Formamide dimers: a computational and matrix isolation study

The dimerization of formamide (FMA) has been investigated by matrix isolation spectroscopy, static ab initio calculations, and ab initio molecular dynamics (AIMD) simulations. Comparison of the experimental matrix IR spectra with the ab initio calculations reveals that two types of dimers A and C are predominantly formed, with two and one strong NH...O hydrogen bonds, respectively. This is in accordance with previously published experiments. In addition, there is also experimental evidence for the formation of the thermally labile dimer B after deposition of high concentrations of FMA in solid xenon. The AIMD simulations of the aggregation process show that in all cases dimer C is initially formed, but rearrangement to the more stable doubly hydrogen-bonded structures A or B occurs for a fraction of collisions on the sub-picosecond time scale.     

Determination of trace levels of total fluorine in water using combustion ion chromatography for fluorine: a mass balance approach to determine individual perfluorinated chemicals in water

Perfluorinated compounds (PFCs) such as perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) have received worldwide attention because of their environmental persistence and widespread distribution. Because of the lack of robust analytical methods and standards to detect all of the PFCs, and their precursors and metabolic intermediates, a mass balance approach involving the determination of total fluorine (TF), followed by fractionation of samples to separately determine inorganic and organic fluorine, is needed. In this study, we have developed a method to determine low microg/L levels of total fluorine (TF) in seawater samples. Further, seawater samples were fractionated into organic and inorganic fractions by extraction with organic solvents, which were then analyzed for TF, extractable organic fluorine (EOF) and inorganic fluorine (IF; i.e., fluoride). Concentrations of known perfluorinated compounds (PFCs) including PFOS and PFOA were also determined in water samples by liquid chromatography-tandem mass spectrometry (LC-MS/MS) to enable calculation of the fraction of fluorine that is contributed by PFCs to TF. A major proportion of fluorine in seawater was in the form of fluoride (>90% in locations not affected by direct discharges). Nevertheless, within the organofluorine fraction, a major percentage (60-90%) of fluorine still remains unknown in water samples, suggesting the occurrence of other fluorinated acids in addition to known perfluorinated acids. Further studies are needed to identify and quantify the unidentified organofluorines in seawater. Mass balance analysis of total organic fluorine (TOF) and EOF is important, if we are to understand transport and fate of fluorinated compounds in the environment, and if we are to identify the sources of unidentified fluorinated compounds.     

Metastable tetragonal phase CdWO4 nanoparticles synthesized with a solvothermal method

CdWO4 has only previously been reported in the monoclinic, or wolframite, phase. Here we report the first metastable, tetragonal or scheelite, CdWO4 nanopowder. The tetragonal CdWO4 was synthesized by a propylene glycol solvothermal method. The scheelite phase is stabilized by a combination of high surface area and surface complexation by the propylene glycol. The CdWO4 is stable at 1 bar to 300 degrees C, and converts back to the monoclinic wolframite phase between 300 and 500 degrees C. The nanopowder exhibits cubic morphology and the average particle size of the nanopowder is around 50 nm.     

Efficient resolution of racemic N-benzyl beta3-amino acids by iterative liquid-liquid extraction with a chiral (salen)cobalt(III) complex as enantioselective selector

The efficient (up to 93% ee) resolution of racemic N-benzyl beta(3)-amino acids has been achieved by an iterative (two cycle) liquid-liquid extraction process using a lipophilic chiral (salen)cobalt(III) complex [Co(III)(1)(OAc)]. As a result of the resolution by extraction, one enantiomer of the N-benzyl beta(3)-amino acid predominated in the aqueous phase, while the other enantiomer was driven into the organic phase by complexation to cobalt. The complexed amino acid was then quantitatively released into an aqueous phase, by a reductive (Co(III)--> Co(II)) counter-extraction using l-ascorbic acid. The reductive cleavage allowed for the recovery of the cobalt(II) selector in up to 90% yield (easily re-oxidable to Co(III) with air/AcOH).     

Photolysis of methylcobalamin: identification of the relevant excited states involved in Co-C bond scission

The relevant excited states involved in the photolysis of methylcobalamin (MeCbl) have been examined by means of time-dependent density functional theory (TD-DFT). The low-lying singlet and triplet excited states have been calculated along the Co-C bond at the TD-DFT/BP86/6-31g(d) level of theory in order to investigate the dissociation process of MeCbl. These calculations have shown that the photodissociation is mediated by the repulsive 3(sigmaCo-C --> sigma*Co-C) triplet state. The key metastable photoproduct involved in Co-C bond photolysis was identified as an S1 state having predominantly dCo --> pi*corrin metal-ligand charge transfer (MLCT) character.     

Preparation and spectroelectrochemical characterization of composite films of poly(3,4-ethylenedioxythiophene) with 4-(pyrrole-1-yl) benzoic acid

The possibility of incorporation of 4-(pyrrole-1-yl) benzoic acid, PyBA, during electrodeposition of poly(3,4-ethylenedioxythiophene), PEDOT, is demonstrated here. The resulting novel composite material has been fabricated as moderately thin (ca 200–300 nm thick) PEDOT/PyBA film on electrode surface. As evidenced from scanning tunneling microscopy (STM) and scanning electron microscopy (SEM), morphology of the composite film is dense and granular, and it is composed of larger granules in comparison to the PyBA-free PEDOT film. It is apparent from infrared reflectance absorption spectroscopy and spectroelectrochemical measurements that the PEDOT/PyBA composite film cannot be viewed as simple mixtures of PEDOT and PyBA components. Some specific (chemical) interactions between PEDOT and PyBA can be expected. The conducting polymer serves as a robust, positively charged conductive polmer matrix for anionic (carboxylate-group derivatized) partially polymerized PyBA structures. Upon incorporation of PyBA, the overall stability of PEDOT film (resistance to dissolution during prolonged voltammetric potential cycling) has been improved. The fact, that the composite PEDOT/PyBA film is capable of preconcentrating (under open circuit conditions) both cations (Cu²⁺) or anions implies the presence of both free (available for binding) carboxylate groups and positively charged PEDOT sites. The presence of PyBA in PEDOT seems to facilitate charge propagation in the composite film. “Contribution to the International Workshop on Electrochemistry of Electroactive Materials (WEEM-2006), Repino, Russia, 24–29 June 2006”.     

The structure of spaces of quasianalytic functions of Roumieu type

It is shown that spaces of quasianalytic ultradifferentiable functions of Roumieu type ℰ_{w}(Ω), on an open convex set , satisfy some new (Ω) -type linear topological invariants. Some consequences for the splitting of short exact sequences of these spaces as well as for the structure of the spaces are derived. In particular, Fréchet quotients of ℰ_{w}(Ω) have property (), while dual Fréchet quotients have property () of Vogt. The work of P. Domański was supported by Committee of Scientific Research (KBN), Poland, grant P03A 022 25.     

Poly(3-alkylthiophenes): new sorption materials for solid phase microextraction of drugs isolated from human plasma

A novel sorbent in solid phase microextraction (SPME) method based on poly(3-alkylthiophenes) was used in the isolation of linezolid from human plasma samples following liquid chromatography determination. The effect of extraction time on the sorption capacity of the SPME process was studied and pointed at 10 min both for adsorption and desorption. Poly(3-methylthiophene) and poly(3-nonylthiophene) were applied for the extraction of linezolid from water solutions. In plasma samples, four coatings including polythiophene and poly(3-penthylthiophene) were investigated. With these measurements, correlation coefficients were calculated in the range from 0.9820 to 0.9995, and the relative standard deviations were below 15%. That allowed claiming that the synthesized and described materials can be successfully applied in the analysis of linezolid also from other matrices such as urine or blood.     

Improvement of tribological properties of co-acting elements by oil pockets creation on sliding surfaces

Sliding experiments were carried out using a block-on-ring friction machine. The tribosystem consists of the stationary block (counter-specimen) pressed at the required load P against the ring (specimen) rotating at the defined speed. The sliding was unidirectional. The block was a part of a bearing sleeve hardened EN-GJS 400-15 cast iron with a hardness value of 50 HRC. The ring samples, 35 mm in diameter, were made from hardened 42CrMo4 steel of hardness 32 HRC. Some variants of specimen surfaces were created by burnishing technique. Two kinds of experiments were done. Seizure tests were conducted at increasing pressure for sliding speeds in the range: 0.27–0.55 m/s. Wear resistance test was carried out under artificially increased dustiness conditions, too. It was found that surface texturing improved seizure resistance for the smallest sliding speed (0.27 m/s) comparing to untextured ground samples. The wear of steel rings with spherical dimples was smaller than of those having dimples of long drop shape for the pit-area ratio range of 7.5–20%.