Poly(ester amide)/clay nanocomposites prepared by in situ polymerization of the sodium salt of N‐chloroacetyl‐6‐aminohexanoic acid

Preparation of nanocomposites of organo‐modified montmorillonites and the biodegradable poly(ester amide) derived from glycolic acid and 6‐aminohexanoic acid has been evaluated by the in situ polymerization technique. The reaction was based on the thermal polycondensation of sodium chloroacetylaminohexanoate, which has the formation of the sodium chloride salt as the driving force of the process. Polymerized samples were studied by means of X‐ray diffraction and transmission electron microscopy. The most dispersed structure was obtained by addition of C25A organoclay. Evaluation of thermal stability and crystallization behavior of these samples showed significant differences between the neat polymer and its nanocomposite with C25A. Isothermal and nonisothermal calorimetric analyses of the polymerization reaction revealed that the kinetics was highly influenced by the presence of the silicate particles. Crystallization of the polymer was observed to occur when the process was isothermally conducted at temperatures lower than 145 °C. In this case, dynamic FTIR spectra and WAXD profiles obtained with synchrotron radiation were essential to study the polymerization kinetics. Clay particles seemed to reduce chain mobility and the Arrhenius preexponential factor. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3616–3629, 2009     

Asymmetric synthesis of (R)- and (S)-4-methyloctanoic acids. A new route to chiral fatty acids with remote stereocenters

The enantioselective synthesis of both enantiomers of 4-methyloctanoic acid, one major aggregation pheromone component of the rhinoceros beetles of the genus Oryctes and an important aroma compound, is described. The key step of the synthesis is based on a stereospecific alkylation with an alcohol-protected alkyl iodide using a pseudoephedrine derivative as a chiral auxiliary followed by subsequent removal of the auxiliary. Both enantiomers are obtained in excellent yields and enantioselectivities (93–94% ee). The strategy outlined allows preparation of a wide variety of enantiopure methyl-branched saturated and unsaturated fatty acids.     

Generic rings for Picard-Vessiot extensions and generic differential equations

Let G be an observable subgroup of GL_n. We produce an extension of differential commutative rings generic for Picard-Vessiot extensions with group G.     

Crystallization kinetics of PGBG4: A sequential poly(ester amide) derived from glycine, 1,4‐butanediol,and adipic acid

Isothermal crystallization kinetics of a new sequential poly(ester amide) derived from glycine, 1,4‐butanediol, and adipic acid was investigated with differential scanning calorimetry and optical microscopy. The Avrami analysis was performed to obtain the kinetic parameters of primary and secondary crystallization. The experimental data indicate a heterogeneous nucleation with spherical growth geometry for the primary crystallization, whereas a linear growth within formed spherulites is characteristic of the last crystallization stages. The Lauritzen–Hoffman analysis was also undertaken to determine the different crystallization regimes, having estimated the corresponding nucleation constants. Temperature dependence of the normalized crystallization‐rate constants was tested with different theoretical equations. These allow an estimation of a temperature close to 90 °C for the maximum crystallization rate. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 903–912, 2003     

Tunable DNA photocleavage by an acridine-imidazole conjugate

We report the synthesis and characterization of photonucleases N,N'-bis[2-[bis(1H-imidazol-4-ylmethyl)amino]ethyl]-3,6-acridinediamine (7) and N-[2-[bis(1H-imidazol-4-ylmethyl)amino]ethyl]-3,6-acridinediamine (10), consisting of a central 3,6-acridinediamine chromophore attached to 4 and 2 metal-coordinating imidazole rings, respectively. In DNA reactions employing 16 metal salts, photocleavage of pUC19 plasmid is markedly enhanced when compound 7 is irradiated in the presence of either Hg(II), Fe(III), Cd(II), Zn(II), V(V), or Pb(II) (low-intensity visible light, pH 7.0, 22 degrees C, 8-50 microM 7). We also show that DNA photocleavage by 7 can be modulated by modifying buffer type and pH. Evidence of metal complex formation is provided by EDTA experiments and by NMR and electrospray ionization mass spectral data. Sodium azide, sodium benzoate, superoxide dismutase, and catalase indicate the involvement of type I and II photochemical processes in the metal-assisted DNA photocleavage reactions. Thermal melting studies show that compound 7 increases the Tm of calf thymus DNA by 10 +/- 1 degrees C at pH 7.0 and that the Tm is further increased upon the addition of either Hg(II), Cd(II), Zn(II), or Pb(II). In the case of Fe(III) and V(V), a colorimetric assay demonstrates that compound 7 sensitizes one electron photoreduction of these metals to Fe(II) and V(IV), likely accelerating the production of type I reactive oxygen species. Our data collectively indicate that buffer, pH, Hg(II), Fe(III), Cd(II), Zn(II), V(V), Pb(II), and light can be used to "tune" DNA cleavage by compound 7 under physiologically relevant conditions. The 3,6-acridinediamine acridine orange has demonstrated great promise for use as a photosensitizer in photodynamic therapy. In view of the distribution of iron in living cells, compound 7 and other metal-binding acridine-based photonucleases should be expected to demonstrate excellent photodynamic action in vivo.     

Sulfur hexafluoride's liquid-vapor coexistence curve, interfacial properties, and diffusion coefficients as predicted by a simple rigid model

We present here molecular-dynamics simulation results of the vapor-liquid coexistence curve, surface tension, and self-diffusion coefficients of sulfur hexafluoride. Sulfur hexafluoride is modeled as a rigid molecule, following the model proposed by Pawley [Mol. Phys. 43, 1321 (1981)]. Vapor-liquid coexistence curve and surface tension are obtained through direct molecular-dynamic simulations in the NVT ensemble. Simulation results are able to reproduce the qualitative shape of the vapor-liquid envelope. However, lower densities, a higher critical temperature, and an overestimated surface tension are obtained here. Those deviations are explained on the basis of the rigidity of the molecular model used. Self-diffusion coefficients are calculated from simulations in the NVE ensemble for different gas states at atmospheric pressure. The rigid model performs better for dynamical properties since simulation results provide very good agreement with available experimental data in this case.     

Towards the effective potential of the littlest Higgs model

We compute the relevant parameters of the combined Higgs and φ scalar effective potential in the littlest Higgs (LH) model. These parameters are obtained as the sum of two kinds of contributions. The first one is the one-loop radiative corrections coming from fermions and gauge bosons. The second one is obtained at tree level from the higher-order effective operators needed for the ultraviolet completion of the model. Finally, we analyze the restrictions that the requirement of reproducing the standard electroweak symmetry breaking of the SM set on the LH model parameters.     

Use of on-line liquid chromatography-nuclear magnetic resonance spectroscopy for the rapid investigation of flavonoids from Sorocea bomplandii

A HPLC method, using photochemically-induced fluorescence detection, is described for the separation and determination of four phenylurea herbicides including diuron, isoproturon, linuron and neburon. A post-column photoreactor, consisting of a reactor knitted around a 4 W xenon lamp, has been included between the column and the detector, in order to transform the non-fluorescent herbicides into fluorophors. The influence of mobile phase composition, flow-rate, pH, and buffer concentration has been studied. An acetonitrile–buffer solution of potassium phosphate dibasic of pH 7 and 0.01 M concentration (60:40, v/v), was selected as optimum. For the fluorimetric detection, optimal excitation/emission wavelengths 324/403, 301/433, 335/411 and 326/385 nm were selected for the determination of diuron, isoproturon, linuron and neburon, respectively. The detection limits ranged between 0.07 and 0.46 μg/ml, according to the compound.     

Unprecedented Blue Intrinsic Photoluminescence from Hyperbranched and Linear Polyethylenimines: Polymer Architectures and pH‐Effects

The intrinsic photoluminescence properties of hyperbranched polyethylenimines (PEIs) and their linear counterpart (LPEIs) have been studied in absence of any classical fluorescent probes. The comparison of the inherent fluorescence emission between hyperbranched polyethylenimines and their linear analogues demonstrates that linear polyamines are capable of producing strong intrinsic photoluminescence species having long excited lifetimes without need of having a tridimensional‐branched structure. The creation of inherently fluorescent polymeric centers from hyperbranched and linear polyethyleimines can be modulated by specific chemical modification and oxidation of amine groups as well as by adjusting the acidity of the polymer.