Summary Silver nanoparticles constitute a very promising approach for the development of new antimicrobial systems. Nanoparticulate objects can bring significant improvements in the antibacterial activity of this element, through specific effect such as an adsorption at bacterial surfaces. However, the mechanism of action is essentially driven by the oxidative dissolution of the nanoparticles, as indicated by recent direct observations. The role of Ag + release in the action mechanism was also indirectly observed in numerous studies, and explains the sensitivity of the antimicrobial activity to the presence of some chemical species, notably halides and sulfides which form insoluble salts with Ag + . As such, surface properties of Ag nanoparticles have a crucial impact on their potency, as they influence both physical (aggregation, affinity for bacterial membrane, etc.) and chemical (dissolution, passivation, etc.) phenomena. Here, we review the main parameters that will affect the surface state of Ag NPs and their influence on antimicrobial efficacy. We also provide an analysis of several works on Ag NPs activity, observed through the scope of an oxidative Ag + release.

The synthesis on the gram scale and characterization of a series of flexible functionalized iron terephthalate MIL-53(Fe) type solids are reported. Chemical groups of various polarities, hydrophilicities, and acidities (-Cl, -Br, -CF(3), -CH(3), -NH(2), -OH, -CO(2)H) were introduced through the aromatic linker, to systematically modify the pore surface. X-ray powder diffraction (XRPD), molecular simulations, thermogravimetric analyses, and in situ IR and (57)Fe Mössbauer spectrometries indicate some similarities with the pristine MIL-53(Fe) solid, with the adoption of the narrow pore form for all solids in both the hydrated and dry forms. Combined XRPD and computational structure determinations allow concluding that the geometry of the pore opening is predominantly correlated with the intraframework interactions rather than the steric hindrance of the substituent. Only (MIL-53(Fe)-(CF(3))(2)) exhibits a nitrogen accessible porosity (S(BET) approximately 100 m(2) g(-1)). The adsorption of some liquids leads to pore openings showing some very specific behaviors depending on the guest-MIL-53(Fe) framework interactions, which can be related to the energy difference between the narrow and large pore forms evaluated by molecular simulation.

A series of conductive porous composites were obtained by the polymerization of 3,4-ethylenedioxythiophene (EDOT) in the cavities of MIL-101(Cr). By controlling the amount of EDOT loaded into the host framework, it was possible to modulate the conductivity as well as the porosity of the composite. This approach yields materials with a reasonable electronic conductivity (1.1 × 10(-3) S·cm(-1)) while maintaining high porosity (SBET = 803 m(2)/g). This serves as a promising strategy for obtaining highly nanotextured conductive polymers with very high accessibility for small gas molecules, which are beneficial to the fabrication of a chemiresistive sensor for the detection of NO2.

The melting behavior of a coordination polymer (CP) crystal was utilized to achieve enhanced and optically switchable proton conductivity in the solid state. The strong acid molecules (triflic acid) were doped in one-dimensional (1D) CP, [Zn(HPO )(H PO ) ](ImH ) (ImH =monoprotonated imidazole) in the melt state, and overall enhancement in the proton conductivity was obtained. The enhanced proton conductivity is assigned to increased number of mobile protons and defects created by acid doping. Optical control over proton conductivity in the CP is achieved by doping of the photo acid molecule pyranine into the melted CP. The pyranine reversibly generates the mobile acidic protons and local defects in the glassy state of CP resulting in the bulk switchable conductivity mediated by light irradiation. Utilization of CP crystal in liquid state enables to be a novel route to incorporate functional molecules and defects, and it provides a tool to control the bulk properties of the CP material.

The uptake of molecular guests, a hallmark of the supramolecular chemistry of cages and containers, has yet to be documented for soluble assemblies of metal nanoparticles. Here we demonstrate that gold nanoparticle-based supraspheres serve as a host for the hydrophobic uptake, transport and subsequent release of over two million organic guests, exceeding by five orders of magnitude the capacities of individual supramolecular cages or containers and rivalling those of zeolites and metal-organic frameworks on a mass-per-volume basis. The supraspheres are prepared in water by adding hexanethiol to polyoxometalate-protected 4 nm gold nanoparticles. Each 200 nm assembly contains hydrophobic cavities between the estimated 27,400 gold building blocks that are connected to one another by nanometre-sized pores. This gives a percolated network that effectively absorbs large numbers of molecules from water, including 600,000, 2,100,000 and 2,600,000 molecules (35, 190 and 234 g l ) of para-dichorobenzene, bisphenol A and trinitrotoluene, respectively.H ost-guest phenomena that involve the uptake of gases and small molecules are associated with the supramolecular chemistry of soluble capsules, cages and containers [1][2][3][4][5] or, alternatively, with heterogeneous reactions of porous solid-state materials such as zeolites 6 and metal-organic frameworks 7 . Only now, however, are organized assemblies of metal nanoparticles beginning to serve in a similar capacity as hosts for molecular guests. In organic solvents, for example, light-induced dipoledipole interactions between gold nanoparticles with azobenzenefunctionalized thiolate ligands were recently used to entrap and catalyse the reactions of polar and alkylaromatic substrates 8 . By design, substrates were entrapped during nanoparticle aggregation to overcome the poor uptake and diffusion of molecular guests into colloidal nanocrystal assemblies. However, the uptake of molecular guests, a trait of supramolecular and solid-state chemistry, has so far not been achieved for colloidal nanoparticle assemblies.For that to occur, a thermodynamically favourable driving force must be combined with a porous structure whose interior architecture features host cavities, along with pathways for the effective diffusion of molecular guests from the exterior (bulk solution) to host domains deeply buried in the assembly's interior. If this were achieved, colloidal metal-nanoparticle assemblies could emerge as a new class of functional nano-engineered structures that are uniquely positioned between supramolecular containers and porous solid-state materials.We report a new class of functional assemblies, wherein the hydrophobic effect 9,10 drives the spontaneous uptake of alkyl and alkylaromatic guests 11 by porous 200 nm diameter supraspheres whose host capacities are orders of magnitude larger than those of individual cages or containers. On a mass-per-volume basis, the level of uptake rivals those of zeolites and metal-organic frameworks, which, for methane at elevated pressures, r...

Separation of high-molecular-weight polymers differing just by one monomeric unit remains a challenging task. Here, we describe a protocol using metal-organic frameworks (MOFs) for the efficient separation and purification of mixtures of polymers that differ only by their terminal groups. In this process, polymer chains are inserted by threading one of their extremities through a series of MOF nanowindows. Selected termini can be adjusted by tuning the MOF structure, and the insertion methodology. Accordingly, MOFs with permanently opened pores allow for the complete separation of poly(ethylene glycol) (PEG) based on steric hindrance of the terminal groups. Excellent separation is achieved, even for high molecular weights (20 kDa). Furthermore, the dynamic character of a flexible MOF is used to separate PEG mixtures with very similar terminal moieties, such as OH, OMe, and OEt, as the slight difference of polarity in these groups significantly changes the pore opening kinetics.

Unlike commonly used molecular recognition techniques, recognition of polymer structures requires an additional aspect of extremely high recognition ability, by which marginal structural differences can be identified in a large polymer chain. Herein we show that metal−organic frameworks (MOFs) can recognize polymer terminal structures, thus enabling the first reported chromatographic separation of polymers. End-functionalized polyethylene glycols (PEGs) are selectively inserted into the MOF channel, the insertion kinetics being dependent on the projection size of the PEG terminus. This size-selective insertion mechanism facilitates precise discrimination of end-functionalized PEGs using liquid chromatography (LC). An MOF-packed column thus provides an efficient and easily accessible method for the separation of such end-functionalized polymers using conventional LC systems.

The development of highly porous metal-organic frameworks (MOFs) is greatly sought after, due to their wide range of applications. As an alternative to the development of new structures, we propose to obtain new stable configurations for flexible MOFs by insertion of polymeric guests. The guests prevent the otherwise spontaneous closing of the host frameworks and result in stable opened forms. Introduced at a fraction of the maximal capacity, polymer chains cause an opening of the occupied nanochannels, and because of the MOF reticular stiffness, this opening is propagated to the neighboring nanochannels that become accessible for adsorption. Composites were obtained by in situ polymerization of vinyl monomers in the nanochannels of an otherwise nonporous MOF, resulting in homogeneously loaded materials with a significant increase of porosity (S = 920 m/g). In addition, by limiting the accessible configurations for the framework and forbidding the formation of a reactive intermediate, the polymeric guest prevented the thermal degradation of the host MOF even at very low loading (as low as 3 wt %) and increased its stability domain by more than 200 °C.