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11.
12.
A phytochemical investigation in plantlets of the Brazilian medicinal tree Virola surinamensis resulted in the isolation and structural determination of four new compounds: 3-hydroxy-4-methyl-2-(11'-piperonyl-n-undecyl)-butenolide; 3-hydroxy-4-methyl-2-(7'-piperonyl-n-heptyl)-butanolide; 9'-(3,4-methylenedioxy-phenyl)-nonanoic acid and 13'-(3,4-methylene-dioxyphenyl)-tridecanoic acid. Thirteen compounds previously isolated from seeds and adult plants were also reported. 相似文献
13.
Angelini N Micali N Mineo P Scamporrino E Villari V Vitalini D 《The journal of physical chemistry. B》2005,109(39):18645-18651
Changes in the UV-vis spectra and induced circular dichroism (ICD) signals observed, in correspondence with the porphyrin Soret region, for aqueous solutions of achiral 5,10,15,20-tetrakis{p-[omega-methoxy poly(oxy-ethylene)]phenyl}porphyrin cobalt (II) (Co-P) and aromatic alpha-L-amino acids (Trp and Phe) give direct evidence for the coordination between the Co-P and amino acids. Considering that Co-P, besides the Co atom (one-fixation-point system), does not contain in the molecule active ligand groups and that no ICD signals have been observed in the case of Co-P/Ala, it has been concluded that hydrophobic interactions or stacking interactions between the aromatic rings of the porphyrin and those of Trp or Phe, acting as further amino acid (AA) fixation points, can strongly reduce the mobility of the chiral guest, thus permitting the generation of ICD signals. The effects of changes of both pH (in the range 2-9) and amino acid structure on the ICD phenomenon have also been investigated. In particular, the following have been observed: (i) strong ICD signals for all of the Co-P/N-acetyl amino acid aqueous solutions at pH 7, (ii) an unexpected ICD band with a bisignate form for the Co-P/Ala solution at pH 9 after long aging, and (iii) an opposite ICD signal when alpha-D-Phe and alpha-D-Trp enantiomers have been used. The data reported in this paper show how the binding mechanism between receptor and AAs changes by modulating properly the pH or the molecular structures and indicate that in these aqueous solutions the coordination Co-N is not the fundamental mechanism giving rise to the formation of the complexes and that the binding can be driven by hydrophobic interactions. These occurrences, through the analysis of the spectroscopic response (and, in particular, the form of the ICD band), can allow the recognition of AAs. 相似文献
14.
García-Río L Leis JR Moreira JA Araujo E Norberto F Ribeiro L 《The Journal of organic chemistry》2003,68(11):4330-4337
A kinetic study was carried out on the hydrolysis of two N-nitrosoguanidines, 1-nitroso-1-methyl-3-tolylsulfonylguanidine (TSGNO) and 1-nitroso-1-methyl-3-benzoylguanidine (BCGNO). We observed an absence of buffer catalysis using H(2)PO(4)(-)/HPO(4)(2)(-), H(3)BO(3)/H(2)BO(3)(-), and HCO(3)(-)/CO(3)(2)(-) regulators and a complex dependency of the rate constant on the pH. We discovered the existence of three simultaneous reaction paths: spontaneous decomposition of the neutral form of the N-nitrosoguanidine, decomposition of the monoanion, and decomposition through the form of the dianion. The analysis of the kinetic data has allowed us to obtain the acidity constant for the formation of the monoanion of the N-nitrosoguanidine, with values of p = 11.5. The reaction rate for the process through the monoanion, k(2), decreases as the acidity increases. The application of the principle of nonperfect synchronization shows that the basicity and reactivity do not correlate when there exists a possibility of stabilization of the negative charge by resonance. This behavior is consistent with the mechanism E1cB whereby the stabler the negative charge, the slower the elimination reaction. When dealing with the case of the elimination through the neutral form we observe that the reaction rate increases together with the capacity of stabilization of the positive charge on the nitrogen atom adjacent to the imino group. For the reaction through the dianion we used a maximum value of k(3) = 10(10) s(-)(1) to estimate the value of p for the formation of the dianion of the N-nitrosoguanidine, obtaining values of p < 24. 相似文献
15.
Lopes NP Stark CB Hong H Gates PJ Staunton J 《Rapid communications in mass spectrometry : RCM》2002,16(5):414-420
Monensin A and B were studied by electrospray ionisation tandem mass spectrometry (ESI-MS/MS) and the fragment ions were confirmed by accurate-mass measurements. Analyses were performed on both a quadrupole time-of-flight (QTOF) and a Fourier-transform ion cyclotron resonance (FTICR) mass spectrometer. The analysis revealed that fragment ions were produced by Grob-Wharton fragmentations and pericyclic rearrangements in addition to various simple neutral losses. A study of the protonated and sodiated sodium salt revealed different fragmentation pathways for these species, thus complementary structural information could be gained. A complete fragmentation pathway of monensin A and B protonated sodium salt [(M-H+Na)+H])+) and sodiated sodium salt [(M-H+Na)+Na](+) is proposed. MS(3) analysis confirmed the separate fragmentation pathways. 相似文献
16.
Jose G. Trujillo‐Ferrara Rosa Luisa Santilln‐Baca Norberto Farfn‐García Itzia I. Padilla‐Martínez Efrn V. García‐Bez 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(3):o125-o128
The molecular and supramolecular structures of 2‐(1,3‐dioxo‐2,3,3a,4,7,7a‐hexahydro‐1H‐isoindol‐2‐yl)phenyl acetate, C16‐H15NO4, (I), and its para isomer, 4‐(1,3‐dioxo‐2,3,3a,4,7,7a‐hexahydro‐1H‐isoindol‐2‐yl)phenyl acetate, (II), are reported. The torsion angle between the succinimide and benzene rings depends on the position of the acetoxy substitution [89.7 (1) and 61.9 (1)° for (I) and (II), respectively]. The twist of the acetoxy group relative to the mean plane of the benzene ring is almost independent of the acetoxy position [66.0 (1) and 70.0 (1)°]. Packing interactions for both compounds include soft C—H⋯X (X = O and Ph) interactions, forming chains of centrosymmetric dimers and interlinked chains for (I) and (II), respectively. In addition, three perpendicular dipole C=O⋯C=O interactions contribute to the supramolecular structure of (II). 相似文献
17.
Gabriella Ieronimo Alessandro Mondelli Francesco Tibiletti Angelo Maspero Giovanni Palmisano Simona Galli Stefano Tollari Norberto Masciocchi Kenneth M. Nicholas Silvia Tagliapietra Giancarlo Cravotto Andrea Penoni 《Tetrahedron》2013
The thermal reaction between nitrosoarenes and alkynes under alkylating conditions produces N-alkoxyindoles as the major products in moderate to good yields and excellent regioselectivity. Various electrophiles are used affording different N–O-protected hydroxyindoles in a multi-component fashion. Privileged acetylenic substrates used in reactions with substituted nitrosoarenes are arylalkynes or propiolates. Potentially bioactive compounds and other classes of highly functionalizable indole products were prepared. Reactions between o-carbomethoxy-nitrosoarenes and arylacetylenes provided tricyclic compounds containing an acylaziridine indoline skeleton. 相似文献
18.
Norberto Manfredi Alberto Bianchi Valerio Causin Riccardo Ruffo Roberto Simonutti Alessandro Abbotto 《Journal of polymer science. Part A, Polymer chemistry》2014,52(5):719-727
The first use of PSn‐b‐PEOm‐b‐PSn block copolymers (PS = polystyrene, PEO = poly(ethylene oxide)) as solid hosts for iodine/iodide electrolytes in dye‐sensitized solar cells (DSSCs) is described. Using the benchmark photosensitizer N719, DSSC based on the quasi solid‐state electrolytes afforded efficiencies up to 6.7%, to be compared with an efficiency of 7.3% obtained in similar conditions with a conventional iodine/iodide liquid electrolyte. By varying the PS:PEO relative volume ratio in the block copolymers different properties and morphologies were obtained. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 719–727 相似文献
19.
20.
Renata Longhini Traudi Klein Marcos Luciano Bruschi Waldir Veríssimo da Silva Jr Juliana Rodrigues Norberto Peporine Lopes João Carlos Palazzo de Mello 《Journal of separation science》2013,36(7):1247-1254
The phenolic compounds are the main phytochemical constituents of the bark of Trichilia catigua and are commonly used for medicinal purposes. An HPLC method for the simultaneous quantification of phenolic compounds (procyanidin B2 (PB2), epicatechin (EPC), chinchonains Ia, Ib, IIa, IIb, catechin, and chrologenic acid) in T. catigua extract was developed and validated. A suitable chromatographic system was selected, which uses a gradient elution with methanol/ACN (75:25), and water both with 0.05% TFA, as mobile phase, column Luna, 280 nm, and flow 0.4 mL/min. Validation of the analytical method was based on the parameters: linearity, precision, LODs and LOQs, accuracy, robustness, and stability. The method showed linearity for PB2 and EPC, in the range 10–120 μg/mL with good correlation coefficients (>0.996). For precision, the repeatability ranged from 1.89 to 3.23%, and the values for accuracy for PB2 and EPC were 95 and 89%, respectively. The LODs and LOQs for PB2 were 1.36 and 4.12 μg/mL, and for EPC were 2.18 and 6.61 μg/mL, respectively. The method was robust under the conditions employed. The proposed method could be employed for quality assessment of T. catigua, as well as pharmaceutical products. 相似文献