We report the nanoscale loading and confinement of aquated Gd3+n-ion clusters within ultra-short single-walled carbon nanotubes (US-tubes); these Gd3+n@US-tube species are linear superparamagnetic molecular magnets with Magnetic Resonance Imaging (MRI) efficacies 40 to 90 times larger than any Gd3+-based contrast agent (CA) in current clinical use.
Crystal growth upon firing of hydrous transition metal oxide gels can be effectively inhibited by replacing the surface hydroxyl group before firing with another functional group that does not condense and that can produce small, secondary-phase particles that restrict advancing of grain boundaries at elevated temperatures. Accordingly, fully crystallized SnO(2), TiO(2), and ZrO(2) materials with mean crystallite sizes of approximately 20, 50, and 15 angstroms, respectively, were synthesized by replacing the hydroxyl group with methyl siloxyl before firing at 500 degrees C. An ultrasensitive SnO(2)-based chemical sensor resulting from the microstructural miniaturization was demonstrated.
Derivatized water-soluble Gd-based metallofullerenes are excellent MRI contrast agents with unusually large proton relaxivities for agents with no direct Gd−OH 2 bonding. In this study, dynamic light scattering (DLS), static light scattering (SLS), and transmission electron microscopy (TEM) have been used to characterize the propensity of two such species, Gd@C 60 [C(COOH) 2 ] 10 and Gd@C 60 (OH) x , to aggregate in aqueous solution, since aggregation is known to enhance proton relaxivities of MRI contrast agents by increasing their rotational correlation times (via more slowly tumbling aggregates). The present aggregation study has been conducted as a function of concentration, temperature, and pH and has revealed that both compounds aggregate at pH ) 9 to form spherical and irregular clusters having sizes between 30 and 90 nm, with little concentration or temperature dependency. Below pH ) 9, the aggregate sizes increase steadily and dramatically, reaching hydrodynamic diameters of 600−1000 nm by pH ) 5. Additionally, the intermolecular forces holding the aggregates together are weaker for Gd@C 60 [C(COOH) 2 ] than for Gd@C 60 (OH) x . We conclude that the tendency of these metallofullerene species to self-assemble into nanoscale aggregates in aqueous solution likely produces their unusually large, outer-sphere, pH-sensitive proton relaxivities.
Cross-shaped and octahedral nanoparticles (hexapods) of MnO in size, and fragments thereof, are created in an amine/carboxylic acid mixture from manganese formate at elevated temperatures in the presence of water. The nanocrosses have dimensions on the order of 100 nm, but with exposure to trace amounts of water during the synthesis process they can be prepared up to about 300 nm in size. Electron microscopy and X-ray diffraction results show that these complex shaped nanoparticles are single crystal face-centered cubic MnO. In the absence of water, the ratio of amine to carboxylic acid determines the nanocrystal size and morphology. Conventionally shaped rhomboehdral/square nanocrystals or hexagonal particles can be prepared by simply varying the ratio of tri-n-octylamine/oleic acid with sizes on the order of 35-40 nm in the absence of added water. If the metal salt is rigorously dried before the synthesis, then "flower-shaped" morphologies on the order of 50-60 nm across are observed. Conventional squareshaped nanocrystals with clearly discernible thickness fringes that also arise under conditions producing the nanocrosses mimic the morphology of the cross-shaped and octahedral nanocrystals and provide clues to the crystal growth mechanism(s), which agree with predictions of crystal growth theory from rough, negatively curved surfaces. The synthetic methodology appears to be general and promises to provide an entryway into other nanoparticle compositions.
Single-source molecular precursors were found to produce iron phosphide materials. In a surfactant system of trioctylamine and oleic acid, H2Fe3(CO)9PtBu reacted to form Fe4(CO)12(PtBu)2, which decomposed to give Fe2P nanorods and "bundles." Control of the morphology obtained was possible by varying the surfactant system; addition of increasing amounts of oleic acid resulted in crystal splitting, while the addition of microliter amounts of an alkane enhanced the crystal splitting to give sheaflike structures. The different morphologies seen were attributed to imperfect crystal growth mechanisms.
Rod-shaped nanostructures of Bi2S3 were synthesized by the solution decomposition of the two new bismuth(III) complexes [Bi6(pydc)8(Hpydc)2(tu)8] (1) and {[Bi2(pydc)3(tsc)(H2O)2]·H2O}∞ (2) (H2pydc = 2,6-pyridinedicarboxylic acid also known as dipicolinic acid; tu = thiourea, tsc = thiosemicarbazide). They were obtained by treatment of Bi2O3 with dipicolinic acid in the presence of the sulfur-containing ligands. The complexes were characterized with the aid of elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction. The dipicolinate anions behave as tridentate ligands toward Bi(III), but two modes of coordination are found. In both cases the ligand serves as a pincer ligand O,N,O-bonded to one bismuth(III) center, but it can also function as a bridging ligand through one carboxylate group that assembles into hexanuclear molecules (1) or a polymeric chain (2). The air-stable complexes 1 and 2 have been used as starting materials in the preparation of bismuth sulfide nanoparticles (NPs) in the presence of different surfactants. Decomposition of 1 and 2 gave Bi2S3 in all cases, but addition of a small amount of 1-dodecanethiol (DT) or 1-octadecanethiol (OT) at 120 °C resulted in better crystallite growth with the observation of nanorods up to several hundreds of nanometers in length. These were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The influence of various reaction conditions on the shape and size of the nanocrystals is discussed. The high resolution (HR) TEM images reveal a number of linear and planar crystal defects and atomic distortions that account for the splitting of bismuth sulfide nanocrystals as observed previously. The growth mechanism is believed to involve decomposition of the precursors and formation of Bi2S3 seeds, followed by the preferential [001] growth of larger particles. Crystal splitting caused by defects and atomic distortions as well as Ostwald ripening processes play important roles in shaping the morphologies of the final Bi2S3 nanostructures.
A new carboxylic acid-terminated alkanethiol having bidentate character, 16-(3,5-bis(mercaptomethyl)phenoxy)hexadecanoic acid (BMPHA), was designed as an absorbate and protectant to form thermally stable carboxylic acid-terminated organic thin films on flat gold and nanoparticles, respectively. The structural features of the organic thin films derived from BMPHA were characterized by ellipsometry, X-ray photoelectron spectroscopy (XPS), and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), and compared to those derived from mercaptohexadecanoic acid (MHA) and 16-(4-(mercaptomethyl)phenoxy)hexadecanoic acid (MMPHA). This study demonstrates that films derived from BMPHA are less densely packed than films derived from MHA and MMPHA. However, the results of solution-phase thermal desorption tests revealed that the carboxylic acid-terminated films generated from BMPHA exhibit an enhanced thermal stability compared to those generated from MHA and MMPHA. Furthermore, as a nanoparticle protectant, BMPHA can be used to stabilize large gold nanoparticles (~45 nm diameter) in solution, and BMPHA-protected gold nanoparticles exhibited a high thermal stability in solution thermolysis studies.
The use of chemotherapeutic drugs in cancer therapy is often limited by problems with administration such as insolubility, inefficient biodistribution, lack of selectivity, and inability of the drug to cross cellular barriers. To overcome these limitations, various types of drug delivery systems have been explored, and recently, carbon nanotube (CNT) materials have also garnered attention in the area of drug delivery. In this study, we describe the preparation, characterization, and in vitro testing of a new ultra-short single-walled carbon nanotube (US-tube)-based drug delivery system for the treatment of cancer. In particular, the encapsulation of cisplatin (CDDP), a widely-used anticancer drug, within US-tubes has been achieved, and the resulting CDDP@US-tube material characterized by high-resolution transmission electron microscopy (HR-TEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and inductively-coupled optical emission spectrometry (ICP-OES). Dialysis studies performed in phosphate-buffered saline (PBS) at 37 °C have demonstrated that CDDP release from CDDP@US-tubes can be controlled (retarded) by wrapping the CDDP@US-tubes with Pluronic-F108 surfactant. Finally, the anticancer activity of pluronic-wrapped CDDP@US-tubes has been evaluated against two different breast cancer cell lines, MCF-7 and MDA-MB-231, and found to exhibit enhanced cytotoxicity over free CDDP after 24 hours. These studies have laid the foundation for developing US-tube-based delivery of chemotherapeutics, with drug release mainly limited to within cancer cells only.
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