Determination of the rate of a fast exchanging coordinated molecule in a lanthanide(III) complex by proton NMR

An elementary procedure is proposed and applied to study the exchange rate of a solvent or solute molecule bound to a complexed paramagnetic Ln(III) ion, other than Gd(III), from the measured longitudinal and transverse relaxation rates and paramagnetic resonance frequency shift at a given temperature.     

Photoprotective activity of propolis

The purpose of this study was to determine the photoprotective properties of propolis. The sun protection factor (SPF) of ethanol extract of propolis was evaluated by an in vitro method, using homosalate as control. This determination is based on the physical determination of the reduction of the energy in the UV range, through a film of product which has previously been spread on an adequate substrate. About 15 mg of O/W emulsion containing propolis at various concentrations were applied on roughened Polymethylmethacrylate (PMMA) plates and the transmission measurements were carried out using a spectrophotometer equipped with integrating sphere. The results may justify their use as a natural sunscreen agent.     

Unraveling the metabolic transformation of tetrazepam to diazepam with mass spectrometric methods

The metabolic transformation pathways of the 1,4-benzodiazepine tetrazepam (C(16)H(17)ClN(2)O, average mass: 288.772) were studied with capillary LC-QqTOF-MS and -MS/MS by analyzing human plasma and urine samples collected from healthy volunteers. Each volunteer took 50 mg of tetrazepam, given in the form of one tablet of Myolastan (Sanofi-Synthelabo, Vienna, Austria). Accurate molecular mass measurements in full-scan mode (scan range: 50-700) were used to survey the collected samples for putative metabolic transformation products. Full-scan fragment ion mass spectra were collected in subsequent LC/MS/MS experiments. Each spectrum was matched to a spectral library containing 3759 MS/MS-spectra of 402 compounds, including eighteen different benzodiazepines, to prove the structural relatedness of a tentative metabolite to tetrazepam. This "similarity search" approach provided a rapid and powerful tool to exclude non-drug-related species, even without any knowledge of the fragmentation chemistry. Interpretation of tandem mass spectrometric data was only required in order to elucidate the site of transformation. Using this strategy, 11 major classes of tetrazepam metabolites were identified. Possible metabolic routes from tetrazepam to diazepam (C(16)H(13)ClN(2)O, average mass: 284.740) via repeated hydroxylation and dehydration of the cylohexenyl moiety were discovered. No evidence for extensive hydroxylation of tetrazepam at position 3 of the diazepine ring was found. In contrast to what is commonly believed, this distinct transformation reaction may be of only minor importance. Furthermore, the occurrence of demethylation, hydration, and glucuronidation reactions was proven.     

1H and 129Xe NMR absorption line shapes in the presence of highly polarized and concentrated xenon solutions in high magnetic field

The presence of highly concentrated dissolved laser-polarized xenon (approximately 1mol/L, polarization up to 0.2) induces numerous effects on proton and xenon NMR spectra. We show that the proton signal enhancements due to (129)Xe-(1)H cross-relaxation (SPINOE) and overall shifts of the proton resonances due to the average dipolar shift created by the intense xenon magnetization are correlated. Protons behave as very useful sensors of the xenon magnetization. Indeed the xenon resonances exhibit many features such as superimposition of narrow lines on the main resonance due to clustering effects, or such as a polarization-dependent line broadening that is tentatively assigned to the effects of temperature fluctuations that decorrelate some distant dipolar field effects from local interactions, transforming xenon spins from "like" to "unlike" spins. These spectral features make difficult the determination of the average dipolar field by means of the xenon resonance but have interesting consequences on the heteronuclear polarization transfer experiment in Hartmann-Hahn conditions (SPIDER).     

The origin of deficiency of the supermolecule second-order Moller-Plesset approach for evaluating interaction energies

Calculations for the complex of thymine and adenine are used to show that the supermolecule second-order Moller-Plesset perturbation theory (MP2) approach for evaluating interaction energies fails in certain cases because of the behavior of one of its components: the uncoupled Hartree-Fock dispersion energy. A simple approach for correcting the MP2 supermolecule interaction energies is proposed. It focuses on correcting a relatively small difference between the MP2 and coupled cluster interaction energies, which is a very appealing feature of the new approach considering a benchmark role played by coupled cluster results.     

Mechanistically inspired catalysts for enantioselective desymmetrizations by olefin metathesis

In asymmetric olefin metathesis reactions, the addition of halide additives is often required to augment enantioselectivities, despite the fact that the additives result in catalysts with diminished reactivities. The preparation of new chiral Ru-based catalysts was accomplished by exploiting previously reported mechanistic studies. The catalysts possess a high level of reactivity and successfully induce high levels of asymmetry in desymmetrization reactions without the use of halide additives.     

Cyclometalation of Phenylpyridines by Rhodium(I) via Room‐temperature C–H Bond Activation

A convenient synthesis of cyclometalated complexes [{Rh(μ‐Cl)(C N)₂}₂] [C N = ppy, 2‐phenylpyridinato ( 2 ); C N = ptpy, 2‐(p‐tolyl)pyridinato ( 3 ); 4‐Clppy = 4‐chloro‐2‐phenylpyridinato ( 4 )] at room temperature is described. The compounds were obtained by the oxidative addition reaction of the corresponding 2‐phenylpyridines to [{Rh(μ‐Cl)(coe)₂}₂] ( 1 ) (coe = cis‐cyclooctene) in dichloromethane solution. The rate of the reaction seems to depend on the electronic influence of the substituents on the phenyl rings of the corresponding 2‐phenylpyridines. The analogous iridium complex of 1 reacted markedly only at higher temperatures in suitable solvents under cyclometalation. The molecular structure of the new compound 4 was additionally confirmed by an X‐ray diffraction study.     

Iron‐Catalyzed Cα?H Oxidation of Tertiary,Aliphatic Amines to Amides under Mild Conditions

De novo syntheses of amides often generate stoichiometric amounts of waste. Thus, recent progress in the field has focused on precious metal catalyzed, oxidative protocols to generate such functionalities. However, simple tertiary alkyl amines cannot be used as starting materials in these protocols. The research described herein enables the oxidative synthesis of amides from simple, noncyclic tertiary alkyl amines under synthetically useful, mild conditions through a biologically inspired approach: Fe‐catalyzed C_α H functionalization. Mechanistic investigations provide insight into reaction intermediates and allow the development of a mild C_α H cyanation method using the same catalyst system. The protocol was further applied to oxidize the drug Lidocaine, demonstrating the potential utility of the developed chemistry for metabolite synthesis.