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"I speak for the trees, for the trees have no tongues." (1) DR. SEUSS, THE LORAX There is increasing scientific, political, and legal concern about the loss of biodiversity and [...]

We have explored the kinetic effect of increasing electron transfer (ET) distance in a biomimetic, proton-coupled electron-transfer (PCET) system. Biological ET often occurs simultaneously with proton transfer (PT) in order to avoid the high-energy, charged intermediates resulting from the stepwise transfer of protons and electrons. These concerted proton–electron-transfer (CPET) reactions are implicated in numerous biological ET pathways. In many cases, PT is coupled to long-range ET. While many studies have shown that the rate of ET is sensitive to the distance between the electron donor and acceptor, extensions to biological CPET reactions are sparse. The possibility of a unique ET distance dependence for CPET reactions deserves further exploration, as this could have implications for how we understand biological ET. We therefore explored the ET distance dependence for the CPET oxidation of tyrosine in a model system. We prepared a series of metallopeptides with a tyrosine separated from a Ru(bpy)32+complex by an oligoproline bridge of increasing length. Rate constants for intramolecular tyrosine oxidation were measured using the flash-quench transient absorption technique in aqueous solutions. The rate constants for tyrosine oxidation decreased by 125-fold with three added proline residues between tyrosine and the oxidant. By comparison, related intramolecular ET rate constants in very similar constructs were reported to decrease by 4–5 orders of magnitude over the same number of prolines. The observed shallow distance dependence for tyrosine oxidation is proposed to originate in part from the requirement for stronger oxidants, leading to a smaller hole-transfer effective tunneling barrier height. The shallow distance dependence observed here and extensions to distance-dependent CPET reactions have potential implications for long-range charge transfers.

Using dye-sensitized water-splitting photoelectrochemical cells is a promising way to satisfy an increasing demand for energy without significant production of greenhouse gases. These cells commonly utilize a large band gap nanoparticulate semiconductor photoelectrode that is sensitized with a photoactive dye. In this paper, we study SnO2nanoparticles (NPs) that are sensitized with either a ruthenium-based dye (RuP) or a porphyrin-based dye (Por). These dyes have a significantly different molar extinction coefficient, resulting in either a high carrier density (Por) or a moderately low density (RuP) within the SnO2NPs. The influence of the dye on charge carrier dynamics and photoconductivity in the NPs has been explored. We present experimental results on samples of five different SnO2film thicknesses, sensitized with either RuPor Por. We find that the injection dynamics are very similar for both dyes, but the trapping dynamics strongly depend on the dye. We conclude that this dependence is linked to dye-induced surface states, electrostatic environment, and defects which increase carrier-trapping at the surface. Frequency-dependent measurements confirm that the dye influences the carrier dynamics in the NPs. This can be seen by the significant change in the Drude–Smith parameter c, which describes backscattering/localization effects at the surface. This parameter is approximately −0.9 for RuPand −0.8 for Por, showing a dependence on the chemical environment and the dye cation after injection.

This study probes a series of linkers and anchoring groups for direct interfacial electron transfer (IET) from high-potential porphyrins into semiconductor surfaces. Eight different linker–anchor combinations of CF3-substituted, high-potential porphyrins were designed, synthesized, and characterized. Specifically, a series of four anchors was examined (carboxylate, hydroxamate, phosphonate, and silatrane), along with two different linkers (phenylene and benzanilidylene), which differ in terms of their electronic conjugation and overall length. The electrochemical and photophysical properties of the porphyrins were evaluated by steady-state and transient spectroscopies in solution and on mesoporous SnO2substrates for use as dye photosensitizers in aqueous photoelectrochemical cells. IET dynamics were measured using time-resolved terahertz (TRTS) and transient absorption spectroscopies. From TRTS measurements, injection yields were determined relative to a commonly used phosphonated ruthenium(II) polypyridyl complex, which is reported to have near quantitative injection yield. We find that IET occurs through space rather than through the linkers, due to the tilted orientation of the adsorbed porphyrins in direct contact with the metal oxide surface. As a result, the anchoring groups have a less significant effect on IET dynamics than for adsorbates exhibiting through-linker injection. Experiments are supported by DFT calculations, including the analysis of different electron-injection pathways. Direct IET offers the advantage of the selection of anchoring groups based solely on chemical/photoelectrochemical stability and synthetic viability, irrespective of the electronic coupling of the anchoring group to the metal oxide surface.

Electron-injection dynamics of dye-sensitized photoelectrochemical cells depend on the length of the linker connecting the molecular photosensitizer to the metal oxide electron acceptor. However, systematic studies of the effect of chromophore–oxide distance are scarce. Here we present the synthesis, characterization, spectroscopy, and computational modeling of electron-injection dynamics from free-base trimesitylporphyrins with varying linker lengths into tin(IV) oxide (SnO2). In each system, the porphyrin core and metal oxide film remain the same while only the linker binding the porphyrin to the carboxylate anchor group is varied. A length range spanning 8.5–17.2 Å is studied by employing phenylene, biphenylene, terphenylene, and benzanilide groups as the linker. We find a clear correlation between linker length and injection rates, providing insights that will be exploited in the optimization of dye-sensitized photoelectrochemical cells.

The transient photoconductive properties of tin(IV) oxide (SnO2) mesoporous films have been studied by time-resolved terahertz (THz) spectroscopy. We gain insight into carrier dynamics by measuring overall injection and trapping lifetimes using optical pump–THz probe spectroscopy, as well as the frequency-dependent complex conductivity at various pump–probe delay times. It is found that the method of charge generation, either direct above band gap excitation (at 267 nm) or dye-sensitized electron injection (at 400 nm), has a dramatic effect on the overall injection and trapping dynamics of mobile charge carriers on the picosecond to nanosecond time scale. In the presence of aqueous electrolyte, direct band gap excitation of nonsensitized SnO2films results in instrument response limited subpicosecond injection lifetimes, while dye-sensitized films require tens of picoseconds for interfacial electron transfer to complete. On the other hand, the rate for trapping of mobile charges is at least 2 orders of magnitude faster in the nonsensitized films compared to the dye-sensitized films, which is likely due to photoinduced charges being more highly concentrated in the nonsensitized films. Finally, we find that the transient photoconductivity deviates from the behavior described by standard conductivity models such as the Drude and Drude–Smith models. This is due to the contribution from a photoinduced change in the permittivity of the SnO2films.

Time-resolved terahertz (THz) spectroscopy and open-circuit photovoltage measurements were employed to examine the size-dependent charge carrier dynamics of tungsten(VI) oxide (WO3) particles for their use as the photoanode in photoelectrochemical cells. Specifically, films of commercially available WO3nanoparticles (NPs) and granular particles (GPs) with diameters of 77 ± 34 and 390 ± 260 nm, respectively, were examined in air and while immersed in 0.1 M Na2SO4electrolyte (pH = 2). Examination of the frequency-dependent transient photoconductivity at short and long time scales indicates the presence of both photoinduced high net transport charge carriers at early times and in some cases low net transport charge carriers at later times. The high net transport charge carriers dominate the photoconductivity signal for ∼100 ps after photoexcitation. Depletion of the short-lived high net transport carriers due to trapping leads to the detection of longer-lived low net transport photoinduced charge carriers that likely contribute to surface chemistry.

Studies of adolescent and young adult males sustaining primary anterior shoulder dislocations reveal the like lihood of recurrence to be virtually always above 50% and as high as 79% to 94%. Common among these investigations is the lack of a specific, rigidly adhered to rehabilitation program.During a 3½ year period, 20 midshipmen at the United States Naval Academy sustained primary anterior shoulder dislocations. All participated in an identical treatment regimen which included a restrengthening program emphasizing the muscles of internal rotation and adduction, plus rigid restrictions of activities until the goals of their rehabilitation program were satisfied. Exercises progressed from isometrics through isoton ics and isokinetics. Goals included return to full active, unrestricted duty and athletic participation which in cluded participation in the sport that resulted in the original dislocation. Patients were followed for an av erage of 35.8 months (with a range of 17 to 45 months). During the period of study there were five recurrences (25%). A success rate of 75% would suggest that adherence to a specific, aggressive postdislocation re habilitation program, plus rigid restrictions of activities until the goals of the program are satisfied, can sub stantially improve the likelihood of a full return to activity without recurrent shoulder dislocation.

The American Cancer Society anticipates the diagnosis of 80,000 new cases of lymphoma in the US in 2013. Cancer Research UK estimates that more than 80% of Hodgkin Lymphoma (HL) patients and more than 60% of Non-Hodgkin Lymphoma (NHL) patients will be alive 5 or more years after diagnosis. As survival rates improve, focus shifts to ensuring quality of life in survivors and decreasing potential toxicity. Radiological procedures play a prominent role in diagnosis, staging and assessment of treatment response. Exposure to ionizing radiation has been linked to an increased risk of malignancy (Pearce et al 2012, Miglioretti et al 2013, Mathews et al 2013). Cumulative exposure in excess of 75mSv has been estimated to increase cancer mortality by 7.3% (Cardis et al 2007). There is a paucity of data in the literature regarding cumulative radiation exposure in patients with lymphoma. In cancer treatment, the aim is individualized management strategies. This should also be the goal for diagnostic procedures (O' Neill et al 2011, Fletcher et al 2012).A retrospective review of all patients on a prospectively maintained database with biopsy proven HL or NHL between January 2009 and July 2012 was conducted in a University hospital group. The cumulative effective radiation dose (CED) was calculated using standardized procedure-specific radiation dose levels.Four hundred and eighty six patients were included in the study. Mean (SD) age at diagnosis was 59 (17) years and 15% were aged < 40. Fifty-nine percent were men. Sixteen percent had HL; 84% had NHL. There were a total of 1127 patient-years of follow-up, with 15% having <1 year and 10% having 5 or more years of follow-up.Ninety-nine per cent of patients had diagnostic imaging. A total of 5748 radiological procedures were performed, equivalent to one procedure every 70 patient days of follow-up.The median estimated total CED ( IQR) per subject was 69mSv (42-118). Forty- six percent had a total CED >75mSv and 14% had a total CED >150mSv – SeeFigure 1. CT contributed 89% of the radiation dose and PET-CT contributed 8%.Patients aged <40 had a median CED (IQR) of 89mSv (55-124). Seventy-five per cent of these patients had a potentially curable malignancy (66% had HL; 5% had Diffuse Large B Cell Lymphoma; 4% had Burkitt Lymphoma). Patients who underwent stem cell transplantation had a median CED (IQR) of 162mSv (135-225) with 59% having radiotherapy as part of their management.Univariate analysis showed that age (p<0.001), duration of lymphoma (p<0.001) and stage (<0.001) were associated with CED.This study highlights the considerable ionizing radiation exposure from diagnostic imaging in patients with lymphoma. This is especially relevant in young people who would be considered the most radiosensitive and at highest risk for secondary malignancies.Low grade lymphomas are relapsing and remitting in nature and frequently require re-staging imaging over many years. Longer follow-up will be required here to potentially explain the non-significant trend between histological subtype and different CED.The American College of Radiology stated in 2013 that when used appropriately, the benefits of ionizing radiation far outweigh the risks. However, to minimize risk, institutions should participate in national dose registries. With the widespread use of Picture Archiving and Communication System (PACS), this will be feasible.Low dose CT imaging has emerged as a mechanism for minimizing CED. Dose reduction strategies incorporating patient-specific information would optimize imaging while minimizing the harmful effects (Shah et al 2012). Novel CT reconstruction algorithms allow diagnostic quality imaging to be obtained at reduced radiation doses without the prohibitive noise that would otherwise be present (Prakash et al 2010).Procedures which do not involve ionizing radiation such as MRI and ultrasound are becoming increasingly popular. There is growing interest in PET-MRI for staging of malignancies (Appenzeller 2013) but as yet, PET-CT remains superior.For patients with potentially curable lymphoma, particularly young patients with higher CED, consideration should be given to these strategies.No relevant conflicts of interest to declare.