Spatial and temporal variations of the inherent and apparent optical properties in a shallow coastal lake

Apparent and inherent optical properties in the coastal lagoon of Fogliano were measured in three seasonal surveys in 2002. Irradiance data from in situ measurements of ultraviolet and visible wavebands permitted to estimate the related attenuation coefficients. Laboratory extinction measurements on filtered (0.22 microm) and unfiltered water samples were also performed. The integrated approach between in situ and laboratory measurements allowed the determination of the role of the suspended and dissolved matter in the attenuation and extinction of ultraviolet and visible radiation within the water column. As noted, the impact of the suspended and dissolved matter on the lake optical quality was influenced by wind resuspension of particulate matter: the relative role of dissolved matter in the absorption of UV and visible radiation was prevailing at low wind velocity conditions (less than 2.2 m s(-1)), while at high wind velocities (3.9 m s(-1)), particulate matter resuspension strongly influenced the attenuation and the extinction measurements. The extinction in the analyzed wavelengths of filtered and unfiltered water samples and the in situ irradiance measurements allowed us to define new optical parameters and important correlations with limnological and classical optical measurements. By sampling at high spatial resolution (18 stations in 4 km2), it was possible to evidence a spatial gradient of the optical and limnological properties, these distributions showed a consistent pattern in all three surveys, and were important for the characterization of the chromophoric dissolved organic matter that was estimated with the spectral slope of the extinction curve spectra. A relatively higher spectral slope was found in the southern basin with respect to the northern, where the maximum values of the attenuation coefficients and limnological parameters were found. These results suggest different sources of dissolved organic matter and/or a different level of photobleaching.     

Acetylene cyclotrimerization by early second-row transition metals in the gas phase. A theoretical study

The acetylene cyclotrimerization reaction mediated by the left-hand-side bare transition metal atoms Y, Zr, Nb, and Mo has been studied theoretically, employing DFT in its B3LYP formulation. The complete reaction mechanism has been analyzed, identifying intermediates and transition states. Both the ground spin state and at least one low-lying excited state have been considered to establish whether possible spin crossings between surfaces of different multiplicity can occur. Our results show that the overall reaction is highly favorable from a thermodynamic point of view and ground state transition states lie always below the energy limit represented by ground state reactants. After the activation of two acetylene molecules and formation of a bis-ligated complex, the reaction proceeds to give a metallacycle intermediate, as the alternative formation of a cyclobutadiene complex is energetically disfavored. All the examined reaction paths involve formation of a metallacycloheptatriene intermediate that in turn generates a metal-benzene adduct from which finally benzene is released. Similarities and differences in the behaviors of the considered four metal atoms have been examined.     

Pressure-tuning of magnetism and linkage isomerism in iron(II) hexacyanochromate

A pressure-induced linkage isomerization of the cyanide anion has been observed in single crystals of a chromium(III)-iron(II) Prussian blue analogue of formula K0.4Fe4[Cr(CN)6]2.8 square1.2.16H2O (1). Upon application of pressure in the 0-1200 MPa range, the cyanide ligand rotates and becomes C-bonded to the iron(II) cations, leading to a stabilization of their diamagnetic low-spin states. The result is a decrease of magnetization and magnetic ordering temperatures from TC = 19 K at ambient pressure to 13 K at 1200 MPa. The initial magnetic properties can be restored on pressure release. The reversible movement of cyanide in the solid state can be exploited as a switch of the magnetic interaction at the molecular level.     

Synthesis of a Tyr-octreotate conjugated closo-carborane [HC2B10H10]: a potential compound for boron neutron capture therapy

A novel Tyr³-octreotate conjugated closo-carborane as a potential compound for boron neutron capture therapy was obtained via Fmoc solid phase peptide synthesis. The boron cluster [C₂B₁₀H₁₁] was introduced through the reaction of 6,9-bis(acetonitrile)decaborane and 5-hexynoic acid yielding a new closo-carborane conjugated carboxylic acid which was coupled subsequently with solid phase conjugated Tyr³-octreotate. The final boron-containing peptide was purified by preparative reverse phase HPLC and structural identity was proved applying MALDI-TOF mass spectrometry.     

Depth profiling of polymer films by confocal Raman spectroscopy

Confocal Raman microspectroscopy has many potential applications in the study of polymer-solvent interactions, including the determination of solvent and polymer-solvent complex depth profiles. This contribution focuses on preventing the formation of polymer-solvent complexes, using surface chemical modification of PVC films. While the surface-specific nature of the film modification is easily demonstrated,^[1] confocal Raman measurements clearly show the effects of film refractive index: the modifier depth profile shows a lack of symmetry and the film thickness is underestimated. A spectral normalisation method is described, and this is shown to result in a modifier depth profile which is in good agreement with data obtained by Raman microspectroscopy following physical cross-sectioning of a sample. Alternative techniques for Raman depth profiling are also discussed.     

Development of a solid-phase microextraction method for the analysis of phenolic flame retardants in water samples

A solid-phase microextraction (SPME) method for the ultra-trace determination of brominated phenols in aqueous samples has been developed and is reported for the first time to the best of our knowledge. 3,5,3',5'-tetrabromobisphenol A (TBBPA), the most widely used brominated flame retardant, and other phenolic flame retardants in commercial use, such as 2,4-dibromophenol (2,4-DBP), 2,4,6-tribromophenol (TBP) and pentabromophenol (PBP) have been included as target analytes. The analytical procedure involves the in situ acetylation-SPME and gas chromatography-mass spectrometry (GC-MS) determination of the target analytes. A multi-factor categorical experimental design was created to study the main parameters affecting the extraction efficiency, allowing also the evaluation of interaction effects between factors. The factors studied were type of fiber, extraction mode, exposing the fiber directly into the sample (DSPME) or into the headspace over the sample (HSSPME), and extraction temperature. Carboxen-polydimethylsiloxane (CAR-PDMS) fiber appeared to be the most suitable of the five fibers tested for the extraction of most compounds, excluding PBP and TBBPA for which polydimethylsiloxane (PDMS) was the most efficient coating. The highest response was achieved for both fibers sampling in headspace mode at 100 degrees C. In order to test the linearity of the method, calibration studies were performed with both CAR-PDMS and PDMS coatings. For both fibers, the method was linear in a range of 2 orders of magnitude, giving relative standard deviation (RSD%) below 10% for most compounds and detection limits at the low pg/mL level. In addition, the feasibility of the method for simultaneous determination of chlorinated and brominated phenols was studied. Finally, the method was applied to several real samples including tap water and effluent and influent waste water samples from an urban treatment plant, in which several phenolic compounds, such as phenol, methylphenols and chlorophenols, could be detected and quantified.     

C-C coupling reactions of aryl bromides and arylsiloxanes in water catalyzed by palladium complexes of phosphanes modified with crown ethers

[reaction: see text] The complexes [PdCl2L2], where L is a crown-ether-containing triarylphosphane, catalyze the formation of biaryls from arylsiloxanes and aryl bromides with high yields in water as solvent and under air. The water-insoluble catalysts [PdCl2(PhCN)2] and [PdCl2(PPh3)2] are also efficient, although they decompose more quickly to form black Pd0.     

Focused ultrasound and molecularly imprinted polymers: a new approach to organotin analysis in environmental samples

There is a high interest in speciation of organotin compounds (OTCs) in biota and marine sediment samples, due to their influence in the transmission of the contamination in the trophic chain. Sample treatment is still the most "compromising" step of speciation analysis. Extraction methods are in general time-consuming due to long extraction times and several analytical steps involved. In addition, in most cases there are problems of low recovery, especially for MBT. These drawbacks, added to the high matrix effects generally present in biota samples, make the sample treatment for organotin analysis a serious challenge for environmental issues. Here we present a novel, fast and efficient two steps method for organotin speciation in mussel and oyster tissue as well as in marine sediments. The first step based on the use of ultrasonic probe extraction for species leaching allowed us to quantitatively extract these compounds in a few minutes. Matrix interferences drastically decreased by applying a clean-up step based on the use of an imprinted polymer especially designed for tributyltin (TBT). This procedure increased accuracy and precision of the GC-FPD analysis and improving the limit of detection, Besides, this new method prevents the use of standard addition calibration method, which is mandatory without the clean-up step. The optimization and validation has been performed by using three reference materials: mussel tissue CRM-477, oyster candidate T-38 and sediment PACS-2.     

Surface characterisation of plasma-modified poly(ethylene terephthalate)

This paper reports the modifications produced by nitrogen and helium cold plasmas on the surface of PET. The changes have been studied by diffuse reflectance Fourier transform spectroscopy (DRIFTS), atomic force microscopy (AFM) and inverse gas-solid chromatography (IGSC). Nitrogen and oxygen atoms seem to appear on the surface of PET as a consequence of the exposure to the atmosphere after the treatments with plasmas. AFM shows that both plasmas altered in different extent the surface of PET as they break the polymer chains producing low molecular products which appear as bumps on the surface. The surface area and the porosity of PET does not change by plasma treatments even after 15 min. The dispersive component of the surface free energy, gamma(s)(d), decreases after long treatments with nitrogen plasma whereas it remains almost unchanged after long treatment with helium plasma.