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1.
Sensors (Basel) ; 22(9)2022 Apr 20.
Artículo en Inglés | MEDLINE | ID: mdl-35590819

RESUMEN

Proposal techniques that reduce financial costs in the diagnosis and treatment of animal diseases are welcome. This work uses some machine learning techniques to classify whether or not cases of canine visceral leishmaniasis are present by physical examinations. For validation of the method, four machine learning models were chosen: K-nearest neighbor, Naïve Bayes, support vector machine and logistic regression models. The tests were performed on three hundred and forty dogs, using eighteen characteristics of the animal and the ELISA (enzyme-linked immunosorbent assay) serological test as validation. Logistic regression achieved the best metrics: Accuracy of 75%, sensitivity of 84%, specificity of 67%, a positive likelihood ratio of 2.53 and a negative likelihood ratio of 0.23, showing a positive relationship in the evaluation between the true positives and rejecting the cases of false negatives.


Asunto(s)
Enfermedades de los Perros , Leishmaniasis Visceral , Animales , Teorema de Bayes , Enfermedades de los Perros/diagnóstico , Perros , Ensayo de Inmunoadsorción Enzimática/métodos , Ensayo de Inmunoadsorción Enzimática/veterinaria , Leishmaniasis Visceral/diagnóstico , Leishmaniasis Visceral/veterinaria , Aprendizaje Automático , Sensibilidad y Especificidad
2.
J Fish Biol ; 99(4): 1524-1528, 2021 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-34159587

RESUMEN

The aim of this study is to provide preliminary observations on the microanatomy of Rhincodon typus skin using histology and electron microscopy analyses. Skin biopsies were obtained from a deceased juvenile male shark (548 cm total length) stranded in La Paz, Mexico, during February 2018. The results of this study evidenced the basic structure of the dermal denticles in the epidermis of the trunk of the shark, as well as the composition of the connective tissue in the hypodermis. Histological images of the hypodermis showed a high concentration of collagen fibres, formed by a large number of fine and wavy fibres of compact shape and little intercellular substance.


Asunto(s)
Tiburones , Animales , Dermis , Epidermis , Masculino , México , Piel
3.
Mol Phylogenet Evol ; 97: 213-223, 2016 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-26802207

RESUMEN

Green tree frogs of the genus Aplastodiscus occur in the Atlantic Forest and Cerrado biomes of South America. The genus comprises 15 medium-sized species placed in three species groups diagnosed mainly by cloacal morphology. A phylogenetic analysis was conducted to: (1) test the monophyly of these species groups; (2) explore the phylogenetic relationships among putative species; and (3) investigate species boundaries. The dataset included eight mitochondrial and nuclear gene fragments for up to 6642 bp per specimen. The results strongly support the monophyly of Aplastodiscus and of the A. albofrenatus and A. perviridis groups. Aplastodiscus sibilatus is the sister taxon of all other species of Aplastodiscus, making the A. albosignatus Group non-monophyletic as currently defined. At least six unnamed species are recognized for Aplastodiscus, increasing the diversity of the genus by 40%. A fourth species group, the A. sibilatus Group is recognized. Aplastodiscus musicus is transferred from the A. albofrenatus Group to the A. albosignatus Group, and A. callipygius is considered a junior synonym of A. albosignatus. Characters related to external cloacal morphology reveal an interesting evolutionary pattern of parallelisms and reversions, suggesting an undocumented level of complexity. We analyze, in light of our phylogenetic results, the evolution of reproductive biology and chromosome morphology in Aplastodiscus.


Asunto(s)
Anuros/clasificación , Anuros/genética , Filogenia , Animales , Cromosomas/genética , Evolución Molecular , Reproducción/genética , América del Sur
4.
Methods Mol Biol ; 2759: 3-8, 2024.
Artículo en Inglés | MEDLINE | ID: mdl-38285134

RESUMEN

Temporary immersion systems (TIS) are technological tools that support plant micropropagation. Given their high efficiency in the in vitro propagation of shoots, a current goal is to update the protocols addressing micropropagation in semisolid culture systems to protocols involving TIS. To this end, different parameters have been evaluated, including TIS types and designs, immersion times, immersion frequencies, and volume of medium per explant, among other characteristics. This has resulted in the improved production of propagules of plants of economic interest and the production of physiologically upgraded plants with high percent survival during acclimatization. TIS are specialized culture flasks that provide countless advantages during the commercial micropropagation of plants.


Asunto(s)
Aclimatación , Inmersión , Reproducción , Tecnología
5.
Methods Mol Biol ; 2759: 247-249, 2024.
Artículo en Inglés | MEDLINE | ID: mdl-38285155

RESUMEN

In vitro propagation protocols that include temporary immersion systems are available for the most economically important plant species. However, these have not been established yet for multiple species. Having protocols validated by the scientific community guarantees the success of the mass production of commercial propagules. Besides, adequate TIS parameters should be established for each plant species to improve the efficiency of micropropagation processes. This book compiles basic and applied aspects of temporal immersion systems used for in vitro plant micropropagation, along with several detailed protocols already established, which may be used as a guide by those interested in this technique, including laboratory technicians, scientists, and other professionals.


Asunto(s)
Personal de Laboratorio , Médicos , Humanos , Inmersión
6.
Methods Mol Biol ; 2759: 9-24, 2024.
Artículo en Inglés | MEDLINE | ID: mdl-38285135

RESUMEN

Technological innovation in the design and manufacture of temporary immersion systems (TIS) has increased in the past decade. Innovations have involved the size, fitting, and replacement of components, as well as manufacturing materials. Air replacement by compressor has also been substituted by air replacement by preset tilting/rotation of culture bottles. This design modification aims to increase the biological yield (number of shoots) produced in these bottles and reduce manufacturing costs. However, the operative principle has remained unchanged through time: promote an environment where explant immersions in the culture medium are programmable. The changes in the TIS design involve advantages and disadvantages, generating the efficiency of one type over another. However, validation to identify the most effective type of TIS should be carried out for each plant species. This chapter lists the different types of temporary immersion available on the market, emphasizing the advantages and disadvantages of each when used for plant micropropagation.


Asunto(s)
Comercio , Inmersión , Medios de Cultivo , Rotación
7.
Plants (Basel) ; 11(13)2022 Jun 21.
Artículo en Inglés | MEDLINE | ID: mdl-35807581

RESUMEN

Vanilla planifolia Jacks. ex Andrews is the vanilla species with the most commercial and greatest economic importance. It has been used as a case study in different cryopreservation studies that involve three vitrification-based approaches: droplet-vitrification (D-V), V-cryoplate (V-Cp) and D-cryoplate (D-Cp). The aim of this study was to compare the impact of these cryogenic techniques on vegetative growth (survival, stem length and leaf number) between cryo-derived plants and in vitro-derived controls during 12 months of greenhouse growth. Genetic stability was also assessed using the inter-simple sequence repeat (ISSR) markers. There were no significant differences found in the survival and stem lengths of the in vitro-derived regenerants and cryo-derived plants. A significant increase in the number of leaves was only detected in cryo-derived plants when using the V-Cp method. The electrophoretic profiles, based on seven ISSR primers, detected low variability: 81 total bands and 27% polymorphism. This is the first report on the assessment of vegetative growth and genetic integrity in cryo-derived V. planifolia plants recovered under greenhouse conditions. Of the three cryogenic approaches, D-Cp appears to yield V. planifolia regenerants plants with more vigorous vegetative growth and a lower level of polymorphism. Future research should focus on the reproductive growth of vanilla regenerants.

8.
Methods Mol Biol ; 2527: 183-201, 2022.
Artículo en Inglés | MEDLINE | ID: mdl-35951192

RESUMEN

The thin cell layer (TCL) culture system was initially reported in relation to the model plant Nicotiana tabacum, giving rise to 47 years of continuous application and investigation on micropropagation and plant breeding of over 100 plant species or hybrids. The small sizes of the tissue sections (100 µm to 1-2 mm in thickness), its classification into transverse TCL (tTCL) or longitudinal TCL (lTCL) categories, and the interaction between the cultured cells and the culture medium are the main drivers of its efficacy in tens of plants for the induction of somatic embryogenesis, relative to the conventional in-vitro culture system. Furthermore, it promotes higher productivity and reduced time in the proliferation of cultures, which is key for the differentiation of cells and plant tissues. This chapter describes the main characteristics of the TCL sections, and the interaction between cells under in-vitro culture. In addition, it highlights the latest findings reporting the success of TCL in ornamental, herbaceous, woody, and recalcitrant plants. In most cases, studies on the use of TCL in combination with techniques such as bioreactors, histology, genetic transformation, and fidelity analysis, provide indisputable evidence that highlights the importance of this technique in plant biotechnology. Finally, the perspectives on TCL use are described, underlining the advantages and constraints of the technique for its continued use and future application.


Asunto(s)
Desarrollo Embrionario , Fitomejoramiento , Medios de Cultivo , Técnicas de Embriogénesis Somática de Plantas/métodos , Plantas , Nicotiana/genética
9.
Sci Rep ; 12(1): 18654, 2022 11 04.
Artículo en Inglés | MEDLINE | ID: mdl-36333416

RESUMEN

In this work, it is proposed the development a new monopole directional antenna, bioinspired in elliptical leaf, with cut by golden ratio, for 4G band application, by the use of the technique of the cut of the radiating element for the increasing of the antenna perimeter, being the first work to use this technique in a bioinspired antenna, promotes resonance frequency turned, and reconfiguring of the antenna parameters as bandwidth, radiation pattern and gain, with the use of the reflector near to the group plane, without the insertion of active devices as the pin diode or change in radiating element. The shape antenna is generated by Gielis formula, built in FR4 substrate, with cuts calculated by golden ratio. To compare the results of the bioinspired monopole on the elliptical sheet, a square-shaped monopole antenna was designed, simulated and measured, the structures were designed in the MATLAB software version 2015(b) and the simulations were performed in the Ansys software version 2016. In the results compared between the square monopole and the bioinspired antenna in the elliptical sheet, it can be seen that the measured bioinspired antenna, compared to the square monopole, presented a bandwidth reduction of 77.27%, a more compact structure, with a reduction of 98%, covering the wireless local area network, and long-time evolution 4G at 2.5 GHz. The proposed technique uses a reflector on the ground plane, to change the parameters of the monopole planar antenna, of omnidirectional radiation pattern to a directional, maintaining the characteristics of the broadband, half-power beamwidth great than 100°, with high current density, and similar gain of a directional antenna. From the results, it has been observed that the elliptical leaf monopole antenna shows broadband characteristics, with a half-power beamwidth of 128°, wideband, the bandwidth of 500 MHz, a gain of 6.28 dBi, a current density of 13.01 A/m2, and circular polarization.


Asunto(s)
Procedimientos de Cirugía Plástica , Tecnología Inalámbrica , Diseño de Equipo , Refracción Ocular , Hojas de la Planta
10.
Biomimetics (Basel) ; 6(1)2021 Jan 04.
Artículo en Inglés | MEDLINE | ID: mdl-33406738

RESUMEN

Different Ag@TiO2 and Ag@ZnO catalysts, with nanowire (NW) structure, were synthesized containing different amounts of silver loading (1, 3, 5, and 10 wt.%) and characterized by FE-SEM, HRTEM, BET, XRD, Raman, XPS, and UV-vis. The photocatalytic activity of the composites was studied by the production of hydrogen via water splitting under UV-vis light and the degradation of the antibiotic ciprofloxacin. The maximum hydrogen production of all the silver-based catalysts was obtained with a silver loading of 10 wt.% under irradiation at 500 nm. Moreover, 10%Ag@TiO2 NWs was the catalyst with the highest activity in the hydrogen production reaction (1119 µmol/hg), being 18 times greater than the amount obtained with the pristine TiO2 NW catalyst. The most dramatic difference in hydrogen production was obtained with 10%Ag@TiO2-P25, 635 µmol/hg, being 36 times greater than the amount reported for the unmodified TiO2-P25 (18 µmol/hg). The enhancement of the catalytic activity is attributed to a synergism between the silver nanoparticles incorporated and the high surface area of the composites. In the case of the degradation of ciprofloxacin, all the silver-based catalysts degraded more than 70% of the antibiotic in 60 min. The catalyst that exhibited the best result was 3%Ag@ZnO commercial, with 99.72% of degradation. The control experiments and stability tests showed that photocatalysis was the route of degradation and the selected silver-based catalysts were stable after seven cycles, with less than 1% loss of efficiency per cycle. These results suggest that the catalysts could be employed in additional cycles without the need to be resynthesized, thus reducing remediation costs.

11.
Cladistics ; 26(3): 227-261, 2010 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-34875782

RESUMEN

The leaf or monkey frogs of the hylid subfamily Phyllomedusinae are a unique group of charismatic anurans. We present a molecular phylogenetic analysis that includes 45 of the 60 species of phyllomedusines using up to 12 genes and intervening tRNAs. The aims were to gain a better understanding of the phylogenetic position of Phrynomedusa, test the monophyly and explore the relationships among several putative lineages (Hylomantis, the H. buckleyi Group, Phasmahyla, the four species groups of Phyllomedusa, and the species of Phyllomedusa that remain unassigned to any group), and to examine the implications of our phylogeny for the evolution of several characters in phyllomedusines. The analyses resulted in a well-supported phylogenetic hypothesis that provides a historical framework for a discussion of the evolution of characters associated with reproductive biology, gliding behaviour, the physiology of waterproofing, and bioactive peptides. Implications include an earlier origin for eggless capsules than for leaf-folding behaviour during amplexus, two independent origins of gliding, and an earlier origin of reduction in evaporative water loss than uricotelism, which is a result that originally was predicted on the basis of physiology alone. Furthermore, our results support the prediction that bioactive peptides from different peptide families are to be expected in all species of Phyllomedusinae. Hylomantis (as recently redefined) is shown to be paraphyletic and the synonymy of Agalychnis is revised to remedy this problem by including both Hylomantis and Pachymedusa. © The Willi Hennig Society 2009.

12.
J Adv Model Earth Syst ; 12(8): e2019MS002025, 2020 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-32999704

RESUMEN

This paper describes the GISS-E2.1 contribution to the Coupled Model Intercomparison Project, Phase 6 (CMIP6). This model version differs from the predecessor model (GISS-E2) chiefly due to parameterization improvements to the atmospheric and ocean model components, while keeping atmospheric resolution the same. Model skill when compared to modern era climatologies is significantly higher than in previous versions. Additionally, updates in forcings have a material impact on the results. In particular, there have been specific improvements in representations of modes of variability (such as the Madden-Julian Oscillation and other modes in the Pacific) and significant improvements in the simulation of the climate of the Southern Oceans, including sea ice. The effective climate sensitivity to 2 × CO2 is slightly higher than previously at 2.7-3.1°C (depending on version) and is a result of lower CO2 radiative forcing and stronger positive feedbacks.

13.
3 Biotech ; 9(8): 307, 2019 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-31355116

RESUMEN

Anthurium has been micropropagated mainly through conventional techniques in semisolid culture medium. However, this culture system involves constraints due to the low number of shoots produced and the high costs of the gelling agent and labor. Temporary immersion systems (TIS) are an alternative for increasing biological performance, reducing costs, and facilitating a semi-automated micropropagation process. The objective of this study was to compare the efficiency of different types of TIS during the in vitro propagation of anthurium. We used 2-cm-long nodal segments from in vitro plants. Explants were cultured in different TIS: temporary immersion bioreactors (TIB®), Ebb-and-Flow bioreactor, and recipient for automated temporary immersion (RITA®), with a 2-min immersion frequency at 12-h intervals. We used Murashige and Skoog (MS) medium supplemented with 3% (w/v) of sucrose and 8.88 µM benzylaminopurine. After 60 days of culture, we evaluated various physiological variables and the percent survival in the different TIS. The largest numbers of shoots per explant were observed in TIB® and Ebb-and-Flow, with 50.83 and 43.16 shoots per explant, respectively; the lowest number of shoots per explant was observed in RITA®, with 30.66. TIB® yielded the highest content of photosynthetic pigments (chlorophyll a, b, and total chlorophyll), stomatal index, and percentage of closed stomata relative to both Ebb-and-Flow and RITA®. The TIB® and RITA® systems showed a 99% shoot survival, while Ebb-and-Flow yielded 86% survival. In conclusion, TIS design and type affect a number of physiological processes and in vitro development, with TIB® as a feasible option for the commercial micropropagation of anthurium.

14.
PeerJ ; 5: e3005, 2017.
Artículo en Inglés | MEDLINE | ID: mdl-28243531

RESUMEN

Three new cryptic species of Chiasmocleis from the Atlantic Forest of Brazil are described. Two of these species occur in the northeastern states of Sergipe and Bahia, whereas the third species is found in the southeastern state of São Paulo. The new species can be distinguished from other congeneric species by the molecular data, as evidenced in the phylogeny, and by a combination of morphological characters including: size, foot webbing, dermal spines, and coloration patterns. Chiasmocleis species differ in osteological traits, therefore we also provide an osteological description of each new species and comparsions with data reported for other species in the genus.

15.
Zookeys ; (642): 115-130, 2017.
Artículo en Inglés | MEDLINE | ID: mdl-28138301

RESUMEN

The genus Aplastodiscus includes 14 nominal species in four monophyletic groups with occurrence in the Atlantic Forest and Brazilian Cerrado (Brazilian Savanna) of South America. A recent study reviewed the taxonomy and phylogenetic relationships of the genus and suggested a third species for the Aplastodiscus perviridis Group. Herein, on the basis of morphology and advertisement call, we describe this species and test its monophyly. The new species is the only Aplastodiscus with endemic occurrence in the Cerrado Biome. In addition, its geographical distribution and conservation status are discussed.

16.
Rev. argent. cir ; 112(4): 517-525, dic. 2020. tab
Artículo en Español | BINACIS, LILACS | ID: biblio-1288164

RESUMEN

RESUMEN Antecedentes: La apendicitis aguda (AA) es una de las principales patologías quirúrgicas en México y el mundo. A pesar de ser una patología frecuente, el manejo quirúrgico presenta una tasa del 10-20% de apendicitis blancas (AB) o hiperplasia folicular linfoide (HPL) por histopatología. Objetivo: Comparar los hallazgos clínicos, de laboratorio y radiológicos de pacientes con sospecha de AA con su diagnóstico por histopatología. Material y métodos: El estudio es retrospectivo, observacional y transversal. Se analizaron los datos de los pacientes con diagnóstico clínico de apendicitis aguda, desde febrero de 2013 hasta diciembre de 2017, atendidos en un hospital de tercer nivel en Monterrey, México. Se compararon los hallazgos de los pacientes con diagnóstico de AA vs. HPL, AA no complicadas vs. AA complicadas y pacientes pediátricos vs. adultos. Se realizó un análisis descriptivo por medio de frecuencias y porcentajes, y mediana y rango intercuartil (RIC), dada la distribución no paramétrica de estas variables. Se compararon los hallazgos por laboratorio mediante la prueba de Mann-Whitney. Se consideró una p< 0,05 como estadísticamente significativa. Resultados: En nuestro medio, ambos sexos tienen la misma frecuencia de presentación de AA. El tiempo de evolución es significativo en la presentación frecuente de AA complicada. Existe asociación entre leucocitosis, neutrofilia total y porcentual y recuento plaquetario mayor en presencia de AA vs. HPL. Conclusión: Los estudios de laboratorio no muestran cambios significativos en pacientes pediátricos con AA. En adultos con AA no complicada vs. apendicitis complicada, el aumento en WBC, NEU y NEU% son estadísticamente significativos.


ABSTRACT Background: Acute appendicitis (AA) is one of the main surgical pathologies in our country and worldwide. Despite being a surgery that is frequently done, it is still reported a 10-20% of negative appendectomies (NA). Objective: The objective of the study is to compare clinical, laboratory and radiology results with the histopathology diagnosis. Material and methods: A retrospective study was done analyzing the data of patients with clinical diagnosis of AA from February 2013 to December 2017, in a tertiary hospital in Monterrey, Mexico. They were classified by their histopathological results into different groups: AA or NA; and the AA was subdivided into complicated AA and uncomplicated AA. Finally, these groups were also subdivided by ages, into pediatric and adult groups of each category. A descriptive analysis was made using frequencies, percentages, median and the interquartile range. Laboratory results were compared with the Mann-Whitney test. Considering a p-value of p < 0.05 as statistically significant. Results: In our group of patients both genders had AA in a similar frequency, the time between the appearance of symptoms and reaching for medical advice was an important factor for having complicated AA. There is a correlation between leukocytosis, neutrophil count and platelet count elevated in presence of AA against NA. Conclusion: Laboratory studies did not report significant changes in pediatric patients with AA. In adults with uncomplicated AA vs. complicated AA, white blood cell count, and neutrophil count are statistically significant.


Asunto(s)
Humanos , Masculino , Femenino , Niño , Adolescente , Adulto , Adulto Joven , Apendicectomía , Apendicitis/diagnóstico , Seudolinfoma/diagnóstico , Apendicitis/diagnóstico por imagen , Tomografía Computarizada por Rayos X , Estudios Transversales , Estudios Retrospectivos , Ultrasonografía , Técnicas de Laboratorio Clínico
17.
Rev. peru. med. integr ; 3(3): 112-117, 2018. tab
Artículo en Español | MTYCI, LILACS | ID: biblio-1145640

RESUMEN

Objetivo. Evaluar el efecto de extractos etanólicos de cinco especies del género Annona y cinco especies del género Piper frente a la línea clonal de referencia de promastigotes de Leishmania braziliensis. Materiales y métodos. Se evaluó el efecto de los extractos etanolicos de Annona hypoglauca, Annona montana, mucosa, Annona nítida, Annona squamosa, Piper acutifolium¸ Piper aduncum, Piper callosum, Piper carpunya y Piper peltatum; sobre cepas de promastigotes de Leishmania braziliensis MHON/ BR/79/M2904. El efecto leishmanicida in vitro se evaluó mediante el cálculo del IC50 por el método probit. Resultados. Las especies con mayor actividad fueron P. acutifolium (IC50=19,40 µg/mL) P. peltatum (IC50=26,6 µg/mL), P. callosum (IC50=21,7 µg/mL), A. mucosa (IC50=30,5 µg/mL) y A. montana (IC50=16,4 µg/mL). Conclusión. Los extractos etanólicos de P. acutifolium, P. peltatum, P. callosum, A. mucosa y A. montana, han mostrado una actividad leishmanicida in vitro. Sin embargo, estos efectos no son superiores a los exhibidos por Anfotericina B.


Objective. To evaluate the effect of ethanolic extracts of five species of genus Annona and five species of genus Piper against a clonal line of reference of Leishmania braziliensis promastigotes. Materials and methods. The ethanolic extracts of Annona hypoglauca, Annona montana, mucosa, Annona nítida, Annona squamosa, Piper acutifolium¸ Piper aduncum, Piper callosum, Piper carpunya and Piper peltatum were evaluated against strains of Leishmania braziliensis promastigotes (MHON/BR/79/ M2904). The in vitro leishmanicidal effect was evaluated through the IC50, which was calculated by the probit method. Results. The species with the highest activity were P. acutifolium (IC50=19,40 µg/ mL) P. peltatum (IC50=26,6 µg/mL), P. callosum (IC50=21,7 µg/mL), A. mucosa (IC50=30,5 µg/mL) and A. montana (IC50=16,4 µg/mL). Conclusion. The ethanolic extracts of P. acutifolium, P. peltatum, P. callosum, A. mucosa and A. montana, had shown some in vitro leishmanicidal activity. However, these effects are not superior to those exhibited by Amphotericin B.


Asunto(s)
Annona , Piper , Leishmania , Perú , Plantas Medicinales , Técnicas In Vitro , Extractos Vegetales , Medicina Tradicional
18.
Dalton Trans ; 41(26): 8175-89, 2012 Jul 14.
Artículo en Inglés | MEDLINE | ID: mdl-22565647

RESUMEN

A rigid NSN-donor proligand, 4,5-bis(2,6-diisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylthioxanthene (H(2)[TXA(2)], 1) was prepared by palladium-catalyzed coupling of 2,6-diisopropylaniline with 4,5-dibromo-2,7-di-tert-butyl-9,9-dimethylthioxanthene. Deprotonation of 1 using (n)BuLi provided Li(2)(DME)(2)[TXA(2)] (2), and subsequent reaction with UCl(4) afforded [Li(DME)(3)][(TXA(2))UCl(3)] (4). The analogous NON-donor ligated complex [(XA(2))UCl(3)K(DME)(3)] [3; XA(2) = 4,5-bis(2,6-diisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylxanthene] was prepared by the reaction of K(2)(DME)(x)[XA(2)] with UCl(4). A cyclic voltammogram (CV) of 3 in THF/[NBu(4)][B(C(6)F(5))(4)] at 200 mV s(-1) showed an irreversible reduction to uranium(III) at E(pc) = -2.46 V versus FeCp(2)(0/+1), followed by a product wave at E(1/2) = -1.83 V. Complex 4 also underwent irreversible reduction to uranium(iii) [E(pc) = -2.56 V], resulting in an irreversible product peak at E(pa) = -1.83 V. One-electron reduction of complexes 3 and 4 using K(naphthalenide) under an argon atmosphere in DME yielded 6-coordinate [(XA(2))UCl(DME)] (5) and the thermally unstable 7-coordinate [(TXA(2))U(DME)Cl(2)Li(DME)(2)] (6), respectively. The U-S distances in 4 and 6 are uncommonly short, the C-S-U angles are unusually acute, and the thioxanthene backbone of the TXA(2) ligand is significantly bent. By contrast, the xanthene backbone in XA(2) complexes 3 and 5 is planar. However, κ(3)-coordination and an approximately meridional arrangement of the ancillary ligand donor atoms is maintained in all complexes. DFT and Atoms in Molecules (AIM) calculations were carried out on 3, 4, 5, 6, [(XA(2))UCl(3)](-) (3B), [(TXA(2))UCl(2)(DME)](-) (6B) and [(TXA(2))UCl(DME)] (6C) to probe the extent of covalency in U-SAr(2) bonding relative to U-OAr(2) bonding.

19.
Dalton Trans ; 39(29): 6626-8, 2010 Aug 07.
Artículo en Inglés | MEDLINE | ID: mdl-20631945

RESUMEN

Methyl and n-butyl thorium complexes of a rigid 2,6-bis(anilidomethyl)pyridine ligand have been prepared; the n-butyl complex is thermally stable, even at 60 degrees C, while the methyl complexes exhibit a high tendency to eliminate methane via sigma-bond metathesis.

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