We present a redox-neutral method for the photocatalytic generation of carbanions. Benzylic carboxylates are photooxidized by single electron transfer; immediate CO
2
extrusion and reduction of the
...in situ
formed radical yields a carbanion capable of reacting with aliphatic aldehydes as electrophiles giving the Grignard analogous reaction product.
We present a redox-neutral method for the photocatalytic generation of carbanions.
DNA-templated molecular (dye) aggregates are a novel class of materials that have garnered attention in a broad range of areas including light harvesting, sensing, and computing. Using DNA to ...template dye aggregation is attractive due to the relative ease with which DNA nanostructures can be assembled in solution, the diverse array of nanostructures that can be assembled, and the ability to precisely position dyes to within a few Angstroms of one another. These factors, combined with the programmability of DNA, raise the prospect of designer materials custom tailored for specific applications. Although considerable progress has been made in characterizing the optical properties and associated electronic structures of these materials, less is known about their excited-state dynamics. For example, little is known about how the excited-state lifetime, a parameter essential to many applications, is influenced by structural factors, such as the number of dyes within the aggregate and their spatial arrangement. In this work, we use a combination of transient absorption spectroscopy and global target analysis to measure excited-state lifetimes in a series of DNA-templated cyanine dye aggregates. Specifically, we investigate six distinct dimer, trimer, and tetramer aggregatesbased on the ubiquitous cyanine dye Cy5templated using both duplex and Holliday junction DNA nanostructures. We find that these DNA-templated Cy5 aggregates all exhibit significantly reduced excited-state lifetimes, some by more than 2 orders of magnitude, and observe considerable variation among the lifetimes. We attribute the reduced excited-state lifetimes to enhanced nonradiative decay and proceed to discuss various structural factors, including exciton delocalization, dye separation, and DNA heterogeneity, that may contribute to the observed reduction and variability of excited-state lifetimes. Guided by insights from structural modeling, we find that the reduced lifetimes and enhanced nonradiative decay are most strongly correlated with the distance between the dyes. These results inform potential tradeoffs between dye separation, excitonic coupling strength, and excited-state lifetime that motivate deeper mechanistic understanding, potentially via further dye and dye template design.
Developing scenarios to explore possible environmental futures is a widely used tool in social-ecological research. Scenario planners working in environmental systems increasingly enlist stakeholders ...to help develop scenarios, but effectively integrating stakeholder participation with scenario analyses and modeling remains a challenge. Using the New England Landscape Futures project as a case study, we explore how a method for codesigning a scenario elicitation process can be used to help balance the needs of both stakeholders and scientists. To illustrate the design process, we document eight influential decisions made with stakeholder input, describe the competing demands that we negotiated, and outline the rationale for the selected approach. We find that three priorities drove most of our decisions: maximizing stakeholder involvement in the scenario development process, efficient use of stakeholder time, and research needs. The outcome was a robust, intense, and highly structured one-day scenario development protocol that engaged stakeholders in the full scenario development process from initial orientation and identification of driving forces through to fleshedout scenarios narratives and quantitative inputs able to inform land-use simulations. Its deployment in six state-specific workshops was successful in eliciting divergent scenarios that stakeholders perceived as being plausible and relevant. Stakeholder responses to the process were positive, though also reflected the compromises made during the codesign process. Research needs were largely met, though initial expectations likely exceeded what could reasonably be elicited from a stakeholder group in one day. Our experiences highlight the importance of process design and how selection of scenario development techniques should follow from the project objectives, problem context, and stakeholder preferences for engagement activities. The use of a codesign framework that recognizes the challenges involved and engages stakeholders in the design process can act as a shared learning experience and contribute to greater effectiveness and impact for participatory social-ecological scenario processes.
Molecular aggregates are of interest to a broad range of fields including light harvesting, organic optoelectronics, and nanoscale computing. In molecular aggregates, nonradiative decay pathways may ...emerge that were not present in the constituent molecules. Such nonradiative decay pathways may include singlet fission, excimer relaxation, and symmetry-breaking charge transfer. Singlet fission, sometimes referred to as excitation multiplication, is of great interest to the fields of energy conversion and quantum information. For example, endothermic singlet fission, which avoids energy loss, has been observed in covalently bound, linear perylene trimers and tetramers. In this work, the electronic structure and excited-state dynamics of dimers of a perylene derivative templated using DNA were investigated. Specifically, DNA Holliday junctions were used to template the aggregation of two perylene molecules covalently linked to a modified uracil nucleobase through an ethynyl group. The perylenes were templated in the form of monomer, transverse dimer, and adjacent dimer configurations. The electronic structure of the perylene monomers and dimers were characterized via steady-state absorption and fluorescence spectroscopy. Initial insights into their excited-state dynamics were gleaned from relative fluorescence intensity measurements, which indicated that a new nonradiative decay pathway emerges in the dimers. Femtosecond visible transient absorption spectroscopy was subsequently used to elucidate the excited-state dynamics. A new excited-state absorption feature grows in on the tens of picosecond timescale in the dimers, which is attributed to the formation of perylene anions and cations resulting from symmetry-breaking charge transfer. Given the close proximity required for symmetry-breaking charge transfer, the results shed promising light on the prospect of singlet fission in DNA-templated molecular aggregates.
Partial anomalous pulmonary venous return (PAPVR) is a rare congenital cardiovascularcondition in which some of the pulmonary veins drain into the systemiccirculation. We report on the cadaveric ...dissection of a 71-year-old Caucasian maledonor who died of chronic obstructive pulmonary disease with hypertension. Wenoted a faint incisional scar on the thorax extending from the parasternal regionat the 4th intercostal level to the midaxillary line. Since the straight-line incisionfollowed the ribs and the scar was quite faint, surgery probably occurred whenthe donor was young. We also observed numerous surgical interventions of theheart, lungs, and vasculature to correct various defects.The morphology of the heart was normal, but was shifted more to the rightside. An atrial septal defect (ASD) was closed with sutures. The right superiorpulmonary vein that drained into the superior vena cava (SVC) was ligated closeto the SVC and the right inferior, left superior, and inferior pulmonary veins alldrained directly into the left atrium. We noticed a dilated coronary sinus enteringthe right atrium adjacent to the ASD; the ostium of the coronary sinus noticeablylacked the normal valve-like structure. We initially thought the right lung wasa “horseshoe” lung, but realised that it was a “hypogenetic” lung with PAPVR andan accessory diaphragm. Compared to the left, the right secondary bronchi weremuch narrower and branched uncharacteristically, as seen in hypogenetic lungsyndrome. The inferior lobe was highly disorganised, severely hypoplastic, andexhibited uncharacteristic morphology. The superior bronchopulmonary segmentwas markedly hypoplastic. The posterior and medial basal segments were notonly hypoplastic and slender, but also extended like a tail to the left pulmonarycavity behind the heart/pericardium and in front of the oesophagus and aorta.The right lung, though hypoplastic, demonstrated patent bronchi and the lobeswere inflatable. Based on the hypogenetic lung and PAPVR, we conclude that thedonor exhibited ‘scimitar’ lung.
This study uses a multimodal analytical approach to evaluate the rates of (co)amorphization of milled drug and excipient and the effectiveness of different analytical methods in detecting these ...changes. Indomethacin and tryptophan were the model substances, and the analytical methods included low-frequency Raman spectroscopy (785 nm excitation and capable of measuring both low- (10 to 250 cm–1) and midfrequency (450 to 1800 cm–1) regimes, and a 830 nm system (5 to 250 cm–1)), conventional (200–3000 cm–1) Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and X-ray powder diffraction (XRPD). The kinetics of amorphization were found to be faster for the mixture, and indeed, for indomethacin, only partial amorphization occurred (after 360 min of milling). Each technique was capable of identifying the transformations, but some, such as low-frequency Raman spectroscopy and XRPD, provided less ambiguous signatures than the midvibrational frequency techniques (conventional Raman and FTIR). The low-frequency Raman spectra showed intense phonon mode bands for the crystalline and cocrystalline samples that could be used as a sensitive probe of order. Multivariate analysis has been used to further interpret the spectral changes. Overall, this study demonstrates the potential of low-frequency Raman spectroscopy, which has several practical advantages over XRPD, for probing (dis-)order during pharmaceutical processing, showcasing its potential for future development, and implementation as an in-line process monitoring method.
Research Highlights: Ecological momentary assessments (EMAs) are a fresh approach to measuring behavior by querying the subject in real time. Typical studies of FFO behavior use self-reported survey ...data. FFOs across the United States collectively own more forested land than any other ownership category, and their actions will impact the public goods these forests provide. Thus, better measures of FFO actions are critical to understanding how these public goods may be affected. Background and Objectives: In this pilot study, we evaluated the potential of ecological momentary assessments to understand family forest owner (FFO) engagement with their woods. We sought to test recruitment, attrition, and participant reaction to the method. Materials and Methods: FFOs belong to woodland owner associations were sent the same questions weekly for a month, asking about woodland engagement. Results: Nearly 90% of participants completed all four surveys and the majority found the method reasonable. Most participants thought about their woods weekly, but a longer time period is needed to measure temporal management trends. Conclusions: This approach may yield real-time and useful information about natural resource engagement to inform conservation-based programming and outreach.
The nonmirror image relationship between absorption and fluorescence spectra of conjugated polymers contrasts with most organic chromophores and is widely considered a signature of interchromopohore ...energy funneling. We apply broad-band ultrafast fluorescence spectroscopy to resolve the evolution of fluorescence spectra for dilute solutions of conjugated oligothiophenes, where no energy transfer is possible. Fluorescence spectra evolve from a mirror image of absorption, which lacks vibronic structure, toward a spectrally narrower and vibronically structured species on the hundreds of femtosecond to early picosecond time scale. Our analysis of this fluorescence spectral evolution shows that a broad distribution of torsional conformers is driven to rapidly planarize in the excited state, including in solid films, which is supported by Raman spectroscopy and quantum chemical modeling. Our data have important implications for understanding different energy-transfer regimes that are delineated by structural relaxation.
Delay in viral production may have a significant impact on the early stages of infection. During the eclipse phase, the time from viral entry until active production of viral particles, no viruses ...are produced. This delay affects the probability that a viral infection becomes established and timing of the peak viral load. Deterministic and stochastic models are formulated with either multiple latent stages or a fixed delay for the eclipse phase. The deterministic model with multiple latent stages approaches in the limit the model with a fixed delay as the number of stages approaches infinity. The deterministic model framework is used to formulate continuous-time Markov chain and stochastic differential equation models. The probability of a minor infection with rapid viral clearance as opposed to a major full-blown infection with a high viral load is estimated from a branching process approximation of the Markov chain model and the results are confirmed through numerical simulations. In addition, parameter values for influenza A are used to numerically estimate the time to peak viral infection and peak viral load for the deterministic and stochastic models. Although the average length of the eclipse phase is the same in each of the models, as the number of latent stages increases, the numerical results show that the time to viral peak and the peak viral load increase.
The ligand-controlled Markovnikov and anti-Markovnikov hydrocarboxylation of styrenes with atmospheric pressure of CO2 at room temperature using dual visible-light-nickel catalysis has been ...developed. In the presence of neocuproine as ligand, the Markovnikov product is obtained exclusively, while employing 1,4-bis(diphenylphosphino)butane (dppb) as the ligand favors the formation of the anti-Markovnikov product. A range of functional groups and electron-poor, -neutral, as well as electron-rich styrene derivatives are tolerated by the reaction, providing the desired products in moderate to good yields. Preliminary mechanistic investigations indicate the generation of a nickel hydride (H-NiII) intermediate, which subsequently adds irreversibly to styrenes.
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