Application of Fluorescence to the Study of Crude Petroleum

Crude petroleum oils are complex mixtures of different compounds (mainly organic), which are obtained from an extensive range of different geological sources. The fluorescence of crude petroleum oils derives largely from the aromatic hydrocarbon fraction, and this fluorescence emission is strongly influenced by the chemical composition (e.g., fluorophore and quencher concentrations) and physical characteristics (e.g., viscosity and optical density) of the oil. The fluorescence spectroscopy (FS) is increasingly used in petroleum technology due the availability of better optical detection techniques, because FS offers high sensitivity, good diagnostic potential, and relatively simple instrumentation. In this work we analyzed crude petroleum at different dilution in Nujol, a transparent mineral oil. The main objective of this work was to verify the possibility to measure crude oil emission spectroscopic without use of volatile solvents. The mixtures of nujol with different -crude oil concentrations were measured with a 10 mm optical path cuvette thus simplifying the fluorescence spectroscopy signal detection. The emission spectra were obtained by exciting the samples with a 400 W Xenon lamp at 350 nm, 450 nm and 532 nm. The emissions of the samples were collected perpendicularly with the excitation axis.     

Simple circuit to improve electric field homogeneity in contour-clamped homogeneous electric field chambers.

We redesigned contour-clamped homogeneous electric field (CHEF) circuitry to eliminate crossover distortion, to set identical potentials at electrodes of each equipotential pair and to drive pairs with transistors in emitter follower stages. An equipotential pair comprised the two electrodes set at the same potential to provide electric field homogeneity inside of the hexagonal array. The new circuitry consisted of two identical circuits, each having a resistor ladder, diodes and transistors. Both circuits were interconnected by diodes that controlled the current flow to electrodes when the array was energized in the 'A' or 'B' direction of the electric field. The total number of transistors was two-thirds of the total number of electrodes. Average voltage deviation from potentials expected at electrodes to achieve a homogeneous electric field was 0.06 V, whereas 0.44 V was obtained with another circuit that used transistors in push-pull stages. The new voltage clamp unit is cheap, generated homogeneous electric field, and gave reproducible and undistorted DNA band patterns.     

Antibacterial and antioxidant properties of mixed linkage beta-oligosaccharides from extracted β-glucan hydrolysed by Penicillium occitanis EGL lichenase

The aim of this study was first to ascertain the chemical composition and the physicochemical properties of cereal extracted β-glucan from barley flour. Secondly, to assess the antioxidant properties and the antibacterial properties of extracted β-glucan hydrolysates. The proximate composition, FT-IR and scanning electron microscopy of extracted β-Glucan were studied. Hydrolysates from extracted β-glucan, obtained by lichenase EG_L from Penicillium occitanis, were a mixed linkage beta-oligosaccharides (MLBO) of trisaccharides and tetrasaccharides. MLBO showed a DPPH radical scavenger with IC50 about 1.8 ± 0.01 mg/mL whereas the IC50 of extracted β-glucan was about 5 ± 0.01 mg/mL. MLBO showed a high antioxidative capacity (175 μmol/mL α-tocopherol equivalents) at 5 mg/mL. The antimicrobial activity was confirmed against all tested bacteria especially at 20 mg/mL of MLBO while no inhibition was observed for all the strains used after the addition of either EG_L or extracted β-glucan.     

Electrochromatography in microchips packed with conventional reversed-phase silica particles

This paper shows the applicability of a disposable and inexpensive microfluidic chip for electrochromatographic separations. The chip, recently developed by us for chip-based LC, was fabricated from PDMS incorporating conventional chromatographic RP silica particles (C18) without the use of frits. Three cephalosporin antibiotics were used to demonstrate the applicability of the chip-based chromatographic packing for electrochromatographic determinations. The used sample injection method utilizes hydrodynamic pressure, thereby, reducing the propensity for sample bias during the injection.     

Building‐Block Approach for the Straightforward Incorporation of a New FRET (Fluorescence‐Resonance‐Energy Transfer) System into Synthetic DNA

The synthesis of the two new phosphoramidites 5 and 8 bearing a carbostyril (=quinolin‐2(1H)‐one) chromophore used as donor entity in our recently developed new FRET (fluorescence‐resonance‐energy transfer) system is described (Schemes 1 and 2) The high stability of the chromophore to basic conditions enables the incorporation of the phosphoramidites directly into DNA during solid‐phase synthesis (Schemes 3 and 4). Since this is also possible for the (bathophenanthroline)ruthenium(II) complex used as acceptor (Scheme 4, Steps d and e), the whole labelling procedure to insert the FRET system into synthetic DNA is straightforward and represents a major improvement to our previous strategy.     

Study of Blood Porphyrin Spectral Profile for Diagnosis of Tumor Progression

Renal cell carcinoma (RCC) accounts for approximately 3% of new cancer incidence and mortality in the United States. Unfortunately many RCC masses remain asymptomatic and nonpalpable until they are advanced. Diagnosis and localization of early carcinoma play an important role in the prevention and curative treatment of RCC. The autofluorescence of blood porphyrin of healthy and tumor induced in male SCID mice was analyzed using fluorescence and excitation spectroscopy. A significant contrast between normal and tumor blood could be established. Blood porphyrin fluorophore showed enhanced fluorescence band (around 630 nm) in function of the tumor growth. This indicates that either the autofluorescence intensity of the blood fluorescence may provide a good parameter for the “first approximation” characterization of the tumor stage.     

Bournonite PbCuSbS3: Stereochemically Active Lone‐Pair Electrons that Induce Low Thermal Conductivity

An understanding of the structural features and bonding of a particular material, and the properties these features impart on its physical characteristics, is essential in the search for new systems that are of technological interest. For several relevant applications, the design or discovery of low thermal conductivity materials is of great importance. We report on the synthesis, crystal structure, thermal conductivity, and electronic‐structure calculations of one such material, PbCuSbS₃. Our analysis is presented in terms of a comparative study with Sb₂S₃, from which PbCuSbS₃ can be derived through cation substitution. The measured low thermal conductivity of PbCuSbS₃ is explained by the distortive environment of the Pb and Sb atoms from the stereochemically active lone‐pair s² electrons and their pronounced repulsive interaction. Our investigation suggests a general approach for the design of materials for phase‐change‐memory, thermal‐barrier, thermal‐rectification and thermoelectric applications, as well as other functions for which low thermal conductivity is purposefully sought.     

The amide bond rotation controlled by an unusual C-H···O hydrogen bonding that favors the 1,4-phenyl radical migration

Experimental evidence in support of the presence of a weak C-H···O hydrogen bonding that favors 1,4-phenyl radical migration in a chiral amide is provided.     

Versatile low-molecular-weight hydrogelators: achieving multiresponsiveness through a modular design

Multiresponsive low-molecular-weight hydrogelators (LMWHs) are ideal candidates for the development of smart, soft, nanotechnology materials. The synthesis is however very challenging. On the one hand, de novo design is hampered by our limited ability to predict the assembly of small molecules in water. On the other hand, modification of pre-existing LMWHs is limited by the number of different stimuli-sensitive chemical moieties that can be introduced into a small molecule without seriously disrupting the ability to gelate water. Herein we report the synthesis and characterization of multistimuli LMWHs, based on a modular design, composed of a hydrophobic, disulfide, aromatic moiety, a maleimide linker, and a hydrophilic section based on an amino acid, here N-acetyl-L-cysteine (NAC). As most LMWHs, these gelators experience reversible gel-to-sol transition following temperature changes. Additionally, the NAC moiety allows reversible control of the assembly of the gel by pH changes. The reduction of the aromatic disulfide triggers a gel-to-sol transition that, depending on the design of the particular LMWH, can be reverted by reoxidation of the resulting thiol. Finally, the hydrolysis of the cyclic imide moieties provides an additional trigger for the gel-to-sol transition with a timescale that is appropriate for use in drug-delivery applications. The efficient response to the multiple external stimuli, coupled to the modular design makes these LMWHs an excellent starting point for the development of smart nanomaterials with applications that include controlled drug release. These hydrogelators, which were discovered by serendipity rather than design, suggest nonetheless a general strategy for the introduction of multiple stimuli-sensitive chemical moieties, to offset the introduction of hydrophilic moieties with additional hydrophobic ones, in order to minimize the upsetting of the critical hydrophobic-hydrophilic balance of the LMWH.