Decisive Influence of Phosphorus Ligands on O2 Oxidations of Alkenes in the Presence of the Iron Nitrato/Iron Nitrosyl Couple

Abstract

Fe(NO)₂XL and Fe(NO)X₂L nitrosyl iron complexes, X = Cl, I, and L = HMPA, dppe, PPh₃, activate molecular O₂ to yield nitrato complexes. The phosphorous ligand is decisive for the oxidative power of these nitrates: with HMPA or dppe, oxygen transfer occurs only to phosphines. On going from HMPA to PPh3 the single nitrato complex obtained, Fe(NO)₂X(OPPh₃)₂ selectively epoxidizes cyclohexene, and this is the first example of oxygen transfer from a nitrato ligand to an olefin.     

Multiple Mechanism of NCA Polymerization: Effect of N-Acetylglycine NCA and Related Additives

Polymerization of α-aminoisobutyric acid NCA by alkaline salts of various basicity as well as amines has been investigated. The study was focused on the effect on the initial polymerization rate of additives such as N-acetylglycine NCA and some other less electrophilic additives (l-acetyl-2-pyrrolidone, 3-acetyl-2-oxazolidone, 1-acetyl-3-methylhydantoin) which are all models of the growing chain end produced by the NCA anion pathway. The acetyl endgroup was detected by 250 MHz ¹H-NMR in all the polymers of α-aminoisobutyric acid NCA obtained in the presence of l-acetyl-3-methylhydantoin and triethyl amine or sodium methoxide initiators, whereas the additives influenced variously the kinetics of polymerization according to the nature of the initiator used. The results were interpreted in the light of a multiple mechanism supposing the simultaneous presence of the initiator anion, its conjugate acid, and NCA anion for basic salt initiation. Thus, the observed effect has to be considered as the sum of an elementary acceleration due to NCA anion and of an elementary deceleration due to the initiator anion. Predominance of the pathways involving NCA anion could be shown this way. This conclusion could be extended to γ-benxyl-L-glutamate NCA which is a more reactive NCA. However, the deceleration observed with some additives led us to believe that a nonnegligible participation of initiator anion during initiation cannot be excluded.     

Synthesis,Photophysics and Nonlinear Optical Properties of Stilbenoid Pyrimidine‐Based Dyes Bearing Methylenepyran Donor Groups

The nonlinear properties and the photophysical behavior of two π‐conjugated chromophores that incorporate an electron‐deficient pyrimidine core (A) and γ‐methylenepyrans as terminal donor (D) groups have been thoroughly investigated. Both dipolar and quadrupolar branching strategies are explored and rationalized on the basis of the Frenkel exciton model. Even though a cooperative effect is clearly observed if the dimensionality is increased, the nonlinear optical (NLO) response of this series is moderate if one considers the nature of the D/A couple and the size of the chromophores (as measured by the number of π electrons). This effect was attributed to a disruption in the electronic conjugation within the dyes’ scaffold for which the geometry deviates from planarity owing to a noticeable twisting of the pyranylidene end‐groups. This latter structural parameter also has a strong influence on the excited‐state dynamics, which leads to a very efficient fluorescence quenching.     

Characterization of the structure of human skin substitutes by infrared microspectroscopy

The skin acts mainly as a protective barrier from the external environment, thanks to the stratum corneum which is the outermost layer of the skin. As in vitro tests on skin are essential to elaborate new drugs, the development of skin models closer to reality becomes essential. It is now possible to produce in vitro human skin substitutes through tissue engineering by using the self-assembly method developed by the Laboratoire d’Organogénèse Expérimentale. In the present work, infrared microspectroscopy imaging analyses were performed to get in-depth morpho-spectral characterization of the three characteristic layers of human skin substitutes and normal human skin, namely the stratum corneum, living epidermis, and dermis. An infrared spectral analysis of the skin is a powerful tool to gain information on the order and conformation of the lipid chains and the secondary structure of proteins. On one hand, the symmetric stretching mode of the lipid methylene groups (2,850 cm^?1) is sensitive to the acyl chain conformational order. The evolution profile of the frequency of this vibrational mode throughout the epidermis suggests that lipids in the stratum corneum are more ordered than those in the living epidermis. On the other hand, the frequencies of the infrared components underneath the envelop of the amide I band provide information about the overall protein conformation. The analysis of this mode establishes that the proteins essentially adopt an α-helix conformation in the epidermis, probably associated with the presence of keratin, while modifications of the protein content are observed in the dermis (extracellular matrix made of collagen). Finally, the lipid organization, as well as the protein composition in the different layers, is similar for human skin substitutes and normal human skin, confirming that the substitutes reproduce essential features of real skin and are appropriate biomimetics.     

Structure of the calcium pyrophosphate monohydrate phase (Ca2P2O7·H2O): towards understanding the dehydration process in calcium pyrophosphate hydrates

Calcium pyrophosphate hydrate (CPP, Ca₂P₂O₇·nH₂O) and calcium orthophosphate compounds (including apatite, octacalcium phosphate etc.) are among the most prevalent pathological calcifications in joints. Even though only two dihydrated forms of CPP (CPPD) have been detected in vivo (monoclinic and triclinic CPPD), investigations of other hydrated forms such as tetrahydrated or amorphous CPP are relevant to a further understanding of the physicochemistry of those phases of biological interest. The synthesis of single crystals of calcium pyrophosphate monohydrate (CPPM; Ca₂P₂O₇·H₂O) by diffusion in silica gel at ambient temperature and the structural analysis of this phase are reported in this paper. Complementarily, data from synchrotron X‐ray diffraction on a CPPM powder sample have been fitted to the crystal parameters. Finally, the relationship between the resolved structure for the CPPM phase and the structure of the tetrahydrated calcium pyrophosphate β phase (CPPT‐β) is discussed.     

Ion chromatograph with three-dimensional printed absorbance detector for indirect ultraviolet absorbance detection of phosphate in effluent and natural waters

An ion chromatography system employing a low-cost three-dimensional printed absorbance detector for indirect ultraviolet detection towards portable phosphate analysis of environmental and industrial waters has been developed. The optical detection cell was fabricated using stereolithography three-dimensional printing of nanocomposite material. Chromatographic analysis and detection of phosphate were carried out using a CS5A 4 × 250 mm analytical column with indirect ultraviolet detection using a 255 nm light-emitting diode. Isocratic elution using a 0.6 mM potassium phthalate eluent combined with 1.44 mM sodium bicarbonate was employed at a flow rate of 0.75 mL/min. A linear calibration range of 0.5 to 30 mg/L PO₄³⁻ applicable to environmental and wastewater analysis was achieved. For retention time and peak area repeatability, relative standard deviation values were 0.68 and 4.09%, respectively. Environmental and wastewater samples were analyzed with the optimized ion chromatography platform and the results were compared to values obtained by an accredited ion chromatograph. For the analysis of environmental samples, relative errors of <14 % were achieved. Recovery analysis was also carried out on both freshwater and wastewater samples and recovery results were within the acceptable range for water analysis using standard ion chromatography methods.     

Optimization of Sr-90 precipitation in nitric acid using design of experiments for radioactive waste characterization method

Journal of Radioanalytical and Nuclear Chemistry - 90Sr radiochemical method using nitric acid for Sr and Ca separation was optimized using design of experiments methodology. Nitric acid...     

Electrochemical behavior of silver thin films interfaced with yttria-stabilized zirconia

Thin silver films (100–800 nm) were deposited by physical vapor deposition (PVD) on yttria-stabilized zirconia solid electrolyte. The electric percolation as a function of the film thickness was studied during deposition and annealing using a two-electrode in-situ resistance measurement technique. Electrical percolation was achieved in as-deposited films greater than 5.4?±?0.4 nm; however, thermal treatment (550 °C in air) resulted in film dewetting for Ag films as thick as 500 nm and formation of electronically isolated Ag nanoparticles, as was confirmed by SEM and XPS. In thermally treated samples, stable electronic conductivity associated with a continuous percolated network was only observed in samples greater than 600 nm in thickness. The effect of polarization on the electrochemical reactions at the three-phase (electrode-gas-electrolyte) and two-phase (electrode-electrolyte) boundaries of the electrode was investigated by solid electrolyte cyclic voltammetry (SECV) at 350 °C and P _O2?=?6 kPa. With the application of positive potential, silver oxide (Ag₂O) was found to form along the three-phase boundary and then extends within the bulk of the electrode with increasing anodic potentials. By changing the hold time at positive potential, passivating oxide layers are formed which results in a shift in favor of the oxygen evolution reaction at the working electrode. This oxide forms according to a logarithmic rate expression with thick oxides being associated with decrease in current efficiency for subsequent oxide formation.     

Ordered Mesoporous ZSM‐5 Employing an Imidazolium‐Based Ionic Liquid

Hierarchically porous ZSM‐5 was achieved by using a simple bottom‐up strategy combining zeolite seeds with imidazolium‐based ionic liquids. The bimodal ZSM‐5 with hexagonal arranged mesopores (3 nm) shows important activity in the acid catalysis of bulky compounds relative to conventional ZSM‐5.