Sequestering ability of some chelating agents towards methylmercury(II)

A study on the interactions between CH₃Hg⁺ and some S, N and O donor ligands (2-mercaptopropanoic acid (thiolactic acid (H₂ TLA)), 3-mercaptopropanoic acid (H₂ MPA), 2-mercaptosuccinic acid (thiomalic acid (H₃ TMA)), d,l-penicillamine (H₂ PSH), l-cysteine (H₂ CYS), glutathione (H₃ GSH), N,N′-bis(3-aminopropyl)-1-4-diaminobutane (spermine (SPER)), 1,2,3,4,5,6-benzenehexacarboxylic acid (mellitic acid (H₆ MLT)) and ethylenediaminetetraacetic acid (H₄ EDTA)) is reported. The speciation models in aqueous solution and the possible structures of the complexes formed are discussed on the basis of potentiometric, calorimetric, UV spectrophotometric and electrospray mass spectrometric results. For the CH₃Hg⁺–S donor ligand systems, the formation of ML^1–z and MLH^2–z complex species is observed, together with a diprotonated MLH ₂ ^3–z species for CYS ^2?, PSH ^2? and GSH ^3? and the mixed hydrolytic one ML(OH)^?z for TLA ^2? and MPA ^2?. The dependence of the stability on ionic strength and on temperature is also analysed. In the other CH₃Hg⁺-L systems (L?=?MLT ^6?, SPER and EDTA ^4?), ML^1–z , MLH^2–z and MLH₂ ^3–z complex species are formed, together with the MLH₃ ^4–z species for SPER, the mixed hydrolytic ML(OH)^–z one for SPER and EDTA, and the M₂L^2–z for EDTA only. On the basis of the speciation models proposed, the sequestering ability of the ligands towards methylmercury(II) cation is evaluated. All S donor ligands show a good sequestering power (at 10^?11?mol?L^?1 level, in the pH range 4 to 8) following the trend MPA ^2??<?PSH ^2??<?GSH ^3??<?TLA ^2??<?CYS ^2??<?TMA ^3?, while significantly lower is the sequestering ability of MLT, SPER and EDTA (at 10^?3–10^?5?mol?L^?1 level, in the pH range 4 to 8).

Interaction of biofunctionalized gold nanoparticles with model phospholipid membranes

The understanding of the interaction of nanoparticles with cell membranes and the penetration of these nano-objects through cell wall is highly required for their biomedical application. In this work were aimed at the study of the interaction of gold nanoparticles with model phospholipid membranes prepared at the air/water interface in a Langmuir trough. Spherical (10 and 15 nm mean diameter) and rod-like gold (aspect ratio: 2.8) nanoparticles were synthesized and biofunctionalized with l-cysteine and l-glutathione. The gold nanoparticles were characterized by TEM images and UV–Vis absorbance measurements. The interaction of the biofunctionalized gold nanoparticles with the model monolayer membrane was studied by surface pressure versus surface area compressional isotherms and by the measurement of the change in surface pressure of a preformed model membrane. The effect of the initial surface pressure of the preformed membrane was evaluated to determine the maximum insertion pressure and synergy. We have found that the driving forces of the bioconjugated Au nanoparticle (NP) or Au nanorod (NR) penetration into the monolayer membrane is mostly determined by electrostatic interaction and orientational van der Waals forces. Monolayer films were transferred with Langmuir–Blodgett technique onto solid substrates and the nanoparticles were visualized with AFM technique. Figure

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Radial symmetry and symmetry breaking for some interpolation inequalities

We analyze the radial symmetry of extremals for a class of interpolation inequalities known as Caffarelli?CKohn?CNirenberg inequalities, and for a class of weighted logarithmic Hardy inequalities which appear as limiting cases of the first ones. In both classes we show that there exists a continuous surface that splits the set of admissible parameters into a region where extremals are symmetric and a region where symmetry breaking occurs. In previous results, the symmetry breaking region was identified by showing the linear instability of the radial extremals. Here we prove that symmetry can be broken even within the set of parameters where radial extremals correspond to local minima for the variational problem associated with the inequality. For interpolation inequalities, such a symmetry breaking phenomenon is entirely new.     

Generalized fiber Fourier optics

A twofold generalization of the optical schemes that perform the discrete Fourier transform (DFT) is given: new passive planar architectures are presented where the 2 × 2 3 dB couplers are replaced by M × M hybrids, reducing the number of required connections and phase shifters. Furthermore, the planar implementation of the discrete fractional Fourier transform (DFrFT) is also described, with a waveguide grating router (WGR) configuration and a properly modified slab coupler.     

Synthesis of derivatives of pyrazolo[1,5-a]pyrrolo[1,2-c][1,3,6]-benzotriazocine,a new class of compounds with potential CNS activity

The synthesis of derivatives of pyrazolo[1,5-a]pyrrolo[1,2-c][1,3,6]benzotriazocine was obtained by the reaction of arylaldehydes with some 1-(2-aminophenyl)-5-(pyrrol-1-yl)pyrazoles, as hydrochlorides. Characterization of this new class of compounds was effected with ir, pmr and ¹³C nmr spectral data.     

Polycondensed nitrogen heterocycles. Part 21. Complete 13C NMR assignment of annelated phenanthridines

Two-dimensional nmr techniques were used for the complete assignment of ¹³C nmr spectra of pyrrolo-[1,2-f]-, pyrazolo[1,5-f]-, and 1,2,4-triazolo[1,5-f]phenanthridines.     

Study of the bidimensional state conformation of polyβ-benzyl-L-aspartate

Summary Huggins' theory of polymer monolayers, considered as bidimensional solutions is applicable to Poly-ß--benzil-L-aspartate films, obtained from two different spreading solvent: a pyridine free solvent and a 80% pyridine one.The spreading isotherms, deduced from the theory agree well with the experimental isotherm; therefore it is possible to deduce theoretical parameters showing the existence of two different macromolecular structures depending on the spreading solvent.In particular, if solvent is pyridine free, it appears that the monolayers have chain with -helix structure, if the solvent contains 80% pyridine they have chains with a more extended structure.

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Zusammenfassung Huggins Theorie der polymeren Monoschichten, als zweidimensionale Lösungen betrachtet, erweist sich als anwendbar auf Monoschichten von Poly--Benzyl-L-Aspartat, die man von zwei verschiedenen Spreitungslösemitteln erhält: ohne Pyridin oder 80% Pyridin enthaltend.Da die Übereinstimmung zwischen den experimentellen Spreitungsisothermen und den theoretisch erhaltenen gut ist, ist es möglich, Parameter abzuleiten, die geeignet sind, zwei verschiedene makromolekulare Strukturen je nach dem benutzten Spreitungslösemitteln zu charakterisieren.Insbesondere, wenn das Lösemittel kein Pyridin enthält, scheint es wahrscheinlich, daß die Monoschichten vorwiegend aus -Spiralen bestehen, wenn das Lösemittel Pyridin enthält, aus Ketten mit einer ausgedehnten Struktur.

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With 2 figures and 1 table     

Selfgravitating electroweak strings

We obtain selfgravitating multi-string configurations for the Einstein-Weinberg-Salam model, in terms of solutions for a nonlinear elliptic system of Liouville type whose solvability was posed as an open problem in Yang (Solitons in Field Theory and Nonlinear Analysis, Springer, New York, 2001).     

On Non-Topological Solutions for Planar Liouville Systems of Toda-Type

In this paper we determine the interaction of diagonal defect clusters in regions of an Aztec rectangle that scale to arbitrary points on its symmetry axis (in earlier work we treated the case when this point was the center of the scaled Aztec rectangle). We use the resulting formulas to determine the asymptotics of the correlation of defects that are macroscopically separated from one another and feel the influence of the boundary. In several of the treated situations this seems not to be accomplishable by previous methods. Our applications include the case of two long neutral strings, which turn out to interact by an analog of the Casimir force, two families of neutral doublets that turn out to interact completely independently of one another, a neutral doublet and a very long neutral string, a general collection of macroscopically separated monomer and separation defects, and the case of long strings consisting of consecutive monomers.