Experimental investigation of the muon transfer reaction from deuterium to helium isotopes

Muon transfer from the ground state of muonic deuterium to a helium atom proceeds mainly via the formation of a muonic molecule in an excited state. A large number of decay X rays ( 6.8 keV) from these (dµHe)^* molecules were observed for the⁴He as well as for the³He case. The time distributions of these X rays allow the determination of the ground state transfer rate. The simultaneous employment of Ge/Si-detectors and CCDs for the same target conditions allows the determination of the branching ratio of radiative to nonradiative decay for the first time.     

A Facile Cell Free Synthesis of Isotopically Labeled (E)‐4‐Hydroxy‐3‐methylbut‐2‐enyl Diphosphate,a Precursor of the Plant Hormone Zeatin

(E)‐4‐Hydroxy‐3‐methylbut‐2‐enyl diphosphate ( 1 ) is a key intermediate of the deoxyxylulose phosphate pathway of isoprenoid biosynthesis and a precursor of the plant hormone zeatin. The availability of this intermediate with various labeling patterns is pivotal for its use in biosynthetic studies. The number of positions, however, that can be easily labeled by chemical synthesis is limited, and the synthesis by means of recombinant enzymes is laborious and time consuming. We demonstrated that chromoplasts from Capsicum annuum, whose enzyme activity was impaired by freeze‐thawing, accumulate 1 . This observation built the basis for the development of a cell‐free system allowing the synthesis of this intermediate with labels in various positions. With 2C‐methyl‐D ‐erythritol 2,4‐cyclodiphosphate ( 5 ) as substrate, yields were in the range of 50%.     

Experience with routine applications of liquid chromatography-mass spectrometry in the pharmaceutical industry

The combination of liquid chromatography and mass spectrometry (LC-MS) has been established to complement gas chromatography (GC)-MS in the analysis of non-volatile and labile drugs in complex materials. The possibilities of LC-MS in the pharmaceutical industry for the analysis of drug substances and dosage forms, metabolism studies and the elucidation of the structures of materials of biological origin are discussed. Instrumental requirements, limitations and applications of LC-MS are considered and experiences with LC-MS in routine applications are reported. Preliminary results obtained with thermospray LC-MS are compared with those using a direct liquid inlet interface.     

Die Tautomeriegleichgewichte von Dihydrochinoxalinen

The primary product of the two step reduction of 2-phenylquinoxaline is the 1,4-dihydrocompound which undergoes a tautomeric rearrangement to the thermodynamically more stable 1,2-dihydro-3-phenylquinoxaline. The 1,4-dihydro compound is an extremely reactive reducing agent whereas the 1,2-dihydro form is almost inert against oxidizing agents. Both dihydro forms are in a kinetically hindered equilibrium. The rearrangement requires a transfer of a proton from a nitrogen to a carbon atom and is therefore relatively slow even at pH 0. The 1,2-dihydro compound cannot take part in redox reactions directly. If this compound is oxidized, the rate determining step is always the reversed tautomeric rearrangement. The effect of the kinetics of the tautomeric rearrangement on the polarographic behavior of the 2-phenylquinoxaline system is discussed.     

Structural characterization of the trans-equatorial isomer of (aqua)(ethylenediamine-N,N,N′-tripropionato)chromium(III) trihydrate,[Cr(edtrp)(H2O)] · 3H2O

The structure of trans-equatorial [Cr(edtrp)(H₂O)] · 3H₂O (edtrp^3– is the anion of ethylenediamine-N,N,N-tripropionic acid) was determined by single crystal X-ray diffraction. The chromium(III) ion is surrounded octahedrally by the two nitrogen and three oxygen atoms of the quinquedentate edtrp^3–, forming a five-membered diamine ring and the three six-membered -propionato chelate rings. The remaining coordination position is occupied by the H₂O ligand. The crystal structure conformation is compared to the result of recent molecular mechanics analysis. The ring strain of R and G chelate rings was found to be in agreement with the previously proposed mechanisms for the C—N bond cleavage and recombination.     

Ion Selective Electrode Determination of Free Versus Total Fluoride Ion in Simple and Fluoroligand Coordinated Hexafluoropnictate (PnF<Subscript>6</Subscript><Superscript>−</Superscript>, Pn = P,As, Sb,Bi) Salts

Interpretation of the results of determinations of free fluoride (F_f⁻) and total fluoride (F_t⁻) obtained with fluoride ISE while conducting elemental chemical analysis of bulk material of newly synthesized inorganic fluoride compounds is of crucial importance for the purpose of determination of purity and stoichiometry of these compounds. Knowledge of the properties and behavior of these compounds in aqueous media is therefore essential. Observations are presented on the determinations of the amounts of F_t⁻ and F_f⁻ in fluorinated compounds, in the particular hexafluoropnictate salts (PnF₆⁻, Pn = P, As, Sb, Bi) as found in aqueous media and in some compounds with XeF₂, AsF₃ ligands. A critical look at the determined amounts of F_f⁻, F_t⁻and calculated amounts of bound fluoride (F_b⁻) is provided.     

Excitonic Emission in van der Waals Nanotubes of Transition Metal Dichalcogenides

Nanotubes (NTs) of transition metal dichalcogenides (TMDs), were first synthesized more than a quarter of a century ago; nevertheless, many of their optical properties have so far remained basically unknown. Herein, the state of the art in the knowledge of the optical properties of TMD NTs is presented. First, general properties of multilayered crystals are evaluated, and available data on related NTs are analyzed. Then, the technology for the formation and the structural characteristics of NTs are represented, focusing on the structures synthesized by chemical transport reaction. The core of this work is the presentation of the ability of synthesized TMD NTs to emit bright photoluminescence (PL), which has been discovered recently. By means of micro‐PL spectroscopy of individual tubes, we show that excitonic transitions relevant to both direct and indirect band gaps contribute to the emission spectra of the NTs despite having the dozens of monolayers in their walls. The performance of the tubes as efficient optical resonators is highlighted, where confined optical modes strongly affect the emission. Finally, a brief conclusion is presented, along with an outlook of the future studies of this novel radiative member of the NTs family, which have unique potential for different nanophotonics applications.