A hydrogen-bonding-modulated molecular rotor: environmental effect in the conformational stability of peptidomimetic macrocyclic cyclophanes

The conformational behavior of 16- to 18-membered ring peptidomimetic p-cyclophanes 1a,b-3a,b has been studied by NMR. The cycles bearing 16 and 17 atoms showed a dynamic process within the NMR time scale, produced by the rotation of the aromatic p-diphenylene moiety with respect to the macrocyclic main plane. The temperature dependence of 1H NMR spectra has been studied in order to get activation parameters of the energetic barrier for the process (VT-NMR and line shape analysis). The rate of the movement clearly depends on the macrocyclic ring size and the nature of the peptidomimetic side chain. Entropic and enthalpic contributions to the free energy of activation are discussed. The rotation of the aromatic ring is closely related to the intramolecular hydrogen bonding pattern, as suggested by temperature factors of NH chemical shifts (DeltadeltaNH/DeltaT) and molecular modeling. The interconnected roles of the solvation and the intramolecular H-bonds have been established by measurements (VT-NMR and DeltadeltaNH/DeltaT) in environments of different polarities and H-bonding abilities. We concluded that the conformational stability of the systems directly depends on the stability of the intramolecular H-bonding pattern. We finally showed how one of these peptidomimetics behaves as a methanol-dependent artificial molecular rotor. In this simple molecular device, the well-defined molecular rotation is tuned by the competition between intramolecular hydrogen bonds and interactions with the solvent.     

Highly collinear three-way photoinduced spectrofluorimetric data arrays modelled with bilinear least-squares: Determination of tetracyclines in surface water samples

A new sensitive method for the determination of three tetracyclines in surface water samples (tetracycline, chlortetracycline and oxytetracycline) using highly collinear data corresponding to photochemical-induced fluorescence excitation emission matrices, modelled with three-way data arrays chemometric tools has been developed. The method involves irradiation of aqueous basic solution of antibiotics with UV light and fluorescence determination of the generated photoproducts after solid phase preconcentration (SPE) with Oasis hydrophilic lipophilic balance (HLB) cartridges. The chemometric models were built by using an eight samples calibration set and samples corresponding to both a validation set and a test set. The latter set containing unsuspected interferents. Considering this latter samples, recoveries of 101.5, 97.9 and 102.2 were obtained for the three analytes. Evaluation of constant and proportional bias and precision were made by using the elliptical joint confidence region (EJCR) test for the estimated intercept and slope.     

Efficient addition reaction of bromonitromethane to aldehydes catalyzed by NaI: a new route to 1-bromo-1-nitroalkan-2-ols under very mild conditions

[Structure: see text] A catalytic NaI-mediated novel synthesis of 1-bromo-1-nitroalkan-2-ols was carried out by reaction of bromonitromethane with a variety of aldehydes, under very mild conditions. When the reaction was performed with chiral N,N-dibenzyl alaninal, the corresponding enantiopure (1S,2S,3S)-3-dibenzylamino-1-bromo-1-nitrobutan-2-ol was obtained with good stereoselectivity. The structure of this enantiopure bromohydrin was established by X-ray analysis.     

Mo(CO)3(NCMe)(PPh3)2: Synthesis, X-ray structure and evaluation of its catalytic activity for the homogeneous hydrogenation of olefins and their mixtures

The complex Mo(CO)₃(NCMe)(PPh₃)₂, was synthesized by the reaction of Mo(NCMe)₃(CO)₃ with two equivalents of PPh₃ and characterized by UV–Vis, IR, NMR and X-ray diffraction. This complex was used as a catalyst precursor for the hydrogenation of 1-hexene, styrene, cyclohexene and 2,3-dimethyl-1-butene and their mixtures under moderate conditions in homogeneous media. Under mild reaction conditions (T = 373 K, P = 60 atm), the substrates showed the following reactivity order: styrene > 1-hexene > cyclohexene > 2,3-dimethyl-1-butene. A quaternary equimolar mixture showed a different hydrogenation order: 1-hexene > cyclohexene > styrene > 2,3-dimethyl-1-butene; the presence of dibenzothiophene or mercury does not interfere with the activity of the catalyst.     

Novel gallium(III) complexes containing phthaloyl derivatives of neutral aminoacids with apoptotic activity in cancer cells

The reaction of N-phthaloylglycine and N-phthaloyl-dl-alanine with trimethylgallium (1:1) yielded the dinuclear complexes [Me₂Ga(μ-O₂CCH₂N(CO)₂C₆H₄)]₂ (1) and RS-[Me₂Ga(μ-O₂CCHMeN(CO)₂C₆H₄)]₂ (2), respectively. The molecular structure of 2 was determined by X-ray diffraction studies. The cytotoxic activity of the organogallium(III) complexes (1 and 2) was tested against human tumour cell lines 8505C anaplastic thyroid cancer, A253 head and neck tumour, A549 lung carcinoma, A2780 ovarian cancer, DLD-1 colon carcinoma and compared with that of cisplatin.The best response of the synthesized gallium complexes, compared with that of cisplatin, was observed against 8505C anaplastic thyroid cancer and DLD-1 colon carcinoma, while the best IC₅₀ values were found for A253 head and neck carcinoma. While the studied carboxylic acids show no proliferative activity, complexes 1 and 2 present very similar cytotoxic activity against all the studied cancer cell lines (IC₅₀ from ca. 5 to 25 μM). The cytotoxicities of complexes 1 and 2 are in all cases higher than that presented by gallium(III) nitrate. In addition DNA laddering method showed that treatment of the studied cell lines with IC₉₀ doses of 1 and 2 resulted in the induction of apoptotic mode of cell death.     

Kernel nonlinearity in heterogeneous evolving networks

In this paper we present an analysis of the interplay between kernel nonlinearity and heterogeneity in preferential attachment (PA) based network models. We define an extended class of heterogeneous PA models where the attachment kernel is a nonlinear function of the connectivity degree of the existing network nodes. Like the original class of heterogeneous PA models, the attachment kernel is also biased by the affinity between the states of pairs of nodes involved in a potential interaction. We show that the class of models exhibit four kinetic regimes in their degree connectivities which are robust against the form of heterogeneity and low-level details of the functional form of the attachment kernel.     

Metastability for small random perturbations of a PDE with blow-up

We study random perturbations of a reaction–diffusion equation with a unique stable equilibrium and solutions that blow-up in finite time. If the strength of the perturbation $\epsilon >0$ is small and the initial data is in the domain of attraction of the stable equilibrium, the system exhibits metastable behavior: its time averages remain stable around this equilibrium until an abrupt and unpredictable transition occurs which leads to explosion in a finite time (but exponentially large in ${\epsilon }^{?2}$). Moreover, for initial data in the domain of explosion we show that the explosion times converge to the one of the deterministic solution.     

Magnetic fields: a tool for the study of organic solar cells

Charge transfer in polymer devices represents a crucial, though highly inaccessible stage of photocurrent generation. In this article we propose studying the properties and behaviour of organic solar cells through the modification of photocurrent generation when an external magnetic field is applied. By allowing the parameters of our theoretical model not to be constrained to any specific material, we are able to show that not only a modest external magnetic field leads to a significant increase in photocurrent intensity, but also how such magnetic field can be used to study in detail the energy levels and transition rates within the polymer compound. Systematic exploration of key properties in organic composites thus can lead to highly optimised devices in which a magnetic field produces an enhancement in the efficiency of polymer solar cells.     

Synchronous scanning derivative spectrofluorimetry for the determination of cadmium with benzyl-2-pyridylketone 2-quinolylhydrazone

Synchronous scanning derivative spectrofluorimetry is used to determine cadmium by means of the fluorescent chelate formed with benzyl-2-pyridylketone 2-quinolylhydrazone at an apparent pH of 11 in 80% (v/v) ethanol. The normal spectrofluorimetric method is also described. The limits of detection are 0.7 and 4.1 ng Cd²⁺ ml^?1, for the first derivative and normal techniques, respectively. Interferences in both methods are reported.