84 research outputs found
Phonon-assisted radiofrequency absorption by gold nanoparticles resulting in hyperthermia
It is suggested that in gold nanoparticles (GNPs) of about 5 nm sizes used in
the radiofrequency (RF) hyperthermia, an absorption of the RF photon by the
Fermi electron occurs with involvement of the longitudinal acoustic vibrational
mode (LAVM), the dominating one in the distribution of vibrational density of
states (VDOS). This physical mechanism helps to explain two observed phenomena:
the size dependence of the heating rate (HR) in GNPs and reduced heat
production in aggregated GNPs. The argumentation proceeds within the
one-electron approximation, taking into account the discretenesses of energies
and momenta of both electrons and LAVMs. The heating of GNPs is thought to
consist of two consecutive processes: first, the Fermi electron absorbs
simultaneously the RF photon and the LAVM available in the GNP; hereafter the
excited electron gets relaxed within the GNP's boundary, exciting a LAVM with
the energy higher than that of the previously absorbed LAVM. GNPs containing
the Ta and/or Fe impurities are proposed for the RF hyperthermia as promising
heaters with enhanced HRs, and GNPs with rare-earth impurity atoms are also
brought into consideration. It is shown why the maximum HR values should be
expected in GNPs with about 5-7 nm size.Comment: proceedings at the NATO Advanced Research workshop FANEM-2015 (Minsk,
May 25-27, 2015). To be published in the final form in: "Fundamental and
Applied NanoElectroMagnetics" (Springer Science + Business Media B.V.
Self-Association of Organic Solutes in Solution: A NEXAFS Study of Aqueous Imidazole
N K-edge near-edge X-ray absorption fine-structure (NEXAFS) spectra of imidazole in concentrated aqueous solutions have been acquired. The NEXAFS spectra of the solution species differ significantly from those of imidazole monomers in the gas phase and in the solid state of imidazole, demonstrating the strong sensitivity of NEXAFS to the local chemical and structural environment. In a concentration range from 0.5 to 8.2 mol L−1 the NEXAFS spectrum of aqueous imidazole does not change strongly, confirming previous suggestions that imidazole self-associates are already present at concentrations more dilute than the range investigated here. We show that various types of electronic structure calculations (Gaussian, StoBe, CASTEP) provide a consistent and complete interpretation of all features in the gas phase and solid state spectra based on ground state electronic structure. This suggests that such computational modelling of experimental NEXAFS will permit an incisive analysis of the molecular interactions of organic solutes in solutions. It is confirmed that microhydrated clusters with a single imidazole molecule are poor models of imidazole in aqueous solution. Our analysis indicates that models including both a hydrogen-bonded network of hydrate molecules, and imidazole–imidazole interactions, are necessary to explain the electronic structure evident in the NEXAFS spectra
The CHUVA Lightning Mapping Campaign
The primary science objective for the CHUVA lightning mapping campaign is to combine measurements of total lightning activity, lightning channel mapping, and detailed information on the locations of cloud charge regions of thunderstorms with the planned observations of the CHUVA (Cloud processes of tHe main precipitation systems in Brazil: A contribUtion to cloud resolVing modeling and to the GPM (GlobAl Precipitation Measurement) field campaign. The lightning campaign takes place during the CHUVA intensive observation period October-December 2011 in the vicinity of S o Luiz do Paraitinga with Brazilian, US, and European government, university and industry participants. Total lightning measurements that can be provided by ground-based regional 2-D and 3-D total lightning mapping networks coincident with overpasses of the Tropical Rainfall Measuring Mission Lightning Imaging Sensor (LIS) and the SEVIRI (Spinning Enhanced Visible and Infrared Imager) on the Meteosat Second Generation satellite in geostationary earth orbit will be used to generate proxy data sets for the next generation US and European geostationary satellites. Proxy data, which play an important role in the pre-launch mission development and in user readiness preparation, are used to develop and validate algorithms so that they will be ready for operational use quickly following the planned launch of the GOES-R Geostationary Lightning Mapper (GLM) in 2015 and the Meteosat Third Generation Lightning Imager (LI) in 2017. To date there is no well-characterized total lightning data set coincident with the imagers. Therefore, to take the greatest advantage of this opportunity to collect detailed and comprehensive total lightning data sets, test and validate multi-sensor nowcasting applications for the monitoring, tracking, warning, and prediction of severe and high impact weather, and to advance our knowledge of thunderstorm physics, extensive measurements from lightning mapping networks will be collected in conjunction with electric field mills, field change sensors, high speed cameras and other lightning sensors, dual-polarimetric radars, and aircraft in-situ microphysics which will allow for excellent cross-network inter-comparisons, assessments, and physical understanding
Enantioselective Catalysis of the Aza-Cope Rearrangement by a Chiral Supramolecular Assembly
The chiral supramolecular catalyst Ga{sub 4}L{sub 6} [L = 1,5-bis(2,3-dihydroxybenzoylamino)naphthalene] is a molecular tetrahedron that catalyzes the 3-aza-Cope rearrangement of allyl enammonium cations. This catalysis is accomplished by preorganizing the substrate in a reactive conformation within the host. This work demonstrates that through the use of enantiopure assembly, its chiral cavity is capable of catalyzing the 3-aza-Cope rearrangement enantioselectively, with yields of 21-74% and enantiomeric excesses from 6 to 64% at 50 C. At lower temperatures, the enantioselectivity improved, reaching 78% ee at 5 C. This is the highest enantioselectivity to date induced by the chiral cavity of a supramolecular assembly
Photochemistry in Japan: the Inoue Photochirogenesis Project -a research profile
The Inoue Photochirogensis Project is part of the ERATO program (Exploratory Research for Advanced Technology) of the Japan Science and Technology Corporation (JST). The project began in 1996, and is located in Toyonaka, Osaka. The project director is Dr. Yoshihisa Inoue, who is a full professor of the Graduate School of Engineering at Osaka University. The project is divided into 3 sub-groups: (1) CPL Photochemistry Group, (2) Asymmetric Photosensitization Group and (3) Supramolecular Photochemistry Group
Amphiphilic amino acids: A key to adsorbing proteins to nanopatterned surfaces?
It has been suggested that amphiphilic amino acids play an important role in the adsorption of proteins on nanostructured surfaces with an ordered, striped domain structure such as those presented by monolayer-protected metal nanoparticles (MPMNs). We have proposed and now further explore this hypothesis by studying the adsorption behaviour of proteins on MPMN surfaces by molecular dynamics (MD) simulations. Our atomistic MD simulations of lysozyme (Lyz) on nanostructured surfaces, including single component surfaces and several theoretical nanopatterns of different spacing, presented here confirm the special role of amino acids containing sidechain amines in facilitating direct protein adsorption to MPMN surfaces. While we have previously demonstrated that an amphiphilic amino acid lysine is responsible for selective adsorption behaviour of Cyt C on nanostructured surfaces, in the case of Lyz it is the amphipathic character of arginine that enables the protein to form close contacts with both polar and non-polar surface ligands simultaneously. This renders it especially important for interactions with surfaces composed of adjacent nano-scale chemical domains. Arg is also capable of forming close contacts with homogeneous hydrophobic and hydrophilic ligand surfaces. We have also found that other amphiphilic amino acids, such as tyrosine and tryptophan, interact with surfaces via water-mediated contacts. Bridging water molecules adopt orientations which differ from those of simple surface-adsorbed waters, with the specificity of their orientations facilitating the protein-surface contacts. Our findings suggest that not only nanopatterned surfaces can be designed to selectively interact with different proteins but proteins may be engineered to specifically interact with nanomaterials by targeted incorporation of synthetic amino acids which can mimic natural amphiphilic amino acids possessing multiple affinities to different chemical motifs
Heterofunctional Poly(ethylene glycol) (PEG) Macroinitiator Enabling Controlled Synthesis of ABC Triblock Copolymers
ABC triblock copolymers
with a polyÂ(ethylene glycol) (PEG) midblock
have attractive properties for biomedical applications because of
PEG’s favorable properties regarding biocompatibility and hydrophilicity.
However, easy strategies to synthesize polymers containing a PEG midblock
are limited. In this study, the successful synthesis of a heterofunctional
PEG macroinitiator containing both an azoinitiator and an atom transfer
radical polymerization (ATRP) initiator is demonstrated. This novel
PEG macroinitiator allows the development of elegant synthesis routes
for PEG midblock-containing ABC copolymers that does not require protection
of initiating sites or polymer end-group postmodification. Polymers
with outer blocks composed of different monomers were synthesized
to illustrate the versatility of this macroinitiator. <i>N</i>-Isopropylacrylamide (NIPAM) was included to obtain thermosensitive
polymers, 2-(dimethylamino)Âethyl methacrylate (DMAEMA) provided pH-sensitive
properties, and 2-hydroxyethyl acrylate (HEA) functioned as a noncharged
hydrophilic block that also allows for postmodifications reactions.
This synthesis approach can further contribute to the design of high-precision
polymers with tailorable block compositions and polymer topologies,
which is highly attractive for applications in nanotechnology
Impact of volcanic ash on anammox communities in deep sea sediments
Subaerial explosive volcanism contributes substantial amounts of material to the oceans, but little is known about the impact of volcanic ash on sedimentary microbial activity. We have studied anammox communities in deep sea sediments near the volcanically active island of Montserrat, Lesser Antilles. The rates of anammox and denitrification in the sediments were measured using 15N isotope pairing incubation experiments, while 16S rRNA genes were used to examine anammox community structures. The higher anammox rates were measured in sediment containing the lower accumulation of volcanic ash in the surface sediments, while the lowest activities were found in sediments with the highest ash deposit. 16S rRNA gene analysis revealed the presence of ‘Candidatus Scalindua spp.’ in the sediments. The lowest diversity of anammox bacteria was observed in the sediments with the highest ash deposit. Overall, this study demonstrates that the deposition of volcanic material in deep sea sediments has negative impacts on activity and diversity of the anammox community. Since anammox may account for up to 79% of N2 production in marine ecosystems, periods of extensive explosive volcanism in Earth history may have had a hitherto unrecognized negative impact on the sedimentary nitrogen removal processes
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