The two new pincer azomethine-thiophene ligands (N,NE',N,NE')-N,N'-(thiophene-2,5-diylbis(methan-1-yl-1-ylidene))bis(naphathalen-2-ylmethanamine) (L1) and (E)-(4,6-dihydropyren-1-yl)-N-((5-((E)-(pyren-1-ylmethylimino)ethyl)thiophen-2-yl)methylene)methanamine (L2), their absorption, fluorescence and MALDI-TOF-MS spectroscopic studies are described. The two systems synthesised combine the emissive probes pyrene and naphthyl with the good chelating properties of a tridentate SN2 donor-set from a thiophene Schiff-base ligand. Both ligands gave analytically pure solid complexes with Ni(II) and Pd(II) salts. The bichromophoric pyrene derivative L2 presents two emission bands in solution, one corresponding to the monomer species and a red-shifted band attributable to the intramolecular excimer. Ni(II) and Pd(II) complexation affects the conformation in solution, increasing the monomer emission at the expense of the excimer band; this effect could be explored in metal ion sensing. System L1 behaves as a non emissive probe. In situ complexation reactions followed by MALDI-TOF-MS spectrometry without matrix support have also been performed; these experiments show that L1 could be a potential chemosensor for Ni(II) and Pd(11). (c) 2007 Elsevier B.V. All rights reserved.

We present a study of the growth of silver clusters on a TiO2(110) substrate in ultra- high vacuum. The growth is monitored in situ by Low Energy Ion Scattering (LEIS) using He+ scattering and X-ray Photoelectron Spectroscopy (XPS) and ex situ by scanning electron microscopy (SEM). Experimental results show that the deposition rate, the substrate temperature and the annealing temperature are key parameters for controlling the size and morphology of the Ag clusters. By changing the deposition rate, the mean cluster diameter can vary from 5 to 20 nm. The growth of Ag at low substrate temperature shows a transition from quasi 2D flat islands to a 3D growth mode at submonolayer coverage. The substrate was annealed at different temperatures and the clusters shape controlled from a quasi 2D flat island to 3D sharp islands with a maximum substrate exposure, prior to cluster desorption.

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In the presentwork we have studied the properties of zinc oxide (ZnO) thin films grown by laser ablation of ZnO targets under different substrate temperature and background oxygen conditions. The ZnO layers were deposited with a Pulsed Laser Deposition (PLD) system on pre-nitrided (0001) sapphire (Al2O3), using the base line of a Nd:YAG laser at 1064 nm. The films were characterized by different structural and optical methods, including X-ray diffraction (XRD), scanning electron microscopy (SEM), optical transmission spectroscopy, and steady-state photoluminescence (PL). XRD analysis with rocking curves and $þeta$–2$þeta$ scans indicates preferential growth along the c-axis direction with a full width at half maximum (FWHM) smaller than 1.5◦. Low-temperature photoluminescence (PL) showed strong excitonic emission near 3.36 eV between 9 and 65 K

Various S = 3/2 EPR signals elicited from wild-type and variant Azotobacter vinelandii nitrogenase MoFe proteins appear to reflect different conformations assumed by the FeMo-cofactor with different protonation states. To determine whether these presumed changes in protonation and conformation reflect catalytic capacity, the responses (particularly to changes in electron flux) of the alpha H195Q, alpha H195N, and alpha Q191 K variant MoFe proteins (where His at position 195 in the alpha subunit is replaced by Gln/Asn or Gln at position alpha-191 by Lys), which have strikingly different substrate-reduction properties, were studied by stopped-flow or rapid-freeze techniques. Rapid-freeze EPR at low electron flux (at 3-fold molar excess of wild-type Fe protein) elicited two transient FeMo-cofactor-based EPR signals within 1 s of initiating turnover under N-2 with the alpha H195Q and alpha H195N variants, but not with the alpha Q191K variant. No EPR signals attributable to P cluster oxidation were observed for any of the variants under these conditions. Furthermore, during turnover at low electron flux with the wild-type, alpha H195Q or alpha H195N MoFe protein, the longer-time 430-nm absorbance increase, which likely reflects P cluster oxidation, was also not observed (by stopped-flow spectrophotometry); it did, however, occur for all three MoFe proteins under higher electron flux. No 430-nm absorbance increase occurred with the alpha Q191K variant, not even at higher electron flux. This putative lack of involvement of the P cluster in electron transfer at low electron flux was confirmed by rapid-freeze Fe-57 Mossbauer spectroscopy, which clearly showed FeMo-factor reduction without P cluster oxidation. Because the wild-type, alpha H195Q and alpha H195N MoFe proteins can bind N-2, but alpha Q195K cannot, these results suggest that P cluster oxidation occurs only under high electron flux as required for N-2 reduction. (C) 2007 Elsevier Inc. All rights reserved.

The simultaneous separation and quantification of two casein peptides (IPP, VPP) presenting potent inhibitory activity of angiotensin-converting-enzyme (ACE) and casein in fermented milks was developed. Gradient elution was carried out at a flow-rate of 1 mL/min, using a mixture of two solvents. Solvent A was 0.1% TFA in water and solvent B was acetonitrile-water-trifluoracetic acid 95:5:0.1. The effluent was monitored by UV detector at 214 nm. Calibration curves were constructed in the interval of 0.01-1.0 mg/mL for VPP, 0.005-1.0 mg/mL for IPP, and 0.05-3.0 mg/mL for casein. R 2 invariably exceeded 0.999. The detection limits were 0.004 for VPP, 0.002 mg/mL for IPP, and 0.02 mg/mL for casein. Repeatability of the method was evaluated by six consecutive injections of two standard solutions containing VPP, IPP, and casein. The RSD values for concentration were all below 5.08%. Recovery studies were carried out to determine the accuracy of the method. Recoveries ranged between 88 and 98.2%. The methodology was applied, not only, for the monitorization of VPP, IPP, and casein in commercial fermented milks labeled as presenting anti hypertensive properties, but also, in milk with different degrees of fermentation by L Helveticus, and in other commercial functional fermented milks, such as, those presenting cholesterol lowering properties.

We report the 98% assignment of the apo-form of an orange protein, containing a novel Mo-Cu cluster isolated from Desulfovibrio gigas. This protein presents a region where backbone amide protons exchange fast with bulk solvent becoming undetectable. These residues were assigned using C-13-detection experiments.

This study describes the characterisation of whey protein hydrolysates obtained from tryptic hydrolysis to assess their application as ingredients with angiotensin-converting-enzyme (ACE) inhibitory action. The levels of a-lactalbumin (alpha-la) and P-lactoglobulin (beta-lg) remaining after hydrolysis were quantified. Peptides were separated by RP-HPLC, and Ala-Leu-Pro-Met-His-Ile-Arg (ALPMHIR), the most potent beta-lg-derived ACE-inhibitory peptide was monitored. A correlation curve was established for the production of this peptide as a function of hydrolysis time. Heat-induced gelation of hydrolysates was studied by small-deformation rheology. The gelation times and the strength of the final gels were highly dependent on the degree of hydrolysis. Smaller peptides liberated by hydrolysis contributed to the inability of whey protein hydrolysates to gel. (c) 2006 Elsevier Ltd. All rights reserved.

Cross-linked polyethylene (XLPE) is currently widely used as an insulating material for power cables due to its good physical properties, however when in use it undergoes an electrical ageing process. Its ability to trap electric charge can give rise to space charge accumulation in the bulk of the polymer and produce localised electric stresses that can lead to cable failure, since the electric field will be increased above the design stress in some regions favouring the initiation of degradation there. In this work the PEA (pulsed electro-acoustic) method was used to compare the charge dynamics in three samples (XLPE cable peelings) aged in different ways (electrothermally in the laboratory, field aged in service and thermally aged in the laboratory). Very different transient behavior was found depending upon the ageing history. This is related to differences in the migration of chemical species in the insulation layer, which are known to act as charge traps. All materials showed heterocharge peaks when the space charge reached stability, the magnitude of which seems to be related to the severity of the ageing. (c) 2007 Elsevier B.V. All rights reserved.