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121.
Claudio Parra Emilio Soto Gloria León Cristian O. Salas Michael Heinrich Carlos Echiburú-Chau 《Natural product research》2018,32(6):719-722
Continuing with our study characterising Senecio nutans Sch. Bip., we have isolated and identified a simple coumarin, scopoletin, that could be relevant for the biological properties of the species related with the ancestral medical uses. This is the first report of scopoletin from S. nutans. In addition, the extract was analysed for its antioxidant activity using the ABTS and FRAP method as well as providing the first nutritional analyses of this plant from northern Chile highlands. 相似文献
122.
In this work we introduce the concept of n
–1-isomorphism between Steiner systems (this coincides with the concept of isomorphism whenever n=1).Precisely two Steiner systems S1
and S2
are said to be n–1-isomorphic if there exist n partial systems S
i
(1)
,...,S
i
(n)
contained in Si, i.{1,2},such that S
1
(k)
and S
2
(k)
are isomorphic for each k{1,..., n}.The n–1-isomorphisms are also used to study nets replacements, see Ostrom [8], and to study the transformation methods of designs and other incidence structures introduced in [9] and generalized in [1] and [10].Work done under the auspicies of G.N.S.A.G.A. supported by 40% grants of M.U.R.S.T. 相似文献
123.
Enhancement of the fluorescence of the blue fluorescent proteins by high pressure or low temperature
Mauring K Deich J Rosell FI McAnaney TB Moerner WE Boxer SG 《The journal of physical chemistry. B》2005,109(26):12976-12981
Green fluorescent proteins bearing the Y66H mutation exhibit strongly blue-shifted fluorescence excitation and emission spectra. However, these blue fluorescent proteins (BFPs) have lower quantum yields of fluorescence (Phi(f) approximately 0.20), which is believed to stem from the increased conformational freedom of the smaller chromophore. We demonstrate that suppression of chromophore mobility by increasing hydrostatic pressure or by decreasing temperature can enhance the fluorescence quantum yield of these proteins without significantly affecting their absorption properties or the shape of the fluorescence spectra. Analysis of the fluorescence lifetimes in the picosecond and nanosecond regimes reveals that the enhancement of the fluorescence quantum yield is due to the inhibition of fast quenching processes. Temperature-dependent fluorescence measurements reveal two barriers ( approximately 19 and 3 kJ/mol, respectively) for the transition into nonfluorescing states. These steps are probably linked with dissociation of the hydrogen bond between the chromophore and His148 or an intervening water molecule and to the barrier for chromophore twisting in the excited state, respectively. The chromophore's hydrogen-bond equilibrium at room temperature is dominated by entropic effects, while below approximately 200 K the balance is enthalpy-driven. 相似文献
124.
Gloria Fernandez-LorenteJose M Palomo Jany CoccaCesar Mateo Paola MoroMarco Terreni Roberto Fernandez-Lafuente Jose M Guisan 《Tetrahedron》2003,59(30):5705-5711
Purified lipases (via interfacial activation on hydrophobic supports) from different microbial extracts have been evaluated in the regio-selective hydrolysis of peracetylated sugars (peracetylated glucose, ribose and sucrose). Among the enzymes tested, lipases from Candida rugosa (CRL) and from Pseudomonas fluorescens (PFL) exhibited the best properties in these reactions.Then, we have prepared two different immobilized lipase preparations obtained by interfacial activation on hydrophobic supports or by covalent attachment on glutaraldehyde agarose. Interfacially activated lipases exhibited a higher activity than covalently attached enzymes (even by a 100-fold factor), giving the higher yields of mono deacetylated sugars (in some instances by more than a threefold factor) in short reaction times. In the hydrolysis of 1,2,3,5-tetra-O-acetyl-β-d-ribofuranose catalyzed by PFL adsorbed on octyl agarosa, hydrolyzed mainly the 3 position (30% of yield) while the CRL gave the hydrolysis only in position 5 (about 50% of yield).Depending on the enzyme immobilized preparation, we have been able also to obtain selective hydrolysis of 1,2,3,4,6-penta-O-acetyl-α/β-d-glucopyranose obtaining a free hydroxyl group in position 1, 4 or 6. Moreover, selective hydrolysis in the 4′ position of peracetylated sucrose was achieved when the hydrolysis is performed with CRL immobilized on octyl-agarose (yield was 77%). 相似文献
125.
Saboury AA Bagheri S Ataie G Amanlou M Moosavi-Movahedi AA Hakimelahi GH Cristalli G Namaki S 《Chemical & pharmaceutical bulletin》2004,52(10):1179-1182
Thermodynamic studies were carried out to evaluate the binding of theophylline on adenosine deaminase (ADA) in 50 mM sodium phosphate buffer pH 7.5, at 300 K, using isothermal titration calorimetry (ITC). A simple method for determination of binding isotherm in the drug--ADA interaction was applied using ITC data. ADA has two binding sites for theophylline, which show positive cooperativity in its sites. The intrinsic association equilibrium constants are 6 and 52 mM(-1) in the first and second binding sites, respectively. Hence, occupation of the first site has produced an appreciable enhancement by 8.7 of the binding affinity of the second site. The molar enthalpies of binding are -12.2 and -14.9 kJ/mol in the first and second binding sites, respectively. 相似文献
126.
Díez-Peña E Frutos G Frutos P Barrales-Rienda JM 《Chemical & pharmaceutical bulletin》2002,50(9):1201-1208
The purpose of the present work was the study of the gentamicin sulphate (GS) release from a commercial acrylic bone cement CMW-1 with the aims of establishing the influence of the slabs preparation as well as the release mechanism and kinetics. The effect of the amount of GS on the release kinetic parameters has been also investigated. In vitro release studies were performed in a buffered saline solution at pH 7.4 and 37 degrees C. The GS concentration was determined using an indirect spectrophotometric method with an o-phthaldialdehyde as a derivatizing reagent. A commercial and three modified samples were tested. The free and fractured surfaces of the GS cement slabs before and after the release studies were observed by means of scanning electron microscopy (SEM). For low GS concentration loading the release was very incomplete because most of the GS beads were encapsulated by the hydrophobic PMMA matrix. A higher amount of antibiotic was released from cement that has a higher amount incorporated. A model and therefore a mechanism of release based on this model have been proposed. It has allowed us to explain the changes in dissolution kinetics of an acrylic matrix type controlled release system up to 12% GS loading. The cumulative amount of GS released M(t)/M(i), was fitted as a function of time. For lower amounts of GS, the regression analysis (R(2)>0.99) revealed that the release is most adequately represented by M(t)/M(i)=b+kt(n), where b represents a burst effect. The goodness of fit decreases as the amount of GS increases. The influence of some other type of release mechanism for higher amounts of GS must be taken into account and a second model for the release, M(t)/M(i)=b+k x [1-exp(-kt)], is proposed. 相似文献
127.
Raffaella Ruffini Alessandro Borghi Roberto Cossio Filippo Olmi Gloria Vaggelli 《Mikrochimica acta》2002,139(1-4):151-158
Quartz is a common phenocryst in acidic volcanic rocks but rarely contributes to the understanding of the magmatic or eruptive
processes due to its apparent chemical homogeneity. Cathodoluminescence studies indicate that volcanic quartz is strongly
zoned with respect to the trace elements. The determination of this zoning can help to elucidate the crystallisation history
of the magmatic rock. Polished thin sections from rhyolitic and dacitic volcanic rocks were examined by cathodoluminescence
mounted on an optical microscope and analysed by electron probe microanalysis. X-ray mapping of the trace elements incorporated
in the zoned quartz was also performed. The interpretation of the data obtained from these different analytical methods provides
useful information on the chemical zoning of single crystals and therefore on the chemico-physical conditions of the melt
from which the quartz crystallised. Quartz from dacitic rock shows a complex cathodoluminescence oscillatory zoning, consisting
of large red-brown and blue bands concentric to a resorbed core. Quartz from rhyolite shows simpler cathodoluminescence zoning,
consisting of dark to bright blue luminescent bands. The EMPA analyses and the X-ray maps combined with the cathodoluminescence
images suggest a clear correlation between the concentrations of some trace element (mainly Al and Ti, acting as activators
of luminescence) and the cathodoluminescence colours pattern zoning. The incorporation of these trace elements during the
growth of the crystals is linked to small variations in the thermo-chemical properties of the magma such as temperature and
chemical composition. 相似文献
128.
Alessandro Borghi Roberto Cossio Filippo Olmi Raffaella Ruffini Gloria Vaggelli 《Mikrochimica acta》2002,139(1-4):17-25
A comparison between major and trace element concentrations in garnet performed by electron microprobe (EPMA) technique is
reported. Quantitative spot analyses and X-ray maps of major elements (Fe, Mg, Mn, Ca) and the trace element yttrium in garnets
from metamorphic rocks are presented. The selected garnet samples come from meta-pelitic and meta-basic specimens belonging
to the tectonic unit of the Monte Rosa Nappe (Western Alps).
In the metapelites, the quantitative Y distribution maps display a prominent increase at the core, the Y abundance varying
by over two orders of magnitude, from about 80 ppm (rim) to over 2100 ppm (core). The Y profiles show well defined patterns
with sharp features that do not correlate with major element distributions. A roughly comparable pattern can be supposed only
with Mn. The Y distribution suggests that the diffusion of Y through the garnet is very slow compared to the major elements,
thus the Y results are suitable for geothermometric estimates.
In the metabasites, the Y spatial distribution is characterised by an increasing content from the core to the rim, displaying
a zoning pattern opposite to the metapelite garnet. Quantitative EPMA analyses range from 1100 ppm at the rim to values lower
than the detection limit at the core.
Therefore, the Y content in the garnet can be related to several chemical and physical variables such as the bulk rock composition
and the phase assemblage. In particular, in the xenotime-bearing metapelitic system the Y distribution seems to be correlated
with metamorphic peak temperature. 相似文献
129.
Francisco Palacios Esther Herrán Concepción Alonso Gloria Rubiales 《Tetrahedron》2006,62(33):7661-7666
Aza-Wittig reaction of N-vinylic phosphazenes with α,β-unsaturated aldehydes leads to the formation of 3-azatrienes through a [2+2]-cycloaddition-cycloreversion process. Subsequent, regioselective [4+2]-cycloaddition of 3-azatrienes with pyrrolidinocycloalkanone affords bicyclic dihydropyridines and pyridines in a regioselective fashion. 2-Heterodiene moiety of azatriene is involved in the formation of the six-membered ring skeleton of pyridine derivatives. 相似文献
130.
F. Feigl und R. A. Rosell 《Fresenius' Journal of Analytical Chemistry》1958,159(5):335-339
Zusammenfassung Gewisse organische Oxydantien können durch Tüpfelreaktionen auf mit Thio-Michlers Keton oder Tetrotan imprägniertem Fallerpapier nachgewiesen werden. Es entstehen blaue Flecke. Die Erfassungsgrenzen der Nachweise liegen zwischen 0,04 und 1,2 g.N-Brom-(Chlor)-succinimid reagiert mit alkalischen TlI-Salzlösungen unter Bildung von braunem Tl O(OH), das einen selektiven Nachweis dieser Verbindungen ermöglicht.Chloramin T kann in alkalischer Lösung neben Alkalihypochlorit nachgewiesen werden nach Zersetzung des Hypochlorites mit Wasserstoffperoxyd und Zinkchlorid und darananschließender Farbreaktion mit Thio-Michlers Keton. 相似文献