Cation exchange at the mineral-water interface: H3O+/K+ competition at the surface of nano-muscovite

This article describes a (39)K nuclear magnetic resonance (NMR) spectroscopic study of K (+) displacement at the muscovite/water interface as a function of aqueous phase pH. (39)K NMR spectra and T 2 relaxation data for nanocrystalline muscovite wet with a solid/solution weight ratio of 1 at pH 1, 3, and 5.5 show substantial liquid-like K (+) only at pH 1. At pH 3 and 5.5, all K (+) appears to be associated with muscovite as inner- or outer-sphere complexes, indicating that H 3O (+) does not displace basal surface K (+) beyond the (39)K detection limit under these conditions. In our pH 1 mixture, only approximately 1/3 of the initial basal surface K (+) population is located more than 3-4 A from the surface. (29)Si and (27)Al MAS NMR spectra and SEM images show no evidence of dissolution during the (39)K experiments, consistent with the liquid-like (39)K fraction originating from displaced basal surface K (+). Assuming no muscovite dissolution or interlayer exchange, the K (+)/H 3O (+) ratio relevant to the solution/surface exchange equilibrium is controlled by the total amount of K (+) on the surface and H 3O (+) in solution (K (+) surf/H 3O (+) aq). These parameters, in turn, depend on the basal surface area, solution pH, and the solid/solution ratio. The results here are consistent with significant displacement of surface K (+) only under conditions where the initial K (+) surf/H 3O (+) aq ratio is less than approximately 1. Computational molecular models of the muscovite/water interface should account for both K (+) and H 3O (+) in the near-surface region.     

Model and simulation of Na+/K+ pump phosphorylation in the presence of palytoxin

The ATP hydrolysis reactions responsible for the Na(+)/K(+)-ATPase phosphorylation, according to recent experimental evidences, also occur for the PTX-Na(+)/K(+) pump complex. Moreover, it has been demonstrated that PTX interferes with the enzymes phosphorylation status. However, the reactions involved in the PTX-Na(+)/K(+) pump complex phosphorylation are not very well established yet. This work aims at proposing a reaction model for PTX-Na(+)/K(+) pump complex, with similar structure to the Albers-Post model, to contribute to elucidate the PTX effect over Na(+)/K(+)-ATPase phosphorylation and dephosphorylation. Computational simulations with the proposed model support several hypotheses and also suggest: (i) phosphorylation promotes an increase of the open probability of induced channels; (ii) PTX reduces the Na(+)/K(+) pump phosphorylation rate; (iii) PTX may cause conformational changes to substates where the Na(+)/K(+)-ATPase may not be phosphorylated; (iv) PTX can bind to substates of the two principal states E1 and E2, with highest affinity to phosphorylated enzymes and with ATP bound to its low-affinity sites. The proposed model also allows previewing the behavior of the PTX-pump complex substates for different levels of intracellular ATP concentrations.     

A study of C-F.M+ interaction: alkali metal complexes of the fluorine-containing cage compound

The C-F.M(+) interaction was investigated by employing a cage compound 1 that has four fluorobenzene units. The NMR ((1)H, (13)C, and (19)F) spectra and X-ray crystallographic analyses of 1 and its metal complexes showed clear evidence of the interaction. Short C-F.M(+) distances (C-F.K(+), 2.755 and 2.727 A; C-F.Cs(+), 2.944 and 2.954 A) were observed in the crystalline state of K(+) subset 1 and Cs(+) subset 1. Furthermore, the C-F bond lengths were elongated by the interaction with the metal cations. By calculating Brown's bond valence, it is shown that the contribution of the C-F unit to cation binding is comparable or greater than the ether oxygen in the crystalline state. Representative spectroscopic changes implying the C-F.M(+) interaction were observed in the NMR ((1)H, (13)C, and (19)F) spectra. In particular, (133)Cs-(19)F spin coupling (J = 54.9 Hz) was observed in the Cs(+) complex.     

Inhibition of gastric H+, K(+)-ATPase activity by compounds from medicinal plants

H+, K(+)-ATPase enzyme is a therapeutic target for the treatment of gastric disturbances. Several medicinal plants and isolated compounds inhibit the acid gastric secretion through interaction with the proton pump. In order to add new properties to some natural constituents, five compounds, a benzylated derivative of vincoside, a diterpene (abietic acid) and three alkaloids (cephaeline, vinblastine and vindoline), were tested for their activities on gastric H+, K(+)-ATPase isolated from rabbit stomach. All the compounds inhibited H+, K(+)-ATPase activity with varied potency. The IC50 value for benzylvincoside was 121 (50-293) microM, and for abietic acid 177 (148-211) microM. The alkaloids cephaeline, vinblastine and vindoline inhibited the H+, K(+)-ATPase activity with IC50 values of 194, 761 and 846 microM, respectively. The results suggest that benzylvincoside, abietic acid and cephaeline can be important sources for the development of anti-secretor agents.     

Synthesis and structure-activity relationships of N-substituted 2-[(2-imidazolylsulfinyl)methyl]anilines as a new class of gastric H+/K(+)-ATPase inhibitors.

A series of N-substituted 2-[(2-imidazolylsulfinyl)methyl]anilines (3) was synthesized and evaluated for its biological activity against gastric H+/K(+)-ATPase prepared from rabbit stomach and gastric acid secretions in Heidenhain pouch dogs. Monoalkyl substituents on the nitrogen atom of the aniline moiety markedly inhibited the enzyme activity to the same degree as omeprazole, a representative H+/K(+)-ATPase inhibitor. Most of these compounds, administered at 3 mg/kg i.v. inhibited histamine-stimulated gastric acid secretion. The inhibitory activity of these derivatives on the enzymes at pH 6.0 was more potent than that at pH 7.4, and was distinctly correlated to stability in aqueous solution at pH 5.0.     

Experimental validation of theoretical potassium and sodium cation affinities of amides by mass spectrometric kinetic method measurements

In this study the theoretical Gaussian-2 K(+)/Na(+) binding affinities (enthalpies) at 0 K (in kJ mol(-1)) for six amides in the order: formamide (109.2/138.5) < N-methylformamide (117.7/148.6) < acetamide (118.7/149.5) < N,N-dimethylformamide (123.9/156.4) < N-methylacetamide (125.6/157.7) < N,N-dimethylacetamide (129.2/162.6), reported previously (Siu et al., J. Chem. Phys. 2001; 114: 7045-7051), were validated experimentally by mass spectrometric kinetic method measurements. By monitoring the collision-induced dissociation (CID) of K(+)/Na(+)-bound heterodimers of the amides, the relative affinities were shown to be accurate to within +/-2 kJ mol(-1). With these six theoretical K(+)/Na(+) binding affinities as reference values, the absolute K(+)/Na(+) affinities of imidazole, 1-methylimidazole, pyridazine and 1,2-dimethoxyethane were determined by the extended kinetic method, and found to be consistent (to within +/-9 kJ mol(-1)) with literature experimental values obtained by threshold-CID, equilibrium high-pressure mass spectrometry, and Fourier transform ion cyclotron resonance/ligand-exchange equilibrium methods. A self-consistent resolution is proposed for the inconsistencies in the relative order of K(+)/Na(+) affinities of amides reported in the literature. These two sets of validated K(+) and Na(+) affinity values are useful as reference values in kinetic method measurements of K(+)/Na(+) affinity of model biological ligands, such as the K(+) affinities of aliphatic amino acids.     

Effect of SiO2 on the dynamics of proton conducting [Nafion/(SiO2)X] composite membranes: a solid-state 19F NMR study

Composite membranes, consisting of Nafion and inorganic oxide additives, are frequently discussed alternative materials to overcome the known low conductivity of pure Nafion at temperatures above 100 °C and at low relative humidity. It has been reported that under dry conditions, these membranes show enhanced water uptake and diffusion as compared to filler-free Nafion. This work focuses on the polymer mobility in Nafion/SiO(2) composites and on the impact of the silica particles on the polymer dynamics. [Nafion/(SiO(2))(X)] composite membranes (with X ranging from 0 to 15 wt%) in the dry and wet states were investigated by variable temperature solid-state (19)F NMR spectroscopy. (19)F T(1) and T(1ρ) relaxation times, and NMR lineshapes (linewidths and spinning sideband intensities) were analyzed to get information about the polymer mobility. It is found that Nafion composite membranes, in general, possess a higher mobility as compared to recast Nafion which is in agreement with previous results from conductivity studies. These findings are attributed to the ability of the SiO(2) particles to keep more water inside the composite membranes which also leads to a higher mobility of the polymer component. The results are further supported by the experimental (19)F{(1)H} CP/MAS NMR spectra. It is also shown that the structure of the composite membranes is more stable after dehydration, and possible condensation reactions are diminished in these membranes. In addition, the decrease in ionic exchange capacity after dehydration is less pronounced for the composite membranes as compared to filler-free Nafion.     

Solid‐state 1H → 19F/19F → 1H CP/MAS NMR study of poly(vinylidene fluoride)

Solid‐state ¹H → ¹⁹F and ¹⁹F → ¹H cross‐polarization magic angle spinning (CP/MAS) NMR spectra have been investigated for a semicrystalline fluoropolymer, namely poly(vinylidene fluoride) (PVDF). The ¹H → ¹⁹F CP/MAS spectra can be fitted by five Lorentzian functions, and the amorphous peaks were selectively observed by the DIVAM CP pulse sequences. Solid‐state spin‐lock experiments showed significant differences in T_1ρ^F and T_1ρ^H between the crystalline and amorphous domains, and the effective time constants, T_HF* and T_1ρ*, which were estimated from the ¹H → ¹⁹F CP curves, also clarify the difference in the strengths of dipolar interactions. Heteronuclear dipolar oscillation behaviour is observed in both standard CP and ¹H → ¹⁹F inversion recovery CP (IRCP) experiments. The inverse ¹⁹F → ¹H CP‐MAS and ¹H → ¹⁹F CP‐drain MAS experiments gave complementary information to the standard ¹H → ¹⁹F CP/MAS spectra in a manner reported in our previous papers for other fluoropolymers. The value of N_F/N_H (where N is a spin density) estimated from the CP‐drain curve is within experimental error equal to unity, which is consistent with the chemical structure. Copyright © 2001 John Wiley & Sons, Ltd.     

51V magic angle spinning NMR spectroscopy of Keggin anions [PVnW12-nO40](3+n)-: effect of countercation and vanadium substitution on fine structure constants

Vanadium environments in Keggin oxopolytungstates were characterized by (51)V solid-state MAS NMR spectroscopy. (C(4)H(9))(4)N(+)-, K(+)-, Cs(+)-, as well as mixed Na(+)/Cs(+)- salts of the mono-, di-, and trivanadium substituted oxotungstates, [VW(11)O(40)](4-), [V(2)W(10)O(40)](5-), and [V(3)W(9)O(40)](6-), have been prepared as microcrystalline and crystalline solids. Solid-state NMR spectra report on the local environment of the vanadium site in these Keggin ions via their anisotropic quadrupolar and chemical-shielding interactions. These (51)V fine structure constants in the solid state are determined by the number of vanadium atoms present in the oxoanion core. Surprisingly, the quadrupolar anisotropy tensors do not depend to any significant extent on the nature of the countercations. On the other hand, the chemical-shielding anisotropy tensors, as well as the isotropic chemical shifts, display large variations as a function of the cationic environment. This information can be used as a probe of the local cationic environment in the vanadium-substituted Keggin solids.     

Tripartilactam, a cyclobutane-bearing tricyclic lactam from a Streptomyces sp. in a dung beetle's brood ball

Tripartilactam, a structurally unprecedented cyclobutane-bearing tricyclic lactam metabolite, was discovered from Streptomyces sp. isolated from a brood ball of the dung beetle, Copris tripartitus. The structure of this compound was elucidated by the combination of NMR, MS, UV, and IR spectroscopy and multistep chemical derivatization. Tripartilactam was evaluated as a Na(+)/K(+) ATPase inhibitor (IC(50) = 16.6 μg/mL).     

Effect of phospholipase A2 on purified gastric vesicles.

The phospholipid and fatty acid composition and role of phospholipids in enzyme and transport function of gastric (H+ + K+)-ATPase vesicles was studied using phospholipase A2 (bee venom). The composition (%) was phosphatidyl-choline (PC) 33%; sphingomyelin (sph) 25%; phosphatidylethanolamine (PE) 22%; phosphatidylserine (PS) 11%; and phosphatidylinositol (PI) 8%. The fatty acid composition showed a high degree of unsaturation. In both fresh and lyophilized preparations, even with prolonged incubation, only 50% of phospholipids were hydrolyzed, but the amount of PE and PS disappearing was increased following lyophilization. There was a marked decrease in K+-ATPase activity (75%) but essentially no loss of the associated K+ p-nitrophenyl phosphatase was found. ATPase activity could be largely restored by various phospholipids (PE greater than PC greater than PS). There was also an increase in Mg2+-ATPase activity, partially reversed in fresh preparations by the addition of phospholipids (PE greater than PS greater than PC). Proton transport activity of the preparation was rapidly inhibited, initially due to a large increase in the HCl permeability of the preparation. Associated with these enzymatic and functional changes, the ATP-induced conformational changes, as indicated by circular dichroism spectra were inhibited.     

Spectroscopic Identification of Adsorbed Intermediates Derived from the CO+H(2)O Reaction on Zeolite-Encapsulated Gold Catalysts

Identification of reaction intermediates in the water-gas shift reaction (WGSR: H(2)O+CO-->H(2)+CO(2)) on Au(n+) (1相似文献   

Investigating the potassium interactions with the palytoxin induced channels in Na+/K+ pump

K(+) has been appointed as the main physiological inhibitor of the palytoxin (PTX) effect on the Na(+)/K(+) pump. This toxin acts opening monovalent cationic channels through the Na(+)/K(+) pump. We investigate, by means of computational modeling, the kinetic mechanisms related with K(+) interacting with the complex PTX-Na(+)/K(+) pump. First, a reaction model, with structure similar to Albers-Post model, describing the functional cycle of the pump, was proposed for describing K(+) interference on the complex PTX-Na(+)/K(+) pump in the presence of intracellular ATP. A mathematic model was derived from the reaction model and it was possible to solve numerically the associated differential equations and to simulate experimental maneuvers about the PTX induced currents in the presence of K(+) in the intra- and extracellular space as well as ATP in the intracellular. After the model adjusting to the experimental data, a Monte Carlo method for sensitivity analysis was used to analyze how each reaction parameter acts during each experimental maneuver involving PTX. For ATP and K(+) concentrations conditions, the simulations suggest that the enzyme substate with ATP bound to its high-affinity sites is the main substate for the PTX binding. The activation rate of the induced current is limited by the K(+) deocclusion from the PTX-Na(+)/K(+) pump complex. The K(+) occlusion in the PTX induced channels in the enzymes with ATP bound to its low-affinity sites is the main mechanism responsible for the reduction of the enzyme affinity to PTX.     

Product binding to the diiron(III) and mixed-valence diiron centers of methane monooxygenase hydroxylase studied by (1,2)H and (19)F ENDOR spectroscopy

The binding of ethanol and 1,1,1-trifluoroethanol (TFE) to both the H(mv) and H(ox) forms of soluble methane monooxygenase (sMMO) in solution has been studied by Q-band (35 GHz) CW and pulsed ENDOR spectroscopy of (1)H, (2)H and (19)F nuclei of exogenous ligands. As part of this investigation we introduce (19)F, in this case from bound TFE, as a new probe for the binding of small molecules to a metalloenzyme active site. The H(mv) form was prepared in solution by chemical reduction of H(ox). For study of H(ox) itself, frozen solutions were subjected to gamma-irradiation in the frozen solution state at 77 K, which affords an EPR-visible mixed-valent diiron center, denoted (H(ox))(mv), held in the geometry of the diiron(III) state. The (19)F and (2)H ENDOR spectra of bound TFE together with (1,2)H ENDOR spectra of bound ethanol indicate that the alcohols bind close to the Fe(II) ion of the mixed-valence cluster in H(mv) and in a bridging or semi-bridging fashion to H(ox). DMSO does not affect the binding of either of the ethanols or of methanol to H(ox), nor of ethanol or methanol to H(mv). It does, however, displace TFE from the diiron site in H(mv). These results provide the first evidence that crystal structures of sMMO hydroxylase into which product alcohols were introduced by diffusion represent the structures in solution.     

Protective effect of Lagenaria siceraria (Mol) against membrane-bound enzyme alterations in isoproterenol-induced cardiac damage in rats

This study was aimed at evaluating the preventive role of the ethanolic extract of Lagenaria siceraria (Mol) fruit on membrane-bound enzymes, such as sodium potassium-dependent adenosine triphosphatase (Na(+)/K(+) ATPase), calcium-dependent adenosine triphosphatase (Ca(2+) ATPase) and magnesium-dependent adenosine triphosphatase (Mg(2+) ATPase) on isoproterenol (ISO)-induced myocardial infarction (MI) in rats. Male albino Wistar rats were pretreated with the ethanolic extract of L. siceraria (Mol) fruit (125, 250 and 500?mg?kg(-1) body weight) for a period of 30 days. After the treatment period, ISO (85mg?kg(-1) body weight) was subcutaneously injected into rats at 24-h intervals for 2 days. ISO-induced rats showed a significant (p?相似文献   

NMR studies of the thermal degradation of a perfluoropolyether on the surfaces of gamma-alumina and kaolinite

Solid-state nuclear magnetic resonance (NMR) methods are used to follow the thermal degradation of Krytox 1506, a common perfluoropolyether, following adsorption onto the surfaces of gamma-Al2O3 and a model clay (kaolinite). The alumina studies are complemented with thermogravimetric analysis (TGA) to follow the degradation process macroscopically. Molecular-level details are revealed through 19F magic-angle spinning (MAS), 27Al MAS, and 19F --> 27Al cross-polarization MAS (CPMAS) NMR. The CPMAS results show the time-dependent formation of probable VIAl(O6 - nFn) (n = 1, 2, 3) species in which the fluorine atoms are selectively associated with octahedrally coordinated aluminum atoms. For the alumina system, the changes in peak shapes of the CP spectra over time suggest the early formation of catalytically active degradation products, which in turn lead to the formation of additional perfluoropolyether degradation products. Similar to the alumina system, the kaolinite system also displays new resonances in both the 27Al MAS and 19F --> 27Al CPMAS spectra after thermal treatment at 300 degrees C for up to 20 h but reveals a more distinct species at -15.5 ppm that forms at the expense of an initial species (3 ppm), which is in greater abundance at shorter heating times.     

Three types of membranous ATPase on rat liver lysosomes.

At least three types of vanadate-insensitive membranous ATPase were identified on rat liver lysosomes: bafilomycin A1-sensitive Mg(2+)-ATPase (H(+)-ATPase), N-ethylmaleimide (NEM)-sensitive but bafilomycin A1-insensitive Mg(2+)-ATPase (ATPase I), and NEM-insensitive Ca2+/Mg(2+)-ATPase (ATPase II). They showed different sensitivity to chemicals and ions with apparent molecular masses of 700-800, 500-650, and 360 kDa, respectively. Of these membranous ATPases, H(+)-ATPase seemed to constitute only one tenth of the ATPase activity on rat liver lysosomes and to be the only ATPase that exposed its active site to the cytoplasmic side of the lysosomal membranes.     

Competition between pi and non-pi cation-binding sites in aromatic amino acids: a theoretical study of alkali metal cation (Li+, Na+, K+)-phenylalanine complexes

To understand the cation-pi interaction in aromatic amino acids and peptides, the binding of M(+) (where M(+) = Li(+), Na(+), and K(+)) to phenylalanine (Phe) is studied at the best level of density functional theory reported so far. The different modes of M(+) binding show the same order of binding affinity (Li(+)>Na(+)>K(+)), in the approximate ratio of 2.2:1.5:1.0. The most stable binding mode is one in which the M(+) is stabilized by a tridentate interaction between the cation and the carbonyl oxygen (O[double bond]C), amino nitrogen (--NH(2)), and aromatic pi ring; the absolute Li(+), Na(+), and K(+) affinities are estimated theoretically to be 275, 201, and 141 kJ mol(-1), respectively. Factors affecting the relative stabilities of various M(+)-Phe binding modes and conformers have been identified, with ion-dipole interaction playing an important role. We found that the trend of pi and non-pi cation bonding distances (Na(+)-pi>Na(+)-N>Na(+)-O and K(+)-pi>K(+)-N>K(+)-O) in our theoretical Na(+)/K(+)-Phe structures are in agreement with the reported X-ray crystal structures of model synthetic receptors (sodium and potassium bound lariat ether complexes), even though the average alkali metal cation-pi distance found in the crystal structures is longer. This difference between the solid and the gas-phase structures can be reconciled by taking the higher coordination number of the cations in the lariat ether complexes into account.     

Analysis of radiation induced degradation in FPC-461 fluoropolymers by variable temperature multinuclear NMR

Solid state nuclear magnetic resonance techniques have been used to investigate aging mechanisms in a vinyl chloride:chlorotrifluoroethylene copolymer, FPC-461, due to exposure to γ-radiation. Solid state ¹H MAS NMR spectra revealed structural changes in the polymer upon irradiation under both air and nitrogen atmospheres. Considerable degradation is seen with ¹H NMR in the vinyl chloride region of the polymer, particularly in the samples irradiated in air. ¹⁹F MAS NMR was used to investigate speciation in the chlorotrifluoroethylene blocks, though negligible changes were seen. ¹H and ¹⁹F NMR at elevated temperature revealed increased segmental mobility and decreased structural heterogeneity within the polymer, yielding significant resolution enhancement over room temperature solid state detection. The effects of multi-site exchange are manifested in both the ¹H and ¹⁹F NMR spectra as a line broadening and change in peak position as a function of temperature.     

Scopadulcic acid B, a new tetracyclic diterpenoid from Scoparia dulcis L. Its structure, H+, K(+)-adenosine triphosphatase inhibitory activity and pharmacokinetic behaviour in rats

The structure of scopadulcic acid B (2, SDB), a major ingredient of the Paraguayan herb "Typychá kurat?" (Scoparia dulcis L.), was elucidated mainly by comparison of its spectral data with that of scopadulcic acid A (1). SDB inhibited both the K(+)-dependent adenosine triphosphatase (ATPase) activity of a hog gastric proton pump (H+, K(+)-ATPase) with a value of 20-30 microM for IC50 and proton transport into gastric vesicles. Pharmacokinetic studies of SDB in rats indicated that plasma SDB concentrations after i.v. injection of the sodium salt of SDB (SDB-Na) were described reasonably well by a two-compartment open model with Michaelis-Menten elimination kinetics. Plasma concentrations after oral administration of SDB-Na or SDB showed a much slower decline than what was expected following the i. v. study. It was suggested that the sustained plasma level of SDB after oral administration of SDB-Na or SDB was accounted for by relatively slow but efficient gastro-intestinal absorption in rats.