Assignment of 29Si NMR lines and determination of 29Si-13C coupling constants in pertrimethylsilylated lignin-related phenol-carboxylic acids by selective heteronuclear INADEQUATE method

1987 ◽  
Vol 52 (8) ◽  
pp. 1985-1991 ◽  
Author(s):  
Jan Schraml ◽  
Jaan Past ◽  
Jüri Puskar ◽  
Tõnis Pehk ◽  
Endel Lippmaa ◽  
...  
Keyword(s):  
Benzene Ring ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
29Si Nmr ◽  
Model Compounds ◽  
Lignin Model ◽  
The One ◽  
Comparable Magnitude ◽  
Unambiguous Assignment

Selective heteronuclear (Si-C) INADEQUATE method has been successfully used to assign all 29Si chemical shifts in six pertrimethylsilylated lignin model compounds. Empirical assignment of the lines in the region δ = 23-25 to trimethylsilyl esters of carboxylic compounds has been confirmed. Selectivity of the method permits unambiguous assignment to trimethylsiloxy groups which differ by their position on the benzene ring only. The assignment is possible despite that 29Si-13C two-bond coupling constants (2·1-3·0 Hz) are of comparable magnitude with the three-bond coupling constants (1-2·3 Hz). The chemical shifts of trimethylsiloxy groups on the benzene ring are sensitive to substituent effect to such an extent that their assignment cannot rely on an empirical rule but requires experimental method such as the one used here.

Determination of chemical shifts in 6-condensed syringylic lignin model compounds

Holzforschung ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Lucas Lagerquist ◽  
Jani Rahkila ◽  
Patrik Eklund
Keyword(s):  
Chemical Shift ◽  
Methoxy Group ◽  
Chemical Shifts ◽  
Model Compounds ◽  
Correlation Peak ◽  
Lignin Model Compounds ◽  
Benzylic Alcohols ◽  
Lignin Model ◽  
C Nmr

Abstract A small library of 6-substituted syringyl model compounds with aliphatic, carboxylic, phenylic, benzylic alcohols and brominated substituents were prepared. The influence of the substituents on the chemical shifts of the compounds was analyzed. All of model compounds showed a characteristic increase in the 13C NMR chemical shift of the methoxy group vicinal to the substitution. This 13C NMR peak and its corresponding correlation peak in HSQC could potentially be used to identify 6-condensation in syringylic lignin samples.

Gradient-Enhanced Inverse-Detected NMR Techniquesfor Determination of 1H-15N Coupling Constants in 2,2-Dimethylpenta-3,4-dienal Derivatives

1997 ◽  
Vol 62 (11) ◽  
pp. 1747-1753 ◽  
Author(s):  
Radek Marek
Keyword(s):  
Double Bond ◽  
Chemical Shifts ◽  
Multiple Bond ◽  
Coupling Constants ◽  
Single Quantum ◽  
Nmr Techniques ◽  
Phase Sensitive ◽  
Heteronuclear Coupling

Determination of 15N chemical shifts and heteronuclear coupling constants of substituted 2,2-dimethylpenta-3,4-dienal hydrazones is presented. The chemical shifts were determined by gradient-enhanced inverse-detected NMR techniques and 1H-15N coupling constants were extracted from phase-sensitive gradient-enhanced single-quantum multiple bond correlation experiments. Stereospecific behaviour of the coupling constants 2J(1H,15N) and 1J(1H,13C) has been used to determine the configuration on a C=N double bond. The above-mentioned compounds exist predominantly as E isomers in deuteriochloroform.

Convenient Sign Determination of Various Coupling Constants in Alkynylplatinum(II) Phosphine Complexes

1991 ◽  
Vol 46 (1) ◽  
pp. 35-38 ◽  
Author(s):  
Bernd Wrackmeyer
Keyword(s):  
Coupling Constants ◽  
Two Dimensional ◽  
Model Compounds ◽  
Standard Equipment ◽  
Phosphine Complexes ◽  
Sign Determination

(1)The utilization of two-dimensional (2 D) 13C /1H , 31P/1H and 195Pt/1H heteronuclear shift correlations for the sign determination of various coupling constants [e.g., 2J(31PPt13C) > 0 (trans), 2J(31PPt13C) < 0 (cis), 3J( 31PPtC13C) > 0 (cis, trans), 4J(31PPtCC1H ) > 0 (trans), 4J(31PCC1H ) < 0 (cis), 3J(195PtCC1H ) > 0, 2J(31PC1H ) < 0, etc.] is demonstrated, using standard equipment. The complexes [trans-(Bu3P)2Pt(C ≡ C -H)2] and [cis-(Et2PCH2CH2PEt2)Pt(C ≡ C - H)2] (2) serve as model compounds.

scholarly journals Determination of the pKa of glucuronic acid and the carboxy groups of heparin by 13C-nuclear-magnetic-resonance spectroscopy

1991 ◽  
Vol 278 (3) ◽  
pp. 689-695 ◽  
Author(s):  
H M Wang ◽  
D Loganathan ◽  
R J Linhardt
Keyword(s):  
Uronic Acid ◽  
Model Compound ◽  
Molecular Size ◽  
Resonance Spectroscopy ◽  
Model Compounds ◽  
Pka Values ◽  
Carboxylate Groups ◽  
13C Nuclear Magnetic Resonance ◽  
Unambiguous Assignment

As part of our continuing studies on heparin, the present paper uses 13C-n.m.r. spectroscopy to examine the acidity of heparin's uronic acid carboxylate groups. Heparin contains three different uronic acids. In porcine mucosal heparin these account for approx. 91, 7 and 2 mol% of the total uronic acid residues. These are alpha-L-idopyranosyluronic acid 2-sulphate, beta-D-glucopyranosyluronic acid and alpha-L-idopyranosyluronic acid. The pKa values of their carboxylate groups were determined as 3.13 (using heparin), 2.79 (using heparin) and 3.0 (predicted by using model compounds) respectively. 18C-n.m.r. spectroscopy, performed at various pH values, provided a convenient method of simultaneously determining the pKa of multiple carboxylate groups, of similar acidity, within heparin D-Glucopyranosyluronic acid and heparin-derived di-, tetra- and hexa-saccharides were used as model compounds to determine pKa values of the different carboxy groups. The results suggested that molecular size had an effect on pKa. Unambiguous assignment of carboxy carbon resonances were accomplished through the use of two-dimensional n.m.r. spectroscopy. Finally, application of this method to the simplest model compound, D-glucopyranosyluronic acid, permitted the determination of the pKa of both its alpha- and beta-anomers.

Studies related to antitumor antibiotics. Part XXIV. High field 1H nmr analysis and conformations of saframycins A and C

1981 ◽  
Vol 59 (20) ◽  
pp. 2945-2952 ◽  
Author(s):  
J. William Lown ◽  
Alummoottil V. Joshua ◽  
Hsiao-Hsiung Chen
Keyword(s):  
High Field ◽  
Chemical Shifts ◽  
Molecular Geometry ◽  
Coupling Constants ◽  
Cytotoxic Action ◽  
Antitumor Antibiotics ◽  
Dna Templates ◽  
H Nmr ◽  
Proton Chemical Shifts ◽  
Unambiguous Assignment

A detailed analysis of the high field (400 MHz) 1H nmr spectra of the basic antitumor antibiotics saframycin A and C in CDCl3, C6D6, and in aqueous DMSO solutions has been carried out. Selective double irradiation experiments permitted the unambiguous assignment of all the proton chemical shifts and coupling constants. Consideration of the magnitudes of the latter together with specific nOe experiments permits assignment of molecular geometry and average conformations in solution. Selective shifts occurring in DMSO–D2O solutions upon addition of CF3COOD identified the 12-N atom as the site of protonation which result bears directly on the acid promoted binding of these antibiotics to DNA templates as part of their cytotoxic action.

The 1H NMR spectra and the conformation of 1,6-anhydro-β-D-hexopyranoses and their triacetates

1979 ◽  
Vol 44 (6) ◽  
pp. 1949-1964 ◽  
Author(s):  
Miloš Buděšínský ◽  
Tomáš Trnka ◽  
Miloslav Černý
Keyword(s):  
Nmr Spectra ◽  
Chemical Shifts ◽  
Shift Reagent ◽  
Point Of View ◽  
Coupling Constants ◽  
Lanthanide Shift Reagent ◽  
Pyranose Ring ◽  
H Nmr ◽  
Vicinal Coupling Constants

The 1H NMR spectra of 1,6-anhydro-β-D-hexopyranoses and their triacetates, measured in hexadeuteriodimethyl sulfoxide or deuteriochloroform, confirmed the existence of these compounds in 1C4(D) conformations, with the pyranose ring partly planarized in dependence on the configuration of the substituents in positions C(2), C(3) and C(4). The effects of the substituents on the chemical shifts and the adjusted relationship for the dependence of vicinal coupling constants on the torsion angle are discussed in detail from the point of view of the determination of the configuration and the conformation of 1,6-anhydro-β-D-hexopyranoses and their derivatives. The 1H NMR spectra of triacetates were also measured in the presence of the lanthanide shift reagent, tris(1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione) europium (III) [Eu.(FOD)3].

A Rapid and Accurate 1HNMR Method for the Identification and Quantification of Major Constituents in Qishen Yiqi Dripping Pills

2020 ◽  
Author(s):  
Qingling Xie ◽  
Limin Gong ◽  
Feibing Huang ◽  
Mengru Cao ◽  
Yongbei Liu ◽  
...  
Keyword(s):  
Simultaneous Determination ◽  
Chemical Shifts ◽  
Salvia Miltiorrhiza ◽  
Proton Nmr ◽  
Herbal Medicines ◽  
Panax Notoginseng ◽  
Hplc Method ◽  
Coupling Constants ◽  
Identification And Quantification

Abstract Background Qishen Yiqi dripping pills (QSYQ), composed of four herbal medicines—Salvia miltiorrhiza, Astragalus membranaceus, Panax notoginseng, and Dalbergiaodorifera—are widely used to treat ischemic cerebrovascular and hemorrhagic cerebrovascular conditions. Objective In this study, a rapid and accurate proton NMR (1HNMR) spectroscopy method was established to control the quality of QSYQ and ensure their clinical efficacy. Method Firstly, different types of metabolites were identified based on the proton signal peaks of chemical shifts, coupling constants, and related information provided through two-dimensional NMR spectroscopy. Secondly, a quantitative 1HNMR method was established for the simultaneous determination of major constituents in QSYQ samples. In addition, an HPLC method was performed to verify the results obtained by the quantitative proton NMR (qHNMR)  method. Results In the present study, 26 metabolites were identified in the 1HNMR spectra of QSYQ. In addition, a rapid and accruate qHNMR method was established for the simultaneous determination of protocatechualdehyde, rosmarinic acid, danshensu, calycosin-7-O-β-D-glucoside, and ononin in ten batches of QSYQ samples for the first time. Moreover, the proposed qHNMR method and HPLC method were compared using Bland-Altman and plots Passing-Bablok regression, indicating no significant differences and a strong correlation between the two analytical methods. Conclusions This method is an important tool for the identification and quantification of major constituents in QSYQ. Highlights Compared with traditional HPLC, the established qHNMR method has the advantages of simple sample preparation, short analysis time, and non-destructive analysis.

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