Simple and fast methods based on solid-phase extraction coupled to liquid chromatography with UV detection for the monitoring of caffeine in natural and waste waters as marker of anthropogenic impact

Two concentration methods for fast and routine determination of caffeine (using HPLC-UV detection) in surface, and wastewater are evaluated. Both methods are based on solid-phase extraction (SPE) concentration with octadecyl silica sorbents. A common “offline” SPE procedure shows that quantitative recovery of caffeine is obtained with 2 mL of an elution mixture solvent methanol-water containing at least 60% methanol. The method detection limit is 0.1 μg L−1 when percolating 1 L samples through the cartridge. The development of an “online” SPE method based on a mini-SPE column, containing 100 mg of the same sorbent, directly connected to the HPLC system allows the method detection limit to be decreased to 10 ng L−1 with a sample volume of 100 mL. The “offline” SPE method is applied to the analysis of caffeine in wastewater samples, whereas the “on-line” method is used for analysis in natural waters from streams receiving significant water intakes from local wastewater treatment plants

Membrane interaction of polymyxin B and synthetic analogues studied in biomimetic systems: implications for antibacterial action

Membrane-active antimicrobial peptides, such as polymyxin B (PxB), are currently in the spotlight as potential candidates toovercome bacterial resistance. We have designed synthetic analogs ofPxB in order to determine the structural requirements for membraneaction. Since the mechanism of action of PxB involves interaction withboth the outer membrane and the cytoplasmic membrane of Gramnegative bacteria, we have used an approach based on mimicking theouter layers of these membranes using monolayers, Langmuir-Blodgettfilms and unilamelar vesicles, and applying a battery of biophysicalmethods in order to dissect the different events of membraneinteraction. Collectively, results indicate that the PxB analogues act inthe bacterial membrane by the same mechanism than PxB, and that cationic amphipathicity determines peptide activity.

Membrane interaction of polymyxin B and synthetic analogues studied in biomimetic systems: implications for antibacterial action

Membrane-active antimicrobial peptides, such as polymyxin B (PxB), are currently in the spotlight as potential candidates toovercome bacterial resistance. We have designed synthetic analogs ofPxB in order to determine the structural requirements for membraneaction. Since the mechanism of action of PxB involves interaction withboth the outer membrane and the cytoplasmic membrane of Gramnegative bacteria, we have used an approach based on mimicking theouter layers of these membranes using monolayers, Langmuir-Blodgettfilms and unilamelar vesicles, and applying a battery of biophysicalmethods in order to dissect the different events of membraneinteraction. Collectively, results indicate that the PxB analogues act inthe bacterial membrane by the same mechanism than PxB, and that cationic amphipathicity determines peptide activity.

Headspace needle-trap analysis of priority volatile organic compounds from aqueous samples: application to the analysis of natural and waste waters

Combining headspace (HS) sampling with a needle-trap device (NTD) to determine priority volatile organic compounds (VOCs) in water samples results in improved sensitivity and efficiency when compared to conventional static HS sampling. A 22 gauge stainless steel, 51-mm needle packed with Tenax TA and Carboxen 1000 particles is used as the NTD. Three different HS-NTD sampling methodologies are evaluated and all give limits of detection for the target VOCs in the ng L−1 range. Active (purge-and-trap) HS-NTD sampling is found to give the best sensitivity but requires exhaustive control of the sampling conditions. The use of the NTD to collect the headspace gas sample results in a combined adsorption/desorption mechanism. The testing of different temperatures for the HS thermostating reveals a greater desorption effect when the sample is allowed to diffuse, whether passively or actively, through the sorbent particles. The limits of detection obtained in the simplest sampling methodology, static HS-NTD (5 mL aqueous sample in 20 mL HS vials, thermostating at 50 °C for 30 min with agitation), are sufficiently low as to permit its application to the analysis of 18 priority VOCs in natural and waste waters. In all cases compounds were detected below regulated levels

Structure, bioactivity and synthesis of natural products with hexahydropyrrolo[2,3-b]indole

Research on natural products containing hexahydropyrrolo[2,3-b]indole (HPI) has dramatically increased during the past few years. Newly discovered natural products with complex structures and important biological activities have recently been isolated and synthesized. This review summarizes the structures, biological activities, and synthetic routes for natural compounds containing HPI, emphasizing the different strategies for assembling this motif. It covers a broad gamut of molecules, from small alkaloids to complex peptides.

Structure, bioactivity and synthesis of natural products with hexahydropyrrolo[2,3-b]indole

Research on natural products containing hexahydropyrrolo[2,3-b]indole (HPI) has dramatically increased during the past few years. Newly discovered natural products with complex structures and important biological activities have recently been isolated and synthesized. This review summarizes the structures, biological activities, and synthetic routes for natural compounds containing HPI, emphasizing the different strategies for assembling this motif. It covers a broad gamut of molecules, from small alkaloids to complex peptides.

Experimental investigation of transient natural convection cooling of high prandtl number fluid with variable viscosity

Report for the scientific sojourn at the James Cook University, Australia, between June to December 2007. Free convection in enclosed spaces is found widely in natural and industrial systems. It is a topic of primary interest because in many systems it provides the largest resistance to the heat transfer in comparison with other heat transfer modes. In such systems the convection is driven by a density gradient within the fluid, which, usually, is produced by a temperature difference between the fluid and surrounding walls. In the oil industry, the oil, which has High Prandtl, usually is stored and transported in large tanks at temperatures high enough to keep its viscosity and, thus the pumping requirements, to a reasonable level. A temperature difference between the fluid and the walls of the container may give rise to the unsteady buoyancy force and hence the unsteady natural convection. In the initial period of cooling the natural convection regime dominates over the conduction contribution. As the oil cools down it typically becomes more viscous and this increase of viscosity inhibits the convection. At this point the oil viscosity becomes very large and unloading of the tank becomes very difficult. For this reason it is of primary interest to be able to predict the cooling rate of the oil. The general objective of this work is to develop and validate a simulation tool able to predict the cooling rates of high Prandtl fluid considering the variable viscosity effects.

Manifestació dels canvis en la interacció entre el medi natural i la societat: la influència del despoblament a Alins i Farrera

L’objectiu principal d’aquest projecte és analitzar les manifestacions dels canvis produïts en els medis natural i social influenciats pel despoblament (a la segona meitat del s.XX), als municipis d’Alins i Farrera, situats al Pallars Sobirà, i fer-ne una comparació, ja que es tracta de municipis de característiques diferents. Per dur a terme l’estudi, es fa un anàlisi de l’evolució del poblament, un anàlisi dels canvis físics, mitjançant l’avaluació dels canvis en les cobertes del sòl i de la transformació del paisatge amb les fotografies, i un anàlisi dels canvis en les activitats i comportaments socials mitjançant la realització d’entrevistes per elaborar un retrat social de cada època, distingint entre les aportacions de la població autòctona respecte de la nouvinguda. Amb tot, es pretén la realització d’una diagnosi transversal que permeti integrar les diferents temàtiques, i definir unes conclusions generals per mitjà d’uns patrons detectats. Finalment, la conclusió que millor permet recollir tota la informació és la que en resulta d’acceptar el fenomen de despoblament generalitzat, combinat amb el d’un canvi de l’estil de vida global, no només local, que és eina de justificació de moltes de les dinàmiques de canvi observades.

Thermodynamics and log–contrast analysis in fluid geochemistry

There are two principal chemical concepts that are important for studying the naturalenvironment. The first one is thermodynamics, which describes whether a system is atequilibrium or can spontaneously change by chemical reactions. The second main conceptis how fast chemical reactions (kinetics or rate of chemical change) take place wheneverthey start. In this work we examine a natural system in which both thermodynamics andkinetic factors are important in determining the abundance of NH+4 , NO−2 and NO−3 insuperficial waters. Samples were collected in the Arno Basin (Tuscany, Italy), a system inwhich natural and antrophic effects both contribute to highly modify the chemical compositionof water. Thermodynamical modelling based on the reduction-oxidation reactionsinvolving the passage NH+4 -& NO−2 -& NO−3 in equilibrium conditions has allowed todetermine the Eh redox potential values able to characterise the state of each sample and,consequently, of the fluid environment from which it was drawn. Just as pH expressesthe concentration of H+ in solution, redox potential is used to express the tendency of anenvironment to receive or supply electrons. In this context, oxic environments, as thoseof river systems, are said to have a high redox potential because O2 is available as anelectron acceptor.Principles of thermodynamics and chemical kinetics allow to obtain a model that oftendoes not completely describe the reality of natural systems. Chemical reactions may indeedfail to achieve equilibrium because the products escape from the site of the rectionor because reactions involving the trasformation are very slow, so that non-equilibriumconditions exist for long periods. Moreover, reaction rates can be sensitive to poorly understoodcatalytic effects or to surface effects, while variables as concentration (a largenumber of chemical species can coexist and interact concurrently), temperature and pressurecan have large gradients in natural systems. By taking into account this, data of 91water samples have been modelled by using statistical methodologies for compositionaldata. The application of log–contrast analysis has allowed to obtain statistical parametersto be correlated with the calculated Eh values. In this way, natural conditions in whichchemical equilibrium is hypothesised, as well as underlying fast reactions, are comparedwith those described by a stochastic approach