NMR detection of intermolecular NH.OP hydrogen bonds between guanidinium protons and bisposphonate moieties in an artificial arginine receptor

Hydrogen bonding plays a major role in the selective recognition of guanidinium groups by receptor molecules. The present NMR investigation provides direct experimental evidence of hydrogen bonds in an artificial arginine receptor complex consisting of alpha-N-benzoylarginine ethyl ester and a bisphosphonate tweezers molecule. trans-Hydrogen bond 2hJHP couplings between the phosphonate moieties and individual guanidinium protons as well as the amide proton have been detected by [1H,31P]-HMBC and [31P,1H]-INEPT experiments. The detected hydrogen bonding network in the investigated artificial arginine receptor shows a symmetrical end-on interaction of the guanidinium moiety, which enables concerted rotations and deviates from the structure proposed for the biological arginine fork.     

Enantioselective Hydrogenation and Transfer Hydrogenation of Bulky Ketones Catalysed by a Ruthenium Complex of a Chiral Tridentate Ligand

A study on the enantioselective hydrogenation of tertiary alkyl ketones catalysed by a novel class of tridentate–Ru complex is reported. In contrast to the extensively studied [RuCl₂(diphos)(di-primary amine)] complexes, this new class of hydrogenation catalyst smoothly reduces these less reactive bulky ketones with up to 94 % ee. The same catalyst system can also selectively reduce other potentially problematic substrates such as bulky heterocyclic ketones. Unusually for a pressure hydrogenation catalyst, similar enantioselectivity can be obtained under transfer hydrogenation conditions. The transfer hydrogenations are somewhat slower than the pressure hydrogenations, but this drawback is readily overcome, since we have discovered that a microwave accelerated transfer hydrogenation of the above ketones occurs within 20 min at about 90 °C with similar selectivity to that obtained in the pressure hydrogenation system.     

Enantioseparation of chiral benzimidazole derivatives by electrokinetic chromatography using sulfated cyclodextrins

Baseline separation of 18 new substituted benzimidazole derivatives, potent AMP‐activated protein kinase (AMPK) activators, with one chiral center, was achieved by CD‐EKC using sulfated and highly sulfated CDs (SCDs and HS‐CDs) as chiral selectors. The influence of the type and concentration of the chiral selectors on the enantioseparations was investigated. The SCDs exhibit a very high enantioselectivity power since they allow excellent enantiomeric resolutions compared to those obtained with the neutral CDs. The enantiomers were resolved with analysis times around 6 min using 25 mM phosphate buffer at pH 2.5 containing either β‐S‐CD, HS‐β‐CD, HS‐γ‐CD (3 or 4% w/v) at 25°C, with a voltage of 20 kV. The apparent association constants of the inclusion complexes were calculated. The study of the solute structure‐enantioseparation relationships seems to show the high contribution of the interactions between the solutes phenyl ring and the CDs to the enantiorecognition process. The optimized method was briefly validated (LOD less than 1%) and the purity of enantiomers of compound 3 was determined. The enantiomer migration shows reversal order depending on the kind of CD.     

Probing platinum degradation in polymer electrolyte membrane fuel cells by synchrotron X-ray microscopy

Synchrotron-based scanning transmission X-ray spectromicroscopy (STXM) was used to characterize the local chemical environment at and around the platinum particles in the membrane (PTIM) which form in operationally tested (end-of-life, EOL) catalyst coated membranes (CCMs) of polymer electrolyte membrane fuel cells (PEM-FC). The band of metallic Pt particles in operationally tested CCM membranes was imaged using transmission electron microscopy (TEM). The cathode catalyst layer in the beginning-of-life (BOL) CCMs was fabricated using commercially available catalysts created from Pt precursors with and without nitrogen containing ligands. The surface composition of these catalyst powders was measured by X-ray Photoelectron Spectroscopy (XPS). The local chemical environment of the PTIM in EOL CCMs was found to be directly related to the Pt precursor used in CCM fabrication. STXM chemical mapping at the N 1s edge revealed a characteristic spectrum at and around the dendritic Pt particles in CCMs fabricated with nitrogen containing Pt-precursors. This N 1s spectrum was identical to that of the cathode and different from the membrane. For CCM samples fabricated without nitrogen containing Pt-precursors the N 1s spectrum at the Pt particles was indistinguishable from that of the adjacent membrane. We interpret these observations to indicate that nitrogenous ligands in the nitrogen containing precursors, or decomposition product(s) from that source, are transported together with the dissolved Pt from the cathode into the membrane as a result of the catalyst degradation process. This places constraints on possible mechanisms for the PTIM band formation process.     

Unusual solid-state behavior in a neutral [2]catenane bearing a hydrolyzable component

A template-directed strategy to forming a bis(diimide) macrocycle through an intermediate asymmetric [2]catenane is reported. Saponification of the ester linkages within the crown ether component is much slower in the mechanically interlocked structure when compared to the free crown. The predominance of a single translational isomer leads to a dimeric structure, resulting in the generation of infinite channels within the crystal lattice. [structure: see text]     

A pyrazine bis‐adduct of a binuclear rhodium(II) carboxylate containing 3,4,5‐triethoxybenzoate as the ­equatorial ligand

The title compound, tetrakis(μ‐3,4,5‐triethoxy­benzoato‐κ²O:O′)­bis­[(pyrazine‐κN)­rhodium(II)](Rh—Rh), [Rh₂(C₁₃H₁₇O₅)₄(C₄H₄N₂)₂], crystallizes on an inversion centre in the triclinic space group . The equatorial carboxyl­ate ligands bridge the two Rh^II atoms, giving a binuclear lantern‐like structure. The pyrazine mol­ecules occupy the two axial coordination sites. The phenyl rings are tilted by ca 10° with respect to the attached carboxyl­ate groups. The pyrazine planes have a torsion angle of ca 19° around the Rh—N bond with respect to the plane of the nearer carboxyl­ate group and are not coplanar with the Rh—Rh bond.     

The Effects of UV Emission from Compact Fluorescent Light Exposure on Human Dermal Fibroblasts and Keratinocytes In Vitro

Compact fluorescent light (CFL) bulbs can provide the same amount of lumens as incandescent light bulbs, using one quarter of the energy. Recently, CFL exposure was found to exacerbate existing skin conditions; however, the effects of CFL exposure on healthy skin tissue have not been thoroughly investigated. In this study, we studied the effects of exposure to CFL illumination on healthy human skin tissue cells (fibroblasts and keratinocytes). Cells exposed to CFLs exhibited a decrease in the proliferation rate, a significant increase in the production of reactive oxygen species, and a decrease in their ability to contract collagen. Measurements of UV emissions from these bulbs found significant levels of UVC and UVA (mercury [Hg] emission lines), which appeared to originate from cracks in the phosphor coatings, present in all bulbs studied. The response of the cells to the CFLs was consistent with damage from UV radiation, which was further enhanced when low dosages of TiO₂ nanoparticles (NPs), normally used for UV absorption, were added prior to exposure. No effect on cells, with or without TiO₂ NPs, was observed when they were exposed to incandescent light of the same intensity.     

Evaluation of the cytotoxicity on breast cancer cell of extracts and compounds isolated from Hyptis pectinata (L.) poit

Abstract

Hyptis pectinata is a herb popularly used in Brazil for the treatment of inflammations, pain, bacterial infections and cancer. In the present study, inflorescences (MPIn), leaves (MPL), branches (MPB), root (MPR) extracts and three compounds isolated from MPIn were assayed against breast tumor cell lines. The structures of the three compounds (pectinolide J, hyptolide and pectinolide E) were determined by means of spectroscopic analysis. Pectinolide J was isolated for the first time. The MPIn, MPL and MPR exhibited specific antiproliferative activity on tumor cell lines when compared to normal cell lines with IC₅₀ of 52.01?±?0.64, 45.91?±?0.02?μg/mL and 82.84?±?0.03?μg/mL, respectively. Although the isolated substances did not present good antiproliferative activity, when the three were associated, a greater biological effect was observed, suggesting a synergistic effect. Hyptolide (5.6?±?0.4?μg/mL) showed IC₅₀ sufficiently low to be considered as a drug prototype.     

Complete assignment of the 1H and 13C NMR spectra of garciniaphenone and keto-enol equilibrium statements for prenylated benzophenones

This article reports the structural elucidation by IR, UV and MS spectroscopic data along with 1H and 13C NMR chemical shift assignments of two benzophenones isolated from the fruit pericarp of Garcinia brasiliensis Mart. (Clusiaceae): garciniaphenone, (1R,5S,7S)-3-benzoyl-4-hydroxy-6,6-dimethyl-5,7-di(3-methyl-2-butenyl)bicyclo[3.3.1]non-3-ene-2,9-dione, a novel triprenylated benzophenone; and 7-epi-clusianone, a tetraprenylated benzophenone that has already been extracted from another species of the same family. Furthermore, the keto-enol tautomeric equilibrium at solution-state was described for these compounds by 1D and 2D NMR spectral methods and one attempt to rationalize the different ratios between the noted tautomers was based on stereochemical features.     

Preparation and crystal structure ofexo-2,exo-6-dihydroxy-2,6-dimethyl-9-oxabicyclo[3.3.1]nonane

In a further exploration of the structural factors causing alicyclic diols such asexo-2,exo-6-dihydroxy-2,6-dimethylbicyclo[3.3.1]nonane (1) to adopt the helical tubuland inclusion host structure, the title compound (8) has been synthesized and its crystal structure determined. This 9-oxa analogue of (1) has a totally different structure [C₁₀H₁₈O₃; orthorhombic;P2₁2₁2;a 18.989(4),b 19.064(3),c 14.256(3) Å;Z 20; with finalR 0.065] due to involvement of the ether oxygen atom in the hydrogen bonding network. The structure of the diol (8) approximatesP¯42₁ c symmetry, and 16 of the 20 molecules per cell create a hostlike structure of this symmetry, which consists of tightly bound hydrogen bonded pillars parallel toc. The remaining guestlike molecules occupy inequivalent pseudo ¯4 sites separated byc/2 to form weakly bound columns parallel toc. Hydrogen bonds also occur between the pillars and columns. An ordered structure with sensible intermolecular contacts can be formed inP2₁2₁2₁ with thec axis doubled. A difference betweena andb axial lengths correlates with a difference in occupancies of pseudo-¯4-related sites for the guest-like component of the structure.