Mass spectral imaging of glycophospholipids, cholesterol, and glycophorin a in model cell membranes

Time of flight secondary ion mass spectrometry (ToF-SIMS) and the Langmuir-Blodgett (LB) technique have been used to create and analyze reproducible membrane mimics of the inner and outer leaflets of a cellular membrane to investigate lipid-protein and lipid-lipid interactions. Films composed of phospholipids, cholesterol and an integral membrane protein were utilized. The results show the outer membrane leaflet mimic (DPPC/cholesterol/glycophorin A LB film) consisting of a single homogeneous phase whereas the inner membrane leaflet mimic (DPPE/cholesterol/glycophorin A LB film) displays heterogeneity in the form of two separate phases. A DPPE/cholesterol phase and a glycophorin A phase. This points to differences in membrane domain formation based upon the different chemical composition of the leaflets of a cell membrane. The reliability of the measurements was enhanced by establishing the influence of the matrix effect upon the measurement and by utlilizing PCA to enhance the contrast of the images.     

Effect of lattice topology on geminate recombination

The molecular theory of geminate recombination is applied to the simple cubic lattice, and the results compared to those obtained previously for the face-centered cubic lattice. The results demonstrate that, for corresponding molecular parameters, lattice topology is a strong determinant of recombination/dissociation efficiency. The implications of this fact for interpretation of experimental data in terms of the Onsager and other continuum approximations are noted.     

Effect of sonication on polymeric membranes

This article studies the effect of 47 kHz ultrasonic (US) waves on polymeric membranes immersed in an aqueous bath. The membranes under study are made from three different polymers: polyethersulfone (PES), polyvinylidenefluoride (PVDF) and polyacrylonitrile (PAN) and present various molecular weight cut-off (MWCO). The evolution of the polymeric structure exposed to US was followed by the measurement of the water permeability and the A_k/Δx parameter which represents the ratio of surface porosity to thickness. Results showed that important variations occurred on certain membranes after irradiation. In addition, microscopic imaging using field emission electron scanning microscopy (FESEM) was performed on irradiated membranes in order to visualize the nature of the degradation. An image analysis method gives the evolution of the pore density, porosity and pore size distribution of a homogeneous area of this membrane before and after irradiation.It has been shown that, over the three materials tested, only the PES is affected by the ultrasonic treatment over all its surface, whereas the others present no significant change in the measured parameters except the PAN (50 kDa) and PVDF (40 kDa) membranes whose edges are affected. In conclusion, in spite of their great efficiency in enhancing filtration processes, ultrasonic waves have to be used with care as the polymeric material itself is sensitive to the ultrasonic waves at the chosen frequency.     

Effect of sulfadiazine on biological model membranes

Summary In this paper the optimization of the kaolin calcination is studied, aiming at using the produced metakaolin as supplementary cementitious material. Representative samples of poor Greek kaolin (Milos island) and a high purity commercial kaolin were tested. Samples were heated at different temperatures during different times. The optimization of calcination conditions was studied by DTA-TG and XRD analysis of the raw and thermal treated kaolin samples, by pozzolanic activity analysis of metakaolins and finally by strength development analysis of cement-metakaolin mixtures. This approach showed that heating at 650°C for 3 h is efficient to convert poor kaolins with low alunite content to highly reactive metakaolins. However in the case of kaolin with a high alunite content, thermal treatment at 850°C for 3 h is required in order to remove undesirable SO₃. Evidence was found that poor kaolins can be efficiently used for the production of highly reactive metakaolins.     

Effect of mechanical treatment on the silicate lattice of kaolinite

X-ray diffraction, differential thermal and chemical analysis have been used to investigate the effect of mechanical treatment on the crystalline lattice of kaolinite. It was established that mechanical treatment leads to amorphization of the mineral and the release of hydroxyl water, but the continuity of kaolinite??s silicate lattice remains intact despite certain deformations, and the phase transformations of the mineral thus occur without any noticeable change in temperature.     

Effect of expanded graphite lattice in exfoliated graphite nanofibers on hydrogen storage

A graphite exfoliation technique, using intercalation of a concentrated sulfuric/nitric acid mixture followed by a thermal shock, has successfully exfoliated a herringbone graphite nanofiber (GNF). The exfoliated GNF retains the overall nanosized dimensions of the original GNF, with the exfoliation temperature determining the degree of induced defects, lattice expansion, and resulting microstructure. High-resolution transmission electron microscopy indicated that the fibers treated at an intermediate temperature of 700 degrees C for 2 min had dislocations in the graphitic structure and a 4% increase in graphitic lattice spacing to 3.5 A. The fibers treated at 1000 degrees C for 36 h were expanded along the fiber axis, with regular intervals of graphitic and amorphous regions ranging from 0.5 to >50 nm in width. The surface area of the starting material was increased from 47 m(2)/g to 67 m(2)/g for the 700- degrees C treatment and to 555 m(2)/g for the 1000- degrees C treatment. Hydrogen uptake measurements at 20 bar indicate that the overall hydrogen uptake and operative adsorption temperature are sensitive to the structural variations and graphitic spacing. The increased surface area after the 1000- degrees C treatment led to a 1.2% hydrogen uptake at 77 K and 20 bar, a 3-fold increase in hydrogen physisorption of the starting material. The uptake of the 700- degrees C-treated material had a 0.29% uptake at 300 K and 20 bar; although low, this was a 14-fold uptake over the starting material and higher than other commonly used pretreatment methods that were tested in parallel. These results suggest that selective exfoliation of a nanofiber is a means by which to control the relative binding energy of the hydrogen interaction with the carbon structure and thus vary the operative adsorption temperature.     

Anisotropic spin lattice relaxation of triplet quinoxaline in a naphthalene host crystal at high magnetic field

The spin lattice relaxation in the excited triplet state of quinoxaline molecules in a perdeutero-naphthalene host crystal was investigated at high magnetic field (B = 5 T) between T = 1.7 K and T = 4.2 K. Relaxation rates were deduced from the non-monoexponential phosphorescence decay of the individual Zeeman sublevels. Besides the so far investigated Δm = 1 transition the Δm = 2 transition was observed and attributed to a purely direct process. Its anisotropy is different to that of the Δm = 1 direct process at 1.7 K. The temperature effect upon Δm = 1 relaxation anisotropy is discussed.     

Bilayer vesicles of amphiphilic cyclodextrins: host membranes that recognize guest molecules

A family of amphiphilic cyclodextrins (6, 7) has been prepared through 6-S-alkylation (alkyl=n-dodecyl and n-hexadecyl) of the primary side and 2-O-PEGylation of the secondary side of alpha-, beta-, and gamma-cyclodextrins (PEG=poly(ethylene glycol)). These cyclodextrins form nonionic bilayer vesicles in aqueous solution. The bilayer vesicles were characterized by transmission electron microscopy, dynamic light scattering, dye encapsulation, and capillary electrophoresis. The molecular packing of the amphiphilic cyclodextrins was investigated by using small-angle X-ray diffraction of bilayers deposited on glass and pressure-area isotherms obtained from Langmuir monolayers on the air-water interface. The bilayer thickness is dependent on the chain length, whereas the average molecular surface area scales with the cyclodextrin ring size. The alkyl chains of the cyclodextrins in the bilayer are deeply interdigitated. Molecular recognition of a hydrophobic anion (adamantane carboxylate) by the cyclodextrin vesicles was investigated by using capillary electrophoresis, thereby exploiting the increase in electrophoretic mobility that occurs when the hydrophobic anions bind to the nonionic cyclodextrin vesicles. It was found that in spite of the presence of oligo(ethylene glycol) substituents, the beta-cyclodextrin vesicles retain their characteristic affinity for adamantane carboxylate (association constant K(a)=7.1 x 10(3) M(-1)), whereas gamma-cyclodextrin vesicles have less affinity (K(a)=3.2 x 10(3) M(-1)), and alpha-cyclodextrin or non-cyclodextrin, nonionic vesicles have very little affinity (K(a) approximately 100 M(-1)). Specific binding of the adamantane carboxylate to beta-cyclodextrin vesicles was also evident in competition experiments with beta-cyclodextrin in solution. Hence, the cyclodextrin vesicles can function as host bilayer membranes that recognize small guest molecules by specific noncovalent interaction.     

Ionic structures as intercalation compound host lattices. An ab initio perturbed ion study on lattice stretching

The effect of lattice expansion along one axis on lattice energy has been analyzed from a theoretical viewpoint. Thirteen ionic structures (LiF, NaF, NaCl, MgO, CsF, CsCl, TiO₂, ZrO₂ (m), ZrO₂ (t), ZrO₂ (c), CaF₂, SrTiO₃ and KMgF₃) have been considered due to their role as potential host lattices for intercalation compounds of the CsF·Br₂ type. Their structural parameters have been optimized and lattice energies evaluated by means of the ab initio perturbed ion method. Results indicate that the most easily stretchable structures based on energy requirements and therefore the best suited as host lattices in this kind of intercalation compound, are those with a rock salt or perovskite type of structure, particularly those formed by low charge ions.     

Controlling disorder in host lattice by hetero-valence ion doping to manipulate luminescence in spinel solid solution phosphors

Phosphor materials have been rapidly developed in the past decades. Developing phosphors with desired properties including strong luminescence intensity and long lifetime has attracted widespread attention. Herein, we show that hetero-valence ion doping can serve as a potent strategy to manipulate luminescence in persistent phosphors by controlling disorder in the host lattice. Specifically, spinel phosphor Zn(Ga_(1-x)Zn_x)(Ga_(1-x)Ge_x)O_4:Cr is developed by doping ZnGa_2O_4:Cr with tetravalent Ge~(~(4+)).Compared to the original ZnGa_2O_4:Cr, the doped Zn(Ga_(1-x)Zn_x)(Ga_(1-x)Ge_x)O_4:Cr possesses significantly enhanced persistent luminescence intensity and prolonged decay time. Rietveld refinements show that Ge~(4+)enters into octahedral sites to substitute Ga~(3+), which leads to the co-substitution of Ga~(3+) by Zn~(2+) for charge compensation. The hetero-valence substitution of Ga~(3+) by Ge~(4+)and Zn~(2+) enriches the charged defects in Zn(Ga_(1-x)Zn_x)(Ga_(1-x)Ge_x)O_4:Cr, making it possible to trap large amounts of charge carriers within the defects during excitation. Electron paramagnetic resonance measurement further confirms that the amount of Cr~(3+) neighboring charged defects increases with Ge~(4+)doping. Thus charge carriers released from defects can readily combine with the neighboring Cr~(3+) to produce bright persistent luminescence after excitation ceases. The hetero-valence ion doping strategy can further be employed to develop many other phosphors and contributes to lighting, photocatalysis and bioimaging.     

Effect of surfactants on the structure of PMMA membranes

In this work, the role played by surfactants in the formation of PMMA membranes was investigated. For a wet inversion process with PMMA as polymer, acetone as solvent, and water as coagulant, delayed demixing was observed and the resulting membrane possessed a sponge-like structure. Adding 1.8 vol% of Tween 80 in the casting solution (PMMA + acetone) could shift the PMMA/acetone/water system from delayed demixing to instantaneous demixing and could induce macrovoids with small pin-holes on the membrane surface. It was found that the affinity of surfactant for coagulant is crucial for the enhancement of the formation of macrovoids. When water was the coagulant, adding the surfactants with high water solubility in PMMA/acetone solution can enhance the formation of macrovoids while adding the surfactants with low water solubility has no effect. On the other hand, for a lipophilic coagulant such as n-hexane, lipophilic surfactants were more effective in changing membrane structure than hydrophillic surfactants. In addition, a mechanism describing the role of surfactants in the formation of macrovoids is proposed: the addition of appropriate surfactants can enhance the affinity between solvent and coagulant, resulting in a shift from delayed demixing to instantaneous demixing, and macrovoids can then be induced.     

Effect of lattice defects on the annealing of γ-irradiation damage in strontium bromate

The role of lattice defects introduced by crushing and doping on the annealing of chemical radiation damage in strontium bromate has been investigated. Crushing of irradiated crystals produces direct recovery and also accelerates the subsequent thermal annealing. The initial damage and the susceptibility to thermal annealing are greater in the doped crystals than that in the untreated samples.     

EPR spectroscopy on irradiated nickel tetracyanide in NaCl host lattice: mechanism for the simultaneous formation of reduced and oxidized species

The kinetics of oxidized and reduced Ni²⁺ complexes produced by X-ray irradiation on single crystals of NaCl doped with [Ni(CN)₄]²⁻ is studied by Electron Paramagnetic Resonance at room temperature. The interdependent generation of these two complexes is attributed to migration of the charge compensating vacancy from the reduced to the oxidized complex in a reversible reaction. At higher X-ray doses, there is a predominant formation of the reduced complex.     

Effect of non-central interactions on energy and lattice dynamics of molecular crystals

Atom-atom, multipole-multipole and three-body potentials have been used to calculate the energy and lattice dynamics of β-paradichlorobenzene, phenanthrene and m-chloronitrobenzene. Non-central interactions are shown to give a significant contribution to the intermolecular interaction energy but have little effect on the phonon spectrum of the crystals.     

Effect of positive background on the ground-state energy of a Wigner lattice

An attempt has been made to study the effect of a nonuniform positive background on the ground-state energy of a nonmagnetic Wigner lattice. The background is modified with a variable “ripple” parameter in the background charge, represented by a Yukawa-type charge distribution. Our calculation shows that a Yukawa-type background leads to a lower ground-state energy value compared to a Gaussian-type and constant positive background. © 1993 John Wiley & Sons, Inc.     

Interaction between glycophorin and phospholipids in recombined systems.

Both the MN-glycoprotein from human erythrocytes and the hydrophobic fragment from the protein isolated with trypsin treatment, T(is), have been recombined with egg phosphatidylcholine in bilayers at various phospholipid/protein ratios. In order to investigate the effect of the protein on the phospholipid headgroups, 31P nuclear magnetic resonance spectra were obtained with the MN-glycoprotein recombined with egg phosphatidylcholine, which revealed two classes of phospholipid environments, one immobilized and one not immobilized. Electron spin resonance (ESR) of fatty acid methyl ester spin labels provided supporting evidence. Computer analysis of the ESR spectra indicate that 4-5 moles of phospholipid are immobilized per mole of protein over a wide range of lipid-to-protein ratios. The immobilization of the phospholipids appears mediated by both the polar headgroups and the hydrocarbon tails of the phospholipid.