Comparative study of surface plasmon scattering by shallow ridges and grooves

We revisit the scattering of surface plasmons by shallow surface defects for both protrusions and indentations of various lengths, which are deemed infinite in one-dimension parallel to the surface. Subwavelength protrusions and indentations of equal shape present different scattering coefficients when their height and width are comparable. In this case, a protrusion scatters plasmons like a vertical point-dipole on a plane, while an indentation scatters like a horizontal point-dipole on a plane. We corroborate that long and shallow asymmetrically-shaped surface defects have very similar scattering, as already found with approximate methods. In the transition from short shallow scatterers to long shallow scatterers the radiation can be understood in terms of interference between a vertical and a horizontal dipole. The results attained numerically are exact and accounted for with analytical models

Design, Synthesis and Biological Evaluation of Novel Analogues of Distamycin

Analogues of distamycin which retain the parent ligand's ability to bind in the DNA minor groove with sequence specificity are widely recognised as potential candidates for drug development. Distamycin binds to DNA with significant, albeit not complete, AT specificity, spanning five base pairs. Its pyrrole rings can partially accommodate the bulky guanine C2-NH2 groups in the minor groove especially at the edges of the binding site, thus leading to some tolerance of GC base pairs. A key objective of this project was to modify a portion of the distamycin structure by substituting its N-terminal pyrrole(-4yl)formamido unit with novel biaryl motifs in an attempt to enhance the AT specificity of the parent ligand. In order to achieve this, solution and solid phase combinatorial approaches were adopted and parallel libraries synthesised using a variety of heterocycles as building blocks. Solid phase combinatorial chemistry, performed on Mimotope Lanterns™, was employed to accelerate the synthesis of polyamides. A protocol for the assembly of the polyamide chain was successfully developed, and Library 3.1 and 3.2 compounds (3.1a-f and 3.2a-f) were prepared rapidly and efficiently. FRET-based DNA melting experiments revealed that some of these molecules are capable of stabilizing a DNA-hairpin oligonucleotide. Library members synthesized in solution phase (2.3a-g) were screened against a 512-member hairpin-DNA oligonucleotide library, containing all possible (non-degenerate) sequences in order to identify recognition events. This screen was based on the ethidium bromide displacement assay reported by Boger, and revealed that enhanced AT sequence selectivity had been achieved with some molecules. In particular, a compound containing the pyrazole-thiazole motif (2.3{5.16}) was found to bind to AT-rich sequences more selectively than distamycin. This result was confirmed by quantitative DNA footprinting experiments using two different DNA fragments in which 2.3{5.16} was shown to bind to TATA sequences with greater selectivity than distamycin, which bound to additional AT- containing sites. Some studies have also been carried out on the synthesis of novel lexitropsins (4.1a-c) specifically designed to target GC sequences. In summary, the results obtained have demonstrated the usefulness of biaryl building blocks in modifying the sequence selectivity of minor-groove binding agents, and lay the foundation for third generation compounds spanning up to five base pairs and designed to have specific recognition of individual bases within their binding site span

2-furyl(phenyl)methanol isolated from Atractilis gummifera rhizome exhibits anti-leishmanial activity

The file attached to this record is the Publisher's final version. Crown copyright.We report for the first time the isolation of 2-furyl(phenyl)methanol (5) from the chloroform extracts of the Atractylis gummifera roots. A. gummifera is a thistle belonging to the Asteraceae family that produces the ent-kaurane diterpenoid glycoside atractyloside (ATR). ATR (1) was isolated and chemically modified to obtain its aglycone atractyligenin (2) and the methylated derivatives ATR-OMe (3) and genine-OMe (4). The compounds 1-5 were structurally characterised and evaluated against the intracellular amastigote, cultured within macrophages, and the extracellular promastigote of Leishmania donovani, the protozoan parasite responsible for the highly infective disease visceral leishmaniasis, which is fatal if untreated. The 2-furyl(phenyl)methanol 5 exhibited notable activity against the promastigote

Synthesis and Biological Evaluation of a Novel C8-Pyrrolobenzodiazepine (PBD) Adenosine Conjugate. A Study on the Role of the PBD Ring in the Biological Activity of PBD-Conjugates

Here we sought to evaluate the contribution of the PBD unit to the biological activity of PBD-conjugates and, to this end, an adenosine nucleoside was attached to the PBD A-ring C8 position. A convergent approach was successfully adopted for the synthesis of a novel C8-linked pyrrolo(2,1-c)(1,4)benzodiazepine(PBD)-adenosine(ADN) hybrid. The PBD and adenosine (ADN) moieties were synthesized separately and then linked through a pentynyl linker. To our knowledge, this is the first report of a PBD connected to a nucleoside. Surprisingly, the compound showed no cytotoxicity against murine cells and was inactive against Mycobacterium aurum and M. bovis strains and did not bind to guanine-containing DNA sequences, as shown by DNase I footprinting experiments. Molecular dynamics simulations revealed that the PBD–ADN conjugate was poorly accommodated in the DNA minor groove of two DNA sequences containing the AGA-PBD binding motif, with the adenosine moiety of the ligand preventing the covalent binding of the PBD unit to the guanine amino group of the DNA duplex. These interesting findings shed further light on the ability of the substituents attached at the C8 position of PBDs to a ect and modulate the biological and biophysical properties of PBD hybrids

Fault behaviour and fault detection in islanded inverter-only microgrids

The increase in popularity of the microgrid concept requires the analysis and solution of the numerous technical issues arising from the operation and integration of the microgrid into the original distribution network. The work presented in this thesis is centred on the study of the fault behaviour of inverter-only microgrids and on the development of a suitable fault detection technique. This task is approached by first understanding the behaviour of a microgrid during a fault and the factors affecting it. A complete description and analysis of the key elements in the study of microgrid fault behaviour is presented. Then, three microgrid models with different inverter control methods (i.e. Synchronous Reference Frame control, Natural Reference Frame control and droop control) and with various current limiting strategies are built in PSCAD and their fault behaviour is simulated, analyzed and compared. It is found that the control of the inverter is able to shape the response of the microgrid in the event of a fault. The constraints to this capability are the inverter’s ratings (current and voltage limits) and the characteristic changes in the network introduced by faults. Moreover, it is found that the control in the Natural Reference Frame gives better fault response, in terms of voltage control and simplicity in implementation, compared with the popular control in the Synchronous Reference Frame. The behaviour of the system is then further analyzed by developing quasi steadystate inverter models suitable for numerical fault analysis. The models are developed starting from the inverter control and analyzing how it changes in the event of a fault. By combining control gains and circuit parameters, they result in being capable of capturing the key features of inverters’ fault behaviour. Depending on the control strategy, some of these models are balanced and therefore are directly applicable in numerical fault analysis based on sequence components. Others are unbalanced and therefore require a fault analysis based on a direct phase coordinates representation of the network. Examples on how to perform numerical fault analysis calculations with balanced and unbalanced models are given and the numerical results well compare with the ones obtained from time-domain simulations using PSCAD. From the knowledge of the microgrid fault behaviour developed analyzing the responses in time-domain simulations and by using the developed inverter models to numerically calculate voltages and currents in the microgrid during different faults at various locations, a fault detection strategy based on voltage sequence components is proposed. Indeed, it is the behaviour of the inverter control during faults which makes the monitoring of voltage sequence components the best discriminator between normal operation and fault operation. The three building blocks of the fault detection strategy which are capable of a fast extraction and comparison of voltage sequence components are described and then the performance of the fault detection strategy for different faults and microgrid operating conditions is tested in PSCAD and discussed. Finally, examples are given on how this voltage detection can be used in the design of a microgrid protection system

Fault behaviour and fault detetion in islanded inverter-only microgrids

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Effect of defect depth on surface plasmon scattering by subwavelength surface defects

10 páginas, 13 figuras, 1 tabla.-- PACS number(s): 42.82.EtSurface plasmon scattering by bidimensional indentations and protrusions is examined, mainly in the optical regime. The width of the defects is fixed, while their height is varied. Both individual defects and arrays of defects are considered. Protrusions mainly reflect the incident plasmons in the optical range. Indentations mainly radiate the incident plasmon out of plane. An indentation produces maximum reflection and out-of-plane radiation at the same wavelength when its interaction with the incident surface plasmon is resonant. Protrusions, in general, exhibit maximum reflection and radiation at different wavelengths. Shallow arrays of either defects produce a photonic band gap, whose spectral width can be broadened by increasing the defects height or depth. At wavelengths inside the band gap, ridge arrays reflect surface plasmon polaritons (SPP’s) better than groove arrays while groove arrays radiate SPP’s better than ridge arrays.The authors acknowledge financial support from the Spanish Ministry of Science and Innovation under Grant Nos. MAT2008-06609-C02, AP2005-5185, and CSD2007- 046-Nanolight.es.Peer reviewe