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Modification Approach (modification + approach)
Selected AbstractsSurface Modification of Exfoliated Layered Gadolinium Hydroxide for the Development of Multimodal Contrast Agents for MRI and Fluorescence ImagingADVANCED FUNCTIONAL MATERIALS, Issue 21 2009Young-su Yoon Abstract A novel method for modifying the surface of magnetic-resonance-contrasting layered gadolinium hydroxide (LGdH) is developed providing them with water- and bio-compatibility and acid-resistance, all of which are essential for medical applications. A stable colloid of exfoliated layers is synthesized by exchanging interlayer anions of LGdH with oleate ions. The delaminated layers are successively coated with phospholipids with poly(ethylene glycol) tail groups, and their effectiveness as a contrast agent for magnetic resonance imaging (MRI) is demonstrated. The adaptability of this surface modification approach for incorporating functional molecules and fabricating a fluorescent colloid of LGdH, which has the potential utility as a multimodal probe, is also demonstrated. This result provides a novel approach for expanding the applications of layered inorganic materials and developing a new class of MRI contrast agents. [source] A pH-Gating Ionic Transport Nanodevice: Asymmetric Chemical Modification of Single NanochannelsADVANCED MATERIALS, Issue 22 2010Xu Hou Inspired by biological ion channels, the generation of artificial nanochannels has strong implications for the simulation of different processes of ionic transport as well as enhance the functionality of biological ion channels. Here, we show plasma asymmetric chemical modification approach to prepare the pH asymmetric gating nanochannel that can achieve pH control for both different ionic rectification and perfect gating function, simultaneously. [source] Characterization of covalently inhibited extracellular lipase from Streptomyces rimosus by matrix-assisted laser desorption/ionization time-of-flight and matrix-assisted laser desorption/ionization quadrupole ion trap reflectron time-of-flight mass spectrometry: localization of the active site serine,JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 12 2004Martin Zehl Abstract A chemical modification approach combined with matrix-assisted laser desorption/ionization (MALDI) mass spectrometry was used to identify the active site serine residue of an extracellular lipase from Streptomyces rimosus R6-554W. The lipase, purified from a high-level overexpressing strain, was covalently modified by incubation with 3,4-dichloroisocoumarin, a general mechanism-based serine protease inhibitor. MALDI time-of-flight (TOF) mass spectrometry was used to probe the nature of the intact inhibitor-modified lipase and to clarify the mechanism of lipase inhibition by 3,4-dichloroisocoumarin. The stoichiometry of the inhibition reaction revealed that specifically one molecule of inhibitor was bound to the lipase. The MALDI matrix 2,6-dihydroxyacetophenone facilitated the formation of highly abundant [M + 2H]2+ ions with good resolution compared to other matrices in a linear TOF instrument. This allowed the detection of two different inhibitor-modified lipase species. Exact localization of the modified amino acid residue was accomplished by tryptic digestion followed by low-energy collision-induced dissociation peptide sequencing of the detected 2-(carboxychloromethyl)benzoylated peptide by means of a MALDI quadrupole ion trap reflectron TOF instrument. The high sequence coverage obtained by this approach allowed the confirmation of the site specificity of the inhibition reaction and the unambiguous identification of the serine at position 10 as the nucleophilic amino acid residue in the active site of the enzyme. This result is in agreement with the previously obtained data from multiple sequence alignment of S. rimosus lipase with different esterases, which indicated that this enzyme exhibits a characteristic Gly-Asp-Ser-(Leu) motif located close to the N-terminus and is harboring the catalytically active serine residue. Therefore, this study experimentally proves the classification of the S. rimosus lipase as GDS(L) lipolytic enzyme. Copyright © 2004 John Wiley & Sons, Ltd. [source] Exploration of ionic modification in dual-layer hollow fiber membranes for long-term high-performance protein separationAICHE JOURNAL, Issue 2 2009Yi Li Abstract Two types of ionic modification approaches (i.e., sulfonation and triethylamination) were applied with the aid of dual-layer hollow fiber technology in this work to fine tune the pore size and pore size distribution, introduce the electrostatic interaction, and reduce membrane fouling for long-term high-performance protein separation. A binary protein mixture comprising bovine serum albumin (BSA) and hemoglobin (Hb) was separated in this work. The sulfonated fiber exhibits an improved BSA/Hb separation factor at pH = 6.8 compared with as-spun fibers but at the expense of BSA sieving coefficient. On the other hand, the triethylaminated fiber reveals the best and most durable separation performance at pH = 4.8. Its BSA/Hb separation factor is maintained above 80 for 4 days and maximum BSA sieving coefficient reaches 33%. Therefore, this study documents that an intelligent combination of both size-exclusion and electrostatic interaction can synergistically enhance protein separation performance in both purity and concentration. © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source] The difference electron density: a probabilistic reformulationACTA CRYSTALLOGRAPHICA SECTION A, Issue 3 2010Maria Cristina Burla The joint probability distribution function P(E, Ep), where E and Ep are the normalized structure factors of the target and of a model structure, respectively, is a fundamental tool in crystallographic methods devoted to crystal structure solution. It plays a central role in any attempt for improving phase estimates from a given structure model. More recently the difference electron density ,q = ,,,p has been revisited and methods based on its modifications have started to play an important role in combination with electron density modification approaches. In this paper new coefficients for the difference electron density have been obtained by using the joint probability distribution function P(E, Ep, Eq) and by taking into account both errors in the model and in measurements. The first applications show the correctness of our theoretical approach and the superiority of the new difference Fourier synthesis, particularly when the model is a rough approximation of the target structure. The new and the classic difference syntheses coincide when the model represents the target structure well. [source] | |||||||||||||