Gelatine/silicate interactions: from nanoparticles to composite gels

The possibility to design new composites associating biopolymers with mineral phases relies on the understanding and control of their mutual interactions. In this work, aqueous solutions of gelatine and sodium silicate were mixed at pH 5, 37 degrees C and left to stand at 20 degrees C for 1 day. At low gelatine and high silicate contents, precipitates were obtained, containing a fixed silicon/polymer molar ratio. Scanning electron microscopy (SEM) reveals that they are formed of large aggregates of platelets, constituted of closely-packed nanoparticles. For high gelatine contents, composite gels were formed consisting of silica particles dispersed in the biopolymer matrix. Swelling studies indicate that the addition of silica decreases the stability of the gels by inducing gelatine depletion in solution. Similar experiments conducted at pH 7 show that at this pH, silicates are more effective at precipitating gelatine. A model is proposed for the formation of the composites, based on the electrostatic interactions arising between silicates and polymer chains. These results are discussed in the context of hybrid biomaterials design and biosilicification processes.     

Coherent Products in a Finite Group along a Linear Ordering

Let C = (C, ) be a linear ordering, E a subset of {(x, y):x< y in C} whose transitive closure is the linear orderingC, and let :E G be a map from E to a finite group G = (G, •).We showed with M. Pouzet that, when C is countable, there isF E whose transitive closure is still C, and such that (p) = (x_o, x₁)•(x₁, x₂)•....•(x_{n– 1}, x_n) G depends only upon the extremities x₀, x_n ofp, where p = (x_o, x₁...,x_n) (with 1 n < ) is a finite sequencefor which (x_i, x_{i + 1}) F for all i < n. Here, we show thatthis property does not hold if C is the real line, but is stilltrue if C does not embed an ₁-dense linear ordering, or evena 2-dense linear ordering when Martin's Axiom holds (it followsin particular that it is independent of ZFC for linear orderingsof size ). On the other hand, we prove that this property isalways valid if E = {(x,y):x < y in C}, regardless of anyother condition on C.     

Rotational band crossings in the actinides

In the actinides bothi _13/2 protons andj _15/2 neutrons are close to the Fermi surface. At rapid rotation these high-j particles will unpair and align their orbital angular momentum along the axis of rotation giving rise tos-bands that cross the ground-state band. Coulomb excitation of the odd nuclei ₂₃₇ ⁹³ Np (established up to the 45/2⁺ state) and ₂₃₅ ⁹² U (established up to the 51/2^? state) provides specific information about these band crossings: From the saturating alignment of the odd high-j particle in both nuclei at intermediate rotational frequencies we find the aligned angular momentum of thei _13/2 protons-band to be 6.6? while the corresponding value for thej _15/2 neutrons-band is 5.5?. At more rapid rotation above ?ω=0.18 MeV we observe additional alignment in²³⁵U. This is ascribed to the interaction of the protons-band. From the gradual onset of the additional alignment we deduce that forZ=92 the protons-band interacts strongly with the ground-state band and from a comparison of the actual amount of alignment with the full value of 6.6? we estimate the crossing to occur around ?gw _c ^p =0.25 MeV.     

Photocatalytic E→Z Contra-Thermodynamic Isomerization of Vinyl Silanes with Lewis Base

Herein, we disclosed the contra-thermodynamic E→Z isomerization of alkenyl silanes, according to the in situ formation of a chromophoric species, in the presence of rac-BINAP as the catalyst. The reaction carried out in DMSO or CH₃CN under irradiation at 405 nm allowed the interconversion of the E-isomers into the Z-congeners in good to excellent yields and outstanding Z/E selectivities, on 18 examples. Finally, the mechanism of this E→Z isomerization was studied to get insight into the reaction mechanism.     

Synthesis of Fibrin-Type I Collagen Biomaterials via an Acidic Gel

Fibrin-Type I collagen composite gels have been widely studied as biomaterials, in which both networks are usually formed simultaneously at a neutral pH. Here, we describe a new protocol in which mixed concentrated solutions of collagen and fibrinogen were first incubated at acidic pH to induce fibrinogen gel formation, followed by a pH change to neutral inducing collagen fiber formation. Thrombin was then added to form fibrin-collagen networks. Using this protocol, mixed gels containing 20 mg.mL⁻¹ fibrin and up to 10 mg.mL⁻¹ collagen could be prepared. Macroscopic observations evidenced that increasing the content of collagen increases the turbidity of the gels and decreases their shrinkage during the fibrinogen-to-fibrin conversion. The presence of collagen had a minor influence on the rheological properties of the gels. Electron microscopy allowed for observation of collagen fibers within the fibrin network. 2D cultures of C2C12 myoblasts on mixed gels revealed that the presence of collagen favors proliferation and local alignment of the cells. However, it interferes with cell differentiation and myotube formation, suggesting that further control of in-gel collagen self-assembly is required to elaborate fully functional biomaterials.     

Lifetimes of high-spin yrast states in 154Er

Lifetimes for high-spin levels (between about 10 and 30 ?) in ¹⁵⁴Er have been measured by the recoil-distance method. Non-collective, moderately collective and collective E2 transitions from states with lifetimes between at most 10 and 400 ps have been found. All available data on this nucleus are discussed within the framework of the oblate coupling scheme with the addition of collective degrees of freedom.     

Hydrogen burning of 17O in classical novae

We report on the observation of a previously unknown resonance at E(lab)(R)=194.1+/-0.6 keV in the 17O(p,alpha)14N reaction, with a measured resonance strength omegagamma(palpha)=1.6 +/- 0.2 meV. We studied in the same experiment the 17O(p,gamma)18F reaction by an activation method and the resonance-strength ratio was found to be omegagamma(palpha)/omegagamma(pgamma) = 470 +/- 50. The corresponding excitation energy in the 18F compound nucleus was determined to be 5789.8 +/- 0.3 keV by gamma-ray measurements using the 14N(alpha, gamma)18F reaction. These new resonance properties have important consequences for 17O nucleosynthesis and gamma-ray astronomy of classical novae.     

Ueber die Einwirkung von Formaldehyd

Ohne Zusammenfassung     

Bacteria encapsulation in colloidal inorganic matrices: Is it a general method?

Zirconium oxyhydroxide nanoparticles prepared by an aqueous route were evaluated for Escherichia coli bacteria encapsulation. A low viability rate was measured 24 hours after immobilization that could be attributed to nanoparticle cytotoxicity. Moreover, the presence of glycerol, a long-term cell-preserving molecule, hindered gel formation, probably due to its adsorption on the nanoparticle surface. A comparison with boehmite and ferrihydrite gels previously synthesized following a similar aqueous colloidal route suggests that the generalization of this method will rely on a careful control of the nanoparticle surface reactivity and may require surface chemical modification.