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101.
102.
Johnson GE Reveles JU Reilly NM Tyo EC Khanna SN Castleman AW 《The journal of physical chemistry. A》2008,112(45):11330-11340
Cationic and anionic cobalt oxide clusters, generated by laser vaporization, were studied using guided-ion-beam mass spectrometry to obtain insight into their structure and reactivity with carbon monoxide. Anionic clusters having the stoichiometries Co2O3(-), Co2O5(-), Co3O5(-) and Co3O6(-) were found to exhibit dominant products corresponding to the transfer of a single oxygen atom to CO, indicating the formation of CO 2. Cationic clusters, in contrast, displayed products resulting from the adsorption of CO onto the cluster accompanied by the loss of either molecular O 2 or cobalt oxide units. In addition, collision induced dissociation experiments were conducted with N 2 and inert xenon gas for the anionic clusters, and xenon gas for the cationic clusters. It was found that cationic clusters fragment preferentially through the loss of molecular O 2 whereas anionic clusters tend to lose both atomic oxygen and cobalt oxide units. To further analyze how stoichiometry and ionic charge state influence the structure of cobalt oxide clusters and their reactivity with CO, first principles theoretical electronic structure studies within the density functional theory framework were performed. The calculations show that the enhanced reactivity of specific anionic cobalt oxides with CO is due to their relatively low atomic oxygen dissociation energy which makes the oxidation of CO energetically favorable. For cationic cobalt oxide clusters, in contrast, the oxygen dissociation energies are calculated to be even lower than for the anionic species. However, in the cationic clusters, oxygen is calculated to bind preferentially in a less activated molecular O 2 form. Furthermore, the CO adsorption energy is calculated to be larger for cationic clusters than for anionic species. Therefore, the experimentally observed displacement of weakly bound O 2 units through the exothermic adsorption of CO onto positively charged cobalt oxides is energetically favorable. Our joint experimental and theoretical findings indicate that positively charged sites in bulk-phase cobalt oxides may serve to bind CO to the catalyst surface and specific negatively charged sites provide the activated oxygen which leads to the formation of CO 2. These results provide molecular level insight into how size, stoichiometry, and ionic charge state influence the oxidation of CO in the presence of cobalt oxides, an important reaction for environmental pollution abatement. 相似文献
103.
Nelly Konopik 《Fresenius' Journal of Analytical Chemistry》1957,155(4):276-278
Ohne Zusammenfassung 相似文献
104.
Gabriel A. Cardoso-Ugarte Nelly Ramírez-Corona Aurelio López-Malo Enrique Palou María Fernanda San Martín-González 《Journal of Dispersion Science and Technology》2018,39(7):1065-1073
Oregano essential oil emulsions (W/O) were prepared using different emulsifiers’ blend concentrations of Tween 80/Span 20, to study their phase separation during storage and to optimize the homogenization processing parameters by minimizing the droplet size of emulsions. Phase separation followed a second-order kinetic model, and relationships between the kinetic parameters and the blend concentrations of emulsifiers were established for determining the best emulsion formulations. The instability mechanism of emulsions demonstrated to be Ostwald ripening; therefore, by means of surface response methodology, mechanical homogenization parameters (11,700?rpm for 12 minutes at 1°C) were specified in order to minimize the droplet size of emulsions (1.02?±?0.12?µm). 相似文献
105.
Anthony W. Coleman Ioannis Nicolis Nelly Keller Jean Pierre Dalbiez 《Journal of inclusion phenomena and macrocyclic chemistry》1992,13(2):139-143
-,- and -Cyclodextrins have been shown to exist as aggregates in solution bound together by a network of hydrogen bonds. Removal of this network by ionisation of the hydroxyl groups leads to a greatly increased solubility and removal of aggregation. The presence of aggregates in solution of structure breaking solutes in which the solubility of-cyclodextrin is greatly enhanced, leads to a proposal that the abnormally low solubility of-CD may be explained by the presence of aggregates and the unfavourable interaction of these aggregates with the hydrogen bonded structure of water. 相似文献
106.
Comprehensive structural characterization of polyisoprene synthesized via cationic mechanism
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Victor A. Rozentsvet Nelly A. Korovina Olesya A. Stotskaya Marianna G. Kuznetsova Frederic Peruch Sergei V. Kostjuk 《Journal of polymer science. Part A, Polymer chemistry》2016,54(15):2430-2442
The microstructure of polyisoprene synthesized with tBuCl/TiCl4 initiating system is investigated using 1D and 2D (HSQC and HMBC) NMR spectroscopy. It is found that trans‐1,4‐units with regular (head‐to‐tail) and inverse (tail‐to‐tail) and (head‐to‐head) enchainments are predominant structures of unsaturated part of polymer chain, while 1,2‐ and 3,4‐units are presented in minor amounts. The new methodology for the quantitative calculation of the content of different structural units in polyisoprene chain including both types of inverse trans‐1,4‐addition (tail‐to‐tail and head‐to‐head) is proposed. It is shown that head groups consist of tert‐butyl group connected to trans‐1,4‐unit of polyisoprene chain. In addition, two types of chlorine‐containing end groups are found (trans‐4,1‐Cl and 4,3‐Cl), while conjugated double bonds at the chain end are totally absent. The methodology for the calculation of number‐average functionality by tert‐butyl head and chlorine end groups, respectively, is developed. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2430–2442 相似文献
107.
Raffaella CincinelliLeonardo Scaglioni Nelly A. ArnoldSabrina Dallavalle 《Tetrahedron letters》2011,52(45):5972-5975
Two novel metabolites have been isolated from the aerial parts of Stachys ehrenberiigii. Their structures and stereochemistry were elucidated using a combination of 13C and 1H homo and heteronuclear 2D NMR experiments and mass analysis. The development of an enantioselective synthesis of 3-(2′-acetoxy-4-phenylbut-3′-enoylamino)propionic acid allowed to confirm the structure and assign the (R) absolute configuration at C-2′ of the natural product. 相似文献
108.
Mariane C. B. Lira Milena S. Ferraz Dáfila G. V. C. da Silva Maria E. Cortes Karina I. Teixeira Nelly P. Caetano Ruben D. Sinisterra Gilles Ponchel Nereide S. Santos-Magalhães 《Journal of inclusion phenomena and macrocyclic chemistry》2009,64(3-4):215-224
In this study β-cyclodextrin (β-CD) was used to improve usnic acid (UA) solubility and the inclusion complex (UA:β-CD) was incorporated into liposomes in order to produce a targeted drug delivery system for exploiting the antimycobacterial activity of UA. A phase-solubility assay of UA in β-CD at pH 7.4 was performed. An apparent stability constant of K1:1 = 234.5 M?1 and a complexation efficiency of 0.005 was calculated. In the presence of 16 mM of β-CD the solubility of UA (7.3 μg/mL) increased more than 5-fold. The UA:β-CD complex was prepared using the freeze-drying technique and characterized through infrared and 1HNMR spectroscopy, X-ray diffraction and thermal analyses. The UA:β-CD inclusion complex presented IR spectral modifications when compared with UA and β-CD spectra. 1HNMR spectrum of UA:β-CD inclusion complex showed significant chemical shifts in proton H5 located inside the cavity of β-CD (Δδ = 0.127 ppm), suggesting that phenyl ring moiety of UA would be expected to be included within the β-CD cavity, interacting with the H-5 proton. A change in UA from its crystalline to amorphous form was observed on X-ray, suggesting the formation of a drug inclusion complex. DSC analysis showed the disappearance of the UA fusion peak UA:βCD complex. No differences between the antimicrobial activity of free UA and UA:βCD were found, supporting the hypothesis that the complexation with cyclodextrin did not interfere with drug activity. Liposomes containing UA:βCD were prepared using hydration of a thin lipid film method with subsequent sonication. Formulations of liposomes containing UA:βCD exhibited a drug encapsulation efficiency of 99.5% and remained stable for four months in a suspension form. Interestingly, the encapsulation of UA:βCD into the liposomes resulted in a modulation of in vitro kinetics of release of UA. Indeed, liposomes containing UA:β-CD presented a more prolonged release profile of free usnic acid compared to usnic acid-loaded liposomes. 相似文献
109.
Nelly N. Mateeva Shihab D. Deiab Edikan E. Archibong Mercedes Jackson Bereket Mochona Madhavi Gangapuram Kinfe K. Redda 《Journal of inclusion phenomena and macrocyclic chemistry》2010,68(3-4):305-312
Three novel aza-crown ether derivatives incorporating 4-amino-7-nitrobenzaoxa-1,3-diazole (NBD) chromophore were synthesized and their structure confirmed by 1H-NMR, IR and elemental analysis. The influence of the solvent polarity and protonation on the photophysical properties of NBD-15-crown-5 was studied by UV/Vis and fluorescence methods. The influence of the investigated cations on the absorption spectra of the ligands was negligible, however emission was strongly affected. Complexation and binding stability of NBD-aza-15-crown-5 and NBD-aza-18-crown-6 were studied using fluorescence spectroscopy. NBD-aza-18-crown-6 exhibits strong selectivity toward Ca2+ and Sr2+ ions with formation constants about 103 times higher than the formation constants with the other ions included in the study. 相似文献
110.
Reliability of biospeckle image analysis 总被引:1,自引:0,他引:1
Roberto Alves Braga Junior Bruno Oliveira Silva Giovanni Rabelo Ricardo Marques Costa Adilson Machado Enes Nelly Cap Hctor Rabal Ricardo Arizaga Marcelo Trivi Graham Horgan 《Optics and Lasers in Engineering》2007,45(3):390
This paper presents an analysis of the time history of speckle patterns (THSP) that is one of the most used procedures to evaluate the biological activity by biospeckle images. THSPs generated by numerical simulations, obtained in a controlled drying of paint experiment and in dead and alive bean seeds under laser illumination were evaluated. We used first- and second-order statistics of the dynamic speckle patterns for different time and spatial amounts of data. We have tested both square and rectangular windows in the space time domain. The results show the agreement with a theoretical curve and comparisons between different window sizes. 相似文献