The development and evaluation of ultrasound in the biocidal treatment of water

The effect of ultrasound upon the destruction of micro-organisms has been studied and reported here. The results obtained from the work carried out has shown that ultrasound can be used effectively for water disinfection and has several advantages. When used in conjunction with chlorine it significantly reduces the number of bacteria present in water samples. Ultrasound also reduces the amount of chlorine required for disinfection. Increasing the power of ultrasound leads to greater efficiency in the destruction of bacterial cells. High frequency ultrasound is more beneficial than low frequency in the disinfection of water.     

Transesterification catalysts to improve clay exfoliation in synthetic biodegradable polyester nanocomposites

We report here on the melt intercalation preparation of polymer/clay nanocomposites based on three commercial synthetic biodegradable polyesters: EastarBio Ultra, Ecoflex, and Bionolle, respectively. The montmorillonite clay addition is performed either by direct dispersion of Cloisite 30B in the polyester matrix or by dispersing a “PCL-grafted Cloisite 30B” masterbatch in the biodegradable polyesters. All obtained nanocomposites display an intercalated morphology as attested by X-ray diffraction measurements. The various analyses clearly show that the Bionolle (BIO) matrix gives the best results. Morphological characterization and mechanical properties of these nanocomposites also show that the “masterbatch route” leads to poor results as a consequence of the very low compatibility between the poly(ε-caprolactone) (PCL) of the masterbatch and the three other polyester matrices. In a second part, nanocomposites based on the BIO matrix are prepared by direct dispersion of the organo-clay in the presence of three different metal-based catalysts with the aim to promote transesterification reactions between the nanocomposite constituents. The mechanical properties and morphological characterization of these nanocomposites show that the tin-based catalyst (Sn) is the more efficient. Indeed, the effectiveness of transesterification reactions taking place between the ester functions of the BIO matrix and the hydroxyl groups of the organo-clay and the resulting “grafting” of BIO chains on the organo-clay surface are confirmed by thermogravimetric analyses performed after the extraction procedure. TEM observations show that this catalyst enhances the clay platelets exfoliation within the BIO matrix as a consequence of the transesterification reactions. Nanocomposites prepared in presence of Sn show better clay dispersion and enhanced stiffness with a 60% increase in Young’s modulus.     

Star‐Pseudopolyrotaxane Organized in Nanoplatelets for Poly(ε‐caprolactone)‐Based Nanofibrous Scaffolds with Enhanced Surface Reactivity

Herein, it is demonstrated that star pseudopolyrotaxanes (star‐pPRs) obtained from the inclusion complexation of α‐cyclodextrin (CD) and four‐branched star poly(ε‐caprolactone) (star‐PCL) organize into nanoplatelets in dimethyl sulfoxide at 35 °C. This peculiar property, not observed for linear pseudopolyrotaxanes, allows the processing of star‐pPRs while preserving their supramolecular assembly. Thus, original PCL:star‐pPR core:shell nanofibers are elaborated by coaxial electrospinning. The star‐pPR shell ensures the presence of available CD hydroxyl functions on the fiber surface allowing its postfunctionalization. As proof of concept, fluorescein isothiocyanate is grafted. Moreover, the morphology of the fibers is maintained due to the star‐pPR shell that acts as a shield, preventing the fiber dissolution during chemical modification. The proposed strategy is simple and avoids the synthesis of polyrotaxanes, i.e., pPR end‐capping to prevent the CD dethreading. As PCL is widely used for biomedical applications, this strategy paves the way for simple functionalization with any bioactive molecules.

     

Thermodynamics of the 3D Hubbard model on approaching the Néel transition

We study the thermodynamic properties of the 3D Hubbard model for temperatures down to the Néel temperature by using cluster dynamical mean-field theory. In particular, we calculate the energy, entropy, density, double occupancy, and nearest-neighbor spin correlations as a function of chemical potential, temperature, and repulsion strength. To make contact with cold-gas experiments, we also compute properties of the system subject to an external trap in the local density approximation. We find that an entropy per particle S/N ≈ 0.65(6) at U/t = 8 is sufficient to achieve a Néel state in the center of the trap, substantially higher than the entropy required in a homogeneous system. Precursors to antiferromagnetism can clearly be observed in nearest-neighbor spin correlators.     

Tetronic Acids and Derivatives Part VIII (1) o-Alkylation of 3-Unsubstituted Tetronic Acids

4-methoxy-(5H)-furan-2-ones 1 are useful starting materials for the synthesis of naturally occuring lactones². In a previous communication we have described an efficient entry to 4-alkoxy-(5H)-furan-2-ones 1–3 (alkyl tetronates) by lactonization of ethyl 4-acetoxy 3-ketoesters 4 using hydrochloric acid in several alcohols¹. The detection of 4-hydroxy-(5H)-furan-2-ones 5 (tetronic acids) during the reaction course³ allowed us to postulate them as intermediates which were subsequently etherified to the products 1–3. In a very recent communication⁴, it was claimed that attempted alkylation of tetronic acids 5 using HC1 in an alcohol or alkyl halides on tetronic acids sodium salts are unsuccessful; moreover, the structure of our compounds 1–3 was questionned by arguing that isomeric 2-alkylated materials     

Gas barrier properties of poly(ε‐caprolactone)/clay nanocomposites: Influence of the morphology and polymer/clay interactions

Poly(ε‐caprolactone)/montmorillonite nanocomposites were prepared maintaining a constant inorganic content with three means: melt blending of poly(ε‐caprolactone) with natural or organomodified clays, in situ polymerization of ε‐caprolactone in the presence of organomodified clays, and initiation of ε‐caprolactone polymerization from the silicate layer with appropriate organomodified montmorillonites and activator. In this last case, the polymer chains were grafted to the silicate layers and it was possible to tune up the grafting density. The presence of clays did not modify the polymer crystallinity. It was shown that the in situ polymerization process from the clay surface improved the clay dispersion. The gas barrier properties of the different composite systems were discussed both as a function of the clay dispersion and of the matrix/clay interactions. The highest barrier properties were obtained for an exfoliated morphology and the highest grafting density. Similar evolution of the permeability and the diffusion coefficients was observed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 205–214, 2005     

Analysis of UV-B-induced DNA damage and its repair in heat-shocked skin cells

The heat-shock response is a cellular defence mechanism against environmental stresses that is evolutionarily conserved from bacteria to man. Numerous reports demonstrate the beneficial effects of heat-shock protein induction on cell survival under toxic or oxidative stress, e.g., in cardiac and cerebral ischemia or prior to organ transplantation. However, there is little data on the effects of heat treatment on damage caused by UV irradiation. Applying three independent techniques, we have tested the influence of thermal pretreatment of skin cells (1 h, 43 degrees C) on the initial extent of UV-B-induced DNA damage and its subsequent repair. For cultured human epidermal keratinocytes and dermal fibroblasts we can show reduced levels of nucleotide-excision-repair-associated DNA strand incision in the comet assay. Moreover, immunostaining and flow cytometric quantitation of thymidine dimers immediately and one day after irradiation, respectively, reveal that the initial DNA damage is not (keratinocytes) or only moderately (fibroblasts) lower in heat-shocked cells as compared to untreated controls. However, excision repair of dimers is significantly attenuated during the first 24 h in both cell types. Furthermore, using a modified host-cell reactivation assay, we are able to demonstrate that repair of UV-B-damaged plasmid DNA is lower if the transfected cells are previously heat shocked. In summary, heat treatment (1 h, 43 degrees C) inducing heat-shock proteins reduces nucleotide excision repair of UV-B-mediated DNA lesions in fibroblasts and keratinocytes during the following 24 h. This is not necessarily caused by elevated heat-shock protein levels themselves. Possibly the direct thermal damage of repair enzymes is more severe than the potential protective effects of heat-shock proteins.     

(Li/Ag)CoO2: a new intergrowth cobalt oxide composed of rock salt and delafossite layers

A new ordered (Li/Ag)CoO(2) layered compound with an unusual oxygen packing combining rock salt and delafossite layers is obtained during the (Li(+), Na(+))/Ag(+) ionic exchange from the OP4-(Li/Na)CoO(2) precursor. This compound is actually an intermediate step to the final D4-AgCoO(2) delafossite and can be isolated thanks to the kinetics difference between the Li(+)/Ag(+) and Na(+)/Ag(+) exchange processes. It crystallizes in the P6(3)/mmc space group with cell parameters a(hex.) = 2.848(3) ? and c(hex.) = 21.607(7) ?. The details of the structure as well as its thermal stability and transport properties are presented and discussed.     

Water exchange of a ProHance MRI contrast agent: isomer-dependent free-energy landscapes and mechanisms

The water-exchange reaction in two diastereoisomers of the clinical magnetic resonance imaging contrast agent [Gd(HP-DO3A)(H(2)O)] (also known as ProHance) has been studied using ab initio simulations. On the basis of the molecular-level details of the mechanism derived from these simulations in aqueous solution, we unravel the underlying difference in the free energies and mechanisms of water exchange in the two diastereoisomers. These findings reveal the crucial role played by hydrogen-bonding dynamics and thus suggest their appropriate control in tailoring improved gadolinium-based constrast agents.     

Theoretical studies of Pt-Ti nanoparticles for potential use as PEMFC electrocatalysts

A theoretical investigation is presented of alloying platinum with titanium to form binary Pt-Ti nanoalloys as an alternative to the expensive pure platinum catalysts commonly used for Proton Exchange Membrane Fuel Cell cathode electrocatalysts. Density Functional Theory calculations are performed to investigate compositional effects on structural properties as well as Oxygen Reduction Reaction kinetics and poisoning effects. High symmetry A(32)-B(6) clusters are studied to investigate structural properties. From these structures binding energies of hydroxyl and carbon monoxide are studied on a range of sites on the surface of the clusters. Promising results are obtained suggesting that the bimetallic Pt-Ti nanoalloys may exhibit enhanced properties compared to pure platinum catalysts.