Enantioselective Catalytic [4+1]-Cyclization of ortho-Hydroxy-para-Quinone Methides with Allenoates

The first highly asymmetric catalytic synthesis of densely functionalized dihydrobenzofurans is reported, which starts from ortho-hydroxy-containing para-quinone methides. The reaction relies on an unprecedented formal [4+1]-annulation of these quinone methides with allenoates in the presence of a commercially available chiral phosphine catalyst. The chiral dihydrobenzofurans were obtained as single diastereomers in yields up to 90 % and with enantiomeric ratios up to 95:5.     

Improved measurement of the hydrogen 1S-2S transition frequency

We have measured the 1S-2S transition frequency in atomic hydrogen via two-photon spectroscopy on a 5.8 K atomic beam. We obtain f(1S-2S) = 2,466,061,413,187,035 (10) Hz for the hyperfine centroid, in agreement with, but 3.3 times better than the previous result [M. Fischer et al., Phys. Rev. Lett. 92, 230802 (2004)]. The improvement to a fractional frequency uncertainty of 4.2 × 10(-15) arises mainly from an improved stability of the spectroscopy laser, and a better determination of the main systematic uncertainties, namely, the second order Doppler and ac and dc Stark shifts. The probe laser frequency was phase coherently linked to the mobile cesium fountain clock FOM via a frequency comb.     

Thermal and photochemical reactivity of oxygen atoms on gold nanocluster surfaces

Reduction of oxidized gold nanoclusters by exposures to foreign gases and irradiation of UV photons has been investigated using X-ray photoelectron spectroscopy. Gold nanoclusters with narrow size distributions protected by alkanethiolate ligands were deposited on a TiO₂(1 1 0) surface with dip coating. Oxygen plasma etching was used for removal of alkanethiolate ligands and oxidization of gold clusters. The oxidized gold clusters were exposed to CO, C₂H₂, C₂H₄, H₂, and hydrogen atoms. Although, C₂H₄ and H₂ did not show any indications of reduction of oxidized gold clusters, CO, C₂H₂, and hydrogen atoms reduced the oxides on gold cluster surfaces. Among them, hydrogen atoms were most effective for reduction. Irradiation of UV photons around 400 nm could also reduce the oxidized gold clusters. The photochemical reduction mechanism was proposed as follows. The photo-reduction was initiated by electronic excitation of gold clusters and oxygen atoms activated reacted with carbon atoms at the surfaces of gold clusters. Carbon species were likely absorbed in gold clusters or remained at the boundaries between gold clusters when gold clusters agglomerated during oxygen plasma exposures. As the photochemical reduction progressed, carbon atoms segregated to the surfaces of gold clusters.     

On the way to sol–gels: an analysis of the intra‐ and intermolecular hydrogen bonding in [Ba(OH)I(H2O)4]

We have been able, via a new synthetic route, to obtain a complete crystal structure of the title compound, tetra­aqua­barium hydro­xide iodide, [Ba(OH)I(H₂O)₄], for which the heavy atoms only were characterized by Kellersohn, ­Beckenkamp & Lutz [Z. Naturforsch. TeilB (1991), 46 , 1279–1286]. In the present results, the H‐atom positions could be located using X‐ray data collection at low temperature. A three‐dimensional network is built up via hydrogen bonds. It was also observed that the title compound undergoes hy­drolysis and might therefore be regarded as an intermediate in the formation of sol–gels, starting from BaI₂ and leading to [Ba(OH)₂(H₂O)_x].     

Monitoring the heterogeneity in single cell responses to drugs using electrochemical impedance and electrochemical noise

Impedance spectroscopy is a widely used technique for monitoring cell–surface interactions and morphological changes, typically based on averaged signals from thousands of cells. However, acquiring impedance data at the single cell level, can potentially reveal cell-to-cell heterogeneity for example in response to chemotherapeutic agents such as doxorubicin. Here, we present a generic platform where light is used to define and localize the electroactive area, thus enabling the impedance measurements for selected single cells. We firstly tested the platform to assess phenotypic changes in breast cancer cells, at the single cell level, using the change in the cell impedance. We next show that changes in electrochemical noise reflects instantaneous responses of the cells to drugs, prior to any phenotypical changes. We used doxorubicin and monensin as model drugs and found that both drug influx and efflux events affect the impedance noise signals. Finally, we show how the electrochemical noise signal can be combined with fluorescence microscopy, to show that the noise provides information on cell susceptibility and resistance to drugs at the single cell level. Together the combination of electrochemical impedance and electrochemical noise with fluorescence microscopy provides a unique approach to understanding the heterogeneity in the response of single cells to stimuli where there is not phenotypic change.

A light addressable single-cell impedance technique for cell adhesion monitoring and measurement of a cell''s drug response based on electrochemical noise is introduced.