Nitrite increases the enantioselectivity of sulfoxidation catalyzed by myoglobin derivatives in the presence of hydrogen peroxide

The effect of nitrite in the sulfoxidation of organic sulfides catalyzed by myoglobin (Mb) in the presence of hydrogen peroxide has been investigated. A general improvement in enantioselectivity was found for the reaction catalyzed by horse heart metMb and a series of sperm whale metMb derivatives including the wild type protein, the active site mutants T67K Mb, T67R Mb, T67R/S92D Mb, and the T67K Mb derivative reconstituted with the modified prosthetic group protohemin-l- histidine methyl ester.     

Nature of urea-fluoride interaction: incipient and definitive proton transfer

1,3-bis(4-nitrophenyl)urea (1) interacts through hydrogen bonding with a variety of oxoanions in an MeCN solution to give bright yellow 1:1 complexes, whose stability decreases with the decreasing basicity of the anion (CH3COO- > C6H5COO- > H2PO4- > NO2- > HSO4- > NO3-). The [Bu4N][1.CH3COO] complex salt has been isolated as a crystalline solid and its molecular structure determined, showing the formation of a discrete adduct held together by two N-H...O hydrogen bonds of moderate strength. On the other hand, the F- ion first establishes a hydrogen-bonding interaction with 1 to give the most stable 1:1 complex, and then on addition of a second equivalent, induces urea deprotonation, due to the formation of HF2-. The orange-red deprotonated urea solution uptakes carbon dioxide from air to give the tetrabutylammonium salt of the hydrogencarbonate H-bond complex, [Bu4N][1.HCO3], whose crystal and molecular structures have been determined.     

A Combined Theoretical and Experimental Approach to the Study of the Structural and Electronic Properties of Curcumin as a Function of the Solvent

Curcumin, a chemical compound present in the well-known Indian spice turmeric, has uses in many different fields ranging from medicinal chemistry to the dye industry. Its poor water solubility, though, makes Curcumin difficult to handle, making it less appealing for potential uses. The principal aim of this work is to perform a computational study of the structural and electronic properties of Curcumin {IUPAC name: 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione} in several solvents, and a comparison with experimental data. Rotameric equilibria, vibrational and thermochemical analysis, and electronic absorption spectra (with ab initio and semi-empirical methodologies) have been studied, both in vacuum and in three selected solvents. Different computational techniques have been applied and the results compared. Combined approaches resulted in very satisfactory results. Interesting results have emerged, which suggest subsequent investigations about the nature of the excited states and potential derivatives of Curcumin that possibly have non-linear optical applications, as a π-core for innovative materials in laser engineering and photonics.     

Synthesis and X-ray structure of the [{Fe3(CO)9(micro3-O)}2H]3- trianion: dimerization of a metal carbonyl cluster via formation of an exceptionally short hydrogen bond

The synthesis, structure and characterization of the [{Fe3(CO)9(micro3-O)}2H]3- trianion in its [Cs(THF)0.33]+ and [NEt4]+ salt are reported. The title dimeric cluster has been obtained by protonation in water or in organic solvent of the [Fe3(CO)9(micro3-O)]2- dianion to the hydroxo [Fe3(CO)9(micro3-OH)]- derivative and crystallization. The solid state structure of [Cs(THF)0.33]3[{Fe3(CO)9(micro3-O)}2H] is based on ionic packing of [Cs(THF)0.33]+ cations and [{Fe3(CO)9(micro3-O)}2H]3- trianions. The fractional formula is due to the particular packing of Cs+ cations, which are at the vertices of fused cuboctahedral and trigonal antiprismatic polyhedrons. Each cuboctahedron encapsulates a [{Fe3(CO)9(micro3-O)}2H]3- trianion, whereas each trigonal antiprism encapsulates a THF molecule. The possibility that the structure of the [{Fe3(CO)9(micro3-O)}2H]3- trianion could be affected by its confinement in the cuboctahedral cage of Cs+ ions and the heavy disorder of the THF molecule urged a further structural determination of the trianion with a completely different cation. The corresponding [NEt4]3[{Fe3(CO)9(micro3-O)}2H] salt has been, therefore, prepared and structurally characterized. The [{Fe3(CO)9(micro3-O)}2H]3- trianion displays an identical structure and almost coincident molecular parameters in both salts. Its most notable feature is represented by the unique hydrogen atom symmetrically bridging the micro3-O atoms of two different [Fe3(CO)9(micro3-O)]2- molecules and displaying one of shortest O...H...O interaction so far reported in organic, inorganic and organometallic literature. The structure of [Cs(THF)]2[Fe4(CO)13], which has been obtained as a by-product of the synthesis of [Cs(THF)0.33]3[{Fe3(CO)9(micro3-O)}2H], is also briefly reported.     

Silica nanoparticles for fluorescence sensing of Zn(II): exploring the covalent strategy

Silica nanoparticles (about 15 nm diameters), which contain a derivative of 6-methoxy-8-(p-toluensulfonamido)-quinoline (TSQ) as a Zn(II) fluorescent probe covalently linked to the silica network, were prepared and studied as Zn(II) fluorescent chemosensors. The systems selectively detect Zn(II) ions in water rich solutions with a submicromolar sensitivity: 0.13 microM concentrations of Zn(II) can be measured with the only interference of Cu(II) and Cd(II) ions. Compared with free TSQ, the nanoparticles based systems have the advantage that they can be employed in aqueous solutions without aggregation problems while at the same time, they maintain a similar Zn(II) affinity and sensing ability. Addition of a second, substrate insensitive, fluorophore to the particles leads to the realization of a ratiometric sensor.     

A dizinc complex for selective fluorescence sensing of uridine and uridine-containing dinucleotides

A dizinc complex with a polyamine macrocycle is able to selectively bind and sense uridine (U) as well as the uridine-containing ribodinucleotides U(3'-5')pU and U(3'-5')pA, thanks to an exciplex emission arising from a pi-stacked complex involving the dipyridine unit and Zn(II)-bound uridine moieties.     

Monitoring the traceability of the pH of a primary tetraborate buffer: comparison of results from primary and secondary apparatus

This paper reports evaluation of the behaviour of different combined glass electrodes applied to measurement of the pH of a primary, 0.01 mol kg⁻¹, tetraborate buffer. Measurements were first performed by use of a primary Harned cell (at 15, 25, and 37 °C); these results were then compared with those obtained for the same solution by use of three combined glass electrodes (25 °C) with different membranes and liquid-junction designs, calibrated by use of commercial pH-metric buffers. The pH of the same solution was also measured in terms of the molal concentration of hydrogen ions, using acid–base titration to evaluate the formal potential difference K of each cell at fixed ionic strength, I, adjusted by addition of KCl or Et₄NI (tetraethylammonium iodide). The reference value from primary measurement, paH = 9.171, was slightly closer to the mean value obtained by determination of concentration, rather than that obtained by direct measurement of activity; the differences were smaller than the extended uncertainty characteristics of the secondary measurements. The importance of evaluation of the ionic strength of the solution under study is emphasised. We verified that for tetraborate buffer slight modification of the value of I used to calculate γ _i (the activity coefficient of a single ion) in the calculation of paH from the acidity function at zero molality of chloride can significantly affect the reference value of the calibrator tool. This is true, in general, for low values of the ionic strength, such as those considered in this work; an approximate value of I can then cause distortions along the pH traceability chain. Application of the concepts of thermodynamics to this traceability chain is discussed.     

Obtaining 4-vinylphenols by decarboxylation of natural 4-hydroxycinnamic acids under microwave irradiation

4-Vinylphenols, useful compounds for industrial applications, were obtained by decarboxylation of 4-hydroxycinnamic acids under microwave irradiation in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as base and basic aluminum oxide as solid support. The reactions were fast (15-30 min). The selective extraction of the final products with ethyl acetate avoids chromatographic purifications. The conversions are quantitative and the yields are satisfactory. Only the unstable 4-vinylcatechol was obtained in moderate yield. This procedure was successfully extended to a natural sample of ferulic acid extracted from wheat bran to get the corresponding 4-vinylguaiacol, a FEMA GRAS (Flavor and Extract Manufacturer's Association; General Regarded as Safe) approved flavoring agent.