scholarly journals Influence of per-O-sulfation upon the conformational behaviour of common furanosides

2019 ◽  
Vol 15 ◽  
pp. 685-694 ◽  
Author(s):  
Alexey G Gerbst ◽  
Vadim B Krylov ◽  
Dmitry A Argunov ◽  
Maksim I Petruk ◽  
Arsenii S Solovev ◽  
...  
Keyword(s):  
Ab Initio Calculations ◽  
Quantum Chemical ◽  
Low Energy ◽  
Coupling Constants ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Ring Conformation ◽  
Nmr Data ◽  
Conformational Investigation ◽  
Conformational Distribution

The studies on the recently discovered pyranoside-into-furanoside rearrangement have led us to conformational investigations of furanosides upon their total sulfation. Experimental NMR data showed that in some cases drastic changes of the ring conformation occurred while sometimes only the conformation of the exocyclic C4–C5 linkage changed. Herein we describe a combined quantum chemical and NMR conformational investigation of three common monosaccharide furanosides as their propyl glycosides: α-mannose, β-glucose and β-galactose. Full exploration of the furanoside ring by means of ab initio calculations was performed and coupling constants were calculated for each of the low-energy conformers. The results demonstrated preferred trans-orientation of H4–H5 protons in the non-sulfated molecules which changed to gauche-orientation upon sulfation. The effect is less pronounced in the galactosides. For all the studied structures changes in the conformational distribution were revealed by quantum mechanical calculations, that explained the observed changes in intraring coupling constants occurring upon introduction of sulfates.

scholarly journals Oxygenated Theonellastrols: Interpretation of Unusual Chemical Behaviors Using Quantum Mechanical Calculations and Stereochemical Reassignment of 7α-Hydroxytheonellasterol

Marine Drugs ◽  
2020 ◽  
Vol 18 (12) ◽  
pp. 607
Author(s):  
A-Young Shin ◽  
Hyi-Seung Lee ◽  
Yeon-Ju Lee ◽  
Jong Seok Lee ◽  
Arang Son ◽  
...  
Keyword(s):  
Chemical Shift ◽  
Chemical Shifts ◽  
Atomic Orbital ◽  
2D Nmr ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Epoxy Alcohol ◽  
Theonella Swinhoei ◽  
Nmr Data ◽  
Chemical Shift Calculations

A total of eight new oxygenated 4-exo-methylene sterols, 1–8, together with one artifact 9 and six known sterols 11–16, were isolated from the marine sponge Theonella swinhoei collected from the Bohol province in Philippines. Structures of sterols 1–8 were determined from 1D and 2D NMR data. Among the sterols, 8α-hydroxytheonellasterol (4) spontaneously underwent an allylic 1,3-hydroxyl shift to produce 15α-hydroxytheonellasterol (9) as an artifact; this was rationalized by quantum mechanical calculations of the transition state. In addition, the 1,2-epoxy alcohol subunit of 8α-hydroxy-14,15-β-epoxytheonellasterol (5) was assigned using the Gauge-Independent Atomic Orbital (GIAO) NMR chemical shift calculations and subsequent DP4+ analysis. Finally, comparison of the 13C chemical shifts of isolated 7α-hydroxytheonellasterol (6) with the reported values revealed significant discrepancies at C-6, C-7, C-8, and C-14, leading to reassignment of the C-7 stereochemistry in the known structure.

scholarly journals Electrochemical and DFT studies of brass corrosion inhibition in 3% NaCl in the presence of environmentally friendly compounds

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Milan B. Radovanović ◽  
Žaklina Z. Tasić ◽  
Marija B. Petrović Mihajlović ◽  
Ana T. Simonović ◽  
Milan M. Antonijević
Keyword(s):  
Quantum Chemical ◽  
Active Sites ◽  
Inhibition Efficiency ◽  
Energy Gap ◽  
Electrochemical Techniques ◽  
Inhibition Mechanism ◽  
Quantum Mechanical ◽  
Chemical Calculation ◽  
Quantum Mechanical Calculations ◽  
Eds Analysis

Abstract The effects of adenine, salicylaldoxime and 4(5)-methylimidazole on brass corrosion in NaCl were investigated. The investigation comprised electrochemical techniques, scanning electron microscopy and quantum chemical calculation. The results obtained by polarization measurements show that the examined compounds successfully inhibited the corrosion of brass. Additionally, the quantum mechanical calculations indicate that there is a correlation between energy gap and inhibition efficiency. Moreover, the inhibition mechanism includes the adsorption of the inhibitor on active sites on the electrode surface, which was confirmed by SEM-EDS analysis of the brass.

Simple Synthesis of Complex Amines from the Diels–Alder Adducts of (–)-Cytisine

Synthesis ◽  
2021 ◽  
Author(s):  
Alexander Shivanyuk ◽  
Alexey Chuyko ◽  
Grygoriy Dolgonos ◽  
Volodymyr Fetyukhin ◽  
Oleg Lukin
Keyword(s):  
Quantum Chemical ◽  
Alder Reaction ◽  
Diels Alder ◽  
Secondary Amines ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Carbonyl Groups ◽  
Model Compounds ◽  
Reaction Progress ◽  
Diels Alder Reaction

AbstractThe Diels–Alder reaction of N-benzylcytisine with N-methyl- and N-benzylmaleimides is 100% endo-selective and gives the corresponding syn- and anti-diastereomers in 11–42% isolated yields. The studies of the reaction progress with LCMS and NMR along with detailed quantum chemical calculations revealed that some Diels–Alder adducts are kinetically and their isomers are thermodynamically controlled products. The Pd/C-catalyzed hydrogenation of benzyl-protected cytisine amine derivatives resulted in the removal of the benzyl group and the addition of hydrogen to the C=C double bond to give the corresponding secondary amines in 45–84% yield. The complete reduction of carbonyl groups in a cytisine derivative with LiAlH4 in THF under reflux afforded the respective tricyclic triamine. Quantum mechanical calculations for the mechanism of the Diels–Alder reaction between the simplest model compounds are presented.

scholarly journals lamaGOET: an interface for quantum crystallography

2021 ◽  
Vol 54 (3) ◽  
Author(s):  
Lorraine A. Malaspina ◽  
Alessandro Genoni ◽  
Simon Grabowsky
Keyword(s):  
Least Squares ◽  
Quantum Chemical ◽  
Theoretical Calculations ◽  
Molecular Orbitals ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
X Ray ◽  
Localized Molecular Orbitals ◽  
Quantum Crystallography

In quantum crystallography, theoretical calculations and crystallographic refinements are closely intertwined. This means that the employed software must be able to perform both quantum-mechanical calculations and crystallographic least-squares refinements. So far, the program Tonto is the only one able to do that. The lamaGOET interface described herein deals with this issue since it interfaces dedicated quantum-chemical software (the widely used Gaussian package and the specialized ELMOdb program) with the refinement capabilities of Tonto. Three different flavours of quantum-crystallographic refinements of the dipetide glycyl-L-threonine dihydrate are presented to showcase the capabilities of lamaGOET: Hirshfeld atom refinement (HAR), HAR-ELMO, namely HAR coupled with extremely localized molecular orbitals, and X-ray constrained wavefunction fitting.

Rydberg transitions as a probe for structural changes and phase transition at polymer surfaces: an ATR-FUV-DUV and quantum chemical study of poly(3-hydroxybutyrate) and its nanocomposite with graphene

2018 ◽  
Vol 20 (13) ◽  
pp. 8859-8873 ◽  
Author(s):  
Krzysztof B. Beć ◽  
Yusuke Morisawa ◽  
Kenta Kobashi ◽  
Justyna Grabska ◽  
Ichiro Tanabe ◽  
...  
Keyword(s):  
Phase Transition ◽  
Quantum Chemical ◽  
Structural Changes ◽  
Quantum Chemical Study ◽  
Chemical Study ◽  
Polymer Surfaces ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Rydberg Transitions

ATR-FUV-DUV (145–300 nm; 8.55–4.13 eV) and quantum mechanical calculations study of PHB and its nanocomposite with graphene.

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