CONFORMATIONS OF 4,5,6-TRIPHENYL-TETRAHYDRO-1,3-THIAZINE-2-THIONES AND THEIR N-ALKYL DERIVATIVES. UNUSUAL THIAZINETHIONE OR AZETIDINE FORMATION UPON REACTION OF 3-AMINO- AND 3-METHYLAMINO-1,2,3-TRIPHENYLPROPYL CHLORIDES WITH POTASSIUM ETHYLXANTHATE

Abstract

Reaction of 3-amino- or 3-methylamino-1,2,3-triphenylpropyl chlorides (6 or 7) with potassium ethylxanthate leads to 4.5.6-triphenyl-tetrahydro-,3-thiazine-2-thione 1 or 1-methyl-2,3,4-triphenylazetidine 8 depending on the N-substitution. Conformational distribution of all possible diastereoisomeric thiazinethiones 1 and their N-alkyl derivatives 2–5 is determined by means of ¹H NMR spectroscopy. Allylic strain caused by N- substituents in the trans,cis-isomers strongly shifts the equilibrium between conformations with a,a,e or e,e,a phenyl groups towards the conformer with an axial neighbouring Ph-4 group. Vicinal couplings data for the diastereoisomeric azetidine 8 show different ring geometry depending on the configuration.     

Gas‐phase tautomerism in hydroxy azo dyes – from 4‐phenylazo‐1‐phenol to 4‐phenylazo‐anthracen‐1‐ol

The tautomeric constants of a series of azo dyes were estimated in the gas phase by using electron ionization mass spectrometry. It was shown that the relative amount of the keto tautomer increases from 4‐phenylazo‐1‐phenol to 4‐phenylazo‐anthracen‐1‐ol, thus confirming the quantum‐chemical predictions. The existence of the enol tautomer of 4‐phenylazo‐anthracen‐1‐ol is shown for the first time by mass spectrometry in the gas phase. This finding is supported by flash photolysis measurements in solution. Copyright © 2010 John Wiley & Sons, Ltd.     

Analysis of current voltage characteristics of MWIR homojunction photodiodes for uncooled operation

Dark currents n⁺/ν/p⁺ Hg_0.69Cd_0.31Te mid wave infrared photodiodes were measured at room temperature. The diodes exhibited negative differential resistance at room-temperature, but with increasing leakage currents as a function of reverse bias. The current–voltage characteristics were simulated and fitted by incorporating trap assisted tunneling via traps and Shockley–Read–Hall generation recombination process due to dislocations in the carrier transport equations. The thermal suppression of carriers was simulated by taking energy level of trap (E_t), trap density (N_t) and the doping concentrations of n⁺ and ν regions as fitting parameters. Values of E_t and N_t were 0.78E_g and ～6–9 × 10¹⁴ cm^?3 respectively for most of the diodes. Variable temperature current voltage measurements on variable area diode array (VADA) structures confirmed the fact that variation in zero bias resistance area product (R₀A) is related to g–r processes originating from variation in concentration and kind of defects that intersect a junction area.     

109Cd → 109Ag and 107Cd → 107Ag β decays

The energies, magnetic dipole and electric quadrupole moments, spectroscopic factors of the ground and excited states of ¹⁰⁹Ag and ¹⁰⁷Ag, the reduced probabilities of electromagnetic transitions between them, and the reduced probabilities of β transitions from the ground states of ¹⁰⁹Cd and ¹⁰⁷Cd to the excited states of ¹⁰⁹Ag and ¹⁰⁷Ag were calculated on the basis of the dynamic collective model. The vacuum fluctuations of quasiparticles and multiphonon (up to 10 phonons) states of the main band of the even-even core were taken into account. The calculation results show good agreement with the experimental data.     

Triple Emission from p‐Dimethylaminobenzonitrile–Cucurbit[8]uril Triggers the Elusive Excimer Emission

The intriguing dual‐emission behavior of p‐ dimethylaminobenzonitrile (DMABN) and the identity of the associated excited states is, arguably, the most extensively investigated and also controversially discussed molecule‐ specific phenomenon of modern photochemistry. We have now found a new, third fluorescence band when DMABN is encapsulated within the water‐soluble molecular container cucurbit[8]uril (CB8). It is centered between the previously observed emissions and assigned to the elusive excimer emission from DMABN through 1:2 CB8:DMABN complex formation. Heating of the CB8 ? (DMABN)₂ complex from 0 to 100 °C results in the dissociation of the ternary complex and restoration of the dual‐emission properties of the monomer. Alternatively, monomer emission can be obtained by selecting cucurbit[7]uril (CB7), a host homologue that is too small to accommodate two DMABN molecules, or by introducing ethyl instead of methyl groups at the amino terminus of the aminobenzonitrile guest.     

Synthesis,Structural Characterization and Physical Properties of a New Member of Ternary Lithium Layered Compounds – Li2RhO3

Li₂RhO₃ was synthesized by solid state reaction and its crystal structure was refined from X‐ray powder data by the Rietveld‐method. The compound was obtained as a black powder and crystallizes in the monoclinic space group C2/m, with unit cell parameters a = 5.1198(1), b = 8.8497(1), c = 5.1030(1) Å, β = 109.61(2) °, V = 217.80(1), and Z = 4. The structure determination shows that the oxygen atoms in Li₂RhO₃ form an approximate cubic close packing, where all octahedral voids are occupied by Rh⁴⁺ and Li⁺ cations. The structure is closely related to the α‐NaFeO₂ and Li₂MnO₃ layered structure types (layered variants of the NaCl‐type), but in Li₂RhO₃ the lithium and rhodium atoms are partially disordered. Li₂RhO₃ behaves as a semiconductor with rather small activation energy of 7.68 kJ · mol^–1 and is thermally stable up to 1273 K in argon atmosphere. According to measurements of the magnetic susceptibility in the temperature range from 2 to 330 K, Li₂RhO₃ is paramagnetic, obeys the Curie–Weiss law at temperatures above 150 K, and has an effective magnetic moment of 1.97 μ_B at 300 K.     

Supramolecular tandem enzyme assays for multiparameter sensor arrays and enantiomeric excess determination of amino acids

The coupling of an enzymatic transformation with dynamic host-guest exchange allows the unselective binding of macrocycles to be used for highly selective analyte sensing. The resulting supramolecular tandem enzyme assays require the enzymatic substrate and its corresponding product to differ significantly in their affinity for macrocycles, for example, cation receptors, and to show a differential propensity to displace a fluorescent dye from its host-guest complex. The enzymatic transformation results in a concomitant dye displacement that can be accurately followed by optical spectroscopy, specifically fluorescence. By exploiting this label-free continuous enzyme assay principle with the fluorescent dye Dapoxyl and the macrocyclic host cucurbit[7]uril, a multiparameter sensor array has been designed, which is capable of detecting the presence of amino acids (e.g. histidine, arginine, lysine, and tyrosine) and their decarboxylases. Only in the presence of both, the particular amino acid and the corresponding decarboxylase, is the amine or diamine product formed. These products are more highly positively charged than the substrate, have a higher affinity for the macrocycle and, therefore, displace the dye from the complex. The extension of the high selectivity and muM sensitivity of the tandem assay principle has also allowed for the accurate measurement of D-lysine enantiomeric excesses of up to 99.98 %, as only the L-enantiomer is accepted by the enzyme as a substrate and is converted to the product that is responsible for the observed fluorescence signal.     

Inclusion of neutral guests by water-soluble macrocyclic hosts – a comparative thermodynamic investigation with cyclodextrins,calixarenes and cucurbiturils

Abstract

The driving forces of association between three different families of macrocycles as hosts, namely cyclodextrins (α-, β-, and γ-), p-sulfonatocalix[n]arenes (n = 4–6) as well as cucurbit[n]urils (n = 6–8), and three different bicyclic azoalkane homologues as guests, namely 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH), 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) as well as 2,3-diazabicyclo[2.2.3]non-2-ene (DBN), were examined by means of calorimetric titrations, NMR spectroscopy and molecular dynamics simulation, all in aqueous solution. The small, spherical and uncharged guests preferably bind inside the cavities of the medium sized hosts. The inclusion complexation by β-cyclodextrin and p-sulfonatocalix[4]arene shows medium binding affinities (millimolar), while cucurbit[7]uril macrocycle shows very strong binding (micromolar). For all types of macrocycles, the complex formation is enthalpically driven (ΔH° < 0), accompanied by slightly unfavourable entropy changes (ΔS° < 0). The results are discussed in terms of the flexibility of the hosts, the hydrophobic character of their cavities and the release of high-energy water upon binding, and generalised by including two additional guests, the ketones cyclopentanone and (+)-camphor.