Elegaphenone and 7-epi-clusianone, the major cytotoxic constituents of Hypericum elegans

Two cytotoxic constituents, namely elegaphenone and 7-epi-clusianone, were isolated from the aerial parts of Hypericum elegans Stepan ex Willd. Elegaphenone was identified as (E)-(2-(3,7-dimethylocta-2,6-dienyloxy)-4,6-dihydroxyphenyl)(phenyl)methanone by means of spectral evidence. Both compounds showed prominent cytotoxicity on HD-MY-Z, K-562 and KE-37 tumour cell lines. The IC(50) values for elegaphenone were 15.9 (HD-MY-Z), 13.9 (K-562) and 16.9 (KE-37) μmol while those of 7-epi-clusianone were 9.8 (HD-MY-Z), 11.8 (K-562) and 13.6 (KE-37) μmol. The established oligonucleosomal deoxyribonucleic acid (DNA) fragmentation of genomic DNA following short-term (6?h) or long-term (24?h) exposure to the tested compounds clearly indicates that the induction of apoptotic cell death is an important component for their cytotoxic mode of action.     

Extraction of chlorides of some lanthanoides by tricaprylylmethylammonium pelargonate

Summary The extraction of some lanthanoides by tricaprylylmethylammonium pelargonate has been investigated in the system ofLnCl₃-Na(H)Cl-R ₄NB-CCl₄ at constant ionic strength =0.1. A mechanism of the extraction process is suggested, which explains the simultaneous extraction of HCl andLnCl₃.

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Extraktion von Chloriden einiger Lanthanoiden mittels Tricaprylylethylmammonium-Pelargonat

Zusammenfassung Es wurde die Extraktion von Lanthanoiden mittels Tricaprylylmethylammonium-Pelargonat in dem SystemLnCl₃-Na(H)Cl-R ₄NB-CCl₄ bei konstanter Ionenstärke =0.1 untersucht. Ein Mechanismus des Extraktionsprozesses wird vorgeschlagen, der die gemeinsame Extraktion von HCl undLnCl₃ erklärt.

     

Continuous-wave stimulated Raman scattering (cwSRS) microscopy

Stimulated Raman scattering (SRS) microscopy is a powerful tool for chemically sensitive non-invasive optical imaging. However, ultrafast laser sources, which are currently employed, are still expensive and require substantial maintenance to provide temporal overlap and spectral tuning. SRS imaging, which utilizes continuous-wave laser sources, has a major advantage, as it eliminates the cell damage due to exposure to the high-intensity light radiation, while substantially reducing the cost and complexity of the setup. As a proof-of-principle, we demonstrate microscopic imaging of dimethyl sulfoxide using two independent, commonly used lasers, a diode-pumped, intracavity doubled 532-nm laser and a He–Ne laser operating at 632.8-nm.     

The syn-oriented 2-OH provides a favorable proton transfer geometry in 1,2-diol monoester aminolysis: implications for the ribosome mechanism

A computational study of 1-formyl 1,2-ethanediol aminolysis predicts a stepwise mechanism involving syn-2-OH-assisted proton transfer. The syn-oriented 2-OH takes over the catalytic role of the external water or amine molecule previously observed in 2-deoxy ester aminolysis. It provides more favorable, that is, more linear, proton transfer geometry for the rate-limiting transition state resulting in an almost billion-fold rate acceleration of the overall reaction. These findings provide structural basis for explanation of the efficiency of the proton shuttling mechanism and imply double proton transfer catalysis by peptidyl tRNA A76 2'-OH as a possible catalytic strategy used by ribosome.     

Predicting adsorption enthalpies on silicalite and HZSM‐5: A benchmark study on DFT strategies addressing dispersion interactions

We evaluated the accuracy of periodic density functional calculations for adsorption enthalpies of water, alkanes, and alcohols in silicalite and HZSM‐5 zeolites using a gradient‐corrected density functional with empirical dispersion corrections (PBE‐D) as well as a nonlocal correlation functional (vdW‐DF2). Results of both approaches agree in acceptable fashion with experimental adsorption energies of alcohols in silicalite, but the adsorption energies for n‐alkanes in both zeolite models are overestimated, by 21?46 kJ mol^?1. For PBE‐D calculations, the adsorption of alkanes is exclusively determined by the empirical dispersion term, while the generalized gradient approximation‐DFT part is purely repulsive, preventing the molecule to come too close to the zeolite walls. The vdW‐DF2 results are comparable to those of PBE‐D calculations, but the latter values are slightly closer to the experiment in most cases. Thus, both computational approaches are unable to reproduce available experimental adsorption energies of alkanes in silicalite and HZSM‐5 zeolite with chemical accuracy. © 2014 Wiley Periodicals, Inc.     

Structure, stability, electronic and magnetic properties of Ni4 clusters containing impurity atoms

Using a gradient-corrected density functional method, we studied computationally how single impurity atoms affect the structure and the properties of a Ni4 cluster. H and O atoms coordinate at a Ni-Ni bond, inducing small changes to the structure of bare Ni4 which is essentially a tetrahedron. For a C impurity, we found three stable structures at a Ni4 cluster. In the most stable geometry, the carbon atom cleaves a Ni-Ni bond of Ni4, binding to all Ni atoms. Inclusion of the impurity atom leads to a partial oxidation of the metal atoms and, in the most stable structures, reduces the spin polarization of the cluster compared to bare Ni4. An H impurity interacts mainly with the Ni 4s orbitals, whereas the Ni 3d orbitals participate strongly in the bonding with O and C impurity atoms. For these impurity atoms, Ni 3d contributions dominate the character of the HOMO of the ligated cluster, in contrast to the HOMO of bare Ni4 where Ni 4s orbitals prevail. We also discuss a simple model which relates the effect of a H impurity on the magnetic state of metal clusters to the spin character (minority or majority) of the LUMO or HOMO of the bare metal cluster.     

New approaches to hyperbranched poly(4‐chloromethylstyrene) and introduction of various functional end groups by polymer‐analogous reactions

A facile way for the synthesis of hyperbranched poly(4‐chloromethylstyrene) [P(4‐CMS)] with adjustable molar mass by classic atom transfer radical polymerization (ATRP) and mechanistically similar procedures is presented. Subsequently, the chlorine functional groups have been modified to obtain polymers with different polarities. On the one hand, the polymer was end‐capped with unpolar groups (e.g., methyl, phenol ether) to obtain chemically inert substances. On the other hand, more complex functional groups have been introduced through azide groups by 1,3‐dipolar cycloaddition reaction (“click chemistry”). Furthermore, a method for the introduction of ester groups under mild conditions using cesium carboxylates is presented, which also allowed the preparation of so‐called hyperstars by attaching COOH functionalized polystyrene chains onto the P(4‐CMS) as core molecule. All these reactions were carried out in high or very high yields. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2224–2235, 2010     

Unusual Reactions of (+)‐Car‐2‐ene and (+)‐Car‐3‐ene with Aldehydes on K10 Clay

The reactions of (+)‐car‐2‐ene ( 1 ) and (+)‐car‐3‐ene ( 2 ) with aldehydes in the presence of montmorillonite clay were studied for the first time (Schemes 3 and 5). The major products of these reactions are optically active, substituted hexahydroisobenzofurans, probably formed as a result of an attack of the protonated aldehyde at the cyclopropane ring. Quite unexpectedly, the products are cis‐configured at the ring‐fusion site; the fact was established by means of quantum‐chemical calculations and NMR data. It appeared that the behavior of the 2 : 3 mixture 1 / 2 in reactions with aldehydes in the presence of K10 clay differed substantially from the reactivities of the corresponding individual monoterpenes.     

Reverse hydrogen spillover on and hydrogenation of supported metal clusters: insights from computational model studies

"Reverse" spillover of hydrogen from hydroxyl groups of the support onto supported transition metal clusters, forming multiply hydrogenated metal species, is an essential aspect of various catalytic systems which comprise small, highly active transition metal particles on a support with a high surface area. We review and analyze the results of our computational model studies related to reverse hydrogen spillover, interpreting available structural and spectral data for the supported species and examining the relationship between metal-support and metal-hydrogen interactions. On the examples of small clusters of late transition metals, adsorbed in zeolite cavities, we showed with computational model studies that reverse spillover of hydrogen is energetically favorable for late transition metals, except for Au. This preference is crucial for the chemical reactivity of such bifunctional catalytic systems because both functions, of metal species and of acidic sites, are strongly modified, in some cases even suppressed - due to partial oxidation of the metal cluster and the conversion of protons from acidic hydroxyl groups to hydride ligands of the metal moiety. Modeling multiple hydrogen adsorption on metal clusters allowed us to quantify how (i) the support affects the adsorption capacity of the clusters and (ii) structure and oxidation state of the metal moiety changes upon adsorption. In all models of neutral systems we found that the metal atoms are partially positively charged, compensated by a negative charge of the adsorbed hydrogen ligands and of the support. In a case study we demonstrated with calculated thermodynamic parameters how to predict the average hydrogen coverage of the transition metal cluster at a given temperature and hydrogen pressure.     

Identification of the related substances of tilmicosin by liquid chromatography/ion trap mass spectrometry

Structures of seven impurities of the veterinary drug tilmicosin have been elucidated by multiple fragmentation with ion trap tandem mass spectrometry. All related compounds possess the main lactone ring of tilmicosin. The differences in their structures are due to the hydroxyl, mycaminose, 3,5-dimethylpiperidine and mycinose groups connected to C(3), C(5), C(6), C(14) of the lactone ring, respectively. The following compounds of the impurity profile of tilmicosin were identified: B - tilmicosin with a hydroxyl group at C(3); C - tilmicosin without a methyl group at the N-atom connected to C(3) of the mycaminose ring; D - tilmicosin with a hydroxyl group at C(6) of the mycaminose ring; E - tilmicosin with a methoxy group at C(3), F - desmicosin; G - 20-dihydrodesmicosin; and H - tilmicosin without a mycaminose ring. Isomers of the compounds B, C, D, E and H were identified by their mass chromatograms and retention times. The concentrations of the impurities varied in the range of 0.1% to 2.9%.