Sensing biological effectors through the response of bridged nucleic acids and polynucleotides fixed in liquid-crystalline dispersions

The formation of three-dimensional structures of double-stranded nucleic acid and polynucleotide molecules, fixed in the structure of liquid-crystalline dispersions and bridged by polymeric chelate complexes is described. The bridging elements consist of alternating daunomycin molecules and copper ions. It is shown that these bridges between nucleic acid molecules stabilize cholesteric structures of the DNA liquid-crystalline dispersion. The formation of polymeric chelate bridges is accompanied by a remarkable increase of the intense circular dichroism (CD) band characteristic of the DNA-daunomycin cholesterics. These bridges are destabilized by a number of biologically relevant compounds and macromolecules, such as ascorbic acid, homocarnosine, bovine serum albumin and lysozyme. The dramatic change in the optical activity of the liquid-crystalline dispersions upon addition of these compounds makes them easily detectable. The sensitivity of the method, in the range of analytic concentration 10(-4)-10(-8) M, depends on the nature of the compound being tested. The response of bridged DNA structures to biological effectors observed here foresees their further development as biosensor devices for detecting the presence of biologically and pharmacologically relevant compounds.     

Structure and fracture of superelastic hard carbon materials produced from fullerites under pressure

The composition and size of fullerites and the structures and fracture surfaces of superelastic hard carbon phase (SHP) particles made from them and reinforcing metal-matrix composite materials are studied by optical microscopy, X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. An inheritance relationship is shown to exist between the optically anisotropic structure of SHP formed under pressure at temperatures above the stability threshold of fullerene molecules and the structure of the original fullerites. The fractographic features of the SHP particles made from C60 fullerenes correlate with a deformed structure of fcc fullerites, whereas the particles made from a soot extract of fullerenes have a fracture surface characteristic of amorphous materials. Reinforcing with SHP particles increases the wear resistance of cobalt by several orders of magnitude and simultaneously decreases its friction coefficient. This effect is most pronounced upon reinforcing by the particles produced from a soot extract of fullerenes.     

Membrane packing geometry of diphytanoylphosphatidylcholine is highly sensitive to hydration: phospholipid polymorphism induced by molecular rearrangement in the headgroup region

Diphytanoylphosphatidylcholine (DPhPC) has often been used in the study of protein-lipid interaction and membrane channel activity, because of the general belief that it has high bilayer stability, low ion leakage, and fatty acyl packing comparable to that of phospholipid bilayers in the liquid-crystalline state. In this solid-state 31P and 2H NMR study, we find that the membrane packing geometry and headgroup orientation of DPhPC are highly sensitive to the temperature studied and its water content. The phosphocholine headgroup of DPhPC starts to change its orientation at a water content as high as approximately 16 water molecules per lipid, as evidenced by hydration-dependent 2H NMR study at room temperature. In addition, a temperature-induced structural transition in the headgroup orientation is detected in the temperature range of approximately 20-60 degrees C for lipids with approximately 8-11 water molecules per DPhPC. Dehydration of the lipid by one more water molecule leads to a nonlamellar, presumably cubic, phase formation. The lipid packing becomes a hexagonal phase at approximately 6 water molecules per lipid. A phase diagram of DPhPC in the temperature range of -40 degrees C to 80 degrees C is thus constructed on the basis of NMR results. The newly observed hydration-dependent DPhPC lipid polymorphism emphasizes the importance of molecular packing in the headgroup region in modulating membrane structure and protein-induced pore formation of the DPhPC bilayer.     

Micropellicular stationary phases for high-performance liquid chromatography of double-stranded DNA

The central role of nucleic acids in biosciences has effectuated the rapid development of numerous techniques for their isolation, separation, characterization and quantitation. Advances in high-performance liquid chromatography, particularly the introduction of novel microparticulate sorbents, have greatly promoted the separation and quantitation of nucleic acids. Because of their favorable mass transfer properties, micropellicular packing materials are advantageous for fast and high-resolution separations of double-stranded (ds) DNA molecules. With micropellicular packings, anion-exchange and ion-pair reversed-phase chromatography are the most popular chromatographic separation modes for dsDNA. The effective separation mechanisms in both chromatographic techniques are preferably described by nonstoichiometric models, that are founded on a better physicochemical background than traditional stoichiometric models. Column efficiency, retention characteristics, and size or sequence dependency of retention of dsDNA are greatly influenced by the chosen operational variables in both chromatographic modes. The applicability of HPLC with micropellicular stationary phases nucleic acids research includes preparative DNA fractionation, DNA restriction mapping, analysis of polymerase chain reaction products and purification of plasmid DNA.     

Effect of refractory nanoparticles on the structural modification of metal-matrix composites

The structure and tribological behavior of composite materials (CMs) filed by dispersed particles and based on aluminum alloys grown by reactive casting with titanium microparticles and SiC nanoparticles or synthetic diamond mixed to the melt have been studied. The composition, size, and volume fraction of the strengthening phases are determined by optical microscopy and x-ray diffraction. The hardness of the CMs is measured. The tribological properties of the CMs are tested during dry friction on a rider made of grade 45 steel. Alloying nanoparticles are shown to affect the morphology, volume fraction, and sizes of the strengthening phases formed in the CMs. The main phases in the CMs are intermetallic compounds Al₃Ti, Al₂₄Ti₉, and AlTi. The introduction of SiC nanoparticles in a CM causes the formation of TiSi₂ (<1%) particles, whereas TiC carbides (<1%) form in a CM containing diamond nanoparticles. CM-steel friction interaction causes the formation of intermediate layers consisting of mechanical mixtures with an ultrafine-grained structure between the sliding surfaces. Their effect on the stable-friction range is discussed.     

Aging processes in precipitation-hardening composite materials based on a D16 aluminum alloy

Aging of composite materials (CMs) based on an aluminum D16 alloy and reinforced by Al₃Ti intermetallic inclusions (0–10 vol %) having formed upon an in situ reaction and by SiC particles (0–30 vol %) ≤3 or 28 μm in size is studied. Oxide ceramic nanoparticles (0.1 wt %) are used to modify the structure of the CMs. The structures of the CMs before and after aging are analyzed by optical microscopy and scanning electron microscopy on a microscope equipped with an X-ray energy dispersive spectrometer. The hardness of the CMs is measured. The overall hardening of aged CMs is shown to result from a competition between the hardening effects induced by the formation of Guinier-Preston zones and the precipitation of the high-temperature θ and S phases. These effects are controlled by the dislocation density in the matrix.     

Synthesis of YAG:Ce3+ Phosphor by Polyacrylamide Gel Method and Promoting Action of α-Al2O3 Seed Crystal on Phase Formation

YAG:Ce3 phosphor particles were prepared using polyacrylamide gel method. The structure evolution of powders during annealing process was followed by X-ray diffraction determination. It is found that some intermediate phases, including θ-Al2O3, YAM and YAP, are formed when calcining polyacrylamide gel, however, the pure YAG phase can be formed directly when calcining polyacrylamide gel with α-Al2O3 as seed crystal. These facts show that the existence of α-Al2O3 seed crystal can block the formation of θ-Al2O3, YAM and YAP, and accelerate its reaction with Y2O3 to form YAG phase directly at lower temperature. The emission peak of prepared YAG:Ce3 phosphor is wide with maximum at 550 nm and the exitation band has two peaks, the major one is around at 460 nm, which matches the blue emission of GaN LED and is suitable for the assemble of white LED. Some fluxes can enhance the photoluminescence intensity of phosphor particles, that can be attributed both to the improvement of crystallization processes of YAG and to the stabilization of trivalence cerium ion in YAG:Ce3 .     

Analysis of the stability of mutant lysozymes at position 15 using X-ray crystallography

His 15 of hen lysozyme is located at the protein surface and is partly buried by the neighboring residues. The side chain of His 15 forms hydrogen bonds with surrounding residues and these hydrogen bonds are somewhat buried. A series of mutant lysozymes at the position 15 (Gly, Ala, Val, and Phe) was prepared, and their stabilities were analyzed by GdnHCl denaturation and X-ray crystallography. The mutants were less stable than the wild type at pH 5.5 and 35 degrees C. In H15G and H15A, X-ray crystallography revealed two fixed water molecules at the mutated region, which formed similar hydrogen bonds to those in the wild type. On the other hand, it was suggested that the hydrogen bonds were disrupted and that several unfavorable van der Waals' contacts occurred in H15V and H15F. Therefore, we concluded that His 15 stabilized the lysozyme structure by forming hydrogen bonds and the best packing with the neighboring residues. Moreover, we found that the method of protein stabilization by increasing the hydrophobicity of an amino acid residue was not always effectively applicable, especially when the residue had formed a hydrogen bond.     

Precursor Dependent Structural Phase Evolution in Hydrothermally Prepared Cu<Subscript>2</Subscript>O Octahedrons and Cu Micro-Flakes and Their Structural and Optical Properties

Cuprous oxide (Cu₂O) and metallic copper particles with different microstructures have been prepared by a single-step hydrothermal method by using copper acetate monohydrate and sodium hydroxide as precursors, d-glucose as reducing agent, and poly (vinylpyrrolidone) as stabilizing agent. It was found that the concentration of the NaOH in the reactant solution played a significant role in the structural phase formation of the product. Further, it was also optimized to get either the single phase of Cu₂O or Cu or the mixed phase of Cu₂O and Cu depending on the NaOH content in the reaction mixture. The product material was systematically investigated by x-ray diffraction (XRD), Rietveld refinement, UV–Vis, Raman spectroscopies, scanning electron microscopy (SEM), and X-ray energy dispersive spectroscopy (XEDS). A thorough analysis of the XRD patterns in a standard method as well as by Rietveld refinement have shown the cubic phases for both Cu₂O and Cu. The same phases have been retained in the mixed phase sample also. Optical band gap was determined through Tauc plot to be 1.95 eV. Microstructural studies by SEM showed that the Cu particles were formed as micro flakes whereas the Cu₂O particles were formed with the well-defined octahedral morphology. The XEDS analysis confirmed the chemical composition in Cu₂O. This work reports the dependence of NaOH concentration in the reactant solution on the type of product (single phase or a mixed phases of Cu₂O and Cu) and their structural and optical properties.     

Allele frequencies of six highly polymorphic DNA loci in the Croatian population

The organization of synthetic oligopeptide trivaline (1) complexes with four types of circular superhelical DNA preparations was studied by electron microscopy. The DNA molecules in the preparations investigated had different sizes ranging from 2.9 kb to 21.0 kb. Two plasmids contained bent DNA sequences from minicircles of kinetoplast DNA of Leishmania gymnodactili and Trypanosoma boissoni. The main structures in all preparations observed were circular compact particles which coincide in their appearance and compaction coefficient (3,5-3,7) with triple rings described earlier. But along with triple rings the new types of compact structures were observed having the shape of a ring with attached rod or the shape of two compact rings attached to each other by a region of compact fiber. The latter structures could be observed in significant quantities in case of DNA preparations longer than 10 kb. The conclusions can be made that due to TVP stimulated compaction of circular DNA molecules compact fibers containing both two or three DNA duplexes arranged side by side can be formed. It is shown that presence of bent DNA sequences stimulates the formation of structures containing more than one triple ring. It demonstrates the possibility of the primary DNA structure influence on the compaction process in case of the circular molecules. The new ways of circular DNA folding described can be of importance for understanding of DNA organization in different cell structures.     

In vitro assembly properties of human immunodeficiency virus type 1 Gag protein lacking the p6 domain

Human immunodeficiency virus type 1 (HIV-1) normally assembles into particles of 100 to 120 nm in diameter by budding through the plasma membrane of the cell. The Gag polyprotein is the only viral protein that is required for the formation of these particles. We have used an in vitro assembly system to examine the assembly properties of purified, recombinant HIV-1 Gag protein and of Gag missing the C-terminal p6 domain (Gag Deltap6). This system was used previously to show that the CA-NC fragment of HIV-1 Gag assembled into cylindrical particles. We now report that both HIV-1 Gag and Gag Deltap6 assemble into small, 25- to 30-nm-diameter spherical particles in vitro. The multimerization of Gag Deltap6 into units larger than dimers and the formation of spherical particles required nucleic acid. Removal of the nucleic acid with NaCl or nucleases resulted in the disruption of the multimerized complexes. We conclude from these results that (i) N-terminal extension of HIV-1 CA-NC to include the MA domain results in the formation of spherical, rather than cylindrical, particles; (ii) nucleic acid is required for the assembly and maintenance of HIV-1 Gag Deltap6 virus-like particles in vitro and possibly in vivo; (iii) a wide variety of RNAs or even short DNA oligonucleotides will support assembly; (iv) protein-protein interactions within the particle must be relatively weak; and (v) recombinant HIV-1 Gag Deltap6 and nucleic acid are not sufficient for the formation of normal-sized particles.     

Microstructural changes on the reduction of imperial smelting furnace sinters

The reduction reactions of Imperial Smelting Furnace (ISF) sinter microstructure were investigated in simulated zinc blast furnace conditions. Initial and partially reduced samples were examined using optical, electron-probe microanalysis, scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX), and X-ray diffraction (XRD) to characterize the struc-tural and compositional changes occurring during the reduction reaction. The reaction mecha-nisms and reduction sequences for the various oxide phases within the sinter structure during reduction of ISF sinters under the system studied are discussed. The reduction of sinters resulted in the structural modification of zincite, franklinite, slag phases, and the formation of new oxide and metallic phases. The rate and sequence of these complex phase transformations were found to be dependent upon reduction time, temperature, and the reacting gas composition.     

A Study of the Effect of Nanosized Particles on Transient Liquid Phase Diffusion Bonding Al6061 Metal–Matrix Composite (MMC) Using Ni/Al2O3 Nanocomposite Interlayer

Transient liquid phase (TLP) diffusion bonding of Al-6061 containing 15 vol pct alumina particles was carried out at 873 K (600 °C) using electrodeposited nanocomposite coatings as the interlayer. Joint formation was attributed to the solid-state diffusion of Ni into the Al-6061 alloy followed by eutectic formation and isothermal solidification of the joint region. An examination of the joint region using an electron probe microanalyzer (EPMA), transmission electron microscopy (TEM), wavelength-dispersive spectroscopy (WDS), and X-ray diffraction (XRD) showed the formation of intermetallic phases such as Al₃Ni, Al₉FeNi, and Ni₃Si within the joint zone. The result indicated that the incorporation of 50 nm Al₂O₃ dispersions into the interlayer can be used to improve the joint significantly.     

Characterization of dispersed intermetallic phases in rapidly quenched Al-Ti-Ce alloys

The microstructures of Al-3Ti-lCe (wt pct) and Al-5Ti-5Ce alloys melt-spun under controlled He atmosphere have been characterized using analytical electron microscopy. The rapidly solidified microstructures comprise uniform, fine-scale dispersions of intermetallic phase in an aluminum matrix, and particular attention has been given to identification of the dispersed phases. In the Al-3Ti-lCe alloy, the dispersed particles are polycrystalline with a complex twinned substructure and a diamond cubic crystal structure(a _o =1.44 ±0.01 nm) and composition consistent with the ternary compound Al₂₀Ti₂Ce (Al₁₈Cr₂Mg₃ structure type, space group Fd3m). In the Al-5Ti-5Ce alloy, there is, in addition to the dispersed ternary phase, a separate uniform array of fine-scale particles of the binary compound Al₁₁Ce₃. The majority of such particles have the body-centered orthorhombic structure of the low-temperature polymorph, α-Al₁₁Ce₃, but there is evidence to suggest that at least some particles developvia initial formation of the high-temperature body-centered tetragonal phase, β-Al₁₁Ce₃. The accumulated evidence suggests that both binary and ternary particles formed as primary phases directly from the melt during rapid solidification, leaving only small concentrations of solute in aluminum matrix solid solution. Both phases are observed to be resistant to coarsening for up to 240 hours at 400 °C. Formerly Research Fellow, Department of Materials Engineering, Monash University.     

How Suspended Particles Affect Surface Morphology in Powder Mixed Electrical Discharge Machining (PMEDM)

The effect of SiC powder mixing into the dielectric liquid on surface topology and structure of interstitial free (IF) steel has been studied. Four process parameters, namely pulse duration, pulse current, concentration of powder, and type of dielectric liquid material, have been selected as varying parameters. Surface modifications due to suspended SiC particles were identified by using optical, scanning electron microscopy, and X-ray diffraction analysis. It was observed that suspended particles around discharge column accelerated and gained sufficient velocity to penetrate to the molten pool before solidification by means of electrophoresis and negative pressure induced after cessation of a discharge, which leads a surface embedded with added fine particles under that prevent formation of penetrating cracks during machining. However, surface cracks that formed due to high transformational stresses developed during solidification were found to be unaffected by means of mechanical action of the particles.     

Influence of rare-earth metals on the high-temperature strength of Ni<Subscript>3</Subscript>Al-based alloys

The influence of the content of reaction- and surface-active alloying elements (rare-earth metals (REMs)) and the method of their introduction into cast high-temperature γ′-Ni₃Al-based intermetallic alloys, which are thermally stable natural eutectic composites, on their structure-phase state and the mechanical properties is studied. The life of low-alloy heterophase γ′ + γ cast high-temperature light Ni₃Al-based alloys is shown can be increased at temperatures exceeding 0.8T _m (T _m is the melting temperature of Ni3Al) due to additional stabilization of the single-crystal structure of these alloys with submicron and nanometer-sized particles of the phases formed by refractory and active REMs. It is also shown that stage-by-stage fractional introduction of all components into alloys during vacuum induction melting with allowance for their reaction activities (most refractory metals are introduced in the form of low-melting-point master alloys at the first stage of vacuum induction melting, and lanthanum is introduced with a master alloy in the optimal contents of 0.1–2 wt % into the charge of VKNA-1V and VKNA-25 alloys at the final stage) leads to the formation of a modified structure stabilized by nanoprecipitates of nickel and aluminum lanthanides and the phases formed by refractory metals. This method increases the life of VKNV-1V-type alloys (0.5 wt % Re) at 1000–1200°C by a factor of ∼1.7 and that of VKNA-25-type alloys (1.2 wt % Re and Co) by a factor of ∼3.     

Characterization of dispersed intermetallic

The microstructures of Al-3Ti-lCe (wt pct) and Al-5Ti-5Ce alloys melt-spun under controlled He atmosphere have been characterized using analytical electron microscopy. The rapidly so- lidified microstructures comprise uniform, fine-scale dispersions of intermetallic phase in an aluminum matrix, and particular attention has been given to identification of the dispersed phases. In the Al-3Ti-lCe alloy, the dispersed particles are polycrystalline with a complex twinned substructure and a diamond cubic crystal structure (α _o = 1.44 ± 0.01 nm) and composition consistent with the ternary compound Al₂₀Ti₂Ce (Al₁₈Cr₂Mg₃ structure type, space group Fd3m). In the Al-5Ti-5Ce alloy, there is, in addition to the dispersed ternary phase, a separate uniform array of fine-scale particles of the binary compound Al₁₁Ce₃. The majority of such particles have the body-centered orthorhombic structure of the low-temperature polymorph, α-Al₁₁Ce₃, but there is evidence to suggest that at least some particles developvia initial formation of the high-temperature body-centered tetragonal phase, β-Al₁₁Ce₃. The accumulated evidence sug- gests that both binary and ternary particles formed as primary phases directly from the melt during rapid solidification, leaving only small concentrations of solute in aluminum matrix solid solution. Both phases are observed to be resistant to coarsening for up to 240 hours at 400 °C. Formerly Research Fellow, Department of Materials Engineering,     

In vitro pharmacology of cryptophycin 52 (LY355703) in human tumor cell lines

Besides parenteral delivery, polymeric nanoparticles have been used for oral drug delivery. In this study, model polymeric nanoparticles (aqueous colloidal polymer dispersions: Eudragit(R) RL 30D, L 30D, NE 30D, or Aquacoat(R)) with different physicochemical properties were incorporated into various solid dosage forms (granules, tablets, pellets or films). The compatibility of the nanoparticles with commonly used tabletting excipients and the redispersibility of the nanoparticles after contact of the solid dosage forms with aqueous media were investigated. Ideally, the nanoparticles should be released from the solid dosage forms with their original properties. The addition of polymeric binders (e.g. polyvinylpyrrolidone, Na carboxymethylcellulose or hydroxypropyl methylcellulose) to the aqueous nanoparticle dispersions prior to wet granulation resulted in phase separation (depletion or bridging flocculation) for many nanoparticle/binder systems. Two critical parameters for the complete redispersibility/release of the nanoparticles with the original particle size properties from the solid dosage forms were a (1) high minimum film formation temperature (MFT) of the polymer dispersion and (2) a good wettability of the dried polymeric nanoparticles. Nanoparticle dispersions with a low MFT were not redispersible, they coalesced into larger agglomerates/films during the drying step. Contact angle measurements correlated well with the redispersibility of the nanoparticles, with ethylcellulose particles having high contact angles and poor redispersibility and Eudragit(R) RL, a polymer stabilized with quaternary ammonium groups, having low contact angles and good redispersibility.     

Exchange and aggregation in dispersions of dimyristoyl phosphatidylcholine vesicles containing myristic acid

Processes occurring in dispersions of dimyristoyl phosphatidylcholine containing myristic acid have been studied by light scattering of dilute dispersions (concn. less than or equal to 1 mg/ml) at temperatures above and below the phase transition temperatures of these dispersions. The transition temperatures increase with increasing mol fraction of myristic acid. Above these temperatures, vesicles with different mol fractions of myristic acid exchange lipid molecules. The exchange process leads to vesicles having phase transition temperatures and radii, which ar both intermediate between the initial transitions and radii, respectively. In contrast with the observations above the phase transitions, it was found that when dimyristoyl phosphatidylcholine/myristic acid vesicles were cooled to a few degrees below the phase transition, larger particles were formed. These observations are consistent with a mechanism consisting of vesicle aggregation followed by fustion of the aggregated vesicles. The aggregation process is of second order in the vesicle concentration, and its rate increases with increasing mol fraction of myristic acid.     

Characterization of dispersed intermetallic Phases in Rapidly Quenched Al-Ti-Ce Alloys

The microstructures of Al-3Ti-lCe (wt pct) and Al-5Ti-5Ce alloys melt-spun under controlled He atmosphere have been characterized using analytical electron microscopy. The rapidly so- lidified microstructures comprise uniform, fine-scale dispersions of intermetallic phase in an aluminum matrix, and particular attention has been given to identification of the dispersed phases. In the Al-3Ti-lCe alloy, the dispersed particles are polycrystalline with a complex twinned substructure and a diamond cubic crystal structure (α _o = 1.44 ± 0.01 nm) and composition consistent with the ternary compound Al₂₀Ti₂Ce (Al₁₈Cr₂Mg₃ structure type, space group Fd3m). In the Al-5Ti-5Ce alloy, there is, in addition to the dispersed ternary phase, a separate uniform array of fine-scale particles of the binary compound Al₁₁Ce₃. The majority of such particles have the body-centered orthorhombic structure of the low-temperature polymorph, α-Al₁₁Ce₃, but there is evidence to suggest that at least some particles developvia initial formation of the high-temperature body-centered tetragonal phase, β-Al₁₁Ce₃. The accumulated evidence sug- gests that both binary and ternary particles formed as primary phases directly from the melt during rapid solidification, leaving only small concentrations of solute in aluminum matrix solid solution. Both phases are observed to be resistant to coarsening for up to 240 hours at 400 °C.