15N Spin Research Articles

Cross sections for the anisotropic interaction of NNO with various molecules

Cross sections for the relaxation of the rotational angular momentum vector of the NNO molecule on collision with CO, Ar, CO2, NNO, Kr, CF4, and Xe, have been measured by 15N spin relaxation in 15N15NO molecules. The relaxation times of the two nuclei are in a ratio 1.86, independent of density, collision partner, or temperature. Except for Ar and CO, the cross sections are larger than the hard sphere cross sections and their temperature dependences range from T−0.8 to T−1.0.

CPMAS polarization transfer methods for superposed chemical exchange and spin diffusion in organic solids

The question of how CPMAS polarization-transfer experiments (CP, cross polarization; MAS, magic-angle spinning) should be conducted in order to distinguish between slow chemical exchange and spin diffusion in the solid state has been studied. Both contributions can be separated by performing different types of polarization-transfer experiments in the laboratory and the rotating frame, since dynamics of spin diffusion but not chemical exchange differs from one experiment to the next. Generally, if both processes are present, polarization transfer is expected to be nonexponential and chemical-exchange as well as spin-diffusion rate constants can be obtained in one series of experiments. If the exchange is symmetric, however, polarization transfer is single exponential and a combination of different pulse experiments is required for obtaining rate constants of both processes. The results for 15N CPMAS NMR polarization-transfer experiments on crystalline meso-tetratolylporphin- 15N 4 (TTP) are presented. Experiments in the laboratory frame show that spin diffusion between the 15N atoms of TTP is characterized by a temperature-independent rate constant. The nature of this process was established by 1H decoupling during the mixing time, which results in quenching of the polarization transfer. Thus, the role of the 1H spin reservoir for laboratory-frame spin diffusion among chemically inequivalent 15N spins in 15N-enriched material is confirmed. At higher temperatures, polarization transfer in the laboratory and the rotating frame is observed due to a symmetric exchange of the nitrogen atoms arising from a double proton transfer which has been previously established. The double proton transfer rates observed with the different polarization-transfer methods agree well with the values predicted from high-temperature lineshape analysis and are found to be very close to the solution data.

Effect of intermolecular interactions on the anisotropic rotational motions of molecules.1H,2H and14N nuclear magnetic resonance relaxation study of the acetonitrile–chloroform liquid system

2 H and 14N spin–lattice relaxation times for the CD3CN and CDCl3 molecules in the CD3CN–CDCl3 liquid system have been determined at temperatures between 250 and 315 K. Analyses of these data led to the determination of rotational diffusion coefficients about the C3 symmetry axis (D‖) and around the axes perpendicular to the symmetry axis (D⊥). Anisotropy of the rotational motions (D‖/D⊥) of CD3CN increases upon addition of CDCl3 to CD3CN liquids and reaches maxima at the mole fraction of CDCl3 to CD3CN liquids and reaches maxima at the mole fraction of CDCl3 to CD3CN liquids and reaches maxima at the mole fraction of CDCl3[x(CDCl3)]= 0.8. Slowing down of the rotational motions of CDCl3 is also observed, and reaches minima at x(CDCl3)= 0.6–0.7.

Rotating frame nuclear magnetic resonance experiments on metal complexes

Measurements of the rate of nuclear magnetic relaxation in the rotating frame (T1ρ) have the potential to provide significant information not readily available by other nmr methods. Some applications to metal complex chemistry are described. The method has been applied to 59Co nmr and used to obtain 59Co–14N spin–spin coupling constants for the tris(ethylenediamine)cobalt(III) and hexanitrocobaltate(III) ions. The larger coupling constant in the latter compound is related to the different hybridization of the nitrogen atom. Proton T1ρ measurements on thiourea and its zinc complex have demonstrated that at room temperature broadening of the 1H resonance is very largely ascribable to scalar relaxation rather than to chemical exchange processes.

Structure of nitroguanidine: Nitroamine or nitroimine? New NMR evidence from 15N‐labeled sample and 15N spin coupling constants

AbstractThe structure of nitroguanidine was investigated by the application of 15N, 1H and 13C NMR spectroscopy of a fully 15N‐labeled sample in DMSO‐d6 and DMF solutions and by 15N CP/MAS NMR in the solid state. These spectra confirm the nitroimine structure which has been suggested by other investigations in recent years, and do not lend any support to the commonly used nitroamine structure or for a tautomeric equilibrium with the nitroamine. Useful 15N spin coupling constants to the 1H and 13C nuclei in the assigned structure are reported.

14N quadrupole double resonance in 2-, 3- and 4-nitrobenzoic acids

14 N quadrupole cross-relaxation spectra of 2-, 3- and 4-nitrobenzoic acids show weak transitions which do not appear in their level-crossing double-resonance spectra. The multiplicity of transitions in 4-nitrobenzoic acid can be understood as originating in disorder in the sense of rotation of the NO2 group with respect to the plane of the aromatic ring. 14N spin–lattice relaxation in the 3- and 4-nitrobenzoic acids appears to be governed by torsional oscillations of the NO2 group about the C—N bond, so that the appearance of lines from the disordered molecules in the cross-relaxation spectra could be due to their lower torsional frequencies and hence shorter relaxation times.

ChemInform Abstract: Sign Determinations and INDO‐MO Calculations of 13C ‐ 15N and 15N ‐ 15N Spin ‐ Spin Coupling Constants of 3‐Methyl‐ and 3,6‐Dimethyl‐pyridazines (I).

Chemischer InformationsdienstVolume 17, Issue 2 Physical Organic Chemistry ChemInform Abstract: Sign Determinations and INDO-MO Calculations of 13C - 15N and 15N - 15N Spin - Spin Coupling Constants of 3-Methyl- and 3,6-Dimethyl-pyridazines (I). Y. KURODA, Y. KURODASearch for more papers by this authorY. FUJIWARA, Y. FUJIWARASearch for more papers by this authorK. MATSUSHITA, K. MATSUSHITASearch for more papers by this author Y. KURODA, Y. KURODASearch for more papers by this authorY. FUJIWARA, Y. FUJIWARASearch for more papers by this authorK. MATSUSHITA, K. MATSUSHITASearch for more papers by this author First published: January 14, 1986 https://doi.org/10.1002/chin.198602050Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume17, Issue2January 14, 1986 RelatedInformation

Determination of the sign of a one-bond15N–15N spin–spin coupling constant for a trans-diazene by selective15N decoupling experiments in13C nuclear magnetic resonance spectroscopy

The sign of the one-bond 15N–15N spin–spin coupling constant, 1J(N–N), of a trans-diazene (4-acetyl-aminoazobenzene) has been determined to test the theoretical prediction that 1J(N–N) would be positive in sign when nitrogens have s-hybridized lone pairs and take a trans conformation. The sign was first determined relative to those of 13C–15N spin-spin coupling constants, nJ(C–N), by selective 15N decoupling experiments and then finally referenced to that of 1J(C–H) in the benzene ring, which undoubtedly bears a positive sign, by selective 15N and 1H decoupling experiments. It was found that the sign of 1J(N–N) of the trans-diazene is negative in contrast to the theoretical prediction. This discrepancy is attributed to the large negative contribution from the orbital–dipole term which was not correctly evaluated in previous calculations for the 1J(N–N) coupling of the NN bond.

Analysis of the proton, carbon, and nitrogen NMR spectra of cis,cis‐ and cis,trans‐1,3,5‐triaminocyclohexane

AbstractThe proton spectrum of the isomeric mixture of cis,cis‐ and cis,trans‐1,3,5‐triaminocyclohexane was assigned with a 2D COSY experiment. Using Forrest's modified equation and the 2D J spectrum results, the conformations of the two isomers were analysed. The six‐membered ring of the cis,trans isomer is flattened by 1,3‐diaxial interactions between two amino substituents; in the cis,cis isomer, ring pucker is increased owing to non‐bonded interaction between the equatorial amino groups and adjacent methylene protons. The 13C and 15N spin—lattice relaxation of the two isomeric 1,3,5‐triaminocyclohexanes was also measured at different pH values; NHx groups rotate faster with decreasing pH. Rotation/jump rates and barriers are reported, determined from the NT1DD ratios between 15N and 13C nuclei.

Molecular ɡ-values, Magnetic Susceptibility Anisotropics, Molecular Electric Quadrupole Moments, improved Molecular Electric Dipole Moments and 14N-Quadrupole Coupling Constants of Acrylonitrile, H2C = CH—CN, and the Magnetic Susceptibility Tensor of the Nitrile Group

The highfield, linear and quadratic Zeeman effect has been observed in Acrylonitrile (Vinyl Cyanide). The Zeeman multiplets are complicated by the presence of the 14N nuclear quadrupole coupling, however the 14N nuclear Zeeman effect effectively uncouples 14N spin from the rotational angular momentum. This uncoupling was used to derive improved molecular electric dipole moments from the Stark-shifts in the 211 ← 202 and 312 ← 303 rotational transitions observed under ΔMj=0 selection rule in the presence of a high magnetic field. They are |μa| = 3.815(12)D and |μb| = 0.894(68)D, respectively. From the zero field hfs multiplets, observed under high resolution conditions, improved 14N quadrupole coupling constants were obtained: χaa N = - 3.7800(21) MHZ, χbb N - χcc N = - 0.4200(89) MHz. They are discussed with reference to the structure of the Nitrile group. From the Zeeman splittings of the 101 ← 000, 110 ← 101, 211 ← 202 and 312 ← 303 rotational transitions observed under ΔMj = 0 and ΔMj = ± 1 selection rule, the diagonal elements of the molecular g-tensor and the anisotropics in the diagonal elements of the molecular magnetic susceptibility tensor were obtained as gaa = -0.17901(33), gbb, = - 0.04585(17), gcc = -0.01820(16) and 2 χaa - χbb - χcc = - 7.22(25) 10-6 erg G-2 mole-1 and 2χbb - χcc - χaa = + 15.90(31) 10-6 erg G-2 mole-1. They are discussed with reference to the molecular electric quadrupole moment, the paramagnetic and diamagnetic contributions to the molecular susceptibilities, and the second moments of the electronic charge distribution. The susceptibility data are also used to derive the magnetic susceptibility tensor contribution of the Nitrile group.

Applicability of vicinal heteronuclear (13C‐1H, 15N‐1H, 13C‐15N) coupling constants for conformational analysis of amino acids: Phenylalanine, α‐aminobutyric acid and β‐alanine

AbstractThe vicinal 13C1H, 15N1H and 13C15N spin coupling constants were obtained from the 1H and 13C NMR spectra of various ionic forms of the amino acids phenylalanine, α‐aminobutyric acid and β‐alanine, and also from their 15N isotopomers. It is concluded that the 13C1H and 15N1H coupling constants are reliable parameters for conformational studies of amino acids, whereas the practical applicability of the 13C15N constants for the same purpose is doubtful.

13C and 15N spin–lattice relaxation and chemical shift studies of pentane‐2,4‐diamine

Abstract13C and 15N NMR chemical shift and spin–lattice relaxation data have been measured for both meso‐ and racemic‐pentane‐2,4‐diamine. At high pH (12), relaxation is consistent with hindered rotation of the NH2 group due, in part, to the formation of intramolecular hydrogen bonds. At low pH (2), relaxation is consistent with relatively unhindered rotation of the NH3+ group. Rotational jump rates and barriers are reported, determined from the NT1 ratios between 15N and 13C nuclei. In all cases, the ratios for the racemic diastereomer are higher than those of the meso compounds; this is interpreted in terms of conformationally more stable intramolecular hydrogen bond formation in the meso compound. Chemical shifts for the diastereomeric amines show that 15N shifts move downfield on protonation along with methyl and methylene carbons, while the methine carbon resonances move upfield.

Lipid-lipid and lipid-protein collision rates in membranes. Determination by evaluation of spin-spin interactions between 15N and 14N spin labels

Lipid-lipid and lipid-protein collision rates in membranes. Determination by evaluation of spin-spin interactions between 15N and 14N spin labels

Nuclear relaxation and molecular motion of pyridine-N-oxide in carbon tetrachloride

Proton spin lattice relaxation of pyridine-N-oxide-2,6-d2 in dilute solution (0·2 M) with carbon tetrachloride has been measured at -12·6, 6·5, and 26·6°C. Using 2H and 14N decoupling, eight transitions were resolved and recovery was monitored after non-selective inversion. In absence of 14N decoupling, scalar relaxation produced clearly visible effects on the proton recovery curves. Combined with measurements of deuterium relaxation of the 2,6-d2 and 4-d derivatives, proton relaxation data (including effects of dipolar cross correlation) were used to determine all three rotational diffusion constants at each temperature. The in-plane spinning motion was found to be ∼four-fold more strongly dependent on viscosity than predicted by the slip rotational diffusion model, while motion about the other two principal axes proceeds at rates within ∼40 per cent of slip predictions. 14N spin lattice relaxation data were combined with the anisotropic reorientation rates in efforts to determine liquid phase values of the 14N quadrupole coupling parameters. A very small decrease from solid phase values provides the best overall fit to the relaxation data.

Nitrogen-14 NMR linewidths as an aid in nitrogen chemical shift assignments

Calculations of electric field gradient tensors using the Townes-Dailey method and the assumption of isotropic rotation are shown to provide information for the assignment of nitrogen chemical shifts from 14N NMR spectra, particularly for the rigid molecular structures of heteroaromatic systems with nonequivalent nitrogen atoms, There are usually serious difficulties in nitrogen chemical shift assignments for such systems. The method seems to be a useful supplement to the existing methods based on considerations of nitrogen chemical shifts themselves and on 15N spin couplings.

Intracellular viscosity of lymphocytes determined by a 15N spin label probe

15N-Tempone was synthesized from (NH 4) 2SO 4 and phorone and was used as a spin label probe to study the protoplasmic viscosity of lymphocytes. The intracellular viscosity was determined to be approximately two times the viscosity of water. 14N-Tempone yielded a similar result. The value of the hyperfine coupling constant for 15N-Tempone in lymphocytes was slightly less than that in water. The EPR signal of the intracellular spin label was observed to decrease exponentially as a function of time with a decay constant of 0.25 ± 0.18 min −1.

Application of doubly decoupled 13C { 1H, 14N}NMR spectroscopy to studies of the conformation and dynamics of the choline headgroup of phospholipids

The high symmetry about the choline nitrogen atom leads to resolvable scalar 13C– 14N coupling in the 13C NMR spectrum of choline. For membranes or model membrane systems containing phosphatidyl choline molecules, this coupling can be partially or completely collapsed due to the slower motion and consequently shorter 14N spin lattice relaxation time of the choline nitrogen. In the present study, this effect has been probed by comparison of the 13C NMR spectra obtained using conventional proton decoupling with spectra obtained using simultaneous 14N and 1H decoupling,i.e., 13C { 1H, 14N} nmR spectroscopy. The results indicate a partially collapsed triplet structure for the choline methyl resonances in several sonicated lipid vesicles as well as in whole Chinese Hamster Ovary cells labeled with a 3 : 3 : 1 mixture of [1- 13C]-, [2- 13C]-, and [ 13CH 3] choline. Further, the sharpening of the choline C-2 resonance resulting from the 14N decoupling makes possible the observation of three bond 13C– 31P scalar coupling and, consequently, a conformational analysis of the rotational isomerism about the choline OC-1 bond.

Stereochemical analysis of aromatic oximes. 13C–15N nuclear spin coupling and 13C shieldings as conformational probes

13C nmr chemical shifts and 13C–15N spin couplings over one, two, and three bonds are reported for six aromatic oximes including two benz annelated compounds. Preferred geometries have been calculated via the GEMO program. Fermi contact contributions to carbon–nitrogen coupling have been evaluated and, in general, agreement between experimental and theoretical values is poor. Vicinal 13C–15N couplings are shown to depend on both dihedral angle and oxime valence angle. Oxime carbon chemical shifts do not provide a measure of deviation from planarity between the oxime group and the aromatic ring.The sign of 1JCN in E-benzaldoxime has been determined to be negative.

Use of nitroxide spin labels in studies of solvent–solute interactions

Complexities imposed on the studies of dynamic polarization of solvent nuclei by the three-line ESR spectrum of solute nitroxide radicals are examined. These include (1) the field dependence of proton polarizations, (2) the unequal magnitude of the polarizations at frequencies corresponding to the nitroxide radical peaks, and (3) the radical concentration dependence of the extrapolated enhancements. These features are analyzed with respect to existing models and with respect to a new mathematical model based on an exchange interaction that couples radicals in different 14N spin states. This model successfully accounts for the nonlinear extrapolation of enhancements as a function of reciprocal radical concentration. The model is tested experimentally using samples of 4-hydroxy-2,2,6,6-tetramethyl piperid-1-yloxy free radical in benzene, with both DNP and relaxation data used in the analysis.

The Long-range1H-14N Spin Coupling in Transition Metal Complexes of Alkyl Isocyanides

Abstract Long-range 1 H—14N spin coupling constants have been observed in the proton nmr spectra of several isocyanides,2 and a coordinated compound, (CH3)3 B · CNC(CH3)3.3 On the other hand, such spin coupling constants, hitherto, have not been observed in the various transition metal complexes of isocyanides.4 A possible explanation for this is that formation of a complex generally introduces an electric field gradient about the 14 N nucleus and consequently the spin-spin coupling disappears.