Synthesis of monomeric Fe(II) and Ru(II) complexes of tetradentate phosphines

rac-Bis[{(diphenylphosphino)ethyl}-phenylphosphino]methane (DPPEPM) reacts with iron(II) and ruthenium(II) halides to generate complexes with folded DPPEPM coordination. The paramagnetic, five-coordinate Fe(DPPEPM)Cl(2) (1) in CD(2)Cl(2) features a tridentate binding mode as established by (31)P{(1)H} NMR spectroscopy. Crystal structure analysis of the analogous bromo complex, Fe(DPPEPM)Br(2) (2) revealed a pseudo-octahedral, cis-α geometry at iron with DPPEPM coordinated in a tetradentate fashion. However, in CD(2)Cl(2) solution, the coordination of DPPEPM in 2 is similar to that of 1 in that one of the external phosphorus atoms is dissociated resulting in a mixture of three tridentate complexes. The chloro ruthenium complex cis-Ru(κ(4)-DPPEPM)Cl(2) (3) is obtained from rac-DPPEPM and either [RuCl(2)(COD)](2) [COD = 1,5-cyclooctadiene] or RuCl(2)(PPh(3))(4). The structure of 3 in both the solid state and in CD(2)Cl(2) solution features a folded κ(4)-DPPEPM. This binding mode was also observed in cis-[Fe(κ(4)-DPPEPM)(CH(3)CN)(2)](CF(3)SO(3))(2) (4). Addition of an excess of CO to a methanolic solution of 1 results in the replacement of one of the chloride ions by CO to yield cis-[Fe(κ(4)-DPPEPM)Cl(CO)](Cl) (5). The same reaction in CH(2)Cl(2) produces a mixture of 5 and [Fe(κ(3)-DPPEPM)Cl(2)(CO)] (6) in which one of the internal phosphines has been substituted by CO. Complexes 2, 3, 4, and 5 appear to be the first structurally characterized monometallic complexes of κ(4)-DPPEPM.     

Debundling, selection and release of SWNTs using fluorene-based photocleavable polymers

Photocleavable polymers based on 9,9-dialkylfluorene backbone and o-nitrobenzylether were designed and synthesized to obtain stable (n,m) enriched suspensions of semiconducting SWNTs in toluene. Photoirradiation of the suspensions triggered the precipitation of the SWNTs and TEM images indicate close packing of SWNTs pointing at partial removal of the coating polymer.     

Pentafluoropyridine as a fluorinating reagent for preparing a hydrocarbon soluble β-diketiminatolead(II) monofluoride

A well-designed method for the preparation of a β-diketiminatolead(II) monofluoride has been developed using LPbNMe(2) (L = [CH{C(Me)(2,6-iPr(2)C(6)H(3)N)}(2)]) and pentafluoropyridine (C(5)F(5)N). The resulting LPbF was used for the synthesis of amidinatosilicon(II) monofluoride. Moreover the activation of a ketone was observed when the LPbF was treated with PhCOCF(3).     

Stigmasterol-based novel low molecular weight/mass organic gelators

Conjugates consisting of stigmasterol and L-phenylalanine, interconnected through short-chained dicarboxylic acyls by ester and amide bonds, respectively, were synthesized as potential low molecular weight/mass organic gelators (LMWGs/LMMGs). Their physico-chemical properties were subjected to investigation, especially their ability to form gels reversibly based on changes of the environmental conditions. Other self-assembly properties detectable by UV-VIS traces were measured in systems consisting of two miscible solvents (water/acetonitrile) with varying solvent ratios and using constant concentrations of the studied compounds. Partition and diffusion coefficients and solubility in water were calculated for the target conjugates. The conjugate 3a was the only compound from this series capable of forming a gel in 1-octanol. All three conjugates 3a-3c displayed supramolecular characteristics in the UV-VIS spectra.     

Application of colloidal palladium nanoparticles for labeling in electron microscopy

The application of palladium nanoparticles as electron-dense markers for labeling in both transmission and scanning electron microscopy requires their conjugation to a specific protein. The conjugation protocol described here includes the dihydrolipoic acid (DHLA) capping of Pd nanoparticles (8 nm equivalent diameter) and their subsequent covalent attachment to functional protein molecules such as streptavidin, protein A, or avidin. The single-step reaction was mediated using the cross-linking agent ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC). The final Pd conjugates were fully functional, as demonstrated by labeling of ultrathin resin sections of either bovine serum albumin or secretory granules of the salivary gland isolated from the partially fed female Ixodes ricinus tick. The results of bovine serum labeling were quantified, statistically evaluated, and compared with results obtained using commercially available gold particle conjugates (10 nm diameter). The highest values of labeling density were achieved using both streptavidin-Pd (106 ± 7 particles/μm2) and protein A-Au conjugates (130 ± 18 particles/μm2) compared to a commercial streptavidin-Au (66 ± 16 particles/μm2) and protein A-Pd conjugates (70 ± 11 particles/μm2). The concentrations of both DHLA and EDC, pH during conjugation, and finally thorough washing away of unbound proteins crucially influenced conjugation.     

Thermodynamics of CO2 adsorption on functionalized SBA-15 silica. NLDFT analysis of surface energetic heterogeneity

Siliceous SBA-15 mesoporous molecular sieves were functionalized with different amounts of 3-aminopropyl-trimethoxysilane. To obtain a more detailed insight into the material properties of the prepared samples, their textural parameters were combined with results of thermal analysis. Adsorption isotherms of carbon dioxide on parent and functionalized SBA-15 were measured in the temperature range from 273 to 333 K. From the temperature dependence of CO(2) isotherms the isosteric adsorption heats of CO(2) were determined and discussed. Information about the surface energetic heterogeneity caused by tethered 3-aminopropyl groups were obtained from CO(2) adsorption energy distributions calculated using the theoretical CO(2) adsorption isotherms derived from the non-local density functional theory. The values of isosteric heats and the energy distributions of CO(2) adsorption detect highly energetic sites and enabled quantification of their concentrations.     

Electronic state selectivity in dication-molecule single electron transfer reactions: NO(2+) + NO

The single-electron transfer reaction between NO(2+) and NO, which initially forms a pair of NO(+) ions, has been studied using a position-sensitive coincidence technique. The reactivity in this class of collision system, which involves the interaction of a dication with its neutral precursor, provides a sensitive test of recent ideas concerning electronic state selectivity in dicationic single-electron transfer reactions. In stark contrast to the recently observed single-electron transfer reactivity in the analogous CO(2)(2+)/CO(2) and O(2)(2+)/O(2) collision systems, electron transfer between NO(2+) and NO generates two product NO(+) ions which behave in an identical manner, whether the ions are formed from NO(2+) or NO. This observed behaviour is in excellent accord with the recently proposed rationalization of the state selectivity in dication-molecule SET reactions using simple propensity rules involving one-electron transitions.     

Methodological study of extraction procedures applied to urban particulate matter

The modified BCR three-step sequential extraction procedure has been applied to two different samples of urban particulate matters (PM). The distribution of selected trace elements As, Cd, Cr, Mn, Ni, Pb, Zn was investigated and, in a comparative study, the presence of common organic air filters in extraction procedures was evaluated. Analytes in separate fractions were determined by ICP-OES and GFAAS, respectively, depending on concentration levels. While, due to air filters, a significant increase of some analytes mobility in individual fractions has been observed in case of the jet-milled PM (tunnel Letna), but in case of the PKC sample such effect was not found. The analyte impurities built in some filters has been tested, and the impact on the reliability of analyte results has been discussed. The arsenic species occurrence and their stability in presence of air filters (size 47 mm) were investigated in both urban PM samples as well, using HPLC-ICP-MS technique. Water soluble and by three-step BCR procedure extractable arsenic forms are shown in chromatograms     

A differential evolution-based regression framework for forecasting Bitcoin price

This research proposes a differential evolution-based regression framework for forecasting one day ahead price of Bitcoin. The maximal overlap discrete wavelet transformation first decomposes the original series into granular linear and nonlinear components. We then fit polynomial regression with interaction (PRI) and support vector regression (SVR) on linear and nonlinear components and obtain component-wise projections. The sum of these projections constitutes the final forecast. For accurate predictions, the PRI coefficients and tuning of the hyperparameters of SVR must be precisely estimated. Differential evolution, a metaheuristic optimization technique, helps to achieve these goals. We compare the forecast accuracy of the proposed regression framework with six advanced predictive modeling algorithms- multilayer perceptron neural network, random forest, adaptive neural fuzzy inference system, standalone SVR, multiple adaptive regression spline, and least absolute shrinkage and selection operator. Finally, we perform the numerical experimentation based on—(1) the daily closing prices of Bitcoin for January 10, 2013, to February 23, 2019, and (2) randomly generated surrogate time series through Monte Carlo analysis. The forecast accuracy of the proposed framework is higher than the other predictive modeling algorithms.