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81.
Solvent effect on the tautomers' stabilities of protonated N,N‐dimethylnitrosamine: The role of hydrogen bonds network 下载免费PDF全文
Railton B. de Andrade Elizete Ventura Silmar A. do Monte 《International journal of quantum chemistry》2017,117(4)
DFT calculations have been applied in order to study the free energies of the structures corresponding to the three different protonation sites of N,N‐dimethylnitrosamine (DMNA). The solvent effect has been taken into account through the study of clusters consisting of protonated DMNA and up to four explicit water molecules, either in the absence or in the presence of a continuum (CPCM) solvation model. Addition of water molecules has been done by a careful screening procedure through which all important hydrogen bonds are likely to be considered. Protonation of DMNA makes all their lone pairs no longer available for hydrogen bond formation with water molecules, such that hydrogen bonds have been observed, for almost all structures, only between water molecules and between one water molecule and the protonated DMNA, in this latter case intermediated by the proton. The stabilities of the solvated structures are governed not only by the number of hydrogen bonds but also by the positions of the water molecules involved in these bonds, as well as by which of them donate or accept H atoms. Our results indicate that oxygen protonation is the most favorable one, regardless of the presence of water molecules. In vacuum protonation at the N‐amino ( 2a ) is approximately as favorable as protonation at the N nitroso ( 2c ). However, in water the former protonation is by far the less favorable one. Our best estimates for the ΔG values in bulk solvent are: ΔG( 2a ) ≈ 17.9, ΔG( 1c ) ≈ 4.3, and ΔG( 2c ) ≈ 4.9 kcal/mol. 相似文献
82.
Maurício Hilgemann Fritz Scholz Heike Kahlert Leandro Machado de Carvalho Marcelo Barcellos da Rosa Ulrike Lindequist Martina Wurster Paulo C. do Nascimento Denise Bohrer 《Electroanalysis》2010,22(4):406-412
A new electrochemical assay has been developed which is based on quantifying the attack of OH. radicals on a self‐assembled thiol monolayer on electrodes in the presence and absence of antioxidants. The OH. radicals were produced in Fenton solutions. The radical scavengers diminish the concentration of the OH. radicals in the Fenton solution, and the extent of thiol layer destruction is monitored with the help of a redox probe in solution, the signal of which is only generated at SAM‐free electrode surface. The results of the electrochemical assay were compared with those of the standard DPPH. assay. In case of each plant extract, an excellent linear correlation was observed between the radical scavenging activity and the concentration of plant extracts; however, the scavenging properties of different plants strongly differ in the electrochemical and the DPPH. assay. Since the proposed new method probes the reactivity of radical scavengers towards OH., one of the most important reactive oxygen radicals in tissues, it is supposed to provide much more relevant information than the DPPH. or other assays. 相似文献
83.
Paula Santos Nunes Marília Santos Bezerra L. P. Costa Juliana Cordeiro Cardoso R. L. C. AlbuquerqueJr. M. O. Rodrigues Gabriela Borin Barin Francilene Amaral da Silva A. A. S. Araújo 《Journal of Thermal Analysis and Calorimetry》2010,99(3):1011-1014
The purpose of this study was to evaluate the physical–chemical properties of collagen (CL) and usnic acid/collagen-based
(UAC) films, using differential thermal analysis (DTA), thermogravimetry (TG/DTG), infrared spectroscopy (FTIR), and scanning
electron microscopy (SEM). Both films were prepared by casting process using polyethylene glycol 1500 (PEG 1500) as plasticizer.
In the spectrum of UAC, similar bands of the usnic acid are observed, indicating that the polymerization (film formation)
did not affect the stability of the drug. Distinctly, DTA curve of UAC did not show an endothermic peak at 201 °C, indicative
that the drug was incorporated into the polymeric system. These results were corroborated by the scanning electron microscopy
(SEM). The TG/DTG curves of UAC presented a different thermal decomposition profile compared to the individual compounds and
CL. These findings suggest the occurrence of molecular dispersion or solubilization of the drug in the collagen film. 相似文献
84.
Gomes de Melo J de Sousa Araújo TA Thijan Nobre de Almeida e Castro V Lyra de Vasconcelos Cabral D do Desterro Rodrigues M Carneiro do Nascimento S Cavalcanti de Amorim EL de Albuquerque UP 《Molecules (Basel, Switzerland)》2010,15(12):8534-8542
The objective of this study was to evaluate antiproliferative activity, antioxidant capacity and tannin content in plants from semi-arid northeastern Brazil (Caatinga). For this study, we selected 14 species and we assayed the methanol extracts for antiproliferative activity against the HEp-2 (laryngeal cancer) and NCI-H292 (lung cancer) cell lines using the (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazole) (MTT) method. In addition, the antioxidant activity was evaluated with the DPPH (2,2-diphenyl-2-picrylhydrazyl) assay, and the tannin content was determined by the radial diffusion method. Plants with better antioxidant activity (expressed in a dose able to decrease the initial DPPH concentration by 50%, or IC50) and with higher levels of tannins were: Poincianella pyramidalis (42.95±1.77 μg/mL IC50 and 8.17±0.64 tannin content), Jatropha mollissima (54.09±4.36μg/mL IC50 and 2.35±0.08 tannin content) and Anadenanthera colubrina (73.24±1.47 μg/mL IC50 and 4.41±0.47 tannin content). Plants with enhanced antiproliferative activity (% living cells) were Annona muricata (24.94±0.74 in NCI-H292), Lantana camara (25.8±0.19 in NCI-H292), Handroanthus impetiginosus (41.8±0.47 in NCI-H292) and Mentzelia aspera (45.61±1.94 in HEp-2). For species with better antioxidant and antiproliferative activities, we suggest future in vitro and in vivo comparative studies with other pharmacological models, and to start a process of purification and identification of the possible molecule(s) responsible for the observed pharmacological activity. We believe that the flora of Brazilian semi-arid areas can be a valuable source of plants rich in tannins, cytotoxic compounds and antioxidant agents. 相似文献
85.
The mechanisms for multimode vibrational couplings in resonant positron annihilation are not well understood. We show that these resonances can arise from positron-induced distortions of the potential energy surface (target response to the positron field). Though these distortions can transfer energy into single- and multiquantum vibrations, they have so far been disregarded as a pathway to resonant annihilation. We also compare the existing annihilation theories and show that the currently accepted model can be cast as a special case of the Feshbach annihilation theory. 相似文献
86.
Search for a standard model Higgs boson in the H→ZZ→ℓ(+)ℓ(-)νν decay channel with the ATLAS detector
Aad G Abbott B Abdallah J Abdelalim AA Abdesselam A Abdinov O Abi B Abolins M Abramowicz H Abreu H Acerbi E Acharya BS Adams DL Addy TN Adelman J Aderholz M Adomeit S Adragna P Adye T Aefsky S Aguilar-Saavedra JA Aharrouche M Ahlen SP Ahles F Ahmad A Ahsan M Aielli G Akdogan T Åkesson TP Akimoto G Akimov AV Akiyama A Alam MS Alam MA Albert J Albrand S Aleksa M Aleksandrov IN Alessandria F Alexa C Alexander G Alexandre G Alexopoulos T Alhroob M Aliev M Alimonti G Alison J Aliyev M Allport PP 《Physical review letters》2011,107(22):221802
A search for a heavy standard model Higgs boson decaying via H→ZZ→→?(+)?(-)νν, where ?=e, μ, is presented. It is based on proton-proton collision data at √s=7 TeV, collected by the ATLAS experiment at the LHC in the first half of 2011 and corresponding to an integrated luminosity of 1.04 fb(-1). The data are compared to the expected standard model backgrounds. The data and the background expectations are found to be in agreement and upper limits are placed on the Higgs boson production cross section over the entire mass window considered; in particular, the production of a standard model Higgs boson is excluded in the region 340相似文献
87.
Eduardo de Almeida Paulo Rogério Massoni Amauri Antonio Menegário Laudi Cunha Leite Dante Pazzanese Duarte Lanna Virgílio Franco do Nascimento Filho 《X射线光谱测定》2011,40(6):424-426
This article describes a comparison of conventional energy‐dispersive X‐ray fluorescence (EDXRF) and synchrotron radiation total‐reflection X‐ray fluorescence (SRTXRF) for Co determination in ruminal fluid from Holstein cow. This element is used as marker for animal nutrition studies. For EDXRF, 200 µl of the sample were dried on 6.35 µm Mylar film at 60 °C. The excitation was carried out using an X‐ray tube with Mo target and Zr filter operated at 30 kV/20 mA. For SRTXRF, 10 µl of the sample were pipetted on a Lucite carrier and dried at 60 °C. In both the techniques, Ga was used as internal standard and the acquisition time was 200 s. The trueness of both techniques was evaluated through the standard addition method, the recoveries obtained by SRTXRF and EDXRF were 76 and 99%, and the limits of detection, 13 and 240 µg l?1, respectively. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
88.
We consider a multidimensional diffusion X with drift coefficient b(α,Xt) and diffusion coefficient ?σ(β,Xt). The diffusion sample path is discretely observed at times tk=kΔ for k=1…n on a fixed interval [0,T]. We study minimum contrast estimators derived from the Gaussian process approximating X for small ?. We obtain consistent and asymptotically normal estimators of α for fixed Δ and ?→0 and of (α,β) for Δ→0 and ?→0 without any condition linking ? and Δ. We compare the estimators obtained with various methods and for various magnitudes of Δ and ? based on simulation studies. Finally, we investigate the interest of using such methods in an epidemiological framework. 相似文献
89.
In the Corridor Allocation Problem, we are given n facilities to be arranged along a corridor. The arrangements on either side of the corridor should start from a common point on the left end of the corridor. In addition, no space is allowed between two adjacent facilities. The problem is motivated by applications such as the arrangement of rooms in office buildings, hospitals, shopping centers or schools. Tabu search and simulated annealing algorithms are presented to minimize the sum of weighted distances between every pair of facilities. The algorithms are evaluated on several instances of different sizes either randomly generated or available in the literature. Both algorithms reached the optimal (when available) or best-known solutions of the instances with n ? 30. For larger instances with size 42 ? n ? 70, the simulated annealing implementation obtained smaller objective values, while requiring a smaller number of function evaluations. 相似文献
90.
We address the question of finding sufficient conditions for existence as well as nonexistence of nonconstant stable stationary solution to the diffusion equation ut=div(a∇u)+f(u) on a surface of revolution with and without boundary. Conditions found relate the diffusivity function a and the geometry of the surface where diffusion takes place. In the case where f is a bistable function, necessary conditions for the development of inner transition layers are given. 相似文献