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排序方式: 共有843条查询结果,搜索用时 15 毫秒
91.
92.
Micelle‐Triggered β‐Hairpin to α‐Helix Transition in a 14‐Residue Peptide from a Choline‐Binding Repeat of the Pneumococcal Autolysin LytA 下载免费PDF全文
Héctor Zamora‐Carreras Dr. Beatriz Maestro Dr. Erik Strandberg Prof. Anne S. Ulrich Dr. Jesús M. Sanz Dr. M. Ángeles Jiménez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8076-8089
Choline‐binding modules (CBMs) have a ββ‐solenoid structure composed of choline‐binding repeats (CBR), which consist of a β‐hairpin followed by a short linker. To find minimal peptides that are able to maintain the CBR native structure and to evaluate their remaining choline‐binding ability, we have analysed the third β‐hairpin of the CBM from the pneumococcal LytA autolysin. Circular dichroism and NMR data reveal that this peptide forms a highly stable native‐like β‐hairpin both in aqueous solution and in the presence of trifluoroethanol, but, strikingly, the peptide structure is a stable amphipathic α‐helix in both zwitterionic (dodecylphosphocholine) and anionic (sodium dodecylsulfate) detergent micelles, as well as in small unilamellar vesicles. This β‐hairpin to α‐helix conversion is reversible. Given that the β‐hairpin and α‐helix differ greatly in the distribution of hydrophobic and hydrophilic side chains, we propose that the amphipathicity is a requirement for a peptide structure to interact and to be stable in micelles or lipid vesicles. To our knowledge, this “chameleonic” behaviour is the only described case of a micelle‐induced structural transition between two ordered peptide structures. 相似文献
93.
Beatriz Lantaño José M. Aguirre Eleonora V. Drago Diego J. de la Faba Nicolás Pomilio Jorge D. Mufato 《Magnetic resonance in chemistry : MRC》2017,55(7):619-633
Here, we studied the influence of the methoxyl groups attached at C‐7 and C‐2′ of natural and synthetic 1‐arylindanes on the chemical shift of the signal of bibenzylic hydrogen and carbon atoms and J1,2 coupling constants. This influence was also analysed in natural 1‐aryltetralins and related compounds that possess methoxyl and/or hydroxyl groups bound at C‐8 and C‐2′. The methoxyl groups attached at C‐7 in indanes or at C‐8 in tetralins produce a deshielding signal at H‐1 and shield at C‐1 and a strong decrease in the value of J1,2 due to the pseudoequatorial location adopted by the aryl group bound at C‐1, avoiding an ‘A1,3 strain’. Furthermore, compounds with hydroxyl or methoxyl groups in C‐2′, in the absence of substituents of C‐7 or C‐8, present a strong deshielding signal at H‐1, strong shield of the C‐1 signal and a decrease in the value of J1,2. This is attributed to the stereoelectronic effects of the methoxyl or hydroxyl groups, which we have called ‘Asarone effect’. NOESY experiments were conducted to confirm the configuration and conformation of some of the compounds included in this work. This study shows that both effects, A1,3 strain and Asarone effect, must be taken into account when the structure of natural indanes and tetralins is analysed by using 1H‐NMR and 13C‐NMR spectra. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
94.
Christian Carrot Jean-Charles Majesté Beatriz Olalla René Fulchiron 《Rheologica Acta》2010,49(5):513-527
The purpose of the presented work was to test the capability of the model proposed by Leonov (J Rheol 34:1039–1068, 1990) for the prediction of secondary plateaus on the storage and loss moduli during small-amplitude oscillatory shear flow experiments
on filled or heterogeneous polymer melts. Though the occurrence of a plateau on the storage modulus can be well explained
in the frame of a filler network, a plateau on the loss modulus can hardly be described with the classical models. In the
Leonov model, the continuum of dissipative processes is attributed to the rupture of flocs of particles. Experiments with
polyolefins filled with magnesium hydroxide show that there is a clear connection between the amount of agglomerates and the
occurrence of a plateau on the loss modulus. However, the value of the critical strain for floc rupture that can be calculated
from the experiment shows that the processes responsible for the low-frequency dissipation are rather changes of configuration
within the agglomerates than floc rupture. These processes are not described by the Leonov model, and the predicted strain
dependence of the plateau is not observed experimentally. 相似文献
95.
M. Beatriz Vázquez-Santos 《Polymer Degradation and Stability》2009,94(1):7-12
The main objective of this work was to investigate porosity development in carbonaceous materials formed by thermal degradation of the high thermal stability polymer, poly(p-phenylene benzobisoxazole) (PBO). Two varieties of PBO, as-spun (AS) and high-modulus (HM) were studied. Chars obtained at various polymer decomposition temperatures (selected on the basis of thermogravimetric and differential thermal analysis results) were characterized by elemental analysis, infrared spectroscopy, X-ray diffraction and CO2 adsorption at 273 K. The obtained adsorbents essentially contained narrow micropores, and maximum pore development took place at ca. 1000 K, when the polymer was not yet completely decomposed. At higher temperatures, there is a certain pore widening along with a displacement towards smaller pore sizes, and the pore volume significantly decreases. 相似文献
96.
Maria Rambla-Alegre Juan Peris-Vicente Sergio Marco-Peiró Beatriz Beltrán-Martinavarro Josep Esteve-Romero 《Talanta》2010,81(3):894-274
Melamine is a toxic triazine, illegally used as an additive in milk to apparently increase the amount of protein. A chromatographic procedure using a C18 column and a micellar mobile phase of sodium dodecyl sulphate (0.05 M) and propanol (7.5%), buffered at pH 3, and a detection set by absorbance at 210 nm, was reported for the resolution and quantification of melamine in liquid and powdered milk samples. In this work, samples were diluted with a SDS solution and were directly injected, thus avoiding long extraction and experimental procedures. Melamine was eluted in nearly 9.3 min without overlapping the protein band or other endogeneous compounds. The optimal mobile phase composition was taken using a chemometrical approach that considers the retention factor, efficiency and peak shape. Validation was performed following the European Commission's indications (European Decision 2002/657/EC), and the main analytical parameters studied were: linearity (0.02-100 ppm; r2 = 0.999), limit of detection (5 ppb), intra- and inter-day precision (R.S.D. <7.6% and <9.7%, respectively) and robustness (R.S.D. <7.4% for retention time and <5.0% for area). Sensitivity was adequate to detect melamine under the safety limits proposed by the US FDA. Finally, recoveries for several milk samples were found in the 85-109% range. 相似文献
97.
Georgina Bassani Pablo Fuciños Guillermo Picó Beatriz Farruggia 《Colloids and surfaces. B, Biointerfaces》2010,75(2):532-537
The interaction between a lipase from Candida rugosa (Lip1) and polyethyleneglycols of different molecular masses was studied using fluorescence and circular dichroism approaches in order to be applied to the analysis of the enzyme partition mechanism in aqueous two-phase systems of polyethyleneglycol–potassium phosphate. The decrease of the partition coefficients with the polyethyleneglycol molecular mass showed that the enzyme partition is driven by the excluded volume effect and not by the enzyme–polymer interaction. The polymer did not affect the secondary and tertiary structure of the enzyme nor its biological activity. The lipase from Candida rugosa lyophilizate was partitioned in favour of the polyethyleneglycol rich phase; PEG 2000 being the system which showed the better enzyme recovery (78.26%) with a purification factor of 2.3. This method could be applied as a first step to isolate the enzyme from a culture medium with good recovery and without modifying the enzymatic capacity and the molecular structure. 相似文献
98.
57Fe Mössbauer spectroscopy is used to study the interactions, geometry, and the coordination characteristics of the Fe-complexes of biopolymers such as chitosan, glucosamine, and chondritin sulfate. In addition, a computational effort is undertaken for predicting the geometries and energies of the metal complexes by the Density Functional Theory (DFT) methods as implemented in the Gaussian 2003 quantum mechanical program. Both experimental and computational results suggest that the structure of the metal complexes resemble closely the structure of the active sites of metalloenzymes in 2+ or 3+ oxidation states and is at least tetracoordinated and can possibly have six ligands. 相似文献
99.
The validity of the paraxial approximation for laser beams in free space is studied via an integral criterion based on the propagation invariants of Helmholtz and paraxial wave equations. This approach allows one to determine the paraxial limit for beams with nondefined spot size and for beams described by more parameters in addition to typical longitudinal wavelength and transverse waist. As examples, the paraxiality of higher-order Hermite, Laguerre, and Bessel-Gaussian beams was completely determined. This method could be extended to nonlinear optics and Bose condensates. 相似文献
100.
Zapico JM Serra P García-Sanmartín J Filipiak K Carbajo RJ Schott AK Pineda-Lucena A Martínez A Martín-Santamaría S de Pascual-Teresa B Ramos A 《Organic & biomolecular chemistry》2011,9(12):4587-4599
A new series of MMP2 inhibitors is described, following a fragment-based drug design approach. One fragment containing an azide group and a well known hydroxamate Zinc Binding Group in a α-sulfone, α-tetrahydropyrane scaffold, has been synthesized. Water-LOGSY, STD and competition-STD experiments indicate that this fragment binds to the active site of the enzyme. A click chemistry reaction was used to connect the azide to lipophilic alkynes selected to interact selectively with the S1' subunit of MMP2, as shown by docking and molecular dynamic experiments of the designed compounds. The most potent compounds 18 and 19 displayed an IC(50) of 1.4 and 0.3 nM against MMP2 respectively, and showed negligible activity towards MMP1 and MMP7, two metalloproteinases which have a shallow S1' subsite. Compound 18 also showed a promising selectivity profile against some antitarget metalloproteinases, such as MMP8, and considerably less activity against MMP14 (IC(50) = 65 nM), and MMP9 (IC(50) = 98 nM), other MMPs characterized by having a deep S1' pocket and, therefore, more similar to MMP2. 相似文献