Revista Cubana de Química

Theoretical study of the thermal decomposition of malonic acid in gas phase and aqueous solution

RESUMEN En este trabajo se presenta el estudio computacional de la reacción de descomposición térmica del ácido malónico. Se modeló mediante dos mecanismos, a cinco temperaturas, en fase gaseosa y en disolución acuosa. Los cálculos fueron realizados mediante la teoría de los funcionales de la densidad. Para las condiciones estudiadas de la reacción, la constante de velocidad fue calculada con la ecuación de Eyring-Polanyi. Los resultados fueron comparados con los valores experimentales reportados. Otro tipo de cálculo realizado fueron los orbitales naturales de enlace. Los resultados obtenidos permitieron discutir diferentes aspectos acerca de los mecanismos de reacción planteados.

ABSTRACT In this work, the computational study of the thermal decomposition of malonic acid is presented. It was followed by two mechanisms, at five temperatures, in gas phase and in aqueous solution. The calculations were carried out by means of the density functional theory. The rate constant of the reaction for the studied conditions was calculated with the Eyring-Polanyi equation. The results were compared with the reported experimental values. Another type of calculation performed were the natural bond orbitals. The results obtained allowed to discuss different aspects about the proposed reaction mechanisms.

Application of the theories of functional density and møller - plesset second order in the study of alcohols acetylation

RESUMEN Se llevó a cabo un estudio teórico comparativo de reactividad de metanol, n-butanol, terc-butanol, fenol, p-nitrofenol y p-metilfenol frente a la reacción de acetilación, a través del análisis de los intermediarios de reacción correspondientes. La acetilación de alcoholes es una de las transformaciones más frecuentemente usadas en síntesis orgánica, ya que proporciona un medio eficiente y económico para proteger el grupo hidroxilo en un proceso sintético. Las energías de activación y las energías de los intermediarios de reacción, se calcularon con dos niveles de teoría DFT (B3LYP) y MP2 combinados con los conjuntos de base 3-21G* y 6-31G*.Los valores obtenidos se compararon con datos de literatura. El metanol presentó la mayor reactividad frente a la acetilación y el método DFT/6-31G* reportó los valores más bajos de energía.

ABSTRACT A comparative theoretical study of reactivity of methanol, n-butyl alcohol, tert-butyl alcohol, phenol.p-nitrophenol and p-methylphenol acetylation, through the analysis of the corresponding reaction intermediates was carried out. The acetylation of alcohols is one of the most frequently used transformations in organic synthesis as it provides an efficient and inexpensive means for protecting hydroxyl group in a synthetic process. The activation energies and the reaction intermediates energies, were calculated with two levels of theory DFT (B3LYP) and MP2 combined with basis set 3-21G* and 6-31G*.The calculated values were compared with literature data. The methanol presented the higher reactivity in the acetylation reaction and the DFT/6-31G* method reported the lower energy values.

Chemical composition and antioxidant activity of Coccoloba cowellii Britton

Abstract The qualitative and quantitative chemical composition (total phenolics, tannins and flavonoids contents), as well as the antioxidant activity of an ethanolic extract of the leaves of Coccoloba cowellii (Polygonaceae) was determined in this study. The extract was prepared by dynamic ultrasound-assisted extraction using firstly petroleum ether:ethyl ether (1:1, v/v) and therefore ethanol:water (8:2, v/v). Quantitative chemical composition (total phenolics, tannins and flavonoids content) was determined using spectroscopic techniques, while the antioxidant activity was determined by means of the 1,1-diphenyl-2-picryl-hydrazyl (DPPH) and ferric reducing power tests. The ethanolic extract showed significant antioxidant activity in both assays, with values of 34,01 % ± 4,03 % in the DPPH and reduced Fe3+ ferricyanide complex to the ferrous form (Fe2+), similar to the ascorbic acid used as standard in both assays. The antioxidant activity of the extract is consistent with the total phenolic, tannins and flavonoid contents of the extract.

Resumen En este trabajo se determinó la composición química cualitativa y cuantitativa (contenido de compuestos fenólicos, taninos y flavonoides totales), así como la actividad antioxidante in vitro de un extracto etanólico de las hojas de Coccoloba cowelli (Polygonaceae). Para ello se realizó una extracción dinámica asistida por ultrasonido con éter de petróleo:éter etílico (1:1, v/v) y luego con etanol:agua (8:2, v/v). En los extractos se cuantificaron los compuestos fenólicos, taninos y flavonoides totales mediante técnicas espectrofotométricas. La actividad antioxidante fue determinada mediante los ensayos del radical 1,1-difenil-2-picrilhidracil (DPPH) y del poder reductor. El extracto etanólico mostró actividad antioxidante significativa en ambos ensayos, con valores de 34,01 % ± 4,03 % en el DPPH y reduciendo el complejo Fe3+ ferricianuro a su forma ferrosa, los que fueron comparables al del ácido ascórbico usado como estándar. La actividad antioxidante es consistente con el contenido de compuestos fenólicos, taninos y flavonoides totales del extracto.

In vitro biosimilarity of ranitidine 300 mg tablets dispensed in peruvian settlers

RESUMEN El estudio estuvo orientado a determinar la biosimilitud in vitro de las tabletas de ranitidina 300 mg multifuente y referente que se prescriben y dispensan en pobladores peruanos. Se utilizaron 12 tabletas procedentes de dos laboratorios (multifuente y referente), que fueron analizadas en tres medios de disolución con buffer pH 1,2; 4,5 y 6,8; para obtener la cantidad de medicamento disuelto en función del tiempo. Los resultados para los medios de disolución indican que los datos se ajustaron al modelo cinético orden uno, el tratamiento estadístico para el tiempo medio de disolución y eficiencia de disolución mediante t student evidenció que no existe diferencia significativa entre el medicamento multifuente y referente. Los valores del factor de similitud f2 fueron 83,3; 75,8 y 71,1 para los pH 1,2; 4,5 y 6,8 respectivamente. Se concluye similitud biológica entre el medicamento multifuente y referente, basado en pruebas de disolución in vitro.

ABSTRACT The study was aimed at determining the in vitro biosimilarity of ranitidine 300 mg multi-source tablets and reference that are prescribed and dispensed in Peruvian residents. Twelve tablets from two laboratories (multi-source and reference) were used, which were analyzed in three dissolution media with buffer pH 1.2; 4.5 and 6.8; to get the amount of medication dissolved as a function of time. The results for the means of dissolution indicate that the data were adjusted to the order kinetic model, the statistical treatment for the mean time of dissolution and dissolution efficiency by student t showed that there is no significant difference between the multi-source drug and the reference. The values of the similarity factor f2 were 83,3; 75,8 and 71,1 for the pH 1,2; 4,5 and 6,8 respectively. Biological similarity between the multi-source drug and the reference based on in vitro dissolution tests is concluded.

Evaluation of adsorption capacity for MN²⁺ by residual biomass from sugar cane (Saccharum officinarum)

RESUMEN El presente trabajo evaluó la tecnología bioadsorción para la remediación de las aguas de La Laguna Azul, en el Cobre en Santiago de Cuba con alto contenido de iones metálicos, empleando la biomasa de caña de azúcar. Para esto, se realizó la caracterización de dos estaciones de monitoreo situadas a los extremos del reservorio acuático. En los análisis se demostró que el agua de la misma no cumple con las regulaciones de la NC: 1021-2014 “Higiene comunal: Fuentes de abastecimiento de agua. Calidad y protección sanitaria”. Los experimentos de adsorción demostraron que la biomasa utilizada en una matriz real es capaz de remover el 5,31 % de Mn2+ en condiciones naturales, el 33,36 % una vez tratada con NaOH y el 58,42 % bajo tratamiento con H3PO4, a un valor de pH de 4,3 y una masa de adsorbente de 0,5 g/50mL.

ABSTRACT The present work, bioadsorption technology was evaluated for the remediation of the waters from “La Laguna Azul”, in the town of El Cobre in Santiago de Cuba with a high content of metal ions, through the use of sugar cane biomass. For this, the characterization of two monitoring stations located at the ends of the aquatic reservoir as carried out. In the analyses it was demonstrated that the water of the same one does not fulfill the regulations of the NC: 1021-2014 “Communal Hygiene. Sources of water supply: Quality and sanitary protection”. The adsorption experiments led to the biomass used in a real matrix being able to remove 5,31 % of Mn2+ ions under natural conditions, 33,36 % once treated with sodium hydroxide and 58,42 % under treatment with phosphoric acid, pH value of 4,3 and a mass of adsorbent of 0,5 g/50mL.

Purification and characterization of human chorionic gonadotropin for diagnosis

RESUMEN En Cuba, el UMELISA HCG, producido por el Centro de Inmunoensayo, detecta la presencia de gonadotropina coriónica humana. Con el objetivo de purificar y caracterizar gonadotropina coriónica humana (hCG) para uso diagnóstico, se desarrolló un procedimiento para su obtención a partir de orina de gestantes, con una etapa de captura y una de purificación por cromatografía de inmunoafinidad, empleando un anticuerpo monoclonal anticadena β hCG. La mayor masa de hCG en el precipitado (74,27 %) se obtuvo al 50 % de saturación del (NH4)2SO4, 22 (C y 3 h de reposo. La actividad específica fue 12 417,65 UI/mg. El PAGE-SDS mostró las bandas de las cadenas α y β, con movilidad similar al control. La pureza por densitometría fue 97,3 %. Por filtración en gel se obtuvo una masa molar de 40 kDa. Con la metodología empleada se obtuvo gonadotropina coriónica humana con la calidad requerida para la obtención de los reactivos biológicos del UMELISAHCG.

ABSTRACT In Cuba, the UMELISA HCG, produced by the Immunoassay Center, detects the presence of human chorionic gonadotropin. With the aim to purify and characterize human chorionic gonadotropin (hCG) for diagnostic use, was developed a procedure for its purification from the urine of pregnant women, with a capture stage and a phase of immune affinity chromatography, using a monoclonal antibody anti-chain β hCG. The highest mass of hCG (74,27 %) in the precipite was obtained at 50 % saturation of (NH4)2SO4, 22 (C and 3 h of rest,. The specific activity was 12 417,65 IU/mg. PAGE-SDS showed the bands of the α and β chains of the hormone, with similar mobility to the control. The purity by densitometry was 97,3 %. By gel filtration a molar mass of 40 kDa was obtained. Using this procedure human chorionic gonadotropin with the required quality to get biological reagents for the UMELISA HCG was obtain.

Physicochemical characterization of distillery vinasse

RESUMEN Se realizó la caracterización fisicoquímica de las vinazas obtenidas en el proceso de producción de alcohol a partir de miel final, en las Destilería “Argeo Martínez “y “Arquímedes Colina” de las Provincias Guantánamo y Granma respectivamente. Fueron determinados parámetros físico-químicos clásicos para evaluar el poder contaminante de la vinaza, y se compararon con la Norma Cubana 521:2007. Los resultados obtenidos muestran que los parámetros: DQO, conductividad eléctrica, pH, temperatura, nitrógeno total y contenido de hierro se encuentran por encima de los límites máximos permisibles. Se demuestra el efecto contaminante de las vinazas estudiadas, corroborándose que es inadecuada la disposición final de este residual a las aguas terrestres y marítimas sin un tratamiento previo.

ABSTRACT Was carried out the physicochemical characterization of the obtained vinasses in the process of alcohol production from final honey in the Argeo Martínez and Arquímedes Distillery Hill of the Guantánamo and Granma Provinces. Representative chemical-physical parameters were determined for evaluate the polluting power of the vinasse, and were compared with the Cuban Standard 521: 2007. The obtained results show that the parameters: DQO, electrical conductivity, pH, temperature, total nitrogen and iron content are above the maximum permissible limits. It´s demonstrated the contaminating effect of the studied vinasses, corroborating that the final disposal of this residual to the terrestrial and maritime waters without prior treatment is inadequate.

Aplicação de doses crescentes de calcário por incubação nos solos da chianga-huambo, Angola

RESUMO Neste trabalho estima-se as doses de calcário para corrigir o solo de uma área da estação experimental da Chianga-Huambo e visou obter doses ideais de calcário, para se elevar o pH a um valor que torna os nutrientes mais disponíveis para as plantas, de modo a padronizar outros métodos de correção. As amostras de solo foram colhidas da superfície até uma profundidade de 20 cm da estação experimental. Com a aplicação das doses crescentes de calcários ao solo, o pH atingiu valores de 5,79 e 5,44 em H2O e CaCl2 respectivamente. O delineamento experimental utilizado foi inteiramente casual, e três épocas de avaliação, 30, 60 e 90 dias após a aplicação no solo. O ião Al3+ reduziu para o valor de 0,2 cmol/l, enquanto que, a capacidade de troca catiónica efectiva, soma de bases aumentarem devido a presença dos catiões de troca no calcário.

ABSTRACT In this work the limestone doses are estimated to correct the soil of an area of the Chianga-Huambo experimental station and aimed at obtaining ideal doses of limestone to raise the pH to a value that makes the nutrients more available to the plants, to standardize other methods of correction. Soil samples were collected from the surface to a depth of 20 cm from the experimental station. With the application of increasing doses of limestone to soil, the pH reached values of 5,79 and 5,44 in H2O and CaCl2, respectively. The experimental design was entirely random, and three evaluation periods, 30, 60 and 90 days after application in the soil. The Al 3+ ion reduced to the value of 0,2 cmol / l, whereas, the effective cation exchange capacity, sum of bases increased due to the presence of the exchange cations in the limestone.

Análise sobre a estabilidade química dos óleos de algumas sementes do cultivo angolano

RESUMO A inquestionável riqueza da flora angolana e a crescente procura de produtos naturais, seja na área medicinal como na alimentar, motivou o estudo sobre o comportamento químico de óleos isolados de seis distintas sementes: gergelim (Sesamun indicum L), pevides de abóbora (Curcubita moschata ) e (Cucumeropsis edulis), pimenta preta (Piper nigrum), gipepe (Monodora myristica) e missange (Xylopia aethiopica), dado o seu valor nutritivo e preventivo na saúde humana.Com estudo espectroscópico Infravermelho de alguns desses óleos verificou-seque mantêm o seu aspecto químico durante o aquecimento da cozedura, garantindo assim a segurança ao consumidor. A realidade actual é um imperativo no recurso aos produtos da nossa flora,como fonte de alimento e fitoquímicosno combate as enfermidades; uma oportunidade para a redução/eliminação da fome e pobreza na nossa sociedade. Os óleos essenciais constituem uma fonte económica para o país.

ABSTRACT The unquestionable richness of our flora and the growing demand for natural products, both in the medicinal and food areas, motivated the study of the chemical behavior of isolated oils of six different seeds: sesame, Curcubita, black pepper, Monodoramyristica and Xylopiaaethiopicain consideration of its nutritive and preventive value in human health. With ainfraredspectroscopic study of some of these oils it was verified that these maintain their chemical aspect during the heating of the cooking, thus assuring the safety to the consumer. The present reality is an imperative in the use of the products of our flora as source of food and phytochemicals in the combat the infirmities; an opportunity for the reduction/elimination of hunger and poverty in our society. Essential oils are an economic source for the country.

Characterization of three bioindicators of pollution by heavy metals

RESUMEN El incremento del turismo en la costa sur de la Península de Guanahacabibes causa preocupación por su posible impacto negativo sobre este ecosistema marino. En esta zona es común la presencia de las especies Syringodium filiforme, Thalassia testudinum y Sargassum buxifolium, reconocidas como bioindicadores descontaminación para metales pesados. En este trabajo fueron caracterizados estos bioindicadores previo a su empleo en estudios de sorción. La caracterización incluyó análisis por Microscopía Electrónica de Barrido con Energía Dispersiva de Rayos X, Espectroscopía Infrarroja por Transformada de Fourier, Espectrometría Óptica de Emisión con Plasma Acoplado Inductivamente, entre otros. Los resultados obtenidos muestran las potencialidades de estos biomateriales para la bioacumulación de metales pesados. Además, con la caracterización fue posible establecer comparaciones entre los tres bioindicadores, así como seleccionar y respaldar algunos de los posibles mecanismos de unión de los metales pesados a la biomasa.

ABSTRACT The increase in tourism on the southern coast of the Guanahacabibes Peninsula causes concern about its possible negative impact on this marine ecosystem. In this zone, the presence of the species Syringodium filiforme, Thalassia testudinum and Sargassum buxifolium, recognized, as bioindicators of contamination by heavy metals is common. In this work, these bioindicators were characterized prior to their use in sorption studies. The characterization included analysis by Scanning Electron Microscopy with Dispersive Energy of X-Rays, Infrared Spectroscopy by Fourier Transform, Optical Spectrometry of Emission with Inductively Coupled Plasma, among others. The results obtained show the potential of these biomaterials for the bioaccumulation of heavy metals. In addition, with the results of the characterization, it was possible to establish comparisons between the three bioindicators, as well as to select and support some of the possible mechanisms of binding of heavy metals to biomass.