Merging gold plasmonic nanoparticles and L-proline inside a MOF for plasmon-induced visible light chiral organocatalysis at low temperature.

Light-driven asymmetric photocatalysis represents a straightforward approach in modern organic chemistry. In comparison to the homogeneous one, heterogeneous asymmetric photocatalysis has the advantages of easy catalyst separation, recovery, and reuse, thus being cost- and time-effective. Here, we demonstrate how plasmon-active centers (gold nanoparticles - AuNPs) allow visible light triggering of chiral catalyst (proline) in model aldol reaction between acetone and benzaldehyde. The metal-organic framework UiO-66-NH2 was used as an advanced host platform for the loading of proline and AuNPs and their stabilization in spatial proximity. Aldol reactions were carried out at a low temperature (-20 °C) under light illumination which resulted in 91% ee with a closed-to-quantitative yield, 4.5 times higher than that without light (i.e. in the absence of plasmon triggering). A set of control experiments and quantum chemical modeling revealed that the plasmon assistance proceeds through hot electron excitation followed by an interaction with an enamine with the formation of anion radical species. We also demonstrated the high stability of the proposed system in multiple catalytic cycles without leaching metal ions, which makes our approach especially promising for heterogeneous asymmetric photocatalysis.

Proton exchange membrane with plasmon-active surface for enhancement of fuel cell effectivity.

The action of fuel cells with proton-exchanged membranes (PEMs) requires the implementation of the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) on the opposite sides of the PEMs. Recently, based on several models of electrochemical reactions a significant decrease in the thermodynamic activation barrier of both reactions under plasmon assistance was reported. In this work, we propose the design of a PEM fuel cell with a plasmon-active catalytic surface providing plasmonic triggering and enhancement of fuel cell efficiency. In particular, we deposited bimetallic (Au@Pt) nanostructures on the PEM surface and integrated them into the fuel cell design. Plasmon excitation occurs on the Au nanostructures under light illumination at the corresponding NIR wavelength, while the Pt shell is responsible for the introduction of catalytic sites. Light illumination results in a significant enhancement of the electric current produced by the fuel cell. In particular, the electric current increased several times. Control experiments indicated that the observed enhancement takes place only when the light wavelength is in compliance with the plasmon absorption band and the contribution from thermal effects is negligible. The present approach for the introduction of plasmon assistance into the design of advanced fuel cells makes them suitable for increasing the fuel cell efficiency under sunlight.

RMS roughness-independent tuning of surface wettability by tailoring silver nanoparticles with a fluorocarbon plasma polymer.

A layer of 14 nm-sized Ag nanoparticles undergoes complex transformation when overcoated by thin films of a fluorocarbon plasma polymer. Two regimes of surface evolution are identified, both with invariable RMS roughness. In the early regime, the plasma polymer penetrates between and beneath the nanoparticles, raising them above the substrate and maintaining the multivalued character of the surface roughness. The growth (ß) and the dynamic (1/z) exponents are close to zero and the interface bears the features of self-affinity. The presence of inter-particle voids leads to heterogeneous wetting with an apparent water contact angle θa = 135°. The multivalued nanotopography results in two possible positions for the water droplet meniscus, yet strong water adhesion indicates that the meniscus is located at the lower part of the spherical nanofeatures. In the late regime, the inter-particle voids become filled and the interface acquires a single valued character. The plasma polymer proceeds to grow on the thus-roughened surface whereas the nanoparticles keep emerging away from the substrate. The RMS roughness remains invariable and lateral correlations propagate with 1/z = 0.27. The surface features multiaffinity which is given by different evolution of length scales associated with the nanoparticles and with the plasma polymer. The wettability turns to the homogeneous wetting state.

Cytotoxicity of Pd nanostructures supported on PEN: Influence of sterilization on Pd/PEN interface.

Non-conventional antimicrobial agents, such as palladium nanostructures, have been increasingly used in the medicinal technology. However, experiences uncovering their harmful and damaging effects to human health have begun to appear. In this study, we have focused on in vitro cytotoxicity assessment of Pd nanostructures supported on a biocompatible polymer. Pd nanolayers of variable thicknesses (ranging from 1.1 to 22.4nm) were sputtered on polyethylene naphthalate (PEN). These nanolayers were transformed by low-temperature post-deposition annealing into discrete nanoislands. Samples were characterized by AFM, XPS, ICP-MS and electrokinetic analysis before and after annealing. Sterilization of samples prior to cytotoxicity testing was done by UV irradiation, autoclave and/or ethanol. Among the listed sterilization techniques, we have chosen the gentlest one which had minimal impact on sample morphology, Pd dissolution and overall Pd/PEN interface quality. Cytotoxic response of Pd nanostructures was determined by WST-1 cell viability assay in vitro using three model cell lines: mouse macrophages (RAW 264.7) and two types of mouse embryonic fibroblasts (L929 and NIH 3T3). Finally, cell morphology in response to Pd/PEN was evaluated by means of fluorescence microscopy.

Gold, Silver and Carbon Nanoparticles Grafted on Activated Polymers for Biomedical Applications.

Organic polymers have been applied successfully in fields such as adhesion, biomaterials, protective coatings, friction and wear, composites, microelectronic devices, and thin-film technology. In general, special surface properties with regard to chemical composition, hydrophilicity, roughness, crystallinity, conductivity, lubricity, and cross-linking density are required for the success of these applications. Polymers very often do not possess the surface properties needed for these applications. For these reasons, surface modification techniques which can transform these inexpensive materials into highly valuable finished products have become an important part of the plastics industry. In case of biomedical polymers is plasma treatment used for enhancing cell adhesion, growth and proliferation and to make them suitable for implants and tissue engineering scaffolds. Nanoparticles fascinated scientists for over a century and are now heavily utilized in chemistry, biology, engineering, and medicine. Nowadays nanoparticles can be synthesized reproducibly, modified with seemingly limitless chemical functional groups, and, in certain cases, characterized with atomic-level precision. In recent years, focus has turned to therapeutic possibilities for such materials. Structures, which behave as drug carriers, antimicrobial agents, and photoresponsive therapeutics have been developed and studied in the context of cells and many debilitating diseases. These structures are not simply chosen as alternatives to molecule-based systems, but rather for their new physical and chemical properties, which confer substantive advantages in cellular and medical applications. In this review, we provide insights into immobilization, toxicity and biomedical applications of gold, silver and carbon nanoparticles and discuss their grafting to polymer substrates and the influence on cell-material interactions. The adhesion and the response of cells in contact with the surface play an important role in the cytocompatibility of the implant. It is thus important to understand how cells interact with their environment. The main properties decisive for colonization of a material with cells are surface chemistry, roughness, morphology and polarity, wettability and electrical charge.

Surface properties of thin gold layers sputtered on polymers.

Thin gold layers were sputtered on the foils of polypropylene-PP, polyethyleneterephthalate-PET, polystyrene-PS, polyethylene-PE and polytetrafluoroethylene-PTFE modified by Ar+ plasma. Surface properties of pristine, plasma treated and gold coated polymers were characterized by two-points method (sheet electrical resistance), electrokinetical analysis (zeta-potential, surface chemistry), goniometry (contact angle), electron paramagnetic resonance (concentration of radicals), atomic force microscopy (AFM, surface morphology and roughness) and scratch test (mechanical properties). Zeta potential and contact angle, as assumed, differ dramatically for plasma treated polymers and for the polymers deposited by Au layers. AFM images indicate that after gold deposition on polymers the surface roughness and the surface morphology change depending on pristine polymer surfaces (roughness and morphology) and sputtering time. Electrical measurements resulted in fact that with increasing layer thickness, the sheet resistance of the gold layer decreases for all polymers with increasing sputtering time. Lower adhesive destruction is observed on the gold layer deposited on plasma treated PE in comparison with pristine.

Plasma-modified and polyethylene glycol-grafted polymers for potential tissue engineering applications.

Modified and grafted polymers may serve as building blocks for creating artificial bioinspired nanostructured surfaces for tissue engineering. Polyethylene (PE) and polystyrene (PS) were modified by Ar plasma and the surface of the plasma activated polymers was grafted with polyethylene glycol (PEG). The changes in the surface wettability (contact angle) of the modified polymers were examined by goniometry. Atomic Force Microscopy (AFM) was used to determine the surface roughness and morphology and electrokinetical analysis (Zeta potential) characterized surface chemistry of the modified polymers. Plasma treatment and subsequent PEG grafting lead to dramatic changes in the polymer surface morphology, roughness and wettability. The plasma treated and PEG grafted polymers were seeded with rat vascular smooth muscle cells (VSMCs) and their adhesion and proliferation were studied. Biological tests, performed in vitro, show increased adhesion and proliferation of cells on modified polymers. Grafting with PEG increases cell proliferation, especially on PS. The cell proliferation was shown to be an increasing function of PEG molecular weight.