Chlorogenic Acid UVA–UVB Photostability

Chlorogenic acid is a natural potent antioxidant. It can be used in cosmetics formulations, but for this purpose its photochemical stability should be determined to ensure that the compound will not be degraded after UV radiation exposure. To evaluate this possibility, the concentration of a chlorogenic acid solution was determined by HPLC before and after UVA and UVB irradiation. The results indicate that chlorogenic acid is not degraded under UVA or UVB irradiation.     

The role of MAPK signal transduction pathways in the response to oxidative stress in the fungal pathogen Candida albicans: implications in virulence

In recent years, Mitogen-Activated Protein Kinase (MAPK) pathways have emerged as major regulators of cellular physiology. In the fungal pathogen Candida albicans, three different MAPK pathways have been characterized in the last years. The HOG pathway is mainly a stress response pathway that is activated in response to osmotic and oxidative stress and also participates regulating other pathways. The SVG pathway (or mediated by the Cek1 MAPK) is involved in cell wall formation under vegetative and filamentous growth, while the Mkc1-mediated pathway is involved in cell wall integrity. Oxidative stress is one of the types of stress that every fungal cell has to face during colonization of the host, where the cell encounters both hypoxia niches (i.e. gut) and high concentrations of reactive oxygen species (upon challenge with immune cells). Two pathways have been shown to be activated in response to oxidative stress: the HOG pathway and the MKC1-mediated pathway while the third, the Cek1 pathway is deactivated. The timing, kinetics, stimuli and functional responses generated upon oxidative stress differ among them; however, they have essential functional consequences that severely influence pathogenesis. MAPK pathways are, therefore, valuable targets to be explored in antifungal research.     

New hydrogels from interpenetrated physical gels of agarose and chemical gels of polyacrylamide: Effect of relative concentration and crosslinking degree on the viscoelastic and thermal properties

In this article, we report on the viscoelastic and thermal properties of agarose–polyacrylamide (PAAm) interpenetrating polymer hydrogels (IPHs) and semi‐IPHs as a function of agarose concentration and PAAm crosslinking degree. The results demonstrated that the agarose is able to gel in the presence of crosslinked and linear IPHs. In addition, the reticulation of PAAm in the presence of agarose is confirmed for the case of IPHs giving rise to systems with dimensional stability at high temperatures. The formation of a fully IPH was ascertained at low agarose concentrations. A study of the morphology and nanoscale elasticity of the different systems has been carried out with atomic force microscopy/ultrasonic force microscopy (UFM). UFM data provide further evidence of interpenetration, allowing us to visualize—if present—phase‐separated domains with nanoscale resolution for the various crosslinking degrees and PAAm and agarose concentrations used during the formation of the IPHs. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Study of the effect of poly(vinyl alcohol) concentration on the gelation point of poly(vinyl alcohol) poly(acrylic acid) semi‐IPN systems as determined by viscoelastic measurements

We report on the determination of the gelation point of semi‐interpenetrating polymer networks (semi‐IPNs) composed of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAAc) formed by a sequential method. The evolution of the viscoelasticity during the gelation reaction of acrylic acid (AAc) in solutions of PVA has been monitored through the sol‐gel transition with dynamic mechanical experiments. The gelation time of the system increased with PVA concentration; however, the molecular structure of the gel, composed of swollen clusters, is rather independent of the presence of PVA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1944–1949, 2005     

Thermal behavior of blends based on a thermoplastic-modified epoxy resin with a crosslinking density variation

The thermal behavior of blends based on a polystyrene (PS) and several epoxy-amine systems where amino groups were provided by a monoamine (MA) and a diamine (DA) mixed in different proportions was investigated. This way, the crosslinking density of epoxy-amine polymer was controlled and continuously changed from a linear polymer (epoxy-MA) to a highly crosslinked polymer (epoxy-DA). The effect of the MA–DA proportion and PS modifier on the thermal stability, glass transition, and polymerization reaction was studied by differential scanning calorimetry and thermogravimetric analysis. The MA–DA ratio and modifier proportion did not affect the reaction heat but affected the reactivity. The thermal stability and glass transition temperature increased by increasing the DA proportion in the blend as a result of the higher degree of crosslinking. A study of miscibility of blends based on glass transitions was performed. The thermoplastic-modified materials generally showed two glass transitions with values close to the those of the pure materials, indicating that the mixtures were separated into phases.     

Synthesis of Fluorinated Graphene Oxide and its Amphiphobic Properties

The richly functionalized basal plane bonded to polar organic moieties makes graphene oxide (GO) innately hydrophilic. Here, a methodology to synthesize fluorinated graphene oxide by oxidizing the basal plane of fluorinated graphite, allowing for tunable hydrophobicity of GO, is reported. Fluorine exists as tertiary alkyl fluorides covalently bonded to graphitic carbons, and using magic‐angle spinning (MAS) ¹³C NMR as a primary tool chemical structures for the two types of synthesized fluorinated graphene oxides (FGOs) with significantly different fluorine contents are proposed. The low surface energy of the C–F bond drastically affects GO's wetting behavior, leading to amphiphobicity in its highly fluorinated form. Ease of solution processing enables the fabrication of inks that are spray‐painted on various porous/non‐porous substrates. These coatings maintain amphiphobicity for solvents with surface tensions down to 59 dyn/cm, thus bypassing existing lithographic means to create similar surfaces. The approach towards fluorinating GO and fabricating graphene‐based surfaces with tunable wettability opens the path towards unique, accessible, carbon‐based amphiphobic coatings.     

Chemical sensing based on the plasmonic response of nanoparticle aggregation: anion sensing in nanoparticles stabilized by amino-functional ionic liquid

We report the synthesis, characterization and modellization of optical anion sensors based on gold nanoparticles (Au NPs) stabilized by amino-functional imidazolium ionic liquids (AFIL). The addition of different salts results in anion exchange of the imidazolium ionic liquid stabilizer leading to a change in the optical response of the original nanoparticle aqueous solution. In all cases except with dodecylbenzenesulfonic acid sodium salt, a sufficient amount of salt concentration (5 times larger than equimolar) leads to the appearance of an absorption band between 600 and 700 nm in the ultravioletvisible (UV-vis) spectrum. The presence of the salt produces aggregation of the particles that localise the optical response and produce a large spectral red shift. Transmission electron microscopy images demonstrated that this optical change was due to the aggregation of the nanoparticles. We simulate the optical response of both situations, before and after salt addition, and interpret the experimental observations in terms of the different response of metallic single nanoparticles and nanoparticle aggregates. Theoretical calculations for single nanoparticle and single nanoparticle dimers demonstrate that the colour change is not due to the enlargement or structural changes of the Au NPs, but due to the formation of NP aggregation. These results show the potential of nanoparticle plasmonics to perform effective chemical sensing.     

Ultradistributional boundary values of harmonic functions on the sphere

We present a theory of ultradistributional boundary values for harmonic functions defined on the Euclidean unit ball. We also give a characterization of ultradifferentiable functions and ultradistributions on the sphere in terms of their spherical harmonic expansions. To this end, we obtain explicit estimates for partial derivatives of spherical harmonics, which are of independent interest and refine earlier estimates by Calderón and Zygmund. We apply our results to characterize the support of ultradistributions on the sphere via Abel summability of their spherical harmonic expansions.     

Fluorescence monitoring of microchip capillary electrophoresis separation with monolithically integrated waveguides

Using femtosecond laser writing, optical waveguides were monolithically integrated into a commercial microfluidic lab-on-a-chip device, with the waveguides intersecting a microfluidic channel. Continuous-wave laser excitation through these optical waveguides confines the excitation window to a width of 12 microm, enabling high-resolution monitoring of the passage of different types of fluorescent analytes when migrating and being separated in the microfluidic channel by microchip capillary electrophoresis. Furthermore, we demonstrate on-chip-integrated waveguide excitation and detection of a biologically relevant species, fluorescently labeled DNA molecules, during microchip capillary electrophoresis. Well-controlled plug formation as required for on-chip integrated capillary electrophoresis separation of DNA molecules, and the combination of waveguide excitation and a low limit of detection, will enable monitoring of extremely small quantities with high spatial resolution.     

CdS plume composition and dynamics of neutral species upon ablation with 532 nm laser light

The neutral species present in CdS ablation plumes upon nanosecond 532 nm laser irradiation at a moderate fluence of 0.5–0.75 J cm⁻² have been studied. Neutral Cd _n S _m clusters have been identified, some as large as (CdS)₃₃₋₃₄ (1–2 nm in diameter). The analysis of the dynamics of neutral species shows an expansion with two components that differ both in composition and dynamics. A fast, high kinetic energy component, dominated by S₂ which acquires free-flow conditions at short distances from the target, is followed by a slower component characterized by similar speeds for all species. This slower component shows dynamic features that are expected to favor aggregation processes leading to effective cluster formation.