Large Organic Ions Research Articles

The permeation of organic cations through cAMP-gated channels in mammalian olfactory receptor neurons.

The permeation of monovalent organic cations through adenosine 3',5'-cyclic monophosphate-(cAMP) activated channels was studied by recording macroscopic currents in excised inside-out membrane patches from the dendritic knobs of isolated mammalian olfactory receptor neurons (ORNs). Current-voltage relations were measured when bathing solution Na+ was replaced by monovalent organic cations. Permeability ratios relative to Na+ ions were calculated from changes in reversal potentials. Some of the small organic cations tested included ammonium (NH4+), hydroxylammonium and formamidinium, with relative permeability ratios of 1.41, 2.3 and 1.01 respectively. The larger methylated and ethylated ammonium ions studied included: DMA (dimethylammonium), TMA (tetramethylammonium) and TEA (tetraethylammonium) and they all had permeability ratios larger than 0.09. Even large cations such as choline, arginine and tris(hydroxymethyl)aminomethane (Tris) were appreciably permeant through the cAMP-activated channel with permeability ratios ranging from 0.19 to 0.7. The size of the permeating cations, as assessed by molecular weight, was a good predictor of the permeability. The permeability sequence of the cAMP-activated channel in our study was PNH4 > PNa > PDMA > PTMA > PCholine > PTEA. Higher permeability ratios of hydroxylammonium, arginine and tris(hydroxymethyl)aminomethane cannot be explained by ionic size alone. Our results indicate that: (i) cAMP-activated channels poorly select between monovalent cations; (ii) the pore dimension must be at least 6.5 x 6.5 A, in order to allow TEA and Tris to permeate and (iii) molecular sieving must be an important mechanism for the permeation of large organic ions through the channels with specific ion binding playing a smaller role than in other structurally similar channels. In addition, the results clearly indicate that cyclic nucleotide-gated (CNG) channels in different cells are not the same, the olfactory CNG channel being different from that of the photoreceptors, particularly with respect to the permeation of large organic cations, which the ORN channels allow to permeate readily.

Light-dependent ion channels in Octopus visual cell membranes: The permeability of large organic ions and effects of cyclic GMP

Electroretinograms (ERG) of Octopus vulgaris were obtained in various physiological solutions containing large organic cations in the place of Na + and large organic anions in the place of Cl − in the normal physiological solution. The permeabilities of the large organic ions to the light-activated membranes were plotted against the maximum spans of the smallest molecular silhouettes of these organic ions. Results suggested that the light-dependent ion channels in the octopus visual cell membranes have a higher permeability to these large organic ions than the Na +-channel and the acetylcholine acceptor. In the planar bilayer, lipid membranes, modified with membrane fractions of microvillar outer segments of octopus visual cells, ion channels of various conductance, 5–400 pS, were observed in 200 mM NACl, but those of the conductance, less than 50 pS, were detected in 200 mM large organic ions (Tris +-Hepes −). Cyclic GMP activated 10 pS-channels and inactivated 20 pS-channels in the lipid membranes. That DBcGMP abolished the fast component of the ERG suggests that the ion channels of 20 pS which can be blocked by cGMP are the most promising candidates for the light-dependent ion channels in the octopus visual cells.

Collision‐induced decomposition of large organic ions and inorganic cluster ions. Effects of pressure on energy losses

AbstractTranslational energy losses ΔE in keV‐collisions have been determined for peptide ions and for caesium iodide cluster ions subsequently decomposing to specific fragment ions, and the dependences of these energies upon transmission have been investigated. Parent ions decomposing to certain fragment ions exhibit energy losses which are independent of transmission, while parent ions associated with other fragment ions show strong dependence of energy loss upon transmission. These findings are interpreted in terms of energy redistributions of tens of eV taking place in single collisions via direct momentum‐transfer.

Ionic solvation in water + co-solvent mixtures: Part 24. Free energies of transfer of single ions from water into water + 1,2-dimethoxyethane mixtures

The spectrophotometric solvent-sorting method for determining the free energy of transfer of the proton from water into water + co-solvent mixtures Δ G t ⊖(H +) has been shown to apply to water-rich mixtures containing, 1,2-dimethoxyethane. Using Δ G t ⊖H +), values for Δ G t ⊖(anion) and Δ G t ⊖(cation) can be derived from the free energies of transfer of acids and salts. The free energy of transfer of the charge alone on large organic ions, Δ G t ⊖(i) e, has been calculated using p K a, values for organic acids in water and in the mixture in conjunction with Δ G t ⊖(H +) values. These values for Δ G t ⊖(i) and Δ G t ⊖(i) e in water + 1,2-dimethoxyethane mixtures are compared with similar free energies of transfer for ions from water into mixtures of similar co-solvents with water. To aid this comparison, values for the relative partial molar volumes of water and 2-methoxyethanol have been calculated for their mixtures.

Radial velocity distributions of secondary ions ejected in electronic sputtering of organic solids

Initial radial velocity distributions of large organic molecular ions as well as low mass contaminant and fragment ions ejected from a solid by impact of 72.3 MeV 127I 13+ have been measured by deflecting the secondary ions by means of a pair of deflection plates placed in the field-free region of a time-of-flight mass spectrometer. The radial velocity distributions have been studied as a function of the angle of incidence of the primary ion for different masses and charge states of the secondary ions. The results indicate that different ejection mechanisms may be involved, applicable in different regions of the secondary ion mass range.

Sputtering of bio-organic samples

In recent years methods based on particle impact on solid and liquid surfaces have been exploited to extend mass spectrometry to high-molecular-weight organic compounds, like biomolecules. One of the most important aspects of these sputtering methods is that one is able to produce ions of whole organic molecules. So far mainly charged ejecta, as exploited in the mass spectrometry applications, have been studied. Since a couple of years, experimental electronic sputtering yields of neutral intact ejecta are available, showing a cubic dependence on deposited energy. Studies of radial velocity distributions of large organic molecular ions show that the ejection angle is related to the angle of incidence of the primary particle. These experimental findings have been reproduced in molecular dynamics simulations of electronic sputtering of large organic molecules. Also an analytical sputtering formula has been derived which describes sputtering by a particle producing a high energy density, in qualitative agreement with experimental data.

Nitroxide radicals as probes for water mobility in perfluorinated membrane

In this paper the properties of water and of large organic ions or neutral molecules confined within the perfluorinated membrane Nafion are studied by electron spin resonance of nitroxide probes. The membrane was used in conditions of full hydration and after exchange with mono- and di-positive ions. The analysis was mainly based on the ESR lineshapes and the correlation times for the motion of positive, neutral, and negative radicals. The dependence of the lineshape on the charge of the probe and on the charge of metal ions was analyzed as a function of temperature. The behavior of adsorbed water was similar to that observed in other systems in which the liquid was finely dispersed. The decreased polarity of sorbed water as a consequence of the lower strength of the hydrogen bond, suggested by A. Falk ( Canad. J. Chem. 58, 1495 (1980)) was confirmed from the A N values of nitroxides. These were located in ionic clusters and were exposed to the interactions with pendant fluorocarbon chains. The extent of these interactions depended on the charge of either the nitroxides or the exchanged metal ion. The ESR patterns invariantly arose from the superposition of many absorptions due to radicals showing different motional rates and in slow exchange among different sites. This indicated the presence of ionic clusters of variable sizes in which water moved with different diffusion coefficients. The comparison between the ESR results and the previously reported NMR results confirmed the nonuniformities in the membrane structure.

Ion-Selectivity of Single Glutamate-Gated Channels in Locust Skeletal Muscle

ABSTRACT The ion-selectivity of the extrajunctional glutamate-gated ion channel in locust extensor tibiae muscle was studied using the patch-clamp technique. The alkali metal ions Li+, Na+, K+, Rb+ and Cs+ were all highly permeant, with reversal potentials close to 0mV. Both complete and partial replacement of Na+ (180 mmol I−1 in standard saline) showed that conductance (γ) increased in the order Li+< Na+< Cs+< Rb+ (approx. 70–125 pS), γK being close to γCs. The channel was impermeable to the large organic monovalent ions tetramethyl ammonium, guanidinium and choline, and permeable to the smaller ammonium ion. Divalent cations (Ca2+ and Mg2+) did not contribute measurably to the ionic current. Indications were obtained that high concentrations of Mg2+ or Ca2+ block the channel. The results suggest that the glutamate-gated channel combines a high conductance with a restricted ion-selectivity, based on ion charge and size, the conductance being dependent on the dehydration energy of the ionic species.

Operation of a hybrid tandem mass spectrometer of BEqQ configuration in scan modes using uncoupled analysers

Experimental methods are described for a tandem BEqQ instrument, which permit exploitation of the unit-mass resolution of the quadrupole mass filter, Q, in conjunction with desirable characteristics of collisionally activated reactions at keV energies. Existing methods require appropriate linked-scans of Q with the electric sector field, E. These linked-scans are difficult to generate accurately over wide scan ranges and, in any case, are inappropriate for cases in which large organic ions suffer appreciable energy-loss shifts upon collisional activation. The present method exploits the properties of Q as a true mass filter. The mass assignments of the fragment-ion peaks thus obtained are wholly independent of any energy shift and the experimental procedure requires absolutely no linkage of E and Q. Problems of reduced absolute sensitivity, encountered in the present exploratory experiments, are described. In addition, a related procedure is described which permits disentangling grand-daughter spectra from a mass-selected parent ion, arising via several daughter ions formed by high-energy CID and thus poorly resolved from one another.

On the detection of large organic ions by secondary electron production

A particle detector based on the detection of secondary electrons ejected at the impact of the particle on the detector surface has been constructed. It has been utilized in plasma desorption time-of-flight mass spectrometry to achieve post-acceleration yielding enhanced detection efficiency and identification of metastable decay channels in the spectrometer. Threshold velocities for electron ejection at the impact of large ions on a surface have been determined. Further, the multiplicity of secondary electrons ejected on the impact of the detected ion on the surface has been determined by energy measurements of the ensemble of ejected electrons.

Outer membrane protein K of Escherichia coli: purification and pore-forming properties in lipid bilayer membranes.

Protein K, a recently described outer membrane protein correlated with encapsulation in Escherichia coli (Paakkanen et al., J. Bacteriol. 139:835-841, 1979), has been purified to apparent homogeneity. Purification was based upon the noncovalent association of protein K with peptidoglycan, and the purified protein was shown to form sodium dodecyl sulfate-resistant oligomers on polyacrylamide gels. Incorporation of small amounts (10(-10) to 10(-11) M) of purified protein K into artificial lipid bilayers resulted in an increase, by many orders of magnitude, in membrane conductance. The increased conductance resulted from the formation of large, water-filled, ion-permeable channels exhibiting single-channel conductance in 1.0 M KCl of 1.83 nS. The membrane conductance showed a linear relationship between current and applied voltage and was not voltage induced or regulated. The channel was permeable to large organic ions (e.g., Tris+ Cl-) and, based upon a pore length of 7.5 nm, a minimum channel diameter of 1.2 nm was estimated; these properties resemble values for other enteric porins. The possible biological role of the pores produced by protein K is discussed.

金属イオンの溶媒抽出に用いられる有機試薬

Organic reagents which are used in the solvent extraction of metal ions are described from the point of view of the relation between their chemical properties and the efficiency of the extraction. What is necessary for good extractions in a two-liquid phase system is first itemized and the liquid-liquid distribution behavior of benzene mono-substituted derivatives is considered as an example. Then the distribution equilibria of several β-diketones and the extraction of zinc (II) with them are demonstrated. Solvent extraction of metal ions as ion-pairs with large organic counter ions and also as solvates with neutral organic reagents is then described. The extractions of lead (II) with two crown ethers with 18 membered ring are compared in order to show the effect of the two phase distribution tendency of the reagent and of the stability and extractability of the metal complex formed in the aqueous phase.

The laser spectroscopy of cool, cold, and very cold molecular ions

Molecular ions have long presented a challenge to spectroscopists. Because of the extreme difficulty in generating molecular ions in high concentrations, sensitivity limitations have restricted work in this field. The technique of laser-induced fluorescence (l.i.f.) has provided us with a means to partially overcome this limitation. L.i.f. spectra of small molecular ions, e.g. N 2 +, CO+ and CO 2 +, show Doppler-limited resolution. Besides their spectroscopic information content, such spectra also serve as quantum-state selective ion detectors, by which dynamical processes involving such ions can be followed. L.i.f. spectra have also been recorded for larger organic ions, e.g. olefinic, acetylenic and benzenoid cations. The large molecular ions’ spectral congestion, caused by the large number of levels populated at room or elevated temperatures, can severely limit the resolution and interpretability of the spectra. As a means of surmounting this problem, we have studied many of the cations at reduced temperatures. The techniques employed include liquid N 2 and free jet expansion cooling in the gas phase, and isolation in solid Ne matrices. The combination of these different spectra lead to a wealth of information about electronic structure, vibrational frequencies, Jahn-Teller effects, etc., in organic molecular ions.

Influence of additives on (hydroxyethyl) methylcellulose properties: relation between gelation temperature change, compressed matrix integrity and drug release profile

Tablets comprising a compressed matrix of a methylcellulose (MC) derivative mixed with various drugs and additives show 3 distinct types of behaviour in a disintegration test: rapid disintegration (D), gradual attrition (A) and maintenance of integrity (ND). Kinetic studies showed that ND matrices gave drug release related to square-root of time (i.e. matrix diffusional model) whereas a typical A matrix (salicylic acid-MC) deviated positively but observed the Hixson-Crowell cube-root equation for dissolutional control, as applicable to polyphase mixtures. In Une with these models, the matrix-controlled system was unaffected by and the dissolution one dependent on stirring conditions. For clarifying the mechanism of matrix behaviour, gelation temperature and viscosity were studied using dilute aqueous systems. Gelation temperature was raised by ND additives, salts containing large organic ions (including sodium benzoate, octanoate, salicylate, tetracaine-HCl. potassium phenoxypenicillin, chlorpheniramine maleate) thiocyanate and iodide. It was lowered by inorganic and small organic ions, lactose and some free organic acids causing A and D behaviour. The elevation, which has not hitherto been noted, is especially interesting. Intrinsic viscosity was raised by sodium salicylate and lowered by sodium chloride, the Huggins' constant being lowered by the former and raised by the latter. These gel point and viscosity changes reflect increased hydration and extension of the macromolecule chain in the former system and dehydration in the latter, such changes being associated with increased or decreased polymer cohesion in the compressed matrix.

Equilibrium exchange selectivity of alkaline earth, quaternary ammonium, and alkane diammonium ions in the release of Co(pn) 33+ from H-Co(pn) 3-bentonite

The selectivity coefficients of the bivalent inorganic ions in the release of Co(pn) 3 3+ from H-Co(pn) 3-bentonite are found to be much lower than those of the organic ions studied. However, both the hydrated ionic radius and the Debye-Hückel parameter a 0 of the alkaline earth metal cations give linear correlation with the relative affinities of the ions for the clay surface. In the lower concentrations of the tetraalkylammonium ions the effectiveness of the exchange of Co(pn) 3 3+ is in the sequence (CH 3) 4N < (C 2H 5) 4N < (C 3H 7) 4N < (C 4H 9) 4N while the order is just reversed at higher concentrations of the ions in solution. This behavior has been attributed to the collapse of the silicate layers in suspension once a critical level of surface coverage by these large organic ions has been achieved. The exchanging ability of the long chain surface active ions and alkane diammonium ions increases with the chain length of the ions. This is probably due to the progressive increase in the magnitude of the van der Waals forces between the clay and the organic ions and changes in hydration of the ions in the clay interlayer. The comparatively smaller bivalent inorganic ions, tetraalkylammonium and alkane diammonium ions desorb a much greater amount of Co(pn) 3 3+ from the clay matrix than the larger cetyltrimethylammonium or cetyl pyridinium ions. The lower displacement of Co(pn) 3 3+ could be caused due to the blocking of some of the exchange sites by the long chain surface active ions lying flat onto the clay surface.

Viscosities of solutions of electrolytes and non-electrolytes in ethylene carbonate at 40�C

The viscosities of dilute solutions of a number of tetraalkylammonium and alkali metal halides, tetraphenylarsonium chloride, sodium tetraphenylborate, tetrabutylammonium tetrabutylborate, water, and 3,3-diethylpentane have been measured in the high-dielectric constant solvent, ethylene carbonate (EC) at 40°C. Crude values of the apparent molar volumes of these solutes have also been obtained. Relative viscosities were fitted to the extended Jones-Dole equation, ηr=17#x002B;Aηc1/2+BηC+Dηc2.The pattern of the Bη coefficients is strikingly similar to that previously observed in the high dielectric constant, linear-chain hydrogen-bonded solvent, N-methylacetamide (NMA). Ionic values for φv and Bη have been obtained using a variety of splitting techniques. Alkali metal ions have large Bη coefficients indicating strong cation solvation with the ‘normal’ order Li>Na>K>Cs. Small anions have positive but much smaller Bη values than in NMA. The observed order does suggest, however, a small degree of anion solvation. Large organic ions do not display the sharp crossing of the Einstein law,Dη=2.5φv, uniquely characteristic in H2O of hydrophobic interaction. The two non-electrolytes have negative Bη coefficients showing that the Einstein law is not valid at the molecular level and that hydrocarbons are not good models for their isoelectronic tetraalkylammonium ion counterparts. An empirical modification of the Einstein law to account for the finite size of the solvent molecules is discussed. As in NMA the Dη coefficients are roughly linear in the square of Bη suggesting that they arise from hydrodynamic origins.

Properties of the large ion-permeable pores formed from protein F of Pseudomonas aeruginosa in lipid bilayer membranes

The incorporation of porin protein F from the outer membrane of Pseudomonas aeruginosa into artificial lipid bilayers results in an increase of the membrane conductance by many orders of magnitude. The membrane conductance is caused by the formation of large ion-permeable channels with a single-channel conductance in the order of 5 nS for 1 M alkali chlorides. The conductance has an ohmic current vs. voltage relationship. Further information on the structure of the pore formed by protein F was obtained by determining the single-channel conductance for various species differing in charge and size, and from zero-current potential measurements. The channel was found to be permeable for large organic ions (Tris +, N(C 2H 5) 4 +, Hepes −) and a channel diameter of 2.2 nm could be estimated from the conductance data (pore length of 7.5 nm). At neutral pH the pore is about two times more permeable for cations than for anions, possibly caused by negative charges in the pore. The consistent observation of large water filled pores formed by porin protein F in model membrane systems is discussed in the light of the known low permeability of the Ps. aeruginosa outer membrane towards antibiotics. It is suggested that this results from a relatively low proportion of open functional porin protein F pores in vivo.

Viscosities of solutions of electrolytes and nonelectrolytes inN-methylacetamide at 35� and 55�C

The viscosities of dilute solutions of a number of tetraalkylammonium and alkali metal halides, tetraphenylarsonium chloride, sodium tetraphenylborate, and tetrabutylammonium tetrabutylborate, as well as several nonelectrolytes have been measured in the high dielectric constant solvent N-methylacetamide (NMA) at 35 and 55°C. The relative viscosities were fitted to the extended Jones-Dole equation, ηГ = 1 + AηC1/2 + BηC + DηC2. The pattern of behavior of the Bη coefficients is roughly similar to that observed in H2O. However, the small ions have exceptionally large Bη values in this solvent due to strong solvation effects, while the large organic ions do not display the sharp crossing of the Einstein law, Bη=2.5 φV, characteristic in H2O of hydrophobic interaction. The Dη coefficients roughly parallel the Bη behavior and display remarkably regular ionic trends. This suggests that they arise largely from hydrodynamic origins. Nonelectrolytes have small or negative Bη coefficients showing that the Einstein law is not applicable at the molecular level and that nonelectrolytes are poor models for structurally similar ions. A simple mixture law is presented as an alternative to the Einstein law to explain the Bη coefficients.

Reversible Topotactic Redox Reactions of Solids by Electron/Ion Transfer

AbstractSolids having suitable structural and electronic properties are able to form intercalation compounds by reversible redox reactions at room temperatureviatopotactic electron/ion transfer processes. The host lattices range from inorganic solids with different structural dimensionality to organic molecular solids. Similarly, depending on the host lattice type, the guest species may vary from protons and metal ions to large inorganic and organic molecular ions. The possibilities of a systematic “tailoring” of new stable or metastable compounds, the controlled modification of physical properties of solids, and the technical application of electronic/ionic conductors, provide a wide and attractive field for academic and applied research in an interdisciplinary area that involves solid state chemistry and physics, molecular chemistry, electrochemistry, and interface science.

Interactions between large organic ions of opposite and unequal charge. III. Enthalpy—entropy linear compensation and application of solvophobic theory

The energetics of complex coacervation between large organic ions of opposite and unequal electrical charge have been determined. The interaction can be described in terms of ion association reinforced by a strong hydrophobic effect. This result has been shown to be a general one for large ion interactions as reflected in unique linear enthalpy—entropy compensation behavior. The temperature versus complex equilibria relationships were found to be complicated but can be reasonably described using Sinanoglu's solvophobic theory which shows that the interaction with respect to temperature is dependent upon the relative magnitude of surface and solvation energy terms and the size of the organic ions.