Association of Radical Chemistry with LanD Flavoprotein Activity for C-Terminal Macrocyclization of a Ribosomal Peptide by Formation of an Unsaturated Thioether Residue.

LanD flavoproteins catalyze oxidative decarboxylation of the C-terminal Cys residue of a peptide to produce an enethiol. This enethiol is highly reactive and can be coupled with an upstream dehydroamino acid through Michael addition to form S-[2-aminovinyl](3-methyl)cysteine, an unsaturated thioether residue known to be characteristic of an array of C-terminally macrocyclized, ribosomally synthesized and posttranslationally modified peptides (RiPPs). Based on a two-stage bioinformatics mining of posttranslational modifications (PTMs) related to C-terminal Cys processing, we report herein that LanD activity can couple with radical S-adenosylmethionine chemistry to provide a new unsaturated thioether residue, S-[2-aminovinyl]-3-carbamoylcysteine, by conjugating the resultant enethiol with Cß of the Asn residue in the C-terminal NxxC motif of a peptide for macrocyclization. This study furthers our understanding of the variety of PTMs involved in creating the structure diversity of macrocyclic RiPPs.

Three-Dimensional Insights into Interfacial Segregation at the Atomic Scale in a Nanocrystalline Glass-Ceramic.

The distribution of dopant atoms plays a key role in the effectiveness of doping, thereby requiring delicate characterizations. In this study, we found that energy-dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS) techniques in scanning transmission electron microscopy (STEM) were not adequate to reveal the distribution of yttrium and the chemical composition of the ZrO2/SiO2 heterophase interface in an yttrium-doped ZrO2-SiO2 nanocrystalline glass-ceramic. Atom probe tomography (APT) is rarely utilized to characterize ceramics due to some inherent difficulties. However, we successfully revealed the three-dimensional distribution of ZrO2 nanocrystallites and SiO2 matrix at the atomic scale with APT under optimized and well-controlled conditions. We also found that the ZrO2 nanocrystallites had a special core-shell structure, with a thin Zr/Si interfacial layer as a shell and a ZrO2 solid solution as a core. Yttrium dopants showed interfacial segregation at both ZrO2 grain boundaries and the ZrO2/SiO2 heterophase interfaces.

Novel oligomeric neolignans with PTP1B inhibitory activity from the bark of Magnolia officinalis var. biloba.

The barks of Magnolia officinalis var. biloba, Magnoliae cortex, have been used as traditional Chinese medicines for several centuries. In this study, phytochemical investigation of M. officinalis var. biloba bark extract afforded five pairs of novel enantiomeric oligomeric neolignans, (±)-mooligomers A-E (1-5). (±)-1 and (±)-2 were two diastereomeric pairs of enantiomers with six C6-C3 subunits, and (±)-4 was a pair of previously unreported tetrameric neolignans bearing eight C6-C3 subunits. (±)-5 is the first example of a naturally occurring trilignan featuring an eight-membered ring with a magnolol moiety. The absolute configurations of (±)-1-(±)-5 were elucidated on the basis of HRESIMS, 1D and 2D NMR spectroscopy and electronic circular dichroism (ECD) calculations. Among the compounds tested for their PTP1B inhibitory activities, (±)-2, (±)-4 and (±)-5 displayed significant PTP1B inhibitory activities with IC50 values of 0.14-2.10 µM. Furthermore, a Molecular docking simulation of PTP1B and active compounds [(±)-2, (±)-4 and (±)-5] exhibited that these active compounds possess low binding affinities ranging from - 5.9 to - 7.7 kcal/mol.

Magmenthanes A-H: Eight new meroterpenoids from the bark of Magnolia officinalis var. Biloba.

Eight new meroterpenoids with different types of monoterpene units, namely, magmenthanes A-H (1-8), were identified from the bark of Magnolia officinalis var. biloba. Magmenthane A (1) possesses a 1,3-dioxabicyclo [4.3.01,5] nonane skeleton, 1-5 possess five pairs of enantiomers and 6 possesses a 1,1'-diallyl-biphenyl fragment. The structures of 1-8 were elucidated on the basis of 1D and 2D NMR, HRESIMS and electronic circular dichroism (ECD) calculations. Compounds 5 and 8 displayed significant PTP1B inhibitory activities with IC50 values of 4.38 and 3.88 µM, respectively.

Two new saponins from the leaves of Panax notoginseng.

Two new saponins, notoginsenosides Ng1 (1) and Ng2 (2), together with seven known compounds (3-9), were isolated from the leaves of Panax notoginseng. Their structures were elucidated by UV, IR, HRESIMS, and NMR experiments. Compounds 6 and 7 showed moderate cytotoxic activities against HCT-116, with IC50 values of 4.98 and 0.64 µmol/L, respectively.

Hepatoprotective glycosides from the rhizomes of Imperata cylindrical.

Three new C-methylated phenylpropanoid glycosides (1, 2), a new 8-4'-oxyneolignan (3), together with two known analogs (4, 5), were isolated from the rhizomes of Imperata cylindrical Beauv. var. major (Nees) C. E. Hubb. Their structures were determined by spectroscopic and chemical methods. Compounds 1, 2, and 5 (10 µM) exhibited pronounced hepatoprotective activity against N-acetyl-p-aminophenol (APAP)-induced HepG2 cell damage in vitro assays. Furthermore, their antioxidant activities against Fe2+-cysteine-induced rat liver microsomal lipid peroxidation and the effects on the secretion of TNF-α in murine peritoneal macrophages (RAW264.7) induced by lipopolysaccharides were evaluated.

Detection of Deepfake Videos Using Long-Distance Attention.

With the rapid progress of deepfake techniques in recent years, facial video forgery can generate highly deceptive video content and bring severe security threats. And detection of such forgery videos is much more urgent and challenging. Most existing detection methods treat the problem as a vanilla binary classification problem. In this article, the problem is treated as a special fine-grained classification problem since the differences between fake and real faces are very subtle. It is observed that most existing face forgery methods left some common artifacts in the spatial domain and time domain, including generative defects in the spatial domain and interframe inconsistencies in the time domain. And a spatial-temporal model is proposed which has two components for capturing spatial and temporal forgery traces from a global perspective, respectively. The two components are designed using a novel long-distance attention mechanism. One component of the spatial domain is used to capture artifacts in a single frame, and the other component of the time domain is used to capture artifacts in consecutive frames. They generate attention maps in the form of patches. The attention method has a broader vision which contributes to better assembling global information and extracting local statistic information. Finally, the attention maps are used to guide the network to focus on pivotal parts of the face, just like other fine-grained classification methods. The experimental results on different public datasets demonstrate that the proposed method achieves state-of-the-art performance, and the proposed long-distance attention method can effectively capture pivotal parts for face forgery.

Towards JPEG-Resistant Image Forgery Detection and Localization Via Self-Supervised Domain Adaptation.

With wide applications of image editing tools, forged images (splicing, copy-move, removal and etc.) have been becoming great public concerns. Although existing image forgery localization methods could achieve fairly good results on several public datasets, most of them perform poorly when the forged images are JPEG compressed as they are usually done in social networks. To tackle this issue, in this paper, a self-supervised domain adaptation network, which is composed of a backbone network with Siamese architecture and a compression approximation network (ComNet), is proposed for JPEG-resistant image forgery detection and localization. To improve the performance against JPEG compression, ComNet is customized to approximate the JPEG compression operation through self-supervised learning, generating JPEG-agent images with general JPEG compression characteristics. The backbone network is then trained with domain adaptation strategy to localize the tampering boundary and region, and alleviate the domain shift between uncompressed and JPEG-agent images. Extensive experimental results on several public datasets show that the proposed method outperforms or rivals to other state-of-the-art methods in image forgery detection and localization, especially for JPEG compression with unknown QFs.

Secure Halftone Image Steganography Based on Feature Space and Layer Embedding.

Syndrome-trellis codes (STCs) are commonly used in image steganographic schemes, which aim at minimizing the embedding distortion, but most distortion models cannot capture the mutual interaction of embedding modifications (MIEMs). In this article, a secure halftone image steganographic scheme based on a feature space and layer embedding is proposed. First, a feature space is constructed by a characterization method that is designed based on the statistics of 4 ×4 pixel blocks in halftone images. Upon the feature space, a generalized steganalyzer with good classification ability is proposed, which is used to measure the embedding distortion. As a result, a distortion model based on a hybrid feature space is constructed, which outperforms some state-of-the-art models. Then, as the distortion model is established on the statistics of local regions, a layer embedding strategy is proposed to reduce MIEM. It divides the host image into multiple layers according to their relative positions in 4 ×4 blocks, and the embedding procedure is executed layer by layer. In each layer, any two pixels are located at different 4 ×4 blocks in the original image, and the distortion model makes sure that the calculation of pixel distortions is independent. Between layers, the pixel distortions of the current layer are updated according to the previous embedding modifications, thus reducing the total embedding distortion. Comparisons with prior schemes demonstrate that the proposed steganographic scheme achieves high statistical security when resisting the state-of-the-art steganalysis.

Robust Estimation of Upscaling Factor on Double JPEG Compressed Images.

As one of the most important topics in image forensics, resampling detection has developed rapidly in recent years. However, the robustness to JPEG compression is still challenging for most classical spectrum-based methods, since JPEG compression severely degrades the image contents and introduces block artifacts in the boundary of the compression grid. In this article, we propose a method to estimate the upscaling factors on double JPEG compressed images in the presence of image upscaling between the two compressions. We first analyze the spectrum of scaled images and give an overall formulation of how the scaling factors along with the parameters of JPEG compression and image contents influence the appearance of tampering artifacts. The expected positions of five kinds of characteristic peaks are analytically derived. Then, we analyze the features of double JPEG compressed images in the block discrete cosine transform (BDCT) domain and present an inverse scaling strategy for the upscaling factor estimation with a detailed proof. Finally, a fusion method is proposed that through frequency-domain analysis, a candidate set of upscaling factors is given, and through analysis in the BDCT domain, the optimal estimation from all candidates is determined. The experimental results demonstrate that the proposed method outperforms other state-of-the-art methods.

Deep Learning-Based Forgery Attack on Document Images.

With the ongoing popularization of online services, the digital document images have been used in various applications. Meanwhile, there have emerged some deep learning-based text editing algorithms which alter the textual information of an image in an end-to-end fashion. In this work, we present a low-cost document forgery algorithm by the existing deep learning-based technologies to edit practical document images. To achieve this goal, the limitations of existing text editing algorithms towards complicated characters and complex background are addressed by a set of network design strategies. First, the unnecessary confusion in the supervision data is avoided by disentangling the textual and background information in the source images. Second, to capture the structure of some complicated components, the text skeleton is provided as auxiliary information and the continuity in texture is considered explicitly in the loss function. Third, the forgery traces induced by the text editing operation are mitigated by some post-processing operations which consider the distortions from the print-and-scan channel. Quantitative comparisons of the proposed method and the exiting approach have shown the advantages of our design by reducing the about 2/3 reconstruction error measured in MSE, improving reconstruction quality measured in PSNR and in SSIM by 4 dB and 0.21, respectively. Qualitative experiments have confirmed that the reconstruction results of the proposed method are visually better than the existing approach in both complicated characters and complex texture. More importantly, we have demonstrated the performance of the proposed document forgery algorithm under a practical scenario where an attacker is able to alter the textual information in an identity document using only one sample in the target domain. The forged-and-recaptured samples created by the proposed text editing attack and recapturing operation have successfully fooled some existing document authentication systems.

Chemical constituents of Psidium guajava leaves and their antibacterial activity.

Seven undescribed compounds, namely (+)-psiflavanone A, (-)-psiflavanone A, (+)-psiflavanone B, (-)-psiflavanone B, (+)-psiketide, (-)-psiketide, and psidinone, were isolated and chirally separated from the 95%-ethanol extract of Psidium guajava leaves. (+)/(-)-Psiflavanone A and (+)/(-)-psiflavanone B are two pairs of rare enantiomeric C-benzoylated flavanones isolated from the title plant for the first time. (+)/(-)-Psiketide are a pair of enantiomeric aromatic polyketides, and psidinone is the first example of a C18 phenanthrenediquinone with an angle-type 6/6/6 tricyclic skeleton. Their structures were identified by extensive analysis of HRESIMS, UV, IR, NMR, and calculated electronic circular dichroism (ECD) data. Particularly, the structures of (+)-psiflavanone A, (-)-psiflavanone A, (+)-psiflavanone B, and psidinone were further confirmed by X-ray diffraction. Psidinone exhibited antibacterial activity against Staphylococcus aureus, Staphylococcus epidermidis, and Mycobacterium Smegmatis mc2 155, with minimum inhibitory concentrations (MICs) of 16, 8, and 0.5 µM, respectively. These results not only highlight the chemical diversity and biological activity of P. guajava but are also expected to pave way for its further expansion to other applications in future.

Discovery of eudesmane-type sesquiterpenoids with neuroprotective effects from the roots of Chloranthus serratus.

Seven eudesmane-type sesquiterpenoids, including three pairs of racemic compounds (1a-3a and 1b-3b) and a sesquiterpenoid lactone (4), were obtained from the roots of Chloranthus serratus. The structures of these sesquiterpenoids were characterized based on spectroscopic analyses, ECD calculations, and X-ray diffraction experiment. Neuroprotection assays of the isolated eudesmane-type sesquiterpenoids were conducted on H2O2 damaged PC12 cells. At the concentration of 10 µM, compounds 1b and 4 increased cell viability from 54.8 ± 3.3% to 76.8 ± 2.3 and 72.7 ± 8.2%, respectively.

New amide alkaloids and carbazole alkaloid from the stems of Clausena lansium.

Five unreported alkaloids including four amide alkaloids (1a, 2a, 3a, and 3b) and one carbazole alkaloid (4) with two known compounds (1b, 2b) were obtained from the stems of Clausena lansium. Their structures were demonstrated by spectroscopic experiments. And the absolute configurations of compounds 1a, 1b, 2b, and 3b were determined by single X-ray diffraction analysis. The neuroprotection assay showed that compound 4 had moderate inhibition effect on PC12 cells induced by serum withdrawal at the concentration of 10 µM. And compounds 1a and 4 had weak protective effects on primary neurons against oxygen glucose deprivation injury at the concentration of 10 µM.

Neuroprotective triterpene saponins from the leaves of Panax notoginseng.

Two new triterpene saponins, namely notoginsenoside Ng5 (1) and notoginsenoside Ng6 (2) were isolated from the leaves of Panax notoginseng, along with five known ones. Their structures were determined by chemical methods, NMR and X-ray experiments. The absolute configuration of compound 3 with four sugar units was confirmed by single crystal X-ray analysis. Compounds 2-4 and 6 inhibited PC12 cell damage induced by serum deprivation, and increased cell viability from 58.7 ± 6.7% to 66.7 ± 4.5%, 76.1 ± 6.1%, 64.7 ± 5.2% and 67.2 ± 5.0% at 10 µM, respectively.

Sesquiterpenoids with neuroprotective activities from the Chloranthaceae plant Chloranthus henryi.

A rare sesquiterpenoid possessing a 6/6 bicyclic system fused with two clustered furan units and a pair of guaiane-type sesquiterpenoids were acquired from the roots of Chloranthus henryi. Their structures with absolute configurations were characterized with spectroscopic data, ECD, and X-ray diffraction analysis. All three sesquiterpenoids showed moderate neuroprotective activities on PC12 cells damaged with hydrogen peroxide.

Oxygen Defects in ß-MnO2 Enabling High-Performance Rechargeable Aqueous Zinc/Manganese Dioxide Battery.

Rechargeable aqueous Zn/manganese dioxide (Zn/MnO2) batteries are attractive energy storage technology owing to their merits of low cost, high safety, and environmental friendliness. However, the ß-MnO2 cathode is still plagued by the sluggish ion insertion kinetics due to the relatively narrow tunneled pathway. Furthermore, the energy storage mechanism is under debate as well. Here, ß-MnO2 cathode with enhanced ion insertion kinetics is introduced by the efficient oxygen defect engineering strategy. Density functional theory computations show that the ß-MnO2 host structure is more likely for H+ insertion rather than Zn2+, and the introduction of oxygen defects will facilitate the insertion of H+ into ß-MnO2. This theoretical conjecture is confirmed by the capacity of 302 mA h g-1 and capacity retention of 94% after 300 cycles in the assembled aqueous Zn/ß-MnO2 cell. These results highlight the potentials of defect engineering as a strategy of improving the electrochemical performance of ß-MnO2 in aqueous rechargeable batteries.

Neuroprotective racemic germacranolides from the roots of Chloranthus henryi.

Three pairs of new germacranolides, (+)/(-)-chlogermacrones A-C, along with two known analogues were obtained from the roots of Chloranthus henryi. Spectroscopic techniques and single-crystal X-ray crystallographic analyses were used for the structure elucidation of the compounds. All of the isolated compounds were tested for their neuroprotective effects on H2O2 damaged PC12 cells, compounds 3 and 5 increased cell viability from 43.4 ± 1.3% to 99.6 ± 8.7 and 68.1 ± 4.8% at 10 µM, respectively.

Dihydroagarofuran sesquiterpenoids esterified with organic acids from the leaves of Tripterygium wilfordii.

Six new and one known dihydroagarofuran sesquiterpenoids esterified with organic acids were obtained from the leaves of Tripterygium wilfordii. Spectroscopic techniques (UV, IR, MS, NMR, ORD and CD) were used for the structure elucidation of the compounds. The structures of compounds 1 and 2 were confirmed by X-ray single crystallographic analyses. The inhibitory effects on NO production in LPS-induced macrophages of 1-7 were conducted. At 10 µmol/L, compounds 1, 2 and 7 showed moderate inhibitory effects on NO production in LPS-induced macrophages with inhibitory rate at 31.2 ±â€¯3.6, 40.9 ±â€¯4.3, and 66.79 ±â€¯3.1%, respectively.

Cytotoxic 9,19-cycloartane Triterpenoids from the Roots of Actaea dahurica.

Eight undescribed 9,19-cycloartane type triterpenoid glycosides (cimdalglnoside A-H) and ten known analogues were obtained from the phytochemical research on the roots of Actaea dahurica (syn. Cimicifuga dahurica). All compounds were characterised by spectroscopic experiments, and chemical method. All the compounds isolated were assayed for cytotoxicity to five human cancer cell lines. Cimdalglnoside G showed promising cytotoxicities against Hela, and MCF-7 cell lines with IC50 values at 7.7 and 12.2 µM.