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A key challenge in the synthesis of multicomponent nanoparticles (NPs) for therapy or diagnosis is obtaining reproducible monodisperse NPs with a minimum number of preparation steps. Here we report the use of microfluidic rapid mixing using hydrodynamic flow focusing in combination with passive mixing structures to realize the self-assembly of monodisperse lipid-polymer and lipid-quantum dot (QD) NPs in a single mixing step. These NPs are composed of a polymeric core for drug encapsulation or a QD core for imaging purposes, a hydrophilic polymeric shell, and a lipid monolayer at the interface of the core and the shell. In contrast to slow mixing of lipid and polymeric solutions, rapid mixing directly results in formation of homogeneous NPs with relatively narrow size distribution that obviates the need for subsequent thermal or mechanical agitation for homogenization. We identify rapid mixing conditions that result in formation of homogeneous NPs and show that self-assembly of polymeric core occurs independent of the lipid component, which only provides stability against aggregation over time and in the presence of high salt concentrations. Physicochemical properties of the NPs including size (35-180 nm) and zeta potential (-10 to +20 mV in PBS) are controlled by simply varying the composition and concentration of precursors. This method for preparation of hybrid NPs in a single mixing step may be useful for combinatorial synthesis of NPs with different properties for imaging and drug delivery applications.
ACS Nano 2010 Mar 23
PMID:Single-step assembly of homogenous lipid-polymeric and lipid-quantum dot nanoparticles enabled by microfluidic rapid mixing. 2016 99

A simplified template-assisted layering approach for preparing catalytic conical tube microjet engines based on sequential deposition of platinum and gold on an etched silver wire template followed by dicing and dissolution of the template is described. The method allows detailed control over the tube parameters and hence upon the performance of the microengine. The recoiling bubble propulsion mechanism of the tubular microengine, associated with the ejection of internally generated oxygen microbubbles, addresses the ionic-strength limitation of catalytic nanowire motors and leads to a salt-independent movement. Similar rates of bubble generation and motor speeds are observed in salt-free and salt-rich media (at elevated ionic-strength environments as high as 1 M NaCl). Plating of an intermediate nickel layer facilitates a magnetically guided motion as well as the pickup and transport of large (magnetic) "cargo". Surfactant addition is shown to decrease the surface tension and offer a more frequent formation of dense smaller bubbles. The new and improved motor capabilities along with the simple preparation route hold great promise for using catalytic micromotors in diverse and important applications.
ACS Nano 2010 Apr 27
PMID:Template-assisted fabrication of salt-independent catalytic tubular microengines. 2042 Apr 69

Single-crystalline rock-salt PbS nanowires (NWs) were synthesized using three different routes; the solvothermal, chemical vapor transport, and gas-phase substitution reaction of pregrown CdS NWs. They were uniformly grown with the [100] or [110], [112] direction in a controlled manner. In the solvothermal growth, the oriented attachment of the octylamine (OA) ligands enables the NWs to be produced with a controlled morphology and growth direction. As the concentration of OA increases, the growth direction evolves from the [100] to the higher surface-energy [110] and [112] directions under the more thermodynamically controlled growth conditions. In the synthesis involving chemical vapor transport and the substitution reaction, the use of a lower growth temperature causes the higher surface-energy growth direction to change from [100] to [110]. The high-resolution X-ray diffraction pattern and X-ray photoelectron spectroscopy results revealed that a thinner oxide-layer was produced on the surface of the PbS NWs by the substitution reaction. We fabricated field effect transistors using single PbS NW, which showed intrinsic p-type semiconductor characteristics for all three routes. For the PbS NW with a thinner oxide layer, the carrier mobility was measured to be as high as 10 cm(2) V(-1) s(-1).
ACS Nano 2010 Apr 27
PMID:Three synthetic routes to single-crystalline PbS nanowires with controlled growth direction and their electrical transport properties. 2034 41

The adhesion between poly(dimethylsiloxane) (PDMS) hemispheres coated with layer-by-layer (LbL) assemblies of polyelectrolytes and rigid, planar substrates was investigated using Johnson, Kendall, and Roberts (JKR) contact mechanics. Measurements were performed against amine-functionalized glass slides both in air and in aqueous solutions of controlled pH. Despite the increased density of negatively charged carboxylate groups, LbL-functionalized PDMS exhibited lower adhesion because of the combined effects of increased surface roughness and the high Young's modulus of the coating. Measurements of coated PDMS in aqueous solutions revealed tunable adhesion behavior dominated by pH-mediated changes in the mechanical properties of the coating. Smoothing the surface of the LbL coatings by aqueous salt annealing led to a significant increase in adhesion. Our results suggest that LbL assembly can be an effective means of surface functionalization for in situ adhesion measurements, but understanding and predicting the adhesion behavior requires comprehensive knowledge of the chemical, mechanical, and topological properties of the coating and how such properties change in response to the ambient environment.
ACS Appl Mater Interfaces 2009 Feb
PMID:In situ adhesion measurements utilizing layer-by-layer functionalized surfaces. 2035 26

Lead sulfide nanocrystals (PbS NCs) were codeposited into two organic films, titanyl phthalocyanine (TiOPc) and alpha-sexithiophene, using cluster beam deposition (CBD). NCs of average diameters of approximately 3-4 nm were evenly distributed in these organic films with average particle spacings of approximately 4 nm, as determined by transmission electron microscopy. The film composition and NC surface chemistry were monitored by X-ray photoelectron spectroscopy (XPS) and other methods. Pb:S stoichiometry in the NC/TiOPc film was determined by XPS to correspond to the PbS cubic rock salt structure. Soft-XPS using 200 eV energy photons determined the NC-organic surface chemistry by resolving the S 2p core level into four distinct components for sulfur. The soft-XPS results found that the PbS NC surface chemistry could be tuned by varying the H(2)S/Ar gas ratio within the CBD source.
ACS Appl Mater Interfaces 2009 Aug
PMID:Cluster beam deposition of lead sulfide nanocrystals into organic matrices. 2035 94

The polyaniline (PANI) base was ball-milled with silver nitrate in the solid state. Samples were prepared at various mole ratios of silver nitrate to PANI constitutional units ranging from 0 to 1.5 for three processing times, 0, 5, and 10 min. The emeraldine form of PANI was oxidized to pernigraniline, and the silver nitrate was reduced to metallic silver. Nitric acid is a byproduct, which may protonate the residual emeraldine and pernigraniline. The changes occurring in the structure of PANI are discussed on the basis of Fourier transform IR and Raman spectroscopies. Raman spectra revealed the formation of pernigraniline salt. The reaction between the two nonconducting components, emeraldine base and silver nitrate, produced a mixture of two conducting components, emeraldine or pernigraniline nitrate and metallic silver. The accompanying conductivity changes were determined. The increase in the conductivity of the original base, 10(-9) S cm(-1), up to 10(-2) S cm(-1) was found to depend on the mole ratio of silver nitrate to PANI base and on the processing time of the components in the ball mill.
ACS Appl Mater Interfaces 2009 Sep
PMID:Solid-state reduction of silver nitrate with polyaniline base leading to conducting materials. 2035 13

A modified polyimide has been created that both senses and absorbs moisture. The material was prepared by introducing cobalt(II) chloride, a well-known moisture sensing and absorbing metal salt, into a polyimide. The final polymer was found to be fully cured, retaining the metal without any leeching, and was thermally stable. Furthermore, the material underwent a visible color change when exposed to moisture and reverted back to the original color when subsequently dried. The total moisture absorbed was measured with a quartz crystal microbalance. The amount of moisture absorption was found to be proportional to the relative humidity, and the modified polymer was found to have up to 3 times greater moisture absorption compared to the unmodified polymer.
ACS Appl Mater Interfaces 2009 May
PMID:Cobalt-containing polyimides for moisture sensing and absorption. 2035 89

We have investigated the influence of a high-concentration salt solution (1 M NaCl) on the aqueous lubrication properties of ethylene glycol-based molecules, namely, alpha-methoxy-omega-mercaptopoly(ethylene glycol) (MW 5000 Da) and alpha-methoxy-omega-mercaptoheptakis(ethylene glycol) (MW 356 Da), which have been end-grafted onto polycrystalline gold surfaces at high surface density. Macroscopic-scale, yet nondestructive, pin-on-disk tribometry experiments revealed that a high concentration of sodium chloride is deleterious to the aqueous lubricating properties of both films under low-sliding-speed conditions. This behavior was observed to be closely associated with the more collapsed conformation of surface-grafted poly(ethylene glycol) polymer chains in concentrated salt solutions, as confirmed by quartz-crystal microbalance measurements.
ACS Appl Mater Interfaces 2009 May
PMID:Influence of salt on the aqueous lubrication properties of end-grafted, ethylene glycol-based self-assembled monolayers. 2035 98

We report the fabrication of a hybrid all semiconductor core/shell nanotetrapod structure consisting of crystalline ZnS:Mn core and amorphous Si shell for the first time. The nanostructures were produced via a catalyst-free rapid thermal evaporation technique. Core/shell nanotetrapods were formed in two steps: (i) formation of the crystalline ZnS:Mn tetrapods and (ii) simultaneous surface adsorption of the in situ formed Si vapor species providing the amorphous shell. Crystalline tetrapod formation was guided by the formation of cubic structured ZnS octahedrons with four active (111) polar growth planes, which served as the favored growth site for the four wurtzite structured legs of the tetrapods. Choice of chloride salt as the source of dopant ion was crucial for the in situ generation of Si vapor. At elevated temperature, chloride salt reacted with the sulfur vapor to produce S2Cl2 gas that etched the Si wafers, generating Si vapor. Suppression of the surface-state-related blue emission was observed in the core/shell structures that clearly supported the formation of a shell layer. Elimination of the surface states ensured efficient energy transfer to the dopant Mn ionic state, resulting in the strong orange emission via (4)T(1)-(6)A(1) electronic transition.
ACS Appl Mater Interfaces 2009 Jul
PMID:Rapid synthesis of core/shell ZnS:Mn/Si nanotetrapods by a catalyst-free thermal evaporation route. 2035 44

Surface chemistry of wood is based on the exposed surface that is the combination of the intact and cut cellular wall material. It is inherently complex and changes with processing history. Modification of wood surfaces through noncovalent attachment of amine containing water soluble polyelectrolytes provides a path to create functional surfaces in a controlled manner. Adsorption of polyethylenimine (PEI) and polydiallydimethylammonium chloride (PDDA) to wood was quantified as a function of solution conditions (pH and ionic strength). Polycation adsorption was maximized under basic pH without the addition of electrolyte. Added salt either had marginal influence or decreased adsorption of polycation, indicating interactions are strongly influenced by Coulombic forces. PEI adsorption could be modeled by both a Langmuir and Freundlich equations, although the wood surface is known to be heterogeneous. After adsorption of polycations, layer-by-layer assembled films were created on the wood surface. Layered films masked ultrastructural features of the cell wall, while leaving the microscale features of wood (cut lumen walls and openings) evident. These findings revealed for the first time that nanoscale films on wood can be deposited without changing the microscopic and macroscopic texture. Functionalized wood surfaces created by nanoscale films may have a future role in adhesives systems for wood composites, wood protection, and creating new functional features on wood.
ACS Appl Mater Interfaces 2009 Mar
PMID:Nanoscale coatings on wood: polyelectrolyte adsorption and layer-by-layer assembled film formation. 2035 76


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