Influence of ligand structure on the stability and oxidation of copper nanoparticles

The stability and oxidation of copper nanoparticles stabilized with various ligands have been studied. Lauric acid-capped copper nanoparticles were prepared by a modified Brust-Schiffrin method. Then, ligand exchange with an excess of different capping agents was performed. Oxidation and stability were studied by UV-vis, XRD, and TEM. Alkanethiols and oleic acid were found to improve air stability. The oxidation resistance of thiol-capped copper nanoparticles was found to increase with the chain length of the thiol. However, excess thiol caused etching of the particles under nitrogen. With oleic acid no etching was observed under nitrogen. After oxidation, no traces of the ligand-exchanged particles were found, suggesting their dissolution due to excess ligand. Oleic acid protected the particles against oxidation better than the tested thiols at large excess (ligand-copper ratio 20:1).     

Development and evaluation of a liquid chromatography-mass spectrometry assay and its application for the assessment of renal function

In the present study we evaluated two commonly used iodinated contrast agents, iohexol and iodixanol, as potential markers of impaired renal function. A reversed phase LC-MS method has been developed in order to separate and quantify the two substances. The assay was linear between 0.02 and 9.7 micromol/L for iohexol and between 0.4 and 49.3 micromol/L for iodixanol (r(2) > 0.998). The recovery during sample preparation ranged from 89.1 to 112.4%. The intra- and inter-assay RSD values were 3.06-13.6% for iohexol and 4.32-12.7% for iodixanol. The validated method was subsequently applied to 17 patients scheduled for angiographic procedure displaying normal and impaired renal function. A mixture of iohexol and iodixanol was intra-arterially injected and their corresponding plasma levels were determined periodically over a 24h period following administration. The elimination of both contrast agents followed by the LC-MS approach allowed us to discriminate between patients with normal and impaired renal function at 4, 8 and 24h after administration. Our preliminary results support the predictive value of iohexol and/or iodixanol clearance in a clinical environment to screen and identify patients at risk of developing CIN.     

Characterisation of complex amphiphilic cyclodextrin mixtures by high-performance liquid chromatography and mass spectrometry

It is established that amphiphilic beta-cyclodextrins chemically modified with alkyl chains on the secondary face exhibit self-organisation properties yielding stable nanospheres or nanoparticles. The ability of these promising colloidal drug carriers to encapsulate drugs being partly related to the internal structure of nanosystems, precise characterisation methods are required to control their synthesis procedure. The present work describes the development of complementary analytical methods based on reversed-phase high-performance liquid chromatography (RPLC) coupled to evaporative light-scattering detection (ELSD) and electrospray ionisation-mass spectrometry (ESI-MS) to characterize various beta-cyclodextrins enzymatically transesterified by vinyl-acyl fatty esters (the number of carbon atom in the acyl chain varying from 4 to 12). LC-ELSD has been used in a preliminary step to optimize the separation on a monolithic octadecylsiloxane-bonded silica stationary phase. A complex fingerprint was achieved for each mixture, revealing the presence of isomers unnoticed by the sole spectrometric (NMR and MS) techniques.     

Synthesis of highly labile SG1-based alkoxyamines under photochemical conditions

Highly labile SG1-based alkoxyamines were synthesized using the photodecomposition of both azo compounds and dithiocarbamates. The former method was a straightforward procedure to obtain the alkoxyamines, but a high [azo]/[nitroxide] ratio is needed. The latter method required only a stoichiometric amount of dithiocarbamate and allowed the recovery of the disulfide after irradiation. This enabled combination of the two methods in a process where only 0.75 equiv of azo compound is needed and where sulfurous compounds acted only as intermediates.     

Evaluating the kinetic indenyl effect of a π-thiaphentalenyl ancillary ligand

The magnitude of the “kinetic indenyl effect” for the π-thiapentalenyl ligand, isoelectronic heteroanalogue of the indenyl ligand, has been tested using the reaction between complex, Rh(η⁵-th)(CO)₂3 (th = 2-ethyl-5-methyl-cyclopenta[b]thienyl or thiapentalenyl) and PPh₃ as a model process. Only moderate “kinetic indenyl effect” of the thiapentalenyl ligand was observed. The rational for such behavior was also supported by DFT computational correlation of ground and transition states for the reaction of carbonyl group substitution by a phosphine in the corresponding indenyl and thiapentalenyl rhodium complexes.     

First Principles Calculations for Hydrogenation of Acrolein on Pd and Pt: Chemoselectivity Depends on Steric Effects on the Surface

The chemoselective hydrogenation of acrolein on Pt(111) and Pd(111) surfaces is investigated employing density functional theory calculations. The computed potential energy surfaces together with the analysis of reaction mechanisms demonstrate that steric effects are an important factor that governs chemoselectivity. The reactions at the C=O functionality require more space than the reactions at the C=C functionality. Therefore the formation of allyl alcohol is more favorable at low coverage, while the reduction of the C=C bond and the formation of propanal becomes kinetically more favorable at higher coverage. The elementary reaction steps are found to follow different reaction mechanisms, which are identified according to terminology typically used in organometallic catalysis. The transition state scaling (TSS) relationship is demonstrated and the origin of multiple TSS lines is linked to variation of an internal electronic structure of a carbon skeleton.     

Evaluation of disaccharide-based ligands for Pd(0)-catalyzed asymmetric allylations

A series of phosphines based on disaccharides containing a d-glucosamine framework were prepared and tested for their abilities as ligands for the palladium(0)-catalyzed asymmetric allylic allylation of racemic 1,3-diphenyl-2-propenyl acetate with various nucleophiles. In contrast to previous results exploiting monosaccharides, the iminophosphines generally afforded higher enantiomeric excesses, up to 99%.     

Structure and orientation changes of omega- and gamma-gliadins at the air-water interface: a PM-IRRAS spectroscopy and Brewster angle microscopy study

Microscopic and molecular structures of omega- and gamma-gliadin monolayers at the air-water interface were studied under compression by three complementary techniques: compression isotherms, polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), and Brewster angle microscopy (BAM). For high molecular areas, gliadin films are homogeneous, and a flat orientation of secondary structures relative to the interface is observed. With increasing compression, the nature and orientation of secondary structures changed to minimize the interfacial area. The gamma-gliadin film is the most stable at the air-water interface; its interfacial volume is constant with increasing compression, contrary to omega-gliadin films whose molecules are forced out of the interface. gamma-Gliadin stability at a high level of compression is interpreted by a stacking model.     

Duplex polarons in DNA

In earlier work we calculated the wavefunction and energy of the solvated polaron in DNA with a simple model in which the charge was taken to be on a single chain of bases at the center of the double helix. To better approximate the actual situation, we have now extended the calculations to the case in which the charge is distributed on two chains of bases, complementary to each other, one on each side of the center. The binding energy of the resulting polaron is somewhat larger than that obtained for the single-chain polaron, the result of each chain of the polaron being closer to some of the polarization charge it induces. Carrying out the calculations for a number of different sequences, we find that the polaron wavefunction is predominantly on one of the two chains, this usually being the one on which the charge was originally placed, despite the availability of lower energy sites on the other chain. This finding is in agreement with recent experiments of Schuster's group(Joy, A.; Ghosh, A. K.; Schuster, G. B. J. Am. Chem. Soc. 2006, 128, 5346-5347). Thus, in contradiction to the ideas of many researchers, there is no transport in which a hole zigzags from one chain to the other, as has been suggested for a sequence of guanines and cytosines (GCGCGC....), for example.