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PubMed2001

Extraction and separation of cationic surfactants from river sediments: application to a spectrophotometric determination of cationic surfactant in an aquatic environment using membrane filters.

The quantitative extraction of cationic surfactant (CS+) in river sediments was studied. Further, the developed method was applied to the spectrophotometric determination of CS+ in urban river sediment samples by solid-phase extraction with membranes. A mixture of methanol and hydrochloric acid was proposed as an eluent. Dried sediment was digested in the eluent under ultrasonic irradiation. After elution, the eluent was evaporated to almost dryness. The residue was dissolved in a small volume of methanol and diluted to a certain volume with water. The pH of the solution was adjusted to 4-5 to separate iron and some other metals as precipitates of hydroxides. The solution was passed through two-piled membranes: first glass-fiber and then polytetrafluoroethylene (PTFE) membranes. A small volume of methanol was passed through the membranes to elute any CS+ retaining on the membranes. After passing the methanol solution through a cationic exchange resin column, the retained CS+ was eluted with methanol containing a high concentration of sodium chloride. Water, Bromophenol Blue (BPB) and hydrochloric acid were added to the solution. The solution was passed through a mixed cellulose ester membrane filter to retain an ion associate of CS+.BPB-. The retained ion associate was dissolved in a small volume of N,N-dimethylformamide together with the membrane filter, followed by the addition of triethanolamine to make the solution alkaline. The absorbance due to BPB2- was measured at 603 nm against a reagent blank. This method was applied to the determination of CS+ in river water and sediment. A cationic surfactant in sediments at 10(-5) mol kg-1 levels was detected with satisfactory precision. It was found that CS+ was about 500-fold enriched in the sediment from water at the place where domestic wastewater was discharged.

Benzalkonium Compounds↗
PubMed1992

Divalent cation-dependent stimulation of ligand binding to the 46-kDa mannose 6-phosphate receptor correlates with divalent cation-dependent tetramerization.

The quaternary structure and binding activity of the murine 46-kDa mannose 6-phosphate receptor (46MPR) were studied in semi-intact murine cells that overexpress the murine receptor. Chemical cross-linking studies showed that the murine 46MPR exists in monomer, dimer, and tetramer forms in membranes of overexpressing murine cells. Treatment of permeabilized cells with Mn2+ increased the tetramer form of 46MPR, and this tetramerization was reversed by removal of Mn2+. Thus, the divalent cations affected the distribution of receptor among the three forms, favoring tetramerization at the expense of dimer and monomer. Low temperature (4 degrees C) also increases the fraction present as tetramer. The binding assay results show that Mn2+ is required for the 46MPR to achieve and retain the ability to bind ligand at 37 degrees C but not at 4 degrees C. Preincubation with Mn2+ produced a 3-fold increase in Man-6-P-specific binding of beta-glucuronidase which paralleled the 3-fold increase in tetramer seen during preincubation with Mn2+. The similarity of the effects of addition and removal of Mn2+ on enzyme binding to the effects of Mn2+ on favoring tetramer formation suggests that divalent cation-dependent tetramerization of the 46MPR contributes to the stimulation of ligand binding to the 46MPR by divalent cations.

Animals↗
PubMed1992

Organic cation transport and cationic drug interactions in freshly isolated proximal tubular cells of the rat.

Freshly isolated proximal tubular cells (PTC) of the rat are used to study the uptake of a prototypical organic cation, tetraethylammonium (TEA), and the influence of other cationic drugs on TEA uptake. The time dependency of 50 microM TEA uptake was determined by incubating PTC for time periods from 10 sec until 60 min. TEA uptake was linear for at least 2 min and reached equilibrium after 30 min. The cell to medium ratio reached a value of 8 after 60 min, indicating marked accumulation of TEA. TEA uptake was concentration dependent and saturable, with an apparent Km of 63 +/- 7 microM and Vmax of 0.57 +/- 0.02 nmol/mg protein.min. In comparison with cells cultured on filters, the overall transport characteristics of TEA in PTC seem to resemble basolateral to apical flux. The concentration-dependent inhibition of some H2 antagonists and various cations on 32 microM TEA uptake was investigated, as well as the interaction with probenecid. Analysis of the log-concentration inhibition curves showed that mepiperphenidol, trimethoprim, famotidine and cimetidine had a high and low IC50 value, whereas ranitidine, nizatidine, cimetidine sulfoxide, N1-methylnicotinamide and probenecid had only a low IC50 value. The data reported here are comparable with those from other preparations, and it is possible to extrapolate to the human in vivo situation. Moreover, the isolation procedure is relatively simple and quick and the yield is high.

Animals↗
PubMed2004

Effect of cationic charge on receptor-mediated transfection using mannosylated cationic liposome/plasmid DNA complexes following the intravenous administration in mice.

The purpose of this study was to evaluate the effect of cationic charge of complexes after intravenous administration of cholesten-5-yloxy-N-[4-[(1-imino-2-D-thiomannosyl-ethyl)amino]butyl]formamide (Man-C4-Chol) containing cationic liposomes/pDNA complexes in mice. Transfection efficiency after intravenous administration of complex at a charge ratio (- : +) of 1.0:2.3 and/or 1.0:3.1 in liver and spleen expressing a mannose receptor on the cell surface were higher than those in lung. When complexes were formed at a charge ratio (- : +) of 1.0:4.7, on the other hand, transfection efficiency in the lung was highest, suggesting a non-specific interaction. Although asialoglycoprotein receptors are expressed on hepatocytes, a liver-selective gene transfection was not achieved by the intravenous administration of pDNA complexed with cholesten-5-yloxy-N-[4-[(1-imino-2-D-thiogalactosyl-ethyl)-amino]butyl]formamide (Gal-C4-Chol)/DOPE liposomes at a charge ratio (- : +) of 1.0 : 2.3. This information supports the design of pDNA/ligands-grafted cationic liposome complexes for cell-specific gene delivery after intravenous administration.

Animals↗
PubMed1990

Uptake and intracellular sequestration of divalent cations in resting and methacholine-stimulated mouse lacrimal acinar cells. Dissociation by Sr2+ and Ba2+ of agonist-stimulated divalent cation entry from the refilling of the agonist-sensitive intracellular pool.

The abilities of various divalent cations to enter the cytoplasm of mouse lacrimal acinar cells was examined under resting and agonist-stimulated conditions, by monitoring their effects on the fluorescence of cytosolic fura-2. In vitro, Ni2+, Co2+, and Mn2+ quenched the fura-2 fluorescence, whereas Sr2+, Ba2+, and La3+ produced an excitation spectrum and maximum brightness similar to Ca2+. Stimulation of mouse lacrimal acinar cells with methacholine (MeCh) caused a biphasic elevation of intracellular Ca2+ concentration [( Ca2+]i) resulting from a release of Ca2+ from intracellular pools followed by a sustained entry of extracellular Ca2+. Neither La3+ nor Ni2+ entered the cells under resting or stimulated conditions, but both blocked Ca2+ entry. Although both Co2+ and Mn2+ entered unstimulated cells, this process was not increased by MeCh. Both Sr2+ and Ba2+ were capable of supporting a sustained increase in fura-2 fluorescence in response to MeCh, indicating that these cations can enter the cells through the agonist-regulated channels. However, Sr2+, but not Ba2+, was capable of refilling the agonist-sensitive intracellular stores. These findings demonstrate dissociation of agonist-induced Ca2+ entry from intracellular Ca2+ pool refilling and thereby provide strong support for the recently modified version of the capacitative Ca2+ entry model according to which influx into the cytoplasm occurs directly across the plasma membrane and does not require a specialized cation channel directly linking the extracellular space and the intracellular Ca2+ stores.

Animals↗
PubMed2005

Mixed micelles of series of monomeric and dimeric cationic, zwitterionic, and unequal twin-tail cationic surfactants with sugar surfactants: a fluorescence study.

Steady state fluorescence measurements have been carried out for binary mixtures of a series of monomeric cationic (MC), zwitterionic (ZI), dimeric cationic (DC), and twin-tail cationic (TC) surfactants with sugar (beta-C8G and beta-C12G) over the whole mole fraction range using pyrene as fluorescence probe. The cmc values thus determined for all the binary mixtures have been further evaluated using the regular solution theory. The various micellar parameters, such as micelle mole fraction (X1), regular solution interaction parameter (beta), micropolarity, and mean micelle aggregation number (Nagg), have been determined for all these series of mixtures. Variation in all these micellar parameters demonstrates that mixed micelles of these surfactants with beta-C8G are mostly synergistic in nature and the synergism increases with the increase in hydrophobicity of the cosurfactant in each case. The mixtures of beta-C12G with various cosurfactants do not show this behavior and instead of it, they show an increase in antagonism with the increase in hydrophobicity of cosurfactants. This discrepancy has been attributed to a large difference in hydrophobicity between beta-C8G and beta-C12G, and the chain folding of the latter is considered to be the reason for the antagonism.

Journal Article↗
PubMed1996

Block of the cGMP-gated cation channel of catfish rod and cone photoreceptors by organic cations.

Tetraalkylammonium compounds and other organic cations were used to probe the structure of the internal and external mouths of the pore of cGMP-gated cation channels from rod and cone photoreceptors. Both rod and cone channels were blocked by tetramethyl- through tetrapentylammonium from the intracellular side in a voltage-dependent fashion at millimolar to micromolar concentrations. The dissociation constant at 0 mV (KD(O)) decreased monotonically with increasing carbon chain length from approximately 80 mM (TMA) to approximately 80 microM (TPeA), where the dissociation constant in rod channels is approximately 50% that of cone channels. N-Methyl-D-glucamine and the buffer Tris also blocked the cone channel in a voltage-dependent fashion at millimolar concentrations, but with lower affinity than similarly sized tetraalkylammonium blockers. Block by tetrahexylammonium (THxA) was voltage-independent, suggesting that the diameter of the intracellular mouth of these channels is less than the size of THxA but larger than TPeA. The location of the binding site for intracellular blockers was approximately 40% across the voltage-drop from the intracellular side. The addition of one carbon to each of the alkyl side chains increased the binding energy by approximately 4 kJ mol-1, consistent with hydrophobic interactions between the blocker and the pore. Cone, but not rod, channels were blocked by millimolar concentrations of extracellular TMA. The location of the extracellular binding site was approximately 13% of the voltage drop from the extracellular side. In cone channels, the two blocker binding sites flank the location of the cation binding site proposed previously.

Animals↗
PubMed2003

Targeted gene delivery into HepG2 cells using complexes containing DNA, cationized asialoorosomucoid and activated cationic liposomes.

Unilamellar activated cationic liposomes containing 3beta[N-(N',N'-dimethylaminopropane)-carbamoyl] cholesterol, dioleoyl phosphatidylethanolamine (DOPE) and the N-hydroxysuccinimide ester of cholesteryl hemisuccinate (4:5:1, molar ratio) have been prepared and their DNA-binding capacity has been assessed in a gel retardation assay. Ternary complexes composed of activated cationic liposomes, carbodiimide-cationized asialoorosomucoid (Me+AOM) and pRSVL plasmid DNA were assembled for receptor-mediated DNA delivery into cells expressing the asialoglycoprotein receptor (ASGP-R). Binding of complexes in which Me+AOM was replaced by fluoresceinated Me+AOM (FMe+AOM) to the human hepatocellular cell line HepG2 at 4 degrees C was severely reduced by co-incubation with asialoorosomucoid (AOM). Moreover, assemblies containing liposomes, pRSVL DNA and Me+AOM (8:1:4, w/w/w) promoted high levels of luciferase activity in this cell line (1.3 x 10(7) relative light units/mg soluble cell protein). Assays conducted in the presence of a hundred-fold excess of the ligand AOM afforded considerably lower levels of transfection (2.5 x 10(5) relative light units/mg soluble cell protein). In contrast, the highest level of luciferase activity achieved with liposome, pRSVL DNA, AOM complexes was only a quarter of the best levels obtained with liposome, pRSVL DNA, Me+AOM assemblies. These findings strongly support the notion that complexes gain entry into hepatocyte-derived cells by ASGP-R mediation and that they are potentially useful gene carriers to liver hepatocytes.

Asialoglycoprotein Receptor↗
PubMed1998

Polycation-DNA complexes for gene delivery: a comparison of the biopharmaceutical properties of cationic polypeptides and cationic lipids.

DNA plasmids formed particulate complexes with a variety of cationic polyamino acids and cationic lipids, which were used to transfect mammalian cells in culture. Complexation was studied by assaying for exclusion of ethidium using a fluorometric assay, which indicated that complexation with cationic polyamino acids took place with utilisation of the majority of charged functional groups. The particle sizes and zeta potentials of a range of complexes were determined. Generally polyamino acids formed uniform particles 80-120 nm in diameter in water, but their particle size increased on dilution of the particles in electrolytes or cell culture media. The efficiency of transfection was compared using complexes of pRSVlacZ, a reporter construct which expressed beta-galactosidase under the control of the Rous sarcoma virus promoter. Positively charged DNA/polyamino acid complexes were taken up by cells but required an endosomolytic agent, such as chloroquine, to facilitate transfection. Polyornithine complexes resulted in the highest levels of expression, in comparison with other homopolyamino acids (polyornithine>poly-L-lysine=poly-D-lysine>polyarginine). Copolyamino acids of lysine and alanine condensed DNA but were less active in transfection experiments. Copoly(L-Lys, L-Ala 1:1) was inactive even in the presence of chloroquine. In contrast DNA/cationic lipid complexes transfected cells spontaneously, and chloroquine did not improve the extent of expression, rather it usually reduced efficiency. There was little correlation between comparative efficiencies of lipid complexes between cell lines suggesting that the nature of the cell membrane and differences in mechanisms of internalisation were determinants of efficiency. In an effort to explore better cell culture models for gene delivery, monolayers of Caco-2 cells were transfected in filter culture. As the cells differentiated and formed a polarized monolayer, expression of beta-galactosidase was reduced until at day 27 expression was not significantly different from basal activity. The Caco-2 filter culture model merits further attention as a model of gene delivery to epithelial surfaces, such as would be encountered in the lung after inhalation.

Animals↗
PubMed2002

The cation cluster of heavier group 14 elements: a free germyl cation with trishomoaromaticity.

The heavier group 14 element cation cluster compound, [(tBu3Si)6Ge10I]+.TTFPB- (3+. TTFPB-; TTFPB- = tetrakis(2,3,5,6-tetrafluorophenyl)borate), was unexpectedly obtained by thermolysis of in situ prepared iodocyclotrigermene, (tBu3Si)3Ge3I, in toluene in the presence of KI and K+.TTFPB-. The molecular structure of 3+.TTFPB- has been unambiguously determined by X-ray crystallography, showing that 3+ is a free germyl cation. The three "naked" cationic germanium atoms in the framework constitute a three-center two-electron (3c-2e) bond with a trishomocyclotrigermenylium character, which is well-supported by a theoretical calculation on the model compound Ge10H7+.

Journal Article↗
PubMed2004

Crystal structures and spectroscopic characterization of radical cations and dications of oligothiophenes stabilized by annelation with bicyclo[2.2.2]octene units: sterically segregated cationic oligothiophenes.

The remarkably stable SbF(6)(-) salts of the radical cations of bithiophene 1(2T) and terthiophene 1(3T), completely surrounded by bicyclo[2.2.2]octene (BCO) units, were obtained by one-electron oxidation of the neutral precursors with NO(+)SbF(6)(-), and their solid-state structures were determined by X-ray crystallography. In these radical cations, the presence of quinoidal character was apparent, as shown by the increased planarity and by comparison of the bond lengths with those of the neutral precursors. The shortest intermolecular pi-pi distances in the crystal structure of 1(2T)(*)(+)SbF(6)(-) (distance between two sp(2) carbon atoms, 4.89 A) and 1(3T)(*)(+)SbF(6)(-) (distance between an sp(2) carbon and a sulfur atom, 3.58 A) were found to be longer than the sums of the van der Waals radii of the corresponding atoms. In accord with this, no apparent change was observed in ESR and UV-vis-NIR spectra of solutions of 1(2T)(*)(+) and 1(3T)(*)(+) upon lowering the temperature, indicating that the pi- (or sigma-) dimer formation is inhibited in solution as well as in the solid state. The dications 1(2T)(2+) and 1(3T)(2+) were generated with the stronger oxidant SbF(5) in CH(2)Cl(2) at -40 degrees C and characterized by NMR spectroscopy. In the (1)H NMR spectra, two conformers were observed for each dication of both 1(2T)(2+) (transoid (t) and cisoid (c)) and 1(3T)(2+) (t,t and c,t) at room temperature due to the high rotational barrier around the inter-ring bond(s) between thiophene rings, which was caused by the enhanced double bond character of these bonds following two-electron oxidation. This is supported by DFT calculations (B3LYP/6-31G(d)), which predicted the rotational barriers in the dications of unsubstituted bithiophene and terthiophene to be 27.6 and 22.9 kcal mol(-)(1), respectively. In the case of quaterthiophene and sexithiophene surrounded by BCO frameworks 1(4T) and 1(6T), oxidation with even one molar equivalent of NO(+)SbF(6)(-) afforded the dication salts 1(4T)(2+)2SbF(6)(-) and 1(6T)(2+)2SbF(6)(-), which were isolated as stable single crystals and allowed the X-ray crystallography. In their crystal structures, the cationic pi-systems became planar again due to the great contribution of quinoidal resonance structures, and the pi-systems, which were arrayed in a parallel geometry, were also segregated by the steric effect of BCO units. The degree and tendency of changes in the bond lengths of thiophene rings of 1(4T)(2+) and 1(6T)(2+) as compared with neutral precursors were similar to those of 1(2T)(*)(+)SbF(6)(-) and 1(3T)(*)(+)SbF(6)(-), respectively, implying that the contribution of quinoidal character is modulated by the amount of positive charge per thiophene unit.

Journal Article↗
PubMed2005

Chiral organic radical cation and dication. A reversible chiroptical redox switch based on stepwise transformation of optically active tetrakis(p-alkoxyphenyl)ethylenes to radical cations and dications.

Optically active tetrakis(p-alkoxyphenyl)ethylenes were found to function as reversible chiroptical switches upon redox transformations. Successive one-electron oxidations of chirally modified tetraarylethylene to the corresponding radical cation and then to the dication led to dramatic changes in the electronic absorption and circular dichroism (CD) spectra. The neutral species showed no color or CD in the visible region, while the radical ion was blue in color and exhibited a weak Cotton effect, with the dication green and giving an intense Cotton effect and a sign opposite that observed for the radical cation, at a longer wavelength. Molecular orbital calculations and X-ray crystallographic studies clearly indicate that the olefinic C=C bond is significantly twisted in the dication to minimize the electrostatic and steric repulsions. By lowering the temperature of the dication, the twist around the double bond is more firmly fixed in either P or M chirality to give a stronger Cotton effect and a larger anisotropy (g) factor. Since the spectral changes are completely reversible and reproducible for multiple redox cycles, this chiral redox system can be used in novel redox-driven chiroptical applications, such as molecular switches and memory devices, in which the information is written/read chiroptically in the ternary mode, giving zero CD signal in the neutral form, positive CD for the radical cation, and negative CD for the dication at a given wavelength.

Journal Article↗
PubMed2003

Cationic arylation through photo(sensitised) decomposition of diazonium salts. Chemoselectivity of triplet phenyl cations.

The photodediazoniation of some 4-X-phenyldiazonium tetrafluoborates in MeCN leads to the singlet phenyl cations (X = H, tert-butyl, NMe2, CN), which add to the solvent yielding the corresponding acetanilides. Triplet sensitisation, however, leads to the triplet phenyl cation, which is reduced in neat solvent and is trapped by pi nucleophiles (allyltrimethylsilane and benzene), resulting in an ionic analogue of the Meerwein or Gomberg arylations. With the 4-nitro derivative intersystem crossing prevails over dediazoniation from the singlet and with the 4-cyano competes with it, so that in those cases the triplet phenyl cation is formed also upon direct irradiation.

Journal Article↗
PubMed1976

Cation-stimulated Adenosine Triphosphatase Activity and Cation Transport in Corn Roots.

ATPase activity of the plasma membrane fraction from primary roots of corn (Zea mays L. WF9 x M14) was activated by Mg(2+) and further stimulated by monovalent cations (K(+) > Rb(+) > Cs(+) > Na(+) > Li(+)). K(+)-stimulated activity required Mg(2+) and was substrate-specific. Maximum ATPase activity in the presence of Mg(2+) and K(+) was at pH 6.5 and 40 C. Calcium and lanthanum (<0.5 mm) were inhibitors of ATPase, but only in the presence of Mg(2+). Oligomycin was not an inhibitor of the plasma membrane ATPase, whereas N,N'-dicyclohexylcarbodiimide was. Activity showed a simple Michaelis-Menten saturation with increasing ATP.Mg. The major effect of K(+) in stimulating ATPase activity was on maximum velocity. The kinetic data of K(+) stimulation were complex, but similar to the kinetics of short term K(+) influx in corn roots. Both K(+)-ATPase and K(+) influx kinetics met all criteria for negative cooperativity. The results provided further support for the concept that cation transport in plants is energized by ATP, and mediated by a cation-ATPase on the plasma membrane.

Journal Article↗
PubMed1991

Effect of external Cd2+ and other divalent cations on carbachol-activated non-selective cation channels in guinea-pig ileum.

1. Inhibitory actions of the external divalent cations, Cd2+, Ni2+, Mn2+ and Co2+ on carbachol (CCh)-induced inward current (Ins,ACh) were investigated in caesium aspartate-loaded single longitudinal smooth muscle cells of guinea-pig ileum, using a rapid solution-switching device, under voltage-clamped conditions. 2. Cd2+ (20-1000 microM), when added to the external solution, reduced Ins,ACh rapidly and reversibly. This effect occurred dose dependently, the relationship being adequately described by a Michaelis-Menten equation with a Hill coefficient (n) of 1.0 and a dissociation constant (Kd) of 98 microM. 3. The inhibitory action of Cd2+ was associated neither with agonist concentration (CCh) nor with changes in reversal potential, and was voltage independent. 4. The appearance and removal of the effect of Cd2+ were both rapid (a few hundred milliseconds), in sharp contrast with a relatively slow time course of atropine or CCh action (of the order of seconds). 5. Other divalent cations (Ni2+, Mn2+, Co2+, Mg2+) applied externally also suppressed Ins,ACh, but less potently. The sequence of apparent potency was Cd2+ (98 microM) greater than or equal to Ni2+ (131 microM) much greater than Co2+ (700 microM) greater than or equal to Mn2+ (1000 microM) much greater than Mg2+ (approximately 10 mM). 6. External Ca2+ increased Ins,ACh dose dependently and antagonized the inhibitory effect of Cd2+. However, this effect may not be a simple competition with Cd2+. 7. These results show that external divalent cations strongly modulate Ins,ACh channels, possibly through direct interaction with the channel protein.

Animals↗
PubMed1974

Induction of morphogenesis in Geodermatophilus by inorganic cations and by organic nitrogenous cations.

Morphogenesis of Geodermatophilus strain 22-68 involves two stages, a motile rod (R form) and an irregularly shaped cluster of coccoid cells (C form). A variety of mono- and divalent cations have been found to induce R-form to C-form morphogenesis and to maintain the organism in the C form. Concentration optima for all cations exceeded 100 mM. Results indicated that uptake of cations was accompanied by extrusion of intracellular protons, causing an increase in intracellular pH. A variety of organic amines also induced morphogenesis. Organic amines were taken up in the dissociated free base form, causing the intracellular pH to rise. None of these compounds was utilized as a carbon or nitrogen source.

Actinomycetales↗
PubMed2005

Synthesis and evaluation of beta-carbolinium cations as new antimalarial agents based on pi-delocalized lipophilic cation (DLC) hypothesis.

Several beta-carbolines including naturally occurring substances and their corresponding cationic derivatives were synthesized and evaluated for antimalarial (antiplasmodial) activity in vitro and in vivo. A tetracyclic carbolinium salt was elucidated for antileishmanial and antitrypanosomal activities in vitro as well as antiplasmodial activity. Quarternary carbolinium cations showed much higher potencies in vitro than electronically neutral beta-carbolines and a good correlation was observed between pi-delocalized lipophilic cationic (DLC) structure and antimalarial efficacy. beta-Carbolinium compounds exhibit medium suppressive activity in vivo against rodent malaria.

Animals↗