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PubMed2003

The major soluble 19.6 kDa protein of the organic shell matrix of the freshwater snail Biomphalaria glabrata is an N-glycosylated dermatopontin.

The major Biomphalaria glabrata shell matrix protein of 19.6 kDa was isolated by preparative electrophoresis and sequenced. The sequence of 148 amino acids showed 32% sequence identity to mammalian dermatopontin sequences and 34-37% identity to two invertebrate dermatopontins described previously. A unique feature of the shell matrix dermatopontin was the presence of a single N-glycosylation consensus sequence, the asparagine of which was completely modified with a pentasaccharide. Sequence analysis of this short N-glycan by mass spectrometry and carbohydrate composition analysis indicated that it was the ubiquitous N-glycan core oligosaccharide with the exception that the terminal mannoses were 3-O-methylated. Dermatopontin is widespread in mammalian extracellular matrices, including the matrix of biominerals such as bone and teeth. Its occurrence in an invertebrate biomineral indicates that such phylogenetically distant biomineral-forming systems as vertebrate bone and mollusk shell share components which have undergone surprisingly few changes during a long evolution.

Amino Acid Sequence↗

PubMed1987

Survival of shelled acanthors of Moniliformis moniliformis (Acanthocephala) under laboratory conditions.

Shelled acanthors (= eggs) of two isolates of Moniliformis moniliformis (Acanthocephala) were tested for their capacity to respond to a hatching stimulus in vitro and for their retention of infectivity to a natural intermediate host (Periplaneta americana). The shelled acanthors were stored for more than 120 weeks (Australian isolate) and for 104 weeks (Texan isolate) together with rat faeces in an incubator maintained at 22.2 +/- 0.1 degrees C. In both cases, infectivity to P. americana was shown to have been retained. In vitro tests of the hatching response were carried out on many occasions during this period of faecal storage. Shelled acanthors continued to respond and no differences were detected either between isolates or within an isolate through time.

Acanthocephala↗

PubMed1994

The role of home-made ice cream as a vehicle of Salmonella enteritidis phage type 4 infection from fresh shell eggs.

A family outbreak of Salmonella enteritidis PT4 infection is described in which home-made ice cream was identified as the vehicle of infection. The ice cream contained approximately 10(5) S. enteritidis PT4 organisms per gm and was probably contaminated by an infected shell egg containing between 10(5)-10(8) organisms. The continued relevance of the Chief Medical Officer's warning on the use of raw shell eggs is highlighted. Home-made ice cream using the same recipe as ice cream that had been incriminated as the cause of the family outbreak of S. enteritidis PT4 infection was used to study the growth of the organism that might have occurred in the 3-4 h it took to prepare the product. When the inoculum was in the stationary phase, as it would be from shell or other cross contamination, there was a lag phase of 3 h before growth occurred at room temperature. Even when actively multiplying organisms were introduced, as may be found in an infected egg, there was less than 3 log(10) increase in the salmonella count in 4 h at room temperature. It was, therefore, given the high S. enteritidis count, unlikely that the ice cream was cross-contaminated. By contrast, raspberry sorbet at pH 3.73 proved to be lethal to a large inoculum of S. enteritidis and may be a relatively safe raw egg containing product.

Animals↗

PubMed2005

Removal of alpha-picoline, beta-picoline, and gamma-picoline from synthetic wastewater using low cost activated carbons derived from coconut shell fibers.

In the present study the ability of activated carbons developed from coconut shell fibers to remove alpha-picoline, beta-picoline, and gamma-picoline from aqueous solution in the broad range of concentrations (1-100 mg/L) is investigated. The derived carbons are designated as FAC (activated carbon derived from coconut shell fibers without any treatment) and ATFAC (activated carbon derived from acid treated coconut shell fibers). Systematic equilibrium and kinetic adsorption studies at different pH, temperatures, particle size, and solid-to-liquid ratio were carried out to determine various parameters necessary to establish the fixed bed reactors. The Langmuir and Freundlich models were applied and the data are not fitted well by the Freundlich and Langmuir equations, but the Langmuir model has an edge over Freundlich model. The monolayer adsorption capacity (Q0) as calculated using Langmuir adsorption isotherm of the activated carbons viz., FAC and ATFAC is found to increase with an increase in temperature confirming the endothermic process. The ATFAC has a higher sorption capacity than FAC. Overall the adsorption of alpha-picoline, beta-picoline, and y-picoline on FAC and ATFAC follow the order FACalpha-picoline < ATFACalpha-picoline < FAC gamma-picoline < ATFACbeta-picoline < FACbeta picoline < ATFAC gamma-picoline. The adsorption of alpha-,beta-, and gamma-picoline followed the pseudosecond-order rate kinetics. On the basis of these studies, various parameters such as effective diffusion coefficients, activation energy, and entropy of activation were evaluated to establish the mechanisms. It was concluded that the adsorption occurred through particle diffusion at low temperatures viz., 10 degrees C and 25 degrees C (except alpha-picoline where it was film diffusion), while at 40 degrees C it occurred through film diffusion. Similarly at concentrations of 25 and 50 mg/L the adsorption was particle diffusion controlled (except for alpha-picoline where it was film diffusion), while at > 50 mg/L it was film diffusion controlled.

Adsorption↗

PubMed2002

Hydrogen and higher shell contributions in Zn2+, Ni2+, and Co2+ aqueous solutions: an X-ray absorption fine structure and molecular dynamics study.

A detailed investigation of the hydration structure of Zn2+, Ni2+, and Co2+ in water solutions has been carried out combining X-ray absorption fine structure (EXAFS) spectroscopy and Molecular Dynamics (MD) simulations. The first quantitative analysis of EXAFS from hydrogen atoms in 3d transition metal ions in aqueous solutions has been carried out and the ion-hydrogen interactions have been found to provide a detectable contribution to the EXAFS spectra. An accurate determination of the structural parameters associated with the first hydration shell has been performed and compared with previous experimental results. No evidence of significant contributions from the second hydration shell to the EXAFS signal has been found for these solutions, while the inclusion of the hydrogen signal has been found to be important in performing a quantitative analysis of the experimental data. The high-frequency contribution present in the EXAFS spectra has been found to be due to multiple scattering (MS) effects inside the ion-oxygen first coordination shell. MD has been used to generate three-body distribution functions from which a reliable analysis of the MS contributions to the EXAFS spectra of these systems has been carried out.

Journal Article↗

PubMed2005

Charge separation and catalytic activity of Ag@TiO2 core-shell composite clusters under UV-irradiation.

Photocatalytic properties of Ag@TiO2 composite clusters have been investigated using steady state and laser pulse excitations. Photoexcitation of TiO2 shell results in accumulation of the electrons in the Ag core as evidenced from the shift in the surface plasmon band from 460 to 420 nm. The stored electrons are discharged when an electron acceptor such as O2, thionine, or C60 is introduced into the system. Charge equilibration with redox couple such as C60/C60*- shows the ability of these core shell structures to carry out photocatalytic reduction reactions. The charge separation, charge storage, and interfacial charge-transfer steps that follow excitation of the TiO2 shell are discussed.

Journal Article↗

PubMed2005

Fabrication of uniform magnetic nanocomposite spheres with a magnetic core/mesoporous silica shell structure.

A novel kind of magnetic core/mesoporous silica shell nanospheres with a uniform particle diameter of ca. 270 nm was synthesized. The inner magnetic core endues the whole nanoparticle with magnetic properties, while the outer mesoporous silica shell shows high enough surface area and pore volume. The synthesized material is expected to be applied to targeted drug delivery and multiphase separation. The storage and release of ibuprofen into and from the pore channels of the mesoporous silica shell, as a typical example, are demonstrated.

Magnetics↗

PubMed2006

Detection of second hydration shells in ionic solutions by XANES: computed spectra for Ni2+ in water based on molecular dynamics.

A general procedure to compute X-ray absorption near-edge structure (XANES) spectra within multiple-scattering theory starting from molecular dynamics (MD) structural data has been developed and applied to the study of a Ni(2+) aqueous solution. This method allows one to perform a quantitative analysis of the XANES spectra of disordered systems using a proper description of the thermal and structural fluctuations. The XANES spectrum of Ni(2+) in aqueous solution has been calculated using the structural information obtained from the MD simulations without carrying out any minimization in the structural parameter space. A very good reproduction of the experimental data was obtained including the second-shell water molecules in the calculation, thus showing that the second hydration shell provides a detectable contribution to the XANES spectra of ionic solutions. The analysis including the first-shell cluster only permitted us to quantitatively determine the effect of disorder on the amplitude of the XANES spectra for molecular complexes. These results simultaneously confirm the reliability of the procedure and the structural results obtained from MD simulations. The combination of MD and XANES is found to be very helpful to get important new insights into the quantitative estimation of structural properties of disordered systems.

Journal Article↗

PubMed2006

Formation and characterization of polyglutamate core-shell microspheres.

The need for organ-targeted delivery of drugs and imaging agents creates an interest in biocompatible, biodegradable vesicles. We make protein microspheres using high-intensity ultrasound; these microspheres have a protein shell and a hydrophobic interior, making them ideal for delivering hydrophobic materials. We have previously shown that various proteins, e.g., bovine serum albumin (BSA), form a microsphere shell stabilized by interprotein cross-linking of cysteine residues. In this study, polyglutamate was used to form core-shell microspheres at slightly basic pH using sonication. These particles are smaller than our previous protein microspheres and are stable under conditions encountered in vivo. The stability of polyglutamate microspheres appears to be due to hydrogen bonding networks and not covalent cross-linking.

Biocompatible Materials↗

PubMed1999

Presence and dehydration of ikaite, calcium carbonate hexahydrate, in frozen shrimp shell.

Ikaite, calcium carbonate hexahydrate, has by means of X-ray diffraction analyses of frozen samples been identified as the mineral component of the white spots formed in the shell of frozen shrimp during storage. When the shrimp thaw and the shell material is dried and kept at room temperature, ikaite rapidly transforms into a mixture of anhydrous calcium carbonate forms. X-ray diffraction analyses and Raman spectra of synthetic ikaite as well as the dehydration product confirm the assignments, and the rate constant for dehydration is approximately 7 x 10(-)(4) s(-)(1) at ambient temperature. Differential scanning calorimetry showed that dehydration of synthetic ikaite is an entropy-driven, athermal process and confirms that a single first-order reaction is rate-determining. Ikaite is found to be stable in aqueous solution at temperatures below 5 degrees C and in the shell of frozen shrimps but decomposes on thawing to form anhydrous calcium carbonates.

Animals↗

PubMed2005

Structure and deformations of Pd-Ni core-shell nanoparticles.

Homogeneous collections of Pd-Ni core-shell nanoparticles have been prepared by decomposition of metal-organic compounds and studied by several electron microscopy techniques: transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), energy-filtered microscopy (EFTEM), and by X-ray photoelectron spectroscopy (XPS). The physical and chemical properties of the Pd shell are supposed to depend on its electronic properties, which are influenced by the presence of the Ni core and by the deformation in the Pd lattice. Here, the interfacial structure of Pd/Ni and the lattice deformations in the core and the shell are studied in detail. The catalytic properties of the pure metal and the bimetallic particles, toward CO oxidation, have been investigated.

Journal Article↗

PubMed2005

A phase-transfer identification of core-shell structures in Ag-Pt nanoparticles.

Ag-Pt nanoparticles with a confirmed core-shell structure could only be formed by the successive reduction method using Ag nanoparticles as the seeds. The core-shell structure could be conveniently inferred from the transferability of the particles from water to toluene. Independent measurements by UV-vis spectroscopy, transmission electron microscopy, energy-dispersive X-ray analysis, and X-ray photoelectron spectroscopy were used to validate the experimental results. The reverse order of synthesis using Pt nanoparticles as the seeds did not result in any core-shell product. Instead a physical mixture of Ag nanoparticles and the original Pt seeds was obtained under the same experimental conditions.

Journal Article↗

PubMed2005

Enhancing the photoluminescence of peptide-coated nanocrystals with shell composition and UV irradiation.

The composition and structure of inorganic shells grown over CdSe semiconductor nanocrystal dots and rods were optimized to yield enhanced photoluminescence properties after ligand exchange followed by coating with phytochelatin-related peptides. We show that, in addition to the peptides imparting superior colloidal properties and providing biofunctionality in a single-step reaction, the improved shells and pretreatment with UV irradiation resulted in high quantum yields for the nanocrystals in water. Moreover, peptide coating caused a noticeable red-shift in the absorption and emission spectra for one of the tested shells, suggesting that exciton-molecular orbital (X-MO) coupling might take place in these hybrid inorganic-organic composite materials.

Cadmium Compounds↗

PubMed2005

Hydration shell exchange dynamics during ion transfer across the liquid/liquid interface.

We examine using molecular dynamics simulations the rate and mechanism of water molecules exchange around the Li(+) and Na(+) ions during ion transfer across the interface between water and nitrobenzene. As the ions are transferred from the water to the organic phase, they keep their first hydration shell and an incomplete second shell. The rate of water exchange between the first shell and the rest of the interfacial water molecule decreases during the transfer, which is consistent with an increase in the barrier along the ion-water potential of mean force. While in bulk water the exchange of water molecules around the Li(+) follows an associative (A) or associative interchange (I(a)) type mechanism, the fraction of exchange events of type A increases at the interface. In contrast, while in bulk water the exchange of water molecules around the six coordinated Na(+) hydrated species mainly follows a dissociative mechanism, the situation at the interface involves an equilibrium interchange between the four- and five-coordinated hydrated ion. Simulation of the reversed process, in which the hydrated Li(+) ion is transferred to the aqueous phase, shows the same general behavior as a function of location from the interface.

Cations, Monovalent↗

PubMed2005

Formation of well-aligned ZnGa(2)O(4) nanowires from Ga(2)O(3)/ZnO core-shell nanowires via a Ga(2)O(3)/ZnGa(2)O(4) epitaxial relationship.

Formation of well-aligned and single-crystalline ZnGa(2)O(4) nanowires on sapphire (0001) substrates has been achieved via annealing of the Ga(2)O(3)/ZnO core-shell nanowires. Ga(2)O(3)/ZnO core-shell nanowires were prepared using a two-step method. The thickness of the original ZnO shell and the thermal budget of the annealing process play crucial roles for preparing single-crystalline ZnGa(2)O(4) nanowires. Structural analyses of the annealed nanowires reveal the existence of an epitaxial relationship between ZnGa(2)O(4) and Ga(2)O(3) phases during the solid-state reaction. A strong CL emission band centered at 360 nm and a small tail at 680 nm are obtained at room temperature from the single-crystalline ZnGa(2)O(4) nanowires.

Journal Article↗

PubMed2005

Prediction of supercritical ethane bulk solvent densities for pyrazine solvation shell average occupancy by 1, 2, 3, and 4 ethanes: combined experimental and ab initio approach.

We introduce a method that addresses the elusive local density at the solute in the highly compressible regime of a supercritical fluid. Experimentally, the red shift of the pyrazine n-pi electronic transition was measured at infinite dilution in supercritical ethane as a function of pressure from 0 to about 3000 psia at two temperatures, one close (35.0 degrees C) to the critical temperature and the other remote (55.0 degrees C). Computationally, stationary points were located on the potential surfaces for pyrazine and one, two, three, and four ethanes at the MP2/6-311++G(d,p) level. The vertical n-pi ((1)B(3u)) transition energies were computed for each of these geometries with a TDDFT/B3LYP/6-311++G(d,p) method. The combination of experiment and computation allows prediction of supercritical ethane bulk densities at which the pyrazine primary solvation shell contains an average of one, two, three, and four ethane molecules. These density predictions were achieved by graphical superposition of calculated shifts on the experimental shift versus density curves for 35.0 and 55.0 degrees C. Predicted densities are 0.0635, 0.0875, and 0.0915 g cm(-3) for average pyrazine primary solvation shell occupancy by one, two, and three ethanes at both 35.0 and 55.0 degrees C. Predicted densities are 0.129 and 0.150 g cm(-3) for occupancy by four ethanes at 35.0 and 55.0 degrees C, respectively. An alternative approach, designed to "average out" geometry specific shifts, is based on the relationship Deltanu = -23.9n cm(-1), where n = ethane number. Graphical treatment gives alternative predicted densities of 0.0490, 0.0844, and 0.120 g cm(-3) for average pyrazine primary solvation shell occupancy by one, two, and three ethanes at both 35.0 and 55.0 degrees C, and densities of 0.148 and 0.174 g cm(-3) for occupancy by four ethanes at 35.0 and 55.0 degrees C, respectively.

Computer Simulation↗

PubMed2005

Core-shell nanorods for efficient photoelectrochemical hydrogen production.

We propose core-shell InP-CdS and InP-ZnTe nanorods as photoelectrodes in the efficient photoelectrochemical hydrogen production. On the basis of our systematic study using strain-dependent k.p theory, we find that in these heterostructures both energies and wave function distributions of electrons and holes can be favorably tailored to a considerable extent by exploiting the interplay between quantum confinement and strain. Consequently, these core-shell nanorods with proper dimensions (height, core radius, and shell thickness) can simultaneously satisfy all criteria for effective photoelectrodes in solar-based hydrogen production.

Electrochemistry↗

PubMed2006

Magnetic core-shell Fe3O4@Ag nanoparticles coated carbon paste interface for studies of carcinoembryonic antigen in clinical immunoassay.

This study demonstrates a novel approach toward development of advanced immunosensors based on chemically functionalized core-shell Fe3O4@Ag magnetic nanoparticles, and the preparation, characterization, and measurement of relevant properties of the immunosensor useful for the detection of carcinoembryonic antigen (CEA) in clinical immunoassay. The immunosensor based on the combination of a magnetic nanocore and an Ag metallic shell shows good adsorption properties for the attachment of the CEA antibody selective to CEA. The core-shell nanostructure presents good magnetic properties to facilitate and modulate the way it was integrated into a carbon paste. Under optimal conditions, the resulting composite presents good electrochemical response for the detection of CEA, and allows detection of CEA at a concentration as low as 0.5 ng.mL(-1). Importantly, the proposed methodology could be extended to the detection of other antigens or biocompounds.

Carbon↗