Synthesis and Characterization of Fluorescent,Nonionic, Water Self-Dispersible Oligothiophenes

Two α-septithiophenes substituted at the third position of the middle ring with polyethyleneglycol of different molecular weights (PEG 1000 and PEG 2000) were synthesized using Suzuki condensation. Their structural characterization was performed by ¹H NMR and FT-IR. The thermal behavior of the new synthesized oligothiophenes was investigated by differential scanning calorimetry (DSC) and thermogravimetrical (TGA) analysis. Photophysical properties in solutions were evaluated by UV-vis and fluorescence measurements using different solvents. The amphiphilic nature of the synthesized oligothiophenes and the presence of the PEG side chains induced self-dispersibility in water and the possibility of fluorescent nanoparticles forming by self-assembling. The size of nanoparticles in water was assessed by DLS and AFM investigations.     

Mesomorphic Behavior of Symmetric Azomethine Dimers Containing Different Chromophore Groups

A series of new azomethine dimers was synthesized by the condensation reaction of flexible bis-benzaldehydes with four aromatic amines containing phenyl, naphthyl, anthracene and pyrene groups. Their right structure was confirmed by FTIR and ¹H-NMR spectroscopy and their thermal properties were investigated by thermogravimetric analysis, differential scanning calorimetry and polarized light optical microscopy. A view on their photophysical behavior was gained by UV-vis and photoluminescence spectroscopy. The dimers containing pyrene and anthracene presented liquid crystalline behavior, while the other dimers were crystalline compounds. Two dimers containing pyrene moieties formed mesomorphic glasses and had intense luminescence, promising properties for applications in building optoelectronic devices.     

Polyelectrolyte complexes. II. Specific aspects of the formation of polycation/dye/polyanion complexes

We report on the formation of the polycation/dye/polyanion (PC/D/PA) complexes by the interaction between nonstoichiometric polycation/dye (PC/D) complexes with polyanions. Polycations differed in their content of the (N,N‐dimethyl‐2‐hydroxypropylene ammonium chloride) units in the main chain. Poly(sodium acrylate) (NaPA), poly(sodium 2‐acrylamido‐2‐methylpropane sulfonate) (NaPAMPS) and poly(sodium styrenesulfonate) (NaPSS) were used as polyanions. Crystal Ponceau 6R (CP6R) and Ponceau 4R (P4R) with two or three sulfonic groups were used as anionic dyes. The interaction between nonstoichiometric PC/D complexes and polyanions was followed by UV‐VIS spectroscopy, viscometry, and conductometry measurements. Formation of PC/D/PA complexes takes place mainly by the electrostatic interaction between the polyanion and the free positive charges of the nonstoichiometric PC/D complex. The stoichiometry and the stability of the tricomponent complexes depended on the polycation structure, the structure and molecular weight of polyanion, the dye structure, and the P/D molar ratio. A high amount of the dye was excluded from the complex before the end point when a branched polycation was used. The higher the solubility of the dye the lower the stability of the PC/D/PA complexes. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 409–418, 1999     

The Melting Temperature of 99.97 wt.% Al Estimated from Activation Energy for Viscous Flow

The viscous flow phenomenon in molten aluminium and the viscosity, in the vicinity of its melting temperature, was analyzed. When the temperature decreases, both the viscosity and the activation energy for viscous flow increase. This is explained on the basis of the atomic rearrangement due to interatomic interactions prior to the separation of the solid phase. The latter was found to be nonlinear as the temperature is decreased wherein the solid phase is separated from the liquid. The second derivative of the activation energy for viscous flow with respect to temperature was found to show discontinuity in the vicinity of the melting temperature. Thus, the second derivative offers a way of estimating the melting temperature of metals. Our estimations indicate that the break of the second derivative vs. temperature could be observed at 938 K.     

A method to convexify functions via curve evolution

This paper is devoted to a new method which allows to compute the convex envelope of a given function, by an evolution equation and techniques of curve evolution. We study the problem in the context of viscosity solutions and we propose numerical algorithms, to convexify a function, in one and two dimensions. In the end, we validate the model by presenting various numerical results. Key words: convex envelope, curve evolution, viscosity solutions, nonlinear second order elliptic and parabolic PDE's, finite differences scheme.     

New insight in the structural features of haloadaptation in α-amylases from halophilic Archaea following homology modeling strategy: folded and stable conformation maintained through low hydrophobicity and highly negative charged surface

Proteins from halophilic archaea, which live in extreme saline conditions, have evolved to remain folded, active and stable at very high ionic strengths. Understanding the mechanism of haloadaptation is the first step toward engineering of halostable biomolecules. Amylases are one of the main enzymes used in industry. Yet, no three-dimensional structure has been experimentally resolved for α-amylases from halophilic archaea. In this study, homology structure modeling of α-amylases from the halophilic archaea Haloarcula marismortui, Haloarcula hispanica, and Halalkalicoccus jeotgali were performed. The resulting models were subjected to energy minimization, evaluation, and structural analysis. Calculations of the amino acid composition, salt bridges and hydrophobic interactions were also performed and compared to a set of non-halophilic counterparts. It clearly appeared that haloarchaeal α-amylases exhibited lower propensities for helix formation and higher propensities for coil-forming regions. Furthermore, they could maintain a folded and stable conformation in high salt concentration through highly negative charged surface with over representation of acidic residues, especially Asp, and low hydrophobicity with increase of salt bridges and decrease in hydrophobic interactions on the protein surface. This study sheds some light on the stability of α-amylases from halophilic archaea and provides strong basis not only to understand haloadaptation mechanisms of proteins in microorganisms from hypersalines environments but also for biotechnological applications.