We compare the singlet fission dynamics of five pentacene derivatives precipitated to form nanoparticles. Two nanoparticle types were distinguished by differences in their solid-state order and ...kinetics of triplet formation. Nanoparticles that comprise primarily weakly coupled chromophores lack the bulk structural order of the single crystal and exhibit nonexponential triplet formation kinetics (Type I), while nanoparticles that comprise primarily more strongly coupled chromophores exhibit order resembling that of the bulk crystal and triplet formation kinetics associated with the intrinsic singlet fission rates (Type II). In the highly ordered nanoparticles, singlet fission occurs most rapidly. We relate the molecular packing arrangement derived from the crystal structure of the pentacene derivatives to their singlet fission dynamics and find that slip stacking leads to rapid, subpicosecond singlet fission. We present evidence that exciton delocalization, coincident with an increased relative admixture of charge-transfer configurations in the description of the exciton wave function, facilitates rapid triplet pair formation in the case of single-step singlet fission. We extend the study to include two hexacene derivatives and find that these conclusions are generally applicable. This work highlights acene derivatives as versatile singlet fission chromophores and shows how chemical functionalization affects both solid-state order and exciton interactions and how these attributes in turn affect the rate of singlet fission.
A range of oxoammonium salt-based oxidation reactions have been explored computationally using density functional theory (DFT), and the results have been correlated with experimentally derived trends ...in reactivity. Mechanistically, most reactions involve a formal hydride transfer from an activated C–H bond to the oxygen atom of the oxoammonium cation. Several new potential modes of reactivity have been uncovered and validated experimentally.
Abstract
Corn with naturally occurring aflatoxin (AF), wheat with naturally occurring doxynivalenol (DON), and barley with naturally occurring zearalenone (ZEA) were used to make rations for feeding ...turkey hen poults to 6 weeks of age. Control rations with equal amounts of corn, wheat, and barley were also fed. The control rations did contain some DON while both sets of rations contained ZEA. Within each grain source, there were 4 treatments: the control ration plus 3 rations each with a different feed additive which were evaluated for the potential to lessen potential mycotoxin effects on bird performance and physiology. The additives were Biomin BioFix (2 lb/ton), Kemin Kallsil (4 lb/ton), and Nutriad UNIKE (3 lb/ton). The mycotoxin rations reduced poult body weight (2.31 vs. 2.08 ± 0.02 kg) and increased (worsened) poult feed conversion (1.47 vs. 1.51 ± 0.01) at 6 wk. Feeding the poults the mycotoxin feed also resulted in organ and physiological changes typical of feeding dietary aflatoxin although a combined effect of AF, DON, and ZEA which cannot be dismissed. The feed additives resulted in improved feed conversion to 6 wk in both grain treatment groups. The observed physiological effect of feeding the additives was to reduce relative gizzard weight for both groups and to lessen the increase in relative kidney weight for the birds fed the mycotoxin feed. In conclusion, the feed additives used in this study did alleviate the effect of dietary mycotoxins to some degree, especially with respect to feed conversion. Further studies of longer duration are warranted.
Tissue engineering scaffolds encourage cell proliferation whilst degrading to facilitate tissue regeneration. Their mechanical properties therefore change, decreasing due to scaffold degradation and ...increasing due to extracellular matrix deposition. This work compares the changing properties of collagen scaffolds incubated in culture medium, with and without human tenocytes, in order to investigate the relationship between degradation and tenocyte proliferation. The material properties of scaffolds are compared over 26 days using mechanical testing, differential scanning calorimetry, infra-red spectroscopy, and histology and biochemical assays. For medium-only scaffolds, the mechanical properties decrease rapidly, while culture medium sulfhydryl content increases significantly, with no significant changes in the denaturation temperature of scaffold collagen content. Conversely, the mechanical properties and collagen content of tenocyte-seeded scaffolds increase significantly while culture medium sulfhydryl content decreases and denaturation temperature remains the same. These results indicate that tenocytes proliferation both reduces the degradation of collagen scaffolds incubated in culture medium and produces scaffolds with improved properties.
A series of tetraphenylethene 9,10‐diphenylanthracene (TPE‐DPA) derivatives have been synthesized, and their photophysical properties studied. Photoluminescence measurements in PMMA, neat films and ...nanoparticle dispersions reveal that different aggregation states are formed, which leads to different photophysical behavior. The triplet excited state properties were studied using Pt(II) octaethylporphyrin (PtOEP) as triplet sensitizer. Upconverted emission from the DPA moiety is observed in nanoparticle dispersions of each derivative. A higher upconverted emission intensity is observed in aerated (compared to deaerated) solutions of the derivatives following irradiation, which is attributed to oxidation of the TPE moiety. These results provide valuable insight for the design of AIE luminogens for triplet‐triplet annihilation upconversion (TTA‐UC).
Bright idea: Tetraphenylethene 9,10‐diphenylanthracenes (TPE‐DPAs) were synthesized and characterized. The TPE‐DPAs displayed aggregation induced emission behavior and were shown to work as emitters in nanoparticle triplet‐triplet annihilation upconversion systems with platinum porphyrin as triplet sensitizer.
The unique chemistry of small, strained carbocyclic systems has long captivated organic chemists from a theoretical and fundamental standpoint. A resurgence of interest in strained carbocyclic ...species has been prompted by their potential as bioisosteres, high fraction of sp
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carbons, and limited appearance in the patent literature. Among strained ring systems, bicyclo1.1.0butane (BCB) stands apart as the smallest bicyclic carbocycle and is amongst the most strained carbocycles known. Despite the fact that BCBs have been synthesized and studied for well over 50 years, they have long been regarded as laboratory curiosities. However, new approaches for preparing, functionalizing, and using BCBs in "strain-release" transformations have positioned BCBs to be powerful synthetic workhorses. Further, the olefinic character of the bridgehead bond enables BCBs to be elaborated into various other ring systems and function as covalent warheads for bioconjugation. This review will discuss the recent developments in the synthesis and functionalization of BCBs as well as the applications of these strained rings in synthesis and drug discovery. An overview of the properties and the historical context of this interesting structure will be provided.
A flurry of reports for preparing, functionalizing, and using bicyclo1.1.0butanes (BCBs) have positioned them to be powerful synthons with numerous applications. This review discusses the recent developments regarding this strained carbocycle.
Both pendant and main chain conjugated MEH-PPV based polymers have been studied at the level of single chains using confocal and widefield fluorescence microscopy techniques. In particular, defocused ...widefield fluorescence is applied to reveal the extent of energy transfer in these polymers by identifying whether they act as single emitters. For main chain conjugated MEH-PPV, molecular weight and the surrounding matrix play a primary role in determining energy transport processes and whether single emitter behaviour is observed. Surprisingly in polymers with a saturated backbone but containing the same pendant MEH-PPV oligomer on each repeating unit, intra-chain energy transfer to a single emitter is also apparent. The results imply there is chromophore heterogeneity that can facilitate energy funneling to the emitting site. Both main chain conjugated and pendant MEH-PPV polymers exhibit changes in orientation of the emission dipole during a fluorescence trajectory of many seconds, whereas a model MEH-PPV oligomer does not. The results suggest that, in the polymers, the nature of the emitting chromophores can change during the time trajectory.
The fissure-sealing of newly erupted molars is an effective caries prevention treatment, but remains underutilized. Two plausible reasons are the financial disincentive produced by the dental ...remuneration system, and dentists’ lack of awareness of evidence-based practice. The primary hypothesis was that implementation strategies based on remuneration or training in evidence-based healthcare would produce a higher proportion of children receiving sealed second permanent molars than standard care. The four study arms were: fee per sealant treatment, education in evidence-based practice, fee plus education, and control. A cost-effectiveness analysis was conducted. Analysis was based on 133 dentists and 2833 children. After adjustment for baseline differences, the primary outcome was 9.8% higher when a fee was offered. The education intervention had no statistically significant effect. ‘Fee only’ was the most cost-effective intervention. The study contributes to the incentives in health care provision debate, and led to the introduction of a direct fee for this treatment.
► Use of AFM to measure ultrastructural differences of bulk tendon samples. ► Assess affect of in vivo loading conditions and preservation techniques. ► Ultrastructure dependent on loading condition, ...regardless of preservation technique. ► Ultrastructural differences between frozen and aldehyde-fixed samples. ► AFM is suitable for bulk analysis but preservation technique must be consistent.
Atomic Force Microscopy (AFM) is a surface characterisation technique which analyses topology. To date, AFM studies of tissue ultrastructure have focussed on single collagen fibrils extracted from different tissues prior to analysis. Using sample preparation techniques used in electron microscopy studies, this work uses AFM to analyse the collagen ultrastructure of bulk samples from bovine deep digital flexor tendons (DDFTs). DDFT ultrastructure in regions of the tendon which experience different loading conditions are compared. Samples are analysed post-freezing and post-aldehyde fixation with either 10% formalin or 4% glutaraldehyde in order to investigate the affect of tissue preservation on tissue ultrastructure. The results demonstrate that both fibril diameter and repeat unit of the tendon vary between different regions in the dorsoventral plane, with regions subjected to both tensile and compressive forces exhibiting smaller fibril diameter and repeat unit compared to regions subjected to tensile forces alone. These differences are detectable regardless of the tissue preservation technique used. However these measured differences do vary with preservation techniques with aldehyde-fixed samples exhibiting smaller fibril diameters and larger repeat units compared to frozen samples. These results demonstrate that AFM is a highly suitable technique for the characterisation of different ultrastructures in bulk samples but that it is important to be consistent in the choice of preservation technique.
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