Proton NMR Spin-lattice Relaxation Research Articles

Proton NMR study on the molecular motion and conformation of polyaniline doped with HCl

Proton NMR spectra and spin-lattice relaxation time (T1) for polyaniline doped with HCl were measured at 90MHz over a temperature range of 110–430K. A narrow line with a width of about 1–2KHz superimposed on broad NMR peak was observed above 210K, and it was tentatively assigned to the protons in dopant and absorbed water. The analysis of linewidths and second moments for the broad lines reveal two distinct relaxation processes with activation energies of 1.9 and 7.8Kcal./mole,respectively. The former may be associated with the motion of the dopant and water absorbed and the latter with the rotation of benzoid ring about C-N bond axis. The second moment data suggest that the twist angle between the adjacent rings decreases with rising the doping ratio. Proton NMR relaxation rate was fitted with a theoretical equation containing the contributions from nuclear dipolar interaction and from electron-proton interaction, Rd and Rp, respectively.Rd is negligible below room temperature and Rp has little change above 100K. The total relaxation rate is dominated by Rp near room temperature.

Determination of ligand lifetimes in the Ni(glycerol)+ complex by proton NMR spin—lattice relaxation time measurements

AbstractThe activation enthalphy and entropy for ligand exchange in the weak complex Ni(glycerol +) were estimated by variable‐temperature proton spin–lattice relaxation time measurements at 9.4 and 6.3 T on a 0.044 molal solution of NiCl2 in glycerol. A description of the dynamic process in terms of a simple two‐site exchange model yields ΔH≠ = 18.4 ± 1 kJ mol−1 and ΔS≠ = −114 ± 3 J mol−1 K−1.

Effects of cytoskeletal inhibitors on water proton relaxation time changes in unfertilized and fertilized sea urchin eggs

Unfertilized and fertilized sea urchin eggs were used for pulsed proton NMR spin-lattice relaxation time (T 1) measurements of cellular water. An 81% increase in T 1 time at fertilization was largely explained by the accumulation of extracellular water in the perivitelline space. To assess the role of microtubule and actin filament assembly and disassembly, eggs were treated with drugs that are known to change these cytoskeletal elements (i.e., colchicine, taxol and cytochalasin β). Egg volume was also monitored in all studies to rule out the influence of water content changes on the observed T 1 relaxation time changes. Neither assembly nor disassembly of microtubules changed the T 1 relaxation time. The role of actin polymerization and depolymerization is discussed as a possible explanation for the observed cell cycle dependent water proton T 1 relaxation time changes.

Proton NMR spin-lattice relaxation studies of hydridometal clusters of ruthenium and osmium

Proton NMR spin-lattice relaxation studies of hydridometal clusters of ruthenium and osmium

A proton NMR spin-lattice relaxation study of the imino proton exchange kinetics in calf-thymus DNA.

AbstractThe results of semiselective 1H‐nmr inversion recovery experiments on sonicated calf thymus DNA fragments are reported. The measurements were conducted in aqueous solutions containing 85% D2O, in order to reduce the dipolar contribution to the observed relaxation rates. In solutions containing 0.2M NaCl, 0.4 mM EDTA, and 10 mM cacodylate at pH = 7.0, the exchange rates of the imino protons in A‐T base pairs confirm values published earlier in the literature, extrapolating to 0.25 s−1 at 25°C. Corresponding values for the G‐C base pairs are published for the first time, and are about sixfold slower. The addition of up to 0.1M Tris buffer (pH = 7.3 at 25°C), caused a striking increase in the measured exchange rates for both the A‐T and G‐C imino protons, resembling the effect recently observed for poly(rA)‐poly(rU) and poly(rI)‐poly(rC), and suggesting that the exchange rates measured for nucleic acid duplexes in low buffer concentrations at neutral pH do not reflect base‐pair opening rates as assumed in the past. Lower limits to the base‐pair opening rates could be estimated from extrapolation of the experimental data to infinite buffer concentration, and are 1 × 103 s−1 for the A‐T, and 50 s−1 for the G‐C, base paris at 62°C.

Magnetic transitions in a molecular metal with embedded local moments: Cu(pc)I

We discuss the low temperature magnetic properties of (phthalocyaninato)-copper(II) iodide (Cu(pc)I). This molecular metal contains conductive stacks that incorporate a one-dimensional array of local Cu +2 moments strongly coupled to conduction electrons. Below 20K, the EPR g-value of the coupled spin system increases anomalously and at 8K the EPR signal broadens abruptly and becomes unobservable. Anomalies in the proton NMR spin-lattice relaxation times are observed at the transition temperature. Preliminary EPR experiments conducted on a newly synthesized series of materials, Cu xNi 1−x(pc)I, indicate the existence of a similar low temperature transition in the presence of various concentrations of loca moments.

The influence of macromolecular polymerization on spin-lattice relaxation of aqueous solutions

The docking or polymerization of globular proteins is demonstrated to cause changes in proton NMR spin-lattice ( T 1) relaxation times. Studies on solutions of lysozyme, bovine serum albumin, actin, and tubulin are used to demonstrate that two mechanisms account for the observed changes in T 1. Polymerization displaces the hydration water sheath surrounding globular proteins in solution that causes an increase in T 1. Polymerization also slows the average tumbling rate of the proteins, which typically causes a contrary decrease in T 1. The crystallization reaction of lysozyme in sodium chloride solution further demonstrates that the “effective” molecular weight can either decrease or increase T 1 depending on how much the protein is slowed. The displacement of hydration water increases T 1 because it speeds up the mean motional state of water in the solution. Macromolecular docking typically decreases T 1 because it slows the mean motional state of the solute molecules. Cross-relaxation between the proteins and bound water provides the mechanism that allows macromolecular motion to influence the relaxation rate of the solvent. Fast chemical exchange between bound, structured, and bulk water accounts for monoexponential spin-lattice relaxation. Thus the spin-lattice relaxation rate of water in protein solutions is a complex reflection of the motional properties of all the molecules present containing proton magnetic dipoles. It is expected, as a result, that the characteristic relaxation times of tissues will reflect the influence of polymerization changes related to cellular activities.

Synthesis, characterization and properties of the new ionic intercalation compound (NH +4) 0.22TiS 0.22−2

The new ionic intercalation compound (NH + 4) 0.22TiS 0.22− 2 has been synthesized by vacuum deintercalation of ammoniated TiS 2, characterized by thermogravimetric analysis and powder X-ray diffraction, and examined by SQUID magnetometry (indirectly), differential scanning calorimetry, incoherent inelastic neutron scattering, and nuclear magnetic resonance. Although the diffraction pattern of this compound resembles a stage-II structure in which every other van der Waals gap is occupied by NH + 4 it cannot be indexed completely on this basis. Magnetic and calorimetric measurements show that one electron is transferred to the host TiS 2 conduction band per NH + 4 cation and that the deintercalation enthalpy of NH + 4 is 22 kcal/mol NH + 4, respectively. Neutron scattering has provided evidence for an NH + 4 torsional fundamental mode at 215 cm −1. The proton NMR linewidth and spin-lattice relaxation time are independent of temperature between 100 and 540 K, and the linewidth of 2.6 ± 0.3 G is in good agreement with that calculated for isotropic reorientation of the NH + 4 cations.

Transition of local moments coupled to itinerant electrons in the quasi one-dimensional conductor, copper phthalocyanine iodide.

Copper phthalocyanine iodide is a molecular metal whose conducting stacks incorporate a one-dimensional array of local moments strongly coupled to conduction electrons. Below 20 K the EPR $g$ value of the coupled system increases anomalously and at 8 K the EPR signal broadens abruptly and becomes unobservable. Anomalies in the proton NMR spin-lattice relaxation are observed at the transition temperature. Magnetic susceptibility measurements and NMR linewidth data both indicate that there is little if any static magnetic order below 8 K.

Proton NMR studies of the interaction of water with lecithin in non-polar organic media

Lecithin-non-polar solvent-water systems are studied by proton NMR spin-lattice ( T 1) and spin-spin relaxation ( T 2) times. T 1 studies indicate that one water molecule is tightly bound to the polar head group. The rotational correlation time ( τ c) of the water pool is shortened as a function of added water, until τ c finally approaches the value of 3 × 10 −12 s for normal, bulk water. The microviscosity of the water environment is very high and falls off rapidly as a function of added water. The water added is solubilized in the polar core of the reverse micelle; this increases the motion of the polar head group but has no effect on the hydrocarbon chains. T 2 studies of those systems reveal that, in addition to intramolecular dipole relaxation, the observed relaxation processes are possibly strongly influenced by exchange narrowing, spin-rotation and chemical shift anisotropy.

The stability, structure and reactivity of the outer sphere complex formed between the hexakis (d 4-methanol) cobalt(II) ion and pyridine in d 4-methanol

Proton NMR spinlattice ( Tι) relaxation times and chemical shifts were used to characterize the outer sphere complex formed between the hexakis (d 4-methanol) cobalt(II) ion and pyridine in d 4-methanol. Analysis of the bulk α-hydrogen Tι data of pyridine resulted in an outer sphere complex stability constant ( K os) which varied from 0.51 ± 0.16 M −1 at −60.0 °C to 0.62 ± 0.17 M −1 at −40.0 °C. The extrapolated K os value at 25.0 °C (1.0 M −1) is almost an order of magnitude larger than predicted larger predicted by theory. The combination of Tι and shift data suggested a preferred orientation of pyridine in the outer sphere of the [Co(CD 3OD) 6] 2+ ion. Further quantitative structural information was obtained by the application of the Solomon-Bloembergen relationship to the system studied. Pyridine dissociation rate constant data were combined with solvent exchange and equilibrium data to obtain values for the interchange probability or statistical factor (f) which ranged from (7.0 ± 3.7) × 10 −3 at −60.0 °C to (9.5 ± 4.7) × 1- −3 at −40.0 °C. These values are more than two orders of magnitude smaller than normally assumed and represent the first direct measurement of an ion-neutral outer sphere complex's reactivity. Implications regarding the relationship between outer sphere complex stability and reactivity are discussed.

Proton NMR dipolar relaxation by delocalized spin density in low-spin ferric porphyrin complexes

The proton NMR spin-lattice relaxation of methyl groups in a series of low-spin ferric, S = 1 2 porphyrin complexes has been analyzed in terms of the paramagnetic influences. The differential porphyrin methyl spin-lattice relaxation rates and the dependence of the difference on the methyl contact shift patterns dictate that both ligand-centered as well as iron-centered dipolar relaxation by unpaired spin density must be considered. For the systems considered, the relaxation by delocalized spin density dominates methyl relaxation for contact shifts greater than 19 ppm. The study shows that delocalized dipolar relaxation must be included in any analysis of differential relaxation data in terms of structure in hemoproteins.

Electron and proton magnetic resonance studies of the effect of rhodopsin incorporation on molecular motion in dimyristoylphosphatidylcholine bilayers

The effect of rhodopsin incorporation on molecular motion in L-α-dimyristoylphosphatidylcholine (DMPC) bilayers is analyzed with nitroxide ESR and proton NMR techniques. A partial, binary phase diagram for DMPC-rhodopsin is constructed by studying the partitioning of 2,2,6,6-tetramethylpiperidine-1-oxyl (Tempo) between polar and hydrophobic domains as a function of temperature and system composition. Proton NMR spin-lattice relaxation measurements show that rhodopsin is associated with a domain of approx. 50 DMPC molecules which have reduced choline methyl mobilities. ESR studies, utilizing nitroxide-labeled fatty acid probes, indicate that rhodopsin immobilizes the outer half of the hydrophobic region in rhodopsin containing DMPC bilayers. Additional ESR studies, involving a nitroxide label placed in the middle of the membrane, as well as proton chain methyl spin-lattice relaxation measurements, indicate only slight rhodopsin-induced immobilization in the central part of the membrane.

Proton magnetic relaxation of proteins in the solid state: molecular dynamics of ribonuclease

Measurements have been made of the proton NMR spin-lattice relaxation at 60, 30 and 18 MHz in solid ribonuclease A from 10 to 300 K, and in α-chymotrypsin, lysozyme and deuterated lysozyme from 120 to 300 K. Reorientation of the methyl groups is the predominant molecular motion causing relaxation. A lognormal distribution of correlation times best characterizes the motions, with a spread of activation energies 14 ± 6 kJ mole .

Simultaneous Fermion and Boson Spin Dynamics in a One-Dimensional Antiferromagnet

The proton NMR spin-lattice relaxation time T/sub 1/ has been measured in the spin-1/2 one-dimensional antiferromagnet (1DAF) ..cap alpha..-bis (N-methylsalicylamidinato) -copper (II) (CuNSal) at low temperatures and high fields. T/sub 1/ is dominated by electron spin fluctuations of the 1DAF, and we show that these fluctuations are described by Fermi-Dirac statistics for the one-magnon contribution to T/sub 1/ but that the two-magnon part is given by Bose-Einstein statistics.

Dynamics of the n-decylammonium chains in the perovskite-type layer structure compound (C10H21NH3)2CdCl4

The two structural phase transitions in the perovskite layer structure compound (C10H21NH3)2CdCl4 at Tc1=35 °C and Tc2=39 °C have been studied by x‐ray diffractional, calorimetric and dielectric measurements, proton NMR spin–lattice relaxation and second moment investigations, 35Cl and 14N quadrupole resonance spectroscopy as well as group theoretical considerations. The results show that the transition (Tc1) from the low temperature phase (P21/n) to the intermediate temperature phase (Pmnn) is basically a dynamic order–disorder transition of rigid alkyl chains, whereas the transition (Tc2) from the intermediate to the high temperature phase (Amaa) is connected with a melting of the alkyl chains. In the intermediate phase the rigid alkyl chains are flipping around their long axes between two equivalent orientations separated by 90°. The two transitions are somewhat analogous to the ones found in the lipid bilayer membranes and can be described by order parameters used for smectic liquid crystals.

The measurement of cross-relaxation effects in the proton NMR spin-lattice relaxation of water in biological systems: Hydrated collagen and muscle

A general procedure for investigating cross relaxation is presented. Experimental evidence derived from proton NMR studies of collagen and muscle clearly shows that cross relaxation between the bulk of the water protons and the bulk of macromolecular protons significantly perturbs water spin-lattice relaxation. These findings have serious implications for interpretations of the molecular dynamics of water molecules in hydrated biological systems. The presence of cross relaxation is direct proof that a fraction of the water protons exchange at a rate slow compared with the Larmor frequency.

Pressure dependence of NMR proton spin–lattice relaxation times and shear viscosity in liquid water in the temperature range −15–10 °C

The NMR proton spin–lattice relaxation times T1 and shear viscosities have been measured as functions of pressure in the temperature interval −15–10 °C. At low temperatures the low pressure boundary of the experiments is ice I, whereas ice V represents the high pressure extreme of our measurements. The initial compression at all temperatures covered in our study results in higher motional freedom of water molecules so that the pressure dependence exhibits a minimum in viscosity and a maximum in T1. This is a consequence of significant distortion of the hydrogen bond network due to compression which also seems to weaken the hydrogen bonds. Further compression leads to restricted motional freedom due to increased packing of the molecules. This anomalous behavior of spin–lattice relaxation and shear viscosity with compression is more pronounced at lower temperatures since the hydrogen bond network is better developed at lower temperatures. In agreement with our earlier data covering the 10–90 °C temperature range, we find that compression under isothermal conditions distorts the random hydrogen bond network, leading to diminished coupling between the rotational and translational motions of water molecules. The data indicate that the Debye equation describes the relationship between the reorientational correlation time and shear viscosity at constant volume but is not applicable to describe the density effects on water reorientation. In general, pressure and temperature have parallel effects on many dynamic properties at temperatures below 40 °C and pressures below 2 kbar, whereas at higher temperatures and pressures their effects are just the opposite. Hard core repulsive interactions become more important than the directional interactions of hydrogen bonding at high compression.

Proton NMR relaxation study on low-spin pyridine complexes of ferriporphyrins

Proton NMR shifts, spin-lattice, and spin-spin relaxation times have been measured on low-spin pyridine complexes of Fe(III)-protoporphyrin(IX)dimethylester and Fe(III)-tetraphenylporphyrine in chloroform between 203 K ⩽ T ⩽ 253 K. Deviations between measured and calculated chemical shifts have been observed for the protons (e.g., methyl group) in Fe(III)-protoporphyrin but not for the pyrrole protons in Fe(III)-tetraphenylporphyrin. These deviations have been analyzed theoretically and it was found that higher-order terms to the pseudocontact shift are too small to explain the deviations observed. Instead, a considerable temperature dependence of the hyperfine coupling constant A for the protons of Fe(III)-protoporphyrin had to be assumed in order to explain the deviations observed, whereas A was found to be independent against temperature variations for Fe-(III)-tetraphenyl-porphyrin. This result was confirmed by independent relaxation time measurements and the values for the hyperfine coupling constants extracted from the two methods were found to be in excellent agreement.

Intramolecular microdynamical and conformational parameters of peptides from 1H and 13C NMR spin-lattice relaxation. Tetragastrin.

Measurements of 1H and 13C spin-lattice relaxation and 13C nuclear Overhauser enhancement factors are reported for dimethyl sulfoxide solutions of tetragastrin, a pharmacologically active tetrapeptide. The use of the dipolar formalism for predicting 1H and quaternary 13C relaxation rates is discussed. Furthermore, the prospect is opened for the use of quaternary 13C and 1H relaxation times to obtain information on the peptide torsion angles phi, psi, and chi in a way supplementing NMR coupling constant methods presently in use.