Tetraethylammonium Cations Research Articles

Rotational isomerism of the tetraethylammonium cation in solution and in the solid state

The tetraethylammonium ion Et4N+ is shown to present rotational isomerism in aqueous or organic solutions between an all-trans conformation (tt.tt or Greek cross) and a trans–gauche one (tg.tg or Nordic cross). The Raman spectra of the two rotamers are distinct and their temperature dependence indicates that (tt.tt) is more stable than (tg.tg) by about 4.1 kJ mol−1, i.e. by a value typical of two trans–gauche rotations. In some investigated solid salts at room temperature, the cation adopts one of these two conformations depending on the crystal structure and local packing effects induced by the anion. However, some other derivatives with bulky anions such as (Et4 N)2 CdBr4 and Et4 N(CF3 SO2)2 N exhibit much more complicated conformational situations for the cation as a function of temperature. Copyright © 2000 John Wiley & Sons, Ltd.

Functional expression of a high affinity mammalian hepatic choline/organic cation transporter

Uptake by the liver of the organic cation and essential nutrient choline is required for the hepatic synthesis of phosphatidylcholine. Uptake of other organic cations is also important for the metabolism and secretion of numerous endobiotics and drugs. Although a high affinity mammalian hepatic choline transporter has been kinetically defined, it has not been previously identified. We have developed stable transfectants of BALB/3T3 cells, using a murine member of the organic cation transporter gene family (mOct1/Slc22a1), and used these cells to characterize the transport of the organic cation choline and model organic cation tetraethylammonium (TEA). Functional expression of mOct1/Slc22a1 in BALB/3T3 cells confers the saturable, temperature-dependent uptake of choline with a Km of 42 μm, and uptake of TEA with a Km of 43 μm. We subsequently used our cell culture uptake system to kinetically define in HepG2 cells a high affinity choline uptake process, which transports choline with a Km similar to that of mOct1/Slc22a1 protein. We also demonstrated that organic cation transport by mOct1/Slc22a1 is inhibited by several organic cations, and that the gene is expressed in the perinatal period, at a time when phosphatidylcholine synthesis increases. We conclude that mOct1/Slc22a1 encodes a high affinity mammalian hepatic choline/organic cation transporter. This transporter may be important for hepatic phosphatidylcholine synthesis, and for the metabolism and secretion of many organic cationic drugs.—Sinclair, C. J., K. D. Chi, V. Subramanian, K. L. Ward, and R. M. Green. Functional expression of a high affinity mammalian hepatic choline/organic cation transporter. J. Lipid Res. 2000. 41: 1841–1848.

Novel Anionic Host Lattices Built of Squarate and Thiourea Molecules

The new inclusion complexes [(C2H5)4N+]2C4O42−·4(NH2)2CS·2H2O (1), [(C2H5)4N+]2C4O42−·6(NH2)2CS (2) and [(C2H5)4N+]2C4O42−·2(NH2)2CS·2H2O (3) have been prepared and characterized by X-ray crystallography. In the crystal structure of (1), infinitely extended squarate–water chains inter-link adjacent puckered thiourea layers to generate a three dimensional host lattice with large uni-directional rectangular channels each containing a double column of well-ordered tetraethylammonium cations. In complex (2), well-ordered tetraethylammonium cations are stacked in single columns within the channel-type thiourea-squarate host lattice constructed by the cross-linkage of two types of layers. In complex (3), well-ordered teteraethylammonium cations are sandwiched between puckered layers generated by the cross-linkage between zigzag (C4O42−·2H2O)∞ chains and singly hydrogen-bonded dimeric thiourea ribbons.

The organic cation transporter OCT2 mediates the uptake of beta-adrenoceptor antagonists across the apical membrane of renal LLC-PK(1) cell monolayers.

Previous studies have shown that beta-adrenoceptor antagonists may be substrates of organic cation transporters in kidney and lung. In this study we examined the transport of the beta-adrenoreceptor antagonists propranolol and metoprolol, in renal LLC-PK(1) cell monolayers. Experiments with BCECF (2', 7'-bis(2carboxyethyl)-5(6)-carboxyfluorescein) loaded LLC-PK(1) cell monolayers demonstrated that metoprolol and propranolol flux across the basolateral membrane was consistent with non-ionic diffusion. Flux across the apical membrane consisted of both non-ionic diffusion and the uptake of the cationic form of the beta-adrenoceptor antagonists. Uptake of the cationic form of metoprolol across the apical membrane was Na(+)-independent, electrogenic and sensitive to external pH. Furthermore, uptake was sensitive to inhibition by Decynium-22 and the organic cations TEA (tetraethylammonium) and MPP(+) (1-methyl 4-phenylpyridinium). These results, allied with the apical location of the uptake mechanism suggest that beta-adrenoceptor antagonists may be substrates for the organic cation transporter, OCT2. To confirm beta-adrenoceptor antagonists as substrates for OCT2, we demonstrate, in cells transiently transfected with an epitope tagged version of hOCT2 (hOCT2-V5):(1) Decynium-22 sensitive [(14)C]-propranolol uptake, (2) cis-inhibition of OCT2 by a range of beta-adrenoceptor antagonists and (3) metoprolol induced intracellular acidification.

Structural and functional characteristics and tissue distribution pattern of rat OCTN1, an organic cation transporter, cloned from placenta

This report describes the structure, function, and tissue distribution pattern of rat OCTN1 (novel organic cation transporter 1). The rat OCTN1 cDNA was isolated from a rat placental cDNA library. The cDNA is 2258 bp long and codes for a protein of 553 amino acids. Its amino acid sequence bears high homology to human OCTN1 (85% identity) and rat OCTN2 (74% identity). When expressed heterologously in mammalian cells, rat OCTN1 mediates Na +-independent and pH-dependent transport of the prototypical organic cation tetraethylammonium. The transporter interacts with a variety of structurally diverse organic cations such as desipramine, dimethylamiloride, cimetidine, procainamide, and verapamil. Carnitine, a zwitterion, interacts with rat OCTN1 with a very low affinity. However, the transport of carnitine via rat OCTN1 is not evident in the presence or absence of Na +. We conclude that rat OCTN1 is a multispecific organic cation transporter. OCTN1-specific mRNA transcripts are present in a wide variety of tissues in the rat, principally in the liver, intestine, kidney, brain, heart and placenta. In situ hybridization shows the distribution pattern of the transcripts in the brain (cerebellum, hippocampus and cortex), kidney (cortex and medulla with relatively more abundance in the cortical-medullary junction), heart (myocardium and valves) and placenta (labyrinthine zone).

NBD-TMA: a novel fluorescent substrate of the peritubular organic cation transporter of renal proximal tubules

Traditionally, the measurement of transport activity has employed radiolabeled compounds. The resulting experimental procedures do not measure transport in real time and are limited in temporal and spatial resolution. The use of epifluorescence microscopy provides the ability to measure transport activity in real time with high temporal and spatial resolution. Using epifluorescence microscopy we characterized the transport of the fluorescent organic cation, [2-(4-nitro-2,1,3-benzoxadiazol-7-yl)aminoethyl]trimethylammonium (NBD-TMA+, MW 266). NBD-TMA+ has structural characteristics common to other secreted organic cations and is fluorescent (lambda(ex)=458 nm; lambda(em)=530 nm). The excitation and emission spectra are insensitive to changes in [Cl-] and minimally sensitive to pH in the physiologically relevant range (pH 5.0-7.4). A microscope equipped with a photon-detection system was used to measure accumulation of NBD-TMA+ by isolated rabbit renal proximal tubules. Accumulation of NBD-TMA+ by proximal tubules was time dependent and saturable (Michaelis-Menten constant Km 12 microM). Proximal tubule accumulation of NBD-TMA+ was inhibited by the organic cations tetraethylammonium (TEA+) (apparent inhibitory constant K(app)TEA 134 microM), cimetidine, and N1-methylnicotinamide (NMN). Our experimental results provide strong evidence that NBD-TMA+ is transported by one or more of the basolateral organic cation transporters involved in the renal secretion of this chemical class of compound. This fluorescent substrate provides a sensitive means of investigating organic cation transport.

Rotational isomerism of the tetraethylammonium cation in solution and in the solid state

The tetraethylammonium ion Et4N+ is shown to present rotational isomerism in aqueous or organic solutions between an all-trans conformation (tt.tt or Greek cross) and a trans–gauche one (tg.tg or Nordic cross). The Raman spectra of the two rotamers are distinct and their temperature dependence indicates that (tt.tt) is more stable than (tg.tg) by about 4.1 kJ mol−1, i.e. by a value typical of two trans–gauche rotations. In some investigated solid salts at room temperature, the cation adopts one of these two conformations depending on the crystal structure and local packing effects induced by the anion. However, some other derivatives with bulky anions such as (Et4 N)2 CdBr4 and Et4 N(CF3 SO2)2 N exhibit much more complicated conformational situations for the cation as a function of temperature. Copyright © 2000 John Wiley & Sons, Ltd.

Transport of thiamine in human intestine: mechanism and regulation in intestinal epithelial cell model Caco-2.

The present study examined the intestinal uptake of thiamine (vitamin B(1)) using the human-derived intestinal epithelial cells Caco-2 as an in vitro model system. Thiamine uptake was found to be 1) temperature and energy dependent and occurred with minimal metabolic alteration; 2) pH sensitive; 3) Na(+) independent; 4) saturable as a function of concentration with an apparent Michaelis-Menten constant of 3.18 +/- 0.56 microM and maximal velocity of 13.37 +/- 0.94 pmol. mg protein(-1). 3 min(-1); 5) inhibited by the thiamine structural analogs amprolium and oxythiamine, but not by unrelated organic cations tetraethylammonium, N-methylnicotinamide, and choline; and 6) inhibited in a competitive manner by amiloride with an inhibition constant of 0.2 mM. The role of specific protein kinase-mediated pathways in the regulation of thiamine uptake by Caco-2 cells was also examined using specific modulators of these pathways. The results showed possible involvement of a Ca(2+)/calmodulin (CaM)-mediated pathway in the regulation of thiamine uptake. No role for protein kinase C- and protein tyrosine kinase-mediated pathways in the regulation of thiamine uptake was evident. These results demonstrate the involvement of a carrier-mediated system for thiamine uptake by Caco-2 intestinal epithelial cells. This system is Na(+) independent and is different from the transport systems of organic cations. Furthermore, a CaM-mediated pathway appears to play a role in regulating thiamine uptake in these cells.

A new layer type anionic host lattice constructed from urea, squarate, bicarbonate, and water molecules

A new inclusion complex bis(tetraethylammonium) squarate-tetraethylammonium hydrogen carbonate-urea-water [(C2H5)4N+ ]2C4O2-4 — 2(C2H5)4N+ HCO-3 — 4(NH2)2CO-6H5O has been prepared and characterized by X-ray crystallography. Crystal data: MoKα radiation, space group P21ln (No. 14), a = 12.283(2), b= 17.287(3), c= 14.898(3) a, υ= 101.27(3)0, Z= 2, R1= 0.055 for 3634 observed MoKα data. In the crystal structure of the title compound, cross linkage between hydrogen-bonded zigzag ribbons of the types [(urea)4(H2O)2]∞ and [(C4O2-4)(H2O)2(HCO-3)2(H20)2]∞ generates urea-anion host layers, with both well-ordered and disordered tetraethylammonium cations occupying the space between them.

Multiple-Scattering EXAFS Analysis of Tetraalkylammonium Manganese Oxide Colloids

X-ray absorption spectroscopy at the Mn K edge was employed to elucidate the structure of colloidal tetraalkylammonium (TAA) manganese oxides in sols and gels obtained by different preparation and heat treatment procedures. Two series of colloidal TAA MnOx prepared with tetrapropylammonium (TPA) and tetraethylammonium (TEA) cations were studied. Several manganese oxides, birnessite, and feitknechtite were also measured and served as model compounds for structural refinements. Near edge structure (XANES) analysis revealed different average valences of the colloidal systems. As synthesized and heat-treated, TAA colloids exhibited an average valence of 3.6−3.7, whereas gelled TAA colloids showed a lower average valence of ∼3.5. Extended absorption fine structure (EXAFS) analysis was carried out to distances of ∼6.0 A around the central Mn atom using theoretical backscattering phases and amplitudes calculated from the ab initio FEFF code. All multiple-scattering (MS) paths with a weight of 2% and more with re...

Layered Intermediates in Zeolite Synthesis: Are Structures Related?

Layered organic−inorganic compounds have been found during the crystallization of zeolites ZSM-48 and beta with hexamethonium and tetraethylammonium cations, respectively. These materials are obtained from gels with relatively high concentrations in organic species but are not stable under hydrothermal conditions. While highly crystalline solids are formed after short synthesis periods, their structure gradually collapses with synthesis time until a completely amorphous compound is formed. The stability of these materials can be increased by lowering the synthesis temperature, but zeolites start to crystallize only after the complete degradation of the layered structures. Even though the synthesis conditions, the gel compositions, and the structure of the final zeolite are different, the two layered materials seem to possess very similar structures, the main difference resulting from the nature of the interlayer organic molecules. These intermediate compounds display interesting intercalation properties t...

Structure of aqueous solutions of tetraethylammonium chloride investigated by positron annihilation and ultrasonic methods

The structure of aqueous solutions of tetraethylammonium chloride was investigated using compressibility and density measurements and positron annihilation methods. The experimental results are different from those obtained earlier for systems where hydrophobic hydration dominates, although some evidences for formation of cage-like hydrates in liquid phase were observed. The results are interpreted, among others, in terms of competition among different hydrates of the tetraethylammonium cations, hydration of chloride anions, and formation of ionic pairs.

Identity of the F52F12.1 gene product in Caenorhabditis elegans as an organic cation transporter

We describe here the cloning and functional characterization of an organic cation transporter from Caenorhabditis elegans (CeOCT1). The CeOCT1 cDNA is 1826 bp long and codes for a protein of 568 amino acids. The oct1 gene is ∼3.2 kb in size and consists of 12 exons. The location of this gene corresponds to the F52F12.1 gene locus on chromosome I. The predicted protein contains 12 putative transmembrane domains. It exhibits significant homology to mammalian OCTs. When expressed in mammalian cells, CeOCT1 induces the transport of the prototypical organic cation tetraethylammonium. The Michaelis–Menten constant for this substrate is 80±16 μM. The substrate specificity of CeOCT1 is broad. This represents the first report on the cloning and functional characteristics of an organic cation transporter from C. elegans.

13C Nuclear magnetic relaxation of tetraethylammonium cation in poly(acrylic acid) solution

The condensation of tetraethylammonium cations on poly(acrylic acid) is a progressive process and its extent is limited; the discontinuity of the titration curve, when α approaches 0.40 (ξ≈1), is probably an indication of several polyion–counterion system internal changes.

Langmuir monolayers of polydimethylsiloxane with controllable surface potential

Interaction of a Langmuir monolayer of polydimethylsiloxane (PDMS) with different hydrophobic ions added to the aqueous subphase was studied using surface pressure–area and surface potential–area isotherm techniques. For strongly hydrophobic tetraphenylborate (TPB) anions and tetraphenylphosphonium (TPP) cations, a pronounced shift of the monolayer surface potential accompanied by modest variations in the surface pressure isotherms was observed. Effects of TPB and TPP ions were found to be almost identical except the sign of a surface potential shift: it was positive for TPP and negative for TPB. An absolute value of this shift increased with concentration of hydrophobic ions and the monolayer surface density, whereas it was not affected by moderate variations of the subphase ionic strength. An effect of less hydrophobic ions (picrate anion and tetraethylammonium cation) was much less pronounced than that of TPP and TPB. A two-phase distribution model was proposed to describe the behaviour of hydrophobic ions in PDMS monolayer/subphase system. In spite of the extreme simplicity, the model appeared to describe rather well all experimental findings. It was shown that hydrophobic ions are located inside the monolayer. Their surface density is low; however, a shift of the surface potential is pronounced due to the low dielectric constant of monolayer material.

Structure of Aqueous Solutions of Tetramethylammonium Chloride Investigated by Positron Annihilation and Ultrasonic Methods

The structure of aqueous solutions of tetraethylammonium chloride was investigated using compressibility and density measurements and positron annihilation methods. The experimental results are different from those obtained earlier for systems where hydrophobic hydration dominates, although some evidences for formation of cage-like hydrates in liquid phase were observed. The results are interpreted, among others, in terms of competition among different hydrates of the tetraethylammonium cations, hydration of chloride anions, and formation of ionic pairs.

Synthesis of a merlinoite-type zeolite with an enhanced Si/Al ratioviapore filling with tetraethylammonium cations

A merlinoite type zeolite with an enhanced Si/Al ratio (around 3.8) compared to known isostructural materials has been synthesised hydrothermally from a gel with Si/Al=5 in the presence of tetraethylammonium and K+ cations. The zeolite has been characterised by a number of techniques and in its calcined form the structure was refined from synchrotron powder X-ray diffraction data [a=14.1291(10), b=14.1308(10), c=9.9274(5)A, Immm]. The different techniques reveal the enhanced Si/Al ratio of the zeolite. Tetraethylammonium is occluded within the tridimensional small pore channels, forcing the K+ and hence the Al content to diminish by 30–50% compared to conventional merlinoite-type zeolites. The thermal stability of the material is greatly improved, although if K+ cations in the zeolite are exchanged by NH4+ the stability decreases as a function of the degree of exchange, suggesting a low stability for the acidic form of merlinoite.

Thermogravimetric Evidence of Cobalt or Manganese Isomorphously Substituted into a Zeolite

Pure silica zeolite ZSM-5 has been synthesised in a slightly acidic aqueous fluoride medium which produces the protonated form of the zeolite ZSM-5 [1]. Tetrahalometallate [2] species of cobalt and manganese have been synthesised and increasing mole fractions incorporated into the zeolite synthesis gel. The products have been analysed and characterised using simultaneous thermogravimetric-derivative thermogravimetric analysis (TG-DTG). The thermal decomposition, under nitrogen of the associated tetraethylammonium (TEA+) and tetrapropylammonium (TPA+) cations occluded within the zeolite channels is indicative and characteristic of the incorporation of the heteroatoms into the zeolitic framework. Analysis by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), and Fourier transform infrared spectroscopy (FTIR) has confirmed the reliability of thermogravimetric (TG) and derived thermogravimetric analysis (DTG) as a diagnostic tool.

Expression Cloning and Characterization of ROAT1: THE BASOLATERAL ORGANIC ANION TRANSPORTER IN RAT KIDNEY

Expression cloning in Xenopus laevis oocytes was used to isolate an organic anion transport protein from rat kidney. A cDNA library was constructed from size-fractionated poly(A)+ RNA and screened for probenecid-sensitive transport of p-aminohippurate (PAH). A 2, 227-base pair cDNA clone containing a 1,656-base pair open reading frame coding for a peptide 551 amino acids long was isolated and named ROAT1. ROAT1-mediated transport of 50 mu M [3H]PAH was independent of imposed changes in membrane potential. Transport was significantly inhibited at 4 degrees C, or upon incubation with other organic anions, but not by the organic cation tetraethylammonium, by the multidrug resistance ATPase inhibitor cyclosporin A, or by urate. External glutarate and alpha-ketoglutarate (1 mM), both counterions for basolateral PAH exchange, also inhibited transport, suggesting that ROAT1 is functionally similar to the basolateral PAH carrier. Consistent with this conclusion, PAH uptake was trans-stimulated in oocytes preloaded with glutarate, whereas the dicarboxylate methylsuccinate, which is not accepted by the basolateral exchanger, did not trans-stimulate. Finally, ROAT1-mediated PAH transport was saturable, with an estimated Km of 70 mu M. Each of these properties is identical to those previously described for the basolateral alpha-ketoglutarate/PAH exchanger in isolated membrane vesicles or intact renal tubules.

Molecular basis for different pore properties of potassium channels from the rat brain Kv1 gene family.

Members of the rat brain Kv1 family of cloned potassium channels are structurally highly homologous, but have diverse conductance and pharmacological characteristics. Here we present data on the effects of mutating residues K533 in the P-region and H471 in the S4-S5 linker of Kv1.4 to their equivalent residues in Kv1.1 and Kv1.6 on single-channel conductance and sensitivity to external tetraethylammonium cations (TEA+) and internal Mg2+. Exchange of residue K533 for its equivalent residue (Y) in Kv1.1 and Kv1.6 increased the single-channel conductance at both negative and positive potentials. This mutation is known to reduce the IC50 for external TEA+ from > 100 mM to 0.6 mM, almost identical to that for Kv1.1 (0.53 mM). We have now found that the additional exchange of residue H471 for the equivalent residue (K) in Kv1.6 increased the IC50 for external TEA+ from 0.6 mM (Kv1.4K533Y) to 2.39 mM; this is very close to that for wild-type Kv1.6 channels (2.84 mM). The mutation H471K alone was ineffective. We thus provide evidence that the S4-S5 linker does contribute to the channel's inner-pore region. Data on the block of Kv1 channels by internal Mg2+ indicate that while the binding site is probably situated within the deep-pore region, its exact location may be channel specific.