P-NMR Studies Research Articles

Characterizing the phosphorus forms extracted from soil by the Mehlich III soil test

Phosphorus (P) can limit crop production in many soils, and soil testing is used to guide fertilizer recommendations. The Mehlich III (M3) soil test is widely used in North America, followed by colorimetric analysis for P, or by inductively coupled plasma-based spectrometry (ICP) for P and cations. However, differences have been observed in M3 P concentrations measured by these methods. Using 31P nuclear magnetic resonance (P-NMR) and mass spectrometry (MS), we characterized P forms in M3 extracts. In addition to the orthophosphate that would be detected during colorimetric analysis, several organic P forms were present in M3 extracts that would be unreactive colorimetrically but measured by ICP (molybdate unreactive P, MUP). Extraction of these P forms by M3 was confirmed by P-NMR and MS in NaOH-ethylenediaminetetraacetic acid extracts of whole soils and residues after M3 extraction. The most abundant P form in M3 extracts was myo-inositol hexaphosphate (myo-IHP, phytate), a compound that may not contribute to plant-available P if tightly sorbed in soil. Concentrations of myo-IHP and other organic P forms varied among soils, and even among treatment plots on the same soil. Extraction of myo-IHP in M3 appeared to be linked to cations, with substantially more myo-IHP extracted from soils fertilized with alum-treated poultry litter than untreated litter. These results suggest that ICP analysis may substantially over-estimate plant-available P in samples with high MUP concentrations, but there is no way at present to determine MUP concentrations without analysis by both colorimetry and ICP. This study also tested procedures that will improve future soil P-NMR studies, such as treatment of acid extracts, and demonstrated that techniques such as P-NMR and MS are complimentary, each yielding additional information that analysis by a single technique may not provide.

Visualization of Electron Paramagnetic Resonance Hyperfine Structure Coupling Pathways

The close relation between the EPR hyperfine coupling constant and NMR indirect spin-spin coupling constant is well-known. For example, the Karplus-type dependence of hyperfine constants on the dihedral angle, originally proposed for NMR spin-spin coupling, is widely used in pNMR studies. In the present work we propose a new tool for visualization of hyperfine coupling pathways based on our experience with visualization of NMR indirect spin-spin couplings. The plotted 3D-function is the difference between the total electron densities when the magnetic moment of the nucleus of interest changes its sign and as such is an observable from the physical point of view. It has been shown that it is proportional to the linear response of the spin density to the nuclear spin (i.e., magnetic moment). In contrast to the widely used visualization of spin density, our new approach depicts only the part of the electron cloud of a molecule that is affected by the interaction of the unpaired electron(s) with the desired nuclear magnetic moment. Because visualization of NMR spin-spin couplings and hyperfine interaction is based on the same ideas and done using similar techniques, it allows a direct comparison of the corresponding pathways for the two phenomena so as to analyze their resemblance and/or dissimilarity.

Why do proton conducting polybenzimidazole phosphoric acid membranes perform well in high-temperature PEM fuel cells?

Transport properties and hydration behavior of phosphoric acid/(benz)imidazole mixtures are investigated by diverse NMR techniques, thermogravimetric analysis (TGA) and conductivity measurements. The monomeric systems can serve as models for phosphoric acid/poly-benzimidazole membranes which are known for their exceptional performance in high temperature PEM fuel cells. 1H- and 31P-NMR data show benzimidazole acting as a strong Brønsted base with respect to neat phosphoric acid. Since benzimidazole's nitrogens are fully protonated with a low rate for proton exchange with phosphate species, proton diffusion and conduction processes must take place within the hydrogen bond network of phosphoric acid only. The proton exchange dynamics between phosphate and benzimidazole species pass through the intermediate exchange regime (with respect to NMR line separations) with exchange times being close to typical diffusion times chosen in PFG-NMR diffusion measurements (ms regime). The resulting effects, as described by the Kärger equation, are included into the evaluation of PFG-NMR data for obtaining precise proton diffusion coefficients. The highly reduced proton diffusion coefficient within the phosphoric acid part of the model systems compared to neat phosphoric acid is suggested to be the immediate consequence of proton subtraction from phosphoric acid. This reduces hydrogen bond network frustration (imbalance of the number of proton donors and acceptors) and therefore also the rate of structural proton diffusion, phosphoric acid's acidity and hygroscopicity. Reduced water uptake, shown by TGA, goes along with reduced electroosmotic water drag which is suggested to be the reason for PBI-phosphoric acid membranes performing better in fuel cells than other phosphoric-acid-containing electrolytes with higher protonic conductivity.

In situ synchrotron radiation X-ray scattering study on the effect of a stearic sucrose ester on polymorphic behavior of a new sunflower oil variety

The effect of the stearic sucrose ester (SE) S-170 on crystallization behavior and polymorphism of two stearins obtained from a new variety of high stearic high oleic sunflower oil was studied by pulsed nuclear magnetic resonance (p-NMR), small (SAXS) and wide (WAXS) angle X-ray scattering using synchrotron light and differential scanning calorimetry (DSC). p-NMR studies showed that there is always a crystallization temperature below which SE S-170 accelerated crystallization and above which SE S-170 delayed nucleation and growth. The effect of SE S-170 strongly depended on supercooling. It was efficient as a seed for high supercooling (low crystallization temperatures) but this efficiency diminished at low supercooling (temperatures close to the melting point) when few crystals were formed. SAXS and WAXS results demonstrated that depending on crystallization temperature SE S-170 promoted crystallization of α and β forms with more polymorphic similarity and inhibited occurrence of β′ forms especially the β′2 polymorph. However, in some conditions SE S-170 favored crystallization of β′1 polymorph. DSC experiments showed that SE S-170 significantly diminished total melting enthalpies when the effect was a delay in crystallization. For other conditions no significant differences were found in melting temperatures or total melting enthalpies. When stearins were stored at 25°C, crystallization in the β2 form was promoted. Depending on crystallization temperature, polymorphic forms β′1 and β2 may be obtained as the main polymorphic forms. This is very relevant from the technological point of view. Depending on the application, SE S-170 may help obtain the required polymorphic form: β′1 form for spreads and β2 polymorph for chocolate production.

Enhancement of superconducting transition temperature due to antiferromagnetic spin fluctuations in iron pnictides LaFe(As1−xPx)(O1−yFy):31P-NMR studies

Systematic P-NMR studies on LaFe(As_{1-x}P_x)(O_{1-y}F_y) with y=0.05 and 0.1 have revealed that the antiferromagnetic spin fluctuations (AFMSFs) at low energies are markedly enhanced around x=0.6 and 0.4, respectively, and as a result, Tc exhibits respective peaks at 24 K and 27 K against the P-substitution for As. This result demonstrates that the AFMSFs are responsible for the increase in Tc for LaFe(As_{1-x}P_x)(O_{1-y}F_y) as a primary mediator of the Cooper pairing. From a systematic comparison of AFMSFs with a series of (La_{1-z}Y_z)FeAsO_{\delta} compounds in which Tc reaches 50 K for z=0.95, we remark that a moderate development of AFMSFs causes the Tc to increase up to 50 K under the condition that the local lattice parameters of FeAs tetrahedron approaches those of the regular tetrahedron. We propose that the T_c of Fe-pnictides exceeding 50 K is maximized under an intimate collaboration of the AFMSFs and other factors originating from the optimization of the local structure.

Coupling of Li motion and structural distortions in olivine LiMnPO4from7Li and31P NMR

We present a detailed $^7$Li- and $^{31}$P-NMR study on single crystalline LiMnPO$_4$ in the paramagnetic and antiferromagnetic phase (AFM, $T_N \sim$ 34 K). This allows us to determine the spin directions in the field-induced spin-flop phase. In addition, the anisotropic dipolar hyperfine coupling tensor of the $^7$Li- and $^{31}$P-nuclei is also fully determined by orientation and temperature dependent NMR experiments and compared to the calculated values from crystal structure data. Deviations of the experimental values from the theoretical ones are discussed in terms of Mn disorder which is induced by Li-disorder. In fact, the disorder in the Mn-sublattice is directly revealed by our diffuse x-ray scattering data. The present results provide experimental evidence for the Li-diffusion strongly coupling to structural distortions within the MnPO$_4$ host, which is expected to significantly affect the Li-mobility as well as the performance of batteries based on this material.

Emergent phases of nodeless and nodal superconductivity separated by antiferromagnetic order in iron-based superconductor (Ca4Al2O6)Fe2(As1−xPx)2:75As- and31P-NMR studies

We report ${}^{31}$P- and ${}^{75}$As-NMR studies on (Ca${}_{4}$Al${}_{2}$O${}_{6}$)Fe${}_{2}$(As${}_{1\ensuremath{-}x}$P${}_{x}$)${}_{2}$ with an isovalent substitution of P for As. We present the novel evolution of emergent phases that the nodeless superconductivity (SC) in $0\ensuremath{\le}x\ensuremath{\le}0.4$ and the nodal one around $x=1$ are intimately separated by the onset of a commensurate stripe-type antiferromagnetic (AFM) order in $0.5\ensuremath{\le}x\ensuremath{\le}0.95$, as an isovalent substitution of P for As decreases a pnictogen height ${h}_{Pn}$ measured from the Fe plane. It is demonstrated that the AFM order takes place under a condition of $1.32\phantom{\rule{4pt}{0ex}}\AA{}\ensuremath{\le}{h}_{Pn}\ensuremath{\le}1.42\phantom{\rule{4pt}{0ex}}\AA{}$, which is also the case for other Fe pnictides with the Fe${}^{2+}$ state in (Fe$Pn$)${}^{\ensuremath{-}}$ layers. This novel phase evolution with the variation in ${h}_{Pn}$ points to the importance of electron correlation for the emergence of SC as well as AFM order.

A fluorophosphate-based inverse Keggin structure

An unusual PFO(3)(2-)-templated "inverse Keggin" polyanion, [Mo(12)O(46)(PF)(4)](4-), has been isolated from the degradation reaction of an {Mo(132)}-type Keplerate to [PMo(12)O(40)](3-) by [Cu(MeCN)(4)](PF(6)) in acetonitrile. (31)P-NMR studies suggest a structure-directing role for [Cu(MeCN)(4)](+) in the formation of the highly unusual all-inorganic inverse Keggin structure.

Dispersion of multi walled carbon nanotubes in a hydrogen bonded liquid crystal

In a newly synthesized self assembled system, namely, hydrogen bonded liquid crystal, multi walled carbon nanotubes (MWCNTs) are dispersed. This self assembly system of liquid crystal is realized by formation of hydrogen bond between levo tartaric acid and undecyloxy benzoic acid. The proposed structure is confirmed by FTIR and P-NMR studies. Thermal and electrical properties of this system dispersed with MWCNT are studied. Alignment of carbon nanotubes in the nematic phase of the self assembled system is responsible for the observation of bistable electrical states namely ON and OFF. Optical textural observations of these two states are recorded and the light intensity complexly decays and unwinding of the helix with the application of external field indicates an optical shuttering action. It is interesting to note that a small threshold value of 3.5 V/μm is sufficient to realize an optical shutter. DSC studied reveals that the enthalpy values pertaining to liquid crystal dispersed with MWCNT is approximately two fold to that of the pure liquid crystal. Results of conductance relating to the liquid crystal with MWCNT dispersion are discussed.

Synthesis, Anti-bacterial and Anti-oxidant Properties of Thiadiazaphosphol-2-ones

4-Amino-5-phenyl-4H-1,2,4-triazole-3-thiol (1) underwent facile condensation with various phosphorus dichlorides (2a-j) in the presence of triethylamine in dry tetrahydrofuran at 60-65 degrees C and afforded corresponding thiadiazaphosphol-2-ones (3a-j). Their chemical structures were characterized using IR, (1)H-, (13)C-, (31)P-NMR and Mass spectral studies. All the title compounds were screened for antioxidant properties by radical scavenging methods such as 1,1-diphenyl-2-picryl hydrazyl (DPPH), hydroxyl and lipid peroxidation. They exhibited potent in vitro antioxidant activity dose dependently. Their bioassay showed them to possess significant antibacterial activity.

The Nuclear Receptor ERRα Is Required for the Bioenergetic and Functional Adaptation to Cardiac Pressure Overload

Downregulation and functional deactivation of the transcriptional coactivator PGC-1alpha has been implicated in heart failure pathogenesis. We hypothesized that the estrogen-related receptor alpha (ERRalpha), which recruits PGC-1alpha to metabolic target genes in heart, exerts protective effects in the context of stressors known to cause heart failure. ERRalpha(-/-) mice subjected to left ventricular (LV) pressure overload developed signatures of heart failure including chamber dilatation and reduced LV fractional shortening. (31)P-NMR studies revealed abnormal phosphocreatine depletion in ERRalpha(-/-) hearts subjected to hemodynamic stress, indicative of a defect in ATP reserve. Mitochondrial respiration studies demonstrated reduced maximal ATP synthesis rates in ERRalpha(-/-) hearts. Cardiac ERRalpha target genes involved in energy substrate oxidation, ATP synthesis, and phosphate transfer were downregulated in ERRalpha(-/-) mice at baseline or with pressure overload. These results demonstrate that the nuclear receptor ERRalpha is required for the adaptive bioenergetic response to hemodynamic stressors known to cause heart failure.

31P-NMR and µSR Studies of Filled Skutterudite Compound SmFe4P12: Evidence for Heavy Fermion Behavior with Ferromagnetic Ground State

The 31P-NMR (nuclear magnetic resonance) and muSR (muon spin relaxation) measurements on the filled skutterudite system SmFe4P12 have been carried out. The temperature T dependence of the 31P-NMR spectra indicates the existence of the crystalline electric field effect splitting of the Sm3+$ (J = 5/2) multiplet into a ground state and an excited state of about 70 K. The spin-lattice relaxation rate 1/T1 shows the typical behavior of the Kondo system, i.e., 1/T1 is nearly T independent above 30 K, and varies in proportion to T (the Korringa behavior, 1/T1 \propto T) between 7.5 K and 30 K. The T dependence deviated from the Korringa behavior below 7 K, which is independent of T in the applied magnetic field of 1 kOe, and suppressed strongly in higher fields. The behavior is explained as 1/T1is determined by ferromagnetic fluctuations of the uncovered Sm3+ magnetic moments by conduction electrons. The muSR measurements in zero field show the appearance of a static internal field associated with the ferromagnetic order below 1.6 K.

Non-Fermi Liquid-Like Behavior in a Heavy Lanthanide Compound YbFe4P12 with Filled Skutterudite Structure Probed by 31P-NMR

We have carried out 31 P-NMR study on a new intermediate-valence compound YbFe 4 P 12 with a filled skutterudite structure which has heavy fermion-like properties below ∼10 K. The Knight shift has a very small value less than 0.05%, and the linewidth exhibits a monotonic increase without exhibiting any singular behavior down to 0.5 K. The nuclear spin–lattice relaxation rate 1/ T 1 T below ∼50 K strongly depends on both the temperature T and applied magnetic field H and follows the power-law relation 1/ T 1 T = A T -α over one decade. The power α∼0.1 at 7.0 T increases with decreasing H and takes the maximum value of ≃0.7 at 0.2 T, which is close to the value 3/4 expected for the non-Fermi liquid (NFL) state associated with antiferromagnetic spin fluctuations. We suggest that YbFe 4 P 12 is an interesting material in which the NFL-like behavior occurs below a rather high temperature of ∼10 K, and a magnetic field of about 0.2 T is sufficient to bring it to its quantum critical point.

Evidence for s-Wave Superconductivity with Antiferromagnetic Fluctuations in Filled Skutterudite LaFe4P12: 139La and 31P-NMR Studies

We have performed 139 La, 31 P-NMR studies on a filled skutterudite superconductor LaFe 4 P 12 with the critical temperature T c =4.1 K. In the normal state, the presence of antiferromagnetic (AFM) fluctuations at finite wave vectors is suggested from the relation between the nuclear spin-lattice relaxation rate 1/ T 1 and the Knight shift. In the superconducting (SC) state, the distinct coherence peak is observed just below T c , and is easily suppressed by applied fields. An exponential decrease of 1/ T 1 is observed, suggestive of the isotropic SC gap with 2Δ/( k B T c )=3.8. Besides, we observed the decrease of the Knight shift, indicative of the singlet-pair formation below T c . These results are clear evidence that LaFe 4 P 12 is a rare s -wave superconductor with significant AFM fluctuations.

The nature and origins of diester phosphates in soils: a 31 P-NMR study

Soils of two climosequences in Russia were investigated by 31 P-NMR spectroscopy. They comprised Dystric Podzoluvisols, Haplic Greyzems, Calcic Cher- nozems, and Gypsic Kastanozems, which are located along temperature and precipitation gradients of the Russian Plain. Another sequence of soils included forest Humic Cambisols and Umbric Leptosols of subalpine and alpine meadows, which are formed in different climatic conditions along a climosequence of the Mt. Malaya Khatipara (northern Caucasus). The results showed that accumulation of DNA was high in the cold, wet, and acid soils (Dystric Podzoluvisol, alpine Umbric Leptosol), while phospholipids and teichoic acids mainly accumulated in the more microbially active soils. We performed a laboratory incubation experiment to test the relationship between microbial biomass P and P species identified in soil extracts. The proportions of P com- pounds resonating at 0.5-3.0 ppm in the NaHCO 3 and H2SO4 extracts from the incubated Humic Cambisol in- creased. The amounts of phosphate diesters resonating at 0 ppm in the same extracts and in the subsequent NaOH extracts decreased after incubation. Based on the results of 31P-NMR spectroscopy of native soils and of the labo- ratory incubation experiment we concluded that signals at 0 ppm in spectra of soil alkaline extracts belong to DNA P which is mainly stabilised in soil organic matter outside microbial cells (at least in soils with relatively low microbial activity). Phospholipids-teichoic acids P extracted with 0.5 M NaHCO 3 seems to be derived from soil microbial biomass, and its proportion can reflect the microbial activity in the soil.

Effects of monovalent cations on phosphate accumulation and storage of the ectomycorrhizal fungus Suillus bovinus.

Comparative in vivo (31)P-NMR studies of the fungus Suillus bovinus (L.: Fr.) O. Kuntze in pure culture have produced interesting new data. To investigate the response of phosphate metabolism to a change in external monovalent cations, samples were exposed to a Hoagland solution containing different monovalent cations Li+, Na+, K+, or Rb+ at 10 mM concentration. A method of nutrient cycling during analysis where the cation was changed and the phosphate kept constant allowed us to determine the kinetics of phosphate accumulation, storage and incorporation into polyphosphate following exposure to the range of test cations. Different external monovalent cations had different effects upon changes in the content of both phosphate and polyphosphate. Treatment with Li+, Na+, or Rb+ resulted in a change in phosphate accumulation to 60, 73, and 107% and in content of the intracellular mobile polyphosphate (polyP) to 119, 112, and 94%, respectively, compared with the control taken as 100%. The effect of each cation is related to its position in the periodic table. Reversing this process, i.e., exchanging with K+, returned phosphate metabolism to normal. Although, the increase in depolarization of the cell membrane should affect the internal pH, fungal metabolism using energy requiring mechanisms appeared necessary to maintain the intracellular pH. Thus, increasing contents of mobile polyP were the consequence of an increasing energy demand. On the other hand, the increasing depolarization of the cell membrane following the sequence Rb+ < K+ < Na+ < Li+ inhibited the net P(i) accumulation. Furthermore, it is postulated that the Pi accumulation was also regulated by the intracellular content in polyP.

Critical oxygen tension in rat brain: a combined (31)P-NMR and EPR oximetry study.

The relationship between cerebral interstitial oxygen tension (Pt(O(2))) and cellular energetics was investigated in mechanically ventilated, anesthetized rats during progressive acute hypoxia to determine whether there is a "critical" brain Pt(O(2)) for maintaining steady-state aerobic metabolism. Cerebral Pt(O(2)), measured by electron paramagnetic resonance oximetry, decreased proportionately to inspired oxygen fraction. (31)P-nuclear magnetic resonance measurements revealed no changes in P(i), phosphocreatine (PCr)/P(i) ratio, or intracellular pH when arterial blood oxygen tension (Pa(O(2))) was reduced from 145.1 +/- 11.7 to 56.5 +/- 4.4 mmHg (means +/- SE). Intracellular acidosis, a sharp rise in P(i), and a decline in the PCr/P(i) ratio developed when Pa(O(2)) was reduced further to 40.7 +/- 2.3 mmHg. The corresponding Pt(O(2)) values were 15.1 +/- 1.8, 8.8 +/- 0.4, and 6.8 +/- 0.3 mmHg. We conclude that over a range of decreasing oxygen tensions, cerebral oxidative metabolism is not sensitive to oxygen concentration. Oxygen becomes a regulatory substrate, however, when Pt(O(2)) is decreased to a critical level.

Phosphorylation state of red and white muscle in tilapia during graded hypoxia: an in vivo (31)P-NMR study.

The aim of this study was to measure the energetic consequences of hypoxia in different types of skeletal muscle within a single tilapia species (n = 5). To that aim, 81.0 MHz (31)P-nuclear magnetic resonance (NMR) spectra were collected, alternately, from three surface coils placed adjacent to the tissues of interest (dorsal white muscle, ventral white muscle, and lateral red muscle) during a graded hypoxia load over 6 h followed by a 5-h recovery period. The fish were contained in a flow cell, enabling us full control of the oxygen content of the bathing medium. The intracellular pH and the concentrations of ATP, phosphocreatine (PCr), and P(i) were determined from the NMR spectra. For normoxia, biochemical differences for [gamma-ATP], [PCr], and [sugar phosphates] (SP) were observed between all three locations, especially between the red and white muscle. During hypoxia stress, loss of phosphorylated compounds (PCr+P(i)+SP) was observed at all locations but was the most severe in red muscle. When the aerobic (respirometry) and anaerobic ((31)P-NMR) ATP production via an energy balance are compared, flexible metabolic depression is demonstrated during anaerobioses. It is concluded that control of the aerobic and anaerobic component of metabolism during metabolic depression is independent of each other.

Synthesis and characterization studies of homopolymers ofN-vinylpyrrolidone, vinyl acetate, and their copolymers

Homopolymers of N-vinylpyrrolidone (VP) and vinyl acetate (VAc) were synthesized by a free-radical solution polymerization technique. Copolymers of VP and VAc in various monomer feed ratios were also synthesized by the same procedure. They were characterized by elemental analysis, FTIR, PNMR, TGA, swelling, and viscosity measurements. The reactivity ratios of the monomers were computed by both Fineman-Ross and Kelen-Tudos methods using data from both PNMR and elemental analysis studies. The activation energy values for various stages of decomposition were calculated from TGA analysis using Broido's method. The viscosity measurements were carried out at four different temperatures: 30, 35, 40, and 45°C. The activation parameters of the viscous flow, voluminosity (V E ), and shape factor (v) were also computed for all systems.

A31P-NMR Study of the Uptake and Compartmentation of Manganese by Maize Roots

The uptake and compartmentation of manganese by maize roots, from solutions containing between 1 /?M and 1 mM Mn2+, was monitored in vivo by 31P nuclear magnetic resonance (NMR) spectroscopy. Qualitatively, NMR provided a convenient method for observing the effects of pH, anoxia, metabolic inhibitors, and competition with magnesium on the uptake of manganese and the results highlighted the role of the vacuole as a sink for Mn2+. Quantitatively, it was established that root tissues could maintain a low concentration of free Mn2+ in the cytoplasm during manganese uptake and that there is a non-equilibrium distribution of Mn2+ between the cytoplasm and the vacuole. Typically exposure to Mn2+ in the range 10-100 iJ.M resulted in a submicromolar pool of Mn2+ in the cytoplasm and a vacuolar pool of 10 and it was concluded that the movement of Mn2+ out of the cytoplasm must be energy consuming. Overall the results draw attention to the similarity between the subcellular distribution of manganese and calcium and provide some support for the suggestion that manganese, like calcium, might have a control function in normal cells.