Cinètica de la reacció de descomposició tèrmica de l’ascaridol en dissolució

Existen diferencias entre los valores de algunas propiedades físicas de ascaridol natural aislado del vegetal denominado vulgarmente «Paico» (Chenopodium ambrosioides L., Chenopodiaceae) y la sustancia sintética obtenida mediante la reacción de fotooxigenación de α-terpineno. Es más, el uso de decocciones de dicha planta, utilizadas como medicina antihelmíntica en los humanos, ha despertado un debate científico debido a las propiedades tóxicas atribuídas a su principio activo (ascaridol), el cual sería responsable de la muy conocida acción beneficiosa. En este trabajo se ha realizado la preparación de esa sustancia por el método de Schenck, pero trabajando a 0 ºC con alcohol isopropílico como solvente y efectuando su separación y purificación a temperatura ambiente por cromatografía en columna preparativa, a fin de prevenir su degradación térmica. De esta manera se obtuvieron excelentes rendimientos de ascaridol (ca. 99% GC-FID), de un alto grado de pureza (> 98% GC; RP-HPLC; 1 H y 13C RMN). Además, se informan aquí los parámetros de activación de la reacción de descomposición térmica de ascaridol en solución de n-hexano, alcohol isopropílico y metanol, en el ámbito de temperaturas de 120ºC a 170ºC. Es evidente también un efecto de solvente en la homólisis unimolecular de esa sustancia.Discrepancies exist between the values of some physical properties of ascaridole isolated from the vegetal named «Paico» (Chenopodium ambrosioides L., Chenopodiaceae) and the synthetic substance obtained by the photoxygenation reaction of α-terpinene. Moreover, the use of decoctions of the above mentioned plant as anthelmintic medicine in humans arouse a scientific debate because of toxic properties attributed to its main active drug (ascaridole), which would be responsible of the well-known beneficial action. This lead to perform here the preparation of that substance by Schenck’s method, but working at 0 ºC with isopropyl alcohol as solvent and doing its separation and purification at room temperature by preparative column chromatography to prevent its thermal degradation. Thus, excellent yields of ascaridole were obtained (ca. 99 % GC-FID) of high degree of purity (> 98% GC; RP-HPLC; 1 H and 13C NMR). Furthermore, the kinetics of the thermal stability of ascaridole in solution is now advanced, reporting the activation parameters values for their decomposition reactions in n-hexane, isopropyl alcohol and methanol, in the 120º170 ºC temperature range. A solvent effect on the unimolecular homolysis of that substance is also evident.  Hi ha diferències entre els valors d’algunes propietats fisiques de l’ascaridol natural, aïllat del vegetal dit vulgarment «Paico» (Chenopodium ambrosioides L., Chenopodiaceae), i la substància sintètica obtinguda mitjançant la reacció de fotooxigenació d’α-terpinè. Encara més, l’ús de decoccions de l’esmentada planta, emprades com a medicina antihelmíntica en humans, ha despertat un debat científic, donades les propietats tòxiques atribuïdes al seu principi actiu (ascaridol), que seria el responsable de la molt coneguda acció beneficiosa. En aquest treball, s’ha realitzat la preparació d’aquesta substància pel mètode de Schenck, però treballant a 0 ºC amb alcohol isopropílic com a dissolvent i efectuant la seva separació i purificació a temperatura ambient mitjançant cromatografia de columna preparativa, per tal de prevenir la seva degradació tèrmica. D’aquesta manera, s’obtenen excel.lents rendiments d’ascaridol (ca. 99% GC-FID), d’un alt grau de puresa (> 98% GC; RP-HPLC; 1 H i 13C RMN). A més, es presenten els paràmetres d’activació de la reacció de descomposició tèrmica de l’ascaridol en dissolució de n-hexà, alcohol isopropílic i metanol, en el marge de temperatures de 120ºC a 170 ºC. Així mateix, és evident un efecte del dissolvent en l’homòlisi unimolecular d’aquesta substància.Fil: Cafferata, Lazaro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Química. Laboratorio de Estudio de Compuestos Orgánicos; ArgentinaFil: Jeandupeux, R.. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Química. Laboratorio de Estudio de Compuestos Orgánicos; ArgentinaFil: Cañizo, Adriana Ines. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Química. Laboratorio de Estudio de Compuestos Orgánicos; Argentin

Agriculture and The Challenge to Reduce Poverty in East Africa

The three East African (EA) countries Tanzania, Kenya and Uganda have a population of about 95 million people and Gross Domestic Product (GDP) of USD 34.2 billion. In recent years efforts has been made among the three East African countries, towards forging economic and regional co-operation by establishing the East African Community (EAC). The premise for economic and regional co-operation has been underpinned for the need for a common market and boost regional trade. The ultimate goal of these efforts is to achieve one of the international development objectives of increasing growth to 7% a year that is required to reduce income poverty. One of the challenges that East African countries need to tackle in the face of globalisation is the ability to participate in international markets. East African countries have to make serious consideration with regards to changing the composition of their exports away from primary products to manufactured exports. Value addition to both agricultural and industrial products is vital to improving the EA economies. This paper examines the composition of East Africa’s economic structure. The aim is to analyse how the economic structure has changed over time, and to assess whether or not East African countries have transformed their agricultural sectors, and what the impact has been on poverty reduction in these economies.Agricultural and Food Policy, Community/Rural/Urban Development, Environmental Economics and Policy, Farm Management, Food Consumption/Nutrition/Food Safety, Food Security and Poverty, International Relations/Trade, Land Economics/Use, Marketing, Productivity Analysis, Research and Development/Tech Change/Emerging Technologies,

Backscatter Transponder Based on Frequency Selective Surface for FMCW Radar Applications

This paper describes an actively-controlled frequency selective surface (FSS) to implement a backscatter transponder. The FSS is composed by dipoles loaded with switching PIN diodes. The transponder exploits the change in the radar cross section (RCS) of the FSS with the bias of the diodes to modulate the backscattered response of the tag to the FMCW radar. The basic operation theory of the system is explained here. An experimental setup based on a commercial X-band FMCW radar working as a reader is proposed to measure the transponders. The transponder response can be distinguished from the interference of non-modulated clutter, modulating the transponder’s RCS. Some FSS with different number of dipoles are studied, as a proof of concept. Experimental results at several distances are provided

Robustness of cultural communities in an open-ended Axelrod's model

We consider an open-ended set of cultural features in the Axelrod's model of cultural dissemination. By replacing the features in which a high degree of consensus is achieved by new ones, we address here an essential ingredient of societies: the evolution of topics as a result of social dynamics and debate. Our results show that, once cultural clusters have been formed, the introduction of new topics into the social debate has little effect on them, but it does have a significant influence on the cultural overlap. Along with the Monte-Carlo simulations, we derive and numerically solve an equation for the stationary cultural overlap based on a mean-field approach. Although the mean-field analysis reproduces qualitatively the characteristic phase transition of the Axelrod's model, it underestimates the cultural overlap, highlighting the role of the local interactions in the Axelrod's dynamics, as well as the correlations between the different cultural features.Comment: 6 pages and 5 figure

A networked voting rule for democratic representation

We introduce a general framework for exploring the problem of selecting a committee of representatives with the aim of studying a networked voting rule based on a decentralized large-scale platform, which can assure a strong accountability of the elected. The results of our simulations suggest that this algorithm-based approach is able to obtain a high representativeness for relatively small committees, performing even better than a classical voting rule based on a closed list of candidates. We show that a general relation between committee size and representatives exists in the form of an inverse square root law and that the normalized committee size approximately scales with the inverse of the community size, allowing the scalability to very large populations. These findings are not strongly influenced by the different networks used to describe the individuals interactions, except for the presence of few individuals with very high connectivity which can have a marginally negative effect in the committee selection process.Comment: Submitted for publicatio

Analysis of a networked social algorithm for collective selection of a committee of representatives

A recent work by Hern\'andez et al. introduced a networked voting rule supported by a trust-based social network, where indications of possible representatives were based on individuals opinions. Individual contributions went beyond a simple vote-counting and were based on proxy voting. These mechanisms generated a high level of representativeness of the selected committee, weakening the possibility of relations of patronage. By incorporating the integrity of individuals and its perception, here we address the question of the trustability of the resulting committee. Our results show that this voting rule provides high representativeness for small committees with a high level of integrity. Furthermore, the voting system displays robustness to a strategic and untruthful application of the voting algorithm.Comment: 7 pages and 8 figures. Submitted for publication. arXiv admin note: text overlap with arXiv:1801.0539

From Genotype to Phenotype:How Enhancers Control Gene Expression and Cell Identity in Hematopoiesis

Blood comprises a wide array of specialized cells, all of which share the same genetic information and ultimately derive from the same precursor, the hematopoietic stem cell (HSC). This diversity of phenotypes is underpinned by unique transcriptional programs gradually acquired in the process known as hematopoiesis. Spatiotemporal regulation of gene expression depends on many factors, but critical among them are enhancers—sequences of DNA that bind transcription factors and increase transcription of genes under their control. Thus, hematopoiesis involves the activation of specific enhancer repertoires in HSCs and their progeny, driving the expression of sets of genes that collectively determine morphology and function. Disruption of this tightly regulated process can have catastrophic consequences: in hematopoietic malignancies, dysregulation of transcriptional control by enhancers leads to misexpression of oncogenes that ultimately drive transformation. This review attempts to provide a basic understanding of enhancers and their role in transcriptional regulation, with a focus on normal and malignant hematopoiesis. We present examples of enhancers controlling master regulators of hematopoiesis and discuss the main mechanisms leading to enhancer dysregulation in leukemia and lymphoma