Swarnalin and cis-swarnalin, two new tetrahydrofuran derivatives with free radical scavenging activity, from the aerial parts of Cuscuta reflexa

The reversed-phase HPLC analysis of a methanol extract of the aerial parts of Cuscuta reflexa afforded a non-separable mixture (55 : 45) of two novel tetrahydrofuran derivatives, named swarnalin (1) and cis-swarnalin (2), and a known coumarin, 5,6,7-trimethoxycoumarin (3). The structures of the compounds were elucidated unequivocally by UV, HRFABMS and a series of 1D and 2D NMR analyses. The mixture of 1 and 2 showed significant free radical scavenging activity in the DPPH assay and the RC50 value was found to be 3.80 x 10(-4) mg mL(-1) for the mixture, compared to 2.88 x 10(-5) mg mL(-1) for the positive control, quercetin.     

Intramolecular O-H...O hydrogen-bond-mediated reversal in the partitioning of conformationally restricted triplet 1,4-biradicals and amplification of diastereodifferentiation in their lifetimes

The photoreactivity and nanosecond transient phenomena have been investigated for a rationally designed set of ketones 4-9 in order to gain comprehensive insights concerning the influence of intramolecular hydrogen bonding on (i) the lifetimes of triplet 1,4-biradicals and (ii) the partitioning of the latter between cyclization and elimination. Comparisons of the photochemical results and lifetime data for the biradicals of ketones 6 versus 8 and 7 versus 9 revealed a remarkable influence of hydrogen bonding when superimposed upon steric factors: while 6 and 7 yielded cyclobutanols in poor yields, cyclization was found to be overwhelmingly predominant for 8-anti and moderately so for 9-anti, with a high stereoselectivity in the formation of cyclobutanols (>95% for 8-anti). The diastereochemistry in the case of 8 permitted the occurrence of fragmentation or cyclization almost exclusively (>90% cyclization for 8-anti and >75% elimination for 8-syn). Significantly, the intramolecular hydrogen bonding in the biradicals of 8 and 9 was found to reverse their partitioning between cyclization and elimination compared with the behavior of the biradicals of ketones 3; the ketones 8-anti and 9-anti underwent cyclization in benzene, predominantly leading to cyclobutanols with syn stereochemistry between the C2 and C3 substituents. In accordance with photoproduct profiles, an unprecedented approximately 2-fold difference in the lifetimes of the intermediate diastereomeric triplet biradicals of ketones 8 in nonpolar solvents (e.g., tau(syn) = 123 ns and tau(anti) = 235 ns in cyclohexane) was observed via nanosecond laser flash photolysis, while no such difference in lifetimes was found for the triplet biradicals of acetoxy ketones 9. The intriguing diastereodifferentiation in the lifetimes of the diastereomeric triplet 1,4-biradicals of 8 and the product profiles of ketones 6, 7, and 9 are best reconciled via a unified mechanistic picture in which superposition of steric factors over varying magnitudes of O-H...O hydrogen bonding selectively facilitates a particular pathway. In particular, the diastereodifferentiation in the photochemical outcomes for the diastereomers of ketone 8 and in the lifetimes of their triplet biradicals can be understood on the basis of rapid deactivation of the 8-syn triplet biradical via fragmentation and slow cyclization of the 8-anti triplet biradical from chair- and twist-boat-like hydrogen-bonded conformations, respectively. The photolysis in polar aprotic solvents such as DMSO and pyridine was found to reverse the chemoselectivity, yielding reactivity paralleling that of ketones 3, for which the steric factors between the C2 and C3 substituents control the photochemical outcome.     

Redetermination of ternifoline‐C at 150 K

The relative stereochemistry of ternifoline‐C (7,20‐epoxy‐ent‐kaur‐16‐ene‐1,6,7,15‐tetrol 1‐acetate), C₂₂H₃₂O₆, previously reported by Wu [FudanXuebaoZir. Kex. (1988), 27 , 61–65], has been redetermined at 150 K. The molecular geometry and crystal packing agree well with the previous study.     

Signature of chaos and multistability in a Thomas-Fermi plasma

The European Physical Journal Special Topics - We propose a dynamical system governing from the nonlinear extension of the electrostatic ion-acoustic waves (IAWs) under the influence of external...     

Hydrothermal synthesis of highly crystalline nanotubes/nanoplates of pure and silver-doped anatase-titania using acid-catalyst-modified sol–gel precursors

Journal of Sol-Gel Science and Technology - Highly crystalline nanotubes/nanoplates of pure and Ag-doped anatase-titania (TiO2) having high aspect-ratio have been synthesized, without the...     

Assimilation of fuzzy clustering approach and EHO‐Greedy algorithm for efficient routing in WSN

The problems related to energy consumption and improvement of the network lifetime of WSN (wireless sensor network) have been considered. The base station (BS) location is the main concern in WSN. BSs are fixed, yet, they have the ability to move in some situations to collect the information from sensor nodes (SNs). Recently, introducing mobile sinks to WSNs has been proved to be an efficient way to extend the lifespan of the network. This paper proposes the assimilation of the fuzzy clustering approach and the Elephant Herding Optimization (EHO)‐Greedy algorithm for efficient routing in WSN. This work considers the separate sink nodes of a fixed sink and movable sink to decrease the utilization of energy. A fixed node is deployed randomly across the network, and the movable sink node moves to different locations across the network for collecting the data. Initially, the number of nodes is formed into the multiple clusters using the enhanced expectation maximization algorithm. After that, the cluster head (CH) selection done through a fuzzy approach by taking the account of three factors of residual energy, node centrality, and neighborhood overlap. A suitable collection of CH can extremely reduce the utilization of energy and also enhancing the lifespan. Finally, the routing protocol of the hybrid EHO‐Greedy algorithm is used for efficient data transmission. Simulation results display that the proposed technique is better to other existing approaches in regard to energy utilization and the system lifetime.     

Dual Reactivity of 1,2,3,4‐Tetrazole: Manganese‐Catalyzed Click Reaction and Denitrogenative Annulation

A general catalytic method using a Mn‐porphyrin‐based catalytic system is reported that enables two different reactions (click reaction and denitrogenative annulation) and affords two different classes of nitrogen heterocycles, 1,5‐disubstituted 1,2,3‐triazoles (with a pyridyl motif) and 1,2,4‐triazolo‐pyridines. Mechanistic investigations suggest that although the click reaction likely proceeds through an ionic mechanism, which is different from the traditional click reaction, the denitrogenative annulation reaction likely proceeds via an electrophilic metallonitrene intermediate rather than a metalloradical intermediate. Collectively, this method is highly efficient and offers several advantages over other methods. For example, this method excludes a multi‐step synthesis of the N‐heterocyclic molecules described and produces only environmentally benign N₂ gas a by‐product.     

Nodosin

Nodosin, or 13-deoxy-5β-hydroxyenmein, C₂₀H₂₆O₆, has been established as a pentacyclic 6,7-seco-ent-kaurane diterpenoid with an enmein skeleton. Two independent intermolecular O—H⃛O hydrogen bonds are present and link each mol­ecule to four neighbours.     

Tuning of nonvolatile bipolar memristive switching in Co(III) polymer with an extended azo aromatic ligand

We have fabricated a unique memristive device by molecular engineering and demonstrated that the leakage current tuning in the device is 100 times more efficient than that in a standard device. Molecular analogs of the memristive matrices used here are an electrochemically active conjugated Co(III) polymer (CP) and a nonconjugated Co(III) polymer (NCP), which have been synthesized in good yield and characterized by (1)H NMR spectroscopy. Redox switching of an organic-metallic hybrid polymer generates bistable states with a large ON/OFF ratio that supports random flip-flops for several hours. Thus, we provide a synthetic solution to leakage current restriction, one of the fundamental problems faced when fabricating state-of-the-art electronic devices.