Application of two-dimensional NMR spectroscopy to the complete analysis of the 1H and 13C NMR spectra of d-biotin in aqueous solution

The ¹H and ¹³C NMR spectra of d-biotin were observed at 400 and 100 MHz, respectively. Various types of two-dimensional NMR spectroscopy were performed to assign the spectra. The previous assignment of ¹³C NMR spectrum of d-biotin reported by Bradbury and Johnson was modified, and the dihedral angles between the C? H bonds of the ring were determined. The populations of the conformers produced by internal rotation around the C-2? C-δ bond were estimated.     

Conformational study of phosphothreonine in aqueous solution. H and 13C NMR results

The 270 MHz ¹H and 22.6 MHz ¹³C NMR spectra of DL -phosphothreonine in D₂O have been measured and analysed as a function of pD. The trans-trans conformation of the fragment H-α? C-α? C-β? O? P predominates at all pD values. The C-β—O gauche contribution is notably larger for pD values in the range 7≤pD<10 than for acidic or more basic solutions which is in accordance with earlier results for phosphoserine (PSer).     

Microenvironmental and conformational structure of triblock copolymers in aqueous solution by 1H and 13C NMR spectroscopy

1H and 13C nuclear magnetic resonance (NMR) spectra of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers in D2O solutions have been systematically investigated. The detailed assignments of various 1H and 13C NMR signals are presented. The hyperfine structure of PO -CH2- protons was clearly assigned, the arising reason of this hyperfine structure was attributed to the influence of the chiral center of -CHCH3- groups and the direct coupling between the PO -CH2- and -CH3 protons. The external standard 2,2-dimethyl-2-silapentane-5-sulfonate sodium salt (DSS) was firstly applied in this system. Accurate chemical shift values referenced to the external standard DSS were obtained. 1H NMR chemical shift of PO -CH2- and -CH3 signals shows a larger decrease in ppm values than that of EO -CH2- signal with the increase of PPO/PEO ratio or temperature indicating that PO segments exist in a more hydrophobic microenvironment. A new resonance signal assigned to the PO -CH2- protons appeared when the temperature is above the CMT, which is attributed to the breakdown of the intra-molecular (C-H)...O hydrogen bond between the PO -CH2- protons and the ester oxygens. The breakdown of this intra-molecular hydrogen bond may result in a decrease of gauche conformers of the PPO chain. The increase of 13C NMR chemical shift of block copolymers validates this conformational change assumption. It can be inferred that the amount of gauche conformers decreases whereas that of trans conformers increases in both PO and EO chains when elevating the PPO/PEO ratio or temperature. The observed 13C NMR chemical shifts of PO segments show a bigger increase than those of EO segments, supporting the formation of a nonpolar microenvironment around PO segments.     

1H NMR study of self-association of actinomycin D in an aqueous solution

This paper presents the results of a proton magnetic resonance study (500 MHz) of self-association of actinomycin D (AMD) antibiotic in an aqueous solution. The equailibrium constants and thermo-dynamic parameters (ΔH, ΔS) of molecular association as well as the limiting values of proton chemical shifts of associate molecules were determined from the concentration and temperature dependences of¹H NMR chemical shifts of AMD. The results were analyzed using dimeric and infinite-dimensional cooperative models of molecular self-association. The value of the cooperativity parameter indicates that AMD self-association is anticooperative, i.e., formation of aggregates larger than dimers is energetically unfavorable. The values of induced proton chemical shifts were used to determine the most probable mutual orientation of chromophores in AMD structure. Sevastopol State Technical University. Berkbeck College, London University. Translated fromZhurnal Struktumoi Khimii, Vol. 36, No. 1, pp. 81–88, January–February, 1995. Translated by L. Smolina     

Investigation of the association of aromatic dyestuff molecules in aqueous solution by1H NMR

We have studied experimentally the proton chemical shifts of the molecules of Acridine Orange and proflavine in aqueous solution as a function of the.concentration of the aromatic ligands. A method is proposed for determining the chemical shifts of the protons in associations from the observed concentration dependence of the proton chemical shifts of dyestuff molecules in solution, which can be used at fairly high concentrations of the interacting molecules. The association constants of the dyestuff molecules and the proton chemical shifts in the association have been calculated. The proton shifts obtained have been used toether with a model of the ring currents to determine the most probable structure for the 1:1 molecular complexes of Acridine Organce and proflavine in aqueous solution.Sevastopol Institute for Instrument Construction. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, No. 1, pp. 83–89, January–February, 1991. Original article submitted February 2, 1988.     

1H NMR spectroscopic study of complexation of citalopram with beta-cyclodextrin in aqueous solution

(1)H NMR spectroscopic study of citalopram (CT) in the absence as well as in the presence of beta-cyclodextrin (beta-CD) in aqueous solution revealed the formation of four 1:1 beta-CD-CT inclusion complexes. The stoichiometry of the complexes was determined by the continuous variation (Job) method, which was further confirmed by Scott's method. The binding constants (K(R) and K(R, S)) were calculated using Scott's method. The structures of all the complexes have been proposed as shown in the diagrams. All the CT proton resonances showed splitting in the presence of beta-CD, owing to chiral discrimination by the beta-CD, between the two enantiomers. The chiral discrimination appears to be due to different modes of binding of the R- and S-CT in the complexes involving a CN-containing aromatic ring.     

Investigation of the self-association of proflavine and acridine orange molecules in aqueous solution by 1H NMR

The chemical shifts of the protons in the proflavine and acridine orange molecules in aqueous solution were measured by ¹H NMR spectroscopy. The equilibrium constants for the association of the molecules and the chemical shifts of the protons in the monomers and associates were obtained from the concentration dependence of the proton chemical shifts. The most probable structures for the dimers of the dyes were calculated on the basis of the obtained chemical shifts, and a comparative analysis was made.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 3, pp. 373–376, May–June, 1987.     

The tautomerism of Omeprazole in solution: a 1H and 13C NMR study

The tautomerism of 5(6)-methoxy-2-([(4-methoxy-3,5-dimethyl-2-pyridinyl)methyl] sulfinyl)-1H-benzimidazole (omeprazole) was determined in solution, K(T) = 0.59 in THF at 195 K, in favor of the 6-methoxy tautomer. The assignment of the signals was made by comparison with its two N-methyl derivatives in acetone-d6 and through theoretical calculations of the absolute shieldings (GIAO/DFT/6-311++G**).     

Complete 1H, 13C{1H}, and 31P NMR spectral parameters of some pyrophosphates

The ¹H, ¹³C{¹H}, and ³¹P NMR spectral parameters of some pyrophosphates were determined in CDCl₃. The most complicated ¹H spectrum can be solved fully only as (A₃MN)R₆XX′R₆′(MNA₃)′, where R₆ (= ―N(CH₃)₂) is coupled only to phosphorus (X). Second‐order coupling between phosphorus was found and solved with iterative analysis. A signal shape of one of the carbon resonance cannot be explained only with couplings. Explanation for exceptional shape was searched from molecular modeling results. Copyright © 2017 John Wiley & Sons, Ltd.     

Differential protonation and dynamic structure of doxylamine succinate in solution using 1H and 13C NMR

A protonation and dynamic structural study of doxylamine succinate, a 1:1 salt of succinic acid with dimethyl-[2-(1-phenyl-1-pyridin-2-yl-ethoxy)ethyl]amine, in solution using one- and two-dimensional 1H and 13C NMR experiments at variable temperature and concentration is presented. The two acidic protons of the salt doxylamine succinate are in 'intermediate' exchange at room temperature, as evidenced by the appearance of a broad signal. This signal evolves into two distinct signals below about -30 degrees C. A two-dimensional 1H-1H double quantum filtered correlation experiment carried out at -55 degrees C shows protonation of one of the acidic protons to the dimethylamine nitrogen. A two-dimensional rotating frame 1H-1H NOE experiment at the same temperature reveals that the other proton remains with the succinate moiety. Comparison of the 1H and 13C chemical shifts and the 13C T1 relaxation times of the salt with those of the free base further substantiate the findings.     

Manifestation of microgel-like particles of styrene-ethylene dimethacrylate copolymers in solution in 1H and 13C NMR spectra

From the integrated intensities of ¹H NMR bands it has been found that in solutions of styrene (St)-ethylene dimethacrylate (EDMA) copolymers, a considerable part of the monomer units do not show directly in high-resolution ¹H NMR spectra and it is suggested that these monomer units form compact structures, probably acting as cores of microgel-like particles. In ¹³C NMR spectra all monomer units are shown, including those which are part of the compact microgel structures. From a comparison of ¹H NMR spectra with other analytical methods (elemental analysis, infrared spectra) it follows that the composition of the copolymer in the core of the microgel is the same as the overall composition of the copolymer. The content of the compact structures in the microgel increases with the content of the EDMA component. The results are discussed from the point of view of structural features and of the motional restrictions of the St/EDMA copolymers in CCl₄ solution. The consequences for ¹H NMR analysis of copolymer composition are also discussed.     

1H and 13C NMR spectra of N-vinylpyrroles

The position of the substituants in 2, 3-dialkyl-1-vinylpyrroles and 7-methyl-1 vinyl-4,5,6,7-tetrahydroindole was established on the basis of the ¹H and ¹³C NMR spectra. It was found that the S-trans conformation of the N-vinyl group is preferred. It is shown that the condensation of ketoximes with acetylene proceeds through the formation of free pyrroles and that vinyl oximes are not intermediates in the condensation.     

1H NMR and calorimetric study on binding ability of cyclodextrins to isomeric pyridinecarboxylic acids in aqueous solution

Complex formation of α- and β-cyclodextrins with isomeric pyridinecarboxylic acids (picolinic, nicotinic and isonicotinic acids) in water were studied by calorimetry and ¹H NMR at 298.15 K. The obtained results revealed the weak 1:1 complex formation governed by the cavity dimensions and position of the carboxylic group in the pyridine ring. It was found that selective inclusion complex formation of α- and β-cyclodextrins with nicotinic and isonicotinic acids takes place. In the case of picolinic acid, the considerable role of external interactions and formation of less stable complexes were detected. The location of the carboxylic group in the meta-position of pyridine ring is more favorable for the effective binding. The pyridinecarboxylic acids are shallow inserted into α-cyclodextrin cavity possessing the smaller diameter, while they are deeply included into β-cyclodextrin cavity. Thermodynamic parameters of complex formation (K, Δ_cG⁰, Δ_cH⁰ and Δ_cS⁰) were calculated and discussed in terms of influence of reagents structure.     

Assignment of the 1H and 13C NMR of tocotrienols

Vitamin E is a family of chromanols that vary by the degree of methylation of the chroman ring as well as the nature of the hydrophobic side chain at C2 that serves to anchor these lipids in biological membranes. The tocopherols contain saturated side chains, whereas the tocotrienols contain three sites of unsaturation and are derived from geranylgeranyl diphosphate. A growing interest in the unique biological activities of the tocotrienols has led us to begin syntheses of isotopically substituted forms and other derivatives that will be useful for probing the metabolism and membrane behavior of the tocotrienols. In order to be certain of our ability to selectively modify sites on the parent molecules it was necessary to make as complete an assignment of the 1H and 13C NMR as possible. Herein we report multidimensional NMR data (HSQC, COSY, ADEQUATE(1,1), C--H HMBC, and NOESY) that have allowed us to assign the identity of almost all the resonances for alpha-, beta-, gamma-, and delta-tocotrienol.     

Molecular motion and 1H NMR relaxation of aqueous poly(N-isopropylacrylamide) solution under high pressure

In order to obtain useful information about the molecular motion and structure of poly(N-isopropylacrylamide) (PNiPAM) in aqueous solution, proton spin-lattice relaxation times, proton spin-spin relaxation times, and volume changes were measured at pressures from 1 to 400 kg/cm² as a function of temperature. We found that the molecular motion and the structure of water and PNiPAM in PNiPAM/water solution transitionally change at gelation temperature (31°C). The effect of pressure on such transitional changes is studied. It is suggested that application of pressure to the system prevents the gelation.     

13C NMR study of D-pantothenic acid complexes with heavy lanthanide ions in aqueous solution

The ¹³C NMR study of the interaction between the trivalent lanthanide ions (from Dy to Lu) and D-pantothenic acid in aqueous solution was presented. The unambiguous resonance assignments were made on the basis of pH dependence and the analysis of molecular geometry. ¹³C paramagnetic shifts were separated into the contact and dipolar components by Reilley's method. The complex stability constant is 12.0 L / mol for the 1:1 ytterbium complex. An analysis of the shift data shows that heavy lanthanide ions form isostructural complexes with the substrate and the hyperfine coupling constant is independent of the ions used in the study. D-pantothenic acid is coordinated to the metal via the two oxygens of the carboxyl group with 2.25Å of Ln—O distances. The electron spin density distribution and the structural details of the complex were elucidated from the shift data. It is stated that contact contributions, while small for nuclei of several bonds away from the metal, should not be dismissed a priori.     

Investigation of the structures of associates of the acridine dye proflavin with deoxytetranucleotides in aqueous solution by 1H NMR spectroscopy

A comparative investigation was made of the complex formation of proflavin with isomeric CG-containing self-complementary deoxytetraribonucleoside triphosphates in aqueous solution by ¹H NMR spectroscopy (500 MHz). Two-dimensional homogeneous 2M-COSY and 2M-NOESY spectroscopy was used for complete assignment of the proton signals of the molecules in solutions and for qualitative analysis of the nature of the reaction of the dye with the tetranucleotides. The concentration dependences of the proton chemical shift of the molecules were measured. The equilibrium constants of the reactions, the relative content of associates of various types, and the limiting values of the chemical shifts of the dye protons in the complex were determined according to the proposed models of complex formation. A comparative analysis was made of the characteristics of binding of the dye to tetranucleotides with various sequences of nitrogen bases and the structural characteristics of the molecular complexes formed in solution.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 28, Nos. 5–6, pp. 424–429, September–December, 1992.