195Pt, 1H and 31P PGSE diffusion studies on platinum complexes

The first example of the use of (195)Pt PGSE diffusion data (D values) to recognize the solvent dependence of aggregation of the hexachloroplatinate dianion in Na(2)PtCl(6) (1) and in H(2)PtCl(6) (2) is reported. In water, the ions are separated; however, in methanol the D values suggest ion pairing and/or aggregation. Additional (1)H and (31)P diffusion data for organometallic Pt complexes trans-PtX(Aryl)(L)(2) (where L = PEt(3) or PPh(3)) and Pt(C(7)H(4)O(2))(L(1))(L(2)) (where L(1) and L(2) = a variety of ligand types) reveal that phenyl phosphines afford relatively large hydrodynamic radii r(h). The presence of a substituent on the aryl ligand of PtX(Aryl)(L)(2) does not markedly affect the D values, whereas a substituent of similar size added to a PPh(3) group in Pt(C(7)H(4)O(2))(L(1))(L(2)) markedly changes both D and r(h) values. There is only a small concentration dependence of the D values in PtX(Aryl)(L)(2) on changing from 2 to 10 mM.     

Extraction processes reduce polyphosphate ion migration,dispersion and diffusion as detected with gel electrophoresis and 31P DOSY NMR

Inorganic polyphosphates (polyPs) have been identified in eukaryotic and prokaryotic cells alike. Various extraction methods have been optimized as a necessary step before identification and measurement of these polymers. Three commercially available sodium polyP glasses were either dissolved or dissolved and extracted by two commonly used polyP extraction techniques – perchloric acid or buffered phenol–chloroform. The products were separated by polyacrylamide gel electrophoresis (PAGE), stained with toluidine blue O, and the migration results quantitatively compared. Both extraction processes reduced the relative migration distances of the peak and leading edges, and the stained band lengths, suggesting reduced polyP migration and dispersion. ³¹P diffusion-ordered spectroscopy nuclear magnetic resonance confirmed that polyP extraction by perchloric acid or phenol–chloroform processes reduced polyP diffusion coefficients and suggested hydrolytic degradation with stronger end-chain signals. Reduced polyP diffusivity after extraction makes possible an overestimation of synthetic polyP chain length assignment when compared to unextracted polyP ladders with PAGE. The mechanism(s) for reduced synthetic polyP diffusion after extraction and intracellular chemical environment effects on migration are not known.     

Observation of a P/M interconversion of a gold-phosphine helicate via 31P NMR

Ligands containing P-CH2-CH2-P elements have been shown to form double-stranded helicates whose axis consists of gold atoms with Au...Au contacts; the interconversion of the P and M forms of the helicate [Au3(mu-pp2)2](OTf)3 (pp2 = PhP(CH2CH2PPh2)2) is monitored via 31P NMR.     

Membrane curvature change induced by an antimicrobial peptide detected by 31P exchange NMR

The influence of an antimicrobial peptide, protegrin-1 (PG-1), on the curvature and lateral diffusion coefficient (D(L)) of phosphocholine bilayers is investigated using one- (1D) and two-dimensional (2D) (31)P exchange NMR. The experiments utilize the fact that lipid lateral diffusion over the curved surface of vesicles changes the molecular orientation and thus the (31)P chemical shift anisotropy. This reorientation is manifested in 2D spectra as off-diagonal intensities and in 1D stimulated-echo experiments as reduced echo heights. The 2D spectra give information on the reorientation-angle distribution while the decay of the stimulated-echo intensity, which closely tracks the second-order correlation function in our experiments, yields the correlation times of the reorientation. The relationships among the 2D exchange spectra, stimulated-echo intensities, the correlation function, and reorientation-angle distributions are analyzed in detail. In the absence of PG-1, both dilaurylphosphotidylcholine (DLPC) and palmitoyloleoylphosphatidylcholine (POPC) vesicles show biexponential decays of the stimulated-echo intensities to equilibrium values of 0.20-0.25, suggesting that the curvature of the lipid vesicles has a bimodal distribution. The addition of PG-1 to DLPC vesicles increased the decay time constants, indicating that D(L) decreases due to peptide binding. In contrast, the addition of PG-1 to POPC vesicles decreased the decay constants by three to fivefold, indicating that the POPC vesicles are fragmented into smaller vesicles. On the basis of the changes in D(L) and the decay constants, we estimate that the radius of the POPC vesicles decreases by threefold due to PG-1 binding. Simulations of the 2D exchange spectra yielded quantitative reorientation-angle distributions that are consistent with the bimodal distributions of the vesicle curvature and the effects of the peptide on the two types of lipid bilayers. Thus, (31)P exchange NMR provides useful insights into the membrane morphological changes induced by this antimicrobial peptide.     

Electron-donating ability of triarylphosphines and related compounds studied by 31P NMR spectroscopy

The influence of aryl, heterocyclic, amide, alkyl, alkoxyl, thioalkoxyl, and ferrocenyl substituents at the phosphorus atom on its electron-donating ability was studied by the measurement of direct ³¹P—⁷⁷Se spin-spin coupling constants for the corresponding selenides. Series of diphenylorganylphosphines and their selenides were studied.     

Phosphorus dendrimers as viewed by 31P NMR spectroscopy; synthesis and characterization

This review emphasizes the role of phosphorus for the elaboration of dendrimers and of various highly sophisticated dendritic structures, and the invaluable role played by ³¹P NMR for their characterization and to ascertain their purity. A few properties, highlighting the importance of phosphorus are reported at the end of this review.     

Multinuclear (11B, 31P) MAS NMR spectroscopy of borophosphates

¹¹B and ³¹P MAS NMR spectroscopy of three borophosphates was used to monitor their phase composition via the isotropic chemical shifts. CaBPO₅ and BPO₄ represent nearly pure samples, SrBPO₅ contains β-Sr₂P₂O₇ as well as BPO₄ as impurities. The anisotropic chemical shift data provide additional information on the geometry and connectivity of the BO₄ and PO₄ building units. Received: 25 July 1996 / Revised: 19 August 1996 / Accepted: 23 August 1996     

Multinuclear (11B, 31P) MAS NMR spectroscopy of borophosphates

¹¹B and ³¹P MAS NMR spectroscopy of three borophosphates was used to monitor their phase composition via the isotropic chemical shifts. CaBPO₅ and BPO₄ represent nearly pure samples, SrBPO₅ contains β-Sr₂P₂O₇ as well as BPO₄ as impurities. The anisotropic chemical shift data provide additional information on the geometry and connectivity of the BO₄ and PO₄ building units. Received: 25 July 1996 / Revised: 19 August 1996 / Accepted: 23 August 1996     

Phospholipids Analysis by 31P NMR

Abstract

Cell membrane phospholipids can be identified and quantitated using ³¹P NMR spectroscopy in conjunction with an analytical reagent composed of chloroform-benzene(d6)/methanol-CsEDTA 2:l ml/ml. 3 ml of this reagent dissolves between 0.01–100 mg crude tissue lipids obtained by the Folch procedure. When the source phospholipids are strongly contaminated with cations, it is necessary to modify the extraction method, backwashing with K-EDTA, 0.6 M, pH 6, instead of KC1. Also if source tissues must be stored for long periods of time, acetone desication is recommended. Using a 500 MHz ³¹PNMR spectrophotometer (magnetic field ?11.75 T), the extracted phospholipids yield narrow Lorenzian signals (1.8–3.2 Hz at half-height), with these widths at half-height corresponding to their 1/πT₂ values. Chemical shifts (δ) at 24 °C, following the IUPAC shift convention and relative to 85% phosphoric acid, were determined as follows:CAEP,21.09;LPG,l,O9;LPA,0.83;LPE plas,0.53;PG,0.50;LPE,0.43; PA,0.25;CL,0.18;LPI,0.10;PE plas,0.07;PE,0.03;PS,?0.O5;SPH,?0.O9; DiMePE,?b.18;LPC plas,?0.20;LPC,?0.28;PI,?0.37; PAF, ?0.70;PC plas,?0.77; PC, ?0.84. This reagent permits assays of high precision and accuracy that use little spectrometer time and that are suitable for automated procedures.     

Monitoring of the insecticide trichlorfon by phosphorus-31 nuclear magnetic resonance (31P NMR) spectroscopy

Trichlorfon is an organophosphorus insecticide, which is extensively being used for protection of fruit crops. Trichlorfon is a thermal labile compound, which cannot be easily determined by gas chromatography (GC) and has no suitable group for sensitive detection by high performance liquid chromatography (HPLC). In this study, a ³¹P nuclear magnetic resonance (³¹P NMR) has been described for monitoring of trichlorfon without any separation step. The quantitative works of ³¹P NMR spectroscopy has been performed in the presence of an internal standard (hexamethylphosphoramide). Limit of detection (LOD) for this method has been found to be 55 mg L⁻¹, without any sample preparation, and the linear working range was 150-5500 mg L⁻¹. Relative standard deviation (R.S.D.%) of the method for three replicates within and between days was obtained ≤9%. The average recovery efficiency was approximately 99-112%. This method was applied for monitoring trichlorfon in a commercial insecticide sample and tomato sample.     

Synthesis and characterization of cyclopalladated complexes of benzylamine by IR and NMR spectroscopy studies

The chloro-bridged dimer [Pd(μ-Cl)(C₆H₄CH₂NH₂-κ²-C,N)]₂ reacts with PPh₂Et, P(p-tolyl)₃, AsPh₃, piper (piper =?C₅H₁₀N) and Py in dichloromethane at room temperature for 24 h in a one-to-two molar ratio and undergoing bridge-splitting reactions to give [PdCl(C₆H₄CH₂NH₂–κ²-C,N)L] (L =?PPh₂Et (1a), P(p-tolyl)₃ (1b), AsPh₃ (1c), piper (1d), C₆H₄CH₂NH₂ (3e) and Py (1f)). Complex 1f in THF at room temperature reacts with a stoichiometric amount of TlTfO (thallium triflate, TfO=CF₃SO₃) and Py (molar ratio 1 : 1 : 1) to afford [Pd(C₆H₄CH₂NH₂)(Py)₂]TfO (2). Infrared and NMR spectroscopies allow unambiguous characterization of these products.     

Slow diffusion by singlet state NMR spectroscopy

Small diffusion coefficients can be measured by using populations of singlet states that have a relaxation time constant, T(s), which can be much longer than the longitudinal relaxation time, T1. Spatial information can be encoded with pulsed field gradients in the manner of stimulated echo sequences. Singlet states can be excited via double-quantum coherences to enhance the efficiency of phase encoding and decoding.     

Determination of coordination modes and estimation of the 31P-31P distances in heterogeneous catalyst by solid state double quantum filtered 31P NMR spectroscopy

To overcome the separation difficulty of the palladium-based homogeneous catalyst, the palladium complex can be anchored on various supports such as silica. However, it is difficult to determine the amounts of the two coordination modes of the Pd nucleus, that is, Pd coordinates with one phosphorus atom and Pd coordinates with two phosphorus atoms. Here a (31)P double-quantum filtered (DQ-filtered) method in solid-state NMR is introduced for the palladium-based heterogenous catalyst system. With the DQ-filtered method, we can not only determine the amounts of the two different kinds of palladium coordination modes, we can also estimate the interatomic distance of two (31)P nuclei bonded to a palladium nucleus. With the help of this method, we can quickly estimate interatomic distances in our designed system and accurately re-design the palladium system to accommodate either one (31)P or two (31)P.     

Application of the attached proton test technique in 31P NMR spectroscopy

Intensity modulated ³¹P NMR spectra were obtained using the pulse sequence published by Patt and Shoolery. This attached proton test (APT) technique for signal assignment could be applied to systems with long-range heteronuclear couplings in P? O? C? H fragments. In a model system derived from the alcoholysis of P₄S₁₀ the six reaction products were assigned to the six signals in the ³¹P NMR spectrum.     

Determination of absolute configuration by 31P NMR

The determination of absolute configuration is crucial for all chiral molecules; therefore many techniques have been developed to serve this purpose. It is especially important for the invention of new medicines, as in some cases only one enantiomer has a positive medical effect, while the other is inactive or even harmful. Herein we present the usefulness of the ³¹P NMR technique in the determination of the absolute configuration of chiral molecules, as an alternative to other methods. The models presented herein, often developed on the basis of ¹H NMR, describe conformations and configurations and following shielding effects in chiral molecules, that can be applied to determine the stereochemistry of a molecule by ³¹P NMR spectroscopy. Numerous examples of the use of some of the described models are presented as well.     

Study of ion exchange selectivity of organic ions by using (31)P NMR spectroscopy

Ion exchange distribution of the phenylphosphoric acid has been studied on various types of chloride form strong base resins as a function of pH at 25 °C, at 0.1 M ionic strength. Equilibrium measurements were supplemented by the study of pH dependence of the ³¹P NMR spectra of the resin-phase phenylphosphate species. Equations were derived to describe the pH dependence of the overall distribution coefficient and the chemical shift of the resin-phase solute species. Experimental data were evaluated by using these model equations and the values of the individual distribution coefficients, ion exchange selectivity coefficients and the resin-phase ³¹P chemical shifts of the mono- and divalent ions have been calculated. Comparison of distribution data of the individual species corroborated the significance of the role of hydrophobic interaction in the selectivity of organic ion exchange processes. A well-defined correlation between the ion exchange selectivity and the resin-phase ³¹P NMR chemical shift data has been pointed out.     

Study of potassium O,O'-Dibutyldithiophosphate combining DFT, 31P CP/MAS NMR and infrared spectroscopy

Dithiophosphates are used in many different industrial applications. To explain their functions and properties in these applications, a fundamental understanding on a molecular level is needed. Potassium O, O'-Dibutyldithiophosphate and its anion have been investigated by means of a combination of DFT and (31)P CP/MAS NMR and infrared spectroscopy. Several low-energy conformations were studied by DFT. Three different conformations with significantly different torsion angles of the O-C bond relative to the O-P-O plane were selected for further studies of infrared frequencies and (31)P NMR chemical-shift tensors. A good agreement between theoretical and experimental results was obtained, especially when the IR spectra or (31)P chemical shift tensor parameters of all three conformations were added, indicating that, because of the low energy difference between the conformations, the molecules are rapidly fluctuating between them.     

Solid-state 31P NMR spectroscopy of precipitated guanine nucleotide-binding protein Ras in complexes with its effector molecules Raf kinase and RalGDS

Liquid-state 31P NMR spectroscopy is a well-established method for the study of guanine nucleotide-binding proteins (GNB proteins) such as the proto-oncogene Ras. Solid-state 31P NMR spectroscopy could meanwhile also be used to study microcrystalline samples of Ras as well as its partial loss-of-function mutants Ras(T35S) and Ras(T35A). However, solid-state NMR studies of the latter mutants in complex with effector molecules such as RalGDS or Raf kinase were so far prevented, since it has been impossible to crystallize these complexes yet. The aim of the present contribution is to make such complexes accessible to solid-state 31P NMR spectroscopy by the application of precipitation methods. The complex formed by Ras(T35S) and Raf kinase is preserved during precipitation. In contrast, the weakly bound complex of Ras(T35S) with RalGDS is dissociated or at least perturbed by the precipitation procedure. Solid-state 31P NMR experiments on precipitates of these complexes deliver spectra of high resolution and signal-to-noise ratio which allows the application of two-dimensional techniques. Precipitates prepared using polyethylene glycol 6000 (PEG) as precipitant were found to exhibit spectra of maximum resolution and signal-to-noise ratio. Interestingly, the 31P signal due to the alpha-phosphate of GppNHp bound to Ras(T35S) in crystalline samples or aged precipitates has a significantly different isotropic chemical shift than in the liquid state or in freshly prepared precipitates. This directly indicates that the crystal structure differs from the equilibrium solution structure at least in the neighborhood of the alpha-phosphate group.     

A comparative study of neighbouring group effects on the isomerization of imines in platinum-imine complexes by 1H, 13C, 31P and 195Pt NMR spectroscopy

¹⁹⁵Pt-, ³¹P-, ¹³C- and ¹H-chemical shifts are reported for the first time for complexes of the type trans-[PtCl₂ (η²-C₂H₄) (imine)], I, trans-[PtCl₂ (η²-C₂H₄) (amine)] II, and trans-[PtCl₂(PR′₃) (imine)] III (the imine ligand being derived from cyclopropyl-2-thienylketone and primary amines; PR′₃ = PBuⁿ₃ and PPh₃; amine; the amine ligand obtained by the reduction of the appropriate imine). The use of multinuclear spectroscopy provides strong evidence for E-Z isomerization of imine ligands coordinated to platinum (II) of the type trans-[PtCl₂ (η²-C₂H₄)(imine)]. Tertiary phosphine ligands trans to imine ligand (III) are not strongly labilizing groups, in contrast to η²-C₂H₄, which shows a strong labilizing effect. The effect of neighbouring groups on E-Z isomerization indicates that increase of the bulky substituents close to the imino group tends to increase the rate of isomerization, and increasing the degree of substitution on the imine carbon atoms slows the rate of isomerization. Furthermore, addition of a trace of amine will catalyze the E-Z isomerization. Also, isomerization takes place in the liquid state to give one isomer during the coordination with platinum.     

31P magic angle spinning NMR spectroscopy of paramagnetic rare-earth-substituted Keggin and Wells-Dawson solids

Paramagnetic rare-earth elements have been examined as NMR structural probes in polyoxoanionic solids, which have a variety of applications as luminescent materials that are usually disordered and therefore intractable by traditional structural methods. Thirteen Keggin and Wells-Dawson polyoxotungstates containing substitutions with lanthanides of different effective magnetic moments have been examined by 31P magic angle spinning NMR spectroscopy. The electron-nuclear dipolar interaction dominating the spinning sideband envelopes is determined by the lanthanide's magnetic moment and was found to be a sensitive probe of the nature of the polyoxoanion, of the positional isomerism, and of the ion stoichiometry. Electron-nuclear dipolar anisotropies computed based on the point-dipole approximation are generally in good agreement with the experimental results. The choice of a specific lanthanide as a structural probe can be tailored to the desired distance range between the phosphorus atoms and the paramagnetic centers to be probed. This approach is expected to be particularly useful in the paramagnetic polyoxoanionic materials lacking long-range order.