Electron Donor Compounds Research Articles

Modified titanium-magnesium nanocatalysts in the polymerization of isoprene

The polymerization of isoprene on titanium-magnesium nanocatalysts modified with electron-donor compounds based on organic phosphines and sulfides has been studied. It was shown that the catalyst modification makes it possible to increase the content of trans-1,4 units in polyisoprene up to 97% (according to the data of 1H NMR spectra). In the case of a catalyst modified with tributylphosphine, the effects of the phosphorus-to-titanium ratio on the polymerization kinetics, on the microstructure of trans-1,4-polyisoprene, and on the molecular mass of the polymer have been estimated.

Graft Copolymeriztion of Glycidyl Methacrylate/Styrene onto Polypropylene in Solid State

Radical grafting of glycidyl methacrylate (GMA) onto polypropylene (PP) powder was studied in this research. The reaction temperature was below the melting point of PP so that the reaction was carried out in solid state. Styrene (St) acting as electron donor compounds was used as grafting comonomer and xylene was used as interfacial agent to swell the PP powder. The effects of monomer and comonomer concentration on the graft degree were investigated. The FT-IR spectra of the grafted PP demonstrated that GMA and St were grafted onto PP backbone successfully and the polarization optical micrographs showed that the grafted chains acted as nucleating agent and speeded up the crystallization process.

Crystal solvates of porphyrins and metalloporphyrins

The published data on the crystal solvates with nonpolar aromatic and electron-donor compounds obtained using different research methods as well as our own experimental results obtained by thermogravimetric analysis of the porphyrins and metalloporphyrins of natural and synthetic origin are generalized. The influence of the molecular structure of the porphyrins and metalloporphyrins on the composition, structural parameters, thermal and energy stability of crystal solvates formed through specific σ-and π-complexes with molecular ligands are considered.

Quaterthiophene-based multipods as promising materials for solution-processible organic solar cells and field effect transistors

The preparation and characterization of novel electron donor compounds with two ( D1) and four ( D2) quaterthiophene-containing arms attached to the flexible carbosilane–siloxane core are described. These materials were investigated in organic field effect transistors and photovoltaic cells. A power conversion efficiency of ∼0.9% obtained for D1:[70]PCBM blends is one of the highest values achieved up to now for solution-processible small molecular bulk heterojunction solar cells with large band-gap oligothiophene-based donor materials comprising no other chromophore units.

Aromatic Electron Acceptors Change the Chirality Dependence of Single-Walled Carbon Nanotube Oxidation

Single-walled carbon nanotubes (SWNTs) dispersed in sodium dodecyl sulfate (SDS) suspensions exhibit diameter-dependent protonation and oxidative quenching of their E11 fluorescence. This nanotube-diameter-based difference in solution chemistry is substantially changed when complexed with aromatic electron-accepting compounds such as nitrobenzene, o-nitrotoluene, 2,4-dinitrotoluene, and 9-nitroanthracene. SWNTs were suspended in aqueous SDS, and their emission spectra were measured as a function of pH and concentration of oxidizing agent (hypochlorite or hydrogen peroxide) to observe their protonation and oxidation behavior. The chirality dependence of the protonation and oxidation behavior became substantially reduced upon the addition of nitroaromatic compounds to the aqueous suspension. This suggests the possibility of forming an electron donor-acceptor (EDA) complex, where the SWNT is the electron donor and nitroaromatic compounds are the acceptor, and the resulting supramolecular complex exhibits different redox behavior than the uncomplexed SWNT.

Synthesis and redox behavior of new ferrocene-π-extended-dithiafulvalenes: An approach for anticipated organic conductors

A number of new ferrocene-π-extended-dithiafulvalenes were successfully synthesized as new electron donor compounds. The chemical structures and electrochemical behaviors of these compounds were investigated using several spectroscopic methods. The synthesis of these compounds was achieved using the modified Wittig–Horner cross-coupling reaction using n-BuLi/THF at temperature varies from −78 °C to 0 °C. These new classes of bis(1,3-dithiafulvalene)ferrocenes have the 1,3-dithiole ring system separated by ferrocene as conjugated spacer. The ferrocene-dithiafulvalenes derivatives 9 and 12 were prepared as side products during the synthesis of the targeted compounds as bis(1,3-dithiafulvalene)ferrocenes 8, 10 and 11 in variable yields. The redox properties of the compounds have been investigated by cyclic voltammetry at ambient temperature using tetra-n-butylammonium perchlorate (TBAP) as the supporting electrolyte compared to ferrocene and the derivative 9. In CH2Cl2 on a Pt working electrode and at ambient temperature, two oxidation waves associated with two reduction waves at scan rates 100 mV s−1 were observed for 9 and 12. In contrast the anodic peak potential of bis(1,3-dithiafulvalene)ferrocenes 8, 10 and 11 exhibited two and three oxidation waves associated with two reduction waves.

“Polydentate phosphine oxides as new electron-donor components of titanium-magnesium catalysts for the synthesis of isotactic poly(1-butene)”

Isotactic poly(1-butene) (PB-1) shows a number of very interesting properties, a unique combination of excellent creep resistance and high flexibility being the most important. The polymer has the lowest flexural modulus of all plastics used for tube manufacturing. Owing to the valuable properties of PB-1, its production is increasing in spite of technological difficulties [1]. The industrial synthesis of poly( α -olefins) utilizes mainly TiCl 4 –MgCl 2 catalysts (TMCs) modified with electron-donor compounds capable of forming chelate complexes to increase isospecificity. At present, alkylalkoxysilanes are mainly used as such compounds (external donors, EDs) introduced with the AlEt 3 cocatalyst [1, 2]. At the same time, a search for other types of electron-donor components providing the necessary combination of catalyst properties is in progress. In this work, we studied for the first time the possibility of using polydentate phosphine oxides as electron-donor components of TMCs for the synthesis of isotactic poly( α -olefins). Here, we report the results of study of the polymerization of 1-butene on TMCs with external donors of the type R n P(O)(CH 2 OR') 3 – n (where R = alkyl; R' = methyl, acyl; n = 1, 2). Phosphine oxides— Me 2 P(O)CH 2 OMe (ED-I) [3], Me 2 P(O)CH 2 OC(O)Me (ED-II) [4], Bu 2 P(O)CH 2 OMe (ED-III) [5], and iso - AmP(O)(CH 2 OMe) 2 (ED-IV) [6]—were obtained by known procedures; commercial tributylphosphine oxide (ED-V) was also used. The polymerization of 1-butene was carried out on the TiCl 4 ‐MgCl 2 ‐dibutyl phthalate catalyst (Ti content was 2.06%) in a 200-mL metallic reactor equipped with a stirrer in n -heptane (110 mL) at 323 K and at a constant monomer concentration during polymerization. The solid component of the TMC was introduced after saturation of the solvent with 1-butene, and then solutions of the AlEt 3 cocatalyst and external donor in n -heptane were added. The polymerization time was 1 h. The catalyst activity was assessed from the ratio of the polymer yield to the amount of Ti, monomer concentration, and process duration. The degree of polymer isotacticity was determined from the content of the fraction insoluble in boiling diethyl ether [7]. The viscosity-average molecular weight M v was determined by viscometry in decalin at 383 K and calculated by the formula [8]

FINE-TUNING CATALYSTS

ELECTRON-DONOR COMPONENTS of commercial Ziegler-Natta polymerization catalysts dictate the structure of the catalyst’s active site, according to a new study ( J. Catal. 2008, 257 , 81). The study provides new avenues for probing details of catalytic reaction mechanisms and may lead to more active and chemically selective catalysts for tailoring molecular properties of polymers. Ziegler-Natta catalysts drive commercial poly-olefin production. They consist of titanium tetrachloride supported on magnesium dichloride crystallites and include aluminum alkyl cocatalysts and organic electron-donor compounds. Although the well-studied catalytic materials mediate polyethylene and polypropylene production on an industrial scale, some aspects of the catalytic system remain poorly understood. For example, researchers have speculated that the electron-donor compounds may play a role in enhancing polymerization by controlling the geometry of MgCl 2 crystals and the orientations of their external surfaces. That proposal...

Photoelectron processes in heterojunctions based on organic films

The photoconductivity and photo emf have been studied in a heterostructure based on thin films of electron donor and acceptor organic compounds. It is established that the main process responsible for the photogeneration and separation of charge carriers is the decay of photoexcited molecular states at the interface between the donor and acceptor materials. The determining influence on the photoelectron processes in the organic heterostructure is produced by the energy structure of electron states at the interface. The role of the photoinduced intermolecular charge transfer in the development of photoconductivity in the given heterostructure is considered.

Influence of Nitrate on Microbial Reduction of Pertechnetate

Factors influencing microbial reduction of Tc(VII) in nitrate and radionuclide contaminated aquifer sediments were investigated using sediment microcosms containing organic electron donor, nitrate and Tc(VII). Microcosms underwent nitrate reduction followed by Tc(VII) reduction. During this transition, the microbial community changed from being dominated by bacteria affiliated with the genus Paenibacillus during the nitrate reduction phase, to those affiliated with genera Agrobacterium, Geothrix, and Desulfosporosinus during the Tc(VII) reduction phase. To investigate the mechanism of Tc(VII) reduction, the nitrate reducing strains Agrobacterium FRC-A2, Azoarcus FRC-B1, and a fermentative Clostridium FRC-C11 were isolated from sediment microcosms undergoing Tc(VII) reduction. Nitrate reducing bacteria reduced Tc(VII) effectively only in the presence of Fe(lll) and after nitrate was reduced, implying a major role for Fe(ll) as an electron shuttle in Tc(VII) reduction. It is likely that accumulation of nitrite blocks Fe(ll) production and hence Tc(VII) reduction during the active nitrate reduction phase. The pure culture of Clostridium FRC-C11 is able to reduce Tc(VII) enzymatically with H2 or glucose as electron donor and deposits insoluble Tc compounds within the cells in a manner that is not significantly influenced by the presence of nitrate. These results provided a possible mechanism for Tc(VII) reduction independent of Fe(III) and not influenced by nitrate.

Reactions of silylium ions with nucleophiles

Transformation of the diethylsilylium cation Et2Si+H into ethyl-and dimethylsilylium ions EtSi+H2 and Me2Si+H in reactions with nucleophiles is induced by electron-donor compounds. Their activity increases in the order Bu2O < BuOH < (Me3Si)2O < C6H6 and is determined by the structure of the intermediate adduct and electron density distribution in it. Qualitative estimation shows that the affinity of the tritiated diethylsilylium cation Et2Si+T for a nucleophile increases in the order C6H6 < BuOH < Bu2O < (Me3Si)2O. The higher affinity of the Et2Si+H cation for hexamethyldisiloxane compared to dibutyl ether, at similar basicity of the nucleophiles, is attributable to the higher charge of the oxygen atom in (Me2Si)2O.

Synthesis of dimethyl carbonate from urea and methanol catalyzed by the metallic compounds at atmospheric pressure

A novel route was proposed for producing dimethyl carbonate (DMC) at atmospheric pressure from urea and methanol catalyzed by the metallic compounds with a high boiling point electron donor compounds (polyethylene glycol dimethyl ether) (PGDE) as solvent. The effects of various operation conditions, such as methanol/urea initial molar ratio, catalyst concentration, urea/PGDE initial mass ratio, flow rate of circulating, reaction temperature, stirring speed and reaction time on DMC yield were investigated, respectively. Experimental results indicate that the using of PGDE as solvent enable this synthesis reaction to reach the requisite temperature and restrain the decomposition of urea and MC; removing the products, DMC and ammonia effectively from the reaction system in time is important to improve the yield of DMC. The DMC yield of 28.8% can be obtained in the optimal reaction conditions. This new process shows some advantages such as easily operating, effectively removing NH 3 from the reaction system and lower cost.

Photoinduced Electron Transfer Research to Build Model Compounds of Artificial Photosynthesis and Solar Energy Conversion

AbstractIn this article various novel synthesized dyads and triad systems containing organic based electron donor and acceptor compounds linked together by flexible and rigid spacers have been described which undergo very fast (˜ ps) charge separation reactions and relatively slow energy destructive charge recombination. Various techniques have been discussed to enhance the survival duration of the charge‐separated products, resulted from photoinduced electron transfer reactions, by retarding the energy wasting charge recombination process. It has been hinted that these systems should form the basis of future artificial photosynthetic and solar energy conversion devices.

Human myeloperoxidase: A potential target for molecular MR imaging in atherosclerosis

Plaque rupture in atherosclerotic disease is the major cause of morbidity and correlates well with myeloperoxidase (MPO) secretion by activated neutrophils and macrophages in humans. We hypothesized that paramagnetic electron donor compounds that rapidly oxidize and polymerize in the presence of MPO could be designed to enable imaging of local MPO activity levels in arterial segments at risk. Several potential substrates for MPO were synthesized and tested. One lead compound consisting of a covalent conjugate of GdDOTA and serotonin (3-(2-aminoethyl)-5-hydroxyindole) was efficiently polymerized in the presence of human neutrophil MPO resulting in a 70-100% increase in proton relaxivity. As a result, we were able to demonstrate MPO activity in enzyme solutions and in a model tissue-like system. These studies suggest that activatable paramagnetic MR imaging agents can be used to directly image MPO activity.

Synthesis and electrochemical properties of 1,1′-bis(benzo-1,3-dithiol-2-ylidene)ferrocene derivatives as novel electron donor compounds

A number of 1,1′-bis(benzo-1,3-dithiol-2-ylidene)ferrocene derivatives 7a– b and 12– 14 based on the strong electron donating ability of 1,3-dithiole and ferrocene moieties were synthesized as new π-donors. The structure and physical properties of these compounds were characterized both by experimental techniques and spectral analysis. These new classes of donor compounds were obtained in very high yields based on modification of the Wittig–Horner reaction and the 1,3-dithiole rings were separated by conjugated spacers including aryl–ferrocenyl–aryl. The electrochemical properties of the new compounds have been studied in comparison to DB-TTF 4 analogues, and the parent ferrocene donor by cyclic voltammetry (CV), using Pt electrode as the working electrode in CH 2Cl 2 solutions at room temperature. Three subsequent oxidation processes are observed as three oxidation waves associated only with two reduction processes. Polycrystalline samples of 14a– b are conducting σ rt 14a=0.2 S cm −1 and σ rt 14b=4.8×10 −4 S cm −1) respectively, while compounds 15 and 16 were found essentially as insulator ( σ rt<10 −10 S cm −1).

Electrospray mass spectra of group 6 (Fischer) carbenes in the presence of electron-donor compounds.

Fischer carbene complexes 1-7 are not ionized under standard electrospray ionization (ESI) conditions. We report here that unsaturated chromium and tungsten (Fischer) carbene complexes can be ionized in an electrospray ion source in the presence of electron-donor compounds such as hydroquinone (HQ) or tetrathiafulvalene (TTF). The addition of these compounds, which seem to act as electron transfer agents, permits the recording and study of their ESI mass spectra in the negative mode of detection. Both chromium and tungsten(0) carbene complexes undergo in the first fragmentation stage a double simultaneous decarbonylation process.

Dinaphtho[2′,3′:5,6][1,4]dithiino[2,3-b:2,3-e]pyridine, its 16-butyl derivative and dinaphtho[2′,3′:5,6][1,4]dioxo[2,3-b:2,3-e]pyridine: novel heterocycles as electron donor compounds

Dinaphtho[2′,3′:5,6][1,4]dithiino[2,3-b:2,3-e]pyridine (4a), its 16-butyl derivative (4b), and dinaphtho[2′,3′:5,6][1,4]dioxo[2,3-b:2,3-e]pyridine (5) have been prepared and fully characterized. The electrochemical properties of 4a, 4b and 5 have been studied by cyclic voltammetry in CH2Cl2∶trifluoroacetic acid (1∶1); in agreement with their donor character, they exhibit a first reversible oxidation wave to their radical cations with very similar potential peak values and a second irreversible wave to their dications, the lowest potential peak value of this second oxidation corresponding to 5. Their radical cations, generated by oxidation of the parent compounds, are relatively stable and have been analyzed in liquid solution by electron paramagnetic resonance (EPR). Spin density distributions in the SOMO have been calculated by the semiempirical MNDO method. Electronic spectra of 4a and 4b in trifluoroacetic acid show peaks at 417 and 401 nm, respectively, and in the presence of thallium(III) trifluoroacetate two characteristic peaks at λmax 411 and 868 nm for 4a˙+, and at 411 and 872 nm for 4b˙+. X-Ray analysis of 4b shows a molecular structure with a stable chair-shaped conformation with interplanar angles between naphthalenes and the pyridine ring of 139.0(1) and 146.4(1)°.

Novel bacterial and archaeal lineages from an in situ growth chamber deployed at a Mid-Atlantic Ridge hydrothermal vent.

The phylogenetic diversity was determined for a microbial community obtained from an in situ growth chamber placed on a deep-sea hydrothermal vent on the Mid-Atlantic Ridge (23 degrees 22' N, 44 degrees 57' W). The chamber was deployed for 5 days, and the temperature within the chamber gradually decreased from 70 to 20 degrees C. Upon retrieval of the chamber, the DNA was extracted and the small-subunit rRNA genes (16S rDNA) were amplified by PCR using primers specific for the Archaea or Bacteria domain and cloned. Unique rDNA sequences were identified by restriction fragment length polymorphisms, and 38 different archaeal and bacterial phylotypes were identified from the 85 clones screened. The majority of the archaeal sequences were affiliated with the Thermococcales (71%) and Archaeoglobales (22%) orders. A sequence belonging to the Thermoplasmales confirms that thermoacidophiles may have escaped enrichment culturing attempts of deep-sea hydrothermal vent samples. Additional sequences that represented deeply rooted lineages in the low-temperature eurarchaeal (marine group II) and crenarchaeal clades were obtained. The majority of the bacterial sequences obtained were restricted to the Aquificales (18%), the epsilon subclass of the Proteobacteria (epsilon-Proteobacteria) (40%), and the genus Desulfurobacterium (25%). Most of the clones (28%) were confined to a monophyletic clade within the epsilon-Proteobacteria with no known close relatives. The prevalence of clones related to thermophilic microbes that use hydrogen as an electron donor and sulfur compounds (S(0), SO(4), thiosulfate) indicates the importance of hydrogen oxidation and sulfur metabolism at deep-sea hydrothermal vents. The presence of sequences that are related to sequences from hyperthermophiles, moderate thermophiles, and mesophiles suggests that the diversity obtained from this analysis may reflect the microbial succession that occurred in response to the shift in temperature and possible associated changes in the chemistry of the hydrothermal fluid.

Reactive processing of polyolefins with MAH and GMA in the presence of various additives

This paper describes the initial results obtained on the study of the reactive processing of polyolefins (LLDPE, PP) with maleic anhydride (MAH) and glycidyl methacrylate (GMA) in the presence of styrene, dimethyl sulfoxide (DMSO), and dimethylacetamide (DMAC). The investigation of the processing torque obtained from the grafting reaction showed that the torque could be used as an indicator for some product properties such as gel content and percentage of grafting. Addition of a monomer such as styrene and electron donor compounds such as DMSO and DMAC showed significant improvement in processing properties in comparison with additive-free systems. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2405–2415, 2000

Fullerene/phthalocyaninatometal complex and their LB films

Buckminsterfullerene(C 60) molecules have been known to form organic charge transfer (CT ) complexes with electron-donor compounds. In this study, we have prepared the complexes of fullerene and 2,3,9,10,16,17,23,24-octakis(octyloxy)-phthalocyaninato metal (MPc(OC 8H 17) 8, M=2H, Cu, Zn) by using the Langmuir-Blodgett ( LB ) technique on the air-water interface for investigating the interaction between C 60 and MPc(OC 8H 17) 8. Monolayers of mixtures of C 60 and MPc(OC 8H 17) 8 were prepared by spreading a benzene solution of C 60 and MPc(OC 8H 17) 8 on the air-water interface at 10 °C. The monolayers were transferred by the horizontal lifting method. These multilayer films were characterized by UV-Vis, polarized UV-Vis and X-ray diffraction measurements.