Carbon-13 Spin-lattice Relaxation Times Research Articles

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.

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.

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.

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.

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.

Carbon-13 solid-state NMR spin-lattice relaxation time measurements of coals

Spin-lattice (T 1 ) relaxation times of 13 C nuclei have been measured on eight different coals in order to determine the best experimental conditions for recording 13 C single-pulse-excitation NMR spectra. It is found that a recycle delay of approximately 100 s is necessary to obtain quantitatively reliable spectra of coals using single-pulse-excitation methods

Interactions between PVC and solvents by longitudinal nuclear relaxation times

PVC/aliphatic ketone systems were investigated by NMR relaxation times such as proton and carbon-13 spin-lattice relaxation time (T1) and proton spin-lattice relaxation time in the rotating frame (T1ϱ). The proton T1 results showed that these systems are homogeneous, while proton T1ϱ indicates the existence of more than one domain.

Carbon-13 nuclear magnetic relaxations and chain local motions of poly(vinyl chloride) in dibutyl phthalate and tetrachloroethane solutions

Carbon-13 spin-lattice relaxation times and NOE values were measured as a function of temperature at two magnetic fields for PVC in dibutyl phthalate (DBP) and 1,1,2,2-tetrachloroethane-d 2 (TCE-d 2 ). The relaxation data were interpreted in terms of chain local motions by using various dynamic models. Among these, the Dejean-Laupretre-Monnerie correlation function appears to be the most appropriate to describe the chain segmental motions of PVC. Simulation paramerters from this model were found to differ for PVC in the two solvents, e.g., the half-angles of the librational motion of the C-H vector for the methine carbon were found to be 27 and 30° in DBP and in TCE-d 2 , respectively

Dynamic response to hydration in a superabsorbing polymer studied by carbon-13 NOE and spin-lattice relaxation times

It is found that in superabsorbing hydrolyzed starch-g-poly(acrylonitrile), steady-state and transient nuclear Overhauser effect (NOE) and spin-lattice relaxation time measurements bring out the dynamic response to hydration. The NOE factor is seen to be sensitive to the hydration level. At low hydrations the NOE behavior is consistent with the process of preferential hydration in this polymer. The NOE does not reach the theetical maximum even when hydrated to 8.0 g/g. Selective 1 H irradiation experiments with MASS bring out the importance of interchain interactions between the pendent groups and starch units

A carbon-13 nuclear magnetic resonance relaxation study of the reentrant 60CB–80CB

The carbon-13 spin-lattice relaxation times of the protonated ring carbons of octyloxycyanobiphenyl (80CB) in a 26 wt.% mixture of perdeuterated hexyloxycyanobiphenyl (60CB–d21) in 80CB are measured as a function of temperature at 22.63 MHz in the nematic (N), smectic A(SA), and reentrant nematic (RN) phases. The deuterium spectral densities of the ring deuterons of 60CB–d21 in the same sample were studied previously, and the diffusion coefficients [Formula: see text] and [Formula: see text] found in that study are used to calculate the theoretical carbon-13 relaxation times of the protonated ring carbons of 60CB. The general agreement of the theoretical values for 60CB with the experimental values for 80CB demonstrates that the two constituent molecules of the reentrant have similar motions. Small differences, similar in nature to those encountered in other studies of this interesting reentrant, however, do exist in the nematic and reentrant nematic phases and are discussed in terms of the molecular pairing model proposed by Cladis. (Phys. Rev. Lett. 35, 48 (1975).)

Temperature Dependence of the Rotational Mobility of the Sugar and Water Molecules in Concentrated Aqueous Trehalose and Sucrose Solutions

Carbon-13 and deuteron spin lattice relaxation times T1 of concentrated solutions of trehalose and sucrose in heavy water are given as function of temperature. From the temperature dependence of the T1 ideal glass transitions temperatures T0 are derived. For both compounds the T0 derived for the disaccharides are at high concentrations larger than the T0 of the water molecules.

NMR and conformational analysis of ganglioside GD1a

One-dimensional TOCSY and 1D NOESY experiments using Gaussian-shaped pulses as well as 2D NOESY and 2D ROESY measurements were carried out to obtain informations for primary and secondary structural characterizations. These techniques combined with 13 C- 1 H correlation measurements were essential for the complete assignment of hydrogen and carbon chemical shifts. Proton and carbon spin-lattice relaxation time measurements were carried out to probe the dynamic behavior of the hexasaccharide. The interresidual hydrogen distances calculated from the 1D NOESY values were found to be in good accord with the lowest energy model suggested by the HSEA calculations, including those for the glycosidic linkages containing the internal sialic acid residue

High-pressure nuclear-magnetic-resonance study of carbon-13 relaxation in 2-ethylhexyl benzoate and 2-ethylhexyl cyclohexanecarboxylate

Natural abundance carbon-13 spin-lattice relaxation times and 13G–1H nuclear Overhauser enhancement (NOE) times of 2-ethyl hexylbenzoate (EHB) and 2-ethyl hexylcyclohexanecarboxylate (EHC) have been measured along isotherms of −20, 0, 20, 40, and 80 °C at pressures of 1–5000 bars using high-pressure, high-resolution NMR techniques. The ability to use pressure as an experimental variable has allowed us to study a wide range of molecular motions from extreme narrowing into the slow motional regime. In addition, the high-resolution capability even at high pressure permits the measurement of 13C and NOE for each individual carbon in the molecules studied. Relaxation in both molecules is successfully analyzed in terms of a model assuming a Cole–Davidson distribution of correlation times. The comparison of parameters used in the model demonstrates the increased flexibility of the EHC ring over the EHB ring and also shows how the presence of the flexible ring contributes to the increased over-all mobility of the EHC molecule. The analysis of molecular reorientations in terms of activation volumes also indicates that EHB motion is highly restricted at low temperature.

13C magnetic relaxation times in isotactic polypropylene

13C spin-lattice relaxation time, T 1, 13C and 1H spin-lattice relaxation times in the rotating frame, T 1ρ( 13 C) and T 1ρ( 1 H) , and the dipolar dephasing behaviour of methylene, methine and methyl carbons of annealed(monoclinic) and quenched(smectic) isotactic polypropylene films were measured using the CP/MAS method. Two T 1s were observed for methylene and methine carbons in the annealed and quenched samples but one T 1 for methyl carbons in both samples. T 1s for methylene and methine carbons in the annealed sample are longer than those in the quenched sample, whereas T 1 for methyl carbons is nearly the same for annealed and quenched samples. There is, however, a small but a definite difference between T 1 of upfield and downfield peaks of methyl carbons in the annealed sample: T 1 for the downfield peak is ca 15–20% shorter than that for the upfield peak. The carbon spin-lattice relaxation time in the rotating frame, T 1ρ( 13 C) , shows rather complicated manner; for the quenched sample, two T 1ρ( 13 C) s were obtained for all carbons but, for the annealed material, one T 1ρ( 13 C) was obtained for methine carbons and the downfield peaks of methylene and methyl carbons and two T 1ρ( 13 C) s were obtained for the upfield peaks of methylene and methyl carbons. For the proton spin-lattice relaxation time in the rotating frame, T 1ρ( 1 H) , two components were observed for all carbons of both samples. There is no large difference in the dipolar dephasing behaviour for annealed and quenched samples and the signal intensity decays as exp[-( t/ T′ 2) 2] for methylene and methyl carbons but as exp(- t/ T′ 2) for methyl carbons.