Synthesis and characterization of three novel perfluoro-oligothiophenes ranging in length from the trimer to the pentamer

In this Article, we report on the synthesis and full characterization of three perfluorinated oligothiophenes, ranging in length from the trimer to the pentamer (PF-nT, with n = 3, 4, or 5). The differential pulse voltammetry (DPV) analysis of the compounds showed that they can be both oxidized and reduced (i.e., they display a dual or amphoteric electrochemical behavior), with the reduction peaks positively shifted relative to those of the corresponding unsubstituted oligothiophenes. The electrochemically determined energy gaps are in agreement with those measured from the UV-vis-NIR absorption spectra in solution. The conjugational properties have been investigated by means of FT-Raman spectroscopy, both as pure solids and as dilute solutes in CH(2)Cl(2), revealing that: (i) pi-conjugation does not still reach saturation with chain length for the longest oligomer, and (ii) conformational distortions from a nearly coplanar arrangement of the successive thiophene units upon solution are not too large. DFT and TDDFT quantum chemical calculations have been performed, at the B3LYP/6-31G level, to assess information about the optimized molecular structure, equilibrium atomic charges distribution, energies and topologies of the frontier molecular orbitals (MO) around the gap, vibrational normal modes associated with the most outstanding Raman scatterings, and vertical one-electron excitations that give rise to the main optical absorptions.     

Molecular photoionization cross sections in electron propagator theory: angular distributions beyond the dipole approximation

Corrections to dipole approximation results for angular distributions in photoionization of first-row hydrides have determined by using Dyson orbitals calculated with ab initio electron propagator theory and by considering the full multipole expansion for the incident photon representation. The relative importance of first-order corrections which consist of electric quadrupole and magnetic dipole terms and of higher-order terms has been estimated as a function of photon energy. Multipole corrections to the dipole approximation depend on photon energy and on the characteristics of the Dyson orbitals.     

Ternary complexes of cimetidine and phenobarbital with Cu(II) in methanolic solution

The formation constants of the binary complexes Cu(CM)²⁺ and Cu(CM) ₂ ²⁺ as well as those of the ternary complexes Cu(CM)L ⁺ and Cu(CM)₂ L ⁺ (CM=Cimetidine=N-Cyano-N-methyl-N[(5-methyl-1H-imidazol-4-yl)methyltioethyl]-guanidine; HL=Phenobarbital=5-ethyl-5-phenyl-barbituric acid) have been determined in 0.1 and 1.0 mol dm^–3 NaClO₄ methanol solutions at 25±0.2°C. The values of logX, log _stat.., and logK confirm the stability of the ternary complexes.

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Ternäre Komplexe von Cimetidin und Phenobarbital mit Cu(II) in methanolischer Lösung

Zusammenfassung Die Stabilitätskonstanten der binären Komplexe Cu(CM)²⁺ und Cu(CM) ₂ ²⁺ sowie die der ternären Komplexe Cu(CM)L ⁺ und Cu(CM)₂ L ⁺ (CM=Cimetidin=N-Cyan-N-methyl-N-[(5-methyl-1H-imidazol-4-yl)methylthioethyl]-guanidin; HL=Phenobarbitalum=5-Ethyl-5-phenyl-barbitursäure) wurden in 0.1 und 1.0M Lösungen von NaClO₄ in Methanol bei 25±0.2°C bestimmt. Die Werte von logX, log _stat. und logK bestätigen die Stabilität der ternären Komplexe.

     

Fast solid-phase extraction-gas chromatography-mass spectrometry procedure for oil fingerprinting. Application to the Prestige oil spill

A rapid and simple fractionation procedure using solid-phase extraction (SPE) cartridges was developed for an accurate determination of aliphatic and polycyclic aromatic hydrocarbons in petroleum residues and further application in chemical fingerprinting of oil spills by gas chromatography-mass spectrometry (GC-MS). Among the adsorbents evaluated, SiO2/C3-CN exhibited the best selectivity, providing, by elution with n-hexane (4 ml) and n-hexane-CH2Cl2 (1:1) (5 ml), two well-resolved aliphatic and aromatic hydrocarbon fractions, with recoveries of 97 +/- 7.2 and 99.7 +/- 13.9%, respectively. The SPE fractionation procedure was compared with the conventional silica-alumina adsorption chromatography showing similar results but practical advantages in terms of reproducibility, analysis time, solvent reduction and cost. Moreover, is particularly suitable for routine analysis with a high sample throughput. The developed methodology was tested in the characterization of fuel-oil samples collected along the Spanish north-west coast, after the Prestige oil spill accident.     

Kinetic analysis of liquid-phase depolymerization of trioxane from programmed temperature data

A sequential kinetic discrimination of potential kinetic models for non-isothermal linear programmed temperature data on the depolymerization of trioxane in a homogeneous liquid phase has been discussed.The influence of the initial concentration on the kinetic curves has been used as an experimental confirmation of the first-order influence of the concentration on the model.Kinetic analysis at constant temperature and conversion permits separation of the effects of concentration and temperature on the kinetic analysis at different levels of the variables.It is provided via non-isothermal kinetic data on the depolymerization of trioxane that nonisothermal experiment's allow a systematic approach to the kinetic behaviour in a wide range of the variables temperature and concentration, leading to maximum knowledge of the reaction model through minimum experimental effort.

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Zusammenfassung Eine sequentielle kinetische Unterscheidung potentieller kinetischer Modelle für die nicht-isotherme, linear temperaturprogrammierte Depolymerisation von Trioxan in homogener flüssiger Phase wird diskutiert. Der Einfluß der Ausgangskonzentration auf die kinetischen Kurven wurde als experimentelle Bestätigung dafür angesehen, daß die Konzentration auf das Modell nach erster Ordnung einwirkt. Die kinetische Analyse bei konstanter Temperatur und Konversion ermöglicht eine Trennung des Einflusses der Konzentration und Temperatur auf die kinetische Analyse bei unterschiedlichen Werten dieser Variablen. In der vorliegenden Arbeit wurde anhand von nichtisothermen kinetischen Daten für die Depolymerisation von Trioxan gezeigt, daß nicht-isotherme Experimente eine systematische Näherung an das kinetische Verhalten in einem weiten Bereich der Variablen Temperatur und Konzentration erlauben und zu einen Maximum an Erkenntnissen über das Reaktionsmodell bei einem Minimum an experimentellen Aufwand führen.

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Influence of the distal his in imparting imidazolate character to the proximal his in heme peroxidase: (1)h NMR spectroscopic study of cyanide-inhibited his42-->ala horseradish peroxidase

The functional higher oxidation states of heme peroxidases have been proposed to be stabilized by the significant imidazolate character of the proximal His. This is induced by a "push-pull" combination effect produced by the proximal Asp that abstracts ("pulls") the axial His ring N(delta)H, along with the distal protonated His that contributes ("pushes") a strong hydrogen bond to the distal ligand. The molecular and electronic structure of the distal His mutant of cyanide-inhibited horseradish peroxidase, H42A-HRPCN, has been investigated by NMR. This complex is a valid model for the active site hydrogen-bonding network of HRP compound II. The (1)H and (15)N NMR spectral parameters characterize the relative roles of the distal His42 and proximal Asp247 in imparting imidazolate character to the axial His. 1D/2D spectra reveal a heme pocket molecular structure that is highly conserved in the mutant, except for residues in the immediate proximity of the mutation. This conserved structure, together with the observed dipolar shifts of numerous active site residue protons, allowed a quantitative determination of the orientation and anisotropies of the paramagnetic susceptibility tensor, both of which are only minimally perturbed relative to wild-type HRPCN. The quantitated dipolar shifts allowed the factoring of the hyperfine shifts to reveal that the significant changes in hyperfine shifts for the axial His and ligated (15)N-cyanide result primarily from changes in contact shifts that reflect an approximately one-third reduction in the axial His imidazolate character upon abolishing the distal hydrogen-bond to the ligated cyanide. Significant changes in side chain orientation were found for the distal Arg38, whose terminus reorients to partially fill the void left by the substituted His42 side chain. It is concluded that 1D/2D NMR can quantitate both molecular and electronic structural changes in cyanide-inhibited heme peroxidase and that, while both residues contribute, the proximal Asp247 is more important than the distal His42 in imparting imidazole character to the axial His 170.     

Melatonin: A Neurotrophic Factor?

Melatonin, N-acetyl-5-hydroxytryptamine, is a hormone that synchronizes the internal environment with the photoperiod. It is synthesized in the pineal gland and greatly depends on the endogenous circadian clock located in the suprachiasmatic nucleus and the retina’s exposure to different light intensities. Among its most studied functions are the regulation of the waking-sleep rhythm and body temperature. Furthermore, melatonin has pleiotropic actions, which affect, for instance, the modulation of the immune and the cardiovascular systems, as well as the neuroprotection achieved by scavenging free radicals. Recent research has supported that melatonin contributes to neuronal survival, proliferation, and differentiation, such as dendritogenesis and axogenesis, and its processes are similar to those caused by Nerve Growth Factor, Brain-Derived Neurotrophic Factor, Neurotrophin-3, and Neurotrophin-4/5. Furthermore, this indolamine has apoptotic and anti-inflammatory actions in specific brain regions akin to those exerted by neurotrophic factors. This review presents evidence suggesting melatonin’s role as a neurotrophic factor, describes the signaling pathways involved in these processes, and, lastly, highlights the therapeutic implications involved.     

Synthesis,In Silico and In Vivo Toxicity Assessment of Functionalized Pyridophenanthridinones via Sequential MW-Assisted Intramolecular Friedel-Crafts Alkylation and Direct C–H Arylation

A rapid, efficient, and original synthesis of novel pyrido[3,2,1-de]phenanthridin-6-ones is reported. First, the key cinnamamide intermediates 8a–f were easily prepared from commercial substituted anilines, cinnamic acid, and 2-bromobenzylbromide in a tandem amidation and N-alkylation protocol. Then, these N-aryl-N-(2-bromobenzyl) cinnamamides 8a–f were subjected to a TFA-mediated intramolecular Friedel-Crafts alkylation followed by a Pd-catalyzed direct C–H arylation to obtain a series of potentially bioactive 4-phenyl-4,5-dihydro-6H,8H-pyrido[3,2,1-de]phenanthridin-6-one derivatives 4a–f in good yields. Finally, the toxicological profile of the prepared final compounds, including their corresponding intermediates, was explored through in silico computational methods, while the acute toxicity toward zebrafish embryos (96 hpf-LC₅₀, 50% lethal concentration) was also determined in the present study.