Selectivity of 1-O-Propargyl-d-Mannose Preparations

Thanks to their ability to bind to specific biological receptors, mannosylated structures are examined in biomedical applications. One of the most common ways of linking a functional moiety to a structure is to use an azide-alkyne click reaction. Therefore, it is necessary to prepare and isolate a propargylated mannose derivative of high purity to maintain its bioactivity. Three known preparations of propargyl-α-mannopyranoside were revisited, and products were analysed by NMR spectroscopy. The preparations were shown to yield by-products that have not been described in the literature yet. Our experiments showed that one-step procedures could not provide pure propargyl-α-mannopyranoside, while a three-step procedure yielded the desired compound of high purity.     

Iron-Mediated Amination of Hydrocarbons in the Gas Phase

FeNH⁺ is chosen as a model system to probe the transition-metal-mediated transfer of imine groups in the gas phase by mass-spectrometric means. Ab initio calculations at the MR-ACPF level predict FeNH⁺ to have a linear sextet ground state (⁶Σ⁺); a bent quartet state (⁴A′) and a linear doublet state (²Δ) are higher in energy by 0.14 eV and 0.51 eV, respectively. The bond-dissociation energy is determined to D(Fe⁺−NH)=69±2 kcal mol⁻¹ using ion-molecule reactions. Charge-stripping experiments combined with ab initio calculations yield an ionization energy of IE(FeNH⁺)=15.7±0.5 eV. The chemical behavior of FeNH⁺ towards oxygen, water, hydrogen, aliphatic hydrocarbons, benzene, and toluene reveals an intrinsically high reactivity of FeNH⁺. Because a transfer of the 〈NH〉 fragment to the substrate is feasible in most cases, attractive amination reactions like methane→methylamine, benzene→aniline, or toluene→benzylidenamine can be afforded by FeNH⁺.     

Easy and efficient deracemization of all trans-1,3-diphenyl-2,4-bis-[α-hydroxybenzyl]-cyclobutane and its bisphenylsulfanyl derivative and the assignment of the absolute configuration

An effective deracemization of all trans-1,3-diphenyl-2,4-bis-[α-hydroxybenzyl]-cyclobutane 1 was achieved by the application of the (R)-(?)-O-acylmandelic acid as a resolving agent, followed by the crystallization of the diastereomeric esters. The kinetic resolution was also observed in the esterification. Racemic 1 was transformed into bisphenylsulfanyl derivative 3. Enantioselective oxidation of 3 with a VO(acac)₂-chiral Schiff Base catalytic system led to a kinetic resolution, and highly enantiomerically enriched bissulfides/bissulfoxides were isolated. Assignment of the absolute configuration was made by spectroscopic methods and chemical correlation. Due to the rigid C₂-symmetric framework, chiral compounds 1 and 3 have strong steric requirements and may be useful in chiral recognition.     

On the theory of diffusion of light interstitials in metals

Using a nonlinear-screening approach the potential energy of positively charged light interstitials in Cu and lattice distortions around these particles have been determined numerically. The calculations predict a marked isotope effect for the lattice distortions around positive muons and protons at octahedral interstitial sites. They indicate that in Cu the diffusion mechanisms for positive muons and for hydrogen isotopes may be different.     

The preparation und unusual rearrangement of triply bridged μ-heteromethylenecobalt complexes. Molecular structure of μ-ethoxycarbonylmethylenebis[carbonyl-(η5-cyclopentadienyl)cobalt] (CoCo)

the μ-heteromethylenecobalt complexes, which have been synthesized by photolysis of (η⁵-C₅H₅)Co(CO)₂ in the presence of the corresponding diazoacetates at < ?90°C in tetrahydrofuran, undergo a novel type of intramolecular irreversible rearrangement yielding two isomers. The structure of one of the isomers has been established by X-ray analysis. A comparison of the structural parameters of all known μ-methylene-transition metal complexes shows that the internal angles α of the cyclopropane-like systems are far less sensitive to the compositions and structures of the molecules than the external angles β. The internal angles cannot be readily correlated with other features of the molecule.     

Zur Definition von Quasiteilchen und Quasiteilcheneigenfunktionen inhomogener Systeme in Anwendung auf innere Elektronenzustände

It is shown that the effective non-hermitean one-particle Hamiltonian H_eff, deduced from many-body theory, is a measurable operator only if H_eff is a normal operator; if H_eff is not a normal operator, quasiparticles and the frequency-dependent quasiparticle-eigenfunctions are defined by the hermitean spectral-operator. Using perturbation-theory, an estimation of the frequency-dependent parts of the core-electron eigenfunctions is given which shows the limitations in defining a core-electron Hilbert subspace.     

Fast quantification of water in single living cells by near-infrared microscopy

We have set up a near-infrared microscope using a tuneable diode laser in the range from 1530 to 1570 nm. This spectral range is close to the peak of the water overtone absorption. We used this new microscope to study liver cells, hepatocytes, showing that quantitative information of the intracellular water concentration in living cells can be extracted.     

The bioequivalence study of baclofen and lioresal tablets using capillary electrophoresis

A simple and robust analytical method for rapid separation and sensitive quantification of baclofen in human plasma by capillary electrophoresis technique was developed. Electrophoretic separation was optimized and successfully performed using simple sodium tetraborate aqueous solution. Observed detection limit in biological material was 10 ng. Using UV detection at 200 nm excellent linearity (r = 0.999) was observed over the concentration range from 0.025 to 1.0 microg mL(-1). The described method has been validated and applied to the quantitative determination of baclofen in human plasma. The bioavailability of Baclofen (Polpharma) and Lioresal (Novartis) in 18 healthy volunteers was investigated. The results indicate bioequivalence of the reference and Baclofen preparations.     

Mild Oxidation of Thiofunctional Polymers to Cytocompatible and Stimuli‐Sensitive Hydrogels and Nanogels

Nanogels consist of three dimensionally cross‐linked hydrophilic polymer chains and can thus be easily modified through functionalization of the polymeric building blocks, for example to yield stimuli‐sensitive materials. For drug transport and intracellular release, redox‐sensitive systems are especially of interest, as the intracellular space is reductive. In this study, parameters that allow preparation of nanogels with tunable size between 150 and 350 nm are systematically evaluated and identified. Most importantly, a new and mild oxidation catalyst, alloxan, is introduced for the preparation of the nanogels. This broadens the range of possible payloads to more‐sensitive molecules. Particle stability, degradation in cytosolic conditions, and cytocompatibility in concentrations up to 10 mg · mL^?1 are demonstrated.