Dipeptides containing N-terminal threonine residues: quantum chemical structural studies on nonionic, zwitterionic and water-clustered systems

2015 ◽  
Vol 26 (4) ◽  
pp. 1025-1037 ◽  
Author(s):  
Gunajyoti Das ◽  
Shilpi Mandal
Keyword(s):  
Quantum Chemical ◽  
Structural Studies ◽  
Clustered Systems

Structural Studies of Chelirubine and Chelilutine Free Bases

1998 ◽  
Vol 63 (7) ◽  
pp. 1045-1055 ◽  
Author(s):  
Jiří Dostál ◽  
Jiří Slavík ◽  
Milan Potáček ◽  
Radek Marek ◽  
Otakar Humpa ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Nmr Spectroscopy ◽  
Quantum Chemical ◽  
2D Nmr ◽  
Molecular Symmetry ◽  
Structural Studies ◽  
Free Base ◽  
2D Nmr Spectroscopy ◽  
Sanguinaria Canadensis ◽  
First Time

The structures of chelirubine and chelilutine free bases have been examined by 2D NMR spectroscopy and mass spectrometry. Chelirubine chloride (1a) upon treatment with Na2CO3 yielded free base which possessed the constitution of bis(5,6-dihydrochelirubin-6-yl) ether (2a). The free base of chelilutine (1b) was determined to be bis(5,6-dihydrochelilutin-6-yl) ether (2b). The aqueous NH3 treatment of chelilutine (1b) produced bis(5,6-dihydrochelilutin-6-yl)amine (3b). 6-Hydroxy-5,6-dihydrochelirubine (4a) and 6-hydroxy-5,6-dihydrochelilutine (4b) were detected only in CDCl3 solution by NMR spectroscopy. In CDCl3, the compound 2b underwent hydrolysis to 4b that was immediately followed by the reverse condensation to a diastereomer of 2b. Pseudokinetics of this reaction was followed by NMR spectroscopy and quantum chemical calculations were carried out to support the suggested type of molecular symmetry alteration. The known alkaloid dihydrochelirubine (5) was isolated for the first time from Sanguinaria canadensis.

scholarly journals RELATIVISTIC CALCULATIONS OF MAGNETORESONSONIC PARAMETERS IN STRUCTURAL STUDIES OF ELEMENTENTORGANIC COMPOUNDS

2020 ◽  
Vol 2018 (1) ◽  
pp. 17-18
Author(s):  
Leonid Krivdin
Keyword(s):  
Quantum Chemical ◽  
Organophosphorus Compounds ◽  
Chemical Shifts ◽  
Relativistic Effects ◽  
Basis Set ◽  
Spin Interaction ◽  
Chemical Calculation ◽  
Structural Studies ◽  
Wide Range ◽  
High Level

Systematic structural studies were carried out in a wide range of nitrogen, silicon, phosphorus, selenium, and organophosphorus compounds by quantum-chemical calculations of a high level of isotropic absolute magnetic-shielding constants (chemical shifts) and spin-spin interaction constants involving 1H, 13C, 15N, 19F, 29Si, 31P, 77Se and 125Te in comparison with the experiment. The analysis of the factors determining the accuracy of the quantum chemical calculation of the discussed magnetoresonance parameters including the level of the theory and the quality of the basis set, the influence of the medium, vibrational corrections, and relativistic effects are analyzed.

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