A new method for estimating the critical current density of a superconductor from its hysteresis loop

The critical current density J_c of some of the superconducting samples, calculated on the basis of the Bean’s model, shows negative curvature for low magnetic field with a downward bending near H = 0. To avoid this problem Kim’s expression of the critical current density, J_c = k/(H₀ + H), where J_c has positive curvature for all H, has been employed by connecting the positive constants k and H₀ with the features of the hysteresis loop of a superconductor. A relation between the full penetration field H_p and the magnetic field H_min, at which the magnetization is minimum, is obtained from the Kim’s theory. Taking the value of J_c at H = H_p according to the actual loop width, as in the Bean’s theory, and at H = 0 according to an enhanced loop width due to the local internal field, values of k and H₀ are obtained in terms of the magnetization values M⁺(?H_min), M^?(H_min), M⁺(H_p) and M^?(H_p). The resulting method of estimating J_c from the hysteresis loop turns out to be as simple as the Bean’s method.     

(20R,22R)-6α,7α-Epoxy-5α,27-dihydroxy-1-oxowitha-2,24-dienolide in Leaves of Withania somnifera: Isolation and its Crystal Structure

Abstract  (20R,22R)-6α,7α-Epoxy-5α,27-dihydroxy-1-oxowitha-2,24-dienolide (27-hydroxy-withanolide B) was isolated from Withania somnifera. The structure of the withanolide was established by spectral analysis and X-ray diffraction studies. The compound crystallizes in the orthorhombic space group P2₁2₁2₁ with unit cell parameters: a = 9.2163(3), b = 11.1828(4), c = 23.6146(9) ?, Z = 4. The crystal structure was refined to R = 0.0495 for 3,284 observed reflections. All the rings of the steroid skeleton are trans connected. Rings A and B exist in a half-chair conformation, ring C a chair, and five membered ring D is intermediate between a half-chair and an envelope. The δ-lactone ring E adopts a distorted sofa conformation. The twist along the length of the steroid nucleus is −6.5°. The characteristic pattern observed in the packing diagram is the appearance of twisted chains of molecules packed together to form layers. Index Abstract  Isolation and crystal structure analysis of (20R,22R)-6α,7α-epoxy-5α,27-dihydroxy-1-oxowitha-2,24-dienolide.      

Biomimetic Synthesis of Silver Nanoparticle Using Leaf Extract of Mangifera Indica and Their Antibacterial Efficacy

The aim of this study to focused on bioinspired synthesis of silver nanoparticles (AgNPs) as a viable alternative to eradicate the existing physicochemical processes. In this context, the bioinspired AgNPs were synthesized using leaf extract of M. indica. Optimization of the experimental conditions for the rapid and high yield of AgNPs in minimum investment of time and expense have been carried out along with their antibacterial efficacy evaluated. For this reason, the variation of parameters like the concentration of the silver precursors, reducing agent, time, pH, and temperature of synthesis were realized. Synthesized AgNPs were characterized by UV-Visible spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM) techniques. UV-Visible spectra gave surface plasmon resonance (SPR) at 440 nm for AgNPs. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) techniques were further confirmed the synthesis and crystalline nature of AgNPs respectively. Transmission electron microscopy (TEM) observed spherical shapes of synthesized AgNPs within range 5～20 nm. The results of the current study indicate that optimization process play a pivotal role in the AgNPs synthesis and biogenic synthesized AgNPs might be used against bacterial pathogens.     

Extraction and Fractionation of Prokinetic Phytochemicals from Chrozophora tinctoria and Their Bioactivities

Chrozophora tinctoria is an annual plant of the family Euphorbiaceae, traditionally used as a laxative, a cathartic and an emetic. A methanolic extract of Chrozophora tinctoria (MEC) whole plant and an n-butanol fraction of Chrozophora tinctoria (NBFC) were analyzed by gas chromatography–mass spectrometry (GC-MS) to detect the phytochemicals. MEC and NBFC were tested for in vitro anti acetylcholinesterase (AChE) potential. The effect of both samples on intestinal propulsive movement and spasmolytic activity in the gastrointestinal tract (GIT) was also studied. About twelve compounds in MEC and three compounds in NBFC were tentatively identified through GC-MS. Some of them are compounds with known therapeutic activity, such as toluene; imipramine; undecane; 14-methyl-pentadecanoic acid methyl ester; and hexadecanoic acid. Both NBFC and MEC samples were checked for acute toxicity and were found to be highly toxic in a dose-dependent manner, causing diarrhea and emesis at 1 g/kg concentration in pigeons, with the highest lethargy and mortality above 3 g/kg. Both the samples of Chrozophora tinctoria revealed significant (p ≤ 0.01) laxative activity against metronidazole (7 mg/kg) and loperamide hydrochloride (4 mg/kg)-induced constipation. NBFC (81.18 ± 2.5%) and MEC (68.28 ± 2.4%) significantly increased charcoal meal intestinal transit compared to distal water (41.15 ± 4.3%). NBFC exhibited a significant relaxant effect (EC₅₀ = 3.40 ± 0.20 mg/mL) in spontaneous rabbit jejunum as compared to MEC (EC₅₀ = 4.34 ± 0.68 mg/kg). Similarly, the impact of NBFC on KCl-induced contraction was more significant than that of MEC (EC₅₀ values of 7.22 ± 0.06 mg/mL and 7.47 ± 0.57 mg/mL, respectively). The present study scientifically validates the folk use of Chrozophora tinctoria in the management of gastrointestinal diseases such as constipation. Further work is needed to isolate the phytochemicals that act as diarrheal agents in Chrozophora tinctoria.     

Visible-light-switchable Chalcone-Flavylium Photochromic Systems in Aqueous Media

The chalcone-flavylium photochromic system switches in aqueous media. However, the chalcone→flavylium conversion requires detrimental ultra-violet (UV) light for the switching which deters their applications in the biological domain. To address this issue, we have synthesized strategically modified chalcone scaffolds that can be reversibly switched to the flavylium forms with visible light ranging from 456 nm (blue) to 640 nm (red).