Tetrasubstituted 2-imidazolones via Ag(I)-catalyzed cycloisomerization of propargylic ureas

A one-pot protocol based on a Ag(I)-catalyzed cycloisomerization of propargylic ureas, derived from secondary propargylamines and isocyanates, was developed for the generation of the 2-imidazolone core.     

Microwave-assisted decarboxylative three-component coupling of a 2-oxoacetic acid, an amine, and an alkyne

A novel and efficient microwave-assisted decarboxylative three-component coupling of a 2-oxoacetic acid, an amine, and an alkyne (OA(2)-coulpling) has been developed. This new multicomponent coupling constitutes an efficient approach for the synthesis of polysubstituted propargylamines in the presence of a catalytic amount of copper(I) catalyst.     

An expeditious route toward pyrazine-containing nucleoside analogues

An improved and convenient methodology for the synthesis of asymmetrically substituted pyrazines starting from 3,5-dichloropyrazin-2(1H)-ones has been elaborated. Several nucleoside analogues have been synthesized containing the pyrazine core as the organic base coupled with the sugar via a triazole linkage. The beneficial effect of microwave irradiation throughout the sequence has been demonstrated.     

Investigation into the enantioselection mechanism of ruthenium-arene-diamine transfer hydrogenation catalysts using fluorinated substrates

The effects of both steric and electronic properties of ketones on the selectivity in asymmetric transfer hydrogenation have been studied with aryl alkyl/fluoroalkyl ketones using four ruthenium based catalysts and two different media. The 1-arylethanones, 1-aryl-2-fluoroethanones and 2,2-difluoroacetophenones could be reduced with medium to high ee (86-99%), while the 1-aryl-2,2,2-trifluoroethanones were reduced with low selectivity in most systems. The change in enantioselectivity upon structural variation has been rationalised aided by regression analysis with substituent constants and the partial charge of the carbonyl carbon as predictors. The steric bulk of the alkyl/fluoroalkyl chain was found to be the major factor in determining selectivity in formic acid/triethylamine, while for reduction of a series of substituted 1-arylethanones and 1-aryl-2-fluoroethanones, the selectivity was found to depend on the electronic properties of the aromatic ring, supporting previous evidence that π-π interaction between the substrate and catalyst is important in determining the selectivity. For reductions in water using sodium formate as the hydrogen donor, altered and more complex selectivity mechanisms were observed. Experiments and regression focused on the variation of the alkyl/fluoroalkyl group of phenyl and 1-naphthyl ketones, showed that the selectivity correlated with the size of the substituent, but also the partial charge of the carbonyl carbon.     

Efficient regioselective protection of myo-inositol via facile protecting group migration

A cis-1,2-cyclohexanediol, 1,4,5,6-tetra-O-benzyl-myo-inositol, was selectively protected at the axial C2-hydroxyl via acid-mediated rearrangement of the corresponding 1,2-orthoacetate, or via the base-induced migration of a protecting group that had previously been easily installed with complete regioselectivity at the adjacent equatorial hydroxyl. Esters 4a-6a were synthesized in high yields (75-82%) while sulfonate 7a and silyl ether 8a were obtained in 85 and 31% yields, respectively. The migration of the esters induced by DBU results in equilibrium between regioisomers favouring the C2 protected isomer, but NaH induced migration of sulfonyl and silyl groups results in complete migration from equatorial to axial hydroxyl groups.     

Energy alignment and surface dipoles of rylene dyes adsorbed to TiO2 nanoparticles

The energy loss in dye-sensitized solar cells calculated from the energy difference between the lowest electronic transition of the dye and the obtained open-circuit voltage is often 1 eV or even more. To minimize this loss, it is important to accurately determine the energy alignment at the TiO(2)/dye/redox-mediator interface. In this study, we compared the results from electrochemistry and photoelectron spectroscopy for determining the energy alignment of three rylene dyes, two of which absorb relatively far in the red. The trends observed with the methods were different, as in the former, the energy alignment is measured relative to an external reference and includes contributions from solvent reorganization energies, while in the latter, it is measured relative to the energetics of the TiO(2) and is lacking such contributions. The influence of the dyes' dipole moments on the energetics of the TiO(2) was also measured and explained some of the differences in trends. Finally, we compared the injection efficiencies of the two red-absorbing dyes and found that the differences in injection efficiencies can be better explained using the energy alignment determined from photoelectron spectroscopy. This shows that the method for measuring the energetics of a DSC should be chosen according to what process one intends to study.     

Microwave spectra and gas phase structural parameters for N-hydroxypyridine-2(1H)-thione

The microwave spectrum for N-hydroxypyridine-2(1H)-thione (pyrithione) was measured in the frequency range 6-18 GHz, providing accurate rotational constants and nitrogen quadrupole coupling strengths for three isotopologues, C(5)H(4)(32)S(14)NOH, C(5)H(4)(32)S(14)NOD, and C(5)H(4)(34)S(14)NOH. Pyrithione was found to be in a higher concentration in the gas phase than the other tautomer, 2-mercaptopyridine-N-oxide (MPO). Microwave spectroscopy is best suited to determine which structure predominates in the gas phase. The measured rotational constants were used to accurately determine the coordinates of the substituted atoms and provided sufficient data to determine some of the important structural parameters for pyrithione, the only tautomer observed in the present work. The spectra were obtained using a pulsed-beam Fourier transform microwave spectrometer, with sufficient resolution to allow accurate measurements of the (14)N nuclear quadrupole hyperfine interactions. Ab initio calculations provided structural parameters and quadrupole coupling strengths that are in very good agreement with measured values. The experimental rotational constants for the parent compound are A = 3212.10(1), B = 1609.328(7), and C = 1072.208(6) MHz, yielding the inertial defect Δ(0) = -0.023 amu·?(2) for the C(5)H(4)(32)S(14)NOH isotopologue. The observed near zero inertial defect clearly indicates a planar structure. The least-squares fit structural analysis yielded the experimental bond lengths R(O-H) = 0.93(2) ?, R(C-S) = 1.66(2) ?, and angle (N-O-H) = 105(4)° for the ground state structure.     

Supported lipid bilayer microarrays created by non-contact printing

Arrays of supported lipid bilayers (SLBs) provide great potential for future drug development and multiplexed biological research, but are difficult to prepare due to the sensitivity of both the lipid and protein structural arrangement to air exposure. A novel way to produce arrays of SLBs is presented based on non-contact dispensing of vesicles to a substrate through a thin surface confined water film. The approach presents many degrees of freedom since it is not limited to a specific substrate, lipid composition, linker or controlled environment. The method allows adjustment of spot size (180-360 μm) by repeated dispensing as well as control over the composition of the spots and subsequent analytes. SLB formation by vesicle adsorption and rupture allows for incorporation of membrane proteins through pre-formed proteoliposomes. Dispensing through a dip-and-rinse water film avoids contamination, disruptive drying and the need for complex buffer compositions. Furthermore, no humidity control is necessary which simplifies the production step and prolongs the life-time of the spotting system. We characterize the method with respect to control over spot size, bilayer mobility and the formation process as well as demonstrate the possibility to fuse bilayer spots with subsequently added vesicles. Since complex lipid compositions and multiple spotting nozzles can be used, this novel technique is expected to be a promising platform for future applications, e.g. patterning to monitor peptide/protein-lipid interactions, for glycomics using glycolipids or lipopolysaccharides, and to study mixing of spatially confined lipid membranes.