The Role of Nonlinear Dynamics in Quantitative Atomic Force Microscopy

Various methods of force measurement with the Atomic Force Microscope (AFM) are compared for their ability to accurately determine the tip-surface force from analysis of the nonlinear cantilever motion. It is explained how intermodulation, or the frequency mixing of multiple drive tones by the nonlinear tip-surface force, can be used to concentrate the nonlinear motion in a narrow band of frequency near the cantilevers fundamental resonance, where accuracy and sensitivity of force measurement are greatest. Two different methods for reconstructing tip-surface forces from intermodulation spectra are explained. The reconstruction of both conservative and dissipative tip-surface interactions from intermodulation spectra are demonstrated on simulated data.Comment: 25 pages (preprint, double space) 7 figure

(3+3)-Annulation of Carbonyl Ylides with Donor-Acceptor Cyclopropanes: Synergistic Dirhodium(II) and Lewis Acid Catalysis

The first (3+3)-annulation process of donor-acceptor cyclopropanes using synergistic catalysis is reported. The Rh2 (OAc)4 -catalyzed decomposition of diazo carbonyl compounds generated carbonyl ylides in situ. These 1,3-dipoles were converted with donor-acceptor cyclopropanes, activated by Lewis acid catalysis, to afford multiply substituted pyran scaffolds in high yield and diastereoselectivity. Extensive optimization studies enabled access to 9-oxabicyclo[3.3.1]nonan-2-one and 10-oxabicyclo[4.3.1]decen-2-ol cores, exploiting solvent effects on intermediate reactivity

Benthic megafauna on steep slopes at the Northern Mid-Atlantic Ridge

The role of small‐scale (<10 km) habitat availability in structuring deep‐sea hard substratum assemblages is poorly understood. Epibenthic megafauna and substratum availability were studied on steep slopes at the Mid‐Atlantic Ridge from May to July 2010 northwest, northeast, southwest and southeast of the Charlie‐Gibbs Fracture Zone (CGFZ; 48–54°N) at between 2095 and 2601 m depth. Megafauna were six times denser north of the CGFZ compared with the south and differences in density were almost entirely driven by sessile fauna. There was no significant difference in habitat availability amongst sites. Rocky substratum made up 48% of the total area surveyed, with individual transects having between 0% and 82% rock. Assemblage structures were different amongst all superstations. The north was dominated by demospongids and hexactinellids, whereas the southern superstations were dominated by anthozoans and hexactinellids. Differences in megafaunal assemblages north and south of the CGFZ primarily reflected variations in demospongid and anthozoan species composition. With 213–1825 individuals·ha−1, and 7–24 species per superstation, hexactinellids were the most species‐rich (36 species) and cosmopolitan taxa at the study site, supporting observations elsewhere along the ridge and in the CGFZ. The absence of significant differences in substrata availability suggested alternative drivers for density or percentage cover. The amount of hard substratum available only limited sessile megafauna density at one transect that was entirely covered with sediments. Species richness was highest for areas with intermediate values of substratum coverage (35–43% rock)

Ring-Opening 1,3-Aminochalcogenation of Donor-Acceptor Cyclopropanes: A Three-Component Approach

A 1,3-aminothiolation was realized by reacting 2-substituted cyclopropane 1,1-dicarboxylates with sulfonamides and N-(arylthio)succinimides. Under Sn(OTf)2 catalysis the transformation proceeded smoothly to the corresponding ring-opened products bearing the sulfonamide in the 1-position next to the donor and the arylthio residue in the 3-position next to the acceptor. The procedure was extended to the corresponding selenium analogues by employing N-(phenylseleno)succinimides as an electrophilic selenium source

Ring-Opening Regio-, Diastereo-, and Enantioselective 1,3-Chlorochalcogenation of Cyclopropyl Carbaldehydes

meso-Cyclopropyl carbaldehydes are treated in the presence of an organocatalyst with sulfenyl and selenyl chlorides to afford 1,3-chlorochalcogenated products. The transformation is achieved by a merged iminium-enamine activation. The enantioselective desymmetrization reaction, leading to three adjacent stereocenters, furnished the target products in complete regioselectivity and moderate to high diastereo- and enantioselectivities (d.r. up to 15:1 and e.r. up to 93:7)

Mining Deep-Ocean Mineral Deposits: What are the Ecological Risks?

A key question for the future management of the oceans is whether the mineral deposits that exist on the seafloor of the deep ocean can be extracted without significant adverse effects to the environment. The potential impacts of mining are wide-ranging and will vary depending on the type of metal-rich mineral deposit being mined. There is, currently, a significant lack of information about deep-ocean ecosystems and about potential mining technologies: thus, there could be many unforeseen impacts. Here, we discuss the potential ecological impacts of deep-ocean mining and identify the key knowledge gaps to be addressed. Baseline studies must be undertaken, as well as regular monitoring of a mine area, before, during, and after mineral extraction