Mechanistic aspects of (CC) isomerization in vinylic rhodium(III) complexes

Observations concerning the (CC) isomerization of several vinylic Rh^III complexes suggest an intramolecular pathway; isomerization occurs at a rate which is affected by the backbonding ability of the metal and the π-acidity of the vinylic ligand in the complex.     

Thermoanalytical investigation of tin and cerium salt mixtures

Summary Oxide materials belonging to the Sn-Ce-O system are very interesting due to their use as solid electrolytes in fuel cells, catalysts, sensors and photoanodes in solar cells. The aim of the present work is to investigate the thermal behaviour of some tin and cerium salt mixtures. Mixtures with different representative Sn:Ce atomic ratio were prepared by classical ceramic method using SnC₂O₄, Ce(SO₄)₂·4H₂O and (NH₄)₂Ce(NO₃)₆ as starting compounds. The samples were investigated by means of TG/DTA methods in flowing and static air atmosphere. SnO₂ and/or CeO₂ were identified by X-ray diffraction and IR spectroscopy in the final decomposition products, depending on the initial composition of the both series. A different crystallinity degree of the solid products was observed depending on the Ce precursor.     

Synthesis of the enantiomer of the structure assigned to the natural product nobilisitine A

The synthesis of the enantiomer of the structure, 1, assigned to the natural product nobilisitine A has been accomplished using the enantiomerically pure cis-1,2-dihydrocatechol 4 as starting material. The (1)H and (13)C NMR spectral data derived from compound ent-1 do not match those reported for the natural product, thus suggesting its structure has been incorrectly assigned.     

“Helter‐Skelter‐Like” Perylene Polyisocyanopeptides

Exciton migration! Spectroscopic analyses and extensive molecular dynamics studies revealed a well‐defined 4₁ helix in which the perylene molecules (see figure) form four “helter‐skelter‐like” overlapping pathways along which excitons and electrons can rapidly migrate.

     

Influence of surface chemistry on the adsorption of oxygenated hydrocarbons on activated carbons

The objective of this work was to study the adsorption of different oxygenated hydrocarbons (methanol, ethanol, 1 and 2-butanol, methyl acetate) on activated carbons from organic mixtures with cyclohexane. Three activated carbons prepared by thermal and chemical treatments of a commercial carbon were employed for this purpose. Their textural properties were found to be similar, whereas their surface chemistries were modified, as shown by temperature-programmed desorption coupled to mass spectrometry (TPD-MS) and X-ray photoelectron spectroscopy (XPS). The adsorption isotherms were obtained by depletion method, and the analysis of adsorbed species was evaluated by TPD-MS to obtain new insight into the interactions between the different hydrocarbons and the carbon surface. Ethanol leads to a high-energy interaction between its hydroxyl function and the oxygenated surface groups and also to a lower energy interaction between the aliphatic part of the molecule and the carbon material. The desorption activation energy for this hydrophilic interaction is high (50 to 105 kJ/mol), and it is related to the nature of the carbon surface groups. The relative importance of these two interactions depend on the size of the alcohol/methanol is similar to ethanol, whereas butanols lead to more dispersive interactions. Methyl-acetate cannot undergo this kind of strong interaction and behaves like cyclohexane, having desorption activation energies ranging between 25 and 45 kJ/mol no matter the molecule and the carbon surface chemistry.     

A sensitive solid-phase fluoroimmunoassay for detection of opiates in urine

An automated flow fluorometer designed for kinetic binding analysis was adapted to develop a solid-phase competitive fluoroimmunoassay for urinalysis of opiates. The solid phase consisted of polymer beads coated with commercial monoclonal antibodies (MAbs) raised against morphine. Fluorescein-conjugated morphine (FL-MOR) was used as the fluorescein-labeled hapten. The dissociation equilibrium constant (K _D ) for the binding of FL-MOR to the anti-MOR MAb was 0.23 nM. The binding of FL-MOR to the anti-MOR MAb reached steady state within minutes and was displaced effectively by morphine and other opiates. Morphine-3-glucuronide (M3G), the major urinary metabolite of heroin and morphine, competed effectively with FL-MOR in a concentration-dependent manner for binding to the antimorphine MAb and was therefore used to construct the calibration curve. The sensitivity of the assay was 0.2 ng/mL for M3G. The assay was effective at concentrations of M3G from 0.2 to 50 ng/mL, with an IC₅₀ of 2 ng/mL. Other opiates and heroin metabolites that showed >50% crossreactivity when present at 1 μg/mL included codeine, morphine-6-glucuronide, and oxycodone. Methadone showed very low crossreactivity (<5%), which is a benefit for testing in patients being treated for opiate addictions. The high sensitivity of the assay and the relatively high cutoff value for positive opiate tests allows very small sample volumes (e.g., in saliva or sweat) to be analyzed. A double-blind comparison using 205 clinical urine samples showed good agreement between this single-step competitive assay and a commercially performed enzyme multiplied immunoassay technique for the detection of opiates and benzoylecgonine (a metabolite of cocaine).     

Kinetics of octadecyltrimethylammonium bromide self-assembled monolayer growth at mica from an aqueous solution

We have studied the growth kinetics of self-assembled monolayers (SAMs) ofoctadecyltrimethylammonium bromide (C18TAB) on mica below the critical micelle concentration at 22, 30, 40, and 50 degrees C. A combination of atomic force microscopy, contact angle goniometry, and transmission infrared spectroscopy was used to follow the growth processes to determine the rates involved in the growth of a C18TAB SAM on mica. The growth of a SAM consisted of four distinct processes: deposition of adsorbate molecules, growth of a disordered 2D liquid phase, nucleation of islands of an ordered 2D solid phase, and subsequent growth of the solid phase. The rates of these various processes are determined, and the activation energies for several processes were calculated including those for the adsorption onto a bare substrate (20 kJ/mol), adsorption into the saturated liquid phase (100 kJ/mol), and nucleation of islands (0.3 kJ/mol). Despite the small activation barrier to island nucleation, the nucleation rate is qualitatively slow, suggesting that entropic effects dominate the nucleation rate.     

Thermal and structural study on the lattice compound 1,4-diammoniumbutane bis(theophyllinate)

Crystalline title compound (1) prepared from aqueous solution of theophylline and 1,4-diaminobutane has been structurally and thermally characterized. Both the two-step TG decomposition curve and elemental analysis of the hexagonal crystals show that it consists of theophylline and 1,4-diaminobutane in 2:1 molar ratio. Actually, presence of one type of both theophyllinate anions and 1,4-diammoniumbutane dication have been indicated by FTIR spectroscopy. The molecular structure of lattice compound (1) has been determined by single crystal X-ray diffraction, where the hydrogen positions have been obtained from differential Fourier maps. It has confirmed that the crystal is really built up from these ionic constituents bound together with an extensive net of hydrogen bonds. The coupled TG-FTIR analysis of the evolved gases has revealed that the diamine is released as a whole molecule in the first decomposition step. Clathrate 1 and the proton migration in it might serve as a structural model of solid aminophylline whose crystal structure is still unknown.