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31.
Molecular dynamics study on the stabilization of dehydrated lipid bilayers with glucose and trehalose 总被引:1,自引:0,他引:1
In this study, we use molecular dynamics simulations to investigate and compare the interactions of DPPC bilayers with and without saccharides (glucose or trehalose) under dehydrated conditions. Results from the simulations indicate that unilamellar bilayers lose their structural integrity under dehydrated conditions in the absence of saccharides; however, in the presence of either glucose or trehalose, the bilayers maintain their stability. Hydrogen bond analysis shows that the saccharide molecules displace a significant amount of water surrounding the lipid headgroups. At the same time, the additional hydrogen bonds formed between water and saccharide molecules help to maintain a hydration layer on the lipid bilayer interface. On the basis of the hydrogen bond distributions, trehalose forms more hydrogen bonds with the lipids than glucose, and it is less likely to interact with neighboring saccharide molecules. These results suggest that the interaction between the saccharide and lipid molecules through hydrogen bonds is an essential component of the mechanism for the stabilization of lipid bilayers. 相似文献
32.
In this work we illustrate the Arnold diffusion in a concrete example — the a priori unstable Hamiltonian system of 2 + 1/2 degrees of freedom H(p, q, I, φ, s) = p 2/2+ cos q ? 1 + I 2/2 + h(q, φ, s; ε) — proving that for any small periodic perturbation of the form h(q, φ, s; ε) = ε cos q (a 00 + a 10 cosφ + a 01 cos s) (a 10 a 01 ≠ 0) there is global instability for the action. For the proof we apply a geometrical mechanism based on the so-called scattering map. This work has the following structure: In the first stage, for a more restricted case (I* ~ π/2μ, μ = a 10/a 01), we use only one scattering map, with a special property: the existence of simple paths of diffusion called highways. Later, in the general case we combine a scattering map with the inner map (inner dynamics) to prove the more general result (the existence of instability for any μ). The bifurcations of the scattering map are also studied as a function of μ. Finally, we give an estimate for the time of diffusion, and we show that this time is primarily the time spent under the scattering map. 相似文献
33.
Dong Yang Jie Zhao Dr. Yanxia Zhao Prof. Yibo Lei Prof. Liping Cao Prof. Xiao‐Juan Yang Dr. Martin Davi Dr. Nader de Sousa Amadeu Prof. Dr. Christoph Janiak Dr. Zhibin Zhang Prof. Yao‐Yu Wang Prof. Biao Wu 《Angewandte Chemie (International ed. in English)》2015,54(30):8658-8661
Caged supramolecular systems are promising hosts for guest inclusion, separation, and stabilization. Well‐studied examples are mainly metal‐coordination‐based or covalent architectures. An anion‐coordination‐based cage that is capable of encapsulating halocarbon guests is reported for the first time. This A4L4‐type (A=anion) tetrahedral cage, [(PO4)4 L 4]12?, assembled from a C3‐symmetric tris(bisurea) ligand ( L ) and phosphate ion (PO43?), readily accommodates a series of quasi‐tetrahedral halocarbons, such as the Freon components CFCl3, CF2Cl2, CHFCl2, and C(CH3)F3, and chlorocarbons CH2Cl2, CHCl3, CCl4, C(CH3)Cl3, C(CH3)2Cl2, and C(CH3)3Cl. The guest encapsulation in the solid state is confirmed by crystal structures, while the host–guest interactions in solution were demonstrated by NMR techniques. 相似文献
34.
Aman ZM Brown EP Sloan ED Sum AK Koh CA 《Physical chemistry chemical physics : PCCP》2011,13(44):19796-19806
The present work uses a micromechanical force apparatus to directly measure cyclopentane clathrate hydrate cohesive force and hydrate-steel adhesive force, as a function of contact time, contact force and temperature. We present a hydrate interparticle force model, which includes capillary and sintering contributions and is based on fundamental interparticle force theories. In this process, we estimate the cyclopentane hydrate tensile strength to be approximately 0.91 MPa. This hydrate interparticle force model also predicts the effect of temperature on hydrate particle cohesion force. Finally, we present the first direct measurements of hydrate cohesive force in the gas phase to be 9.1 ± 2.1 mN/m at approximately 3 °C (as opposed to 4.3 ± 0.4 mN/m in liquid cyclopentane). 相似文献
35.
Luiz F. A. Santos Amadeu H. Iglesias Fabio C. Gozzo 《Journal of mass spectrometry : JMS》2011,46(8):742-750
The use of mass spectrometry coupled with chemical cross‐linking of proteins has become one of the most useful tools for proteins structure and interactions studies. One of the challenges in these studies is the identification of the cross‐linked peptides. The interpretation of the MS/MS data generated in cross‐linking experiments using N‐hydroxy succinimide esters is not trivial once a new amide bond is formed allowing new fragmentation pathways, unlike linear peptides. Intermolecular cross‐linked peptides occur when two different peptides are connected by the cross‐linker and they yield information on the spatial proximity of different domains (within a protein) or proteins (within a complex). In this article, we report a detailed fragmentation study of intermolecular cross‐linked peptides, generated from a set of synthetic peptides, using both ESI and MALDI to generate the precursor ions. The fragmentation features observed here can be helpful in the interpretation and identification of cross‐linked peptides present in cross‐linking experiments and be further implemented in search engine's algorithms. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
36.
Pubill-Ulldemolins C Bonet A Bo C Gulyás H Fernández E 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(4):1121-1126
Bases play an important role in organocatalytic boron conjugate addition reactions. The sole use of MeOH and a base can efficiently transform acyclic and cyclic activated olefins into the corresponding β-borated products in the presence of diboron reagents. Inorganic and organic bases deprotonate MeOH in the presence of diboron reagents. It is concluded, on the basis of theoretical calculations, NMR spectroscopic data, and ESI-MS experiments, that the methoxide anion forms a Lewis acid-base adduct with the diboron reagent. The sp(2) B atom of the methoxide-diboron adduct gains a strongly nucleophilic character, and attacks the electron-deficient olefin. The methanol protonates the intermediate, generating the product and another methoxide anion. This appears to be the simplest method to activate diboron reagents and make them suitable for incorporation into target organic molecules. 相似文献
37.
Martins N Mateus N Vinci D Saidi O Brigas A Bacsa J Xiao J 《Organic & biomolecular chemistry》2012,10(20):4036-4042
A new ferrocenyl oxazaphospholidine oxide 3 was synthesized together with its P-epimer 2 in the reaction of ferrocene lithium with phosphoramidite chloride 1. 3 was successfully derivatized into planar chiral 1,2-ferrocenes, including phosphine ligands, via highly diastereoselective ortho-lithiation and subsequent functionalization; these compounds display opposite planar chirality to those obtained from 2. Some of these 1,2-ferrocenes were further lithiated, allowing for the introduction of a free phosphine group at the oxazaphospholidine ring. The X-ray structures of the compounds 2 and 3 as well as those of the new 1,2-ferrocenes 4 and 7 have been determined. 相似文献
38.
Micromechanical cohesion force measurements to determine cyclopentane hydrate interfacial properties
Aman ZM Joshi SE Sloan ED Sum AK Koh CA 《Journal of colloid and interface science》2012,376(1):283-288
Hydrate aggregation and deposition are critical factors in determining where and when hydrates may plug a deepwater flowline. We present the first direct measurement of structure II (cyclopentane) hydrate cohesive forces in the water, liquid hydrocarbon and gas bulk phases. For fully annealed hydrate particles, gas phase cohesive forces were approximately twice that obtained in a liquid hydrocarbon phase, and approximately six times that obtained in the water phase. Direct measurements show that hydrate cohesion force in a water-continuous bulk may be only the product of solid-solid cohesion. When excess water was present on the hydrate surface, gas phase cohesive forces increased by a factor of three, suggesting the importance of the liquid or quasi-liquid layer (QLL) in determining cohesive force. Hydrate-steel adhesion force measurements show that, when the steel surface is coated with hydrophobic wax, forces decrease up to 96%. As the micromechanical force technique is uniquely capable of measuring hydrate-surface forces with variable contact time, the present work contains significant implications for hydrate applications in flow assurance. 相似文献
39.
A new heterodinuclear Fe(III)Zn(II) complex which mimics the active site of the hydrolytic enzyme red kidney bean purple acid phosphatase was synthesized and characterized by IR, CHN and X-ray crystallographic analyses. This complex, [FeIIIZnII(μ-OH)bpbpmp-CH3](ClO4)2, containing the ligand (H2bpbpmp-CH3 = {2-[bis(2-pyridylmethyl)aminomethyl]-6-[(2-hydroxy-5-methylbenzyl) (2-pyridyl-methyl) aminomethyl]-4-methyl-phenol}) was employed in the construction of a biomimetic sensor and used in the determination of rosmarinic acid in plant extract samples. The response parameters and optimization of the biomimetic sensor design were evaluated. The best performance of this sensor was obtained for 75:15:10% (w/w/w) of the graphite powder:nujol:Fe(III)Zn(II) complex, 0.1 mol L−1 phosphate buffer solution (pH 7.5), 1.19 × 10−4 mol L−1 hydrogen peroxide with frequency, pulse amplitude, and scan increment at 30 Hz, 100 mV, and 0.6 mV, respectively. The rosmarinic acid concentration was linear in the range of 2.98 × 10−5 to 3.83 × 10−4 mol L−1 (r = 0.9991) with a detection limit of 2.30 × 10−6 mol L−1. This biomimetic sensor demonstrated long-term stability (300 days; 900 determinations) and reproducibility, with a relative standard deviation of 12.0%. The recovery study of rosmarinic acid in plant extract samples gave values from 90.3 to 98.3% and the concentrations determined showed agreement when compared with those obtained using capillary electrophoresis at the 95% confidence level. 相似文献
40.
Albert Farre Kaline Soares Rachel A. Briggs Dr. Angelica Balanta Dr. David M. Benoit Dr. Amadeu Bonet 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(49):17552-17556
The generation of in situ sp2–sp3 diboron adducts has revolutionised the synthesis of organoboranes. Organocatalytic diboration reactions have represented a milestone in terms of unpredictable reactivity of these adducts. However, current methodologies have limitations in terms of substrate scope, selectivity and functional group tolerance. Here a new methodology based on the use of simple amines as catalyst is reported. This methodology provides a completely selective transformation overcoming current substrate scope and functional/protecting group limitations. Mechanistic studies have been included in this report. 相似文献