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91.
Rita C. Almeida‐Lafet Marcelo J. P. Ferreira Vicente P. Emerenciano Maria A. C. Kaplan 《Helvetica chimica acta》2010,93(12):2478-2487
In the first phytochemical study of the Aureliana genus (Solanaceae), two new withanolides, 1 and 2 , together with two known sterols, were isolated from the MeOH extract of the leaves of Aureliana fasciculata var. fasciculata. The structures were established as (4S,22R)‐16α‐acetoxy‐5β,6β‐epoxy‐4β,17α‐dihydroxy‐1‐oxowitha‐2,24‐dienolide (aurelianolide A) and (4S,22R)‐16α‐acetoxy‐4β,17α‐dihydroxy‐1‐oxowitha‐2,5,24‐trienolide (aurelianolide B). The new compounds possessed the unusual 16α,17α‐dioxygenated group and were fully characterized by spectroscopic techniques, including 1H‐ and 13C‐NMR (DEPT), as well as 2D‐NMR (HMBC, HMQC, 1H,1H‐COSY, NOESY) experiments, and HR‐MS. 相似文献
92.
Filgueira Dde M Guterres LP Votto AP Vargas MA Boyle RT Trindade GS Nery LE 《Photochemistry and photobiology》2010,86(6):1278-1284
The purpose of this study was to verify the occurrence of pigment dispersion in retinal pigment cells exposed to UVA and UVB radiation, and to investigate the possible participation of a nitric oxide (NO) pathway. Retinal pigment cells from Neohelice granulata were obtained by cellular dissociation. Cells were analyzed for 30 min in the dark (control) and then exposed to 1.1 and 3.3 J cm−2 UVA, 0.07 and 0.9 J cm−2 UVB, 20 n m β-PDH (pigment dispersing hormone) or 10 μ m SIN-1 (NO donor). Histological analyses were performed to verify the UV effect in vivo . Cultured cells were exposed to 250 μ m L-NAME (NO synthase blocker) and afterwards were treated with UVA, UVB or β-PDH. The retinal cells in culture displayed significant pigment dispersion in response to UVA, UVB and β-PDH. The same responses to UVA and UVB were observed in vivo . SIN-1 did not induce pigment dispersion in the cell cultures. l-NAME significantly decreased the pigment dispersion induced by UVA and UVB but not by β-PDH. All retinal cells showed an immunopositive reaction against neuronal nitric oxide synthases. Therefore, UVA and UVB radiation are capable of inducing pigment dispersion in retinal pigment cells of Neohelice granulata and this dispersion may be nitric oxide synthase dependent. 相似文献
93.
Marcelo Kobelnik Douglas Lopes Cassimiro Clóvis Augusto Ribeiro Diógenes dos Santos Dias Marisa Spirandeli Crespi 《Journal of Thermal Analysis and Calorimetry》2010,102(3):1167-1173
Two ONNO type naphtaldehyde derivative Schiff base compounds were reduced and two symmetric phenol-amine ligands containing
naphthalene groups were obtained; bis-N,N′[(2-hydroxy-1-naphtyl) methyl]-1,3-propanediamine (NAFLH) and bis-N,N′[(2-hydroxy-1-naphtyl) methyl]-2,2′-dimetyhyl-1,3-propanediamine (NAFLDMH). Homotrinuclear Ni(II) complexes of these ligands were prepared. The solid-state molecular structures of representative
nickel complex of NAFLDMH were determined using single crystal X-ray diffraction analysis. The terminal Ni(II) ions were found to be situated in between
the donor atoms of the organic ligand. The central Ni(II) ion was observed to be bonded via two different μ-bridges. The phenolic
oxygens and carboxylate ion were seen to form two different μ-bridges. TG analysis proved that the compounds have different
thermal characteristics than those cited in literature. The complexes showed extreme exothermic degradation reactions in inert
atmosphere. The complexes are ruptured with a two stepped exothermic reaction which appears huge heat over 300 °C. The heat
appeared in O2 atmosphere is observed to be higher than the heat appeared in inert atmosphere. Revealed heat is observed to be higher than
the conventional explosive materials. 相似文献
94.
95.
Rodrigo S. Corrêa Marcelo H. dos Santos Tanus J. Nagem Javier Ellena 《Structural chemistry》2010,21(3):555-563
Oxygenated xanthones have been extensively investigated over the years, but there are few reports concerning their crystal
structure. Our chemical investigations of Brazilian plants resulted in the isolation of four natural products named 1-hydroxyxanthone
(I), 1-hydroxy-7-methoxyxanthone (II), 1,5-dihydroxy-3-methoxyxanthone (III), and 1,7-dihydroxy-3,8-dimethoxyxanthone (IV).
The structures of these compounds were established on the basis of single crystal X-ray diffraction. The xanthone nucleus
conformation is essentially planar with the substituents adopting the orientations less sterically hindered. In addition,
classical intermolecular hydrogen bonds (O–H···O) present in III and IV give rise to infinite ribbons. However, the xanthone
I does not present any intermolecular hydrogen bonds, meanwhile the xanthone II presents only a non-classical one (C–H···O).
The crystal packing of all xanthone structures is also stabilized by π–π interactions. The fingerprint plots, derived from
the Hirshfeld surfaces, exhibited significant features of each crystal structures. 相似文献
96.
Simas ER Gehlen MH Pinto MF Siqueira J Misoguti L 《The journal of physical chemistry. A》2010,114(47):12384-12390
Polyfluorene end-capped with N-(2-benzothiazole)-1,8-naphthalimide (PF-BNI) is a highly fluorescent material with fluorescence emission modulated by solvent polarity. Its low energy excited state is assigned as a mixed configuration state between the singlet S(1) of the fluorene backbone (F) with the charge transfer (CT) of the end group BNI. The triexponential fluorescence decays of PF-BNI were associated with fast energy migration to form an intrachain charge-transfer (ICCT) state, polyfluorene backbone decay, and ICCT deactivation. Time-resolved fluorescence anisotropy exhibited biexponential relaxation with a fast component of 12-16 ps in addition to a slow one in the range 0.8-1.4 ns depending on the solvent, showing that depolarization occurs from two different processes: energy migration to form the ICCT state and slow rotational diffusion motion of end segments at a longer time. Results from femtosecond transient absorption measurements agreed with anisotropy decay and showed a decay component of about 16 ps at 605 nm in PF-BNI ascribed to the conversion of S(1) to the ICCT excited state. From the ratio of asymptotic and initial amplitudes of the transient absorption measurement, the efficiency of intrachain ICCT formation is estimated in 0.5, which means that, on average, half of the excited state formed in a BNI-(F)(n)-BNI chain with n = 32 is converted to its low energy intrachain charge-transfer (ICCT) state. 相似文献
97.
Marcelo H. Gehlen 《Cellulose (London, England)》2010,17(2):245-252
The acid hydrolysis of cellulose with crystalline and amorphous fractions is analyzed on the basis of autocatalytic model
with a positive feedback of acid production from the degraded biopolymer. In the condition of low acid rate production compared
with hydrolysis rate, both fraction of cellulose decrease exponentially with linear and cubic time dependence, and the normalized
number of scissions per cellulose chain follows a sigmoid behavior with reaction time. The model predicts that self generated
acidic compounds from cellulose accelerate the degradation of the biopolymer. However, if the acidic compounds produced are
volatile species, then their release under low pressure will reduce the global rate of degradation of cellulose toward its
intrinsic rate value determined by the residual acid catalyst present in the starting material. 相似文献
98.
Tests such as Bell's inequality and Hardy's paradox show that joint probabilities and correlations between distant particles in quantum mechanics are inconsistent with local realistic theories. Here we experimentally demonstrate these concepts in the time domain, using a photonic entangling gate to perform nondestructive measurements on a single photon at different times. We show that Hardy's paradox is much stronger in time and demonstrate the violation of a temporal Bell inequality independent of the quantum state, including for fully mixed states. 相似文献
99.
In this work, the influence of synthesis parameters on the synthesis efficiency of tin oxide nanomaterials was studied by
using the carbothermal reduction method in a sealed tube furnace. The parameters were the starting material, temperature and
time of synthesis as well as the gas flux. The starting material was tin dioxide mixed with carbon black in a molar proportion
of 1.5:1 and 1:1. The temperature range was from 950 to 1,125 °C with a step of 25 °C, and the synthesis times used were 15,
30, 45, 60, 75, 90, and 120 min. Using optimum values of the above parameters, the gas flux was changed to verify its influence.
After completion of the syntheses, we found a grayish-black material inside the tube which was characterized by X-ray diffraction
and scanning electron microscopy. The results showed that the collected material is composed of nanobelts (with width around
60 nm) and disks that grew preferentially in the SnO phase. A model based on the oxide vapor pressure was proposed to evaluate
the efficiency of the process, and the results showed good agreement between experimental data and the proposed model. Based
on the results obtained, the best conditions to obtain a homogeneous material with 95% efficiency is using a starting material
in the molar proportion Sn:C of 1.5:1, a temperature of 1,132 °C for 75 min, and a N2 gas flux of 80 sccm. 相似文献
100.
Marcelo G. Honnicke Jeffrey W. Keister Raymond Conley Konstantine Kaznatcheev Peter Z. Takacs David Scott Coburn Leo Reffi Yong Q. Cai 《Journal of synchrotron radiation》2011,18(6):862-870
Characterization and testing of an L‐shaped laterally graded multilayer mirror are presented. This mirror is designed as a two‐dimensional collimating optics for the analyzer system of the ultra‐high‐resolution inelastic X‐ray scattering (IXS) spectrometer at National Synchrotron Light Source II (NSLS‐II). The characterization includes point‐to‐point reflectivity measurements, lattice parameter determination and mirror metrology (figure, slope error and roughness). The synchrotron X‐ray test of the mirror was carried out reversely as a focusing device. The results show that the L‐shaped laterally graded multilayer mirror is suitable to be used, with high efficiency, for the analyzer system of the IXS spectrometer at NSLS‐II. 相似文献