Biomedical subjects

Peter H Dinolfo

Publications and source records attributed to Peter H Dinolfo.

10 recordsLinked to original sources

PubMed2006

A new class of mixed-valence systems with orbitally degenerate organic redox centers. Examples based on hexa-rhenium molecular prisms.

The ligand-centered mixed-valence (LCMV) properties of two supramolecular complexes are reported: triangular prisms of the form ([Re(CO)3]2X)3-mu,mu',mu' '-[tPyTz]2, where X is 2,2'-bisbenzimidazolate (1) or a pair of benzylthiols (2), and tPyTz is tri-(4-pyridyl)-1,3,5-triazine. Cyclic voltammetry demonstrates that the redox-accessible bridging ligands, tPyTz, are reduced in sequential, one-electron reactions. The singly reduced prisms, which represent an unusual type of mixed-valence compound in which the tPyTz ligands themselves are the redox centers, show intense, broad intervalance transfer (IT) bands in the NIR, consistent with highly coupled MV species. Electroabsorption (Stark spectroscopy) measurements reveal small dipole moment changes associated with intervalence excitation (|Deltamu12| = 0.30 +/- 0.02 eA for 1- and 0.48 +/- 0.02 eA for 2-), as well as noncollinear transition dipole moment (mu12) and dipole moment change vectors (zeta approximately 45 degrees ). DFT electronic structure calculations support this unusual result, along with a through-space electronic interaction mechanism. The neutral complexes (D3h symmetry) possess doubly degenerate, but spatially distinct, LUMO and LUMO+ orbitals. The orbital degeneracy of the tPyTz ligands is lifted in the MV forms, resulting in nonsymmetrical charge redistribution within the molecules upon on optical IT.

Journal Article↗

PubMed2006

Active-site models of bacterial nitric oxide reductase featuring tris-histidyl and glutamic acid mimics: influence of a carboxylate ligand on Fe(B) binding and the heme Fe/Fe(B) redox potential.

Active-site models of bacterial nitric oxide reductase (NOR) featuring a heme Fe and a trisimidazole- and glutaric acid-bound non-heme Fe (Fe(B)) have been synthesized. These models closely replicate the proposed active site of native NORs. Examination of these models shows that the glutamic acid mimic is required for both Fe(B) retention in the distal binding site and proper modulation of the redox potentials of both the heme and non-heme Fe's.

Bacterial Proteins↗

PubMed2006

Underlying spin-orbit coupling structure of intervalence charge transfer bands in dinuclear polypyridyl complexes of ruthenium and osmium.

The mixed-valence systems meso- and rac-[{M(bpy)2}2(mu-BL)]5+ {M = Ru, Os; BL = a series of polypyridyl bridging ligands such as 2,3-bis(2-pyridyl)benzoquinoxaline (dpb)} are characterized by multiple intervalence charge transfer (IVCT) and interconfigurational (IC) bands in the mid-infrared and near-infrared (NIR) regions. Differences in the relative energies of the IC transitions for the fully oxidized (+6) states of the osmium systems demonstrate that stereochemical effects lead to fundamental changes in the energy levels of the metal-based dpi orbitals, which are split by spin-orbit coupling and ligand-field asymmetry. An increase in the separation between the IC bands as BL is varied reflects the increase in the degree of electronic coupling through the series of ruthenium and osmium complexes. The increase in the IVCT bandwidths for the former is therefore attributed to the increase in the separation of the three underlying components of the bands. Stark effect measurements reveal small dipole moment changes accompanying IVCT excitation in support of the localized-to-delocalized or delocalized classification for the dinuclear ruthenium and osmium systems.

Journal Article↗

PubMed2006

Efficient synthesis of trisimidazole and glutaric acid bearing porphyrins: ligands for active-site models of bacterial nitric oxide reductase.

Ligands (1) for active-site models of bacterial nitric oxide reductase (NOR) have been efficiently synthesized. These compounds (1) feature three imidazolyl moieties and one carboxylic acid residue at the FeB site, which represent the closest available synthetic model ligands of NOR active center. The stereo conformations of these ligands are established on the basis of steric effects and 1H NMR chemical shifts under the ring current effect of the porphyrin.

Bacteria↗

PubMed2006

Selective functionalization of independently addressed microelectrodes by electrochemical activation and deactivation of a coupling catalyst.

We demonstrate selective functionalization of independently addressed microelectrodes by electrochemical activation and deactivation of a coupling catalyst. 1,2,3-Triazole formation between terminal acetylenes and organic azides is efficiently catalyzed by copper(I) complexes (a Sharpless "click" reaction), while the oxidized copper(II) complexes are inactive. By electrochemically activating or deactivating the catalyst by switching its redox state, we demonstrate control over triazole formation between surface-immobilized azides and ethynylferrocene. The reaction proceeds on the time scale of minutes using submicromolar concentration of reactants and catalyst, requires mild potentials for catalyst activation and deactivation, and works in aqueous and mixed aqueous-organic solvents. By appropriate biasing of each electrode, we selectively modify one of two chemically identical 10-mum-wide electrodes separated by 10 mum in an interdigitated array. The ability to switch on or off the reaction by electrical addressing together with the chemoselectivity of this reaction makes Cu(I)-catalyzed triazole formation an ideal method for the chemical modification of multielectrode arrays.

Catalysis↗

PubMed2005

C- and Z-shaped coordination compounds. synthesis, structure, and spectroelectrochemistry of cis- and trans-[Re(CO)3(L)]2-2,2'-bisbenzimidizolate with L = 4-phenylpyridine, 2,4'-bipyridine, or pyridine.

A series of C- and Z-shaped complexes of the form cis- and trans-[Re(CO)3(L)]2BiBzIm, where L = 4-phenylpyridine, 2,4'-bipyridine, or pyridine and BiBzIm = 2,2'-bisbenzimidizolate, have been synthesized by the reaction of [Re(CO)4]2BiBzIm with a slight excess of L in refluxing tetrahydrofuran. Five of the six compounds have been isolated and crystallographically and electrochemically characterized. Formation of the sixth, the cis form of the [Re(CO)3(4-phenylpyridine)]2BiBzIm, is evidently inhibited by the torsional steric demands of proximal 4-phenylpyridines. The compounds are acyclic analogues of recently studied tetrarhenium molecular rectangles and are of interest, in part, because of their potential to form ligand-centered mixed-valence (LCMV) compounds upon reduction by one electron. Spectroelectrochemical measurements corroborated the formation of a LCMV version of cis-[Re(CO)3(L)]2BiBzIm but failed to uncover a ligand-based intervalence transition. Electrochemical measurements revealed isomer-dependent L/L electrostatic effects, resulting in greater mixed-valence ion comproportionation for C-shaped assemblies versus Z-shaped assemblies.

Journal Article↗

PubMed2005

Borderline class II/III ligand-centered mixed valency in a porphyrinic molecular rectangle.

A molecular rectangle of the form ([Re(CO)(3)](2)BiBzIm)(2)-mu,mu'-(LL)(2), where BiBzIm is 2,2'-bisbenzimidazolate and LL are cofacially aligned [5,15-bis(4-ethynylpyridyl)-10,20-bis(n-hexyl)-porphyrinato]zinc ligands, has been examined via electrochemical, spectroelectrochemical, and electronic Stark effect methods. The rectangle displays three electrochemically accessible reductions assigned as LL based. The singly reduced rectangles are part of an unusual class of mixed-valence complexes where cofacial ligands, in this case porphyrins, comprise the degenerate redox centers. Absorption spectra for the singly reduced rectangle show two intense and narrow absorption bands in the near-infrared (NIR) region; the lower energy band is assigned as an intervalence transition. Time-dependent density functional theory electronic structure calculations support the assignment. Curiously, the transition displays a non-Marcus-type solvent dependence. NIR region electroabsorbance measurements of the singly reduced rectangle reveal a small but readily measurable dipole moment change of 0.56 +/- 0.05 eA. On the basis of spectroelectrochemical and electroabsorption measurements, the singly reduced rectangle is assigned as a borderline class II/class III mixed-valence species.

Journal Article↗

PubMed2004

Tetra-rhenium molecular rectangles as organizational motifs for the investigation of ligand-centered mixed valency: three examples of full delocalization.

Molecular rectangles having the form ([Re(CO)3]2(X)2)(2)-mu,mu'-(LL)2, where X is either a bridging alkoxide or phenylthiolate group and LL is 4,4'-bipyridine or pyrazine, are characterized by cofacial LL pairs that are in van der Waals contact across the "long" side of the rectangle. Cyclic voltammetry shows that the redox-accessible bridging ligands, LL, are reduced in sequential, one-electron reactions. The singly reduced rectangles represent an unusual type of mixed-valence compound in which the LL ligands themselves are the redox centers. Spectroelectrochemical measurements for mixed-valence forms of these rectangles reveal intense, asymmetric absorption bands in the near-infrared region, assigned as intervalence transitions. Electroabsorption (Stark spectroscopy) measurements reveal minute changes in dipole moment and therefore a lack of significant charge transfer upon intervalence excitation. Thus, the rectangles are unusual examples of class III (fully valence delocalized) molecular mixed-valence species that employ direct donor-orbital/acceptor-orbital overlap rather than covalent-bond-mediated superexchange to achieve the large electronic coupling strengths required for delocalization.

Journal Article↗

PubMed2004

Rhenium-based molecular rectangles as frameworks for ligand-centered mixed valency and optical electron transfer.

A series of six neutral, tetrametallic, molecular rectangles has been synthesized that have the form ([Re(CO)(3)](2)BiBzIm)(2)-mu,mu'-(LL)(2), where BiBzIm is 2,2'-bisbenzimidazolate and LL is a reducible, dipyridyl or diazine ligand. X-ray crystallographic studies of the six show that the rectangle frameworks, as defined by the metal atoms, range in size from 5.7 A x 7.2 A to 5.7 A x 19.8 A. The singly reduced rectangles are members of an unusual category of mixed-valence compounds in which the ligands themselves are the redox centers and interligand electronic communication is controlled by direct ligand orbital overlap rather than by superexchange through the metal ions. Despite nominally identical coordination-defined ligand positioning, the spectrally determined electronic strengths, H(ab)2, vary by roughly 100-fold. As shown by X-ray crystallography and computational modeling, the observed differences largely reflect detailed geometric configurational differences that can either facilitate or frustrate productive direct orbital overlap.

Journal Article↗

PubMed2002

Shape-selective transport through rectangle-based molecular materials: thin-film scanning electrochemical microscopy studies.

Microporous thin films (approximately equal to 50 to 400 nm) composed of discrete, cavity-containing molecular rectangles have been prepared. The films, which contain both amorphous and microcrystalline domains, display shape-selective transport behavior. They are permeable to small molecules and to molecules that are short or narrow in at least one dimension--for example, elongated planar molecules--but are impermeable to molecules lacking a narrow dimension. However, the shape selectivity is based on transport through intramolecular rather than intermolecular cavities. By using redox-active probe molecules, rates of transport through the rectangle-based material have been extracted from electrochemical measurements. Spatially resolved measurements obtained via scanning electrochemical microscopy have permitted transport through individual microcrystals to be evaluated semiquantitatively. The measurements reveal that transport is roughly two orders of magnitude slower than observed with thin microcrystalline films of molecular squares featuring similar-sized cavities. The differences likely reflect the fact that cavities within the square-based materials, but not the rectangle-based material, align to form simple one-dimensional channels.

Carbon↗