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Ohne Zusammenfassung     

Searchability in merging and implicit data structures

We introduce the notion ofsearchability as a property of an in place merging algorithm. We show that a pair of sorted arrays can be merged in place in linear time, so that a search can be performed in logarithmic time at any point during the merging process. We apply this method to devise an implicit data structure which can support searches inO(log² n) time in the worst case, andO(logn) on the average, and insertions inO(logn) time, in the worst case.This research was partly supported by NSERC under grant A8237 and presented in preliminary form at the 10th International Colloquium on Automata, Languages and Programming.On leave from the University of Chile.     

Development of tip-enhanced optical spectroscopy for biological applications: a review

Tip-enhanced optical spectroscopy is an approach that holds a good deal of promise for the nanoscale characterisation of matter. Tip-enhanced Raman spectroscopy (TERS) has been demonstrated on a variety of samples: inorganic, organic and biological. Imaging using TERS has been shown for carbon nanotubes due to their high scattering efficiency. There are a number of compelling motivations to consider alternative approaches for biological samples; most importantly, the potential for heat damage of biomolecules and long acquisition times. These issues may be addressed through the development of tip-enhanced coherent anti-Stokes Raman scattering microscopy.     

Unconventional hydrogen bonding and π‐stacking in two substituted pyridine carboxamides

The crystal structures of two para‐substituted aryl derivatives of pyridine‐2‐carboxamide, namely N‐(4‐fluorophenyl)pyridine‐2‐carboxamide, C₁₂H₉FN₂O, (I), and N‐(4‐nitrophenyl)pyridine‐2‐carboxamide, C₁₂H₉N₃O₃, (II), have been studied. Compound (I) exhibits unconventional aryl–carbonyl C—H...O and pyridine–fluorine C—H...F hydrogen bonding in two dimensions and well defined π‐stacking involving pyridine rings in the third dimension. The conformation of (II) is more nearly planar than that of (I) and the intermolecular interactions comprise one‐dimensional aryl–carbonyl C—H...O hydrogen bonds leading to a stepped or staircase‐like progression of loosely π‐stacked molecules. The close‐packed layers of planar π‐stacked molecules are related by inversion symmetry. Two alternating interplanar separations of 3.439 (1) and 3.476 (1) Å are observed in the crystal lattice and are consistent with a repetitive packing sequence, ABA′B′AB…, for the π‐stacked inversion pairs of (II).     

Assessing Number Sense of Students in Australia,Sweden, Taiwan,and the United States

This paper reports selected findings from a study of number sense proficiency of students aged 8 to 14 years in Australia, Sweden, United States, and Taiwan. It comments on the meaning and importance of number sense, the development of the assessment instruments, and student responses to the items. Some implications for classrooms of the findings are then discussed.     

Polymersomes Prepared from Thermoresponsive Fluorescent Protein–Polymer Bioconjugates: Capture of and Report on Drug and Protein Payloads

Polymersomes provide a good platform for targeted drug delivery and the creation of complex (bio)catalytically active systems for research in synthetic biology. To realize these applications requires both spatial control over the encapsulation components in these polymersomes and a means to report where the components are in the polymersomes. To address these twin challenges, we synthesized the protein–polymer bioconjugate PNIPAM‐b‐amilFP497 composed of thermoresponsive poly(N‐isopropylacrylamide) (PNIPAM) and a green‐fluorescent protein variant (amilFP497). Above 37 °C, this bioconjugate forms polymersomes that can (co‐)encapsulate the fluorescent drug doxorubicin and the fluorescent light‐harvesting protein phycoerythrin 545 (PE545). Using fluorescence lifetime imaging microscopy and Förster resonance energy transfer (FLIM‐FRET), we can distinguish the co‐encapsulated PE545 protein inside the polymersome membrane while doxorubicin is found both in the polymersome core and membrane.     

Attenuation technique for measuring sediment displacement levels

A technique for obtaining accurate, high (spatial) resolution measurements of sediment redeposition levels is described. In certain regimes, the method may also be employed to provide measurements of sediment layer thickness as a function of time. The method uses a uniform light source placed beneath the layer, consisting of transparent particles, so that the intensity of light at a point on the surface of the layer can be related to the depth of particles at that point. A set of experiments, using the impact of a vortex ring with a glass ballotini particle layer as the resuspension mechanism, are described to test and illustrate the technique.

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Multifrequency electron paramagnetic resonance characterization of PpoA, a CYP450 fusion protein that catalyzes fatty acid dioxygenation

PpoA is a fungal dioxygenase that produces hydroxylated fatty acids involved in the regulation of the life cycle and secondary metabolism of Aspergillus nidulans . It was recently proposed that this novel enzyme employs two different heme domains to catalyze two separate reactions: within a heme peroxidase domain, linoleic acid is oxidized to (8R)-hydroperoxyoctadecadienoic acid [(8R)-HPODE]; in the second reaction step (8R)-HPODE is isomerized within a P450 heme thiolate domain to 5,8-dihydroxyoctadecadienoic acid. In the present study, pulsed EPR methods were applied to find spectroscopic evidence for the reaction mechanism, thought to involve paramagnetic intermediates. We observe EPR resonances of two distinct heme centers with g-values typical for Fe(III) S = (5)/(2) high-spin (HS) and Fe(III) S = (1)/(2) low-spin (LS) hemes. (14)N ENDOR spectroscopy on the S = (5)/(2) signal reveals resonances consistent with an axial histidine ligation. Reaction of PpoA with the substrate leads to the formation of an amino acid radical on the early millisecond time scale concomitant to a substantial reduction of the S = (5)/(2) heme signal. High-frequency EPR (95- and 180-GHz) unambiguously identifies the new radical as a tyrosyl, based on g-values and hyperfine couplings from spectral simulations. The radical displays enhanced T(1)-spin-lattice relaxation due to the proximity of the heme centers. Further, EPR distance measurements revealed that the radical is distributed among the monomeric subunits of the tetrameric enzyme at a distance of approximately 5 nm. The identification of three active paramagnetic centers involved in the reaction of PpoA supports the previously proposed reaction mechanism based on radical chemistry.     

Biomimetic mineralisation of polymeric scaffolds using a combined soaking approach: adaptation with various mineral salts

Biomimetic strategies which utilise hydrogels have been targeted due to favourable hydrogel characteristics such as the presentation of a large surface area for crystal nucleation within a structured yet responsive scaffold. Chitosan hydrogels were prepared and mineralised using a combined method which involves alternate soaking of the films with precursor solutions, followed by treatment with saturated mineral solution. This method has been shown to be effective for the synthesis of calcium carbonate-chitosan composite materials with tensile strength comparable to nacre. The ratio of organic to inorganic is readily controlled through the presoaking solution concentrations. The ubiquity of this method is shown here with respect to switching out both the anion (CaHPO(4)) and the cation (BaSO(4)). Cation doping is also readily achieved allowing formation of Mg-rich CaCO(3). Poly(acrylic acid) added to (Mg,Ca)CO(3)-chitosan systems induces the formation of two polymorphs (vaterite and calcite) which coexist within the composite material. The mineralised scaffolds were analysed by SEM and powder XRD. The successful mineralisation of chitosan templates with various inorganic compounds shows that this combined approach is widely applicable as a biomimetic approach.     

Interactions of halichondrin B and eribulin with tubulin

Compounds that modulate microtubule dynamics include highly effective anticancer drugs, leading to continuing efforts to identify new agents and improve the activity of established ones. Here, we demonstrate that [(3)H]-labeled halichondrin B (HB), a complex, sponge-derived natural product, is bound to and dissociated from tubulin rapidly at one binding site per αβ-heterodimer, with an apparent K(d) of 0.31 μM. We found no HB-induced aggregation of tubulin by high-performance liquid chromatography, even following column equilibration with HB. Binding of [(3)H]HB was competitively inhibited by a newly approved clinical agent, the truncated HB analogue eribulin (apparent K(i), 0.80 μM) and noncompetitively by dolastatin 10 and vincristine (apparent K(i)'s, 0.35 and 5.4 μM, respectively). Our earlier studies demonstrated that HB inhibits nucleotide exchange on β-tubulin, and this, together with the results presented here, indicated the HB site is located on β-tubulin. Using molecular dynamics simulations, we determined complementary conformations of HB and β-tubulin that delineated in atomic detail binding interactions of HB with only β-tubulin, with no involvement of the α-subunit in the binding interaction. Moreover, the HB model served as a template for an eribulin binding model that furthered our understanding of the properties of eribulin as a drug. Overall, these results established a mechanistic basis for the antimitotic activity of the halichondrin class of compounds.