Zinaida B. Shifrina

Magnetically Recoverable Catalysts Based on Polyphenylenepyridyl Dendrons and Dendrimers

Here, a systematic study of magnetite nanoparticle (NP) formation in the presence of functional polyphenylenepyridyl dendrons and dendrimers of different generations and structures (such as focal groups, periphery and a combination of phenylene and pyridyl moieties) has been reported. For certain dendron/dendrimer concentrations and structures, well-dispersible, multi-core, flower-like crystals are formed which display ferrimagnetic-like behavior. It is noteworthy that the least complex second generation polyphenylenepyridyl dendrons with a carboxyl focal group already allow formation of flower-like crystals. Magnetically recoverable catalysts were obtained via Pd NP formation in the dendron/dendrimer shells of magnetite NP and tested in selective hydrogenation of dimethylethynylcarbinol to dimethylvinylcarbinol. Dependences of catalytic activity and selectivity on the dendron/dendrimer generation and structure, type of Pd species, and Pd NP size have been demonstrated. High selectivity and activity of these catalysts along with easy catalyst recovery and successful repeated use make them promising in catalytic hydrogenation.

Functionalization of Magnetic Nanoparticles with Amphiphilic Block Copolymers: Self-Assembled Thermoresponsive Submicrometer Particles

For the first time the four block copolymers derived from 1-alkyl[2-(acryloyloxy)ethyl]dimethylammonium bromides with hexyl (ADA) or cetyl (ADHA) groups and 2-hydroxyethylacrylate (HEA) or N-isopropylacrylamide (NIPAM) were synthesized and employed for functionalization of monodisperse iron oxide nanoparticles (NPs). The polyADA (pADA) or polyADHA (pADHA) block consists of long hydrophobic tails (C(6) or C(16)) connected to a positively charged quaternary ammonium group, making this block amphiphilic. The second block was either fully hydrophilic (pHEA) or thermoresponsive (pNIPAM). The dependence of the NP coating on the length of the hydrophobic tail in the amphiphilic block, the composition of the hydrophilic block, and the NP sizes have been studied. Unusual self-assembling of iron oxide NPs into well-defined composite submicrometer particles was observed for pADHA-b-pNIPAM in the wide range of concentrations (at the pADHA repeating unit concentrations of 0.065 × 10(-2)-2.91 × 10(-2) mmol/mL per 1 mg/mL NPs) but only two concentrations, 1.62 × 10(-2) and 1.94 × 10(-2) mmol/mL, led to regular spherical particles. The thermoresponsive behavior of these composite particles was tested using ζ-potential and dynamic light scattering measurements, while the morphology of particles was characterized by transmission electron microscopy. Coating of NPs with pADHA-b-pHEA results in the formation of individually coated NPs. The different composite particle morphologies are explained by different properties of pHEA and pNIPAM. It is demonstrated that the composite particles based on pADHA-b-pNIPAM are responsive to a magnetic field and can be recommended as magnetic stoppers in biorelated membrane separations. The incorporation of Pd species in submicrometer particles makes them promising candidates for catalytic applications as magnetically recoverable catalysts with a high magnetic response.

Ru-Containing Magnetically Recoverable Catalysts: A Sustainable Pathway from Cellulose to Ethylene and Propylene Glycols.

Biomass processing to value-added chemicals and biofuels received considerable attention due to the renewable nature of the precursors. Here, we report the development of Ru-containing magnetically recoverable catalysts for cellulose hydrogenolysis to low alcohols, ethylene glycol (EG) and propylene glycol (PG). The catalysts are synthesized by incorporation of magnetite nanoparticles (NPs) in mesoporous silica pores followed by formation of 2 nm Ru NPs. The latter are obtained by thermal decomposition of ruthenium acetylacetonate in the pores. The catalysts showed excellent activities and selectivities at 100% cellulose conversion, exceeding those for the commercial Ru/C. High selectivities as well as activities are attributed to the influence of Fe3O4 on the Ru(0)/Ru(4+) NPs. A facile synthetic protocol, easy magnetic separation, and stability of the catalyst performance after magnetic recovery make these catalysts promising for industrial applications.

Proof of Concept: Magnetic Fixation of Dendron-Functionalized Iron Oxide Nanoparticles Containing Palladium Nanoparticles for Continuous-Flow Suzuki Coupling Reactions

A new concept for the magnetic immobilization of catalytically active material has been developed for continuous-flow Suzuki cross-coupling reactions. The reversible immobilization of the magnetic catalyst material inside a novel capillary microreactor has been achieved by utilizing a newly designed reactor housing with 208 small permanent magnets. As a catalyst material, magnetic Fe3O4 nanoparticles decorated with polyphenylenepyridyl dendrons and loaded with Pd nanoparticles have been employed. Both batch and continuous-flow experiments prove the activity of the catalyst and the applicability of this new microreactor concept.

Zinc-Containing Magnetic Oxides Stabilized by a Polymer: One Phase or Two?

Here we developed a new family of Zn-containing magnetic oxides of different structures by thermal decomposition of Zn(acac)2 in the reaction solution of preformed magnetite nanoparticles (NPs) stabilized by polyphenylquinoxaline. Upon an increase of the Zn(acac)2 loading from 0.15 to 0.40 mmol (vs 1 mmol of Fe(acac)3), the Zn content increases, and the Zn-containing magnetic oxide NPs preserve a spinel structure of magnetite and an initial, predominantly multicore NP morphology. X-ray photoelectron spectroscopy (XPS) of these samples revealed that the surface of iron oxide NPs is enriched with Zn, although Zn species were also found deep under the iron oxide NP surface. For all the samples, XPS also demonstrates the atom ratio of Fe(3+)/Fe(2+) = 2:1, perfectly matching Fe3O4, but not ZnFe2O4, where Fe(2+) ions are replaced with Zn(2+). The combination of XPS with other physicochemical methods allowed us to propose that ZnO forms an ultrathin amorphous layer on the surface of iron oxide NPs and also diffuses inside the magnetite crystals. At higher Zn(acac)2 loading, cubic ZnO nanocrystals coexist with magnetite NPs, indicating a homogeneous nucleation of the former. The catalytic testing in syngas conversion to methanol demonstrated outstanding catalytic properties of Zn-containing magnetic oxides, whose activities are dependent on the Zn loading. Repeat experiments carried out with the best catalyst after magnetic separation showed remarkable catalyst stability even after five consecutive catalytic runs.

Disruption of Amyloid Prion Protein Aggregates by Cationic Pyridylphenylene Dendrimers

Disruption of amyloid protein aggregates is one of the potential therapies for treatment of neurodegenerative disorders such as prion diseases. Here, for the first time we report that pH-independent cationic pyridylphenylene dendrimers are able to disrupt amyloid protein aggregates at physiological pH as exemplified by inclusion bodies of ovine prion protein. The results show that exposure of inclusion bodies to the dendrimers leads to its partial disaggregation and release of the nanosize protein-dendrimer complexes. The complexes were characterized by SDS PAGE, DLS, and Western blotting methods. Thioflavin T fluorescence clearly demonstrated a decrease of amyloidogenic capability of the prion protein upon exposure to the dendrimers. The complexes formed are stable and do not show further aggregation.

Interaction of water-soluble polypyridylphenylene dendrimers with a polymethacrylate anion

Cationic water-soluble dendrimers have been prepared by the alkylation of pyridyl groups in polypyridylphenylene dendrimers of the first four generations, and their interaction with a polymethacrylate anion has been studied. The stability of polyelectrolyte complexes in aqueoussaline solutions has been studied by fluorimetric titration with the use of the pyrenyl-tagged polyanion, and it has been shown that the stability of these complexes significantly increases with the dendrimer generation number and the content of hydrophobic phenylene groups. Based on sedimentation analysis and turbidimetric titration, it is inferred that a significant part of charged groups of dendrimers are inaccessible to interaction with the polyanion and that water-soluble nonstoichiometric polyelectrolyte complexes develop in mixtures of higher generation dendrimers. Modeling results of this study may be useful for designing efficient cationic dendrimer carriers of genetic material and hydrophobic physiologically active compounds.

Enhancing the Catalytic Activity of Zn-Containing Magnetic Oxides in a Methanol Synthesis: Identifying the Key Factors

A new family of Ni-, Co-, and Cr-doped Zn-containing magnetic oxide nanoparticles (NPs) stabilized by polyphenylquinoxaline (PPQ) and hyperbranched pyridylphenylene polymer (PPP) has been developed. These NPs have been synthesized by thermal decomposition of Zn and doping metal acetylacetonates in the reaction solution of preformed magnetite NPs, resulting in single-crystal NPs with spinel structure. For the PPQ-capped NPs, it was demonstrated that all three types of metal species (Fe, Zn, and a doping metal) reside within the same NPs, the surface of which is enriched with Zn and a doping metal, while the deeper layers are enriched with Fe. The Cr-doped NPs at the high Cr loading are an exception due to favored deposition of Cr on magnetite located in the NP depth. The PPP-capped NPs exhibit similar morphology and crystallinity; however, the detailed study of the NP composition was barred due to the high PPP amount retained on the NP surface. The catalyst testing in syngas conversion to methanol demonstrated outstanding catalytic properties of doped Zn-containing magnetic oxides, whose activities are dependent on the doping metal content and on the stabilizing polymer. The PPP stabilization allows for better access to the catalytic species due to the open and rigid polymer architecture and most likely optimized distribution of doping species. Repeat experiments carried out after magnetic separation of catalysts from the reaction mixture showed excellent catalyst stability even after five consecutive catalytic runs.

Hyperbranched pyridylphenylene polymers based on the first-generation dendrimer as a multifunctional monomer

An A6 + B2 approach was applied for the first time to synthesize novel hyperbranched pyridylphenylene polymers by Diels–Alder cyclocondensation reaction. For this, the first-generation pyridylphenylene dendrimer with six ethynyl functionalities (A6) was used as a branching core for the molecule growth. The phenyl-substituted bis(cyclopentadienone)s (B2) of different structures were used as co-monomer in the reaction. A careful choice of reaction conditions allowed us to obtain high molecular weight polymers without undesirable gelation. The molecular weight of the polymers varied in the range of 10 800–80 100 with a polydispersity degree of 1.69 to 4.07 according to SEC analysis. The 1H and inverse-gated decoupling 13C NMR combined with heteronuclear single quantum correlation and heteronuclear multiple bond correlation measurements were used to estimate the branching degree of the polymers synthesized.

Multicore iron oxide mesocrystals stabilized by a poly(phenylenepyridyl) dendron and dendrimer: role of the dendron/dendrimer self-assembly.

We report the formation of multicore iron oxide mesocrystals using the thermal decomposition of iron acetyl acetonate in the presence of the multifunctional and rigid poly(phenylenepyridyl) dendron and dendrimer. We thoroughly analyze the influence of capping molecules of two different architectures and demonstrate for the first time that dendron/dendrimer self-assembly leads to multicore morphologies. Single-crystalline ordering in multicore NPs leads to cooperative magnetic behavior: mesocrystals exhibit ambient blocking temperatures, allowing subtle control over magnetic properties using a minor temperature change.