oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2019 ( 44 )

2018 ( 67 )

2017 ( 77 )

2016 ( 118 )

Custom range...

Search Results: 1 - 10 of 57946 matches for " Alberto Rojas-Hernández "
All listed articles are free for downloading (OA Articles)
Page 1 /57946
Display every page Item
Preparation and Characterization of Holmium-Beta-Cyclodextrin Complex  [PDF]
Ana Rosa Rojas-Mena, Hilario López-González, Alberto Rojas-Hernández
Advances in Materials Physics and Chemistry (AMPC) , 2015, DOI: 10.4236/ampc.2015.53011
Abstract: The purpose of this study was to prepare and characterize of holmium-beta-cyclodextrin complex (Ho-β-CD) in order to increase the solubility and stability of Holmium. To achieve this goal, Ho-β-CD complex was prepared by evaporation method of holmium and beta cyclodextrin solutions in a proportion (1:1) and (1:3), respectively. Infrared (IR) and Raman spectroscopy, X-Ray Diffraction were performed to identify the complex. Morphology of the Ho, β-CD, and Ho-β-CD were studied using Scanning Electron Microscopy (SEM).
Hydrolysis of Trivalent Holmium in Aqueous Solutions of 2 M Ionic Strength by Spectrophotometric and Potentiometric Methods  [PDF]
Miguel Angel Hernández-García, Hilario López-González, Alberto Rojas-Hernández
Advances in Materials Physics and Chemistry (AMPC) , 2015, DOI: 10.4236/ampc.2015.55017
Abstract: The first hydrolysis constants of trivalent holmium in 2 M NaClO4 and 2 M NaCl at 303 K and in CO2 free conditions were determined. The pCH borderlines of precipitation and first hydrolysis were determined by means of a spectrophotometric method and last one with the program SQUAD. Independently, the stability constant for the first hydrolytic species was determined, by means of potentiometric pH titrations whose data were treated with the program SUPERQUAD. The hydrolysis constants obtained were: \"\"?and \"\". These values attained by both methods are the same. The log10β1,Cl constants for the species HoCl2+ was also calculated for 2 M ionic strength and 303 K from the hydrolysis constant obtained in both perchlorate and chloride media. This value was logβ1,Cl = -0.56.
Chemical Speciation of the Fe(III)-piroxicam and Fe(III)-tenoxicam Systems in Aqueous Solution
Rosario Moya-Hernández,Rodolfo Gómez-Balderas,Alberto Rojas-Hernández
Revista de la Sociedad Química de México , 2011,
Abstract: Se realizó un estudio de especiación de los fármacos antiinflamatorios piroxicam y tenoxicam con el ion metálico Fe(III), bajo condiciones pseudofisiológicas (T = 37oC y I = 0.15 M). Las constantes de formación de las especies Fe(III)-oxicam fueron obtenidas a partir de datos de espectrofotometría UV/VIS, utilizando para ello el programa computacional SQUAD. Se determinaron también las constantes de hidrólisis de Fe(III) en agua bajo las mismas condiciones experimentales. Para tenoxicam se refinaron las constantes de las especies Fe(H2tenox)2 5+, Fe(Htenox)2 3+, Fe(OH)2(Htenox)2 +, Fe(OH)2(tenox)2 -, FeH2tenox4+, FeHtenox3+, Fe(OH)2Htenox+, Fe(OH)2tenox; un modelo análogo fue refinado para piroxicam. Para todas estas especies, se calcularon sus coeficientes de absortividad molar.
Spectrophotometric Determination of the First Hydrolysis Constant of Praseodymium (III)
González-Mendoza, Roberto;López-González, Hilario;Rojas-Hernández, Alberto;
Journal of the Mexican Chemical Society , 2010,
Abstract: the behavior of the trivalent ion praseodymium in 2m of nacl at 303 k and in co2 free conditions, was studied. spectrophotometric titrations of the soluble species were used, in order to obtain the value of the first hydrolysis constant of pr(iii). the data obtained were treated with both the program squad and by a graphic method, respectively. the result obtained using squad was log* β1 = -8.94 ± 0.03, while it was log*β1 = -8.77 ± 0.03, when calculated graphically. these results are similar to the value obtained previously with the potentiometric method.
Spectrophotometric Determination of the First Hydrolysis Constant of Praseodymium (III)
Roberto González-Mendoza,Hilario López-González,Alberto Rojas-Hernández
Revista de la Sociedad Química de México , 2010,
Abstract: Se estudió el comportamiento del ion trivalente praseodimio, en el medio 2M de NaCl a 303 K y en condiciones libres de CO2. Para obtener el valor de la primera constante de hidrólisis del Pr(III), se empleó la titulación espectrofotométrica de las especies solubles. Los datos obtenidos fueron tratados con el programa de cómputo SQUAD y un cálculo gráfico, respectivamente. El valor obtenido con el programa de cómputo SQUAD fue log*β1 = -8.94 ± 0.03, en tanto que el calculado gráficamente fue log*β1 = -8.77 ± 0.03. Estos resultados para el valor de la primera constante de hidrólisis del praseodimio son similares al valor obtenido previamente con el método potenciométrico.
Molecular Speciation Effect on Docking and Drug Design. A Computational Study for Mangiferin, a Carbohydrate-Polyphenol Bioconjugate as a Test Case
Gómez-Zaleta, Berenice;González-De la Rosa, Claudia Haydée;Pérez-Hernández, Gerardo;Beltrán, Hiram I.;Aparicio, Felipe;Rojas-Hernández, Alberto;Rojo-Domínguez, Arturo;
Journal of the Mexican Chemical Society , 2008,
Abstract: a study to evaluate the effect of molecular speciation considering methodologies to assign partial charges and conformational search processes for a docking test was made with mangiferin (mgf). this compound was selected as a model to explore speciation effects on drug design due to the speciation studies previously performed, and because it is a bioconjugate containing carbohydrate and polyphenolic xanthonoid groups, both moieties important as potential-drug candidates. peoe (partial equalization of orbital electronegativity) resulted the best method to assign partial charges, with a good compromise between precision and computational cost, among different classical molecular force fields and quantum mechanics methods that were compared with density functional theory calculations as the reference methodology. the number of conformations in energy minima showed to be extremely dependent upon partial charge assignation, as well as their geometry. in docking simulations of mgf on albumin drug-site 1, it was showed the relevance of choosing the properly expected chemical species for the ph value of interest since neutral mgf or deprotonated at the hydroxyl group on position 1 results in orientations significantly different from those predicted for the species deprotonated at the hydroxyl group on position 6, which is the predominant deprotonation site in accordance with the speciation study. the first two species present a tendency to expose the carbohydrate region to solvent occupying the same region in the binding site, while the molecule deprotonated in position 6 exhibits a preference for a different region of the site with its xanthonoid moiety exposed. carbohydrate-polyphenol bioconjugates, such as mgf combine two types of bioactive molecules being both important as leaders for drug design.
Equilibrium Constants Determination of the Species Formation in the Al(III)-H2O System by Integration of 27Al-NMR Signals and Fitting with Species Fractions
Rojas-Hernández, Alberto;Botello, Julio César;Pacheco-Hernández, Ma de Lourdes;Gutiérrez, Atilano;Domínguez, José Manuel;Espinosa, Gabriela;Ramírez-Silva, María Teresa;
Journal of the Mexican Chemical Society , 2008,
Abstract: a quantitative methodology to determine formation constants that takes into consideration the 27al-nmr signals of al(iii)-h2o systems has been analyzed, where area fractions beneath the peaks recorded were associated with the corresponding species fractions. the values of the formation constants were compared with the model obtained by potentiometric studies. in agreement with previous reports, the -log*β values obtained by nmr and potentiometry, at 0.020 m ≤ [al(iii)]total ≤ 0.500 m are 12.96 ± 0.02 for al(oh)3, 13.50±0.02 for al3(oh)45+, and 109.70±0.09 for al13(oh)327+, by assuming that al(oh)2+ has a value of 5.29. additionally the equilibrium constant values obtained allowed fitting of the conductimetry titrations in the 6.00(10-3) m ≤ [al(iii)]total ≤ 0.120 m. the algorithm presented in this work gives a support to establish that the area fractions of nmr signals are proportional to the species concentration fractions.
MONITORING OF THE pH USING ISFET SENSORS IN ELECTROPLATING PROCESSES
Alvarez Romero,Ramírez-Silva, M. T.,Rojas-Hernández,Hernández-Rodríguez, P. R.
Journal of applied research and technology , 2005,
Abstract: It is well known that electroplating with metals has achieved quite a significant importance and has become alucrative area. The present paper looks at the electroplating processes as a part of the metallurgical industry that arecarried out with diverse aims. The quality and characteristics of the metal deposit depend on the electrochemicalconditions imposed, such as pH. During an industrial electroplating process, when an undesirable change isdetected first in the metal coating attained, is a common occurrence that a complete change of the plating bath iscarried out. Due to this, the application of analytical systems to enable in situ precise monitoring of anycompositional changes of the bath during the electroplating process, is an unquestionable need to be carefullysatisfied. The design of such systems should allow close control of the concentrations of specific componentsduring the process, constituting thus a desirable aim entailing both, financial and time savings. In the present work,the construction of an analytical system based on the coupling of a continuous sampling system with pH ISFETsensors is described. Comparative studies between a glass electrode and the proposed analytical system in copper,silver and nickel electroplating baths are carried out.
Estudio de eliminación de arsénico con resinas de intercambio iónico en agua potable de Zimapán, Estado de Hidalgo, México
Pérez-Moreno, F.,Prieto-García, F.,Rojas-Hernández, A.,Marmolejo-Santillán, Y.
Revista de Metalurgia , 2006,
Abstract: Anionic exchange resins were research with respect its capacity for removal arsenic content in water. Water of well V from Zimapán Hidalgo Mexico was used to make this research, because this water have a mean concentration of 480 ± 11 μg·L-1 of arsenic and it is available as drinking water. The exchange resins employed were two strong anionic, one macroreticular (IRA-900) and other gel type (IRA-400), as soon as one third anionic weak macroreticular type (IRA-96). The experiments carried with this resins showing that IRA-900 has highest efficient in the process of arsenic removal from drinking water, because, it showed a treatment capacity of 700 Vagua·Vres-1; while that capacities of IRA-400 e IRA-96 resins were 320 and 52 Vagua·Vres-1 respectively. The mean concentration of arsenic residue in the treatise water was 24 μg·l-1 and it is within the maximum level permissible by Mexican official norm for drinking water. Se investigaron resinas de intercambio aniónico con respecto a su capacidad para la eliminación de arsénico contenido en agua. Se utilizó agua del pozo V de Zimapán, Hidalgo, México, cuya concentración promedio es de 480 ± 11 μg·l-1 de arsénico y es utilizada para consumo humano. Se emplearon dos reinas aniónicas fuertes; una, de tipo macro reticular (IRA-900) y la otra de tipo gel (IRA-400), así como una tercera, aniónica débil, de tipo macro reticular (IRA-96). Los experimentos realizados con estas resinas muestran que la IRA-900 es la que mostró la más alta eficiencia en la eliminación de arsénico del agua potable, debido a que presentó una capacidad de tratamiento de 700 Vagua·Vres-1, mientras que las capacidades de las resinas IRA-400 e IRA-96 fueron de 320 y 52 Vagua·Vres-1, respectivamente. La concentración promedio de arsénico remanente en el agua tratada fue de 24 μg·l-1 y está dentro del límite máximo permisible por la norma oficial mexicana para agua potable.
Identificación, usos y medición de leguminosas arbóreas forrajeras en ranchos ganaderos del sur del Estado de México
Olivares-Pérez, J.;Avilés-Nova, F.;Albarrán-Portillo, B.;Rojas-Hernández, S.;Castelán-Ortega, O. A;
Tropical and subtropical agroecosystems , 2011,
Abstract: the aim of the study was to identify fodder legume trees species, it's uses, density, frequency, abundance and dasometrics measures; as well as to evaluate foliage production (kg dm tree-1) of pithecellobium dulce, gliricidia sepium and haematoxylum brasiletto, and its preference by farmers as a source of forage in farms in south of mexico state. fruit production (kg tree-1 dm) of acacia cochliacantha and pithecellobium dulce was also evaluated. trees uses and preferences were obtained throughout structured interviews applied to 69 farmers representing 83% of the population. measurements of the trees were made in six farms. data were analyzed using descriptive statistics. twelve trees species were identified, were acacia cochliacantha, lysiloma divaricata, pithecellobium dulce, gliricidia sepium and haematoxylum brasiletto were the most important having higher density, frequency and abundance. ruminants consume foliage and fruit of 46.6% of identified trees, in 20% of the trees only foliage is consumed. eighty percent of species identified had between five to 8 different uses different form forages, being: firewood, poles, shade, living fence, medicinal, human consumption, material for crafts and wood. the largest trees were caesalpinia coriaria, pithecellobium dulce, leucaena esculenta and enterolobium cyclocarpum according to their basal diameter (bd) (between 47.1 to 57.2 cm), diameter at breast height (dbh) was between 49.3 to 50.3 cm and height (h) between 7.4 to 14.5 m, therefore preferred as a shadow. foliage production was 44.5, 8.8 and 8.4 kg dm tree-1 for the pithecellobium dulce, gliricidia sepium and haematoxylum brasiletto respectively. fruit production was 63.9 and 21.7 kg dm tree-1 for pithecellobium dulce and acacia cochliacantha, respectively. the 12 leguminous trees identified in the area are recognized by farmers as multipurpose fodder trees being a source of food for cattle during the rainy; fruit becomes an important source of food during the dr
Page 1 /57946
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.