scholarly journals A 300-fold enhancement of imino nucleic acid resonances by hyperpolarized water provides a new window for probing RNA refolding by 1D and 2D NMR

2020 ◽  
Vol 117 (5) ◽  
pp. 2449-2455 ◽  
Author(s):  
Mihajlo Novakovic ◽  
Gregory L. Olsen ◽  
György Pintér ◽  
Daniel Hymon ◽  
Boris Fürtig ◽  
...  
Keyword(s):  
Nmr Spectra ◽  
Chemical Exchange ◽  
Solvent Accessibility ◽  
2D Nmr ◽  
Rapid Acquisition ◽  
H Nmr ◽  
Rapid Monitoring ◽  
Nmr Sensitivity ◽  
A Site ◽  
Aptamer Domain

NMR sensitivity-enhancement methods involving hyperpolarized water could be of importance for solution-state biophysical investigations. Hyperpolarized water (HyperW) can enhance the 1H NMR signals of exchangeable sites by orders of magnitude over their thermal counterparts, while providing insight into chemical exchange and solvent accessibility at a site-resolved level. As HyperW’s enhancements are achieved by exploiting fast solvent exchanges associated with minimal interscan delays, possibilities for the rapid monitoring of chemical reactions and biomolecular (re)folding are opened. HyperW NMR can also accommodate heteronuclear transfers, facilitating the rapid acquisition of 2-dimensional (2D) 15N-1H NMR correlations, and thereby combining an enhanced spectral resolution with speed and sensitivity. This work demonstrates how these qualities can come together for the study of nucleic acids. HyperW injections were used to target the guanine-sensing riboswitch aptamer domain (GSRapt) of the xpt-pbuX operon in Bacillus subtilis. Unlike what had been observed in proteins, where residues benefited of HyperW NMR only if/when sufficiently exposed to water, these enhancements applied to every imino resonance throughout the RNA. The >300-fold enhancements observed in the resulting 1H NMR spectra allowed us to monitor in real time the changes that GSRapt undergoes upon binding hypoxanthine, a high-affinity interaction leading to conformational refolding on a ∼1-s timescale at 36 °C. Structural responses could be identified for several nucleotides by 1-dimensional (1D) imino 1H NMR as well as by 2D HyperW NMR spectra acquired upon simultaneous injection of hyperpolarized water and hypoxanthine. The folding landscape revealed by this HyperW strategy for GSRapt, is briefly discussed.

E-Homolupane Derivatives Substituted in Position 17 and 22a. 1H NMR, 13C NMR and IR Spectra

1995 ◽  
Vol 60 (4) ◽  
pp. 619-635 ◽  
Author(s):  
Václav Křeček ◽  
Stanislav Hilgard ◽  
Miloš Buděšínský ◽  
Alois Vystrčil
Keyword(s):  
Nmr Spectra ◽  
2D Nmr ◽  
Coupling Constants ◽  
Side Chain ◽  
Oxidation Reactions ◽  
H Nmr ◽  
Complete Assignment ◽  
Nmr Techniques ◽  
Intramolecular Association ◽  
C Nmr

A series of derivatives with various oxygen functionalities in positions 17,22a or 19,20 was prepared from diene I and olefin XVI by addition and oxidation reactions. The structure of the obtained compounds was confirmed by 1H NMR, 13C NMR and IR spectroscopy. The kind of intramolecular association of the 17α-hydroxy group was studied in connection with modification of the side chain and substitution in position 22a. Complete assignment of the hydrogen signals and most of the coupling constants was accomplished using a combination of 1D and 2D NMR techniques. The 1H and 13C NMR spectra are discussed.

scholarly journals Reactions of 3-(p-substituted-phenyl)-5-chloromethyl-1,2,4-oxadiazoles with KCN leading to acetonitriles and alkanes via a non-reductive decyanation pathway

2018 ◽  
Vol 14 ◽  
pp. 3011-3017
Author(s):  
Akın Sağırlı ◽  
Yaşar Dürüst
Keyword(s):  
Nmr Spectra ◽  
2D Nmr ◽  
Synthetic Route ◽  
X Ray ◽  
H Nmr ◽  
2D Nmr Spectra ◽  
Tof Ms ◽  
C Nmr

The present work describes an unfamiliar reaction of 5-(chloromethyl)-3-substituted-phenyl-1,2,4-oxadiazoles with KCN affording trisubstituted 1,2,4-oxadiazol-5-ylacetonitriles and their parent alkanes, namely, 1,2,3-trisubstituted-1,2,4-oxadiazol-5-ylpropanes. To the best of our knowledge, the current synthetic route leading to decyanated products will be the first in terms of a decyanation process which allows the transformation of trisubstituted acetonitriles into alkanes by the incorporation of KCN with the association of in situ-formed HCN and most likely through the extrusion of cyanogen which could not be detected or isolated. In addition, the plausible mechanisms were proposed for both transformations. The structures of the title compounds were identified by means of IR, 1H NMR, 13C NMR, 2D NMR spectra, TOF–MS and X-ray measurements.

Studies of structure and dynamics in a nominally symmetric twisted amide by NMR and electronic structure calculations

2006 ◽  
Vol 84 (3) ◽  
pp. 421-428 ◽  
Author(s):  
Alex D Bain ◽  
Hao Chen ◽  
Paul H.M Harrison
Keyword(s):  
Electronic Structure ◽  
Nmr Spectra ◽  
Chemical Exchange ◽  
Electronic Structure Calculations ◽  
Amide Bond ◽  
Electronic Effects ◽  
H Nmr ◽  
Line Shape Analysis ◽  
Structure Calculations ◽  
C Nmr

Amides that are twisted around the C—N bond show unusual spectroscopy and reactivity when compared with planar amides. The diacyl derivatives of 3,4,7,8-tetramethyl-2,5-dithioglycoluril are intriguing examples of this class, since the crystal structures show that the two acyl groups are twisted by different amounts on either side of the molecule owing to a combination of steric and electronic effects. However, the 1H NMR spectra in solution at room temperature exhibit only one acyl resonance, so there must be fast interconversion among pairs of equivalent structures of each compound. We have prepared a number of derivatives with different acyl groups, both on the glycoluril framework as well as on its dithio analogue. The chemical exchange in solution was slowed down sufficiently by cooling to see individual sites for only two compounds: the dithiodipivaloyl and the dithiodiadamantyl derivatives. The barriers were estimated at 41 kJ mol–1 for the dipivaloyl derivative and 45 kJ mol–1 for diadamantyl derivative. The results show that rotation around the twisted amide bond is slowed by both the steric size of the acyl group and the presence of the thioureido group vs. the ureido group in the glycoluril core. In the solid-state 13C NMR spectra, there is no evidence for any dynamics, even for the diacetyl derivative at ambient temperature. Electronic structure calculations predict a geometry for the dipivaloyl derivative very close to that observed in the crystal structure. These results indicate that the crystal confines, but does not distort the molecule. A mechanism for the exchange is proposed. The relevance of these results to the mechanism of Claisen-like condensations in diacylglycolurils is also discussed.Key words: 1H and 13C NMR, exchange, dynamics, CP/MAS, solids, line shape analysis, amides, twisted amides, atropisomers, glycoluril.

Structure of a pentacyclic triterpenyl angelate from Loeseliamexicana. 1H 2D-NMR data and stereochemistry

1989 ◽  
Vol 67 (12) ◽  
pp. 2071-2077 ◽  
Author(s):  
M. Jiménez E. ◽  
K. Velézquez ◽  
A. Lira-Rocha ◽  
A. Ortega ◽  
E. Díaz ◽  
...  
Keyword(s):  
Nmr Spectra ◽  
Parent Compound ◽  
2D Nmr ◽  
X Ray Diffraction ◽  
Pentacyclic Triterpene ◽  
Nmr Structure Determination ◽  
X Ray ◽  
H Nmr ◽  
Nmr Data ◽  
Unambiguous Assignment

The total assignment of 1H NMR spectra of a pentacyclic triterpene from Loeseliamexicana was performed using selected 2D-NMR experiments (COSY, NOE). X-ray diffraction data were obtained from the parent compound as supplemental information to the NMR investigations. The data allowed for the unambiguous assignment of the structure and the stereochemistry of the title compound. Keywords: pentacyclic triterpene NMR, 2D NMR of terpenes, X-ray of triterpenes, triterpenyl angelate NMR, X-ray -2D NMR structure determination.

X-ray structural and nuclear magnetic resonance study of open chain and macrocyclic thioether complexes

1990 ◽  
Vol 68 (8) ◽  
pp. 1357-1363 ◽  
Author(s):  
C. Robert Lucas ◽  
Shuang Liu ◽  
Michael J. Newlands ◽  
Eric J. Gabe
Keyword(s):  
Nmr Spectra ◽  
Chemical Exchange ◽  
Variable Temperature ◽  
Low Frequency ◽  
Nuclear Magnetic Resonance Study ◽  
Conformational Exchange ◽  
Open Chain ◽  
H Nmr ◽  
Chain Complexes ◽  
C Nmr

Preparations of the thiophenophane and open chain thioether complexes MX2•BBTE(M = Pd; X = Cl, I)(M = Pt; X = Cl) (BBTE = 1,2-bis(benzylthio)ethane) and MX2•L (M = Pd; X = Cl, Br, I, SCN) (M = Pt; X = Cl) (L = 2,5,8-trithia[9](2,5)thiophenophane) are described. The molecular structure of PdBr2•L which contains a weak thiophene-sulfur-to-palladium interaction has been determined: space group P21/n, a = 8.3569(3), b = 16.3254(15), c = 11.1462(3) Å, β = 92.833(4)°, Z = 4, Rf = 0.060, Rw = 0.058. The electronic, low frequency ir, and 13C nmr spectra are described. Variable temperature 1H nmr spectra are discussed and it is concluded that the open chain complexes undergo rapid conformational exchange at room temperature but are configurationally rigid unless the temperature is increased. In contrast, the macrocyclic complexes undergo very limited conformational and no configurational exchange up to their decomposition temperatures. They are also nonfluxional in the same temperature range. Chemical exchange of acidic ligand hydrogens and a metal–ligand dissociative equilibrium were also detected when X = SCN. Keywords: thiophene, thioether, macrocyclic metal complexes.

Conformational structure of ethylene glycol dibenzoate. Vibrational and NMR spectra

1981 ◽  
Vol 46 (8) ◽  
pp. 1913-1929 ◽  
Author(s):  
Bohdan Schneider ◽  
Pavel Sedláček ◽  
Jan Štokr ◽  
Danica Doskočilová ◽  
Jan Lövy
Keyword(s):  
Ethylene Glycol ◽  
Vibrational Spectra ◽  
Nmr Spectra ◽  
Coupling Constants ◽  
Conformational Structure ◽  
Infrared And Raman Spectra ◽  
H Nmr ◽  
Liquid States ◽  
Crystalline Forms ◽  
C Nmr

It was found that three crystalline forms of ethylene glycol dibenzoate can be prepared. Infrared and Raman spectra of these three forms, as well as of the glassy and liquid states, were measured. From 3JHH coupling constants obtained by analysis of the 13C satellite band of the -CH2- group in 1H NMR spectra, and from the 3JCH coupling constants of the -CO.O.CH2- fragment obtained by analysis of the carbonyl band in 13C NMR spectra it was found that in the liquid state the -CH2-CH2- group exists predominantly in the gauche conformational structure, and the bonds C-O-C-C assume predominantly a trans orientation. The results of the analysis of NMR and vibrational spectra were used for the structural interpretation of conformationally sensitive bands in vibrational spectra of ethylene glycol dibenzoate.

Preparation and absolute configuration at C(20) of 21-nor-5α-chol-22-en-24→20-olide derivatives

1981 ◽  
Vol 46 (4) ◽  
pp. 917-925 ◽  
Author(s):  
Vladimír Pouzar ◽  
Miroslav Havel
Keyword(s):  
Absolute Configuration ◽  
Nmr Spectra ◽  
Lithium Salt ◽  
H Nmr ◽  
Chemical Correlation ◽  
Unsaturated Lactones

Reaction of the aldehyde I with the lithium salt of 1-(2-tetrahydropyranyloxy)-2-propyne yielded the compounds II and IV. From the compound II the lactone XII was prepared via the intermediates III and X, the lactone XVIII was prepared from the substance IV via the intermediates V and XVI. The unsaturated lactones XII and XVIII were also prepared by sulfenylation and dehydrosulfenylation of the saturated lactones XIII and XIX. Based on chemical correlation and 1H-NMR spectra analyses of the compounds II and IV, the lactone XII was assigned the 20R-configuration whereas the lactone XVIII was allotted the 20S-configuration.

New type of addition to 5-substituted 4-arylidene-2-(4,5-dihydrofurfurylidene)-N,N-dimethyliminium bisperchlorates. Preparation of 4-substituted 5-(N,N-dimethylamino)-2-furancarbaldehydes

1986 ◽  
Vol 51 (3) ◽  
pp. 573-580 ◽  
Author(s):  
Tibor Gracza ◽  
Zdeněk Arnold ◽  
Jaroslav Kováč
Keyword(s):  
Nmr Spectra ◽  
Addition Reaction ◽  
H Nmr ◽  
Organic Bases ◽  
New Type

4-Arilidene-5-(N,N-dimethyliminium)-2-(4,5-dihydrofurfurylidene)-N,N-dimethyliminium bisperchlorate I undergoes a 1,4-addition reaction with organic bases under re-formation of the furan nucleus; this behaviour has been utilized in the preparation of new 4-substituted 5-(N,N-dimethylamino)-2-furancarbaldehydes II, III. The structure of the prepared compounds has been confirmed by 13C and 1H NMR spectra.

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