Hydrogen-bonded coordination network in crystal structures of [Cu(3-PM)4Cl2] and [Cu(4-PM)4Cl]Cl, (PM = pyridylmethanol)

The crystal and molecular structures of [Cu(3-PM)₄Cl₂] (1) and [Cu(4-PM)₄Cl]Cl (2) have been determinated by X-ray crystallography. Complex 1 crystallizes in the triclinic system, space group P–1, with lattice parameters a = 7.972(2) Å, b = 8.293(2) Å, c = 10.707(2) Å, = 105.73(3)°, = 90.04(3)°, = 110.38(3)°, and Z = 1 at 100 K. The coordination geometry of each Cu atom is approximately octahedral formed by four nitrogen atoms of pyridine rings of 3-pyridylmethanol molecules in the equatorial plane and two chlorine atoms occupying the axial positions. The O—HsO, C—HsCl, and O—HsCl intermolecular hydrogen bonds and s stacking link the molecules in 3-D hydrogen-bonded coordination network. Complex 2 crystallizes in the tetragonal system, space group P4/n, with lattice parameters a = 10.464(1) Å, c = 11.339(2) Å, and Z = 2 at 217 K and a = 10.352(1) Å, c = 11.201(2) Å, and Z = 2 at 293 K. The coordination geometry of Cu atom in the [Cu(4-PM)₄Cl]⁺ ion is approximately square pyramidal formed by four nitrogen atoms of pyridine rings of 4-pyridylmethanol molecules in equatorial plane and one chlorine atom in axial position. The O—HsCl and C—HsCl intermolecular hydrogen bonds link the molecules in 2-D hydrogen-bonded coordination network.     

A Coupled Chemical Kinetic and Nucleation Model of Fume Formation in Metal–Inert-Gas/Metal–Active-Gas Welding

A computational model of the formation of welding fume in arc plasmas, under conditions occurring in metal–inert-gas (MIG) and metal–active-gas (MAG) welding, is presented. The model couples the chemical kinetics occurring in high-temperature mixtures of iron vapour, oxygen and argon with a moment model of the nucleation and growth by condensation of iron and iron oxide nanoparticles. Results are presented for different iron vapour concentrations, oxygen-to-argon ratios, and quench rates. It is found that the presence of oxygen has important effects on the gas-phase chemistry and the properties of the nanoparticles. FeO nanoparticles are preferentially nucleated, and have smaller diameter than the Fe nanoparticles that are produced in the absence of oxygen. The final composition of the nanoparticles depends on the relative concentrations of iron and oxygen in the plasma. A three-dimensional arc model that includes vaporization of the wire electrode is used to predict temperature, velocity and iron vapour mass fraction distributions in typical MIG and MAG welding conditions. Calculations of nanoparticle formation and growth along streamlines confirm the importance of oxygen in determining the fume particle properties.     

Correlation of capillary zone electrophoresis with continuous free-flow zone electrophoresis: application to the analysis and purification of synthetic growth hormone releasing peptide

Two carrier-free electrophoretic separation methods, capillary zone electrophoresis (CZE) and continuous free-flow zone electrophoresis (FFZE), have been applied to both microanalysis at the nanogram level and preparative fractionation, with a throughput of 30 mg/h, of synthetic growth hormone releasing peptide (GHRP). A crude product of GHRP, a hexapeptide with the sequence His-D-Trp-Ala-Trp-D-Phe-Lys-NH2, synthesized by the solid phase methodology, was desalted and analyzed by CZE. Based on the results of analytical CZE the separation was converted into a preparative purification procedure by continuous FFZE, employing the same separation medium (0.5 mol/L acetic acid, pH 2.6). The purifity of peptide fractions obtained by FFZE was reevaluated by CZE. The combination of these two techniques proved to be a valuable tool for both peptide analysis and peptide purification. A close correlation of CZE and FFZE, resulting from the fact that both methods are based on the same separation principle (zone electrophoresis) and that both are performed in a free solution of the same composition, was confirmed. However, when transforming data from CZE to FFZE, the different electroosmotic flow, temperature and electric field intensity in the capillary and in the flow-through cell, respectively, have to be taken into account and corresponding corrections have to be made.     

Crystallization and Melting of β-Nucleated Isotactic Polypropylene

Ca salts of suberic (Ca-Sub) and pimelic acid (Ca-Pim) were synthesized and used as β-nucleating agents in different grades of isotactic polypropylene (IPP). Propylene homo-, random- and block-copolymers containing these additives crystallize principally in pure β-modification as demonstrated in isothermal and non-isothermal crystallization experiments. Ca-Sub proved the most effective β-nucleating agent known, so far. It broadens the upper crystallization temperature range of pure β-IPP formation up to 140°C. The effect of the additives on the crystallization and melting characteristics of the polymers was studied. The degree of crystallinity of the β-modification was found to be markedly higher than that of α-IPP. High temperature melting peak broadening was first observed and discussed in literary results regarding the same phenomenon for α-IPP. This revised version was published online in August 2006 with corrections to the Cover Date.     

Comparative Study of Efficiency of Nucleating Agents in PA-6

The isothermal and anisothermal crystallization of nucleated polyamide-6 (PA-6) was investigated by DSC. A comparative study was made of twelve potential nucleating agents, including some commercial products for PA-6 and polypropylene. The amide wax processing aid lubricant originally introduced into the polymer was found to exhibit a marked nucleation ability. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of molecular weight on the perforation impact behavior of injection-molded plaques of α-and β-phase isotactic polypropylenes

This study was devoted to the instrumented falling weight impact (IFWI) behavior of injection-molded a-and β-phase isotactic polypropylene (iPP) homopolymers. The perforation impact response of iPP with various melt flow indices (MFIs), and thus molecular weight (MW) characteristics, was studied at two different temperatures (T = 23°C and T =?40°C) and incident impact speeds (v_inc = 5 and 10 m/s). The impact resistance of β-iPP was superior to the α-modification. The absolute resistance to perforation increased with increasing MW or decreasing MFI, whereas the relative toughness improvement between the β-and α-iPPs followed an opposite tendency. The molding-induced skin-core morphology did not affect practically the out-of-plane response of the impacted plaques. Changes in the fractograms (viz. force-time curves) under various experimental conditions were traced to variations in the failure mode, showing a competition between radial and circumferential cracking with respect to the clamping ring. In the case of the more ductile β-iPP. circumferential cracking was favored.     

Monte Carlo simulation of light propagation in adult brain: influence of tissue blood content and indocyanine green

Near-infrared spectroscopy (NIRS), applied to a human head, is a noninvasive method in neurointensive care to monitor cerebral hemodynamics and oxygenation. The method is particularly powerful when it is applied in combination with indocyanine green (ICG) as a tracer substance. In order to assess contributions to the measured optical density (OD) which are due to extracerebral circulation and disturb the clinically significant intracerebral signals, we simulated the light propagation in an anatomically representative model of the adult head derived from MRI measurements with the aid of Monte Carlo methods. Since the measured OD signal depends largely on the relative blood content in various transilluminated tissues, we weighted the calculated densities of the photon distribution under baseline conditions within the tissues with the changes and aberrations of the relative blood volumes which we expect to prevail under physiological conditions. Furthermore, the influence of the IGC dye as a tracer substance was assessed. We conclude that up to about different 70% of the measured OD signal may have its origin in the tissues of interest under optimal conditions, which is mainly due to the extrapolated high relative blood content of brain tissue along with the influence of ICG.     

Near-infrared spectroscopy extended with indocyanine green dye dilution for cerebral blood flow measurement: Median values in healthy volunteers

The cerebral blood flow (CBF) is an important vital parameter in neurointensive care. Currently, there is no non-invasive method for its measurement that can easily be applied at the bedside. A new tool to determine CBF is based on near-infrared spectroscopy (NIRS) applied together with indocyanine green (ICG) dye dilution. From a bilateral measurement on selected regions on the head of infrared (IR) absorption at various wavelengths during the dilution maneuver, the vascular perfusion characteristics of the two brain hemispheres can be determined in terms of mean transit time (mtt) of ICG, cerebral blood volume (CBV) and CBF. So far, on nine healthy volunteers, NIRS ICG dye dilution bihemispheric measurements were performed, which yielded to mtt given as median (range) of 9.3 s (5.1–16.3 s), CBV of 3.5 ml/100 g (1.7–4.1 ml/100 g), and CBF of 18.2 ml/(100 g×min) [11.1–48.6 ml/(100 g×min)]. Additionally, the blood flow index (BFI) was calculated with BFI= 13.8 mg/(100 g×s) [6.6–15.2 mg/(100 g×s)]. The Spearman rank correlation coefficient between CBF and BFI was R_S = 0.76. However, as the Bland & Altman plot between CBFNIRS and the CBF_BFI documents, the limits of agreement are rather wide (21.9±6.7). Under physiological conditions in healthy volunteers, no differences could be detected between the hemispheres.     

Electrospinning through the prism of time

Electrospinning is a versatile and flexible technique for the preparation of ultrafine fibers. The present study aims to provide a comprehensive overview of electrospinning, as a complex technique, its evolution toward the high-throughput techniques, including the basic principles, parameters influencing the fibers production process, methods applied to solve the alignment difficulties, commonly used polymers and solvents, and the applications of the electrospun materials. We begin with an insight into the history of electrospinning, followed by its theoretical background and typical apparatus. Then, its renaissance over the past two decades as a powerful technology for the production of nanofibers suitable for industrial scale is presented. Afterward, we briefly discuss the applications of electrospun fibers, including use in different fields of industry, energy harvesting/conversion/storage, photonic and electronic devices, as well as biomedical applications. In the end, we also offer perspectives on the challenges and new directions for developments in electrospinning.