Efecto de la Longitud de onda de la radiación UV sobre la seda de araña

En el presente trabajo se continúa el análisis de la influencia de la radiación UV sobre las propiedades mecánicas de las fibras de seda de araña. Para ello se ha empleado la seda producida por la glándula ampollácea mayor de la especie Argiope trifasciata y se ha estudiado el comportamiento en tracción simple de fibras de seda sometidas a diferentes tiempos de irradiación con luz UV de longitudes de onda de 254, 312 y 365 nm. Se ha encontrado que la radiación ultravioleta disminuye la tensión de rotura y la deformación de rotura modificando, en algunos casos, el aspecto general de las curvas tensión-deformación. Además se ha hecho uso de la radiación UV de longitud de onda de 254 nm para introducir daño en las fibras con objeto de realizar un análisis fractográfico sistemático. El estudio se complementa con la evaluación del efecto producido por la irradiación en el fenómeno de supercontracción

The variability and interdependence of spider viscid line tensile properties

True stress-true strain curves of naturally spun viscid line fibers retrieved directly from the spiral of orb-webs built by Argiope trifasciata spiders were measured using a novel methodology. This new procedure combines a method for removing the aqueous coating of the fibers and a technique that allows the accurate measurement of their cross sectional area. Comparison of the tensile behaviour of different samples indicates that naturally spun viscid lines show a large variability, comparable to that of other silks, such as major ampullate gland silk and silkworm silk. Nevertheless, application of a statistical analysis allowed identifying two independent parameters that underlie the variability and characterize the observed range of true stress-true strain curves. Combination of this result with previous mechanical and microstructural data suggested the assignment of these two independent effects to the degree of alignment of the protein chains and to the local relative humidity which, in turn, depends on the composition of the viscous coating and on the external environmental conditions

Influencia de la radiación UV en las propiedades mecánicas y en el comportamiento en fractura de un polimero artificial bioinspirado en la seda de araña

En el presente trabajo se estudia la influencia de la radiación UV sobre las propiedades mecánicas y las superficies de fractura de un polímero artificial bioinspirado en la seda de araña. Las fibras de seda de araña constituyen un material enormemente atractivo ya que su elevada resistencia y deformabilidad lo convierten en el material con mayor trabajo hasta rotura de los conocidos hasta el momento. Además se ha encontrado que posee una elevada biocompatibilidad y un comportamiento biodegradable. Debido a estas excelentes propiedades se han dedicado importantes esfuerzos a intentar producir fibras inspiradas en la seda de araña. Fruto de estos esfuerzos es el polímero artificial estudiado en este trabajo. Dicho polímero presenta una secuencia de aminoácidos inspirada en la spidroína 1, que es una de las dos proteínas que conforman la seda de araña natural. Uno de los factores más perjudiciales para los polímeros es la radiación ultravioleta (UV), de presencia ubicua en aplicaciones al aire libre, ya que puede provocar la modificación de sus enlaces covalentes y, como consecuencia, modificar sus propiedades mecánicas. Para evaluar el efecto de la radiación UV sobre el material bioinspirado se ha estudiado el comportamiento a tracción simple de fibras sometidas a diferentes tiempos de irradiación con luz UV de longitud de onda de 254 nm. Se ha observado que la radiación UV de 254 nm modifica considerablemente las propiedades mecánicas de este material a tiempos de exposición elevados (a partir de 3 días de irradiación). Además se ha estudiado el comportamiento a fractura de este material cuando es irradiado con luz UV. Se ha observado que a medida que aumenta el tiempo de irradiación las superficies de fractura comienzan a ser cada vez más planas, obteniéndose un aspecto extremadamente especular para muestras irradiadas durante 16 día

Ultrasound measurement of the effects of high, medium and low hip long-axis distraction mobilization forces on the joint space width and its correlation with the joint strain

Background: No study has evaluated the mechanical effect of different magnitudes of long axis-distraction mobilization (LADM) force on hip joint space width (JSW) or the association between the separation of joint surfaces and the strain on hip capsular ligaments. Objective: To compare the joint separation when applying three different magnitudes of LADM forces (low, medium and high) and to analyse the correlation between joint separation, strain on the inferior ilio-femoral ligament and magnitude of applied force. Design: Repeated measures controlled laboratory cadaveric study. Methods: Three magnitudes of force were applied to 11 cadaveric hip joints (mean age 73 years). Ultrasound images were used to measure joint separation, and strain gauges recorded inferior ilio-femoral ligament strain during each condition. Results: The magnitude of joint separation was significantly different between low (0.23 ± 0.19 mm), medium (0.72 ± 0.22 mm) and high (2.62 ± 0.43 mm) forces (p 0.723; p < 0.001). Conclusion: Hip joint separation and ligament strain during LADM are associated with the magnitude of the applied force

Exploring the oil prices and exchange rates nexus in some African economies

This paper investigates the relationship between oil prices and exchange rates in three African countries using a Vector AutoRegressive (VAR) model. We use daily dataset on nominal exchange rates, oil prices and short term interbank interest rates from 01/12/2003 to 02/07/2014. The results suggest that the exchange rate of three selected countries displayed differing in the event of an oil price shock, not only before and after the oil peak of July of 2008, but also between each other, implying that no general rule can be made for net oil importing sub-Saharan countries, such as Botswana, Kenya and Tanzania. From our analysis we conclude that after an oil price peak, the Botswanan pula clearly appreciates against the US dollar, the Kenyan and Tanzanian shilling

Comparación de la Resistencia mecánica y disipación de energía de la seda de seguridad y de la seda víscida de araña

Las fibras de seda son materiales biológicos estructurales que presentan excelentes propiedades mecánicas. Las fibras de seda del hilo de seguridad producido por las arañas presentan unas propiedades mecánicas sólo superadas –en algunas propiedades– por las fibras sintéticas de altas prestaciones. Estas excelentes propiedades, y el hecho de que la biotecnología permite en la actualidad producir fibras bioinspiradas, fundamentan el interés de estudiar las propiedades de diferentes sedas, relacionando la composición y el comportamiento mecánico. El presente artículo aborda el estudio de las propiedades de los hilos de seda víscida, comparándolos con los hilos de seguridad. Al mismo tiempo se ha estudiado la relación entre las propiedades de los hilos de seda víscida y su situación en las telarañas, con el fin de analizar estas construcciones desde el punto de vista estructural. Los resultados muestran una enorme variabilidad de propiedades dentro de la telaraña, sin correlación con la situación. Además se ha encontrado una sorprendente similitud entre las propiedades mecánicas de ambos hilos

Stereoselective synthesis and reactivity of cis- and trans- dimolybdenum nitrosyl derivatives with the bridging bis(dimethylsilanediyl)di(η5-cyclopentadienyl) ligand. X-ray molecular structures of cis-[{Mo(CO)2(NO)}2(μ-(η5-C5H3)2(SiMe2)2}], trans-[(Mo(CO)(NO)(CNtBu)}2(μ-(η5-C5H3)2(SiMe2)2}], cis-[{Mo2(CO)3(NO)2(PMe3)}{μ-(η5-C 5H3)2(SiMe2)2}] and trans-[{Mo(NO)(CNtBu)2}2(μ-(η5-C5H3)2(SiMe2)2}]

New dimolybdenum nitrosyl [Mo(CO)2(NO)2μ-(η5-C5H3)2(SiMe2)2] cis-3 and trans-3 complexes have been isolated from the reaction of the previously reported cis-[Mo(CO)3H2μ-(η5-C5H3)2(SiMe2)2] cis-1 and trans-K2[Mo(CO)32μ-(η5-C5H3)2(SiMe2)2] trans-2 respectively, with p-CH3C6H4SO2N(NO)(CH3) (diazald). The reaction of [Mo(CO)2(NO)2μ-(η5-C5H3)2(SiMe2)2] cis-3 and trans-3 with Lewis bases L (L = tert-butylisocyanide and trimethylphosphine) under appropriate conditions gave monosubstituted [Mo2(CO)3(NO)2Lμ-(η5-C5H3)2(SiMe2)2] complexes (L = CNtBu cis-4; PMe3cis-5 and trans-5), disubstituted [Mo(CO)(NO)L2μ-(η5-C5H3)2(SiMe2)2] (L = CNtBu, cis-6, trans-6; PMe3cis-7 and trans-7) and tetrasubstituted [Mo(NO)L22μ-(η5-C5H3)2(SiMe2)2] complexes (L = CNtBu, cis-8 and trans-8), which were isolated in moderate yields and fully characterized by conventional analytical and spectroscopic methods. Addition of PCl5 under appropriate conditions to a diethyl ether solution of cis-3 or trans-3 afforded the dichloronitrosyl derivatives cis- and trans-[MoCl2(NO)2μ-(η5-C5H3)2(SiMe2)2] cis-9 and trans-9. The 13C and variable temperature 1H NMR spectra of complex cis-9 are consistent with the formation of 18 electron metal centres bridged by two chlorine atoms, providing two cis- and trans-nitrosyl isomers, which interchange rapidly in solution at room temperature through a postulated 16 electron intermediate. Treatment of cis-8 and trans-8 with stoichiometric amounts of PCl5 gave the tetrahalo derivatives [Mo(NO)(CNtBu)Cl22μ-(η5-C5H3)2(SiMe2)2] cis-10 and trans-10 respectively, whereas the oxidation of trans-6 with PCl5 under similar conditions gave a mixture of trans-10 and trans-[Mo2(CO)(NO)2(CNtBu)Cl4μ-(η5-C5H3)2(SiMe2)2] (trans-11). In addition, single crystal X-ray crystallographic analyses were performed for cis-3, cis-5, trans-6 and trans-8. All the complexes show two metal fragments bridged by the μ-(η5-C5H3)2(SiMe2)2 ligand, with different dispositions of the metal fragments. Stereoselective synthesis and reactivity of cis- and trans- dimolybdenum nitrosyl derivatives with the bridging bis(dimethylsilanediyl)di(η5-cyclopentadienyl) ligand. X-ray molecular structures of cis-[Mo(CO)2(NO)2μ-(η5-C5H3)2(SiMe2)2], trans-[Mo(CO)(NO)(CNtBu)2μ-(η5-C5H3)2(SiMe2)2], cis-[Mo2(CO)3(NO)2(PMe3)μ-(η5-C5H3)2(SiMe2)2] and trans-[Mo(NO)(CNtBu)22μ-(η5-C5H3)2(SiMe2)2]. Available from: http://www.researchgate.net/publication/256790936_Stereoselective_synthesis_and_reactivity_of_cis-_and_trans-_dimolybdenum_nitrosyl_derivatives_with_the_bridging_bis(dimethylsilanediyl)di(5-cyclopentadienyl)_ligand._X-ray_molecular_structures_of_cis-Mo(CO)2(NO)2-(5-C5H3)2(SiMe2)2_trans-Mo(CO)(NO)(CNtBu)2-(5-C5H3)2(SiMe2)2_cis-Mo2(CO)3(NO)2(PMe3)-(5-C5H3)2(SiMe2)2_and_trans-Mo(NO)(CNtBu)22-(5-C5H3)2(SiMe2)2 [accessed Nov 23, 2015].We acknowledge financial support from DGICYT (Project 92-0178-C). R.G-G acknowledges CAM for a fellowship

Unexpected behavior of irradiated spider silk links conformational freedom to mechanical performance

Silk fibers from Argiope trifasciata and Nephila inaurata orb-web weaving spiders were UV irradiated to modify the molecular weight of the constituent proteins. Fibers were characterized either as forcibly silked or after being subjected to maximum supercontraction. The effect of irradiation on supercontraction was also studied, both in terms of the percentage of supercontraction and the tensile properties exhibited by irradiated and subsequently supercontracted fibers. The effects of UV exposure at the molecular level were assessed by polyacrylamide gel electrophoresis and mass spectrometry. It is shown that UV-irradiated fibers show a steady decrease in their main tensile parameters, most notably, tensile strength and strain. The combination of the mechanical and biochemical data suggests that the restricted conformational freedom of the proteins after UV irradiation is critical in the reduction of these properties. Consequently, an adequate topological organization of the protein chains emerges as a critical design principle in the performance of spider silk

Sequential origin in the high performance properties of spider dragline silk

Major ampullate (MA) dragline silk supports spider orb webs, combining strength and extensibility in the toughest biomaterial. MA silk evolved ~376 MYA and identifying how evolutionary changes in proteins influenced silk mechanics is crucial for biomimetics, but is hindered by high spinning plasticity. We use supercontraction to remove that variation and characterize MA silk across the spider phylogeny. We show that mechanical performance is conserved within, but divergent among, major lineages, evolving in correlation with discrete changes in proteins. Early MA silk tensile strength improved rapidly with the origin of GGX amino acid motifs and increased repetitiveness. Tensile strength then maximized in basal entelegyne spiders, ~230 MYA. Toughness subsequently improved through increased extensibility within orb spiders, coupled with the origin of a novel protein (MaSp2). Key changes in MA silk proteins therefore correlate with the sequential evolution high performance orb spider silk and could aid design of biomimetic fibers

Multiple approaches at admission based on lung ultrasound and biomarkers improves risk identification in COVID-19 patients

Background: Risk stratification of COVID-19 patients is fundamental to improving prognosis and selecting the right treatment. We hypothesized that a combination of lung ultrasound (LUZ-score), biomarkers (sST2), and clinical models (PANDEMYC score) could be useful to improve risk stratification. Methods: This was a prospective cohort study designed to analyze the prognostic value of lung ultrasound, sST2, and PANDEMYC score in COVID-19 patients. The primary endpoint was in-hospital death and/or admission to the intensive care unit. The total length of hospital stay, increase of oxygen flow, or escalated medical treatment during the first 72 h were secondary endpoints. Results: a total of 144 patients were included; the mean age was 57.5 ± 12.78 years. The median PANDEMYC score was 243 (52), the median LUZ-score was 21 (10), and the median sST2 was 53.1 ng/mL (30.9). Soluble ST2 showed the best predictive capacity for the primary endpoint (AUC = 0.764 (0.658–0.871); p = 0.001), towards the PANDEMYC score (AUC = 0.762 (0.655–0.870); p = 0.001) and LUZ-score (AUC = 0.749 (0.596–0.901); p = 0.002). Taken together, these three tools significantly improved the risk capacity (AUC = 0.840 (0.727–0.953); p = 0.001). Conclusions: The PANDEMYC score, lung ultrasound, and sST2 concentrations upon admission for COVID-19 are independent predictors of intra-hospital death and/or the need for admission to the ICU for mechanical ventilation. The combination of these predictive tools improves the predictive power compared to each one separately. The use of decision trees, based on multivariate models, could be useful in clinical practice. © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/)