Stereodefined ring contraction-rearrangement of thiocoumarins to new fused benzo[b]thiophene derivatives

Mesoionic 1,3-oxazolium-5-olates (münchnones) react with thiocoumarins having an electron-withdrawing group at the 3-position to afford stereodefined fused polycyclic thienopyrroles. The reaction sequence seems to be triggered by a regiospecific dipolar cycloaddition followed by ring opening of the initial 1:1 cycloadduct and intramolecular rearrangement with an unusual ring contraction.     

Fast and stable photochromic oxazines for fluorescence switching

The stringent limitations imposed by diffraction on the spatial resolution of fluorescence microscopes demand the identification of viable strategies to switch fluorescence under optical control. In this context, the photoinduced and reversible transformations of photochromic compounds are particularly valuable. In fact, these molecules can be engineered to regulate the emission intensities of complementary fluorophores in response to optical stimulations. On the basis of this general design logic, we assembled a functional molecular construct consisting of a borondipyrromethene fluorophore and a nitrospiropyran photochrome and demonstrated that the emission of the former can be modulated with the interconversion of the latter. This fluorophore-photochrome dyad, however, has a slow switching speed and poor fatigue resistance. To improve both parameters, we developed a new family of photochromic switches based on the photoinduced opening and thermal closing of an oxazine ring. These compounds switch back and forth between ring-closed and -open isomers on nanosecond-microsecond timescales and tolerate thousands of switching cycles with no sign of degradation. In addition, the attachment of appropriate chromophoric fragments to their switchable oxazine ring can be exploited to either deactivate or activate fluorescence reversibly in response to illumination with a pair of exciting beams. Specifically, we assembled three dyads, each based on either a borondipyrromethene or a coumarin fluorophore and an oxazine photochrome, and modulated their fluorescence in a few microseconds with outstanding fatigue resistance. The unique photochemical and photophysical properties of our fluorophore-photochrome dyads can facilitate the development of switchable fluorophores for superresolution imaging and, ultimately, provide valuable molecular probes for the visualization of biological samples on the nanometer level.     

Solubility of metal atoms in helium droplets: exploring the effect of the well depth using the coinage metals Cu and Ag

We report a theoretical investigation of the solution properties of Cu and Ag atoms dissolved in He clusters. Employing our recent ab initio ground state pair potential for Me-He (Me = Ag, Cu), we simulated the species Me@He (n) (n = 2-100) by means of diffusion Monte Carlo (DMC) obtaining exact information on their energetics and the structural properties. In particular, we investigated the sensitivity of structural details on the well depth of the two interaction potentials. Whereas Ag structures the first He solvation layer similarly, to some extent, to a positive ion such as Na(+), Cu appears to require the onset of a second solvation shell for a similar dense structure to be formed despite an interaction well of 28.4 μhartree. An additional signature of the different solution behavior between Ag and Cu appears also in the dependence of the energy required to evaporate a single He atom on the size of the MeHe(n) clusters. The absorption spectrum for the (2)P ← (2)S excitation of the metals was also simulated employing the semi-classical Lax approximation to further characterize Me@He(n) (n = 2-100) using novel accurate interaction potentials between He and the lowest (2)P state of Ag and Cu in conjunction with the Diatomic-in-Molecules approach. The results indicated that Ag exciplexes should not form via a direct vertical excitation into an attractive region of the excited manifolds and that there is an interesting dependence of the shape of the Cu excitation bands on the local structure of the first solvation shell.     

Silver nanoparticles as potential antiviral agents

Virus infections pose significant global health challenges, especially in view of the fact that the emergence of resistant viral strains and the adverse side effects associated with prolonged use continue to slow down the application of effective antiviral therapies. This makes imperative the need for the development of safe and potent alternatives to conventional antiviral drugs. In the present scenario, nanoscale materials have emerged as novel antiviral agents for the possibilities offered by their unique chemical and physical properties. Silver nanoparticles have mainly been studied for their antimicrobial potential against bacteria, but have also proven to be active against several types of viruses including human imunodeficiency virus, hepatitis B virus, herpes simplex virus, respiratory syncytial virus, and monkey pox virus. The use of metal nanoparticles provides an interesting opportunity for novel antiviral therapies. Since metals may attack a broad range of targets in the virus there is a lower possibility to develop resistance as compared to conventional antivirals. The present review focuses on the development of methods for the production of silver nanoparticles and on their use as antiviral therapeutics against pathogenic viruses.     

A successful chemical strategy to induce oligothiophene self-assembly into fibers with tunable shape and function

Functional supramolecular architectures for bottom-up organic nano- and microtechnology are a high priority research topic. We discovered a new recognition algorithm, resulting from the combination of thioalkyl substituents and head-to-head regiochemistry of substitution, to induce the spontaneous self-assembly of sulfur overrich octathiophenes into supramolecular crystalline fibers combining high charge mobility and intense fluorescence. The fibers were grown on various types of surfaces either as superhelices or straight rods depending on molecular structure. Helical fibers directly grown on a field effect transistor displayed efficient charge mobility and intrinsic 'memory effect'. Despite the fact that the oligomers did not have chirality centers, one type of hand-helicity was always predominant in helical fibers, due to the interplay of molecular atropisomerism and supramolecular helicity induced by terminal substituents. Finally, we found that the new sulfur overrich oligothiophenes can easily be prepared in high yields through ultrasound and microwave assistance in green conditions.     

Photogenerated defects in shape-controlled TiO2 anatase nanocrystals: a probe to evaluate the role of crystal facets in photocatalytic processes

The promising properties of anatase TiO(2) nanocrystals exposing specific surfaces have been investigated in depth both theoretically and experimentally. However, a clear assessment of the role of the crystal faces in photocatalytic processes is still under debate. In order to clarify this issue, we have comprehensively explored the properties of the photogenerated defects and in particular their dependence on the exposed crystal faces in shape-controlled anatase. Nanocrystals were synthesized by solvothermal reaction of titanium butoxide in the presence of oleic acid and oleylamine as morphology-directing agents, and their photocatalytic performances were evaluated in the phenol mineralization in aqueous media, using O(2) as the oxidizing agent. The charge-trapping centers, Ti(3+), O(-), and O(2)(-), formed by UV irradiation of the catalyst were detected by electron spin resonance, and their abundance and reactivity were related to the exposed crystal faces and to the photoefficiency of the nanocrystals. In vacuum conditions, the concentration of trapped holes (O(-) centers) increases with increasing {001} surface area and photoactivity, while the amount of Ti(3+) centers increases with the specific surface area of {101} facets, and the highest value occurs for the sample with the worst photooxidative efficacy. These results suggest that {001} surfaces can be considered essentially as oxidation sites with a key role in the photoxidation, while {101} surfaces provide reductive sites which do not directly assist the oxidative processes. Photoexcitation experiments in O(2) atmosphere led to the formation of Ti(4+)-O(2)(-) oxidant species mainly located on {101} faces, confirming the indirect contribution of these surfaces to the photooxidative processes. Although this work focuses on the properties of TiO(2), we expect that the presented quantitative investigation may provide a new methodological tool for a more effective evaluation of the role of metal oxide crystal faces in photocatalytic processes.     

Water evaporation from gel beads

Hydrogels are characterized by properties which make them ideal candidates for applications in several fields, such as drug delivery, biomedicine, and functional foods. Molecular diffusion out of a hydrogel matrix depends on their hydrodynamic radii and the mesh sizes within the matrix of the gel. A quantitative experimental and mathematical understanding of interactions, kinetics, and transport phenomena within complex hydrogel systems assists network design by identifying the key parameters and mechanisms that govern the rate and extent of solute release. In this article a calorimetric differential scanning calorimetry (DSC) study reports on the approach to parallel water effusion from a hydrogel matrix to the release of a model protein. The measurement of the water evaporation is taken as the simplest routine determination of a phenomenon that is basically due to a diffusive process through the porous structure of the gel and thermodynamically governed by the difference in the water chemical potential inside and outside of the bead. The analysis of the experimental calorimetric curves is made with the purpose of extracting several numerical parameters characteristic of each curve. The rationale is to develop a simple methodology to understand the release properties of the porous structure of the complex gel matrix by means of DSC.     

A priori estimates for rough PDEs with application to rough conservation laws

We introduce a general weak formulation for PDEs driven by rough paths, as well as a new strategy to prove well-posedness. Our procedure is based on a combination of fundamental a priori estimates with (rough) Gronwall-type arguments. In particular this approach does not rely on any sort of transformation formula (flow transformation, Feynman–Kac representation formula etc.) and is therefore rather flexible. As an application, we study conservation laws driven by rough paths establishing well–posedness for the corresponding kinetic formulation.     

Embedding a novel objective function in a two-phased local search for robust vertex coloring

In this paper, we propose a two-phased local search for vertex coloring. The algorithm alternately executes two closely interacting functionalities, i.e., a stochastic and a deterministic local search. The stochastic phase is basically based on biased random sampling that, according to a probability matrix storing the probability a vertex can be assigned to a color, iteratively constructs feasible colorings. The deterministic phase, instead, consists in assigning sequentially, according to a given ordering, each vertex to the color which causes the lowest increase of the solution penalty, and then, when the schedule is constructed, swap operations are executed to improve the performance. The interaction between the two phases is implemented by tunnelling information of what happened during a phase to the successive ones. Beyond the algorithm scheme, the novelty of the approach stems from the fact that the objective function is not minimizing the number of colors but a new penalty function. The proposed approach is tested on known benchmarks for the studied problem available on the public domain. From a comparison to the state of the art it appears that the proposed approach is robust and is able to achieve best known results.     

Synthesis of novel rigid-rod and tripodal azulene chromophores

Two novel azulene chromophores 1 and 2 were synthesized to study dynamics of ultrafast electron injection at the interface of TiO₂ semiconductor nanoparticles. Fluorescence quenching was observed upon binding.