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In this paper, we report novel ferroelectric properties of a new form of ice inside single-walled carbon nanotubes (SWCNTs). These are called "ice nanotubes" (ice NTs) and they consist of polygonal water rings stacked one-dimensionally along the SWCNT axis. We performed molecular dynamics (MD) calculations for the ice NTs under an external electric field and in a temperature range between 100 and 350 K. It is revealed that ice NTs show stepwise polarization with a significant hysteresis loop as a function of the external field strength. In particular, pentagonal and heptagonal ice NTs are found to be the world's smallest ferroelectrics with spontaneous polarization of around 1 microC/cm(2). The n-gonal ice NT, where n = 5, 6, or 7, has (n + 1)-polarized structures with different polarizations. These findings suggest potential applications of SWCNTs encapsulating dielectric materials for the fabrication of the smallest ferroelectric devices. Experimental evidence for the presence of ice NTs inside SWCNTs is also discussed in great detail.
ACS Nano 2009 May 26
PMID:Dielectric properties of water inside single-walled carbon nanotubes. 1938 4

We report a simple, economical method for generating water-soluble, biocompatible nanocrystals that are colloidally robust and have a small hydrodynamic diameter. The nanocrystal phase transfer technique utilizes a low molecular weight amphiphilic polymer that is formed via maleic anhydride coupling of poly(styrene-co-maleic anhydride) with either ethanolamine or Jeffamine M-1000 polyetheramine. The polymer encapsulated water-soluble nanocrystals exhibit the same optical spectra as those formed initially in organic solvents, preserve photoluminescence intensities, are colloidally stable over a wide pH range (pH 3-13), have a small hydrodynamic diameter, and exhibit low levels of nonspecific binding to cells.
ACS Nano 2009 May 26
PMID:The preparation of colloidally stable, water-soluble, biocompatible, semiconductor nanocrystals with a small hydrodynamic diameter. 1938 61

We demonstrate a straightforward strategy to fabricate a multilayer inorganic/organic polarized light-emitting diode device based on highly ordered arrays of rod-shaped nanocrystals as the active species. We have developed a simple and effective method that allows colloidal CdSe/CdS core/shell nanorods to be laterally aligned in smectic or nematic phases on the surface of water. A floating film of such ordered nanorods has been collected by a poly(dimethylsiloxane) (PDMS) stamp pad and transferred by contact printing onto previously evaporated organic layers. Thanks to the lateral nanorod alignment the as-prepared film exhibited strong polarized photoluminescence and it has been used as emissive layer in the polarized electroluminescent device.
ACS Nano 2009 Jun 23
PMID:Polarized light emitting diode by long-range nanorod self-assembling on a water surface. 1944 70

Water-soluble single-walled nanotubes (SWNTs) are being tested as contrast agents for medical imaging and for the delivery of therapeutically active molecules to target cells. However, before they become used commercially, it will be essential to establish their subcellular distribution and whether they are cytotoxic. Here we characterize uptake of unlabeled, acid-treated, water-soluble SWNTs by human monocyte derived macrophage cells using a combination of Raman spectroscopy and analytical electron microscopy and compare our findings to previous work on unpurified SWNTs. Raman spectroscopy demonstrated that acid-treated SWNTs had a greater number of functional groups on the carbon walls than nontreated SWNT. The acid-treated SWNTs were less aggregated within cells than unpurified SWNTs. Bundles, and also individual acid-treated SWNTs, were found frequently inside lysosomes and also the cytoplasm, where they caused no significant changes in cell viability or structure even after 4 days of exposure.
ACS Nano 2009 Jun 23
PMID:Uptake of noncytotoxic acid-treated single-walled carbon nanotubes into the cytoplasm of human macrophage cells. 1945 22

How primitive enzymes emerged from a primordial pool remains a fundamental unanswered question with important practical implications in synthetic biology. Here we show that a de novo evolved ATP binding protein, selected solely on the basis of its ability to bind ATP, mediates the regiospecific hydrolysis of ATP to ADP when crystallized with 1 equiv of ATP. Structural insights into this reaction were obtained by growing protein crystals under saturating ATP conditions. The resulting crystal structure refined to 1.8 A resolution reveals that this man-made protein binds ATP in an unusual bent conformation that is metal-independent and held in place by a key bridging water molecule. Removal of this interaction using a null mutant results in a variant that binds ATP in a normal linear geometry and is incapable of ATP hydrolysis. Biochemical analysis, including high-resolution mass spectrometry performed on dissolved protein crystals, confirms that the reaction is accelerated in the crystalline environment. This observation suggests that proteins with weak chemical reactivity can emerge from high affinity ligand binding sites and that constrained ligand-binding geometries could have helped to facilitate the emergence of early protein enzymes.
ACS Chem Biol 2009 Aug 21
PMID:A synthetic protein selected for ligand binding affinity mediates ATP hydrolysis. 1952 80

A broad array of water-insoluble compounds has displayed therapeutically relevant properties toward a spectrum of medical and physiological disorders, including cancer and inflammation. However, the continued search for scalable, facile, and biocompatible routes toward mediating the dispersal of these compounds in water has limited their widespread application in medicine. Here we demonstrate a platform approach of water-dispersible, nanodiamond cluster-mediated interactions with several therapeutics to enhance their suspension in water with preserved functionality, thereby enabling novel treatment paradigms that were previously unrealized. These therapeutics include Purvalanol A, a highly promising compound for hepatocarcinoma (liver cancer) treatment, 4-hydroxytamoxifen (4-OHT), an emerging drug for the treatment of breast cancer, as well as dexamethasone, a clinically relevant anti-inflammatory that has addressed an entire spectrum of diseases that span complications from blood and brain cancers to rheumatic and renal disorders. Given the scalability of nanodiamond processing and functionalization, this novel approach serves as a facile, broadly impacting and significant route to translate water-insoluble compounds toward treatment-relevant scenarios.
ACS Nano 2009 Jul 28
PMID:Nanodiamond-mediated delivery of water-insoluble therapeutics. 1953 85

Understanding transport phenomena of fluids through nanotubes (NTs) is of great interest in order to enable potential application of NTs as separation devices, encapsulation media for molecule storage and delivery, and sensors. Single-walled metal oxide NTs are interesting materials because they present a well-defined solid-state structure, precisely tunable diameter and length, as well as a hydrophilic and functionalizable interior for tuning transport and adsorption selectivity. Here, we study the transport properties of hydrogen-bonding liquids (water, methanol, and ethanol) through a single-walled aluminosilicate NT to investigate the influence of liquid-surface and liquid-liquid interactions and the effects of competitive transport of different chemical species using molecular dynamics (MD) simulations. The self-diffusivities (D(s)) for all the three species decrease with increasing loading and are comparable to bulk liquid diffusivities at low molecular loadings. We show that the hydrogen-bond network associated with water makes its diffusion behavior different from methanol and ethanol. Mixtures of water and methanol show segregation in the NT, with water located closer to the tube wall and the alcohol molecules localized near the center of the NT. D(s) values of water in an analogous aluminogermanate NT are larger than those in the aluminosilicate NT due to a larger pore diameter.
ACS Nano 2009 Jun 23
PMID:Self-diffusion of water and simple alcohols in single-walled aluminosilicate nanotubes. 1954 68

The presence of E. coli in foodstuffs and drinking water is a chronic worldwide problem. The worldwide food production industry is worth about U.S. $578 billion, and the demand for biosensors to detect pathogens and pollutants in foodstuffs is growing day by day. Driven by the need, we report for the first time that two-photon Rayleigh scattering (TPRS) properties of gold nanorods can be used for rapid, highly sensitive and selective detection of Escherichia coli bacteria from aqueous solution, without any amplification or enrichment in 50 colony forming units (cfu)/mL level with excellent discrimination against any other bacteria. TPRS intensity increases 40 times when anti- E. coli antibody-conjugated nanorods were mixed with various concentrations of Escherichia coli O157:H7 bacterium. The mechanism of TPRS intensity change has been discussed. This bionanotechnology assay could be adapted in studies using antibodies specific for various bacterial pathogens for the detection of a wide variety of bacterial pathogens used as bioterrorism agents in food, clinical samples, and environmental samples.
ACS Nano 2009 Jul 28
PMID:Gold Nanorod Based Selective Identification of Escherichia coli Bacteria Using Two-Photon Rayleigh Scattering Spectroscopy. 1957 19

Particle lithography is a practical approach to generate millions of organosilane nanostructures on various surfaces, without the need for vacuum environments or expensive instrumentation. This report describes a stepwise chemistry route to prepare organosilane nanostructures and then apply the patterns as a spatially selective foundation to attach gold nanoparticles. Sites with thiol terminal groups were sufficiently small to localize the attachment of clusters of 2-5 nanoparticles. Basic steps such as centrifuging, drying, heating, and rinsing were used to generate arrays of regular nanopatterns. Close-packed films of monodisperse latex spheres can be used as an evaporative mask to spatially direct the placement of nanoscopic amounts of water on surfaces. Vapor phase organosilanes deposit selectively at areas of the surface containing water residues to generate nanostructures with regular thickness, geometry, and periodicity as revealed in atomic force microscopy images. The area of contact underneath the mesospheres is effectively masked for later synthetic steps, providing exquisite control of surface coverage and local chemistry. By judicious selection in designing the terminal groups of organosilanes, surface sites can be engineered at the nanoscale for building more complex structures. The density of the nanopatterns and surface coverage scale predictably with the diameter of the mesoparticle masks. The examples presented definitively illustrate the capabilities of using the chemistry of molecularly thin films of organosilanes to spatially define the selectivity of surfaces at very small size scales.
ACS Nano 2009 Jul 28
PMID:Engineering the spatial selectivity of surfaces at the nanoscale using particle lithography combined with vapor deposition of organosilanes. 1957 52

Dendrimers have successfully proved themselves as functional nanodevices for drug delivery because they can render drug molecules a greater water solubility, bioavailability, and biocompatibility. It has recently been suggested that the structural changes of cell membranes (e.g., local lipid density and actual pore or hole) could affect the permeability across them for dendrimers. However, to understand these effects requires direct measurements in a single cell and is thus very difficult and more challenging. Here we use mesoscopic simulations to investigate the tension-mediated complexes comprising charged dendrimers and lipid bilayer membranes. The structures of membranes are alternated by adjusting their surface tensions. Our simulations demonstrate that the permeability of charged dendrimers can be effectively enhanced in the tense membranes, and the permeability in the actual hole is several times higher than that in the lipid-poor section. The possible mechanism of charged dendrimer-induced pore nucleation in the tense membranes is evaluated. The findings have implications in tuning intracellular delivery rates and amounts in nanoscale complex and chemotherapeutics.
ACS Nano 2009 Aug 25
PMID:Enhanced permeability of charged dendrimers across tense lipid bilayer membranes. 1958 48


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