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201.
Diastereomeric gamma-dilactones isolated from Pterogorgia spp allowed the establishment of (13)C NMR-based empirical rules to determine the relative stereochemistry of 3-alkyl-4-hydroxy-5-methyl-2(5H)-dihydrofuranones, gamma-lactone moieties ubiquitous in many bioactive synthetic and natural products. An NMR-based method using Pirkle's reagent at low temperature allowed the absolute configuration of the naturally occurring dibutenolides to be unambiguously determined. A biogenetic pathway that involves oxidation of long-chain (C16:0 and C18:0) fatty acids is proposed. [structure: see text] 相似文献
202.
M.S. Baptista E.J. Ngamga Paulo R.F. Pinto Margarida Brito 《Physics letters. A》2010,374(9):1135-1140
Observing how long a dynamical system takes to return to some state is one of the most simple ways to model and quantify its dynamics from data series. This work proposes two formulas to estimate the KS entropy and a lower bound of it, a sort of Shannon's entropy per unit of time, from the recurrence times of chaotic systems. One formula provides the KS entropy and is more theoretically oriented since one has to measure also the low probable very long returns. The other provides a lower bound for the KS entropy and is more experimentally oriented since one has to measure only the high probable short returns. These formulas are a consequence of the fact that the series of returns do contain the same information of the trajectory that generated it. That suggests that recurrence times might be valuable when making models of complex systems. 相似文献
203.
Dynamic clustering for interval data based on L
2 distance 总被引:2,自引:0,他引:2
Francisco de A. T. de Carvalho Paula Brito Hans-Hermann Bock 《Computational Statistics》2006,21(2):231-250
Summary This paper introduces a partitioning clustering method for objects described by interval data. It follows the dynamic clustering
approach and uses and L
2 distance. Particular emphasis is put on the standardization problem where we propose and investigate three standardization
techniques for interval-type variables. Moreover, various tools for cluster interpretation are presented and illustrated by
simulated and real-case data. 相似文献
204.
205.
Synthesis of Pyridazinones through the Copper(I)‐Catalyzed Multicomponent Reaction of Aldehydes,Hydrazines, and Alkynylesters
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Anderson C. Mantovani Tales A. C. Goulart Prof. Dr. Davi F. Back Prof. Dr. Gilson Zeni 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(39):12663-12668
The copper‐catalyzed multicomponent cyclization reaction, which combined aldehydes, hydrazines, and alkynylesters, was applied in the synthesis of pyridazinones. The reaction was regioselective and gave only six‐membered pyridazinones in the complete absence of five‐membered pyrazoles or a regioisomeric mixture. During this investigation, the use of 2‐halobenzaldehyde as the starting material, under identical reaction conditions, gave 6‐(2‐ethoxyphenyl)pyridazinones after sequential Michael addition/1,2‐addition/Ullmann cross‐coupling reactions. 相似文献
206.
Adding Remnant Magnetization and Anisotropic Exchange to Propeller‐like Single‐Molecule Magnets through Chemical Design
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Kátia Cristina M. Westrup Dr. Marie‐Emmanuelle Boulon Dr. Pasquale Totaro Dr. Giovana G. Nunes Dr. Davi F. Back Dr. Andersson Barison Dr. Martin Jackson Dr. Carley Paulsen Prof. Dante Gatteschi Dr. Lorenzo Sorace Prof. Andrea Cornia Prof. Jaísa F. Soares Prof. Roberta Sessoli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(42):13681-13691
The selective replacement of the central iron(III) ion with vanadium(III) in a tetrairon(III) propeller‐shaped single‐molecule magnet has allowed us to increase the ground spin state from S=5 to S=13/2. As a consequence of the pronounced anisotropy of vanadium(III), the blocking temperature for the magnetization has doubled. Moreover, a significant remnant magnetization, practically absent in the parent homometallic molecule, has been achieved owing to the suppression of zero‐field tunneling of the magnetization for the half‐integer molecular spin. Interestingly, the contribution of vanadium(III) to the magnetic anisotropy barrier occurs through the anisotropic exchange interaction with iron(III) spins and not through single ion anisotropy as in most single‐molecule magnets. 相似文献
207.
Ana Frangolho Bruno E. Correia Daniela C. Vaz Zaida L. Almeida Rui M. M. Brito 《Molecules (Basel, Switzerland)》2020,25(23)
One of the molecular hallmarks of amyloidoses is ordered protein aggregation involving the initial formation of soluble protein oligomers that eventually grow into insoluble fibrils. The identification and characterization of molecular species critical for amyloid fibril formation and disease development have been the focus of intense analysis in the literature. Here, using photo-induced cross-linking of unmodified proteins (PICUP), we studied the early stages of oligomerization of human transthyretin (TTR), a plasma protein involved in amyloid diseases (ATTR amyloidosis) with multiple clinical manifestations. Upon comparison, the oligomerization processes of wild-type TTR (TTRwt) and several TTR variants (TTRV30M, TTRL55P, and TTRT119M) clearly show distinct oligomerization kinetics for the amyloidogenic variants but a similar oligomerization mechanism. The oligomerization kinetics of the TTR amyloidogenic variants under analysis showed a good correlation with their amyloidogenic potential, with the most amyloidogenic variants aggregating faster (TTRL55P > TTRV30M > TTRwt). Moreover, the early stage oligomerization mechanism for these variants involves stepwise addition of monomeric units to the growing oligomer. A completely different behavior was observed for the nonamyloidogenic TTRT119M variant, which does not form oligomers in the same acidic conditions and even for longer incubation times. Thorough characterization of the initial steps of TTR oligomerization is critical for better understanding the origin of ATTR cytotoxicity and developing novel therapeutic strategies for the treatment of ATTR amyloidosis. 相似文献
208.
Danitza Vargas Ivn Brito Andrea Reyes Alejandro Crdenas Matías Lpez‐Rodríguez 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(1):o48-o50
The structure of title compound, C6H16N+·C14H8N3O7S−, comprises discrete ions which are interconnected by N—H⋯O− and N—H+⋯O− hydrogen bonds, leading to a neutral one‐dimensional network along [100]. These hydrogen bonds appear to complement the Coulombic interaction and help to stabilize the structure further. 相似文献
209.
210.