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James W Canary

Publications and source records attributed to James W Canary.

At least 19 recordsLinked to original sources
PubMed2006

Redox-triggered interconversion between piperidine chair conformations in a Cu(I/II) complex.

A redox-induced six-membered ring chair-chair conformational interconversion in a copper-coordinated trans-piperidine tripodal ligand is demonstrated. Each group of the 1,2,3-substituted ring can potentially ligate the metal; two equatorial groups ligate the metal in the Cu(I) state leaving a disassociated, axial group. However, all three groups (two axial and one equatorial) ligate the metal in the Cu(II) state. Exciton-coupled circular dichroism (ECCD) and 2D NMR were used to characterize the structures.

Copper↗
PubMed2006

Redox-induced ligand reorganization and helicity inversion in copper complexes of N,N-dialkylmethionine derivatives.

N,N'-Dipicolyl, bis(stilbylvinylpyridylmethyl), and diquinaldyl methionine derivatives form stable Cu(II) complexes with metal ligation by three nitrogen atoms and the carboxylate. One-electron reduction results in the exchange of carboxylate for sulfide in the complexes. This ligand reorganization is accompanied by inversion of the helical orientation of the two arms containing nitrogen heterocycles, resulting in nearly mirror image circular dichroism spectra. This paper provides details for the synthesis of these complexes and the evidence for the remarkable stereochemical interconversion that accompanies the reduction reaction. Detailed analysis of the electronic spectra of the ligands and metal complexes is provided along with X-ray crystallographic structures of Cu(II) and Zn(II) complexes of the N,N'-dipicolylmethionine complexes.

Journal Article↗
PubMed2006

A sensitive probe for the detection of Zn(II) by time-resolved fluorescence.

A new, highly sensitive fluorescent sensor for Zn(II) ion (a tris(2-pyridylmethyl)amine derivative) shows very strong binding and Zn(II) concentration-dependent biexponential time-resolved fluorescence (TRF) decay profiles that can be used for ratiometric estimates of Zn(II) concentrations. The ligand-metal complexes were characterized in solution by spectroscopic techniques and in the solid state by X-ray crystallography. The TRF studies revealed that the sensor aggregates in the absence of Zn(II) in a ligand concentration-dependent manner, a complication that is discerned by TRF but not by steady-state fluorescence ratiometric sensing techniques. It is shown that the same TRF methods are highly useful for monitoring Zn(II) concentrations in A549 epithelial lung cells in vitro and that the results were consistent with those in solution.

Cations, Divalent↗
PubMed2006

Viral nanoparticles donning a paramagnetic coat: conjugation of MRI contrast agents to the MS2 capsid.

A nanoparticle magnetic resonance imaging (MRI) contrast agent was developed by conjugation of more than 500 gadolinium chelate groups onto a viral capsid. The high density of paramagnetic centers and slow tumbling rate of modified MS2 capsids provided enhanced T1 relaxivities up to 7200 mM-1s-1 per particle. A bimodal imaging agent was generated by sequential conjugation of fluorescein and Gd3+ chelate. These results illustrate the potential for engineering natural protein assemblies to address bionanotechnology applications.

Binding Sites↗
PubMed2005

An electrochiroptical molecular switch: mechanistic and kinetic studies.

Previously, we reported the synthesis and preliminary characterization of Cu(I/II) complexes of N,N-bis(2-quinilylmethyl)-(l)-methionine (Zahn, S.; Canary, J. W. Science 2000, 288, 1404-7). The chemically oxidized and reduced forms of the complexes gave nearly mirror image circular dichroism (CD) spectra as a result of reorganization of the inner coordination sphere of the copper atom. The reorganization involved exchange of oxygen for sulfur in proceeding from the Cu(II) to Cu(I) oxidation state and corresponding ligand conformational changes required to accommodate this exchange. In this paper, we demonstrate that the complex can be triggered by electrochemical means. The electrochemical and stereochemical details of the redox-induced ligand reorganization were probed by independent synthesis of alternative chemical intermediates, CD spectroelectrochemistry, curve fitting of cyclic voltammograms, CD titration, and scanning electrochemical microscopy (SECM). A square-type mechanism was most consistent with the data: the Cu(II) complex is reduced followed by a ligand reorganization step to give the stable reduced form of the complex. The Cu(I) complex is then oxidized in a fast step followed by another ligand reorganization. A millisecond time scale rate was found by SECM for one of the key conformational conversion steps.

Journal Article↗
PubMed2005

Ratiometric displacement approach to Cu(II) sensing by fluorescence.

A chelation-enhanced fluorescence method for the detection of paramagnetic copper(II) ions is developed. Two dyes with unequal metal ion binding constants are used, each giving strong fluorescence enhancement in the presence of a diamagnetic reporter ion such as cadmium(II). Upon presentation of copper(II) to a 1:1:1 mixture of the two dyes and cadmium(II), the Cd(II) is displaced from one dye to the other, resulting in quenching of one dye by the Cu(II) and enhancement of the weaker binding dye by complexation of the Cd(II). Although several criteria must be met, this method holds promise for analysis of a wide range of analytes.

Acetates↗
PubMed2005

Ternary ligand-zinc-hydroxamate complexes.

Because of the importance of the hydroxamic acid functional group in zinc protease inhibitors, we have measured the stability constants of the ternary complex LMG, where L is series of tridentate and tetradentate ligands containing amino, carboxylate, pyridyl, and/or imidazolyl groups as enzyme models and G is the guest molecule, acetohydroxamate or N-methylacetohydroxamate. All measurements were determined by pH titration which gave reproducible and reasonable results. A general correlation between binding of LMG and that of LM showed ligands that strongly chelated zinc gave less LMG formation. Surprisingly, no correlation was observed between ligand charge and LMG formation even though the guest, acetohydroxamate, is anionic. The pH value of the maximum formation of the ternary complex is also correlated to the acidity of zinc-bound water; more acidic zinc-bound water results in a maximum ternary complex formation at lower pH value.

Binding Sites↗
PubMed2005

Rigidified tripodal chiral ligands in the asymmetric recognition of amino compounds.

Chiral rigidified piperidine and quinuclidine analogues of tris(2-pyridylmethyl)amine (TPA) derivatives were examined for asymmetric recognition of amino compounds by cyclic voltammetry and fluorescence. A Cu(II) complex of a piperidine analogue discriminated the enantiomers of some chiral amines and amino alcohols, giving differences in electrochemical potential for diastereomeric complexes. Protonated piperidine and quinuclidine analogues were able to differentiate the two enantiomers of certain amino alcohols by fluorescence spectroscopy. The quinuclidine analogue gave a 3-fold difference in response to the two enantiomers of phenyglycinol.

Journal Article↗
PubMed2005

Chiral nanotechnology.

A review of chiral, nanoscale science and technology is presented, with the subject divided into two topics. The first discusses nanotechnology in the service of asymmetric synthesis, chiral separations, and analysis. The second topic concerns broader research in the nanotechnology realm, where molecular chirality plays a role in the properties of materials, including molecular devices, chiral supramolecules, chiral nanotubes, chiral fullerenes, and DNA nanotechnology.

Journal Article↗
PubMed2004

Detection of zinc ions by differential circularly polarized fluorescence excitation.

A new chiroptical spectroscopic approach, differential circularly polarized fluorescence excitation (CPE), can be used to provide a selective method for detecting the presence of zinc ions. The approach utilizes the same instrumentation as fluorescence-detected circular dichroism and provides strong contrast in metal detection due to response to both chelation-enhanced fluorescence and circular dichroism upon metal ion binding. The observed contrast is therefore better than either of the parent spectroscopic detection methods. CPE also provides a strategy to reduce interference from background such as protein-based tryptophan fluorescence.

Animals↗
PubMed2003

Geometry-dependent phosphodiester hydrolysis catalyzed by binuclear copper complexes.

Two isomeric binuclear ligands PBTPA and MBTPA and their copper(II) complexes were prepared and examined for hydrolysis of a model phosphodiester substrate: bis(p-nitrophenyl)phosphate. A bell-shaped pH vs rate profile, which is in agreement with one mechanism proposed for bimetallonucleases/phosphatases, was observed for the binuclear complex of copper(II) and PBTPA. At pH 8.4, a maximum rate of 1.14 x 10(-6) s(-1)--more than 10(4)-fold over uncatalyzed reactions--was achieved. However, the analogous complex of MBTPA did not show significant rate enhancement. The binuclear complex of copper(II) and PBTPA also showed 10-fold acceleration over mononuclear complex of copper(II) and tris(2-pyridylmethyl)amine (TPA) catalyzed reaction. A phage phiX174 DNA assay showed that the complex of copper(II) and PBTPA promoted supercoiled phage phiX174 DNA relaxation under both aerobic and anaerobic conditions, in contrast to the hydrolytic inactivity of the mononuclear complex of copper(II) and TPA.

Catalysis↗
PubMed2003

Nylon/DNA: Single-stranded DNA with a covalently stitched nylon lining.

The synthesis of DNA/nylon ladder oligomers is described. Three stages of the development are addressed: the synthesis of 2'-beta-substituted phosphoramidites, the deprotection/purification protocols of ODNs modified with both amino and carboxyl groups, and amide bond-forming reactions on the ODNs. The established technology and the novel DNA-based ladder oligomer structure opens a pathway to the synthesis of topological molecular objects and networks templated by DNA through versatile DNA nanotechnology. The DNA-based ladder oligomers may find application in the antisense area.

Alkylation↗
PubMed2003

Stability and acidity constants for ternary ligand-zinc-hydroxo complexes of tetradentate tripodal ligands.

Four series of tetradentate tripodal ligands containing pyridyl, 2-imidazolyl, 4-imidazolyl, amino, and/or carboxylic groups were synthesized as hydrolytic zinc enzyme models in order to elucidate the effect of various coordination environments on zinc binding and the acidity of zinc-bound water. In aqueous solution, ligands with same charges showed a good correlation between zinc binding (log K(ZnL)) and zinc-bound water acidity (pK(a) of LZnOH(2)); the stronger the zinc binding, the higher the pK(a). The zinc-bound water acidity decreased as pyridyl groups were replaced by carboxylate groups. However, exchanging amino groups for carboxylate groups gave no change in zinc-bound water acidity regardless of the charge of the atoms in the inner coordination sphere of the metal ion. The results are consistent with the conventional notion that negatively charged carboxylate groups inherently increase zinc binding and result in decreasing zinc-bound water acidity, but also suggest that environmental effects may modulate or dominate control of acidity.

Electric Conductivity↗
PubMed2003

Derivatization, complexation, and absolute configurational assignment of chiral primary amines: application of exciton-coupled circular dichroism.

We report here a sensitive method for the determination of the absolute configurations of primary amines using exciton-coupled circular dichroism (ECCD). The method works on a microgram scale by derivatization of chiral amines with quinoline chromophores. Complexation of the chiral ligands with metal ion fixes the geometry of the chromophores, resulting in a twist that is governed by the asymmetric carbon configuration and steric environment of the amine. The absolute configurations of the primary amines can be interpreted from the couplets of the ECCD spectra of the derivatized complexes. Crystal structures, 2D NMR studies, and semiempirical calculations provide structural evidence for our model.

Journal Article↗
PubMed2002

Crystal-driven distortion of ligands in copper coordination complexes: conformational pseudo-enantiomers.

The ligand in [Cu(6)CH3CN]-(ClO4)2 adopts two conformations that may be described as "pseudo-enantiomers" in that they possess approximately mirror-image molecular helicity, although they differ in the orientation of a single methyl substituent. The two conformations differ in energy as judged by analogy to other compounds studied previously, computation of the relative free energies of formation of the isomers, and measurement of solution circular dichroism spectra. The solid-state structures of both single enantiomer and racemic forms of the complex were determined by X-ray crystallography. In the chiral complex, a quasi-racemate was observed with both pseudo-enantiomeric conformers present in the asymmetric unit. Packing forces induce a higher energy conformation in order to achieve higher apparent symmetry in the solid state. In contrast, the racemic complex only displayed a single conformation corresponding to the lower energy one of the two observed in the single enantiomer structure.

Journal Article↗
PubMed2002

Cu(I/II) redox control of molecular conformation and shape in chiral tripodal ligands: binary exciton-coupled circular dichroic states.

This manuscript describes the design, synthesis, and characterization of a coordination complex that demonstrates reversible interconversion between two redox states that show very different chiroptical properties. Reported here are three chiral N(4)-tetradentate ligands, prepared in enantiopure form by asymmetric synthesis, and their circular dichroic and other properties, as well as those of numerous Cu(I) and Cu(II) complexes. While the chiroptical spectra of the free ligands are unremarkable, the CD spectra of the complexes are very intense, and spectral features indicate that they derive from exciton coupling. Comparison of complexes with one, two, or three chromophores provides strong supportive evidence for this assignment, and semiquantitative correlation with intensity as rationalized by additivity. A Cu(I)(L)/Cu(II)(L) redox couple was identified that showed dramatically different circular dichroic properties that was further shown to be easily oxidized and reduced chemically between two states with remarkable retention of signal. A structural hypothesis for the interconversion is given and supported by a variety of spectroscopic evidence.

Journal Article↗