Rational Functionalization Towards Redox-Active TEMPO Stable Free-Radical-Hydrochar Composites.

Although both stable free organic radicals and biomass-derived hydrochars have emerged as appealing, green, multifunctional materials, their association has not been explored. In this study, strength is found to lie in their union, which primarily leads to stable redox-active free-radical-hydrochar composites that can generate unexpected opportunities for the development of advanced metal-free sustainable materials. The composites are obtained by a straightforward green one-pot hydrothermal procedure. The loading of stable free radicals of nitroxide type and their localization is engineered by the nature of the carbohydrate and the reaction status; vigorous reaction parameters promote faster nucleation and growth kinetics of the hydrochar products, leading to a covalent immobilization of redox species on the surface of the carbonaceous microspherical aggregates. The nitroxide free-radical-hydrochar materials demonstrate enhancements in terms of both electrocatalytic activity and capacitive features.

Self-assembled zinc oxide hierarchical structures with enhanced antibacterial properties from stacked chain-like zinc oxalate compounds.

Single ZnO crystallites assembled into porous hierarchical structures have been prepared by topotactic thermal decomposition of in situ obtained zinc oxalate precursors, whose synthesis involves a redox reaction between 1,2-ethanediol and nitrate ion. For the first time it was demonstrated that post-synthesis protocols of the precursors (e.g. ultrasound irradiation, hydrolytic decomposition) master the hydrogen bonds formed between oxalate chains, allowing that way the adjustment of materials properties (morphology, porosity and optical) and a rational introduction of different dopants (Eu3+/Er3+). The ZnO surface reactivity is confirmed by the significant biocidal activity of the obtained materials against Gram-positive and Gram-negative planktonic and biofilm-embedded cells, superior to those reported in the literature for other ZnO-based materials or antibiotics, associated also with a good biocompatibility.

Eco-friendly synthesized spherical ZnO materials: Effect of the core-shell to solid morphology transition on antimicrobial activity.

ZnO materials with spherical morphology, core-shell and solid, disperse or interconnected, were obtained by a completely green synthesis via a carbohydrate-template route. Morphology, structure and optical properties, as well as antimicrobial potential and cytocompatibility were investigated. The antimicrobial efficiency of the obtained materials was screened against a large spectrum of reference and clinical microbial strains, both susceptible and exhibiting resistance phenotypes of clinical and epidemiological interest, in planktonic and biofilm state. Their biocidal activity is strongly dependent of material's characteristics and target microorganism. One of the most valuable findings of our study is the good antibiofilm activity of the obtained nanostructures, which in some cases was superior to that noted against planktonic cells, despite the well-known high tolerance of biofilm-embedded cells to different stressor agents. Another important finding is the excellent efficiency against three Gram-negative, respectively Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae and two Gram-positive species, i.e. Staphylococcus aureus and Enteroccus faecium included in the ESKAPE list of the most dangerous resistant pathogens, requiring global surveillance and urgent need for the development of novel antimicrobial agents. Our study offers the first insight regarding the high therapeutic potential of ZnO nanoparticles against the fearful nosocomial pathogen A. baumannii. The cytocompatibility of the developed materials in terms of cell morphology, viability and proliferation, revealed a comparable dose-dependent cellular response, at the active antimicrobial concentrations, only a low effect on cell viability is evidenced. Overall, our data demonstrated the potential of the materials for antimicrobial applications and also that their biotoxicity can be modulated directly through their morpho-structural characteristics.

Sustainable one-pot integration of ZnO nanoparticles into carbon spheres: manipulation of the morphological, optical and electrochemical properties.

ZnO-carbon composite spheres were synthesized via starch hydrothermal carbonization (HTC) in the presence of a soluble zinc salt (acetate), followed by thermal processing under an argon atmosphere. Besides sustainability, the one-pot procedure represents a scalable synthesis of tailored carbon-metal oxide spheres with a structurally-ordered carbon matrix obtained at a relatively low temperature (700 °C). The ability of zinc cations to develop different linkages with starch's hydrophilic functional groups and to act as external nucleators determines an increase in HTC yield; the effect is obvious even in the presence of small concentrations of zinc in the reaction medium (0.005 M), thus providing a way to improve the carbonization process efficiency. It is also shown that zinc content is the control vector of the spherical composite's properties: a variation from 0.3 to 4.8 at% not only induces a variation in their size (200 nm-10 µm), interconnectivity (from disperse spheres to necklace-like aggregations), surface area and connected porosity (from micro- to mesoporosity), but also of their electrochemical and white light adsorption and emission features. Since the variation in zinc content is made by a simple adjustment of the raw material concentrations, the functionality of these carbon-based materials can be modulated in a straightforward manner.

Tunable ZnO spheres with high anti-biofilm and antibacterial activity via a simple green hydrothermal route.

A family of distinct ZnO morphologies - hollow, compartmented, core-shell and full solid ZnO spheres, dispersed or interconnected - is obtained by a simple hydrothermal route, in the presence of the starch biopolymer. The zinc-carbonaceous precursors were characterized by infrared spectroscopy, thermal analysis and scanning electron microscopy, while the ZnO spheres, obtained after the thermal processing, were investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, UV-VIS spectroscopy, photoluminescence measurements, antimicrobial, anti-biofilm and flow cytometry tests. The formation mechanism proposed for this versatile synthesis route is based on the gelling ability of amylose, one of the starch template constituents, responsible for the effective embedding of zinc cations into starch prior to its hydrothermal carbonization. The simple variation of the raw materials concentration dictates the type of ZnO spheres. The micro-sized ZnO spheres exhibit high antibacterial and anti-biofilm activity against Gram-positive (Staphylococcus aureus, Bacillus subtilis) and Gram-negative (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa) reference and methicillin resistant clinical strains especially for Gram-negative biofilms (P. aeruginosa), demonstrating great potential for new ZnO anti-biofilm formulations.

Spatial control of 3D energy transfer in supramolecular nanostructured host-guest architectures.

Systematic control of 3D energy transfer (ET) dynamics is achieved in supramolecular nanostructured host-guest systems using spacer-functionalized guest chromophores. Quantum chemistry-based Monte Carlo simulations reveal the strong impact of the spacer length on the ET dynamics, efficiency, and dimensionality. Remarkably high exciton diffusion lengths demonstrate that there is ample scope for optimizing oligomeric or polymeric optoelectronic devices.