Simple mercury fractionation in biological samples by CV AAS following microwave-assisted acid digestion or TMAH pre-treatment

A simple and reliable method to determine total and inorganic mercury in biological certified reference material (CRM) by cold vapor atomic absorption spectrometry (CV AAS) is proposed. After the CRM treatment at room temperature with tetramethylammonium hydroxide (TMAH), inorganic mercury is determined by CV AAS. Total mercury is measured by the same technique, after sample acid digestion in a microwave oven. Organic mercury, basically methylmercury, is obtained by difference. In both procedures, the quartz tube is kept at room temperature. By means of analysis of the following reference materials: pig kidney, lobster hepatopancreas, dogfish liver and mussel tissue, it was clear that the difference between the total and inorganic mercury concentrations agrees with the methylmercury concentration. Only one calibration curve against aqueous standards in acidic medium was carried out for both procedures. The concentrations obtained by both procedures are in agreement with the certified values according to the t-test at a 95% confidence level. The relative standard deviations were lower than 3.0% for digested CRM and 6.0% for CRM treated with TMAH for most of the samples. The limits of detection in the samples were 0.02 µg g^{− 1} and 0.04 µg g^{− 1} for inorganic and total Hg, respectively, since the sample mass for total mercury was half of that for inorganic mercury determination. Simplicity and high efficiency without using chromatographic techniques are some of the qualities of the proposed method, being adequate for fractionation analysis of mercury in biological samples.     

Bis(trifluoromethyl)phosphinous acid (CF3)2P-O-H: an example of a thermally stable phosphinous acid--synthesis, gas-phase structure, and rotational isomers

The bis(trifluoromethyl)phosphinous acid, (CF3)2P-O-H, is the only known example of a thermally stable phosphinous acid. Although this compound has been known since 1960, little is known about the chemistry of this extraordinary compound; this might be due to the tedious, and in some part risky, synthesis that was originally published. An improved, simple, and safe synthesis that is based on the treatment of the easily accessible (CF3)2PNEt2, with at least three equivalents of p-toluene sulfonic acid, is presented. The reaction results in a complete conversion to the phosphinous acid, which is isolated in almost 90 % yield. The compound exists in an equilibrium of two P--OH rotational isomers, a fact which is supported by quantum chemical calculations. The relative enthalpy difference of 6.4 kJ mol(-1), calculated at the B3PW91/6-311G(3d,p) level, is in excellent agreement with the experimental value of 5.9 kJ mol(-1), which was determined from the temperature dependence of the nu(OH) bands of the two rotational isomers. The complete experimental vibrational spectra of both rotamers, their predicted vibrational spectra obtained by using quantum chemical calculations, and an attempt at photoinduced isomerization of matrix-isolated (CF3)2POH is presented. The experimental structure, obtained from an electron-diffraction study in the gas phase, is reproduced very well by ab initio and density functional theory (DFT) methods.     

Co-conformational mechanoisomerism in a calix[6]arene-based [2]rotaxane

The synthesis of a [2]rotaxane, comprising a calix[6]arene-wheel and a dibenzyl-ammonium axle, is here reported. By virtue of its inherent directionality, the calix-wheel makes non-degenerate two equivalent stations of the symmetrical axle. In this way, the neutral rotaxane shows two co-conformations, named endo-alkyl and endo-benzyl, in which an alkyl or benzyl moiety of the axle are included inside the calix-cavity, respectively. NMR and DFT studies showed that the co-conformation preferred by the neutral mechanomolecule is the ‘endo-alkyl’ one, which is more stabilized by C-H···π interactions between the included alkyl chain and the aromatic wall of the calix-cavity.     

Characterization of Biodegradable Nanocomposite Films Prepared with Glutelin from Jatropha curcas L. by Response Surface Methodology and Infrared Spectroscopy

The water vapor permeability (WVP) and hardness of biodegradable nanocomposite films based on glutelin from Jatropha curcas L. were determined and the results were analyzed by response surface methodology (RSM). The effects of independent variables constituted by the plasticizer (glycerol), nanofiller (cloisite), and pH on the physical parameters were evaluated. The regression models obtained for each physical property adequately described the measurements used in the experimental design, with regression coefficients of 0.9513 and 0.9421 for WVP and hardness. The regression coefficients show that pH has the most significant effect on the WVP, whereas the cloisite content has the largest influence on the hardness of the nanocomposite film. Fourier transform infrared spectroscopy provided confirmation of the results obtained by RSM. Corroboration that the gluteline structure is in a similar form as the WVP and primarily influenced by pH was obtained using conventional and second derivative infrared spectra. However, the hardness of the film primarily depends on the cloisite content. This methodology may be useful for the design and elaboration of nanocomposite films based on J. curcas L. with specific barrier and mechanical properties.     

Analytic solutions of axisymmetric problems in elastic cylinders

Summary A general scheme encompassing expansion methods for the sleeve is presented: one homogeneous condition for each contour portion establishes real eigenvalues ensuring orthogonality to Fourier-Bessel expansions. Solutions by integral equations may be regarded as limiting cases, with summations replaced by integrations. Special attention is devoted to the alternative use of complex eigensolutions, subjected to two homogeneous conditions on the cylindrical boundary.

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Sommario Si presenta uno schema generale che inquadra i metodi di risoluzione attraverso sviluppi, per cilindri cavi: imponendo una condizione omogenea su ciascuna parte, piana o cilindrica, di contorno, si definiscono le autosoluzioni reali, ortogonali, per gli sviluppi in serie di Fourier-Bessel. Rientrano come casi particolari quelli di lunghezza o raggio infinito. Si esamina inoltre l'uso di autosoluzioni complesse, definite da due condizioni omogenee sul contorno cilindrico.

     

Quasi-cylindrical translation shells

Summary For shells generated by translation of an arbitrary profile along an arc of finite rise and large chord, as compared with the dimensions of , an elastic theory is developed on three-dimensional basis by the method of parametric expansions.

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Sommario Per il guscio generato dalla traslazione di una curva generica lungo un arco di monta finita e corda grande a fronte delle dimensioni di A, è sviluppata su base tridimensionale una teoria elastica col metodo degli sviluppi parametrici.

     

13C NMR spectra of some N-substituted 1,2-dihydro-3,1-benzoxazin-4-ones

The natural abundance ¹³C NMR spectra of a series of hitherto unknown l-atyl-methyl-1,2-dihydro-3,1-benzoxazin-4-ones have been recorded. The assignments of the various resonances have been made from chemical shift arguments, by the analysis of the fine splittings caused by one-bond and long-range couplings and also by comparison with model compounds.     

Asymptotic properties of steep solutions in shells

Summary Analogies in formulation and discrepancies in admissibile simplifications in application, between theories for stress states in shallow shells and for steep solutions in non-shallow shells, are noticed.Distributions of external forces or dislocations along the normals to the midsurface for which particular solutions can be constructed by means of the differential system under consideration, are defined in asymptotic form.

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Sommario La teoria del guscio piatto presenta analogia con quella degli stati con distribuzione ripida nel guscio curvo: tuttavia le semplificazioni ammissibili nelle due accezioni presentano differenze che l'analisi asintotica mette in rilievo.Si indicano le distribuzioni di forze esterne o dislocazioni lungo le normali alla superficie media per le quali soluzioni particolari sono costruibili mediante il sistema differenziale in esame.

     

Hydrodynamic and Thermophoretic Effects on the Supramolecular Chirality of Pyrene‐Derived Nanosheets

Chiroptical properties of two‐dimensional (2D) supramolecular assemblies (nanosheets) of achiral, charged pyrene trimers ( Py₃ ) are rendered chiral by asymmetric physical perturbations. Chiral stimuli in a cuvette can originate either from controlled temperature gradients or by very gentle stirring. The chiroptical activity strongly depends on the degree of supramolecular order of the nanosheets, which is easily controlled by the method of preparation. The high degree of structural order ensures strong cooperative effects within the aggregates, rendering them more susceptible to external stimuli. The samples prepared by using slow thermal annealing protocols are both CD and LD active (in stagnant and stirred solutions), whereas for isothermally aged samples chiroptical activity was in all cases undetectable. In the case of temperature gradients, the optical activity of 2D assemblies could be recorded for a stagnant solution due to migration of the aggregates from the hottest to the coldest regions of the system. However, a considerably stronger exciton coupling, coinciding with the J‐band of the interacting pyrenes, is developed upon subtle vortexing (0.5 Hz, 30 rpm) of the aqueous solution of the nanosheets. The sign of the exciton coupling is inverted upon switching between clockwise and counter‐clockwise rotation. The supramolecular chirality is evidenced by the appearance of CD activity. To exclude artefacts from proper CD spectra, the contribution from LD to the observed CD was determined. The data suggest that the aggregates experience asymmetrical deformation and alignment effects because of the presence of chiral flows.     

Biomolecular Fishing for Calixarene Partners by a Chemoproteomic Approach

MS‐based chemical‐proteomics technology is introduced herein as a third general strategy to study the biomolecular recognition properties of given calixarene derivatives. In particular, we demonstrate that a simply designed calix[4]arene derivative 1 a bearing acetamido groups at the exo rim (pAC), when linked to a solid support, is able to fish out a specific protein (PDI protein) from a crude extract of HeLa cells. Western blot and surface plasmon resonance studies confirmed the direct interaction between PDI and the linker‐free pAC derivative 1 b with considerable affinity, and in vitro tests showed its inhibition of PDI chaperone activity. In accordance with the role of PDI in a variety of human cancers, biological tests showed that pAC 1 b was cytotoxic and cytostatic toward CAL‐27 and PC‐3 cancer cell lines in vitro. Docking studies showed that H bonds and hydrophobic interactions contribute to the stabilization of the PDI/pAC complex.