Reversible addition-fragmentation chain transfer polymerization of N-isopropylacrylamide: a comparison between a conventional and a fast initiator

The reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide (NIPAM) was studied to determine the reasons for deviation of experimental molecular weights to lower molecular weight at high monomer conversion when S-1-dodecyl-S-(alpha,alpha'-dimethyl-alpha' '-acetic acid)trithiocarbonate (CTAm) and S,S-bis(alpha,alpha'-dimethyl-alpha' '-acetic acid)trithiocarbonate (CTAd) were used as RAFT agents at 65 degrees C. For this purpose, experiments were performed in N,N'-dimethylformamide (DMF) at the NIPAM/CTA ratio of 200 with initiators capable of yielding fast and slow initiation, respectively by photochemical and thermal process, either at ambient temperature or at 65 degrees C. When the polymerization of NIPAM was conducted under these conditions with Irgacure-2959 (IRGC) as photoinitiator, a continuing supply of primary radicals by incremental initiator addition was required to achieve reasonably high conversion. This effect was also apparent by the loss of linearity of the first-order kinetic plot with a conventional initiator (4,4-azobis(4-cyanovaleric acid) (ACVA) as azo-initiator, 10h (t1/2) decomposition at 65 degrees C) indicating that steady-state concentration of the macroradical decreases significantly with the initiator consumption. Nevertheless, polymers with predictable number-average molecular weight Mn (i.e., based on [monomer]/([CTA] + [initiator]) ratio) and narrow polydispersities were obtained (PDIs < 1.2) with CTAm indicating that the process of chain growth was controlled. When CTAd was used, instead of CTAm, the polymers obtained were characterized by a larger polydispersity (1.2 < PDIs < 1.3). The so-called "living steady-state concentration" in chain equilibration together with the linear dependence of Mn vs conversion was observed only when the 200/1 NIPAM/CTA mixture in DMF was subjected to a permanent photoirradiation at 65 degrees C. With ACVA, the deviation of the experimentally measured molecular weights at high conversion was accounted for by the simultaneous self-initiated polymerization of NIPAM with the controlled process in the presence of CTA at 65 degrees C. Similar drift from the linear dependence Mn vs conversion was also observed at 65 degrees C when a significant number of low molecular weight polymer chains were generated intentionally by photodecomposition of IRGC.     

Crystal structure of monomethylammonium monochlorodibromomercurate(II)

The crystal structure of monomethylammonium monochlorodibromomercurate (II) was refined from single crystal X-ray data including the fractional contribution of centrosymmetric domains. The refinement converged toR=0.05 in space groupC2. The fraction of structure and its inverse were detected in the refinement. The structure is one-dimensional consisting of distorted tetrahedra (HgCl₂Br₂) connected together by chlorine atoms, The CH₃NH ₃ ⁺ groups are connected to the chains by hydrogen bonds to the halogen atoms contributing to the cohesion of the crystal.     

Crystal structure of monomethylammonium monochlorodibromomercurate(II)

The crystal structure of monomethylammonium monochlorodibromomercurate (II) was refined from single crystal X-ray data including the fractional contribution of centrosymmetric domains. The refinement converged toR=0.05 in space groupC2. The fraction of structure and its inverse were detected in the refinement. The structure is one-dimensional consisting of distorted tetrahedra (HgCl₂Br₂) connected together by chlorine atoms, The CH₃NH ₃ ⁺ groups are connected to the chains by hydrogen bonds to the halogen atoms contributing to the cohesion of the crystal.     

New Sobolev-Weinstein Spaces and Applications

In this paper, we consider the generalized Weinstein operator $\Delta_{W}^{d,\alpha,n}$, we introduce new Sobolev-Weinstein spaces denoted $\mathscr H_{\alpha,d,n}^{s}(\mathbb{R}_{+}^{d+1}),$ $s\in\mathbb{R},$ associated with the generalized Weinstein operator and we investigate their properties. Next, as application, we study the extremal functions on the spaces $\mathscr H_{\alpha,d,n}^{s}(\mathbb{R}_{+}^{d+1})$ using the theory of reproducing kernels.     

Synthesis and reactivity of two new trichloromethyl substituted dihydroisoquinoline-derived oxaziridines

N-Alkyl oxaziridines may be used as reagents for the oxidation of sulfides in acid-promoted reactions. This article reports on a simple and efficient synthesis of two new trichloromethyl substituted dihydroisoquinoline oxaziridines, a new family of organic oxidizing agents. Their oxygen transfer capability with respect to sulfides as model substrates and in the absence of acid is investigated.     

Local nonlinear dynamics of MEMS arches actuated by fringing-field electrostatic actuation

Nonlinear Dynamics - The nonlinear dynamic behavior of a resonant MEMS arch microbeam actuated by fringing electric actuation is investigated in this paper. The arch microbeam is loaded with DC and...     

Synthesis and characterization of Ni (II), Cu (II), Fe (II) and Fe3O4 nanoparticle complexes with tetraaza macrocyclic Schiff base ligand for antimicrobial activity and cytotoxic activity against cancer and normal cells

This work describes a simple synthesis of complexes of the type [M(C₃₂H₂₈N₄)Cl₂], where M = Ni (II), Cu (II) and Fe (II) and a novel complex of magnetite nanoparticle (Fe₃O₄NP) inside (INS) tetraaza macrocyclic Schiff base ligand (C₃₂H₂₈N₄): [Fe₃O₄NP‐INS‐(C₃₂H₂₈N₄)], which was prepared by using a novel co‐precipitation method of coordinated ferric ion (Fe³⁺) in the complex [Fe(C₃₂H₂₈N₄)Cl₂] under mild conditions. The synthesized compounds were characterized and compared with a various physic‐chemical techniques like: Fourier transform infrared (FT‐IR), ultraviolet–visible spectroscopic techniques (UV–Vis), 1‐dimensional (1D) ¹H‐NMR, ¹³C‐NMR spectroscopic techniques, mass spectra, Powder X‐ray diffraction (PXRD), Vibrating sample magnetometer (VSM), Scanning electron microscopy (SEM), elemental analysis and molar conductance measurements. Furthermore, the highest saturation magnetization was 26.56 emu.g^?1 obtained from [Fe₃O₄NP‐INS‐(C₃₂H₂₈N₄)] (diameter of Fe₃O₄NPs~20.87 nm) that prove easy separation by an external magnetic field. In vitro screening of all the compounds against different species of bacteria and fungi shows that [Fe₃O₄NP‐INS‐(C₃₂H₂₈N₄)] is effective against the tested strains as compared to the tetraaza macrocyclic ligand and selected complexes. The cytotoxic activity of the all compounds was also examined in 3 human tumor cell lines as U87, MDA‐MB‐231 and LS‐174. The complex [Fe₃O₄NP‐INS‐(C₃₂H₂₈N₄)] shows moderate and strong cytotoxic activity against brain cancer, colon cancer and breast cancer (U87, MDA‐MB‐231 and LS‐174 respectively), without showing cytotoxicity towards peripheral blood mononucleocyte (PBMC) cells.     

Blue Highly Fluorescent Boranil Derived From Anil Ligand: Synthesis,Characterization, Experimental and Theoretical Evaluation of Solvent Effect on Structures and Photophysical Properties

In this study, we report the design and the synthesis of a Schiff base; Anil and its corresponding Boron Difluoride complexe; Boranil. The synthesis procedure was carried out adopting new, optimized reaction conditions. The Boranil dye presents the advantage to be emissive in solution. 1H and 19F NMR along with FTIR confirmed both compound's structure. To gain a better understanding of the solvatochromic behavior of Anil and Boranil, the dependence of the absorption spectra on the solvent's polarity was studied in depth. Thus, UV–Vis spectroscopy was performed in five selected solvents. In addition to the solvent's polarity effect, the influence of BF2 moiety introduction on the molecule's photophysical properties was also evaluated. When examining different absorption spectra, we found that the title fluorescent dye exhibited weak solvatochromic (11 nm in THF) as well as a slight redshift broader and relatively more structured absorption spectra after complexation. Besides, we investigate the obtained key structure–property relationships through DFT and TD-DFT calculations using a 6–311++ G (d, p) basis set. Quantum chemical calculations allowed confirming proposed structures and understanding their electronic structure in larger details. Theoretical results also showed good agreement with the experimental findings. Finally, the frontier molecular orbitals were investigated to illustrate the pi-conjugation and charge transfer effect.     

MEIR-KEELER TYPE CONTRACTIONS FOR TRIPLED FIXED POINTS

In 2011,Berinde and Borcut [6] introduced the notion of tripled fixed point in partially ordered metric spaces.In our paper,we give some new tripled fixed point theorems by using a generalization of Meir-Keeler contraction.