Determination of Acetylamantadine by γ-Cyclodextrin-Assisted α-HL Nanopore for Potential Cancer Prediagnosis.

The high expression of Spermidine/spermine N1-acetyltransferase (SSAT-1) is an important indicator in early cancer diagnosis. Here, we developed a nanopore-based methodology with γ-cyclodextrin as an adaptor to detect and quantify acetylamantadine, the specific SSAT-1-catalyzed product from amantadine, to accordingly reflect the activity of SSAT-1. We employ γ-cyclodextrin and report that amantadine cannot cause any secondary signals in γ-cyclodextrin-assisted α-HL nanopore, while its acetylation product, acetylamantadine, does. This allows γ-cyclodextrin to practically detect acetylamantadine in the interference of excessive amantadine, superior to the previously reported ß-cyclodextrin. The quantification of acetylamantadine was not interfered with even a 50-fold amantadine and displayed no interference in artificial urine sample analysis, which indicates the good feasibility of this nanopore-based methodology in painless cancer prediagnosis. In addition, the discrimination mechanism is also explored by 2-D nuclear magnetic resonance (NMR) and nanopore experiments with a series of adamantane derivatives with different hydrophilic and hydrophobic groups. We found that both the hydrophobic region matching effect and hydrophilic interactions play a synergistic effect in forming a host-guest complex to further generate the characteristic signals, which may provide insights for the subsequent design and study of drug-cyclodextrin complexes.

DFT mechanistic study of biomimetic diiron complex catalyzed dehydrogenation: Unexpected Fe(III)Fe(III)-1,1-µ-hydroperoxy active species for hydride abstraction.

The diiron active site is pivotal in catalyzing transformations in both biological and chemical systems. Recently, a range of biomimetic diiron catalysts have been synthesized, drawing inspiration from the active architecture of soluble methane monooxygenase (sMMO). These catalysts have been successfully deployed for the dehydrogenation of indolines, marking a significant advancement in the field. Using density functional theory (DFT) calculations, we have identified a novel mechanistic pathway that governs the dehydrogenation of indolines catalyzed by a biomimetic diiron complex. Specifically, this reaction is facilitated by the transfer of a hybrid atom from the C1 position of the substrate to the distal oxygen atom of the Fe(III)Fe(III)-1,1-µ-hydroperoxy active species. This transfer serves as the rate-limiting step for the heterolytic cleavage of the OO bond, ultimately generating the substrate cation. The mechanism we propose aligns well with mechanistic investigations incorporating both kinetic isotope effect (KIE) measurements and evaluations of stereochemical selectivity. This research contributes to the broader scientific understanding of catalysis involving biomimetic diiron complexes and offers valuable insights into the catalytic behaviors of non-heme diiron metalloenzymes.

Recognition of Oligonucleotide C by Polydopamine-Coated Solid-State Nanopores.

Selective recognition of short oligonucleotides at the single-molecule level is particularly important for early disease detection and treatment. In this work, polydopamine (PDA)-coated nanopores were prepared via self-polymerization as a solid-state nanopore sensing platform for the recognition of oligonucleotide C (PolyC). The PDA coating possesses abundant active sites, such as indole, amino, carboxyl, catechol, and quinone structures, which had interactions with short oligonucleotides to slow down the translocation rate. PDA-coated nanopores selectively interact with PolyC20 by virtue of differences in hydrogen bonding forces, generating a larger blocking current, while polyA and polyT demonstrated very small blockings. At the same time, PDA-coated nanopores can sensitively distinguish PolyC with different lengths, such as 20, 14, and 10 nt. The functionalization of PDA on the solid-state nanopore provides an opportunity for the rational design of the recognition surface for biomolecules.

Solid-State Nanopore Distinguishes Ferritin and Apo-Ferritin with Identical Exteriors through Amplified Flexibility at Single-Molecule Level.

Protein identification and discrimination at the single-molecule level are big challenges. Solid-state nanopores as a sensitive biosensor have been used for protein analysis, although it is difficult to discriminate proteins with similar structures in the traditional discrimination method based on the current blockage fraction. Here, we select ferritin and apo-ferritin as the model proteins that exhibit identical exterior and different interior structures and verify the practicability of their discrimination with flexibility features by the strategy of gradually decreasing the nanopore size. We show that the larger nanopore (relative to the protein size) has no obvious effect on discriminating two proteins. Then, the comparable-sized nanopore plays a key role in discriminating two proteins based on the dwell time and fraction distribution, and the conformational changes of both proteins are also studied with this nanopore. Finally, in the smaller nanopore, the protein molecules are trapped rather than translocated, where two proteins are obviously discriminated through the current fluctuation caused by the vibration of proteins. This strategy has potential in the discrimination of other important similar proteins.

O-O Bond Formation and Oxygen Release in Photosystem II Are Enhanced by Spin-Exchange and Synergetic Coordination Interactions.

The photosystem II (PSII)-catalyzed water oxidation is crucial for maintaining life on earth. Despite the extensive experimental and computational research that has been conducted over the past two decades, the mechanisms of O-O bond formation and oxygen release during the S3 ∼ S0 stage remain disputed. While the oxo-oxyl radical coupling mechanism in the "open-cubane" S4 state is widely proposed, recent studies have suggested that O-O bond formation may occur from either the high-spin water-unbound S4 state or the "closed-cubane" S4 state. To gauge the various mechanisms of O-O bond formation proposed recently, the comprehensive QM/MM and QM calculations have been performed. Our studies show that both the nucleophilic O-O coupling from the Mn4 site of the high-spin water-unbound S4 state and the O5-O6 or O5-OW2 coupling from the "closed-cubane" S4 state are unfavorable kinetically and thermodynamically. Instead, the QM/MM studies clearly favor the oxyl-oxo radical coupling mechanism in the "open-cubane" S4 state. Furthermore, our comparative research reveals that both the O-O bond formation and O2 release are dictated by (a) the exchange-enhanced reactivity and (b) the synergistic coordination interactions from the Mn1, Mn3, and Ca sites, which partially explains why nature has evolved the oxygen-evolving complex cluster for the water oxidation.

Theoretical studies on the structural and spectral properties of two specific C54 isomers and the chlorinated species C54Cl8.

X-ray photoelectron (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectra as well as the ground-state electronic/geometrical structures of #540C54 captured in experiment and the most controversial isomer #369C54 (C 2v- and C s-symmetry, respectively) have been calculated at the density functional theory (DFT) level. After chlorination, significant changes were observed in the electronic structure and X-ray spectra. Both XPS and NEXAFS spectra showed strong isomer dependence. The results indicated that the "fingerprints" in the X-ray spectra afforded an effective way to identify the fullerene isomers mentioned above. Ultraviolet-visible (UV-Vis) absorption spectroscopy of C54Cl8 was also simulated at the time-dependent (TD) DFT level, and the simulated UV-Vis spectrum was in accordance with the experimental result. The results of this study can provide valuable information for further experimental and theoretical studies of new fullerenes and their derivatives through X-ray and ultraviolet spectroscopy. The study of newly synthesized fullerene isomers and their derivatives using X-ray and UV-Vis spectra offers valuable information for further experimental and theoretical exploration.