Synthesis, characterization, and photoinduced electron transfer in functionalized single wall carbon nanohorns

Single-wall carbon nanohorns (SWNHs) are a new class of material that is closely related to single-wall carbon nanotubes. Here, we describe the synthesis and characterization of a series of SWNHs functionalized with ethylene glycol chains and porphyrins. Functionalization of carbon nanohorns has been achieved using two different synthetic protocols: (1) direct attack of a free amino group on the nanohorn sidewalls (nucleophilic addition) and (2) amidation reaction of the carboxylic functions in oxidized nanohorns. The nanohorn derivatives have been characterized by a combination of several techniques, and the electronic properties of the porphyrin/nanohorn assemblies (SWNH/H2P) have been investigated by electrochemistry, spectroelectrochemistry, and a series of steady-state and time-resolved spectroscopy. The cyclic voltammetry curve of nanohorn/porphyrin conjugate 6 showed a continuum of faradic and pseudocapacitive behavior, which is associated with multiple-electron transfers to and from the SWNHs. Superimposed on such a pseudocapacitive current, the curve also displays three discrete reduction peaks at -2.26, -2.57, and -2.84 V and an oxidation peak at 1.12 V (all attributed to the porphyrin moiety). Steady-state and time-resolved fluorescence demonstrated a quenching of the fluorescence of the porphyrin in SWNH/H2P conjugates 5 and 6 compared to the reference free base porphyrin. Transient absorption spectra permitted the electron-transfer process between the porphyrins and the carbon nanostructures to be highlighted.     

From rooted to floating vegetal species in lagoons as a consequence of the increases of external nutrient load: An analysis by model of the species selection mechanism

In this paper, the substitution mechanism of rooted aquatic plants (as eelgrass) with floating species (as Ulva r.) in lagoons are inquired by using a eutrophication model.     

Analytical characterization of chitosan nanoparticles for peptide drug delivery applications

Chitosan-cyclodextrin hybrid nanoparticles (NPs) were obtained by the ionic gelation process in the presence of glutathione (GSH), chosen as a model drug. NPs were characterized by means of transmission electron microscopy and zeta-potential measurements. Furthermore, a detailed X-ray photoelectron spectroscopy study was carried out in both conventional and depth-profile modes. The combination of controlled ion-erosion experiments and a scrupulous curve-fitting approach allowed for the first time the quantitative study of the GSH in-depth distribution in the NPs. NPs were proven to efficiently encapsulate GSH in their inner cores, thus showing promising perspectives as drug carriers.     

Pd nanoparticles catalyzed stereospecific synthesis of beta-aryl cinnamic esters in ionic liquids

Reaction of the catalyst 1 or Pd(OAc)(2) with tetrabutylammonium acetate, dissolved in tetrabutylammonium bromide, leads to a fast formation of Pd nanoparticles which efficiently catalyze the stereospecific reaction of cinnamates with aryl halides to give beta-aryl-substituted cinnamic esters. The role of tetrabutylammonium acetate is crucial in determining the formation of nanoparticles and stereospecificity of the C-C coupling process.     

On almost revlex ideals with Hilbert function of complete intersections

Ricerche di Matematica - In this paper, we investigate the behavior of almost reverse lexicographic ideals with the Hilbert function of a complete intersection. More precisely, over a field K, we...     

Reduction of spectral interferences using ultraclean gold nanowire arrays in the LDI-MS analysis of a model peptide

The surface chemistry of gold nanowires (AuNWs) has been systematically assessed in terms of contamination and cleaning processes. The nanomaterial’s surface quality was correlated to its performance in the matrix-free laser desorption ionization mass spectrometry (LDI-MS) analysis of low molecular weight analytes. Arrays of AuNWs were deposited on glass slides by means of the lithographically patterned nanowire electrodeposition technique. AuNWs were then characterized in terms of surface chemical composition and morphology using X-ray photoelectron spectroscopy, scanning electron microscopy and atomic force microscopy. AuNWs were subjected to a series of well-known cleaning procedures with the aim of producing the best performing surfaces for the LDI-MS detection of leucine enkephalin, chosen as a model analyte with a molar mass below 1,000 g/mol. Prolonged cyclic voltammetry in 2 M sulfuric acid and, most of all, oxygen plasma cleaning for 5 min provided the best results in terms of simpler (interference-free) and more intense mass spectrometry spectra of the reference compound. The analyte always ionized as the sodiated adduct, and leucine enkephalin limits of detection of 0.5 and 2.5 pmol were estimated for the positive and negative analysis modes, respectively. This study points out the tight correlation existing between the chemical status of the nanostructure surface and the AuNW-assisted LDI-MS performance in terms of reproducibility of spectra, intensity of analyte ions and reduction of interferences.

Sugarcane bagasse cellulose fibres and their hydrous niobium phosphate composites: synthesis and characterization by XPS,XRD and SEM

Cellulose fibres obtained from sugarcane bagasse were submitted to a purification process, which consisted of an acid hydrolysis for elimination of the major part of lignin and hemicellulose. This was followed by a delignification process carried out in two steps to yield crude cellulose (CCell) fibres in the first one and with a subsequent bleaching in order to yield bleached cellulose fibres (BCell). Composites of crude and bleached cellulose fibres with hydrous niobium phosphate, cell/NbOPO₄·nH₂O, were subsequently synthesized. Scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction characterization of the obtained materials showed CCell/NbOPO₄·nH₂O and BCell/NbOPO₄·nH₂O are real composites. The nature of the cellulose (CCell or BCell) has an important role on the composites obtained, namely on the niobium salt composition at the composite surface. The synthesis of membranes of both cellulose and mixed matrix cellulose/NbOPO₄·nH₂O was only possible when the bleached cellulose was used.     

Facile decoration of functionalized single-wall carbon nanotubes with phthalocyanines via "click chemistry"

We describe the functionalization of single-wall carbon nanotubes (SWNTs) with 4-(2-trimethylsilyl)ethynylaniline and the subsequent attachment of a zinc-phthalocyanine (ZnPc) derivative using the reliable Huisgen 1,3-dipolar cycloaddition. The motivation of this study was the preparation of a nanotube-based platform which allows the facile fabrication of more complex functional nanometer-scale structures, such as a SWNT-ZnPc hybrid. The nanotube derivatives described here were fully characterized by a combination of analytical techniques such as Raman, absorption and emission spectroscopy, atomic force and scanning electron microscopy (AFM and SEM), and thermogravimetric analysis (TGA). The SWNT-ZnPc nanoconjugate was also investigated with a series of steady-state and time-resolved spectroscopy experiments, and a photoinduced communication between the two photoactive components (i.e., SWNT and ZnPc) was identified. Such beneficial features lead to monochromatic internal photoconversion efficiencies of 17.3% when the SWNT-ZnPc hybrid material was tested as photoactive material in an ITO photoanode.     

Microcirculation within grooved substrates regulates cell positioning and cell docking inside microfluidic channels

Immobilization of cells inside microfluidic devices is a promising approach for enabling studies related to drug screening and cell biology. Despite extensive studies in using grooved substrates for immobilizing cells inside channels, a systematic study of the effects of various parameters that influence cell docking and retention within grooved substrates has not been performed. We demonstrate using computational simulations that the fluid dynamic environment within microgrooves significantly varies with groove width, generating microcirculation areas in smaller microgrooves. Wall shear stress simulation predicted that shear stresses were in the opposite direction in smaller grooves (25 and 50 microm wide) in comparison to those in wider grooves (75 and 100 microm wide). To validate the simulations, cells were seeded within microfluidic devices, where microgrooves of different widths were aligned perpendicularly to the direction of the flow. Experimental results showed that, as predicted, the inversion of the local direction of shear stress within the smaller grooves resulted in alignment of cells on two opposite sides of the grooves under the same flow conditions. Also, the amplitude of shear stress within microgrooved channels significantly influenced cell retainment in the channels. Therefore, our studies suggest that microscale shear stresses greatly influence cellular docking, immobilization, and retention in fluidic systems and should be considered for the design of cell-based microdevices.     

Silver nanofractals: electrochemical synthesis, XPS characterization and application in LDI-MS

Silver nanofractals (Ag-NFs) have been electrosynthesized and characterized by means of morphological and spectroscopic analytical techniques. In particular, X-ray photoelectron spectroscopy has been used to assess the nanomaterial surface chemical state. Ag-NFs show interesting perspectives in bioanalytical applications, particularly as non-conventional desorption and ionization promoters in laser desorption ionization mass spectrometry.