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At least 685 records · Page 38Linked to original sources
PubMed1998

Crystal Engineering in [(12C4)(2)Na][Cd(SCN)(3)]: First Example of an Anionic Cadmium Thiocyanate Coordination Solid with a Sandwich [(12C4)(2)Na](+) Cation as Spacer/Controller, Resulting in a Hexagonal Arrangement of Antiparallel Zigzag [Cd(SCN)(3)(-)](infinity) Chains.

This paper reports the synthesis, characterization, and structure of [(12C4)(2)Na][Cd(SCN)(3)] (3). The title compound 3 represents the first example of an anionic cadmium thiocyanate coordination solid in which a sandwich [(12C4)(2)Na](+) monocation serves as the spacer/controller, giving rise to a hexagonal array of antiparallel infinite zigzag [Cd(SCN)(3)(-)](infinity) chains with the cations occupying the triangular channels. The title compound 3 crystallizes in a monoclinic unit cell of P2(1)/n space group symmetry with lattice parameters of 13.204(2) Å, 10.692(2) Å, 21.036(1) Å, 95.520(8) degrees, and Z = 4. A detailed comparison of the title structure (3) with that of [(18C6)(2)Na(2)(H(2)O)(2)](1/2)[Cd(SCN)(3)] (1) and [(18C6)K][Cd(SCN)(3)] (2) revealed that the arrangement and the alignment of the infinite anionic [Cd(SCN)(3)(-)](infinity) zigzag chains are dictated by the dimensions and symmetry, respectively, of the cations. The infinite anionic [Cd(SCN)(3)(-)](infinity) chains in 1 and 2 form an approximate tetragonal array, creating square channels which are filled with the dimeric [(18C6)(2)Na(2)(H(2)O)(2)](2+) (in 1) or with two monomeric [(18C6)K](+) (in 2) cations while the infinite anionic [Cd(SCN)(3)(-)](infinity) chains in 3 adopt an approximate hexagonal arrangement with the triangular channels filled by the smaller [(12C4)(2)Na](+) cations (the dimension effect). The relative alignment (either parallel or antiparallel) of the anionic chains is dictated by the symmetry or approximate symmetry of the cations. Thus, both the dimeric cation in 1 and the sandwich cation in 3 give rise to antiparallel alignment of the anionic [Cd(SCN)(3)(-)](infinity) chains with the centrosymmetric space group P2(1)/n whereas the disklike cation in 2 gives rise to parallel alignment of [Cd(SCN)(3)(-)](infinity) chains with noncentrosymmetric space group Cmc2(1) (the symmetry effect).

Journal Article↗
PubMed2000

Crystal supramolecular motifs: columns of embracing Ph3PMe+ or Ph3PCI+ cations controlling formation of.

The crystal structures of (Ph3PCl)2[Cu3Cl8] (1) (triclinic, space group P1, a = 9.480(6) A, b = 10.243(8) A, c = 11.232(6) A, alpha = 86.76(4) degrees, beta = 66.62(5) degrees, gamma = 83.92(4) degrees, Z = 1) and (Ph3PMe)2[Cu3Br8] (2) (triclinic, space group P1, a = 9.795(4) A, b = 10.472(4) A, c = 11.392(4) A, alpha = 86.67(3) degrees, beta = 66.67(3)degrees, gamma = 83.14(3) degrees, Z = 1), reported here, demonstrate a new supramolecular motif for cations of the type Ph3PY+ where Y is CH3 or Cl. The crystals contain columns of cations propagated by alternating 6-fold phenyl embraces (6PE) and pseudo-6PE: the pseudo-6PE described here contains four phenyl rings and two hetero groups (Cl or CH3), and is symbolized as 4P2Y. The zigzag sequence of cations engaged in ...6P...4P2Y...6P...4P2Y... is similar to the zigzag chain of infinite 6-fold phenyl embraces (ZZI6PE) frequently adopted by Ph4P+ cations in crystals. One-dimensionally nonmolecular anion chains with repeat unit [Cu3X8] run parallel to and between the columns of cations. The coordination geometry in the [Cu3X8(2-)]1 to infinity chain has not been observed in crystals with other cations, and it is postulated that the attractive interactions between cations in the pseudo-ZZI6PE crystal supramolecular motif control the geometry of the anions through the requirement for commensurability of cation columns and anion chains.

Journal Article↗
PubMed2001

Stability of Zn(II) cations in chabazite studied by periodical density functional theory.

The location of the Zn(2+) cation in Zn-exchanged chabazite has been studied by the periodical density functional method. Chabazite was chosen as a zeolite model, because it contains three different types of rings commonly found in the zeolite structures: four-, six-, and eight-membered rings. Two aluminum atoms have been employed to substitute the silicon atoms in the same D6R unit cell of the zeolite framework. This leads to different arrangements for the Brønsted site pair and the Zn(II) cation. The two Brønsted sites are found to be more stable when placed in the small ring (4T ring) than in the other rings. This suggests that the most reactive Brønsted sites are located in the large rings. Two Brønsted sites are most stable when the O(H)-Al-O-Si-O(H)-Al sequence is followed in the same ring instead of being located in two different rings. This resembles the aluminum distribution in the small four-membered ring and agrees with bond order conservation rules. The cation stability is markedly influenced by the distortions of the framework. Other factors that also contribute to the stabilization are the aluminum content near the cation and the stability of the original Brønsted sites. The Zn(2+) cation is more stable in the large rings than in the small ones, the six-membered one being the most stable configuration. In the small rings, the cation is, therefore, more reactive. Two different probe molecules have been used to study the interaction with the Zn(II) cation: water and methane. These probe molecules can extract the active center from its original position. For the water molecule, this effect is large and leads to a high framework relaxation. The value of the binding energy of this molecule to the active sites is influenced by these framework relaxations as well as by the cationic position environment. For weakly interacting methane, these effects are significantly less.

Journal Article↗
PubMed2002

Formation and decomposition of N,N,N-trimethylanilinium cations on zeolite H-Y investigated by in situ stopped-flow MAS NMR spectroscopy.

Methylation of aniline by methanol on zeolite H-Y has been investigated by in situ (13)C MAS NMR spectroscopy under flow conditions. The in situ (13)C continuous-flow (CF) MAS NMR experiments were performed at reaction temperatures between 473 and 523 K, molar methanol-to-aniline ratios of 1:1 to 4:1, and modified residence times of (13)CH(3)OH between 20 and 100 (g x h)/mol. The methylation reaction was shown to start at 473 K. N,N,N-Trimethylanilinium cations causing a (13)C NMR signal at 58 ppm constitute the major product on the catalyst surface. Small amounts of protonated N-methylaniline ([PhNH(2)CH(3)](+)) and N,N-dimethylaniline ([PhNH(CH(3))(2)](+)) were also observed at ca. 39 and 48 ppm, respectively. After increase of the temperature to 523 K, the contents of N,N-dimethylanilinium cations and ring-alkylated reaction products strongly increased, accompanied by a decrease of the amount of N,N,N-trimethylanilinium cations. With application of the in situ stopped-flow (SF) MAS NMR technique, the decomposition of N,N,N-trimethylanilinium cations on zeolite H-Y to N,N-dimethylanilinium and N-methylanilinium cations was investigated to gain a deeper insight into the reaction mechanism. The results obtained allow the proposal of a mechanism consisting of three steps: (i) the conversion of methanol to surface methoxy groups and dimethyl ether (DME); (ii) the alkylation of aniline with methanol, methoxy groups, or DME leading to an equilibrium mixture of N,N,N-trimethylanilinium, N,N-dimethylanilinium, and N-methylanilinium cations attached to the zeolite surface; (iii) the deprotonation of N,N-dimethylanilinium and N-methylanilinium cations causing the formation of N,N-dimethylaniline (NNDMA) and N-methylaniline (NMA) in the gas phase, respectively. The chemical equilibrium between the anilinium cations carrying different numbers of methyl groups is suggested to play a key role for the products distribution in the gas phase.

Journal Article↗
PubMed2004

A new rearrangement process in tert-amyl cation.

13C NMR spectroscopy of the 2-methyl-2-butyl-1-13C cation (13C-labeled tert-amyl cation) indicates that interchange of the inside and outside carbons occurs via a barrier of 19.5 +/- 2.0 kcal/mol. A plausible mechanism involves hydride migration in the proposed 2-pentyl cation 4 to form 3-pentyl cation 5. Via the protonated cyclopropane intermediate 6, which undergoes degenerate corner-to-corner hydride shift, the secondary 3-pentyl cation 5' with the label shifted to the central carbon atom is formed. The tert-amyl cation obtained from 5' in the reverse process has the 13C label on an inside carbon atom. All intermediates and transition structures were located on the PES theoretically at the MP2/6-31G(d,p) level of theory. The rearrangement rate of the doubly labeled tert-amyl cation (methyl-13C-butyl-1-13C cation), followed by means of 13C NMR, revealed that the process that interchanges inside and outside carbons has the highest barrier. Comparison of the initial rates revealed that isotopomer 1e arises considerably more slowly than other isotopomers, indicating that in the overall rearrangement process transition structure 5-TS has the highest energy.

Journal Article↗
PubMed2004

Generation and absolute reactivity of an aryl enol radical cation in solution.

Laser flash photolysis of 1-bromo-1-(4-methoxyphenyl)acetone in acetonitrile leads to the formation of the alpha-acyl 4-methoxybenzyl radical that under acidic conditions rapidly protonates to give detectable amounts of the radical cation of the enol of 4-methoxyphenylacetone. This enol radical cation is relatively long-lived in acidic acetonitrile (tau approximately equal to 200 micros), which is on the same order of magnitude as the radical cations of other 4-methoxystyrene derivatives. Rate constants for deprotonation of the radical cation and the acid dissociation constant for the enol radical cation were also determined using time-resolved absorption spectroscopy. Deprotonation is rapid, taking place with a rate constant of 3.9 x 10(6) s(-1), but the enol radical cation is found to be only moderately acidic in acetonitrile having a pK(a) = 3.2. The lifetime of the enol radical cation was also found to be sensitive to the presence of oxygen and chloride. The sensitivity toward oxygen is explained by oxygen trapping the vinyloxy radical component of the enol radical cation/vinyloxy equilibrium, while chloride acts as a nucleophile to trap the enol radical cation.

Journal Article↗
PubMed2006

Intermediates of halogen addition to phenylethynes and protonation of phenylethynyl halides. Open halovinyl cations, bridged halonium, or phenyl-bridged ions: a substituent effect study by DFT and GIAO-DFT.

Formation of alpha-phenyl-beta-halovinyl cation, beta-phenyl-alpha-halovinyl cation, as well as the halogen-bridged and the spirocyclic phenyl-bridged cations as intermediates of protonation of phenylethynyl halides or by halogen addition to phenylethynes was evaluated by DFT at B3LYP/6-31+G(d) and, for comparison in representative cases, by B3LYP/6-311++G(d,p). Relative stabilities of the resulting minima were gauged as a function of substituents on the phenyl group with p-OH, p-OMe, p-H, p-CF3, p-CN, and p-NO2 and with p-OMeH+, p-NO2H+, and p-N2+. In the majority of cases, the alpha-aryl-beta-halovinyl cations were identified as the most likely intermediates, irrespective of X and for most R groups. For R = p-N2+ (with X = Br and Cl), R = CNH+ (with X = Cl), and R = MeOH+ (with X = Br), the corresponding beta-aryl-alpha-halovinyl cations become more stable than alpha-aryl-beta-halovinyl cations (but in most cases with a relatively small stability difference). Whereas competitive formation of the spirocyclic aryl bridged cations via this route appears remote, with R = N2+ and R = NO2H+ as substituents (with X = Br), cyclic halonium ions could intervene, since their relative stabilities are within approximately 4 kcal/mol of the lowest energy vinyl cations. Geometrical features, GIAO NMR chemical shifts, and NPA-derived charges were used to gain insight into the structural/electronic features in the resulting mono and dications. The study provides a basis for stable ion and solvolytic/kinetic studies on a series of substituted phenylethynyl halides that are being synthesized.

Journal Article↗
PubMed1996

Trishomocyclopropenylium Cations. Structure, Stability, Magnetic Properties, and Rearrangement Possibilities.

Potentially trishomoaromatic cations possessing the 6-X-bicyclo[3.1.0]hex-3-yl (X = CH(2), BH, NH, O) or bicyclo[3.2.0]hept-3-yl unit have been investigated at the Hartree-Fock, second-order, third-order, and fourth-order (single, double, quadruple excitations) Møller-Plesset perturbation level employing the 6-31G(d) basis set. IGLO/6-31G(d) chemical shift calculations have been carried out at optimized geometries. Through-space interactions between the symmetric Walsh orbital of the three-membered ring and ppi(C3) orbital have been analyzed as a function of orbital energies and orbital overlap. The best indicators for trishomoaromaticity are NMR chemical shifts and magnetic susceptibility. There is a simple relationship between the conformation of the trishomocyclopropenylium cation, its charge distribution, and delta(13)C3, which can be used to determine the conformation or the C1C3 interaction distance from NMR measurements. Trishomocyclopropylium cations investigated can rearrange to an envelope form of higher energy where the height of the inversion barrier and the chair-envelope energy difference are a measure for the homoaromatic stabilization energy. The bicyclo[3.1.0]hex-3-yl cation in its envelope form can rearrange with a barrier of just 1 kcal/mol to the bicyclo[3.1.0]hept-2-yl cation. In the case of the bicyclo[3.2.0]hept-3-yl cation, there exists just the envelope form, which can rearrange to a ethano-bridged center-protonated spirocyclopentyl cation. The later cation should be an interesting target of chemical synthesis since it contains a pentacoordinated carbon atom and possesses unusual properties.

Journal Article↗
PubMed1998

Intramolecular Binaphthyl Formation from Radical Cations of Tri-1-naphthyl Phosphate and Related Compounds in Photoinduced Electron-Transfer Reactions Sensitized by 9,10-Dicyanoanthracene.

The photoinduced electron transfer of tri-1-naphthyl phosphate and related compounds sensitized by 9,10-dicyanoanthracene (DCA) in acetonitrile produces 1,1'-binaphthyl and the corresponding biaryl. The quenching rate constant of the DCA fluorescence is calculated to be equal to the diffusion-controlled rate constant from the Stern-Volmer analysis and the fluorescence lifetime measurement. The free energy change calculated from the redox potentials and excitation energy of the singlet excited DCA indicates that the quenching process occurs exergonically to give the tri-1-naphthyl phosphate radical cation and DCA radical anion through electron transfer from tri-1-naphthyl phosphate to the singlet excited DCA at the diffusion-controlled rate. On the basis of spectroscopic and kinetic studies with laser flash photolysis, pulse radiolysis, and gamma-radiolysis, the radical cation of tri-1-naphthyl phosphate forms an intramolecular pi-dimer radical cation with face-to-face interaction between the two naphthyl groups within 8 ns of the electron pulse. The 1,1'-binaphthyl radical cation is eliminated at the rate constant of k(r) = 5.3 x 10(5) s(-)(1) from the intramolecular pi-dimer radical cation. Branching ratios of the reaction pathways are estimated for the reactive intermediates such as the tri-1-naphthyl phosphate radical cation and its intramolecular pi-dimer radical cation from the rate constants and quantum yields. The electron-withdrawing character of the P(O) group in the O-P(O)-O spacer is responsible for the elimination of the binaphthyl radical cation. The DCA-sensitized photoinduced electron-transfer reaction of the tri-1-naphthyl phosphate is compared with the direct photoreaction.

Journal Article↗
PubMed2006

Cation migration upon adsorption of methanol in NaY and NaX faujasite systems: a molecular dynamics approach.

Molecular dynamics simulations have been carried out to address the question of cation migration upon adsorption of methanol in NaY and NaX faujasite systems as a function of the loading. For NaY, it has been shown that, at low and intermediate loadings, SII cations can migrate toward the center of the supercage due to strong interactions with the adsorbates, followed by a hopping of SI' from the sodalite cage into the supercage to fill the vacant SII site. A SI' cation can also migrate across the double six ring and takes a SI' vacant position. SI cations mainly remain trapped in their initial sites whatever the loading. At high loading, only limited motions are observed for SII cations due to steric effects induced by the presence of adsorbates within the supercage. For NaX, the SIII' cations which occupy the most accessible adsorption sites are significantly moving upon coordination to the methanol molecules; the extent of this mobility exhibits a maximum for 48 methanol molecules per unit cell before decreasing at higher loadings due to steric hindrance. In addition, the SI' and SII cations remain almost trapped in their initial sites whatever the loading. Indeed, the most probable migration mechanism involves SIII' cation displacements into nearby SIII' sites.

Journal Article↗
PubMed2006

Band gap variation in Prussian Blue via cation-induced structural distortion.

The charge-transfer band gap of the iron cyanide framework material Prussian Blue and its dependence on the type and location of the charge-compensating interstitial cations (K(+), Rb(+), Cs(+)) are investigated via periodic density functional (DF) calculations. The calculated variation in the band gap magnitude with respect to cation type confirms recent experimental results on cation-induced spectral shifts. The role of both the cation interaction with the framework and the cation-induced lattice expansion are examined with respect to their influence on the band gap. The gap magnitude is related to the cation type but is found to be more strongly affected by cation-induced lattice distortion as the cation passes through the material. Our results support the possibility of engineering the electronic structure of Prussian Blue type materials through guest-induced host-framework distortion.

Journal Article↗
PubMed1998

Cationic liposome--plasmid DNA complexes used for gene transfer retain a significant trapped volume.

The goal of this study is to determine whether cationic liposomes retain any trapped volume after their complexation to plasmid DNA. This serves two purposes: to further the understanding of the physical nature of liposome/plasmid DNA complexes used in gene therapy and to investigate the potential for codelivery of other encapsulated molecules with the liposome-DNA complexes. Cationic liposomes composed of N,N-dioleoyl-N,N-dimethylammonium chloride and dioleoylphosphatidylethanolamine (DODAC/DOPE, 50/50 mol %) encapsulating an aqueous trap marker were used to prepare liposome-DNA complexes at various charge ratios. The trapped volume before and after DNA binding was measured by two methods: dialysis and filtration. The effect of tissue culture medium on trapped volume was also investigated. A lipid-mixing assay was employed to further characterize the aggregation events that influence trap volume. The trapped volume (Vt) of neutral control liposomes was 1.1 +/- 0.04 microL/mumol, which was not affected by the addition of DNA. For cationic liposomes in the absence of DNA the Vt was 1.45 +/- 0.46 and 1.54 +/- 0.08 microL/mumol, as measured by the filtration and dialysis methods, respectively. After addition of DNA, the residual trapped volume (RVt) decreased to 0.43 +/- 0.1 microL/mumol and 0.47 +/- 0.05 microL/mumol, as determined by each method, respectively. RVt increased as the ratio of cationic lipid to DNA (nmol of lipid/mg of DNA) was increased above 10, a ratio that corresponds to a charge ratio (positively charged lipids to negatively charged phosphate groups) of 1.62. Aggregation and lipid-mixing were greatest at charge ratios coinciding with the lowest trapped volume. In the presence of tissue culture medium, the Vt of cationic liposomes but not neutral liposomes was reduced, suggesting that the salts have a direct effect on cationic liposomes in the absence of DNA. The RVt of both neutral and cationic liposomes in the presence of DNA, however, was not different from that of the liposomes in the absence of DNA. These results suggest that a significant trapped volume is retained by cationic liposomes after binding to plasmid DNA. This is an important finding with regard to the potential use of DNA/liposome complexes in the codelivery of other bioactive molecules at the time of cell transfection.

Culture Media↗
PubMed2005

Synergism in the spreading of hydrocarbon-chain surfactants on polyethylene film-anionic and cationic mixtures by a two-step procedure.

A study has been made of the adsorption, interaction, and spreading of mixtures of anionic and cationic surfactants at the aqueous solution/polyethylene (PE) interface. When a drop of an aqueous solution of an anionic or cationic hydrocarbon-chain surfactant is placed on a highly hydrophobic PE film (contact angle of water > 90 degrees ), it spreads to an area very little larger than that of a drop of water of the same volume. If the anionic and cationic hydrocarbon-chain surfactant solutions are mixed prior to being applied to PE film, synergism is small, if any, and the reproducibility of the experimental results is poor. However, when the cationic and anionic aqueous solutions are applied on the PE film in a sequential manner, a remarkable synergism in spreading is observed and the results are very reproducible. The area spread by an aqueous solution of the anionic-cationic mixture may be more than 400 times that of aqueous solutions of the same volume and surfactant concentration of the individual surfactant components. Previous work in this laboratory on surfactant systems showing synergism in spreading on PE film, but only weak interaction at the aqueous solution/air interface, showed that the synergy was due to changes at the aqueous solution/PE interface and not to the changes at the aqueous solution/air or PE/air interface. Investigation of the adsorption behavior at the aqueous solution/solid interface of two of the anionic-cationic mixtures studied here indicates the reason for differences in spreading behavior observed with different anionic-cationic mixtures. The more similar the adsorption tendencies at the solid/aqueous solution interface of the anionic and cationic surfactants, and the closer their adsorption to an equimolar monolayer there, the stronger their interaction there and the greater their enhancement of the spreading. A mechanism is proposed for the synergy in spreading observed, based upon the difference between the surface tension in the precursor film at the spreading interface and that at the top of the spreading drop.

Journal Article↗
PubMed2005

Role of exchangeable cations on geometrical and energetic surface heterogeneity of kaolinites.

Textural and energetic proprieties of kaolinite were studied by low-pressure argon adsorption at 77 K. The heterogeneity of four kaolinites (two low-defect and two high-defect samples) modified on their surface by cation exchange with Li+, Na+, or K+ was studied by DIS analysis of the derivative argon adsorption isotherms. The comparison between the derivative adsorption isotherms shows that the nature of the surface cation influences the adsorption phenomena on edge and basal faces. In the case of basal faces, two adsorption domains are observed: for the first one, argon adsorption is slightly sensitive to the nature of the surface cation; for the second one, argon adsorption energy depends on the nature of surface cation suggesting their presence on theoretically uncharged basal faces. This study also shows that the shape of elementary particles, as derived from basal and edge surface areas, changes with the nature of cation. This anomalous result is due to the decrease of edge surface area with increasing the size of the cation. This surface cation dependence can be accounted for the area occupied by the edge surface cations in the first argon monolayer.

Journal Article↗
PubMed1998

Target specific optimization of cationic lipid-based systems for pulmonary gene therapy.

PURPOSE: Cationic lipids are capable of transferring foreign genes to the pulmonary epithelium in vivo. It is becoming increasingly clear that factors other than lipid molecular structure also influence efficiency of delivery using cationic lipid systems. This study is aimed at evaluating the effect of formulation variables such as cationic lipid structure, cationic lipid/DNA ratio, particle size, co-lipid content and plasmid topology on transgene expression in the lung. METHODS: The effect of varying the surface and colloidal properties of cationic lipid-based gene delivery systems was assessed by intratracheal instillation into rats. An expression plasmid encoding chloramphenicol acetyl transferase (CAT) was used to measure transgene expression. RESULTS: Cationic lipid structure, cationic lipid/DNA ratio, particle size, co-lipid content and topology of the plasmid, were found to significantly affect transgene expression. Complexation with lipids was found to have a protective effect on DNA integrity in bronchoalveolar lavage fluid (BALF). DNA complexed with lipid showed enhanced persistence in rat lungs as measured by quantitative polymerase chain reaction. CONCLUSIONS: Fluorescence microscopy analysis indicated that the instilled formulation reaches the lower airways and alveolar region. Data also suggests cationic lipid-mediated gene expression is primarily localized in the lung parenchyma and not infiltrating cells isolated from the BALF.

Animals↗
PubMed2000

Voltage-dependent inhibition of the muscarinic cationic current in guinea-pig ileal cells by SK&F 96365.

The effects of SK&F 96365 on cationic current evoked either by activating muscarinic receptors with carbachol or by intracellularly applied GTPgammaS (in the absence of carbachol) were studied using patch-clamp recording techniques in single guinea-pig ileal smooth muscle cells. SK&F 96365 reversibly inhibited the muscarinic receptor cationic current in a concentration-, time- and voltage-dependent manner producing concomitant alteration of the steady-state I-V relationship shape which could be explained by assuming that increasing membrane positivity increased the affinity of the blocker. The inhibition was similar for both carbachol- and GTPgammaS-evoked currents suggesting that the cationic channel rather than the muscarinic receptor was the primary site of the SK&F 96365 action. Increased membrane positivity induced additional rapid inhibition of the cationic current by SK&F 96365 which was more slowly relieved during membrane repolarization. Both the inhibition and disinhibition time course could be well fitted by a single exponential function with the time constants decreasing with increasing positivity for the inhibition (e-fold per about 12 mV) and approximately linearly decreasing with increasing negativity for the disinhibition. At a constant SK&F 96365 concentration, the degree of cationic current inhibition was a sigmoidal function of the membrane potential with a potential of half-maximal increase positive to about +30 mV and a slope factor of about -13 mV. Increasing the duration of voltage steps at -80 or at 80 mV, increased the percentage inhibition; the degree of inhibition was almost identical at both potentials providing evidence that the same cationic channel was responsible for the cationic current both at negative and at positive potentials. It is concluded that the distinctive and unique mode of SK&F 96365 action on the muscarinic receptor cationic channel is a valuable tool in future molecular biology studies of this channel.

Animals↗
PubMed2001

Successive non-suppressed ion chromatography of common cations and anions using dual columns with single eluent.

A successive non-suppressed ion chromatography (IC) system for the determination of common cations (Na+, K+, Mg2+, Ca2+) and anions (Cl-, Br-, NO3-, SO4(2-)) was developed, using two separation columns and a single eluent. 5-Sulfoisophthalic acid eluent was very suitable for such separations with a commercially available cation-exchange column for the mono- and di-valent cations and with an ODS column coated with cetyltrimethylammonium for the anions. Both cations and anions were detected with conductimetrically high sensitivity without any suppressor. After injecting an aliquot of sample solution, the solvent front from the cation-exchange column, including most of the anionic species, was firstly accumulated into the additional 2 ml accumulation loop for 60 s, while the cation IC was performed. Subsequently, the accumulated fraction was introduced into the anion-exchange column and chromatographed. Relative standard deviations (RSDs) of retention times and conductimetric area responses for common cations were within 6% and within 4%, respectively. The linear relationships between molar concentration and detector response ranged from 0.01 to 1.00 mM with r2 of 0.9994 for Na+, 0.9992 for K+, 0.9993 for Mg2+, and 0.9988 for Ca2+. The successive anion IC through the accumulating process was also quantitative, with 95% recovery or over for each analyte. The linear ranges were between 0.01 and 1.00 mM with r2 of 0.9996 for Cl-, 0.9997 for Br-, 0.9993 for NO3-, and 0.9984 for SO4(2-). The method was applied to the determination of common cations and anions in several mineral waters and a hot spring water.

Journal Article↗
PubMed2005

Fluorometric sensing of alkali metal and alkaline earth metal cations by novel photosensitive monoazacryptand derivatives in aqueous micellar solutions.

Novel monoazacryptand-type fluorescent chemosensors, (derived from an 18-crown-6) and (derived from a 15-crown-5) both with a pyrene ring as their photoresponsive moiety, were synthesized. Their fluorescence properties for alkali metal and alkaline earth metal cations in water were then examined. The detection of metal cations was accomplished by a change in the fluorescence intensity of the host compounds, based on a photoinduced electron transfer (PET) mechanism. In aqueous solution, showed little fluorescence upon the addition of Ba2+ because of the very weak complexation with Ba2+, but the presence of micelles of polyoxyethylene(10) isooctylphenyl ether (Triton X-100) enabled to show highly sensitive and selective Ba2+ detection among alkali metal and alkaline earth metal cations. With respect to the selective fluorescent detection of important metal cations (Na+, K+, Mg2+, Ca2+) relevant to living organisms, was found to detect K+ with high selectivity in aqueous micellar solutions of polyoxyethylene(20) sorbitan monostearate (Tween-60). The selectivity for metal cations was mainly dependent on the goodness of fit of the host cavity and the metal cation size. In the presence of anionic surfactants, detected alkaline earth metal cations more effectively than alkali metal cations.

Journal Article↗