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Mass Spectrometric Analysis
Published in Adorjan Aszalos, Modern Analysis of Antibiotics, 2020
This technique has also been called “direct chemical ionization,” “direct exposure,” “plasma desorption ionization,” and “surface ionization.” Introduced by Baldwin and McLafferty in 1973 [18] and recently reviewed [19–21], desorption CI was developed as a more accessible alternative to field desorption to obtain mass spectra from nonvolatile samples. Samples are applied to the surface of a desorption CI probe tip (often a coiled wire) that is inserted directly inside the chemical ionization source. In earlier experiments, the probe was not heated but simply inserted into a heated source. The technique has been improved by using probe tips of inert material to reduce the binding energy of the sample to the surface and by rapid heating. Both approaches make desorption more competitive with decomposition processes. Materials used for probe tips include copper [22], gold [22], glass [18], quartz [23–26], Teflon [27], and Vespel [28,29]. Coiled platinum wire [30] and field desorption emitter wires of tungsten [31] have also been used. These latter probe tips can be rapidly heated by passing a current through them. Molecular ion adducts of compounds that readily dehydrate under desorption CI conditions are obtained by adding amines to the reagent gas [32]. Adduct ions are easily recognized using a 1:1 mixture of pyridine-d5 and pyridine. A similar method uses a 1:1 mixture of tetramethylsilane-d12 and tetramethylsilane to produce trimethylsilyl adducts [33].
ISOLATION OF β-SITOSTEROL FROM Crotalaria longipes WIGHT & ARN: PHARMACOLOGICAL USES
Published in V. R. Mohan, A. Doss, P. S. Tresina, Ethnomedicinal Plants with Therapeutic Properties, 2019
K. Paulpriya, P. S. Tresina, V. R. Mohan
The aerial parts of C. longipes were collected from Kotagiri, Nilgiri Biosphere Reserve, Western Ghats, Tamil Nadu, India. Hexane, petroleum ether, chloroform, ethyl acetate, acetone, methanol, and ethanol of analytical grade were procured from Merck. Column chromatography was performed on column (length 50 and diameter 150 mm), silica gel (60–120 mesh), and Merck TLC readymade sheets 20 cm × 20 cm. The spectrophotometer systems used were Shimadzu UV spectrophotometer, Shimadzu spectrum 1 FT-IR spectrometer, and ESI-MS analysis (Tof Spec 2E MALDI time of flight, TOF) instrument (Micromass, Manchester, UK). 1H-NMR and 13C-NMR spectra were recorded on Bruker spectrometer using CDCl3 as solvent and tetramethylsilane (TMS) as internal standard. The observed chemical shifts were recorded in parts per million and the coupling constants (J) were recorded in Hertz.
Introduction to Combining MRI with PET
Published in George C. Kagadis, Nancy L. Ford, Dimitrios N. Karnabatidis, George K. Loudos, Handbook of Small Animal Imaging, 2018
Volkmar Schulz, Jakob Wehner, Yannick Berker
The B0 distortion map is measurable within the MRI using the phase images of two gradient echo (GRE) sequences with two different echo times TE,1 and TE,2 (TE extension: ΔTE = TE,2 − TE,1). A large phantom filling the FOV under investigation is used. In a given pixel, the phase advance between both measurements is given by Δϕ = 2πΔfΔTE, whereby Δf is proportional to ΔB0, the local B0 modification. Thus, via subtraction of both phase images and rescaling, the B0 distortion map can be reconstructed. However, the B0 map contains information only about the field homogeneity and not about the absolute B0 field at a given point. The absolute scale of B0 could be shifted and has to be measured separately by determining the resonance frequency using, for example, spectroscopic methods. A well-defined phantom material with a clear resonance spectrum (e.g., no peak splitting due to chemical shifts) is preferred to quantitatively measure any shifts. Tetramethylsilane (TMS), for example, is widely accepted in NMR spectroscopy as reference material since it provides single-peak spectra for 1H, 13C, and 29Si nuclei due to its highly symmetric structure and thus might be a suitable choice (Mohrig et al. 2006).
Design, synthesis, and evaluation of novel O-alkyl ferulamide derivatives as multifunctional ligands for treating Alzheimer’s disease
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2022
Gaofeng Zhu, Ping Bai, Keren Wang, Jing Mi, Jing Yang, Jiaqi Hu, Yujuan Ban, Ran Xu, Rui Chen, Changning Wang, Lei Tang, Zhipei Sang
Unless otherwise noted, the reagents required for the chemical synthesis were obtained from Shanghai Titan Scientific Co., Ltd. and were used without purification. All new compounds provided satisfactory 1H NMR and 13 C NMR spectra were recorded on a Varian INOVA spectrometer and used CDCl3 as a solvent, referenced to Tetramethylsilane (TMS). Chemical shifts (δ) are reported in ppm. Splitting patterns are designated as s, single; d, doublet; dd, double-doublet; t, triplet; m, multiplet. The purity of the final synthesised products was evaluated by HPLC analyses which were conducted with a Waters X-Bridge C18 column (4.6 mm × 150 mm, 5 μm) at a flow ratio of 0.8 ml/min. Mobile phase: A: 0.12%TFA in H2O, B: 0.1% TFA in CH3CN. The high-resolution mass spectra were obtained by Waters Xevo G2-XS-Qtof mass spectrometer.
Positional scanning of natural product hispidol’s ring-B: discovery of highly selective human monoamine oxidase-B inhibitor analogues downregulating neuroinflammation for management of neurodegenerative diseases
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2022
Ahmed H. E. Hassan, Hyeon Jeong Kim, Min Sung Gee, Jong-Hyun Park, Hye Rim Jeon, Cheol Jung Lee, Yeonwoo Choi, Suyeon Moon, Danbi Lee, Jong Kil Lee, Ki Duk Park, Yong Sup Lee
General: All solvents and reagents have been purchased from commercial suppliers and used without any further purification. NMR spectra were acquired on Bruker Avance 400 spectrometer (400 MHz) or JEOL JNM-ECZ500R spectrometer (500 MHz). 1H NMR spectra were referenced to tetramethylsilane (δ = 0.00 ppm) as an internal standard. High-resolution mass spectra (HRMS) were recorded on Jeol AccuTOF (JMS-T100TD) equipped with a DART (direct analysis in real time) ion source from ionsense, Tokyo, Japan in the positive modes. TLC was carried out using glass sheets pre-coated with silica gel 60F254 purchased by Merk and spots were visualised under UV lamp or using staining solutions, such as p-anisaldehyde solution, ninhydrin solution. 6-Methoxy-3-coumaranone and compounds 1a, 1b, 1d, 1e, 1f, 1h–1t, and v–1y were in agreement with reported literature (Supplementary materials)43,49,53–58.
Cytotoxic furanosesquiterpenoids and steroids from Ircinia mutans sponges
Published in Pharmaceutical Biology, 2021
Fatemeh Heidary Jamebozorgi, Morteza Yousefzadi, Omidreza Firuzi, Melika Nazemi, Somayeh Zare, Jima N. Chandran, Bernd Schneider, Ian T. Baldwin, Amir Reza Jassbi
NMR spectra of the purified compounds were recorded on a Bruker Avance 500 spectrometer (Bruker Biospin, Karlsruhe, Germany), operating at resonance frequencies of 500 MHz for 1H and 125 MHz for 13C, respectively. Standard Bruker pulse sequences were used for measuring 1H NMR, 13C APT, 1H-1H COSY, 1H-13C HSQC and 1H-13C HMBC spectra. Tetramethylsilane (TMS) was used as an internal standard for referencing 1H and 13C NMR spectra. Data acquisition and processing was accomplished using Bruker Topspin 2.1. EI-MS spectra were recorded on an Agilent 5975 C inert GC/MS instrument. For isolation and purification of the sponge’s metabolites, different chromatographic separations were performed, including silica gel open column chromatography (CC: 0.063–0.200 mm particle size), flash column chromatography (FCC: 0.040–0.063 mm particle size) and TLC using silica gel 60 F254 pre-coated plates (0.25 mm film thickness). The adsorbents were purchased from Merck, Darmstadt, Germany. For further purification of the fractions, reversed-phase (RP-18) HPLC analyses were performed using a Knauer semi-preparative HPLC with a K-1050 pump and a four wavelength K-2600 UV detector set at λ 210 nm (Jassbi et al. 2014a). The semi-preparative HPLC column (Phenomenex RP-18, 250 × 10 mm) was eluted with 95% acetonitrile (solvent B) and 5% in ultrapure water (solvent A). The flow rate of the mobile phase was set at 4.5 mL/min.