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51.
52.
The Importance of Methyl Positioning and Tautomeric Equilibria for Imidazole Nucleophilicity
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Renan B. Campos Leociley R. A. Menezes Prof. Dr. Andersson Barison Prof. Dr. Dean J. Tantillo Prof. Dr. Elisa S. Orth 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(43):15521-15528
Imidazole (IMZ) rings catalyze many biological dephosphorylation processes. The methyl positioning effect on IMZs reactivity has long intrigued scientists and its full understanding comprises a promising tool for designing highly efficient IMZ‐based catalysts. We evaluated all monosubstituted methylimidazoles (xMEI) in the reaction with diethyl 2,4‐dinitrophenyl phosphate by kinetics studies, NMR analysis and DFT calculations. All xMEI showed remarkable rate enhancements, up to 1.9×105 fold, compared with spontaneous hydrolysis. Unexpectedly, the electron‐donating methyl group acts to decrease the reactivity of the xMEI compared to IMZ, except for 4(5)methylimidazole, (4(5)MEI). This behavior was attributed to both electronic and steric effects. Moreover, reaction intermediates were monitored by NMR and surprisingly, the reactivity of the two different 4(5)MEI tautomers was distinguished. 相似文献
53.
54.
João Pedro A. Souza Dr. Leociley R. A. Menezes Dr. Francielle P. Garcia Dr. Débora B. Scariot Dr. Pamela T. Bandeira Mateus B. Bespalhok Dr. Siddhartha O. K. Giese Dr. David L. Hughes Prof. Dr. Celso V. Nakamura Prof. Dr. Andersson Barison Prof. Dr. Alfredo R. M. Oliveira Prof. Dr. Renan B. Campos Prof. Dr. Leandro Piovan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(58):14427-14437
Inspired by the synthetic and biological potential of organotellurium substances, a series of five- and six-membered ring organotelluranes containing a Te−O bond were synthesized and characterized. Theoretical calculations elucidated the mechanism for the oxidation-cyclization processes involved in the formation of the heterocycles, consistent with chlorine transfer to hydroxy telluride, followed by a cyclization step with simultaneous formation of the new Te−O bond and deprotonation of the OH group. Moreover, theoretical calculations also indicated anti-diastereoisomers to be major products for two chirality center–containing compounds. Antileishmanial assays against Leishmania amazonensis promastigotes disclosed 1,2λ4-oxatellurane LQ50 (IC50=4.1±1.0; SI=12), 1,2λ4-oxatellurolane LQ04 (IC50=7.0±1.3; SI=7) and 1,2λ4-benzoxatellurole LQ56 (IC50=5.7±0.3; SI=6) as more powerful and more selective compounds than the reference, being up to four times more active. A stability study supported by 125Te NMR analyses showed that these heterocycles do not suffer structural modifications in aqueous-organic media or at temperatures up to 65 °C. 相似文献
55.
Renan Tunalıoğlu Çağrı Koç Tolga Bektaş 《The Journal of the Operational Research Society》2016,67(7):1012-1024
The process by which olive oil is produced yields two by-products, one of which is the brown-coloured Olive Oil Mill Wastewater (OMWW) and has no direct use. OMWW is generally disposed of into soil or rivers, potentially contaminating the environment. OMWW can be treated using ultrafiltration facilities, but this requires that OMWW is collected from oil mills and delivered to the treatment facilities using a fleet of vehicles in an economically viable manner. Such considerations give rise to a multiperiod location-routing problem. This paper formally introduces the problem and proposes an adaptive large neighbourhood search metaheuristic for its solution. The algorithm is applied on a case study drawn from one of the major olive oil producing countries. The paper presents computational and managerial results. 相似文献
56.
Daniela Pinheiro Gaspar Gilson Celso Albuquerque Chagas Junior Eloisa Helena de Aguiar Andrade Lidiane Diniz do Nascimento Renan Campos Chist Nelson Rosa Ferreira Luiza Helena da Silva Martins Alessandra Santos Lopes 《Molecules (Basel, Switzerland)》2021,26(13)
In addition to the vast diversity of fauna and flora, the Brazilian Amazon has different climatic periods characterized by periods with greater and lesser rainfall. The main objective of this research was to verify the influence of climatic seasons in the Brazilian Amazon (northeast of Pará state) concerning the aromatic and bioactive profiles of fermented and dried cocoa seeds. About 200 kg of seeds was fermented using specific protocols of local producers. Physicochemical analyzes (total titratable acidity, pH, total phenolic compounds, quantification of monomeric phenolics and methylxanthines) and volatile compounds by GC-MS were carried out. We observed that: in the summer, the highest levels of aldehydes were identified, such as benzaldehyde (6.34%) and phenylacetaldehyde (36.73%), related to the fermented cocoa and honey aromas, respectively; and a total of 27.89% of this same class was identified during winter. There were significant differences (p ≤ 0.05, Tukey test) in the profile of bioactive compounds (catechin, epicatechin, caffeine, and theobromine), being higher in fermented almonds in winter. This study indicates that the climatic seasons in the Amazon affect the aromatic and bioactive profiles and could produce a new identity standard (summer and winter Amazon) for the cocoa almonds and their products. 相似文献
57.
A. Siber J. Marien Th. Koch P. Ziemann 《Applied Physics A: Materials Science & Processing》1993,57(3):267-270
Al/Au multilayers (average composition Al2Au, individual layer thicknesses 1 nm Al and 0.71 nm Au) are prepared at 90 K by ion beam sputtering. The electrical resistance of the growing films is monitored in situ. From the results obtained in this way it can be concluded that interface reactions occur transforming the ultrathin layers into an amorphous phase, which is stable up to 255 K.For larger individual layer thicknesses (2.1 nm Au and 3 nm Al), the interface reaction into the amorphous state is incomplete. Based on a simple parallel-resistor model, one finds that the interface reaction into the amorphous phase is restricted to a thickness of less than 3.5 nm. The temperature dependence of the resistance of such thicker multilayers indicates the onset of interdiffusion of the yet unreacted material at T=200 K resulting in the crystalline Al2Au-phase. 相似文献
58.
Ana Cláudia M. Oliveira Marluce S. Santos Luma M. S. Brandão R. M. Navarro Yerga J. L. G. Fierro Manuela S. Leite Eliane B. Cavalcantia Renan Tavares Figueiredo 《Chemical Papers》2017,71(6):1129-1141
This work reports the reforming of bio-ethanol on chitosan–TiO2 hybrid photocatalysts at ambient temperature. The influence of chitosan composition on the photocatalytic performance of chitosan–TiO2 hybrid was studied. The hybrids were characterized by CHN elemental analysis, nitrogen adsorption–desorption isotherms, thermogravimetric analysis, diffuse reflectance spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that the preparation variables used for the incorporation of chitosan on TiO2 promoted changes in the morphology, superficial area, crystal size and porosity of the photocatalyst, affecting the band gap of this semiconductor and consequently the reactivity of the chitosan–TiO2 hybrids. The catalysts were evaluated for hydrogen production from ethanol under visible light. It was demonstrated that the calcination temperature of 623 K and a chitosan content of 20% were the most appropriate preparation conditions and the resulting product displays a pore size of 1.9 nm, crystal size of 11.3 nm, BET area of 178 m2 g?1 and band gap of 2.92 eV. The calcination temperature of 623 K and incorporation of 20% of chitosan obtained the same results in the conversion rate of hydrogen in comparison to the pure TiO2 P25. 相似文献
59.
Moritz Trautvetter Ulf Wiedwald Heiko Paul Alexander Minkow Paul Ziemann 《Applied Physics A: Materials Science & Processing》2011,102(3):725-730
Solid-phase epitaxy is demonstrated for the metallic binary alloy AlFe. Stoichiometric thin films are deposited at ambient
temperature onto c-cut sapphire by pulsed laser deposition (PLD), resulting in smooth amorphous films as revealed by X-ray diffraction (XRD)
and atomic force microscopy (AFM). By annealing at 600°C, still smooth epitaxial AlFe films are obtained exhibiting the B2
phase with the (110) direction parallel to the substrate normal and an in-plane orientation as given by AlFe[001]||Al2O3[11[`2]0]\mbox{AlFe}[001]\|\mbox{Al}_{2}\mbox{O}_{3}[11\bar{2}0]. While ferromagnetism is observed for the amorphous phase, the formation of the B2 structure is accompanied by paramagnetic
behavior, confirming the high structural quality. 相似文献
60.
Cariou R Dahcheh F Graham TW Stephan DW 《Dalton transactions (Cambridge, England : 2003)》2011,40(18):4918-4925
The tridentate bis-phosphinimine ligands O(1,2-C(6)H(4)N=PPh(3))(2)1, HN(1,2-C(2)H(4)N=PR(3))(2) (R = Ph 2, iPr 3), MeN(1,2-C(2)H(4)N=PPh(3))(2)4 and HN(1,2-C(6)H(4)N=PPh(3))(2)5 were prepared. Employing these ligands, monometallic Pd and Ni complexes O(1,2-C(6)H(4)N=PPh(3))(2)PdCl(2)6, RN(1,2-CH(2)CH(2)N=PPh(3))(2)PdCl][Cl] (R = H 7, Me 8), [HN(1,2-CH(2)CH(2)N=PiPr(3))(2)PdCl][Cl] 9, [MeN(1,2-CH(2)CH(2)N=PPh(3))(2)PdCl][PF(6)] 10, [HN(1,2-CH(2)CH(2)N=PPh(3))(2)NiCl(2)] 11, [HN(1,2-CH(2)CH(2)N=PR(3))(2)NiCl][X] (X = Cl, R = iPr 12, X = PF(6), R = Ph 13, iPr 14), and [HN(1,2-C(6)H(4)N=PPh(3))(2)Ni(MeCN)(2)][BF(4)]Cl 15 were prepared and characterized. While the ether-bis-phosphinimine ligand 1 acts in a bidentate fashion to Pd, the amine-bis-phosphinimine ligands 2-5 act in a tridentate fashion, yielding monometallic complexes of varying geometries. In contrast, initial reaction of the amine-bis-phosphinimine ligands with base followed by treatment with NiCl(2)(DME), afforded the amide-bridged bimetallic complexes N(1,2-CH(2)CH(2)N=PR(3))(2)Ni(2)Cl(3) (R = Ph 16, iPr 17) and N(1,2-C(6)H(4)N=PPh(3))(2)Ni(2)Cl(3)18. The precise nature of a number of these complexes were crystallographically characterized. 相似文献