Carbon-13 Longitudinal Relaxation Research Articles

Inclusion of Chloromethane Guests Affects Conformation and Internal Dynamics of Cryptophane-D Host

Cryptophane-D is composed of two nonequivalent cyclotribenzylene caps bound together by three OCH2CH2O bridges in a syn arrangement. Host-guest complexes with chloroform and dichloromethane were investigated in solution by NMR spectroscopy. Variable temperature NMR (1)H and (13)C spectra showed effects of chemical exchange between the free and bound guest and of conformational exchange for the host, strongly and specifically affected by guest binding. We found in particular that the carbon-13 chemical shifts for the linkers connecting the two cyclotribenzylene units are very informative. The NMR results were supported by DFT calculations. The guest exchange was also studied quantitatively, either by EXSY measurements (for chloroform as guest) or by line-shape analysis (for dichloromethane as guest). In the case of chloroform guest, we also investigated cross-relaxation between the guest and host protons, as well as carbon-13 longitudinal relaxation and heteronuclear NOE at three different fields. The results were interpreted in terms of orientation and dynamics of the guest inside the host cavity. Putting together various types of evidence resulted in remarkably detailed insight into the process of molecular recognition of the two guests by cryptophane-D host.

Morphology and molecular dynamics of hard α-keratin under pressure by 1H and 13C solid-state NMR

The effect of uniaxial pressure on phase composition, aminoacid side-chain and backbone dynamics, as well as rigid domain sizes of hard α-keratin from human fingernail clippings was investigated by 1H solid-state and 13C cross-polarization MAS NMR spectroscopy. Proton spin–diffusion NMR experiments revealed that the rigid-domain sizes increased upon compression. The 13C carbonyl resonance components were shown to be very sensitive to the transition of α-helices to β-sheets induced by uniaxial compression. Carbon-13 longitudinal relaxation in the rotating frame showed dynamic heterogeneity of aminoacid residues especially during the α-helix to β-sheet transition.

Solvent Dynamical Behavior in an Organogel Phase As Studied by NMR Relaxation and Diffusion Experiments

An organogelation process depends on the gelator-solvent pair. This study deals with the solvent dynamics once the gelation process is completed. The first approach used is relaxometry, i.e., the measurement of toluene proton longitudinal relaxation time T(1) as a function of the proton NMR resonance frequency (here in the 5 kHz to 400 MHz range). Pure toluene exhibits an unexpected T(1) variation, which has been identified as paramagnetic relaxation resulting from an interaction of toluene with dissolved oxygen. In the gel phase, this contribution is retrieved with, in addition, a strong decay at low frequencies assigned to toluene molecules within the gel fibers. Comparison of dispersion curves of pure toluene and toluene in the gel phase leads to an estimate of the proportion of toluene embedded within the organogel (found around 40%). The second approach is based on carbon-13 T(1) and nuclear Overhauser effect measurements, the combination of these two parameters providing direct information about the reorientation of C-H bonds. It appears clearly that reorientation of toluene is the same in pure liquid and in the gel phase. The only noticeable changes in carbon-13 longitudinal relaxation times are due to the so-called chemical shift anisotropy (csa) mechanism and reflect slight modifications of the toluene electronic distribution in the gel phase. NMR diffusion measurements by the pulse gradient spin-echo (PGSE) method allow us to determine the diffusion coefficient of toluene inside the organogel. It is roughly two-thirds of the one in pure toluene, thus indicating that self-diffusion is the only dynamical parameter to be slightly affected when the solvent is inside the gel structure. The whole set of experimental observations leads to the conclusion that, once the gel is formed, the solvent becomes essentially passive, although an important fraction is located within the gel structure.

Behavior of Cesium and Thallium Cations inside a Calixarene Cavity As Probed by Nuclear Spin Relaxation. Evidence of Cation−π Interactions in Water

We have studied the complexes formed between the p-sulfonatocalix[4]arene and cesium or thallium metal cation, first by carbon-13 longitudinal relaxation of the calixarene molecule at two values of the magnetic field B(0). From the longitudinal relaxation times of an aromatic carbon directly bonded to a proton, thus subjected essentially to the dipolar interaction with that proton, we could obtain the correlation time describing the reorientation of the CH bond. The rest of this study has demonstrated that it is also the correlation time describing the tumbling of the whole calixarene assembly. From three non-proton-bearing carbons of the aromatic cycles (thus subjected to the chemical shift anisotropy and dipolar mechanisms), we have been able to determine the variation of the chemical shift anisotropy when going from the free to the complex form of the calixarene. These variations not only provide the location of the cation inside the calixarene cavity but also constitute a direct experimental proof of the cation-pi interactions. These results are complemented by cesium and thallium relaxation measurements performed again at two values of the magnetic field B(0). An estimation of the mean distance between the cation and the calixarene protons could be obtained. These measurements have also revealed an important chemical shift anisotropy of thallium upon complexation.

Solution structure investigation of Ru(II) complex ion pairs: quantitative NOE measurements and determination of average interionic distances.

The structure of the Ru(II) ion pairs trans-[Ru(COMe)[(pz(2))CH(2)](CO)(PMe(3))(2)]X (X(-) = BPh(4)(-), 1a; BPh(3)Me(-), 1b; BPh(3)(n-Bu)(-), 1c; BPh(3)(n-Hex)(-), 1d; B(3, 5-(CF(3))(2)(C(6)H(3)))(4)(-), 1e; PF(6)(-), 1f; and BF(4)(-), 1g; pz = pyrazol-1-yl-ring) was investigated in solution from both a qualitative (chloroform-d, methylene chloride-d(2), nithromethane-d(3)) and quantitative (methylene chloride-d(2)) point of view by performing 1D- and 2D-NOE NMR experiments. In particular, the relative anion-cation localization (interionic structure) was qualitatively determined by (1)H-NOESY and (19)F, (1)H-HOESY (heteronuclear Overhauser effect spectroscopy) NMR experiments. The counteranion locates close to the peripheral protons of the bispyrazolyl ligand independent of its nature and that of the solvent. In complexes 1c and 1d bearing unsymmetrical counteranions, the aliphatic chain points away from the metal center as indicated by the absence of NOE between the terminal Me group and any cationic protons. An estimation of the average interionic distances in solution was obtained by the quantification of the NOE build-up versus the mixing time under the assumption that the interionic and intramolecular correlation times (tau(c)) are the same. Such an assumption was checked by the experimental measurements of tau(c) from both the dipolar contribution to the carbon-13 longitudinal relaxation time T(DD-1)and the comparison of the intramolecular and interionic cross relaxation rate constant (sigma) dependence on the temperature. Both the methodologies indicate that anion and cation have comparable tau(c) values. The determined correlation time values were compared with those obtained for the neutral trans-[Ru(COMe)[(pz(2))BH(2)](CO)(PMe(3))(2)] complex (2), isosteric with the cation of 1. They were significantly shorter (approximately 3.8 times), indicating that the main contribution to dipolar relaxation processes comes from the overall ion pair rotation. As a consequence, the determined average interionic distances appear to be accurate. By using such interionic distances, it was possible to verify that the counteranion in complex 1b also orients the BMe group far away from the metal center.

Spatially Resolved Crystalline and Amorphous Components of Polymeric Materials by Carbon-13 Chemical Shift Imaging Performed with Radio-Frequency Field Gradients

It is shown that chemical shift imaging can be easily adapted to high-resolution solid-state experiments by means of radio-frequency field gradient technology. (The gradient is delivered by a two-turn flat coil, the axis of which coinciding with the rotor axis.) The resulting two-dimensional diagram involves chemical shift information in one dimension and spatial information (along the rotation axis) in the other dimension. Different procedures (physical filters) have been considered in order to enhance specific properties of the crystalline and amorphous components in high-density polyethylene (hdpe). Two of them rely on differences in cross-polarization or in cross-polarization inversion processes, while a third one is based on carbon-13 longitudinal relaxation times. The latter is shown to be especially efficient for effectively obtaining separate images of the amorphous and crystalline components and ultimately unraveling their distribution within the sample. In particular, it is demonstrated that two structurally distinct amorphous phases are spatially separated in the sample under investigation.

Carbon-13 Nuclear Magnetic Relaxation Study of Solvent Effects on Chain Local Dynamics of Poly(N-vinylcarbazole) in Dilute Solution

Carbon-13 longitudinal relaxation times and NOE values were measured as a function of temperature at three magnetic fields for poly(N-vinylcarbazole) (PNVC) in five solvents, covering viscosities differing by a factor of 5. The relaxation data of the backbone carbons were interpreted in terms of chain local motions by using the bimodal time-correlation function of the Dejean−Laupretre−Monnerie (DLM) model. The molecular correlation times obtained from the DLM model follow a linear relationship with solvent viscosity with unit slope, indicating that the hydrodynamic behavior of PNVC can be described by Kramers' theory. Several time-correlation functions describing internal motion failed to reproduce the experimental relaxation data of the protonated aromatic carbons of the carbazole side-group. It was concluded that the internal motion of the carbazole group is highly restricted due to strong steric effects from neighboring rings and the backbone chain. Finally, on the basis of our data some general conclu...

Carbon-13 and mercury-199 nuclear spin relaxation study on solution dynamics of the bis(phenylethynyl)mercury molecule and shielding anisotropy of its acetyleniccarbon and mercury nuclei

Carbon-13 longitudinal relaxation times and nuclear Overhauser effect enhancement factors at two magnetic fields and three temperatures were measured for a DMSO solution of bis(phenylethynyl)mercury and interpreted in terms of molecular mobility of the solute molecule. The problem of the effective C— H bond length, crucial for the quantitative treatment of the relaxation data, was especially addressed. Then, using relaxation data for acetylenic carbons and additionally measured longitudinal relaxation times of mercury-199, the shielding anisotropy parameters for these nuclei were calculated. Copyright © 2000 John Wiley & Sons, Ltd.

Effect of solvent isotopic labelling on proton and carbon-13 longitudinal relaxation

The coupled 1H and 13C nuclear magnetic relaxation in dichloromethane has been studied in acetone and deuterated acetone. The dynamical parameters have been found to be the same in the two media (Dxx = 4·1 × 10-10, Dyy = 2·0 × 10-10 Dzz = 8·6 × 10-10 s-1). The ratio of the random field spectral densities in the two solvents is lower than the theoretical value. This discrepancy has been ascribed to the different internal dynamics of the CD3 and CH3 groups. The isotopic content of the medium is shown to affect the relaxation times of the proton as well as the carbon nuclei.

Nuclear magnetic resonance study of alkylammonium chlorides: 3. Micelles characterization and dynamic properties determined by proton and carbon-13 longitudinal relaxation

Alkylammonium chloride/D 2O systems have been studied by NMR proton longitudinal relaxation, proton linewidth, carbon-13 longitudinal relaxation, and carbon-13 nuclear Overhauser enhancement at three different temperatures: 25, 40, and 70°C. The investigated surfactants include normal chains with n c = 6, 8, 10, and 14 carbon atoms (denoted C nc ), octyl-oxy-propylammonium chloride (denoted OC 12), and octyl-amino-propylammonium chloride (denoted NC 12). Proton T 1 of monomers can be simply interpreted on the basis of the Stokes-Einstein law. Proton T 1 profiles, as a function of concentration, allow determination of the critical micellar concentration, and discrimination between two types of micelles: (A) involving a well-defined packing of surfactant molecules inside the aggregate in such a way that their dynamic properties are independent of concentration and chain length and (B) ill-defined micelles whose dynamic properties continuously change with concentration and depend on chain length. Proton linewidth permits detection of an eventual transition from globular to elongated micelles. This occurs only for type (A) micelles. Carbon-13 relaxation data are analyzed in terms of (i) fast motions arising from rotational isomerism with which is associated a correlation time τ Gi at the ith carbon in the chain and (ii) a slower overall motion of the surfactant molecule. τ G profiles provide a detailed picture of mobility along the alkyl chain and are also shown to be characteristic of the micelle type ((A) and (B)) as defined above but independent of the aggregate shape for a given long chain surfactant at a given temperature. C 12, C 14 at all temperatures, C 10 at 25 and 40°C, and OC 12 at 25°C are of type (A) whereas C 6, C 8, NC 12 at all temperatures, C 10 at 70°C, and 0C 12 at 40 and 70°C are of type (B).

Nuclear magnetic resonance studies of alkylammonium chlorides in aqueous solution. II. Carbon-13 longitudinal relaxation times and nuclear overhauser enhancements in isotropic micellar media and in the lamellar mesophase

Carbon-13 longitudinal relaxation times ( T 1), and nuclear Overhauser enhancements (η) of a series of n-alkylammonium chlorides (with 8, 10, and 12 carbons in the aliphatic chain) have been measured at two concentrations in D 2O corresponding to globular and rod-shaped micelles. In addition, due to its macroscopic orientation, the lamellar lyotropic mesophase of dodecylammonium chloride could be investigated. Data have been analyzed at the local level in terms of a correlation time τ G i , associated to fast internal motions, a correlation time τ R representing the overall surfactant molecule reorientation, and an angle θ i defining the position of an effective rotation axis with respect to each C iH vector. It has been observed that mobility is quasi-independent on the considered aggregate. In the case of decyl and dodecylammonium chlorides, the τ G i correlation times exhibit a “plateau” (at value of the order of 10 ps) up to three carbons from the chain extremity and then decrease rapidly to reach ∼ 1 ps. On the contrary, for octylammonium chloride a monotonic decrease from 10 to 1 ps is observed for the polar head toward the chain extremity. The slow motion ( τ R ∼ 10 −7 to 10 −8 sec ) is attributed to fluctuations of the surfactant molecule with respect to an average position inside the aggregate.

Information obtainable from N.M.R. longitudinal relaxation as measured by a non-selective pulse sequence in an ABC system

From proton and carbon-13 longitudinal relaxation and 13C Overhauser enhancement measurements, the diffusion constants for the molecule acrylonitrile dissolved in carbon disulphide are found to be: Dxx =(0·11±0·06) × 1012 s-1; Dyy = (0·38 ± 0·12) × 1012 s-1; Dzz = (0·25 ± 0·02) × 1012 s-1 (the z axis is perpendicular to the molecular plane; the y axis is almost parallel to the C≡N bond). The diffusion and inertial principal axis systems are shown to be nearly coincident. From these diffusion constants, the nitrogen-14 quadrupolar coupling constant was calculated to be (4·9±0·8) MHz. Notwithstanding the fact that we can study more relaxation rates due to the presence of more lines in the proton ABC spectrum, as compared to an AB 2 or AX 2 system, we obtain less information. This is a result of the fact that the unknown spectral densities occur in linear combinations in the expression for the recovery rates. A procedure to obtain the maximum available information is described.

Analysis of carbon-13 longitudinal relaxation times and nuclear overhauser enhancements in alkyl chains

A simple procedure is proposed which yields, from carbon-13 longitudinal relaxation times and nuclear Overhauser enhancements, information concerning the local mobility of a given CH vector in an alkyi chain. This method is based on the definition of an effective rotation axis related to internal motions and makes use of Woessner's equations. It yields a correlation time τ R characteristic of the overall reorientation. In addition, for each carbon C i a correlation time τ G i , associated with the fast motion of the C i H vector, and an angle θ i , between C i H and an effective rotation axis, are determined. The effect of cross-correlation spectral densities is discussed. This model is used for analysing relaxation data of decylammonium chloride micelles. It is further checked by interpreting experimental results at two different observation frequencies.

Paramagnetic ion binding to amino acids : the structure of the manganese (II)-L-proline complex from carbon-13 relaxation data

Abstract Carbon-13 longitudinal relaxation times T 1 of aqueous solutions of proline at pH=11 containing 10 −4 –10 −5 M manganese(II) perchlorate are measured at 62.86 MHz and 60°C. Under these conditions, the Mn 2+ cation is bound to three proline molecules in their dibasic form to form the complex [Mn(L-PRO − ) 3 ] − . The relaxation of carbons α, β, γ, δ in this complex is shown to be dipolar. The relevant correlation time is rotational τ r =4.3×10 −11 s (at 60°C). A method is given to compute the Mn 2+ - 13 C distances in the complex from the paramagnetic relaxation rates 1/T 1M of carbons α to δ and an assumed geometry of the proline molecule. The manganese (II) cation may be positioned with respect to each proline ligand, thus determining the structure of the hexacoordinated complex. The sites of coordination are the uncharged nitrogen and one carboxylic oxygen atom of the proline molecules, their distance to the Mn 2+ cation are respectively 2.22 and 1.97 a.

Nuclear spin dipolar relaxation in paramagnetic systems undergoing multiple internal motions

A theoretical treatment is proposed for the relaxation induced by the dipolar interaction between two spins separated by several bonds about which jump motions occur among three sites, two of them at least being equivalent. The influence of the internal and overall molecular motions upon the carbon-13 longitudinal relaxation is discussed for the model of n-butylamine coordinated to a paramagnetic ion having a comparatively long T 1e like Mn2+. The 13C paramagnetic dipolar relaxation appears to be mainly dependent upon the ratios of the transition rates among the different conformers. A computer program has been written to analyse the 13C longitudinal dipolar relaxation in terms of internal motions and transient conformations for flexible and partially rigid molecules such as butylamine, allylamine and benzylamine coordinated to Mn(AA)2 and Gd(DPM)3. The extension of these calculations to complexes where the nuclear relaxation is governed by the electron spin relaxation times is examined for the example of...

ChemInform Abstract: CARBON‐13 LONGITUDINAL RELAXATION TIMES OF ACETATE ION IN THE PRESENCE OF METAL‐SUBSTITUTED BOVINE CARBONIC ANHYDRASES

Chemischer InformationsdienstVolume 9, Issue 3 Physical Organic Chemistry ChemInform Abstract: CARBON-13 LONGITUDINAL RELAXATION TIMES OF ACETATE ION IN THE PRESENCE OF METAL-SUBSTITUTED BOVINE CARBONIC ANHYDRASES I. BERTINI, I. BERTINISearch for more papers by this authorC. LUCHINAT, C. LUCHINATSearch for more papers by this authorA. SCOZZAFAVA, A. SCOZZAFAVASearch for more papers by this author I. BERTINI, I. BERTINISearch for more papers by this authorC. LUCHINAT, C. LUCHINATSearch for more papers by this authorA. SCOZZAFAVA, A. SCOZZAFAVASearch for more papers by this author First published: January 17, 1978 https://doi.org/10.1002/chin.197803070AboutPDF 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. Volume9, Issue3January 17, 1978 RelatedInformation

Carbon-13 longitudinal relaxation times of acetate ion in the presence of metal-substituted bovine carbonic anhydrases

Longitudinal relaxation times T1 have been determined for both carbons of 13C-enriched acetate in the presence of bovine apo-, zinc(II), cobalt(II), and manganese(II) carbonic anhydrase, and the factors affecting them have been analyzed. The existence of a further interaction besides the binding at the metal atom has been confirmed by measuring T1 in the presence of excess of a strong inhibitor like toluene-p-sulphonamide. By use of the Solomon–Bloembergen analysis, distances and orientations of acetate with respect to the metal ion have been estimated both at the metal binding site and when unco-ordinated.

Carbon-13 relaxation in doubly labeled sodium acetate

Carbon-13 longitudinal relaxation times of singly and doubly 13C-labeled sodium acetates are presented and compared. In this system, in which the 13C indirect coupling is weak, the effect of the second 13C is just that expected on introduction of the 13C 13C dipolar interaction as an additional relaxation mechanism. This effect is quite small, and dipolar cross relaxation between 13C's is negligible.