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81.
Francisco Palacios Concepción Alonso Gloria Rubiales Maite Villegas 《Tetrahedron letters》2004,45(21):4031-4034
A method for the preparation of 3-fluoroalkyl substituted 2-aza-butadienes by aza-Wittig reaction of N-vinylic phosphazenes and aldehydes is reported. [4+2] Cycloaddition reaction with enamines affords fluoralkyl substituted pyridine derivatives in a regioselective fashion. 相似文献
82.
83.
Domingues MR Domingues P Reis A Fonseca C Amado FM Ferrer-Correia AJ 《Journal of the American Society for Mass Spectrometry》2003,14(4):406-416
New oxidation products and free radicals derived from tryptophan (Trp) oxidation under Fenton reaction conditions were identified
using mass spectrometry. After the oxidation of tryptophan using hydrogen peroxide and iron (II) system (Fenton reaction),
mono- and dihydoxy tryptophans and N-formylkynurenine were identified using electrospray mass spectrometry (ES-MS) and ES-MS/MS.
Besides these products, new products resulting from the reaction of tryptophan and oxidized tryptophan and 3-methyl indole
derivatives were also identified. The 3-methyl indole derivatives resulted, most probably, from the oxidation process and
not from in-source processes. A dimer formed by cross-linking between two Trp radicals (Trp-Trp), similar to the previously
described tyrosine dimer was observed, as well as the corresponding monohydroxy-dimer (Trp-Trp-OH). Tandem mass spectrometry
was used to identify the structures of these new oxidation products. Free radicals derived from tryptophan oxidation under
Fenton reaction were detected using as spin trap the DMPO. The free radical species originated during the oxidation reaction
formed stable adducts with the spin trap, and these adducts were identified by ES-MS. New adducts of oxidized tryptophan radicals,
namely monohydroxy-tryptophan and dihydroxy-Trp dimer radicals, with one and two DMPO spin trap molecules where identified.
Tandem mass spectrometry was used to confirm the proposed structure of the observed adducts. 相似文献
84.
Castro K Sarmiento A Maguregui M Martínez-Arkarazo I Etxebarria N Angulo M Barrutia MU González-Cembellín JM Madariaga JM 《Analytical and bioanalytical chemistry》2008,392(4):755-763
A complete study of several English polychromed alabaster sculptures is presented. The support, pigment, and binders were
characterised by combining μEDXRF, μRaman, and FTIR spectroscopies. Among the pigments, minium, vermilion, lead white, carbon
black, red iron oxide, and a degraded green copper pigment were determined, together with gold leaf. The presence of the rare
mineral moolooite (copper oxalate) was also found as a degradation product in the green areas, where weddellite (calcium oxalate
dihydrate) was also determined. These facts, together with degradation of the green copper pigment, suggest microbiological
degradation of the original materials. Remains of glue and a varnish were also determined by FTIR spectroscopy and principal-components
analysis (PCA) of the spectra. Finally, PCA analysis was carried out to confirm whether the pieces came from the same quarry. 相似文献
85.
Fiuza SM Amado AM Marques MP de Carvalho LA 《The journal of physical chemistry. A》2008,112(14):3253-3259
In the light of the recognized anticancer properties of cisplatin-type inorganic systems, the exact knowledge of their conformational preferences is of the utmost importance for understanding their biological activity. The present study reports the use of theoretical (quantum mechanical) calculations for achieving this goal. An alternative calculation method to the use of the AE basis sets, both accurate and computationally feasible, was presently tested for the conformational and vibrational study of cis-diamminedichloroplatinum(II). Effective core potentials (ECPs) were used, within the HF methodology and, within the B3LYP and mPW1PW DFT protocols. The DFT methods (particularly mPW1PW) were found to be the best choice for describing cDDP (as compared to the HF methodology). 相似文献
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Positivity - We introduce both the notions of tensor product of convex bodies that contain zero in the interior, and of tensor product of 0-symmetric convex bodies in Euclidean spaces. We prove... 相似文献
89.
90.
José M. Matés José M. Segura Cristina Pérez-Gómez Maite Asenjo Miguel Blanca 《Research on Chemical Intermediates》2001,27(3):297-304
Although oxidative status has been related to several pathophysiologic processes, there is not a well established connection between antioxidant defense and allergy. An imbalance of reactive oxygen species is related to inflammation in allergic diseases. Antioxidant enzymes are involved in cell detoxification. This primary antioxidant defence system might work against allergic's symptoms. In this work, arguments in favour of the potential of free radical scavengers in antioxidant therapy for allergic patients are discussed. 相似文献