Interpreting “Acidity” as a Global Property Controlling Comonomer Reactivity in Olefin Polymerization

A possible rationale for the different catalytic behaviors of systems based on <i>rac</i>-(ethylenebis­(1-indenyl))zirconium dichloride (<i>rac</i>-EBIZrCl₂), <i>rac</i>-(ethylenebis­(1-indenyl))­hafnium dichloride (<i>rac</i>-EBIHfCl₂), and <i>rac</i>-(isopropylidenebis­(1-indenyl))zirconium dichloride (<i>rac</i>-iPrBIZrCl₂) toward ethene–styrene copolymerization has been sought by studying related active systems. For this purpose, the metallocene ion pairs (IPs) <i>rac</i>-EBIZrMeMeB­(C₆F₅)₃, <i>rac</i>-EBIHfMeMeB­(C₆F₅)₃, and <i>rac</i>-iPrBIZrMeMeB­(C₆F₅)₃ have been synthesized and their structures in solution explored with ROESY and pulsed gradient NMR spectroscopy. The energetics of dynamical processes relevant for catalysis that can be used as indicators of the cation acidity have been studied with variable-temperature NMR experiments and density functional theory (DFT). NMR experiments successfully provided IP structural details in solution and also indicated the presence of an intricate dynamic behavior for all the IPs. DFT results, instead, indicated quantitatively how changing the metal and/or the ancillary ligand bridge influences the energetics of the active species and modifies the reaction energy profile. The theoretical results also drew attention to the fact that finding a rationale for the ligand influence on the catalytic behavior of <i>rac</i>-EBIZrCl₂/MAO and <i>rac</i>-iPrBIZrCl₂/MAO in ethene–styrene copolymerization requires not only considering the steric effects but also determining how subtle changes in the ligand sphere affect the capability of the metal center to accept electrons from the counteranion or the olefins

Modulating Antimicrobial Activity by Synthesis: Dendritic Copolymers Based on Nonquaternized 2-(Dimethylamino)ethyl Methacrylate by Cu-Mediated ATRP

The synthesis of novel star-like heteroarms polymers A­(BC)_<i>n</i> containing m-PEG (block A), methylmethacrylate (MMA), and nonquaternized 2-(dimethylamino)­ethyl methacrylate (DMAEMA) (blocks BC) is here reported. We demonstrated that copolymer films with comparable amounts of DMAEMA have antimicrobial properties strongly depending on the topological structure (i.e., the number of arms) of the composing copolymers. We interpret the highest antimicrobial activity of A­(BC)₂ with respect to A­(BC)₄ and linear copolymers (respectively, A­(BC)₂ ≥ A­(BC)₄ > A­(BC)) as probably due to the formation of strong hydrogen bonds between close amino-ammonium groups in the A­(BC)₂ film. Strong hydrogen bonds seem to be somewhat disfavored in the case of the linear species by the difference in both polymer architecture and film morphology compared with the A­(BC)₂ and A­(BC)₄ architectures

pH-sensitive polymersomes: controlling swelling via copolymer structure and chemical composition

<p>pH-sensitive vesicles used as drug delivery systems (DDSs) are generally composed of protonable copolymers. The disaggregation of these nanoparticles (NPs) during drug release implies the dispersion of positively charged cytotoxic polyelectrolytes in the human body. To alleviate such issue, we synthesised A(BC)<i>_n</i> amphiphilic block copolymers with linear (<i>n</i> = 1) and branched (<i>n</i> = 2) architectures to obtain pH-sensitive vesicles capable of releasing drugs in acidic conditions via controlled swelling instead of disaggregation. We obtained this feature by fine-tuning the relative amount of pH-sensitive and hydrophobic monomers. We studied pH-driven swelling by measuring NPs size in neutral and acidic conditions, the latter typical of tumours or inflamed tissues (pH∼6) and lysosomes (pH∼4.5). Dynamic light scattering (DLS) and zeta potential data provided useful indications about the influence of architecture and chemical composition on NPs swelling, stability and polycation release. Results demonstrated that vesicles made of linear copolymers with ∼22–28% in mol of protonable monomers in the ‘BC’ block swelled more than other species following a pH change from pH 7.4 to pH 4.5. We finally evaluated the cytotoxicity of vesicles composed of linear species, and paclitaxel (PTX) release from the latter in both cancer and normal cells.</p

Dicopper(II) Mozobil^TM: a dinuclear receptor for the pyrophosphate anion in aqueous solution

<p>In this work, we investigated the dicopper(II) complex of Mozobil^TM as a potential receptor for anions in MeOH and MeOH/water mixture. The results were compared with those obtained for the mononuclear complex, copper(II) benzyl-cyclam as a model system. Experimental investigations were also supported by computational studies on both the dinuclear and the mononuclear species. Among the investigated anionic guests, the dicopper complex showed an outstanding affinity for the pyrophosphate anion, leading to the formation of a stable adduct in MeOH solution. Our computational studies strongly suggested a 2:2 stoichiometry for the adduct. At least in MeOH, this dimeric structure, with two pyrophosphate anions sandwiched between two dicopper Mozobil^TM units, is stabilized by H-bonding interactions between the receptor and pyrophosphate. In MeOH:water mixture, beside the strong competition of solvent, the affinity toward the anion was preserved. We exploited this property to develop a novel indicator displacement assay (IDA) for pyrophosphate in aqueous solution, using Pyrocatechol Violet (PV) as the indicator.</p

Different Insight into Amphiphilic PEG-PLA Copolymers: Influence of Macromolecular Architecture on the Micelle Formation and Cellular Uptake

One constrain in the use of micellar carriers as drug delivery systems (DDSs) is their low stability in aqueous solution. In this study “tree-shaped” copolymers of general formula mPEG-(PLA)_n (<i>n</i> = 1, 2 or 4; mPEG = poly­(ethylene glycol) monomethylether 2K or 5K Da; PLA = atactic or isotactic poly­(lactide)) were synthesized to evaluate the architecture and chemical composition effect on the micelles formation and stability. Copolymers with mPEG/PLA ratio of about 1:1 wt/wt were obtained using a “core-first” synthetic route. Dynamic Light Scattering (DLS), Field Emission Scanning Electron Microscopy (FESEM), and Zeta Potential measurements showed that mPEG_2K-(PD,LLA)₂ copolymer, characterized by mPEG chain of 2000 Da and two blocks of atactic PLA, was able to form monodisperse and stable micelles. To analyze the interaction among micelles and tumor cells, FITC conjugated mPEG-(PLA)_<i>n</i> were synthesized. The derived micelles were tested on two, histological different, tumor cell lines: HEK293t and HeLa cells. Fluorescence Activated Cells Sorter (FACS) analysis showed that the FITC conjugated mPEG_2K-(PD,LLA)₂ copolymer stain tumor cells with high efficiency. Our data demonstrate that both PEG size and PLA structure control the biological interaction between the micelles and biological systems. Moreover, using confocal microscopy analysis, the staining of tumor cells obtained after incubation with mPEG_2K-(PD,LLA)₂ was shown to be localized inside the tumor cells. Indeed, the mPEG_2K-(PD,LLA)₂ paclitaxel-loaded micelles mediate a potent antitumor cytotoxicity effect