Conformational equilibria and photoinduced tautomerization in 2-(2′-pyridyl)pyrrole

Depending on the polarity and protic abilities of the solvent, 2-(2′-pyridyl)pyrrole can exist in either syn or anti rotameric forms. In nonpolar solvents, intramolecular excited state single proton transfer is observed, manifested by the appearance of low-energy tautomeric emission. The solvent-assisted excited state double proton transfer reaction is also detected. DFT calculations confirm low barriers for both single and double proton transfer processes in the lowest excited singlet state and show different character of the tautomerization in both cases: in the intramolecular reaction, mutual approach of two nitrogen atoms plays an important role.     

The analysis of the zero-order and the second derivative spectra of retinol acetate, tocopherol acetate and coenzyme Q10 and estimation of their analytical usefulness for their simultaneous determination in synthetic mixtures and pharmaceuticals

The aim of the present work was to develop a simple and rapid method of retinol acetate, tocopherol acetate and coenzyme Q(10) determination in pharmaceuticals without involving any preparation operations like separation or masking. The values of second derivative amplitude at 212 nm for tocopherol, 351 nm for retinol and 222 nm for coenzyme were used for construction of calibration graphs. Beer's law is obeyed in the concentration range 0.5-20, 0.5-7.5 and 0.5-30 microg ml(-1) for retinol acetate, tocopherol acetate and coenzyme, respectively. The elaborated procedures were successfully applied to the simultaneous determination of studied compounds in their binary synthetic mixtures and in commercial preparations with high reliability and repeatability. Spectral properties of retinol acetate allows to determine its contents in ternary mixture which includes Vitamin E and coenzyme Q(10).     

Application of organolithium and related reagents in synthesis,Part XII. Synthesis of phenyl- and pyridylpyridopyridazinones and their derivatives

Summary The preparation of the pyridazinones10a,10b,11a,11b, and12a,12b from the ketoamides7,8, and9 and hydrazine hydrate is described. It was found that from ketoamides8b and9b in addition to the expected pyridopyridazinones11b and12b also aminopyridopyridazines14 and15 were formed and that ketoamide7b gave exclusively aminopyridopyridazine13. The pyridopyridazinones10b,11b, and12b were alkylated with alkyl iodides.

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Anwendungen von Organolithium und verwandten Reagenzien in organischen Synthesen, Teil XII. Synthese von Phenyl- und Pyridylpyridopyridazinonen und ihren Derivaten

Zusammenfassung Die Darstellung der Pyridazinone10a,10b,11a,11b und12a,12b aus Ketoamiden7,8 und9 und Hydrazinhydrat wird beschrieben. Es wurde festgestellt, daß aus Ketoamiden8b und9b außer den erwarteten Pyridopyridazinonen11b und12b auch Aminopyridopyridazine14 und15 enstanden und daß das Ketoamid7b ausschließlich ins Aminopyridopyridazin13 überführt wurde. Die Pyridopyridazinone10b,11b und12b wurden mit Alkyljodiden alkyliert.

     

Gas-phase solvation of protonated aliphatic amines: methyl,ethyl, n-propyl,and iso-propylamine

The thermodynamic quantities K_{n?1 n}, ΔG⁰_{n?1, n} and ΔS⁰_n?1, n for the gas phase equilibrium reactions RNH⁺₃(RNH₂)_n?1 + RNH₂ = RNH⁺₃(RNH₂)_n, where n ? 3 and R indicates an alkyl group (CH₃, C₂H₅, n-C₃H₇ and iso-C₃H₇), have been determined.     

Crystal structures and magnetic properties of two low-dimensional materials constructed from [Mn(III)(salen)H2O]+ and [M(CN)8](3-/4-) (M = Mo or W) precursors

The syntheses, X-ray structures, and magnetic behaviors of two new cyano-bridged assemblies, the molecular [Mn(III)(salen)H2O]3[W(V)(CN)8].H2O (1) and one-dimensional [Mn(salen)(H2O)2]2[[Mn(salen)(H2O)][Mn(salen)]2[Mo(CN)(8)]].0.5ClO4.0.5OH.4.5H2O (2), are presented. Compound 1 crystallizes in the monoclinic system, has space group P2(1)/c, and has unit cell constants a = 13.7210(2) A, b = 20.6840(4) A, c = 20.6370(2) A, and Z = 4. Compound 2 crystallizes in the triclinic system, has space group P, and has unit cell dimensions a = 18.428(4) A, b = 18.521(3) A, c = 18.567(4) A, and Z = 2. The structure of 1 consists of the asymmetric V-shaped Mn-NC-W-NC-Mn-O(phenolate)-Mn molecules, where W(V) coordinates with [Mn(salen)H2O] and singly phenolate-bridged [Mn(salen)H2O]2 moieties through the neighboring cyano bridges. The [W(V)(CN)8]3- ion displays distorted square-antiprism geometry. The structure of 2 consists of the cyano-bridged [Mn3(III)Mo(IV)]n- repeating units linked by double phenolate bridges into one-dimensional zigzag chains. The Mn(III) centers are bound to Mo(IV) of square-antiprism geometry through the neighboring cyano bridges. The magnetic studies of 1 reveal the antiferromagnetic intramolecular interactions through the CN and phenolate bridges and the relatively weak intermolecular interactions. Compound 1 becomes antiferromagnetically ordered below TN = 4.6 K. The presence of the magnetic anisotropy is documented with the MH measurements carried out for both polycrystalline and single-crystal samples. At T = 1.9 K, the spin-flop transition is observed in the field of 18 kOe applied parallel to the bc plane, which is the easy plane of magnetization. Field dependence of magnetization of 1 shows field-induced metamagnetic behavior from the antiferromagnetic ground state of ST = 3/2 to the state of ST = 5/2. The magnetic properties of 2 indicate a weak antiferromagnetic interaction between Mn(III) centers in double-phenolate-bridged [Mn(III)(salen)]2 dinuclear subunits and a very weak ferromagnetic interaction between them through the diamagnetic [Mo(IV)(CN)8]4- spacer.     

Nanogel nanosecond photonic crystal optical switching

We developed a robust nanosecond photonic crystal switching material by using poly(N-isopropylacrylamide) (PNIPAM) nanogel colloidal particles that self-assemble into crystalline colloidal arrays (CCAs). The CCA was polymerized into a loose-knit hydrogel which permits the individual embedded nanogel PNIPAM particles to coherently and synchronously undergo their thermally induced volume phase transitions. A laser T-jump from 30 to 35 degrees C actuates the nanogel particle shrinkage; the resulting increased diffraction decreases light transmission within 900 ns. Additional transmission decreases occur with characteristic times of 19 and 130 ns. Individual NIPAM sphere volume switching occurs in the approximately 100 ns time regime. These nanogel nanosecond phenomena may be useful in the design of fast photonic crystal switches and optical limiting materials. Smaller nanogels will show even faster volume phase transitions.     

Evaluation of the residual stability of polyurethane automotive coatings by DSC

Degradation of poly(ester-urethanes), poly(ether-urethanes) and poly(acrylic-urethanes), as a base for automotive paintings in interior applications, has been studied by DSC. The samples were clearcoat and black-pigmented paints, unstabilized and stabilized with HALS Tinuvin 292, UV absorber Tinuvin 1130 and antioxidant Hostanox O3, exposed to weathering in Xenotest and in Arizona desert. From the dependences of oxidation onset temperature on the heating rate, the kinetic parameters enabling to calculate the oxidation induction time for a chosen temperature have been obtained. From the values of oxidation induction time, the protection factors of the additives and the residual stability of the polymer after an ageing stress has been evaluated. It has been shown that the equivalence between the two methods of weathering depends on the polymer composition. A new criterion for the evaluation of synergism/antagonism of additives in the stabilizing mixture has been proposed.     

The furan approach to oxacycles. Part 5: Synthesis of a chiral butenolide, building block towards biologically interesting natural products

We describe an efficient new approach for the synthesis of a chiral butenolide that is based on the oxidation of a chiral furan ring with singlet oxygen in the presence of Hünig’s base, followed by Luche reduction and in situ lactonization.     

Multipeak distributions of first passage times in bistable dynamics in a model of a thermochemical system.

A master equation is used to study transitions between the stable limit cycle and stable focus in the two-variable bistable system. The distribution function of the mean first passage time between these attractors and the relative dispersion of the mean first return time from the stable focus to itself as a function of the intensity of fluctuations are calculated and discussed. A coherence resonance is observed for the return time from the focus to itself.     

Free-electron attachment to coronene and corannulene in the gas phase

Electron attachment to the polyaromatic hydrocarbons coronene and corannulene is studied in the electron energy range of about 0-14 eV using a high-resolution crossed electron-neutral beam setup. The major anions observed are the parent anions peaking at about 0 eV with cross sections of 3.8 x 10(-20) and 1 x 10(-19) m(2), respectively. The only fragment anions formed in coronene and corannulene are the dehydrogenated coronene and corannulene anions. Other anions observed in the negative mass spectra at about 0 eV can be ascribed to impurities of the sample. High-level quantum-mechanical studies are carried out for the determination of electron affinities, hydrogen binding energies, and structures of both molecules. The behavior of coronene and corannulene upon electron attachment is compared with that of other polyaromatic hydrocarbons studied previously.