Resonance Raman Spectroscopy of the T1 Triplet Excited State of Oligothiophenes.

The characterization of triplet excited states is essential for research on organic photovoltaics and singlet fission. We report resonance Raman spectra of two triplet oligothiophenes with n-alkyl substituents, a tetramer and hexamer. The spectra of the triplets are more complex than the ground state, and we find that density functional theory calculations are a useful starting point for characterizing the bands.

Photogeneration and Quenching of Tryptophan Radical in Azurin.

Tryptophan and tyrosine can form radical intermediates that enable long-range, multistep electron transfer (ET) reactions in proteins. This report describes the mechanisms of formation and quenching of a neutral tryptophan radical in azurin, a blue-copper protein that contains native tyrosine (Y108 and Y72) and tryptophan (W48) residues. A long-lived neutral tryptophan radical W48• is formed upon UV-photoexcitation of a zinc(II)-substituted azurin mutant in the presence of an external electron acceptor.

Mechanism of carotenoid coloration in the brightly colored plumages of broadbills (Eurylaimidae).

The plumage carotenoids of six species from five genera of broadbills (Eurylaimidae) have been examined. These plumages are crimson, violet, purple-maroon, or yellow. Two genera also have brilliant green plumages that are produced by a combination of structural coloration and unknown carotenoids.

Resonance Raman spectra of a perylene bis(dicarboximide) chromophore in ground and lowest triplet states.

Resonance Raman spectroscopy is employed to probe the ground (S0) and lowest triplet (T1) excited states of a perylene bis(dicarboximide) (PDI) dimer. Four bands at ~1324, 1507, ~1535, and 1597 cm(-1) are signatures of the T1 excited state; a fifth band at ~1160 cm(-1) is tentatively assigned. Density functional calculations of an asymmetrically substituted PDI monomer match the experimental bands of the PDI dimer in both S0 and T1 states.

Vibrational and electronic spectroscopy of the retro-carotenoid rhodoxanthin in avian plumage, solid-state films, and solution.

Rhodoxanthin is one of few retro-carotenoids in nature. These chromophores are defined by a pattern of single and double bond alternation that is reversed relative to most carotenoids. Rhodoxanthin is found in the plumage of several families of birds, including fruit doves (Ptilinopus, Columbidae) and the red cotingas (Phoenicircus, Cotingidae).

Width of the cervical intervertebral neuroforamina after total disc replacement with the Cerkinetic prosthesis: a three-dimensional simulation using a computer-aided design model.

Introduction: Physiological cervical intervertebral motion inherently induces a neuroforaminal volume change. Integration of an artificial motion component within this intervertebral kinematic system may cause neuroforamina to lose their ability for continuous and instantaneous volume adaptation, inducing foraminal stenosis. The purpose of the current study is to virtually simulate a newly developed cervical total disc replacement (TDR) to evaluate the neuroforaminal dimensions at rest and during motion.

Raman microspectroscopy and vibrational sum frequency generation spectroscopy as probes of the bulk and surface compositions of size-resolved sea spray aerosol particles.

Sea spray aerosol (SSA) represents one of the largest aerosol components in our atmosphere. SSA plays a major role in influencing climate; however the overall impacts remain poorly understood due to the overall chemical complexity. SSA is comprised of a mixture of inorganic and organic components in varying proportions that change as a function of particle size and seawater composition.

Characterization of carotenoid aggregates by steady-state optical spectroscopy.

The carotenoids have low-lying triplet excited states and can self-assemble in some solvents to form weakly or strongly coupled aggregates. These qualities make carotenoid aggregates useful for studies of singlet fission, where an outstanding goal is the correlation of interchromophoric coupling to the dynamics and yield of triplet excited states from a parent singlet excited state. Three aggregates of zeaxanthin, two weakly coupled and one strongly coupled, are characterized by steady-state spectroscopic methods including temperature-dependent absorption, fluorescence, and resonance Raman spectroscopy.

Rapid self-healing hydrogels.

Synthetic materials that are capable of autonomous healing upon damage are being developed at a rapid pace because of their many potential applications. Despite these advancements, achieving self-healing in permanently cross-linked hydrogels has remained elusive because of the presence of water and irreversible cross-links. Here, we demonstrate that permanently cross-linked hydrogels can be engineered to exhibit self-healing in an aqueous environment.

Hydrogen bonding of tryptophan radicals revealed by EPR at 700 GHz.

Redox-active tryptophans are important in biological electron transfer and redox biochemistry. Proteins can tune the electron transfer kinetics and redox potentials of tryptophan via control of the protonation state and the hydrogen-bond strength. We examine the local environment of two neutral tryptophan radicals (Trp108 on the solvent-exposed surface and Trp48 buried in the hydrophobic core) in two azurin variants.

Infrared nanoscopy of dirac plasmons at the graphene-SiO₂ interface.

We report on infrared (IR) nanoscopy of 2D plasmon excitations of Dirac fermions in graphene. This is achieved by confining mid-IR radiation at the apex of a nanoscale tip: an approach yielding 2 orders of magnitude increase in the value of in-plane component of incident wavevector q compared to free space propagation. At these high wavevectors, the Dirac plasmon is found to dramatically enhance the near-field interaction with mid-IR surface phonons of SiO(2) substrate.

High-yield singlet fission in a zeaxanthin aggregate observed by picosecond resonance Raman spectroscopy.

We report high-yield triplet generation by singlet fission upon photoexcitation of a new aggregate of the carotenoid all-trans 3R,3'R-zeaxanthin. The yield is determined by picosecond time-resolved resonance Raman spectroscopy, which allows direct characterization and quantification of triplet excited-state signatures and ground-state depletion. The technique and analysis reveals that triplets form within picoseconds.

Spectroscopic comparison of photogenerated tryptophan radicals in azurin: effects of local environment and structure.

Tryptophan radicals play a significant role in mediating biological electron transfer. We report the photogeneration of a long-lived, neutral tryptophan radical (Az48W*) from the native residue tryptophan-48 in the hydrophobic core of azurin. The optical absorption, electron paramagnetic resonance, and resonance Raman spectra strongly support the formation of a neutral radical, and the data are consistent with direct electron transfer between tryptophan and the copper(II) center.

Dye-sensitized solar cell constructed with titanium mesh and 3-D array of TiO2 nanotubes.

We have designed and constructed dye sensitized solar cells based on new, 3-D configurations of TiO(2) nanotubes. The overall efficiency of our best cells is 5.0% under standard air mass 1.

Toward an n-type molecular wire: electron hopping within linearly linked perylenediimide oligomers.

A series of linearly linked perylenediimide (PDI) dimers and trimers were synthesized in which the PDI pi systems are nearly orthogonal. These oligomers and several model compounds were singly reduced, and intramolecular electron hopping between the PDI molecules was probed by electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) spectroscopy. When the functional groups attached to the ends of the oligomers were chosen to make each PDI molecule electronically equivalent, the single electron hops between the PDI molecules with rates that significantly exceed 10(7) s(-1).

Resonance Raman characterization of a stable tryptophan radical in an azurin mutant.

Tryptophan radicals play a significant role in mediating biological electron transfer and catalytic processes. Here, we employ visible and UV resonance Raman, EPR, and absorption spectroscopy along with pH/isotope studies and calculations to probe a neutral closed-shell tryptophan and its oxidized radical counterpart in a modified azurin protein. Comparison of the resonance Raman spectra of the radical and closed-shell species combined with vibrational analysis reveals important structural differences between these two tryptophan species.

Effect of micrometer-scale roughness of the surface of Ti6Al4V pedicle screws in vitro and in vivo.

Background: Titanium implants that have been grit-blasted and acid-etched to produce a rough microtopography support more bone integration than do smooth-surfaced implants. In vitro studies have suggested that this is due to a stimulatory effect on osteoblasts. It is not known if grit-blasted and acid-etched Ti6Al4V implants also stimulate osteoblasts and increase bone formation clinically.

Use of instrumented pedicle screws to evaluate load sharing in posterior dynamic stabilization systems.

Background Context: Dynamic stabilization is an alternative to fusion intended to eliminate or at least minimize the potential for adjacent level degeneration. Different design approaches are used in pedicle screw-based systems that should have very different effects on the loading of the posterior column and intervertebral disc. If the implant system distributes these loads more evenly, loads in the pedicle screws will be reduced, and screw loosening will be prevented.

Degradation of azo dyes by oxidative processes--laccase and ultrasound treatment.

Azo dyes are of synthetic origin and their environmental fate is not well understood. They are resistant to direct aerobic bacterial degradation and form potentially carcinogenic aromatic amines by reduction of the azo group. This study shows that applying the oxidative processes of enzymatic treatment with laccase and ultrasound treatment, both alone and in combination, leads to dye degradation.

Controlling energy and charge transfer in linear chlorophyll dimers.

A series of linkers constructed from combinations of phenyl and ethynyl groups is shown to permit ultrafast energy transfer between two chlorophylls, while allowing control over radical cation migration between them.

Structure and dynamics of the solvated electron in alcohols from resonance Raman spectroscopy.

Resonance Raman (RR) spectroscopy is used to probe the structure and excited-state dynamics of the solvated electron in the primary liquid alcohols methanol (MeOH), ethanol (EtOH), n-propanol (n-PrOH), and n-butanol (n-BuOH). The strong resonance enhancements (>or=10(4) relative to pure solvent) of the libration, CO stretch, COH bend, CH3 bend, CH2 bend, and OH stretch reveal significant Franck-Condon coupling of the intermolecular and intramolecular vibrational modes of the solvent to the electronic excitation of the solvated electron. All enhanced bands are fully accounted for by a model of the solvated electron that is comprised of several nearby solvent molecules that are only perturbed by the presence of the electron; no new molecular species are required to explain our data.