Influence Of Ion-pair Formation Research Articles

Thermodynamics of Fullerenes Reduction Revisited

The thermodynamics of fullerene C60 electroreduction, and 2′-ferrocenylpyrrolidino [3′,4′;1,2][C60]fullerene electroreduction and electrooxidation has been studied in different aprotic solvents containing tetra(alkyl)ammonium perchlorates as supporting electrolytes using dc cyclic voltammetry and square-wave voltammetry. Obtained values of formal potential were corrected for diffusion potential drop. The electrode processes of C60 reduction are accompanied by the ion pair formation. In each reduction step, one cation of supporting electrolyte is involved. The strength of ionic interaction increase with decrease in the interacting ions size. The association constant of ion pair formation, Ka, also depends on the solvent dielectric constant. A linear relationship between ln Ka and 1/ɛs has been found. The association constants obtained on the base of these relations depend on the solvents dielectric properties. The influence of ion pair formation process on the reduction and oxidation of 2′-ferrocenylpyrrolidino [3′,4′;1,2][C60]fullerene has also been compared. Both, anion formed during fullerene cage reduction and cation produced during ferrocene moiety oxidation are associated with one counter-ion from supporting electrolyte. The cation formed during oxidation much stronger interacts with perchlorate ions in comparison to the anion formed by electroreduction. The influence of ion pair formation on the donor-acceptor energy gap has been also discussed.

Influence of Ion-pair Formation on the Pharmacokinetic Properties of Drugs. Pharmacokinetic Interactions of Bretylium and Hexylsalicylic Acid in Rabbits

The simultaneous i.v. administration of equimolar doses of bretylium and hexylsalicylic acid results in an increase in plasma area under the curve value of both substances in comparison with their separate administration. The higher plasma levels of both compounds were associated with a reduced renal excretion and an increased biliary elimination. However, the increase in biliary excretion did not compensate for the reduced elimination of bretylium and hexylsalicylic acid via the kidney. The results presented in this paper give further evidence that ion-pairing in-vivo may result in altered pharmacokinetics of drugs particularly due to changes in biliary or renal excretion.

The Influence of Ion Pair Formation on the Phase Behavior of Polyelectrolyte Solutions

In this paper we calculate the phase diagrams of polyelectrolyte solutions taking into account the possibility of ion pair formation between counterions and ions on polymer chains with their subsequent aggregation in multiplets. Multiplets play a role of reversible physical crosslinks between different polymer chains. Furthermore, we assume that the dielectric constant, and hence the binding energy of ion pairs and multiplets, depends on the volume fraction of polymer in the solution. We have shown that ion pairing and multiplet formation leads to instability of the homogeneous phase, so that at some conditions the phase separation can proceed even in doog solvent. Another qualitatively new feature of the behavior of polyelectrolyte solutions is the emergence of a triple point on the phase diagram. The effect of the solvent polarity and the polarity of the dry polymer on the general form of the phase diagram is studied in detail.

Prediction of Distribution Coefficients from Structure. The Influence of Ion Pair Formation as Reflected in Experimental and Calculated Values

Prediction of Distribution Coefficients from Structure. The Influence of Ion Pair Formation as Reflected in Experimental and Calculated Values

Use of microelectrodes and spectroelectrochemical techniques in the study of redox properties of organometallic complexes: “Costa-type” coenzyme B 12 models

The electrochemical behaviour of the “Costa-type” coenzyme B 12 model neopentyl- N 2, N 2'-propane-diylbis (2,3-butanedione-2-imine-3-oxime) Co(III) perchlorate complex has been studied using a platinum inlaid disk microelectrode techniques over a wide range of supporting electrolyte concentrations, and thin-layer absorption spectroelectrochemistry. In the former case, the separation of the two single electron transfers leading to Co(I) increased with decreasing supporting electrolyte concentration and, at the same concentration of the supporting electrolyte, with increasing radius of the cation. The likely explanation for this behaviour is the influence of ion-pair formation on the reduction potential of the redox couple involved in the second electron transfer that leads to a Co(I) complex bearing a negative charge. It has been demonstrated that the plot of the derivative of the steady-state current with respect to the electrode potential vs. E is morphologically identical to the derivative of the absorbance in thin-layer spectroelectrochemistry, and that the correlation between the results obtained using the two different techniques is useful for a better understanding of the electrochemical process.

Deactivation behaviour of Photoexcited Aryltropylium Ions. IV. Influence of Ion Pair Formation

AbstractAryltropylium salts exhibit an unusually effective self quenching of fluorescence in dependence on their concentration in dichlòromethane. The quenching process is investigated by static and time resolved fluorescence measurements. The observed biexponential fluorescence decay is interpreted by the emissions of ion pairs and free cations. The rate constant of fluorescence quenching by formation ion pair is two orders of magnitude greater than the diffusion constant.

Hepatic uptake and biliary excretion of organic cations—II: The influence of ion pair formation

The influence of an anorganic anion iodide (I −) and an organic anion tetraphenylborate (TPB −) on the hepatic uptake and biliary excretion of three organic cations, triethylmethyl ammonium (TEMA), tripropylmethyl ammonium (TPMA) and tri- n-butylmethyl ammonium (TBuMA) was studied. The compounds were injected as a bolus (D = 1 μmole) and studied in isolated perfused livers. In the perfusion medium 25% of the amount of NaCl (3 mmole) was replaced by NaI, whereas in two other experiments TPB − was added to the medium in two concentrations (2 μM and 200, μM). NaI did not affect the biliary output of the three quaternary ammonium compounds (QACs) although an increased net rate of hepatic uptake was found for all compounds, most likely due to a decreased liver to plasma transport. Liver to plasma concentration ratios were increased, while the ratios between bile to liver and bile to plasma were not affected. TP − in catalytic amounts added to the medium (2 μM) decreased the biliary output of TEMA and TBuMA, whereas the kinetic profile of TPMA was unchanged. The decreased biliary excretion rate of TEMA was explained by a decreased plasma level (due to the increased liver uptake) assuming that the small molecular weight compounds can enter the bile directly from plasma via the junctional complexes between the cells. The bile to plasma (B/P) ratio was not affected. In contrast, the bile to plasma (B/P) ratio and the bile to liver (B/L) ratio of TBuMA were decreased, compared with the control, probably due to an increased reabsorption from the bile, whereas the back transport from the liver into the plasma was also decreased. A large amount of TPB − (200 μM), added to the perfusion medium, dramatically changed the kinetic profile of the three QACs. Ion pair formation between the QACs and TPB − was supposed to be responsible for this effect. Plasma levels dropped more rapidly as a result of an increased rate of liver uptake. The biliary excretion of all compounds was greatly reduced (the excretion rates were 0.022, 0.19 and 0.18 nmole/min, compared with 0.047, 0.71 and 7.5 nmole/min for the controls). It is concluded that ion pair formation may play a role in the hepatobiliary transport. The rate of liver uptake of the QACs is enhanced in the presence of an anion, which is due to an increase in plasma to liver transport ( k 12) and a reduced liver to plasma transport ( k 21). The increased net uptake into the hepatocytes however does not result in an increased biliary output. In fact the effects of ion pair formation on the biliary output can be strongly negative. The intra membrane potential hill, which is supposed to be influenced by TPB −, may be a barrier for liver uptake of QACs with low lipophilicity and also for reabsorption from the biliary tree of QACs with a high lipophilicity. The remarkable decrease in biliary transport of the QACs caused by TPB − may therefore be explained by reduction of the effective concentration for the canalicular transport of onium compounds within the cells, due to ion pair formation and/or an increased intracellular binding or alternatively to an increased bile to liver transport (increased biliary reabsorption).

Optical and NMR investigations on alkali ion pairs of carbanions and nitranions

Abstract The ion pair formation of some cyclic conjugated carbanions and nitranions has been studied by absorption and fluorescence spectroscopy. From the spectra, recorded as a function of temperature, solvent and counter ion it becomes clear that the absorption spectra of contact ion pairs are always shifted to high energy with respect to the spectra of solvent separated ion pairs, but in the fluorescence spectra shifts in both directions have been found. The observed phenomena can be explained satisfactorily by theoretical π-electron charge distributions in the ground and first excited states. Also with 1H and 13C NMR spectroscopy valuable information concerning the ion pairing has been obtained. An apparent discrepancy between the structure of the contact ion pair of the carbanion indenyl inferred from calculations and from 1H NMR is resolved by a theoretical examination of the effects of the cationic field on the proton chemical shifts. The 13C NMR data support the interpretation of the temperature dependence of the 1H chemical shifts in terms of a “direct” and an “indirect” effect of the cation. In order to explain the 1H chemical shifts of some anions with 16 π-electrons the occurrence of paramagnetic ring currents has to be postulated. 7Li NMR data give evidence for the structure of the contact ion pairs, σ- or π-complex. The influence of ion pair formation on the reaction rate of the symmetrical proton exchange reaction between a carbanion and its parent molecule has been studied from the exchange line broadening for the system indene/indenyl in various solvents.

Electrochemical reduction mechanism of phthalimide in DMF

Summary The electrochemical behaviour of phthalimide in DMF solutions and kinetics of the subsequent reactions has been examined by polarographic, chronopotentiometric and chronovoltammetric methods. Two possible mechanisms including second-order reactions have been considered, the first includes dismutation between two radical anions: RH + e = RH ⨪ 2 RH ⨪ → RH 2 − + R − RH 2 − + RH = RH 3 + R − and the second one includes dismutation between protonated radical and radical anion: RH + e = RH ⨪ RH ⨪ + RH = RH 2 · + R − RH 2 · + RH ⨪ → RH 2 − + RH RH 2 − + RH = RH 3 + R − The influence of ion-pair formation on the kinetics has been discussed.