A highly selective hydrogen-deuterium exchange in indolium heptamethine cyanines

Chemical shift assignments in ¹H nmr spectra of four tricarbocyanines have been made. Studies by ¹H nmr have shown a rapid acid-catalyzed proton exchange at positions 1′,7′ and a much slower exchange at positions 3′,5′ of the heptamethine chain. Base catalysis results in a slow exchange at positions 1′,7′ only.     

Importance of exchange effects in the deformation of interacting ions

In calculations for liquids or solids one often considers a limited cluster of atoms or molecules in the electrostatic field of their environment. In this paper possibilities of improving this model by inclusion of the exchange deformation potential are shown. The reported numerical results for the LiF and NaF molecules as well as for the LiF and NaF perfect crystals indicate the importance of the exchange deformation effects.     

The spirooxirane route to trans-fused γ-lactones

Convenient access to $\text{trans}$-fused γ-lactones is provided by sodium benzenethiolate promoted ring opening of appropriate γ,δ-spiroepoxyesters.     

Preparation and properties of Ba1−xCaxTiO3 nanopowders obtained by mechanochemical synthesis

ABSTRACT

The calcium-substituted barium titanate nanopowders Ba_1?xCa_xTiO₃ (0.2 ≤ x ≤ 0.3) have been obtained at room temperature by mechanochemical synthesis. The formation of the perovskite phase was controlled by X-ray diffraction studies at various milling duration. The powders possess the perovskite crystallographic structure directly after milling longer than 10 h. The dielectric properties of the ceramics obtained by sintering of the nanopowders were investigated in the temperature range between 300 and 500 K. The temperature dependence of permittivity exhibited a single anomaly, which corresponds to the ferroelectric–paraelectric phase transition.     

Syntheses, structure, and reactivity of chiral titanium compounds: procatalysts for olefin polymerization

Titanium complexes with chelating alkoxo ligands have been synthesised with the aim to investigate titanium active centres in catalytic ethylene polymerisation. The titanium complexes cis-[TiCl2(eta2-maltolato)2] (1, 89%), and cis-[TiCl2(eta2-guaiacolato)2] (2, 80%) were prepared by direct reaction of TiCl4 with maltol and guaiacol in toluene. The addition of maltol to [Ti(OiPr)4] in THF results in the formation of species [Ti(OiPr)2(maltolato)2] (3, 82%). The titanium compound cis-[Ti(OEt)2(eta2-maltolato)2] (4, 74%) was obtained by the transesterification reaction of species 3 with CH3CO2Et. When compound 4 is dissolved in THF a dinuclear species [Ti2(mu-OEt)2(OEt)4-(eta2-maltolato)2] (5, 45%) is formed. Reaction of [Ti(OiPr)4] with crude guaiacol in THF yields a solid, which after recrystallisation from acetonitrile gives [Ti4(mu-O)4(eta2-guaiacolato)] x 4CH3CN (6, 55%). In contrast, reaction of TiCl4 with crude guaiacol in tetrahydrofuran affords [Ti2(mu-O)Cl2(eta2-guaiacolato)4] (7, 82%). Crystallographic and electrochemical analyses of these complexes demonstrate that maltolato and guaiacolato ligands can be used as a valuable alternative for the cyclopentadienyl ring. These complexes have been shown to be active catalysts upon combination with the appropriate activator.     

Synthesis of water‐soluble near‐infrared cyanine dyes functionalized with [(succinimido)oxy]carbonyl group

Two hetamethine cyanine dyes suitable for labeling of biomolecules at a primary amino group with a near‐infrared chromophore/fluorophore (λ_max/(λ_em = 800/830 nm and 837/864 nm) have been synthesized from readily available starting materials. Despite the high molecular complexity of intermediate and final products, all these compounds have been obtained in an analytically pure form by using crystallization only.     

Investigation of the spectral properties of a squarylium near-infrared dye and its complexation with Fe(III) and Co(II) ions.

The spectral features of the squarylium dye NN525 in different solutions and its complexation with several metal ions were investigated. The absorbance maximum of the dye is at 669 nm in tetrahydrofuran. This value matches the output of a commercially available laser diode (650 nm), thus making use of such a source practical for excitation. The emission maximum of the dye in tetrahydrofuran is at 676 nm. The addition of either Fe(III) ion or Co(II) ion resulted in fluorescence quenching of the dye. The detection limit is 6.24 x 10(-8) M for Fe(III) ion and 1.55 x 10(-8) M for Co(II) ion. The molar ratio of the metal to the dye was established to be 1:1 for both metal ions. The stability constant Ks of the metal-dye complex was calculated to be 3.14 x 10(6) M(-1) for the Fe-dye complex and 2.64 x 10(5) M(-1) for the Co-dye complex.     

X-ray diffraction, DFT theoretical, and IR polarized spectroscopic studies of the crystal-like E-mesophase of 4′-hexyloxy-isothiocyanatotolane (6OTOLT)

The dynamics of 6OTOLT molecules was analyzed based on IR absorption spectra and DFT calculations. Of particular interest was the mode ascribed to the ν_as(NCS) vibrations, the transition dipole moment of which is directed along the long axes of the molecules. Polarized IR spectra in the region of this mode allowed a characterization of the ordering of molecules in the analyzed phases. In a case of the smectic E phase, a random distribution of molecules aligned laterally in two-dimensional space between KRS-5 windows was found. The crystals of 6OTOLT were successfully grown and are characterized by an interesting Pc space group. The molecules are parallely arranged in layers and cross the adjoining ones underneath at an angle of 86.04°. The distance between the ring planes is 3.48 Å. The packing of molecules indicates a tendency to maintain short contacts between NCS groups and alkyl chains. The crystals grown do not correspond to the ordering of the smectic E phase and thus to the solid state obtained after cooling the smectic phase. Calculations of the interaction energy for three possible arrangements of dimeric species show a predominance of the core-to-core units. It was also shown that in this case an increase in ν_as(NCS) frequency should be expected, in good agreement with experimental data.