BF<Subscript>3</Subscript>OEt<Subscript>2</Subscript>-coinitiated cationic polymerization of cyclopentadiene in the presence of water at room temperature

The cationic polymerization of cyclopentadiene (CPD) with 1-(4-methoxyphenyl)ethanol (1)/BF₃OEt₂ initiating system in CH₂Cl₂:CH₃CN 4:1 (v/v) mixture at room temperature and in the presence of water ([H₂O]/[BF₃OEt₂] up to 8) is reported. The number-average molecular weights of obtained polymers increased in direct proportion to monomer conversion or initial monomer concentration (M _n ≤ 4,000 g mol⁻¹) in agreement with calculated values, and were inversely proportional to initiator concentration. Polymer MWDs were relatively narrow (M _w/M _n = 1.4–1.7) up to 60% of monomer conversion. It was also shown that regioselectivity of CPD polymerization with 1/BF₃OEt₂ initiating system did not depend significantly on water, monomer, or initiator concentration (1,4-structures content was nearly 60% in all cases).     

Ruthenium Complexes with 2-Pyridin-2-yl-1H-benzimidazole as Potential Antimicrobial Agents: Correlation between Chemical Properties and Anti-Biofilm Effects

Antimicrobial resistance is a growing public health concern that requires urgent action. Biofilm-associated resistance to antimicrobials begins at the attachment phase and increases as the biofilms maturate. Hence, interrupting the initial binding process of bacteria to surfaces is essential to effectively prevent biofilm-associated problems. Herein, we have evaluated the antibacterial and anti-biofilm activities of three ruthenium complexes in different oxidation states with 2-pyridin-2-yl-1H-benzimidazole (L₁ = 2,2′-PyBIm): [(η⁶-p-cymene)Ru^IIClL₁]PF₆ (Ru(II) complex), mer-[Ru^IIICl₃(CH₃CN)L₁]·L₁·3H₂O (Ru(III) complex), (H₂L₁)₂[Ru^IIICl₄(CH₃CN)₂]₂[Ru^IVCl₄(CH₃CN)₂]·2Cl·6H₂O (Ru(III/IV) complex). The biological activity of the compounds was screened against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa strains. The results indicated that the anti-biofilm activity of the Ru complexes at concentration of 1 mM was better than that of the ligand alone against the P. aeruginosa PAO1. It means that ligand, in combination with ruthenium ion, shows a synergistic effect. The effect of the Ru complexes on cell surface properties was determined by the contact angle and zeta potential values. The electric and physical properties of the microbial surface are useful tools for the examined aggregation phenomenon and disruption of the adhesion. Considering that intermolecular interactions are important and largely define the functions of compounds, we examined interactions in the crystals of the Ru complexes using the Hirshfeld surface analysis.     

Electrosynthesis of polyfuran in acetonitrile–boron trifluoride–ethyl ether mixture and its device application

Electrochemical polymerization of furan was achieved in acetonitrile/boron trifluoride/ethyl ether (CH₃CN/BF₃/EE) mixture in the presence of tetrabutylammonium tetrafluoroborate via constant potential electrolysis at 1.4 V versus Ag/AgCl. Electrochemical behavior of furan was investigated in the same solvent mixture of varying ratios, utilizing cyclic voltammetry. Free‐standing polyfuran (PFu) films were obtained in CH₃CN/BF₃/EE mixture (2/4/4; v/v/v) and characterized using FTIR spectroscopic technique. Spectroelectrochemical behavior of the PFu film was investigated by recording the electronic absorption spectra, in situ, in monomer‐free solution. It is observed that PFu film can be reversibly cycled between –0.1 V (gray) and + 0.6 V versus Ag‐wire (gray color); however, this behavior diminishes in the presence of water. Electrochromic device application of PFu film with poly(ethylene dioxythiophene) was also studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 871–876, 2007     

Preparation and characterization of poly[Ni(salen)(crown receptor)]/multi-walled carbon nanotube composite films

Nanocomposite films comprising multi-walled carbon nanotubes (MWCNTs) embedded within poly[Ni(3-Mesalophen-b15-c5)] were deposited on Pt and ITO electrode surfaces by the potentiodynamic polymerisation of [Ni(3-Mesalophen-b15-c5)] from solutions containing dispersed MWCNTs. Composites incorporating carbon nanotubes subject to a range of oxidising pre-treatments were compared with those incorporating untreated carbon nanotubes and with the pure polymer. In both cases, the use of CH₃CN and CH₂Cl₂ as fabrication and characterization media were explored. Films were characterized by voltammetry, electrochemical impedance spectroscopy and scanning electron microscope (SEM). The coating of the carbon nanotubes with polymer varied significantly with pre-treatment and solvent medium; this influenced the final composite morphology and electrical properties. Performance enhancement of the polymer component by the presence of the carbon nanotubes was manifested through the ability to store charge and the ease with which this could be accomplished; these were parameterized via increased redox capacitance and decreased charge-transfer resistance, respectively. Correlation of impedance parameters with SEM images provided a morphological rationale for composite electrical properties.     

A recommended esterification method for gas chromatographic measurement of conjugated linoleic acid

The effect of the methylation method on isomerization of conjugated linoleic acid (CLA) in gas chromatographic analysis was studied. Among methylation methods examined, the magnitude of isomerization of CLA was greatest with BF₃ catalyst, followed by HCI and H₂SO₄ catalyst. Short-time methylation did not extensively change the CLA composition in all methods, and c,t and t,c isomers were essentially maintained, while the appearance of t,t isomers and unknown peaks was practically restricted. After 120 min of methylation, there was essentially no conversion in the H₂SO₄ method, in contrast to a marked change in the BF₃ method. The antioxidants butylated hydroxytoluene, ascorbic acid, β-carotene, and α-tocopherol did not suppress conversion, while dimethylsulfoxide (DMSO) and dimethylformamide (DMF) attenuated the changes in CLA composition. Suppression was more effective in the H₂SO₄ method than in the BF₃ method. Thus, methylation with H₂SO₄ in the presence of a proper amount of DMSO or DMF is recommended for esterification of CLA.     

Evaluating acid and base catalysts in the methylation of milk and rumen fatty acids with special emphasis on conjugated dienes and total trans fatty acids

Milk analysis is receiving increased attention. Milk contains conjugated octadecadienoic acids (18∶2) purported to be anticarcinogenic, low levels of essential fatty acids, and trans fatty acids that increase when essential fatty acids are increased in dairy rations. Milk and rumen fatty acid methyl esters (FAME) were prepared using several acid-(HCl, BF₃, acetyl chloride, H₂SO₄) or base-catalysts (NaOCH₃, tetramethylguanidine, diazomethane), or combinations thereof. All acid-catalyzed procedures resulted in decreased cis/trans (Δ9c, 11t-18∶2) and increased trans/trans (Δ9t, 11t-18∶2) conjugated dienes and the production of allylic methoxy artifacts. The methoxy artifacts were identified by gas-liquid chromatography (GLC)-mass spectroscopy. The base-catalyzed procedures gave no isomerization of conjugated dienes and no methoxy artifacts, but they did not transesterify N-acyl lipids such as sphingomyelin, and NaOCH₃ did not methylate free fatty acids. In addition, reaction with tetramethylguanidine coextracted material with hexane that interfered with the determination of the short-chain FAME by GLC. Acid-catalyzed methylation resulted in the loss of about 12% total conjugated dienes, 42% recovery of the Δ9c,11t-18∶2 isomer, a fourfold increase in Δ9t,11t-18∶2, and the formation of methoxy artifacts, compared with the base-catalyzed reactions. Total milk FAME showed significant infrared (IR) absorption due to conjugated dienes at 985 and 948 cm⁻¹. The IR determination of total trans content of milk FAME was not fully satisfactory because the 966 cm⁻¹ trans band overlapped with the conjugated diene bands. IR accuracy was limited by the fact that the absorptivity of methyl elaidate, used as calibration standard, was different from those of the other minor trans fatty acids (e.g., dienes) found in milk. In addition, acid-catalyzed reactions produced interfering material that absorbed extensively in the trans IR region. No single method or combination of methods could adequately prepare FAME from all lipid classes in milk or rumen lipids, and not affect the conjugated dienes. The best compromise for milk fatty acids was obtained with NaOCH₃ followed by HCl or BF₃, or diazomethane followed by NaOCH₃, being aware that sphingomyelins are ignored. For rumen samples, the best method was diazomethane followed by NaOCH₃.     

Nitric oxide species as oxidising agents and adducts for soft scorpionates

Bis-(κ³-H,S,S-dihydrobis-(methimazolyl)borato)ruthenium(II), [Ru(Bm^Me)₂], has been prepared and tested as a nitric oxide scavenger using NO, NOBF₄ and NOBr. The products isolated show that, NO and NO⁺ are good one electron oxidising agents towards the ruthenium complexes but NO is not coordinated to the metal. The oxidised species, [Ru(Bm^Me)₂]BF₄ has been isolated and characterised. Reaction of “Ru(NO)Cl₃” with NaBm^Me results in the removal of the borohydride from the ligand and formation of [Ru(mtH)₃(mt)(NO)Cl]⁺.     

Solvent effect on the nucleation and growth mechanisms of poly(thiophene)

Applying the step potential method, the effect of parameters such as solvent, potential, electrolyte and monomer concentration on the nucleation and growth processes of poly(thiophene) on Pt electrode in tetrabuthylammonium hexafluorophosphate-acetonitrile or dichloromethane has been studied. The j/t transients were generally fitted by means of a mathematical equation that considers different contributions. In acetonitrile the j/t transient (0<t<30 s) present three contributions corresponding to the following mechanisms: two-dimensional instantaneous nucleation (IN2D), three-dimensional progressive nucleation (PN3D_CT) under charge transfer control and three-dimensional progressive nucleation (PN3D_dif) under diffusion control. Similar results were obtained in dichloromethane, but in this case the 3D_CT nucleus presented an instantaneous nucleation mechanism (IN3D_ct). A second wave has been observed in the j/t transients obtained in CH₃CN at t>30 s, which was fitted by a mathematical equation that included two contributions corresponding to a PN3D_CT and PN3D_dif mechanisms. In general, the charge associated to each contribution depended on the solvent, the monomer and electrolyte concentration and the applied potential. However, the PN3D_CT (CH₃CN) or IN3D_CT (CH₂Cl₂) mechanisms were always the more important contributions. The scanning electron microscopy (SEM) analysis of the deposits morphology are in agreement with the nucleation and growth models that are proposed by this method.     

Synthesis,characterization and crystal structure of a zinc bis-dithiocarboxylate derivative

The zinc(II) complex, Zn(3,5-di-t-butyl-4-hydroxybenzene-dithiocarboxylate)₂(pyridine) (3) was obtained by the reaction of Zn(CH₃CN)₄(BF₄)₂ with the sodium salt of 3,5-di-t-butyl-4-hydroxybenzene-dithiocarboxylate (1) with subsequent recrystallization from pyridine. The latter salt (1) was prepared by the deprotonation of 2,6-di-t-butylphenol with NaH in THF, followed by reaction with carbon disulfide at ambient temperature. The structure of complex 3 was established by X-ray crystallography and shown to be of a distorted trigonal bipyramidal geometry with one sulfur atom from each of the dithiocarboxylate ligands occupying the axial sites. By way of contrast, Na(2,4-di-t-butylphenolate) was found to react with CS₂ to afford the xanthate derivative, Na(O-2,4-di-t-butylphenyldithiocarbonate) (4).     

Ruthenium Catalysts for Controlled Mono‐ and Bis‐Allylation of Active Methylene Compounds with Aliphatic Allylic Substrates

The allylation of 1,3‐dicarbonyl compounds and malononitrile with aliphatic allylic substrates is achieved under mild conditions in the presence of new ruthenium catalysts. The ruthenium complex [Ru(C₅Me₅)(2‐quinolinecarboxylato)(CH₂CHCH‐n‐Pr)] [BF₄] as a precatalyst, allows the synthesis of mono‐allylated branched derivatives. On the other hand, the parent complex [Ru(C₅Me₅)(MeCN)₃] [PF₆] as a precatalyst, straightforwardly favours the bis‐allylation of the procarbonucleophiles leading to bis‐allylated bis‐linear products. The involvement of the two precatalysts provides a sequential synthesis of unsymmetrical mixed linear‐branched bis‐allylated derivatives.     

CH3 and Cl2 coadsorbed on Si/Cu(100)

X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) studies were used to investigate the reactions of coadsorbed CH₃ and Cl₂ on Si/Cu(100). TPD results showed that the individual exposure of Si/Cu(100) to CH₃ and Cl₂ resulted primarily in the desorption of (CH₃)₃SiH and SiCl₄, respectively. Coadsorption of CH₃ and Cl₂ at specific surface concentrations on Si/Cu(100) resulted in the desorption of (CH₃)_4-xSiCl_x (x ranges from 1 to 3) species. The relative surface concentration of CH₃ and Cl (resulting from Cl₂ dissociation), however, controlled the stoichiometry of the methylchlorosilane product. XPS results suggested that more Si was removed from the Si/Cu(100) surface as gaseous product when CH₃ and Cl₂ were coadsorbed on the surface than when CH₃ and Cl₂ were adsorbed alone.     

Polymerization of N-substituted 2-propynamides with transition metal catalysts

Summary Polymerization of N-substituted 2-propynamides proceeded in the presence of Pd(II) catalysts such as [Pd(CH₃CN)₄](BF₄)₂, PdCl₂(PhCN)₂-n-BuLi, and PdCl₂(nbd)-n-BuLi. The molecular weights of the obtained polymers ranged 8,500 to 14,000, depending on the catalysts. From the ¹H NMR spectra, these polymers were found to have alternating double bonds in the main chain. Received: 25 December 2000/Revised version: 17 January 2001/Accepted: 19 January 2001     

Metal-free isotactic-specific radical polymerization of N-alkylacrylamides with 3,5-dimethylpyridine N-oxide: The effect of the N-substituent and solvent on the isotactic specificity

Radical polymerization of N-methylacrylamide (NMAAm), N-n-propylacrylamide, N-isopropylacrylamide (NIPAAm) and N-benzylacrylamide was investigated in CHCl₃, CH₂Cl₂ and CH₃CN, in the presence of 3,5-dimethylpyridine N-oxide (35DMPNO) to examine the effects of the N-substituent and the solvent on the isotactic specificity induced by 35DMPNO. With addition of 35DMPNO to radical polymerization of N-alkylacrylamides in CHCl₃, isotactic specificity was significantly induced in NIPAAm polymerization but only slightly induced in NMAAm polymerization. Furthermore, mixed solvents of CH₃CN and halomethanes such as CHCl₃ and CH₂Cl₂ enhanced the ability of 35DMPNO to induce isotactic specificity, and poly(NIPAAm) with 74% meso dyad was obtained.     

Dicopper(I) and disilver(I) complexes of a thiophene-derived Schiff base macrocycle

Dicopper(I) and disilver(I) complexes of a tetraimine Schiff base macrocycle derived from the cyclocondensation of thiophene-2,5-dicarbaldehyde with 1,4,7-triazaheptane (1) have been synthesised and characterised. The structure of Cu₂(1)(BF₄)₂·2CH₃CN is given.     

Band-gap tuning of carbazole-containing donor-acceptor type conjugated polymers by acceptor moieties and π-spacer groups

Carbazole-containing donor-acceptor type conjugated polymers were prepared by Sonogashira cross-coupling reaction of 3,6-diethynyl-9-hexadecylcarbazole and arylene dibromides, and the optical and electrochemical properties were extensively investigated. Copolymerization with 4,7-dibromo-2,1,3-benzothiadiazole furnished the orange-colored polymer with a charge-transfer band at 440 nm in CH₂Cl₂, indicating efficient intramolecular donor-acceptor interactions. On the other hand, the color of the copolymer with 2,5-dibromopyridine was ocher and the longest wavelength absorption band was 381 nm in CH₂Cl₂, suggesting almost negligible donor-acceptor interactions. This difference was also reflected by the emission spectra, solvatochromic behaviors, and electrochemical redox potentials. Comparison of the ethynylene spacer between the donor and acceptor moieties to other π-spacers revealed that the ethynylene spacer serves as a more efficient π-spacer than vinylene and direct connection (without spacer) for strong donor-acceptor coupling in this polymer system.     

Structure,Luminescence, and Vapochromism of Bridged Cationic Copper(I) Dimers and Polymers

The dimeric complex of Cu(I) [Cu₂(PPh₃)₄(MeCN)₂(Bpy)](BF₄)₂ (1a, Bpy = 4,4′-dipyridyl) self-assembles in CH₂Cl₂ or acetone and shows intense photoluminescence (excitation λ_max = 356 nm, emission λ_max = 486 nm, ? = 0.47). The MeCN ligands are readily removed from 1a, producing [Cu₂(PPh₃)₄(Bpy)](BF₄)₂ (1b) and altering the photophysical behavior (excitation λ_max = 336 nm, emission λ_max = 568 nm, ? = 0.07). The desolvated compound 1b reversibly absorbs many vapor phase nucleophiles, as revealed by thermogravimetry. Intense luminescence emission is restored for 1b/Nu, Nu = MeCN (1a), acetone, tetrahydrothiophene (THT), and Et₂S. Films of 1b are produced when CH₂Cl₂ solutions of 1a are cast onto glass. The films also react with Nu vapor, again producing intense emission. The pyrazine-bridged dimer [Cu₂(PPh₃)₄(MeCN)₂(Pyz)](BF₄)₂ (2a) is produced in CH₂Cl₂, while [Cu₂(PPh₃)₄(MeCN)(acetone)(Pyz)](BF₄)₂?½[Cu₂(PPh₃)₄(MeCN)₂(Pyz)](BF₄)₂ (2b) is formed in acetone. The crystal structure of the polymer {[Cu(PPh₃)₂(Bpy)](BF₄)?acetone} _n (3) is reported, as is the mixed polymer/dimer structure {[Cu(PPh₃)₂(Pyz)](BF₄)} _n ?½n[Cu₂(PPh₃)₄(BF₄)₂(Pyz)] (4b) in which the dimer units show Cu–FBF₃ coordination. The Pyz dimer and the Pyz and Bpy polymers show much weaker luminescence behavior than that of Bpy dimers 1a and the related 1b/Nu adducts. Nucleophile adduct structures [Cu₂(PPh₃)₄(THT)₂(Bpy)](BF₄)₂?½ethyl ether (5) and [Cu₂(PPh₃)₄(Py)₂(Bpy)](BF₄)₂?CH₂Cl₂ (6) confirmed the coordination of one Nu per Cu to 1b.     

Polymerization of vinyl chloride with Cp*Ti(OPh)3/MAO catalyst in toluene

Polymerization of vinyl chloride (VC) with a Cp*Ti(OPh)₃/MAO catalyst in toluene was investigated. The polymerization rate was lower than that in CH₂Cl₂, and the mm triad concentration of the PVC obtained in toluene was somewhat higher than that of the PVC obtained in CH₂Cl₂. As the polymerization in toluene proceeded at a considerable rate, a kinetic study of this polymerization was undertaken. The polymer yield increased with reaction time, and the molecular weight of the polymer increased with increasing polymer yield. The M_w/M_n ratio of the polymer decreased with increasing polymerization temperature. The initiator efficiency of the catalyst was low at the initial stage of the polymerization in toluene, but it reached nearly 100% when the polymerization was carried out for more than 30 h. The control of both themolecular weight of PVC and its main‐chain structure was found to be possible in the polymerization of VC with the Cp*Ti(OPh)₃/MAO catalyst in toluene. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers     

Synthesis and properties of conjugated copolymers having a tricarbonyl(arene)chromium and thiophene units in the main chain

Summary Palladium-catalyzed polymerization of η ⁶-(1,4-diethynylbenzene)tricarbonyl chromium (1) with 3-alkyl-2,5-dibromothiophene (2a-c) was carried out to give the corresponding alternating conjugated copolymers (5a-c) in good yields. The structures of the polymers were supported by ¹H NMR and IR spectra. The polymers obtained were soluble in common solvents such as THF, CH₂Cl₂, CHCl₃ and toluene. The molecular weights of the polymers were determined by GPC. Their thermal, optical and electrical properties were investigated in detail. Received: 18 March 2002 /Accepted: 1 April 2002     

Migratory insertion reaction in alkenyl ruthenium(II) complexes containing a trifluoroacetate ligand. X-ray structure of the Ru(η2- O2CCF3)(η1-OCCHCHtBu)(CO)(PPh3)2 complex

Reaction of compound Ru(O₂CCF₃)(CHCH^tBu)(CO)(PPh₃)₂ with CO gives the η¹-alkeneacyl complex Ru(O₂CCF₃)(OCCHCH^tBu)(CO)(PPh₃)₂, which is in equilibrium with the dicarbonyl Ru(O₂CCF₃)(CHCH^tBu)(CO)₂(PPh₃)₂ derivative in CH₂Cl₂ solution. The η¹-acyl form involves an η¹-coordination of the O₂CCF₃ ligand, whereas the dicarbonyl form contains the carboxylate ligand η²-coordinated to the metal. The same mixture of carbonylated compounds can be obtained from the reaction of Ru(CHCH^tBu)Cl(CO)₂(PPh₃)₂ with Na[O₂CCF₃] in a CH₂Cl₂/MeOH solution. These reactions reveal the significance of ancillary bidentate ligands for the η-nature of the acyl–metal bond. The molecular structure of the complex Ru(O₂CCF₃)(OCCHCH^tBu)(CO)(PPh₃)₂ was established by X-ray diffraction study of a monocrystal obtained from a CH₂Cl₂/MeOH solution of the mixture of carbonylated compounds.     

Bmim ionic liquids as media for the electrochemical oxidation of 2,6-di-<Emphasis Type="Italic">t</Emphasis>-butylphenol

The electrochemical oxidation of the substituted phenol 2,6-di-t-butylphenol is studied at platinum electrodes using a number of 1-butyl-3-methylimidazolium (bmim) ionic liquids (BF₄, PF₆ and N(CF₃SO₂)₂), and compared with the oxidation obtained using a traditional solvent/electrolyte system (CH₃OH/CH₂Cl₂ and LiClO₄). The electrolysis leads to anodic coupling, resulting in the corresponding diphenoquinone, which upon reduction produces the biphenol. Best results were obtained for the conventional solvent and electrolyte, where the oxidation was found to take place via an indirect method. It was found that the ionic liquids performed better upon dilution with a suitable solvent such as acetonitrile, yielding higher conductivities due to ion separation. Dilution studies were performed with acetonitrile, methanol, dichloromethane and acetone and the resulting increase in conductivity of the ionic liquid was in the order: acetonitrile > methanol > acetone > dichloromethane. This trend is in line with the dielectric constant and the dipole moment of the solvent used. It was found that the electrolysis proceeded best in the following order: conventional solvent/electrolyte > ionic liquid suitably diluted > ionic liquid. Among the ionic liquids, best results were obtained for [bmim][BF₄]. Cyclic voltammetry data was used to further explain the electrolysis as a function of dilution.