Tetraphenylborate Anion Research Articles

Potentiometric Dipyridamole Sensors Based on Lipophilic Ion Pair Complexes and Native Ionic Polymer Membranes

ABSTRACT The construction and general performance characteristics of three novel potentiometric PVC membrane sensors responsive to the dipyridamole cation are described. These sensors are based on the use of the ion -association complexes of dipyridamole cation with tetraphenylborate and Reineckate counter anions as ion exchange sites in a plasticized PVC matrix.A plasticized native polymer (e.g., carboxylated polyvinyl chloride) is also used. These sensor exhibit linear and near- Nernstian response for 1×10−2 - 1×10−6 M dipyridamale with cationic slopes of 53.4 ? 55.1 mv/decade and the working pH range is 2-5. No interference are caused by many inorganic and organic cations due to complete dissolution and high exchange equiliburium of the ion-association electroactive complexes in the membrane phase. Fairly good thermodynamic ionic exchange process at the membrane/drug solution interface and good mechanical and thermal stability are obtained up to 60C. The sensor proved useful for determining dipyridamole in various dosage forms with an average recovery of 98.7% and a means standard deviation of0.6%.

Sputtering of Tetrafluoro- and Tetraphenylborate Anions Adsorbed to an Amine-Terminated Self-Assembled Monolayer Surface

Secondary ion mass spectrometry was used to monitor the exchange of tetrafluoro- and tetraphenylborate anions to the surface of an amine-terminated self-assembled monolayer. The exchanged surfaces were prepared by soaking aminoethanethiol (AET) monolayers on Au in solutions of the respective sodium salts. The mass spectra produced from the monolayer surface and those from Au blank and propanethiol monolayers soaked in the same salt solutions demonstrate that the protonated amine terminus of the AET monolayer is important to the uptake of the inorganic anion. The exchanged monolayer surfaces were used to measure secondary ion yields produced from ultrathin films by (CsI)nCs+ (n = 0−2) projectiles at the limit of single-ion impacts. The yield trends produced from the monolayer surface as a function of projectile complexity and energy differ dramatically from those generated from thicker targets of solid NaBF4 and NaB(Ph)4. Nonlinear enhancements (expressed as an increase in the secondary ion yield per proje...

Modeling the Proposed Intermediate in Alkane Carbon−Hydrogen Bond Activation by Cp*(PMe3)Ir(Me)OTf: Synthesis and Stability of Novel Organometallic Iridium(V) Complexes

Addition of HX to CH2Cl2 solutions of Cp*IrMe4 (Cp* = η5-C5Me5) at low temperature provided Cp*Ir(Me)3X (X = Cl, 5; X = OSO2CF3 = OTf, 6). Both complexes are very thermally sensitive yet proved to be useful precursors for novel cationic iridium(V) complexes. Treatment of 6 with a variety of trisubstituted phosphines, arsines, and stibines (L) afforded compounds 7−12, [Cp*(L)IrMe3][OTf] (L = PMe3, 7; L = PEt3, 8; L = PPh3, 9; L = AsEt3, 10; L = AsPh3, 11; L = SbPh3, 12). Metathesis of the triflate anion of antimony complex 12 for the tetraphenylborate anion afforded [Cp*(SbPh3)IrMe3][BPh4] (13). The molecular structure of 13 was determined by single-crystal X-ray diffraction analysis. Complex 7 is a potential model for the proposed intermediate on the methane carbon−hydrogen bond activation reaction pathway by Cp*(PMe3)Ir(Me)OTf, and its relevance to this reaction is discussed. Complex 7 decomposed by reductive elimination of MeCp*. The remaining iridium fragment was trapped by added phosphine to form [cis-{PMe3}4IrMe2][OTf] (14) as an impure mixture. Reaction of 6 with excess dppm (dppm = Ph2PCH2PPh2) afforded [cis-{η2-Ph2PCH2PPh2}2IrMe2][OTf] (15). The molecular structure of 15 was determined by single-crystal X-ray structure analysis.

Preparation, Structure, and Properties of a Mixed-Valent NiIINiIII Amine-Selenolate Complex

Two dinuclear nickel amine-selenolate complexes of the tridentate amine-selenolate ligand, 4-tert-butyl-2,6-di(aminomethyl)selenophenol (1b), have been synthesized and their properties characterized. The green complex [NiII2(1b)3]Cl (4a) is readily prepared from 1b, NiCl2 · 6 H2O, and NaOMe in methanol or by reaction of coordinatively unsaturated [NiII2(1b)2][BPh4]2 (2b) with another one equivalent of 1b in the presence of triethylamine. The face-sharing, bioctahedral structure of 4a is derived from UV/Vis spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction of its oxidation product, [NiIINiIII(1b)3]2+. The dication was prepared by air-oxidation of 4a in MeOH and isolated as the dark-brown BPh4− salt, [NiIINiIII(1b)3][BPh4]2 · CH3OH (4b). Mixed-valent complex 4b consists of a dinuclear, face-sharing bioctahedral dication with a central N3NiII(μ2-SeR)3NiIIIN3 core and well-separated tetraphenylborate anions. Distortions from D3h symmetry suggest that 4b is a trapped-valence compound in the solid-state. On the CV time scale complex 4a undergoes two reversible one-electron oxidations at E11/2 = –0.15 and at E21/2 = +0.29 V vs SCE, affording 4b and the thermally not stable trication [NiIII2(1b)3]3+, respectively. The EPR spectrum of a powdered sample of 4b reveals an S = 3/2 ground state of the mixed-valent NiIINiIII complex.

Neutral carrier-type ion sensors based on sol-gel-derived membranes incorporating a bis(crown ether) derivative by covalent bonding.

Sol-gel-derived membranes incorporating crown ether neutral carriers by covalent bonding have been designed for durable, nontoxic neutral carrier-type ion sensors by sol-gel processing using tetraethoxysilane, diethoxydimethylsilane, and their corresponding alkoxysilylated neutral carriers. A tetraphenylborate anion was also bound chemically to the neutral carrier-type sol-gel-derived membranes for suppressing anion interference and membrane impedance. Ion-sensitive field effect transistors (ISFETs) based on the sol-gel-derived membranes modified chemically by crown ether derivatives, such as 16-crown-5 and bis(12-crown-4) derivatives, showed high performance, high sensitivity in wide cation activity ranges, short response time, and high electrode durability. Specifically, high ion selectivities of practical use in biological systems were attained in the sodium ISFETs based on the chemically modified bis(12-crown-4), which has been successfully applied to sodium assay in blood sera.

Interaction of DPPC monolayer at air–water interface with hydrophobic ions

Interaction of a Langmuir monolayer of dipalmitoylphosphatidylcholine (DPPC) with different hydrophobic ions added to the aqueous subphase was studied using surface pressure-area and surface potential-area isotherm techniques. Strongly hydrophobic tetraphenylborate (TPB) anions cause marked expansion of the monolayer and drastic decrease of surface potential. Both effects grow gradually with the TPB concentration, the first shows also an increase with the ionic strength. The influence of the less hydrophobic picrate anions is qualitatively similar, but essentially weaker than that of TPB. The results obtained can be described in terms of the competition of two effects: (i) both the hydrophobic interaction and local electrostatic attraction between anions and ammonium moiety of DPPC promote incorporation of hydrophobic ions into the monolayer, that results in its charging; (ii) long-range electrostatic repulsion between the charged monolayer and ions prevents further incorporation of the later. In contrast to TPB anions, the strongly hydrophobic tetraphenylphosphonium (TPP) cations have only a minor influence on the DPPC monolayer. This marked difference can be explained by taking into account dissimilarities in the degree of hydration, charge density and migration ability between the negatively-charged phosphate and the positively-charged ammonium moieties of DPPC head group.

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.

The effects of covalent binding of the electroactive components in durable CHEMFET membranes—impedance spectroscopy and ion sensitivity studies

The effects of covalent attachment of the electroactive components (i.e. the cation receptor molecules and the tetraphenylborate anions) in durable CHEMFET membranes is described. CHEMFETs for monovalent cations having either one or both electroactive components covalently bound in the membrane matrix exhibit Nernstian responses and good selectivities for Na+, or K+ ions, however, covalent attachment of borate in the membrane results in non-functioning sensors. Durability studies with CHEMFETs modified with polysiloxane membranes which are selective for Na+, K+ and Pb2+ ions show long lifetimes upon continuous exposure to a water stream. Na+ selective CHEMFETs with covalently attached Na+ ionophores and free borate in the membrane are still Na+ selective after 82 weeks of continuous exposure to water. Similar K+ and Pb2+ selective polysiloxane CHEMFETs showed good selectivities for at least 26 and 19 weeks, respectively. Impedance measurements showed that in all cases the lowest membrane resistance and the most stable CHEMFETs were obtained with polysiloxane membranes containing covalently attached ion-selective calix[4]arene-based receptor molecules and free anionic sites.

Ultrafast dynamics of photogenerated styrylpyridinyl radical and its dimer radical cation with styrylpyridinium cation studied by femtosecond laser flash photolysis

Ultrafast photoinduced electron transfer reaction and dimer radical cation formation have been studied at room temperature in less polar solvents by femtosecond laser flash photolysis of ion-pair charge-transfer complexes between a styrylpyridinium cation and a tetraphenylborate anion. In addition to the visible absorption due to the styrylpyridinyl radicals, the charge resonance absorption band (CR band) due to the electronic interaction between the photogenerated styrylpyridinyl radical and the styrylpyridinium cation was observed in the near infrared region. Transient absorptions of both radicals and the CR band showed very rapid rise in less than 1 ps, which was limited by the time resolution of the flash photolysis system. No interaction of styrylpyridinium cations was observed before photoexcitation. These results strongly suggested that the electronic interaction between the styrylpyridinium ion and its reduced form occurred without a diffusion process immediately after photoinduced electron transfer. From the decay dynamics, the dimer radical cation was found to show a faster back electron transfer than the radical itself.

Wechselwirkungen in Kristallen. 136. Protonierte Di(pyrid-2-yl)amin-Salze mit verschiedenen Anionen: Monomeres Tetraphenylborat sowie Bis(trifluormethylsulfonat), dimeres Squarat und polymeres Chlorid-Dihydrat

Interactions in Crystals. 136. Protonated Dipyridylamine Salts with Different Anions: Monomeric Tetraphenylborate as well as Bis(trifluormethylsulfonate), Dimeric Squarate and Polymeric Chloride Dihydrate Di(pyrid-2-yl)amine is monoprotonated by acetic, squaric as well as hydrochloric acid and diprotonated by trifluoromethylsulfonic acid. To explore the anion and hydrogen-bridge dependency of its salts, crystals of the monomeric tetraphenylborate, the dimeric squarate as well as the bis(trifluoromethylsulfonate) and the polymeric chloride hydrate have been grown and their structures determined: Separated by bulky tetraphenylborate anions, pyrid-2-yl(2′-pyridinium) amine cation contains an intramolecular hydrogen bridge N⊕H…︁N and is slightly folded. The squarate salt dimer exhibits additional bridges, NH…︁O⊖ and OH…︁O. The severely twisted di(2-pyridinium)amine dication is connected to its trifluormethylsulfonate counter anions by altogether three H-bridges, two N⊕H…︁O and one NH…︁O. The chloride dihydrate crystallizes in layers of 16-membered rings, formed from three Cl anions and five water molecules. The diversity of the hydrogen-bridge dominated salt structures is discussed based on comparison with selected literature examples and on PM3 calculations.

Tetraphenylborate adducts of lead(II) co-ordinated by imidazole-functionalized 1,4,7-triazacyclononanes: crystal and molecular structures

The new functionalized macrocycles 1-(1-methylimidazol-2-ylmethyl)-1,4,7-triazacyclononane, L1, 1,4-bis(1-methylimidazol-2-ylmethyl)-1,4,7-triazacyclononane, L2, and 1,2-bis[4,7-bis(1-methylimidazol-2-ylmethyl)-1,4,7-triazacyclonon-1-yl]ethane, L3, have been synthesized. The reaction of hydrated lead(II) acetate with these compounds in the presence of sodium tetraphenylborate afforded the complexes [PbL1Cl(BPh4)]·0.5MeCN, [PbL2(BPh4)]BPh4 and [Pb2L3(BPh4)2][BPh4]2·4MeCN which were characterized in the solid state by elemental analyses and X-ray crystallography. The lead(II) atoms are co-ordinated by the nitrogens of the macrocyclic ring, by the nitrogen donor(s) of the pendant imidazole group(s) and, in the complex with the L1 ligand, also by a chlorine atom. In each of the three complexes a phenyl group of a tetraphenylborate anion lies at close contact distance from the lead and completes its co-ordination.

Hydration and Covalence of the Ln2+ and An2+ Ions vs. Alkaline Earth Ions as Reflected in Solubility and Cocrystallization of Their Sulfates

Solubilities of some divalent lanthanide and actinide sulfates were evaluated and compared with the solubilities of alkaline earth sulfates. It has been concluded that the shift of the solubilities of LnSO4 and AnSO4 towards the solubility of BaSO4 is a consequence of differences in the aquo ion structure between [Ln(OH2)9]aq 2+, [An(OH2)9]aq 2+, [Ba(OH2)9]aq 2+ and [Ra(OH2)9]aq 2+ vs. [Sr(OH2)8]aq 2+ and [Ca(OH2)8]aq 2+. This difference in the primary hydration number throws light on the problem of the nomadic behavior of Eu(II) which, depending on the system, migrates from Ca(II) to Ba(II) on plots of the Gibbs solution and complexation energies. The virtual absence of the covalent shortening in the Euaq 2+ aquo ion slightly enlarges the Eu2+ ion, and this makes its primary hydration number higher by 1 than that of the Sr2+ ion. The increase in the coordination number (CN) for the Euaq 2+ species with respect to the Sraq 2+ species is supported by the solution enthalpy and entropy values of the respective sulfates. In particular, the difference in the primary hydration explains why the solubility product of EuSO4 is about two orders of magnitude lower than that of SrSO4 and close to BaSO4, while the stability of the Eu(II) complexes with EDTA, DCTA and 2-picolinic acid is close to that for the respective Ca complexes. The stronger interactions in the octaaquaions(II) than in the nonaaquaions(II) is the reason why, in oposition to Sr2+, the ions of Eu2+, Yb2+ and Es2+ form inner sphere complexes with tetraphenylborate anions in aqueous-ethanolic solutions. The same reason elucidates why, contrary to the Lnaq 2+ and Anaq 2+ species, Sraq 2+ does not form complexes with o-phenantroline and dipirydyl.

Interaction of Hydrophobic Ions with a Langmuir Monolayer of Dioctadecyldimethylammonium Bromide

Interaction of a positively charged dioctadecyldimethylammonium bromide monolayer with three different single-charged hydrophobic anions, namely, hexafluorophosphate (HFP), picrate, and tetraphenylborate (TPB), was studied by surface pressure, surface potential isotherm, and ellipsometric techniques. Two models of monolayer−ion interaction were considered: adsorption to the head groups and incorporation into the monolayer. It was shown that the nature of ion−monolayer interaction depends on the hydrophobic properties of ions. The least hydrophobic HFP anion adsorbs to the head groups of the monolayer. This leads to a moderate decrease of the surface potential and more close packing of the monolayer. Ellipsometric data as well agree with the adsorption model. More hydrophobic picrate and strongly hydrophobic TPB anions incorporate into the monolayer. It reveals a drastic drop of the surface potential, which is due to the formation of an additional double electric layer inside the monolayer. Variations of ...

Diphenhydramine‐selective plastic membrane sensor and its pharmaceutical applications

AbstractDifferent types of PVC‐matrix ion‐selective electrodes (ISEs) that respond to the cationic form of diphenhydramine (Dph) are described. Three ion‐pairing agents, namely tetraphenylborate (TPB), phosphotungstate (PT), reineckate (RN) are investigated. The best PVC polymeric membrane contains Dph‐TPB as active material. The electrode, based on the ion‐pair complex with TPB anion shows near‐Nernstian response in the concentration range 10−2 to 3.5 × 10−5 M (Dph.HCl). Changing pH within the range 2.0–7.5 did not affect the electrode performance. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coeffcient of the electrode (0.00156 V/°C) The electrode showed a good selectivity for Dph with respect to a large number of inorganic and organic cations. The standard addition method and potentiometric titration were applied to determine Dph amounts in pharmaceutical preparations. The Dph selective membrane electrode was also applied to the determination of the dissolution profile of Dph tablets. The dissolution results were compared with spectrophotometrically determined ones.

Exchange Coupling in an Isostructural Series of Face-Sharing Bioctahedral Complexes [LM(II)(&mgr;-X)(3)M(II)L]BPh(4) (M = Mn, Fe, Co, Ni, Zn; X = Cl, Br; L = 1,4,7-Trimethyl-1,4,7-triazacyclononane).

The reaction of the divalent metal halides ZnCl(2), ZnBr(2), MnCl(2).4CH(3)CN, MnBr(2), FeCl(2).4CH(3)CN, CoCl(2).4CH(3)CN, CoBr(2), NiCl(2).6H(2)O, and NiBr(2), respectively, with the macrocycle 1,4,7-trimethyl-1,4,7-triazacyclononane (L) (1:1) in anhydrous acetonitrile, acetone, chloroform, or ethanol affords upon additon of NaBPh(4) the isomorphous series of complexes [LM(II)(&mgr;-X)(3)M(II)L]BPh(4): 1, M = Zn, X = Cl; 2, Zn, Br; 3, Mn, Cl; 4, Mn, Br; 5, Fe, Cl; 6, Co, Cl; 7, Co, Br; 8, Ni, Cl; 9, Ni, Br. Six of these complexes have been structurally characterized by single-crystal X-ray crystallography; they crystallize in the triclinic space group P&onemacr; (No. 2) with Z = 4. Crystal data are as follows 1, a = 16.654(1), b = 17.042(1), c = 17.684(1) Å, alpha = 97.30(1), beta = 93.58(1), gamma = 117.46(1) degrees; 3, a = 16.632(8), b = 17.012(8), c = 17.855(5) Å, alpha = 97.16(3), beta = 93.37(3), gamma = 117.24(3) degrees; 5, a = 16.658(3), b = 17.064(3), c = 17.741(4) Å, alpha = 97.32(3), beta = 93.47(3), gamma = 117.36(3) degrees; 6, a = 16.640(3), b = 17.040(3), c = 17.686(4) Å, alpha = 97.39(3), beta = 93.58(3), gamma = 117.39(3) degrees; 8, a = 16.608(3), b = 16.995(3), c = 17.555(3) Å, alpha = 97.36(1), beta = 93.52(1), gamma = 117.52(1) degrees; 9, a = 16.680(3), b = 17.016(2), c = 17.715(3)Å, alpha = 96.99(1), beta = 93.70(1), gamma = 117.42(1) degrees. All complexes consist of a dinuclear, face-sharing bioctahedral monocation with three &mgr;(2)-Cl or &mgr;(2)-Br bridging ligands and two LM fragments and well-separated tetraphenylborate anions (1:1). The cations cocrystallize in two different forms: an enantiomeric form with (lambdalambdalambda) (or (deltadeltadelta)) conformation at both LM fragments and a meso form with an (lambdalambdalambda) conformation at one LM fragment and (deltadeltadelta) at the other (ratio 1:1). From temperature-dependent magnetic susceptibility measurements (2-293 K) it was established that the spins of the unpaired electrons in 3 (d(5)d(5) high spin), 4 (d(5)d(5)), 6 (d(7)d(7) high spin), 7 (d(7)d(7)), 8 (d(8)d(8)), and 9 (d(8)d(8)) are intramolecularly, weakly antiferromagnetically coupled in each case. Surprisingly, the spins order ferromagnetically in 5 (d(6)d(6) high spin). This is in contrast to the previously reported complex [(thf)(3)Fe(II)(&mgr;-Cl)(3)Fe(II)(thf)(3)][SnCl(5)(thf)] (thf = tetrahydrofuran)(5) for which a new analysis of the temperature-dependence of the magnetic susceptibility and of field-dependent Mössbauer spectra establish a weak intramolecular antiferromagnetic coupling. The origin of this difference is analyzed.

Narrow and Wide EPR Lines of C60 −

C60 is photochemically reduced in the presence of tetraphenylborate anion to C60 −. The primary products A and B are characterized with narrow EPR lines (< 0.1 mT), and then, consecutively, radical C with a 3 mT wide EPR line is observed, which correlates with the formation of a sediment.

Protonation of porphyrins in liquid PVC membranes: Effects of anionic additives and application to pH-sensing

We report on a study on the protonation of representative porphyrins, metalloporphyrins, porphyrin-ketones and a Pd-porphyrin Schiff base in aqueous solution and when dissolved in plasticized PVC membranes. The respective protolytic forms were characterized by absorption and emission spectra as well as apparent p K a values. It is shown that the protonation of porphyrins dissolved in PVC membranes is much more difficult than in solution, resulting in an extraordinarily large decrease in the apparent p K a values which can be as large as 5 units when compared to the corresponding data for the porphyrins in solution. In certain cases, no protonation at all occurred within the pH 2–12 range. At the same time, N-MeEP which is much more basic (its intrinsic p K being 11.2) can be protonated in such membranes into the monocation at weakly acidic pH, but the apparent p K a also is lowered by about 6 units. On addition of a tetraphenylborate anion to the PVC membranes, protonation was found to proceed much easier. Both the monocation and dication was identified in case for the porphyrins, while for the prophyrin-ketones protonation into dication took place, and N-methyl-etioprophyrin was present as the monocation over the whole pH 2–12 range. Membranes composed of solutions of porphyrin-ketones or the Pd-porphyrin Schiff base in plasticized PVC were identified as being useful for purposes of continuously sensing pH in the physiological range. Their response time, calibration curves, signal stability and effects of buffer ionic strength and temperature were investigated in more detail.

Wechselwirkungen in Kristallen. 98. Mitt. Protonierte Hexamethylmelamin-Salze mit verschiedenen Anionen: Monomeres Tetraphenylborat, dimeres Trifluoracetat und polymeres Chlorid-Dihydrat

Interaction in Crystals. 98. Protonated Hexamethylmelamin Salts with Different Anions: Monomeric Tetraphenylborate, Dimeric Trifluoracetate and Polymeric Chloride-Dihydrate Hexamethylmelamin (2,4,6-tris(dimethylamino)-1,3,5-triazine), on monoprotonation at one of the triazine nitrogens keeps its close to planar skeleton. Its salts with different anions reflect biochemically interesting hydrogen-bridge networks: Crystallization of the hydrochloride from isopropanol solution containing Li⊕ [B⊖(C6H5)4], yields “naked” molecular cations, packed in herringbone fashion in between the lattice-dominating bulky, phenyl-shielded and non-protonable tetraphenylborate anions. From trifluoroacetic acid, crystals with sandwich-like subunits connected by hydrogen-bridged anions [F3CCOO⊖…︁HOOCCF3] are obtained. The hydrochloride salt, prepared by adding aqueous HCl to a diethylether solution, crystallizes in stacks of triazinium cation dimers with an intermolecular bridge N⊕-H…︁Cl⊖…︁H⊕N in between chloride-bydrate strands (…︁Cl⊖…︁HOH…︁O(H)H…︁Cl⊖…︁). Together, the structures of the three different hexamethyl-melaminium salts further illustrate the influence of anions on the crystallization of protonated nitrogen heterocycles and complement that of counter cation cation solvation in molecular anion salts.

Evidence for ion chain mechanism of the nonlinear charge transport of hydrophobic ions across lipid bilayers

The conductivity across a lipid bilayer by tetraphenylborate anion is increased 10-fold on the photoformation of lipophilic porphyrin cations. The cations alone have negligible conductivity. This nonlinear photogenerated increase of ion conductivity is termed the photogating effect. Substitution of H by Cl in the para position of tetraphenylborate leads to a 100-fold enhancement of conductivity, whereas the dark conductivities for this and other substituted borates are the same. Moreover, the halo-substituted borates show a large enhancement of conductivity in the low concentration range (10(-8) M), whereas that of tetraphenylborate is small and space charge is negligible. The enhanced ion conductivity has great structural sensitivity to the structure of the anion, the cation, and the lipid, whereas the partition coefficient of all the borates and the concentration of photoformed cations are only slightly affected. The photogated ion transport has a twofold larger activation energy than transport in the dark. Time-resolved photocurrents and voltages demonstrate that the translocation rate of the porphyrin cation is also enhanced 100-fold by the Cl-borate anion but only 10-fold by the H-borate anion. For these reasons the nonlinear gating effect cannot be explained by electrostatics alone, but requires an ion chain or ion aggregate mechanism. Kinetic modeling of the photoinduced current with a mixed cation-anion ion chain can fit the data well. The photogating effect allows the direct study of ion interactions within the bilayer.

Interaction of hydrophobic ions with amphiphile monolayers at the air-water interface

The interaction of monolayers of stearylamine (SAM) and dioctadecyldimethylammonium (DODA) at the air-water interface with hydrophobic ions in the water phase was investigated by using the techniques of two-dimensional pressure isotherms and the surface electrostatic potential. In both cases the interaction with tetraphenylborate anions results in the formation of mixed monolayers whose properties sharply differ from those of the original monolayers. The effect of sulaphase composition on the formation of mixed monolayers has been studied. A qualitative description of the interaction under study has been given. A model including the phase inhomogeneity of the mixed monolayer and the formation of multilayer structures from the areas of the “surface salt” has been suggested. The strong effect of hydrophobic ions on the monolayers is not only due to Coulomb interaction; their hydrophobic properties also play an important role.