Nonfickian effect in time and space for diffusion processes

Diffusion processes are usually simulated using the classical diffusion equation. In certain scenarios, such equation induces anomalous behavior and consequently several improvements were introduced in the literature to overcome them. One of the most popular was the replacement of the diffusion equation by an integro‐differential equation. Such equation can be established considering a modification of Fick's mass flux where a delay in time is introduced. In this article, we consider mathematical models for diffusion processes that take into account a memory effect in time and space. © 2015 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 31: 1589–1602, 2015     

New Acetogenins from the Seeds of Annona coriacea

From the hexane and MeOH extracts of Annona coriacea Mart . (Annonaceae) seeds, two novel acetogenins, coriapentocins A and B ( 1 and 2 , resp.) were isolated. The known acetogenin bullacin ( 3 ) was also isolated from the hexane extract. The structures of compounds 1 – 3 were elucidated by NMR and MS analysis, and relative configurations were established by comparison with literature data.     

A convenient [2+2] cycloaddition-cycloreversion reaction for the synthesis of 1,1-dicyanobuta-1,3-diene-scaffolded peptides as new imaging chromophores

We report on the chemoselective coupling between colorless peptide fragments functionalized with a mutually reactive electron-rich N^α-(4-ethynylphenyl)-N^α-(methyl)-glycyl- and an electron-deficient [4-(2,2-dicyanovinyl)]benzoyl moiety. The resulting donor-substituted 1,1-dicyanobuta-1,3-dienes represent a new class of orange-red colored (λ_max = 450-500 nm, with molar extinction coefficients (ε) above 5,000 mol⁻¹ dm³ cm⁻¹) peptide-based imaging chromophores.     

Magnetic and electrokinetic manipulations on a microchip device for bead-based immunosensing applications

The combination of electrophoretic and magnetic manipulations with electrochemical detection for a versatile microfluidic and bead-based biosensing application is demonstrated. Amperometric detection is performed in an off-channel setup by means of a voltammetric cell built at the microchannel outlet and using a gold working electrode. Superparamagnetic particles are introduced and handled inside the channel by means of an external permanent magnet in combination with the electrogenerated flow which allows reproducible loading. The specific detection of phenol as electroactive alkaline phosphatase product is used in this study as proof of concept for a sensitive protein quantification. Characterizations and optimization of different parameters have been carried out in order to achieve the best detection signal. The applicability of the device has been finally demonstrated by the detection of rabbit IgG as model protein after an immunoassay performed on magnetic particles as immobilization platform. A comparison between the electrochemical detection using the developed device and the optical standard detection revealed similar performances with, however, extremely lower amount of reagent used and shorter analysis time. The developed electrophoretic- and magnetic-based chip may open the way to several other biosensing applications with interest not only for other proteins but also for DNA analysis, cell counting, and environmental control.     

Investigation of Cs(I) adsorption on densely crosslinked poly(sodium methacrylate) from aqueous solutions

In this study, a crosslinked copolymer bearing sodium methacrylate functional groups has been proposed to remove Cs(I) ions from aqueous solutions. For this purpose, the crosslinked copolymer of ethylene glycol dimethacrylate (EGDM) and methacrylic acid (MA) containing 25% MA as weight percentage was synthesized by using benzoyl peroxide (BPO)-N,N-dimethyl aniline initiator system. The available carboxyl groups in copolymer were converted to the groups of sodium methacrylate using 2 N NaOH. The adsorption behavior of cesium ions on the densely crosslinked poly(sodium methacrylate) from aqueous solutions were investigated by the technique of ICP-MS measurements of cesium ions in solutions. Batch adsorption method was used to analyze the Cs(I) adsorption as a function of parameters such as the amount of adsorbent, contact time, pH of solution, initial Cs(I) concentration and temperature. The adsorption data were evaluated by the Freundlich, Langmuir and Dubinin–Radushkevich (D–R) isotherms. The adsorption capacity and free energy change were calculated by using D–R isotherm. The adsorption data obtained from experimental results have been tested by the fractional power, the Elovich, the pseudo-first order and the pseudo-second order kinetic models.     

An expeditious,environment-friendly,and microwave-assisted synthesis of 5-isatinylidenerhodanine derivatives

A series of nine 5-arylidenerhodanine derivatives was prepared in good yields and purity without the use of a solvent or catalyst under microwave-assisted condensation with some substituted isatins. All 5-arylidenerhodanines were evaluated as possible inhibitors of the CK1α/β, CDK5/p25, and GSK-3α/β kinases. None of them showed substantive inhibitory activity against these kinases when evaluated at the concentration of 10 μM.     

Green synthesis of gold nanoparticles using glycerol-incorporated nanosized liposomes

There has been enormous interest in the last decade in development methods for the inorganic synthesis of metallic nanoparticles of desired sizes and shapes because of their unique properties and extensive applications in catalysis, electronics, plasmonics, and sensing. Here we report on an environmentally friendly, one-pot synthesis of metallic nanoparticles, which avoids the use of organic solvents and requires mild experimental conditions. The developed method uses liposomes as nanoreactors, where the liposomes were prepared by encapsulating chloroauric acid and exploited the use of glycerol, incorporated within the lipid bilayer as well as in its hydrophilic core, as a reducing agent for the controlled preparation of highly homogeneous populations of gold nanoparticles. The effects of temperature, the presence of a capping agent, and the concentration of glycerol on the size and homogeneity of the nanoparticles formed were investigated and compared with solution-based glycerol-mediated nanoparticle synthesis. Well-distributed gold nanoparticle populations in the range of 2-8 nm were prepared in the designed liposomal nanoreactor with a clear dependence of the size on the concentration of glycerol, the temperature, and the presence of a capping agent whereas large, heterogeneous populations of nanoparticles with amorphous shapes were obtained in the absence of liposomes. The particle morphology and sizes were analyzed using transmission electron microscopy imaging, and the liposome size was measured using photon correlation spectroscopy.     

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.     

SERS detection of streptavidin/biotin monolayer assemblies

A two-dimensional array of gold nanotriangles inscribed onto glass coverslips were optimized for the surface-enhanced Raman detection of streptavidin/biotin monolayer assemblies. The nanostructures were fabricated by electron beam lithography, and its optical parameters were optimized to be probed under a Raman microscope with a linearly polarized He-Ne laser with an excitation wavelength of λ = 632.8 nm. The platforms were first tested against a monolayer of biotinylated alkanethiols (BAT) functionalized over the gold nanostructure, showing that good-quality spectra could be acquired with a short acquisition time. The supramolecular interaction of streptavidin (strep) with BAT showed subsequent modification of the Raman spectrum that implies a change in the secondary structure of the host biomolecule (streptavidin). Compared to gold surfaces without nanoscale structures, the local enhancement that results from our nanostructured surfaces allows one to detect the vibrational signal of monolayers within a time on the order of seconds and under modest laser intensity, further demonstrating the utility of using plasmonic metallic nanostructures for molecular recognition.     

A new method to analyze copolymer based superplasticizer traces in cement leachates

Enhancing the flowing properties of fresh concrete is a crucial step for cement based materials users. This is done by adding polymeric admixtures. Such additives have enabled to improve final mechanicals properties and the development of new materials like high performance or self compacting concrete. Like this, the superplasticizers are used in almost cement based materials, in particular for concrete structures that can have a potential interaction with drinking water. It is then essential to have suitable detection techniques to assess whether these organic compounds are dissolved in water after a leaching process or not. The main constituent of the last generation superplasticizer is a PolyCarboxylate-Ester copolymer (PCE), in addition this organic admixture contains polyethylene oxide (free PEO) which constitutes a synthesis residue. Numerous analytical methods are available to characterize superplasticizer content. Although these techniques work well, they do not bring suitable detection threshold to analyze superplasticizer traces in solution with high mineral content such as leachates of hardened cement based materials formulated with superplasticizers. Moreover those techniques do not enable to distinguish free PEO from PCE in the superplasticizer.Here we discuss two highly sensitive analytical methods based on mass spectrometry suitable to perform a rapid detection of superplasticizer compounds traces in CEM I cement paste leachates: MALDI-TOF mass spectrometry, is used to determine the free PEO content in the leachate. However, industrial copolymers (such as PCE) are characterized by high molecular weight and polymolecular index. These two parameters lead to limitation concerning analysis of copolymers by MALDI-TOFMS. In this study, we demonstrate how pyrolysis and a Thermally assisted Hydrolysis/Methylation coupled with a triple-quadrupole mass spectrometer, provides good results for the detection of PCE copolymer traces in CEM I cement paste leachates.