matrix, the difference being equal to d ₀ Δd/d ₀ ≈ 2 × 10^?5. This layer contains mainly vacancy-type microdefects. The angle between the reflecting planes and the local surface relief is Δψ = (7 ± 1) arcmin.     

EXAFS study on poly-Si1−XGeX films prepared by reactive thermal CVD method

Extended X-ray absorption fine structure analyses were carried out on Si_1−XGe_X films of different thicknesses, prepared by the reactive thermal chemical vapor deposition (CVD) method. From a Rutherford backscattering measurement, the Ge fraction was found to be high near the substrate interface. The Ge coordination ratio, Ge–Ge bond length and Ge–Si bond length decreased with increasing film thickness. The Ge fraction dependences of these parameters were found to be different from the results of previous studies on Si_1−XGe_X films prepared by molecular beam epitaxy. Our results are considered to be caused by the local structure formation around the Ge atoms during the reactive thermal CVD process.     

Growth and study of single crystals of Pb1 − x BaxSc0.5Nb0.5O3 solid solutions

Crystals of Pb_{1 ? x} Ba_xSc_0.5Nb_0.5O₃ solid solutions with 0 ≤ x ≤ 0.58 have been grown by the method of mass crystallization from flux. It is established that, unlike the concentration dependence of the corresponding ceramic, the concentration dependence of the temperature T _m (the maximum dielectric constant ε in crystals) does not attain saturation. Cooling of crystals with x ≤ 0.04 resulted in a spontaneous transition from the relaxor to the macrodomain ferroelectric state. In crystals with a higher barium content, the relaxor state is “locked in.”     

The crystal structure of racemicdl-penicillamine and a spectroscopic study ofd-(−)-penicillamine

The X-ray crystal structure of a racemic mixture of D- and L-penicillamine has been determined. Crystals are monoclinic,P2₁/c (No. 14), with cell dimensionsa=11.624(3),b=5.919(1),c=11.482(2) Å,β=114.48(2)°, andZ=2, based on the racemate. The structure was determined by standard methods and refined toR ₁=0.0666,R ₂=0.0726 for 985 independent reflections. Bond lengths and bond angles do not differ from those in similar structures. Mass spectra and¹H and¹³C NMR spectra are reported ford-penicillamine, and detailed infrared and Raman spectra are reported for solidd-penicillamine hydrochloride,d ₅-d-penicillamine hydrochloride,d-penicillamine,d ₄-d-penicillamine, anddl-penicillamine. The Raman spectrum ofd-penicillamine in H₂O solution as a function of pH is also reported.     

The 1:1 crystal complex of salicylic acid and urea

The 1∶1 crystal complex of salicylic acid (C₇H₆O₃) and urea (CH₄N₂O), mp 121° C, is monoclinic, with space groupC2/c (C ₂ ⁶ h, No. 15) and unit cell dimensionsa=22.206(3),b=5.108(1),c=17.177(2) Å,β=106.18(1)°.d _calc=1.407 g cm^?3,d _meas=1.41 g cm^?3 forZ=8. The structure was determined by direct methods and refined by a full-matrix least-squares procedure to giveR=0.057 andR _w =0.050 for 1652 integrated intensities above 2σ(I). The structure contains a strong OH?O hydrogen bond with O?O distance 2.54 Å in which the carboxyl OH group is donor and urea oxygen atom is acceptor. There are two NH?O intermolecular hydrogen bonds with N?O distances of 2.90 and 2.96 Å. Additionally, the salicyclic acid contains an intramolecular OH?O hydrogen bond of 2.56 Å.