New triorganotin (IV) derivatives of dipeptides as models for metal-protein interactions: synthesis, structural characterization and biological studies

New non-electrolytic triorganotin(IV) derivatives of dipeptides with general formulae R3Sn(HL), where R = Ph and HL = monoanion of glycylisoleucine (H2L-1), valylvaline (H2L-2), alanylvaline (H2L-3), leucylalanine (H2L-4), leucylleucine (H2L-5); R = n-Bu and HL = monoanion of glycylisoleucine (H2L-1) and leucylalanine (H2L-4); and R = Me and HL = monoanion of leucylalanine (H2L-4) have been synthesized and characterized on the basis of infrared, multinuclear 1H, 13C and 119Sn NMR and 119Sn M?ssbauer spectroscopic studies. These investigations suggest that all the ligands in R3Sn(HL) act as monoanionic bidentates coordinating through the COO- and NH2 groups. The 119Sn M?ssbauer studies, together with the NMR data, indicate that, for these polymeric derivatives, the polyhedron around tin in R3Sn(HL) is a trigonal-bipyramid with the three organic groups in the equatorial positions, while the axial positions are occupied by a carboxylic oxygen and the amino nitrogen atom from the adjacent molecule. The anti-inflammatory and cardiovascular activities and toxicity of all these compounds have been determined. Four of the complexes have also been screened against some of the chosen bacterial and fungal strains. The Ph3Sn(IV) compounds exhibit better anti-inflammatory and cardiovascular activities in comparison to the Me3Sn(IV) and n-Bu3Sn(IV) analogues. n-Bu3Sn(Gly-Ile) and Ph3Sn(Ala-Val) exhibit good antibacterial activity against all the chosen strains.     

Diode laser wavelength modulated spectroscopy of I(2) at 675 nm

A free-running diode laser has been used to examine the spectrum of 127I(2) near 675 nm using wavelength modulation spectroscopy. Twelve transitions have been observed in the region between 14818.0 and 14819.3 cm(-1), all of which are accounted for by previously published constants. Changes in quadrupole coupling constants, DeltaeQq, have been determined for all lines. Pressure broadening and shift coefficients have been determined for two unblended lines for broadening by air, argon, and water vapor.     

Dynamics of two-phase bubble-droplets in immiscible liquids

This paper describes an experimental study of two-phase bubble-droplets of butane in distilled water. In the process of direct-contact heat transfer between two immiscible liquids, and with change of phase, evaporation occurs within a liquid droplet to form an interior bubble which ultimately may expand to absorb the entire droplet. The so-called stopped-evaporation two-phase bubble-droplets were formed by such evaporating droplets of butane rising in a column of water by application of pressure on the surface of the water to stop the evaporation. The configurations of such bubble-droplets, which depend on the ratio of mass of the vapor to mass of the liquid, are discussed. Results are also given for the rise velocity, and comparisons are made between the rise velocity of stopped-evaporation droplets and those of evaporating droplets.

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Dynamik zweiphasiger Blasen-Tropfen in unmischbaren Flüssigkeiten

Zusammenfassung Die experimentelle Untersuchung von zweiphasigen Blasen-Tropfen aus Butan in destilliertem Wasser wird beschrieben. Bei direktem Wärmeaustausch mit Phasenänderung zwischen zwei unmischbaren Flüssigkeiten beginnt die Verdampfung innerhalb eines Flüssigkeitstropfens und bildet eine innere Blase, die sich schließlich ausdehnt und den Tropfen absorbiert. Ein Ende der Verdampfung konnte beim Aufsteigen von Butantropfen in eine Wassersäule durch Anlegen von Druck an der Wasseroberfläche erreicht werden. Die Struktur dieser Blasen-Tropfen, die abhängt vom Verhältnis der Massen des Dampfes und der Flüssigkeit, wird diskutiert. Außerdem werden Ergebnisse für die Aufstiegsgeschwindigkeit gegeben und die Aufstiegsgeschwindigkeiten der verdampfenden Tropfen mit denen bei beendeter Verdampfung verglichen.

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Nomenclature d Equivalent spherical diameter of initial droplet (mm) - D Equivalent spherical diameter of bubble-droplet (mm) - m₀₀ Initial mass of droplet (kg) - m _v Mass of vapour (kg) - Re _c Reynolds number based on water properties (Re_c=UD/) - t Time (s) - T _c Temperature of water (°C) - U Rise velocity (m/s) - Z Position of bubble-droplet (mm) - t ₀ Overall temperature difference (C deg) - Density (kg/m³) - Viscosity (kg/m s)     

Encouraging problem-solving disposition in a Singapore classroom

In this article, we share our learning experience as a Lesson Study team. The Research Lesson was on Figural Patterns taught in Year 7. In addition to helping students learn the skills of the topic, we wanted them to develop a problem-solving disposition. The management of these two objectives was a challenge to us. From the lesson observation and the students’ classwork, it turned out better than we expected.     

Highly Hydrogenated Graphene through Microwave Exfoliation of Graphite Oxide in Hydrogen Plasma: Towards Electrochemical Applications

Hydrogenated graphenes exhibit a variety of properties with potential applications in devices, ranging from a tunable band gap to fluorescence, ferromagnetism, and the storage of hydrogen. We utilize a one‐step microwave‐irradiation process in hydrogen plasma to create highly hydrogenated graphene from graphite oxides. The procedure serves the dual purposes of deoxygenation and concurrent hydrogenation of the carbon backbone. The effectiveness of the hydrogenation process is investigated on three different graphite oxides (GOs), which are synthesized by using the Staudenmaier, Hofmann, and Hummers methods. A systematic characterization of our hydrogenated graphenes is performed using UV/Vis spectroscopy, SEM, AFM, Raman spectroscopy, FTIR spectroscopy, X‐ray photoelectron spectroscopy (XPS), combustible elemental analysis, and electrical conductivity measurements. The highest hydrogenation extent is observed in hydrogenated graphene produced from the Hummers‐method GO, with a hydrogen content of 19 atomic % in the final product. In terms of the removal of oxygen groups, microwave exfoliation yields graphenes with very similar oxygen contents despite differences in their parent GOs. In addition, we examine the prospective application of hydrogenated graphenes as electrochemical transducers through a cyclic voltammetry (CV) study. The highly hydrogenated graphenes exhibit fast heterogeneous electron‐transfer rates, suggestive of their suitability for electrochemical applications in electrodes, supercapacitors, batteries, and sensors.     

Proteomic analysis of Pseudomonas aeruginosa grown under magnesium limitation

In this study, large-scale qualitative and quantitative proteomic technology was applied to the analysis of the opportunistic bacterial pathogen Pseudomonas aeruginosa grown under magnesium limitation, an environmental condition previously shown to induce expression of various virulence factors. For quantitative analysis, whole cell and membrane proteins were differentially labeled with isotope-coded affinity tag (ICAT) reagents and ICAT reagent-labeled peptides were separated by two-dimensional chromatography prior to analysis by electrospray ionization-tandem mass spectrometry (ESI-MS/MS) in an ion trap mass spectrometer (ITMS). To increase the number of protein identifications, gas-phase fractionation (GPF) in the m/z dimension was employed for analysis of ICAT peptides derived from whole cell extracts. The experiments confirmed expression of 1331 P. aeruginosa proteins of which 145 were differentially expressed upon limitation of magnesium. A number of conserved Gram-negative magnesium stress-response proteins involved in bacterial virulence were among the most abundant proteins induced in low magnesium. Comparative ICAT analysis of membrane versus whole cell protein indicated that growth of P. aeruginosa in low magnesium resulted in altered subcellular compartmentalization of large enzyme complexes such as ribosomes. This result was confirmed by 2-D PAGE analysis of P. aeruginosa outer membrane proteins. This study shows that large-scale quantitative proteomic technology can be successfully applied to the analysis of whole bacteria and to the discovery of functionally relevant biologic phenotypes.     

Inter versus intra-molecular photoinduced charge separation in solid films of donor-acceptor molecules

We report on photoinduced charge separation in solid films of two perylene diimides; intramolecular charge separation and recombination is correlated with a reduction in the yield of long-lived, intermolecular charge-separated species.     

Structure and reactivity of the calcite-water interface

The zetapotential of calcite in contact with aqueous solutions of varying composition is determined for pre-equilibrated suspensions by means of electrophoretic measurements and for non-equilibrium solutions by means of streaming potential measurements. Carbonate and calcium are identified as charge determining ions. Studies of the equilibrium solutions show a shift of isoelectric point with changing CO(2) partial pressure. Changes in pH have only a weak effect in non-equilibrium solutions. The surface structure of (104)-faces of single crystal calcite in contact to solutions corresponding to those of the zetapotential investigations is determined from surface diffraction measurements. The results reveal no direct indication of calcium or carbonate inner-sphere surface species. The surface ions are found to relax only slightly from their bulk positions; the most significant relaxation is a ～4° tilt of the surface carbonate ions towards the surface. Two ordered layers of water molecules are identified, the first at 2.35±0.05? above surface calcium ions and the second layer at 3.24±0.06? above the surface associated with surface carbonate ions. A Basic-Stern surface complexation model is developed to model observed zetapotentials, while only considering outer-sphere complexes of ions other than protons and hydroxide. The Basic-Stern SCM successfully reproduces the zetapotential data and gives reasonable values for the inner Helmholtz capacitance, which are in line with the Stern layer thickness estimated from surface diffraction results.     

金属离子负载修饰阳离子树脂在酯化反应中的研究

将催化精馏中常用作催化填料的强酸性阳离子交换树脂用金属离子负载修饰后，考察了树脂催化性能的改变及树脂结构对催化性能的影响。实验表明，经修饰后树脂的催化能力都高于原树脂，在不分水的情况下，合成乙酸乙酯时乙酸的转化率最高可达73％，具有很好的选择性，金属离子能与树脂的磺酸基团产生络合，提高了树指的催化性能，所形成的新酸中心不会被阳离子交换而失活。