Cephanolides A–D are cephalotane-type diterpenoids featuring a novel 6/6/6/5 tetracyclic core embedded with a bridged δ-lactone. The asymmetric and divergent total syntheses of cephanolides A–D have ...been accomplished, proceeding in 11–14 steps from a known alcohol. The salient features of the present work include (i) a substrate-controlled diastereoselective intermolecular Diels–Alder reaction to form the 6–6 cis-fused rings, (ii) a palladium-catalyzed formal bimolecular 2 + 2 + 2 cycloaddition reaction via a partially intermolecular cascade reaction sequence involving multiple carbometalations to rapidly install the key tetracyclic skeleton, and (iii) lactonization and late-stage oxidative diversification to complete total syntheses of the four benzenoid cephanolides.
Abstract Tetraglycidyl diamino diphenyl methane (TGDDM) and its carbon fiber composite are widely studied and used because of their heat resistance and high performance. In order to obtain efficient ...reinforcing effects in a simple manner, we adopt the idea of molecular composite—uniformly dispersing the rigid‐rod macromolecules in the TGDDM matrix. Herein, we prepared fully aminated‐poly( p ‐phenylene terephthalamide) by direct polycondensation and hydrogenation reduction as the reinforcing agent. The fully aminated‐PPTA is distributed uniformly in the cross‐linked epoxy resin (EP) network by chemical bonds, and achieves efficient reinforcement. With the addition of only 0.5 wt% fully aminated‐PPTA, the tensile strength and Young's modulus of EP are improved to 127.7 ± 7.4 MPa (+28%) and 3.36 ± 0.15 GPa (+44%); the flexural strength and modulus are improved to 209.6 ± 9.4 MPa (+42%) and 3.70 ± 0.14 GPa (+37%); the notch impact strength is improved by 32%. Crucially, the heat resistance of EP almost remains unchanged. Furthermore, the flexural properties and interlaminar shear strength of the carbon fiber composite are also comprehensively increased. Compared with other modified fillers, the fully aminated‐PPTA is simple to prepare and blend, and is an efficient reinforcing agent for TGDDM and its carbon fiber composite benefitting from its rigid‐rod main chain and amino side groups. Highlights Molecular composite can achieve excellent strengthen and toughen effects. Fully aminated‐PPTA is embedded uniformly in EP network by chemical bonds. TGDDM is effectively reinforced without deteriorated heat resistance. Fully aminated‐PPTA is also a comprehensive reinforcement for EP/CF composite.
•Histone modification is an important mechanism that regulates chromatin dynamics and accessibility.•Histone ubiquitylation mainly occurs on H2A and H2B.•H2A ubiquitylation is induced by DNA damage, ...and functions in recruiting downstream DDR proteins.•H2B ubiquitylation and deubiquitylation are important for double strand break repair and transcription-coupled repair, respectively.
DNA in human cells is constantly assaulted by endogenous and exogenous DNA damaging agents. It is vital for the cell to respond rapidly and precisely to DNA damage to maintain genome integrity and reduce the risk of mutagenesis. Sophisticated reactions occur in chromatin surrounding the damaged site leading to the activation of DNA damage response (DDR), including transcription reprogramming, cell cycle checkpoint, and DNA repair. Histone proteins around the DNA damage play essential roles in DDR, through extensive post-translational modifications (PTMs) by a variety of modifying enzymes. One PTM on histones, mono-ubiquitylation, has emerged as a key player in cellular response to DNA damage. In this review, we will (1) briefly summarize the history of histone H2A and H2B ubiquitylation (H2Aub and H2Bub, respectively), (2) discuss their roles in transcription, and (3) their functions in DDR.
Graphdiyne (GD), a novel carbon allotrope with a 2D structure comprising benzene rings and carbon–carbon triple bonds, is successfully integrated with ZnO nanoparticles by a wet chemistry method. An ...ultraviolet photodetector based on these graphdiyne:ZnO nanocomposites exhibits significantly enhanced performance in comparison with a conventional ZnO device. GD may have diverse applications in future optoelectronics.
Due to their wide tunable bandgaps, high absorption coefficients, easy solution processabilities, and high stabilities in air, lead sulfide (PbS) quantum dots (QDs) are increasingly regarded as ...promising material candidates for next‐generation light, low‐cost, and flexible photodetectors. Current single‐layer PbS‐QD photodetectors suffer from shortcomings of large dark currents, low on–off ratios, and slow light responses. Integration with metal nanoparticles, organics, and high‐conducting graphene/nanotube to form hybrid PbS‐QD devices are proved capable of enhancing photoresponsivity; but these approaches always bring in other problems that can severely hamper the improvement of the overall device performance. To overcome the hurdles current single‐layer and hybrid PbS‐QD photodetectors face, here a bilayer QD‐only device is designed, which can be integrated on flexible polyimide substrate and significantly outperforms the conventional single‐layer devices in response speed, detectivity, linear dynamic range, and signal‐to‐noise ratio, along with comparable responsivity. The results which are obtained here should be of great values in studying and designing advanced QD‐based photodetectors for applications in future flexible optoelectronics.
A bilayer lead‐sulfide‐quantum‐dot‐only photodetector is designed, which significantly outperforms conventional single‐layer devices in response speed, detectivity, linear dynamic range, and signal‐to‐noise ratio. Careful investigation finds that junction‐controlled carrier separation and recombination is responsible for the superiority of the bilayer device. The bilayer devices also signal their great potential in future flexible optoelectronics.
The rapid and sensitive detection of trace‐level viruses in a simple and reliable way is of great importance for epidemic prevention and control. Here, a multi‐functionalized floating gate carbon ...nanotube field effect transistor (FG‐CNT FET) based biosensor is reported for the single virus level detection of SARS‐CoV‐2 virus antigen and RNA rapidly with a portable sensing platform. The aptamers functionalized sensors can detect SARS‐CoV‐2 antigens from unprocessed nasopharyngeal swab samples within 1 min. Meanwhile, enhanced by a multi‐probe strategy, the FG‐CNT FET‐based biosensor can detect the long chain RNA directly without amplification down to single virus level within 1 min. The device, constructed with packaged sensor chips and a portable sensing terminal, can distinguish 10 COVID‐19 patients from 10 healthy individuals in clinical tests both by the RNAs and antigens by a combination detection strategy with an combined overall percent agreement (OPA) close to 100%. The results provide a general and simple method to enhance the sensitivity of FET‐based biochemical sensors for the detection of nucleic acid molecules and demonstrate that the CNT FG FET biosensor is a versatile and reliable integrated platform for ultrasensitive multibiomarker detection without amplification and has great potential for point‐of‐care (POC) clinical tests.
A multi‐probe functionalized floating gate carbon nanotube field effect transistor (FG‐CNT FET) based biosensor is reported for the on‐site single virus level detection of SARS‐CoV‐2 with a portable sensing system. The biosensors can detect SARS‐CoV‐2 antigens and the unamplified long chain RNA down to 0.05 copies µL−1 within 1 min by using multi‐probes to enhance the sensitivity and clinical accuracy.
Helix-distorting DNA lesions, including ultraviolet (UV) light-induced damage, are repaired by the global genomic-nucleotide excision repair (GG-NER) and transcription coupled-nucleotide excision ...repair (TC-NER) pathways. Previous studies have shown that histone post-translational modifications (PTMs) such as histone acetylation and methylation can promote GG-NER in chromatin. Whether histone PTMs also regulate the repair of DNA lesions by the TC-NER pathway in transcribed DNA is unknown. Here, we report that histone H3 K36 methylation (H3K36me) by the Set2 histone methyltransferase in yeast regulates TC-NER. Mutations in Set2 or H3K36 result in UV sensitivity that is epistatic with Rad26, the primary TC-NER factor in yeast, and cause a defect in the repair of UV damage across the yeast genome. We further show that mutations in Set2 or H3K36 in a GG-NER deficient strain (i.e., rad16Δ) partially rescue its UV sensitivity. Our data indicate that deletion of SET2 rescues UV sensitivity in a GG-NER deficient strain by activating cryptic antisense transcription, so that the non-transcribed strand (NTS) of yeast genes is repaired by TC-NER. These findings indicate that Set2 methylation of H3K36 establishes transcriptional asymmetry in repair by promoting canonical TC-NER of the transcribed strand (TS) and suppressing cryptic TC-NER of the NTS.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We present the results of a thorough study of wet chemical methods for transferring chemical vapor deposition grown graphene from the metal growth substrate to a device-compatible substrate. On the ...basis of these results, we have developed a “modified RCA clean” transfer method that has much better control of both contamination and crack formation and does not degrade the quality of the transferred graphene. Using this transfer method, high device yields, up to 97%, with a narrow device performance metrics distribution were achieved. This demonstration addresses an important step toward large-scale graphene-based electronic device applications.
Cisplatin is a chemotherapeutic drug used for the treatment of a number of cancers. The efficacy of cisplatin relies on its binding to DNA and the induction of cytotoxic DNA damage to kill cancer ...cells. Cisplatin-based therapy is best known for curing testicular cancer; however, treatment of other solid tumors with cisplatin has not been as successful. Pre-clinical and clinical studies have revealed nucleotide excision repair (NER) as a major resistance mechanism against cisplatin in tumor cells. NER is a versatile DNA repair system targeting a wide range of helix-distorting DNA damage. The NER pathway consists of multiple steps, including damage recognition, pre-incision complex assembly, dual incision, and repair synthesis. NER proteins can recognize cisplatin-induced DNA damage and remove the damage from the genome, thereby neutralizing the cytotoxicity of cisplatin and causing drug resistance. Here, we review the molecular mechanism by which NER repairs cisplatin damage, focusing on the recent development of genome-wide cisplatin damage mapping methods. We also discuss how the expression and somatic mutations of key NER genes affect the response of cancer cells to cisplatin. Finally, small molecules targeting NER factors provide important tools to manipulate NER capacity in cancer cells. The status of research on these inhibitors and their implications in cancer treatment will be discussed.
High-density semiconducting aligned carbon nanotube (A-CNT) arrays have been demonstrated with wafer-scale preparation of materials and have shown high performance in P-type field-effect transistors ...(FETs) and great potential for applications in future digital integrated circuits (ICs). However, high-performance N-type FETs (N-FETs) have not yet been implemented with A-CNTs, making development of complementary metal-oxide–semiconductor (CMOS) technology, a necessary component for modern digital ICs, impossible. In this work, we reveal the mechanism hindering the realization of A-CNT N-FETs contacted by low-work-function metals and develop corresponding solutions to promote the performance of N-FETs to that of P-type FETs (P-FETs). The fabricated scandium (Sc)-contacted A-CNT N-FET with a 100 nm gate length exhibits an on-state current (I on) of 800 μA/μm and a peak transconductance (g m) of 250 μS/μm, representing the highest performance of CNT-based N-FETs to date. Moreover, CMOS technology has been developed to realize N- and P-FETs with symmetric high performance based on A-CNTs. The fabricated A-CNT CMOS FETs show electron and hole mobilities of 325 and 241 cm2 V–1 s–1, respectively, which are slightly higher than the corresponding values of Si CMOS transistors. Our scalable fabrication of A-CNT CMOS FETs with comparable electronic performance to Si CMOS will promote the application of CNT-based electronics in digital ICs.
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