Zobrazení zdroje stránky Romeroernstsen5159

Finally, our results indicate a switch from preferential cleavage of the pro-(R) to the pro-(S) carboxylate group in the CLG-IPL variant of AMDase for all substrates studied. This appears to be due to the emergence of a new hydrophobic pocket generated by the insertion of the six amino acid substitutions, into which the pro-(S) carboxylate binds. Our results allow insight into the tight interaction network determining AMDase selectivity, which in turn provides guidance for the identification of target residues for future enzyme engineering.A new mononuclear vanadium peroxido complex [VO(O2)(phen)(quin)]·H2O (1) exhibiting an unprecedented isomerism of its ligands was isolated from a two-component water-acetonitrile solvent system. DFT computations aimed at inspecting the stability of all possible isomers of complexes [VO(O2)(L1)(L2)], where L1 and L2 are NN+ON, OO+ON, NN+OO, and ON+ON donor atom set ligands, suggested that every complex characterized so far was the one preferred thermodynamically. However, the particular case of complex [VO(O2)(phen)(quin)] reported herein poses a notable exception to this rule, as this complex yielded single crystals of the isomer with total energy above the anticipated isomer, although both of these isomers could be observed concurrently in solution and also in the solid state. 51V NMR spectroscopy suggested these isomers to be present both in the crystallization solution and in the acetonitrile solution of 1. The coexistence of two isomers is a consequence of their small computed energy difference of 2.68 kJ mol-1, while the preferential crystallization favoring the unexpected isomer is likely to be triggered by solvent effects and the effects of different solubility and/or crystal packing. The coordination geometry of the unusual isomer also manifests itself in FT-IR and Raman spectra, which were corroborated with DFT computations targeted at band assignments.A facile method to prepare difluoromethylenes, including α,α-difluorobenzyl chlorides, by single C-F transformations of benzotrifluorides is disclosed. The C-F cleavage followed by chlorination proceeded smoothly using trityl chloride through the generation of trityl cation as an activator and chloride anion as a nucleophile. Diverse difluoromethylenes such as difluorobenzyl ethers were efficiently prepared by virtue of the good versatility of the resulting chloro and fluorosilyl groups.An enantioselective synthesis of the C(1)-C(15) segment of the marine natural product amphidinolide C has been accomplished by a route that includes a stereoselective boron-Wittig reaction to furnish a trisubstituted alkenylboronate. In addition, the route employs enantioselective alkene diboration to install the C(6) hydroxyl group which undergoes intramolecular conjugate addition to establish a tetrahydrofuran ring. Lastly, a catalytic Suzuki-Miyaura cross-coupling is accomplished to construct the C(9)-C(10) bond.Lithium niobate is an excellent and widely used material for nonlinear frequency conversion due to its strong optical nonlinearity and broad transparency region. Here, we report the fabrication and experimental investigation of resonant nonlinear metasurfaces for second-harmonic generation based on thin-film lithium niobate. In the fabricated metasurfaces, we observe pronounced Mie-type resonances leading to enhanced second-harmonic generation in the direction normal to the metasurface. We find the largest second-harmonic generation efficiency for the resonance dominated by the electric contributions because its specific field distribution enables the most efficient usage of the largest element of the lithium niobate nonlinear susceptibility tensor. This is confirmed by polarization-resolved second-harmonic measurements, where we study contributions from different elements of the nonlinear susceptibility tensor to the total second-harmonic signal. [https://www.selleckchem.com/products/rp-6685.html DNA inhibitor] Our work facilitates establishing lithium niobate as a material for resonant nanophotonics.Four chalcogenophene-fused acenes containing O, S, Se, or Te, respectively, were presented, and the chalcogenophene effect on linear and nonlinear optics was systematically investigated. Their excited-state absorption performance and two-photon absorption (TPA) capacity could be modulated by the incorporating chalcogen atoms. The experimental results showed that the heavy chalcogen facilitated the intersystem crossing resulting in the presence of the triplet state absorption for PyPSe and PyPTe, and the TPA capacity gradually increased with the atomic size of the chalcogens. The theoretical calculation inferred that their nonlinear optical performance was closely related to the contributions of the chalcogenophene component to heterotwistacenes in the final excited state. In addition, PyPTe was able to work under various laser pulses from femtoseconds to nanoseconds.Perovskites have attracted much attention due to their remarkable optical properties. While it is well established that excitons dominate their optical response, the impact of higher excitonic states and formation of phonon sidebands in optical spectra still need to be better understood. Here, we perform a theoretical study of excitonic properties of monolayered hybrid organic perovskites-supported by temperature-dependent photoluminescence measurements. Solving the Wannier equation, we obtain microscopic access to the Rydberg-like series of excitonic states including their wave functions and binding energies. Exploiting the generalized Elliot formula, we calculate the photoluminescence spectra demonstrating a pronounced contribution of a phonon sideband for temperatures up to 50 K, in agreement with experimental measurements. Finally, we predict temperature-dependent line widths of the three energetically lowest excitonic transitions and identify the underlying phonon-driven scattering processes.Penisarins A (1) and B (2), sesquiterpene coumarins with an unusual tricyclic sesquiterpene system, were isolated from endophytic Penicillium sp. KMU18029. Their structures were elucidated on the basis of spectroscopic methods, single-crystal X-ray diffraction, and electronic circular dichroism calculations. Compound 2 showed significant cytotoxicities against two human cancer cell lines, HL-60 and SMMC-7721, with IC50 values of 3.6 ± 0.2 and 3.7 ± 0.2 μM, respectively.