Carbon-13 Spin-lattice Relaxation Research Articles

Solution dynamics of the natural bioactive molecule capsaicin: a relaxation study

Nuclear magnetic resonance spectroscopy is a straightforward technique for studying molecular dynamics that range in timescale from picosecond (motions faster than molecular reorientation) to those that occur in real-time. This approach is important to highlight the behavior of bioactive molecules in solution, and to acquire information about action mechanisms and potential pharmacological effects. Proton and carbon-13 spin–lattice relaxation experiments were performed to calculate the reorientational correlation time for protonated carbons. Capsaicin showed complex dynamical properties and the results revealed two regions with different dynamical properties: the aliphatic region with fast reorientation motions and the aromatic region with slow motions.

First solid-state NMR spectroscopy evaluation of complexes of benznidazole with cyclodextrin derivatives

Complexation of benznidazole (BZL), a drug of choice for the treatment of Chagas’neglected disease, with cyclodextrin (CD) derivatives was analyzed by solid-state NMR. 13C cross polarization/magic angle spinning spectra were recorded from BZL and from BZL:β-CD, BZL:methyl β-CD and BZL:hydroxypropyl β-CD complexes, which were obtained by the solvent evaporation technique. No significant evidence was obtained on BZL inclusion complexes involving either β-CD or hydroxypropyl β-CD. Conversely, BZL:methyl β-CD displayed BZL resonances characteristic of an amorphous drug and data analysis confirmed the presence of stable BZL:methyl β-CD inclusion complexes, with benzene encapsulated into the host cavity. Further evidences on complex structure and dynamics were obtained from proton and carbon spin–lattice relaxation times in the rotating frame. These data are consistent with a common guest–host spin reservoir. The BZL interaction with methyl β-CD provided a route to stabilize amorphous BZL. Physical mixtures with identical BZL and CD compositions were also studied for comparison.

Nuclear spin–lattice relaxation and complex motion of macromolecules in solution

The NMR spectral densities of a complex motion consisting of a combination of anisotropic overall motion and internal motion have been derived. Two approximations of the equations derived for the cases of slow, Jslow (ω), and fast, Jfast (ω), internal motions are presented. These equations imply that reduction in spectral density of overall motion can be observed if the maxima of internal and overall motions spectral densities versus temperature are well separated, as for fast internal motion. Slow intramolecular motion influences the values of spectral densities of the overall motion if one of the two spins performs a motion, for example a proton in double minimum of the 15N-H ··· N hydrogen bond. The analysis presented reveals small differences between the temperature dependencies of spectral densities of the isotropic and anisotropic overall motions. The theory is illustrated by the 13C protonated carbon spin-lattice relaxation of α-cyclodextrin macromolecule, using the expected motional parameters: D ∥/D ⊥ ≈ 5 at room temperature and for a fast or slow internal motion.

Solid-state NMR study of biodegradable starch/polycaprolactone blends

Abundant literature exists on starch or modified starch blended with biodegradable polyesters to achieve good performance with cheap compost plastics. The level of miscibility in these blends is one of the most relevant parameters. In the present study, solid-state 1H and 13C NMR spectra, as well as carbon spin-lattice relaxation times T 1(C) and proton spin-lattice relaxation times T 1(H) and proton spin-lattice relaxation times in the rotating frame T 1ρ(H) of biodegradable starch (or starch formate)/polycaprolactone (PCL) (or polyester (PE) oligomers) blends and samples of the neat components were measured. From the T 1ρ(H) and T 1(H) relaxation times it follows that blends starch/PCL, starch/PE-oligomers and starch formate/PE-oligomers are phase separated even on the scale of 20–110 nm. On the contrary starch formate/PCL blend is phase separated on the scale 2.5–12 nm but homogeneously mixed on the scale 20–90 nm. Moreover, shorter T 1(C) and especially T 1ρ(H) values found for the starch or starch formate component in all these blends in comparison with neat samples show that molecular mobility of starch and starch formate segments is affected by blending. This indicates some miscibility also in phase separated blends which can happen in amorphous channels of starch.

NMR characterization of paclitaxel/poly (styrene-isobutylene-styrene) formulations

TAXUS™ is a coronary drug-eluting stent system utilizing a formulation consisting of cellular-target drug paclitaxel and poly (styrene-isobutylene-styrene) (SIBS). The present study investigates the interaction and interfacial dynamics of paclitaxel incorporated in a nano-polymeric matrix system. Solution and solid-state CP/MAS NMR experiments were designed to characterize the microstructure of heterogeneous drug–polymer mixtures in terms of its composition, molecular mobility, molecular order, paclitaxel–SIBS molecular interactions, and molecular mobility of the drug in the polymer matrix. The NMR spectra demonstrated unchanged chemical shifts between the neat and incorporated paclitaxel, and suggested that the level of the interactions between paclitaxel and SIBS is limited to non-bonding interactions or physical interactions between paclitaxel and SIBS when mixed in solution under NMR detection. Carbon spin-lattice relaxation time and proton spin-lattice relaxation time in the rotating frame offer further confirmation that the mobility of paclitaxel is increased in the paclitaxel–SIBS mixture. The results also indicate that a change occurs from crystalline packing to amorphous packing in paclitaxel due to its intermolecular interaction with SIBS. Our studies were used in understanding the detailed structure, morphology, and molecular motion of paclitaxel in the paclitaxel–SIBS system and to probe chemical and physical heterogeneity down to the nanometer scale.

Dynamics and packing mode of long-chained n-alkane molecules in the nano-channel of MCM-41

High-resolution solid-state 13C NMR spectra of long-chained n-alkanes included in the nano-channel of MCM-41 have been observed. Each spectrum has two sets of peaks: one from very flexible molecules and the other from molecules with no significant flexibility. These molecules are characterized by carbon spin lattice relaxation times, T 1, of < 1 s and > 10 s, respectively. This phenomenon is ascribed to phase separation of the alkanes in the nano-channel, i.e., the amorphous and crystalline phases, respectively. The mechanism of this phase separation and the dynamics of these molecules in the nano-channel are discussed.

Influence of methanol conditioning and physical aging on carbon spin-lattice relaxation times of poly(1-trimethylsilyl-1-propyne)

Molecular-level changes in poly(1-trimethylsilyl-1-propyne) [PTMSP] were observed using solid-state 13C NMR. These changes are attributed to the effect of polymerization catalyst on polymer configuration and the influence of methanol conditioning and physical aging on chain mobility. Chain mobility is deduced from carbon spin-lattice relaxation times ( T 1). In the solid-state 13C NMR spectrum of TaCl 5-synthesized PTMSP, the α-methyl carbon resonance is split into two peaks (25.5 and 29.5 ppm), indicating the existence of both cis and trans isomers. In the spectrum of the NbCl 5-catalyzed polymer, however, the peak assigned to the trans isomer is absent, suggesting that PTMSP synthesized with NbCl 5 catalyst has a more regular configuration than PTMSP prepared with TaCl 5 catalyst. For all PTMSP films, T 1 values decrease during methanol conditioning and then increase upon aging, indicating that molecular motion is enhanced by methanol treatment and reduced by aging. Methanol conditioning enhances carbon molecular motion by a similar amount in both NbCl 5- and TaCl 5-synthesized PTMSP, except for the mobility of carbons assigned to the trans isomer (which notably exhibits the largest percentage decrease in relaxation time). In the initial state, the presence of the trans isomer, which has less rotational freedom than the cis isomer, resulted in TaCl 5-synthesized PTMSP having higher T 1 values than the NbCl 5-catalyzed counterpart. Although the trans isomer present in the TaCl 5-catalyzed membrane imparts rigidity, it also induces disorder in chain packing. As the TaCl 5-catalyzed PTMSP membrane was previously shown to be more permeable than the NbCl 5-catalyzed PTMSP, disorder in chain packing seems to be more important than polymer mobility when high permeability is desired.

Supramolecular association of acid-terminated polydimethylsiloxanes. IV. NMR investigation of hydrogen bonding interactions and apparent molecular weight in the bulk state

Carbon-13 spin-lattice relaxation time measurements were used to probe the existence of hydrogen bonding interactions in bulk for a diacid-terminated oligosiloxane at temperatures well above its glass transition and melting temperatures. The behavior of the corresponding monoacid-terminated oligosiloxane, which can form dimers only, diester-terminated oligosiloxane, which cannot undergo any hydrogen bonding interactions, and two higher molecular weight covalent polymers, which serve as models for the supramolecular polymer, was also studied. The degree of association of the diacid-terminated oligosiloxane was estimated by investigating its transverse relaxation derived from 1H NMR and comparing the results thus obtained with data from a series of polydimethylsiloxane samples with different molecular weights.

Chemometric solid-state 13C NMR analysis of morphology and dynamics in irradiated crosslinked polyolefin cable insulation

The relative concentrations and carbon spin–lattice relaxation constants ( T 1,C) of the amorphous, intermediate, and crystalline phases of unaged crosslinked polyolefin cable insulation (ultimate elongation, e=310%), 60Co γ-irradiated ( e=22%), and irradiated+annealed ( e=220%) samples were determined by chemometric analyses of directly polarized solid-state 13C NMR spectra. The T 1,C relaxation curves of the intermediate and amorphous components were found to be mono-exponential. The intermediate component contains 23±5% of the CH 2 segments in the unaged sample and has an T 1,C relaxation constant of 1.4±0.3 s. γ-Irradiation caused a slight decrease in the amount of intermediate component to 19±5% and an increase of the relaxation constant to 1.8±0.3 s. The subsequent annealing of the irradiated sample resulted in an additional increase of the relaxation constant to 2.1 s and a slight loss of crystallinity. The amorphous T 1,C relaxation constants were found to be identical in all three samples and have a value of 0.38±0.03 s. At ambient temperature, the crystalline phase was found to relax via chain diffusion from the intermediate component. The rate of helical jumps was twice as fast in the irradiated and irradiated+annealed samples compared with the unaged material.

Carbon-13 Spin-Lattice Relaxation Time (T1) for Assignment of Brominated Carbons

Carbon-13 Spin-Lattice Relaxation Time (T1) for Assignment of Brominated Carbons

Characterization of Molecular Motion in the Solid State by Carbon-13 Spin–Lattice Relaxation Times

Relaxation calculations for rapidly spinning samples show that spin–lattice relaxation time (T1Z) anisotropy varies with the angle between the rotor spinning axis and the external field. When the rate of molecular motion is in the extreme narrowing limit, the measurement of T1Z anisotropies for two different values of the spinning angle allows the determination of two linear combinations of the three static spectral densities, J0(0), J1(0), and J2(0). These functions are sensitive to molecular geometry and the rate and trajectory of motion. The utility of these linear combinations in the investigation of molecular dynamics in solids has been demonstrated with natural abundance 13C NMR experiments on ferrocene. In an isolated 13C–1,2H group, the dipole–dipole interaction has the same orientational dependence as the quadrupole interaction. Thus, the spectral densities that are responsible for dipolar relaxation of 13C are the same as those responsible for deuteron quadrupolar relaxation. For ferrocene-d10, deuteron T1Z and T1Q anisotropies and the relaxation time of the 13C magic angle spinning peak provide sufficient information to determine the orientation dependence of all three individual spectral densities.

Gas transport properties and molecular motions of 6FDA copolyimides

The gas transport properties of 6FDA copolyimide membranes have been studied by examining their interaction such as the charge transfer complex between donor and acceptor molecules or the π–π aromatic stacking and their molecular motion in the solid-state. The interaction and the molecular motion in the membranes have been measured using fluorescence spectroscopy and solid-state 13C NMR spectroscopy, respectively. The gas permeability and selectivity of CO 2, O 2, N 2, and CH 4 for the membranes have been measured at 35°C and at pressures up to 10 atm. The gas permeability of the copolyimide membranes was significantly dependent on the gas diffusion, and the diffusion selectivity was a principal factor that dominates the determination of the gas selectivity in the membranes. A good correlation was found between the gas transport properties and the carbon spin–lattice relaxation time associated with the molecular motion of the CF 3 group in the copolyimide membranes.

Discussion

Selective one-dimensional ROE experiments were applied to study the host-guest interactions of cyclomaltohexaose with p-nitrophenol and the solution structure of 3A-(4-methylamino-3-nitrobenzyl)-cyclomaltoheptaose. The line selective excitation of the aromatic signals of p-nitrophenol gave intense ROE enhancements on the cyclomaltohexaose multiplets (H3 and H5), indicating deep complexation inside the cavity. The results on 3A-(4-methylamino-3-nitrobenzyl)-cyclomaltopheptose showed that the aromatic moiety covers the wider base of the cyclomaltoheptaose cone. The rotational correlation time for this compound was calculated to be 2.9 x 10-(-10)s using carbon-13 spin-lattice relaxation data. Quantitative analysis of the measured enhancements was performed and proton-proton distances were obtained between the aromatic and cyclomaltoheptoase protons as well as interglycosidic distances inside the cyclomaltoheptaose moiety.

Internal dynamics of human ubiquitin revealed by 13C-relaxation studies of randomly fractionally labeled protein

The use of random, fractional 13C-enrichment combined with low pass filtration has allowed the determination of NMR relaxation parameters at an unprecedented number of sites within recombinant human ubiquitin. Essentially complete 1H, 13C, and 15N resonance assignments for the protein are reported. Carbon spin lattice and heteronuclear NOE relaxation data have been analyzed in the context of the Lipari-Szabo model free formalism. The generalized order parameters for 56 main chain alpha C-H vectors have been determined and are found to correspond to the highly restricted motion seen in previous studies of the motion of amide N-H vectors. In distinct contrast, the analysis presented here indicates an unexpected range of dynamics within the interior of the protein. The generalized order parameters of 45 methyl groups of human ubiquitin have been determined. The methyl groups of Thr and Ala residues show generalized order parameters ranging from the Woessner limit (0.111) to below 0.01. Generalized order parameters for all methyl groups of the seven isoleucine residues were determined. With one exception, the generalized order parameters of the gamma methyls were equal to or greater than the corresponding delta methyls, indicating higher mobility away from the main chain. Generalized order parameters for 11 methyl groups of leucine residues were also determined. In six of the seven cases where the generalized order parameters of both prochiral methyl groups were determined, the pro-R methyl consistently shows a higher value than the pro-S methyl group. Generalized order parameters for seven methyl groups of four valines were also determined. There is no apparent correlation of methyl group prochirality with the value of the generalized order parameter. These data have several implications and generally indicate that the interior of the protein is heterogeneously dynamic.

Characterization of EPDM/atactic polypropylene blends by high-resolution solid-state NMR

The study of EPDM/atactic polypropylene blend compatibility was investigated by cross-polarization/magic angle spinning carbon-13 NMR spectra, variation contact time experiment analysis, proton spin-lattice relaxation time in the rotating frame, carbon-13 spin-lattice relaxation time, and a dipolar dephasing experiment. The data are discussed in terms of mobility and compatibility of polymeric blends. © 1996 John Wiley & Sons, Inc.

Internal dynamics of human ubiquitin revealed by 13C-relaxation studies of randomly fractionally labeled protein.

The use of random, fractional 13C-enrichment combined with low pass filtration has allowed the determination of NMR relaxation parameters at an unprecedented number of sites within recombinant human ubiquitin. Essentially complete 1H, 13C, and 15N resonance assignments for the protein are reported. Carbon spin lattice and heteronuclear NOE relaxation data have been analyzed in the context of the Lipari-Szabo "model free" formalism. The generalized order parameters for 56 main chain alpha C-H vectors have been determined and are found to correspond to the highly restricted motion seen in previous studies of the motion of amide N-H vectors. In distinct contrast, the analysis presented here indicates an unexpected range of dynamics within the interior of the protein. The generalized order parameters of 45 methyl groups of human ubiquitin have been determined. The methyl groups of Thr and Ala residues show generalized order parameters ranging from the Woessner limit (0.111) to below 0.01. Generalized order parameters for all methyl groups of the seven isoleucine residues were determined. With one exception, the generalized order parameters of the gamma methyls were equal to or greater than the corresponding delta methyls, indicating higher mobility away from the main chain. Generalized order parameters for 11 methyl groups of leucine residues were also determined. In six of the seven cases where the generalized order parameters of both prochiral methyl groups were determined, the pro-R methyl consistently shows a higher value than the pro-S methyl group. Generalized order parameters for seven methyl groups of four valines were also determined. There is no apparent correlation of methyl group prochirality with the value of the generalized order parameter. These data have several implications and generally indicate that the interior of the protein is heterogeneously dynamic.

Comparative conformational and dynamical study of some N-quaternarized UV filters: structure–activity relationships

A comparative conformational and dynamical study of a series of structurally related molecules with UV-filtering properties, i.e. N,N-dimethyl-N-[2-(4-benzoyl-2-hydroxyphenoxy)ethyl]-N-dodecyl ammonium bromide 2, N,N-dimethyl-N-[6-(4-benzoylphenoxy)hexyl]-N-dodecyl ammonium bromide 3 and N,N-dimethyl-N-[3-(salicyloylamino)propyl]-N-dodecyl ammonium bromide 5, has been performed in CDCl3 and [2H6] DMSO solutions. The main conformers of 2 and 3 (extensively folded conformations) and 5 (‘linear’ conformations) were determined by means of selective spin-lattice proton relaxation rates, carbon spin-lattice relaxation rates and 1D nuclear Overhauser effects. On the basis of these results a possible correlation between conformation and antibacterial activity is discussed.

Carbon relaxation analysis in proton coupled spin systems

Selective, non-selective and biselective carbon spin-lattice relaxation measurements were determined in methyl-salicylate DMSO-d 6 solution. The frequency dependence of biselective relaxation measurements of protonated aromatic carbons showed the effects of J-scalar modulation. The dipolar contribution induced by asymmetric selective proton inversion of the spin population of a single satellite peak could be useful for investigating of the Shimizu-Fujiwara-Mackor-Maclean relaxation rate. Analysis of the ratios is also proposed for the calculation of dipolar relaxation mechanism efficiency.

New approach to study fast and slow motions in lipid bilayers: application to dimyristoylphosphatidylcholine-cholesterol interactions

Natural abundance 13C solid-state nuclear magnetic resonance spectroscopy was used to investigate the effect of the incorporation of cholesterol on the dynamics of dimyristoylphosphatidylcholine (DMPC) bilayers in the liquid-crystalline phase. In particular, the use of a combination of the cross-polarization and magic angle spinning techniques allows one to obtain very high resolution spectra from which can be distinguished several resonances attributed to the polar head group, the glycerol backbone, and the acyl chains of the lipid molecule. To examine both the fast and slow motions of the lipid bilayers, 1H spin-lattice relaxation times as well as proton and carbon spin-lattice relaxation times in the rotating frame were measured for each resolved resonance of DMPC. The use of the newly developed ramped-amplitude cross-polarization technique results in a significant increase in the stability of the cross-polarization conditions, especially for molecular groups undergoing rapid motions. The combination of T1 and T1 rho measurements indicates that the presence of cholesterol significantly decreases the rate and/or amplitude of both the high and low frequency motions in the DMPC bilayers. This effect is particularly important for the lipid acyl chains and the glycerol backbone region.

Soluble Spin-Label as a NMR Relaxation Probe in the Study of the Enzyme-Substrate Complexes

Abstract The paramagnetic contributions induced by TEMPOL soluble spin-label on gentiobiose carbon spin-lattice relaxation rates are analyzed. Selective effects in the β(1–6) glycosidic bond region were observed. The possibility of using soluble spin-label to determine the stereochemistry of the substrate-enzyme interaction was then explored. The results obtained with different diamagnetic and paramagnetic systems enabled us to distinguish the region of gentiobiose most involved in interaction with the enzyme, and the region of the disaccharide molecule located on the surface of the enzyme and most exposed to the nitroxide. The results obtained could be used to model the enzyme surface of the gentiobiose binding site. Soluble spin-labels have been widely used in the investigation of the conformational and dynamical properties of biomolecules in solution (1–4). The main effects of nit oxide spin-labels, like TEMPO or TEMPOL, is the increase in NMR spin-lattice relaxation rates of solvent exposed nuclei. In...