Solid-state synthesis of a conducting polythiophene via an unprecedented heterocyclic coupling reaction

Prolonged storage ( approximately 2 years) or gentle heating (50-80 degrees C) of crystalline 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT) affords a highly conducting, bromine-doped poly(3,4-ethylenedioxythiophene) (PEDOT), as confirmed by solid-state NMR, FTIR, CV, and vis-NIR spectroscopies. The novel solid-state polymerization (SSP) does not occur for 2,5-dichloro-3,4-ethylenedioxythiophene (DCEDOT), and requires a much higher temperature (>130 degrees C) for 2,5-diiodo-3,4-ethylenedioxythiophene (DIEDOT). X-ray structural analysis of the above dihalothiophenes reveals short Hal.Hal distances between adjacent molecules in DBEDOT and DIEDOT, but not in DCEDOT. The polymerization may also occur in the melt but is significantly slower and leads to poorly conductive material. Detailed studies of the reaction were performed using ESR, DSC, microscopy, and gravimetric analyses. SSP starts on crystal defect sites; it is exothermic by 14 kcal/mol and requires activation energy of approximately 26 kcal/mol (for DBEDOT). The temperature dependence of the conductivity of SSP-PEDOT (sigma(rt) = 20-80 S/cm) reveals a slight thermal activation. It can be further increased by a factor of 2 by doping with iodine. Using this approach, thin films of PEDOT with conductivity as high as 20 S/cm were fabricated on insulating flexible plastic surfaces.     

Template-synthesized LiCoO2, LiMn2O4, and LiNi0.8 Co0.2 O2 nanotubes as the cathode materials of lithium ion batteries

The first point of this work is to synthesize LiCoO2, LiNi0.8 Co0.2 O2, and LiMn2O4 nanotubes with the template of porous anodic aluminum oxide by thermal decomposition of sol-gel precursors. The as-synthesized materials were open-ended nanotubes with uniform shape and size based on the analysis of scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. An "in situ reaction from nanoparticle to nanotube" mechanism was discussed for the formation process of the nanotubes. The second point of this paper is to investigate the electrochemical properties of the as-synthesized nanotubes for the cathode materials of lithium ion batteries. It was found that the nanotube electrodes exhibited better reversibility and higher discharge capacities than that of their nanocrystalline counterparts. The reason for the improved electrochemical performance of the nanotube electrodes was also interpreted.     

Coupling of chromatographic ion-exchange reaction with change-partner reaction. Presumed mechanism on the ion-ion interaction of inorganic ions in Sephadex G-15 columns

A sample solution containing sodium or potassium dihydrogenphosphate or disodium or dipotassium hydrogenphosphate was eluted from a Sephadex G-15 column with either sodium or potassium chloride solution in various sample-eluent systems, and every one of the four kinds of ions employed was determined in the eluate. Then, the elution profiles showed the phenomenon that a negative peak of chloride ion coexisted in the fractions of a positive peak of phosphate ion, in all sample-eluent systems employed. This phenomenon was assumed to occur by the coupled reaction of change-partner and ion-exchange reactions including ion exclusion.     

Inducible stable DNA replication (iSDR) and the uvr-dependent tolerance of pyrimidine dimers in UV-irradiated Escherichia coli are two uncoupled processes

Inducible stable DNA replication (iSDR) is dependent on recombination and is supposed to play a role in DNA repair of Escherichia coli. Our previous data suggested that iSDR may be involved in the tolerance of UV lesions, which remain unexcised in excision-proficient E. coli exposed to some UV pretreatments. Now, the tolerance of unexcised lesions has been followed in E. coli recB21 and in E. coli priA1 sup mutants, incapable of iSDR. The obtained data do not confirm the previous hypothesis about the involvement of iSDR in the putative uvr-dependent lesion tolerance. They rather suggest that iSDR and the uvr-dependent lesion tolerance are two uncoupled processes.     

Formation of Small Silica Aggregates by Turbulent Aggregation

Aggregation of silica powder in water has been experimentally studied by turbidimetry. Aggregation was carried out in a stirred tank under physicochemical conditions corresponding to attractive interparticle forces. The effects of different primary particle sizes and stirring rates on aggregation dynamics have been studied. The scattering cross sections of silica aggregates were calculated in the framework of the anomalous diffraction approximation of light scattering theory. Aggregation has been studied by using Kusters's and Brakalov's approaches. By comparison between experimental and theoretical turbidity changes with time it has been shown that aggregates are small and slightly porous. The aggregation process is characterized by a weak fractal dimension D(wf) and an aggregate limit size L.D(wf) is found in the range 2.4-2.5. D(wf) (respectively L) is a weakly increasing (respectively decreasing) function of the stirring rate or of the shear rate. Copyright 2001 Academic Press.     

A route to heat resistant solid membranes with performances of liquid electrolytes

The confinement of ionic liquids within a porous silica matrix was performed by a one-step non-hydrolytic sol-gel route, leading to hybrid materials (called "ionogels") featuring both the mechanical and transparency properties of silica gels and the high ionic conductivity and thermal stability of ionic liquids.     

Langmuir films of (alpha-amino) phosphorus amphiphiles on various ion-containing subphases

Monolayers of amphiphilic (alpha-amino)phosphonocarboxylic and (alpha-amino)phosphonic acids have been formed by adsorption at the air/water interface. The influence of both the ionic strength and the pH of the subphase on the stability and compactness of the monolayers have been studied. The stability and the compactness of the Langmuir films are enhanced by introduction of metallic ions such as Ca(2+) or Mg(2+) in the subphases. These effects are more pronounced with Ca(2+). These metal ions can form dimeric complexes with the phosphorus moieties of the surfactant polar heads and therefore bring the amphiphiles closer. For the less hydrophobic derivative, complexation with Ca(2+) or Mg(2+) is required to ensure the formation of a stable monomolecular film. For both phosphonocarboxylic and phosphonic compounds, models have been proposed to represent the complexation phenomenon at the air/water interface.     

First total synthesis of leucamide A

The first total synthesis of marine bioactive cyclic heptapeptide Leucamide A has been accomplished, including a simple method for construction of the 4,2-bisheterocycle tandem pair substructure that employs a DAST-mediated cyclization of beta-hydroxy amide and final HBTU-promoted ring closing.     

Heterometallic hexanuclear cluster with an S = 8 spin ground state: MnII[MnII(hfac)2]3[NiII(pao)3]2 (hfac- = hexafluoroacetylacetonate,pao- = pyridine-2-aldoximate)

The heterometallic Mn(II)(4)Ni(II)(2) title compound has been synthesized and characterized by X-ray crystallography. The compound consists of a Ni-Mn-Ni linear moiety, [[Ni-(mu-NO)(3)](2)-Mn], linked by oximate bridges and three Mn(II) hfac terminal units attached by oximate oxygens in a di-mu-oxo fashion, forming a novel heterometallic cluster: Mn[Mn(hfac)(2)](3)[Ni(pao)(3)](2) (1). Magnetic measurements reveal the antiferromagnetic nature of the oximate pathway between Mn(II) and Ni(II) metal ions, which imposes an unusual high-spin ground state (S = 8) for 1.     

Photoinduced electron transfer in platinum(II) terpyridinyl acetylide complexes connected to a porphyrin unit

A series of six new dyads consisting of a zinc or magnesium porphyrin appended to a platinum terpyridine acetylide complex via a para-phenylene bisacetylene spacer are described. Different substituents on the 4' position of the terpyridinyl ligand were explored (OC7H15, PO3Et2, and H). The ground-state electronic properties of the dyads are studied by electronic absorption spectroscopy and electrochemistry, and they indicate some electronic interactions between the porphyrin subunit and the platinum complex. The photophysical properties of these dyads were investigated by steady-state, time-resolved, and femtosecond transient absorption spectroscopy in N,N-dimethylformamide solution. Excitation of the porphyrin unit leads to a very rapid electron transfer (2-20 ps) to the nearby platinum complex followed by an ultrafast charge recombination, thus preventing any observation of the charge separated state. The variation in the rate of the photoinduced electron transfer in the series of dyads is consistent with Marcus theory. The results underscore the potential of the para-phenylene bisacetylene bridge to mediate a rapid electron transfer over a long donor-acceptor distance.