OCH CH Research Articles

Ionic environment and hydrogen bonding in di-ureasil ormolytes doped with lithium triflate

Di-urea cross-linked sol–gel derived poly(oxyethylene) (POE)/siloxane hybrids (di-ureasils) doped with a wide concentration range of lithium triflate (LiCF 3SO 3) were studied by infrared and Raman spectroscopies with the primary objective of examining in detail the Li +/cross-link and hydrogen bonding interactions. Another goal of this work was to find additional data that confirmed previous conclusions regarding the Li +/polymer and Li +/anion bonding. Xerogels with ∞> n≥1 (where n, called salt composition, is the molar ratio OCH 2CH 2/Li +) were analyzed. The analysis of the ‘amide I’ and ‘amide II’ regions provided solid evidences that the Li + ions bond to the urea carbonyl oxygen atoms in the entire range of salt concentration studied. The changes detected in the CH 2 rocking region indicate that the alkali metal cations are also coordinated to the ether oxygen atoms of the POE chains at n≤20. Proofs of the formation of a POE/LiCF 3SO 3 crystalline compound at n≤10 were also found. The anionic configurations detected in the FT-IR SO 3 symmetric stretching region are in perfect agreement with those deduced from the FT-Raman spectra.

Ion conductive characteristics of cross-linked network polysiloxane-based solid polymer electrolytes

A series of cross-linked network polysiloxanes containing oligoethylene oxide units, (OCH 2CH 2) n , as internal free chains have been synthesized by performing hydrosilylation of partially PEO-substituted polysiloxane precursor with α, ω-diallyl terminated poly(ethylene glycol). The polymer electrolytes were formed by complexing with LiN(CF 3SO 2) 2 electrolyte salt and exhibited superior conductive property. The σ RT of the network polymer electrolytes is in the range of 2.50×10 −5 to 1.62×10 −4 S/cm and depends on the cross-linking density (in terms of Si–H amount of the siloxane precursor), repeating unit number of internal oligoethylene oxide and chain length of the cross-linker. The significant enhancement of the conductivity was observed when low molecular weight dimethyl poly(ethylene glycol) was added as plasticizer. The temperature dependence of the ionic conductivity was also studied, following the Vogel–Tamman–Fulcher (VTF) equation.

Synthesis of hyperbranched carbosiloxane macromolecule with triallyloxysilane and applications to the dendritic core

A hyperbranched carbosiloxane macromolecule (AB 3-type with Si–O bonds) was prepared by the self-hydrosilation of triallyloxysilane (H–Si(OCH 2CH=CH 2) 3) in the presence of a platinum catalyst. The prepared AB 3-type hyperbranched carbosilane was used for the carbosilane dendrimer as the core, which was progressed until the second generation by the use of iterative controlled methods such as hydrosilation and alcoholysis. NMR, MALDI mass and GPC identified the triallyloxysilane-based hyperbranched carbosilanes and dendrimers. To cite this article: C. Kim, H. Kim, C. R. Chimie 7 (2004) .

Synthesis and characterisation of phosphane-substituted Co 3C clusters having a pendant allyl side-chain

Substituted μ 3-carbido-capped tricobalt carbonyl clusters have been synthesised by reaction of [Co 3(μ 3-C(O)OCH 2CHCH 2)(CO) 9] with a range of monodentate and chelating phosphane ligands. The products have been characterised by microanalysis, IR and NMR spectroscopy, mass spectrometry and, in the case of [Co 3(μ 3-CR)(CO) 7(dppe)], [Co 3(μ 3-CR)(CO) 7(dppm)], [Co 3(μ 3-CR)(CO) 7(PPh 3) 2], [Co 3(μ 3-CR)(CO) 7(PMe 3) 2] and [Co 3(μ 3-CR)(CO) 6(PEt 3) 3] (R=C(O)OCH 2CHCH 2), single crystal X-ray diffraction.

Thermodynamics of micellization of tapered statistical copolymers of ethylene oxide and propylene oxide in water

Two tapered statistical copolymers were prepared by the oxyanionic polymerization of ethylene oxide and propylene oxide and characterized by gel permeation chromatography and 13C NMR spectroscopy. We denote the copolymers t-E/P38 and t-E/P30, where E = oxyethylene, OCH 2CH 2, and P = oxypropylene, OCH 2CH(CH 3), and the number denotes the mole percentage P. In each case the copolymer chain length was ca. 100 oxyalkylene units. The association of the copolymers to form micelles in aqueous solution was checked by dynamic light scattering. The critical micelle temperatures (cmt) of the copolymers at several concentrations were determined by static light scattering and dye solubilization, and values of the apparent standard enthalpy of micellization (Δ mic H 0 app) were obtained. For both copolymers, a low value of Δ mic H 0 app was found when the copolymer concentration exceeded ca. 150 g dm −3.

Preparation and dilute solution properties of model gemini nonionic surfactants

Dimeric poly(ethylene oxide) surfactants (or nonionic gemini surfactants) with the structure (C n−2 H 2 n−3 CHCH 2O(CH 2CH 2O) m H) 2(CH 2) 6 (or Gem n E m ), where n is the alkyl length and m is the average number of ethylene oxides per head group, were synthesized. Surfactants were synthesized with alkyl chain lengths n=12, 14, and 20 and m=5, 10, 15, 20, and 30. Water solubilities and cloud temperatures at 1 wt% were determined by measuring turbidity as a function of temperature. Cloud temperatures increase with m and decrease with n, as observed for conventional surfactants. For large m the cloud temperatures were all above 100 °C. Surfactants with small m (i.e., n=12, 14, m=5 and n=20, m=10) were insoluble at room temperature, forming two-phase mixtures. Critical micelle concentrations (CMCs) were measured using a pyrene fluorescence method and are all in the range of 10 −7 to 10 −6 M, with the lowest values from the surfactants with large n and small m. CMCs of mixtures with both anionic and nonionic conventional (monomeric) surfactants were well described by an ideal mixing model.

Different deswelling behavior of temperature-sensitive microgels of poly( N-isopropylacrylamide) crosslinked by polyethyleneglycol dimethacrylates

Polymerization of N-isopropylacrylamide (NIPAM) with polyethyleneglycol dimethacrylates ( nG, n representing the number of CH 2CH 2O units in polyethyleneglycol dimethacrylates) through surfactant-free radical polymerization was used to prepare the temperature-sensitive microgels. The morphology, dispersity, and deswelling behavior of the microgels were investigated by means of transmission electron microscopy (TEM), ultraviolet–visible spectroscopy, differential scanning calorimetry (DSC), and dynamic light scattering (DLS) techniques. TEM micrographs revealed that it was feasible to obtain regular spherical microgels for crosslinking agents with short chain. Turbidity, DSC, and DLS analysis showed that in marked contrast to 1G and 3G crosslinked microgels, the collapse of microgels crosslinked by 9G, 14G, and 23G proceeded in a two-step mechanism. The amide groups dehydrated at the lower temperature leading to the first-step transition. In the transition, the hydrophilic long (CH 2CH 2O) n  segments could be enriched on the surface of the microgels, which was further verified by variable temperature 1H NMR spectroscopy. The hydrophilic long (CH 2CH 2O) n  segments can be dehydrated at the higher temperature.

Solution properties, electrochemical behavior and protein interactions of water soluble triosmium carbonyl clusters

The synthesis and solution chemistry of the water soluble clusters [Os 3(CO) 9(μ-η 2-Bz)(μ-H)L +] (HBz=quinoxaline, L +=[P(OCH 2CH 2NMe 3) 3I 3], 1) along with its negatively charged analog [Os 3(CO) 9(μ-η 2-Bz)(μ-H)L −] (L −=[P(C 6H 4SO 3) 3Na 3], 2) are reported. In addition, we have examined the reduction potentials of the complexes [Os 3(CO) 9(μ-η 2-Bz)(μ-H)L] (HBz=phenanthridine, L=L + ( 3); HBz=5,6 benzoquinoline, L=L + ( 4); HBz=3-amino quinoline, L=L + ( 5); HBz=3-amino quinoline, L=L − ( 6). The neutral analog of 1 and 2 [Os 3(CO) 9(μ-η 2-Bz)(μ-H) PPh 3] (Bz=quinoxaline, 7) was also examined for comparison. Both compounds 1 and 2 show pH dependent NMR spectra that are interpreted in terms of the extent of protonation of the uncoordinated quinoxaline nitrogen which impacts the degree of aggregation of the clusters in aqueous solution. Compound 1 undergoes a reversible 1e − reduction in water while 2 undergoes a quasi-reversible 1e − reduction at more negative potentials as expected from the difference in charge on the phosphine ligand. Compound 7 undergoes a marginally reversible CV in methylene chloride at a potential intermediate between the positively and negatively charged clusters. The overall stability of the radical anions of 1, 2 and 7 is somewhat less than the corresponding decacarbonyl [Os 3(CO) 10(μ-η 2-Bz)(μ-H)] (HBz=quinoxaline). While complexes 1 and 2 show reversible 1e − reductions, all the other complexes examined show 1e − and/or two 1e − irreversible reductions in aqueous and non-aqueous solvents. The potentials for these complexes follow expected trends relating to the charge on the phosphine and the pH of the aqueous solutions. The ligand dependent trends are compared with those of the previously reported corresponding decacarbonyls. The interactions of the positively and negatively charged clusters with albumin have been investigated using the transverse and longitudinal relaxation times of the hydride resonances as probes of binding to the protein. Evidence of binding is observed for both the positive and negative clusters but the positive and negative clusters exhibit distinctly different rotational correlation times. Two additional complexes [Os 3(CO) 9(μ-η 2-Bz)(μ-H)L] (HBz=2-methylbenzimidazole, L=L + ( 8); L=L − ( 10) and HBz=quinoline-4-carboxaldehyde, L=L + ( 9); L=L − ( 11)) are reported in connection with these studies.

A DFT study on the intramolecular dissociation pathways of ethyl fluoroformate radical cation in the gas phase; I. Enol path

A ground-state intramolecular gas-phase enol dissociation pathway of ethyl fluoroformate radical cation (FCOOCH 2CH 3 + ) is studied using conventional ab initio and density functional molecular orbital methods. Initial geometries are optimized using the 6-31G* basis set. Electron correlation is incorporated by optimizing the geometries at the MP2 and B3LYP levels using the 6-31G** basis set. Stationary points are characterized by frequency calculation at the same level of theory and basis set except for MP2 where only HF/6-31G* corrections were applied. A new dissociation mechanism, a so-called enol path is proposed. Initially, the α-distonic radical cation undergoes a barrierless isomerization to a more stable γ-distonic enol form FC +(OH)OCH 2CH 2 . This is followed by a rate-determining self-induced cleavage of the ester linkage yielding FCOOH+C 2H 4 + in the second step of an Ei (elimination, intramolecular) scheme which is at the same time the first step of an E1 β-elimination mechanism. The enol pathway is terminated by a slow elimination of a proton from C 2H 4 + by FCOOH which acts as a base. The proposed mechanism is drawn from the results of density functional (UB3LYP/6-31G**) calculations as the conventional ab initio treatment [UHF/6-31G* and UMP2(Full)/6-31G**//UHF/6-31G*] gave erroneous energetics due to severe spin-contamination of the wavefunction.

Decomposition of vinyl ethers by alkalide K −, K +(15-crown-5) 2 via organopotassium intermediates

The structure of vinyl ethers determines the direction of the C–O bond cleavage by alkalide K −, K +(15-crown-5) 2 1. Highly reactive organopotassium compounds are intermediate products formed in the system containing phenyl vinyl ether, butyl vinyl ether, ethylene glycol butyl vinyl ether or triethylene glycol methyl vinyl ether. Vinylpotassium and butylpotassium react with 15-crown-5. The oxacyclic ring of the latter is opened in this case. Organopotassium ethers possessing CH 2CH 2O units eliminate ethylene. It results in various potassium alkoxides. The reaction of 1 with butyl vinyl ether occurs very slow as compared to other vinyl ethers and most of other reagents used till now.

The effect of properties of water–organic solvent mixtures on the solvation enthalpy of 12-crown-4, 15-crown-5, 18-crown-6 and benzo-15-crown-5 ethers at 298.15 K

Crown ethers are preferential solvated by organic solvents in the mixtures of water with formamide, N-methylformamide, acetonitrile, acetone and propan-1-ol. In these mixed solvents the energetic effect of the preferential solvation depends quantitatively on the structural and energetic properties of mixtures. The energetic properties of the mixtures of water with hydrophobic solvents ( N, N-dimethylformamide, dimethylsulfoxide, N, N-dimethylacetamide, hexamethylphosphortriamide) counteract the preferential solvation of the crown ether molecules. The effect of the hydrophobic and acid–base properties of the mixture of water with organic solvent on the solvation of 12-crown-4, 15-crown-5, 18-crown-6 and benzo-15-crown-5 ethers was discussed. The solvation enthalpy of one –CH 2CH 2O– group in water, N,N-dimethylformamide and hexamethylphosphortriamide is equal to −24.21, −16.04 and −15.91 kJ/mol, respectively. The condensed benzene ring with 15-crown-5 ether molecule brings about an increase in the exothermic effect of solvation of the crown ether in the mixtures of water with organic solvent.

Direct liquid injection metal-organic chemical vapor deposition of HfO 2 thin films using Hf(dimethylaminoethoxide) 4

Hf(OCH 2CH 2NMe 2) 4, [Hf(dmae) 4] (dmae=dimethylaminoethoxide) was synthesized and used as a chemical vapor deposition precursor for depositing Hf oxide (HfO 2). Hf(dmae) 4 is a liquid at room temperature and has a moderate vapor pressure (4.5 Torr at 80 °C). It was found that HfO 2 film could be deposited as low as 150 °C with carbon level not detected by X-ray photoelectron spectroscopy. As deposited film was amorphous but when the deposition temperature was raised to 400 °C, X-ray diffraction pattern showed that the film was polycrystalline with weak peak of monoclinic (020). Scanning electron microscope analysis indicated that the grain size was not significantly changed with the increase of the annealing temperature. Capacitance–voltage measurement showed that with the increase of annealing temperature, the effective dielectric constant was increased, but above 900 °C, the effective dielectric constant was decreased due to the formation of interface oxide. For 500 Å thin film, the dielectric constant of HfO 2 film annealed at 800 °C was 20.1 and the current–voltage measurements showed that the leakage current density of the HfO 2 thin film annealed at 800 °C was 2.2×10 −6 A/cm 2 at 5 V.

Characterization of Ti 6O 4(O 2C 4H 5) 8(OCH 2CH 3) 8 by electrospray time of flight mass spectrometry

A titanium oxide molecular cluster prepared by hydrolysis of titanium tetraethoxide in the presence of methacrylic acid, can be characterized by electrospray time of flight mass spectrometry (ESMS-TOF). The chemistry of such systems is not well known and ESMS is a powerful technique for studying the reactions of clusters in solution. The fingerprint of the cluster fragmentation suggests formation of Ti xO y core fragments that represent commonly observed structural constructs in bulk titanium oxide metallates. The fragmentation steps provide insight into the hydrolytic conversion of this molecular sol gel intermediate into bulk TiO 2. While MS has been applied to the study of metal alkoxide hydrolysis mechanisms, mass spectra of isolated individual titanium oxide clusters have not previously been reported.

In vitro assay of singlet oxygen generation in the presence of water-soluble derivatives of C 60

Singlet oxygen ( 1 Δ g ) is a very efficient oxidizing agent that targets numerous molecules in living cells. We report a comprehensive in vitro study of 1 Δ g -generation in the presence of two fullerene-based water-soluble sensitizers, fullerol C 60(OH) n and fullerene-core star-like polymer, C 60 [>N-CH 2CH 2(OCH 2CH 2) 2OCH 3] 6. Efficiencies of the photodynamic generation of 1 Δ g in the presence of C 60-derivatives and a reference sensitizer, the amino acid protoporphyrin IX-derivative, PP(Ala) 2(Arg) 2, were measured using electron spin resonance (ESR). Subsequently, atomic force microscopy (AFM) experiments were performed to measure the local elastic properties of living and glutaraldehyde-fixed cells exposed to the toxic action of 1 Δ g . Remarkably, the Young's modulus values obtained for four different cell lines revealed a pronounced drop as a function of exposure to 1 Δ g . Thus, our ESR and AFM results bring the evidence that the multi-functionalized fullerene-based compounds are efficient 1 Δ g -generators in aqueous media and might be implemented as oxidizing agents in biological systems. Moreover, we also show that AFM can be used as a sensitive tool for detecting early changes occurring to the subcellular structures under exposure to the oxidative stress.

Cationic and anionic environments in mono-urethanesil hybrids doped with magnesium triflate

Sol–gel derived poly(oxyethylene), POE/siloxane hybrids (mono-urethanesils) with a wide range of magnesium triflate (Mg(CF 3SO 3) 2) concentrations were analyzed by infrared and Raman spectroscopies with the goal of examining the cation/polymer, cation/cross-link, hydrogen bonding and cation/anion interactions. In the host matrix of these xerogels short CH 3-terminated POE segments are covalently bonded to the siliceous backbone through urethane linkages. Samples with ∞> n≥6 (where n is the molar ratio of (OCH 2CH 2) moieties per Mg 2+ ion) were synthesized. The spectral data obtained provided conclusive evidence that the ether oxygen atoms of the polymer chains of the host structure complex the alkaline-earth ions in materials with n≤60. “Free” triflate ions and weakly coordinated anions were detected over the whole range of salt concentration examined. The coordinated triflate species are formed in two different bonding environments. Contact ion pairs appear in materials with n≤60. This work confirms previous studies that suggested that the nature of the cations added to the mono-urethanesil-type framework plays a key-role in the properties of these composites.

Glyme-based nonaqueous electrolytes for rechargeable lithium cells

Poly(ethylene glycol)dimethyl ethers [(CH 3O(CH 2CH 2O) n CH 3, n = 1, 2, 3, and 4)] are generally known as “glymes”. This study examines the conductivity, lithium ion solvation state and charge–discharge cycling efficiency of lithium metal anodes in glyme-based electrolytes for rechargeable lithium cells. 1 M (M: mol l −1) LiPF 6 was used as the solute. The properties of the glymes were investigated by using a ternary mixed solvent consisting of n-glyme, ethylene carbonate (EC) and methylethylcarbonate (MEC). This was because the solubility of LiPF 6 is far less than 1 M in an n-glyme single solvent. The glyme solutions exhibited higher conductivity and higher lithium cycling efficiency than EC/MEC. The conductivity tended to increase with decreases in ethylene oxide chain number ( n) and solution viscosity. The decrease in the solution viscosity resulted from the change in the lithium ion solvation structure that occurred when a glyme was added to EC/MEC. The selective solvation of the glyme with respect to lithium ions was clearly demonstrated by 13 C -NMR measurements. The lithium cycling efficiency value depended on the charge–discharge current ( I ps). When n increased there was an increase in lithium cycling efficiency at a low I ps and a decrease in the reduction potential of the glymes. When the conductivities including those at low temperature (below 0 °C), and charge–discharge cycling at a high current are taken into account, di- or tri-glyme is superior to the other glymes tested here.

Computational approach to estimate layer structures of organic derivatives of boehmite

The observed basal spacings of the alkyl derivatives of boehmite, AlO(OH) 1− x (OR) x , obtained by the reaction of aluminum metal or aluminum alkoxides with alcohols at 250–300 °C was only slightly affected by the population ( x) of the alkyl groups ( x=0.39−0.21) (Chem. Mater. 12 (2000) 55). In order to clarify the origin of this independency, the molecular mechanics (MM) calculation was carried out, and the effect of the alkyl population upon the basal spacing of the butyl derivative of boehmite, AlO(OH) 1− x (OCH 2CH 2 CH 2CH 3) x , was examined in a range of x=0.00–0.30. The calculated results clearly suggested that in the range of x from 0.3 to 0.2, the boehmite derivative has the bilayer arrangement of the alkyl groups with essentially all-trans conformation. In this range, the basal spacing was only slightly affected by the population of the alkyl groups because it is determined by the most crowded part of the assembly of the alkyl chains. Since the alkyl chains are fixed to the host layers through the covalent bonding, decrease in the alkyl population does not affect essential feature of the alkyl derivatives of layered inorganics.

Synthesis and Characterization of N-Methyl-Substituted Germocanes. Crystal Structure of MeN(CH2CH2O)2GeBr2

The reaction of GeHal4 with MeN(CH2CH2OSiMe3)2 affords dihalogermocanes MeN(CH2 CH2O)2GeHal2 (1, Hal = Br; 2, Hal = Cl). Treatment of Me2Ge(NMe2)2 with MeN(CH2CH2OH)2 leads to dimethylgermocane MeN(CH2CH2O)2GeMe2 (3). The composition and structure of 1-3 were established by elemental analyses, 1H, 13C NMR spectroscopy, and mass spectrometry. The crystal structure of 1 is reported; structural data obtained from geometry DFT optimization on 1 are in good agreement with experimental results. Values of the electron density in the N→Ge bond critical point and the Laplacian of charge density for 1-3 indicate a closed-shell interaction between the Ge and N atoms.

Golden crowns: cation binding by macrocyclic gold(I) crown ether derivatives

The polyether bis(alkynes) α,ω-bis( O-propargyl)triethylene glycol and α,ω-bis( O-4-propargyloxyphenoxy)triethylene glycol reacted with [AuCl(SMe 2)] in the presence of base to form the corresponding oligomeric gold(I) acetylide complexes (AuCCCH 2O(CH 2CH 2O) 3CH 2CCAu) n and (AuCCCH 2OC 6H 4O(CH 2CH 2O) 3C 6H 4OCH 2CCAu) n . These digold(I) diacetylide complexes reacted with diphosphine ligands to give macrocyclic digold(I) complexes of the type [Au 2(μ-CC)(μ-PP)], where CC is the diacetylide and PP is a diphosphine ligand. These digold(I) complexes bind the cations Li +, Na +, K + and Cs +, as studied by electrospray mass spectrometry.

Ate complexes of Ge(II) and Sn(II) with bidentate ligands [LiE 14(OCH 2CH 2NMe 2) 3] 2 (E 14=Ge, Sn): synthesis and structure

The reaction of equimolar quantities of LiOCH 2CH 2NMe 2 and E 14(OCH 2CH 2NMe 2) 2 (E 14=Ge, Sn) in ether yielded new ate complexes [LiE 14(OCH 2CH 2NMe 2) 3] 2 (E 14=Ge ( 1), Sn ( 2)) with bidentate ligands. The compounds 1 and 2 are white crystalline substances which are highly soluble in THF and pyridine and very sensitive to the traces of oxygen and moisture. The structures of these compounds are studied by X-ray diffraction analysis. The ate complexes 1 and 2 are powerful nucleophiles and may be employed as ligands (neutral) in the coordination chemistry of the transition metals. The electronegative O-substituents at the divalent E 14 atoms render them less oxidizable than alkyl- or aryl-substituted derivatives, and the bidentate ligands, owing to intramolecular donor–acceptor interactions, make them more thermodynamically stable compared to monodentate ligands.