Analysis of etimicin sulfate by liquid chromatography with pulsed amperometric detection

A new method for determination of etimicin's (ETM) purity and content is developed by liquid chromatography (LC) and pulsed amperometric detection (PAD). A reversed-phase ion-pair LC method with pulsed amperometric detection on a gold electrode after post-added NaOH is described. The mobile phase consisted of an aqueous solution containing 0.033 mol L(-1) oxalic acid, 0.012 mol L(-1) heptafluorobutyric acid, and 210 mL L(-1) acetonitrile with pH 3.40 adjusting by dilute NaOH solution. The total analysis time was not more than 30 min. The effects of the different chromatographic parameters on the separation were also investigated. A number of commercial samples of etimicin sulfate were analyzed using this method.     

Determination of soluble toxic arsenic species in alga samples by microwave-assisted extraction and high performance liquid chromatography-hydride generation-inductively coupled plasma-atomic emission spectrometry

A microwave-based procedure for arsenic species extraction in alga samples (Sargassum fulvellum, Chlorella vulgaris, Hizikia fusiformis and Laminaria digitata) is described. Extraction time and temperature were tested in order to evaluate the extraction efficiency of the process. Arsenic compounds were extracted in 8 ml of deionised water at 90 degrees C for 5 min. The process was repeated three times. Soluble arsenic compounds extracted accounted for about 78-98% of total arsenic. The results were compared with those obtained in a previous work, where the extraction process was carried out by ultrasonic focussed probe for 30 s. Speciation studies were carried out by high performance liquid chromatography-hydride generation-inductively coupled plasma-atomic emission spectrometry (HPLC-HG-ICP-AES). The chromatographic method allowed us to separate As(III), As(V), monomethylarsonic acid and dimethylarsinic acid in less than 13 min. The chromatographic analysis of the samples allowed us to identify and quantify As(V) in Hizikia sample and Sargasso material, while the four arsenic species studied were found in Chlorella sample. In the case of Laminaria sample, none of these species was identified by HPLC-HG-ICP-AES. However, in the chromatographic analysis of this alga by HPLC-ICP-AES, an unknown arsenic species was detected.     

Study of the critical points in lobenzarit disodium hydrophilic matrices for controlled drug delivery

Percolation theory is a multidisciplinary theory that studies chaotic systems. It has been applied in the pharmaceutical field since 1987. The application of this theory to study the release and hydration rate of hydrophilic matrices allowed for first time to explain the changes in release and hydration kinetic of swellable matrices type controlled delivery systems. The objective of the present paper is to estimate the percolation threshold of HPMC K4M in matrices of lobenzarit disodium and to apply the obtained result to the design of hydrophilic matrices for the controlled delivery of this drug. The materials used to prepare the tablets were Lobenzarit disodium (LBD) and HPMC of viscosity grade K4M. The drug mean particle size was 42+/-0.61 mum and the polymer was sieved and 150-200 microm granulometric fraction was selected. The formulations studied were prepared with different excipient contents in the range of 10-80% w/w. Dissolution studies were carried out using the paddle method and the water uptake measurements were performed using a modified Enslin apparatus. In order to estimate the percolation threshold, the behaviour of the kinetic parameters with respect to the volumetric fraction of each component at time zero, was studied. According to percolation theory, the critical points observed in dissolution and water uptake studies are attributed to the existence of an excipient percolation threshold. This threshold was situated between (18.58 to 24.33% v/v of HPMC). Therefore, the LBD-HPMC K4M matrices with a relative HPMC particle size of should be formulated with an excipient content above 24.33% v/v of HPMC, to obtain a control of the drug release from these systems.     

UV Index on tilted surfaces

Solar ultraviolet erythemal irradiance (UVER) has been studied on inclined planes with different orientations in Valencia, Spain. To do this a platform was designed that could turn through 90 degrees on its own axis. The radiometers were inclined at an angle close to the latitude of Valencia (39.5 degrees N). Using two timers the platform could be turned through 90 degrees every 5 min. On clear or partially cloudy days, including those with different turbidity values, it was observed that the UVER showed a maximum at 1200 h GMT, very close to solar noon, in the north and south positions, while the maximum for east and west orientations was found at approximately one hour before and one hour after midday respectively. It was also observed how the irradiance for the south orientation was greater and for the north was less than for the horizontal plane, as well as the opposite performances of the east and west orientations, for four days close to the summer and winter solstices and each equinox. Some experimental results were also compared with the results from the SMARTS2.9 model for the same conditions. It was found that the model frequently overestimated the experimental data. With respect to the maximum calculated UV Index in the different planes this was always higher for the south orientation than for the north, while it was similar for east and west orientations throughout the year. Finally the accumulated erythemal dosage for the considered period was obtained as a function of phototype and orientation, confirming that the accumulated erythemal dosage decreased by around 37% in the north orientation compared to the horizontal value, while in the south position it was only 6% less and some 20% and 15% less in the east and west positions, respectively.     

Self-assembled monolayers of aromatic thiols stabilized by parallel-displaced pi-pi stacking interactions

Parallel-displaced pi-pi stacking interactions have been known to be the dominant force in stabilizing the double helical structure of DNA and the tertiary structure of proteins. However, little is known about their roles in self-assembled monolayers of other large pi molecules such as aromatic thiols. Here we report on a systematic study of the self-assembled monolayers of four kinds of anthracene-based thiols, 9-mercaptoanthracene (MA), (4-mercaptophenyl) (9-anthryl) acetylene (MPAA), (4-mercaptophenyl) (10-nitro-9-anthryl) acetylene (MPNAA), and (4-mercaptophenyl) (10-carboxyl-9-anthryl) acetylene (MPCAA) on Au(111), in which a spacer and different functional groups (NO2 and COOH) are intentionally designed to introduce and thus allow the investigation of various intermolecular interactions, in addition to pi-pi interactions in the base molecules. We find that all molecules form long-range-ordered monolayers and, more interestingly, that these assembled monolayers exhibit essentially the same fundamental packing structure. On the basis of high-resolution scanning tunneling microscopy observations, we propose the space-filling models for the observed superstructures and demonstrate that all superstructures can be understood in terms of the parallel-displaced pi-pi stacking interactions, despite the presence of competing dipole-dipole and H-bonding interactions associated with these specially designed functional groups.     

Thermal control over the electrophoresis of soft colloidal particles

We study the electrophoresis of surface-charged thermosensitive microgel particles based on poly-N-isopropylacrylamide (PNIPAM); these deswell with increasing temperature T. Our results show that the electrophoretic mobility mu is affected by the temperature-induced volume phase transition. It increases with increasing temperature, as a result of the charge density increase induced by particle deswelling. Temperature thus allows control of mu, in contrast to the more conventional charged hard spheres for which mu is T independent. Salt also affects the mu behavior and gives rise to rich phenomenology, sharing common characteristics with charged hard spheres and polyelectrolyte-coated colloids depending on whether the microgels are swollen or deswollen. We interpret the effects of salt concentration n by considering that particle charges are located in an external shell, as confirmed by titrations, and that it is this shell-salt-induced compression that affects the resulting mu behavior.     

Seeded growth of submicron Au colloids with quadrupole plasmon resonance modes

A modified seeded growth process has been used for the controlled synthesis of quasispherical, CTAB-stabilized gold nanoparticles from 12 up to 180 nm with narrow size distributions. The UV-visible spectra of the aqueous colloids show distinct bands corresponding to dipole and quadrupole plasmon modes, for diameters above 100 nm, in close agreement with predictions based on Mie theory. The assignment of the modes is demonstrated by calculation of near field enhancement maps based on the boundary element method. Apart from other applications, since absorption is drastically reduced above 600 nm, while scattering is largely increased, these particles open new possibilities for construction of highly efficient photonic structures.     

Synthesis of extended triphenylenes by palladium-catalyzed [2+2+2] cycloaddition of triphenylynes

The synthesis of ortho-(trimethylsilyl)triphenylenyl triflates 7 is described. Fluoride-induced decomposition of these triflates leads to the generation of didehydrotriphenylenes (triphenylynes) 6. These arynes undergo [4+2] cycloadditions with dienes to afford the corresponding Diels-Alder adducts or palladium-catalyzed formal [2+2+2] cycloadditions to afford extended triphenylenes.     

Quantification and confirmation of anionic, cationic and neutral pesticides and transformation products in water by on-line solid phase extraction-liquid chromatography-tandem mass spectrometry

Two on-line SPE-LC-ESI-MS/MS methods have been developed for the rapid determination and confirmation of 18 polar pesticides and nine transformation products (TPs) in water samples. Given the very different physico-chemical characteristics of the analytes, it was not feasible the simultaneous determination of all selected compounds in only one method. Thus, it was necessary to use heptafluorobutyric acid and formic acid in order to obtain good retention in the SPE cartridge for basic and acidic analytes, respectively. The developed analytical methodology based on the direct injection of 2 mL of water sample in the system allowed the quantification of all analytes at the 25 ng/L level (LOQ) with limits of detection normally lower than 5 ng/L. Satisfactory recoveries (70-110%) were obtained for most compounds in ground and surface water samples. Some exceptions were found mainly in surface water, due to the ion suppression produced by the higher amount of matrix interferents in these samples. The acquisition of two MS/MS transitions for each compound allowed the reliable confirmation of positive findings even at the LOQ level. The developed methodology was applied to real ground and surface water samples showing the interest of including TPs in monitoring methods, as several of them were found at concentrations higher than that of parent compounds.     

Novel nylon-supported organic-inorganic hybrid membrane with hierarchical pores as a potential immobilized metal affinity adsorbent

Chitosan-based porous organic-inorganic hybrid membranes supported by microfiltration nylon membranes were prepared, in which gamma-glycidoxypropyltrimethoxysilane (GPTMS) was used as an inorganic source as well as crosslinking reagent. Polyethylene glycol (PEG) with different molecular weight and content was used as imprinting molecule for morphology control. In situ crosslinking of chitosan and simultaneous polymerization of GPTMS in PEG template environment endowed the hybrid membrane with specific characteristics. Distinct hybrid effect between chitosan (CS) and GPTMS was revealed by shifting in X-ray diffraction (XRD) pattern, decomposition in simultaneous thermogravimetry and differential scanning calorimetry (TG/DSC) testing. As manifested by scanning electron microscopy (SEM), the molecular weight and content of PEG had remarkable effect on the resulting surface morphology of the hybrid membrane and a given surface morphology could be obtained by extracting of the imprinted PEG molecular. Among three types of porogen used: PEG 400, PEG 4000 and PEG 20000, only PEG 20000 could result in a porous surface. Moreover, a special porous surface with three-dimensional (3D) hierarchical structure-in-structure pore fashion was obtained when content of PEG 20000 was controlled at 15%. Experimental results also showed that the hybrid membrane had low swelling ratio and high stability in acidic solution. After conveniently coordinated with copper ions, the porous metal chelating hybrid membrane could effectively adsorb the model protein, bovine serum albumin (BSA). As expected, the hybrid membrane imprinted with 15% PEG 20000 had remarkably high copper ion binding and BSA adsorption capacity, which might result from the large surface area, high ligand density and suitable interconnected 3D hierarchical porous surface.