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1.
Comput Methods Biomech Biomed Engin ; 26(9): 1008-1017, 2023 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-35862582

RESUMO

The classification of sEMG signals is fundamental in applications that use mechanical prostheses, making it necessary to work with generalist databases that improve the accuracy of those classifications. Therefore, synthetic signal generation can be beneficial in enriching a database to make it more generalist. This work proposes using a variant of generative adversarial networks to produce synthetic biosignals of sEMG. A convolutional neural network (CNN) was used to classify the movements. The results showed good performance with an increase of 4.07% in a set of movement classification accuracy when 200 synthetic samples were included for each movement. We compared our results to other methodologies, such as Magnitude Warping and Scaling. Both methodologies did not have the same performance in the classification.


Assuntos
Membros Artificiais , Redes Neurais de Computação , Eletromiografia/métodos , Movimento
2.
Entropy (Basel) ; 24(11)2022 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-36421519

RESUMO

An exact solution of the Ising model on the simple cubic lattice is one of the long-standing open problems in rigorous statistical mechanics. Indeed, it is generally believed that settling it would constitute a methodological breakthrough, fomenting great prospects for further application, similarly to what happened when Lars Onsager solved the two-dimensional model eighty years ago. Hence, there have been many attempts to find analytic expressions for the exact partition function Z, but all such attempts have failed due to unavoidable conceptual or mathematical obstructions. Given the importance of this simple yet paradigmatic model, here we set out clear-cut criteria for any claimed exact expression for Z to be minimally plausible. Specifically, we present six necessary-but not sufficient-conditions that Z must satisfy. These criteria will allow very quick plausibility checks of future claims. As illustrative examples, we discuss previous mistaken "solutions", unveiling their shortcomings.

3.
Pest Manag Sci ; 78(12): 5150-5163, 2022 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-36070208

RESUMO

BACKGROUND: Brazil is the largest grower of the world's 26 million ha of sugarcane, Saccharum officinarum. Pest damage mainly by the sugarcane borer, Diatraea saccharalis (F.), is a great challenge to the sugarcane industry. To control D. saccharalis, Brazil launched the world's first commercial use of Bt sugarcane in 2017. As part of the resistance management programs for Bt sugarcane planting, 535 F2 isoline families of D. saccharalis collected from three major sugarcane planting states (Goiás, Minas Gerais and São Paulo) in Brazil during 2019-2020 were screened for resistance to two Bt sugarcane varieties: CTC20BT expressing Cry1Ab and CTC9001BT expressing Cry1Ac. Here we report the results of the first study related to Bt resistance in a sugarcane cropping system. RESULTS: Larval survivorships of these families in an F2 screen on CTC20BT were highly correlated with their survival on CTC9001BT, whereas the Cry1Ac tissues exhibited greater insecticidal activities than Cry1Ab. Resistance allele frequencies (RAFs) for populations from Goiás and Minas Gerais were relatively low at 0.0034 for Cry1Ab and 0.0045 to Cry1Ac. By contrast, RAFs for São Paulo populations were considerably greater (0.0393 to Cry1Ab, 0.0245 to Cry1Ac). CONCLUSIONS: RAFs to Cry1Ab and Cry1Ac varied among Brazilian D. saccharalis populations. Prior selection resulting from an intensive use of single-gene Bt maize under low compliance of refuge planting could be a main factor contributing to the high RAF in São Paulo. The results suggest that mitigation measures including sufficient non-Bt maize refuge planting, effective resistance monitoring, and use of pyramided Bt sugarcane traits should be implemented promptly to prevent further increase in the RAF to ensure the sustainable use of Bt sugarcane in Brazil. MINI ABSTRACT: To control Diatraea saccharalis, Brazil launched the world's first commercial use of Bt sugarcane in 2017. As part of the resistance management programs for Bt sugarcane planting in Brazil, 535 F2 isoline families of D. saccharalis collected from three major sugarcane planting states (Goiás, Minas Gerais and São Paulo) in Brazil during 2019-2020 were screened for resistance to Cry1Ab and Cry1Ac sugarcane plants Resistance allele frequencies (RAFs) for the populations from Goiás and Minas Gerais were relatively low at 0.0034 for Cry1Ab and 0.0045 to Cry1Ac. By contrast, RAFs for the São Paulo populations were considerably greater (0.0393 to Cry1Ab, 0.0245 to Cry1Ac). Prior selection resulting from an intensive use of single-gene Bt maize under low compliance of non-Bt maize refuge planting could be a main factor contributing to the high RAF in São Paulo. The results suggest that effective mitigation measures including sufficient non-Bt maize refuge planting, effective resistance monitoring and use of pyramided Bt sugarcane traits should be implemented promptly to prevent further increase in the RAF to ensure the sustainable use of Bt sugarcane in Brazil. © 2022 Society of Chemical Industry.


Assuntos
Mariposas , Saccharum , Animais , Toxinas de Bacillus thuringiensis , Proteínas Hemolisinas/farmacologia , Endotoxinas/farmacologia , Brasil , Alelos , Proteínas de Bactérias/farmacologia , Zea mays/genética , Grão Comestível , Plantas Geneticamente Modificadas
4.
Pest Manag Sci ; 78(12): 5243-5250, 2022 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-36054418

RESUMO

BACKGROUND: Intercropping is commonly implemented as a way of promoting sustainable agriculture. Some of the benefits of intercropping include improving resource-use efficiency and soil quality as well as promoting pest control. As for pest control, intercropping can often engender pest repellency/confusion and promote natural biological control. Nevertheless, intercropping is not always a win-win strategy for pest management, with chances of sometimes either favoring or hampering pests and their natural enemies. Brazilian farmers commonly row-intercrop maize with brachiaria with the intent of forming a grass pasture for the feeding of livestock after maize harvest. However, very little is known about whether this intercropping can influence key pests and natural enemies in the maize agroecosystem. The overall aim of this study was to investigate how multiple groups of maize pests and natural enemies respond in terms of temporal abundance to this intercropping. RESULTS: Defoliation caused by caterpillars was higher in the intercropping treatment. Intercropping appeared to promote Dalbulus maidis while hampering aphids and Diabrotica speciosa. In general, the abundance of natural enemies was favored by intercropping. There was a reduction in maize productivity (i.e. fresh weight) in the intercropping treatment. Most results were season dependent. CONCLUSION: We believe that by considering together the pros and cons of intercropping maize and brachiaria in terms of pest management and soil conservation/fertility, the benefits of implementing this intercropping shall still outweigh its potential challenges. Nevertheless, the results and ensuing recommendations should be considered under the context of time and arthropod species. © 2022 Society of Chemical Industry.


Assuntos
Brachiaria , Zea mays , Agricultura/métodos , Solo , Controle de Pragas
5.
Pharmaceuticals (Basel) ; 15(8)2022 Jul 30.
Artigo em Inglês | MEDLINE | ID: mdl-36015096

RESUMO

The interest in 3,4-dihydropyrimidine-2(1H)-(thio)ones is increasing every day, mainly due to their paramount biological relevance. The Biginelli reaction is the classical approach to reaching these scaffolds, although the product diversity suffers from some limitations. In order to overcome these restrictions, two main approaches have been devised. The first one involves the modification of the conventional components of the Biginelli reaction and the second one refers to the postmodification of the Biginelli products. Both strategies have been extensively revised in this manuscript. Regarding the first one, initially, the modification of one of the components was covered. Although examples of modifications of the three of them were described, by far the modification of the keto ester counterpart was the most popular approach, and a wide variety of different enolizable carbonylic compounds were used; moreover, changes in two or the three components were also described, broadening the substitution of the final dihydropyrimidines. Together with these modifications, the use of Biginelli adducts as a starting point for further modification was also a very useful strategy to decorate the final heterocyclic structure.

6.
Sensors (Basel) ; 22(6)2022 Mar 10.
Artigo em Inglês | MEDLINE | ID: mdl-35336343

RESUMO

Unmanned aerial vehicle (UAV) applications have evolved to a wide range of fields in the last decade. One of the main challenges in autonomous tasks is the UAV stability during maneuvers. Thus, attitude and position control play a crucial role in stabilizing the vehicle in the desired orientation and path. Many control techniques have been developed for this. However, proportional integral derivative (PID) controllers are often used due their structure and efficiency. Despite PID's good performance, different requirements may be present at different mission stages. The main contribution of this research work is the development of a novel strategy based on a fuzzy-gain scheduling mechanism to adjust the PID controller to stabilize both position and altitude. This control strategy must be effective, simple, and robust to uncertainties and external disturbances. The Robot Operating System (ROS) integrates the proposed system and the flight control unit. The obtained results showed that the proposed approach was successfully applied to the trajectory tracking and revealed a good performance compared to conventional PID and in the presence of noises. In the tests, the position controller was only affected when the altitude error was higher, with an error of 2% lower.

7.
Sensors (Basel) ; 21(4)2021 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-33562647

RESUMO

Path planning is one of the most important issues in the robotics field, being applied in many domains ranging from aerospace technology and military tasks to manufacturing and agriculture. Path planning is a branch of autonomous navigation. In autonomous navigation, dynamic decisions about the path have to be taken while the robot moves towards its goal. Among the navigation area, an important class of problems is Coverage Path Planning (CPP). The CPP technique is associated with determining a collision-free path that passes through all viewpoints in a specific area. This paper presents a method to perform CPP in 3D environment for Unmanned Aerial Vehicles (UAVs) applications, namely 3D dynamic for CPP applications (3DD-CPP). The proposed method can be deployed in an unknown environment through a combination of linear optimization and heuristics. A model to estimate cost matrices accounting for UAV power usage is proposed and evaluated for a few different flight speeds. As linear optimization methods can be computationally demanding to be used on-board a UAV, this work also proposes a distributed execution of the algorithm through fog-edge computing. Results showed that 3DD-CPP had a good performance in both local execution and fog-edge for different simulated scenarios. The proposed heuristic is capable of re-optimization, enabling execution in environments with local knowledge of the environments.

8.
Sensors (Basel) ; 21(2)2021 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-33467417

RESUMO

Different practical applications have emerged in the last few years, requiring periodic and detailed inspections to verify possible structural changes. Inspections using Unmanned Aerial Vehicles (UAVs) should minimize flight time due to battery time restrictions and identify the terrain's topographic features. In this sense, Coverage Path Planning (CPP) aims at finding the best path to coverage of a determined area respecting the operation's restrictions. Photometric information from the terrain is used to create routes or even refine paths already created. Therefore, this research's main contribution is developing a methodology that uses a metaheuristic algorithm based on point cloud data to inspect slope and dams structures. The technique was applied in a simulated and real scenario to verify its effectiveness. The results showed an increasing 3D reconstructions' quality observing optimizing photometric and mission time criteria.

9.
Angew Chem Int Ed Engl ; 60(16): 8728-8732, 2021 Apr 12.
Artigo em Inglês | MEDLINE | ID: mdl-33476411

RESUMO

A method for the synthesis of ketones from aldehydes and boronic acids via a transition-metal-free C-H functionalization reaction is reported. The method employs nitrosobenzene as a reagent to drive the simultaneous activation of the boronic acid as a boronate and the activation of the C-H bond of the aldehyde as an iminium species that triggers the key C-C bond-forming step via an intramolecular migration from boron to carbon. These findings constitute a practical, scalable, and operationally straightforward method for the synthesis of ketones.

10.
An Acad Bras Cienc ; 92(suppl 2): e20191241, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-33174914

RESUMO

Ecological restoration is a traditional option for recovering biodiversity and ecosystem functions. Birds perform pollination, seed dispersal, and pest-control services, which catalyze increases in habitat structure. Habitat complexity changes bird composition, but there is little evidence of its effects on bird functional diversity in Neotropical restorations. We tested whether bird functional diversity and composition respond to increased habitat complexity. Point-counts were performed (January-December 2015) in an area undergoing restoration (536 ha) in the Atlantic Forest of southeastern Brazil, in restorations with less and more structured vegetation and pastures and forest-fragments. The functional bird traits considered were diet, habitat, biomass, environmental sensitivity, and foraging strata. Increased habitat complexity was evaluated using plant characteristics (exotic grass, canopy, herbaceous cover, and diameter at breast height). A total of 172 bird species (5% endemic; 12% migratory) were recorded. Increased vegetation structure in both restored sites and forest-fragments drove a reorganization and addition of functional bird traits, which positively influenced functional richness, dispersion, and evenness. Shifts in plant-characteristics rearranged bird functional traits (diet-forest-dependence and diet-strata-foraging). The rapid development of vegetation structure is a key factor for restoration because it provides additional habitat for semi-dependent forest birds and enhances resilience and sustainability in new man-made forests.


Assuntos
Ecossistema , Florestas , Animais , Biodiversidade , Aves , Brasil , Conservação dos Recursos Naturais
11.
Chem Soc Rev ; 49(15): 5159-5177, 2020 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-32627787

RESUMO

This tutorial review describes recent developments in carbon-nitrogen bond-forming reactions (amination, amidation, nitration and nitrosation) that involve the use of boronic acids and some of their derivatives as carbon-nucleophiles in the absence of transition-metals. Issues pertaining to reagents and mechanisms are discussed.

12.
ACS Omega ; 4(9): 13943-13953, 2019 Aug 27.
Artigo em Inglês | MEDLINE | ID: mdl-31497712

RESUMO

The selective synthesis of mono-N-methyl aromatic amines was achieved by the reaction of aromatic nitroso compounds with methylboronic acid promoted by triethylphosphite under transition metal-free conditions. The target compounds are constructed efficiently without overmethylation, under environmentally benign reaction conditions that do not require bases or reductants and therefore are of interest in pharmaceutical, agricultural, and chemical industries.

13.
J Org Chem ; 83(18): 11425-11436, 2018 09 21.
Artigo em Inglês | MEDLINE | ID: mdl-30036474

RESUMO

The repertoire of synthetic transformations of the products of the Achmatowicz rearrangement has been expanded by exploring their reactivity with potassium organotrifluoroborates in the absence of transition metals. Depending on the reaction conditions and the substitution pattern of the starting material, the reaction may lead to the stereoselective synthesis of dihydropyranones (2,6- trans), tetrahydropyranones (2,3- cis-2,6- cis) or functionalized 1,4-dicarbonyl compounds. The method has also been adapted for the one-pot synthesis of functionalized pyrroles.

14.
Dement Neuropsychol ; 12(2): 205-211, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29988357

RESUMO

Cognitive Impairment (CI) is a common and distressing problem in Multiple Sclerosis (MS). Its identification is complicated and sometimes omitted in the routine evaluation by neurologists. The BICAMS (Brief International Cognitive Assessment for Multiple Sclerosis) is a promising tool to overcome this difficulty. However, there is some concern regarding the subjectivity in scoring of the BVMT-R (Brief Visuospatial Memory Test - Revised), one of its components. OBJECTIVE: To evaluate the reliability of the BVMT-R in a sample of Brazilian MS patients, with the measure being administered and scored by neurologists. METHODS: BICAMS was applied to seventy subjects comprising forty patients diagnosed with MS and thirty healthy controls. In the MS patients group, the coefficients of agreement between three different raters, using the same protocols, and the internal consistency of the BVMT-R were assessed. Also, the coefficients of correlation of the BVMT-R with the other tests of the BICAMS, CVLT II (California Verbal Learning Test II) and SDMT (Symbol Digit Modalities Test), and their respective effect sizes were calculated. RESULTS: the BVMT-R presented a moderate inter-rater coefficient of agreement (k=0.62), an excellent Intraclass Correlation Coefficient (ICC=0.85), and high internal consistency (α=0.92). The correlation between the BVMT-R and CVLT II was moderate (ρ=0.36; p<0.025), but strong with the SDMT (ρ=0.60; p<0.01), with a large effect size. CONCLUSION: The BVMT-R is a reliable instrument for assessing CI in patients with MS, having a significant association with information processing speed, an aspect which should be considered when evaluating its score.


O declínio cognitivo (DC) é um problema comum na esclerose múltipla (EM), mas sua identificação é complexa, por vezes sendo omitida na avaliação de rotina pelos neurologistas. O BICAMS é uma bateria breve de testes neuropsicológicos que visa superar tais dificuldades. No entanto, uma possível subjetividade no sistema de pontuação do BVMT-R, um dos seus componentes, é um ponto frágil desta ferramenta. OBJETIVO: Avaliar a confiabilidade do BVMT-R em pacientes portadores de EM, aplicado e aferido por neurologistas. MÉTODOS: Os testes do BICAMS foram administrados a setenta indivíduos, quarenta pacientes portadores de EM e trinta controles saudáveis. No grupo de pacientes com EM foram calculados os coeficientes de concordância dos resultados entre três diferentes avaliadores e a consistência interna do BVMT-R. Também foram calculados os coeficientes de correlação do BVMT-R com os demais testes componentes do BICAMS e seus respectivos tamanhos de efeito. RESULTADOS: O BVMT-R apresentou um coeficiente de concordância entre examinadores moderado (k=0,62), um excelente Coeficiente de Correlação Intraclasse (ICC=0,85) e uma alta consistência interna (α=0,92). A correlação entre o BVMT-R foi moderada (CVLT II: ρ=0,36; p<0,025) ou forte (SDMT: ρ=0,60; p<0,01), com grande tamanho de efeito. CONCLUSÃO: O BVMT-R é um instrumento confiável para avaliar o DC na EM, apresentando uma associação significativa com a velocidade de processamento da informação, o que deve ser considerado na interpretação de seus resultados.

15.
Dement. neuropsychol ; 12(2): 205-211, Apr.-June 2018. tab, graf
Artigo em Inglês | LILACS | ID: biblio-952965

RESUMO

ABSTRACT: Cognitive Impairment (CI) is a common and distressing problem in Multiple Sclerosis (MS). Its identification is complicated and sometimes omitted in the routine evaluation by neurologists. The BICAMS (Brief International Cognitive Assessment for Multiple Sclerosis) is a promising tool to overcome this difficulty. However, there is some concern regarding the subjectivity in scoring of the BVMT-R (Brief Visuospatial Memory Test - Revised), one of its components. Objective: To evaluate the reliability of the BVMT-R in a sample of Brazilian MS patients, with the measure being administered and scored by neurologists. Methods: BICAMS was applied to seventy subjects comprising forty patients diagnosed with MS and thirty healthy controls. In the MS patients group, the coefficients of agreement between three different raters, using the same protocols, and the internal consistency of the BVMT-R were assessed. Also, the coefficients of correlation of the BVMT-R with the other tests of the BICAMS, CVLT II (California Verbal Learning Test II) and SDMT (Symbol Digit Modalities Test), and their respective effect sizes were calculated. Results: the BVMT-R presented a moderate inter-rater coefficient of agreement (k=0.62), an excellent Intraclass Correlation Coefficient (ICC=0.85), and high internal consistency (α=0.92). The correlation between the BVMT-R and CVLT II was moderate (ρ=0.36; p<0.025), but strong with the SDMT (ρ=0.60; p<0.01), with a large effect size. Conclusion: The BVMT-R is a reliable instrument for assessing CI in patients with MS, having a significant association with information processing speed, an aspect which should be considered when evaluating its score.


RESUMO: O declínio cognitivo (DC) é um problema comum na esclerose múltipla (EM), mas sua identificação é complexa, por vezes sendo omitida na avaliação de rotina pelos neurologistas. O BICAMS é uma bateria breve de testes neuropsicológicos que visa superar tais dificuldades. No entanto, uma possível subjetividade no sistema de pontuação do BVMT-R, um dos seus componentes, é um ponto frágil desta ferramenta. Objetivo: Avaliar a confiabilidade do BVMT-R em pacientes portadores de EM, aplicado e aferido por neurologistas. Métodos: Os testes do BICAMS foram administrados a setenta indivíduos, quarenta pacientes portadores de EM e trinta controles saudáveis. No grupo de pacientes com EM foram calculados os coeficientes de concordância dos resultados entre três diferentes avaliadores e a consistência interna do BVMT-R. Também foram calculados os coeficientes de correlação do BVMT-R com os demais testes componentes do BICAMS e seus respectivos tamanhos de efeito. Resultados: O BVMT-R apresentou um coeficiente de concordância entre examinadores moderado (k=0,62), um excelente Coeficiente de Correlação Intraclasse (ICC=0,85) e uma alta consistência interna (α=0,92). A correlação entre o BVMT-R foi moderada (CVLT II: ρ=0,36; p<0,025) ou forte (SDMT: ρ=0,60; p<0,01), com grande tamanho de efeito. Conclusão: O BVMT-R é um instrumento confiável para avaliar o DC na EM, apresentando uma associação significativa com a velocidade de processamento da informação, o que deve ser considerado na interpretação de seus resultados.


Assuntos
Humanos , Disfunção Cognitiva/diagnóstico , Reprodutibilidade dos Testes , Esclerose Múltipla , Testes Neuropsicológicos
16.
Org Lett ; 20(6): 1667-1671, 2018 03 16.
Artigo em Inglês | MEDLINE | ID: mdl-29493243

RESUMO

The synthesis of di(hetero)arylamines by a transition-metal-free cross-coupling between nitrosoarenes and boronic acids is reported. The procedure is experimentally simple, fast, mild, and scalable and has a wide functional group tolerance, including carbonyls, nitro, halogens, free OH and NH groups. It also permits the synthesis of sterically hindered compounds.

17.
Int J STD AIDS ; 29(7): 658-664, 2018 06.
Artigo em Inglês | MEDLINE | ID: mdl-29393006

RESUMO

The objective of this study was to investigate risk behaviors for sexually transmitted infections (STIs) in noninjecting drug users (NIDUs), using STI diagnosis history as an indicator. A cross-sectional study was conducted in 323 NIDUs of two facilities for alcohol and/or drug dependence treatment in the Goiás State, Central Brazil. All participants were interviewed about risk behaviors and STI history. Multivariable analysis was performed in order to identify predictors of STIs. Adjusted prevalence ratio (APR) with confidence intervals of 95% was obtained using a Poisson regression model. Prevalence of self-reported STIs in the previous 12 months was 25.4% (95% confidence interval [95% CI]: 21.0-30.4%). A multivariable model verified that age (APR: 1.01; 95% CI: 1.00-1.01), sexual contact with partners diagnosed with STIs (APR: 1.27; 95% CI: 1.12-1.45) and injecting drug users (IDUs) (APR: 1.14; 95% CI: 1.14; 95% CI: 1.01-1.31), exchange sex for money and/or drugs (APR: 1.12; 95% CI: 1.02-1.21), and a history of sexual violence (APR: 1.04; 95% CI: 1.04-1.32) were predictors of STIs. Elevated rates of STI history and risk behaviors were observed in NIDUs, supporting the vulnerability of this group for these infections. Public policies and health outreach should be intensified in this population, principally regular STI testing of individuals in treatment for drug dependence and their sexual partners.


Assuntos
Usuários de Drogas/psicologia , Assunção de Riscos , Comportamento Sexual , Infecções Sexualmente Transmissíveis/epidemiologia , Transtornos Relacionados ao Uso de Substâncias/epidemiologia , Adolescente , Adulto , Brasil/epidemiologia , Usuários de Drogas/estatística & dados numéricos , Feminino , Humanos , Drogas Ilícitas , Masculino , Fatores de Risco , Infecções Sexualmente Transmissíveis/diagnóstico , Transtornos Relacionados ao Uso de Substâncias/psicologia
18.
Phys Chem Chem Phys ; 20(3): 1395-1407, 2018 Jan 17.
Artigo em Inglês | MEDLINE | ID: mdl-29297520

RESUMO

Polyelectrolyte-surfactant mixtures and their interactions with fluid interfaces are an important research field due to their use in technological applications. Most of the existing knowledge on these systems is based on models in which the polyelectrolyte concentration is around 50 times lower than that used in commercial formulations. The present work marks a step to close the gap on the understanding of their behavior under more practically-relevant conditions. The adsorption of concentrated mixtures of poly(diallyldimethyl-ammonium) chloride and sodium N-lauroyl-N-methyltaurate at the water/vapor interface with a crude mixing protocol has been studied by different surface tension techniques, Brewster angle microscopy, neutron reflectometry, and several bulk characterization techniques. Kinetically-trapped aggregates formed during mixing influence the interfacial morphology of mixtures produced in the equilibrium one-phase region, yet fluctuations in the surface tension isotherm result depending on the tensiometric technique applied. At low bulk surfactant concentrations, the free surfactant concentration is very low, and the interfacial composition matches the trend of the bulk complexes, which is a behavior that has not been observed in studies on more dilute mixtures. Nevertheless, a transition to synergistic co-adsorption of complexes and free surfactant is observed at the higher bulk surfactant concentrations studied. This transition appears to be a special feature of these more concentrated mixtures, which deserves attention in future studies of systems with additional components.

19.
Org Lett ; 19(22): 6236-6239, 2017 11 17.
Artigo em Inglês | MEDLINE | ID: mdl-29112447

RESUMO

The transition-metal-free diastereoselective C(sp2)-C(sp3) cross-coupling between unprotected diols and boronic acids or potassium organotrifluoroborates is reported. Depending on the reaction conditions, the syn or the anti reaction products are obtained in a stereocomplementary fashion. This type of coupling is developed with alkenyl-, heteroaryl- and arylboron compounds as carbon nucleophiles.

20.
Org Lett ; 17(6): 1605-8, 2015 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-25738233

RESUMO

The transition-metal-free intermolecular direct 1,2-carboboration reaction of heteroarylacetylenes using boronic acids as reagents is achieved by utilizing tartaric acid as promoter. The reaction proceeds with excellent regioselectivity and anti stereoselectivity to afford boroxole frameworks. The resulting compounds are of use for the stereoselective preparation of polysubstituted alkenylheteroarenes.

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