Molecular organization in binary mixtures of derivatives of naphthalenebicarboxylic acid and naphthoylenebenzimidazole with a liquid crystal in two-dimensional layers

Langmuir films of some dichroic dyes, namely derivatives of naphthalenebicarboxylic acid and derivatives of naphthoylenebenzimidazole, as well as of their mixtures with the liquid crystals 4-octyl-4′-cyanobiphenyl (8CB) and 4-pentyl-4″-cyano-p-terphenyl (5CT) were prepared. Surface pressure/mean molecular area isotherms were recorded from which some information about the alignment of molecules in a monomolecular layer at an air–water interface could be deduced. It was found that the properties of the monolayer are highly sensitive to the molecular structure of the side groups substituted on the main skeleton of the dye molecule, and to the mixture composition. Moreover, information about the miscibility or the phase separation of the two components in Langmuir films formed from dye/liquid crystal mixtures was obtained by using the excess area criterion and surface pressure rules.     

Aliphatic and Aromatic Hydrocarbons in the Mediterranean Aerosol

Abstract

The atmospheric transport of organic pollutants over long distances and their effect on the biological cycles of the sea are two major questions of concern in environmental chemistry. These processes are of particular importance in the Mediterranean Sea because of its semi-enclosed characteristics, which determine the accumulation of the pollutants entering into the system.

In order to get some insight into these processes a project (PHYCEMED), was developed for the evaluation of the atmospheric budget of organic and inorganic substances in the Western Mediterranean and for the investigation of the exchange mechanisms of these materials across the air/sea interface.

A high volume air sampling system including a cascade impactor was placed on board of the R/V le Suroit for collecting the acrosols along several transects parallel to the French, Spanish and North-African coasts, facing areas of different population densities and industrial activities. The cruise was realised on October 1983 and the particulate material was fractionated into the following sizes: 7.2, 3.0, 1.5, 0.96, and 0.03 μm. Quantitative and qualitative analyses of the aliphatic and the aromatic hydrocarbons present in these fractions were performed by high resolution gas chromatography and gas chromatography-mass spectrometry.

Total non-aromatic hydrocarbon concentrations are in the range 30-57 ng/m³ (10-14ng/m³ for n-alkanes). The distribution of n-alkanes indicates that most of the aerosol mass is associated with small particles < 1 μm.Polycyclic aromatic hydrocarbons are identified from phenanthrene to benzo(ghi)perylene with fluoranthene and pyrene as dominant compounds. Concentrations for individual PAH vary in the range 4.1 pg/m³ for benzo(a)anthracene up to 100 pg/m³ for fluoranthene. The evaluation of different contributions such as land plant waxes or soil sources and various anthropogenic sources is discussed from n-alkanes and PAH distribution patterns.     

Vesicles in ionic liquids

The formation of vesicles from 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) in several room-temperature ionic liquids, namely, 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF(4)), 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimNTf(2)), and N-benzylpyridinium bis(trifluoromethylsulfonyl)imide (BnPyNTf(2)), as well as in a water/BmimBF(4) mixture, was investigated. In pure ionic liquids, observations by staining transmission electron microscopy demonstrated clearly the formation of spherical structures with diameters of 200-400 nm. The morphological characteristics of these vesicles in ionic liquids, in particular, the membrane thicknesses, were first investigated by small-angle neutron scattering measurements. The mean bilayer thickness was found to be ～63 ± 1 ? in a deuterated ionic liquid (BnPyNTf(2)-d). This value was similar to that observed in water. The effect of ILs on the modification of the phase physical properties of multilamellar vesicles (MLVs) was then investigated by differential scanning calorimetry. In pure IL as in water, DPPC exhibited an endothermic pretransition followed by the main transition. These transition temperatures and the associated enthalpies in ILs were higher than those in water because of a reduction of the electrostatic repulsion between zwitterionic head groups. To better understand the effect of ionic liquid on the formation of multilamellar vesicles, mixtures of BmimBF(4) and water, which are miscible in all proportions, were analyzed (BmimBF(4)/water ratio from 0% to 100%). SANS and DSC experiments demonstrated that the bilayer structure and stability were strongly modified by the IL content. Moreover, matching SANS experiments showed that BmimBF(4) molecules prefer to be located inside the DPPC membrane rather than in water.     

An electrochemical immunosensor based on covalent immobilization of okadaic acid onto screen printed carbon electrode via diazotization-coupling reaction

In this work, an electrochemical method based on the diazonium-coupling reaction mechanism for the immobilization of okadaic acid (OA) on screen printed carbon electrode was developed. At first, 4-carboxyphenyl film was grafted by electrochemical reduction of 4-carboxyphenyl diazonium salt, followed by terminal carboxylic group activation by N-hydroxysuccinimide (NHS), N-(3-dimethylaminopropyle)-N′-ethyle-carbodiimide hydrochloride (EDC). Hexamethyldiamine was then covalently bound by one of its terminal amine group to the activated carboxylic group. The carboxyl group of okadaic acid was activated by EDC/NHS and then conjugated to the second terminal amine group on other side of the hexamethyldiamine through amide bond formation. After immobilization of OA, an indirect competitive immunoassay format was employed to detect OA. The immunosensor obtained using this novel approach allowed detection limit of 1.44 ng/L of OA, and was also validated with certified reference mussel samples.     

C5-functionalized DNA, LNA, and α-L-LNA: positional control of polarity-sensitive fluorophores leads to improved SNP-typing

Single nucleotide polymorphisms (SNPs) are important markers in disease genetics and pharmacogenomic studies. Oligodeoxyribonucleotides (ONs) modified with 5-[3-(1-pyrenecarboxamido)propynyl]-2'-deoxyuridine monomer X enable detection of SNPs at non-stringent conditions due to differential fluorescence emission of matched versus mismatched nucleic acid duplexes. Herein, the thermal denaturation and optical spectroscopic characteristics of monomer X are compared to the corresponding locked nucleic acid (LNA) and α-L-LNA monomers Y and Z. ONs modified with monomers Y or Z result in a) larger increases in fluorescence intensity upon hybridization to complementary DNA, b) formation of more brightly fluorescent duplexes due to markedly larger fluorescence emission quantum yields (Φ(F)=0.44-0.80) and pyrene extinction coefficients, and c) improved optical discrimination of SNPs in DNA targets. Optical spectroscopy studies suggest that the nucleobase moieties of monomers X-Z adopt anti and syn conformations upon hybridization with matched and mismatched targets, respectively. The polarity-sensitive 1-pyrenecarboxamido fluorophore is, thereby, either positioned in the polar major groove or in the hydrophobic duplex core close to quenching nucleobases. Calculations suggest that the bicyclic skeletons of LNA and α-L-LNA monomers Y and Z influence the glycosidic torsional angle profile leading to altered positional control and photophysical properties of the C5-fluorophore.     

Monitoring the buckling threshold of drying colloidal droplets using water-ethanol mixtures

We visualize the drying of droplets of colloids suspended in a mixture of two miscible solvents, namely water and ethanol. After a period of isotropic shrinkage, droplets suddenly buckle like elastic shells. For a fixed colloid solid fraction, the buckling threshold evolves as a function of ethanol content, due to changes of the solvent mixture physical properties, such as viscosity and evaporation rate. A simplified model predicting the qualitative behavior of the buckling threshold as a function of the initial ethanol mass fraction has been developed that fits well experimental results.