31P NMR Chemical Shifts Research Articles

Crystallinity and compositional changes in carbonated apatites: Evidence from 31P solid-state NMR, Raman, and AFM analysis.

Solid-state (magic-angle spinning) NMR spectroscopy is a useful tool for obtaining structural information on bone organic and mineral components and synthetic model minerals at the atomic-level. Raman and 31P NMR spectral parameters were investigated in a series of synthetic B-type carbonated apatites (CAps). Inverse 31P NMR linewidth and inverse Raman PO43- ν1 bandwidth were both correlated with powder XRD c-axis crystallinity over the 0.3-10.3 wt% CO32- range investigated. Comparison with bone powder crystallinities showed agreement with values predicted by NMR and Raman calibration curves. Carbonate content was divided into two domains by the 31P NMR chemical shift frequency and the Raman phosphate ν1 band position. These parameters remain stable except for an abrupt transition at 6.5 wt% carbonate, a composition which corresponds to an average of one carbonate per unit cell. This near-binary distribution of spectroscopic properties was also found in AFM-measured particle sizes and Ca/P molar ratios by elemental analysis. We propose that this transition differentiates between two charge-balancing ion-loss mechanisms as measured by Ca/P ratios. These results define a criterion for spectroscopic characterization of B-type carbonate substitution in apatitic minerals.

Coplanar Tetracyclic π‐Excess σ2P Ligands

AbstractThe acid‐catalyzed reactions of 5‐methyl‐2‐phosphanylaniline (1) with dialdehydes were studied. Whereas the reaction with glyoxal provides a mixture of two 1H‐1,3‐benzazaphospholes, 2 and 3, by concomitant reduction of a CHO group and C–C bond cleavage, respectively, the reaction with o‐phthalic dicarbaldehyde provided in excellent yield the tetracyclic planar benzazaphosphole 4, which was characterized by crystal structure analysis. The active hydrogen atoms, delivered by aromatization of a dihydrobenzazaphosphole intermediate, forms an N–CH2 bridge by reductive N‐alkylation. Pyridine‐2,6‐dicarbaldehyde reacts analogously but not chemoselectively and, thus, gives two isomers 5 and 6. Condensation with pyridine‐2,6‐dicarbaldehyde afforded the bis(benzazaphosphole)pyridine pincer ligand 7, but along with 2‐(benzazaphospholyl)‐6‐tolylpyridine (8) by partial P–C bond cleavage. The high upfield 31P NMR chemical shift of 4 compared to those of normal benzazaphospholes indicates it to be a particularly π‐rich σ2P ligand.

The synthesis and characterization of 4-isopropylanilino derivatives of cyclotriphosphazene

Hexachlorocyclotriphosphazene N3P3Cl6 and gem-disubstituted cyclotriphosphazene derivatives N3P3Cl4X2 (X=Ph, PhS, PhNH) were reacted with 4-isopropylaniline to give geminal tetra and hexa substituted compounds (1a–4a, 1b–4b). The compounds (1a–4a, 1b–4b) were separated by column chromatography on silica gel and analyzed by elemental analysis, mass spectrometry, and 31P and 1H NMR spectroscopies, and also crystal structures of 2a and 3b were determined by X-ray crystallography. Compounds were prepared to cover the normal ranges of C-, S- and N-substituents in cyclophosphazene (X=Cl, Ph, SPh, NHPh). Compounds (1a–4a, 1b–4b) were reported for the first time. We additionally investigated the effect of substituent (Cl, Ph, SPh, NHPh) on 31P NMR chemical shifts of neighboring phosphorus atoms.

31P solid-state NMR based monitoring of permeation of cell penetrating peptides into skin

The main objective of the current study was to investigate penetration of cell penetrating peptides (CPPs: TAT, R8, R11, and YKA) through skin intercellular lipids using 31P magic angle spinning (MAS) solid-state NMR. In vitro skin permeation studies were performed on rat skin, and sections (0–60, 61–120, and 121–180μm) were collected and analyzed for 31P NMR signal. The concentration-dependent shift of 0, 25, 50, 100, and 200mg/ml of TAT on skin layers, diffusion of TAT, R8, R11, and YKA in the skin and time dependent permeation of R11 was measured on various skin sections using 31P solid-state NMR. Further, CPPs and CPP-tagged fluorescent dye encapsulate liposomes (FLip) in skin layers were tagged using confocal microscopy. The change in 31P NMR chemical shift was found to depend monotonically on the amount of CPP applied on skin, with saturation behavior above 100mg/ml CPP concentration. R11 and TAT caused more shift in solid-state NMR peaks compared to other peptides. Furthermore, NMR spectra showed R11 penetration up to 180μm within 30min. The results of the solid-state NMR study were in agreement with confocal microscopy studies. Thus, 31P solid-state NMR can be used to track CPP penetration into different skin layers.

Intrinsic 31P NMR Chemical Shifts and the Basicities of Phosphate Groups in a Short-Chain Imino Polyphosphate

The stepwise protonation constants of two linear triphosphate ligand anions, triphosphate, {text{P}}_{3} {text{O}}_{10} ^{5 - } and di-imidotriphosphate, {text{P}}_{3} {text{O}}_{8} left( {text{NH}} right)_{2}^{5 - } , were investigated by potentiometric titration, and the intrinsic chemical shifts of the stepwise protonated species of these anions were determined from the pH-dependence of the 31P NMR chemical shifts. All stepwise protonation constants of {text{P}}_{3} {text{O}}_{8} left( {text{NH}} right)_{2}^{5 - } were found to be larger than those of {text{P}}_{3} {text{O}}_{10}^{5 - } , and the 31P NMR signals due to P3O8(NH)2 always appeared at a lower magnetic field compared to the signals due to P3O10. These results indicate higher basicity of the P3O8(NH)2 ligand, because it contains two imino groups in the ligand molecule. The 31P NMR signals for the end phosphate groups appear at a lower magnetic field than those for the middle phosphate groups, indicating that the basicity of the end phosphate group is higher than that of the middle phosphate group. It can be expected that the high basicity of the P3O8(NH)2 ligand brings about the formation of high stability complexes with various metal ions. Furthermore, the only 31P NMR signal due to the middle phosphate group of P3O8(NH)2 ligand molecule clearly showed a low-field shift in the range of pH < 2.5. The reason for this peculiar low-field shift should be the change of the localization of imino protons around the nitrogen atom in P3O8(NH)2.Graphical

Slow tumbling but large protrusion of phospholipids in the cell sized giant vesicle

Lipid membrane dynamics in cell sized vesicles (CSVs) in water is characterized by the solution-state NMR. CSV is successfully prepared by natural swelling method using osmotic effect. Broad 1H NMR signal and large 31P NMR chemical shift anisotropy show the slow tumbling of the lipid with the rotational correlation time 0.2–2.8s in CSV of 10–20μm-diameters. The 1H–1H nuclear Overhauser effect enhancement reveals the proximity between the lipid headgroup and alkyl chains, in which the close distance, ∼0.4nm. The proximity is due to the large protrusion of the lipids in the vertical direction to the CSV surface.

Acceptor number of halogenated solvents and its potential as a criterion for the ability of halogen bonding as a specific solvent effect using the 31P NMR chemical shift of triethylphosphine oxide as a probe

Acceptor numbers (AN) of several halogenated and perfluorohalogenated solvents were determined using 31P NMR of triethylphosphine oxide (Et3PO) as a probe. The halogen and/or hydrogen bonding complex, C–X⋯OPEt3 or C–H⋯OPEt3, between the probe and solvent molecules was simulated by MP2 and DFT methods. The halogen bonding energies of perfluorohalogenated solvents and iodobenzene with the probe show a good linear correlation to the AN. The results indicate that the AN can act as a possible criterion for the ability of halogen bonding as a specific solvent effect.

Differently Saturated Fatty Acids Can Be Differentiated by 31P NMR Subsequent to Derivatization with 2-Chloro-4,4,5,5-tetramethyldioxaphospholane: A Cautionary Note

The analysis of free fatty acid (FFA) mixtures is a very important but, even nowadays, challenging task. This particularly applies as the so far most commonly used technique-gas chromatography/mass spectrometry (GC/MS)-is tedious and time-consuming. It has been convincingly shown ( Spyros, A.; Dais, P. J. Agric. Food Chem. 2000, 48, 802 - 5) that FFA may be analyzed by (31)P NMR subsequent to derivatization with 2-chloro-4,4,5,5-tetramethyldioxaphospholane (CTDP). However, it was also indicated that differently unsaturated FFAs result in the same (31)P NMR chemical shift and cannot be differentiated. Therefore, only the overall fatty acid content of a sample can be determined by the CTDP assay. In contrast, we will show here by using high-field NMR (600 MHz spectrometer, i.e., 242.884 MHz for (31)P) that the CTDP assay may be used to differentiate FFAs that have pronounced differences in their double bond contents: saturated fatty acids (16:0), moderately unsaturated (18:1, 18:2), highly unsaturated (20:4), and extremely unsaturated fatty acids (22:6) result in slightly different chemical shifts. The same applies for oxidized fatty acids. Finally, it will also be shown that the CTDP derivatization products decompose in a time-dependent manner. Therefore, all investigations must adhere to a strict time regime.

Tuning the Homo–Lumo Gap in Π-Bridged Bis(Phosphaalkenes)

The HOMO–LUMO gap in a series of π-bridged bis(phosphaalkenes) is investigated by theoretical methods. The deshielding of the experimental 31P-NMR chemical shifts of a selection of these compounds does not correlate with a decrease of their calculated HOMO–LUMO gaps.

Synthesis, characterization, thermal, electrochemical, and DFT studies of mononuclear cyclopalladated complexes containing bidentate phosphine ligands and their biological evaluation as antioxidant and antibacterial agents

Abstract The non-symmetric phosphorus ylides and their Pd(II) complexes have been synthesized as potential antioxidant and antibacterial compounds and their structures were elucidated using a variety of physicochemical techniques. The reaction of 1 equiv non-symmetric phosphorus ylides, Ph2PCH2PPh2C(H)C(O)PhX (X = Br (Y1), Cl (Y2), NO2 (Y3), OCH3 (Y4)) with [Pd(dppe)Cl2] (M1), followed by treatment with 2 equiv AgOTf led to monomeric chelate complexes, [(dppe)Pd(Ph2PCH2PPh2C(H)C(O)PhX)] (OSO2CF3)2 (X = Br (C1), Cl (C2), NO2 (C3), OCH3 (C4)), which contain a five-membered P,P chelate ring in one side and a five-membered P,C chelate ring in the other side. Palladium ion complexes were synthesized and investigated by cyclic voltammetry, FT-IR, UV–visible, multinuclear (1H, 31P and 19F) NMR, thermal analysis and ESI-mass spectroscopic studies. Some complexes and ligands have been studied by powder XRD and single crystal X-ray diffraction techniques. FT-IR and 31P NMR studies revealed that the ylides Y are coordinated to the metal ions via the terminal phosphorus (Pc) of the ylides and methene group (CH). The proposed coordination geometry around the Pd atom in these complexes is defined as slightly distorted square planar by UV-Visible and DFT studies. Thermal stability of all complexes was also shown by TG/DTG methods. Furthermore, the electrochemical behavior of the complexes was investigated by cyclic voltammetry. The results indicate that all complexes are successfully synthesized from the initial ligands. All complexes were analyzed for their antioxidant properties by DPPH free radical scavenging assay. In addition, the antibacterial effects of the hexane-solved complexes were investigated by disc diffusion method against four Gram positive and negative bacteria. All complexes represented antibacterial activity against bacteria tested especially on Gram positive ones. A theoretical study on the structure, 1H and 31P NMR chemical shifts and the interaction energy between the Pd2+ ion and ligands dppe and ylide Y is also reported.

Quantum-chemical calculations of chemical shifts in NMR spectra of organic molecules: V. Stereochemical structure of unsaturated phosphonic acids dichlorides from 31P NMR spectral data

The stereochemical structure of unsaturated phosphonic acids dichlorides containing fragments C=C-POCl2 and C=N-POCl2 was investigated by 31P NMR spectroscopy and quantum chemistry. Starting from the experimental measurement and theoretical calculation of 31P NMR chemical shifts configurations were assigned and the conformational composition of compounds under study was determined.

Scalar Relativistic Computations and Localized Orbital Analyses of Nuclear Hyperfine Coupling and Paramagnetic NMR Chemical Shifts.

A method is reported by which calculated hyperfine coupling constants (HFCCs) and paramagnetic NMR (pNMR) chemical shifts can be analyzed in a chemically intuitive way by decomposition into contributions from localized molecular orbitals (LMOs). A new module for density functional calculations with nonhybrid functionals, global hybrids, and range-separated hybrids, utilizing the two-component relativistic zeroth-order regular approximation (ZORA), has been implemented in the parallel open-source NWChem quantum chemistry package. Benchmark results are reported for a test set of few-atom molecules with light and heavy elements. Finite nucleus effects on (199)Hg HFCCs are shown to be on the order of -11 to -15%. A proof of concept for the LMO analysis is provided for the metal and fluorine HFCCs of TiF3 and NpF6. Calculated pNMR chemical shifts are reported for the 2-methylphenyl-t-butylnitroxide radical and for five cyclopentadienyl (Cp) sandwich complexes with 3d metals. Nickelocene and vanadocene carbon pNMR shifts are analyzed in detail, demonstrating that the large carbon pNMR shifts calculated as +1540 for Ni (exptl.: +1514) and -443 for V (exptl.: -510) are caused by different spin-polarization mechanisms. For Ni, Cp to Ni π back-donation dominates the result, whereas for vanadocene, V to Cp σ donation with relaxation of the carbon 1s shells can be identified as the dominant mechanism.

Pt L2,3 - Edge X-ray absorption spectroscopy investigation of zerovalent [Pt(PPh3)2(η2-L)] {L = C2H4, C60 and C2(CN)4} compounds

X-ray absorption spectra at the Pt L2,3-edges have been measured for three [Pt(PPh3)2(η2-L)] {L = C2H4, C60 and C2(CN)4} compounds. The spectral features are effective for measuring the π*-acid strength of ligands (L) coordinated to the Pt(PPh3)2 fragment. The energies of the dπ-orbitals are quantitatively determined using the difference between the edge jumping and the edge maximum shifts of the L2,3-white lines in the second derivatives of the spectra. The dπ-orbital energies follow the order [Pt(PPh3)2(η2-C2H4)] < [Pt(PPh3)2(η2-C60)] < [Pt(PPh3)2{η2-C2(CN)4}]. These dπ-orbital energies are in good agreement with the changes in the bound olefinic carbon bond lengths and the 31P NMR chemical shifts of the coordinated phosphines. Furthermore, the experimental values are in good agreement with available dπ-orbital interaction energy terms calculated using density functional theory for model [Pt(PH3)2(η2-L)] compounds.

Quantum-chemical calculations of NMR chemical shifts of organic molecules: IV. Effect of intermolecular coordination on 31P NMR shielding constants and chemical shifts of molecular complexes of phosphorus pentachloride with azoles

Intermolecular coordination effects on the 31P NMR spectra of molecular complexes of N-vinylimidazole and 1-allyl-3,5-dimethylpyrazole with phosphorus pentachloride were studied by theoretical and experimental methods. The formation of intermolecular dative N→P bond was shown to be accompanied by upfield shift of the phosphorus resonance signal by more than 200 ppm. Appreciable contribution of relativistic effects to 31P NMR chemical shifts was revealed; the spin-orbital contribution to 31P shielding constant was estimated at >210 ppm. Consideration of solvent effect was found to be crucial while studying steric structure of molecular complexes of azoles with phosphorus pentachloride and intermolecular coordination effects on 31P NMR chemical shifts.

Quantum-chemical calculation of NMR chemical shifts of organic molecules: III. Intramolecular coordination effects on the 31P NMR chemical shifts of phosphorylated N-vinylazoles

Theoretical and experimental studies on magnetic shielding of the phosphorus nucleus in trichloro-[2-(1H-pyrazol-1-yl)ethenyl]phosphonium hexachlorophosphate(V) and 1,1,1,1-tetrachloro-1H-1λ6-pyrazolo-[1,2-a][1,2,3]diazaphosphol-8-ium-1-ide showed that intramolecular coordination of the phosphorus atom in the chlorophosphonium group to the nitrogen atom in the pyrazole ring leads to upfield shift of the phosphorus signal (to δP 170 ppm) and that the contribution of the spin-orbital contribution to the 31P chemical shift reaches 15%. Relativistic effects and effects of the medium are determining in the theoretical calculation of 31P NMR chemical shifts.

Interaction of hydrated protons with octyl-phenyl-N,N-diisobutylcarbamoylmethyl phosphine oxide (CMPO): NMR and theoretical study

Interaction of octyl-phenyl-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO, the 'classical' rare metal extraction agent) with fully ionized hydrated protons (HP) was studied in acetonitrile-d(3) using (1)H, (13)C, (31)P NMR, PFG NMR and magnetic relaxation. The experimental results were confronted with high-precision ab initio DFT calculations. Relative chemical shifts of NMR signals of CMPO (0.01 mol/L) under the presence of HP in the molar ratio β = 0-2.0 mol/mol show binding between CMPO and HP. Self-diffusion measurements using (1)H PFG NMR demonstrate that larger complexes with higher content of CMPO are generally formed at β < 0.75. Analyzing the collective dependence of (13)C and (31)P NMR chemical shifts on β by the use of program LETAGROP, we obtained very good fitting for the assumed coexistence of two complexes (CMPO)(2)·HP (C(2)) and CMPO.HP (C(1)). The logarithms of the respective stabilization constants log K(i) were found to be 7.518 (C(2)) and 4.581 (C(1)). The system dynamics was studied by measuring the transverse (1)H NMR relaxation using CPMG sequence with varying delays t(p) between the π pulses in the mixtures with β = 0.4-0.8. The following exchange correlation times were obtained: τ(10) = 2.35 × 10(-5), τ(20) = 0.82 × 10(-4), τ(21) = 0.45 × 10(-3) s. The DFT calculations support the conclusion that the complexes C(1) and C(2) are the main species in the mixtures of CMPO with HP. They also agree with the NMR and FTIR observation that the main site to which H(3) O(+) is bound is the P=O group, whereas the amide group does not form a strong bond with the ion when excess water molecules are present.

Prediction of 31P-NMR Chemical Shifts Using Empirical Models with Modest Methods and Optimally Selected Basis Sets

The performance of the ab initio and density functional theory (DFT) functional, B3LYP and PBEPBE, in conjunction with selected basis sets for the prediction of 31P shielding constants for small phosphorous-containing molecules is assessed. The effects of applied factors are discussed. By including the electron correlation treatment, B3LYP and PBEPBE are the most accurate methods to compute the chemical shielding for a set of small phosphines that was studied. Also, additional improvements of DFT were obtained by empirical scaling of basis sets in calculation of chemical shifts. For molecules containing only phosphorous and carbon atoms with sp3 hybridization, the PBEPBE/6-311G(d,p) level of theory has been shown to provide reliable 31P chemical shifts. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. GRAPHICAL ABSTRACT

Crystalline O, O′-di- sec-butyl and O, O′-diethyl dithiophosphate platinum(II) complexes: Synthesis, 13C and 31P CP/MAS NMR, single crystal X-ray diffraction studies and thermal behaviour

Crystalline bis( O, O′-di- sec-butyldithiophosphato)platinum(II) was prepared and studied by means of 13C, 31P CP/MAS NMR spectroscopy and single-crystal X-ray diffraction. The unit cell of the platinum(II) compound is comprised of one centrosymmetric mononuclear molecule [Pt{S 2P(O- sec-C 4H 9) 2} 2], in which the dithiophosphate groups display structural equivalence in both 31P NMR and XRD data. A pair of the dithiophosphate ligands exhibit the same S, S′-bidentate chelating structural function and form two planar four-membered chelate rings, [PtS 2P], in this molecule. The planar configuration of the [PtS 4] chromophore in structure 1 is governed by the dsp 2-hybrid state of platinum(II). The structural states of the dithiophosphate groups in two different samples of complex 1 (one crystallised from ethanol and the other one precipitated from an aqueous solution) are all characterised by almost rhombic 31P chemical shift tensors. The observed essential dispersion of the 31P NMR chemical shift is caused by a coexistence of six optical isomers of molecule 1. The thermal behaviour of this compound was studied by means of simultaneous thermal analysis (a combination of TG and DSC) under an argon atmosphere. The thermal behaviour shows that the mass of 1 is lost in three steps, involving successive thermal decompositions of the organic and inorganic parts of this compound with platinum(II) dithio- meta-phosphate and reduced metallic platinum as the intermediate and the final products, respectively.

Quantum-chemical calculations of NMR chemical shifts of organic molecules: II. Influence of medium, relativistic effects, and vibrational corrections on phosphorus magnetic shielding constants in the simplest phosphines and phosphine chalcogenides

The influence of solvent nature, relativistic effects, and vibrational corrections on the accuracy of calculation of 31P chemical shifts of the simplest phosphines, phosphine oxides, phosphine sulfides, and phosphine selenides was studied. Consideration of the above factors at the stage of both geometry optimization and calculation of magnetic shielding constants was found to appreciably improve the accuracy of calculation of 31P NMR chemical shifts in the series of phosphines and phosphine chalcogenides.

QUANTUM CHEMISTRY STUDIES ON THE Fe-Hg INTERACTIONS AND 31P NMR IN [Fe(CO)3(RPhPpy)2 (HgCl2)] (R = Me, Et, Ph)

In order to study the effects of R group on Fe-Hg interactions and 31P NMR, the structures of mononuclear complexes [Fe(CO)3(RPhPpy)2] (1: R = Me; 2: R = Et; 3: R = Ph) and binuclear complexes [Fe(CO)3(RPhPpy)2(HgCl2)] (4: R = Me; 6: R = Et; 6: R = Ph) were calculated by density functional theory (DFT) PBE0 method. Moreover, the 31P NMR chemical shifts were calculated by PBE0-GIAO method. The replacement of Ph group in Ph2Ppy ligands with Me or Et group results in higher stabilities and stronger Fe-Hg interactions. The stabilities of binuclear complexes follow the order of 5 &gt; 4 &gt;6. Although the electrostatic interactions in 5 are weaker, the weaker repulsion interactions and stronger orbital interactions lead to the highest stability. The strength of Fe → Hg interactions, which mainly attribute to σFe-P → nHg and σFe-C → nHg charge-transfer interactions, follows the order of 5 &gt; 4 &gt; 6. The 31P NMR chemical shifts in mononuclear complexes 1 ~ 3 or binuclear complexes 4 ~ 6 increase with the increase of electron-withdrawing effect of R group following the order of Me &lt; Et &lt; Ph. Due to Fe → Hg interactions, the charge-transfer from R groups towards the P , Fe and Hg atoms increases the electron density on P nucleus in binuclear complexes. Besides, the stronger σFe-C → nP charge-transfer in binuclear complexes can also increase the electron density of P nucleus. As a result, compared with corresponding mononuclear complexes, the 31P chemical shifts in binuclear complexes show some reduction.