CHARACTERIZATION OF BIOACTIVE PHYTOCHEMICALS FROM THE STEM BARK OF AFRICAN MAHOGANY Khaya senegalensis (MELIACEAE)

ABSTRACT African mahogany Khaya senegalensis (Desr.) A. Juss (Meliaceae) is a large tree growing mainly in the sub-Saharan savannah forests from Senegal to Uganda. This plant is one of the most popular medicinal meliaceous plants in traditional African remedies, used as a bitter tonic, folk and popular medicine against malaria, fever, mucous diarrhea, and venereal diseases as well as an anthelmintic and a taeniacide remedy. Its extracts and chemical constituents have been the subject of extensive phytochemical and pharmacological investigations since 1960s. Anti-inflammatory, anti-bacterial, anthelmintic, and antiplasmodial activities of plant extracts have been reported. Limonoids with anti-feeding, feeding deterrent and growth inhibitory properties, anti-fungal, and anti-sickling activity, as well as dimeric flavonoids with immunostimulating activity have been isolated from different parts of this plant. However, none of extracts or pure chemicals has been screened for biological activity such as antioxidant activity and anti-proliferative capacity against human cancer cell lines. Therefore, the main object of this study was to screen bioactive ingredients with anticancer and antioxidant activities from the plant through purification, isolation, structural elucidation, and bioassays. Eleven natural products were isolated from the methanolic extract of stem bark of Khaya senegalensis after extraction and purification, especially through crystallization and modern column chromatographic techniques using normal phase and reverse phase silica gel columns, Sephadex LH-20, MCI CHP20P, prep-HPLC, etc. Their structures were determined to be two ring D-seco limonoids 3, 7-dideacetylkhivorin (1) and 1, 3, 7-trideacetylkhivorin (2), mexicanoloid limonoid khayanone (3), five khayanolide limonoids 1-O-deacetylkhayanolide B (4), khayanolide B (5), khayanolide E (6), 1-O-deacetylkhayanolide E (7), and novel 6-dehydroxykhayanolide E (8), three lignans (-)-lyoniresinol (9), (-)-lyoniresin-9-yl-D-xylopyranoside (10), and (-)-lyoniresin-4\u27-yl-D-glucopyranoside (11), respectively, through various spectroscopic methods including IR, EI-MS (HREI-MS), LC-ESI-MS (accurate ESI-MS), extensive 1D and 2D NMR (1H , 13C, DEPT, 1H-1H COSY, HMQC or HSQC, HMBC, NOESY), and X-ray diffraction experiments. The structures and stereochemistry of 1, 2, 3, 4, 6, and 8 were confirmed through X-ray crystallography. Based on the X-ray diffraction analyses and NMR data, two reported khayanolides 12 and 13 are, in fact, 1-O-acetylkhayanolide B 4 and khayanolide B 5, respectively, and two reported phragmalins 14 and 15 are, in fact, khayanolide E 6 and 1-O-deacetylkhayanolide E 7, respectively. In the anti-proliferative bioassay, 1 and 2 showed significant growth inhibitory activities against MCF-7, SiHa, and Caco-2 tumor cells with IC50 values in the range of 35-69 microgram/ml, while other compounds did not show anticancer activity even at high concentration 200 microgram/ml; 9, 10, 11 exhibited strong antioxidant activities comparable to that of BHT, regarding the DPPH free scavenging activity

Chlorinated Withanolides from Withania somnifera

A chlorinated withanolide, 6α-chloro-5β,17α-dihydroxywithaferin A (1), and nine known withanolides, 6α-chloro-5β-hydroxywithaferin A (2), (22R)-5β-formyl-6β,27-dihydroxy-1-oxo-4-norwith-24-enolide, withaferin A, 2,3-dihydrowithaferin A, 3-methoxy-2,3-dihydrowithaferin A, 2,3-didehydrosomnifericin, withanone, withanoside IV and withanoside X, were isolated from Withania somnifera (Solanaceae). All structures were elucidated on the basis of spectroscopic methods (IR, HRESIMS, 1D/2D NMR). X-ray crystallography confirmed the absolute configuration of 1

PsyAttention: Psychological Attention Model for Personality Detection

Work on personality detection has tended to incorporate psychological features from different personality models, such as BigFive and MBTI. There are more than 900 psychological features, each of which is helpful for personality detection. However, when used in combination, the application of different calculation standards among these features may result in interference between features calculated using distinct systems, thereby introducing noise and reducing performance. This paper adapts different psychological models in the proposed PsyAttention for personality detection, which can effectively encode psychological features, reducing their number by 85%. In experiments on the BigFive and MBTI models, PysAttention achieved average accuracy of 65.66% and 86.30%, respectively, outperforming state-of-the-art methods, indicating that it is effective at encoding psychological features

Magnetic reconnection-driven turbulence and turbulent reconnection acceleration

This paper employs an MHD-PIC method to perform numerical simulations of magnetic reconnection-driven turbulence and turbulent reconnection acceleration of particles. Focusing on the dynamics of the magnetic reconnection, the properties of self-driven turbulence, and the behavior of particle acceleration, we find that: (1) when reaching a statistically steady state of the self-driven turbulence, the magnetic energy is almost released by 50\%, while the kinetic energy of the fluid increases by no more than 15\%. (2) the properties of reconnection-driven turbulence are more complex than the traditional turbulence driven by an external force. (3) the strong magnetic field tends to enhance the turbulent reconnection efficiency to accelerate particles more efficiently, resulting in a hard spectral energy distribution. Our study provides a particular perspective on understanding turbulence properties and turbulent reconnection-accelerated particles.Comment: 12 pages, 10 figures and 1 table. Accepted for publication in Ap

Experimental observation of superscattering

Superscattering, induced by degenerate resonances, breaks the fundamental single-channel limit of scattering cross section of subwavelength structures; in principle, an arbitrarily large total cross section can be achieved via superscattering. It thus provides a unique way to strengthen the light-matter interaction at the subwavelength scale, and has many potential applications in sensing, energy harvesting, bio-imaging (such as magnetic resonance imaging), communication and optoelectronics. However, the experimental demonstration of superscattering remains an open challenge due to its vulnerability to structural imperfections and intrinsic material losses. Here we report the first experimental evidence for superscattering, by demonstrating the superscattering simultaneously in two different frequency regimes through both the far-field and near-field measurements. The underlying mechanism for the observed superscattering is the degenerate resonances of confined surface waves, by utilizing a subwavelength metasurface-based multilayer structure. Our work paves the way towards practical applications based on superscattering

Polarity Information Coded Flip-OFDM for Intensity Modulated Systems

A polarity-information-coded flip orthogonal frequency division multiplexing (PIC-flip-OFDM) is proposed for intensity modulation/direct detection (IM/DD) optical communications in this letter. In the proposed scheme, the modulated signals in the frequency domain are not constrained to have Hermitian symmetry. The real and imaginary parts of the timedomain complex signals are separated, and the polarities of the real and imaginary parts are jointly encoded and modulated. The transmit strategy and the receive algorithm of the proposed scheme are analyzed in detail. The major advantage of the proposed scheme is that its spectral and optical power efficiencies are higher than existing schemes, which is validated in simulation

Exploring the Role of Gender on Bloggers\u27 Switching Behaviors

Blog has become an increasingly popular form of new information technology (IT) in recent years. Many world famous web sites (e.g., Microsoft, Yahoo!, and Google) are providing blog services on the Internet. Bloggers, therefore, can easily establish and maintain their blogs through such services. However, research on blogs’ adoption and diffusion is rare. In this study, we attempt to study bloggers’ post-adoption behaviors. We examine bloggers’ intention to switch their blog services building upon the marketing and IS literature. Particularly, the role of gender is explored and an online survey is conducted to test the research model. Findings confirm that bloggers’ intention to switch their blog services is strongly associated with three factors: satisfaction, sunk costs, and attractive alternatives. Meanwhile, gender is found to moderate the relationship between satisfaction and intention to switch the blog service. Implications for both researchers and practitioners are provided