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Phosphorylation is an essential mechanism of protein control and plays an important role in biology. The two-component system (TCS) is a bacterial regulation mechanism mediated by a response regulator (RR) protein and a kinase protein, which synchronize the regulatory circuit according to the environment. Phosphorylation is a key element in TCS function as it controls RR activity. In the present study, we characterize the behavior of MorR, an RR associated with Mo homeostasis, upon acetylphosphate and phosphoramidate treatment in vitro . Our results show that MorR was phosphorylated by both phospho-donors. Fluorescence experiments showed that MorR tryptophan emission is quenched by phosphoramidate. Furthermore, theoretical and computational results demonstrate that phosphorylation by phosphoramidate is more favorable than that by acetylphosphate. In conclusion, phosphorylated MorR is a monomeric protein and phosphorylation does not appear to induce observable conformational changes in the protein structure. [ABSTRACT FROM AUTHOR]

Aggregation of heat unstable wine proteins is responsible for the economically and technologically detrimental problem called wine protein haze. This is caused by the aggregation of thermally unfolded proteins that can precipitate in bottled wine. To study the influence of SO 2 in this phenomenon, wine proteins were isolated and thaumatins were identified has the most prone to aggregate in the presence of this compound. Isolated wine thaumatins aggregation was followed by dynamic light scattering (DLS), circular dichroism (CD), fluorescence spectroscopy and size exclusion chromatography (SEC). Our experimental results demonstrate that protein thermal unfolding after exposure of the protein to 70 °C does not present differences whether SO 2 is present or not. Conversely, when the protein solution is cooled to 15 °C (after heat stress) significant analytical changes can be observed between samples with and without SO 2 . A remarkable change of circular dichroism spectra in the region 220–230 nm is observed (which can be related to S-S torsion angles), as well as an increase in tryptophan fluorescence intensity (absence of fluorescence quenching by S-S bonds). Formation of covalently-linked dimeric and tetrameric protein species were also detected by SEC. The ability to dissolve the aggregates with 8 M urea seems to indicate that hydrophobic interactions are prevalent in the formed aggregates. Also, the reduction of these aggregates with tris (2-carboxyethyl) phosphine (TCEP) to only monomeric species reveals the presence of intermolecular S-S bonds. [ABSTRACT FROM AUTHOR]

Iron oxide nanoparticles (Fe 3 O 4 , IONPs) are promising candidates for several biomedical applications such as magnetic hyperthermia and as contrast agents for magnetic resonance imaging (MRI). However, their colloidal stability in physiological conditions hinders their application requiring the use of biocompatible surfactant agents. The present investigation focuses on obtaining highly stable IONPs, stabilized by the presence of an oleic acid bilayer. Critical aspects such as oleic acid concentration and pH were optimized to ensure maximum stability. NPs composed of an iron oxide core with an average diameter of 9 nm measured using transmission electron microscopy (TEM) form agglomerates with an hydrodynamic diameter of around 170 nm when dispersed in water in the presence of an oleic acid bilayer, remaining stable (zeta potential of −120 mV). Magnetic hyperthermia and the relaxivities measurements show high efficiency at neutral pH which enables their use for both magnetic hyperthermia and MRI. [ABSTRACT FROM AUTHOR]

Abstract: The mechanism of electron-transfer from aluminium tetrasulfonated phthalocyanine triplet state to cytochrome c was investigated in this work. This reaction successfully quenches the dye triplet state due to the formation of complexes between the solute and the protein at the active site. The electron-transfer rate constant is around 3×107 s−1, and is in accordance with previous results for the singlet excited state quenching [C.A.T. Laia, S.M.B. Costa, D. Phillips, A. Beeby. Electron-transfer kinetics in sulfonated aluminum phthalocyanines/cytochrome c complexes, J. Phys. Chem. B 108 (2004) 7506–7514.] in the framework of the Marcus theory, with a reorganization energy equal to 0.94 eV. The complex formation is diffusion controlled, but heterogeneities of the protein surface charge distribution lead to quenching rate constants smaller than predicted on a hard-spheres model with electrostatic interactions. Also the binding equilibrium constant is strongly affected by this phenomenon. Ionic strength plays an important role on the complex formation, but its effect on the unimolecular electron-transfer rate constant is negligible within experimental error. [Copyright &y& Elsevier]

The thermal back isomerization of 5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimidacarbocyanine cis photoisomers studied by nanosecond laser flash photolysis is reported in polar solvents and at different temperatures. The data show the formation of a cis isomer after laser excitation, which disappears afterwards in the microsecond timescale with first-order kinetics, forming again the trans conformer. The reaction rate constant does not depend on the solvent viscosity, but exhibits strong polarity dependence. Accordingly, the activation energy exhibits a parabolic polarity dependence, which is attributed to the charge transfer nature of the transition state. Such effect may be enhanced by stereochemical hindrance in the cis photoisomer. [Copyright &y& Elsevier]

Despite the extensive research performed during the last decades, the multifactorial mechanism responsible for white wine protein haze formation is not fully characterized. A model is proposed, which is essentially based on two postulates: the experimental identification of sulfur dioxide as the non-proteinaceous factor, and the inference from reliable data available in the literature of the dynamic chemistry played by wine protein sulfhydryl groups. Unlike other reducing agents, addition of SO 2 to must/wine upon heating cleaves intraprotein disulfide bonds, hinders thiol-disulfide exchange during protein interactions, and leads to formation of novel interprotein disulfide bonds. These bonds are ultimately responsible for wine protein aggregation following a nucleation-growth kinetic model, as shown by Dynamic Light Scattering experiments. The model was tested in wine model solution (using total and fractionated wine proteins) and validated under real wine conditions. The results achieved may open the way to develop techniques that will find wide application in the wine industry. [ABSTRACT FROM AUTHOR]

Abstract: Flavylium is the basic structure of anthocyanins, an important family of natural dyes responsible for the color in many flowers and fruits. While anthocyanins in vitro are involved in a pH dependent equilibrium between a flavylium cation (acidic species) and a hemiketal (as major basic species), some synthetic flavylium compounds present the trans-chalcone as the major basic species. In this case irradiation of the trans-chalcone leads to appearance of colored products, either a flavylium cation and/or a quinoidal base, via cis-chalcone and hemiketal. Taking profit from the complexity of the network it is possible to design photochromic systems, exhibiting a thermal back reaction, or models for optical memories, when the back reaction is prevented. The flavylium photochromism was also observed in ionic liquids, gels, micelles and reversed micelles opening up possible applications. In this work an overview of the photochromism of synthetic flavylium compounds is presented, from the first observations of the light effect to recent developments. [Copyright &y& Elsevier]

Graphical abstract Highlights • Fluorescence emission of a fluorescein derivative decreased in acid pH. • Fluorescence anisotropy of fluorescein derivative increased in acid pH. • The monoanionic species of fluorescein derivative predominates under physiological pH. • A constant fluorescence emission of fluorescein derivative is a prerequisite for binding studies. Abstract Fluorescence spectroscopy is a powerful tool to comprehend macromolecules interaction. The characteristics of the fluorophore as well its behavior under the experimental conditions are central to ascertain the results. The present work characterizes the fluorescence emission and anisotropy of a fluorescein derivative linked to a double strand DNA containing 67 base pairs (named as 6-FAM-67-mer) under different pH conditions. The results show that fluorescence emission and anisotropy of this fluorescein derivative varies according to pH (as the pH becomes more acidic, the total fluorescence emission decreases). The decrease in fluorescence emission intensity is accompanied by an increase in anisotropy. The monoanionic form of fluorescein derivative is the predominant species from pH 7.5 to 9.2. Our main conclusion is that a constant fluorescein derivative emission is a prerequisite to determine association constants between macromolecules. [ABSTRACT FROM AUTHOR]

[Display omitted] • trans -Chalcones derived from 2-phenyl-1-benzopyrylium cations exist in solution as multistate systems involving several species. • trans -n-Pyridinechalcones (n=2′,3′,4′) exhibit similar multistate systems with slower kinetics and where flavylium is absent. • Both types of chalcones undergo photoisomerization and/or photo-ring closure reactions depending on pH. • Depending on the solvent, trans -2′-pyridinechalcone may give rise to new compounds in the multistate. • The new compounds were fully characterized and pave the way to applications in photochromism and biological applications. The kinetics and thermodynamics of the pH-dependent multistate of species generated by the trans -chalcone of n-pyridinebenzopyrylium (n = 2′, 3′) were studied by UV–vis spectroscopy, 1H NMR and HPLC-MS, and the results compared with those reported for n = 4′. Due to the slow kinetics of the multistate species interconversion, the conjugation of these techniques has shown to be a powerful tool to investigate the behaviour of these systems. The species involved in the multistate are mutatis mutandis the same observed in anthocyanins and related compounds except for the flavylium cation, which was not observed in these systems even in very acidic medium. The rates of the interconversion of the multistate species upon pH stimuli are much slower than in anthocyanins. The compound bearing the pyridine nitrogen in position 2′ gives two novel products absorbing in the visible. Formation of the new products is particularly efficient from the thermal evolution of the photochemical products obtained upon light irradiation of the protonated trans -chalcone in a mixture of methanol:acidic water (1:1). This confirms the unique capacity of the substituents in position 2′ in giving intramolecular reactions involving the benzopyrylium core. Crystal structures for the three pyridine chalcone compounds (n = 2′, 3′, 4′) were obtained and the respective structures discussed. [ABSTRACT FROM AUTHOR]

Poly(3,4-ethylenedioxythiophene) (PEDOT) has been electrochemically polymerized from 3,4-ethylenedioxythiophene (EDOT) monomers through a vertically oriented mesoporous silica matrix previously formed on FTO electrodes. The mesoporous silica thin films with pore channels of 3 nm in diameter, closely packed in a hexagonal arrangement, were obtained by electrochemically-assisted self-assembly (EASA). The mesoporous silica/PEDOT films were characterized by SEM and TEM microscopy and by cyclic voltammety. They were also used to construct electrochromic devices (ECDs), which were fully characterized for switching speed, coloration efficiencies, and cycling and voltammetric responses. [ABSTRACT FROM AUTHOR]

Three new complexes based on lanthanide(III) tetrakis(β-diketonate) with a tetraalkylphosphonium as counterion [P 6,6,6,14 ][Ln(NTA) 4 ] (Ln = Dy ( 1 ), Tb ( 2 ), Gd ( 3 ); NTA = naphthoyltrifluoroacetone; P 6,6,6,14 = trihexyl(tetradecyl)phosphonium) were synthesized. The complexes were fully characterized and their spectroscopic, thermal and magnetic properties were evaluated, together with the Eu ( 4 ) analogue. The Dy ( 1 ) compound showed solvatochromic properties, the Tb ( 2 ) compound presented an unprecedented solid state polymorphism never observed in an organometallic compound and all complexes presented paramagnetic behavior with no interactions between the magnetic moments. [ABSTRACT FROM AUTHOR]

Abstract: Soda-lime glasses doped with Eu3+ were synthesized using a variety of compositions, namely changing the fraction of CaO or Eu2O3. Those glasses were characterized with several techniques, including ellipsometry, UV–vis–NIR absorption spectroscopy, steady-state photoluminescence spectroscopy and time-resolved luminescence. The compositions' effects on optical properties such as refraction indexes, Eu3+ oscillator strengths and luminescence lifetimes were accessed from the analysis of the experimental results. Judd–Ofelt theory was used to analyze all these aspects, which allow the detection of a mismatch of optical properties from absorption and emission spectroscopy. This mismatch was confirmed from the time-resolved data, showing the existence of two different spectroscopic Eu3+ species. From those results it is concluded that there is evidence for lanthanide aggregation, giving rise to self-quenching effects that may be described through resonance energy transfer mechanisms. The difference between luminescence lifetimes for isolated and aggregated Eu(III) is interpreted as due to different interactions with oxygen in the matrix, namely degree of covalency of the Eu–O bond and point group symmetry of the lanthanide. [Copyright &y& Elsevier]

Highlights: [•] Photostationary state of the flavylium network of chemical reactions is analyzed. [•] A energy diagram is proposed to visualize the photostationary state. [•] The model compound 4′,7-dihydroxyflavylium was used to test the model. [ABSTRACT FROM AUTHOR]

Highlights: [•] We deposited IZO by DC Sputtering on heat sensitive substrates such as paper. [•] The materials displayed high electric conductivity and optical transparency. [•] Electrochromic materials were deposited using screen-printing. [•] Solid-state electrochromic devices were assembled, showing an excellent performance. [ABSTRACT FROM AUTHOR]

Abstract: Selective interaction between Crystal Violet Lactone and Fe3+/Fe2+ in methanol leads to a reversible ionochromic colour change. This interaction can be controlled electrochemically, in order to achieve reversible colour changes with high contrast between colourless and dark blue solutions. The presented system is proposed as an alternative electrochromic solution. [Copyright &y& Elsevier]

Abstract: Chalcones possessing a hydroxyl group in position 2 cyclize to form flavylium salts in acidic media, this reaction being reversible under neutral–basic conditions. On the other hand, chalcones possessing a hydroxyl group in position 2′ cyclize to form flavanones in basic media. By synthesizing 2′-hydroxyflavylium tetrafluoroborate, it was possible to obtain trans-2,2′-dihydroxychalcone that in solution can evolve to 2′-hydroxyflavanone or back to 2′-hydroxyflavylium depending on the pH. The several equilibria established in aqueous solution were fully characterized. The importance of including flavanones into the flavylium network of chemical reactions is briefly exploited. [Copyright &y& Elsevier]