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

Supramolecularly directed rotary motion in a photoresponsive receptor

Stimuli-controlled motion at the molecular level has fascinated chemists already for several decades. Taking inspiration from the myriad of dynamic and machine-like functions in nature, a number of strategies have been developed to control motion in purely synthetic systems. Unidirectional rotary motion, such as is observed in ATP synthase and other motor proteins, remains highly challenging to achieve. Current artificial molecular motor systems rely on intrinsic asymmetry or a specific sequence of chemical transformations. Here, we present an alternative design in which the rotation is directed by a chiral guest molecule, which is able to bind non-covalently to a light-responsive receptor. It is demonstrated that the rotary direction is governed by the guest chirality and hence, can be selected and changed at will. This feature offers unique control of directional rotation and will prove highly important in the further development of molecular machinery

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

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

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

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

Ordering Surfaces on the Nanoscale: Implications for protein adsorption

Monolayer-protected metal nanoparticles (MPMNs) are a newly discovered class of nanoparticles with an ordered, striped domain structure that can be readily manipulated by altering the ratio of the hydrophobic to hydrophilic ligands. This property makes them uniquely suited to systematic studies of the role of nanostructuring on biomolecule adsorption, a phenomenon of paramount importance in biomaterials design. In this work, we examine the interaction of the simple, globular protein cytochrome C (Cyt C) with MPMN surfaces using experimental protein assays and computational molecular dynamics simulations. Experimental assays revealed that adsorption of Cyt C generally increased with increasing surface polar ligand content, indicative of the dominance of hydrophilic interactions in Cyt C-MPMN binding. Protein-surface adsorption enthalpies calculated from computational simulations employing rigid-backbone coarse-grained Cyt C and MPMN models indicate a monotonic increase in adsorption enthalpy with respect to MPMN surface polarity. These results are in qualitative agreement with experimental results and suggest that Cyt C does not undergo significant structural disruption upon adsorption to MPMN surfaces. Coarse-grained and atomistic simulations furthermore elucidated the important role of lysine in facilitating Cyt C adsorption to MPMN surfaces. The amphipathic character of the lysine side chain enables it to form close contacts with both polar and nonpolar surface ligands simultaneously, rendering it especially important for interactions with surfaces composed of adjacent nanoscale chemical domains. The importance of these structural characteristics of lysine suggests that proteins may be engineered to specifically interact with nanomaterials by targeted incorporation of unnatural amino acids possessing dual affinity to differing chemical motifs