Nitrogen-15 NMR Study Research Articles

Nitrogen-15 NMR study on the incorporation of nitrogen into aquatic NOM upon chloramination

Nitrogen-15 NMR study on the incorporation of nitrogen into aquatic NOM upon chloramination

Self-Assembly of DNA and RNA Building Blocks Explored by Nitrogen-14 NMR Crystallography: Structure and Dynamics.

The isotopic enrichment of nucleic acids with nitrogen-15 is often carried out by solid-phase synthesis of oligonucleotides using phosphoramidite precursors that are synthetically demanding and expensive. These synthetic challenges, combined with the overlap of chemical shifts, explain the lag of nitrogen-15 NMR studies of nucleic acids behind those of proteins. For the structural characterization of DNA and RNA-related systems, new NMR methods that exploit the naturally occurring 99.9 % abundant nitrogen-14 isotope are therefore highly desirable. In this study, we have investigated nitrogen-14 spectra of self-assembled quartets based on the nucleobase guanine in the solid state by means of magic-angle spinning NMR spectroscopy. The network of dipolar proton-nitrogen couplings between neighboring stacked purine units is probed by 2D spectra based on 1 H→14 N→1 H double cross-polarization. Interplane dipolar contacts are identified between the stacked G quartets. The assignment is supported by density functional theory (DFT) calculations of the anisotropic chemical shifts and quadrupolar parameters. The experimental spectra are fully consistent with internuclear distances obtained in silico. Averaging of chemical shifts due to internal motions can be interpreted by semiempirical calculations. This method can easily be extended to synthetic G quartets based on nucleobase or nucleoside analogs and potentially to oligonucleotides.

Solid-State Nitrogen-15 NMR and Quantum Chemical Study ofN,N-Dimethylaniline Derivatives

In this study the components of the nitrogen chemical shift (CS) tensor are examined for a series of para substituted N,N-dimethylaniline derivatives. This is done through measurement of the 15N NMR spectra of powder samples and through quantum chemical calculations on the isolated molecules. Experiments and calculations show that the isotropic CS, delta(iso), decreases with increasing electron donating ability of the para substituent, in agreement with previous solution studies. More importantly, this study shows that this decrease in the isotropic (solution) CS is due to decreasing values of the CS tensor component delta(11) and component delta(33). The component delta(22) is essentially invariant to the electron donating/withdrawing ability of the para substituent. Through Ramsey's theory of nuclear magnetic shielding, it can be seen that the variation in delta(11) and delta(33), and hence delta(iso), is due to changes in the n-pi* and the sigma-pi* energy gaps in N,N-dimethylaniline. This, in turn, is a result of the change in the energy of the pi* molecular orbital with change in the pi-electron donating ability of the para substituent. The effects of nitrogen inversion on the components of the nitrogen CS tensor components are also discussed. This study also shows the feasibility of performing 15N cross-polarization experiments on nonspinning powder samples at natural isotopic abundance.

A nitrogen-15 NMR study of hydrogen bonding in 1-alkyl-4-imino-1,4-dihydro-3-quinolinecarboxylic acids and related compounds

The title compounds contain groups (amine, amide, imine, carboxylic acid) that are capable of forming intramolecular hydrogen bonds involving a six-membered ring. In compounds where the two interacting functional groups are imine and carboxylic acid, the imine is protonated to give a zwitterion; where the two groups are imine and amide, the amide remains intact and forms a hydrogen bond to the imine nitrogen. The former is confirmed by the iminium 15N signal, which shows the coupling of 1J(15N,1H) -85 to -86.8 Hz and 3J(1H,1H) 3.7-4.2 Hz between the iminium proton and the methine proton of a cyclopropyl substituent on the iminium nitrogen. Hydrogen bonding of the amide is confirmed by its high 1H chemical shift and by coupling of the amide hydrogen to (amide) nitrogen [(1J(15N,1H) -84.7 to -90.7 Hz)] and to ortho carbons of a phenyl substituent. Data obtained from N,N-dimethylanthranilic acid show 15N-1H coupling of (-)8.2 Hz at 223 K (increasing to (-)5.3 Hz at 243 K) consistent with the presence of a N... H-O hydrogen bond.

A Direct Carbon-13 and Nitrogen-15 NMR Study of Praseodymium(III)- and Neodymium(III)-Isothiocyanate Complex Formation in Aqueous Solvent Mixtures

Multinuclear magnetic resonance spectroscopic studies of the trivalent lanthanide complexes with isothiocyanate have been completed for the praseodymium(III) and neodymium(III) ions. In water–acetone–Freon mixtures, at temperatures low enough to slow ligand exchange, usually −85 to −125°C for isothiocyanate, separate carbon-13 and nitrogen-15 NMR signals can be observed for free anion and NCS- in each metal–ion complex. For both metal ions, 15N NMR signals are observed for four complexes, displaced about +1500 ppm downfield from free NCS- for Pr3+ and about +2000 ppm for Nd3+. In the 13C NMR spectra, only three peaks are observed for the complexes of both metal anions, with signal overlap obscuring the resonance for the fourth complex. However, the metal ion coordination numbers, obtained by integration of the resonance signals, are comparable in the 15N and 13C spectra, approaching a maximum value of about 3. These spectral data indicate the formation of Ln(NCS)2+ through Ln(NCS)41- occurs for both lanthanides in these solvent systems, a result also observed previously for Ce3+, Sm3+, and Eu3+ in our laboratory. Attempts to study these complexes in water–methanol were unsuccessful, due to the inability to achieve low enough temperatures to slow ligand exchange sufficiently. Results for NCS- and Cl- competitive-binding studies by 35Cl NMR for both metal ions will also be described.

A Direct Carbon-13 and Nitrogen-15 NMR Study of Cerium(III)–Isothiocyanate Complexation in Aqueous Solvent Mixtures

A study of lanthanide complexation with isothiocyanate is underway using a multinuclear magnetic resonance technique. For isothiocyanate solutions in water–acetone–Freon mixtures at low temperature, −85–−125°C, ligand exchange is slow enough to permit the observation of 13C and 15N NMR signals for coordinated and free anions. For the Ce3+–NCS− system, four coordinated anion signals, displaced from the free anion signal by about +450 to +550 ppm for 15N and +50 to +80 ppm for 13C, are observed. The 13C and 15N spectral data are complementary, showing a signal area concentration dependence and measured coordination numbers consistent with the formation of Ce(NCS)2+ through Ce(NCS)1-4. In water–methanol, the extent of complexing is decreased, presumably because of the higher dielectric constant of this medium. In addition, the results of a competitive study of NCS− and Cl− ion binding, carried out using 35Cl NMR, is presented.

A direct carbon-13 and nitrogen-15 nmr study of europium(iii)-isothiocyanate complex formation in aqueous solvent mixtures

A continuation of the contact ion-pairing studies of the trivalent lanthanides by direct, low-temperature, multinuclear magnetic resonance techniques has been completed for the europium(III)-isothiocyanate system. In water-acetone-Freon-22 solvent mixtures, ligand exchange is sufficiently slow at — 100°C to - 125°C to permit the observation of13C and15N NMR signals for Eu3+-NCS- contact ion-pair complexes. With each nuclide, signals for four complexes are observed, displaced approximately 250 ppm upfield from free anion in the13C spectra, and 2,500 ppm upfield from bulk NCS- in the15N spectra. The concentration dependence of the signal areas is consistent with the formation of Eu(NCS)2+ through Eu(NCS) 4 1- , with water molecules completing the solvation shell. In the15N NMR spectra, the large chemical shifts identified the nitrogen atom as the NCS- binding site. Also, the observation of two15N NMR signals for isomers of Eu(NCS) 2 1+ was possible in several spectra. In methanol, a medium of higher dielectric constant, complex formation was diminished, with signal area integrations confirming the dominance of Eu(NCS) 1 2+ . A comparative binding study of Cl- and NCS- also was made by35C1 NMR chemical shift and linewidth measurements in water-methanol mixtures. The much stronger coordinating ability of NCS- was evident in these experiments, but there is a strong possibility of Eu3+-Cl- ion-pairing in the absence of this anion.

A direct hydrogen-1, carbon-13, and nitrogen-15 NMR study of lutetium(III)-isothiocyanate complexation in aqueous solvent mixtures

A direct, low-temperature hydrogen-1, carbon-13, and nitrogen-15 nuclear magnetic resonance study of lutetium(III)-isothiocyanate complex formation in aqueous solvent mixtures has been completed. At −100°C to −120°C in water-acetone-Freon mixtures, ligand exchange is slowed sufficiently to permit the observation of separate1H,13C, and15N NMR signals for coordinated and free water and isothiocyanate ions. In the13C and15N spectra of NCS−, resonance signals for five complexes are observed over the range of concentrations studied. The13C chemical shifts of complexed NCS− varied from −0.5 ppm to −3 ppm from that of free anion. For the same complexes, the15N chemical shifts from free anion were about −11 ppm to −15 ppm. The magnitude and sign of the15N chemical shifts identified the nitrogen atom as the binding site in NCS−. The concentration dependence of the13C and15N signal areas, and estimates of the fraction of anion bound at each NCS−:Lu3+ mole ratio, were consistent with the formation of [(H2O)5Lu(NCS)]2+ through [(H2O)Lu(NCS)5]2−. Although proton and/or ligand exchange and the resulting bulk-coordinated signal overlap prevented accurate hydration number measurements, a good qualitative correlation of the water1H NMR spectral results with those of13C and15N was possible.

Nitrogen-15 NMR studies of hydrogen bonding and proton transfer in complexes of pyridineN-oxides with dichloroacetic acid in CDCl3

The 15N NMR chemical shifts of eight substituted pyridine N-oxides (B) and their complexes (AHB) with methanol and dichloroacetic and trifluoromethanesulfonic acids were measured in chloroform-d at the natural abundance level. The measured chemical shifts are strongly affected by substituents, hydrogen bond strength and protonation. The plot of the relative chemical shifts, Δδ(15N) = δ(AHB) − δ(B), against ΔpKa gives a titration curve that reflects the variation of the hydrogen bond strength and the proton moves from the acid to the N-oxide. According to previous IR data, in the complexes from the inversion region (ΔpKa = 1·26), the proton is either delocalized (B…H…A) or more likely the lifetime is so short (⩽10−13 s) that the method does not recognize the B…H-A and B+H…A− species. Protonation of pyridine N-oxides shifts the nitrogen signal ca 50 ppm to lower frequencies compared with the ca 123 ppm for pyridines.

A direct carbon-13 and nitrogen-15 NMR study of europium(III) complexation-nitrate and europium(III)-isothiocyanate complexation in aqueous solvent mixtures

A direct, low-temperature nuclear magnetic resonance spectroscopic study of europium(III)-nitrate contact ion-pairing has been completed, and preliminary results for europium(III)-isothiocyanate have been obtained. In water-acetone-Freon mixtures, at −110°C to −120°C, four15N NMR signals are observed for coordinated nitrate ion. Area evaluations of the signals and their concentration dependence indicate the formation of Eu(NO3)2+, Eu(NO3) 2 1+ , and two higher complexes, possibly the tetra-, with either the penta-or hexanitrato. This correlates well with similar15N NMR results obtained for Ce(III), Pr(III), Nd(III), and Sm(III). As a result of a higher dielectric constant, complex formation is significantly less in water-methanol mixtures, wheein only three complexes form with Eu(NO3) 2 1+ dominating at the highest anion concentrations. Competitive complexing experiments in water-methanol also were made by35Cl NMR chemical shift and linewidth measurements, as well as15N NMR. Initial experiments with the Eu3+-NCS− system show four coordinated anion signals, displaced from the bulk anion peak by about −250 ppm and −2,500 ppm in the13C and15N NMR spectra, respectively. Area evaluations are consistent with the presence of Eu(NCS)2+ through Eu(NCS) 4 1- in these solutions. A consideration of the chemical shifts identified the nitrogen atom as the site of binding in the NCS−. A discussion of these preliminary results, as well as those for several other metal-ions, will be presented.

Oxygen–nitrogen ordering in yttrium nitrogen melilite

Nitrogen-15 NMR studies of yttrium nitrogen melilite (Y2Si3O3N4) show that, contrary to previous work based only on 29Si NMR results, the oxygen and nitrogen atoms are ordered in a way that is entirely consistent with Pauling's rules. Nitrogen atoms occupy bridging sites and oxygen atoms occupy terminal sites in the Si2(O,N)7 units, while for the remaining two tetrahedra in the unit cell, oxygen and nitrogen atoms are disordered but with an overall composition of three nitrogens and one oxygen in each tetrahedron. This type of ordering behaviour is consistent with O/N ordering observed in other crystalline Y–Si–O–N ceramics.

Direct hydrogen-1, carbon-13, and nitrogen-15 NMR study of magnesium(II)-isothiocyanate complexing

A hydrogen-1, carbon-13, and nitrogen-15 NMR study of magnesium(II)-isothiocyanate complexation in aqueous mixtures has been completed. At temperatures low enough to slow proton and ligand exchange, separate1H,13C, and15N NMR signals are observed for coordinated and bulk water molecules and anions. The1H NMR spectra reveal signals for the hexahydrate and the mono-through triisothiocyanato complexes, as well as two small signals attributed to [Mg(H2O)5(OH)]1+ and [Mg(H2O)4(OH)(NCS)]. Accurate hydration numbers were obtained from signal area integrations at each NCS− concentration. In the15N NMR spectra, signals also were observed for the mono-through triisothiocyanato complexes, and a small signal believed to be due to [Mg(H2O)4(OH)(NCS)]. Coordination number contributions for NCS− were measured from these spectra and when combined with the hydration numbers they totalled essentially six at each anion concentration. Signals for [Mg(H2O)5(NCS)]1+ through [Mg(H2O)3(NCS)3]1− also were observed in the13C NMR spectra and the area evaluations were comparable to the15N NMR results. An analysis of the magnitude and sign of the coordinated NCS− chemical shifts identified the nitrogen atom as the anion binding site. All spectra indicated [Mg(H2O)5(NCS)]1+ and [Mg(H2O)4(NCS)2] were the dominat isothiocyanato complexes over the entire range of anion concentrations. The inability to detect evidence for complexes higher than the triisothiocyanato reflects the competitive binding ability of water molecules and perhaps the decreased electrostatic interaction between NCS− and negatively charged higher complexes.

A direct carbon-13 and nitrogen-15 NMR study of samarium(III) complexation with nitrate and isothiocyanate in aqueous solvent mixtures

The extent of inner-shell, contact ion-pairing between samarium(III)-nitrate and in a preliminary manner, samarium(III)-isothiocyanate, has been determined by a direct, low-temperature, multinuclear magnetic resonance technique. In water-acetone mixtures containing Freon-12 or Freon-22, the slow exchange condition is achieved at −110 to −120°C, permitting the observation of15N NMR resonance signals for bulk and coordinated nitrate. In these mixtures, signals are observed for Sm(NO3)2+, Sm(NO3) 2 + , and two higher complexes, possibly the tetranitrato with either the penta-or hexanitrato.1H NMR signals for bound water molecules in these mixtures were observed, but accurate hydration numbers can not yed be determined. In anhydrous or aqueous methanol mixtures,15N NMR signals for only three complexes are observed, with the dinitrato clearly dominating. Using15N and35Cl NMR chemical shift and linewidth measurements, the superior complexing ability of nitrate compared to perchlorate and chloride, was demonstrated. Successful preliminary13C and15N NMR measurements of Sm3+-NCS− interactions in water-acetone-Freon-22 mixtures also have been made. The13C NMR spectra reveal signals for five complexes, presumably Sm(NCS)2+ through Sm(NCS) 5 2− . In the15N NMR spectra, signals for only three complexes are observed (the result of insufficient spectral resolution.) displaced about +240 ppm from bulk anion.

A Hydrogen-1, Nitrogen-15, and Yttrium-89 NMR-Study of Yttrium(III)-Isothiocyanate Complexes in Aqueous Solvent Mixtures

Abstract A direct, low-temperature hydrogen-1, nitrogen-15, and yttrium-89 NMR study of inner-shell complex formation between yttrium(III) and isothiocyanate ion in aqueous solvent mixtures has been completed. At −105 to −115°C in water-acetone-Freon 12 mixtures, ligand exchange is slow enough to permit the observation of separate 15 N NMR signals for the mono-, di-, and triisothiocyanato complexes of Y(III), displaced upheld by 14 to 17 ppm from the free anion signal. Coordination to 89 Y is strong enough to produce observable J coupling of about 14 Hz in the 15 N signals. This coupling and an analysis of the magnitude and sign of the 15 N chemical shifts indicate binding occurs at the anion nitrogen atom. Area integrations of these signals indicated an overall total of 2 mol of SCN − complexed per mole of Y(III), with the diisothiocyanate complex dominating even at the highest anion concentrations studied. The 1 H spectra of these solutions revealed multiple coordinated water signals, the areas of which led to Y(III) hydration numbers of six in the absence of SCN − to about four at the highest concentrations of this anion. The 89 Y NMR spectra of these systems also revealed a maximum of three complexes, with signals appearing upheld from that of the free metal ion by 3 to 15 ppm. Preliminary 15 N NMR results are presented for the isothiocyanate complexes of lanthanum(III), lutetium(III), aluminum(III), magnesium(II), and paramagnetic samarium(III).

The importance of binding energy in catalysis of hydride transfer by UDP-galactose 4-epimerase: a 13C and 15N NMR and kinetic study.

UDP-galactose 4-epimerase contains NAD+ irreversibly but noncovalently bound to the active site. Uridine nucleotides bind to the substrate site and induce a protein conformational change that increases the chemical reactivity of NAD+ at the coenzyme site. Activation of NAD+ by uridine nucleotides perturbs the 15N and 13C NMR chemical shifts of selectively enriched NAD+ bound to the coenzyme site. The proton-decoupled 15N NMR signal for enzyme-bound [carboxamide-15N]NAD+ does not change upon addition of UDP, indicating that activation is not brought about by a change in the binding of the carboxamide group. The 15N NMR signal of enzyme-bound [nicotinamide-1-15N]NAD+ is shifted upfield 3.0 ppm and the 13C NMR signal for [nicotinamide-4-13C]NAD+ is shifted downfield 3.4 ppm downfield by the binding of UDP at the substrate site. These changes are consistent with the induction of a distortion into the nicotinamide ring, in which positive charge is transferred from N-1 to C-4. The kinetic and thermodynamic effects of these perturbations are significant, as indicated by the nonenzymatic chemical reactivities of a series of N-alkyl nicotinamides differing in the inductive electron withdrawing effects of the alkyl substituents. A downfield change of 3.4 ppm in the 4-13C chemical shifts brought about by electron withdrawal in the model compounds corresponds to a 3200-fold increase in the rate of reduction by NaBH3CN in water, a 15,000-fold increase in 86% ethanol, and a 152 mV more positive reduction potential in this series. The distortion of NAD+ by the binding of UDP is a long-range effect that is transmitted from the substrate binding site to the coenzyme through the protein conformational change. This apparently distorts the pi-electron distribution in the nicotinamide ring and reduces the activation energy for its reduction. Activation of enzyme-bound NAD+ toward reduction apparently arises from a destabilization in the nicotinamide ring structure rather than from a stabilization of the transition state through attractive interactions between the nicotinamide ring and the enzyme.

A solid-state nitrogen-15 NMR study of the phase transitions in ammonium nitrate

The five solid phases of NH 4 NO 3 and transitions between these phases are studied using solid-state 15 N magic angle spinning (MAS) and static NMR. The thermal behavior of this substance is explored by means of the MAS chemical shifts. A magnetic nonequivalence in the NO 3 - ions of phase V is observed. The principal values of the chemical shift tensors of the NO 3 - in all five phases are determined. The evidence of crystal packing deformations is seen in the static NO 3 - spectra of phases V through II

Heteronuclear NMR studies of cobalt corrinoids. 14. Amide proton and nitrogen-15 NMR studies of base-on cobalamins

The amide 15 N and 1 H NMR resonances of a series of nine base-on cobalamins in DMSO-d 6 have been observed by inverse-detected 1 H, 15 N HMQC spectroscopy, in order to evaluate the possibility of the use of 15 N NMR as a probe of axial nucleotide ligation in macromolecular complexes of cobalt corrinoids with proteins. While the chemical shifts of the nucleotide loop amide nitrogen atoms fail to correlate with the strength of axial nucleotide coordination, the chemical shifts of the nucleotide loop amide proton show a smooth, if nonlincar, dependence on the free energy of formation of the babe-on species.

Solid-state nitrogen-15 NMR studies of the nitroso group in the nitrosobenzene dimer and p-nitroso-N,N-dimethylaniline

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSolid-state nitrogen-15 NMR studies of the nitroso group in the nitrosobenzene dimer and p-nitroso-N,N-dimethylanilineMike D. Lumsden, Gang Wu, Roderick E. Wasylishen, and Ronald D. CurtisCite this: J. Am. Chem. Soc. 1993, 115, 7, 2825–2832Publication Date (Print):April 1, 1993Publication History Published online1 May 2002Published inissue 1 April 1993https://doi.org/10.1021/ja00060a032RIGHTS & PERMISSIONSArticle Views356Altmetric-Citations43LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (825 KB) Get e-Alerts Get e-Alerts

Heteronuclear NMR studies of cobalt corrinoids. 13. Amide proton and nitrogen-15 NMR studies of diastereomerism and the base-on/base-off reaction in 5'-deoxyadenosylcobalt corrinoids

Inverse detected 1 H, 15 N HMQC spectroscopy in DMSO-d 6 has been used to observe the 1 H and 15 N NMR resonances and establish the H-N connectivities of the peripheral amides of a series of five 5'-deoxyadenosylcobalt corrinoids including the β cobalamin (i.e., coenzyme B 12 ) and its α diastereomer (in which the 5'-deoxyadenosyl ligand is in the «lower» axial ligand position), the diastereomeric α- and β-5'-deoxyadenosylcobinamides (in which the axial 5,6-dimethylbenzimidazole nucleotide has been removed by phosphodiester hydrolysis), and the base-off analogue of the coenzyme, in which the coordinating nitrogen of the axial nucleotide is methylated

Kinetic, isotopic, and nitrogen-15 NMR study of N-hydroxybenzenesulfonamide decomposition: an nitrosyl hydride (HNO) source reaction

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTKinetic, isotopic, and nitrogen-15 NMR study of N-hydroxybenzenesulfonamide decomposition: an nitrosyl hydride (HNO) source reactionFrancis T. Bonner and Younghee KoCite this: Inorg. Chem. 1992, 31, 12, 2514–2519Publication Date (Print):June 1, 1992Publication History Published online1 May 2002Published inissue 1 June 1992https://doi.org/10.1021/ic00038a038RIGHTS & PERMISSIONSArticle Views442Altmetric-Citations74LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (711 KB) Get e-Alerts Get e-Alerts