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We present a novel and scalable approach to tailored ligand exchange in stable suspensions of nanoparticles and nanoparticle clusters which is applicable to a wide range of nanoparticle types. Comp...

The multistep synthesis of a versatile new 4-substituted 3,5-bis(2-pyridyl)-1,2,4-triazole (Rdpt) ligand, 4-[4-(2-aminomethyl)phenyl]-3,5-bis(2-pyridyl)-4 H-1,2,4-triazole (apdpt), is reported, which features a reactive aminomethyl para-substituent on the phenyl group that points "out of the back" of the triazole. This enables further functionalisation under mild conditions by using a range of esters to form an amide link. Specifically, this proof of principle study demonstrates the synthesis of apdpt successfully appended with gold-binding thioctic acid (tpdpt), graphene-binding/emissive pyrene/propylpyrene (prdpt/pbdpt), and a Langmuir-Blodgett film-forming polyethylene glycol (PEG) tail (pgdpt). These ligands are subsequently reacted with [Fe(pyridine)4 (NCBH3 )2 ] to give the mononuclear iron(II) complexes [Fe(Rdpt)2 (NCBH3 )2 ]⋅solvent, in which Rdpt/solvent is tpdpt/2.5 H2 O (1), prdpt/0.5 CHCl3 ⋅H2 O (2), and pbdpt/0.5 CHCl3 ⋅2 H2 O (3), as red powders. Magnetic studies on these powders indicate that the complexes undergo only very gradual and incomplete spin crossover, from completely or mostly high spin at 300 K, to half or three-quarters high spin at 50 K. Gold nanoparticles are successfully functionalised with the thioctic acid tpdpt ligand to give tpdpt@Au with an average diameter (as determined by TEM) of (3.1±0.7) nm. Preliminary studies on the two pyrene systems in dimethylformamide show that upon excitation at λ=345 nm the blue fluorescence observed for the free ligands is retained, essentially unaffected, in the respective complexes.

A novel silver nanoparticle (AgNP) formulation was developed as a targeted application for the disinfection of carious dentine. Silver nitrate (AgNO3) was chemically reduced using sodium borohydrate (NaBH4) in the presence of sodium dodecyl sulfate (SDS) to form micelle aggregate structures containing monodisperse 6.7- to 9.2-nm stabilized AgNPs. AgNPs were characterized by measurement of electrical conductivity and dynamic light scattering, scanning electron microscopy, transmission electron microscopy, and inductively coupled plasma mass spectrometry. Antimicrobial activity of AgNPs was tested against planktonic cultures of representative gram-positive and gram-negative oral bacteria using well diffusion assays on tryptic soy broth media and monoculture biofilms grown with brain heart infusion ± sucrose anaerobically at 37°C on microtiter plates. Biofilm mass was measured by crystal violet assay. Effects were compared to silver diamine fluoride and chlorhexidine (negative controls) and 70% isopropanol (positive control) exposed cultures. In the presence of AgNPs, triplicate testing against Streptococcus gordonii DL1, C219, G102, and ATCC10558 strains; Streptococcus mutans UA159; Streptococcus mitis I18; and Enterococcus faecalis JH22 for planktonic bacteria, the minimum inhibitory concentrations were as low as 7.6 µg mL-1 and the minimum bacteriocidal concentrations as low as 19.2 µg mL-1 silver concentration. Microplate readings detecting crystal violet light absorption at 590 nm showed statistically significant differences between AgNP-exposed biofilms and where no antimicrobial agents were used. The presence of sucrose did not influence the sensitivity of any of the bacteria. By preventing in vitro biofilm formation for several Streptococcus spp. and E. faecalis, this AgNP formulation demonstrates potential for clinical application inhibiting biofilms.

Nonporous coordination polymers (CPs) constructed from flexible bridging ligands have seldom been utilized in practical applications, owing to limited solubility and/or stability in most solvents. Here we have produced nanocrystal coordination polymers (NCPs) with identical crystalline structure to their macroscale counterparts, high solvent dispersibility, and large effective surface area for catalytic application. A microemulsion system has been developed for the mild synthesis of the ZnII- and CuII-NCPs, resulting in control over the size, morphology, and reactivity. Both ZnII- and CuII-NCPs demonstrated high catalytic activity in a ring opening reaction of cyclohexene oxide with aniline; furthermore, reduced Cu-NCPs were employed as efficient, reusable catalysts for an azide–alkyne cycloaddition “click” reaction in the nonpolar solvent heptane. In contrast, all macroscale CP equivalents, prepared by conventional methods, were catalytically inactive.

The synthesis and specific surface functionalization of antimicrobial silver nanoparticles (AgNPs) and their incorporation into an alginate hydrogel is described. Divalent cation-mediated ionic crosslinking was used to disperse the AgNPs throughout the gel, made possible by -COO- cross-linking sites provided by the surface-enhanced nanoparticles, inspired by the classic egg-box model crosslinking of calcium alginate. An AgNP concentration, 10-20 μg g-1 increased hygrogel elasticity, viscosity, and shear resistance by 45, 30, and 31% respectively. Cryo-TEM revealed evenly distributed AgNP assemblies of discrete AgNPs throughout the gel matrices. FTIR-ATR indicated AgNPs were involved in alginate carboxylate-Ca2+-COO-AgNP crossbridging, which was not achieved through mixing of AgNPs into preformed gels. Live/dead fluorometric assays determined a minimal bactericidal concentration of 25 μg g-1 Ag for 6 microorganisms. Anti-biofilm assays showed species-dependent cell death of 44 -61%, with limited silver ion release of 0.41% and 1.1% after 7 days for Gram positive and negative bacteria, respectively.

We present a novel approach for the preparation of magnetic nanoparticle clusters of controlled size and selectable magnetic anisotropy, which provides materials with properties selectable for biomedical applications and as components in magnetically responsive nanocomposites. The assembly process is based on a ligand desorption strategy and allows selection of nanoparticle size and temporal control over final cluster size. Detailed NMR analysis of the suspensions pinpoints the role of particle size in controlling the interparticle interactions, within the clusters, which effectively determine the anisotropy. Colloidal interaction modelling confirms this interpretation and provides a means to predict both colloidal stability and magnetic anisotropy.

Diffusion-ordered NMR spectroscopy (DOSY) and nuclear Overhauser effect spectroscopy (NOESY) have been used to explore the diffusion and partitioning behavior of secondary surfactants added to suspensions of reverse micelles (RMs) containing either silver or gold nanoparticles (NPs), with an aim of advancing our understanding of the mechanism of metal NP extraction and/or surface functionalization with specific capping agents as performed during a microemulsion-based synthesis. We have coupled these NMR techniques with corresponding dynamic light scattering (DLS) measurements of RMs, with and without encapsulated metal NPs, upon addition of secondary surfactants. Using oleylamine (OAm), oleic acid (OA), dodecylamine (DDAm), and dodecanethiol (DDT), we show that all four secondary surfactants can rapidly diffuse into/out of the RM environment with their head groups in close proximity to the RM interior and encapsulated water molecules; however, surfactant molecules containing a terminal -NH2 or -COOH group undergo a persistent association with the molecules of the RMs, thus solubilizing and partially sequestering a portion of the total concentration of these secondary agents within the RM interface for a lengthened period of time (in relation to the time frame of the DOSY experiments) and slowing their rate of exchange with freely diffusing molecules in the bulk solvent. The extraction of Ag or Au NPs from RMs into organic phase was determined to be critically dependent on the type and concentration of secondary surfactant added to the system, with DDT proving to be most efficient for the extraction of Ag NPs, while OA was shown to be most efficient for Au NPs. Consideration of the results obtained from this particular combination of techniques has provided new knowledge with respect to dynamic metal NP-containing microemulsion systems.

A series of ditopic ω-di(2-pyridylmethyl)amine carboxylic acid ligands incorporating a range of n-alkyl linkers (CnCOOH, n = 3–5, 7, 10 and 11) have been synthesised. Solution phase studies showed a 1 : 1 coordination stoichiometry between the ligands and M(ClO4)2·6H2O (M = ZnII or CuII) in all cases. The ZnII and CuII complexes were subsequently crystallised by liquid–liquid diffusion and the solid-state structures investigated by X-ray crystallography. The crystal structures obtained are entirely consistent with the 1 : 1 metal–ligand ratio of the solution-phase adducts. However, the coordination geometries and complex topologies are dependent on the alkyl chain length of the ligand CnCOOH. The ZnII and CuII complexes of the short alkyl chain ligands (n ≤ 5) exhibit 1D coordination polymeric structures with somewhat different conformations for {[Zn(C3COO)(H2O)](ClO4)·3.5H2O}n (1), {[Zn(C4COO)(H2O)]4(ClO4)4·1.5H2O}n (2), {[Zn(C5COO)(H2O)](ClO4)}n (3), {[Cu(C3COO)](ClO4)·MeOH}n (4), {[Cu(C4COO)(H2O)]2(ClO4)2·2H2O}n (5) and {[Cu(C5COO)(H2O)](ClO4)·2H2O}n (6). In contrast, the ligands with longer alkyl chains (n ≥ 7) participate in Zn2L2 metallomacrocyclic structures {[Zn(C7COO)(H2O)](ClO4)}2 (7), [Zn2(C10COO)2(H2O)2](ClO4)2·2H2O·MeOH (8) and {[Zn2(C11COO)2(H2O)2][Zn2(C11COO)2](ClO4)4·H2O}n (9). The formation of metallomacrocycles instead of the 1D coordination polymers is a persistent trend and, with identical crystal growth conditions and a non-coordinating anion employed, appears to be an effect of the longer alkyl chain.

In this work we identify an effective cmc boundary for a model ionic surfactant/metal salt system (sodium dodecylsulfate/silver nitrate; SDS/AgNO 3 ), and demonstrate the importance of this boundary with respect to surfactant- and/or micelle-templated synthesis of metal nanoparticles. By preparing SDS-stabilized silver nanocomposite materials using an SDS/AgNO 3 ratio at the identified cmc boundary, we observe the formation of silver nanocomposite assemblies; the extent of assembly can be varied by altering the initial AgNO 3 concentration. Finally, we describe the mechanism of formation and morphology of the nanocomposite materials when the structures are prepared at , above and/or below the effective cmc boundary.

A highly stable and processable macrocyclic Single-Molecule Magnet (SMM) containing one Tb III and three Cu II ions in the core structure was covalently grafted onto gold nanoparticles pre-functionalised with carboxylate terminated tethers. The modified microemulsion method allowed production of small and monodisperse nanoparticles (about 3.5 nm in diameter) for the chemisorption of a huge amount of molecules, with retention of the SMM behavior in the final hybrid system.

In a proof-of-principle study, a soluble macrocyclic single-molecule magnet (SMM) containing a Cu

New methods to study dynamics in lipid bilayers are of interest particularly where they may bridge the gap between conventional experimental techniques and molecular dynamics simulations. Fast field cycling nuclear magnetic resonance relaxometry can provide valuable information as it is sensitive to dynamic processes that occur over a broad time scale. By analysis of data recorded for large unilamellar liposomes composed of 1,2-dimyristoyl-sn-glycero-3-posphocholine (DMPC) or 1,2-dioleoyl-sn-glycero-3-posphocholine (DOPC) at different temperatures and sizes, we validate an evidence-based approach to studying dynamics by relaxometry. Specifically, the number and form of the spectral density contributions from a range of dynamic processes are determined. This success of the approach strongly suggests its general applicability for the study of dynamics in membranes of more complex composition and for parameterizing molecular dynamics simulations.

We present a new route to stable magnetic-plasmonic nanocomposite materials with exceptional control over composite size and very high monodispersity. The method involves the assembly of magnetic iron oxide nanoparticles, of any size in the superparamagnetic size range, whose steric repulsion is gradually reduced by competitive stabilizer desorption arising from the presence of a tertiary silica phase. Subsequent addition of gold nanoparticles results in hierarchical assemblies in the form of gold-decorated magnetic nanoparticle clusters, in a range of possible sizes from 20 to 150 nm, selected by the timing of the addition. This approach adds plasmonic and chemical functionality to the magnetic clusters and improves the physical robustness and processability of the suspensions. Most critically, detailed NMR relaxation analysis demonstrates that the effect of the gold NPs on the interaction between bulk solvent and the magnetic moments of the cluster is minimal and that the clusters remain superparamagnetic in nature. These advantages enhance the potential of the materials as size-selected contrast agents for magnetic resonance imaging. The possibility of generalizing the approach for the production of hierarchical assemblies of variable composition is also demonstrated.

Polyelectrolyte-stabilised cobalt ferrite magnetic fluids demonstrate high relaxivity values at low fields. The magnetic suspensions are composed of compact metal oxide nanocomposites arranged in micelle-like structures which demonstrate an inverse correlation between relaxivity and hydrodynamic diameter (see graph). They can be aligned into linear arrays using an external magnet.

Stable aqueous suspensions of phospholipid-coated superparamagnetic Fe3O4 nanoparticles, or magnetoliposomes (MLs), were prepared and were separated by magnetic chromatography into size monodisperse fractions over a broad size range (50–130 nm). This development facilitated the first study of the size dependence of the MRI relaxation enhancements (relaxivity) of the ML suspensions. The iron oxide surface was stabilised by a primary layer of phosphatidylglycerol, but a range of lipids could be used to complete the bilayer, ensuring water dispersibility and control of ML surface properties. This work establishes for the first time that the outer lipid headgroup has a strong influence on the water relaxation time. Thus our approach provides multiple means to tailor both the biodistribution and the relaxivity of ML suspensions for biomedical applications as contrast agents for MRI, or as magnetically actuated delivery vehicles.

We report the preparation of monodisperse maghemite (gamma-Fe2O3) nanoparticle suspensions in heptane, by thermal decomposition of iron(III) acetylacetonate in the presence of oleic acid and oleylamine surfactants. By varying the surfactant/Fe precursor mole ratio during synthesis, control was exerted both over the nanocrystal core size, in the range from 3 to 6 nm, and over the magnetic properties of the resulting nanoparticle dispersions. We report field-cycling 1H NMR relaxation analysis of the superparamagnetic relaxation rate enhancement of nonaqueous suspensions for the first time. This approach permits measurement of the relaxivity and provides information on the saturation magnetization and magnetic anisotropy energy of the suspended particles. The saturation magnetization was found to be in the expected range for maghemite particles of this size. The anisotropy energy was found to increase significantly with decreasing particle size, which we attribute to increased shape anisotropy. This study can be used as a guide for the synthesis of maghemite nanoparticles with selected magnetic properties for a given application.

BACKGROUND: In late January 2003, some blood centers and hospitals throughout the US voluntarily sus-pended the use of some RBC and plasma units for trans-fusion due to the presence of unknown white particulate matter (WPM) in these units. To better understand the WPM phenomena, a number of technologies were used to establish the nature of the particulates observed in Terumo Collection sets. STUDY DESIGN AND METHODS: All AS-5 nonleuko-reduced RBCs and plasma units were visually inspected for WPM by placing the bags on a flat counter, undisturbed, for approximately 10 minutes and then perform-ing a visual examination for particles. Particles were isolated and placed on microscope slides or in plastic tubes for further analysis. Electron microscopy, bright field microscopy, differential interference contrast microscopy, infrared spectroscopy, and flow cytometry procedures were performed to establish the nature of the particulate matter. In addition, leukoreduction filters and blood transfusion sets were used on RBCs units with WPM. RESULTS: The particles were mostly composed of PLTs and WBCs, and fragments of these cells. All macroscopic WPM was removed from RBCs with leukoeduction and transfusion filters. CONCLUSIONS: WPM originated from PLTs and WBCs. Foreign matter (e.g., plastic) was not observed in any of the units. Leukoreduction and transfusion filters can be used to remove macroscopic WPM.

A strategy to prevent and treat tooth decay, which utilises electrophoretic movement of charged, antibacterial silver nanocomposite structures to infiltrate human dentine to target bacteria contained within the dentine tubules, has been developed and evaluated. Scanning electron microscopy and energy-dispersive X-ray spectroscopy have confirmed high affinity of the nanocomposite structures for tooth tissue, and enhanced penetration of the nanostructures into the tubules under the influence of direct current. It is anticipated that this strategy could be used to sterilise dentine prior to the placement of a dental restorative material.

The general applicability of fast field-cycling nuclear magnetic resonance relaxometry in the study of dynamics in lipid bilayers is demonstrated through analysis of binary unilamellar liposomes composed of 1,2-dioleoyl-sn-glycero-3-posphocholine (DOPC) and cholesterol. We extend an evidence-based method to simulating the NMR relaxation response, previously validated for single-component membranes, to evaluate the effect of the sterol molecule on local ordering and dynamics over multiple timescales. The relaxometric results are found to be most consistent with the partitioning of the lipid molecules into affected and unaffected portions, rather than a single averaged phase. Our analysis suggests that up to 25 mol%, each cholesterol molecule orders three DOPC molecules, providing experimental backup to the findings of many molecular dynamics studies. A methodology is established for studying dynamics on multiple timescales in unilamellar membranes of more complex compositions. Fil: Fraenza, Carla Cecilia. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Meledandri, Carla J.. Universidad de Dublin; Irlanda. University of Otago; Nueva Zelanda Fil: Anoardo, Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Brougham, Dermot F.. Universidad de Dublin; Irlanda

Fast field-cycling (FFC) and rotating-frame nuclear magnetic resonance relaxometry were used to study molecular and collective dynamics in unilamellar liposome systems. Relaxation data for liposomes of diameter about 100 nm composed of 1,2-dimyristoyl-sn-glycero-3-posphocholine (DMPC) or 1,2-dioleoyl-sn-glycero-3-posphocholine (DOPC) were obtained. The Larmor frequency dependence of the spin-lattice relaxation rates was interpreted in terms of clearly defined relaxation mechanisms associated with the underlying molecular dynamics. The physical parameters obtained from the analysis are consistent with values available in the literature obtained from a range of experimental techniques. This work establishes the potential of our approach to study dynamics in liposomal samples of more complex lipid composition.

Using a one-step procedure we have prepared magnetic fluids comprising of polyelectrolyte stabilized magnetite nanoparticles. These nanocomposites are comprised of linear, chain-like assemblies of magnetic nanoparticles, which can be aligned in parallel arrays by an external magnetic field. We have shown the potential use of these materials as contrast agents by measuring their MR response in live rats. The new magnetic fluids have demonstrated good biocompatibility and potential for in vivo MRI diagnostics.

We present a new twist on a conventional nanoparticle preparation method, which allows the one-pot synthesis of two fractions of size-controlled, spherical, monodisperse silver nanoparticles (Ag NPs), one fraction of which can be suspended in organic solvent, and the other can be suspended in aqueous or other polar solvents, with no significant change to the core diameter of the suspended particles. Furthermore, we demonstrate that the careful selection of capping agents enables the tailoring of the NP surface and optical properties and controls the extent of partitioning between the organic and aqueous phases. This study can serve as a guide for the preparation of NPs with independent control over particle size, composition, surface coating and dispersing medium, thus allowing the contributions of each of these factors to the NP properties to be isolated and investigated individually.

In recent years there has been rapid progress in the development of nanomaterials, and in particular magnetic nanomaterials, for magnetic resonance imaging and other biomedical applications. Using selected highlights from recent literature we describe the magnetic resonance methods that are used to measure the effects of agents on image contrast. We also show how these methods offer new insight into magnetic order in the colloidal state, a critical factor for all biomedical applications.