Modulation of optical properties of dissolved humic substances by their molecular complexity

In this study, we show that several UV-Vis absorbance, steady-state and time-resolved fluorescence parameters of a series of dissolved humic substances (DHS) from different sources (e.g. terrestrial fulvic and humic acids, and humic acid-like molecules extracted from composted and vermicomposted wastes) correlate with the molar absorptivity at 280 nm per mole of organic carbon (ε(280)), which in turn is proportional to the molecular complexity (e.g. molecular size, aromaticity and oxidation degree) of the DHS. Both absorbance and fluorescence spectral responses were sensitive to the molecular complexity associated with the maturation degree of the DHS. Depending on the DHS, different emitting responses by excitation at the UVA (340 nm) and VIS (460 nm) regions of the absorption spectra were observed. The results were explained in terms of the extent of intramolecular electronic interactions between electron donor groups, such as polyhydroxylated aromatics and indoles, and more oxidized acceptor groups (e.g. quinones or other oxidized aromatics) as the molecular complexity of the DHS increased.     

Thermochemiluminescence as a fast method to detect and characterize hydroperoxide moieties in novel 3-hydroperoxyisothiazole 1,1-dioxides

Hydroperoxy compounds are important for selective oxidation of organic precursors in the chemical industry. Moreover, novel 3-hydroperoxyisothiazole 1,1-dioxides (N-phthalimidyl sultams) have been shown to be potent and specific inhibitors of acetylcholinesterase (AChE) an important enzyme in the neurotransmitter process. The inhibitory potential of these novel compounds is clearly linked to the hydroperoxide moiety. Hydroperoxides are known for their chemi- and thermochemiluminescent reactivity. In this study we tested thermochemiluminescence (TCL) as a fast method to detect and characterize the hydroperoxide moiety in structurally different synthetic organic hydroperoxides.     

Generation of chemisorbed benzyl radicals on silica nanoparticles

Functionalized silica nanoparticles (NP) were obtained by esterification of the silanol groups of fumed silica nanoparticles with benzyl alcohol. These particles were characterized by Fourier transform infrared spectroscopy, ¹³C and ²⁹Si NMR spectroscopy, thermogravimetry, total organic carbon, Brunauer–Emmett–Teller analysis, UV-visible spectroscopy, and transmission electron microscopy. NP suspensions in water/acetonitrile mixtures were used as quenchers of benzophenone (BP) phosphorescence in time-resolved experiments at the excitation wavelength of 266 nm. The phosphorescence signals obtained in the presence of the nanoparticles were fitted to biexponential decays. Both decays were accelerated in the presence of increasing amounts of NP. A model, including the reversible adsorption of BP on the NP, which was supported by computer simulations accounts for the observed results. Laser flash-photolysis experiments with excitation at 266 nm of NP suspensions in water/acetonitrile in the presence of BP generated benzyl radicals that were attached to the silica surface. These radicals were detected at their absorption maxima (320 nm) by transient optical techniques.     

Derivatization of GSSG by pHMB in alkaline media. Determination of oxidized glutathione in blood

Chromatographic determination of glutathione disulfide (GSSG) without any preliminary reduction has been presented using GSSG derivatization by p-hydroxymercuribenzoate (pHMB) in strong alkaline medium followed by the determination of GS-pHMB complex by reversed phase chromatography coupled to chemical vapour generation and atomic fluorescence detector (RPC-CVGAFS). A detection limit of 35 nM for GSSG (corresponding to 1.8 pmol) detected as GS-pHMB species was achieved based on a signal-to-noise ratio of 3 in buffer and in blood. The proposed method was applied to the determination of GSSG in whole blood and validated by the classical determination of GSSG by derivatization after reduction with dithiothreitol (DTT).     

Stereoselective synthesis of 2-O-MEM-2,3-unsaturated-β-O-glycosides and elaboration to useful synthetic tools

The glycosylation of alcohols by the new 2-O-MEM-substituted d-galactal-derived allyl epoxide affords the corresponding alkyl 2-O-MEM-3-deoxy-β-d-threo-hex-2-enopyranosides through a completely 1,4-regio- and a highly to completely substrate-dependent stereoselective glycosylation processes. The glycosides obtained can be regioselectively transformed into corresponding 3-deoxy-β-O-glycosides, 3-deoxy-β-d-threo-hexopyranosid-2-uloses, and 3,4-dideoxy-β-d-glycero-hex-3-enopyranosid-2-uloses, which are useful synthetic tools for further transformations.     

Simultaneous determination of nine endogenous steroids in human urine by polymeric-mixed micelle capillary electrophoresis

A new CE system based on the use of polymeric-mixed micelles (cholic acid, SDS and the poloxamine Tetronic(?) 1107) was developed for the simultaneous determination of nine steroids in human urine. This method allows the baseline separation and quantitation of cortisol, androstenedione, estriol, dehydroepiandrosterone sulfate, testosterone, dehydroepiandrosterone, estrone, progesterone and estradiol in less than 25 min showing to be sensitive enough to detect low concentrations of these steroids in urine samples (5-45 ng/mL). The optimized electrophoretic conditions were performed using a 50 cm × 75 μm capillary, 18 kV, 25°C, with 44 mM cholic acid, 10 mM SDS, 0.05% w/v tetronic(?) 1107, 2.5% v/v methanol, 2.5% v/v tetrahydrofuran in 5 mM borate - 5 mM phosphate buffer (pH=8.0) as a background electrolyte and a dual 210/254 UV-detection. The method can simultaneously determine 0.1-120 μg/mL, which corresponds to 5-6000 ng/mL of steroids in 2 mL urine. The recoveries ranged between 82.4 and 101.5%. Due to its simplicity, speed, accuracy and reliability, the proposed method could be a potential alternative to the traditional methodologies used with clinical purposes.     

Unambiguous characterization and tissue localization of Pru P 3 peach allergen by electrospray mass spectrometry and MALDI imaging

The lipid transfer protein (LTP), Pru p 3, has been identified as the major allergen present in peach, and its sequence obtained by direct amino acid sequencing has been previously reported. However, several sequences, obtained from c‐DNA and available in databases, show differences among them and from the originally proposed structure. In this paper, we report the fast and unambiguous determination of the structure of Pru p 3 protein, extracted from three different varieties of peach, by electrospray ionization mass spectrometry (ESI‐MS), both coupled to single stage (quadrupole) or advanced (FT‐HRMS) analyzers. The structure was identical to one of the cDNA‐derived sequences and different in two positions from the previously reported structure obtained by amino acid sequencing. Moreover, the exclusive localization of the protein in the outer part of the fruits was assessed by Matrix‐Assisted Laser Desorption Ionization Mass Spectrometry Imaging (MALDI MSI). The results reported here demonstrate the full potential of mass spectrometry for rapidly obtaining high quality structural data of relevant food proteins. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis,Structure, and Complexation Properties of Partially and Completely Reduced meso‐Octamethylporphyrinogens (Calix[4]pyrroles)

New tricks for an old dog : Calixpyrroles bind anions efficiently and can be transformed into transition‐metal complexes only under forcing conditions. Reducing the macrocycle creates a ligand that easily forms classical Werner complexes with copper, nickel, and palladium ions. The metal complexes present an array of four directed hydrogen bonds, which specifically bind the counterions (see picture; blue N, white H, green Cl, red Cu, Ni, or Pd).

     

Helical‐Ribbon Formation by a β‐Amino Acid Modified Amyloid β‐Peptide Fragment

An addition to the family : The introduction of β‐amino acid residues into a modified amyloid β peptide fragment resulted in well‐defined helical nanoribbons (see cryo‐TEM image) comprising β strands mainly oriented perpendicular to the ribbon axis. The nanoribbons order into a flow‐aligning nematic phase at higher concentration. The β‐strand nanoribbon structure is an addition to the known set of secondary structures adopted by β‐peptides.

     

Small-scale vorticity filaments and structure functions of the developed turbulence

We develop a theory of turbulence based on the Navier-Stokes equation, without using dimensional or phenomenological considerations. A small scale vortex filament is the main element of the theory. The theory allows to obtain the scaling law and to calculate the scaling exponents of Lagrangian and Eulerian velocity structure functions in the inertial range. The obtained results are shown to be in very good agreement with numerical simulations and experimental data. The introduction of stochasticity into the equations and derivation of scaling exponents are discussed in details. A weak dependence on statistical propositions is demonstrated. The relation of the theory to the multifractal model is discussed.