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21.
Macarena Eugui Katerine Rasquin Andrés López Radcenco Leopoldo Suescun Guillermo Moyna 《Tetrahedron letters》2018,59(16):1560-1563
We describe a novel pericyclic/anionic cascade reaction on tropolonic substrates that combines a Diels-Alder reaction, an oxa-Michael addition, and an acyloin rearrangement to afford tricyclic α-hydroxy-β-methoxyketones. Spectroscopic, crystallographic, and mechanistic studies indicate that the process requires stabilization of reaction intermediates through intramolecular H-bonding to take place, and suggest that the conjugate addition step involves a catalytic cycle with initial formation of an ammonium enolate and sustained by an alkoxide ion pair. Given the rich functionality and structural complexity generated in a single step, the process could be exploited in the preparation of natural product-like compound libraries. 相似文献
22.
23.
Juan Alfonso Redondo Enrique Martínez‐Campos Laetitia Plet Mnica Prez‐Perrino Rodrigo Navarro Guillermo Corrales Abhay Pandit Helmut Reinecke Alberto Gallardo Jos Luis Lpez‐Lacomba Alfonso Fernndez‐Mayoralas Carlos Elvira 《Macromolecular rapid communications》2016,37(7):575-583
The incorporation of cyclodextrins (CDs) to nonviral cationic polymer vectors is very attractive due to recent studies that report a clear improvement of their cytocompatibility and transfection efficiency. However, a systematic study on the influence of the CD derivatization is still lacking. In this work, the relevance of β‐CD permethylation has been addressed by preparing and evaluating two series of copolymers of the cationic N‐ethyl pyrrolidine methacrylamide (EPA) and styrenic units bearing pendant hydroxylated and permethylated β‐CDs (HCDSt and MeCDSt, respectively). For both cell lines, CDs permethylation shows a strong influence on plasmid DNA complexation, “in vitro” cytocompatibility and transfection efficiency of the resulting copolymers over two murine cell lines. While the incorporation of the hydroxylated CD moiety increased the cytotoxicity of the copolymers in comparison with their homopolycationic counterpart, the permethylated copolymers have shown full cytocompatibility as well as superior transfection efficiency than the controls. This behavior has been related to the different chemical nature of both units and tentatively to a different distribution of units along the polymeric chains. Cellular internalization analysis with fluorescent copolymers supports this behavior.
24.
Dr. Oscar Bertran Dr. Guillermo Revilla‐López Dr. Jordi Casanovas Dr. Luis J. del Valle Dr. Pau Turon Prof. Dr. Jordi Puiggalí Prof. Dr. Carlos Alemán 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(19):6631-6636
In spite of the clinical importance of hydroxyapatite (HAp), the mechanism that controls its dissolution in acidic environments remains unclear. Knowledge of such a process is highly desirable to provide better understanding of different pathologies, as for example osteoporosis, and of the HAp potential as vehicle for gene delivery to replace damaged DNA. In this work, the mechanism of dissolution in acid conditions of HAp nanoparticles encapsulating double‐stranded DNA has been investigated at the atomistic level using computer simulations. For this purpose, four consecutive (multi‐step) molecular dynamics simulations, involving different temperatures and proton transfer processes, have been carried out. Results are consistent with a polynuclear decalcification mechanism in which proton transfer processes, from the surface to the internal regions of the particle, play a crucial role. In addition, the DNA remains protected by the mineral mold and transferred proton from both temperature and chemicals. These results, which indicate that biomineralization imparts very effective protection to DNA, also have important implications in other biomedical fields, as for example in the design of artificial bones or in the fight against osteoporosis by promoting the fixation of Ca2+ ions. 相似文献
25.
Laila D. Kazimierski Guillermo Abramson Marcelo N. Kuperman 《The European Physical Journal B - Condensed Matter and Complex Systems》2016,89(10):232
We study a simple model of a foraging animal that modifies the substrate on which itmoves. This substrate provides its only resource, and the forager manages it by taking alimited portion at each visited site. The resource recovers its value after the visitfollowing a relaxation law. We study different scenarios to analyze the efficiency of themanaging strategy, corresponding to control the bite size. We observe the non trivialemergence of a home range, that is visited in a periodic way. The duration of thecorresponding cycles and the transient until it emerges is affected by the bite size. Ourresults show that the most efficient use of the resource, measured as the balance betweengathering and traveled distance, corresponds to foragers that take larger portions butwithout exhausting the resource. We also analyze the use of space determining the numberof attractors of the dynamics, and we observe that it depends on the bite size and therecovery time of the resource. 相似文献
26.
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María Jesús Lerma‐García Ernesto F. Simó‐Alfonso Guillermo Ramis‐Ramos José M. Herrero‐Martínez 《Electrophoresis》2008,29(22):4603-4611
A method for the determination of sterols in vegetable oils by CEC with UV–Vis detection, using methacrylate ester‐based monolithic columns, has been developed. To prepare the columns, polymerization mixtures containing monomers of different hydrophobicities were tried. The influence of composition of polymerization mixture was optimized in terms of porogenic solvent, monomers/porogens and monomer/crosslinker ratios. The composition of the mobile phase was also studied. The optimum monolith was obtained with lauryl methacrylate monomer at 60:40% (wt:wt) lauryl methacrylate/ethylene dimethacrylate ratio and 60 wt% porogens with 20 wt% of 1,4‐butanediol (12 wt% 1,4‐butanediol in the polymerization mixture). Excellent resolution between sterols was achieved in less than 7 min with an 85:10:5 v/v/v ACN–2‐propanol–water buffer containing 5 mM Tris at pH 8.0. The limits of detection were lower than 0.04 mM, and inter‐day and column‐to‐column reproducibilities at 0.75 mM were better than 6.2%. The method was applied to the determination of sterols in vegetable oils with different botanical origins and to detect olive oil adulteration with sunflower and soybean oils. 相似文献
28.
Francisco Palacios Ana M. Ochoa de RetanaSergio Pascual Guillermo Fernández de Trocóniz 《Tetrahedron》2011,67(8):1575-1579
A simple and efficient synthesis of fluoroalkylated α-amino nitrile (4) derivatives by regioselective 1,2-addition of trimethylsilyl cyanide to fluoroalkylated α,β-unsaturated imines (1) is described. Fluoroalkylated β-amino nitriles (7) are also prepared by regioselective 1,2-addition of α-carbanions derived from acetonitrile to fluoroalkylated α,β-unsaturated imines (1). Fluoroalkylated α-(4) and β-amino nitriles (7) are also prepared through an ‘one pot’ procedure by reaction of enaminophosphonate 2 with BuLi, addition of aldehydes and subsequent addition of either trimethylsilyl cyanide or α-carbanion derived from acetonitrile. Basic hydrolysis of α-(4) and β-amino nitriles (7) gives fluoroalkylated α-(5) and β-amino acids (8). 相似文献
29.
Pierozan MK Oestreicher EG Oliveira JV Oliveira D Treichel H Cansian RL 《Applied biochemistry and biotechnology》2011,165(1):75-86
The objective of this study was to provide some features on immobilization and partial characterization of lipases from wheat
seeds. The optimum pH and temperature were found to be 5.5 and 32–37 °C, respectively. The stability of the concentrated enzymatic
extract to high temperatures (25, 35, 45, and 55 °C) showed that the incubation of the extract at 55 °C led to its complete
inactivation. The concentrated enzymatic extract kept 90% of its hydrolytic and esterification activities until 70 and 40 days
of storage at 4 °C, respectively. The extract presented higher hydrolytic specificity to substrates of medium and long chains
and higher esterification affinity to fatty acids of short and medium chains and alcohols with two and three carbon atoms.
After the immobilization process using activated coal and sodium alginate as supports, an enhancement of about threefold in
lipase activity was observed. The development of the present work permitted us to point out some characteristics of lipases
from wheat seeds necessary for the proposition of new future industrial applications for this important biocatalyst. 相似文献
30.
We describe the topology, structure, and stability of giant fullerenes exhibiting various symmetries (I, I
h
, D
2h
, T). Our results demonstrate that it is possible to create two new families of nested chiral icosahedral (I) fullerenes namely C260@C560@C980@C1520@, ...,and C140@C380@C740@C1220@ ..., which exhibit interlayer separations of ca. 3.4 Å. These chiral fullerenes are thought to possess metalliclike conduction properties. We discuss in detail the transformation of polyhedral graphitic particles into quasispherical nested giant fullerenes by reorganization of carbon atoms, which result in the formation of additional pentagonal and heptagonal carbon rings. These spherical structures are metastable and we believe they could be formed under extreme conditions, such as those produced by high-energy electron irradiation. There is circumstantial experimental evidence for the presence of heptagonal rings within these spherical fullerenes. 相似文献