ABSTRACT
Artificial light-harvesting systems in aqueous media which mimic nature are of significant importance; however, they are often restrained by the solubility and the undesired aggregation-caused quenching effect of the hydrophobic chromophores. Here, we report a generalized strategy toward the construction of efficient artificial light-harvesting systems based on supramolecular peptide nanotubes in water. By molecularly aligning the hydrophobic chromophores along the nanotubes in a slipped manner, an artificial light-harvesting system with a two-step sequential Förster resonance energy transfer process is successfully fabricated, showing an energy transfer efficiency up to 95% and a remarkably high fluorescence quantum yield of 30%, along with high stability. Furthermore, the spectral emission could be continuously tuned from blue through green to orange, as well as outputted as a white light continuum with a fluorescence quantum yield of 29.9%. Our findings provide a versatile approach of designing efficient artificial light-harvesting systems and constructing highly emissive organic materials in aqueous media.
ABSTRACT
Molecular flavins are one of the most versatile photocatalysts. They can coordinate single and multiple electron transfer processes, gift hydrogen atoms, form reversible covalent linkages that support group transfer mechanisms, and impart photonic energy to ground state molecules, priming them for downstream reactions. But one mechanism that has not featured extensively is the ability of flavins to act as photoacids. Herein, we disclose our proof-of-concept studies showing that electrophotochemistry can transform fully oxidized flavin quinones to super-oxidized flavinium photoacids that successfully guide proton-transfer and deliver acid-catalyzed products. We also show that these species can adopt a second mechanism wherein they react with water to release hydroxyl radicals that facilitate hydrogen-atom abstraction and sp3C-H functionalization protocols. Together, this unprecedented bimodal reactivity enables electro-generated flavinium salts to affect synthetic chemistries previously unknown to flavins, greatly expanding their versatility as catalysts.
ABSTRACT
Child abuse is a serious concern that can cause the death of a child. In such cases the medico-legal evidence is often pivotal but complex, drawing across multiple medical disciplines and techniques. One key specialism is histopathology, which is considered the gold standard for estimating the age of individual fractures. Another is micro-CT imaging, which can visualise the location of trauma across the body. This case report demonstrates how micro-CT was used to contextualise the histological evidence in the Criminal Justice Proceedings of a fatal child abuse case. This was achieved by overlaying the aged fracture evidence from histopathology onto the visuals rendered from micro-CT imaging. The case was a suspected child abuse of a deceased 1-month old infant who was reported unresponsive by their parents. The child was taken to hospital where they were pronounced dead. Suspicion was raised and post-mortem imaging confirmed head trauma and rib fractures, and the case was escalated for a forensic investigation. This case report details how the micro-CT imaging was merged with the gold standard of histopathology for visualisation of trauma, and how the court presentation was planned alongside Senior Investigating Officers and various medical experts. The presentation was used in court by the histopathologist to present the evidence. The resulting presentation provided additional clarity to jury members regarding the location, severity, frequency, and timings of the injuries. From the perspective of the investigating police force, the resulting presentation was crucial in ensuring understanding of the medico-legal evidence of how the infant died. The prosecuting lawyer noted that combining the histological and micro-CT evidence in this way allowed the evidence to be presented in a sensitive, clear, and impactful manner.
Subject(s)
Child Abuse , Rib Fractures , X-Ray Microtomography , Humans , Infant , Child Abuse/diagnosis , Forensic Pathology/methods , Rib Fractures/diagnostic imaging , Rib Fractures/pathologyABSTRACT
Many photoactivated processes involve a change in oxidation state during the reaction pathway and formation of highly reactive photoactivated species. Isolating these reactive species and studying their early-stage femtosecond to nanosecond (fs-ns) photodynamics can be challenging. Here we introduce a combined ultrafast transient absorption-spectroelectrochemistry (TA-SEC) approach using freestanding boron doped diamond (BDD) mesh electrodes, which also extends the time domain of conventional spectrochemical measurements. The BDD electrodes offer a wide solvent window, low background currents, and a tuneable mesh size which minimises light scattering from the electrode itself. Importantly, reactive intermediates are generated electrochemically, via oxidation/reduction of the starting stable species, enabling their dynamic interrogation using ultrafast TA-SEC, through which the early stages of the photoinduced relaxation mechanisms are elucidated. As a model system, we investigate the ultrafast spectroscopy of both anthraquinone-2-sulfonate (AQS) and its less stable counterpart, anthrahydroquinone-2-sulfonate (AH2QS). This is achieved by generating AH2QS in situ from AQS via electrochemical means, whilst simultaneously probing the associated early-stage photoinduced dynamical processes. Using this approach we unravel the relaxation mechanisms occurring in the first 2.5 ns, following absorption of ultraviolet radiation; for AQS as an extension to previous studies, and for the first time for AH2QS. AQS relaxation occurs via formation of triplet states, with some of these states interacting with the buffered solution to form a transient species within approximately 600 ps. In contrast, all AH2QS undergoes excited-state single proton transfer with the buffered solution, resulting in formation of ground state AHQS- within approximately 150 ps.