Spatial Coordination of Cooperativity in Silica-Supported Cu/TEMPO/Imidazole Catalytic Triad

Multifunctional catalysts obtained by the covalent immobilization of discrete molecular species on porous supports represent a unique approach to emulate some of the design principle and performances of enzymes. However, it is decisive in such systems to control the stoichiometry, spatial distribution, and proximity between the grafted catalytic centers to satisfy the chemical and geometrical requirements for cooperativity. Here, we present strategies to optimize the activity of a catalytic triad on mesoporous silica particles in the representative aerobic oxidation of benzyl alcohol and show that, in contrast with the more-traditional mixed-monolayer approach, activity can be amplified by tuning the spatial distribution of the co-catalysts to maximize the probability of full synergistic pairings

Sequence and Surface Confinement Direct Cooperativity in Catalytic Precision Oligomers

Confinement and cooperativity are important design principles used by Nature to optimize catalytic activity in enzymes. In these biological systems, the precise sequence of the protein encodes for specific chain folding to preorganize critical amino acid side chains within defined binding pockets, allowing synergistic catalytic activation pathways to be expressed and triggered. Here we show that short synthetic precision oligomers with the optimal sequence of catalytic units, spatially arranged by dense surface grafting to form confined cooperative “pockets”, display an up to 5-fold activity improvement compared to a “mismatched” sequence or free oligomers using the (pyta)­Cu/TEMPO/NMI-catalyzed aerobic selective oxidation of alcohols as a model reaction. We thus demonstrate that, in analogy with enzymes, sequence definition combined with surface grafting induce the optimized distribution, both radially (interchain) and axially (intrachain), of a catalytic triad, and that the impressive improvement of catalytic efficiency results predominantly from “matched” interchain interactions in the surface-confined system, thereby outperforming the homogeneous system. The concept presented here hence uncovers a new paradigm in the design of multifunctional molecular assemblies to control functions at a level approaching biological precision

Nanofibrillar Patches of Commensal Skin Bacteria

We demonstrate entrapment of the commensal skin bacteria Staphylococcus epidermidis in mats composed of soft nanotubes made by membrane-templated layer-by-layer (LbL) assembly. When cultured in broth, the resulting nanofibrillar patches efficiently delay the escape of bacteria and their planktonic growth, while displaying high steady-state metabolic activity. Additionally, the material properties and metabolic activity can be further tuned by postprocessing the patches with additional polysaccharide LbL layers. These patches offer a promising methodology for the fabrication of bacterial skin dressings for the treatment of skin dysbiosis while preventing adverse effects due to bacterial proliferation

Nanofibrillar Patches of Commensal Skin Bacteria

We demonstrate entrapment of the commensal skin bacteria Staphylococcus epidermidis in mats composed of soft nanotubes made by membrane-templated layer-by-layer (LbL) assembly. When cultured in broth, the resulting nanofibrillar patches efficiently delay the escape of bacteria and their planktonic growth, while displaying high steady-state metabolic activity. Additionally, the material properties and metabolic activity can be further tuned by postprocessing the patches with additional polysaccharide LbL layers. These patches offer a promising methodology for the fabrication of bacterial skin dressings for the treatment of skin dysbiosis while preventing adverse effects due to bacterial proliferation

Integrating Proteins in Layer-by-Layer Assemblies Independently of their Electrical Charge

Layer-by-layer (LbL) assembly is an attractive method for protein immobilization at interfaces, a much wanted step for biotechnologies and biomedicine. Integrating proteins in LbL thin films is however very challenging due to their low conformational entropy, heterogeneous spatial distribution of charges, and polyampholyte nature. Protein–polyelectrolyte complexes (PPCs) are promising building blocks for LbL construction owing to their standardized charge and polyelectrolyte (PE) corona. In this work, lysozyme was complexed with poly­(styrenesulfonate) (PSS) at different ionic strengths and pH values. The PPCs size and electrical properties were investigated, and the forces driving complexation were elucidated, in the light of computations of polyelectrolyte conformation, with a view to further unravel LbL construction mechanisms. Quartz crystal microbalance and atomic force microscopy were used to monitor the integration of PPCs compared to the one of bare protein molecules in LbL assemblies, and colorimetric assays were performed to determine the protein amount in the thin films. Layers built with PPCs show higher protein contents and hydration levels. Very importantly, the results also show that LbL construction with PPCs mainly relies on standard PE–PE interactions, independent of the charge state of the protein, in contrast to classical bare protein assembly with PEs. This considerably simplifies the incorporation of proteins in multilayers, which will be beneficial for biosensing, heterogeneous biocatalysis, biotechnologies, and medical applications that require active proteins at interfaces

Structure and Ferroelectric Properties of Nanoimprinted Poly(vinylidene fluoride-<i>ran</i>-trifluoroethylene)

Nanoimprint lithography (NIL) was used to shape thin films of a ferroelectric copolymer of vinylidene fluoride and trifluoroethylene (PVDF-TRFE), using a variety of molding shapes and imprinting conditions. The morphology of the layers was characterized by atomic force microscopy (AFM), and preferential orientation of the crystallographic axes was monitored by infrared microspectroscopy; in addition, the local ferroelectric properties were obtained by piezoresponse force microscopy (PFM). When the sample is imprinted in its paraelectric phase in conditions leading to complete confinement, in cavities of size lower than the natural lamellar length observed in a continuous thin film, the crystallographic <i>a</i> axis aligns preferentially parallel to the substrate, and the crystalline lamellae are of significantly reduced length. These characteristics translate in a strongly decreased coercive field and accelerated ferroelectric switching, which is in part ascribed to the improved coupling between the electric field and the properly oriented dipole moments. When decreasing the confinement either by leaving a residual film connecting the nanopillars, or by increasing the lateral size of the nanopillars above the natural lamellar length, or by using line molds where confinement only exists in one direction, or by using continuous films, the preferential orientation becomes less visible and the lamellar length increases, resulting in increased coercive and switching fields. Interestingly, the average length of the crystalline lamellae tends to correlate with the value of the coercive field. Finally, if the sample is imprinted in the melt, a flat-on setting of the crystalline lamellae ensues, with a vertical chain axis which is unfavorable for ferroelectric properties probed with a vertical electric field

Controlling the Growth of Staphylococcus epidermidis by Layer-By-Layer Encapsulation

Commensal skin bacteria such as Staphylococcus epidermidis are currently being considered as possible components in skin-care and skin-health products. However, considering the potentially adverse effects of commensal skin bacteria if left free to proliferate, it is crucial to develop methodologies that are capable of maintaining bacteria viability while controlling their proliferation. Here, we encapsulate S. epidermidis in shells of increasing thickness using layer-by-layer assembly, with either a pair of synthetic polyelectrolytes or a pair of oppositely charged polysaccharides. We study the viability of the cells and their delay of growth depending on the composition of the shell, its thickness, the charge of the last deposited layer, and the degree of aggregation of the bacteria which is varied using different coating proceduresamong which is a new scalable process that easily leads to large amounts of nonaggregated bacteria. We demonstrate that the growth of bacteria is not controlled by the mechanical properties of the shell but by the bacteriostatic effect of the polyelectrolyte complex, which depends on the shell thickness and charge of its outmost layer, and involves the diffusion of unpaired amine sites through the shell. The lag times of growth are sufficient to prevent proliferation for daily topical applications

Room-Temperature Magnetic Switching of the Electric Polarization in Ferroelectric Nanopillars

Magnetoelectric layers with a strong coupling between ferroelectricity and ferromagnetism offer attractive opportunities for the design of new device architectures such as dual-channel memory and multiresponsive sensors and actuators. However, materials in which a magnetic field can switch an electric polarization are extremely rare, work most often only at very low temperatures, and/or comprise complex materials difficult to integrate. Here, we show that magnetostriction and flexoelectricity can be harnessed to strongly couple electric polarization and magnetism in a regularly nanopatterned magnetic metal/ferroelectric polymer layer, to the point that full reversal of the electric polarization can occur at room temperature by the sole application of a magnetic field. Experiments supported by finite element simulations demonstrate that magnetostriction produces large strain gradients at the base of the ferroelectric nanopillars in the magnetoelectric hybrid layer, translating by flexoelectricity into equivalent electric fields larger than the coercive field of the ferroelectric polymer. Our study shows that flexoelectricity can be advantageously used to create a very strong magnetoelectric coupling in a nanopatterned hybrid layer

The Ferro- to Paraelectric Curie Transition of a Strongly Confined Ferroelectric Polymer

Nanopillars of ferroelectric polymers are of strong interest for the fabrication of low-cost nanoscale actuators and memories of high density. However, a limiting factor of polymers compared to inorganic ferroelectric materials is their low ferro- to paraelectric Curie transition, a problem compounded by the possible further decrease of the Curie temperature in nanostructures as was suggested by previous studies. Here we develop a methodology based on piezoresponse force microscopy to study the thermal stability of data stored in free-standing poled and annealed nanopillars of ferroelectric poly­(vinylidene fluoride-<i>ran</i>-trifluoroethylene), P­(VDF-TrFE), and thereby demonstrate that the Curie transition of a properly processed strongly confined ferroelectric polymer is not significantly modified compared to the bulk material, at least down to a mass as small as ca. 560 attograms corresponding to ca. 1500 chains only

Highly Versatile Approach for Preparing Functional Hybrid Multisegmented Nanotubes and Nanowires

The membrane-templating method was successfully combined with electrodeposition and layer-by-layer assembly to create various multisegmented nanostructures composed of metal, polymers, synthetic and biological polyelectrolytes, and colloids. The electrochemical approach offers the control over the architectural parameters of the resulting structures (in particular the segment length and morphology), whereas the LbL adsorption technique permits to integrate nonconducting materials, including biomacromolecules, within the nanostructures. A supplementary degree of complexity can be reached by capping or loading the LbL nanotubes with colloidal particles. The ability to easily generate such hybrid anisotropic nanoparticles with spatially resolved chemical, physical, and biochemical functionalities is a boon for the synthesis of nanostructures, which is of tremendous importance for electronic, sensing, drug delivery, and modern biomedical and biotechnological applications