Structural Analysis of Defects in Layered Double Hydroxides and Related Mixed Oxides

Russian Journal of General Chemistry - Results of studying the structural defects in MgAl and NiAl layered double hydroxides and in the products of their thermal decomposition to 1000°C,...     

Asymptotic Behavior of the Solutions of a Functional-Differential Equation with Linearly Transformed Argument

Ukrainian Mathematical Journal - We establish new properties of the solutions of a functional-differential equation with linearly transformed argument.     

Decreased optical nonlinearities upon CF3 substitution on tricyanofuran acceptors

Replacement of the tricyanofuran (TCF) acceptor by its stronger analogue CF 3-TCF results in decreased second-order optical nonlinearities in merocyanines bearing a proaromatic 1,3-dithiole donor. The TCF-containing derivatives display exceptionally high mu beta values up to 31,000 x 10(-48) esu, unprecedented for 1,3-dithiole-based NLO-phores.     

Vibrational analysis of amino acids and short peptides in hydrated media. 3. Successive KL repeats induce highly stable beta-strands capable of forming non-H-bonded aggregates

Circular dichroism (CD) and Raman scattering were applied to the aqueous solution of minimalist LK peptides constructed with successive KL repeats leading to the following generic primary sequence: (KL)nK. Three peptides of this family, a 3-mer (n=1), a 9-mer (n=4), and a 15-mer (n=7), are analyzed in this report. Raman spectra of the 3-mer (KLK, a random chain) and its labile-hydrogen deuterated species yield a set of interesting information for analyzing longer peptides of this series. Although the CD spectrum of the 9-mer (KLKLKLKLK) reveals a signal traditionally assigned to a random structure, the corresponding Raman spectrum allows finding a mixture of conformations in solution, adopting predominantly beta-type structures. This fact proves the utility of Raman spectroscopy to eliminate eventual ambiguity concerning conformational assignments in peptides based only on the use of CD technique. Finally, the 15-mer (KLKLKLKLKLKLKLK) gives rise to CD and Raman spectra clearly assignable to a beta-type structure. On the basis of all the observed results on the 15-mer, we can confirm that this peptide may exist as isolated beta-strands at low concentration (sub-micromolar), flat-oriented at the air/water interface, whereas at high concentrations (millimolar), non-H-bonded immersible aggregates might be formed. A hypothetical model for these beta-strand aggregates could be proposed as stabilized by an interior hydrophobic core and a hydrophilic external face, formed by leucine and lysine side chains, respectively.     

Analytical evaluation of three-center nuclear-attraction integrals over s-Slater orbitals for asymmetrical conformations of the centers

Analytical formulas for three-center nuclear-attraction integrals over Slater orbitals are given for any location of the three atomic centers. In the mathematical derivations the Neumann expansion has been used and new general auxiliary integrals which depend on the elliptical coordinates of one of the centers are defined. The orbital exponents within the integrals may be different.     

Iminium salts of omega-dithiafulvenylpolyenals: an easy entry to the corresponding aldehydes and doubly proaromatic nonlinear optic-phores

A short, high-yielding route to omega-dithiafulvenylpolyenals (1) via the corresponding iminium salts (2) and starting from trimethyl-1,3-dithiolium tetrafluoroborate is reported. The Knoevenagel reactions of either 1 or 2 with isoxazolone-containing acceptors afford merocyanines 7 and 9, in a process that is often accompanied by a vinylene-shortening side reaction. Experimental and theoretical studies reveal that compounds 7 and 9, featuring two proaromatic end groups, are strongly polarized and show good second-order nonlinear optical responses.     

Reactions of glycosylamines with diphenylphosphine oxide and ethyl and phenyl phenylphosphinates

A novel procedure has been proposed for the synthesis of chiral α-aminophosphoryl compounds from glycosylamines and PH compounds (diphenylphosphine oxide and ethyl and phenyl phenylphosphonates) under mild conditions. The reaction is accompanied by dehydration of the carbohydrate moiety in unprotected monosaccharides to form furan ring.     

Effect of salt modification on adsorption properties of acid-activated montmorillonite and kaolinite

Effect of modification of a layered aluminosilicate, montmorillonite, and rigid-structure kaolinite activated by sulfuric acid with solutions of magnesium chloride was studied in order to obtain sorbents for wastewater treatment to remove organic compounds.     

Full NMR analysis of annomontine, methoxy- annomontine and N-hydroxyannomontine pyrimidine-beta-carboline alkaloids

Using modern NMR techniques, including 1H--13C and 1H--15N heteronuclear correlation experiments, the complete and unambiguous 1H, 13C, and 15N NMR chemical shift assignments of annomontine, methoxyannomontine, and N-hydroxyannomontine pyrimidine-beta-carboline alkaloids were performed. All 1H--1H scalar coupling constants and signal multiplicities were determined, and all nOe observations were also included.     

Light-induced excited-state spin trapping in tetrazole-based spin crossover systems

Ab initio calculations have been performed on Fe (II) (tz) 6 (tz = 1- H-tetrazole) to establish the variation of the energy of the electronic states relevant to (reverse) light-induced excited-state spin trapping (LIESST) as function of the Fe-ligand distance. Equilibrium distances and absorption energies are correctly reproduced. The deactivation of the excited singlet is proposed to occur in the Franck-Condon region through overlap of vibrational states with an intermediate triplet state or an intersystem crossing along an asymmetric vibrational mode. This is followed by an intersystem crossing with the quintet state. Reverse LIESST involves a quintet-triplet and a triplet-singlet intersystem crossing around the equilibrium distance of the high-spin state. The influence of the transition metal is studied by changing Fe (II) for Co (II), Co (III), and Fe (III). The calculated curves for Fe (III) show remarkable similarity with Fe (II), indicating that the LIESST mechanism is based on the same electronic conversions in both systems.