Origin of the nonadhesive properties of fibrinogen matrices probed by force spectroscopy

The deposition of a multilayered fibrinogen matrix on various surfaces results in a dramatic reduction of integrin-mediated cell adhesion and outside-in signaling in platelets and leukocytes. The conversion of a highly adhesive, low-density fibrinogen substrate to the nonadhesive high-density fibrinogen matrix occurs within a very narrow range of fibrinogen coating concentrations. The molecular events responsible for this transition are not well understood. Herein, single-cell and molecular force spectroscopy were used to determine the early steps in the formation of nonadhesive fibrinogen substrates. We show that the adsorption of fibrinogen in the form of a molecular bilayer coincides with a several-fold reduction in the adhesion forces generated between the AFM tip and the substrate as well as between a cell and the substrate. The subsequent deposition of new layers at higher coating concentrations of fibrinogen results in a small additional decrease in adhesion forces. The poorly adhesive fibrinogen bilayer is more extensible under an applied tensile force than is the surface-bound fibrinogen monolayer. Following chemical cross-linking, the stabilized bilayer displays the mechanical and adhesive properties characteristic of a more adhesive fibrinogen monolayer. We propose that a greater compliance of the bi- and multilayer fibrinogen matrices has its origin in the interaction between the molecules forming the adjacent layers. Understanding the mechanical properties of nonadhesive fibrinogen matrices should be of importance in the therapeutic control of pathological thrombosis and in biomaterials science.     

Isomorphous substitutions of rare earth elements for calcium in synthetic hydroxyapatites

Polycrystalline hydroxyapatites Ca(10-x)REE(x)(PO(4))(6)(OH)(2-x)O(x) were synthesized and studied by X-ray powder diffraction, infrared absorption, diffuse-reflectance spectroscopy, and thermogravimetry. The solubility limits x(max) of rare earth elements (REE) in Ca hydroxyapatites decreases with an increasing REE atomic number from x(max) = 2.00 for La, Pr, and Nd to x(max) = 0.20 for Yb at 1100 °C. Refinements of X-ray diffraction patterns by the Rietveld method show that REE atoms substitute for Ca preferentially at the Ca(2) sites of the apatite structure. The substitution decreases the Ca(2)-O(4) atomic distances in the calcium coordination polyhedra and increases the Ca(2)-O(1,2,3) distances. This observation shows that interatomic distances depend not only on radii of the ions involved in the substitution but also on their charges.     

A model proton-transfer system in the condensed phase: NH4(+)OOH(-), a crystal with short intermolecular H-bonds

The crystal structure of NH(4)(+)OOH(-) is determined from single-crystal x-ray data obtained at 150 K. The crystal belongs to the space group P2(1)/c and has four molecules in a unit cell. The structure consists of discrete NH(4)(+) and OOH(-) ions. The OOH(-) ions are linked by short hydrogen bonds (2.533 A?) to form parallel infinite chains. The ammonium ions form links between these chains (the N?O distances vary from 2.714 to 2.855 A?) giving a three-dimensional network. The harmonic IR spectrum and H-bond energies are computed at the Perdew-Burke-Ernzerhof (PBE)/6-31G(??) level with periodic boundary conditions. A detailed analysis of the shared (bridging) protons' dynamics is obtained from the CPMD simulations at different temperatures. PBE functional with plane-wave basis set (110 Ry) is used. At 10 K the shared proton sits near the oxygen atom, only a few proton jumps along the chain are detected at 70 K while at 270 K numerous proton jumps exist in the trajectory. The local-minimum structure of the space group Cc is localized. It appears as a result of proton transfer along a chain. This process is endothermic (～2?kJ/mol) and is described as P2(1)/c?2Cc. The computed IR spectrum at 10 K is close to the harmonic one, the numerous bands appear at 70 K while at 270 K it shows a very broad absorption band that covers frequencies from about 1000 to 3000?cm(-1). The advantages of the NH(4)(+)OOH(-) crystal as a promising model for the experimental and DFT based molecular dynamics simulation studies of proton transfer along the chain are discussed.     

Comparison of Sepharose CL-2B and CL-4B Matrices in Purification of the Hepatitis B Surface Antigen by Affinity Chromatography

Sepharose CL-4B and Sepharose CL-2B with immobilized CB.Hep-1 monoclonal antibody were compared for studying the matrix efficiency in the immunopurification of the recombinant hepatitis B surface antigen (rHBsAg). The elution capacities of both matrices were similar over eight chromatographic cycles, significant differences were only observed in the first purification cycles. A high percentage of the adsorbed rHBsAg was not eluted from both matrices. The rHBsAg purity was not affected by matrix characteristics (pore size and percentage of agarose) and differences between Sepharose CL-4B and Sepharose CL-2B do not provoke differences in the antibody released from the matrices under defined experimental conditions.     

BaTiO3 and PbTiO3 perovskite as catalysts for methane combustion

Unsupported and γ-Al₂O₃-supported Ba and Pb titanate catalysts were prepared, characterized and studied in the combustion of methane, as a test reaction for VOCs’ catalytic combustion. They present good catalytic activities, and after dispersion (5%) on γ-Al₂O₃ the specific activity of the supported perovskite phase increased 25 and 30 times, respectively, compared with the unsupported samples. PbTiO₃/γ-Al₂O₃ shows the best catalytic properties among the tested samples.     

Luminescence properties of three structures built from 3‐cyano‐4‐dicyanomethylene‐5‐oxo‐4,5‐dihydro‐1H‐pyrrol‐2‐olate and alkaline metals (Na,K and Rb)

The structures of three salts of 3‐cyano‐4‐dicyanomethylene‐5‐oxo‐4,5‐dihydro‐1H‐pyrrol‐2‐olate with alkali metals (Na, K and Rb) are related to their luminescence properties. The Rb salt, rubidium(I) 3‐cyano‐4‐dicyanomethylene‐5‐oxo‐4,5‐dihydro‐1H‐pyrrol‐2‐olate, Rb⁺·C₈HN₄O₂⁻, is isomorphous with the previously reported potassium salt. For the Na compound, sodium(I) 3‐cyano‐4‐dicyanomethylene‐5‐oxo‐4,5‐dihydro‐1H‐pyrrol‐2‐olate dihydrate, Na⁺·C₈HN₄O₂⁻·2H₂O, two independent sodium ions, located on inversion centers, are coordinated by four water molecules each and additionally by two cyano groups for one and two carbonyl groups for the other. The luminescence spectra in solution are unaffected by the nature of the cation but vary strongly with the dielectric constant of the solvent. In the solid state, the emission maxima vary with structural features; the redshift of the maximum luminescence varies inversely with the distance between the stacked anions.     

From small structural modifications to adjustment of structurally dependent properties: 1‐methyl‐3,5‐bis[(E)‐2‐thienylidene]‐4‐piperidone and 3,5‐bis[(E)‐5‐bromo‐2‐thienylidene]‐1‐methyl‐4‐piperidone

The molecules of the title compounds, C₁₆H₁₅NOS₂, (I), and C₁₆H₁₃Br₂NOS₂, (II), are E,E‐isomers and consist of an extensive conjugated system, which determines their molecular geometries. Compound (I) crystallizes in the monoclinic space group P2₁/c. It has one thiophene ring disordered over two positions, with a minor component contribution of 0.100 (3). Compound (II) crystallizes in the noncentrosymmetric orthorhombic space group Pca2₁ with two independent molecules in the unit cell. These molecules are related by a noncrystallographic pseudo‐inversion center and possess very similar geometries. The crystal packings of (I) and (II) have a topologically common structural motif, viz. stacks along the b axis, in which the molecules are bound by weak C—H...O hydrogen bonds. The noncentrosymmetric packing of (II) is governed by attractive intermolecular Br...Br and Br...N interactions, which are also responsible for the very high density of (II) (1.861 Mg m⁻³).     

Optimum extraction process of polyphenols from Bridelia grandis stem bark using experimental design

Euphorbiaceae barks are known to contain an appreciable amount of polyphenolic compounds responsible for several biological activities. Preliminary extraction from Bridelia grandis stem bark afforded high content of polyphenols, determined by spectrophotometric methods such as Folin–Ciocalteu (for total phenols, TP) and n‐butanol‐HCl (for condensed tannins, CT). A preliminary Plackett–Burman screening design was used to identify the key factors that influence the TP and CT extraction. Between all the variables known to influence the extraction from vegetable matrixes, six were selected; maceration was chosen as traditional extraction methodology. To investigate the effect of solvents and extraction method, methanol, acetone 70% (v/v in water), centrifugation and ultrasound were chosen. A full factorial design 2³ was applied to optimize the extraction procedure. The responses were obtained analyzing the extracts for their TP and CT contents determined by the above‐mentioned spectrophotometric methods. The results confirm that, within the explored domain, the optimum solvent is methanol and the optimum method is one‐cycle centrifugation. Finally, it was also compared with the effect of maceration on the considered responses. It has never given results better than centrifugation, whereas in the case of CT it represents an advantage to employ a three‐cycle centrifugation instead of one.