Ferrell Lawson (classdime77)
Finally, we end this review with a look into the remaining challenges and future perspectives of single-atom photocatalysts. We anticipate that this review will provide some inspiration for the future discovery of the single-atom photocatalysts, manifestly stimulating the development in this emerging research area.A tridentate [PPP] ligand has been used to construct a series of dimeric cobalt complexes and explore cooperative multielectron redox processes that are both metal- and ligand-centered. Reduction of (PPClP)CoCl2 (1) with excess magnesium affords the CoICoI N-heterocyclic phosphido (NHP-)-bridged symmetric dimer [(μ-PPP)Co]2 (2). Two-electron oxidation of 2 with FcPF6 generates an asymmetrically bridged dication [(μ-PPP)Co]2[PF6]2 (3) in which the oxidation has occurred in a delocalized fashion throughout the Co2P2 core. In contrast, [(μ-PPP)Co]2+ (5), which can be generated either by one-electron oxidation of 2 with FcPF6 or comportionation of 2 and 3, features an asymmetric geometry and localized mixed valence. Treatment of 1 with the milder reductants CoCp2 and KBEt3H does not lead to formation of 2, 3, or 5 but instead generates dimeric species [(PPP)CoCl]2 (6) and [(PPP)CoH]2 (7). Unlike 2-5, where the phosphine side arms of the tridentate [PPP] ligand span the two Co centers, complex 6 and 7 are connected solely by NHP- ligands that bridge the two (PPP)Co fragments.Ribonucleotide reductases (RNRs) catalyze the conversion of nucleotides (NDP) to deoxynucleotides (dNDP), in part, by controlling the ratios and quantities of dNTPs available for DNA replication and repair. The active form of Escherichia coli class Ia RNR is an asymmetric α2β2 complex in which α2 contains the active site and β2 contains the stable diferric-tyrosyl radical cofactor responsible for initiating the reduction chemistry. Each dNDP is accompanied by disulfide bond formation. We now report that, under in vitro conditions, β2 can initiate turnover in α2 catalytically under both "one" turnover (no external reductant, though producing two dCDPs) and multiple turnover (with an external reductant) assay conditions. In the absence of reductant, rapid chemical quench analysis of a reaction of α2, substrate, and effector with variable amounts of β2 (1-, 10-, and 100-fold less than α2) yields 3 dCDP/α2 at all ratios of α2β2 with a rate constant of 8-9 s-1, associated with a rate-limiting conformational change. Stopped-flow fluorescence spectroscopy with a fluorophore-labeled β reveals that the rate constants for subunit association (163 ± 7 μM-1 s-1) and dissociation (75 ± 10 s-1) are fast relative to turnover, consistent with catalytic β2. When assaying in the presence of an external reducing system, the turnover number is dictated by the ratio of α2β2, their concentrations, and the concentration and nature of the reducing system; the rate-limiting step can change from the conformational gating to a step or steps involving disulfide rereduction, dissociation of the inhibited α4β4 state, or both. The issues encountered with E. coli RNR are likely of importance in all class I RNRs and are central to understanding the development of screening assays for inhibitors of these enzymes.This paper introduces the concept of "Drawing-PADs" (Drawing paper-based microfluidic analytical devices) allowing to intuitively evaluate the urinary albumin (Alb) index, a clinically important parameter used for the early detection of renal deficiencies related to diabetes, among others. To enable regular monitoring of the Alb index, a simple examination method suitable for self-diagnosis is highly desirable. The Drawing-PADs rely on the simultaneous naked eye detection of Alb and creatinine (Cre) on a single device according to the distance-based microfluidic PAD (μPAD) approach. The Alb index is visualized by simply drawing a straight line connecting the top of two color-changed assay channel sections (Alb and Cre channels), followed by visually confirming the position o
