Determination of Polyphenolic Phytochemicals using Highly Deshielded -OH 1 H-NMR Signals

2016 ◽  
Vol 28 (3) ◽  
pp. 159-170 ◽  
Author(s):  
Pantelis Charisiadis ◽  
Vassiliki G. Kontogianni ◽  
Constantinos G. Tsiafoulis ◽  
Andreas G. Tzakos ◽  
Ioannis P. Gerothanassis
Keyword(s):  
H Nmr ◽  
Nmr Signals

Zusammensetzung von Rohsulfan, Nachweis der Sulfane H2S9 bis H2S35 Composition of Crude Sulfane Oil, Identification of the Sulfanes H2S9 to H2S35

1985 ◽  
Vol 40 (2) ◽  
pp. 263-272 ◽  
Author(s):  
Josef Hahn
Keyword(s):  
Narrow Range ◽  
Benzene Solution ◽  
Chemical Shifts ◽  
Upfield Shift ◽  
Downfield Shift ◽  
H Nmr ◽  
Intramolecular Hydrogen ◽  
Hydrogen Bondings ◽  
Nmr Signals

In benzene solution the position of the 1H NMR signals of sulfanes, H2Sn, strongly depends on the sulfur chain length and on the sulfane concentration. Under proper conditions all sulfanes in a mixture are characterized by well-resolved NMR signals showing a downfield shift with increasing length of the sulfur chain. The shift differences between the higher homologues ( n > 8 ) remain nearly constant, thus allowing the assignment of the signals up to H2S35 and the determination of the complete sulfane distribution in crude oils. In sulfane mixtures without solvent as well as in CS2 and CCl4 solutions, however, H2S8 shows the largest downfield shift. The signals of the higher sulfanes overlap in a narrow range at slightly higher field and cannot be characterized except for the CCl4 solution where an assignment up to H2S11 is possible. The chemical shifts are interpreted in terms of inter- and intramolecular hydrogen bondings. The upfield shift caused by benzene is attributed to the formation of H2Sn · benzene complexes.

21,22-Disubstituted 18α,19βH-Ursane Derivatives with Oxabicyclooctane System in Ring E

1993 ◽  
Vol 58 (1) ◽  
pp. 173-190 ◽  
Author(s):  
Eva Klinotová ◽  
Jiří Klinot ◽  
Václav Křeček ◽  
Miloš Buděšínský ◽  
Bohumil Máca
Keyword(s):  
Spectral Data ◽  
Spin Systems ◽  
Coupling Constants ◽  
Complete Analysis ◽  
Nmr Spectrum ◽  
Proton Proton ◽  
H Nmr ◽  
Proton Coupling ◽  
C Nmr

Reaction of 3β-acetoxy-21,22-dioxo-18α,19βH-ursan-28,20β-olide (IIIa) and 20β,28-epoxy-21,22-dioxo-19α,19βH-ursan-3β-yl acetate (IIIb) with diazomethane afforded derivatives XII-XIV with spiroepoxide group in position 21 or 22, which were further converted into hydroxy derivatives XV and XVII. Ethylene ketals VIII-X were also prepared. In connection with the determination of position and configuration of the functional groups at C(21) and C(22), the 1H and 13C NMR spectral data of the prepared compounds are discussed. Complete analysis of two four-spin systems in the 1H NMR spectrum of bisethylenedioxy derivative Xb led to the proton-proton coupling constants from which the structure with two 1,4-dioxane rings condensed with ring E, and their conformation, was derived.

Determination of the Accurate Values of the Rate Constant and Thermodynamic Parameters for the Rotation About the C(sp2)-C(aryl) Bond; Adamantan-1-yl 3-Bromo-2,4,6-trimethylphenyl Ketone

1998 ◽  
Vol 63 (7) ◽  
pp. 955-966
Author(s):  
Eva Přibylová ◽  
Miroslav Holík
Keyword(s):  
Thermodynamic Parameters ◽  
Shape Analysis ◽  
Rate Constants ◽  
Line Shape ◽  
Microsoft Excel ◽  
Hindered Rotation ◽  
H Nmr ◽  
Line Shape Analysis ◽  
Coalescence Temperature

Four programs for the 1H NMR line shape analysis: two commercial - Winkubo (Bruker) and DNMR5 (QCPE 165) and two written in our laboratory - Newton (in Microsoft Excel) and Simtex (in Matlab) have been tested in order to get highly accurate rate constants of the hindered rotation about a single bond. For this purpose four testing criteria were used, two of them were also developed by us. As supplementary determinations the rate constants obtained for the coalescence temperature and for the thermal racemization of chromatographically separated enantiomers were used which fitted well the temperature dependence of the rate constants determined by the line shape analysis. As a test compound adamantan-1-yl 3-bromo-2,4,6-trimethylphenyl ketone was prepared and studied. It was shown that supermodified simplex method used in our algorithm (Simtex), though time consuming, gives the most accurate values of the rate constants and consequently the calculated thermodynamic parameters Ea, ∆H≠, and ∆S≠ lay in relatively narrow confidence intervals.

scholarly journals 13C and 1H NMR Spectra of Synthetic (25R)-5α-Spirostanes

1999 ◽  
Vol 23 (1) ◽  
pp. 48-49
Author(s):  
Martín A. Iglesias Arteaga ◽  
Carlos S. Pérez Martinez ◽  
Roxana Pérez Gil ◽  
Francisco Coll Manchado
Keyword(s):  
1H Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
1H Nmr Spectra ◽  
H Nmr ◽  
C 23 ◽  
Main Effects ◽  
Nmr Signals

The assignment of 13C and 1H NMR signals of synthetic (25 R)-5α-spirostanes is presented; the main effects on chemical shifts due to substitution at C-23 are briefly discussed.

scholarly journals Darstellung und Charakterisiening der Spezies R-C7H7Mo(CO)3 und die Röntgenstrukturanalyse von / Synthesis and Characterisation of the Species R-C7H7Mo(CO)3 and the X-ray Structure Determination of

1978 ◽  
Vol 33 (4) ◽  
pp. 361-365 ◽  
Author(s):  
Margret Sommer ◽  
Klaus Weidenhammer ◽  
Henning Wienand ◽  
Manfred L. Ziegler
Keyword(s):  
Carbon Atom ◽  
Structure Determination ◽  
Nmr Spectra ◽  
X Ray ◽  
Ethyl Group ◽  
H Nmr

The species R−C7H7Mo(CO)3 (R=−CH2COCH3,−CH(CH3)COCH3,−CH(CH)(CH3)2COCH3) have been synthesized by electrolysing [η7-C7H7Mo(CO)3]+, η7-C7H7Mo(CO)2Br and the dimers [C7H7Mo(CO)3]2 and (C7H7)2Mo(CO)3, respectively, in suitable ketones and HBr. 1H NMR spectra and the X-ray structure determination of (CH3−CO−CH(CH3)−C7H7)Mo(CO)3 revealed the CH3−CO−CH(CH3)-group being bonded to the cycloheptatriene ligand via the α-carbon atom of the ethyl group.

Differentiation of enantiomeric anions by NMR spectroscopy with chiral bisurea receptors

2018 ◽  
Vol 16 (2) ◽  
pp. 213-222 ◽  
Author(s):  
Suguru Ito ◽  
Manami Okuno ◽  
Masatoshi Asami
Keyword(s):  
Nmr Spectroscopy ◽  
H Nmr ◽  
Nmr Signals

Enantiomeric 1H NMR signals of chiral anions are separated by forming 1 : 1 and 1 : 2 host–guest complexes with chiral bisurea.

scholarly journals New Sensitive Kinetic Spectrophotometric Methods for Determination of Omeprazole in Dosage Forms

2009 ◽  
Vol 2009 ◽  
pp. 1-11 ◽  
Author(s):  
Ashraf M. Mahmoud
Keyword(s):  
Reference Method ◽  
Fixed Time ◽  
Dosage Forms ◽  
Charge Transfer Complexes ◽  
Specific Rate ◽  
Spectrophotometric Methods ◽  
H Nmr ◽  
Nmr Techniques ◽  
Kinetic Spectrophotometric

New rapid, sensitive, and accurate kinetic spectrophotometric methods were developed, for the first time, to determine omeprazole (OMZ) in its dosage forms. The methods were based on the formation of charge-transfer complexes with both iodine and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The variables that affected the reactions were carefully studied and optimized. The formed complexes and the site of interaction were examined by UV/VIS, IR, and1H-NMR techniques, and computational molecular modeling. Under optimum conditions, the stoichiometry of the reactions between OMZ and the acceptors was found to be 1 : 1. The order of the reactions and the specific rate constants were determined. The thermodynamics of the complexes were computed and the mechanism of the reactions was postulated. The initial rate and fixed time methods were utilized for the determination of OMZ concentrations. The linear ranges for the proposed methods were 0.10–3.00 and 0.50–25.00   with the lowest LOD of 0.03 and 0.14   for iodine and DDQ, respectively. Analytical performance of the methods was statistically validated; RSD was <1.25% for the precision and <1.95% for the accuracy. The proposed methods were successfully applied to the analysis of OMZ in its dosage forms; the recovery was 98.91–100.32%  0.94–1.84, and was found to be comparable with that of reference method.

Synthesis and antiaromatic character of alkyl-substituted di-peri-dinaphthoporphyrin Ni(II) complex

2017 ◽  
Vol 21 (12) ◽  
pp. 850-856 ◽  
Author(s):  
Masataka Umetani ◽  
Koji Naoda ◽  
Takayuki Tanaka ◽  
Atsuhiro Osuka
Keyword(s):  
Cyclic Voltammetry ◽  
Solid State ◽  
Potential Difference ◽  
Planar Structure ◽  
H Nmr ◽  
Antiaromatic Character ◽  
Homo Lumo ◽  
Nmr Signals

Antiaromatic molecules have recently been proven to display unique properties such as small HOMO–LUMO gaps, ambipolar carrier transporting and [Formula: see text]-stack-induced aromatic stabilizations. These intriguing properties have been demonstrated by stable antiaromatic molecules that exhibit a distinct antiaromatic character. Di-peri-dinaphthoporphyrins are peripherally [Formula: see text]-extended porphyrinoids that exhibit a planar structure and a distinct antiaromatic character stemming from their 24[Formula: see text] electron circuit. Herein, we report an alkyl-substituted di-peri-dinaphthoporphyrin Ni(II) complex 5Ni bearing less peripheral bulkiness as compared with phenyl-substituted ones. 5Ni displayed upfield-shifted [Formula: see text]H NMR signals due to [Formula: see text]-protons, indicating its distinct antiaromaticity, and a slightly shorter intermolecular packing distance (ca. 3.402 Å) in the solid state. Cyclic voltammetry shows a larger potential difference between the first and second oxidation waves, implying that this molecule tends to stack favorably in its oxidized state.

Supramolecular complexation between cucurbit[7]uril and folate and analytical applications

2021 ◽  
pp. 174751982110664
Author(s):  
Jue Chen ◽  
Tengmei Gao ◽  
Yinxia Chang ◽  
Yanming Wei ◽  
Yonghui Wang
Keyword(s):  
Fluorescence Spectra ◽  
Fluorescence Probe ◽  
H Nmr ◽  
Fluorescent Method ◽  
Inclusion Interaction ◽  
Spiked Plasma ◽  
Direct Fluorescence ◽  
Supramolecular Complexation

Folate (FA) plays a key role in the biosynthesis of amino acids, purines, and pyrimidines in the human body, and intracellular folate metabolism has become an attractive target of tumor chemotherapy. In this work, an inclusion interaction was found between FA and cucurbit[7]uril (CB[7]), and the formation of a CB[7]-FA 2:1 supramolecular inclusion complex was confirmed by fluorescence spectra, UV-Vis absorption spectroscopy, 1H NMR, and molecular modeling calculations. In addition, FA is generally determined through the indirect fluorescent method because it shows weak fluorescence in aqueous solution. Therefore, a simple, direct fluorescence probe method for rapidly measuring FA was investigated, and the linear equation of FA was ΔF = 14.691C + 37.366 within the concentration ranges of 0.82 ~ 18.31 µg mL–1. The proposed direct fluorescence method was applied to the determination of spiked plasma. We demonstrated that this method could provide an experimental basis for the targeted administration of the CB[7]-FA complex, and it could be extended as a promising fluorescence detection method for drugs in vivo.

Determination of Clay Bound Water in Shales from NMR Signals: The Fractal Theory

2021 ◽  
Author(s):  
Kouqi Liu ◽  
Zhijun Jin ◽  
Lianbo Zeng ◽  
Yujie Yuan ◽  
Mehdi Ostadhassan
Keyword(s):  
Fractal Theory ◽  
Bound Water ◽  
Nmr Signals
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