Functional syndiotactic poly(β‐hydroxyalkanoate)s via stereoselective ring‐opening copolymerization of rac‐β‐butyrolactone and rac‐allyl‐β‐butyrolactone

The copolymerization of racemic β‐butyrolactone (rac‐BL^Me) with racemic “allyl‐β‐butyrolactone” (rac‐BL^allyl) in toluene, catalyzed by the discrete amino‐alkoxy‐bis(phenolate) yttrium‐amido complex 1 , gave new poly(β‐hydroxyalkanoate)s with unsaturated side chains. The poly(BL^Me‐co‐BL^allyl) copolymers produced have a highly syndiotactic backbone structure (P_r = 0.80–0.84) with a random enchainment of monomer units, as evidenced by ¹³C NMR, and high molecular weight (M_n up to 58,000 g mol^?1) with a narrow polydispersity (M_w/M_n = 1.07–1.37), as determined by GPC. The comonomer incorporation (5–50 mol % rac‐BL^allyl) was a linear function of the feed ratio. The pendant vinyl bond of the side‐chains in those poly(BL^Me‐co‐BL^allyl) copolymers allowed the effective introduction of hydroxy or epoxy groups via dihydroxylation, hydroboration‐oxidation or epoxidation reactions. NMR studies indicated that all of these transformations proceed in an essentially quantitative conversion and do not affect the macromolecular architecture. Some thermal properties (T_m, ΔH_m, T_g) of the prepared polymers have been also evaluated. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3177–3189, 2009     

Localized surface plasmon resonance interfaces coated with poly[3-(pyrrolyl)carboxylic acid] for histidine-tagged peptide sensing

The paper reports on a novel localized surface plasmon resonance (LSPR) substrate architecture for the immobilization and detection of histidine-tagged peptides. The LSPR interface consists of an ITO (indium tin oxide) substrate coated with gold nanostructures. The latter are obtained by thermal deposition of a thin (2 nm thick) gold film followed by post-annealing at 500 °C. The LSPR interface was coated with poly[3-(pyrrolyl)carboxylic acid] thin films using electrochemical means. The ability of the LSPR interfaces coated with poly[3-(pyrrolyl)carboxylic acid] to chelate copper ions was investigated. Once loaded with metal ions, the modified LSPR interface was able to bind specifically to histidine-tagged peptides. The binding process was followed using LSPR.     

‘ClickCarb’: modular sugar based ligands via click chemistry

Reported is a modular approach for the synthesis of a number of structurally diverse ligands derived from carbohydrates. The use of the highly functional hydroxy amino azide 1 derived from glucosamine allows the synthesis of a number of useful ligands for organic and organometallic catalyses. The key step of the approach is the Huisgen cycloaddition of the anomeric sugar azide and diverse alkynes.     

New secoiridoid from olive mill wastewater

A new secoiridoid, olenoside A (1a) and its known epimer olenoside B (1b), were isolated from olive mill wastewater as a mixture of two isomers. Their structures, 1-methyl-7-oxo-6,6a,8,8a-tetrahydro-1H,3H-pyrano[3,4-c]pyran-4-carboxylic acid methyl ester, were determined by spectroscopic methods including 2-D NMR. The structure of major compound 1a was confirmed by X-ray diffraction.     

Computation of the electronic structure and direct-gap absorption spectra in Ge-rich Si<Subscript>1−x</Subscript> Ge<Subscript>x</Subscript>/Ge/Si<Subscript>1−x</Subscript>Ge<Subscript>x</Subscript> type-I quantum wells

This paper presents the results of conduction band discontinuities calculation for strained/relaxed Si_1?x Ge _x /Si_1?y Ge _y heterointerfaces in Γ _15C , Γ _2′C and L upper bands minima, as well as the room-temperature strained (vs. relaxed) band gaps deduced from the classical model-solid theory. Based upon the obtained data, we propose a type-I W-like Si_1?y Ge _y /Si_1?x Ge _x /Ge/Si_1?x Ge _x /Si_1?y Ge _y quantum wells heterostructure optimized in terms of compositions and thicknesses. Electronic states and wave functions are found by solving Schrödinger equation without and under applied bias voltage. An accurate investigation of the optical properties of this heterostructure is done by calculating the energies of the interband transitions and their oscillator strengths. Moreover, a detailed computation of the bias-voltage evolution of the absorption spectra is presented. These calculations prove the existence of type-I band alignment at Γ _2′C point in compressively strained Ge quantum wells grown on relaxed Ge-rich Si_1?y Ge _y buffers. The strong absorption coefficient (> 8 × 10³ cm^-1) and the large Stark effect (0.1 eV @ 2 V) of the Γ _2′C transitions thresholds open up perspectives for application of these heterostructures for near-infrared optical modulators.     

Effect of Si doping on optical and thermal properties of MOVPE GaN thin layers

Photothermal deflection spectroscopy is used to investigate thermal and optical properties of MOVPE grown GaN thin layers deposited on sapphire substrate. The effects of Si doping on absorption spectrum and gap energy are revealed. Also, doping-induced free carrier absorption is extracted from absorption in the sub-gap region. Moreover, the variations of photothermal signal versus modulation frequency are used to determine thermal properties of these films. The measured thermal conductivity is clearly decreased by Si doping, the main reason should be the phonon scattering on point defects.     

Determination of free-carrier and phonon-assisted absorptions for Si-doped GaSb thin layers

Photothermal deflection spectroscopy is used in order to investigate near- and sub-band gap absorption of Si-doped GaSb epilayers deposited by MBE on a semi-insulating GaAs substrate. The optical absorption spectra show an extra absorption on the transparency region below the bandgap due to free-carrier absorption. However, for energies above the gap, we notice a linear behavior of the square root of the absorption coefficient versus the heating beam energy, which is attributed to phonon-assisted absorption. From interpolation of the phonon absorption to low energies we have determined the free-carrier absorption that is found to follow the Drude law.     

The structural transformation of monoclinic [(R)-C5H14N2][Cu(SO4)2(H2O)4]·2H2O into orthorhombic [(R)-C5H14N2]2[Cu(H2O)6](SO4)3: crystal structures and thermal behavior

Single crystals of [(R)-C₅H₁₄N₂][Cu(SO₄)₂(H₂O)₄]·2H₂O (1) were grown through the slow evaporation of a solution containing H₂SO₄, (R)-C₅H₁₂N₂ and CuSO₄·5H₂O. These crystals spontaneously transform to [(R)-C₅H₁₄N₂]₂[Cu(H₂O)₆](SO₄)₃ (2) over the course of four days at room temperature. The same single crystal on the same mounting was used for the determination of the structure of (1) and the unit cell determination of (2). A second single crystal of the transformed batch has served for the structural determination of (2). Compound 1 crystallizes in the noncentrosymmetric space group P2₁ (No. 4) and consists of trimeric [Cu(SO₄)₂(H₂O)₄]^2? anions, [(R)-C₅H₁₄N₂]²⁺ cations and occluded water molecules. Compound 2 crystallizes in P2₁2₁2 (No. 18) and contains [Cu(H₂O)₆]²⁺ cations, [SO₄]^2? anions and occluded water molecules. The thermal decompositions of compounds 1 and 2 were studied by thermogravimetric analyses and temperature-dependent X-ray diffraction.     

ESI-MS/MS Analysis of Phenolic Compounds from Aeonium arboreum Leaf Extracts and Evaluation of their Antioxidant and Antimicrobial Activities

Aeonium is a genus of succulents belonging to the Crassulaceae family. Their importance in traditional medicine has stimulated both pharmacological and chemical research. In this study, we optimized extraction, separation, and analytical conditions using a high performance liquid chromatographic method coupled with electrospray ionization mass spectrometry by the negative mode (HPLC-ESI-MS) in order to, for the first time, determine thirty-four compounds from Aeonium arboreum leaves. Twenty-one of them are assigned among which are sixteen flavonoids and five phenolic acids. FRAP, TAC, DPPH, and ABTS^•+ radical scavenging were used to evaluate antioxidant activity. The obtained IC₅₀ values ranged from 0.031 to 0.043 mg.mL⁻¹ for DPPH and between 0.048 and 0.09 mg·mL⁻¹ for ABTS^•+. Antimicrobial activity was also assessed. The obtained minimum inhibitory concentrations (MIC) of these extracts ranged from 12.5 to 50 µg·mL⁻¹ against Micrococcus luteus, Listeria ivanovii, Staphylococcus aureus, Salmonella enterica, Escherichia coli, Pseudomonas aeruginosa, Aspergillus niger, and Fusarium oxysporum, and from 25 to 50 µg·mL⁻¹ against Candida albicans. Therefore, these extracts can be considered as a potential source of biological active compounds.     

Influence of hydrogen and residual disorder on the optical and electrical properties of microcrystalline silicon

The total hydrogen content, Raman diffusion, optical absorption α(hν) and electrical conductivity σ(1/T) of silicon films prepared by glow discharge between 250°C and 500°C were measured. A model is presented according to which α(hν) and σ(1/T) are controlled by the grain boundaries of microcrystalline Si.