31P Nuclear Magnetic Resonance Spectroscopy Research Articles

Reactive phosphorus via simulated lightning discharge: A role for fulgurites in pre-biotic chemistry

Apatite is the most common phosphorus-bearing mineral in primary igneous rocks. Despite its early and ubiquitous presence in such rocks at the Earth's surface, its phosphorus exhibits a low reactivity in prebiotic chemosynthesis. This situation may change radically upon the transformation of phosphorus from orthophosphates to pyrophosphates or phosphides which are, in contrast, highly reactive in such scenarios. Pyrophosphates and phosphides are today however, scarce on Earth, generally not being stabilized in rock-forming processes. Noticeable exceptions are lightning-struck rocks (i.e., fulgurites). Here, we present the first evidence of reactive phosphorus (P) in a fulgurite which has been experimentally generated under controlled conditions from natural apatite. Crushed apatite was transformed into a fulgurite through the application of controlled high voltage electrical discharges. We document both the apatite (pre-experiment) and the fulgurite (post-experiment) texture, state, and chemistry. 31P and 19F nuclear magnetic resonance spectroscopy reveals the presence of a reactive P phase (pyrophosphate) in the fulgurite. Our results support the speculation that frequent lightning activity under early Earth conditions may have provided more than 100–10.000 kg/yr of reactive P on early Earth through the generation of reactive P-bearing fulgurites. Their presence may have enabled the chemosynthesis of vital prebiotic components such as RNA and lipids for the emergence of life on Earth.

Hepta‐nuclear Zinc Tungstophosphate Nano‐cluster [Zn7(H2O)2(OH)2P2W25O94]16−: Synthesis, Characterization and its Catalytic Application in Alcohol Oxidation

AbstractA new hepta‐nuclear Zinc tungstophosphate nano‐cluster of formula K14[Zn7(H2O)2(OH)2P2W25O94]Zn(H2O)4 ⋅ 35H2O (1 a) was synthesized under environment‐friendly conditions in a one‐pot reaction procedure. The isolated crystalline compound was synthesized by reacting Zn(NO3)2 ⋅ 6H2O with the potassium salt of tungstophosphate precursor, K14[P2W19O69(H2O)] ⋅ 24H2O in the presence of Ce(NO3)3 ⋅ 6H2O in a solution of potassium chloride. The synthesized compound was characterized by instrumentation techniques such as fourier transform infrared (FT‐IR) spectroscopy, single crystal X‐ray diffraction (SC‐XRD), 31P nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), powder X‐ray diffraction (P‐XRD) and energy dispersive X‐ray (EDX) spectroscopy.The compound also shows a good catalytic activity for the oxidation of alcohols.

Phosphorus speciation and colloidal phosphorus responses to short-term cessation of fertilization in a lime concretion black soil

Long-term excessive mineral fertilizer application led to soil acidification and phosphorus (P) accumulation, increasing the risk of P loss and environmental pollution. The cessation of fertilization was widely considered as a cost-effective management strategy to relieve the situation, however, how the fertilization cessation influences the speciation and concentrations of P in bulk soil and the colloidal fractions, and whether the declining P concentration could maintain soil fertility are unclear. In this study, the effect of long-term fertilization (~40 years) and short-term cessation of fertilization (~16 months) on inorganic P, organic P, and colloidal P in lime concretion black soil were investigated with P sequential fractionation and 31P nuclear magnetic resonance spectroscopy (NMR). After long-term fertilization, available P, Ca2-P, Fe-P, orthophosphate monoesters, and orthophosphate diesters increased significantly, but soil pH decreased by ~2.8 pH units, indicating that long-term fertilization caused soil acidification and P accumulation as well as changed P speciation dramatically. In contrast, fertilization cessation in short term brought the increase of soil pH (~0.8 pH units) and decreased slightly for available P and inorganic P. The available P after fertilization cessation was 22.9-29.8 mg kg−1, which was still sufficient for crop growth requirements. In addition, fertilization cessation brought increases in the proportions of fine colloids (100-450 nm, including nontronite and some amorphous Fe oxides) and drove the significant release of Fe/Al oxides nanoparticles (1-100 nm) and associated P with the species of orthophosphate and pyrophosphate. In summary, fertilization cessation in short term could alleviate soil acidification and inorganic P accumulation effectively, at the same time maintain soil P fertility and improve the potential mobilization of P associated with microparticles.

Combined Use of MALDI-TOF Mass Spectrometry and 31P NMR Spectroscopy for the Analysis of (Phospho)Lipids.

Lipids are important and abundant constituents of all biological tissues and body fluids. In particular, phospholipids (PLs) constitute a major part of the cellular membrane and play a role in signal transduction, and some selected PLs are increasingly considered as potential disease markers. Unfortunately, methods of lipid analysis are less established in comparison to techniques of protein analysis. Mass spectrometry (MS) is an increasingly used technique to analyze lipids, especially in combination with electrospray ionization MS, which is the most commonly used ionization technique in lipidomics. Matrix-assisted laser desorption/ionization coupled to time-of-flight MS (MALDI-TOF MS) has itself proven to represent a useful tool in the field of lipid analysis. 31P nuclear magnetic resonance (NMR) spectroscopy, another powerful method for PL analysis, represents a direct quantitative method and does not suffer from suppression effects.This paper gives an overview of methodological aspects of MALDI-TOF MS and 31P NMR in lipid research and summarizes the specific advantages and drawbacks of both methods. In particular, suppression effects in MS will be highlighted, and possible ways to overcome this problem, e.g., the use of different matrices and separation of the relevant lipid mixture prior to analysis, will be discussed.

Multiplicity of Th(IV) and U(VI) HEH[EHP] Chelates at Low Temperatures from Concentrated Nitric Acid Extractions

Organophosphorus extractants have been widely investigated for lanthanide recovery from ore and for application in the reprocessing of spent nuclear fuel, such as in Advanced TALSPEAK schemes. Determining the speciation of the extracted metal complex in the organic phase remains a significant challenge. A better understanding of the variability of HEH[EHP]-actinide complexes and the speciation of chelates for tetra- and hexavalent actinides can improve the predictability of actinide phase transfer in such biphasic systems. In this study, the extraction of Th(IV) and U(VI) from nitric acid media using HEH[EHP] in heptane is examined. The distribution ratio as a function of nitric acid concentration was quantified using UV-vis spectroscopy, and then the speciation of HEH[EHP]-metal complexes in the organic phase was investigated using Fourier transform infrared (FTIR) spectroscopy and low-temperature 31P nuclear magnetic resonance (NMR) spectroscopy. In addition to perturbation of the vibrational modes proximal to the phosphonic moiety in HEH[EHP] in the FTIR spectra, the appearance of a nitrate signal was found in the organic phase following extraction from the highest acidity conditions for U(VI). The 31P NMR spectra of the organic phase at a low temperature (-70 °C) exhibited a surprising number (n) of resonances (n ≥ 7 for Th(IV) and n ≥ 11 for U(VI)), with the distribution between these resonances changing with the initial concentration of nitric acid in the aqueous phase. These results indicate that the compositions of the inner and outer spheres of the extracted actinides in the organic phase are more diverse than initially thought.

Ruthenium Catalyzed Oxidative Cleavage of High Oleic Sunflower Oil: Considerations Regarding the Synthesis of a Fully Biobased Triacid

AbstractTricarboxylic acids are molecules of interest for the synthesis of highly cross‐linked polymers, for instance, for the curing of epoxy resins. Herein, a synthesis route to a novel high oleic sunflower oil based triacid is described by applying a ruthenium catalyzed oxidative cleavage of its double bonds. A statistical concept is devised for the prediction of the yields of mono‐, di‐, and trifunctional derivatives that can be formed from high oleic sunflower oil, depending on the overall conversion of double bonds into this functional group and the overall oleic acid content of the used oil. This concept proved to be highly useful for the explanation of seemingly moderate triacid yields, which are inherently dependent on the unsaturated fatty acid content of the used oil. All obtained sunflower oil based polyacids are fully analyzed by attenuated total reflection infrared spectroscopy (ATR‐IR), electrospray ionization mass spectrometry (ESI‐MS), 1H, 13C, and quantitative 31P nuclear magnetic resonance (NMR) spectroscopy. In addition, a more sustainable purification procedure is developed to obtain a polymerizable mixture of polyacids containing more than 2.0 carboxylic acids per molecule in average.Practical applications: Tricarboxylic acids are valuable monomers for the synthesis of cross‐linked polymers. The herein reported procedure represents a hitherto unknown synthesis route towards a new triacid and polyacid mixture directly from high oleic sunflower oil.

Phosphorus application promoted the sequestration of orthophosphate within soil microorganisms and regulated the soil solution P supply in a temperate grassland in northern China: A 31P NMR study

Anthropogenic activities have made phosphorus (P) a new sustainability issue globally. To better understand the mechanisms of soil P dynamics responding to inorganic P fertilization (0–12.5 g P m−2yr−1), we conducted a 2-year field experiment in a temperate grassland in northern China. The P fertilizer was added once per year before the growth period as NaH2PO4. We randomly collected topsoil samples (0–10 cm) and analyzed the soil properties, microbial community, and extracellular enzyme activities, and quantified the soil P fractions using solution 31P nuclear magnetic resonance (31P NMR) spectroscopy. P application promoted transformation from organic P to inorganic P driven by microbial carbon (C) demand and regulated by altered soil properties and microbial characteristics. P addition decreased orthophosphate diesters, especially DNA, due to increased hydrolysis under increased soil pH. This may increase hydrolysates such as α-glycerophosphate and choline phosphate. Orthophosphate monoesters, especially myo-inositol hexaphosphate, also decreased following increased P availability. This could be explained by increased alkaline phosphatase activity and reduced sorption due to a decreased metal (Ca, Al, and Fe) content. Furthermore, P fertilization increased soil NH4+-N, thereby increasing the growth of phosphonate-solubilizing microorganisms (Bacillus, Streptomyces, Bradyrhizobium, Mesorhizobium, Penicillium, Aspergillus, and Fusarium). Their increased growth also contributed to inorganic P solubilization and organic P mineralization due to their P-solubilizing specificity. Together, these factors increased inorganic P, especially orthophosphate, which was temporarily immobilized in microbial cells, to regulate the soil-solution P supply, and created a potentially available P sink in the grassland.

One-step synthesis of heteropolyacid ionic liquid as co-extraction agent for recovery of lithium from aqueous solution with high magnesium/lithium ratio

The novel heteropolyacid ionic liquid 1-methylimidazolium silicotungstate ([Mmim]4SiW12O40) was synthesized using a one-step method and subsequently characterized. This compound was then employed as a co-extractant for the removal of lithium from salt lake brine having a high Mg/Li molar ratio, in conjunction with tributyl phosphate (TBP) and γ-heptanolide as the extractant and diluent, respectively. The optimal extraction conditions gave a single-stage lithium ion extraction efficiency of approximately 60 %. More environmentally friendly and efficient processes were also developed. In one approach, a portion of the aqueous phase containing only HCl and LiCl after stripping was used for washing along with an aqueous HCl solution as the stripping agent and Mg(OH)2 for regeneration. In the alternative method, NaCl and LiCl were used as washing agents while Na2CO3 was employed for stripping and regeneration, reducing the time required without the need for strong acids or bases. This system showed good extraction efficiency stability over 10 consecutive cycles. The mechanism of this process was explored using Fourier transform infrared spectroscopy and 31P nuclear magnetic resonance spectroscopy and the binding capacity of TBP for the metals was found to decrease in the order of Li+ > Na+ > Mg2+ > K+.

Soil colloidal particles in a subtropical savanna: Biogeochemical significance and influence of anthropogenic disturbances

Soil colloids (diameter < 1000 nm) are comprised mainly of clay minerals and organic matter, and play major roles in determining ion exchange capacity and in regulating key biogeochemical processes. Consequently, it is important to understand how soil colloids and their functions are influenced by land cover and anthropogenic disturbances. In grasslands, savannas, and other dryland ecosystems across the globe, woody plants are encroaching due to livestock grazing, fire suppression, elevated CO2 concentrations, and climate change. These major land cover changes could influence soil colloidal properties, with implications for soil C, N, and P cycles. We assessed how woody encroachment, livestock grazing, and fire interact to influence soil colloidal properties in a juniper-oak savanna. Surface soils (0–10 cm) from the southern Great Plains (Texas, USA) were collected from long-term treatments differing in grazing intensity (none, moderate, and heavy) and fire history. Within each treatment, soil samples were taken under grass, juniper, and oak canopies. Water dispersible soil colloids (WDC, d < 500 nm) were isolated and analyzed by asymmetric flow field-flow fractionation and their P species by liquid-state 31P-nuclear magnetic resonance spectroscopy (31P NMR). Soil beneath oak and juniper canopies had smaller WDC and elevated colloidal organic carbon (OC) and P concentrations, especially in nanocolloid (<30 nm) and fine colloid (30–160 nm) size fractions. Woody encroachment enriched Ca, Fe, Al, Si and Mg in WDC in the ungrazed control, but not in any of the other grazed or burned areas. Colloidal soil P mainly occurred as orthophosphate and orthophosphate diesters, and was present as OC-Ca-P complexes in fine and medium colloid fractions (30–500 nm), while P in the nanocolloid fraction (<30 nm) was in direct association with Ca. Moderate grazing did not affect the retention of colloidal P, while heavy grazing potentially increased the loss risk of colloidal P. Fire accelerated soil P loss from colloid fractions only in woody areas. Our findings highlight that woody encroachment strengthens the retention of OC and P by soil colloids, consequently increasing overall C and P pools in savanna soils.

Synthesis of new photo-cured phosphorus-containing oligoestermethacrylates with a spacer in the structure

Objectives. To synthesize phosphorus-containing oligoestermethacrylates spatially separated by spacers of aliphatic or aromatic structure and evaluate their effect on photocuring kinetics.Methods. For determining the qualitative and quantitative composition of the synthesized compounds, the following methods were used: thin layer chromatography; chromatographic and mass spectrometry; infrared spectroscopy; 1H, 13C, 31P nuclear magnetic resonance spectroscopy; differential scanning calorimetry. The dielectric loss tangent was determined on a specially designed optical cell with an ultraviolet (UV) light source to an immittance meter. Elemental analysis was performed on an energy dispersive X-ray fluorescence spectrometer.Results. Spatially separated oligoestermethacrylates based on phosphorus trichloride containing aliphatic or aromatic spacers in the structure were synthesized. During the interaction of glycidyl methacrylate with phosphorus trichloride in the mass of the latter, reaction products were shown to be formed both according to the Krasusky rule from the side of the α-carbon atom, as well as against this rule with the formation of isomeric products. Obtaining these compounds in bulk is possible only in the presence of a homopolymerization inhibitor. The influence of the spacer structure on the curing rate of oligoestermethacrylates under the action of UV radiation has been established. It has been shown that the introduction of a spacer into the oligomer structure is accompanied by an increase in the induction period by a factor of 39 compared to a sample without a spacer.Conclusions. The results obtained indicate the possibility of obtaining new oligoestermethacrylates with aliphatic and aromatic spacers in the structure. The influence of the structure of the spacer on the kinetics of photocuring is determined.

Phosphorus speciation along a soil to kettle hole transect: Sequential P fractionation, P XANES, and 31P NMR spectroscopy

Phosphorus (P) is an essential element for all living organisms but can also be an important factor in the eutrophication of aquatic/marine ecosystems. Kettle holes are often situated in regions under intense agricultural land use where there is a high risk of nutrient transfer to larger waterbodies. The chemical speciation of soil P influences its rate of transfer from arable fields to aquatic environments. However, there is a paucity of information on the P speciation in kettle holes and their effect on the P cycle. Thus, we investigated the P composition of arable soils and kettle hole sediments in surface and subsurface layers along a transect of an agricultural field. Multiple P analyses were carried out including modified sequential Hedley P fractionation, P K-edge X-ray absorption near edge structure (XANES) spectroscopy, and 31P nuclear magnetic resonance (NMR) spectroscopy. The Pt concentrations ranged from 680 to 1123 mg kg−1 in the soils and 797 to 2591 mg kg−1 in the sediments. A predominance of the residual-P fraction, characterized as not extractable P, occluded P or stable forms of organic P (Po) was determined by sequential fractionation, ranging from 37 to 67 % followed by 3 to 38 % H2SO4-Pi and 3 to 16 % NaOH-Po of total P (Pt) in the soils and sediments. Analyses with P K–edge XANES spectroscopy assigned 61 to 100 % Fe- and Al-P, 0 to 14 % Ca-P, and 0 to 39 % Po in the arable soils and 46 to 74 % Fe- and Al-P, 14 to 43 % Ca-P, and 0 – 38 % Po in the adjoining kettle hole sediments. Solution 31P NMR spectra on alkaline extracts revealed a broad signal in the phosphomonoester region, which was the most abundant form of organic P across all samples. Besides, the proportion of ‘complex’ phosphomonesters (broad signal) to that of total extractable P was about 2-fold greater in the kettle hole sediments than in soils. Complex forms of organic P are known to be strongly associated with organic matter (OM) and appear to accumulate on a decadel timeframe. Therefore, it is desirable that kettle hole sediments are conserving P (and carbon), which will help reduce the transfer of P from agricultural fields to other, more vulnerable aquatic/marine ecosystems.

Molecular-Level Insights into Phosphorus Transformation Mechanisms in Entisol Soils under Multiple Long-Term Fertilization Regimes

Improving phosphorus (P) fertilization strategies benefits mitigating future global P shortage and reducing legacy P loss risk in agricultural lands. In this study, the molecular transformation mechanisms of P in Entisol soils under multiple long-term fertilization regimes including PK; NK; NPK; NPK with pig manure (NPKM); and NPK with rice straw return (NPKS) were investigated by sequential fractionation (SF), synchrotron-based P K-edge X-ray absorption near-edge structure (P-XANES) and solution 31P nuclear magnetic resonance (P-NMR) spectroscopy. Compared with conventional NPK fertilization, a higher accumulation of total P occurred in soils under the PK, NPKM and NPKS treatments. By SF, there were relatively higher contents of NaHCO3-extracted inorganic P (Pi) fractions for the soils under PK (52.5 mg/kg) and NPKM (35.5 mg/kg) fertilization relative to the NPK (23.3 mg/kg) treatment. Consistently, P-XANES analysis revealed that there was a higher proportion of brushite, as a bioavailable P form, in soil under the PK and NPKM treatments compared with the NPK treatment, indicating higher P availability in the Entisol soils under PK and NPKM fertilizations. By P-NMR, long-term PK fertilization resulted in relatively a higher ratio of orthophosphate diesters to orthophosphate monoesters after correction compared with the NPK fertilization, which strongly suggested that N deficiency enhanced the biodegradability of soil organic P (Po) pools, thus providing new molecular-level insights into soil Po transformation. Collectively, these results, obtained from a long-term experimental study, facilitates the comprehensive understanding of P availability and transformation mechanisms in Entisol soils under multiple fertilization regimes, and thus benefits the improvement of fertilization strategies in agricultural soils.

Functional Characterization of a HAD Phosphatase Involved in Capsular Polysaccharide Biosynthesis in Campylobacter jejuni.

Campylobacter jejuni is a Gram-negative, pathogenic bacterium found in the intestinal tracts of chickens and many other farm animals. C. jejuni infection results in campylobacteriosis, which can cause nausea, diarrhea, fever, cramps, and death. The surface of the bacterium is coated with a thick layer of sugar known as the capsular polysaccharide. This highly modified polysaccharide contains an unusual d-glucuronamide moiety in serotypes HS:2 and HS:19. Previously, we have demonstrated that a phosphorylated glucuronamide intermediate is synthesized in C. jejuni NCTC 11168 (serotype HS:2) by cumulative reactions of three enzymes: Cj1441, Cj1436/Cj1437, and Cj1438. Cj1441 functions as a UDP-d-glucose dehydrogenase to make UDP-d-glucuronate; then Cj1436 or Cj1437 catalyzes the formation of ethanolamine phosphate or S-serinol phosphate, respectively, and finally Cj1438 catalyzes amide bond formation using d-glucuronate and either ethanolamine phosphate or S-serinol phosphate. Here, we investigated the final d-glucuronamide-modifying enzyme, Cj1435. Cj1435 was shown to catalyze the hydrolysis of the phosphate esters from either the d-glucuronamide of ethanolamine phosphate or S-serinol phosphate. Kinetic constants for a range of substrates were determined, and the stereoselectivity of the enzyme for the hydrolysis of glucuronamide of S-serinol phosphate was established using 31P nuclear magnetic resonance spectroscopy. A bioinformatic analysis of Cj1435 reveals it to be a member of the HAD phosphatase superfamily with a unique DXXE catalytic motif.

Metal-Support Interactions in Molecular Single-Site Cluster Catalysts.

This study provides atomistic insights into the interface between a single-site catalyst and a transition metal chalcogenide support and reveals that peak catalytic activity occurs when edge/support redox cooperativity is maximized. A molecular platform MCo6Se8(PEt3)4(L)2 (1-M, M = Cr, Mn, Fe, Co, Cu, and Zn) was designed in which the active site (M)/support (Co6Se8) interactions are interrogated by systematically probing the electronic and structural changes that occur as the identity of the metal varies. All 3d transition metal 1-M clusters display remarkable catalytic activity for coupling tosyl azide and tert-butyl isocyanide, with Mn and Co derivatives showing the fastest turnover in the series. Structural, electronic, and magnetic characterization of the clusters was performed using single crystal X-ray diffraction, 1H and 31P nuclear magnetic resonance spectroscopy, electronic absorption spectroscopy, cyclic voltammetry, and computational methods. Distinct metal/support redox regimes can be accessed in 1-M based on the energy of the edge metal's frontier orbitals with respect to those of the cluster support. As the degree of electronic interaction between the edge and the support increases, a cooperative regime is reached wherein the support can deliver electrons to the catalytic site, increasing the reactivity of key metal-nitrenoid intermediates.

Validated quantitative 31P NMR spectroscopy for positional isomeric impurity determination in L-α-glycerylphosphorylcholine (L-α-GPC)

In this study a quantitative 31P nuclear magnetic resonance (31P NMR) spectroscopy method was described to determine positional isomeric impurity β-GPC in commercial products of L-α-GPC. The samples were dissolved in D2O and trimethyl phosphate (TMP) was selected as an internal calibrant. The measurements were performed on a Bruker 500 MHz spectrometer and the spectra were recorded under optimized process conditions. A good linear relationship was constructed for β-GPC in the range of 62.7–528.0 µg·mL−1, i.e. 0.03–0.25 % (w/w %, in relative to L-α-GPC) with a correlative coefficient of 0.9996. The limit of quantification (LOQ) and limit of detection (LOD) were 62.7 µg·mL−1 and 20.9 µg·mL−1 with signal to noise of 3 and 10, respectively. The spiked recoveries were in the range of 98.17–99.78 % with the relative standard deviation (RSD %) less than 1.0 %. Therefore, it could be supposed that the 31P NMR was a promising alternative method for sensitive determination of β-GPC for strict quality control of L-α-GPC.

Characteristics and controls of inorganic and organic phosphorus transformation during long-term paddy soil evolution

Information on phosphorus (P) transformation during long-term paddy soil evolution is important for maintaining rice yield and nutrient management. This study was aimed to reveal the characteristics and controls of inorganic and organic P transformation during paddy soil evolution over a millennial time scale using both sequential chemical extraction and solution 31P nuclear magnetic resonance spectroscopy. Results show that the rate and trajectory of P evolution in the topsoil differ markedly from that of the illuvial horizon. The amount of apatite P, non-occluded P, occluded P and total P in the topsoils increased rapidly during the early stage of paddy soil evolution (< 50 yrs) due to anthropogenic P additions, but declined in the older paddy soils due to the leaching loss of P sorbents (CaCO3 and Fe/Al oxides); thus, the added P cannot be efficiently retained by the older paddy soils. Total organic P including phosphate monoester in the topsoils reached maximum in the 300-yr paddy soil and declined thereafter. However, the phosphate diester pool (including DNA) and its proportion in the topsoil increased continuously across the paddy soil chronosequence, suggesting that long-term paddy cultivation promoted labile organic P accumulation. In the deeper soil horizons with less human impacts, the temporal trends in inorganic and organic P across the paddy soil chronosequence can be fully predicted by previous established P transformation models during natural pedogenesis, although the rates of P changes differ among different sites. Our study demonstrates that long-term paddy cultivation alters the rate and trajectory of inorganic and organic P transformation in the topsoils over a millennial time scale, and highlights the importance of labile organic P activation for nutrient supply in the older paddy soils.

Dissolved organic phosphorus molecular weight fractionation and apparent bioavailability quantified via coupled sequential ultrafiltration and enzyme hydrolysis

AbstractAquatic organisms utilize dissolved organic phosphorus (DOP) when phosphate levels are insufficient to satisfy their P‐demand. Its critical role in supporting primary production has motivated efforts to characterize DOP composition and gain insight into its bioavailability. 31P nuclear magnetic resonance (31P‐NMR) spectroscopy, the principal tool currently used by aquatic geochemists to identify compositional aspects of the bulk marine DOP pool, has provided limited compositional detail beyond the immediate P‐bonding environment, and does not provide quantitative information on potential bioavailability of DOP. As a result, the DOP pool remains poorly characterized, limiting predictive power relative to DOP bioavailability. We have developed a sequential ultrafiltration (SUF) method to segregate the DOP pool into four distinct molecular weight ranges. The concentrated molecular weight fractions are then incubated with phosphohydrolytic enzymes to determine the potential bioavailability of monoester‐ and diester‐bound P. DOP molecular weight segregation was verified using commercially available DOP compounds of known molecular weight as analogues for naturally occurring DOP. We have applied the SUF method to surface water samples from a nearshore transect in Kāne'ohe Bay, Hawai'i, and surface waters from oligotrophic Station ALOHA (Hawai'i Ocean Time Series). Results of these field tests indicate that the coupled SUF‐bioavailability method reveals greater compositional complexity of the marine DOP pool than has been resolved by 31P‐NMR studies. Notably, the SUF‐bioavailability method does not require expensive, technically complicated instrumentation (e.g., 31P‐NMR), and thus is readily accessible to researchers wishing to probe marine DOP composition who do not have access to or expertise in 31P‐NMR.

Coordination of Palladium(II) and Platinum(II) Complexes to One Vacant Site in an α-Keggin-Type Polyoxotungstate.

A palladium-platinum bimetal complex containing a mono-lacunary α-Keggin-type polyoxotungstate is demonstrated. The bimetallic complex Cs2.5{PdII(bpy)}0.25[α-PW11O39{PdII(bpy)}{cis-PtII(NH3)2}]·12H2O·2CH3CN (bpy = 2,2'-bipyridine) (PdPt) was synthesized by the reaction of Cs4.9K0.1[α-PW11O39{cis-PtII(NH3)2}]·10H2O (Pt1) with PdII(bpy)Cl2 in aqueous solution. The compound PdPt was characterized via elemental analysis, thermogravimetric/differential thermal analysis, and Fourier transform infrared, ultraviolet-visible, cold-spray ionization mass, and solution (1H, 13C, and 31P) nuclear magnetic resonance spectroscopies. The coordination of {cis-PtII(NH3)2} and {PdII(bpy)} moieties to the mono-vacant site of [PW11O39]7- resulted in an asymmetric, monomeric compound. A unique exchange reaction between the counter cation [PdII(bpy)]2+ and {cis-PtII(NH3)2} moiety in [α-PW11O39{PdII(bpy)}{cis-PtII(NH3)2}]3- in a dimethylsulfoxide solution was also observed.

Changes in chemical form of phosphorus in rice bran during fermentation process as determined by 31P nuclear magnetic resonance spectroscopy

ABSTRACT Rice bran contains appreciable amount of phosphorus (P), which can be used as P fertilizers. The efficiency of the P in the rice bran to plants, however, is low, and the fermentation of the rice bran is proposed to improve the P availability for plants. In the present study, 20 kg of rice bran was aerobically fermented by adding 5 kg of rice husk, 0.025 kg of mulch, and 7 L of water and incubating for 35 days with 6 times of stirring, and the changes in the chemical form of P during the fermentation process were investigated by 31P nuclear magnetic resonance spectroscopy and chemical extraction. Most part (84%) of P in the raw rice bran was myo-inositol-1,2,3,4,5,6-hexaphosphate (I6P), which is not available for plants. During the fermentation process, I6P was degraded and transformed into plant-available phosphate anions (orthophosphate). The proportions of the orthophosphate increased to 68% after incubating for 19 days with two times of stirring and 92% after incubating for 35 days with six times of stirring. After the fermentation, the orthophosphate was present as plant available precipitates associated with magnesium and the other monovalent cations. In conclusion, rice bran contains low-available I6P as a major P form, and the fermentation of rice bran accelerates the cleavage of the ester bond of I6P and results in the increased proportion of orthophosphate with high availability to plants.

Phosphatic metabolism in dark- and light-adapted rat retinas

This study defines retinal phosphatic metabolites and their adjustment to illumination in rat retinas under conditions that preserve retinal function. Metabolic data are measured using high-performance liquid chromatography (HPLC) and 31P nuclear magnetic resonance (31P NMR) spectroscopy after 10 min of light exposure in vivo compared with retinas from dark-adapted rats. Multiple high-energy and low-energy phosphatic metabolites of intermediary metabolism were quantified. The concentration of the high-energy phosphate adenosine triphosphate (ATP) remained unchanged from dark- to light-adaptation. Under the same conditions the concentrations of the high-energy phosphates guanosine triphosphate (GTP) and creatine phosphate increased, whereas the inorganic phosphate decreased. Comparing dark-adapted controls with retinas light-adapted either in vitro or in vivo, the evidence is consistent with a light-dependent increase in GTP and a decrease in cyclic guanosine monophosphate. Although cyclic adenosine monophosphate (cAMP) levels were lower in retinas light-adapted in vivo than in the dark-adapted controls, this did not seem to be an effect of light, as cAMP levels decreased similarly after 10 min incubation in dark or light in parallel with recovery of ATP/adenosine diphosphate ratios. This study: (1) reports on retinal metabolic changes with adjustment in illumination, (2) provides baseline measurements of retinal phosphatic metabolites in whole retinas, and (3) reports on the validity of chromatographic and spectroscopic methods used for studying retinal metabolism establishing a high correlation among measurements made using HPLC and 31P NMR.