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The effective water dispersion of highly uniform nanoparticles synthesized in organic solvents is a major issue for their broad applications. In an effort to overcome this problem, iron oxide and cadmium selenide nanocrystals were surrounded by lipid bilayers to create stable, aqueous dispersions. The core inorganic particles were originally generated in oleic acid and 1-octadecene. When these organic solutions were mixed with water and a sparing amount of excess fatty acid, up to 70% of the nanoparticles transferred into the aqueous phase. This simple approach was applied to two different nanocrystal types, and nanocrystal diameters ranging from 5 to 15 nm. In all cases, the resulting materials were stable, nonaggregated suspensions that retained their original magnetic and optical properties. The phase transfer efficiency is maximum when very little oleic acid is added (e.g. 0.2 w/w %). At higher concentrations, above the critical micelle concentration, the formation of micelles begins to compete with bilayer generation leading to less effective phase transfer. Unlike other approaches for water dispersion that rely on amphiphiles with significant water solubility, the fatty acids used in this work are only sparingly soluble in water. As a result, there is minimal dynamic exchange between free and bound surface agents and the resulting aqueous solutions contain little residual free organic carbon. Thermogravimetric analysis (TGA) confirmed the presence of bilayers around the nanocrystal cores. The particle size, size distribution, process yield, and colloidal stability were found using a suite of methods including transmission electron microscopy, small angle X-ray scattering, dynamic light scattering, inductively coupled plasma-optical emission spectroscopy, and ultraviolet-visible spectroscopy. Bilayer-nanocrystal complexes possess many of the same size-dependent features as the original materials, and as such offer new avenues for exploring and exploiting the interface between nanocrystals and biology.
ACS Nano 2009 Aug 25
PMID:Bilayers as phase transfer agents for nanocrystals prepared in nonpolar solvents. 1959 66

We present the layer-by-layer assembly of an electroactive polymer nanocomposite thin film containing cationic linear poly(ethyleneimine) (LPEI) and 68 vol % anionic Prussian Blue (PB) nanoparticles, which allow for electrochemical control over film thickness and mechanical properties. Electrochemical reduction of the PB doubles the negative charge on the particles, causing an influx of water and ions from solution to maintain electroneutrality in the film; concomitant swelling and increased elastic compliance of the film result. Reversible swelling upon reduction is on the order of 2-10%, as measured via spectroscopic ellipsometry and electrochemical atomic force microscopy. Reversible changes in the Young's elastic modulus of the hydrated composite film upon reduction are on the order of 50% (from 3.40 to 1.75 GPa) as measured with in situ nanoindentation, and a qualitative increase in viscous contributions to energy dissipation upon redox is indicated by electrochemical quartz crystal microbalance. Electrochemical stimuli maintain a mild operating environment and can be applied rapidly, reversibly, and locally. We maintain that electrochemical control over the swelling and mechanical behavior of polymer nanocomposites could have important implications for responsive coatings of nanoscale devices, including mechanically tunable surfaces to modulate behavior of adherent cells.
ACS Nano 2009 Aug 25
PMID:Electrochemically controlled swelling and mechanical properties of a polymer nanocomposite. 1962 48

We have investigated formation of a proteolipid membrane surrounding mesoporous silica particles with a diameter of 550 nm and pore sizes of 3.0 nm. A multisubunit redox-driven proton pump, cytochrome c oxidase, was incorporated into the membrane, and we show that the enzyme is functional, both with respect to catalysis of O(2) reduction to water, and charge separation across the membrane. The orientation of cytochrome c oxidase in the membrane was found to be the same ( approximately 70%) in the lipid vesicles and in the silica-particle-supported lipid membrane, which provides information on the mechanism by which the vesicles adsorb to the surface. Furthermore, cytochrome c oxidase could maintain a proton electrochemical gradient across the supported proteomembrane, that is, the membrane system was proton tight, defining an interior particle compartment that is separated from the surrounding aqueous media. Such a biofunctional cellular interface, supported onto a colloid that has a connected interior cytoskeleton-like pore structure, provides a basis for functional studies of membrane-bound transport proteins, and also for applications within pharmaceutical drug delivery.
ACS Nano 2009 Sep 22
PMID:A membrane-reconstituted multisubunit functional proton pump on mesoporous silica particles. 1965 79

Droplet-based microfluidic systems are an expansion of the lab on a chip concept toward flexible, reconfigurable setups based on the modification and analysis of individual droplets. Superhydrophobic surfaces are one suitable candidate for the realization of droplet-based microfluidic systems as the high mobility of aqueous liquids on such surfaces offers possibilities to use novel or more efficient approaches to droplet movement. Here, copper-based superhydrophobic surfaces were produced either by the etching of polycrystalline copper samples along the grain boundaries using etchants common in the microelectronics industry, by electrodeposition of copper films with subsequent nanowire decoration based on thermal oxidization, or by a combination of both. The surfaces could be easily hydrophobized with thiol-modified fluorocarbons, after which the produced surfaces showed a water contact angle as high as 171 degrees +/- 2 degrees . As copper was chosen as the base material, established patterning techniques adopted from printed circuit board fabrication could be used to fabricate macrostructures on the surfaces with the intention to confine the droplets and, thus, to reduce the system's sensitivity to tilting and vibrations. A simple droplet-based microfluidic chip with inlets, outlets, sample storage, and mixing areas was produced. Wire guidance, a relatively new actuation method applicable to aqueous liquids on superhydrophobic surfaces, was applied to move the droplets.
ACS Nano 2009 Sep 22
PMID:Easy route to superhydrophobic copper-based wire-guided droplet microfluidic systems. 1968 79

In the present study, we report the novel application of polyhydroxylated fullerenes (fullerenols) in cancer drug delivery. The facile synthetic procedure for generating multiple hydroxyl groups on the fullerene cage offers scope for high drug loading in addition to conferring hydrophilicity. Doxorubicin, a first line cancer chemotherapeutic, was conjugated to fullerenols through a carbamate linker, achieving ultrahigh loading efficiency. The drug-fullerenol conjugate was found to be relatively stable in phosphate buffer saline but temporally released the active drug when incubated with tumor cell lysate. The fullerenol-doxorubicin conjugate suppressed the proliferation of cancer cell-lines in vitro through a G2-M cell cycle block, resulting in apoptosis. Furthermore, in an in vivo murine tumor model, fullerenol-doxorubicin exhibited comparable antitumor efficacy as free drug without the systemic toxicity of free doxorubicin. Additionally, we demonstrate that the fullerenol platform can be extended to other chemotherapeutic agents, such as the slightly water-soluble cisplatin, and can emerge as a new paradigm in the management of cancer.
ACS Nano 2009 Sep 22
PMID:Fullerenol-cytotoxic conjugates for cancer chemotherapy. 1968 36

A general method is described for the deposition of metal nanoparticles selectively either inside or outside of carbon nanotubes (CNTs). The method is based on the difference in the interface energies of organic and aqueous solutions with the CNT surface. Because of their lipophilic character, the organic solvent better wets the surface of the nanotubes compared to water and penetrates into the inner volume. The precise control of the volume of each phase allows filling the CNT with the organic phase and covering its outer surface with the aqueous one. Hence, metal nanoparticles can be put with high selectivity either inside or outside the CNT, just by choosing in which solvent the metal precursor is dissolved. SEM, TEM, and 3D-TEM investigations show that a selectivity in localization close to 75% can be reached by this technique. The nanoparticles are homogeneously dispersed and present a narrow size distribution, centered on 5 nm. In this way, one can decorate either the inner or the outer surface of open CNTs, without the need of discriminating the diameter of the opening and without any further step of functionalization than a treatment with nitric acid.
ACS Nano 2009 Aug 25
PMID:Selective deposition of metal nanoparticles inside or outside multiwalled carbon nanotubes. 1970 19

In this work we demonstrate a facile means to generate fluorescent carbon nanoribbons, nanoparticles, and graphene from graphite electrode using ionic liquid-assisted electrochemical exfoliation. A time-dependence study of products exfoliated from the graphite anode allows the reconstruction of the exfoliation mechanism based on the interplay of anodic oxidation and anion intercalation. We have developed strategies to control the distribution of the exfoliated products. In addition, the fluorescence of these carbon nanomaterials can be tuned from the visible to ultraviolet region by controlling the water content in the ionic liquid electrolyte.
ACS Nano 2009 Aug 25
PMID:One-pot synthesis of fluorescent carbon nanoribbons, nanoparticles, and graphene by the exfoliation of graphite in ionic liquids. 1970 26

The adsorption, mobility, and vibration of water in ion-exchanged rho-zeolite-like metal-organic frameworks (ZMOFs) are investigated using atomistic simulations. Because of the high affinity for the ionic framework and nonframework ions, water is strongly adsorbed in rho-ZMOFs with a three-step adsorption mechanism. At low pressures, water is preferentially adsorbed onto Na(+) ions, particularly at site II; with increasing pressure, adsorption occurs near the framework and finally in the large cage. Upon water adsorption, Na(+) ions are observed to redistribute from site I to site II and gradually hydrated with increasing pressure. In Li-, Na-, and Cs-exchanged rho-ZMOFs, the adsorption capacity and isosteric heat decrease with increasing ionic radius attributed to the reduced electrostatic interaction and free volume. The mobility of water in Na-rho-ZMOF increases at low pressures but decreases upon approaching saturation. With sufficient amount of water present, the mobility of Na(+) ions is promoted. The vibrational spectra of water in Na-rho-ZMOF exhibit distinct bands for librational motion, bending, and stretching. The librational motion has a frequency higher than bulk water due to confinement. With increasing loading and hence stronger coordinative attraction, the bending frequency shows a blue shift. Symmetric and asymmetric modes are observed in the stretching as a consequence of the strong water-ion interaction. This study provides a fundamental microscopic insight into the static and dynamic properties of water in charged ZMOFs and reveals the subtle interplay between water and nonframework ions.
ACS Nano 2009 Sep 22
PMID:Atomistic insight into adsorption, mobility, and vibration of water in ion-exchanged zeolite-like metal-organic frameworks. 1970 39

The ability of 20-50 nm nanoparticles to target and modulate the biology of specific types of cells will enable major advancements in cellular imaging and therapy in cancer and atherosclerosis. A key challenge is to load an extremely high degree of targeting, imaging, and therapeutic functionality into small, yet stable particles. Herein we report approximately 30 nm stable uniformly sized near-infrared (NIR) active, superparamagnetic nanoclusters formed by kinetically controlled self-assembly of gold-coated iron oxide nanoparticles. The controlled assembly of nanocomposite particles into clusters with small primary particle spacings produces collective responses of the electrons that shift the absorbance into the NIR region. The nanoclusters of approximately 70 iron oxide primary particles with thin gold coatings display intense NIR (700-850 nm) absorbance with a cross section of approximately 10(-14) m(2). Because of the thin gold shells with an average thickness of only 2 nm, the r(2) spin-spin magnetic relaxivity is 219 mM(-1) s(-1), an order of magnitude larger than observed for typical iron oxide particles with thicker gold shells. Despite only 12% by weight polymeric stabilizer, the particle size and NIR absorbance change very little in deionized water over 8 months. High uptake of the nanoclusters by macrophages is facilitated by the dextran coating, producing intense NIR contrast in dark field and hyperspectral microscopy, both in cell culture and an in vivo rabbit model of atherosclerosis. Small nanoclusters with optical, magnetic, and therapeutic functionality, designed by assembly of nanoparticle building blocks, offer broad opportunities for targeted cellular imaging, therapy, and combined imaging and therapy.
ACS Nano 2009 Sep 22
PMID:Small multifunctional nanoclusters (nanoroses) for targeted cellular imaging and therapy. 1971 44

Applications of water-soluble quantum dots (QDs) in the life sciences are limited by their poor colloidal stability in physiological media and nonspecific interaction with biomatter, particularly cell membranes. We have studied colloidal stability and nonspecific interactions with living cells for zwitterionic d-penicillamine-coated QDs (DPA-QDs) and the traditionally used carboxylated 11-mercaptoundecanoic acid-coated QDs (MUA-QDs) and found clear advantages of DPA-QDs. In single molecule fluorescence experiments, DPA-QDs showed no aggregation over the physiologically relevant pH range of 5-9, whereas MUA-QDs showed significant aggregation below pH 9. Upon exposure to living Mono Mac 6 cells, DPA-QDs, which possess overall charge-neutral surfaces, exhibited weak interactions with the cell membrane and were easily removed by flushing with buffer. By contrast, the highly charged MUA-QDs strongly associated with the cells and could not be removed even by extensive rinsing with buffer solution. DPA-QDs exhibit a high chemical stability even in strongly oxidizing conditions, in contrast to cysteine-coated QDs reported earlier. This beneficial property may arise from reduced interactions between DPA ligands due to steric effects of the methyl groups on their beta-carbon atoms.
ACS Nano 2009 Sep 22
PMID:Zwitterionic biocompatible quantum dots for wide pH stability and weak nonspecific binding to cells. 1971 85


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