Experimental measurements and theoretical calculations of the chemical shifts and coupling constants of three azines (benzalazine, acetophenoneazine and cinnamaldazine)

2008 ◽  
Vol 46 (9) ◽  
pp. 859-864 ◽  
Author(s):  
Artur M. S. Silva ◽  
Regina M. S. Sousa ◽  
María Luisa Jimeno ◽  
Fernando Blanco ◽  
Ibon Alkorta ◽  
...  
Keyword(s):  
Theoretical Calculations ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Experimental Measurements

scholarly journals Estudo do tautomerismo ceto-enólico da 7-epi-clusianona através de cálculos teóricos de deslocamentos químicos de RMN

2020 ◽  
Author(s):  
Ana Carolina Ferreira de Albuquerque ◽  
José Walkimar de Mesquita Carneiro ◽  
Fernando Martins dos Santos Junior
Keyword(s):  
Natural Products ◽  
Structural Characterization ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spectroscopic Techniques ◽  
Chemical Structures ◽  
Nmr Parameters

The properties of natural products, including their biological and pharmacological activities, are directly correlated with their chemical structures. Thus, a correct structural characterization of these compounds is a crucial step to the understanding of their biological activities. However, despite the recent advances in spectroscopic techniques, structural studies of natural products can be challenging. This way, theoretical calculations of Nuclear Magnetic Resonance (NMR) parameters (such as chemical shifts and coupling constants) have proven to be a powerful and low-cost tool for the aid to experimental techniques traditionally used for the structural characterization of natural products. One of the several applications of quantum-mechanical calculations of NMR parameters is the study of tautomerism. Since chemical shifts are sensitive to the tautomeric equilibrium, this technique can provide crucial informations. In this work, it was applied a protocol for theoretical calculations of ¹³C chemical shifts in order to study the tautomerism of the natural product 7-epi-clusianone, isolated from Rheedia gardneriana. This protocol consists in a Monte Carlo conformational search, followed by geometry optimization and shielding tensors calculations, both using a density functional level of theory. After comparison of theoretical and experimental data, it was possible to confirm the two tautomers present in equilibrium in the experimental solution. Furthermore, this study highlights how this theoretical protocol can be an effective method in identifying the preferred tautomeric form in solution.

Conformational Energy Calculations on the Eosinophil Chemotactic Peptide Analog Val-Gly-Ala-Glu: Comparison of Theory and Experiment

1988 ◽  
Vol 41 (12) ◽  
pp. 1841
Author(s):  
J Bremer ◽  
GL Mendz
Keyword(s):  
Theoretical Calculations ◽  
Chemical Shifts ◽  
Minimum Energy ◽  
Conformational Energy ◽  
Coupling Constants ◽  
Amide Proton ◽  
Energy Calculations ◽  
Peptide Analog ◽  
Conformational Energy Calculations ◽  
Nuclear Overhauser

Conformational energy calculations have been employed to obtain minimum energy conformations of the peptide Val- Gly-Ala-Glu , an analogue of eosinophil chemotactic tetrapeptides. The calculated conformations of the peptide can be described as an ensemble of structures in which the C-terminal and N-terminal regions of the molecule are in close proximity. The charge state of the peptide showed a marked effect on the calculated conformation, and the results were also sensitive to the electrostatic environment. The calculations performed on the dianionic form of the molecule showed good agreement with experimental n.m.r . Data on coupling constants, amide-proton resonance chemical shifts and temperature coefficients, nuclear Overhauser effects, side-chain rotamer populations, and binding of paramagnetic ions, obtained in dimethyl sulfoxide solutions. The calculations demonstrate some of the inherent problems facing theoretical calculations of peptide structure.

Conformational and Structural characterization of carbohydrates and their interactions studied by NMR

2021 ◽  
Vol 28 ◽  
Author(s):  
Francisco Javier Cañada ◽  
Ángeles Canales ◽  
Pablo Valverde ◽  
Beatriz Fernández de Toro ◽  
Mónica Martínez-Orts ◽  
...  
Keyword(s):  
Structural Information ◽  
Theoretical Calculations ◽  
Chemical Shifts ◽  
Structural Complexity ◽  
Coupling Constants ◽  
Resonance Spectroscopy ◽  
Additional Information ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects

: Carbohydrates, either free or as glycans conjugated with other biomolecules, participate in many essential biological processes. Their apparent simplicity in terms of chemical functionality hides an extraordinary diversity and structural complexity. Deeply deciphering at the atomic level their structures is essential to understand their biological function and activities, but it is still a challenging task in need of complementary approaches and no generalized procedures are available to address the study of such complex, natural glycans. The versatility of Nuclear Magnetic Resonance spectroscopy (NMR) often makes it the preferred choice to study glycans and carbohydrates in solution media. The most basic NMR parameters, namely chemical shifts, coupling constants and nuclear Overhauser effects, allow defining short or repetitive chain sequences and characterize their structures and local geometries either in the free state or when interacting with other biomolecules, rendering additional information on the molecular recognition processes. The increased accessibility to carbohydrate molecules extensively or selectively labeled with 13C boosts the resolution and detail that analyzed glycan structures can reach. In turn, structural information derived from NMR, complemented with molecular modeling and theoretical calculations can also provide dynamic information on the conformational flexibility of carbohydrate structures. Furthermore, using partially oriented media or paramagnetic perturbations, it has been possible to introduce additional long-range observables rendering structural information on longer and branched glycan chains. In this review, we provide examples of these studies and an overview of the recent and most relevant NMR applications in the glycobiology field.

Carbon-13 and nitrogen-14 NMR spectra of 1-(substituted phenyl)pyridinium salts

1980 ◽  
Vol 45 (10) ◽  
pp. 2766-2771 ◽  
Author(s):  
Antonín Lyčka
Keyword(s):  
Heavy Water ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Pyridinium Salts ◽  
Nmr Signals ◽  
C Nmr

The 13C and 14N NMR spectra of 1M solutions of 1-(substituted phenyl)pyridinium salts (4-CH3, 4-OCH3, H, 4-Cl, 4-Br, 4-I, 3-NO2, 4-NO2, 2,4-(NO2)2 (the 13C NMR only)) have been measured in heavy water at 30 °C. The 13C and 14N chemical shifts, the 1J(CH) coupling constants, some 3J(CH) coupling constants, and values of half-widths Δ 1/2 of the 14N NMR signals are given. The 13C chemical shifts of C(4) correlate with the σ0 constants (δC(4) = (1.79 ± 0.097) σ0 + (147.67 ± 0.041)), whereas no correlation of the nitrogen chemical shifts with the σ constants has been found. The half-widths Δ 1/2 correlate with the σ0 constants (Δ 1/2 = (76.2 ± 4.9) σ0 + (106.4 ± 2.2)) except for 1-phenylpyridinium chloride.

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.

1H, 13C and 15N NMR Spectra of Coupling Products of Benzenediazonium Salts with Aliphatic Nitro Compounds and Study of Their E/Z Isomerism

1996 ◽  
Vol 61 (4) ◽  
pp. 589-596 ◽  
Author(s):  
Antonín Lyčka
Keyword(s):  
Dimethyl Sulfoxide ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Nitro Compounds ◽  
Coupling Constants ◽  
15N Nmr ◽  
Geometrical Isomers ◽  
Sodium Salts ◽  
Aliphatic Nitro Compounds ◽  
Tautomeric Forms

The 1H, 13C and 15N NMR spectra have been measured of coupling products of benzenediazonium salts with nitromethane, nitroethane, 1-nitropropane, 2-nitroethanol and of their sodium salts, and the chemical shifts have been unambiguously assigned. The coupling products have been found to exist only in their hydrazone tautomeric forms. Stereospecific behaviour of the coupling constants 2J(15N,1H) and 2J(15N,13C) in the 15N isotopomers and NOESY have been used to differentiate between the E and Z geometrical isomers. The above-mentioned compounds exist as Z isomers in deuteriochloroform and predominantly (>95%) as E isomers in dimethyl sulfoxide, while the sodium salts are present only as E isomers in dimethyl sulfoxide.

The High Resolution NMR Spectra of Pesticides. II. The DDT-Type Compounds

1969 ◽  
Vol 52 (5) ◽  
pp. 1074-1092 ◽  
Author(s):  
L H Keith ◽  
A L Alford ◽  
A W Garrison
Keyword(s):  
Nuclear Magnetic Resonance ◽  
High Resolution ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Aromatic Rings ◽  
Nuclear Magnetic Resonance Spectra ◽  
High Resolution Nmr ◽  
Related Compounds ◽  
Deshielding Effect

Abstract The high resolution nuclear magnetic resonance spectra of the DDT class of pesticides and related compounds are discussed, including a study of the resonances of the aromatic protons as they are affected by various substiluents. The CCl3 moiety on the α-carbon strongly deshields the ortho protons on the aromatic rings, and this deshielding effect is greatly enhanced by substitution of a chlorine ortho rather than para on the aromatic ring. These deshielding effects are explained by a consideration of the electronegativity of the substituents and the stereochemistry of the molecule. The chemical shifts and coupling constants are tabulated.

Structural Characterization of Natural Products By Means of Quantum Chemical Calculations of NMR Parameters: New insights

2021 ◽  
Author(s):  
Fabio Luiz Paranhos Costa ◽  
Ana Carolina Ferreira de Albuquerque ◽  
Rodolfo Goetze Fiorot ◽  
Luciano Morais Lião ◽  
Lucas Haidar Martorano ◽  
...  
Keyword(s):  
Natural Products ◽  
Structural Characterization ◽  
Quantum Chemical ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Nmr Parameters ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The calculation of NMR parameters for natural products was pioneered by Bifulco and coworkers in 2002. Since then, modelling 1H and 13C chemical shifts and spin-spin coupling constants for this...

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