Synthesis and Luminescence Properties of Near-Infrared N-Heterocyclic Luciferin Analogues for In Vivo Optical Imaging

As a means of achieving highly sensitive bioluminescence imaging of deep tissues utilizing the firefly luciferin-luciferase (L-L) reaction, we previously reported a luciferin analogue, AkaLumine, which exhibits high cell-permeability and emits near-infrared (NIR) light with high tissue-penetration by the L-L reaction. However, while AkaLumine enables us to observe targets in deep tissues, its poor solubility in aqueous media limits its utility for in vivo imaging. Herein, to address this issue, we have synthesized three AkaLumine derivatives with N-heterocyclic aromatic rings as new red luciferin analogues that have substantially higher solubility than that of AkaLumine in phosphate buffered saline solution. One of the derivatives (herein termed seMpai) exhibits an emission maximum at 675 nm upon L-L reaction with Photinus pyralis luciferase and presents an activity in mouse-tissue imaging similar to that of AkaLumine. It is hoped that seMpai will extend the application of high-sensitivity NIR bioluminescence imaging in a wide range of biomedical research fields

Environment-driven variability in absolute band edge positions and work functions of reduced ceria

The absolute band edge positions and work function (Φ) are the key electronic properties of metal oxides that determine their performance in electronic devices and photocatalysis. However, experimental measurements of these properties often show notable variations, and the mechanisms underlying these discrepancies remain inadequately understood. In this work, we focus on ceria (CeO2), a material renowned for its outstanding oxygen storage capacity, and combine theoretical and experimental techniques to demonstrate environmental modifications of its ionization potential (IP) and Φ. Under O-deficient conditions, reduced ceria exhibits a decreased IP and Φ with significant sensitivity to defect distributions. In contrast, the IP and Φ are elevated in O-rich conditions due to the formation of surface peroxide species. Surface adsorbates and impurities can further augment these variabilities under realistic conditions. We rationalize the shifts in energy levels by separating the individual contributions from bulk and surface factors, using hybrid quantum mechanical/molecular mechanical (QM/MM) embedded-cluster and periodic density functional theory (DFT) calculations supported by interatomic-potential-based electrostatic analyses. Our results highlight the critical role of on-site electrostatic potentials in determining the absolute energy levels in metal oxides, implying a dynamic evolution of band edges under catalytic conditions

Backtracked and paused transcription initiation intermediate of Escherichia coli RNA polymerase.

Initiation is a highly regulated, rate-limiting step in transcription. We used a series of approaches to examine the kinetics of RNA polymerase (RNAP) transcription initiation in greater detail. Quenched kinetics assays, in combination with gel-based assays, showed that RNAP exit kinetics from complexes stalled at later stages of initiation (e.g., from a 7-base transcript) were markedly slower than from earlier stages (e.g., from a 2- or 4-base transcript). In addition, the RNAP-GreA endonuclease accelerated transcription kinetics from otherwise delayed initiation states. Further examination with magnetic tweezers transcription experiments showed that RNAP adopted a long-lived backtracked state during initiation and that the paused-backtracked initiation intermediate was populated abundantly at physiologically relevant nucleoside triphosphate (NTP) concentrations. The paused intermediate population was further increased when the NTP concentration was decreased and/or when an imbalance in NTP concentration was introduced (situations that mimic stress). Our results confirm the existence of a previously hypothesized paused and backtracked RNAP initiation intermediate and suggest it is biologically relevant; furthermore, such intermediates could be exploited for therapeutic purposes and may reflect a conserved state among paused, initiating eukaryotic RNA polymerase II enzymes