31P Spin-lattice Relaxation Times Research Articles

Contrasting Trivalent Lanthanide and Actinide Complexation by Polyoxometalates via Solution-State NMR.

Deciphering the solution chemistry and speciation of actinides is inherently difficult due to radioactivity, rarity, and cost constraints, especially for transplutonium elements. In this context, the development of new chelating platforms for actinides and associated spectroscopic techniques is particularly important. In this study, we investigate a relatively overlooked class of chelators for actinide binding, namely, polyoxometalates (POMs). We provide the first NMR measurements on americium-POM and curium-POM complexes, using one-dimensional (1D) 31P NMR, variable-temperature NMR, and spin-lattice relaxation time (T1) experiments. The proposed POM-NMR approach allows for the study of trivalent f-elements even when only microgram amounts are available and in phosphate-containing solutions where f-elements are typically insoluble. The solution-state speciation of trivalent americium, curium, plus multiple lanthanide ions (La3+, Nd3+, Sm3+, Eu3+, Yb3+, and Lu3+), in the presence of the model POM ligand PW11O397- was elucidated and revealed the concurrent formation of two stable complexes, [MIII(PW11O39)(H2O)x]4- and [MIII(PW11O39)2]11-. Interconversion reaction constants, reaction enthalpies, and reaction entropies were derived from the NMR data. The NMR results also provide experimental evidence of the weakly paramagnetic nature of the Am3+ and Cm3+ ions in solution. Furthermore, the study reveals a previously unnoticed periodicity break along the f-element series with the reversal of T1 relaxation times of the 1:1 and 1:2 complexes and the preferential formation of the long T1 species for the early lanthanides versus the short T1 species for the late lanthanides, americium, and curium. Given the broad variety of POM ligands that exist, with many of them containing NMR-active nuclei, the combined POM-NMR approach reported here opens a new avenue to investigate difficult-to-study elements such as heavy actinides and other radionuclides.

Structural and Dynamical Origin of Ionic Conductivity As Studied By Solid-State NMR

Ionic conductors are promising electrolyte of solid-state batteries. Their major advantages are high ionic conductivity, electrochemical stability and inflammability. Various works have been done to explain the origin of high ionic conductivity. For example, the high ionic conductivity in the order of 10-3 Scm-1 at room temperature of Li7P3S11 metastable crystal, which is synthesized by annealing (Li2S)70(P2S5)30 glass at 513 K [1, 2], has attracted much interest. By analyzing its synchrotron X-ray powder diffraction pattern, Yamane et al. showed that Li ions are situated in the conduction pathways formed by PS4 tetrahedra and P2S7 ditetrahedra units [3]. The conduction pathway has been attributed to as the structural origin of high conductivity. We thus applied 6/7Li and 31P solid-state NMR to examine structural/dynamical origins of high conductivity of glass and glass-ceramics Li2S-P2S5 samples. (Li2S) x (P2S5)100 – x (mol %; x = 70 and 75) glasses were prepared by mechanical milling. Li2S and P2S5 crystalline powders were used as the starting materials. The glass-ceramics sample was prepared by heating the glass at 290 °C for 2 h. All the processes were performed in a dry Ar atmosphere. The NMR measurements were made using a JEOL ECA600 NMR spectrometer at 14 T. The MAS NMR spectra were observed by using a single pulse with the Hahn-echo. The spin-lattice relaxation times (T 1) were measured under MAS by using the conventional saturation-recovery method. To examine the origin of the linewidth of signals of 31P NMR, we applied the two-dimensional (2D) Radio Frequency Driven Recoupling (2D-RFDR). It was performed with an experimentally optimized p pulse length of 2.2 ms using XY16 phase cycling. While 6/7Li and 31P spin-lattice relaxation times exhibit that 31P relaxation of the glass sample is governed by 7Li motion, those of the glass-ceramics sample indicate 31P motion is appreciable at temperatures higher than ca. 310 K. The results showed that dynamics of the PS4 tetrahedra and P2S7 ditetrahedra units in (Li2S)70(P2S5)30 glass-ceramic is not appreciable at temperatures below ca. 310 K, where the ionic conductivity is low. At higher temperatures, however, significant motion especially for the P2S7 ditetrahedra unit is apparent in both of 31P-T 1 and 31P MAS lineshapes. High-resolution 31P MAS NMR spectra of the glass-ceramics sample bear the 31P signals of PS4, P2S7, and P2S6. In addition to these signals reported previously, we found two signals, which have not yet been assigned. Interestingly, these two signals are merged into the P2S7 signal at higher temperatures. Further, we applied 31P-31P dipolar correlation experiment to examine the 31P linewidth, which is reduced by motion at higher temperatures. It was shown that the linewidth of the P2S7 unit is attributable to distribution of local structures of and around the P2S7 ditetrahedra unit. With these, we concluded that the significant motional fluctuation of the P2S7ditetrahedra unit at above 310 K allows facile diffusive motion of lithium ions, leading to the high ionic conductivity [4]. As has been described, NMR is a powerful tool to correlate the local environment of ions and ion transportation (= ionic conductivity) and can be applied to other systems including F- (or other ion) conductive systems. 1) F. Mizuno et al., Adv. Mater. 17, 918-921 (2005). 2) F. Mizuno et al., Electrochem. Solid-State Lett. 8, A603-A606 (2005). 3) H. Yamane et al., Solid State Ionics 178, 1163–1167 (2007). 4) M. Murakami et al., J. Phys. Chem. C 119, 24248-2425 (2015). Acknowledgment: This work was financially supported by the RISING project of the New Energy and Industrial Technology Development Organization (NEDO).

Solid-state NMR study of discrete environments of bone mineral nanoparticles using phosphorus-31 relaxation

Bone mineral nanoparticles, residing between collagenous fibres, contain a crystalline apatite core (CAC) covered by an amorphous hydrated surface layer (AHSL). The main objectives of this work were to characterize the nanoparticles of human bone mineral and their discrete CAC and AHSL regions and relate this information to bone diseases. This pilot study involved 18 postmenopausal women suffering from osteoarthritis together with osteoporosis or osteopenia. Trabecular tissue specimens were acquired from the femoral intertrochanteric region during total hip arthroplasty. The specimens of whole bone were examined by 31P solid-state NMR (ssNMR) to measure the concentration ratio of phosphorus in the AHSL and CAC locations, together with their 31P linewidths and spin-lattice relaxation times. It was found that the AHSL region of the studied specimens contained 13–24% apatite phosphorus. The magnitude, hydration and structural order of AHSL and CAC were dependent on the progress of the pertinent diseases. Thus, the 31P ssNMR spectroscopy can be used ex vivo to selectively analyse the discrete nanoapatite environments in whole bone specimens and possibly assist in postoperative medical diagnostics.

Solid-state 1H and 31P NMR and FTIR spectroscopy study of static and dynamic structures in sol-gel derived calcium hydroxyapatites

Calcium hydroxyapatite containing amorphous phosphate phase (ACP-CaHA) and nano-structured hydroxyapatite (CaHA) have been prepared by two sol-gel synthesis routes. The structural organization of hydroxyl groups in both materials has been determined by means of 1H MAS NMR and FTIR spectroscopy. It has been shown that the amount of structural –OH groups in nano-structured CaHA is significantly higher than that from adsorbed water and vice versa in ACP-CaHA. A precise signal shape analysis has been carried out for both studied samples. The 31P NMR signals have been found being Voigt-shaped in the wide-line as well as in MAS spectra. The 1H and 31P spin-lattice and spin-spin relaxation time measurements have revealed that the fast spin motion takes place in ACP-CaHA. The corresponding correlation time τ ~ 7 · 10–7 s at ~300 K has been determined. The effect of MAS rate on the 31P signal shape also confirms that this motion runs in the time scale of microseconds or even nanoseconds. The magnitude of the anisotropic broadening 1220 ± 20 Hz determined for nano-structured CaHA is very close to the maximum of the dipolar 1H–31P coupling distribution profile estimated using CP MAS kinetics. The dynamics of 1H–31P spin interactions in nano-structured CaHA (τ ~ 3.3 · 10–5 s) is much slower than in ACP-CaHA.

1H and 31P nuclear spin-lattice relaxation in C-phosphorylated oximes

The 1H spin-lattice relaxation times of the proton-bearing groups and the 31P spin-lattice relaxation times in C-phosphorylated oximes R1C(=NOH)P(=O)R2R3 (R1 = Ph, R2 = R3 = OMe; R1 = Ph, R2 = OMe, R3 = OCH2CH2Br; R1 = PhCH2, R2 = R3 = OCHMe2) and dioxime R2P(=O)C(=NOH)(CH2)4C(=NOH)P(=O)R2 (R = OMe) in DMSO-d6 were measured. The characteristic reorientation times of the whole molecules were estimated using the measured values of the 1H relaxation times and the results of semiempirical PM3 quantum chemical calculations of the molecular geometries. The reorientation times were used to identify the contributions of different relaxation mechanisms to the rate of 31P spin-lattice relaxation. The anisotropy of the chemical shielding of 31P nuclei was evaluated from the difference between the 31P relaxation rates measured at 101.27 and 161.92 MHz.

Valence structure and magnetic interaction in MMX-type 1D complexes, A 4[Pt 2I(P 2O 5H 2) 4]· nH 2O, studied by 31P solid NMR

31P MAS-NMR spectra and spin-lattice relaxation time T 1 in solid were measured on A 4 [Pt 2 I(P 2 O 5 H 2 ) 4 ].nH 2 O (A: Cs, Rb, K, Na and Li). Continuous spectrum changes in both line and splitting widths were observed with changing the cation size and the number of crystalline water. Complexes with A: Cs (n=0) and Rb (n=2) afforded two kinds of 31 P resonance lines with chemical shifts close to those in the Pt 3+ and Pt 2+ monomer complexes indicating a mixed valence structure. On the other hand, complexes with A: Na (n=2) and Li (n=4) yielded a broad single line suggesting the formation of paramagnetic Pt sites with an averaged valence of Pt 2.5+ . An analogous continuous change was observed in 31 P T 1 in consistent with the above analysis. The observed spectra and T 1 depending on the cation size and the H 2 O number suggest valence fluctuation due to spin jumps in and between Pt-Pt units sensitively influenced by crystal packings and hydrogen bonding.

Dynamic Properties and Phase Transitions in A2ZnBr4(A= (CH3)4 N and (CH3)4P) as Studied by 79Br NQR and Multinuclear NMR

Abstract In order to understand the mechanism of ferroelastic phase transitions in A2ZnBr4 (A = (CH3)4 N and (CH3)4 P), the temperature dependences of 79Br NQR frequencies and the spin-lattice relaxation times were measured. The temperature dependences of the 1H and 31P spin-lattice relaxation times were measured as well for a possible correlation between the cation dynamics and the phase transition. Although the phase transition temperatures of these two compounds differ much (~ 100 K), the correlation times for the cation reorientation at the individual transition temperatures amount to some 10-11 s for both compounds.

DETERMINATION OF THE31P NMR CHEMICAL SHIELDING TENSOR ANISOTROPY OF SOME MOLECULES IN SOLUTION

Abstract The chemical shielding tensor anisotropy of the 31P nucleus in tris(piperidino)phosphine oxide and triphenylphosphine sulfide molecules was determined in solution from 31P and 13C spin-lattice relaxation time measurements. The quadrupolar coupling constant χ of the 17O nucleus of tris(piperidino)phosphine oxide was also deduced from these experiments and 17O NMR spectra. The δ[sgrave] value for triphenylphosphine sulfide is compared to those reported in the literature. The δ[sgrave] and χ parameters for tris(piperidino)phosphine oxide are discussed in terms of the influence of the piperidino substituent on the electronic distribution in the PO bond.

31P spin lattice relaxation time measurements of the amphiphilic ligands [Ph 2P (CH 2) nPMe 3] + in solution and tethered to a solid cationic exchange resin via the tetra-alkylphosphonium groups

31P spin lattice relaxation time data and, thence, assessments of relative molecular mobilities are obtained for the amphiphilic tertiary phosphines [Ph 2P(CH 2) n PMe 3] + ( n = 2, 3, 6, 10) in aqueous (D 2O) solution and on tethering via the tetra-alkylphosphonium groups to a cation exchange resin; immersion of the resin-sorbed ligands in D 2O results in sufficient shortening of the correlation times for molecular tumbling that well-resolved 31P{ 1H} NMR spectra of the solid materials may be observed.

High-pressure 31P NMR study of dipalmitoylphosphatidylcholine bilayers.

High-pressure 31P NMR was used for the first time to investigate the effects of pressure on the structure and dynamics of the phosphocholine headgroup in pure 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) multilamellar aqueous dispersions and in DPPC bilayers containing the positively charged form of the local anesthetic tetracaine (TTC). The 31P chemical shift anisotropies, delta sigma, and the 31P spin-lattice relaxation times, T1, were measured as a function of pressure from 1 bar to 5 kbar at 50 degrees C for both pure DPPC and DPPC/TTC bilayers. This pressure range permitted us to explore the rich phase behavior of DPPC from the liquid-crystalline (LC) phase through various gel phases such as gel I (P beta'), gel II (L beta'), gel III, gel IV, gel X, and the interdigitated, Gi, gel phase. For pure DPPC bilayers, pressure had an ordering effect on the phospholipid headgroup within the same phase and induced an interdigitated Gi gel phase which was formed between the gel I (P beta') and gel II (L beta') phases. The 31P spin-lattice relaxation time measurements showed that the main phase transition (LC to gel I) was accompanied by the transition between the fast and slow correlation time regimes. Axially symmetric 31P NMR lineshapes were observed at pressures up to approximately 3 kbar but changed to characteristic axially asymmetric rigid lattice lineshapes at higher pressures (3.1-5.1 kbar).(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphorus-31 magnetic resonance imaging of hydroxyapatite: a model for bone imaging.

One-dimensional 31P nuclear magnetic resonance images (projections) of synthetic calcium hydroxyapatite, Ca10(OH)2(PO4)6, have been obtained for samples on the order of 0.5 to 1.0 cm in linear extent at 7.4 T magnetic field strength. Because of the solid state nature of these samples, short 31P spin-spin relaxation times under 1 ms occur, necessitating echo times of 1 ms and phase-encoding magnetic field gradient pulses shorter than 500 microseconds. Optimal projection quality and shortest acquisition times result from pulsed gradient phase-encoding of the spatial dimension, using a compensating gradient pulse to cancel the distorting effects of gradient waveform transients. The exceedingly long 31P spin-lattice relaxation times could lead to potentially intolerable image acquisition times; these have been reduced with a flipback pulse technique. In addition to holding great potential as a novel research tool in the study of biomineralization of those organisms containing calcium phosphate solid phases, these methods should be of general utility in the multinuclear imaging of a wide variety of solids of interest in biophysics and materials science.

Dynamics of the phosphate group in phospholipid bilayers. A 31P-1H transient Overhauser effect study

Two recent studies have addressed the question of the dynamics of the phosphate in egg phosphatidylcholine multilayers by measurement and interpretation of 31P NMR spin-lattice relaxation. In the first (Milburn, M. P., and K. R. Jeffrey. 1987. Biophys. J. 52:791-799), the temperature dependences of the two contributions to the 31P relaxation rate, a dipolar interaction of the phosphorus with neighboring protons and a time-dependent anisotropic chemical shielding interaction were separately measured. A further study (Milburn, M. P., and K. R. Jeffrey. 1989. Biophys. J. 56:543-549) incorporated the anisotropic nature of phospholipid motions into the dynamic model of the headgroup motion by measuring the 31P spin-lattice relaxation time in oriented samples as a function of angle between the bilayer normal and the magnetic field. These angular dependent measurements were made at high field so that analysis could by made using the chemical shielding interaction because the 31P-1H dipolar interaction in phospholipid systems is complex and as such poorly understood. Nuclear Overhauser effect (NOE) studies have attempted to identify the important proton species contributing to the 31P-1H dipolar interaction (Yeagle, P. L., W. C. Hutton, C. Huang, and R. B. Martin. 1975. Biochemistry. 15:2121-2124) and despite some controversy in interpretation (Burns, R. A., R. E. Stark, D. A. Vidusek, and M. F. Roberts. 1983. Biochemistry. 22:5084-5090), it was generally agreed that the choline methyl and methylene protons are the major contributors to the 31P-1H NOE. To further understand the nature of the 31P-1H dipolar interaction, we carried out 31P-1H Transient Overhauser effect (TOE) measurements on egg phosphatidylcholine multilayers. Protons from both the lipids and water are important in understanding the TOE measurements in both D20 dispersions and H20 dispersions of egg PC. A quantitative analysis of the TOE has enabled the cross-relaxation rate between the phosphorus and the two proton types to be determined. It is suggested that these TOE experiments are a direct observation of the interaction between the phospholipid phosphate and surrounding water protons. The correlation time describing the relative motion of the phosphate group and the water molecules is on the order of 10- 11 s. The TOE measurements in phospholipid dispersions can be easily understood in terms of a straight forward model of the dipolar interaction and provide complementary information to NOE and T1 measurements.

Dynamics of the phosphate group in phospholipid bilayers. A 31P angular dependent nuclear spin relaxation time study

To understand 31P relaxation processes and hence molecular dynamics in the phospholipid multilayer it is important to measure the dependence of the 31P spin-lattice relaxation time on as many variables as the physical system allows. Such measurements of the 31P spin-lattice relaxation rate have been reported both as a function of Larmor frequency and temperature for egg phosphatidylcholine liposomes (Milburn, M.P., and K.R. Jeffrey. 1987. Biophys. J. 52:791-799). In principle, the spin-lattice relaxation rate in an anisotropic environment such as a bilayer will be a function of the angle between the bilayer normal and the magnetic field. However, the measurement of this angular dependence has not been possible because the rapid (on the time-scale of the spin-lattice relaxation rate) diffusion of the lipid molecules over the curved surface of the liposome average this dependence (Milburn, M.P., and K.R. Jeffrey. 1987. Biophys. J. 52:791-799; Brown, M.F., and J.H. Davis. 1981. Chem. Phys. Lett. 79:431-435). This paper reports the results of the measurement of the 31P spin-lattice relaxation rate as a function of this angle, beta', (the angle between the bilayer normal and the external magnetic field) using samples oriented between glass plates. These measurements were made at high field (145.7 MHz) where the spin-lattice relaxation processes are dominated by the chemical shielding interaction (Milburn, M.P., and K.R. Jeffrey. 1987. Biophys. J. 52:791-799). A model of molecular motion that includes a fast axially symmetric rotation of the phosphate group (tau i approximately 10(-9) s) and a wobble of the head group tilt with respect to this rotation axis has been used to describe both the angular dependence of the spin-lattice relaxation and the spectral anisotropy. Cholesterol is seen to have a negligible effect on the motional properties of the phospholipid phosphate segment as measured by the orientation dependence of the spin-lattice relaxation.

A nuclear magnetic resonance study of 1H, 23Na, and 31P relaxation and molecular dynamics in the sodium salts of some pyrophosphates

Proton second moments and spin-lattice relaxation times in the laboratory and rotating frames and 31P and 23Na spin-lattice relaxation times in the laboratory frame have been measured over the temperature region 295 > T > 100 K for the sodium pyrophosphate salts, Na2P2O7∙10H2O and Na2H2P2O7. Laboratory-frame 31P and 23Na spin-lattice relaxation times have also been measured over the same temperature range for Na4P2O7. In the case of Na4P2O7∙10H2O, the results show clearly that the H2O molecules execute a twofold jump motion at higher temperatures. The potential barriers to these motions range from 30 to 40 kJ/mol. The 31P and 23Na relaxations are also influenced by these motions. The [Formula: see text] ion in Na2H2P2O7 is stationary over the temperature range studied. T1(Na) is most probably dominated by acoustical lattice vibrations. The [Formula: see text] ion in Na4P2O7 is not involved in a molecular reorientation. A shallow T1(P) minimum of 55 s is associated with a limited motion of the pyrophosphate molecule.

1H, 23Na and 31P N.M.R. in the disodium salt of glucose 1-phosphate

1H, 23Na and 31P spin-lattice relaxation times in the laboratory frame and the 1H spin-lattice relaxation time in the rotating frame have been measured as a function of temperature (295 ⩾ T ⩾ 100K) in polycrystalline Na2C6H11O9. 3·5H2O. In addition the proton second moment has also been measured over the same temperature region. The results show that the glucose 1-phosphate molecule is stationary over the entire temperature region while the water molecules execute twofold reorientations. The relaxation of the 31P nuclei is via the proton spin reservoir while the 23Na nuclei relax by means of the quadrupolar mechanism.

Spin-lattice relaxation and molecular motions in amorphous fructose 6-phosphate

1H, 23Na and 31P spin-lattice relaxation times and the 1H second moment of an amorphous sample of fructose 6-phosphate have been measured. The motional parameters of the water molecule have been extracted by employing a model in which the motions are characterized by a Gaussian distribution of correlation times.

Nuclear spin relaxation in some phenyl phosphorus compounds

13C and 31P spin-lattice relaxation times ( T1) and nuclear Overhauser effects were measured in triphenylphosphine, triphenylphosphine oxide, triphenylphosphine sulphide, and triphenylphosphine selenide, over a temperature, range −40°C to +55°C. Isotropic reorientation correlation times were calculated from the dipolar relaxation times for phosphorus and that for the para carbon. The spin-rotation mechanism is the dominant relaxation mechanism for phosphorus in triphenylphosphine, whereas the chemical shift anisotropy is the dominant mechanism in triphenylphosphine oxide at low temperatures. In triphenylphosphine sulphide and triphenylphosphine selenide, the dipolar and the chemical shift anisotropy mechanisms are important in phosphorus relaxation. The motional anisotropy of internal rotation of phenyl rings and overall tumbling is determined from the ratio of T 1's of ortho or meta carbon to para carbon, and is found to increase with the decrease in temperature and with the increase in mol. wt. The angular momentum correlation times were calculated from phosphorus spin-rotation relaxation rates. From viscosity data, reduced correlation times were calculated and compared with that calculated using Stokes-Einstein-Debye, Gierer-Wirtz, and Hu-Zwanzig models.

Association of ferri- and ferro-cytochrome c with lipid multilayers: a 31P solid-state NMR study

The 31P nuclear magnetic resonance anisotropies of dispersions of diacylphosphatidic acid and diacylphosphatidylserine were slightly increased in the presence of cytochrome c: no increase was observed with cardiolipin. However, the 31P spin-lattice relaxation times ( T 1) for all of these lipids were reduced markedly by the protein. As similar effects were observed with ferri-cytochrome c and with the reduced protein, which is diamagnetic, we suggest that the changes in T 1 reflect a reduction in the spectral density of fast motions for the lipid headgroups attendant on binding of protein, rather than paramagnetic relaxation of the phosphorus nuclear spin.

Investigation of 4f-magnetism in CeNi 2P 2, EuNi 2P 2 and YbNi 2P 2 by susceptibility and NMR studies

The results of 31P NMR Knight shift (KS) and spin-lattice relaxation time (T 1) as well as magnetic susceptibility ( ξ) measurements in the temperature interval 4.2–300K are reported for the compounds RENi 2 P 2( RE = Ce, Eu and Yb) in order to understand the nature of the 41 magnetism in these compounds. The KS results conclusively establish that all these compounds exhibit non-magnetic ground states. There is a low-temperature upturn in ξ for CeNi 2P 2 and YbNi 2P 2 presumably due to magnetic impurities. The estimated spin fluctuation temperatures (T sf) for EuNi 2P 2 above 50K agree qualitatively with those obtained earlier from Mössbauer and ξ data employing ionic interconfigurational fluctuation model, but seem to disagree at low temperatures. Implications of this result are discussed.

Gated in vivo examination of cardiac metabolites with 31P nuclear magnetic resonance.

Phosphorus-31 nuclear magnetic resonance (31P NMR) spectroscopy was used to study the temporal aspects of metabolism of canine heart in vivo. An NMR catheter coil was passed through the jugular vein of a dog into the apex of the right ventricle, and spectra were recorded at four points in the cardiac cycle by triggering from the blood pressure trace of the animal. The 31P spin-lattice relaxation times of phosphocreatine (PC) and the gamma-, alpha-, and beta-phosphates of ATP at 1.89 Tesla are 4.4, 1.8, 1.7, and 1.6 s, respectively. The ratio of PC to ATP is 2.0. No changes in PC/ATP were noted in any of the four portions of the cardiac cycle examined, and difference spectra exhibited no observable signals, in contrast to previously reported results for glucose-perfused rat hearts. On the assumption that intracellular pH and the total creatine pool were constant, the equilibrium expression for the creatine kinase reaction was used to deduce that free ADP concentrations were invariant throughout the cardiac cycle. This is in apparent disagreement with the proposed regulatory role for ADP in heart oxidative phosphorylation.