An MEDT study of the mechanism and selectivities of the [3+2] cycloaddition reaction of tomentosin with benzonitrile oxide

The [3+2] cycloaddition (32CA) reaction of tomentosin with benzonitrile oxide yielding a spiro-isoxazoline has been studied within the Molecular Electron Density Theory at the B3LYP/6-31(d,p) computational level. Given the multifunctionality of tomentosin, this 32CA reaction can take place along 16 competitive reaction paths. The chemo-, regio-, and stereoisomeric reaction paths involving the two C C double bonds of tomentosin have been studied. Density functional theory (DFT) calculations account for the total chemo- and regioselectivity, in complete agreement with the experimental outcomes, being suggestive of low diastereofacial selectivity. Analysis of the conceptual DFT indices accounts for the nonpolar character of this 32CA reaction. On the other hand, the topological analysis of the electron localization function of the selected points of the intrinsic reaction coordinate associated with the formation of the C C and C O single bonds emphasizes the zw-type reactivity of the phenyl nitrile oxide; the reaction taking place through a non-concerted two-stage one-step mechanism initialized with the formation of the C C single bond involving the β-conjugated carbon of tomentosin.     

Structure-based virtual screening to identify inhibitors against Staphylococcus aureus MurD enzyme

Structural Chemistry - The MurD enzyme of Staphylococcus aureus is an attractive drug target as it is essential and ubiquitous in bacteria but absent in mammalian cells. In the present study, we...     

Rapid Photolysis-Mediated Folding of Disulfide-Rich Peptides

Structure–activity relationship studies are a highly time-consuming aspect of peptide-based drug development, particularly in the assembly of disulfide-rich peptides, which often requires multiple synthetic steps and purifications. Therefore, it is vital to develop rapid and efficient chemical methods to readily access the desired peptides. We have developed a photolysis-mediated “one-pot” strategy for regioselective disulfide bond formation. The new pairing system utilises two ortho-nitroveratryl protected cysteines to generate two disulfide bridges in less than one hour in good yield. This strategy was applied to the synthesis of complex disulfide-rich peptides such as Rho-conotoxin ρ-TIA and native human insulin.     

Influence of Alkoxy Chain Length on the Properties of Two-Dimensionally Expanded Azulene-Core-Based Hole-Transporting Materials for Efficient Perovskite Solar Cells

A series of two-dimensionally expanded azulene-core-based π systems have been synthesized with different alkyl chain lengths in the alkoxy moieties connected to the partially oxygen-bridged triarylamine skeletons. The thermal, photophysical, and electronic properties of each compound were evaluated to determine the influence of the alkyl chain length on their effectiveness as hole-transporting materials (HTMs) in perovskite solar cells (PSCs). All the synthesized molecules showed promising material properties, including high solubility, the formation of flat and amorphous films, and optimal alignment of energy levels with perovskites. In particular, the derivatives with methyl and n-butyl in the side chains retained amorphous stability up to 233 and 159 °C, respectively. Such short alkoxy chains also resulted in improved electrical device properties. The PSC device fabricated with the HTM with n-butyl side chains showed the best performance with a power conversion efficiency of 18.9 %, which compares favorably with that of spiro-OMeTAD-based PSCs (spiro-OMeTAD=2,2′,7,7′-tetrakis[N,N-bis(p-methoxyphenyl)amino]-9,9′-spirobifluorene).     

Synthesis of thioether‐functional poly(olefin)s via ruthenium‐alkylidene initiated ring‐opening metathesis polymerization

Ring‐opening metathesis polymerization (ROMP) of thioether‐derived oxanorbornene imide ( M1 ) and its copolymerization with various cycloolefin comonomers such as cyclopentene ( M2 ), cyclopent‐3‐en‐1‐ol ( M3 ), cycloheptene ( M4 ), and cyclooctene ( M5 ) using Hoveyda–Grubbs second generation catalyst has been investigated. Polymerizations were performed at two different temperatures (0 and 25 °C) and the obtained functional poly(olefin)s were characterized by nuclear magnetic resonance ¹H and ¹³C (NMR), and infrared spectroscopy as well as size exclusion chromatography, differential scanning calorimetry, and thermogravimetric analysis analyses. Additionally, the dependence of the polymer composition on the reaction temperature and monomer feed was studied with time‐dependent ¹H NMR experiments. Copolymerization of M1 with a five‐membered cycloolefin monomer M2 showed relatively low ROMP reactivity irrespective of the reaction conditions in comparison to M3 , M4 , and M5 monomers. In general, the degree of monomer incorporation into poly(olefin)s were determined in the order of M5 > M3 > M4 > M2 , and that sheds light on the effect of cycloolefin ring strain energies in the ruthenium‐alkylidene initiated ROMP. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1741–1747     

Discovery of New S‐Glycosides and N‐Glycosides of Pyridine‐biphenyl System with Antiviral Activity and Induction of Apoptosis in MCF7 Cells

Glycosylation of small molecule‐based drugs can dramatically improve the biological activities of the parent scaffold. In the current study, S‐glycosides and N‐glycosides of polyfunctionalized pyridine‐biphenyl system tethered with benzotriazole moiety were designed and synthesized. S‐Glycosides of pyridine‐2‐thione derivatives 5a – h and N‐glycosides of pyridine‐2‐one derivatives 9a , b were synthesized by a facile, convenient, and high‐yielding procedure. The epimers glucose and galactose, acetylated or deacetylated, were used to form the glycone part. The structures of these compounds were confirmed by microanalysis and spectroscopic data (IR, ¹ H–NMR, and ¹³C‐NMR). The anticancer activities of the target compounds, in comparison with standard cisplatin, were assessed by MTT assay against MCF7 cell line. Compounds 4f , 4g , 5f , and 5h exhibited the highest cytotoxic effect on MCF7. The anticancer effect of these four compounds induced the apoptosis as evident by the up‐regulated expression of the apoptotic genes Bax and p53 and down‐regulated expression of the anti‐apoptotic gene BCl₂. S‐Glycoside derivatives are more active than N‐glycosides. Moreover, the nontoxic doses of the tested compounds were evaluated in MA104, FRHK4, BGM, Hep2, and Vero cells. Compounds 4a – d and 5a – d were also evaluated for their antiviral effect against HSV‐1, HAV, and rotavirus Wa strain. The compounds' results showed less, moderated, and high antiviral activities. The docking study for these compounds with MDM2 revealed that deacetylated galactose is important for binding with the receptor as it facilitates the formation of hydrogen bond in the receptor. Rapid overlay of chemical structures analysis was employed to understand the compounds' similarity on the basis of their shape structure using the Tanimoto scores.     

Traffic-aware auto-configuration protocol for service oriented low-power and lossy networks in IoT

Wireless Networks - Many diversified services can be offered by smart objects, referred to herein by nodes, in low-power and lossy networks (LLNs) contributing to the Internet of Things (IoT). A...     

Green transmission for C-RAN based on SWIPT in 5G: a review

Wireless Networks - C-RAN is a promising new design for the next generation, an important aspect of it in the energy efficiency consideration. Hence, it is considering an innovative candidate to...     

Gaussian distribution model for gate-to-channel capacitance for carbon nanotube field-effect transistor

ABSTRACT

In this paper, a carbon nanotube (CNT) field-effect transistor gate-to-channel capacitance Gaussian distribution model is proposed. The proposed model is based on the assumption of random placement of CNTs within the channel region, in lieu of the traditional uniform distribution exhibited in the literature. The proposed model is inspired from the fact that the nanotubes in the central region along the channel that are more closely packed together yield a lower capacitance value over those that are widely spaced towards the edges. The Gaussian model as presented in this paper offers more accuracy to simulation results, where simulation results reveal that this model provides more practical answers for gate-to-channel capacitance, with higher percentages of improvement regarding energy consumption by the transistor. Moreover, the effects of several parameters such as type of material, tube diameter and the tube–gate distance have been evaluated using the proposed model.     

Relay selection schemes for secure transmission in cognitive radio networks

The security in cognitive radio networks (CRNs) has been attracting continuously growing attention due to the open and dynamic nature of cognitive radio architecture. In this paper, we propose new relay selection schemes to improve the physical layer security in CRNs. A trusted decode-and-forward relay is selected to help the secondary user (SU) transmission and improve the secrecy rate in the presence of multiple eavesdroppers and multiple primary users (PUs). The secrecy rate of the SU is characterized under both its own transmit power constraint as well as a set of interference power constraints imposed at each PU, in order to preserve its quality of service. The performance of the proposed schemes is analyzed in terms of the achievable secrecy rate and the intercept probability. Closed form expressions for the asymptotic intercept probability at high source-relays channel variances are also derived. Moreover, new derivations of some existing traditional schemes are presented and compared. The performance comparison of the proposed schemes with the schemes proposed in the literature reveals the superior of the proposed schemes.