31P T1 Research Articles

Spin diffusion in the Phosphorus-31 NMR relaxation in a layered crystalline α-Sn(IV) phosphate contaminated by paramagnetic impurities

The study of a layered crystalline Sn(IV) phosphate by solid-state NMR has demonstrated that the 31P T1 relaxation of phosphate groups, dependent on spinning rate is completely controlled by the limited spin diffusion to paramagnetic ions found by EPR. The spin-diffusion constant, D(SD), was estimated as 2.04 10−14 cm2s−1. The conclusion was supported by the 31P T1 time measurements in zirconium phosphate 1–1, also showing paramagnetic ions and in diamagnetic compound (NH4)2HPO4.

Paramagnetic Relaxation Agents for Enhancing Temporal Resolution and Sensitivity in Multinuclear FlowNMR Spectroscopy.

Sensitivity in FlowNMR spectroscopy for reaction monitoring often suffers from low levels of pre-magnetisation due to limited residence times of the sample in the magnetic field. While this in-flow effect is tolerable for high sensitivity nuclei such as 1 H and 19 F, it significantly reduces the signal-to-noise ratio in 31 P and 13 C spectra, making FlowNMR impractical for low sensititvity nuclei at low concentrations. Paramagnetic relaxation agents (PRAs), which enhance polarisation and spin-lattice relaxation, could eliminate the adverse in-flow effect and improve the signal-to-noise ratio. Herein, [Co(acac)3 ], [Mn(acac)3 ], [Fe(acac)3 ], [Cr(acac)3 ], [Ni(acac)2 ]3, [Gd(tmhd)3 ] and [Cr(tmhd)3 ] are investigated for their effectiveness in improving signal intensity per unit time in FlowNMR applications under the additional constraint of chemical inertness towards catalytically active transition metal complexes. High-spin Cr(III) acetylacetonates emerged as the most effective compounds, successfully reducing 31 P T1 values four- to five-fold at PRA concentrations as low as 10 mM without causing adverse line broadening. Whereas [Cr(acac)3 ] showed signs of chemical reactivity with a mixture of triphenylphosphine, triphenylphosphine oxide and triphenylphosphate over the course of several hours at 80° C, the bulkier [Cr(tmhd)3 ] was stable and equally effective as a PRA under these conditions. Compatibility with a range of representative transition metal complexes often used in homogeneous catalysis has been investigated, and application of [Cr(tmhd)3 ] in significantly improving 1 H and 31 P{1 H} FlowNMR data quality in a Rh-catalysed hydroformylation reaction has been demonstrated. With the PRA added, 13 C relaxation times were reduced more than six-fold, allowing quantitative reaction monitoring of substrate consumption and product formation by 13 C{1 H} FlowNMR spectroscopy at natural abundance.

Phosphorus-Containing Polymers as Sensitive Biocompatible Probes for 31P Magnetic Resonance

The visualization of organs and tissues using 31P magnetic resonance (MR) imaging represents an immense challenge. This is largely due to the lack of sensitive biocompatible probes required to deliver a high-intensity MR signal that can be distinguished from the natural biological background. Synthetic water-soluble phosphorus-containing polymers appear to be suitable materials for this purpose due to their adjustable chain architecture, low toxicity, and favorable pharmacokinetics. In this work, we carried out a controlled synthesis, and compared the MR properties, of several probes consisting of highly hydrophilic phosphopolymers differing in composition, structure, and molecular weight. Based on our phantom experiments, all probes with a molecular weight of ~3-400 kg·mol-1, including linear polymers based on poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), poly(ethyl ethylenephosphate) (PEEP), and poly[bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)]phosphazene (PMEEEP) as well as star-shaped copolymers composed of PMPC arms grafted onto poly(amidoamine) dendrimer (PAMAM-g-PMPC) or cyclotriphosphazene-derived cores (CTP-g-PMPC), were readily detected using a 4.7 T MR scanner. The highest signal-to-noise ratio was achieved by the linear polymers PMPC (210) and PMEEEP (62) followed by the star polymers CTP-g-PMPC (56) and PAMAM-g-PMPC (44). The 31P T1 and T2 relaxation times for these phosphopolymers were also favorable, ranging between 1078 and 2368 and 30 and 171 ms, respectively. We contend that select phosphopolymers are suitable for use as sensitive 31P MR probes for biomedical applications.

Motions of Trimethylphosphine Oxide in Carbon Nanotubes as Revealed by Solid‐state NMR

Trimethylphosphine (TMP) has been adsorbed in carbon nanotubes and oxidized to trimethylphosphine oxide (TMPO). 31P spin–lattice relaxation T1 measurements at temperatures from 203 to 333 K have been employed to investigate the motions of TMPO. The 31P T1 is found to be monoexponential and isotropic. The activation energy is measured as 4.4 ± 0.3 kcal•mol−1, which is comparable to that of TMP adsorbed on Lewis acid sites in zeolites.

31P Solid-State NMR Relaxation in the Zirconium Phosphate Network in the Presence of Paramagnetic Centers: A Detailed Relaxation Study in Static and Rotating Samples of Layered Zirconium Phosphate Materials

The careful study of MAS effects on the spin–lattice and spin–spin phosphorus NMR relaxation in two layered zirconium phosphate materials, α-ZrP and m-PEG-PO3/Zr(IV)/DOX/ZrP, has clearly shown that the fast spin-diffusion and limited spin-diffusion mechanisms are completely negligible in spite of the presence of paramagnetic centers detected in these materials by EPR. The 31P T1 relaxation is always nonexponential in static and spinning samples as well. The 31P T1 relaxation in α-ZrP follows a stretched exponential law to show the presence of a 31P T1 distribution. The 31P T1 time remarkably depends on spinning rates only in a 7 mm NMR probe head due to the frictional heating effects in 7 mm rotors but not due to the spin-diffusion mechanism. In accord, the 31P T1 and T2 times are independent of MAS rates in the experiments performed with 2.5 mm rotors. All the 31P T1 and T2 relaxation data support well the interpretation of the 31P T1 times in the zirconium phosphate network by dipolar proton–phosphorus interactions and justify the application of the 31P T1 and 31P T1/T2 approaches to probing molecular mobility in zirconium phosphate materials.

Probing the interaction of the potassium channel modulating KCNE1 in lipid bilayers via solid-state NMR spectroscopy.

KCNE1 is known to modulate the voltage-gated potassium channel α subunit KCNQ1 to generate slowly activating potassium currents. This potassium channel is essential for the cardiac action potential that mediates a heartbeat as well as the potassium ion homeostasis in the inner ear. Therefore, it is important to know the structure and dynamics of KCNE1 to better understand its modulatory role. Previously, the Sanders group solved the three-dimensional structure of KCNE1 in LMPG micelles, which yielded a better understanding of this KCNQ1/KCNE1 channel activity. However, research in the Lorigan group showed different structural properties of KCNE1 when incorporated into POPC/POPG lipid bilayers as opposed to LMPG micelles. It is hence necessary to study the structure of KCNE1 in a more native-like environment such as multi-lamellar vesicles. In this study, the dynamics of lipid bilayers upon incorporation of the membrane protein KCNE1 were investigated using 31 P solid-state nuclear magnetic resonance (NMR) spectroscopy. Specifically, the protein/lipid interaction was studied at varying molar ratios of protein to lipid content. The static 31 P NMR and T1 relaxation time were investigated. The 31 P NMR powder spectra indicated significant perturbations of KCNE1 on the phospholipid headgroups of multi-lamellar vesicles as shown from the changes in the 31 P spectral line shape and the chemical shift anisotropy line width. 31 P T1 relaxation times were shown to be reversely proportional to the molar ratios of KCNE1 incorporated. The 31 P NMR data clearly indicate that KCNE1 interacts with the membrane. Copyright © 2017 John Wiley & Sons, Ltd.

31P, 1H NMR Relaxation and Molecular Mobility in Layered α-Zirconium Phosphate: Variable-Temperature NMR Experiments

Internal rotations in HPO4– groups and proton transfer between them have been characterized in static α-zirconium phosphate by variable-temperature measurements of 31P T1 and 1H T1ρ times. The 1H T1ρ times have been obtained by the kinetic of phosphorus–proton cross-polarization treated with the I-I*-S model. The calculations of the temperature T1 relaxation dependences have resulted in the rotational activation energy of 2.6 kcal/mol (or 3.9 kcal/mol in account for the τC distribution) and the proton transfer activation energy of 5.5 kcal/mol. Thus, two types of motions have been found in α-zirconium phosphate: the low-frequency proton transfer with the correlation time τc of 1.5 × 10–5 s at 295 K and the high-frequency rotation in P–OH groups with the correlation time τc of 2.2 × 10–8 s at 295 K.

Membrane interactions in small fast-tumbling bicelles as studied by 31P NMR

Small fast-tumbling bicelles are ideal for studies of membrane interactions at molecular level; they allow analysis of lipid properties using solution-state NMR. In the present study we used 31P NMR relaxation to obtain detailed information on lipid head-group dynamics. We explored the effect of two topologically different membrane-interacting peptides on bicelles containing either dimyristoylphosphocholine (DMPC), or a mixture of DMPC and dimyristoylphosphoglycerol (DMPG), and dihexanoylphosphocholine (DHPC). KALP21 is a model transmembrane peptide, designed to span a DMPC bilayer and dynorphin B is a membrane surface active neuropeptide. KALP21 causes significant increase in bicelle size, as evidenced by both dynamic light scattering and 31P T2 relaxation measurements. The effect of dynorphin B on bicelle size is more modest, although significant effects on T2 relaxation are observed at higher temperatures. A comparison of 31P T1 values for the lipids with and without the peptides showed that dynorphin B has a greater effect on lipid head-group dynamics than KALP21, especially at elevated temperatures. From the field-dependence of T1 relaxation data, a correlation time describing the overall lipid motion was derived. Results indicate that the positively charged dynorphin B decreases the mobility of the lipid molecules – in particular for the negatively charged DMPG – while KALP21 has a more modest influence. Our results demonstrate that while a transmembrane peptide has severe effects on overall bilayer properties, the surface bound peptide has a more dramatic effect in reducing lipid head-group mobility. These observations may be of general importance for understanding peptide–membrane interactions.

Reversible Assembly of β-Sheet Nanocrystals within Caddisfly Silk

Nuclear magnetic resonance (NMR) and X-ray diffraction (XRD) experiments reveal the structural importance of divalent cation-phosphate complexes in the formation of β-sheet nanocrystals from phosphorylated serine-rich regions within aquatic silk from caddisfly larvae of the species Hesperophyla consimilis. Wide angle XRD data on native caddisfly silk show that the silk contains a significant crystalline component with a repetitive orthorhombic unit cell aligned along the fiber axis with dimensions of 5.9 Å × 23.2 Å × 17.3 Å. These nanocrystalline domains depend on multivalent cations, which can be removed through chelation with ethylenediaminetetraacetic acid (EDTA). A comparison of wide angle X-ray diffraction data before and after EDTA treatment reveals that the integrated peak area of reflections corresponding to the nanocrystalline regions decreases by 15-25% while that of the amorphous background reflections increases by 20%, indicating a partial loss of crystallinity. (31)P solid-state NMR data on native caddisfly silk also show that the phosphorylated serine-rich motifs transform from a rigid environment to one that is highly mobile and water-solvated after treatment with EDTA. The removal of divalent cations through exchange and chelation has therefore caused a collapse of the β-sheet structure. However, NMR results show that the rigid phosphorus environment is mostly recovered after the silk is re-treated with calcium. The (31)P spin-lattice (T1) relaxation times were measured at 7.6 ± 3.1 and 1 ± 0.5 s for this calcium-recovered sample and the native silk sample, respectively. The shorter (31)P T1 relaxation times measured for the native silk sample are attributed to the presence of paramagnetic iron that is stripped away during EDTA chelation treatment and replaced with diamagnetic calcium.

Solid-state NMR investigations of peptide–lipid interactions of the transmembrane domain of a plant-derived protein, Hcf106

The chloroplast twin arginine translocation system transports highly folded precursor proteins across the thylakoid using the protonmotive force as its only energy source. Hcf106 and another thylakoid protein, cpTatC compose the precursor receptor complex. Hcf106 is predicted to contain a single amino terminal transmembrane domain (TMD) followed by a Pro–Gly hinge, an amphipathic α-helix, and a loosely structured carboxyl terminus. Hcf106 has been shown biochemically to insert spontaneously into thylakoid membranes; however, how this occurs is not understood. To investigate how Hcf106 inserts itself into the membrane unassisted, solid-state NMR spectroscopy was used to investigate the membrane activity of the TMD. A synthetic peptide of the Hcf106 TMD was incorporated into multilamellar vesicles made of 100% 1-palmitoyl-2-oleoyl-sn-glycero-phosphocholine (POPC) or 85%:15% ratio with monogalactosyl diacylglycerol (POPC/MGDG) to probe peptide–lipid interaction. Solid-state 31P NMR and 2H NMR spectroscopic techniques were used to reveal peptide perturbations of the phospholipid membranes. Changes in spectral lineshape, chemical shift anisotropy width, 31P T1 relaxation time and SCD order parameters demonstrated that the Hcf106 TMD peptide interacted with the phospholipids. Furthermore, the comparison between POPC and POPC/MGDG multilamellar vesicles indicated that lipid bilayer composition affected the peptide–lipid interaction with the peptide interacting preferentially with vesicles that more closely mimic the thylakoid.

Probing the interaction of Arg9Cys mutated phospholamban with phospholipid bilayers by solid-state NMR spectroscopy

Phospholamban (PLB) is a 52 amino acid integral membrane protein that interacts with the sarcoplasmic reticulum Ca2+ ATPase (SERCA) and helps to regulate Ca2+ flow. PLB inhibits SERCA impairing Ca2+ translocation. The inhibition can be relieved upon phosphorylation of PLB. The Arg9 to Cys (R9C) mutation is a loss of function mutation with reduced inhibitory potency. The effect R9C PLB has on the membrane surface and the hydrophobic region dynamics was investigated by 31P and 2H solid-state NMR spectroscopy in multilamellar vesicles (MLVs). The 31P NMR spectra indicate that, like the phosphorylated PLB (P-PLB), the mutated R9C-PLB protein has significantly less interaction with the lipid bilayer headgroup when compared to wild-type PLB (WT-PLB). Similar to P-PLB, R9C-PLB slightly decreases 31P T1 values in the lipid headgroup region. 2H SCD order parameters of 2H nuclei along the lipid acyl chain decrease less dramatically for R9C-PLB and P-PLB when compared to WT-PLB. The results suggest that R9C-PLB interacts less with the membrane surface and hydrophobic region than WT-PLB. Detachment of the cytoplasmic domain of R9C-PLB from the membrane surface could be related to its loss of function.

Interactions of lipopolysaccharide with lipid membranes, raft models — A solid state NMR study

Lipopolysaccharide (LPS) is a major component of the external leaflet of bacterial outer membranes, key pro-inflammatory factor and an important mediator of host–pathogen interactions. In host cells it activates the complement along with a pro-inflammatory response via a TLR4-mediated signalling cascade and shows preference for cholesterol-containing membranes. Here, we use solid state 13C and 31P MAS NMR to investigate the interactions of LPS from three bacterial species, Brucella melitensis, Klebsiella pneumoniae and Escherichia coli, with mixed lipid membranes, raft models. All endotoxin types are found to be pyrophosphorylated and Klebsiellar LPS is phosphonylated, as well. Carbon-13 MAS NMR indicates an increase in lipid order in the presence of LPS. Longitudinal 31P relaxation, providing a direct probe of LPS molecular and segmental mobility, reveals a significant reduction in 31P T1 times and lower molecular mobility in the presence of ternary lipid mixtures. Along with the ordering effect on membrane lipid, this suggests a preferential partitioning of LPS into ordered bilayer sphingomyelin/cholesterol-rich domains. We hypothesise that this is an important evolutionary drive for the selection of GPI-anchored raft-associated LPS-binding proteins as a first line of response to membrane-associated LPS.

A solid-state NMR study of the interaction of fish antifreeze proteins with phospholipid membranes

Fish antifreeze proteins and glycoproteins (AF(G)Ps) prevent ice crystal growth and are able to protect mammalian cells and tissues from hypothermic damage in the sub-zero Polar oceans. This protective mechanism is not fully understood, and further data is required to explain how AF(G)Ps are able to stabilize lipid membranes as they pass through their phase transition temperatures. Solid-state NMR spectroscopy was used as a direct method to study the interaction of the 37-residue alpha-helical type I AFP, TTTT, and the low molecular weight fraction glycoprotein, AFGP8, with dimyristoylphosphatidylcholine membranes above and below the gel-fluid phase transition temperature. In contrast to previous studies in fluid phase bilayers these experiments have provided direct information regarding both the mobility of the phosphate headgroups and perturbation of the acyl chains at a range of temperatures under identical conditions on the same sample. At 5 degrees C changes in the 2H and 31P spectra and a dramatic increase in the 31P T1 relaxation times were consistent with a significant disruption of the membrane by TTTT. Heating to 30 degrees C appeared to expel the peptide from the lipid and re-cooling showed that the interaction of TTTT was not reversible. By contrast, 31P spectra of the membranes with AFGP8 were consistent with interaction with the phosphate headgroups at both 5 and 30 degrees C. Although both peptides interact with the phospholipid bilayer surface, which may stabilize the membrane at lower temperatures, the longer 31P T1 values and the 2H NMR data obtained for TTTT compared with AFGP8 suggest that TTTT causes a greater reduction of phosphate headgroup mobility and has a greater effect on the lipid acyl chains at 5 degrees C.

Syntheses and Characterization of Upper Rim 1,2- and 1,3-Diphosphinated Calix[4]arenes and Their Corresponding 1,5-Cyclooctadienylrhodium(I) Complexes: Comparison of the Catalytic Hydroformylation Properties of Terminal Alkenes

The 5,11- (1,2-isomer) and 5,17-bis(dialkylphosphino)-25,26,27,28-tetra-n-propoxycalix[4]arene (1,3-isomer) ligands (alkyl = Me, i-Pr) have been prepared and coordinated to Rh(COD)+ fragments (COD = 1,5-cyclooctadiene). The ligands 5,17-bis(diphenylphosphino)-11,23-dibromo-25,26,27,28-tetra-n-propoxycalix[4]arene and 5,11-bis(diphenylphosphino)-25,26,27,28-tetra-n-propoxycalix[4]arene have been coordinated to M(COD)+ (M = Rh, Ir) and RhCl(CO) fragments, as well. On the basis of mass spectrometry and 31P NMR spin−lattice relaxation time measurements (T1), all of the complexes are found to be dimers. Molecular modeling provides evidence that ring stress favors the dimer over the monomer, and the modeled structures for both 1,2- and 1,3-isomers have been corroborated by the comparison of the photophysics of the Ir(COD)+ species at 77 K. The decrease in emission lifetimes of the P2Ir(CC)2+ lumophore in the presence of 1-hexene is more pronounced for the 1,3-isomer, indicating reduced steric hindrance about the metallic center. The catalytic hydroformylation of five terminal alkenes using all six Rh(COD)+ catalyst precursors has been investigated under various conditions in order to extract the turnover frequencies (tof as defined as the number of moles of products divided by the total number of moles of rhodium used per hour) and the ratios of the product distribution (n/i, normal vs internal). The comparison of the data suggests that the basicity and the cone angle of the phosphines influence the n/i ratios. The tof's are generally larger for the 1,2-series for 1-hexene, but depend on the nature of the phosphine for styrene, vinyl acetate, vinyl benzoate, and vinyl p-tert-butylbenzoate. All in all, these complexes are good catalysts with respect to literature data, notably those containing the (i-Pr2P)− groups. During the course of this study, one hydride carbonyl complex has been synthesized and characterized from 1H and 31P NMR, IR, and T1 measurements.

Rhenium-(III) and -(V) hydride complexes with modified poly(pyrazolyl)borates

The hydrides [ReH2{κ3-(OR)(µ-OR)B(pz)2}(PPh3)2] (R = Me 1 or Et 2) and [ReH4{κ3-(H)(µ-OR)B(3,5-Me2pz)2}(PPh3)] (R = Me 3 or Et 4) have been obtained by treating [ReOCl3(PPh3)2] with Na[H2B(pz)2] or Na[H2B(3,5-Me2pz)2] in alcohols (ROH, R = Me or Et) at room temperature. The same type of reaction with Na[Ph2B(pz)2], using methanol as solvent, gave [ReO(OMe){κ2-Ph2B(OMe)(pz)}2] 5, although in a very low yield. The characterization of the new compounds involved IR and 1H NMR spectroscopies, 31P-{1H} NMR, variable temperature 1H and 31P NMR studies, T1 and JH-D measurements. The crystal structures of the complexes 1, 4 and 5 were also determined. The structural parameters of the hydride ligands in 1 and 4 have not been obtained, but were tentatively assigned by X-ray diffraction associated with molecular orbital calculations of ab initio and extended Huckel type.

Synthesis, Characterization, and Reactivity of Cationic Molecular Hydrogen Complexes of Manganese(I)

Hydride complexes MnH(CO)3P2 (1), MnH(CO)2P3 (2), and MnH(CO)P4 (3) (P = P(OEt)3 (a), PPh(OEt)2 (b), PPh2OEt (c), PPh(OiPr)2 (d) were prepared by allowing the MnH(CO)5 species to react with an excess of phosphine upon UV irradiation or under reflux conditions. Their formulation and geometry in solution were established by IR and 1H, 13C, and 31P NMR spectroscopy. Protonation reactions with HBF4·Et2O of the monocarbonyls MnH(CO)P4 (3) afford isolable dihydrogen derivatives [Mn(η2-H2)(CO)P4]BPh4 (5), which were characterized by variable-temperature 1H and 31P NMR spectra, T1 measurements, and JHD values. Thermally unstable (above 0 °C) [Mn(η2-H2)(CO)2P3]+ (4) cations were also prepared by protonation of the dicarbonyl hydrides MnH(CO)2P3 (2) and fully characterized in solution. Evolution of H2 from 4 and 5 results in the formation of the unsaturated complexes [Mn(CO)2P3]BPh4 (6) and [Mn(CO)P4]BPh4 (7), which are probably stabilized by an agostic interaction between the metal center and a C−H proton of the p...

HeteroTOCSY-based experiments for measuring heteronuclear relaxation in nucleic acids and proteins

While both 31P and 113Cd are present at locations of interest in many different macromolecular systems, heteronuclear-detected relaxation measurements on these nuclei have been restrained by limitations in either resolution or signal-to-noise ratio. We have developed heteroTOCSY-based methods to overcome both of these problems. Two-dimensional versions of these experiments were utilized to measure 31P T1 and T2 values in DNA oligonucleotides; the additional resolution offered by a second dimension allowed determination of these values for most of the 31P resonances in a DNA dodecamer. The results from the experiments indicated that there was little significant variation in T1 values for the different phosphates in the DNA dodecamer; however, the T2 values showed a clear pattern, with lower values in the interior of the sequence than at the ends of the helix. Furthermore, a significant correlation between 31P chemical shifts and T2 values was observed. One-dimensional, frequency-selective versions of these experiments were also developed for use on systems containing a smaller number of heteronuclear spins. These methods were applied to investigate the heteronuclear relaxation properties of 113Cd in 113Cd2LAC9(61), a Cys6Zn2 DNA-binding domain. Data from the experiments confirm biochemical evidence that more significant differences occur in the metal-protein interactions between the two metal-binding sites than has been previously identified for proteins containing this motif.

Optimum flip-angles for exciting NMR with uncertain T1 values.

T1 is often ill-determined. This means that an Ernst angle excitation often cannot be precisely defined for the simple pulse and acquire experiment. Here, published 31P T1 values of metabolites in human muscle, liver, heart, and brain are archived, some new data on heart and brain added, and overall confidence intervals determined. Strategies for setting the flip-angle based on the confidence intervals are examined, and an optimum flip-angle derived which minimizes the signal loss relative to what could have been realized if T1 were precisely known. With such optimized pulses, signal loss can be limited to < or = 14% for up to a 10-fold variation in T1, with TR < or = T1. The effect that an uncertainty in T1 by a factor of two has on the saturation corrected signal is limited to < or = 20% in the optimum flip-angle experiment. Adiabatic B1-independent rotation phase-cycled (BIRP) excitation pulses are ideal as optimum flip-angle pulses as they can be prescribed without calibration.

31P NMR relaxation does not affect the quantitation of changes in phosphocreatine, inorganic phosphate, and ATP measured in vivo during complete ischemia in swine brain.

Ischemia-induced changes in 31P NMR relaxation were examined in 16 piglets. NMR spectra were acquired under control conditions and during complete cerebral ischemia induced via cardiac arrest. Changes in T1 were assessed directly in six animals during control conditions and after 30-45 min of complete ischemia when changes in brain Pi levels had reached a plateau. The T1 for Pi did not change, i.e., 2.3 +/- 0.5 s during control conditions versus 2.4 +/- 1.0 s during ischemia. To evaluate phosphocreatine and ATP, two types of spectra, with a long (25-s) or short (1-s) interpulse delay time, were collected during the first 10 min of ischemia (n = 10). Both types of spectra showed the same time course of changes in phosphocreatine and ATP levels, implying that the T1 relaxation times do not change during ischemia. There were no changes in the linewidths of phosphocreatine, ATP, or Pi during ischemia, implying that the T2* values remain constant. Our results suggest that the 31P T1 and T2* for phosphocreatine, Pi, and ATP do not change during ischemia, and therefore changes in 31P NMR peak intensity accurately reflect changes in metabolite concentrations.

Phosphorus‐31 NMR studies of polymer‐supported highly reactive copper reagents

AbstractThe chemistry of highly reactive zerovalent copper species represents an active area of research. Recently, active metal chemistry has been successfully accomplished using polymer‐supported triphenylphosphine–copper(I) coordination complexes as precursors. Since the materials are solids, detailed examination of the reagents at vaious stages of chemical reaction can be problematic, since the primary means of examination has historically been proton, 13C and 31P NMR methods. In this study, cross‐polarization magic angle spinning (CPMAS) experiments, combined with 31P T1 relaxation measurements (via proton cross‐polarization), provided data which allowed the determination of the role of the phosphine species in the overall chemistry of these materials. Although it is known that the type of phosphine affects the chemistry, it was found here that there is no observable interaction between the reduced copper species and the polymer‐supported triphenylphosphine.