k‐Nearest neighbors optimization‐based outlier removal

Datasets of molecular compounds often contain outliers, that is, compounds which are different from the rest of the dataset. Outliers, while often interesting may affect data interpretation, model generation, and decisions making, and therefore, should be removed from the dataset prior to modeling efforts. Here, we describe a new method for the iterative identification and removal of outliers based on a k‐nearest neighbors optimization algorithm. We demonstrate for three different datasets that the removal of outliers using the new algorithm provides filtered datasets which are better than those provided by four alternative outlier removal procedures as well as by random compound removal in two important aspects: (1) they better maintain the diversity of the parent datasets; (2) they give rise to quantitative structure activity relationship (QSAR) models with much better prediction statistics. The new algorithm is, therefore, suitable for the pretreatment of datasets prior to QSAR modeling. © 2014 Wiley Periodicals, Inc.     

Abraham model expressions for describing water-to-organic solvent and gas-to-organic solvent partition coefficients for solute transfer into anhydrous poly(ethylene glycol) dialkyl ether solvents at 298.15 K

Henry’s law constants and infinite dilution activity coefficients were compiled from the published chemical and engineering literature for gaseous solutes and organic liquids in butyl diglyme, butyl triglyme and tetraglyme. The published literature values were converted into water-to-liquid and gas-to-liquid partition coefficients using standard thermodynamic relationships. The calculated partition coefficients were correlated mathematically with the Abraham solvation parameter model. The derived Abraham model correlations can be used to predict the partitioning behaviour of additional solutes into dry, anhydrous butyl diglyme, butyl triglyme and tetraglyme.     

Quartz tuning fork based portable sensor for vapor phase detection of methanol adulteration of ethanol by using aniline-doped polystyrene microwires

The authors describe a sensor capable of detecting methanol adulteration of ethanol. The sensor is based on the use of quartz tuning forks (QTFs) that were functionalized with polymer wires made from a combination of polystyrene (PS) and aniline. Exposure to organic vapors causes the resonance frequency of the functionalized QTF to change, and this can be used to identify the type and concentration of the analyte. A mixture of methanol and ethanol vapors in varying concentrations was exposed to the QTF polymer system. The resulting shift in the resonance frequency of the QTF was firstly used to determine the concentration of alcohol vapor, which is reflected in the amount of shift. Secondly, the nature of change in resonance frequency was used to determine the type of alcohol exposed to the sensor. The sensitivity and selectivity of the sensors to ethanol and methanol vapors has been investigated. A portable hand-held prototype sensor has been developed which displays the percentage of two alcohols it is exposed to. It can detect ethanol adulteration where the methanol concentration is as low as 5%.

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Graphical abstract Spring loaded Quartz Tuning Fork sensors functionalized with polystyrene-aniline wires exhibit opposite responses (increase and decrease in frequency) to vapors of ethanol and methanol respectively.The methanol adulteration of ethanol solutions may thus be detected by sensing their vapors.

     

Abraham model ion-specific equation coefficients for the 1-butyl-2,3-dimethyimidazolium and 4-cyano-1-butylpyridinium cations calculated from measured gas-to-liquid partition coefficient data

Partition coefficient and gas solubility data have been assembled from the published chemical and engineering literature for solutes dissolved in anhydrous 1-butyl-3-methylimidazolium dicyanamide, 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, and 4-cyano-1-butylpyrridinium bis(trifluoromethylsulfonyl)imide. More than 60 experimental data points were gathered for each IL solvent. The compiled experimental data were used to derive Abraham model correlations for describing the solute transfer properties into the three anhydrous IL solvents from both the gas phase and water. The derived mathematical correlations described the observed solute transfer properties, expressed as the logarithm of the water-to-IL partition coefficient and logarithm of the gas-to-IL solvent partition coefficient, to within standard deviations of 0.125 log units (or less). Abraham model ion-specific equation coefficients are also calculated for the 1-butyl-2,3-dimethylimidazolium and 4-cyano-1-butylpyridinium cations.     

Photoinduced Cross‐Linking of Dynamic Poly(disulfide) Films via Thiol Oxidative Coupling

Initially developed as an elastomer with an excellent record of barrier and chemical resistance properties, poly(disulfide) has experienced a revival linked to the dynamic nature of the S–S covalent bond. A novel photobase‐catalyzed oxidative polymerization of multifunctional thiols to poly(disulfide) network is reported. Based solely on air oxidation, the single‐step process is triggered by the photodecarboxylation of a xanthone acetic acid liberating a strong bicyclic guanidine base. Starting with a 1 μm thick film based on trithiol poly(ethylene oxide) oligomer, the UV‐mediated oxidation of thiols to disulfides occurs in a matter of minutes both selectively, i.e., without overoxidation, and quantitatively as assessed by a range of spectroscopic techniques. Thiolate formation and film thickness determine the reaction rates and yield. Spatial control of the photopolymerization serves to generate robust micropatterns, while the reductive cleavage of S–S bridges allows the recycling of 40% of the initial thiol groups.

     

Role of the hydroxyl-water hydrogen-bond network in structural transitions and selectivity toward cesium in Cs0.38(D1.08H0.54)SiTi2O7.(D0.86H0.14)2O crystalline silicotitanate

The crystal structure of the selective Cs+ ion exchanger D1.6H0.4Ti2SiO7.D2.66H0.34O1.5, known as crystalline silicotitanate or CST, has been determined in both native (D-CST) and in the Cs+-exchanged forms ((Cs, D)-CST) from angle-dispersive and time-of-flight neutron diffraction studies. The final fully exchange Cs+ form transformed from D-CST with unit cell parameters a = 11.0704(3) A c = 11.8917(5) A and space group P42/mbc, to one with a = 7.8902(1) A c = 11.9051(4) A and space group P42/mcm. Rietveld structure refinements of both D-CST and (Cs, D)-CST suggest the transition, and ultimately the selectivity, is driven by changes in the positions of water molecules, in response to the initial introduction of Cs+. The changes in water position appear to disrupt the D-O-O-D dihedral associated with the CST framework in space group P42/mbc which ultimately leads to the structural transition. The new geometric arrangement of the water-deuteroxyl network in (Cs, D)-CST suggests that Dwater-Ddeuteroxyl repulsion forced by Cs+ exchange drives the structural transformation.     

Characterization of the sorption of gaseous and organic solutes onto polydimethyl siloxane solid-phase microextraction surfaces using the Abraham model

Water-to-polydimethylsiloxane (PDMS) and gas-to-PDMS sorption coefficients have been compiled for 170 gaseous and organic solutes. Both sets of sorption coefficients were analyzed using the Abraham solvation parameter model. Correlations were obtained for both "dry" headspace solid-phase microextraction and conventional "wet" PDMS coated surfaces. The derived equations correlated the experimental water-to-PDMS and gas-to-PDMS data to better than 0.17 and 0.18 log units, respectively. In the case of the gas-to-PDMS sorption coefficients, the experimental values spanned a range of approximately 11 log units.     

Hydrophobic interaction chromatography of proteins. I. The effects of protein and adsorbent properties on retention and recovery

The contributions of protein and adsorbent properties to retention and recovery were examined for hydrophobic interaction chromatography (HIC) using eight commercially available phenyl media and five model proteins (ribonuclease A, lysozyme, alpha-lactalbumin, ovalbumin and BSA). The physical properties of the adsorbents were determined by inverse size exclusion chromatography (ISEC). The adsorbents examined differ from each other in terms of base matrix, ligand density, porosity, mean pore radius, pore size distribution (PSD) and phase ratio, allowing systematic studies to understand how these properties affect protein retention and recovery in HIC media. The proteins differ in such properties as adiabatic compressibility and molecular mass. The retention factors of the proteins in the media were determined by isocratic elution. The results show a very clear trend in that proteins with high adiabatic compressibility (higher flexibility) were more strongly retained. For proteins with similar adiabatic compressibilities, those with higher molecular mass showed stronger retention in Sepharose media, but this trend was not observed in adsorbents with polymethacrylate and polystyrene divinylbenzene base matrices. This observation could be related to protein recovery, which was sensitive to protein flexibility, molecular size, and conformation as well as the ligand densities and base matrices of the adsorbents. Low protein recovery during isocratic elution could affect the interpretation of protein selectivity results in HIC media. The retention data were fitted to a previously published retention model based on the preferential interaction theory, in terms of which retention is driven by release of water molecules and ions upon protein-adsorbent interaction. The calculated number of water molecules released was found to be statistically independent of protein retention strength and adsorbent and protein properties.     

Layered ruthenium hexagonal perovskites: The new series [Ba2Br2−2x(CO3)x][Ban+1RunO3n+3] with n=2, 3, 4, 5

Single crystals of the title compounds were prepared by solid state reactions from barium carbonate and ruthenium metal using a BaBr₂ flux and investigated by X-ray diffraction method using Mo(Kα) radiation and a Charge Coupled Device (CCD) detector. A structural model for the term n=2, Ba₅Ru₂Br₂O₉ (1) was established in the hexagonal symmetry, space group P6₃/mmc, a=5.8344(2) Å, c=25.637(2) Å, Z=2. Combined refinement and maximum-entropy method (MEM) unambiguously show the presence of CO₃²⁻ ions in the three other compounds (2, 3, 4). Their crystal structures were solved and refined in the trigonal symmetry, space group , a=5.8381(1) Å, c=15.3083(6) Å for the term n=3, Ba₆Ru₃Br_1.54(CO₃)_0.23O₁₂ (2), and space group , a=5.7992(1) Å, c=52.866(2) Å and a=5.7900(1) Å, c=59.819(2) Å for the terms n=4, Ba₇Ru₄Br_1.46(CO₃)_0.27O₁₅ (3), and n=5, Ba₈Ru₅Br_1.64(CO₃)_0.18O₁₈ (4), respectively. The structures are formed by the periodic stacking along [0 0 1] of (n+1) hexagonal close-packed [BaO₃] layers separated by a double layer of composition [Ba₂Br_2−2x(CO₃)_x]. The ruthenium atoms occupy the n octahedral interstices created in the hexagonal perovskite slabs and constitute isolated dimers Ru₂O₉ of face-shared octahedra (FSO) in 1 and isolated trimers Ru₃O₁₂ of FSO in 2. In 3 and 4, the Ru₂O₉ units are connected by corners either directly (3) or through a slab of isolated RuO₆ octahedra (4) to form a bidimensional arrangement of RuO₆ octahedra. These four oxybromocarbonates belong to the family of compounds formulated [Ba₂Br_2−2x(CO₃)_x][Ba_n+1Ru_nO_3n+3] where n represents the thickness of the octahedral string in hexagonal perovskite slabs. These compounds are compared to the oxychloride series.