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991.
Irene T. S. Garcia Fabiane G. da S. Porto Queila D. F. do Amaral Neftalí L. V. Carreño Márcio M. Martins Martin Wallau 《Surface and interface analysis : SIA》2008,40(5):899-905
Amino acids and polypeptides thin films, pure or attached to polymers, present large application as sensors and biosensors. The interactions between such films and the supports, their sensorial properties, as well as the development of techniques to produce thin regular films, are still challenges in the area. In this work, we present the preparation of L ‐glutamine thin films on silicon substrates, the factors that determine amino acid/silicon substrate interaction, and the morphology of the films. For this purpose, a 24 factorial design is used, taking into account the effects of the solvent system, the glutamine concentration, the temperature, as well as the pretreatment of the substrate surface. The contact angles between a drop of glutamine solution and the silicon substrate were taken for the preliminary evaluation of the affinity between the amino acid and the substrate. The results have shown six promising experimental combinations with oxidized silicon as substrate to improve the solution/substrate interaction. Three of these promising conditions involved aqueous solution of L ‐glutamine and three alkalis solution. The obtained films were characterized by scanning electron microscopy (SEM), Rutherford backscattering (RBS), and Fourier transform infrared (FTIR) spectroscopy. The selected experimental conditions permitted to prepare a variety of films with L ‐glutamine, like small crystals, lamellas, needles, and smoothed regular films. The systems prepared in presence of alkalis solution yielded regular and smooth films. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
992.
Danilo Eduardo Martins Sérgio E. Galembeck 《International journal of quantum chemistry》2024,124(1):e27325
Despite the ubiquitous presence of amine oxides in chemistry, there is no consensus about the nature of the N O bond in these compounds. In this work, we have used electron density analysis to investigate the nature of this bond in substituted amine oxides, R3NO, and have compared it with the nature of the N O bond in hydroxylamines, R2NOR, and model molecules that have well-established chemical bond character. The results showed that the N O bond length and relative stability are proportional to the inductive effect of the substituents. Quantum chemical topology, natural bond orbitals (NBO), and natural resonance theory (NRT) analyses indicated that the N O bond is polar covalent in all the studied amine oxides, but the ionic contribution is different. NBO and NRT analyses revealed that molecules with more electronegative substituents have strongly delocalized N O and N R bonds, whereas molecules with electropositive substituents have localized bonds. 相似文献
993.
A new modified carbon paste electrode based on multi-walled carbon nanotubes and a synthesized Schiff base of N,N'-bis(2-hydroxybenzylidene)-2,2'(aminophenylthio) ethane, acting as a chelating agent for Ag(I) ions, is described. The electroanalytical procedure for the determination of Ag(I) was comprised of two steps: the chemical accumulation of the analyte under open-circuit conditions followed by replacing the medium with a 0.1 M HCl solution where the accumulated Ag(I) was reduced for 20 s in -0.7 V. The potential was then scanned from -0.2 to +0.2 V to obtain the voltammetric peak. The effective parameters in the sensor response were examined. Under optimized operational conditions, a linear response range from 0.5-200 ng mL(-1) was obtained. The detection limit for silver determination was 0.092 ng mL(-1). For 7 successive determinations of 15.0 and 60.0 ng mL(-1) of Ag(I), relative standard deviations of 2.2% and 1.2% were obtained, respectively. The procedure was applied in determining Ag(I) in X-ray photographic films and water samples. 相似文献
994.
The insertion of isocyanates in (Bn(2)Cyclam)ZrX(2) is regioselective; (Bn(2)Cyclam)Zr(OR)(2) produces urea-like moieties by the insertion of RN═C═O in the Zr-N(amido) bonds of the cyclam ring. Depending on the bulkiness of the isocyanate R groups, O- and N-bound ureates are formed. (Bn(2)Cyclam)Zr(NH(t)Bu)(2) reacts with MesN═C═O at the terminal Zr-N bonds. 相似文献
995.
Andrea Vasas Edvárd Sulyok Ana Martins Dóra Rédei Peter Forgo Zoltán Kele István Zupkó Joseph Molnár Gyula Pinke Judit Hohmann 《Tetrahedron》2012,68(4):1280-1285
Two new and one known cyclomyrsinane-type diterpenes (1–3) were isolated from the methanol extract of the whole, undried plant of Euphorbia falcata, native to Hungary. The structures and relative configuration of the compounds were established on the basis of extensive spectroscopic analysis, including HRESIMS and one- and two-dimensional NMR techniques. These compounds are hexa- and heptaesters of diterpene polyols, esterified with acetic, propanoic, isobutanoic, 2-methylbutanoic, and benzoic acids. This type of diterpenes was previously detected only in three Euphorbia species (Euphorbia teheranica, Euphorbia seguieriana, and Euphorbia prolifera). The compounds, together with premyrsinanes isolated previously from this plant were evaluated for their antiproliferative activity against HeLa, Ishikawa, and MCF7 mouse lymphoma cells, and for their capacity to modulate resistance to doxorubicin in L5178 mouse lymphoma cells that over-express the MDR1 efflux pump. Compounds did not show substantial antiproliferative activity against any of the tested cell lines. However all compounds act in a mild to a very strong synergism with doxorubicin against the MDR mouse lymphoma cell line. 相似文献
996.
Emerson A. Guarda Mara R.B. Marzari Clarissa P. Frizzo Patrícia M. Guarda Nilo Zanatta Helio G. Bonacorso Marcos A.P. Martins 《Tetrahedron letters》2012,53(2):170-172
Synthesis of 4-alkoxy-1,1-dichloro-3-alken-2-ones [CHCl2C(O)C(R2)C(R1)-OR, where R, R1, R2 = Et, H, H; Me, Me, H; Et, H, Me; Me, –(CH2)2–; Me, –(CH2)3–; Et, Et, H; Et, Bu, H; Et, i-Pr, H; Et, i-Bu, H; Me, Ph, H; Me, thien-2-yl, H] from acylation of enol ethers and acetals with dichloroacetyl chloride, in ionic liquid ([BMIM][BF4] or [BMIM][PF6]) is reported. The synthesis of alkenones [R3–C(O)C(R2)C(R1)-OR], where R/R1/R2/R3 = Et/H/H/Ph, t-Bu/H/H/Ph, Me/-(CH2)4/Ph, Me/-(CH2)4/Me] from the reaction of enol ethers with benzoyl chloride or acetyl chloride, in ionic liquid [BMIM][BF4], is also reported. Last products are described for the first time. 相似文献
997.
998.
V. Gokulakrishnan S. Parthiban E. Elangovan K. Jeganathan D. Kanjilal K. Asokan R. Martins E. Fortunato K. Ramamurthi 《Radiation Physics and Chemistry》2012,81(6):589-593
Molybdenum (0.5 at%) doped indium oxide thin films deposited by spray pyrolysis technique were irradiated by 100 MeV O7+ ions with different fluences of 5×1011, 1×1012 and 1×1013 ions/cm2. Intensity of (222) peak of the pristine film was decreased with increase in the ion fluence. Films irradiated with the maximum ion fluence of 1×1013 ions/cm2 showed a fraction of amorphous nature. The surface microstructures on the surface of the film showed that increase in ion fluence decreases the grain size. Mobility of the pristine molybdenum doped indium oxide films was decreased from ~122 to 48 cm2/V s with increasing ion fluence. Among the irradiated films the film irradiated with the ion fluence of 5×1011 ions/cm2 showed relatively low resistivity of 6.7×10?4 Ω cm with the mobility of 75 cm2/V s. The average transmittance of the as-deposited IMO film is decreased from 89% to 81% due to irradiation with the fluence of 5×1011 ions/cm2. 相似文献
999.
1000.
João Marcos do Ó Abiel Costa Macedo 《Calculus of Variations and Partial Differential Equations》2014,51(1-2):195-215
This paper brings a generalization of the Lions concentration–compactness principle to the Sobolev space \(W_0^{m,p}(\Omega )\) when \(mp=n\) and \(\Omega \subset \mathbb {R}^n \, (n \ge 2)\) is a smooth domain with finite \(n\) -measure. Moreover, our result sharpens an inequality by D. Adams improving its best exponent. The proof is established using the decreasing rearrangement and comparison principle due to Talenti combined with the maximum principle. It is also shown how this concentration–compactness principle yields the existence of critical points of mountain-pass type for an energy functional associated with a class of polyharmonic problems. 相似文献