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排序方式: 共有139条查询结果,搜索用时 31 毫秒
81.
Grimaneza Teixeira Ana R. Santana M. Salomé Pais Alda Clemente 《Applied biochemistry and biotechnology》2000,88(1-3):299-312
We report on the screening of different enzymes such as arylamidases, lipases, proteinases, and glucosidases in plant extracts
of the Cactaceae family, genus Opuntia, as well as on a newly purified plant proteases from O. ficus-indica fruit extracts. These proteinases showed the maximum activity at pH 5.2 and 55°C and FTC-casein was the best of the escreened
substrates. Proteolytic activities were activated by anti-oxidant compounds and by some divalent cations. These proteinases
were efficiently inhibited by cystein proteinase inhibitors and by 1,10-phenanth roline. The estimated M
t for the main proteolytic activity was about 23.2 kDa. The results on milk clotting characteristics suggest a potential use
of the fruit cystein enzymes of this plant in dairy industries. 相似文献
82.
ZDM – Mathematics Education - Blended learning, which combines face-to-face workshops with self-directed online learning, is becoming a good alternative in designing and deploying... 相似文献
83.
M. Sánchez-Cabezudo R. M. Masegosa C. Salom M. G. Prolongo 《Journal of Thermal Analysis and Calorimetry》2010,102(3):1025-1033
The mechanical properties of poly(vinyl acetate) (PVAc)/epoxy thermosets as a function of the PVAc content were investigated
through dynamic mechanical thermal analysis from −100 to 220 °C and through tensile tests at room temperature. The morphology
of the thermosets was examined by scanning electron microscopy. Cured PVAc/epoxy blends are phase separated, arising two phases
that correspond to a PVAc-rich phase and to the epoxy rich-phase. The morphology evolves from nodular to inverted as the PVAc
content increases. Intermediate compositions present combined morphologies, in which nodular and inverted regions are detected.
The tensile properties at room temperature reveal that combined morphologies present the most ductile behaviour. The glass
transition temperatures (T
g) of PVAc and of epoxy phases in the blends are different from those of the neat polymers. The profile of the loss modulus
(E″)–temperature curves are correlated with the change in morphology that appears increasing the PVAc content. The storage modulus
(E′)–temperature curves are highly dependent on the morphology of the samples. The E′-composition dependence is predicted using several models for two-phase composites. The low-temperature β-relaxation of the
epoxy is slightly modified by the presence of PVAc. The activation energies of the α and β-relaxations are not dependent on
the blend morphology. 相似文献
84.
Rodríguez-Morgade MS Torres T Atienza-Castellanos C Guldi DM 《Journal of the American Chemical Society》2006,128(47):15145-15154
A novel supramolecular electron donor-acceptor hybrid (1) has been designed through axial coordination of a perylenebisimide moiety [BPyPDI], bearing two 4-pyridyl substituents at the imido positions, to the ruthenium(II) metal centers of two phthalocyanines [Ru(CO)Pc]. This modular protocol enables access to electron donor-acceptor hybrids with potentially great design flexibility. The new array (1) has been characterized by standard spectroscopic methods, and its photophysical behavior has been established by using ultrafast and fast time-resolved techniques. Photoexcitation of either chromophore leads to a product that is essentially identical for both pathways, that is, evolving from the [Ru(CO)Pc] or [BPyPDI] singlet excited state. Features of the photoproduct are new transient maxima at 530 and 725 nm, plus transient minima at 580 nm and 650 nm. Based on the radiolytically generated [BPyPDI*-] (i.e., one-electron reduction of [BPyPDI]) and [Ru(CO)Pc*+] (i.e., one-electron oxidation of [Ru(CO)Pc]) features, which in the 300 and 900 nm range remarkably resemble those noted for photoexcited 1, we attribute the photolytically generated species to the composite spectrum of the [Ru(CO)Pc*+ -BPyPDI*- -RuCOPc] radical ion pair state. Its lifetime, which is on the order of 115 +/- 5 ns, reveals a significant stabilization and confirms that the strongly exothermic charge recombination dynamics are placed deeply in the inverted region of the Marcus parabola. 相似文献
85.
Nieto-Oberhuber C López S Jiménez-Núñez E Echavarren AM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(23):5916-5923
Three pathways actually compete in metal-catalyzed cyclizations of enynes in which the metal selectively activates the alkyne: an endocyclic process and two exo-cyclizations, one proceeding by anti attack of the alkene and a second one resulting in a syn addition. Although cyclobutenes may be formed in transition-metal-catalyzed cyclization of some enynes, particularly, 1,7-enynes, these compounds are not necessarily the intermediates in the skeletal rearrangement. Cyclobutenes are formed by ring expansion of syn-cyclopropyl metal-carbenes formed in the syn pathway. 相似文献
86.
High Frequency Solutions for the Singularly-Perturbed One-Dimensional Nonlinear Schrödinger Equation
Patricio Felmer Salomé Martínez Kazunaga Tanaka 《Archive for Rational Mechanics and Analysis》2006,182(2):333-366
This article is devoted to the nonlinear Schrödinger equation when the parameter ε approaches zero. All possible asymptotic behaviors of bounded solutions can be described by means of envelopes, or alternatively by adiabatic profiles. We prove that for every envelope, there exists a family of solutions reaching that asymptotic behavior, in the case of bounded intervals. We use a combination of the Nehari finite dimensional reduction together with degree theory. Our main contribution is to compute the degree of each cluster, which is a key piece of information in order to glue them. 相似文献
87.
Jiménez AJ Marcos ML Hausmann A Rodríguez-Morgade MS Guldi DM Torres T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(50):14139-14146
Phthalocyanine (Pc) dimers connected through trans-platinum(II) diacetylide linkers have been prepared by reaction of the corresponding ethynylphthalocyanines with trans-bis(triethylphosphine)platinum(II) chloride. Special emphasis was placed on the analysis of the ground- and excited-state features of these compounds in relation to butadiyne-bridged Pc dimers and the corresponding monomers. Both Zn(II)-containing Pc dimers exhibit long-lived triplet excited states. The insertion of σ-bonded trans-platinum(II) diacetylide spacers decoupled the two Pc groups and led to an appreciable acceleration (by a factor of up to 10) of the radiative and nonradiative decay rate of the singlet and triplet excited states. 相似文献
88.
S. Calvo J. Escribano M. G. Prolongo R. M. Masegosa C. Salom 《Journal of Thermal Analysis and Calorimetry》2011,103(1):195-203
The effect of a low profile additive, poly(ε-caprolactone) (PCL), on the thermal and mechanical properties of unsaturated
polyester resins (UP) was investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA),
and tensile tests. The morphology of the systems has been studied by scanning electronic microscopy (SEM). Two PCL molecular
mass were selected (PCL2: M
n = 2000 g mol−1 and PCL50: M
n = 50000 g mol−1) to analyze the influence of the molecular mass and the content of PCL on the UP resins and to establish the relation between
thermomechanical behavior and morphology. DSC and DMTA glass transition temperatures (T
g) of the UP cured samples containing PCL indicate that PCL2 is miscible with UP whereas for UP + PCL50 system, T
g values are very close to the ones corresponding to neat UP. Besides in UP + PCL2 systems, one phase morphology is observed
in which PCL2 would act as solvent of the reacting mixture along curing process; however, UP + PCL50 systems present phase-separated
morphology. The presence of PCL2 and PCL50 in UP resin leads to a decrease of the tensile strength and the Young′s modulus
as much notorious as the PCL concentration increases. For UP + PCL2 system the elongation at fracture increases in relation
to neat UP, increasing as well with the PCL content. 相似文献
89.
90.
Eckert AK Rodríguez-Morgade MS Torres T 《Chemical communications (Cambridge, England)》2007,(40):4104-4106
Genuine B-B linked subphthalocyanine dimers are synthesized through Wurtz coupling of readily accessible chlorosubphthalocyanines. 相似文献