Buffers for the Physiological pH Range: Studies of 4-(N-Morpholino)butanesulfonic Acid (MOBS) from 5 to 55 °C

In this study, we report the pH values of two buffer solutions without chloride ion and eight buffer solutions with NaCl with an ionic strength I=0.16 mol?kg^?1. Electromotive force (emf) techniques have been used to get the cell potentials at 12 temperatures from 5 to 55?°C, including 37?°C. An extended form of the Bates-Guggenheim convention is used in the entire ionic strength range, 0.04 to 0.16?mol?kg^?1. The residual liquid junction potentials (??E _j ) of the buffer solutions of MOBS have been estimated from previous measurements with a flowing junction cell. These values of ??E _j have been used for correction in order to ascertain the operational pH values of four buffer solutions of MOBS at 25 and 37?°C. These solutions are recommended as pH standards for physiological application in the pH range 7.4 to 7.7.     

Calcium rubies: a family of red-emitting functionalizable indicators suitable for two-photon ca(2+) imaging

We designed Calcium Rubies, a family of functionalizable BAPTA-based red-fluorescent calcium (Ca(2+)) indicators as new tools for biological Ca(2+) imaging. The specificity of this Ca(2+)-indicator family is its side arm, attached on the ethylene glycol bridge that allows coupling the indicator to various groups while leaving open the possibility of aromatic substitutions on the BAPTA core for tuning the Ca(2+)-binding affinity. Using this possibility we now synthesize and characterize three different CaRubies with affinities between 3 and 22 μM. Their long excitation and emission wavelengths (peaks at 586/604 nm) allow their use in otherwise challenging multicolor experiments, e.g., when combining Ca(2+) uncaging or optogenetic stimulation with Ca(2+) imaging in cells expressing fluorescent proteins. We illustrate this capacity by the detection of Ca(2+) transients evoked by blue light in cultured astrocytes expressing CatCh, a light-sensitive Ca(2+)-translocating channelrhodopsin linked to yellow fluorescent protein. Using time-correlated single-photon counting, we measured fluorescence lifetimes for all CaRubies and demonstrate a 10-fold increase in the average lifetime upon Ca(2+) chelation. Since only the fluorescence quantum yield but not the absorbance of the CaRubies is Ca(2+)-dependent, calibrated two-photon fluorescence excitation measurements of absolute Ca(2+) concentrations are feasible.     

A Direct CH/ArH Coupling Approach to Oxindoles,Thio‐oxindoles, 3,4‐Dihydro‐1 H‐quinolin‐2‐ones,and 1,2,3,4‐Tetrahydroquinolines

A copper(II)‐catalysed approach to oxindoles, thio‐oxindoles, 3,4‐dihydro‐1H‐quinolin‐2‐ones, and 1,2,3,4‐tetrahydroquinolines via formal C?H, Ar?H coupling is described. In a new variant, copper(II) 2‐ethylhexanoate has been identified as an inexpensive and efficient catalyst for this transformation, which utilises atmospheric oxygen as the re‐oxidant.     

Functionalized Graphene as a Gatekeeper for Chiral Molecules: An Alternative Concept for Chiral Separation

We propose a new method of chiral separation using functionalized nanoporous graphene as an example. Computational simulations based on density functional theory show that the attachment of a suitable chiral “bouncer” molecule to the pore rim prevents the passage of the undesired enantiomer while letting its mirror image through.     

One‐Pot Synthesis of O‐Allylhydroxylamines through the Organocatalytic Oxidation of Tertiary Allylic Amines Followed by a [2,3]‐Meisenheimer Rearrangement

A cheap, green, and highly efficient one‐pot method for the synthesis of O‐protected allylic alcohols is described. By utilizing 2,2,2‐trifluoroacetophenone as the organocatalyst and H₂O₂ as the oxidant, a variety of allylic amine N‐oxides were synthesized, which upon heating are converted to the final products through a [2,3]‐Meisenheimer rearrangement.     

Adsorption of the first row of transition metals on the perfect and defective MgO(1 0 0) surface

We present DFT calculations for adsorption of the first row of transition metal atoms on a MgO(1 0 0) surface and on a surface exhibiting defects. Some atoms exhibit a high adsorption energy on the defect (e.g. Co, Ni and Cu), but others (Ca, Sc) rather adsorb on a clean surface and another set is indifferent to the presence of defect. The adsorption becomes energetically unfavorable when the σ anti-bonding orbitals become populated; this is worse on a defective surface than on a terrace. The π back-donation to the surface contributes to favor the adsorption on the center.     

The influence of calcination on the size of nanocrystals, porous structure and acid–base properties of mesoporous anatase used as catalytic support

Mesoporous anatase was prepared following sol–gel and using urea as template. The influence of calcination temperature on the phase stability, nanocrystal/aggregate size, pore size distribution and specific surface area as well as on the acid–base behavior in aqueous solutions was studied using X-ray diffraction, laser-Raman and diffuse reflectance spectroscopies, scanning electron microscopy and laser scattering as well as N₂ adsorption–desorption isotherms and potentiometric mass titrations.The crystal structure was kept constant upon calcination over the whole temperature range, 200–500 °C. In this range anatase is constituted from primary nanocrystals. These are assembled into larger, rather spherical, clusters of about 30–40 nm and then into aggregates of various sizes (0.2–0.3 μm and 2–100 μm) with a distribution centered at about 12 μm. Increase of the calcination temperature caused an increase in the size of the primary nanocrystals from 8.1 nm at 200 °C to 17.1 nm at 500 °C, whereas calcination does not influence the morphology at micro-scale. Moreover, increase of the calcination temperature from 200 °C to 500 °C brings about a shift in the mean pore diameter from 47 nm to 91 nm accompanied by a decrease in the specific surface area and pore volume. The above effects were related with the aforementioned increase in the size of the primary nanocrystals. The value of pzc and the values of surface charge determined at various pH do not practically depend on the calcination temperature. The absence of pore space confinement effects was explained in terms of the structure and size of the interface development between the anatase surface and the electrolytic solution.     

Direct C-glycosylation by indium-mediated alkynylation on sugar anomeric position

Indium-mediated alkynylation reaction was studied for the direct preparation of C-glycosides. Easily available starting sugar derivatives with an acetyl group at the anomeric position were tested as electrophiles toward alkynylindium reagents under Barbier conditions. Good yields and stereoselectivities were observed during the reaction. The alkynylation was applied to the synthesis of an alpha-(1-->6)-C-disaccharide analogue of isomaltoside.     

Asymmetric Transfer Hydrogenation of gem-Difluorocyclopropenyl Esters: Access to Enantioenriched gem-Difluorocyclopropanes

Catalytic enantioselective access to disubstituted functionalized gem-difluorocyclopropanes, which are emerging fluorinated motifs of interest in medicinal chemistry, was achieved through asymmetric transfer hydrogenation of gem-difluorocyclopropenyl esters, catalyzed by a Noyori–Ikariya (p-cymene)-ruthenium(II) complex, with (N-tosyl-1,2-diphenylethylenediamine) as the chiral ligand and isopropanol as the hydrogen donor. The resulting cis-gem-difluorocyclopropyl esters were obtained with moderate to high enantioselectivity (ee=66–99 %), and post-functionalization reactions enable access to valuable building blocks incorporating a cis- or trans-gem-difluorocyclopropyl motif.