Browsing by Type "Journal"
  • Publication
    1T-Phase Tungsten Chalcogenides (WS2, WSe2, WTe2) Decorated with TiO2 Nanoplatelets with Enhanced Electron Transfer Activity for Biosensing Applications
    ( 2018-12-28)
    Rahmanian E.
    ;
    Mayorga-Martinez C.
    ;
    Malekfar R.
    ;
    Luxa J.
    ;
    Sofer Z.
    ;
    Pumera M.
    Layered transition metal dichalcogenides (TMDs) have received a great deal of attention due to fact that they have varied band gap, depending on their metal/chalcogen composition and on the crystal structure. Furthermore, these materials demonstrate great potential application in a myriad of electrochemical technologies. Heterogeneous electron transfer (HET) abilities of TMD materials toward redox-active molecules occupy a key role in their suitability for electrochemical devices. Herein, we introduce a promising biosensing strategy based on improved heterogeneous electron transfer rate of WS2, WSe2, and WTe2 nanosheets exfoliated using tert-butyllithium (t-BuLi) and n-butyllithium (n-BuLi) intercalators decorated with vertically aligned TiO2 nanoplatelets. By comparison of all the nanohybrids, decoration of TiO2 on t-BuLi WS2 (TiO2@t-BuLi WS2) results in the fastest HET rate of 5.39 × 10-3 cm s-1 toward ferri/ferrocyanide redox couple. In addition, the implications of decorating tungsten dichalcogenides (WX2) with TiO2 nanoplatelets in enzymatic biosensor applications for H2O2 detection are explored. TiO2@t-BuLi WS2 outperforms all other nanohybrid counterparts and is demonstrated to be an outstanding sensing platform in enzyme-based biosensor with wide linear range, low detection limit, and high selectivity. Such conceptually new electrocatalytic detection systems shall find the way to the next generation biosensors. ©
  • Publication
    A fortuitous ant-fern association in the Amazon lowlands of Peru
    ( 2010-08-01)
    León B.
    ;
    Young K.R.
    Myrmecophyly is best documented among tropical epiphytes, and myrmecotrophy occurs especially among domatia-forming plants. We report the case of Polytaenium cajenense with “external” domatia and its use by the same symbiont ant as its host Cordia nodosa. This case is interpreted as the result of stochastic events and their relations to pre-existing adaptations of all species involved.
  • Publication
    A global atmospheric electricity monitoring network for climate and geophysical research
    ( 2019-03-01)
    Nicoll K.A.
    ;
    Harrison R.G.
    ;
    Barta V.
    ;
    Bor J.
    ;
    Brugge R.
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    Chillingarian A.
    ;
    Chum J.
    ;
    Georgoulias A.K.
    ;
    Guha A.
    ;
    Kourtidis K.
    ;
    Kubicki M.
    ;
    Mareev E.
    ;
    Matthews J.
    ;
    Mkrtchyan H.
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    Odzimek A.
    ;
    Raulin J.P.
    ;
    Robert D.
    ;
    Silva H.G.
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    Tacza J.
    ;
    Yair Y.
    ;
    Yaniv R.
    The Global atmospheric Electric Circuit (GEC) is a fundamental coupling network of the climate system connecting electrically disturbed weather regions with fair weather regions across the planet. The GEC sustains the fair weather electric field (or potential gradient, PG) which is present globally and can be measured routinely at the surface using durable instrumentation such as modern electric field mills, which are now widely deployed internationally. In contrast to lightning or magnetic fields, fair weather PG cannot be measured remotely. Despite the existence of many PG datasets (both contemporary and historical), few attempts have been made to coordinate and integrate these fragmented surface measurements within a global framework. Such a synthesis is important in order to fully study major influences on the GEC such as climate variations and space weather effects, as well as more local atmospheric electrical processes such as cloud electrification, lightning initiation, and dust and aerosol charging. The GloCAEM (Global Coordination of Atmospheric Electricity Measurements) project has brought together experts in atmospheric electricity to make the first steps towards an effective global network for atmospheric electricity monitoring, which will provide data in near real time. Data from all sites are available in identically-formatted files, at both 1 s and 1 min temporal resolution, along with meteorological data (wherever available) for ease of interpretation of electrical measurements. This work describes the details of the GloCAEM database and presents what is likely to be the largest single analysis of PG data performed from multiple datasets at geographically distinct locations. Analysis of the diurnal variation in PG from all 17 GloCAEM sites demonstrates that the majority of sites show two daily maxima, characteristic of local influences on the PG, such as the sunrise effect. Data analysis methods to minimise such effects are presented and recommendations provided on the most suitable GloCAEM sites for the study of various scientific phenomena. The use of the dataset for further understanding of the GEC is also demonstrated, in particular for more detailed characterization of day-to-day global circuit variability. Such coordinated effort enables deeper insight into PG phenomenology which goes beyond single-location PG measurements, providing a simple measurement of global thunderstorm variability on a day-to-day timescale. The creation of the GloCAEM database is likely to enable much more effective study of atmospheric electricity variables than has ever been possible before, which will improve our understanding of the role of atmospheric electricity in the complex processes underlying weather and climate.
  • Publication
    A microgrid energy management system based on chance-constrained stochastic optimization and big data analytics
    ( 2020-05-01)
    Marino C.A.
    ;
    Marufuzzaman M.
    A Microgrid (MG) is a promising distributed technology to solve todays energy challenges. They are changing how electricity is produced, transmitted, and distributed, enabling to capture massive amounts of data from sensors, and other electrical infrastructures. However, recent advances in modeling and optimization of MG neither integrate the use of big data technologies aggressively nor focus on developing an optimal operational strategy for a single building. To bridge this gap, this research proposes to use Apache Spark to enhance the performance of a scalable stochastic optimization model for an MG for multiple buildings, and to ensure that a significant portion of the wind power output will be utilized. The decision model is formulated as a chance constraint two-stage optimization problem to obtain operation decisions for a behind-the-meter topology. The comparison between the current practice of using historical data and integrating Apache Spark technologies demonstrates the superiority of the streaming data as energy management strategy. Experiments under different settings show that using big data strategy, the model can (1) achieve more cost savings of the total system, (2) increase resiliency to power disturbances, and (3) build a data analytics framework to enhance the decision-making process.
  • Publication
    A new locality, range extension and record of Batrachochytrium dendrobatidis in the endangered terrestrial breeding frog Pristimantis katoptroides Flores, 1988 (Anura: Craugastoridae) in Peru
    ( 2015-01-01)
    Cusi J.C.
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    Barboza A.C.
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    Vredenburg V.
    ;
    Von May R.
    We provide a new record of the poorly known and endangered Pristimantis katoptroides from the Cordillera Central in Peru, based on a specimen collected in the Alto Mayo Protected Forest, San Martin Department. We provide notes on the morphology and coloration of the species and two other specimens previously collected in Peru, as well as photographs and an updated map indicating the known localities of P. katoptroides. This record represents an extension of 210 km in the southern limit of the geographic range. Additionally, we report the presence of the chytrid fungus in this species.
  • Publication
    A new species of Thomasomys (Muridae: Sigmodontinae) from the Andes of southeastern Peru
    ( 2002-08-01)
    Luna L.
    ;
    PACHECO TORRES, VICTOR RAUL
    We describe a new species of Thomasomys from the Vilcabamba Cordillera, Cuzco, Peru. This thomasomyine is a medium-sized, small-eared, and long-tailed rodent similar in external and cranial features to Thomasomys silvestris, a species from the western Andean slopes of Ecuador. The new species presents a unique combination of characters that includes the absence of genal vibrissae, absence of a "gap" between the hypothenar and thenar pads, short incisive foramina, and a primitive pattern of carotid circulation. The proposed new species is known only from the type locality, suggesting that its restricted distribution could be attributed to the existence of a relict fauna in the area.
  • Publication
    A Note on the Relation Between the Metric Entropy and the Generalized Fractal Dimensions of Invariant Measures
    ( 2022-06-01)
    Condori A.
    ;
    Carvalho S.L.
    We investigate in this work some situations where it is possible to estimate or determine the upper and the lower q-generalized fractal dimensions Dμ±(q), q∈ R, of invariant measures associated with continuous transformations over compact metric spaces. In particular, we present an alternative proof of Young’s Theorem by Young (Ergod. Theory Dyn. Syst. 2(1):109–124, 1982) for the generalized fractal dimensions of the Bowen-Margulis measure associated with a C1+α-Axiom A system over a two-dimensional compact Riemannian manifold M. We also present estimates for the generalized fractal dimensions of an ergodic measure for which Brin-Katok’s Theorem is pointwise satisfied, in terms of its metric entropy. Furthermore, for expansive homeomorphisms (like C1-Axiom A systems), we show that the set of invariant measures such that Dμ+(q)=0 (q≥ 1), under a hyperbolic metric, is generic (taking into account the weak topology). We also show that for each s∈ [0 , 1) , Dμ+(s) is bounded above, up to a constant, by the topological entropy, also under a hyperbolic metric. Finally, we show that, for some dynamical systems, the metric entropy of an invariant measure is typically zero, settling a conjecture posed by Sigmund (Trans. Am. Math. Soc. 190:285–299, 1974) for Lipschitz transformations which satisfy the specification property.
  • Publication
    A pH optode based on thymol blue: Application to determination of co2 using flow injection analy sis system
    ( 2010-01-01)
    Sotomayor M.D.P.T.
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    Raimundo J.M.
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    Rohwedder J.J.R.
    ;
    Neto G.O.
    An optode based on thymol blue (TB), an acid-based indicator, has been constructed and evaluated as a detector in FIA system for CO2determination. The dye was chemically immobilised on the surface of a bifurcated glass optical fibre bundle, using silanisation in organic media. In FIA system, hydrogen carbonate or carbonate samples are injected in a buffer carrier solution, and then are mixed with phosphoric acid solution to generate CO2, which diffuses through a PTFE membrane, in order to be collected in an acceptor carrier fluid, pumped towards to detection cell, in which the optode was adapted. The proposed system presents two linear response ranges, from 1.0 x 10-3to 1.0 x 10-2mol l-1, and from 2.0 x 10-2to 0.10 mol l-1. The sampling frequency was 11 sample h-1, with good repeatability (R.S.D < 4 %, n = 10). In flow conditions the optode lifetime was 170 h. The system was applied in the analysis of commercial mineral water and the results obtained in the hydrogen carbonate determination did not differ significantly from those obtained by potentiometry, at a confidence level of 95 %.
  • Publication
    A prebiotic diet based on dandelion (Taraxacum officinale) improves the productive performance and intestinal morphology of laying hens
    ( 2021-09-01)
    Saenz F.M.C.
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    Saucedo-Uriarte J.A.
    ;
    Sotelo-Mendez A.
    ;
    Zamora-Huamán S.J.
    The inclusion of Dandelion meal [DL] (Taraxacum officinale) in the diet of laying hens and its effect on productive performance, intestinal morphology and dry matter content in feces was evaluated. Ninety-six 35-week-old brown Hisex hens were distributed in 6 treatments. Gradual levels of DM meal (1%, 2%, 3% and 4%) were compared with a diet based on the mixture of antibiotics (CAB; 0.03% Zinc bacitracin + 0.03% colistin sulfate) and another based of 0.20% sodium butyrate (CPB). DM and CPB improved egg production (p < 0.05) compared to CAB, but feed consumption and egg weight decreased with the use of 4% DM (p < 0.05), without affecting the feed conversion ratio (p > 0.05). In general, DM (1% - 4%) improved intestinal morphology parameters (p < 0.05). Higher quantity and content of dry matter in feces was observed in 4% DM compared to CAB. The incorporation of up to 3% DM improved the productive indexes on the feeding of laying hens and managed to have the best prebiotic effect, as it was evidenced in the intestinal morphology and goblet cells.
  • Publication
    A randomized double-blind study of caspofungin versus fluconazole for the treatment of esophageal candidiasis
    ( 2002-08-01)
    Villanueva A.
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    Gotuzzo E.
    ;
    Arathoon E.
    ;
    Noriega L.
    ;
    Kartsonis N.
    ;
    Lupinacci R.
    ;
    Smietana J.
    ;
    DiNubile M.
    ;
    Sable C.
    BACKGROUND: Candida esophagitis remains an important cause of morbidity in patients with advanced human immunodeficiency virus (HIV) infection. Fluconazole is widely regarded as the treatment of choice for this condition. METHODS: The efficacy and safety of caspofungin were compared with fluconazole in adult patients with Candida esophagitis in a double-blind randomized trial. Eligible patients had symptoms compatible with esophagitis, endoscopic demonstration of mucosal plaques, and microscopic demonstration of Candida from the esophageal lesions. Patients were randomly assigned to receive caspofungin (50 mg) or fluconazole (200 mg) intravenously once daily for 7 to 21 days. The primary endpoint was the combined response of symptom resolution and significant endoscopic improvement 5 to 7 days after discontinuation of treatment. Data were analyzed with a modified intention-to-treat analysis, which excluded 2 ineligible patients. RESULTS: Most patients (154/177; 87%) had HIV infection, with a median CD4 count of 30 cells/mm3. Candida albicans was the predominant isolate. Favorable response rates were achieved in 66 (81%) of the 81 patients in the caspofungin arm and in 80 (85%) of the 94 patients in the fluconazole arm (difference = -4%; 95% confidence interval: -15% to +8%). Symptoms had resolved in >50% of patients in both groups by the fifth day of treatment. No patient in the caspofungin group developed a serious drug-related adverse event; therapy was only discontinued in 1 patient (receiving fluconazole) due to a drug-related adverse experience. Four weeks after stopping study drug, symptoms had recurred in 18 (28%) of 64 patients given caspofungin and in 12 (17%) of 72 patients given fluconazole (P = 0.19). CONCLUSION: In this study, caspofungin appeared to be as efficacious and generally as well tolerated as fluconazole in patients with advanced HIV infection and documented Candida esophagitis. © 2002 by Excerpta Medica, Inc.
  • Publication
    A review on the controversial physiognomic classification of the Linhares Forest, northern Espírito Santo
    ( 2017-10-01)
    Saiter F.Z.
    ;
    Rolim S.G.
    ;
    Filho S.J.
    ;
    De Oliveira-Filho A.T.
    We present a review of the controversial points of view concerning the physiognomic classification of Linhares Forest, which is defined here as the forest over coastal tablelands that is found between the Rio Doce and the Rio Barra Seca, in the north of Espírito Santo. We compiled information about the seasonal climate of such region and analyzed the relationship of both the interannual variation and the seasonality of the rainfall with the ecological attributes of the forest. Our interpretations unveiled that the average monthly rainfall does not express the reality of the biologically dry periods year after year nor does it express the consequences on the vegetation physiognomy. We perceived that Linhares Forest may manifest itself as semideciduous or evergreen, depending on the drought severity within a given period. Thus, we propose that the flexibility of Linhares Forest leaf flush regime must be considered in its classification. We suggest a double classification for the forest: one as a seasonal semideciduous forest during annual or supra-annual periods that are characterized by pronounced water deficit and the other as a seasonal evergreen forest during annual or supra-annual periods with no significant water deficit.
  • Publication
    A risk characterization model of Salmonella Typhimurium in Irish fresh pork sausages
    ( 2012-03-01)
    Gonzales-Barron U.A.
    ;
    Redmond G.
    ;
    Butler F.
    A second-order simulation model was built to estimate the risk of Salmonella Typhimurium associated with the consumption of Irish fresh pork sausages. To select appropriate hazard characterization models, an initial appraisal of the current dose-response models was conducted. The cooking modality of grilling was associated with a higher mean risk of infection per serving (1.399×10 ?6; 95% CI: 7.54×10 ?7-2.65×10 ?6) than frying (6.246×10 ?7, 95% CI: 2.78×10 ?7-1.17×10 ?6). When the risk was extrapolated over the consumption in a year period, the mean risk of infection increased considerably to 8.541×10 ?5 with an expected number of infections and illnesses of 184.3 (95% CI: 26-664) and 17 (95% CI: 2-63), respectively. Results highlighted the importance of consumer education, as scenario analysis predicted that, for the current level of Salmonella in pork sausage, decreasing the product's cold storage by approximately 8h and cooking for an additional half minute can reduce the current risk level by ?50%. © 2010 Elsevier Ltd.
  • Publication
    A simple and efficient method for highquality total RNA isolation from oleaginous microalgae
    ( 2017-01-01)
    Castro J.C.
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    Rodríguez H.N.
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    Maddox J.D.
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    Jiu B.
    ;
    Petterman J.B.
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    Marapara J.L.
    ;
    Cobos M.
    Microalgae are a very diverse group of microorganisms with great potential for biotechnological applications. To best exploit these organisms is necessary to expand our knowledge at its molecular levels. To realize these studies, however, it is essential to have efficient and reproducible methods for total RNA isolation. The objective of this research was to develop a method for high-quality total RNA isolation from three oleaginous microalgae species promissories for biotechnological applications. Three strains Ankistrodesmus sp., Chlorella sp., and Scenedesmus sp. were cultured on CHU-10 medium. Then, were harvested by centrifugation and total RNA was isolated with three commercial kits, one previously published method, and our improved CTAB-LiCl method. Quality and quantity of total RNA isolated were assayed with standard spectrophotometric and electrophoretic techniques. The highest quality (A260/A280: 1.95-2.02, A260/A230: 1.12-1.84) and yield (16.40-93.63 μg/g fresh weight) of total RNA from the three microalgae strains were obtained with our improved CTAB-LiCl method. In addition, the time required to complete the isolation process and the cost were relatively lowest. In conclusion, the improved CTAB-LiCl method, in contrast to frequently used commercial kits, and a previously published method, is effective and reliable to produce total RNA of high quality and quantity that is suitable for cDNA synthesis and polymerase chain reaction.
  • Publication
    A study of some lyotropic cholesteric mesophases by circular and linear dichroism and by circular intensity differential scattering
    ( 1988-01-01)
    Spada G.P.
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    Gottarelli G.
    ;
    Samori B.
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    Bustamante C.J.
    ;
    Wells K.S.
    The handedness of lyotropic cholesterics formed by decylammonium chloride, ammonium chloride, water and chiral dopants was determined by circular and linear dichroism and, independently, by circular intensity differential scattering. From the study of the twisting power of a few dopants and from the magnetic orientation of cholesterics with long and short pitches, it is concluded that distortion of the micelles is likely to be determinant for the formation of the cholesteric phase. © 1988 Taylor & Francis Group, LLC.
  • Publication
    A survey of the clinicopathological and molecular characteristics of patients with suspected Lynch syndrome in Latin America
    ( 2017-09-05)
    Rossi B.M.
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    Palmero E.I.
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    López-Kostner F.
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    Sarroca C.
    ;
    Vaccaro C.A.
    ;
    Spirandelli F.
    ;
    Ashton-Prolla P.
    ;
    Rodriguez Y.
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    de Campos Reis Galvão H.
    ;
    Reis R.M.
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    Escremim de Paula A.
    ;
    Capochin Romagnolo L.G.
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    Alvarez K.
    ;
    Della Valle A.
    ;
    Neffa F.
    ;
    Kalfayan P.G.
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    Spirandelli E.
    ;
    Chialina S.
    ;
    Gutiérrez Angulo M.
    ;
    Castro-Mujica M.d.C.
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    Sanchez de Monte J.
    ;
    Quispe R.
    ;
    da Silva S.D.
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    Rossi N.T.
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    Barletta-Carrillo C.
    ;
    Revollo S.
    ;
    Taborga X.
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    Morillas L.L.
    ;
    Tubeuf H.
    ;
    Monteiro-Santos E.M.
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    Piñero T.A.
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    Dominguez-Barrera C.
    ;
    Wernhoff P.
    ;
    Martins A.
    ;
    Hovig E.
    ;
    Møller P.
    ;
    Dominguez-Valentin M.
    Background: Genetic counselling and testing for Lynch syndrome (LS) have recently been introduced in several Latin America countries. We aimed to characterize the clinical, molecular and mismatch repair (MMR) variants spectrum of patients with suspected LS in Latin America. Methods: Eleven LS hereditary cancer registries and 34 published LS databases were used to identify unrelated families that fulfilled the Amsterdam II (AMSII) criteria and/or the Bethesda guidelines or suggestive of a dominant colorectal (CRC) inheritance syndrome. Results: We performed a thorough investigation of 15 countries and identified 6 countries where germline genetic testing for LS is available and 3 countries where tumor testing is used in the LS diagnosis. The spectrum of pathogenic MMR variants included MLH1 up to 54%, MSH2 up to 43%, MSH6 up to 10%, PMS2 up to 3% and EPCAM up to 0.8%. The Latin America MMR spectrum is broad with a total of 220 different variants which 80% were private and 20% were recurrent. Frequent regions included exons 11 of MLH1 (15%), exon 3 and 7 of MSH2 (17 and 15%, respectively), exon 4 of MSH6 (65%), exons 11 and 13 of PMS2 (31% and 23%, respectively). Sixteen international founder variants in MLH1, MSH2 and MSH6 were identified and 41 (19%) variants have not previously been reported, thus representing novel genetic variants in the MMR genes. The AMSII criteria was the most used clinical criteria to identify pathogenic MMR carriers although microsatellite instability, immunohistochemistry and family history are still the primary methods in several countries where no genetic testing for LS is available yet. Conclusion: The Latin America LS pathogenic MMR variants spectrum included new variants, frequently altered genetic regions and potential founder effects, emphasizing the relevance implementing Lynch syndrome genetic testing and counseling in all of Latin America countries.
  • Publication
    A tobacco asparagine synthetase gene responds to carbon and nitrogen status and its root expression is affected under boron stress
    ( 2010-03-01)
    Beato V.
    ;
    REXACH BENAVIDES , JESÚS
    ;
    Navarro-Gochicoa M.
    ;
    Camacho-Cristóbal J.
    ;
    Herrera-Rodríguez M.
    ;
    Maldonado J.
    ;
    González-Fontes A.
    To date, one asparagine synthetase (AS) mRNA has been identified in Nicotiana tabacum. Our results point out that this gene encodes an actual AS protein. This proposal is supported by the following facts. (i) Blast analysis indicates that tobacco AS gene shows increased percent identity with several AS genes of different plant species. (ii) Leaf and root AS mRNA levels were inversely correlated with soluble carbohydrate concentrations, both in the presence of light and in darkness, and the addition of exogenous sucrose repressed the root AS gene expression. (iii) In light, a positive correlation between AS transcript levels and ammonium content was observed in both leaves and roots. (iv) A direct correlation between leaf AS gene expression and asparagine (Asn) concentration has been found. Furthermore, quantitative real-time PCR analyses showed that this gene expression was increased under boron (B) deficiency in roots, but not in leaves. Interestingly, soluble B concentration in roots of plants subjected to B deficiency was significantly lower than that of control plants. However, in leaves, there was no significant difference in soluble B content between both B treatments. We discuss the possible role of soluble B deficiency in the regulation of AS gene expression in tobacco roots. © 2010 Elsevier Ireland Ltd. All rights reserved.
  • Publication
    A top-down analysis of Xa- and Xi-territories reveals differences of higher order structure at ≥20 Mb genomic length scales
    ( 2011-01-01)
    Teller K.
    ;
    Illner D.
    ;
    Thamm S.
    ;
    Casas-Delucchi C.S.
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    Versteeg R.
    ;
    Indemans M.
    ;
    Cremer T.
    ;
    Cremer M.
    The active and inactive X (Xa;Xi) territory with its seemingly highly compacted Barr body in nuclei of female mammalian cells provide a key example for studies of structure/function relationships in homologous chromosomes with different functional properties. Here we used about 300 human X-specific large insert clones to generate probe sets, which target physically or functionally defined sub-chromosomal segments. We combined 3D multicolor FISH with quantitative 3D image analysis in order to compare the higher order organization in Xi-and Xa-territories in human diploid fibroblasts (HDFs) at various length scales ranging from about 50 Mb down to 1 Mb. Xi-territories were characterized by a rounder shape as compared to the flatter and more extended shape of Xa-territories. The overall compaction of the entire Xi-territory, including the Barr body, was only 1.2-fold higher than the Xa-territory. Significant differences, however, were noted between distinct subchromosomal segments: At 20 Mb length scales higher compaction in Xi-territories was restricted to specific segments, but higher compaction in these segments was not correlated with gene density, transcriptional activity, LINE content or histone markers locally enriched in Xi-territories. Notably, higher compaction in Xi-territories observed for 20 Mb segments was not reflected accordingly by inclosed segments of 1-4 Mb. We conclude that compaction differences result mainly from a regrouping of ~1 Mb chromatin domains rather than from an increased condensation of individual domains. In contrast to a previous report, genes subject to inactivation as well as escaping from inactivation were not excluded from the interior of the Barr body. © 2011 Landes Bioscience.
  • Publication
    Ab initio static and molecular dynamics study of 4-styrylpyridine
    ( 2007-06-25)
    Lawson Daku L.M.
    ;
    Linares J.
    ;
    Boillot M.L.
    We report an in-depth theoretical study of 4-styrylpyridine in its singlet S0 ground state. The geometries and the relative stabilities of the trans and cis isomers were investigated within density functional theory (DFT) as well as within Hartree-Fock (HF), second-order Møller-Plesset (MP2), and coupled cluster (CC) theories. The DFT calculations were performed using the B3LYP and PBE functionals, with basis sets of different qualities, and gave results that are very consistent with each other. The molecular structure is thus predicted to be planar at the energy minimum, which is associated with the trans conformation, and to become markedly twisted at the minimum of higher energy, which is associated with the cis conformation. The results of the calculations performed with the post-HF methods approach those obtained with the DFT methods, provided that the level of treatment of the electronic correlation is high enough and that sufficiently flexible basis sets are used. Calculations carried out within DFT also allowed the determination of the geometry and the energy of the molecule at the biradicaloid transition state associated with the thermal cis=trans isomerization and at the transition states associated with the enantiomerization of the cis isomer and with the rotations of the pyridinyl and phenyl groups in the trans and cis isomers. Car-Parrinello molecular dynamics simulations were also performed at 50, 150, and 300K using the PBE functional. The studies allowed us to evidence the highly flexible nature of the molecule in both conformations. In particular, the trans isomer was found to exist mainly in a nonplanar form at finite temperatures, while the rotation of the pyridinyl ring in the cis isomer was incidentally observed to take place within ≈ 1 ps during the simulation carried out at 150K on this isomer. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.
  • Publication
    Ab initio study of the lowest energy conformera and IR spectra of poly(amidoamine)-G0 dendrimers
    ( 2004-10-14)
    Tarazona-Vasquez F.
    ;
    Balbuena P.B.
    A systematic sequential procedure is implemented to find local minimum conformers corresponding to the lowest generation (G0), -NH 2- and -OH-tenninated, poly(amidoamine) (PAMAM) dendrimers, and their IR vibrational spectra using ab initio (Hartree-Fock and density functional theory) techniques. It is found that the most stable conformations of PAMAM-G0 dendrimers in the gas phase have all their secondary amide groups in the trans conformation. Interbranch interactions including intramolecular H-bonds play a definite role in providing structural stability. The calculated electronic density spatial distribution reveals the existence of three regions where appropriate environments would attract either an ion or a metal atom: the core, the amide, and the terminal group (NH 2 or OH) sites. A detailed analysis of the IR spectra for the lowest energy conformers of PAMAMPolym-NH 2: and PAMAM-OH is thoroughly analyzed and compared with experimental data when available.
  • Publication
    Abdominal Tuberculosis in children and adolescents. A diagnostic challenge
    ( 2015-10-01)
    Reto Valiente L.
    ;
    Pichilingue Reto C.
    ;
    Pichilingue Prieto O.
    ;
    Dolores Cerna K.
    OBJECTIVE: To present our experience with abdominal tuberculosis in children and adolescents treated in our hospital from 2003 - 2014.