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61.
Mg/Al hydrotalcite acts as an efficient heterogeneous basic catalyst for the synthesis of 4H-pyrano[2,3-c]pyrazoles via a multicomponent reaction of aromatic hydrazine hydrate, ethyl acetoacetate, aldehydes, and malononitrile in ethanol at ambient temperature. The hydrotalcite catalyst was easily separated from the reaction mixture and can be reused.
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Helane?MS?Costa Augusto?CV?Freitas Júnior Ian?PG?Amaral Izaura?Y?Hirata Patrícia?MG?Paiva Luiz?B?CarvalhoJr Vitor?Oliveira Ranilson?S?BezerraEmail author 《Chemistry Central journal》2013,7(1):166
Background
Over the past decades, the economic development and world population growth has led to increased for food demand. Increasing the fish production is considered one of the alternatives to meet the increased food demand, but the processing of fish leads to by-products such as skin, bones and viscera, a source of environmental contamination. Fish viscera have been reported as an important source of digestive proteases with interesting characteristics for biotechnological processes. Thus, the aim of this study was to purify and to characterize a trypsin from the processing by-products of crevalle jack (Caranx hippos) fish.Results
A 27.5 kDa trypsin with N-terminal amino acid sequence IVGGFECTPHVFAYQ was easily purified from the pyloric caeca of the crevalle jack. Its physicochemical and kinetic properties were evaluated using N-α-benzoyl-DL-arginine-p-nitroanilide (BApNA) as substrate. In addition, the effects of various metal ions and specific protease inhibitors on trypsin activity were determined. Optimum pH and temperature were 8.0 and 50°C, respectively. After incubation at 50°C for 30 min the enzyme lost only 20% of its activity. K m , kcat, and k cat /K m values using BApNA as substrate were 0.689 mM, 6.9 s-1, and 10 s-1 mM-1, respectively. High inhibition of trypsin activity was observed after incubation with Cd2+, Al3+, Zn2+, Cu2+, Pb2+, and Hg2+ at 1 mM, revealing high sensitivity of the enzyme to metal ions.Conclusions
Extraction of a thermostable trypsin from by-products of the fishery industry confirms the potential of these materials as an alternative source of these biomolecules. Furthermore, the results suggest that this trypsin-like enzyme presents interesting biotechnological properties for industrial applications.64.
Linear and weakly non-linear analyses of convection in a second-order fluid is investigated. The Rivlin-Ericksen constitutive equation is considered to give viscoelastic correction to the momentum equation. The linear and non-linear analyses are, respectively, based on the normal mode technique and truncated representation of Fourier series. The linear theory reveals that the critical eigenvalue is independent of viscoelastic effects and the principle of exchange of stabilities holds. An autonomous system of differential equations representing cellular convection arising in the non-linear study is solved numerically. The non-linear analysis reveals that finite amplitudes have random behaviour. The effect of viscoelasticity on the non-linear solutions is analysed by considering different projections in the phase-space. Also, the transient behaviour concerning the variations of the Nusselt number with time has been investigated. The onset of chaotic motion is also discussed in this paper. 相似文献
65.
van Dongen PG 《Physical review letters》1989,63(12):1281-1284
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The effect of thermal modulation on the onset of convection in a horizontal, anisotropic porous layer saturated by a viscoelastic
fluid is investigated by a linear stability analysis. Darcy’s law with viscoelastic correction is used to describe the fluid
motion. The perturbation method is used to find the critical Rayleigh number and the corresponding wavenumber for small amplitude
thermal modulation. The stability of the system characterized by a correction Rayleigh number is calculated as a function
of the thermal and mechanical anisotropy parameters, the viscoelastic parameters and the frequency of modulation. It is found
that the onset of convection can be delayed or advanced by the factors represented by these parameters. The results of the
problem have possible implications in mantle convection. 相似文献
69.
B. S. Bhadauria P. G. Siddheshwar Jogendra Kumar Om P. Suthar 《Transport in Porous Media》2012,92(3):633-647
The effect of time-periodic temperature/gravity modulation on thermal instability in a fluid-saturated rotating porous layer
has been investigated by performing a weakly nonlinear stability analysis. The disturbances are expanded in terms of power
series of amplitude of convection. The Ginzburg–Landau equation for the stationary mode of convection is obtained and consequently
the individual effect of temperature/gravity modulation on heat transport has been investigated. Further, the effect of various
parameters on heat transport has been analyzed and depicted graphically. 相似文献
70.
Siddheshwar W. Kshirsagar 《Tetrahedron letters》2010,51(21):2924-811
A multicomponent one-pot reaction of aromatic aldehyde, malononitrile, and nitromethane is carried out in the presence of HTs (different Mg/Al ratios) and other solid bases, where 2-amino-5-nitro-4,6-diphenylcyclohex-1-ene-1,3,3-tricarbonitriles are obtained. HT with Mg/Al = 5 is the best catalyst for the reaction. The reaction gives best results under solvent-free condition. The catalyst can be easily separated and is recyclable. Other parameters were optimized. 相似文献