Revista de Ciencias

Evaluation of the Electrogenic Potential of Coastal Sediments of La Azufrada Beach, Gorgona Island

Resumen El presente trabajo exploratorio, evaluó la respuesta electrogénica de sedimentos costeros colectados en la Playa La Azufrada en la Isla Gorgona; se comparó con la respuesta electrogénica de lodos y aguas provenientes del lago de la microestación del Departamento de Biología del Campus Universitario Meléndez de la Universidad del Valle. Los sustratos fueron evaluados en celdas de combustible microbianas (MFC por su nombre en inglés) mediante curvas de densidad de potencia. Los sustratos ambientales fueron utilizados como inoculo y único sustrato energético. Al finalizar los ensayos, se realizó microscopía electrónica a los ánodos de las MFC. Se reportaron valores de densidad de potencia máximas de 3.1 mW/m2 en el día 19 de operación para el caso de las MFC alimentadas con sedimentos de lago y de 0.67 mW/m2 en el día 15 para el caso de los sedimentos marinos. Las observaciones mediante microscopía electrónica muestran diferencias en la formación de la biopelícula de los dos ambientes. Los ánodos de las MFC alimentadas con sedimentos marinos mostraron una formación de biopelícula insipiente. Los ensayos demuestran que los sedimentos marinos colectados presentan actividad electrogénica, lo cual abre la posibilidad de realizar estudios sobre las poblaciones bacterianas electrogénicas y las aplicaciones que puedan tener las MFC en estos ambientes.

Abstract The present exploratory work evaluated the electrogenic response of shore sediments collected on La Azufrada Beach in Gorgona Island. It was compared with the electrogenic response of mud and water from the micro-station lake of the Department of Biology of the Melendez University of Valle Campus. The substrates were evaluated in Microbial fuel cells (MFC) through power density curves. The environmental substrates were used as inoculated and only energetic substrate. Scanning electron microscope was performed on the anodes of the MFC at the end of the trials. Values of maximum power density of 3.1 mW/m2 were reported on the 19th day of operation for the case of the MFC feed with lake sediments and a maximum power density of 0.67 mW/m2 was reported on the 15th day for the case of marine sediments. Electron microscopic observations showed differences in the formation of incipient bio-film. The results suggested that the collected marine sediments present electrogenic activity which opens the possibility to perform studies on the electrogenic bacterial populations and the applications the MFC could have in those environments.

The use of Entanglement Entropy to Classify Quantum Phase Transitions in 1d Ultracold Spinor Bosons

Abstract In this paper, we discuss a novel method based on a quantum-information-tool suitable to identify and characterize quantum-phases and phase transitions in a broad set of lattice models relevant in condensed-matter systems. The method relies on the entanglement entropy which, for instance, can be calculated using the Matrix Product State (MPS) algorithm, or any other method, for several system sizes to perform an appropriate scaling. Particularly, this advanced method has been applied for a finite 1D system of repulsively interacting spin-1 bosons and obtaining the universality class via the calculation of the central charge for the external field-induced phase transition between the dimerized phase and the XY-nematic phase in the antiferromagnetic regime. Finally, we briefly discuss how this method has been recently used to identify topological phases.

Diffusion and Deposition Rates in a Colloidal Model for Epitaxial Growth

Abstract We analyze the dynamical properties of a two-dimensional colloidal suspension model, whose particles are slowly deposited on a one-dimensional substrate due to the influence of an external field. Once the particles are deposited on the substrate they can laterally diffuse on it. Using an analytical model based on the Langevin and the Fokker- Plank equations, the dynamics of a particle in the suspension and on the substrate, are studied. In particular, we evaluate the average deposition rate on the substrate, ℱ, as well as the diffusion constant of the particles on the substrate D. The proposed analytical model gives results that agree well with those found using numerical simulations based on molecular dynamics. This simple model allows to explore the possibility to use colloids for the formation of structures through the epitaxial growth technique, which is relevant in several application fields.

Resumen Se estudian las propiedades dinámicas de un modelo de suspensión coloidal bidimensional cuyas partículas son depositadas lentamente sobre un sustrato unidimensional bajo la acción de un campo externo. Una vez que las partículas son depositadas en el sustrato pueden difundirse lateralmente sobre este último. Usando un modelo analítico basado en las ecuaciones de Langevin y de Fokker-Plank se estudia la dinámica de una partícula en la suspensión y sobre el sustrato. En particular, se calculan la tasa de deposición promedio sobre el sustrato, ℱ, así como también la constante de difusión de las partículas sobre el sustrato, D. Los resultados del modelo analítico propuesto presentan un buen acuerdo con los encontrados usando simulaciones numéricas basadas en dinámica molecular. Este modelo sencillo permite explorar la posibilidad de usar coloides para la formación de estructuras mediante la técnica de crecimiento epitaxial, la cual es relevante en distintos campos de aplicación.

𝑝-cycles, S ₂ -sets and Curves with Many Points

Abstract We construct S 2-sets contained in the integer interval I q-1 = [1,q - 1] with q = 𝑝 n , 𝑝 a prime number and n ∈ Z+, by using the 𝑝-adic expansion of integers. Such sets come from considering 𝑝-cycles of length n. We give some criteria in particular cases which allow us to glue them to obtain good S 2-sets. After that we construct algebraic curves over the finite field 𝔽 q with many rational points via minimal (𝔽𝑝, 𝔽𝑝)-polynomials whose exponent set is an S 2-set.

Standardization of a Method for Analysis of Cocaine in Urine Samples Using Solid-Phase Extraction (SPE) and High Performance Liquid Chromatography (HPLC)

Resumen Los altos costos que implica el consumo de cocaína pura, llevó a la producción de base de cocaína o bazuco (crack), un producto de menor valor económico, gran demanda y generalmente más usado por consumidores de bajo nivel socioeconómico. El bazuco es una sustancia blanca, o pardusca, semisólida o sólida, cuyo principio activo es la cocaína. La cocaína es un alcaloide con una larga historia de uso y abuso. Su determinación, tanto en muestras no biológicas como en fluidos biológicos continúa siendo una tarea de primer orden. En el presente trabajo se reporta la validación de un método de extracción de la cocaína en muestras de orina, usando la técnica de extracción en fase sólida (SPE). Porcentajes de recuperación entre el 99.4 y el 99.8 % fueron obtenidos para cocaína empleando SPE. La técnica cromatográfica fue estandarizada, empleando una columna C18, un detector ultravioleta (254 nm), una fase móvil de agua-acetonitrilo-ácido acético (58-40-2) a un flujo de 0.4 mL/min. El rango de linealidad estuvo entre 0.01 (g/mL y 1.0 (g/mL. Se crearon tres curvas de cuantificación: 10 - 20 ppb, 20 - 100 ppb y 100 - 1,000 ppb con coeficientes de determinación r2 de 0.9965, 0.9947 y 0.9973 respectivamente. El método fue aplicado en muestras de orina de un grupo de personas voluntarias que consumen bazuco en la ciudad de Popayán, Cauca, Colombia.

Abstract The high costs of the consumption of pure cocaine, led to the production of cocaine base or bazuco (crack), a product of lower economic value, high demand and generally more used by consumers of low socioeconomic level. Bazuco is a white or brownish, semisolid or solid substance, whose active principle ingredient is cocaine. Cocaine is an alkaloid with a long history of use and abuse. Determination of both, in non-biological samples as well as in biological fluids remains a top priority task. In this work, the validation of the extraction method of cocaine in urine samples is reported, using the technique of solid phase extraction (SPE). Recovery rates between 99.4 and 99.8 % were obtained using SPE to cocaine. The technique was standardized using chromatographic column C18, an ultraviolet detector (254 nm), a mobile phase of acetonitrile-acetic acid-water (58-40-2) at a flow of 0.4 mL/min. The linearity range was between 0.01 ug/mL and 1.0 ug/mL. Three quantification curves were created: 10 - 20 ppb, 20-100 ppb and 100-1000 ppb with determination coefficients r2 of 0.9965, 0.9947 and 0.9973 respectively. The method was applied to urine samples from a group of volunteers who consumed crack in the city of Popayán, Cauca, Colombia.

Preparation and Characterization of Chitosan Based Gels for Possible Biomedical Applications

Resumen Los geles poliméricos tienen un rango amplio de aplicaciones biomédicas incluyendo su uso para el crecimiento de tejidos, la liberación controlada de fármacos, la inmovilización de enzimas, entre muchas otras. Debido a la capacidad que tienen los geles para almacenar agua en su interior y a la conducción iónica que se puede generar a través de grupos funcionales ionizables, estos materiales pueden llegar a tener aplicaciones en el diagnóstico clínico y la electroterapia. En la presente investigación se prepararon geles conductores a base de quitosano, el cual es un polímero biodegradable y biocompatible, usando glutaraldehído como agente entrecruzante. Los geles de quitosano se caracterizaron por espectroscopia infrarroja con transformada de Fourier (FTIR) y se determinaron además sus valores de viscosidad (μ), conductividad eléctrica (κ) y pH. Estas propiedades variaron conforme se modificó el grado de entrecruzamiento. Una de las muestras con valores comparables con los geles de formulación comercial presentó una viscosidad absoluta de 365x103 cP, una conductividad iónica de 0.2140 Sm-1 y un pH de 3.5, valores prometedores para su aplicación en geles comerciales con aplicaciones biomédicas.

Abstract The polymeric gels have a wide range of biomedical applications including their use for tissue growth, controlled drug release, enzyme immobilization, among others. Due to the ability of the gels to store water inside and the ionic conductivity that could be generated through ionizable functional groups, these materials may have applications in clinical diagnosis and in electro-therapy. In the present research, conductive gels based on chitosan (a biodegradable and biocompatible polymer) were prepared using glutaraldehyde as crosslinking agent. Chitosan gels were characterized by infrared spectroscopy with Fourier transform (FTIR) and it was also determined the values for their viscosity (μ), electric conductivity (κ) and pH. These properties vary as the crosslinking degree changed. One of the samples with comparable values to those of the commercial gels presented an absolute viscosity of 365x103 cP, ionic conductivity of 0.2140 Sm-1 and pH of 3.5, which are promising values for their use in commercial gels with biomedical applications.

An Electrochemical Desalination Cell Based On Conducting Polymers

Abstract Insufficient access to potable water is becoming one of the major threats to sustainable development around the globe. The implementation of water conservation policies and the use of mature and novel desalination technologies are key to address the water demand for an increasing population. Desalination systems based on electrochemical cells are of current interest. This paper discusses an electrochemical cell based on carbon electrodes modified with polypyrrole and a polypyrrole/polystyrene sulfonate composite which have anion and cation exchange properties, respectively. The cell was used to substantially decrease the concentration of sodium chloride solution in the 10-1 and the 10-2 M concentration range. The long term stability of this cell is also discussed.

Electrochemical studies of grid and linear type M2+ (M=Zn, Cd and Pb) complexes of a bis-(hydrazone) bearing two symmetric carboxylic groups

Abstract Herein we present the preparation of a bis-(hydrazone) containing a pyridine-pyrimidine- pyridine framework. This compound can be visualized as a double arm system able of coordinating two metal ions in a terpyridine-like manner. By NMR (1D and 2D) it was determined a transoid conformation and an E configuration around the two imine double bonds. Complexation with M2+ (M = Zn, Cd, and Pb) ions resulted in grid and linear type structures which were studied by cyclic and squared wave voltammetry at different temperatures. No linear correlations of the redox potentials as a function of temperature were observed. The latter is likely due to rearrangements in the structure or to spin crossover events. The present results deserve further studies on the electronic properties of these types of compounds for the development of smart materials.

5-Deazaflavins: Chemical Synthesis

Resumen Las 5-Deazaflavinas, están involucradas en reacciones enzimáticas redox de una variedad de sistemas biológicosyguardan similitud estructuralconla riboflavina. Laspropiedadeselectroquímicas y fotoquímicas son resultado de la sustitución del N-5 del anillo de la isoaloxazina por un átomo de carbono. En esta revisión, se describen los avances en la obtención de 5-deazaflavinas y análogos a partir de ácido barbitúrico, análogos de uracilo, triamino-tricloropirimidinas y quinolincarbonitrilos. El grado y tipo de sustitución de las 5-deazaflavinas, se obtiene a través de los aldehídos y aminas utilizadas, vía reacciones clásicas, simples y convergentes. Comparando las diferentes estrategias sintéticas reportadas, para la construcción de 5-deazaflavinas y análogos, estas se clasifican en dos estrategias generales: i) la construcción del anillo de quinolina sobre el anillo pirimidínico o ii) la construcción del anillo pirimidínico sobre el anillo quinolínico.

Abstract 5-Deazaflavinas are involved in enzymatic redox reactions from a variety of biological systems and have structural similarity with riboflavin. Electrochemical and photochemical properties are the result of the substitution of N-5 of the isoalloxazine ring for a carbon. Herein, we described the progress in obtaining 5-deazaflavins analogues starting from barbituric acid, uracil analogues, three amino-threechloropirimidines and quinolincarbonitriles. Molecular diversity was obtained using both appropriately substituted aldehydes and amines, via conventional, simple and convergent reactions. When comparing the different synthetic reported strategies for the construction of the 5-desflavines and analogues, these are classified into two general strategies: i) construction of the quinoline ring over pyrimidine moiety or ii) construction of the pyrimidine ring over quinoline moiety.

Evolutionary Relationships of the Fish Prochilodus reticulatus and Prochilodus magdalenae (Characiformes: Prochilodontidae)

Resumen Se realizó un estudio filogenético entre las especies Prochilodus reticulatus (Valenciennes, 1850) y P. magdalenae (Steindachner, 1879) de gran valor socioeconómico en el país. Inicialmente, las especies fueron colectadas para la extracción del ADN y su posterior caracterización mediante RAPD-PCR para establecer sus relaciones filogenéticas empleando el coeficiente de Jaccard y el método UPGMA. El análisis filogenético de P. reticulatus y P. magdalenae mostró una estrecha relación genética, lo que sugiere que las diferencias encontradas entre ellas pueden considerarse no significativas.

Abstract A phylogenetic study was carried out between the species Prochilodus reticulatus (Valenciennes, 1850) and P. magdalenae (Steindachner, 1879) of great socioeconomic value in the country. Initially, the species were collected for DNA extraction and subsequent characterization by RAPD-PCR to establish their phylogenetic relationships using the Jaccard coefficient and the UPGMA method. The phylogenetic analysis of P. reticulatus and P. magdalenae showed a close genetic relationship, which suggests that the differences found between them may not be considered significant.