Biomedical subjects

James E Hutchison

Publications and source records attributed to James E Hutchison.

15 recordsLinked to original sources

PubMed2006

Convenient synthesis of 6,6-bicyclic malonamides: a new class of conformationally preorganized ligands for f-block ion binding.

A general synthetic approach was developed for the preparation of a series of 6,6-bicyclic malonamides, a class of ligands that provide a preorganized binding site for f-block ions (particularly trivalent lanthanides). The approach described is convenient to introduce a variety of functional groups at the amide nitrogens to tune the properties of the ligand without altering the preorganized binding. Each of the ten derivatives (that represent a range of functionality, including R = alkyl, hydroxy, phenyl, ester, perfluorocarbon) reported here derives from a single, readily prepared dialdehyde intermediate. This intermediate is converted to the final products via reductive amination with an appropriately functionalized benzylamine, followed by hydrogenolysis and lactam formation. Because derivatization occurs late in the synthesis, the approach is general, requiring only modification of the purification procedures for each new derivative. To aid in the purification of the bicyclic malonamides, we report a novel complexation-based purification method that takes advantage of the high affinity of the ligand for f-block metals.

Journal Article↗

PubMed2006

Spectral diffusion in the tunneling spectra of ligand-stabilized undecagold clusters.

We report diffusion in the tunneling spectra of isolated, ligand-stabilized undecagold (Au11) clusters immobilized by attachment to alpha,omega-alkanedithiolate tethers inserted into alkanethiolate self-assembled monolayers. We use scanning tunneling microscopy and spectroscopy at cryogenic (UHV, 4 K) conditions to measure these clusters' conductance with complete control of their chemical and physical environment; additionally, thermal broadening of their electronic states as well as their mobility is minimized. At low temperature, the Au11 clusters demonstrate Coulomb blockade behavior, with zero-conductance gaps resulting from quantum size effects. Surprisingly, chemically identical and even single particles produced different families of tunneling spectra, comparable to previous results for heterogeneous distributions of particles. We hypothesize that, while these particles are chemically attached to the surface of the SAM for measurement, these assemblies may still be sufficiently dynamic to affect their transport properties significantly.

Journal Article↗

PubMed2006

Rapid purification and size separation of gold nanoparticles via diafiltration.

Purification and size-based separation of nanoparticles remain significant challenges in the preparation of well-defined materials for fundamental studies and applications. Diafiltration shows considerable potential for the efficient and convenient purification and size separation of water-soluble nanoparticles, allowing for the removal of small-molecule impurities and for the isolation of small nanoparticles from larger nanostructures in a single process. Herein, we report studies aimed at assessing the suitability of diafiltration for (i) the purification of water-soluble thiol-stabilized 3-nm gold nanoparticles, (ii) the separation of a bimodal distribution of nanoparticles into the corresponding fractions, and (iii) the separation of a polydisperse sample into fractions of differing mean core diameter. NMR, thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) measurements demonstrate that diafiltration produces nanoparticles with a much higher degree of purity than is possible by dialysis or a combination of solvent washes, chromatography, and ultracentrifugation. UV-visible spectroscopic and transmission electron microscopic (TEM) analyses show that diafiltration offers the ability to separate nanoparticles of disparate core size. These results demonstrate the applicability of diafiltration for the rapid and green preparation of high-purity gold nanoparticle samples and the size separation of heterogeneous nanoparticle samples. They also suggest the development of novel diafiltration membranes specifically suited to high-resolution nanoparticle size separation.

Journal Article↗

PubMed2006

Solution and structural investigations of ligand preorganization in trivalent lanthanide complexes of bicyclic malonamides.

This report describes an investigation into the coordination chemistry of trivalent lanthanides in solution and the solid state with acyclic and preorganized bicyclic malonamide ligands. Two experimental investigations were performed: solution binding affinities were determined through single-phase spectrophotometric titrations and the extent of conformational change upon binding was investigated with single-crystal X-ray crystallography. Both experimental methods compare the bicyclic malonamide (BMA), which is designed to be preorganized for binding trivalent lanthanides, to an analogous acyclic malonamide. Results from the spectrophotometric titrations indicate that BMA exhibits a 10-100x increase in binding affinity to Ln(III) over acyclic malonamide. In addition, BMA forms compounds with high ligand-metal ratios, even when competing with water and nitrate ligands for binding sites. The crystal structures exhibit no significant differences in the nature of the binding between Ln(III) and the BMA or acyclic malonamide. These results support the conclusion that rational ligand design can lead to compounds that enhance the binding affinities within a ligand class.

Bridged Bicyclo Compounds↗

PubMed2006

Substrates for direct imaging of chemically functionalized SiO2 surfaces by transmission electron microscopy.

A significant challenge in materials characterization is the determination of the structure of nanoparticle assemblies that have been deposited on solid substrates, such as SiO2. The best method for obtaining quantitative information about structure, size, and spacing on the nanometer-length scale is TEM; however, commercially available TEM grids offer a limited range of substrate materials. In addition, the compositions of these grids do not permit much chemical processing. Here we describe silicon-based grids with electron-transparent SiO2 windows suitable for use as substrates for high-resolution TEM that can be easily fabricated using standard silicon microfabrication techniques. These grids are physically and chemically robust and exhibit the same surface chemistry and chemical stability as an oxide grown on a silicon wafer. Thus, the grids make possible the concurrent investigation of chemical and structural information on the same sample. Convenient modification of the surfaces of the grids provides access to a wide range of new substrates for the direct imaging of chemically modified surfaces by TEM. We demonstrate the utility of these grids by aligning DNA on the chemically modified SiO2 surface in order to direct the assembly of linear arrays of nanoparticles. Using these grids, we are able to quantify the effects of assembly conditions on nanoparticle size, spacing, and dispersity in the arrays.

DNA↗

PubMed2005

Molecular engineering of the polarity and interactions of molecular electronic switches.

We have investigated and learned to control switching of oligo(phenylene ethynylene)s embedded in amide-containing alkanethiol self-assembled monolayers on Au{111}. We demonstrate bias-dependent switching of the oligo(phenylene ethynylene)s as a function of the interaction between the dipole moment of the oligo(phenylene ethynylene)s and the electric field applied between the scanning tunneling microscope tip and the substrate. We are able to invert the polarity of the switches by altering their design-inverting their dipole moments. For appropriately designed switches and matrix molecules, the conductance states are stabilized by intermolecular hydrogen bonding. These results further support the hypothesis that conductance switching in these molecules is due to hybridization changes at the molecule-substrate bonds due to tilting of the switch molecules.

Journal Article↗

PubMed2005

Thiol-functionalized undecagold clusters by ligand exchange: synthesis, mechanism, and properties.

Ligand exchange of phosphine-stabilized undecagold precursor particles, Au11(PPh3)8Cl3, with omega-functionalized thiols provides a convenient and general approach for the rapid preparation of large families of thiol-stabilized, subnanometer (dCORE approximately 0.8 nm) particles. The approach permits rapid incorporation of specific functionality into the stabilizing ligand shell, is tolerant of a wide range of functional groups, and provides convenient access to new materials inaccessible by other methods. Mechanistic studies and trapping experiments give insight into the progression of the ligand exchange, providing evidence that the core size of the phosphine-stabilized undecagold precursor particles is preserved during ligand exchange. The optical properties of the thiol-stabilized nanoparticles depend strongly on the composition of the ligand shell, and a series of studies suggests that this dependence is a result of the ligand shell's influence on the electronic structure of the particle core, as opposed to a structural change within the nanoparticle core.

Journal Article↗

PubMed2005

Electrochemical detection of nanoscale phase separation in binary self-assembled monolayers.

Developing methods to probe the nature and structure of nanoscale environments continues to be a challenge in nanoscience. We report a cyclic voltammetry investigation of the internal, hydrogen-bond-driven phase separation of amide-containing thiols and alkanethiols. Amide-containing thiols with a terminal ferrocene carboxylate functional group were investigated in two binary monolayers, one homogeneously mixed and the other phase separated. The electrochemical response of the ferrocene probe was used to monitor adsorbate coverage, environment, and phase separation within each of these monolayers. The results demonstrate that the behavior of ferrocene-containing monolayers can be used to probe nanoscale organization.

Journal Article↗

PubMed2005

Thiol-functionalized, 1.5-nm gold nanoparticles through ligand exchange reactions: scope and mechanism of ligand exchange.

Ligand exchange reactions of 1.5-nm triphenylphosphine-stabilized nanoparticles with omega-functionalized thiols provides a versatile approach to functionalized, 1.5-nm gold nanoparticles from a single precursor. We describe the broad scope of this method and the first mechanistic investigation of thiol-for-phosphine ligand exchanges. The method is convenient and practical and tolerates a surprisingly wide variety of technologically important functional groups while producing very stable nanoparticles that essentially preserve the small core size and size dispersity of the precursor particle. The mechanistic studies reveal a novel three-stage mechanism that can be used to control the extent of ligand exchange. During the first stage of the exchange, AuCl(PPh3) is liberated, followed by replacement of the remaining phosphine ligands as PPh3 (assisted by gold complexes in solution). The final stage involves completion and reorganization of the thiol-based ligand shell.

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PubMed2004

Bicyclic and acyclic diamides: comparison of their aqueous phase binding constants with Nd(III), Am(III), Pu(IV), Np(V), Pu(VI), and U(VI).

This report describes affinity measurements for two, water-soluble, methyl-alkylated diamides incorporating the malonamide functionality, N,N,N',N' tetramethylmalonamide (TMMA) and a bicyclic diamide (1a), toward actinide metal cations (An) in acidic nitrate solutions. Ligand complexation to actinides possessing oxidation states ranging from +3 to +6 was monitored through optical absorbance spectroscopy, and formation constants were obtained from the refinement of the spectrophotometric titration data sets. Species analysis gives evidence for the formation of 1, 4, 1, and 2 spectrophotometrically observable complexes by TMMA to An(III, IV, V, and VI), respectively, while for 1a, the respective numbers are 3, 4, 2, and 2. Consistent with the preorganization of 1a toward actinide binding, a significant difference is found in the magnitudes of their respective formation constants at each complexation step. It has been found that the binding affinity for TMMA follows the well-established order An(V) < An(III) < An(VI) < An(IV). However, with 1a, Np(V) forms stronger complexes than Am(III). The complexation of 1a with Np(V) and Pu(VI) at an acidity of 1.0 M is followed by reduction to Np(IV) and Pu(IV), whereas TMMA does not perturb the initial oxidation state for these dioxocations. These measurements of diamide binding affinity mark the first time single-component optical absorbance spectra have been reported for a span of actinide-diamide complexes covering all common oxidation states in aqueous solution.

Journal Article↗

PubMed2004

In situ deprotection and assembly of s-tritylalkanethiols on gold yields monolayers comparable to those prepared directly from alkanethiols.

In this paper we describe a systematic study comparing the properties of self-assembled monolayers (SAMs) formed by in situ deprotection and assembly of S-triphenylmethyl (trityl)- and thiolacetate-protected alkanethiols to those of SAMs formed from the parent alkanethiols. The two in situ deprotections were carried out in trifluoroacetic acid and THF/ammonium hydroxide, respectively. Monolayers of octadecanethiol (ODT) and the peptide-containing alkanethiol 3-mercapto-N-n-pentadecylpropionamide (1ATC15) were assembled on gold using the two in situ methods and characterized by contact angle goniometry, X-ray photoelectron spectroscopy, polarization modulation infrared reflection absorption spectroscopy, and electrochemical characterization methods to assess how the monolayer properties compare to those of monolayers prepared by traditional methods. The results for the in situ deprotection of the trityl-protected molecules demonstrate that this method can afford high-quality monolayers that are nearly indistinguishable from those prepared directly from alkanethiols. The quality of the monolayers prepared using this method is shown to depend on the solubility of the trityl-protected compound in trifluoroacetic acid. The results for the in situ deprotection of acetyl-ODT indicate this method yields low-quality monolayers that contain mixtures of adsorbates bound as thiolates and thiolacetates. In situ trityl deprotection is a useful approach for monolayer formation that greatly simplifies the purification, handling, and assembly of thiol-containing monolayer precursors.

Gold↗

PubMed2004

Mediating stochastic switching of single molecules using chemical functionality.

We have studied oligo(phenylene-ethynylene)s inserted into amide-containing alkanethiol self-assembled monolayers using scanning tunneling microscopy to demonstrate switching based on chemical functionality of the environment of the inserted molecules. The molecules show stability in two conductance states: an ON and an OFF state. We demonstrate bias-dependent switching due to hydrogen bonding between the inserted oligo(phenylene-ethynylene) and the matrix molecules. In addition, the inserted molecules exhibit fewer switching events than previously reported for alkanethiol matrixes, which we attribute to the rigidity of the hydrogen-bonded matrix.

Journal Article↗

PubMed2004

Molecular-level control of feature separation in one-dimensional nanostructure assemblies formed by biomolecular nanolithography.

In this paper, we present a convenient and reliable method to organize small gold nanoparticles (d(CORE) = 1.5 nm) into linear chains with precisely controlled interparticle spacing over a range of 1.5-2.8 nm through biomolecular nanolithography. Controlling the feature separations of 1 to a few nanometers with angstrom-level precision is a key requirement in electronic and optical applications of nanostructures to tune the properties of the nanostructures and manipulate the interactions between neighboring structures. Here, chains are formed in solution by utilizing functional-group-directed self-assembly to organize ligand-stabilized gold nanoparticles onto DNA templates. The spacing between neighboring nanoparticles can be controlled chemically and tuned at the molecular level by utilizing nanoparticles possessing ligand shells of varying thickness to achieve angstrom-level resolution at spacings of 1.5, 2.1, and 2.8 nm. The small standard deviation (< or = 20%) in the values for the interparticle spacing illustrates the reproducibility of the approach. Because the interparticle spacing is enforced by the ligand shell rather than the scaffold, the spacing is uniform even in nonlinear sections of the chain. We further show that the assembly process is robust and produces extended linear nanoparticle chains of up to 1 microm in length and a total coverage of > 90%. All structures and interparticle spacings were analyzed using transmission electron microscopy. Our results demonstrate the potential of scaffold-assisted assembly approaches for patterning features with tunable dimensions on a length scale that is important for future applications of these materials in nanoscale electronics and optics.

DNA↗

PubMed2003

Linear assemblies of nanoparticles electrostatically organized on DNA scaffolds.

A significant challenge faced in the use of nanoscale building blocks is developing parallel methods for interconnecting and patterning assemblies of the individual components. Molecular or polymeric scaffolds hold promise as a means of preparing closely spaced, specifically arranged nanoscale assemblies. Here we show how a biopolymer, DNA, can be used as a scaffold for the assembly of extended, close-packed, ligand-stabilized metal nanoparticle structures, including several desirable architectures (such as lines, ribbons, and branches). Electrostatic binding of ligand-stabilized nanoparticles to the DNA backbone results in extended linear chain-like structures, ribbon-like structures composed of parallel nanoparticle chains, and branched structures. High-resolution transmission electron microscopy shows that the particles are evenly spaced, separated only by the 15 A imposed by the intervening ligand shell. These studies demonstrate that biomolecular nanolithography (the arrangement of nanoscale building blocks on biomolecular scaffolds) is a viable approach to interconnecting individual devices into extended, closely spaced assemblies.

DNA, Viral↗

PubMed2002

Deliberate design of ligand architecture yields dramatic enhancement of metal ion affinity.

Evaluation of the malonamide substructure with respect to binding site preorganization and complementarity for lanthanide metal ions suggests a new ligand architecture specifically designed to enhance lanthanide ion affinity. Consideration of conformational reorganization, restricted bond rotation, and donor group orientation suggests that typical malonamide structures, for example, N,N,N'N'-tetrahexylpropane-1,3-diamide (1), N,N'-dibutyl-N,N'-dimethyl-2-tetradecylpropane-1,3-diamide (2), or N,N,N'N'-tetramethylpropane-1,3-diamide (6), are poorly organized for metal ion complexation. Molecular mechanics analyses show that the unfavorable enthalpic and entropic terms are eliminated by the use of the novel bicyclic architecture found in 3,9-diaza-3,9-dimethylbicyclo[4.4.0]decane-2,10-dione (7). Diamide 7 was prepared, and the X-ray crystal structure of the complex [Eu(7)(2)(NO(3))(3)] exhibits the same chelate conformation predicted by the molecular mechanics model. A hydrophobic derivative, 3,9-diaza-3,9-dioctylbicyclo[4.4.0]decane-2,10-dione (8), was prepared, and solvent extraction studies reveal that the preorganized architecture of 8 gives a dramatic enhancement in binding affinity, exhibiting Eu(3+) distribution coefficients that are 7 orders of magnitude larger than a typical malonamide ligand, 1.

Journal Article↗