Two-step numerical procedure for complex permittivity retrieval of dielectric materials from reflection measurements

A two-step measurement procedure has been proposed for measurement of complex permittivity of dielectric materials using one-port reflection measurements. In the procedure, as a first step, a graphical method is applied to analyze on the complex reflection-coefficient plane the general pattern of dielectric behavior of the sample. Then, as a second step, optimization algorithms are utilized for retrieving electrical properties of samples. The procedure requires measurement of complex reflection scattering parameters of at least two samples with different lengths. It has been validated by X-band measurements of three polyvinyl chloride samples with lengths 5, 10, and 20 mm.     

Effect of epoxidized palm oil on the mechanical and morphological properties of a PLA–PCL blend

In this study, the effects of epoxidized palm oil (EPO) on the mechanical and morphological properties of a blend of two types of biodegradable polymer, poly(lactic acid) (PLA) and polycaprolactone (PCL), were investigated. The solution-casting process, with chloroform as a solvent, was used to prepare samples. Addition of EPO reduced the tensile strength and modulus but increased elongation at break for the PLA–PCL blend. The highest elongation at break was observed for the blend with 10 % (w/w) EPO content. Scanning electron microscopy (SEM) indicated that the fractured surface morphology of the PLA–PCL blend became more stretched and homogeneous in PLA–PCL–EPO. Possible interactions between the PLA–PCL blend and EPO were also characterized by use of Fourier-transform infrared (FTIR) spectroscopy. Thermal stability was studied by differential scanning calorimetry and thermogravimetric analysis. The results from FTIR and SEM revealed that the miscibility of the PLA–PCL blend was improved by addition of EPO.     

Cyanobuta‐1,3‐dienes as Novel Electron Acceptors for Photoactive Multicomponent Systems

The synthesis, electrochemical, and photophysical properties of five multicomponent systems featuring a Zn^II porphyrin (ZnP) linked to one or two anilino donor‐substituted pentacyano‐ (PCBD) or tetracyanobuta‐1,3‐dienes (TCBD), with and without an interchromophoric bridging spacer (S), are reported: ZnP‐S‐PCBD ( 1 ), ZnP‐S‐TCBD ( 2 ), ZnP‐TCBD ( 3 ), ZnP‐(S‐PCBD)₂ ( 4 ), and ZnP‐(S‐TCBD)₂ ( 5 ). By means of steady‐state and time‐resolved absorption and luminescence spectroscopy (RT and 77 K), photoinduced intramolecular energy and electron transfer processes are evidenced, upon excitation of the porphyrin unit. In systems equipped with the strongest acceptor PCBD and the spacer ( 1 , 4 ), no evidence of electron transfer is found in toluene, suggesting ZnP→PCBD energy transfer, followed by ultrafast (<10 ps) intrinsic deactivation of the PCBD moiety. In the analogous systems with the weaker acceptor TCBD ( 2 , 5 ), photoinduced electron transfer occurs in benzonitrile, generating a charge‐separated (CS) state lasting 2.3 μs. Such a long lifetime, in light of the high Gibbs free energy for charge recombination (ΔG_CR=?1.39 eV), suggests a back‐electron transfer process occurring in the so‐called Marcus inverted region. Notably, in system 3 lacking the interchromophoric spacer, photoinduced charge separation followed by charge recombination occur within 20 ps. This is a consequence of the close vicinity of the donor–acceptor partners and of a virtually activationless electron transfer process. These results indicate that the strongly electron‐accepting cyanobuta‐1,3‐dienes might become promising alternatives to quinone‐, perylenediimide‐, and fullerene‐derived acceptors in multicomponent modules featuring photoinduced electron transfer.     

Theoretical study of hydrolysis of an imine oxime in aqueous solution and crystal structure and spectroscopic characterization of a platinum(II) complex containing the hydrolysis product

The hydrolysis of an imine oxime (ppeieoH) in neutral and acidic aqueous solutions was studied using DFT at the B3LYP/6-311G(d,p) level. The rate-determining step at the neutral and acidic aqueous solutions is the nucleophilic attack of the water molecules to the neutral or protonated imine C atom of ppeieoH. The activation energy is much lower in the acidic hydrolysis. The hydrolysis of ppeieoH results in the parent carbonyl oxime (inapH) and amine compounds with ΔG _cal values of 8.66 and 11.02 kJ mol^?1 in the neutral and acidic solutions, respectively. The hydrolysis of ppeieoH was observed experimentally during its reaction with K₂[PtCl₄] in an aqueous solution. The reaction yielded [PtCl(inap)(DMSO)], which contains only the hydrolysis product inap. The new platinum(II) complex was characterized spectroscopic techniques and X-ray diffraction. The platinum(II) ion is coordinated by chlorido, carbonyl oxime (inap), and DMSO ligands forming a distorted square-planar arrangement. The molecules of the platinum(II) complex were connected by weak non-conventional C–H···O and C–H···π hydrogen bonds.     

Insights into directing group ability in palladium-catalyzed C-H bond functionalization

This paper describes a detailed investigation of factors controlling the dominance of a directing group in Pd-catalyzed ligand-directed arene acetoxylation. Mechanistic studies, involving reaction kinetics, Hammett analysis, kinetic isotope effect experiments, and the kinetic order in oxidant, have been conducted for a series of different substrates. Initial rates studies of substrates bearing different directing groups showed that these transformations are accelerated by the use of electron-withdrawing directing groups. However, in contrast, under conditions where two directing groups are in competition with one another in the same reaction flask, substrates with electron-donating directing groups react preferentially. These results are discussed in the context of the proposed mechanism for Pd-catalyzed arene acetoxylation.     

Modulation of the ligand-field anisotropy in a series of ferric low-spin cytochrome c mutants derived from Pseudomonas aeruginosa cytochrome c-551 and Nitrosomonas europaea cytochrome c-552: a nuclear magnetic resonance and electron paramagnetic resonance study

Cytochromes of the c type with histidine-methionine (His-Met) heme axial ligation play important roles in electron-transfer reactions and in enzymes. In this work, two series of cytochrome c mutants derived from Pseudomonas aeruginosa (Pa c-551) and from the ammonia-oxidizing bacterium Nitrosomonas europaea (Ne c-552) were engineered and overexpressed. In these proteins, point mutations were induced in a key residue (Asn64) near the Met axial ligand; these mutations have a considerable impact both on heme ligand-field strength and on the Met orientation and dynamics (fluxionality), as judged by low-temperature electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) spectra. Ne c-552 has a ferric low-spin (S = 1/2) EPR signal characterized by large g anisotropy with g(max) resonance at 3.34; a similar large g(max) value EPR signal is found in the mitochondrial complex III cytochrome c1. In Ne c-552, deletion of Asn64 (NeN64Delta) changes the heme ligand field from more axial to rhombic (small g anisotropy and g(max) at 3.13) and furthermore hinders the Met fluxionality present in the wild-type protein. In Pa c-551 (g(max) at 3.20), replacement of Asn64 with valine (PaN64V) induces a decrease in the axial strain (g(max) at 3.05) and changes the Met configuration. Another set of mutants prepared by insertion (ins) and/or deletion (Delta) of a valine residue adjacent to Asn64, resulting in modifications in the length of the axial Met-donating loop (NeV65Delta, NeG50N/V65Delta, PaN50G/V65ins), did not result in appreciable alterations of the originally weak (Ne c-552) or very weak (Pa c-551) axial field but had an impact on Met orientation, fluxionality, and relaxation dynamics. Comparison of the electronic fingerprints in the overexpressed proteins and their mutants reveals a linear relationship between axial strain and average paramagnetic heme methyl shifts, irrespective of Met orientation or dynamics. Thus, for these His-Met axially coordinated Fe(III), the large g(max) value EPR signal does not represent a special case as is observed for bis-His axially coordinated Fe(III) with the two His planes perpendicular to each other.     

Electronic spectrum of TaO and its hyperfine structure

The B (2)Phi(5/2)-X(1) (2)Delta(3/2)(0,0) band at 778 nm and the C (2)Delta(3/2)-X(1) (2)Delta(3/2)(0,0) band at 737 nm of tantalum oxide (TaO) were recorded by laser excitation spectroscopy using a hollow cathode sputtering source to generate the molecules. The hyperfine structure arising from the (181)Ta (I=72) nucleus was measured at sub-Doppler resolution using the technique of intermodulated fluorescence spectroscopy. The hyperfine structure was assigned and fitted in order to derive accurate values for the magnetic dipole and electric quadrupole interactions. The magnetic hyperfine constant for the ground electronic state was also calculated using the density functional theory as h(3/2)=625 MHz, in good agreement with the experimental value of 647+/-10 MHz. This result suggests that the X (2)Delta ground state of TaO is well described by a pure deltasigma(2) electronic configuration, where the unpaired electron is located in a Ta 5ddelta orbital.     

An optimized extraction and gas chromatography analysis method for the quantification of diluent hydrocarbons in froth treatment tailings

Froth treatment tailings are one type of waste stream generated during the extraction of surface-mined oil sands bitumen. To remove water and solids from bitumen froth recovered during the water-based extraction process, hydrocarbon diluent is added, and settling and/or centrifugation are applied to the diluted bitumen froth, producing diluted bitumen and froth treatment tailings. While recovery processes are in place to remove and recycle the diluent from froth treatment tailings, some residual diluent can remain. Since tailings are stored in outdoor ponds, the residual diluent can have implications for methanogenic microbial processes and resulting greenhouse gas emissions. This work presents a methodology to accurately extract and quantify diluent hydrocarbons from froth treatment tailings using gas chromatography. A cold-start temperature program is used to separate diluent hydrocarbons from any residual bitumen in the sample, and diluent is quantified using commercial standards as well as unprocessed diluent. A series of extraction parameters were tested and results from multiple conditions are shown with a rationale for the selected optimized parameters. Quantification of diluent in tailings samples is demonstrated from 60 to 5329 μg/g, and results from quality control standards show an average diluent recovery of 100 ± 10%.     

New potential humic acid stationary phase toward drug components: Development of a chemometric‐assisted RP‐HPLC method for the determination of paracetamol and caffeine in tablet formulations

A new humic acid based stationary phase has been used, for the first time, to achieve the separation and quantification of paracetamol and caffeine in pharmaceutical preparations under reversed‐phase high‐performance liquid chromatography conditions. Central composite design was applied as a powerful tool to optimize the most dominant parameters that influence the resolution of reversed‐phase high‐performance liquid chromatography, that is, mobile phase composition (acetonitrile percentage in water), flow rate, and column temperature. The optimum conditions were obtained as 21.69%, 1.5 mL/min, and 15°C, respectively, with the aid of a second‐order quadratic model and desirability function. Under the optimum conditions, the peaks could be baseline separated within 10 min. For the developed reversed‐phase high‐performance liquid chromatography method, the linearity was investigated in the concentration ranges of 2–160 mg/mL (R² = 0.999) for paracetamol and 2–9.9 mg/mL (R² = 0.991) for caffeine. Mean recoveries for paracetamol and caffeine were 95.90 and 95.68%, respectively. The limits of detection and quantification were 4.1 × 10^‐4 and 1.3 × 10^‐3 mg/mL for paracetamol and 1.6 × 10^‐4 and 5.0 × 10^‐4 mg/mL for caffeine. The results showed that the new humic acid based stationary phase is very suitable for the separation of paracetamol and caffeine in pharmaceutical preparations and, thus it can be used effectively in the pharmaceutical industry.     

The electrochemical detection of droplets in microfluidic devices

This paper presents a new electrochemical method for the detection and characterisation of aqueous droplets in an organic carrier fluid (1,2-dichloroethane) formed in flow-focusing microfluidic devices. The devices consist of a conventional flow-focusing channel 250 microm wide and 250 microm deep cast out of poly(dimethylsiloxane) (PDMS) which is sealed onto a glass substrate containing a set of microelectrodes 100 microm long. Chronoamperometric analysis of a suitable electrolyte contained in the organic phase is presented for characterising the droplet frequency and size. This chronoamperometric method is then extended to a dual working electrode approach in order to determine the velocity of the droplet. Good agreement between experimental measurements and theory was observed.