Polytetrafluoroethylene surface modification by impregnation with iron and manganese oxides

Polytetrafluoroethylene (PTFE) surfaces can be modified by impregnation with Fe and Mn oxides by procedures based on Fe(CO)₅ sorption in the polymer and followed by oxidation with H₂O₂ or KMnO₄. The effect of some variables (reagent concentrations and temperature) on the amount of oxides deposited was examined. The oxides incorporated in PTFE can be only partly removed by acid cleaning. Water–PTFE contact angles and PTFE surface resistivity are altered. Electron and x-ray diffractograms of the oxides were obtained but unambiguous identification was not achieved. Transmission electron microscopy examination of surface replicas showed that impregnation with oxides which covered most of the PTFE surface was fairly uniform.     

A new method for estimating the importance of hydrogen-bonding groups in the binding site of a protein

We introduce a new method to estimate the importance of hydrogen-bonding sitepoints in the binding site of a protein as part of a structure-based design strategy. Our method identifies hydrogen-bonding sitepoints within a binding pocket and ranks them according to both the accessibility of their hydrogen bonding regions to incoming ligands and their hydrogen-bonding strength. The combination of these components produces a prioritised list of sitepoints that are more likely to be involved in hydrogen bonding with an incoming ligand. A dataset of known protein-ligand interactions was used to compare the prioritisation of sitepoints identified by our method with those observed to be engaged in hydrogen bonding in their crystal structures. Our method was able to remove those sitepoints unable to bind the ligand due to a low accessibility or an unfavourable orientation and to award significantly higher hydrogen-bonding ranking values to those sitepoints observed to form hydrogen bonds. Our method can thus be used to identify hydrogen-bonding sitepoints that should be targeted preferentially in a drug design strategy.     

Gold nanoparticle embedded, self-sustained chitosan films as substrates for surface-enhanced Raman scattering

In this work, self-sustained, biocompatible, biodegradable films containing gold nanostructures have been fabricated for potential application in nanobioscience and ultrasensitive chemical and biochemical analysis. We report a novel synthesis of gold nanoparticles mediated by the biopolymer chitosan. Self-supporting thin films are formed from the resultant gold-chitosan nanocomposite solutions and characterized by UV-visible surface plasmon absorption, transmission electron microscopy, atomic force microscopy, infrared absorption, and Raman scattering measurements. Results demonstrate control over the size and distribution of the nanoparticles produced, which is promising for several applications, including the development of biosensors. As a proof of principle, we demonstrate that gold-chitosan films can be employed in trace analysis using surface-enhanced Raman scattering.     

Electron propagator theory and application

Summary The electron propagator theory is presented with somewhat of a historical perspective and the working equations are developed with the aim of taking advantage of molecular point group symmetry. A new electron propagator code, the vectorized electron propagator program (VEP), is introduced without full details about its structure and capabilities (such details are being published elsewhere). Applications to the (UV) photoelectron spectra of some donor-acceptor complexes of borane with carbon monoxide and water are presented at the level of second-order theory as an illustration of the theory and the VEP code.     

Metallcarbonyl-synthesen: XIII. Eine mangan—mangan-dreifachbindung

Photolysis of the manganese half-sandwich complex (η⁵-C₅Me₅)Mn(CO)₃ (1) in tetrahydrofuran (THF) yields cleanly the solvent complex (η⁵-C₅Me₅)(Mn(CO)₂THF (2). Compound 2 undergoes spontaneous elimination of carbon monoxide to give at ambient temperature in approx. 20 h, or upon removal of solvent in vacuo, the novel dinuclear derivative (η⁵-C₅Me₅)₂Mn₂(μ-CO)₃ (3). Elemental analyses and infrared and mass as wel as the ¹H and ¹³C NMR spectra unequivocally demonstrate this compound to adopt a triply carbonyl-bridged structure containing the first example of a manganesemanganese multiple bond.     

The determination of trace metals in lubricating oils by atomic spectrometry

The determination of trace metals in lubricating oils using atomic spectrometric methods is reviewed. The importance of such analyses for technical diagnostics as well as the specific sample characteristics related to the analyte form (metallo-organic and metal particles) is discussed. Problems related to sample pre-treatment for appropriate sample introduction and calibration are addressed as well as the strategies to overcome them. Recent trends aimed at simplifying sample manipulation are presented. The applications and scope of AAS, ICP OES and ICP MS techniques for the determination of trace metals in lubricating oil is individually discussed, as well as some present instrumental trends.     

Unfolding Tin–Cobalt Interactions in Oxide‐Based Composite Electrodes for Li‐Ion Batteries by Mössbauer Spectroscopy

With a view to the development of new composite electrodes for lithium-ion batteries with electroactive tin and cobalt, Co-doped tin dioxide samples are studied. The role played by oxygen and cobalt atoms in the electrochemical behavior of tin-based electrodes for Li-ion batteries is examined by the powerful and selective (119)Sn M?ssbauer spectroscopy. For the discharged electrodes, the oxygen atoms in the lithia matrix tend to destabilize the Sn(0) atoms. In contrast, the presence of cobalt atoms helps to form a matrix that stabilizes the reduced tin atoms. Cobalt-tin interactions in electrochemical reduced Co(x)Sn(1-x)O(2) electrodes are deduced from the electrochemical and M?ssbauer results.     

Continuous organelle separation in an insulator-based dielectrophoretic device

Heterogeneity in organelle size has been associated with devastating human maladies such as neurodegenerative diseases or cancer. Therefore, assessing the size-based subpopulation of organelles is imperative to understand the biomolecular foundations of these diseases. Here, we demonstrated a ratchet migration mechanism using insulator-based dielectrophoresis in conjunction with a continuous flow component that allows the size-based separation of submicrometer particles. The ratchet mechanism was realized in a microfluidic device exhibiting an array of insulating posts, tailoring electrokinetic and dielectrophoretic transport. A numerical model was developed to elucidate the particle migration and the size-based separation in various conditions. Experimentally, the size-based separation of a mixture of polystyrene beads (0.28 and 0.87 $\mu$m) was accomplished demonstrating good agreement with the numerical model. Furthermore, the size-based separation of mitochondria was investigated using a mitochondria mixture isolated from HepG2 cells and HepG2 cells carrying the gene Mfn-1 knocked out, indicating distinct size-related migration behavior. With the presented continuous flow separation device, larger amounts of fractionated organelles can be collected in the future allowing access to the biomolecular signature of mitochondria subpopulations differing in size.     

Metal-ion induced amplification of three receptors from dynamic combinatorial libraries of peptide-hydrazones

Three building blocks of general structure (MeO)2 CH-aromatic linker-Pro-amino acid-NHNH2 have been prepared and tested in acid-catalysed dynamic combinatorial libraries. Exposure of these libraries to LiI and NaI led to the amplification of three macrocyclic pseudopeptide receptors. The receptors were isolated and their interactions with LiI and NaI were analysed using NMR, IR and ITC. Binding of the metal ions to the receptors is invariably entropy-driven. Nevertheless, all receptors were found to be flexible with substantial conformational rearrangements accompanying guest binding. This type of receptor is extremely difficult to access through rational design and the fact that dynamic combinatorial chemistry allows facile access to these challenging molecules underlines the power of the dynamic approach.     

Crystal structure and pseudosymmetry analysis of the triclinic prodrug cloxazolam (Z′ = 4)

The prodrug cloxazolam [systematic name: 13‐chloro‐2‐(2‐chlorophenyl)‐3‐oxa‐6,9‐diazatricyclo[8.4.0.0^2,6]tetradeca‐1(10),11,13‐trien‐8‐one], C₁₇H₁₄Cl₂N₂O₂, crystallizes in the triclinic space group P, with four chemically identical independent molecules in the asymmetric unit. However, in order to facilitate the analysis of the striking pseudosymmetry relating the four independent molecules, the structure has been analysed and reported in the nonconventional centred B space‐group setting. Pseudosymmetry is an eminently local property, valid only in the realm of the unit‐cell boundary and not propagating to the whole crystal structure. It has been analyzed using the MP procedure described in the preceding article [Baggio (2019). Acta Cryst. C 75 , 837–850]. The molecules consist of a rigid core made up of three rings (five‐, six‐ and seven‐membered) and an extra six‐membered ring joined to the latter group by a single C—C bond, together with a clamping intramolecular C—H…O interaction preventing free rotation and providing additional rigidity. The four molecules in the asymmetric unit pair into dimers with almost exact twofold pseudosymmetry, further linked into (001) slabs as the building bricks of the structure. Interpenetration of slabs finally leads to a three‐dimensional structure of unusual compactness for an organic structure, with a Kitaigorodskii packing index of ca 0.71.