Activity

ConspectusThe fundamental repeating unit of chromatin, the nucleosome, is composed of DNA wrapped around two copies each of four canonical histone proteins. Nucleosomes possess 2-fold pseudo-symmetry that is subject to disruption in cellular contexts. For example, the post-translational modification (PTM) of histones plays an essential role in epigenetic regulation, and the introduction of a PTM on only one of the two “sister” histone copies in a given nucleosome eliminates the inherent symmetry of the complex. Similarly, the removal or swapping of histones for variants or the introduction of a histone mutant may render the two faces of the nucleosome asymmetric, creating, if you will, a type of “Janus” bioparticle. Over the past decade, many groups have detailed the discovery of asymmetric species in chromatin isolated from numerous cell types. However, in vitro biochemical and biophysical investigation of asymmetric nucleosomes has proven synthetically challenging. Whereas symmetric nucleosomes are readily to biochemically interrogate a plethora of asymmetric nucleosome species. We conclude with a discussion of remaining challenges, particularly that of endogenous asymmetric nucleosome detection.Counterfeits in the supply chain of high-value advanced materials such as graphene and their derivatives have become a concerning problem with a potential negative impact on this growing and emerging industry. Recent studies have revealed alarming facts that a large percentage of manufactured graphene materials on market are not graphene, raising considerable concerns for the end users. The common and recommended methods for the characterization of graphene materials, such as transmission electron microscopy (TEM), atomic force microscopy (AFM), and Raman spectroscopy based on spot analysis and probing properties of individual graphene particles, are limited to provide the determination of the properties of “bulk” graphene powders at a large scale and the identification of non-graphene components or purposely included additives. These limitations are creating counterfeit opportunities by adding low-cost black carbonaceous materials into manufactured graphene powders. To address this problem, it is critical to have reliable characterization methods, which can probe the specific properties of graphene powders at bulk scale, confirm their typical graphene signature, and detect the presence of unwanted additional compounds, where the thermogravimetric analysis (TGA) method is one of the most promising methods to perform this challenging task. This paper presents the evaluation of the TGA method and its ability to detect low-cost carbon additives such as graphite, carbon black, biochar, and activated carbon as potential counterfeiting materials to graphene materials and their derivatives such as graphene oxide (GO) and reduced GO. The superior performance of the TGA method is demonstrated here, showing its excellent capability to successfully detect these additives when mixed with graphene materials, which is not possible by two other comparative methods (Raman spectroscopy and powder X-ray diffraction (XRD)), which are used as the common characterization methods for graphene materials.Wetting of metal surfaces plays an important role in fuel cells, corrosion science, and heat-transfer devices. It has been recently stipulated that Cu surface is hydrophobic. In order to address this issue we use high purity (1 1 1) Cu prepared without oxygen, and resistant to oxidation. Using the modern Fringe Projection Phase-Shifting method of surface roughness determination, together with a new cell allowing the vacuum and thermal desorption of samples, we define the relation between the copper surface roughness and water contact angle (WCA). Next by a simple extrapolation, we determine the WCA for the perfectly smooth copper surface (WCA = 34°). Additionally, the kinetics of airborne hydrocarbons adsorption on copper was measured. It is shown for the first time that the presence of surface hydrocarbons strongly affects not only WCA, but also water droplet evaporation and the temperature of water droplet freezing. The different behavior and features of the surfaces were observed once the atmosphere of the experiment was changed from argon to air. The evaporation results are well described by the theoretical framework proposed by Semenov, and the freezing process by the dynamic growth angle model.Cisplatin, which selectively binds to N7 atoms of purines to inhibit normal replication and transcription, is a widely applied chemotherapeutic drug in the treatment of cancer. Though direct identification of cisplatin lesions on DNA is of great significance, existing sequencing methods have issues such as complications of preamplification or enrichment-induced false-positive reports. Direct identification of cisplatin lesions by nanopore sequencing (NPS) is in principle feasible. However, relevant investigations have never been reported. By constructing model sequences (83 nucleotides in length) containing a sole cisplatin lesion, identification of corresponding lesions by NPS is achieved with less then 10 ng of input sequencing library. Moreover, characteristic high-frequency noises caused by cisplatin lesions are consistently observed during NPS, clearly identifiable in corresponding high-pass filtered traces. This feature is, however, never observed in any other combinations of natural DNA bases and could be taken as a reference to identify cisplatin lesions on DNA. Further investigations demonstrate that cisplatin stalls the replication of phi29 DNA polymerase, which appears as a ∼5 pA level fluctuation in the single-molecule resolution. These results have confirmed the feasibility of NPS to identify cisplatin lesions at the genomic level and may provide new insights into understanding the molecular mechanism of platinum-based drugs.Organic-inorganic hybrid perovskites hold great potential for various optoelectronic devices with exceptional properties. Although the direct generation of circularly polarized emission from perovskites would enable various compact devices, achieving a large degree of circular polarization (DCP) at room temperature still remains challenging. Herein, we demonstrate that DCP can be strongly enhanced at the narrow mode position of chiral Fano resonances. In our design, a perovskite film is spin-coated on a symmetry-broken structure with a relatively large feature size. A large DCP of more than 0.5 is achieved at room temperature without the direct patterning of the perovskite layer. Reciprocity calculation reveals that chiral field enhancement enables the emission of opposite helicity to couple into counter-propagating slab modes and leads to a large DCP. Our design is very general and scalable. Our work may lead to circularly polarized light sources based on various perovskite materials.Solvent engineering and antisolvent methods have been used extensively to achieve high-quality, homogeneous, and crystalline perovskite thin films. Usually, highly concentrated (>1.1 M) precursor solutions are used to achieve the maximum power conversion efficiency (PCE), and most fabrication studies focus on iodide-based metal halide perovskites (MHPs). However, high concentrations of precursors are not suitable for semitransparent (ST) MHP solar cells (STPSCs), which require thinner films to achieve a high average visible transmittance (AVT). The deposition of high-quality perovskites with variable concentrations in a one-step method is challenging due to the complexity of the antisolvent crystallization process. Here, we have developed an in situ technique based on photoluminescence (PL) measurements to identify the optimum delay time for antisolvent crystallization in formamidinium lead bromide (FAPbBr3). By monitoring the in situ PL, the nucleation, crystal growth, and early perovskite formation phases are easily identified for a range of concentrations. Subsequently, we fabricated opaque and ST solar cells with optically clear, ST perovskite films formed from precursors with varying concentrations. These all-solution-processed STPSCs achieved AVTs of up to 35.6, 42.5, and 49.2%, with the corresponding PCEs of 5.71, 3.25, and 1.86% in p-i-n type, FAPbBr3 perovskite solar cells with transparent Ag nanowire electrodes. These devices show good stability over several weeks and an impressive Voc as high as 1.24 V for STPSCs and 1.38 V for opaque cells produced with a thick Ag electrode. This work demonstrates the potential use of in situ spectroscopy to tailor the film growth of halide perovskites with varying concentrations and the feasibility of using wide-band-gap perovskites for ST solar cells with exceptional clarity and higher Voc.Chalcogenides with diamond-like (DL) structures are a treasury of infrared nonlinear optical (NLO) materials. Here, a ternary Hg-based chalcogenide with a defect DL structure, Hg3P2S8, is synthesized by solid-state reaction. D-AP5 Driven by the highly distorted [HgS4] tetrahedra, this compound displays an interesting structural symmetry degradation from tetragonal to orthorhombic compared with its analogue Zn3P2S8. Meanwhile, the overall performances of Hg3P2S8 are quite remarkable, including a very strong phase-matchable second-harmonic generation (SHG) response (4.2 × AgGaS2), large band gap (2.77 eV), wide IR transparent range (0.45-16.7 μm), and high laser-induced damage threshold (4 × AGS). Furthermore, the theoretical analysis and local dipole moment calculations elucidate that the highly distorted [HgS4] tetrahedra contribute a lot to the enhancement of the SHG effect. This discovery will motivate the exploration of other DL Hg-based chalcogenides serving as high-performing mid-IR NLO materials.Perovskite oxynitride semiconductors have attracted huge interest recently as promising photoelectrode materials for photoelectrochemical (PEC) water splitting. Depicted by, the extensive studies of the PEC activity of oxynitride powder-based photoelectrodes and/or deposited thin-film electrodes. High-crystalline-quality, oxynitride thin films grown by physical vapor deposition are ideal model systems to study the fundamental physical and chemical properties of the surface of these materials, including their evolution. In this work, using a combination of high-sensitivity low-energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS), we monitor surface evolution of LaTiOxNy (LTON) and CaNbOxNy (CNON) thin films before and after the PEC characterizations. The as-prepared epitaxial LTON films show a preferential LaO termination at the surface layers, followed by a Ti-enriched subsurface. Whereas, the polycrystalline CNON thin films exhibit a non-uniform surface, with a mixed surface termination and a significant Ca-segregated subsurface. After the PEC characterizations, additional precipitated LaO species are found on the outer surface of the LTON epitaxial films. However, no significant surface change is observed on the polycrystalline CNON films by LEIS. The XPS analysis shows, an increase of the oxidized Ti and Nb cations (Ti4+ and Nb5+) after the PEC reaction in the LTON and CNON films, respectively. The initial drops in photocurrent for the LTON and CNON films are attributed to the changes in the surface chemical status. This work provides insight into the surface characteristics and evolution of LTON and CNON oxynitride thin films as photoelectrodes for PEC applications.