Spectroellipsometric Characterization of Multilayer Sol-Gel Fe2O3 Films

Multilayer Fe₂O₃ films were deposited by the sol-gel method on glass substrates using three successive deposition procedures. The films were thermally treated for 1 h at 300°C.The optical and microstructural properties of these films were investigated by spectroscopic ellipsometry (SE) in the 500–1000 nm range. The optical gap was found by fitting the dispersion of the film refractive index (n) with the Wemple-DiDomenico (WDD) formula.The ellipsometric measurements showed also that the Fe₂O₃ films are anisotropic. The birefringence values (n) of the sol-gel films (0.05–0.08) are smaller than the large values of the Fe₂O₃ (which are around 0.28) but increase with the crystalization of the films. AFM mesurements showed that the films treated at 300°C start to crystallize.     

Photodegradation of azodyes: comparison of different catalytic systems and control of the effective mineralisation

Three different azodyes were used as target molecules to test the efficiency of the photodegradation process catalysed by titanium dioxide under UV irradiation. A comparison of different catalytic systems was performed using the catalyst both free in solution (system I) and immobilised in a polymeric membrane (system II). Iron oxalate and a conducting polymer (polyaniline, PA) were added to the I and II systems respectively to check an eventual synergetic effect. The research evolved through three different steps involving each one the use of a different analytical method. Shortly, the UV spectrophotometry were preliminarily used to monitor the bleaching process and allowed to choose the best catalytic system, HPLC and GC/MS were used to monitor the appearance and disappearance of the photodegradation intermediates and, lastly, the effective mineralisation was tested by an indirect ICP (Inductively Coupled Plasma) determination of the produced carbon dioxide.     

The gas phase acidity of oligofluorobenzenes and oligochlorobenzenes: about the additivity or non-additivity of substituent effects

The deprotonation energies of benzene, fluorobenzene, all di-, tri-, and tetrafluorobenzenes, pentafluorobenzene, chlorobenzene, all di-, tri-, and tetrachlorobenzenes, and pentachlorobenzene have been calculated at various levels of second-order Moller-Plesset and density functional theory. Taking the previously determined experimental data as a benchmark, good agreement was achieved in the chloro series even with moderate computational effort, whereas more extended basis sets have to be used to obtain meaningful numbers in the fluoro series. Apparently, most extensive electron correlation is required to avoid artifacts caused by the proximity of nonbonding lone pairs at the carbanionic center and at the fluorine atoms. When two or more fluorine substituents were introduced in the same aromatic ring, their individual effects (as defined by position-dependent acidity increments) proved to be perfectly additive in the entire series. In contrast, the acidifying effect of chloro substituents was found to level off when the number of such halogens increases. Additivity or non-additivity of element effects cannot be ascertained after having merely compared the acidity of mono- and disubstituted substrates, but only after having moved to higher degrees of substitution.     

A selective experiment for the sequential protein backbone assignment from 3D heteronuclear spectra

Two modifications of the triple-resonance CANCO sequence, designed for backbone assignment in proteins [Angew. Chem. Int. Ed. 43 (2004) 2257], are presented here. These two new sequences display the intra-residue Ca-CO correlation selectively, while in the original sequence both the inter- and the intra-residue correlations were present. In addition, one of the two variants benefits from an improved sensitivity. Both sequences are a useful complement to the CANCO sequence for facile sequence-specific protein assignment by protonless NMR.     

Determination of total organic carbon – an overview of current methods

This article summarizes the most important and current methods for the determination of total organic carbon (TOC) in solid samples. The methods presented are chemical oxidation, combustion, acid treatment and ashing. We discuss the advantages of the different methods as well as problems that can be encountered during analysis. We give additional information on the detection techniques used for TOC determination and on the topic of volatile organic carbon (VOC) that deserves particular attention when carrying out TOC determinations, in particular with solid samples. We have compiled a concise survey of the literature covering 60 reports and tabulated the relevant analytical parameters.     

13C-13C NOESY: an attractive alternative for studying large macromolecules

13C direct detection provides a valuable alternative to 1H detection to overcome fast relaxation because of its smaller magnetic moment. 13C-13C NOESY spectra were acquired for a dimeric protein of molecular mass 32 000 and for a monomeric analogue. With increasing molecular mass, the quality of 13C-13C NOESY spectra improves while the scalar-based experiments become less sensitive, as predicted by the increase in the molecular mass. 13C-13C NOESY spectra of the dimer were acquired with different mixing times. The mixing time can be tuned to detect mainly one-bond correlations, or it can be increased to also detect correlations between nuclei at longer distances. It is proposed that 13C-13C dipolar-based experiments provide a promising tool for signal detection and assignment in large macromolecules, such as multimeric species and macromolecular complexes, for which scalar-based experiments become less effective.     

Analysis of drying oils used as binding media for objects of art by capillary electrophoresis with indirect UV and conductivity detection

Capillary electrophoresis (CE) was applied to analyse the long-chain fatty acid composition of vegetable oils, and their degradation products formed upon ageing when drying oils are used as binding media. The analytes were detected with contactless conductivity detection (CCD) and indirect UV absorption, both detectors positioned on-line at the separation capillary. The long-chain fatty acids were resolved in a background electrolyte (BGE) consisting of phosphate buffer (pH = 6.86, 15 mM) containing 4 mM sodium dodecylbenzensulfonate, 10 mM Brij 35, 2% (v/v) 1-octanol and 45% (v/v) acetonitrile. As in this system dicarboxylic analytes, the products of oxidative degradation of unsaturated fatty acids, cannot be determined, a suitable background electrolyte was developed by the aid of computer simulation program PeakMaster. It makes use of a 10 mM salicylic acid, 20 mM histidine buffer, pH 5.85, which combines buffering ability with the optical properties obligatory for indirect UV detection. This buffer avoids system eigenpeaks, which are often impairing the separation efficiency of the system. Separation of the dicarboxylic analytes was further improved by a counter-directed electroosmotic flow (EOF), obtained by dynamically coating the capillary wall with 0.2 mM cetyltrimethylammonium bromide. Long-chain fatty acids and their decomposition products could be determined in recent and aged samples of drying oils, respectively, and in samples taken from two paintings of the 19th century.     

Effect of Photodynamic Pretreatment on the Susceptibility of Murine Tumor Cells To Macrophage Antitumor Mechanisms

Abstract— In vitro photodynamic treatment of YAC-1 murine T-lymphoma cells with the hematoporphyrin derivative Photosan 3 and red light resulted in dose-dependent phototoxicity. Photodynamic pretreatment, however, did not render these cells more susceptible to macrophage-me-diated tumor cytotoxicity or the cytotoxic effects of mac-rophage-derived antitumor mediators like tumor necrosis factor aL (TNF-aL) or interferon bT (IFN-bT). Independent of the degree of photosensitization used, the cytotoxicity values obtained with macrophages or the different mediators were shifted by the respective values for phototoxicity, suggesting these effects to be additive and thus not interdependent. These data show that while higher overall tumor cytotoxicity can be achieved by a combination of photodynamic treatment and macro-phage-mediated tumor destruction, this apparently is not a result of enhanced sensitivity of photodynamically treated tumor cells to macrophage antitumor mechanisms in general     

Oxygen-bridged borate anions from tris(pentafluorophenyl)borane: synthesis, NMR characterization, and reactivity

The previously known anion [(C6F5)3B(mu-OH)B(C6F5)3]- (2) has been prepared by a two-step procedure, involving deprotonation of (C6F5)3BOH2 to give [B(C6F5)3OH]- (1), followed by addition of B(C6F5)3. The solution structure and the dynamics of 2 have been investigated by 1H and 19F NMR spectroscopy. The reaction of [NHEt3]2 with NEt3 resulted in the formation of [NHEt3]+ [(C6F5)3BOH]-, [NHEt3]+ [(C6F5)3BH]-, and (C6F5)3B- (CH2CH=N+ Et2). This indicates that in the presence of a nucleophile anion 2 can dissociate to B(C6F5)3 and 1. The reaction of [HDMAN]2 with 1,8-bis(dimethylamino)naphthalene (DMAN) confirmed this trend. In the presence of water, 2 transformed into the adduct [(C6F5)3BO(H)H...O(H)B(C6F5)3]- (3), containing the borate 1 hydrogen-bonded to a water molecule coordinated to B(C6F5)3. The same compound is formed by treating (C6F5)3BOH2 with 0.5 equiv of a base. A competition study established that for 1 the Lewis acid-base interaction with B(C6F5)3 is about 5 times preferred over H-bonding to (C6F5)3BOH2. The X-ray single-crystal analysis of [2-methyl-3H-indolium]3 provided the first experimental observation of an asymmetric H-bond in the [H3O2]- moiety, the measured O-H and H...O bond distances being significantly different [1.14(2) vs 1.26(2) A]. The reaction of NEt3 with an equimolar mixture of B(C6F5)3 and bis(pentafluorophenyl)borinic acid, (C6F5)2BOH, afforded the novel borinatoborate salt [NHEt3]+ [(C6F5)3BOB(C6F5)2]- ([NHEt3]4). X-ray diffraction showed that the B-O bond distances are significantly shorter than in [(C6F5)3B(mu-OH)B(C6F5)3]-. Variable-temperature 19F NMR revealed high mobility of the five aryl rings, at variance with the more crowded anion 2. 2D NMR correlation experiments showed that in CD2Cl2 the two anions [(C6F5)3BOH]- and [(C6F5)3BH]- form tight ion pairs with [NHEt3]+, in which the NH proton establishes a conventional (BO...HN) or an unconventional (BH...HN), respectively, hydrogen bond with the anion. The diborate anions 2-4, on the contrary, gave loose ion pairs with the ammonium cation, due both to the delocalized anionic charge and to the more sterically encumbered position of the oxygen atoms that should act as H-bond acceptors.