Imidazolium-based ionic liquids binding to DNA: Mechanical effects and thermodynamics of the interactions.

We performed a robust characterization of the molecular interactions between the DNA molecule and two imidazolium-based ionic liquids (ILs): 1-Butyl-3-methylimidazolium chloride ([bmim]Cl) and 1-Octyl-3-methylimidazolium chloride ([omim]Cl), using single molecule approaches (optical and magnetic tweezers) and bulk techniques (isothermal titration calorimetry and conductivity measurements). Optical and magnetic tweezers allowed us to obtain the changes on the mechanical properties of the DNA complexes formed with both ILs, as well as the relevant physicochemical (binding) parameters of the interaction. Despite the weak binding measured between DNA and the two ILs, we identify a transition on the regime of polymer elasticity of the complexes formed, which results in a relevant DNA compaction for high IL concentrations. In addition, isothermal titration calorimetry and conductivity complemented the single molecule investigation, giving a complete thermodynamic characterization of the interactions and allowing the identification of the most relevant driving forces at various different concentration ranges of the ILs. Based on the results obtained with all the employed techniques, we propose a model for the binding schemes involving DNA and both [bmim]Cl and [omim]Cl.

Bessel beam optical tweezers for manipulating superparamagnetic beads.

We propose a Bessel beam optical tweezers setup that can stably trap superparamagnetic beads. The trap stiffness measured is practically independent of the radius of the Bessel beam and of the bead height (distance from the coverlip of the sample chamber), indicating that the beads can be trapped with high accuracy within a wide range of such parameters. On the other hand, the trap stiffness exhibits the expected linear increase with the laser power, despite the non-negligible absorption coefficient of the superparamagnetic beads. A geometrical optics model that considers spherical aberration and light absorption by the beads was used to predict the optical forces and trap stiffness, showing excellent agreement with the experimental data. We believe the results presented here advance the field of optical trapping manipulation of absorbing magnetic particles, and future applications will involve, for example, the design of new hybrid optomagnetic tweezers.

Dodecyltrimethylammonium bromide surfactant effects on DNA: Unraveling the competition between electrostatic and hydrophobic interactions.

We present a new study on the interaction of the DNA molecule with the surfactant dodecyltrimethylammonium bromide (DTAB), performed mainly with optical tweezers. Single-molecule force spectroscopy experiments performed in the low-force entropic regime allowed a robust characterization of the DNA-DTAB interaction, unveiling how the surfactant changes the mechanical properties of the biopolymer, the binding parameters, and the competition of the two mechanisms involved in the interaction: electrostatic attraction between the cationic surfactant heads and the negative phosphate backbone of the DNA and hydrophobic interactions between the tails of the bound DTAB molecules, which can result in DNA compaction in solution depending on the quantity of bound surfactant. Finally, force clamp experiments with magnetic tweezers and gel electrophoresis assays confirm that DTAB compacts DNA depending not only on the surfactant concentration but also on the conformation of the biopolymer in solution. The present study provides new insights on general aspects of the DNA-surfactant complexes formation, contributing to the fundamental knowledge of the physics of such interactions.

Silicon microparticles as handles for optical tweezers experiments.

We study the behavior of silicon microparticles in a 1064 nm Gaussian-beam optical tweezers, showing that this semiconductor can be used to perform different types of optical manipulation experiments. Depending on the focal position and the laser power used, the particles can present an oscillatory dynamics in the tweezers or can be stably 3D-trapped with a trap stiffness that allows the application of femtoNewton forces with accuracy. A new, to the best of our knowledge, interpretation based on the photoexcitation of electrons in the valence band is proposed to explain the oscillations, and the quantities associated with such dynamics (e.g., amplitude, period, etc.) were characterized as a function of relevant parameters to optical tweezers setups.

Estado nutricional en pacientes hospitalizados en el Hospital Regional de Talca / Nutritional status in hospitalized patients in the Talca Regional Hospital

La prevalencia de desnutrición intrahospitalaria varía entre 40 y 50 porciento según distintos estudios. sin embargo, datos internacionales muestran que la obesidad ha desplazado a la desnutrición. no existen datos nacionales actuales al respecto. metodologia: se evaluó el estado nutricional de 385 pacientes ingresados al hospital y se comparó la realidad entre los servicios de medicina y cirugía. resultados: se encontró desnutrición en 23 porciento de los pacientes; 13,7 porciento presentó desnutrición calórica y 16,5 porciento, proteica. la desnutrición fue mas frecuente en el servicio de medicina. no se encontró diferencia significativa al relacionar la prevalencia de desnutrición con el diagnóstico de ingreso. el 51,3 porciento de los pacientes eran obesos, siendo más obesas las mujeres y los pacientes en el servicio de cirugía. conclusiones: el estado nutricional de nuestros pacientes se relaciona al servicio de ingreso y al sexo del paciente. la desnutrición intrahospitalaria es muy frecuente, sin embargo, la obesidad es más prevalente, siguiendo el mismo patrón de distribución por sexo que en la población general. estos datos apoyan la necesidad de crear programas nacionales, incluyendo un enfoque intrahospitalario, dirigidos a la prevención y tratamiento de la obesidad, con el objetivo de prevenir las enfermedades crónicas relacionadas.

Insulinorresistencia en mujeres obesas afrovenezolanas / Insulin resistance in women obesas afrovenezuelan

Se ha demostrado que los factores genéticos se ven influenciados por la raza, donde las de origen africano presentan tendencia a poseer índice de masa corporal (IMC) elevado con perfil lipídico normal (HDL-c elevado y triglicéridos bajos). El objetivo de este estudio fue analizar el grado de insulino-resistencia utilizando para ello el modelo matemático Homeostasis Model Assessment (HOMA) en 2 pobalciones venezolanas de origen africano. La muestra estuvo conformada por 72 mujeres afrovenezolanas de las poblaciones de Santa María (SM) y San José (SJ), Venezuela, con edades comprendidas entre 36 y 48 años, a las cuales se les realizó historia médica y se les calculó IMC para dividirlas en grupos de mujeres obesas y mujeres no obesas; se determinó glicemia, perfil lipídico y HOMA-IR. Al comparar el grupo de mujeres obesas de las dos poblaciones con las no obesas, no se observó diferencia estadísticamente significativa en la Glicemia (obesas 85,1 ± 3,5 SM y 83 ± 2,9 SJ; no obesas 77,3 ± 2,2 SM y 190,1 ± 9,1 SJ; no obesas 184,4 ± 8.8 SM y 193,4 ± 7,4 mg/dl), Triacilglicéridos (obesas 109,8 ± 16,3 SM y 114,8 ± 21,9 SJ; no obesas 64,9 ± 7,6 SM y 77,5 ± 10,8 SJ mg/dl), LDL-c (obesas 126,6 ± 14,8 SM y 126,9 ± 8,6 Sj; no obesas 115,5 ± 133,6 ± 11,4 SJ mg/dl) y HDL-c séricos (obesas 46,3 ± 4,0 SM y 40,2 ± 3,4 SJ; no obesas 55,5 ± 2,8 SM y 44,1 ± 2,3 SJ mg/dl). Igualmente no hubo diferencia significativa entre el HOMA IR del grupo de mujeres obesas de ambas poblaciones (3,3 ± 0,2 SM y 3,2 ± 0,1 SJ) y el del grupo de no obesas (2,8 ± 0,1 SM y 3,1 ± 0,1 SJ). En conclusión, los grupos de mujeres obesas de las poblaciones de Santa María y San José presentaron HDL-c deprimidas y HOMA IR sobre los límites normales

Influence of acute hypophysectomy on the natriuresis of dogs submitted to expansion of the extracellular fluid volume.

Three days after creating an access to the turcica on the sphenoid bone, twelve anesthetized mongrel dogs, after control collections, were submitted to extracellular volume expansion with saline. Thereafter, maintained constant the rate of saline infusion, the dura-mater covering the pituitary gland was incised in all dogs, the hypohysis being removed in seven and remaining untouched in the other five dogs. Pharmacological doses of pitressin, glycocorticoids and mineralocorticoids were administered to all dogs. It was shown, for the same filtered sodium load(p is greater than 0.05), that hypophysectomy produces a significant reduction (p is less than 0.05) in urinary sodium excretion previously elevated by the extracellular volume expansion, while durostomy only, without removal of th hypophysis, did not change (p is greater than 0.05) the rate of sodium excretion. Thus, the pituitary gland could be considered as contributing to natriuresis during extracellular volume expansion, all other factors related to this expansion remaining constant in both, hypophysectomized and sham operated dogs.