Nature Publishing GroupCorma Canós, A.; Concepción Heydorn, P.; Boronat Zaragoza, M.; Sabater Picot, MJ.; Navas Escrig, J.; Yacaman, MJ.; Larios, E.... (2013). Exceptional oxidation activity with sizecontrolled supported gold clusters of low atomicity. Nature Chemistry. 5 (9) SummaryThe catalyticic activity of gold depends on particle size, with reactivity increasing as particle diameter decreases. Investigation of the trends in the subnanometer regime, where gold exists as small clusters of a few atoms, is now starting thanks to recent advances in synthesis and characterization techniques. An easy method to prepare isolated gold atoms supported on functionalized carbon nanotubes and their performance in the oxidation of thiophenol with O 2 are described. Single gold atoms are not active and they aggregate under reaction conditions into gold clusters of low atomicity, which show a catalytic activity comparable to that sulfhydryl oxidase enzymes. When clusters grow into larger nanoparticles, catalyst activity drops to zero.Theoretical calculations show that gold clusters are able to simultaneously activate thiophenol and O 2 , while larger nanoparticles become passivated by strongly adsorbed thiolates. The combination of an optimum for reactants activation and product desorption makes gold clusters excellent catalysts. Main TextGold has attracted wide interest as catalyst in the last years due to its unexpected activity and, specially, to its high selectivity in organic reactions. [1][2][3] The catalytic properties of gold depend on several factors that in some cases are intimately related:gold particle size and morphology, metal-oxide support interaction, oxidation state of the active sites, etc. 4-8 The influence of particle size has been extensively investigated, and a volcano type curve with a maximum in activity at an optimum diameter has been reported for CO oxidation, 7 alkane oxidation, 9 or propene epoxidation with O 2 and H 2 , 10 while in other cases an exponential increase in activity with decreasing particle size has been observed. 5,11,12 However, the trends in catalytic activity when the particle diameter While it appears that in order to control reactivity, the atomicity control of the gold clusters is crucial, the synthesis of size-selected metal clusters and their deposition over a solid support is a challenging task. 26 The wet-chemistry methods for preparing supported metal clusters involve the anchoring of well defined precursors to an adequate support, 27,28 followed by removal of the ligands by post-synthesis treatments, trying to prevent cluster agglomeration during these steps. 9,[29][30][31]32 Soft landing of monodisperse metal clusters grown in the gas phase and with precise size selection by mass spectrometry is a more straightforward method, but it requires sophisticated equipment, and the scaling up of the process is a major drawback. 20,23,33 In The chemical nature of these isolated atoms has been investigated by X-ray absorption spectroscopy (XAS) and X-ray photoelectron spe...

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Bacteria often colonize in-dwelling medical devices and grow as complex biofilm communities of cells embedded in a self-produced extracellular polymeric matrix, which increases their resistance to antibiotics and the host immune system. During biofilm growth, bacterial cells cooperate through specific quorum-sensing (QS) signals. Taking advantage of this mechanism of biofilm formation, we hypothesized that interrupting the communication among bacteria and simultaneously degrading the extracellular matrix would inhibit biofilm growth. To this end, coatings composed of the enzymes acylase and α-amylase, able to degrade bacterial QS molecules and polysaccharides, respectively, were built on silicone urinary catheters using a layer-by-layer deposition technique. Multilayer coatings of either acylase or amylase alone suppressed the biofilm formation of corresponding Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus. Further assembly of both enzymes in hybrid nanocoatings resulted in stronger biofilm inhibition as a function of acylase or amylase position in the layers. Hybrid coatings, with the QS-signal-degrading acylase as outermost layer, demonstrated 30% higher antibiofilm efficiency against medically relevant Gram-negative bacteria compared to that of the other assemblies. These nanocoatings significantly reduced the occurrence of single-species (P. aeruginosa) and mixed-species (P. aeruginosa and Escherichia coli) biofilms on silicone catheters under both static and dynamic conditions. Moreover, in an in vivo animal model, the quorum quenching and matrix degrading enzyme assemblies delayed the biofilm growth up to 7 days.

Bacteria use a signaling mechanism called quorum sensing (QS) to form complex communities of surface-attached cells known as biofilms. This protective mode of growth allows them to resist antibiotic treatment and originates the majority of hospital-acquired infections. Emerging alternatives to control biofilm-associated infections and multidrug resistance development interfere with bacterial QS pathways, exerting less selective pressure on bacterial population. In this study, biologically stable coatings comprising the QS disrupting enzyme acylase were built on silicone urinary catheters using a layer-by-layer technique. This was achieved by the alternate deposition of negatively charged enzyme and positively charged polyethylenimine. The acylase-coated catheters efficiently quenched the QS in the biosensor strain Chromobacterium violaceum CECT 5999, demonstrated by approximately 50% inhibition of violacein production. These enzyme multilayer coatings significantly reduced the Pseudomonas aeruginosa ATCC 10145 biofilm formation under static and dynamic conditions in an in vitro catheterized bladder model. The quorum quenching enzyme coatings did not affect the viability of the human fibroblasts (BJ-5ta) over 7 days, corresponding to the extended useful life of urinary catheters. Such enzyme-based approach could be an alternative to the conventional antibiotic treatment for prevention of biofilm-associated urinary tract infections.

Catheter associated urinary tract infections are common during hospitalization due to the formation of bacterial biofilms on the indwelling device. In this study, we report an innovative biotechnology-based approach for the covalent functionalization of silicone catheters with antifouling zwitterionic moieties to prevent biofilm formation. Our approach combines the potential bioactivity of a natural phenolics layer biocatalytically conjugated to sulfobetaine-acrylic residues in an enzymatically initiated surface radical polymerization with laccase. To ensure sufficient coating stability in urine, the silicone catheter is plasma-activated. In contrast to industrial chemical methods, the methacrylate-containing zwitterionic monomers are polymerized at pH 5 and 50 °C using as an initiator the phenoxy radicals solely generated by laccase on the phenolics-coated catheter surface. The coated catheters are characterized by X-ray photoelectron spectroscopy (XPS), Fourier transformed infrared (FTIR) analysis, atomic force microscopy (AFM), and colorimetrically. Contact angle and protein adsorption measurements, coupled with in vitro tests with the Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus in static and dynamic conditions, mimicking the operational conditions to be faced by the catheters, demonstrate reduced biofilm formation by about 80% when compared to that of unmodified urinary catheters. The zwitterionic coating did not affect the viability of the human fibroblasts (BJ-5ta) over seven days, corresponding to the extended useful life of urinary catheters.

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Textiles are good substrates for growth of microorganisms especially under moisture and temperature conditions found in hospitals. Microbial shedding from the body occurs continuously at contact of the patient with textile materials used in medical practices, contributing to the occurrence of hospital acquired infections. Thus, the use of efficient antimicrobial textiles is necessary to prevent the transfer of pathogens and the infection incidence. In this work, hybrid antimicrobial coatings were generated on cotton fabrics by means of a one-step simultaneous sonochemical deposition of ZnO nanoparticles (NPs) and chitosan. The process was further optimized in terms of reagents concentration and processing time in order to improve the antibacterial properties of the fabric and ensure their biocompatibility. The highest antibacterial activity of the fabrics against two medically relevant bacterial species was achieved in a 30 min sonochemical coating process using 2 mM ZnO NPs suspension. When chitosan was simultaneously deposited with the same amount of ZnO, the obtained hybrid NPs coating displayed higher by 48 and 17% antibacterial activity against Staphylococcus aureus and Escherichia coli, respectively. The presence of biopolymer also improved the durability of the antimicrobial effect of the coatings by 21% for Staphylococcus aureus and 40% for Escherichia coli, evaluated after applying multiple washing cycles at hospital laundering regimes. Finally, 87% biocompatibility improvement supported by fibroblast viability was observed for the hybrid ZnO/chitosan coating compared to the steady decrease of cells viability over one week in contact with the fabrics coated with ZnO alone.

Small gold nanoclusters in a very narrow size distribution (1.1 ± 0.5 nm) have been stabilized onto multiwalled carbon nanotubes (MWCNT). Theoretical studies supported by XPS and (16)O(2)/(18)O(2) isotopic exchange experiments have shown that, on small gold nanoparticles (0.9-1.5 nm), dissociation of molecular O(2) and formation of a surface oxide-like layer is energetically favorable and occurs at room temperature, while O(2) recombination and desorption involves a larger activation barrier. CO titration experiments and theoretical studies demonstrate that the reactivity of the oxidized particles toward CO does not only depend on particle size but also on oxygen coverage. The oxidation-reduction process described is reversible, and the oxidized nanoparticles are active in the epoxidation of styrene with air.