G-quadruplexes (G4s) are versatile catalytic DNAs when combined with hemin. Despite the repertoire of catalytically competent G4/hemin complexes studied so far, little is known about the detailed catalytic mechanism of these biocatalysts. Herein, we have carried out an in-depth analysis of the hemin binding site within the G4/hemin catalysts, providing the porphyrinic cofactor with a controlled nucleotidic environment. We intensively assessed the position-dependent catalytic enhancement in model reactions and found that proximal nucleobases enhance the catalytic ability of the G4/hemin complexes. Our results allow for revisiting the mechanism of the G4/hemin-based catalysis, especially gaining insights into the rate-limiting step, demonstrating how both the G4 core and the proximal nucleotides dA and/or dC concomitantly activate the Compound 0 → 0* prototropic cleavage of H 2 O 2 to foster Compound 1 formation. These results provide mechanistic clues as to how the properties of G4-based catalysts can be improved to ultimately make them competitive with proteinaceous enzymes.

Recent studies indicate that i-DNA, afour-stranded cytosine-richD NA also knowna st he i-motif,i sa ctually formed in vivo;however,asystematic study on sequence effects on stability has been missing. Herein, an unprecedented number of different sequences ( 271) bearing four runs of 3-6 cytosines with different spacer lengths has been tested. While i-DNAstability is nearly independent on total spacer length, the central spacer plays as pecial role on stability.S tability also depends on the length of the C-tracts at both acidic and neutral pHs.T his study provides ag lobal picture on i-DNAs tability thanks to the large size of the introduced data set;i tr eveals unexpected features and allows to conclude that determinants of i-DNAstability do not mirror those of G-quadruplexes.Our results illustrate the structural roles of loops and C-tracts on i-DNAs tability,c onfirm its formation in cells,a nd allow establishing rules to predict its stability.

Lead-free double perovskites (DPs) with excellent moisture, light, and heat stability have been explored as alternatives to toxic lead halide perovskite (APbX 3 ) (A for monovalent cation and X for Cl, Br, or I). However, the bandgaps of the current DPs are generally larger and either indirect or direct forbidden, which leads to weak visible light absorption and limitation for photovoltaic and other optoelectronic applications. Herein, we demonstrate the first synthesis of Cu 2+ -doped Cs 2 AgInCl 6 double perovskite nanocrystals via a facile hot-injection solution approach. The electronic bandgap can be dramatically tuned from ∼3.60 eV (Cs 2 AgInCl 6 , parent) to ∼2.19 eV (Cu 2+ -doped Cs 2 AgInCl 6 ) by varying the Cu 2+ doping amount. We conclude that the decrease of bandgap is attributed to the overlap of the Agd/In-p/Cl-p orbitals and the Cu-3d orbitals in the valence band. The wide tunability of the optical and electronic properties makes Cu 2+ -Doped Cs 2 AgInCl 6 DP NCs promising candidates for future optoelectronic device applications.

The quadruplex-based DNAzyme system is one of the most useful artificial enzymes or catalysts; their unique properties make them reliable alternatives to proteins for performing catalytic transformation. The first prototype of a thermally stable DNAzyme system is presented. This thermophilic DNAzyme is capable of oxidizing substrates at high temperatures (up to 95 °C) and long reaction times (up to 18 h at 75 °C). The catalytic activity of the DNAzymes were investigated with the standard peroxidase-mimicking oxidation of 2,2'-azino-bis(3-ethylbenzothiozoline-6-sulfonic acid) (ABTS) by H O . The step-by-step design of this unique heat-activated G-quadruplex/hemin catalyst, including the modification of adenines at both ends of G-tracts, the choice of cation, and its concentration for DNAzyme stabilization, is described. This work investigates thoroughly the molecular basis of these catalytic properties and provides an example of an industrially relevant application.

The catalytic activity of G-quadruplex/hemin is much lower than that of proteinous enzymes, so it is very important to increase its activity. Very recently, flanking sequences, which can be regarded as an external part of G-quadruplexes, were found to enhance the activity of G-quadruplex/hemin DNAzyme. However, little is known about the effect of internal parts, such as loop sequences and linkers, on the activity. In the present study, adenine repeats were incorporated into several designed G-quadruplex structures either in the loops, bulges, or linkers, and the constructed G-quadruplex/hemin DNAzyme exhibit about fivefold improvement in peroxidase-mimicking activity in some cases. The enhancement effect may result from the formation of compound I, protoporphyrin⋅Fe =O , accelerated by dA repeats, which was demonstrated by H O decay kinetics and pH dependency analysis. The novel enhancement methods described here may help in the development of high-activity DNAzymes, illustrated by a dimer G-quadruplex with flanking adenine at one end, a relatively long adenine run in one loop, and another adenine run in the linker.