Spectrophotometric study of a hafnium-hematein chelate

A spectrophotometric study of an analytically useful hafnium chelate of hematein is presented. The stoichiometry, the formation constant, the optimal pH range and the free energy of formation of the chelate are described. Beer's law is obtained in the range 3–25 μg of hafnium(IV).The red-brown chelate, of probable formula HfO[hematein]₂, can be used for the colorimetric determination of hafnium in the presence of zirconium, if the molar concentrations of both metals are the same. The molar absorptivity of the hafnium chelate is 5.8·10⁴ 1 mole^-1 cm^-1 at 520 nm and pH 2.0 at room temperature.     

Structure, spectroscopic properties, and reversible solid-to-solid reactions of metal complexes of 5-nitro-pyrimidin-2-olate

In searching for coordination polymers containing the highly polarized 5-nitro-pyrimidin-2-olate ligand (NP), a number of species containing 3d transition metals have been prepared and characterized, namely Co(NP)2(H2O)4, [Co(NP)2]n, Ni(NP)2(H2O)4, [Ni(NP)2]x, and [Zn(NP)2]n. Their structures have been determined by X-ray powder diffraction methods. The hydrated compounds contain mononuclear M(NP)2(H2O)4 units interconnected by means of a three-dimensional (3D) network of hydrogen bonds. The homoleptic species, at variance from the already known metal(II) pyrimidin-2-olate ones, crystallize as two-dimensional (2D) slabs, where the metal coordination is of the MN3O kind. The electron-withdrawing nitro group, never bound to the metal ion, is likely to influence the observed stereochemistry through steric and dipolar effects within the crystal lattice. The thermal, spectroscopic, and magnetic properties of these species are presented. The M(NP)2(H2O)4/[M(NP)2]x,n systems interconvert reversibly upon dehydration/rehydration processes.     

Texture discrimination and multi-unit recording in the rat vibrissal nerve

Background  

Rats distinguish objects differing in surface texture by actively moving their vibrissae. In this paper we characterized some aspects of texture sensing in anesthetized rats during active touch. We analyzed the multifiber discharge from a deep vibrissal nerve when the vibrissa sweeps materials (wood, metal, acrylic, sandpaper) having different textures. We polished these surfaces with sandpaper (P1000) to obtain close degrees of roughness and we induced vibrissal movement with two-branch facial nerve stimulation. We also consider the change in pressure against the vibrissa as a way to improve the tactile information acquisition. The signals were compared with a reference signal (control) – vibrissa sweeping the air – and were analyzed with the Root Mean Square (RMS) and the Power Spectrum Density (PSD).     

Gas‐phase dissociation of 1,4‐naphthoquinone derivative anions by electrospray ionization tandem mass spectrometry

Gas‐phase dissociation pathways of deprotonated 1,4‐naphthoquinone (NQ) derivatives have been investigated by electrospray ionization tandem mass spectrometry (ESI‐MS/MS). The major decomposition routes have been elucidated on the basis of quantum chemical calculations at the B3LYP/6‐31 + G(d,p) level. Deprotonation sites have been indicated by analysis of natural charges and gas‐phase acidity. NQ anions underwent an interesting reaction under collision‐induced dissociation conditions, which resulted in the radical elimination of the lateral chain, in contrast with the even‐electron rule. Possible pathways have been suggested, and their mechanisms have been elucidated on the basis of Gibbs energy and enthalpy values for the anions previously described at each pathway. Copyright © 2009 John Wiley & Sons, Ltd.     

Porphyrin deposition induced by UV irradiation

Simple irradiation by UV light of porphyrin TpyP and its zinc(II) and manganese(III) metal derivatives in chlorinated solvents leads to the deposition on silica of mesoscale aggregates. The process is due to the photochemical decomposition of the solvent with generation of HCl, which causes the precipitation of a protonated form. The morphology of the resulting objects is driven by the nature of the inserted metal ion.     

Determination of caffeine and its metabolites in urine by capillary electrophoresis-mass spectrometry

The caffeine content of foods and beverages varies considerably, interfering with our ability to obtain valid interpretations in many human studies with regard to the mechanism of action(s) of caffeine and/or its metabolites. The rate of metabolism of caffeine and other xanthine drugs also varies greatly from one individual to another. Therefore, it is extremely important to develop accurate, reliable analytical methods to quantify caffeine and its metabolites in simple and complex matrixes. A simple method is described for the separation and characterization of caffeine and its major metabolites employing capillary electrophoresis (CE) coupled to ultraviolet-absorption and mass spectrometry (MS) detection. After optimization of the electrophoresis separation conditions, a reliable separation of caffeine and 11 of its major metabolites was achieved in 50 mM ammonium carbonate buffer, pH 11.0. The volatile aqueous electrolyte system used with a normal electroosmotic flow polarity also provided an optimal separation condition for the characterization of the analytes by MS. The CE method achieved baseline resolution for all 12 compounds in less than 30 min. The CE-MS method is suitable for use as a routine procedure for the rapid separation and characterization of caffeine and its metabolites. The usefulness of this method was demonstrated by the extraction, separation, and identification of caffeine and its 11 metabolites from normal urine samples. The urine specimens were first acidified to obtain optimum binding efficiency to the sorbents of the off-line, solid-phase extraction procedure employed here, and an acidified eluent solvent was employed for the desorption step to maximize the recovery of the bound analytes.     

Total assignment of 1H and 13C NMR data for the sesquiterpene lactone 15-deoxygoyazensolide

We describe a complete analysis of the 1H and 13C spectra of the anti-inflamatory, schistossomicidal and trypanosomicidal sesquiterpene lactone 15-deoxygoyazensolide. This lactone, with a structure similar to other important ones, was studied by NMR techniques such as COSY, HMQC, HMBC, Jres and NOE experiments. The comparison of the data with some computational results led to an unequivocal assignment of all hydrogen and carbon chemical shifts, even eliminating some previous ambiguities. We were able to determine all hydrogen coupling constants (J) and signal multiplicities and to confirm the stereochemistry. A new method for the determination of the relative position of the lactonization and the position of the ester group on a medium-sized ring by NMR was developed.     

Synthesis and characterization of two cyclic organosiloxanes by multinuclear NMR spectroscopy and X-ray crystallography

1,3-[2′,6′-Pyridinebis(methyleneoxy)]-1,3-bis(diphenyl)cyclodisiloxane (9) and 2,6-pyridinebis(1,1-diphenylethoxy)diphenylsilane (11) were obtained from 2,6-pyridinediol derivatives with dichlorodiphenylsilane. An N→Si interaction is present in 2,6-pyridinebis(1,1-diphenylethoxy)diphenylsilane, which also shows fluxional behavior. The activation energy of 13.2 kcal mol⁻¹ for 11 was obtained for the intramolecular exchange between the phenyl groups from a variable-temperature ¹H-NMR study. The compounds were characterized by ¹H-, ¹³C- and ²⁹Si-NMR and their structures were established by X-ray crystallographic studies.     

Combination of GC-MS Molecular Networking and Larvicidal Effect against Aedes aegypti for the Discovery of Bioactive Substances in Commercial Essential Oils

Dengue is a neglected disease, present mainly in tropical countries, with more than 5.2 million cases reported in 2019. Vector control remains the most effective protective measure against dengue and other arboviruses. Synthetic insecticides based on organophosphates, pyrethroids, carbamates, neonicotinoids and oxadiazines are unattractive due to their high degree of toxicity to humans, animals and the environment. Conversely, natural-product-based larvicides/insecticides, such as essential oils, present high efficiency, low environmental toxicity and can be easily scaled up for industrial processes. However, essential oils are highly complex and require modern analytical and computational approaches to streamline the identification of bioactive substances. This study combined the GC-MS spectral similarity network approach with larvicidal assays as a new strategy for the discovery of potential bioactive substances in complex biological samples, enabling the systematic and simultaneous annotation of substances in 20 essential oils through LC₅₀ larvicidal assays. This strategy allowed rapid intuitive discovery of distribution patterns between families and metabolic classes in clusters, and the prediction of larvicidal properties of acyclic monoterpene derivatives, including citral, neral, citronellal and citronellol, and their acetate forms (LC₅₀ < 50 µg/mL).