Pamela Pasetto

Elaboration of Monodisperse Spherical Hollow Particles with Ordered Mesoporous Silica Shells via Dual Latex/Surfactant Templating: Radial Orientation of Mesopore Channels

Monodisperse spherical hollow nanoparticles of mesoporous silica featuring mesopores with a radial orientation in the silica shell were synthesized via a dual-templating method. Specifically designed polystyrene latexes with anionic or cationic surface charges acted as the core templates, while cetyltrimethylammonium bromide served as a co-template to structure the mesopore formation during tetraethoxysilane hydrolysis/condensation. The particles were well-separated and presented homogeneous mesoporous silica shells. Average particle diameters were less than 200 nm, and the particles displayed high values of specific surface area and pore volume. The shell thickness and the hollow core diameter could be tuned independently while the radial pore structure was preserved. A detailed analysis of the nitrogen adsorption-desorption isotherms proved that the central cavity was completely isolated from the external medium, that is, only accessible through the radial mesopores of the shell. Consequently, our particles gather the advantages of a well-defined structure, straight penetrating channels across the silica shell, and a high accessible porous volume of the central core. These properties make them far better candidates than simple mesoporous particles for any storage and/or controlled release applications.

A fluorescence polarisation molecular imprint sorbent assay for 2,4-D: a non-separation pseudo-immunoassay.

The first pseudo-immunoassay which employs a molecularly imprinted receptor and a fluorescent probe, and quantifies the bound analyte directly using the fluorescence anisotropy of the polymer-probe-analyte suspension, is described.

On the effect of using RAFT and FRP for the bulk synthesis of acrylic and methacrylic molecularly imprinted polymers

Molecularly imprinted polymers (MIPs) are synthetic polymeric receptors, capable of specifically binding a target molecule, just like a biological antibody. There has been a recent trend to improve the properties of these materials by using modern methods of controlled radical polymerization (CRPs) for their synthesis. Despite the recognized advantages associated with their “living character”, the effect of the “controlled nature” has still to be clearly demonstrated. This is far from obvious as the high amounts of short cross-linkers normally used for their synthesis complicate the formation of homogeneous polymer networks. In order to gain more insights into the potential benefits for the binding properties of MIPs resulting from the use of CRPs, the imprinting of a model target (S-propranolol) has been used to compare reversible addition–fragmentation chain transfer polymerisation (RAFT) and free-radical polymerisation (FRP) on acrylic and methacrylic matrices. While most MIPs are based on methacrylates, we used acrylates as a “difficult imprinting matrix” for comparison. In fact, the absence of the methyl groups in their polymer back-bone reduces their entanglement, resulting in a more flexible network. This renders the material more difficult to imprint, and at the same time makes it easier to evaluate the effects of RAFT polymerization and FRP on structural parameters and thus binding properties. Moreover, we also progressively reduced the amount of cross-linking in order to explore the effects of RAFT and FRP on a wider range of scaffold rigidities. Although MIPs are normally highly cross-linked, some recent emerging applications require lower degrees of cross-linking. Binding experiments, SEM, BET, DMA, swelling and nanoindentation analyses revealed that RAFT is effective in promoting the synthesis of more homogeneous networks compared to FRP, even at very high cross-linker contents, which results in higher target affinities, especially in the case of acrylates.

Simple spectroscopic method for titration of binding sites in molecularly imprinted nanogels with hydrolase activity

In this investigation we report the preparation of soluble molecularly imprinted catalytic nanogels with hydrolytic activity. The nanogels were imprinted using a stoichiometric non-covalent approach, employing a phosphate transition state analogue as template and polymerizable tyrosine and arginine units as functional monomers, for catalysis of a carbonate hydrolysis reaction. Full characterization of the rebinding and of the hydrolytic activity was performed, with particular emphasis on a novel titration method developed for the measurement of active site concentrations and the subsequent calculation of accurate catalytic parameters. Considering the features of the template molecule and the functional monomers used, an original method for performing rebinding experiments is described, taking advantage of the change of the visible spectrum evident on binding the sodium salt of the template to the arginine residue present in the nanogel.

Marennine, Promising Blue Pigments from a Widespread Haslea Diatom Species Complex

In diatoms, the main photosynthetic pigments are chlorophylls a and c, fucoxanthin, diadinoxanthin and diatoxanthin. The marine pennate diatom Haslea ostrearia has long been known for producing, in addition to these generic pigments, a water-soluble blue pigment, marennine. This pigment, responsible for the greening of oysters in western France, presents different biological activities: allelopathic, antioxidant, antibacterial, antiviral, and growth-inhibiting. A method to extract and purify marennine has been developed, but its chemical structure could hitherto not be resolved. For decades, H. ostrearia was the only organism known to produce marennine, and can be found worldwide. Our knowledge about H. ostrearia-like diatom biodiversity has recently been extended with the discovery of several new species of blue diatoms, the recently described H. karadagensis, H. silbo sp. inedit. and H. provincialis sp. inedit. These blue diatoms produce different marennine-like pigments, which belong to the same chemical family and present similar biological activities. Aside from being a potential source of natural blue pigments, H. ostrearia-like diatoms thus present a commercial potential for aquaculture, cosmetics, food and health industries.

Novel imprinted soluble microgels with hydrolytic catalytic activity

The synthesis and kinetic characterisation of soluble imprinted acrylamide based microgels incorporating arginine and tyrosine derivatives as additional functional monomers is reported.

Preparation and Properties of Bio-based Polyurethane Containing Polycaprolactone and Natural Rubber

Novel polyurethanes were successfully synthesized by a one-shot polymerization. They contained poly(ε-caprolactone) diol (PCL diol) and hydroxyl telechelic natural rubber (HTNR) as the soft segment. The effect of the NCO:OH molar ratio (0.75:1.00–2.25:1.00), chain extender and PCL:HTNR molar ratio (1:1, 0.7:0.3 and 0.3:0.7) on the thermal and mechanical properties of the resulting polyurethane were investigated. FTIR analysis showed the presence of urethane linkages and crosslinking or chain branching. The derived polyurethanes demonstrated excellent mechanical properties, which depended on their chemical composition. Their tensile behavior seemed to have typical elastomeric characteristics. Polyurethanes became amorphous and showed a phase separation between the PCL diol and HTNR segments. The phase separation between the soft and the hard segments was observed by the DMTA technique whereas DSC results showed only the glass transition temperatures of the soft segment. The longer and more flexible chain and non-polarity of HTNR was responsible of a decrease in the mechanical properties and transition temperatures.

Antimicrobial Compounds from Eukaryotic Microalgae against Human Pathogens and Diseases in Aquaculture

The search for novel compounds of marine origin has increased in the last decades for their application in various areas such as pharmaceutical, human or animal nutrition, cosmetics or bioenergy. In this context of blue technology development, microalgae are of particular interest due to their immense biodiversity and their relatively simple growth needs. In this review, we discuss about the promising use of microalgae and microalgal compounds as sources of natural antibiotics against human pathogens but also about their potential to limit microbial infections in aquaculture. An alternative to conventional antibiotics is needed as the microbial resistance to these drugs is increasing in humans and animals. Furthermore, using natural antibiotics for livestock could meet the consumer demand to avoid chemicals in food, would support a sustainable aquaculture and present the advantage of being environmentally friendly. Using natural and renewable microalgal compounds is still in its early days, but considering the important research development and rapid improvement in culture, extraction and purification processes, the valorization of microalgae will surely extend in the future.

Bacterial adhesion and growth reduction by novel rubber-derived oligomers

In the medical field, attached bacteria can cause infections associated with catheters, incisions, burns, and medical implants especially in immunocompromised patients. The problem is exacerbated by the fact that attached bacteria are ∼1000 times more resistant to antibiotics than planktonic cells. The rapid spread of antibiotic resistance in these and other organisms has led to a significant need to find new methods for preventing bacterial attachment. The goal of this research was to evaluate the effectiveness of novel polymer coatings to prevent the attachment of three medically relevant bacteria. Tests were conducted with Pseudomonas aeruginosa, Staphylococcus epidermidis, and Staphylococcus aureus for oligomers derived from modifications of natural rubber (cis 1,4-polyisoprene). The different oligomers were: PP04, with no quaternary ammonium (QA); MV067, one QA; PP06, three QA groups. In almost all experiments, cell attachment was inhibited to various extents as long as the oligomers were used. PP06 was the most effective as it decreased the planktonic cell numbers by at least 50% for all bacteria. Differences between species sensitivity were also observed. P. aeruginosa was the most resistant bacteria tested, S. aureus, the most sensitive. Further experiments are required to understand the full extent and mode of the antimicrobial properties of these surfaces.

Synthesis and Properties of New Biodegradable Polyurethane Containing Natural Rubber and Poly(lactic Acid): Effect of NR and PLA Ratio

Biodegradable polyurethane was synthesized using poly(DL-lactic acid) diol and hydroxytelechelic natural rubber as hydroxyl containing precursor, 1,4-butane diol as chain extender, isophorone diisocyanate and dibutyltin dilaurate as catalyst. Poly(DL-lactic acid) diol was prepared by condensation polymerization of DL-lactic acid using 1,4-butane diol as initiator and stannous octoate as catalyst. Hydroxyltelechelic natural rubber synthesized via oxidative degradation of natural rubber and then reduced carbonyl end group to hydroxyl group. Chemical structure of products was characterized by 1H-NMR. Molecular weight and polydispersity determined by SEC. Thermal properties was characterized by DSC and TGA. Segmented polyurethane show two Tgs and two degradation steps corresponding to natural rubber and poly(DL-lactic acid) segment. Polyurethane containing poly(lactic acid) more than 40%mol are become brittle. This result caused by brittle characteristic of PLA. Moreover, mechanical properties increased as content of PLA increased.