Flow microcalorimetry: Experimental development and application to adsorption of heavy metal cations on silica

Sorption of metal ions at the oxide mineral-water interfaces is a complex process involving many various contributions that can be explained using thermodynamics. The aim of this study is to obtain experimental thermodynamic data on adsorption of two heavy metal ions (Cd(II) and Pb(II)) on macroporous silica. Thermal signals of adsorption are studied by flow microcalorimetry which has been preferred because physico-chemicals conditions (pH, equilibrium concentration,…) can be controlled (the routine configuration was optimized in order to get a very stable pressure baseline and avoid important fluctuations in the determination of heat). Mechanisms driving the adsorption have been explained. The calculation of the effective charge of ions determined from the speciation diagrams and of the surface charges shows that the interactions between the two metals and the silica surface are mainly electrostatic. The differential enthalpies of adsorption Δ_adsH have been experimentally measured. The heat of cadmium adsorption is low, endothermic and quantitatively equivalent to that of desorption. In the case of lead, the adsorption is athermal. Free energies and entropic effects related to cation adsorption have then been deduced according to the Gibbs’law. The entropy is positive during the adsorption process and at this temperature (298 K) is quite equivalent to free energy. This entropy is due to modification of hydration shell of the ions during their insertion into the interfacial region.     

Experimental and numerical analysis of fretting crack formation based on 3D X-FEM frictional contact fatigue crack model

Nowadays, numerical simulation of 3D fatigue crack growth is easily handled using the eXtended Finite Element Method coupled with level set techniques. The finite element mesh does not need to conform to the crack geometry. Most difficulties associated to complex mesh generation around the crack and the re-meshing steps during the possible propagation are hence avoided. A 3D two-scale frictional contact fatigue crack model developed within the X-FEM framework is presented in this article. It allows the use of a refined discretization of the crack interface independent from the underlying finite element mesh and adapted to the frictional contact crack scale. A stabilized three-field weak formulation is also proposed to avoid possible oscillations in the local solution linked to the LBB condition when tangential slip is occurring. Two basic three-dimensional numerical examples are presented. They aim at illustrating the capacities and the high level of accuracy of the proposed X-FEM model. Stress intensity factors are computed along the crack front. Finally an experimental 3D ball/plate fretting fatigue test with running conditions inducing crack nucleation and propagation is modeled. 3D crack shapes defined from actual experimental ones and fretting loading cycle are considered. This latter numerical simulation demonstrates the model ability to deal with challenging actual complex problems and the possibility to achieve tribological fatigue prediction at a design stage based on the fatigue crack modeling.     

High order harmonic balance formulation of free and encapsulated microbubbles

The radial responses of free and encapsulated microbubbles excited by an ultrasonic plane wave with a large wavelength in comparison with the bubble size are governed by NonLinear Ordinary Differential Equations (NL-ODEs). The nonlinear frequency response gives the harmonic content of the time response and constitutes the expected outcome of a high order harmonic analysis. In this paper, high order harmonic balance analysis of modified “RPNNP” (bubble), Hoff and Marmottant (contrast agents) models is performed with an open-source software program. For this purpose, the original NL-ODEs are recast into nonlinear systems in which the nonlinearities are at most quadratic. In the spectral domain, this recast provides close form and aliasing-free solutions of arbitrarily large numbers of harmonics. Relevant quantities such as primary and secondary resonances and the nonlinear amplitude threshold of the excitation wave are evaluated. The frequency curves drawn up characterize the bending and quantify the jump frequencies and amplitudes of each harmonic component. The results obtained with this predictive method confirm that it should provide a useful tool for nonlinear bubble detection and sizing and for contrast agent designing.     

Deciphering the structure of isomeric oligosaccharides in a complex mixture by tandem mass spectrometry: Photon activation with vacuum ultra-violet brings unique information and enables definitive structure assignment

Carbohydrates have a wide variety of structures whose complexity and heterogeneity challenge the field of analytical chemistry. Tandem mass spectrometry, with its remarkable sensitivity and high information content, provides key advantages to addressing the structural elucidation of polysaccharides. Yet, classical fragmentation by collision-activated dissociation (CAD) in many cases fails to reach a comprehensive structural determination, especially when isomers have to be differentiated. In this work, for the first time, vacuum ultra-violet (VUV) synchrotron radiation is used as the activation process in tandem mass spectrometry of large oligosaccharides. Compared to low energy CAD (LE-CAD), photon activated dissociation brought more straightforward and valuable structural information. The outstanding feature was that complete series of informative ions were produced, with only minor neutral losses. Moreover, systematic fragmentation rules could be drawn thus facilitating the definitive assignments of fragment identities. As a result, most of the structures present in a complex mixture of oligogalacturonans could be comprehensively resolved, including many isomers differing in the position of methyl groups along the galacturonic acid backbone.     

Allowed and forbidden d-d transitions in poly(3,5-dimethylpyrazolyl)methane complexes of nickel(II)

Absorption spectra of four nickel(II) complexes with poly(pyrazolyl)methane ligands are presented in the NIR-VIS-UV region and the band system corresponding to the lowest-energy spin-allowed and spin-forbidden transitions is analyzed. A quantitative theoretical model involving coupled electronic states provides precise energies for the lowest-energy triplet and singlet excited states and allows comparisons between complexes with a variable number of nitrogen and oxygen ligator atoms. Singlet energies between 12,840 and 13,000 cm(-1) are determined for heteroleptic complexes. These energies are in an intermediate range between those for homoleptic complexes with either nitrogen or oxygen ligator atoms with singlet states at approximately 12,000 and 14,000 cm(-1), respectively. The new theoretical approach is compared to the traditional ligand-field parameters obtained from the maxima of the broad, spin-allowed absorption bands.     

Solid phase synthesis of a redox delivery system with the aim of targeting peptides into the brain

A solid phase approach for the preparation of peptides attached to a redox chemical delivery system derived from stable annulated NADH models is reported. The synthesis starts with the grafting on a Merrifield resin of quinoline 4b, precursor of the redox carrier. From the resulting quinoline supported resin 4d, the stepwise SPPS of both octapeptide OP (RPGLLDLK) and octadecaneuropeptide ODN (QATVGDVNTDRPGLLDLK), two neuropeptides exhibiting anorexigenic effects, was successfully achieved by conventional methods. Quaternization of the quinoline moiety prior to cleavage of the modified OP and ODN peptides from the resin, led to the expected quinolinium salt 8a and 8b respectively linked to OP or ODN peptides. Finally, the reduction with NaBH4 monitored by UV-vis, provided the desired annulated NADH models as peptides carriers with either the OP (11a,b) or ODN (12a,b) moiety.     

Synthesis of a benzomacrolactone-based somatostatin mimetic

The benzomacrolactone is a framework found in numerous natural products. The synthesis of an orthogonally functionalized benzomacrolactone from D-glucosamine and a salicylic acid derivative is described. This macrolactone was used for the synthesis of a somatostatin mimetic that has submicromolar affinity for the human somatostatin receptor 4 (hSSTR4).     

Experimental determination of L fluorescence yields of gadolinium

The fluorescence yields are useful X-ray atomic fundamental parameters for X-ray spectrometric purposes but suffer from large tabulated uncertainties, and this is the first time to our knowledge that all three subshell parameters are measured together. We determined the three L partial fluorescence yields and the associated Coster-Kronig transition probabilities of gadolinium, by selectively ionizing the three L subshells with a tunable monochromatic photon beam. We found ω₁ = 0.099(3) , ω₂ = 0.162(4) , and ω₃ = 0.159(3) that are in good agreement with tabulated values, but our derived uncertainties are significantly reduced.     

Nano-scale metallodendritic complexes in electron-transfer processes and catalysis

Nano-sized metallodendrimers in which the equivalent metal fragments are located at the periphery can be assembled covalently, by H-bonding (supramolecular) or onto dendronized nanoparticles. They can be used as electron-reservoirs, i.e. molecular batteries, redox catalysts and sensors for the recognition of biologically relevant anions. They can also be deposited on metal surfaces or electrodes, which optimizes their use as recoverable sensors.