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Significant Perturbation (significant + perturbation)
Selected AbstractsSi-doped GaN/AlN quantum dot superlattices for optoelectronics at telecommunication wavelengthsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2006F. Guillot Abstract We report on the controlled growth of Si doped GaN/AlN quantum dot (QD) superlattices, in order to tailor their intersubband absorption within the 1.3,1.5 µm telecommunication wavelengths. The QD size is tuned by modifying the amount of GaN in the QDs and the growth temperature. Silicon can be incorporated in the QDs to populate the first electronic level, without significant perturbation of the QD morphology. As a proof of the capability of these structures for infrared detection, a quantum-dot intersubband photodetector at 1.38 µm with lateral carrier transport is demonstrated. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Binding of quercetin with human serum albumin: A critical spectroscopic studyBIOPOLYMERS, Issue 6 2003Bidisa Sengupta Abstract Flavonols are plant pigments that are ubiquitous in nature. Quercetin (3,3,,4,,5,7-pentahydroxyflavone) and other related plant flavonols have come into recent prominence because of their usefulness as anticancer, antitumor, anti-AIDS, and other important therapeutic activities of significant potency and low systemic toxicity. Quercetin is intrinsically weakly fluorescent in aqueous solution, showing an emission maximum at ,538 nm. Upon binding to human serum albumin (HSA), quercetin undergoes dramatic enhancement in its fluorescence emission intensity, along with the appearance of dual emission behavior, consisting of normal and excited-state proton transfer (ESPT) fluorescence. In addition, the occurrence of a third emitting species has been noted for the first time. This is attributed to a electronic ground-state complex formed in the protein environment. High values of the fluorescence anisotropy (r) are obtained in the presence of HSA for the ESPT tautomer (r = 0.18), as well as the complex species (r = 0.37) of quercetin, indicating that the precursor ground-state molecules for both these emitting species of quercetin molecules are located in the motionally constrained sites of HSA. The steady-state emission data suggest that quercetin binds to two distinct sites in HSA from which the emissions from the normal tautomer and complex species take place. The preliminary results of studies on emission decay kinetics are also reported herein. Studies by far-UV circular dichroism spectroscopy reveal that binding of quercetin induces no significant perturbation in the secondary structure of HSA. © 2003 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy), 2003 [source] Selective Binding of Imidazolium Cations in Building Multi-Component LayersCHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2010Irene Ling Abstract Addition of 1-alkyl-3-methylimidazolium (Cn -mim) cations 3,5 to a mixture of bis-phosphonium cation 2 and sodium p -sulfonatocalix[4]arene (1) in the presence of lanthanide ions results in the selective binding of an imidazolium cation into the cavity of the calixarene. The result is a multi-layered solid material with an inherently flexible interplay of the components. Incorporating ethyl-, n -butyl- or n -hexyl-mim cations into the multi-layers results in significant perturbation of the structure, the most striking effect is the tilting of the plane of the bowl-shaped calixarene relative to the plane of the multi-layer, with tilt angles of 7.2, 28.9 and 65.5°, respectively. The lanthanide ions facilitate complexation, but are not incorporated into the structures and, in all cases, the calixarene takes on a 5, charge, with one of the lower-rim phenolic groups deprotonated. ROESY NMR experiments and other 1H,NMR spectroscopy studies establish the formation of 1:1 supermolecules of Cn -mim and calixarene, regardless of the ratio of the two components, and indicate that the supermolecules undergo rapid exchange on the NMR spectroscopy timescale. [source] Selenium Derivatization of Nucleic Acids for X-Ray Crystal-Structure and Function StudiesCHEMISTRY & BIODIVERSITY, Issue 4 2010Jia Sheng Abstract It is estimated that over two thirds of all new crystal structures of proteins are determined via the protein selenium derivatization (selenomethionine (Se-Met) strategy). This selenium derivatization strategy via MAD (multi-wavelength anomalous dispersion) phasing has revolutionized protein X-ray crystallography. Through our pioneer research, similarly, Se has also been successfully incorporated into nucleic acids to facilitate the X-ray crystal-structure and function studies of nucleic acids. Currently, Se has been stably introduced into nucleic acids by replacing nucleotide O-atom at the positions 2,, 4,, 5,, and in nucleobases and non-bridging phosphates. The Se derivatization of nucleic acids can be achieved through solid-phase chemical synthesis and enzymatic methods, and the Se-derivatized nucleic acids (SeNA) can be easily purified by HPLC, FPLC, and gel electrophoresis to obtain high purity. It has also been demonstrated that the Se derivatization of nucleic acids facilitates the phase determination via MAD phasing without significant perturbation. A growing number of structures of DNAs, RNAs, and protein,nucleic acid complexes have been determined by the Se derivatization and MAD phasing. Furthermore, it was observed that the Se derivatization can facilitate crystallization, especially when it is introduced to the 2,-position. In addition, this novel derivatization strategy has many advantages over the conventional halogen derivatization, such as more choices of the modification sites via the atom-specific substitution of the nucleotide O-atom, better stability under X-ray radiation, and structure isomorphism. Therefore, our Se-derivatization strategy has great potentials to provide rational solutions for both phase determination and high-quality crystal growth in nucleic-acid crystallography. Moreover, the Se derivatization generates the nucleic acids with many new properties and creates a new paradigm of nucleic acids. This review summarizes the recent developments of the atomic site-specific Se derivatization of nucleic acids for structure determination and function study. Several applications of this Se-derivatization strategy in nucleic acid and protein research are also described in this review. [source] Millennial-scale variability in the oceans: an ocean modelling viewJOURNAL OF QUATERNARY SCIENCE, Issue 4 2001Grant R. Bigg Abstract Climate and ocean-only models have shown that the ocean will respond abruptly to significant perturbations in surface forcing. Centennial-scale oscillation is a characteristic of circulation in large semi-enclosed ocean basins such as the Arctic, whereas millennial-scale adjustment to changes in surface forcing has been found in the global ocean component of climate models. We show that the millennial time-scale in climate models is likely to be intrinsic to the ocean through its presence in an ocean-only model. The strength of the thermohaline circulation is shown to be very sensitive to the magnitude of ice albedo and, to a lesser extent, perturbation in the surface freshwater flux. Modelled glacial ocean circulation, in contrast to present-day simulations, requires an enhanced freshwater flux over the northern Atlantic, even in its non-Heinrich state, to obtain realistic overturning in the North Atlantic. Copyright © 2001 John Wiley & Sons, Ltd. [source] Changes in Plasma Cortisol, Glucose, and Selected Blood Properties in the Summer Flounder Paralichthys dentatus Associated with Sequential Movement to Three Experimental ConditionsJOURNAL OF THE WORLD AQUACULTURE SOCIETY, Issue 3 2003James A. Sulikowski To determine the changes in blood chemistry associated with sequential transfer of summer flounder Paralichthys dentatus (320,480 g), 300 hatchery-reared fish were moved to three different environmental conditions during a 20-d period. Fish were transferred in progression from a recirculating seawater system (22 ppt, 22.5 C) to a flow-thru seawater system (31 ppt, 20.0 C), to three small coastal net pens (33 ppt, 15.5 C), and finally to a large open ocean net pen (33 ppt, 16.0 C). For this study, eight random fish were captured at each progressive step (environmental condition), anesthetized (MS222), and bled from the caudal vein (2 mL). Transferred flounder were bled every 12 h for 48 h to collect plasma cortisol and glucose samples. Fish were bled 24 h after transport and every 3 d thereafter for osmolarity, hematocrit, hemoglobin concentration, mean corpuscular hemoglobin content, glucose, cortisol, and the electrolytes Cl - Na+, K+ and Ca+. The most significant perturbations to blood chemistry (P < 0.05) occurred within 24 h of initial transfer from the recirculating to flow-thru seawater systems, suggesting an osmoregulatory rather than handling or transfer related stress. Osmolarity, electrolyte, and hematological parameters fluctuated and then recovered to stable levels by day 8 in the flow-thru seawater system. However, unlike the initial transfer, successive movement to the coastal and then the open ocean net pens produced transient increases in both plasma cortisol and glucose levels, suggesting a high level of stress associated with extended flounder handling and transfer. [source] A hydrogen-bonding network is important for oxidation and isomerization in the reaction catalyzed by cholesterol oxidaseACTA CRYSTALLOGRAPHICA SECTION D, Issue 11 2009Artem Y. Lyubimov Cholesterol oxidase is a flavoenzyme that catalyzes the oxidation and isomerization of 3,-hydroxysteroids. Structural and mutagenesis studies have shown that Asn485 plays a key role in substrate oxidation. The side chain makes an NH..., interaction with the reduced form of the flavin cofactor. A N485D mutant was constructed to further test the role of the amide group in catalysis. The mutation resulted in a 1800-fold drop in the overall kcat. Atomic resolution structures were determined for both the N485L and N485D mutants. The structure of the N485D mutant enzyme (at 1.0,Å resolution) reveals significant perturbations in the active site. As predicted, Asp485 is oriented away from the flavin moiety, such that any stabilizing interaction with the reduced flavin is abolished. Met122 and Glu361 form unusual hydrogen bonds to the functional group of Asp485 and are displaced from the positions they occupy in the wild-type active site. The overall effect is to disrupt the stabilization of the reduced FAD cofactor during catalysis. Furthermore, a narrow transient channel that is shown to form when the wild-type Asn485 forms the NH..., interaction with FAD and that has been proposed to function as an access route of molecular oxygen, is not observed in either of the mutant structures, suggesting that the dynamics of the active site are altered. [source] | ||||||||||