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Biomedical subjects

Vincent M Lynch

Publications and source records attributed to Vincent M Lynch.

At least 19 recordsLinked to original sources
PubMed2007

Dipyrrolyl-functionalized bipyridine-based anion receptors for emission-based selective detection of dihydrogen phosphate.

New cationic anion receptors, based on the use of pyrrole-substituted bipyridine and coordinated to transition metals, are described. Specifically, polypyridine-ruthenium and -rhodium cores have been functionalized to generate an anion binding site. The design was chosen to probe the influence of the pyrrole-to-pyrrole separation on anion-binding affinities and selectivities; this distance is greater in the new systems of this report (receptors 1 and 2) relative to that present in related dipyrrolyl quinoxaline based receptors 3 and 4. Solution-phase anion-binding studies, carried out by means of (1)H NMR spectroscopic titrations in [D(6)]DMSO and isothermal titration calorimetry (ITC) in DMSO, reveal that 1 and 2 bind most simple anions with substantially higher affinity than either 3 or 4. In the case of chloride anion, structural studies, carried out by means of single-crystal X-ray diffraction analyses, are consistent with the solution-phase results and reveal that receptors 1 and 2 are both able to stabilize complexes with this halide anion in the solid state.

2,2'-Dipyridyl↗
PubMed2006

Calix[4]pyrrole as a chloride anion receptor: solvent and countercation effects.

The interaction of calixpyrrole with several chloride salts has been studied in the solid state by X-ray crystallography as well as in solution by isothermal titration calorimetry (ITC) and (1)H NMR spectroscopic titrations. The titration results in dimethylsulfoxide, acetonitrile, nitromethane, 1,2-dichloroethane, and dichloromethane, carried out using various chloride salts, specifically tetraethylammonium (TEA), tetrapropylammonium (TPA), tetrabutylammonium (TBA), tetraethylphosphonium (TEP), tetrabutylphosphonium (TBP), and tetraphenylphosphonium (TPhP), showed no dependence on method of measurement. The resulting affinity constants (K(a)), on the other hand, were found to be highly dependent on the choice of solvent with K(a)'s ranging from 10(2)-10(5) M(-1) being recorded in the test solvents used for this study. In dichloromethane, a strong dependence on the countercation was also seen, with the K(a)'s for the interaction with chloride ranging from 10(2)-10(4) M(-1). In the case of TPA, TBA, and TBP, the ITC data could not be fit to a 1:1 binding profile.

Anions↗
PubMed2006

Tetrathiafulvalene-calix[4]pyrroles: synthesis, anion binding, and electrochemical properties.

The syntheses of monotetrathiafulvalene-calix[4]pyrrole 5 and bistetrathiafulvalene-calix[4]pyrrole 6, prepared from the acid-catalyzed condensation of monopyrrolo[3,4-d]tetrathiafulvalene (MPTTF, 7) with acetone in the presence of tripyrrane 8 and dipyrromethane 9, respectively, are described. Compound 5 and the previously reported tetrathiafulvalene-calix[4]pyrrole 4 both adopt a 1,3-alternative conformation in the solid state, as determined from X-ray crystallographic analysis. The anion binding properties of the tetrathiafulvalene-calix[4]pyrroles 5 and 6, as well as those of the parent meso-octamethylcalix[4]pyrrole (1), were investigated in acetone using (1)H NMR spectroscopic and isothermal titration calorimetry (ITC) techniques and, within the error limits of the methods, were generally found to give concordant results. On the basis of the results of the ITC studies carried out in 1,2-dichloroethane, increasing the number of tetrathiafulvalene units annulated to the calix[4]pyrrole system serves to enhance the anion binding affinities substantially but at the price of lowered selectivity. Cyclic voltammetry (CV) studies, carried out in 1,2-dichloroethane, provided evidence of an anion-dependent electrochemical response with Cl(-) and Br(-) ions. This response was particularly dramatic in the case of the monotetrathiafulvalene-calix[4]pyrrole 5, with a DeltaE(max) of -145 mV being seen after the addition of approximately 1 equiv of Cl(-) ion.

Anions↗
PubMed2006

A structural investigation of the N-B interaction in an o-(N,N-dialkylaminomethyl)arylboronate system.

o-(Pyrrolidinylmethyl)phenylboronic acid (4) and its complexes with bifunctional substrates such as catechol, alpha-hydroxyisobutyric acid, and hydrobenzoin have been studied in detail by X-ray crystallography, (11)B NMR, and computational analysis. The N-B interactions in analogous boronic acids and esters have been extensively cited in molecular recognition and chemosensing literature. The focal point of this study was to determine the factors that are pertinent to the formation of an intramolecular N-B dative bond. Our structural study predicts that the formation of an N-B dative bond, and/or solvent insertion to afford a tetrahedral boronate anion, depends on the solvent and the complexing substrate present. Specifically, from (11)B NMR studies, complexation of 4 with electron-withdrawing and/or vicinally bifunctionalized substrates promotes both the formation of N-B dative bonds and the solvation of sp(2) boron to a tetrahedral sp(3) boronate. In the solid state, the presence of an N-B dative bond in the complex of 4 and catechol (7) depends on the solvent from which it crystallizes. From chloroform, an N-B bond was observed, whereas from methanol, a methoxylated boronate was formed, where the methoxy group is hydrogen-bonded with the neighboring tertiary ammonium ion. The structural optimization of compounds 4 and 7 using density functional theory in a simulated water continuum also predicts that complexation of 4 and catechol promotes either the formation of an N-B bond or solvolysis if 1 equiv of water is present. The conclusion from this study will help in the design of future chemosensing technologies based on o-(N,N-dialkylaminomethyl)arylboronate scaffolds that are targeting physiologically important substances such as saccharides, alpha-hydroxycarboxylates, and catecholamines.

Boron↗
PubMed2005

Synthesis and anion binding properties of 2,5-diamidothiophene polypyrrole Schiff base macrocycles.

[reaction: see text] Two easy-to-synthesize polypyrrolic 2,5-diamidothiophene Schiff base macrocycles are reported, along with their anion binding properties as determined via UV-vis spectroscopic titrations carried out in dichloroethane. There is a striking difference between the interactions with anions of the two macrocycles, a finding ascribed to differences in their rigidity. For example, the more flexible dipyrromethane-derived macrocycle displays a 1.2:1 hydrogen sulfate versus nitrate selectivity, while its more rigid bipyrrole-derived congener shows a 7.4:1 selectivity in favor to hydrogen sulfate.

Journal Article↗
PubMed2005

Calix[4]pyrrole Schiff base macrocycles: novel binucleating ligands for Cu(I) and Cu(II).

New bimetallic copper(I) and copper(II) complexes of dipyrromethane-derived Schiff base macrocycles are reported. Two different structural motifs were identified, providing support for the notion that ligands of this type can support a variety of coordination modes. In the case of the Cu(I) complexes, the metal centers were found to have a distorted tetrahedral geometry and be coordinated to two imine nitrogens on each side of the ligand, with the exact structure depending on the choice of Schiff base macrocycle. In contrast to what is seen for Cu(I), with Cu(II) as the coordinated cation the Cu(II) metal centers assumed distorted square planar geometries, and both pyrrole N-Cu and imine N-Cu interactions were confirmed by single-crystal X-ray diffraction analysis. This structural analysis revealed a copper-copper distance of 3.47 A, while SQUID magnetic susceptibility data provided evidence for antiferromagnetic coupling between the two metal centers.

Copper↗
PubMed2005

"Naked-eye" detection of histidine by regulation of Cu(II) coordination modes.

The association of various alpha-amino acids with four new, coordinatively unsaturated metal complexes ([Cu(5)]2+, [Cu(6)]2+, [Cu(7)]2+, and [Zn(8)]2+) was examined. The receptors [Cu(5)]2+ and [Cu(7)]2+ were found to discriminate histidine (His) from other zwitterionic alpha-amino acids by means of indicator-displacement assays (IDAs) using 5(6)-carboxyfluorescein as an indicator in buffered methanol/water (3:1) solvent. The colorimetric detection of His was achieved by using this IDA method, which appears to owe its selectivity to a unique process involving disruption of the host complex to form a 2:1 His/Cu(II) complex rather than simple indicator displacement. The occurrence of distinct intermolecular coordination processes in response to the introduction of a different amino acid is observed. X-ray crystal structures of the host metal complexes were obtained and exhibit the adoption of a variety of coordination geometries about the metal center.

Copper↗
PubMed2005

Fine tuning the anion binding properties of 2,6-diamidopyridine dipyrromethane hybrid macrocycles.

The synthesis, characterization, and anion-binding properties of a series of 2,6-diamidopyridine dipyrromethane hybrid macrocycles is presented. As part of this work, a new method for effecting the oxidation of dipyrromethane-based macrocycles in organic solvents has been developed. The macrocyclic frameworks presented here stand out because of their ease of synthesis and tunable anion-binding properties. Evidence for anion binding was obtained from UV-vis spectroscopic titrations carried out in acetonitrile. The results clearly indicate that by changing the flexibility, cavity size, and directionality of anion-binding moieties in the macrocyclic framework the anion selectivity may be changed dramatically. These results are in accord with density functional theory molecular modeling calculations performed on one member of the series.

Journal Article↗
PubMed2005

Anion binding studies of fluorinated expanded calixpyrroles.

The anion binding properties of fluorinated calix[n]pyrroles (n = 4-6) in aprotic solvents (acetonitrile and DMSO) and modified reaction conditions allowing for the synthesis and isolation of the hitherto missing dodecafluorocalix[6]pyrrole from the condensation of 3,4-difluoro-1H-pyrrole and acetone are described. In acetonitrile solution containing 2% water, the association constants for the 1:1 binding interaction between octafluorocalix[4]pyrrole and chloride anion obtained with isothermal titration calorimetry (ITC) and (1)H NMR titration methods were found to match reasonably well. As compared to its nonfluorinated congener, octafluorocalix[4]pyrrole was found to display enhanced binding affinities for several representative anions in pure acetonitrile as judged from ITC analyses. Similar analyses of the fluorinated calix[n]pyrroles revealed an increase in the relative affinity for bromide over chloride with increasing macrocycle size, as manifest in a decrease in the binding ratio K(a(Cl))/K(a(Br)). Anion binding studies in the solid state, involving single-crystal X-ray diffraction analyses of the chloride and acetate anion complexes of octafluorocalix[4]pyrrole and decafluorocalix[5]pyrrole, respectively, confirmed the expected hydrogen bond interactions between the pyrrolic NH protons and the bound anions.

Journal Article↗
PubMed2005

An artificial siderophore for the detection of iron(III).

An artificial siderophore in the form of a squaraine dye (1) has been synthesized. The bidentate ligand chelates to Fe(III) between the deprotonated hydroxyl group on the ortho position of the ring adjacent to the carbonyl group of the cyclobutadiene ring. The optical response is due to a subtle geometry change of 1 on chelation to Fe(III). This artificial siderophore forms a 2 ratio 1 ligand ratio metal complex, as indicated by a sigmoidal isotherm (K(a)= 10(7) M(-1)). The optical response on the addition of Fe(III) is observed at low concentrations in comparison to other metal salts. The X-ray crystal structure and calculated structures of dye (1) are also included, and will be discussed.

Cations↗
PubMed2005

Colorimetric enantiodiscrimination of alpha-amino acids in protic media.

A new method is described for the determination of optical purity of alpha-amino acid samples in protic media. No derivatization of the analyte or multistep synthesis is required, and high accuracy is obtained from the colorimetric output. Chiral discrimination is achieved through the use of an optically pure trans-1,2-diaminocyclohexane-derived Cu(II)-containing host that differentiates amino acid enantiomers by a factor of about 2. Enantioselective signaling arises from the implementation of an indicator displacement assay based on competitive Cu(II) coordination involving the chiral Cu(II)-containing host, the amino acid guest, and a metal ion indicator. The molecular structure of the host/guest complex was determined by X-ray analysis and exhibits chelation of the Cu(II) center by the amino acid to provide substrate organization.

Amino Acids↗
PubMed2005

Facile syntheses of quater-, penta-, and sexipyrroles.

alpha,alpha-Linked oligopyrroles are attractive precursors for both expanded porphyrin and conducting polymer chemistry. We demonstrate facile methods for synthesizing quater-, penta-, and sexipyrroles from more readily available bi- and terpyrrole intermediates. These products demonstrate stability in their brightly colored oxidized forms, while reduction using borohydride reagents gives the corresponding all-pyrrole oligomers, which oxidize readily in air. The oxidized quater- and sexipyrroles were characterized by single-crystal X-ray diffraction analysis.

Journal Article↗
PubMed2005

Large pKa shifts of alpha-carbon acids induced by copper(II) complexes.

A series of synthetic receptors (4-6) incorporating metal ions, specifically copper(II), were examined for their ability to enhance the acidity of active methylene compounds. The copper(II) complexes were observed to reduce the pKa of 1,3-diketone carbon acids in acetonitrile by as much as 12 pKa units. The relatively large pKa reduction achieved by the complex is attributed to the electrostatic interaction between the anionic pi system of the enolate and the copper(II) ions. The cage structure and hydrogen bonding sites in receptors 4 and 5 lead to a very modest further enhancement of the acidity relative to that with 6. This study provides insight into the way in which metalloenzymes stabilize an enolate intermediate.

Acids↗