Solvent Effects on the Absorption Spectrum of the Product and the Equilibrium Constant for the Proton Transfer Reaction from 1-Phenacylquinolinium Bromide to Amines

The equilibrium constants, K ₂, have been determined for the proton-transfer reactions of 1-phenacylquinolinium ion, PHQ⁺, with several amines {triethylamine (TEA), N,N,N′,N′-tetramethylethylenediamine (ED), N,N,N′, N′-tetramethylpropanediamine (PD), N,N,N′,N′-tetramethylbutanediamine (BD), and 1,8-bis(dimethylamino-naphthalene (DMAN)} in acetonitrile (AN), AN-tetrahydrofuran (THF) and AN-ethanol (EtOH) mixtures. The reaction was followed spectrophotometrically using a stopped-flow technique. The K ₂ value decreased for DMAN and increased for TEA with increasing vol-% of THF in AN-THF mixtures. The changes in the K ₂ value for ED, PD and BD changed in the order: ED, PD and BD from a pattern similar to TEA to a pattern similar to DMAN. The change in the K ₂ value for DMAN with increasing vol-% of THF in AN-THF mixtures was explained by the effect of polarity on the stability of P⁻Q⁺ (the deprotonated product of PHQ⁺). The effect of THF on the K ₂ value is consistent with that of the peak wavelength of the absorption spectrum of P⁻Q⁺. The change in the K ₂ value for TEA, ED, PD and BD depended on the structures of the protonated bases, one of the products for this reaction. The effect of EtOH on the K ₂ value for DMAN was examined in ternary EtOH-THF-AN mixtures that contain different amounts of EtOH and whose relative permittivities were adjusted to that of EtOH. The K ₂ value increased with increasing vol-% of EtOH because of the stabilization of P⁻Q⁺ upon the formation of the hydrogen-bonded complex with EtOH. The absorption spectrum of P⁻Q⁺ demonstrated a blue shift as the vol-% of EtOH increased.     

Capillary electrophoretic study of thiolated α-cyclodextrin-capped gold nanoparticles with tetraalkylammonium ions

Capillary zone electrophoresis (CZE) has been employed to characterize nanometer-sized thiolated α-cyclodextrin-capped gold nanoparticles (α-CD-S-AuNPs). The addition of tetrabutylammonium (Bu₄N⁺) ions to the run buffer greatly narrows the migration peak of α-CD-S-AuNP. The optimal run buffer was determined to be 10 mM Bu₄N⁺ in 30 mM phosphate buffer at pH 12 and an applied voltage of 15 kV. The effect of various tetraalkylammonium ions on the peak width and electrophoretic mobility (μ_e) of α-CD-S-AuNP was studied in detail. Bu₄N⁺ ions assist in inter-linking the α-CD-S-AuNPs and narrowing the migration peak in CZE. This observation can be explained by the fact that each Bu₄N⁺ ion can simultaneously interact with several hydrophobic cavities of the surface-attached α-CDs on AuNPs. The TEM images show that α-CD-S-AuNPs with Bu₄N⁺ are linked together but in the absence of Bu₄N⁺, they are more dispersed. The migration mechanism in CZE is based on the formation of inclusion complexes between Bu₄N⁺ and α-CD-S-AuNPs which induces changes in the charge-to-size ratio of α-CD-S-AuNPs and μ_e. An inverse linear relationship (r² > 0.998) exists between the μ_e and size of α-CD-S-AuNPs in the core range 1.4–4.1 nm. The CZE analyses are rapid with migration time less than 4 min. A few nanoliters of each of the α-CD-S-AuNP samples were injected hydrodynamically at 0.5 psi for 5 s. Our work confirms that CZE is an efficient tool for characterizing the sizes of α-CD-S-AuNPs using Bu₄N⁺ ions.     

Tetraalkylammonium Picrates in the Dichloromethane–Water System: Ion-Pair Formation and Liquid–Liquid Distribution of Free Ions and Ion Pairs

Equilibria concerning picrates of tetraalkylammonium ions (Me₄N⁺, Et₄N⁺, Pr₄N⁺, Bu₄N⁺, Bu₃MeN⁺) in a dichloromethane−water system have been investigated at 25 ^∘C. The 1:1 ion-pair formation constants (K _IP,o ^o) in dichloromethane at infinite dilution were conductometrically determined. The distribution constants (K _D ^o) of the ion pairs and the free cations between the solvents were determined by a batch-extraction method. The K _IP,o ^o value varies in the cation sequence, Bu₄N⁺ ≈ Pr₄N⁺ ≈ Et₄N⁺ < Bu₃MeN⁺ < < Me₄N⁺; this trend is explained by the electrostatic cation−anion interaction taking into account the structures of the ion pairs determined by density functional theory calculations. For the ion pairs of the symmetric R₄N⁺ cations, there is a linear positive relationship between log₁₀ K _D ^o and the number of methylene groups in the cation (N _{CH 2}). The ion pair of asymmetric Bu₃MeN⁺ has a higher distribution constant than that expected from the above log₁₀ K _D ^o versus N _{CH 2} relationship. These cation dependencies of log₁₀ K _D ^o for the ion pairs are explained theoretically by using the Hildebrand-Scatchard equation. For all the cations, the log₁₀ K _D ^o value of the free cation increases linearly with N _{CH 2}; the variation of log₁₀ K _D ^o is discussed by decomposing the distribution constant into the Born-type electrostatic contribution and the non-Born one, and attributed to the latter that is governed by the differences in the molar volumes of the cations. The cation dependencies of the ion-pair extractability and ion pairing in water are also discussed. An erratum to this article can be found at     

Steric Control in the π‐Dimerization of Oligothiophene Radical Cations Annelated with Bicyclo[2.2.2]octene Units

A Two series of oligothiophenes 2 (nT) (n=4,5), annelated with bicyclo[2.2.2]octene (BCO) units at both ends, and quaterthiophenes 3 a – c , annelated with various numbers of BCO units at different positions, were newly synthesized to investigate the driving forces of π‐dimerization and the structure–property relationships of the π‐dimers of oligothiophene radical cations. Their radical‐cation salts were prepared through chemical one‐electron oxidation by using nitrosonium hexafluoroantimonate. From variable‐temperature electron spin resonance and electronic absorption measurements, the π‐dimerization capability was found to vary among the members of the 2 (nT)^{+ .} SbF₆^? series and 3 ^{+ .} SbF₆^? series of compounds. To examine these results, density functional theory (DFT) calculations at the M06‐2X/6‐31G(d) level were conducted for the π‐dimers. This level of theory was found to successfully reproduce the previously reported X‐ray structure of ( 2 (3T))₂²⁺ having a bent π‐dimer structure with cis–cis conformations. The absorption bands obtained by time‐dependent DFT calculations for the π‐dimers were in reasonable agreement with the experimental spectra. The attractive and repulsive forces for the π‐dimerization were divided into four factors: 1) SOMO–SOMO interactions, 2) van der Waals forces, 3) solvation, and 4) Coulomb repulsion, and the effects of each factor on the structural differences and chain‐length dependence are discussed in detail.     

The Surface Activity of the Hydrated Proton Is Substantially Higher than That of the Hydroxide Ion

The behavior of hydroxide and hydrated protons, the auto‐ionization products of water, at surfaces is important for a wide range of applications and disciplines. However, it is unknown at which bulk concentration these ions start to become surface active at the water–air interface. Here, we report changes in the D₂O–air interface in the presence of excess D⁺_hyd/OD^?_hyd determined using surface‐sensitive vibrational sum‐frequency generation (SFG) spectroscopy. The onset of the perturbation of the D₂O surface occurs at a bulk concentration as low as 2.7±0.2 mm D⁺_hyd. In contrast, a concentration of several hundred mm OD^?_hyd is required to change the D₂O surface. The hydrated proton is thus orders of magnitude more surface‐active than hydroxide at the water–air interface.     

Structure of aminonitrones and electronic effect of substituents on their acid-base properties

A series of para-substituted aromatic aminonitrones p-RC₆H₄C(NH₂)=N⁺(Me)O^– (R = NMe₂, H, Br, Cl, CF₃) have been prepared. Acidity constants of the conjugate acids RC₆H₄C(NH₂)N⁺(Me)OH at 25°C in a EtOH–H₂O mixture (5: 95) have been determined by potentiometric titration. A linear correlation between log (k_R/k_H) and σ_para values has been revealed, and a ρ²⁹⁸(σ_para) parameter has been determined as of 0.635.     

Conductance of 1,1-electrolytes in acetonitrile solutions from −40° to 35°C

Conductance data for perchlorates of Li⁺, K⁺, Me₄N⁺, Et₄N⁺, Pr₄N⁺, Bu₄N⁺, iodides of K⁺, Me₄N⁺, i-Am₃BuN⁺, and tetraphenylborates of Na⁺, Bu₄N⁺ and i-Am₃BuN⁺ in acetonitrile solution in the temperature range −40° to 35°C are reported. Λ_° (limiting molar conductance) and K_A (association constant) are evaluated for several temperatures using a conductance equation based on the chemical model of electrolyte solutions including short range forces. Limiting molar ion conductances, λ _ΰ ⁱ , at −35°, −25°, −15°, −5°, 5°, 15° and 25°C are evaluated from temperature dependent limiting transference numbers. Enthalpies and entropies of association, obtained from the temperature dependence of the association constants, are also presented. Dedicated to the memory of Professor Raymond M. Fuoss.     

Cellulose wet wiper sheets prepared with cationic polymer and carboxymethyl cellulose using a papermaking technique

Carboxymethyl cellulose (CMC)-rich cellulose sheets were prepared with a cationic retention aid, poly[N,N,N-trimethyl-N-(2-methacryloxyethyl)ammonium chloride] (PTMMAC), using a papermaking technique. When 5% PTMMAC and 5% CMC were added to cellulose slurries, approximately 94% of the polymers were retained in the sheets by formation of polyion complexes between the two polymers. When the PTMMAC/CMC/cellulose sheets were soaked in solutions consisting of ethanol, water and calcium chloride (EtOH/H₂O/CaCl₂) with a weight ratio of 75:24:1, almost all PTMMAC and CMC molecules remained in the sheets, forming the structures of PTMMAC-N⁺Cl⁻ and CMC-COO⁻Ca²⁺Cl⁻ without dissolution of these molecules in the soaking solution. Thus, PTMMAC, CMC and calcium contents in the sheets were able to be determined on the basis of these PTMMAC and CMC structures from analytical data such as nitrogen, calcium and chlorine contents. The trade-off properties between sufficient wet strength in use and water-disintegrability after use can be added to the PTMMAC/CMC/cellulose sheets by selecting weight ratios of the EtOH/H₂O/CaCl₂ solution used as the impregnation liquid.     

Dissociative photoionization of isoprene: experiments and calculations

Vacuum ultraviolet (VUV) dissociative photoionization of isoprene in the energy region 8.5–18 eV was investigated with photoionization mass spectroscopy (PIMS) using synchrotron radiation (SR). The ionization energy (IE) of isoprene as well as the appearance energies (AEs) of its fragment ions C₅H₇⁺, C₅H₅⁺, C₄H₅⁺, C₃H₆⁺, C₃H₅⁺, C₃H₄⁺, C₃H₃⁺ and C₂H₃⁺ were determined with photoionization efficiency (PIE) curves. The dissociation energies of some possible dissociation channels to produce those fragment ions were also determined experimentally. The total energies of C₅H₈ and its main fragments were calculated using the Gaussian 03 program and the Gaussian‐2 method. The IE of C₅H₈, the AEs for its fragment ions, and the dissociation energies to produce them were predicted using the high‐accuracy energy model. According to our results, the experimental dissociation energies were in reasonable agreement with the calculated values of the proposed photodissociation channels of C₅H₈. Copyright © 2009 John Wiley & Sons, Ltd.     

钾离子掺杂对石墨型氮化碳光催化剂能带结构及光催化性能的影响

以双氰胺和氢氧化钾为原料制备了能带可控的钾离子掺杂石墨型氮化碳(g-C3N4)光催化剂,并与碱处理的g-C3N4及g-C3N4/KOH复合催化剂进行了对比。采用X射线衍射(XRD)光谱、紫外-可见(UV-Vis)光谱、傅里叶变换红外(FTIR)光谱、N2吸附、电感耦合等离子体-原子发射光谱(ICP-AES)、荧光(PL)光谱、X 光电子能谱(XPS)等分析手段对制备的催化剂进行了表征。结果表明,钾离子含量对氮化碳催化剂的价带及导带位置有显著影响。此外,钾离子的引入抑制了氮化碳晶粒的生长,提高了氮化碳的比表面积以及对可见光的吸收,降低了光生电子-空穴对的复合几率。以染料罗丹明B的降解为探针反应系统研究了钾离子掺杂对g-C3N4在可见光下催化性能的影响,研究了光催化反应机理。结果表明,钾离子掺杂后氮化碳的光催化性能显著提高。制备的钾离子掺杂氮化碳催化剂表现出良好的结构及催化稳定性。     

Adsorption phenomena on a mercury electrode in aqueous cryptand[2.2.2] solutions by the background of tetraalkylammonium salts

The electrochemical behavior of cryptand[2.2.2] (Cry) is studied on a mercury electrode in aqueous solutions of tetraalkylammonium tetrafluoroborates (Me₄N⁺, Et₄N⁺, and Bu₄N⁺). Cryptand [2.2.2] is shown to exhibit high surface activity in Me₄ NBF₄ nd Et₄NBF₄ solutions. Based on the model of two parallel capacitors supplemented by the Frumkin adsorption isotherm, the adsorption parameters of Cry by the background of Me₄BNF₄ were calculated using the regression analysis methods. The calculated dependences of the differential capacitance on the potential adequately agree with experimental curves. The adsorption characteristics of Cry in the studied solutions are compared with those in MgSO₄ solutions. By the background of Bu₄NBF₄, Cry molecules and Bu₄N⁺ cations exhibit very close surface activity and form a mixed adsorption layer.     

Interactions between apolar,basic and acidic model oils and a calcite surface

Abstract

In this study, the atomic force microscopy colloidal probe technique was employed to investigate the interaction between apolar, basic and acidic model oil probes and a calcite surface in solutions containing different concentrations of NaCl, CaCl₂ and Na₂SO₄. In the presence of SO₄^2?, hydration and structural forces were observed between apolar model oil probes and a calcite surface on approach. Relatively low adhesion forces were observed between the basic model oil probes and the calcite surface, while higher adhesion forces were observed between the acidic model oil probes and the calcite surface. Furthermore, the adhesion forces between the basic model oil probes and the calcite surface significantly increased in the presence of SO₄^2?, while the adhesion force between the acidic model oil probes and the calcite surface decreased in the presence of Ca²⁺ or SO₄^2?. The differences in the adhesion forces are related to electrostatic attraction and ion bridging forces between the model oil probes and the calcite surface.     

Interaction of the Benzenium Ion with Inert Ligands: IR Spectra of C6H7+?Ln Cluster Cations (L=Ar,N2, CH4, H2O)

IR photodissociation spectra of mass‐selected clusters composed of protonated benzene (C₆H₇⁺) and several ligands L are analyzed in the range of the C? H stretch fundamentals. The investigated systems include C₆H₇⁺? Ar, C₆H₇⁺? (N₂)_n (n=1–4), C₆H₇⁺? (CH₄)_n (n=1–4), and C₆H₇⁺? H₂O. The complexes are produced in a supersonic plasma expansion using chemical ionization. The IR spectra display absorptions near 2800 and 3100 cm^?1, which are attributed to the aliphatic and aromatic C? H stretch vibrations, respectively, of the benzenium ion, that is, the σ complex of C₆H₇⁺. The C₆H₇⁺? (CH₄)_n clusters show additional C? H stretch bands of the CH₄ ligands. Both the frequencies and the relative intensities of the C₆H₇⁺ absorptions are nearly independent of the choice and number of ligands, suggesting that the benzenium ion in the detected C₆H₇⁺? L_n clusters is only weakly perturbed by the microsolvation process. Analysis of photofragmentation branching ratios yield estimated ligand binding energies of the order of 800 and 950 cm^?1 (≈9.5 and 11.5 kJ mol^?1) for N₂ and CH₄, respectively. The interpretation of the experimental data is supported by ab initio calculations for C₆H₇⁺? Ar and C₆H₇⁺? N₂ at the MP 2/6‐311 G(2df,2pd) level. Both the calculations and the spectra are consistent with weak intermolecular π bonds of Ar and N₂ to the C₆H₇⁺ ring. The astrophysical implications of the deduced IR spectrum of C₆H₇⁺ are briefly discussed.     

Enantiomer separation of rac-2,2′-dihydroxy-1,1′-binaphthyl (BNO) by inclusion complexation with racemic or achiral ammonium salts and a novel transformation of a 1:1:1 racemic complex of BNO, Me4N·Cl and MeOH into a conglomerate complex in the solid state

The complete simultaneous and mutual enantiomer resolution of 2,2′-dihydroxy-1,1′-binaphthyl (BNO) and N-(3-chloro-2-hydroxypropyl)-N,N,N-trimethylammonium chloride, Me₃N⁺CH₂CH(OH)CH₂Cl·Cl⁻ into their enantiomers by inclusion complexation between their racemates in EtOH in the presence of a chiral seed crystal is reported. The enantiomer resolution of the rac-BNO was also accomplished easily by inclusion complexation with achiral ammonium salts, N-(2-hydroxyethyl)-N,N,N-trimethylammonium chloride, Me₃N⁺CH₂CH₂OH·Cl⁻ and tetramethylammonium chloride, Me₄N⁺·Cl⁻. Inclusion complexation of the rac-BNO with Me₃N⁺ CH₂CH₂OH·Cl⁻ gave only a 1:1 conglomerate inclusion complex but not a racemic complex. Recrystallization of the rac-BNO and an equimolar amount of Me₄N⁺·Cl⁻ from MeOH (7 ml) and MeOH (15 ml) gave a 1:1:1 racemic complex, BNO·Me₄N⁺·Cl⁻·MeOH and a 1:1 conglomerate complex, BNO·Me₄N⁺·Cl⁻, respectively. Novel transformation of the former racemate into the latter conglomerate occurred by heating or by exposure to MeOH vapor in the solid state.     

Effects of Ionic Liquid [Me3NC2H4OH]+[ZnCl3]− on γ‐Radiation Polymerization of Methyl Methacrylate in Ethanol and N,N‐Dimethylformamide

Summary: Radiation‐induced polymerization of methyl methacrylate (MMA) in ethanol (EtOH) and N,N‐dimethylformamide (DMF) in the presence of ionic liquid [Me₃NC₂H₄OH]⁺[ZnCl₃]⁻ is reported. A substantial increase in monomer conversion and molecular weight is observed at room‐temperature ionic liquid (RTIL) >60 vol.‐%, and the resulting PMMA has a broad multimodal MWD. A clear difference in the MWD pattern is noted between EtOH/RTIL and DMF/RTIL systems, probably due to the complicated interactions between the solvent and ionic liquid.

Gel permeation chromatography traces of poly(methyl methacrylate) obtained by radiation polymerization in EtOH/RTIL and DMF/RTIL mixed solvent. Organic/RTIL (v/v): 1) 100:0; 2) 80:20; 3) 60:40; 4); 40:60; 5) 0:100.     

Adsorption of ions onto polymer surfaces and its influence on zeta potential and adhesion phenomena

 The adhesion behavior that governs many technologically and biologically relevant polymer properties can be investigated by zeta potential measurements with varied electrolyte concentration or pH. In a previous work [1] it was found that the difference of the adsorption free energies of Cl^- and K⁺ ions correlates with the adhesion force caused by van der Waals interactions, and that the decrease of adhesion strength by adsorption layers can be elucidated by zeta potential measurements. In order to confirm these interrelations, zeta potential measurements were combined with atomic force microscopy (AFM) measurements. Force–distance curves between poly(ether ether ketone) and fluorpolymers, respectively, and the Si₃N₄ tip of the AFM device in different electrolyte solutions were measured and analysed. The adsorption free energy of anions calculated from the Stern model correlates with their ability to prevent the adhesion between the polymer surface and the Si₃N₄ tip of the AFM device. These results demonstrate the influence of adsorption phenomena on the adhesion behavior of solids. The results obtained by AFM confirm the thesis that the electrical double layer of solid polymers in electrolyte solutions is governed by ion adsorption probably due to van der Waals interactions and that therefore van der Waals forces can be detected by zeta potential measurements. Received: 18 November 1997 Accepted: 19 January 1998     

Surface‐Roughness Evolution During the Cementation of Silver Ions on Solid Copper in Aqueous Sulfuric Acid Solution

The evolution of the surface roughness during cementation of Ag⁺ conducted either in O₂‐free or O₂‐saturated aqueous H₂SO₄/CuSO₄ was investigated at two different initial concentrations of Ag⁺. The kinetics data of the process determined previously in the rotating cylinder were linked directly with scanning‐electron‐microscope (SEM) images and surface‐height‐distribution diagrams calculated for various cementation times. It was found that, at the beginning of the process, the surface roughness decreases due to formation of a flat Ag layer on the top of the surface, independent of the presence or absence of O₂ in the system. With increasing reaction time, an increase in the surface roughness was observed. The rate enhancement of the process is mainly responsible for the increase of the surface roughness in the O₂‐saturated solutions, especially at the higher initial Ag⁺ concentration (100 mg/dm³). The rate enhancement observed at a latter stage of the process, connected with the increase of the effective surface area of the cathodic sites, was separated from the rate enhancement induced by the competitive chemical process occurring in O₂‐free solution. The difference in the mechanisms of the processes conducted under aerobic and anaerobic conditions was reflected in the surface‐heigth distributions calculated from the SEM images.     

Studies on the effect of the cation nature on the kinetics of the isotopic exchange reaction between chloride ion and O,O-diphenylphosphorochloridothionate in acetonitrile

Rate constants and activation parameters for the isotopic exchange reactions between (PhO)₂PSCl and M³⁶Cl (M = Me₄N⁺, Et₄N⁺, n-Bu₄N⁺, Et₃HN⁺, EtH₃N⁺, Li⁺) in acetonitrile were measured in order to find the effect of the cation nature onthe kinetics of the reaction. The rate constants measured for a range of concentrations of Et₃HN³⁶Cl, EtH₃N³⁶Cl, and Li³⁶Cl were analyzed using the Acree equation. The equivalent conductance of LiCl in acetonitrile was determined. The nature of the cation has no effect on the mechanism of the reaction. The cation changes only the experimental rate constant proportionally to the dissociation degree of the salt. Smaller values of the rate constant and smaller activation parameters ΔH? and ΔS? for the reaction with Li³⁶Cl indicate the existenceof the intermolecular interaction between lithium ions and O,O-diphenylphosphorochloridothionate.     

Determination of the surface acidity of a free-base corrole in a self-assembled monolayer

Mixed self-assembled monolayers (SAMs) containing a corrole moiety have been prepared to examine their electrochemical properties and surface acidity, with the eventual goal of biosensor development. Mixed SAMs consisting of 6-mercapto-hexanol (6-MHO) and 8-amino-1-octanethiol (8-AOT) in varying ratios were modified with a free-base corrole and characterized via Osteryoung square-wave voltammetry and contact angle measurements. The surface acidity of the free-base corrole was determined using an electrochemical titration method, with pK _a values established at 6.4 when using Fe(CN) ₆ ^4? /Fe(CN) ₆ ^3? as a redox probe and at 6.7 when using iodide, and assigned to the CorH₄ ⁺ ? CorH₃ + H⁺ equilibrium.     

Solvent Effect on Rotational Correlation Times of Symmetric Tetraalkylammonium Ions

The overall rotational correlation times of symmetric tetraalkylammonium ions, R ₄N⁺ (R = ethyl, n-propyl, n-butyl, and n-pentyl), in various solvents were determined by the measurements of the ¹³C NMR spin-lattice relaxation times and the nuclear Overhauser enhancement factors of each α-carbon, considering the contribution of the internal rotation around the N—C bond. Except in water, the observed solvent dependencies of the rotational correlation times, τ_r, showed good correlations with those predicted from an electrohydrodynamic (Hubbard–Onsager–Felderhof) model. The correlation times of R ₄N⁺ increased as the size of the alkyl groups became larger. In the case of the n-Bu₄N⁺ and the n-Pen₄N⁺ ion, the τ _r values were similar to or even higher than those predicted by the HOF model under the stick hydrodynamic boundary condition, in spite of the fact that the ions were too small to allow the solvent to be regarded as a hydrodynamic or a dielectric continuum. A comparison of the results with the rotations of other pseudotetrahedral ions, e.g., tetraphenylborate and tetraphenylarsenium ions and with the translation of the R ₄N⁺ ions suggests that a considerable part of the rotational friction for R ₄N⁺ is brought about by pushing aside the solvent in the spaces between the alkyl groups of R ₄N⁺. A significant slowing in the rotation in water was observed for the n-Pr₄N⁺, n-Bu₄N⁺, and n-Pen₄N⁺ions; the extent of this effect increased with increasing size of the alkyl group. The increase in friction was related to the hydrophobic hydration of the R ₄N⁺ ions.