Resonances on-demand for plasmonic nano-particles

A method for designing plasmonic particles with desired resonance spectra by exploiting the interaction of local geometry with surface charge distribution and applying evolutionary algorithm is presented. The method is based on repetitive perturbations of an initial particle's shape while calculating the eigenvalues of the various quasistatic resonances. Novel family of particles with collocated dipole-quadrupole resonances was designed, as an example for the unique power of the method.     

Experimental demonstration of a single-molecule electric motor

For molecules to be used as components in molecular machines, methods that couple individual molecules to external energy sources and that selectively excite motion in a given direction are required. Significant progress has been made in the construction of molecular motors powered by light and by chemical reactions, but electrically driven motors have not yet been built, despite several theoretical proposals for such motors. Here we report that a butyl methyl sulphide molecule adsorbed on a copper surface can be operated as a single-molecule electric motor. Electrons from a scanning tunnelling microscope are used to drive the directional motion of the molecule in a two-terminal setup. Moreover, the temperature and electron flux can be adjusted to allow each rotational event to be monitored at the molecular scale in real time. The direction and rate of the rotation are related to the chiralities of both the molecule and the tip of the microscope (which serves as the electrode), illustrating the importance of the symmetry of the metal contacts in atomic-scale electrical devices.     

Identification and characterization of five new classes of chlorogenic acids in burdock (Arctium lappa L.) roots by liquid chromatography/tandem mass spectrometry

Burdock (Arcticum lappa L.) roots are used in folk medicine and also as a vegetable in Asian countries especially Japan, Korea, and Thailand. We have used LC-MS(n) (n = 2-4) to detect and characterize in burdock roots 15 quantitatively minor fumaric, succinic, and malic acid-containing chlorogenic acids, 11 of them not previously reported in nature. These comprise 3-succinoyl-4,5-dicaffeoyl or 1-succinoyl-3,4-dicaffeoylquinic acid, 1,5-dicaffeoyl-3-succinoylquinic acid, 1,5-dicaffeoyl-4-succinoylquinic acid, and 3,4-dicaffeoyl-5-succinoylquinic acid (M(r) 616); 1,3-dicaffeoyl-5-fumaroylquinic acid and 1,5-dicaffeoyl-4-fumaroylquinic acid (M(r) 614); 1,5-dicaffeoyl-3-maloylquinic acid, 1,4-dicaffeoyl-3-maloylquinic acid, and 1,5-dicaffeoyl-4-maloylquinic acid (M(r) 632); 1,3,5-tricaffeoyl-4-succinoylquinic acid (M(r) 778); 1,5-dicaffeoyl-3,4-disuccinoylquinic acid (M(r) 716); 1,5-dicaffeoyl-3-fumaroyl-4-succinoylquinic acid and 1-fumaroyl-3,5-dicaffeoyl-4-succinoylquinic acid (M(r) 714); dicaffeoyl-dimaloylquinic acid (M(r) 748); and 1,5-dicaffeoyl-3-succinoyl-4-dimaloylquinic acid (M(r) 732). All the structures have been assigned on the basis of LC-MS(n) patterns of fragmentation, relative hydrophobicity, and analogy of fragmentation patterns if compared to caffeoylquinic acids.     

Design and synthesis of novel fluorescence sensing perylene diimides based on photoinduced electron transfer

Two novel tetraester- and PAMAM-branched perylene diimides were synthesized and configured as “fluorophore-spacer-receptor” systems based on photoinduced electron transfer. Due to their long alkylester and alkylamine terminal groups the examined compounds were well soluble in organic solvents. Photophysical characteristics of the dyes were investigated in DMF and water/DMF (1:1, v/v) solution. The ability of the synthesized perylene diimides to detect cations was evaluated by the changes in their fluorescence intensity in the presence of metal ions (Zn²⁺, Co²⁺, Cu²⁺, Fe³⁺, Pb²⁺, Hg²⁺, Ag⁺ and Ni²⁺) and protons. The dyes under study displayed “off-on” switching in its fluorescence as a function of pH, which is attributed to disallowing photoinduced electron transfer from the receptor moiety to the fluorophore. PAMAM-branched dye displayed a good pH sensor activity (FE = 6.4), however the pH sensing ability of tetraester was substantially higher (FE = 184). In the presence of Cu²⁺ and Pb²⁺ ions tetraester quenched its fluorescence intensity (FQ = 22 and 12 respectively), while PAMAM-branched dye enhanced its fluorescence intensity with pronounced selectivity to Cu²⁺ and Fe³⁺ (FE = 3.2 and 4.9, respectively). The results obtained indicate the potential of the novel compounds as fluorescent detectors for metal ions with pronounced selectivity towards Cu²⁺, Pb²⁺ and Fe³⁺ ions and highly efficient “off-on” pH switches, especially a tetraester-branched perylene diimide.     

The Ketosynthase Domain Controls Chain Length in Mushroom Oligocyclic Polyketide Synthases

The nonreducing iterative type I polyketide synthases (NR-PKSs) CoPKS1 and CoPKS4 of the webcap mushroom Cortinarius odorifer share 88 % identical amino acids. CoPKS1 almost exclusively produces a tricyclic octaketide product, atrochrysone carboxylic acid, whereas CoPKS4 shows simultaneous hepta- and octaketide synthase activity and also produces the bicyclic heptaketide 6-hydroxymusizin. To identify the region(s) controlling chain length, four chimeric enzyme variants were constructed and assayed for activity in Aspergillus niger as heterologous expression platform. We provide evidence that the β-ketoacyl synthase (KS) domain determines chain length in these mushroom NR-PKSs, even though their KS domains differ in only ten amino acids. A unique proline-rich linker connecting the acyl carrier protein with the thioesterase domain varies most between these two enzymes but is not involved in chain length control.     

Premixed flame propagation in a free straight vortex

The paper presents experimental and numerical investigations of the Combustion Induced Vortex Breakdown (CIVB) in a free straight turbulent vortex. The velocity field was measured using the Laser-Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV) methods. The flame propagation is estimated from analysis of pictures taken by a high speed camera. Numerical simulations have been performed using the Large Eddy Simulations (LES). Two different types of the flame propagation along the vortex were identified depending on the equivalence ratio and the swirl number. It was shown that the Combustion Induced Vortex Breakdown takes place if the swirl number exceeds a certain threshold at a constant value of the equivalence ratio. LES simulations confirmed the fact that the CIVB appears in the vortex configuration considered. Detailed analysis of the LES data allows to estimate contributions of different physical mechanisms to the CIVB.     

Point defect configurations of supersaturated Au atoms inside Si nanowires

Aberration-corrected scanning transmission electron microscopy (STEM) is used to reveal individual Au atom configurations inside Si nanowires grown by Au-catalyzed vapor-liquid-solid (VLS) molecular beam epitaxy (MBE). We identify a substitutional and three distinct interstitial configurations, one of which has not been previously identified. We confirm the stability of the observed point defect configurations by density functional theory (DFT) calculations. The observed number densities of the various configurations are in accord with their calculated formation energies. The concentration of Au atoms is larger than the solubility limit, but the effect may be caused by the STEM beam.     

Symmetry breaking in a plasmonic metamaterial at optical wavelength

We numerically study the effect of structural asymmetry in a plasmonic metamaterial made from gold nanowires. It is reported that optically inactive (i.e., optically dark) particle plasmon modes of the symmetric wire lattice are immediately coupled to the radiation field, when a broken structural symmetry is introduced. Such higher order plasmon resonances are characterized by their subradiant nature. They generally reveal long lifetimes and distinct absorption losses. It is shown that the near-field interaction strongly determines these modes.     

Recognition of proteins by crystallization patterns in an array of reporter solution microdroplets

A new technique is described for specific recognition of protein analytes by observing protein-induced changes in the drying/crystallization patterns (DCP) of an array of microdroplets containing solutions of different reporter substances. Recognition is based on a difference in interaction of the protein analyte crystalline elements (planes, edges, defects, etc.) in the growing reporter crystals. Using a set of natural L-amino acids as reporters and denoting the amino acid solutions displaying substantial protein-induced changes in the DCP as "1" and those that show no or small changes as "0", a digital binary code was determined for several proteins at multiple concentrations. It was demonstrated that globular proteins can be reliably identified using this code as a "signature" when only 2-100 ng of protein was added to amino acid microdroplets.     

Tumour Stem Cells in Breast Cancer

Tumour stem cells (CSCs) are a self-renewing population that plays important roles in tumour initiation, recurrence, and metastasis. Although the medical literature is extensive, problems with CSC identification and cancer therapy remain. This review provides the main mechanisms of CSC action in breast cancer (BC): CSC markers and signalling pathways, heterogeneity, plasticity, and ecological behaviour. The dynamic heterogeneity of CSCs and the dynamic transitions of CSC⁻ non-CSCs and their significance for metastasis are considered.