Synthesis of Polysubstituted Symmetrical BODIPYs via Fischer Carbene Complexes: Theoretical,Photophysical and Electrochemical Evaluation

A series of new symmetrical highly substituted BODIPYs 6 a – l was synthesized through a prefunctionalization approach in 35 %–89 % yields from the pyrrole core. This strategy allowed modulation of the substituents at the different positions based on the choice of Fischer's alkynyl carbenes, oxazolones and aldehydes used as precursors. The substituent variation at positions 2, 6, 3 and 5 had the greatest effect on the modulation of their photophysical properties such as absorption (λ_abs) and emission (λ_em) wavelengths, extinction coefficient (ϵ), quantum yields (ϕ), Stokes shifts (Δν), fluorescence decay, radiative (k_rad) and non-radiative (k_nr) constants and the CIE 1931 coordinates. Theoretical calculations allowed to corroborate the effect of the substituents of meso-position on the modification of the dihedral angles. Cyclic voltammetry studies revealed that the BODIPY series presents similar redox potential behavior, being electrochemically active even in successive cycles, which suggests that transport by diffusion is the dominant process.     

Structural Elucidation of an Atropisomeric Entcassiflavan-(4β→8)-Epicatechin Isolated from Dalbergia monetaria L.f. Based on NMR and ECD Calculations in Comparison to Experimental Data

A rare dihydoxyflavan-epicatechin proanthocyanidin, entcassiflavan-(4β→8)-epicatechin, was isolated from Dalbergia monetaria, a plant widely used by traditional people from the Amazon to treat urinary tract infections. The constitution and relative configuration of the compound were elucidated by HR-MS and detailed 1D- and 2D-NMR measurements. By comparing the experimental electronic circular dichroism (ECD) spectrum with the calculated ECD spectra of all 16 possible isomers, the absolute configuration, the interflavan linkage, and the atropisomers could be determined.     

Analysis of potential toxic elements in soil of the Czech dump-side

Journal of Radioanalytical and Nuclear Chemistry - The mass fractions of V, Cr, Co, Ni, Cu, Zn, As, Br, Mo, Cd, W, Hg, and Pb in soil of the Czech dump-side were measured by instrumental neutron...     

Intramolecularly coordinated organoantimony(III) carboxylates

The reactions of organoantimony chlorides L^1,2SbCl₂1 and 2 ([2,6-(ROCH₂)₂C₆H₃]⁻, R = Me; L¹ and R = t-Bu; L²) with silver salts of selected carboxylic acids resulted to corresponding organoantimony carboxylates L^1,2Sb(OOCR′)₂, 1a-c (for L¹) and 2a-c (for L²), where R′ = CH₃ for 1a, 2a; R′ = CHCH₂ for 1b, 2b and R′ = CF₃ for 1c, 2c. All compounds were characterized by the help of elemental analysis, ESI-MS, ¹H and ¹³C NMR spectroscopy. The solid state structure investigation using single crystal X-ray diffraction techniques (2a, c) and IR spectroscopy revealed significant differences in coordination mode of both O,C,O chelating ligand and carboxylic groups in this set of compounds. The structure of all compounds in solution of non-coordinating solvent (CDCl₃) was determined by means of variable temperature ¹H, ¹³C, ¹⁹F NMR spectroscopy and IR spectroscopy.     

8-Dioxane ferra(III) bis(dicarbollide): A paramagnetic functional molecule as versatile building block for introduction of a Fe(III) centre into organic molecules

The synthesis of a new, paramagnetic closo-[(8-(-CH₂CH₂O)₂-1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)-3,3′-Fe]⁰ (3) is reported. This compound can serve as a versatile building block for construction of both anionic and zwitterionic derivatives, as exemplified by the synthesis of a series of compounds of general formula closo-[(8-X-(CH₂CH₂O)₂-1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)-3,3′-Fe], bearing organic end groups (X = NC₅H₅ (4), (C₆H₅)₃P (5), OH (6), and 2-O(1-CH₃O-C₆H₄) (7)) attached to the cluster by a diethyleneglycol spacer. Molecular structures of 3, 4, 5 and 7 were determined by single-crystal X-ray diffraction analysis and by the long-time neglected method of paramagnetic, high field NMR (¹H, ¹³C and ¹¹B) spectroscopy.     

Hybrid neural network model of an industrial ethanol fermentation process considering the effect of temperature

In this work a procedure for the development of a robust mathematical model for an industrial alcoholic fermentation process was evaluated. The proposed model is a hybrid neural model, which combines mass and energy balance equations with functional link networks to describe the kinetics. These networks have been shown to have a good nonlinear approximation capability, although the estimation of its weights is linear. The proposed model considers the effect of temperature on the kinetics and has the neural network weights reestimated always so that a change in operational conditions occurs. This allow to follow the system behavior when changes in operating conditions occur.     

Investigation of potential-sensitive fluorescent dyes for application in nitrate sensitive polymer membranes

The applicability of various potential-sensitive dyes (PSD) for optical sensing of anions is reported. Specifically, nitrate-responsive polymer membranes have been developed which are composed of a plasticized polymer, an anion exchange catalyst, and a fluorescent dye. On exposure to nitrate, the fluorescence intensity of such membranes increases, while the wavelengths of the excitation and emission maxima remain virtually unchanged. The membranes typically are 2–4 μm thick and exhibit highest sensitivity to nitrate in the 2 to 200 mgl^–1 range. Signal changes on exposure to 100 mmol/l nitrate can be as high as +300%. The detection limit is 0.2 mgl^–1. The cationic PSD octadecyl acridine organe was tested in combination with a tin-organic and an indium-organic anion carrier rather than with tridodecylmethylammonium chloride, but both carriers were found to display no improved selectivity. Received: 2 December 1995 / Revised: 28 March 1996 / Accepted: 5 April 1996     

Bacterial Photosensory Proteins and Their Role in Plant–pathogen Interactions

Light is an important environmental signal for almost all living organisms. The light perception is achieved by photoreceptor proteins. As can be observed from the great number of bacterial genomes sequenced, plant pathogenic bacteria encode for a large number of photoreceptor proteins. The physiological implications of these photoreceptors are still poorly characterized. However, recent studies revealed the participation of these photosensory proteins in the pathogenic process. Here, we summarize what is known about these proteins and their role during the virulence process, concluding that the light environment modulates the plant–pathogen interaction.     

Quinol-containing ligands enable high superoxide dismutase activity by modulating coordination number,charge, oxidation states and stability of manganese complexes throughout redox cycling

Reactivity assays previously suggested that two quinol-containing MRI contrast agent sensors for H₂O₂, [Mn(H2qp1)(MeCN)]²⁺ and [Mn(H4qp2)Br₂], could also catalytically degrade superoxide. Subsequently, [Zn(H2qp1)(OTf)]⁺ was found to use the redox activity of the H2qp1 ligand to catalyze the conversion of O₂˙⁻ to O₂ and H₂O₂, raising the possibility that the organic ligand, rather than the metal, could serve as the redox partner for O₂˙⁻ in the manganese chemistry. Here, we use stopped-flow kinetics and cryospray-ionization mass spectrometry (CSI-MS) analysis of the direct reactions between the manganese-containing contrast agents and O₂˙⁻ to confirm the activity and elucidate the catalytic mechanism. The obtained data are consistent with the operation of multiple parallel catalytic cycles, with both the quinol groups and manganese cycling through different oxidation states during the reactions with superoxide. The choice of ligand impacts the overall charges of the intermediates and allows us to visualize complementary sets of intermediates within the catalytic cycles using CSI-MS. With the diquinolic H4qp2, we detect Mn(iii)-superoxo intermediates with both reduced and oxidized forms of the ligand, a Mn(iii)-hydroperoxo compound, and what is formally a Mn(iv)-oxo species with the monoquinolate/mono-para-quinone form of H4qp2. With the monoquinolic H2qp1, we observe a Mn(ii)-superoxo ↔ Mn(iii)-peroxo intermediate with the oxidized para-quinone form of the ligand. The observation of these species suggests inner-sphere mechanisms for O₂˙⁻ oxidation and reduction that include both the ligand and manganese as redox partners. The higher positive charges of the complexes with the reduced and oxidized forms of H2qp1 compared to those with related forms of H4qp2 result in higher catalytic activity (k_cat ∼ 10⁸ M⁻¹ s⁻¹ at pH 7.4) that rivals those of the most active superoxide dismutase (SOD) mimics. The manganese complex with H2qp1 is markedly more stable in water than other highly active non-porphyrin-based and even some Mn(ii) porphyrin-based SOD mimics.

Manganese complexes with polydentate quinol-containing ligands are found to catalyze the degradation of superoxide through inner-sphere mechanisms. The redox activity of the ligand stabilizes higher-valent manganese species.