Phytotoxins from <i>Tithonia diversifolia</i>

<i>Tithonia diversifolia</i> (Mexican sunflower) is a dominant plant of the Asteraceae family, which suggests it produces allelochemicals that interfere with the development of surrounding plants. The study described herein was conducted to identify the compounds that have phytotoxic activity in <i>T. diversifolia</i> extracts. Ethyl acetate extracts of the leaves, stems, and roots showed significant inhibition of wheat coleoptile growth, and the leaf extract had similar inhibitory effects to a commercial herbicide. Fourteen compounds, 12 of which were sesquiterpene lactones, have been isolated. Two sesquiterpene lactones are reported for the first time and were isolated as an inseparable mixture of 8β-<i>O</i>-(2-methylbutyroyl)­tirotundin (<b>4</b>) and 8β-<i>O</i>-(isovaleroyl)­tirotundin (<b>5</b>). Their structures were determined by spectroscopic analysis, including NMR techniques and mass spectrometry. The sesquiterpene lactones 1β-methoxydiversifolin (<b>6</b>), tagitinin A (<b>7</b>), and tagitinin C (<b>8</b>) were the major products identified. These compounds were active on etiolated wheat coleoptiles, seed germination, and the growth of STS and weeds. The phytotoxic activity shown by these sesquiterpene lactones indicates that they are the compounds responsible for the activity exhibited by the initial extracts

Direct Atomic Observation in Powdered 4H-Ba_0.8Sr_0.2Mn_0.4Fe_0.6O_2.7

A new hexagonal polytype in the BaMn_1‑<i>x</i>Fe_<i>x</i>O_3‑δ system has been stabilized. Powdered Ba_0.8Sr_0.2Mn^IV_0.4Fe^III_0.6O_2.70 crystallizes in the 4H hexagonal polytype (space group <i>P</i>6₃/<i>mmc</i>) according to X-ray diffraction. HAADF images and chemical maps with atomic resolution have been obtained by combining Cs-corrected electron microscopy and EELS spectroscopy. The structure is formed by dimers of face-sharing octahedra linked by corners. EELS data show a random distribution of the transition metals ions identified by Fe and Mn-L2,3 chemical maps. A systematic difference in contrast observed in the O–K signal mapping suggests that anion deficiency is randomly located along the hexagonal layers in agreement with ND data. The magnetic structure consists of ferromagnetic sheets with the magnetic moments aligned along the <i>x</i>-axis and coupled antiferromagnetically along the <i>c</i>-axis

High-Performance Implantable Sensors based on Anisotropic Magnetoresistive La_0.67Sr_0.33MnO₃ for Biomedical Applications

We present the design, fabrication, and characterization of an implantable neural interface based on anisotropic magnetoresistive (AMR) magnetic-field sensors that combine reduced size and high performance at body temperature. The sensors are based on La0.67Sr0.33MnO3 (LSMO) as a ferromagnetic material, whose epitaxial growth has been suitably engineered to get uniaxial anisotropy and large AMR output together with low noise even at low frequencies. The performance of LSMO sensors of different film thickness and at different temperatures close to 37 °C has to be explored to find an optimum sensitivity of ∼400%/T (with typical detectivity values of 2 nT·Hz–1/2 at a frequency of 1 Hz and 0.3 nT·Hz–1/2 at 1 kHz), fitted for the detection of low magnetic signals coming from neural activity. Biocompatibility tests of devices consisting of submillimeter-size LSMO sensors coated by a thin poly(dimethyl siloxane) polymeric layer, both in vitro and in vivo, support their high suitability as implantable detectors of low-frequency biological magnetic signals emerging from heterogeneous electrically active tissues