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Biomedical subjects

Harry L Anderson

Publications and source records attributed to Harry L Anderson.

At least 19 recordsLinked to original sources
PubMed2007

Insulated molecular wires.

An astonishing assortment of structures have been described as "insulated molecular wires" (IMWs), thus illustrating the diversity of approaches to molecular-scale insulation. These systems demonstrate the scope of encapsulation in the molecular engineering of optoelectronic materials and organic semiconductors. This Review surveys the synthesis and structural characterization of IMWs, and highlights emerging structure-property relationships to determine how insulation can enhance the behavior of a molecular wire. We focus mainly on three IMW architectures: polyrotaxanes, polymer-wrapped pi systems, and dendronized polymers, and compare the properties of these systems with those of conjugated polymers threaded through mesoporous frameworks and zeolites. Encapsulation of molecular wires can enhance properties as diverse as luminescence, electrical transport, and chemical stability, which points to applications in electroluminescent displays, sensors, and the photochemical generation of hydrogen.

Journal Article↗
PubMed2006

Homo- and hetero-[3]rotaxanes with two pi-systems clasped in a single macrocycle.

Here we present the first synthesis of a [3]rotaxane with two dumbbell components threaded through a single gamma-cyclodextrin macrocycle. This synthesis is carried out in two steps: first one dumbbell is synthesized threaded through the macrocycle to give a [2]rotaxane, then a second dumbbell is synthesized through the remaining cavity of the [2]rotaxane. We have synthesized a hetero- [3]rotaxane with one stilbene and one cyanine dye threaded through gamma-cyclodextrin, which exhibits quantitative energy transfer between the two encapsulated dyes. The stilbene [2]rotaxane intermediate in this synthesis has a remarkably high affinity for suitably shaped hydrophobic guests in aqueous solution, facilitating the synthesis of [3]rotaxanes and suggesting possible applications in sensors.

Journal Article↗
PubMed2006

Strong cooperative enhancement of two-photon absorption in double-strand conjugated porphyrin ladder arrays.

We present the two-photon absorption (2PA) spectra of a series of conjugated porphyrin oligomers containing N = 2, 4, 8, and ca. 13 monomer units, meso-meso connected with butadiyne linkers. We demonstrate that, in the coplanar double-strand arrays, self-assembled upon addition of 4,4'-bipyridyl, the conjugation length increases dramatically, leading to very strong cooperative enhancement of 2PA. We analyze the scaling of 2PA in both the double-strand and rotationally free single-strand arrays and show how the effective conjugation length in both cases is linked to the observed 2PA properties. By introducing a "conjugation signature" for the 2PA strength, we show that, in double-strand arrangement, the conjugation embraces the whole molecule up to the tetramer level, whereas in single-strand arrangement, it is always less than N, except for N = 2, but keeps increasing until N = 8. Our finding of extremely strong 2PA cross section, sigma2 approximately 105 GM, in double-strand oligomers peaking at 1.3 mum can find use for signal processing in fiber-optic devices.

Journal Article↗
PubMed2005

Synthesis, crystal structure, and nonlinear optical behavior of beta-unsubstituted meso-meso E-vinylene-linked porphyrin dimers.

[structure: see text] A vinylene-linked porphyrin dimer, with no substituents at the beta-positions, has been synthesized by CuI/CsF promoted Stille coupling. In the crystal structure of this dimer, the C(2)H(2) bridge is twisted by 45 degrees relative to the plane of the porphyrins. The absorption, emission spectra, and electrochemistry reveal substantial porphyrin-porphyrin pi-conjugation. The triplet excited-state absorption spectrum of this dimer makes it suitable for reverse saturable absorption at 710-900 nm.

Journal Article↗
PubMed2005

Extremely strong near-IR two-photon absorption in conjugated porphyrin dimers: quantitative description with three-essential-states model.

Two-photon absorption spectra (2PA) of a series of conjugated dimers and the corresponding monomer were studied in the near-IR region. All of the dimers show very large peak cross section values, sigma(2) = (3-10) x 10(3) GM (1 GM = 1 x 10(-50) cm(4) s photon(-1)), which is several hundred times larger than that obtained for the corresponding monomer in the same region. We explain such dramatic cooperative enhancement by a combination of several factors, such as strong enhancement of the lowest one-photon Q-transition, better resonance conditions in the three-level system, dramatic enhancement of the excited-state singlet-singlet transition, and parallel arrangement of consecutive transitions in dimers, as compared to perpendicular arrangement in the monomer. We show that the absolute values of the 2PA cross section in these molecules are quantitatively described by a quantum-mechanical expression, derived for the three-level model. We also demonstrate the possibility of singlet oxygen generation upon one- and two-photon excitation of these dimers, which makes them particularly attractive for photodynamic therapy.

Absorption↗
PubMed2004

Understanding strong two-photon absorption in pi-conjugated porphyrin dimers via double-resonance enhancement in a three-level model.

We present the two-photon absorption (2PA) spectra of a series of conjugated porphyrin dimers and show that they possess extremely large intrinsic (femtosecond) peak 2PA cross sections, up to sigma2 = 1 x 104 GM in the near-IR region; these are among the highest values measured for any organic molecule. Moreover, we demonstrate that the second-order perturbation theory applied to a simple three-level model gives a perfect quantitative description of the observed 2PA cross section. By comparing all the factors of the three-level model for dimers with those of corresponding monomer (for which sigma2 = 20 GM), we explain an approximately 500-fold cooperative enhancement in sigma2 and find that the most important factor is the strength of excited-state transition. The matrix element of dipole moment of this transition amounts gigantic values of 30-40 D for conjugated porphyrin dimers, which can be accounted for a large delocalization radius (large electron-hole separation) in this state. We also demonstrate efficient generation of singlet oxygen upon one- and two-photon excitation of these porphyrin dimers, which can be useful for two-photon initiated photodynamic therapy of cancer.

Journal Article↗
PubMed2003

Synthesis of conjugated polyrotaxanes.

A series of conjugated polyrotaxane insulated molecular wires are synthesised by aqueous Suzuki polymerisation, using hydrophobic binding to promote threading of the cyclodextrin units. These polyrotaxanes have conjugated polymer cores based on poly(para-phenylene), polyfluorene, and poly(diphenylene-vinylene), threaded through 0.9-1.6 cyclodextrins per repeat unit. Bulky naphthalene-3,6-disulfonate endgroups prevent the macrocycles from slipping off the conjugated polymer chains. Dialysis experiments show that the cyclodextrins become unthreaded only if smaller stoppers are used. MALDI TOF mass spectra detect oligomers with up to ten threaded cyclodextrins, and reveal the presence of some defects that result for oxidative homo-coupling of boronic acids. Weight-average molecular weights were determined by analytical ultracentrifugation, demonstrating that step-growth polymerisation is efficient enough to achieve degrees of polymerisation up to approximately 20 repeat units (84 para-phenylenes). The fluorescence spectra of these polyrotaxanes indicate that the presence of the threaded cyclodextrin macrocycles reduces the flexibility of the conjugated polymer pi-systems. Both the solution and the solid-state photoluminescence quantum yields are enhanced upon threading of the conjugated polyaromatic cores through alpha- or beta-cyclodextrins, and the emission spectra of the polyrotaxanes are blue-shifted compared to the corresponding unthreaded polymers. The greater weight of the 0-0 transition in the emission spectra, as well as the smaller Stokes shift, indicate that the polyrotaxanes are more rigid than the unthreaded polymers.

Cyclodextrins↗
PubMed2003

Hindered fluorescence quenching in an insulated molecular wire.

A [3]rotaxane 2 within 1(2) consisting of an anionic phenylene ethynylene dumbbell 2(4-) threaded through two cationic cyclophanes 1(2+) has been prepared using aqueous Glaser coupling. Stern-Volmer analysis of the fluorescence quenching using three different electron-acceptors (methyl viologen 13(2+), dipropyl-4,4'-bipyridinium disulfonate 14 and anthraquinone-2,6-disulfonate 15(2-)) shows that the threaded cyclophanes inhibit electron-transfer from the excited state of the dumbbell by steric shielding, and by electrostatic shielding in the case of methyl viologen.

Journal Article↗
PubMed2003

Surfaces designed for charge reversal.

We have created surfaces which switch from cationic at pH < 3 to anionic at pH > 5, by attaching aminodicarboxylic acid units to silica and gold substrates. Charge reversal was demonstrated by monitoring the adsorption of cationic dyes (methylene blue and a tetracationic porphyrin) and an anionic sulfonated porphyrin, at a range of pH using UV-vis absorption and reflection spectroscopy. The cationic dyes bind under neutral conditions (pH 5-7) and are released at pH 1-4, whereas the anionic dye binds under acidic conditions (pH 1-4) and is released at pH 5-7. Gold surfaces were functionalized with two different amphoteric disulfides with short (CH(2))(2) and long (CH(2))(10)CONH(CH(2))(6) linkers; the longer disulfide gave surfaces exhibiting charge reversal in a narrower pH range. Adsorption is much faster on the functionalized gold (t(1/2) = 62 s) than on functionalized silica (t(1/2) = 6900 s), but the final extents of coverage on both surface are similar, for a given dye at a given pH, with maximal coverages of around 2 molecules nm(-)(2). These charge-reversal processes are reversible and can be repeatedly cycled by changing the pH. We have also created surfaces which undergo irreversible proton-triggered charge switching, using a carbamate-linked thiol carboxylic acid which cleaves in acid. These surfaces are versatile new tools for controlling electrostatic self-assembly at surfaces.

Journal Article↗
PubMed2003

Contracted and expanded meso-alkynyl porphyrinoids: from triphyrin to hexaphyrin.

The boron trifluoride-catalyzed Rothemund condensation of triisopropylsilyl (TIPS) propynal 1 with 3,4-diethylpyrrole in dichloromethane, followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) generates a mixture of products, including [15]triphyrin(1.1.3) H3, corrole H(3)4, porphyrin H(2)2, [24]pentaphyrin(1.1.1.1.1) H(4)5, [28]hexaphyrin(1.1.1.1.1.1) H(4)6, and two linear tripyrromethenes H(2)7 and H(2)8. We report the spectroscopic characteristics of these unusual chromophores, together with the crystal structures of triphyrin H3 (and its zinc complex ZnCl3), porphyrin H(2)2 (and its metal complexes Zn2, Ni2 and Pt2), hexaphyrin H(4)6, and tripyrromethene nickel(II) complex Ni7. When the condensation is catalyzed with trifluoroacetic acid, rather than boron trifluoride, the triphyrin H3 become the main product (26% yield). This novel macrocycle is linked with a TIPS-substituted exocyclic double bond. This C=C bond makes an eta(2)-interaction with the zinc center in ZnCl3 with C-Zn distances of 2.863 and 3.025 A. The porphyrin H(2)2 is severely ruffled, and its absorption spectrum is red-shifted and broadened compared with the analogous compound without ethyl substituents. The hexaphyrin H(4)6 adopts a figure-of-eight conformation with virtual C(2) symmetry in the solid state and C(2) symmetry in solution on the NMR time scale. Oxidation with DDQ appears to convert this nonaromatic [28]hexaphyrin into an aromatic [26]hexaphyrin with a strongly red-shifted absorption spectrum, but the oxidized macrocyle is too unstable to isolate.

Journal Article↗
PubMed2003

Functional outcomes in octogenarian trauma.

BACKGROUND: Outcome data on geriatric trauma patients (GTPs) (age >or= 65) focus on mortality and resource use. We examined mortality and outcome in GTPs and octogenarian trauma patients (OTPs) (age >or= 80). We hypothesized that OTPs would have worse functional outcomes than GTPs as defined by functional independence measurement (FIM) scales. METHODS: Our study was a 13-year retrospective analysis of a statewide trauma database. Isolated hip fractures and intubation with Glasgow Coma Scale scores of 3 at admission were excluded. Demographic data, preexisting conditions, complications, discharge destination, mortality, and FIM were analyzed. RESULTS: OTPs constituted 17742 (40.9%) of 43297 GTPs admitted to trauma centers. Falls (64.4%) and motor vehicle collisions (24.5%) were predominant. Average Injury Severity Score (ISS) was higher in GTPs (11.5 +/- 9.2 vs. 10.8 +/- 8.3, p = 0.001). Cardiac disease was the most common preexisting condition. Diabetes, obesity, and pulmonary disease were more common in GTPs than in OTPs (p = 0.001). Dementia, congestive heart failure, and hematologic disease were more common in OTPs than in GTPs (p = 0.001). Pulmonary and infectious complications were most common and occurred with equal frequency in OTPs and GTPs. Mortality rates were higher (10.0% vs. 6.6%, p = 0.001) for OTPs overall and when stratified into low (<10), moderate (11-20), and high (>20) ISS subgroups (p = 0.001). Discharge destination was most often home (53.3% vs. 28.8%, p = 0.001) or a rehabilitation facility (20.0% vs. 17.4%, p = 0.001) for GTPs versus OTPs. OTPs were discharged to skilled nursing facilities (37.2% vs. 14.9%, p = 0.001) far more often than GTPs. FIM at discharge was lower in all categories for OTPs. Modified dependence in locomotion and transfer was seen for OTPs but not GTPs overall and when stratified by ISS subgroups (p = 0.001). Some dependence in feeding was seen for OTPs but not GTPs with high injury severity (p = 0.001). Otherwise, feeding, expression, and social independence were preserved for both OTPs and GTPs. CONCLUSION: Functional outcomes after blunt trauma are worse for OTPs; however, functional independence in feeding and social interaction are preserved in OTPs even with moderate injury severity.

Activities of Daily Living↗
PubMed2002

Amplified optical nonlinearity in a self-assembled double-strand conjugated porphyrin polymer ladder.

Addition of 4,4'-bipyridyl to a solution of a meso-meso butadiyne-linked conjugated zinc porphyrin polymer in chloroform results in self-assembly of a double-strand ladder complex. Excess ligand causes this duplex to dissociate into single strands. These binding processes were elucidated by near-IR and NMR titrations, as well as by gel permeation chromatography and small-angle neutron scattering. Ladder-making and -breaking are highly cooperative, with Hill coefficients of 3.0 and 3.7, respectively. Self-assembly of the ladder holds the pi-system in a planar conformation, enhancing the conjugation, resulting in a red-shift and intensification of the Q-band. Both the real and imaginary parts of the third-order susceptibility per macrocycle are amplified by ladder formation, as revealed by degenerate four-wave mixing measurements at 1064 nm. At this wavelength, the double-strand polymer complex has |chi(3)xyyx| = 6.0 x 10-17 m2 V-2 per macrocycle, compared with 6.6 x 10-18 m2 V-2 for the single-strand polymer under the same conditions.

Journal Article↗
PubMed2002

Fusion and planarization of a quinoidal porphyrin dimer.

The crystal structure, near-infrared spectrum and electrochemistry of a quinoidal triply-linked porphyrin dimer are compared with those of its singly-linked precursor; fusing the two porphyrins planarizes the pi-system and reduces the optical HOMO-LUMO gap while increasing the gap between the first oxidation and reduction potentials.

Journal Article↗