Transition Metal Complexes of a Salen–Fullerene Diad: Redox and Catalytically Active Nanostructures for Delivery of Metals in Nanotubes

A covalently‐linked salen–C₆₀ (H₂L) assembly binds a range of transition metal cations in close proximity to the fullerene cage to give complexes [M(L)] (M=Mn, Co, Ni, Cu, Zn, Pd), [MCl(L)] (M=Cr, Fe) and [V(O)L]. Attaching salen covalently to the C₆₀ cage only marginally slows down metal binding at the salen functionality compared to metal binding to free salen. Coordination of metal cations to salen–C₆₀ introduces to these fullerene derivatives strong absorption bands across the visible spectrum from 400 to 630 nm, the optical features of which are controlled by the nature of the transition metal. The redox properties of the metal–salen–C₆₀ complexes are determined both by the fullerene and by the nature of the transition metal, enabling the generation of a wide range of fullerene‐containing charged species, some of which possess two or more unpaired electrons. The presence of the fullerene cage enhances the affinity of these complexes for carbon nanostructures, such as single‐, double‐ and multiwalled carbon nanotubes and graphitised carbon nanofibres, without detrimental effects on the catalytic activity of the metal centre, as demonstrated in styrene oxidation catalysed by [Cu(L)]. This approach shows promise for applications of salen–C₆₀ complexes in heterogeneous catalysis.     

Boronate Ligands in Materials: Determining Their Local Environment by Using a Combination of IR/Solid‐State NMR Spectroscopies and DFT Calculations

Boronic acids (R‐B(OH)₂) are a family of molecules that have found a large number of applications in materials science. In contrast, boronate anions (R‐B(OH)₃^?) have hardly been used so far for the preparation of novel materials. Here, a new crystalline phase involving a boronate ligand is described, Ca[C₄H₉‐B(OH)₃]₂, which is then used as a basis for the establishment of the spectroscopic signatures of boronates in the solid state. The phase was characterized by IR and multinuclear solid‐state NMR spectroscopy (¹H, ¹³C, ¹¹B and ⁴³Ca), and then modeled by periodic DFT calculations. Anharmonic OH vibration frequencies were calculated as well as NMR parameters (by using the Gauge Including Projector Augmented Wave—GIPAW—method). These data allow relationships between the geometry around the OH groups in boronates and the IR and ¹H NMR spectroscopic data to be established, which will be key to the future interpretation of the spectra of more complex organic–inorganic materials containing boronate building blocks.     

A Step-Forward Method of Quantitative Analysis of Enzymatically Produced Isomaltooligosaccharide Preparations by AEC-PAD

In this paper, anion exchange chromatography coupled with pulsed amperometric detection has been successfully applied for the fine analysis of isomaltooligosaccharides (IMO) syrups where previous reported methods suffered from a lack of homologue oligosaccharides resolution. These syrups are made of a very complex mixture of glucose oligosaccharides characterized at the same time by their DP value (from 2 to ~15) and linkage types [α-(1–2, 3 or 6) and non-IMO α-(1–4)] and position. A mix of available commercial standards (17 species) was completely separated on a CarboPac PA-100 column at a flow rate of 1 mL min^?1 and with a gradient of sodium acetate in 100 mM sodium hydroxide. The method was validated according to calibration curve, precision, recovery tests, limits of detection and quantitation. Calibration curves presented correlation coefficients greater than 0.98. The analytical method has been applied on real syrups, keeping a high performance separation of structurally close molecules and giving, for six determinations, very low relative SD for the available standard molecules (0.3–5.8%). The accuracy of the proposed method was tested by recovery measurements: first by spiking maltose on three different syrups and then by spiking six different sugar standards (20, 50 and 75% of the initial content) on a single syrup. Good recovery results (respectively, 96.5–99.7 and 97.1–102.7%) were found. The method was found sensible with limits of detection (signal-to-noise ratio of 3) between 0.048 and 0.124 μg mL^?1 and limits of quantification (signal-to-noise ratio of 10) between 0.159 and 0.412 μg mL^?1.     

Theoretical and experimental investigation of the structural and spectroscopic properties of coumarin 343 fluoroionophores

A joint theoretical-experimental investigation has been carried out to unravel the details of the complexation of cations by fluoroionophores based on coumarin 343 and to interpret the modifications in the ligand and also in the coumarin structural, electronic, magnetic, and vibrational properties. It is confirmed that C343-dea (1) complexes the cations by both the lactone and the amide oxygen atoms whereas for C343-crown (2) and C343-dibenzocrown (3), the cations are complexed by the oxygen atoms of the lactone as well as those of the crown ligand. These complexations induce geometric modifications, which are delocalized over the coumarin backbone and are related to electronic reorganizations that modify the spectroscopic signatures. This paper analyzes these signatures and shows how they are related as well as how they can be used to monitor the complexation process. Upon complexation, the UV-visible absorption spectra display a bathochromic shift of the most intense electronic transition; this shift is generally larger for the most flexible compound 1 as well as when complexing divalent cations. NMR spectra bear many signatures of the complexation, of which the most remarkable ones are the large shielding of C(1) and the large deshieldings of C(9) and C(16). Additional makers of complexation are highlighted in the IR vibrational spectra, in particular the bands associated with the lactone and amide CO vibrations, which are downshifted when the corresponding CO is involved in the complexation mode and, otherwise, upshifted. A high degree of consistency characterizes the different geometrical, electronic, magnetic, and vibrational signatures, which substantiates the assignment of the modes of complexation in 1-3. In addition, the agreement between the experimental data and the theoretical values is rather satisfactory, in that it at least enables us to interpret the spectral signatures.     

2D silver nanocrystal ordering modulated by various substrates and revealed using oxygen plasma treatment

Here, 5 nm Ag nanocrystals are deposited, using the same procedure, on various substrates differing by their rms roughness, wetting properties and nanoparticle-substrate interactions leading, consequently, to different nanocrystal orderings. Theoretical calculations are carried out to understand how these parameters influence the size of the nanocrystal organizations on the substrate surface. When these nanocrystal arrays are subjected to an oxygen plasma treatment, the nanocrystals perfectly assembled in hexagonal networks remain intact, while the nanocrystals that are not well-packed coalesce to form larger particles independently on the used substrate. This phenomenon is observed on the entire substrate surface. This procedure gives an innovative way of using oxygen plasma generated by the reactive ion etching technique, as a new method to reveal defects in 2D Ag nanocrystal self-assemblies.     

A joint theoretical and experimental investigation on the 13C and 1H NMR chemical shifts of coumarin derivatives

¹H and ¹³C NMR chemical shifts of coumarin derivatives have been determined using first principles approaches with and without accounting for the effects of the solvent and compared to experiment in order to assess their reliability. Good linear relationships are obtained between theory and experiment, which allows correcting the calculated values for systematic errors. This is particularly the case when using the PCM scheme to model the solvent effects because the δ values larger than 150 ppm are more difficult to reproduce. The final accuracy of the method amounts to about 1 ppm for ¹³C and 0.05 ppm for ¹H.     

Magnetization of Fe‐oxide based nanocomposite tuned by surface charging

Aiming at a voltage‐control of magnetism, the magnetization of a porous γ‐Fe₂O₃–Pt nanocomposite is studied under the influence of charging the surfaces of the porous structure in an electrolyte. Reversible variations of the magnetization of up to 10.4% could be achieved upon charging in the regime where electrochemical adsorption and desorption occurs. The observed variation of the magnetization with electrochemical charging is assigned to the γ‐Fe₂O₃ nanoparticles whereas the conductive network of Pt nanoparticles is necessary for charging. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

PSAQ™ standards for accurate MS–based quantification of proteins: from the concept to biomedical applications

Absolute protein quantification, i.e. determining protein concentrations in biological samples, is essential to our understanding of biological and physiopathological phenomena. Protein quantification methods based on the use of antibodies are very effective and widely used. However, over the last ten years, absolute protein quantification by mass spectrometry has attracted considerable interest, particularly for the study of systems biology and as part of biomarker development. This interest is mainly linked to the high multiplexing capacity of MS analysis, and to the availability of stable‐isotope‐labelled standards for quantification. This article describes the details of how to produce, control the quality and use a specific type of standard: Protein Standard Absolute Quantification (PSAQ?) standards. These standards are whole isotopically labelled proteins, analogues of the proteins to be assayed. PSAQ standards can be added early during sample treatment, thus they can correct for protein losses during sample prefractionation and for incomplete sample digestion. Because of this, quantification of target proteins is very accurate and precise using these standards. To illustrate the advantages of the PSAQ method, and to contribute to the increase in its use, selected applications in the biomedical field are detailed here. Copyright © 2012 John Wiley & Sons, Ltd.