Anselmo del Prado

Control over the synthesis of anisotropic nanoparticles is crucial as slight differences in their size, shape, sharpness, or the number of tips in the case of gold nanostars, has an inordinate influence on their properties and functionality for future applications. Herein, we show that the supplier and purity of polyvinylpyrrolidone (PVP) can significantly alter the synthesis of gold nanostars, demonstrating that impurities, not PVP itself, are the main factor responsible for star-like shape formation. We demonstrate that in the presence of pure PVP and N,N-dimethylformamide, the use of hydrazine leads to the formation of branched nanoparticles. This synthetic approach opens the door to solving issues associated with the use of commercial PVP during the synthesis of gold nanostars.

Non-viral vectors are a safety tool for gene therapy to deliver therapeutic genes. Among the different non-viral vectors, polyvinylpyrrolidone (PVP), a well-known hydrosoluble, neutral, and non-toxic polymer, satisfies the requirements and becomes a suitable candidate for gene delivery. In this study, we describe the preparation of polyvinylpyrrolidones decorated with pyrrolidine, piperidine, and piperazine groups, and evaluate them in vitro as non-viral gene carriers. The properties of these new systems are compared with those of hyperbranched polyethyleneimine (PEI) used as a positive control. Their ability to complex DNA at different N/P molar ratios, from 1:1 up to 10:1, was studied through agarose gel electrophoresis and dynamic light scattering. The resulting complexes (polyplexes) were characterized and evaluated in vitro with murine fibroblast (Swiss 3T3) as non-viral gene carriers, using luciferase as the reporter gene and a calcein cytocompatibility assay. All the copolymers condensed DNA to a particle average size between 100–400 nm when used at N/P ratios of 4:1 or higher. The copolymers with piperidine groups showed higher transfection efficiency than the pyrrolidine and piperazine modified copolymers, and even higher than the positive control of PEI at N/P ratios of 4:1 or higher. All the synthesized polyplexes from an aminated PVP displayed a general tendency of high cytocompatibility (75–95%) in comparison with the positive control PEI (55%).

Dynamic and reversible non‐covalent interactions endow synthetic systems and materials with smart adaptive functions that allow them to response to diverse stimuli, interact with external agents, or repair structural defects. Inspired by the outstanding performance and selectivity of DNA in living systems, scientists are increasingly employing Watson−Crick nucleobase pairing to control the structure and properties of self‐assembled materials. Two sets of complementary purine‐pyrimidine pairs (guanine:cytosine and adenine:thymine(uracil)) are available that provide selective and directional H‐bonding interactions, present multiple metal‐coordination sites, and exhibit rich redox chemistry. In this review, we highlight several recent examples that profit from these features and employ nucleobase interactions in functional systems and materials, covering the fields of energy/electron transfer, charge transport, adaptive nanoparticles, porous materials, macromolecule self‐assembly, or polymeric materials with adhesive or self‐healing ability.

In analogy to covalent reactions, the understanding of noncovalent association pathways is fundamental to influence and control any supramolecular process. Following an approach that is reminiscent of covalent methodologies, we study here, for the first time, the mechanism of G‐quadruplex formation in organic solvents. Our results support a reaction pathway in which the cation shifts the equilibrium towards a G‐quartet transient intermediate, which then acts as a template in the formation of the G‐quadruplex product.

In analogy to covalent reactions, the understanding of noncovalent association pathways is fundamental to influence and control any supramolecular process. Following an approach that is reminiscent of covalent methodologies, we study here, for the first time, the mechanism of G‐quadruplex formation in organic solvents. Our results support a reaction pathway in which the cation shifts the equilibrium towards a G‐quartet transient intermediate, which then acts as a template in the formation of the G‐quadruplex product.

The stimuli-responsiveness of supramolecular polymers has recently been exploited for the development of adhesives that can be (de)bonded on demand when heated or exposed to UV-light. However, it remains difficult to combine competitive solid-state mechanical properties and very low melt viscosity in one material. Here we report a new supramolecular polymer adhesives platform based on soybean oil as a multifunctional low-molecular weight monomer (~1500 g/mol) and isophthalic acid (IPA) groups that show hydrogen bonding and promote the formation of a reversible network. The polarity difference between the triglyceride backbone and the IPA groups leads to microphase separation, and the crystalline IPA domains act as physical cross-links. Heating the polymer above the melting temperature of the IPA-rich domains results in a dramatic viscosity reduction to 8 Pa·s at 120 ºC. Once cooled to room temperature, the material properties are fully recovered, as a result of the reassembly of the supramolecular network. Single lap joint adhesive tests performed at room temperature using glass and stainless steel substrates reveal shear strength values of 1.2 and 1.7 MPa, respectively, and heat and UV-light can be used as external stimuli to debond on command. In addition, composites were prepared by adding 5 or 10 wt%) microcrystalline cellulose (MCC), to the polymer and this led to an increase of strength and modulus below the glass transition by up to 80% and 170%, respectively. Because the introduction of MCC partially hinders the crystallization of the matrix, the the stiffness and tensile strength are reduced above the glass transition, while the elongation at break is significantly increased.

A well‐known approach toward mechanochromic polymers relies on the incorporation of excimer‐forming fluorophores into a matrix polymer and the disruption of aggregated chromophores when such materials undergo macroscopic mechanical deformation. However, the required aggregates and stress‐transfer processes have so far only been realized with select dye/polymer combinations. As demonstrated here, the utility of this approach can be extended by tethering an excimer‐forming cyano‐substituted oligo(p‐phenylene vinylene) fluorophore to the two ends of a telechelic poly(ethylene‐co‐butylene) and blending small amounts (0.1–2 wt%) of the resulting aggregachromic macromolecule into polymer matrices such as poly(ε‐caprolactone), poly(isoprene), or poly(styrene‐b‐butadiene‐b‐styrene). All blends display mechanofluorochromic responses, and the ratio between the monomer and excimer emission intensities can be used to correlate the luminescence signal to the extent of deformation and to follow subsequent relaxation processes. The developed approach significantly expands the scope of blend‐based mechanoresponsive luminescent materials.

In the present paper, we describe the synthesis of novel monomers prepared by regioselective Michael addition to asymmetric divinylic compounds. This chemoselectivity was experimentally studied employing different reaction conditions and theoretically calculated using chemical global and local descriptors. The global reactivity data show that incoming nucleophilic secondary amines preferentially attack the acrylic derived units acrylate and acrylamide, while deactivated methacrylate and N-vinyl-pyrrolidone require harder reaction conditions, which leads to the formation of by-products. Moreover, it is demonstrated that the presence of two vinyl units within a studied divinylic agent leads to a significant increase in its global reactivity parameters. Besides, the local reactivity parameters of asymmetric divinyl compounds show a preference for an attack at the C_β of activated units compared to the C_β center of deactivated units. Based on these results, asymmetric divinyl compounds are very interesting starting materials for the preparation of new functionalized monomers.