Effect of ionic liquid on diffusion in P123 gel: fluorescence correlation spectroscopy

The effect of two room-temperature ionic liquids (RTILs) on the diffusion of three fluorescent dyes in the gel phase of a triblock copolymer, (PEO)(20)-(PPO)(70)-(PEO)(20) [Pluronic P123; poly ethylene oxide (PEO), poly propylene oxide (PPO)], was studied by using fluorescence correlation spectroscopy (FCS). We used three dyes, 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM), coumarin 480 (C480), and coumarin 343 (C343). By field-emission scanning electron microscopy (FESEM), it was observed that the macroscopic structure of the P123 gel remained unaffected upon addition of RTIL. In the absence of RTIL, the diffusion coefficient (D(t)) of the hydrophobic dye DCM (1 μm(2) s(-1) at the core) is smaller than that of the other two hydrophilic dyes (7 μm(2) s(-1) for C480 and C343). On addition of RTIL, the D(t) values of all of the dyes increase, indicating a decrease in local viscosity (η(eff)). The η(eff) of the core of the RTIL-P123 gel estimated from the D(t) of DCM is lower than that of both the P123 gel (at the core η=90 cP) and RTIL (η=110 cP). It is shown that the RTIL affects the structure of the gel by modifying the size of the micellar aggregates and by penetrating the core.     

Cancer Cell Imaging Using in Situ Generated Gold Nanoclusters

In situ generated fluorescent gold nanoclusters (Au‐NCs) are used for bio‐imaging of three human cancer cells, namely, lung (A549), breast (MCF7), and colon (HCT116), by confocal microscopy. The amount of Au‐NCs in non‐cancer cells (WI38 and MCF10A) is 20–40 times less than those in the corresponding cancer cells. The presence of a larger amount of glutathione (GSH) capped Au‐NCs in the cancer cell is ascribed to a higher glutathione level in cancer cells. The Au‐NCs exhibit fluorescence maxima at 490–530 nm inside the cancer cells. The fluorescence maxima and matrix‐assisted laser desorption ionization (MALDI) mass spectrometry suggest that the fluorescent Au‐NCs consist of GSH capped clusters with a core structure (Au_8‐13). Time‐resolved confocal microscopy indicates a nanosecond (1–3 ns) lifetime of the Au‐NCs inside the cells. This rules out the formation of aggregated Au–thiolate complexes, which typically exhibit microsecond (≈1000 ns) lifetimes. Fluorescence correlation spectroscopy (FCS) in live cells indicates that the size of the Au‐NCs is ≈1–2 nm. For in situ generation, we used a conjugate consisting of a room‐temperature ionic liquid (RTIL, [pmim][Br]) and HAuCl₄. Cytotoxicity studies indicate that the conjugate, [pmim][AuCl₄], is non‐toxic for both cancer and non‐cancer cells.     

Photoinduced electron transfer between various coumarin analogues and N,N-dimethylaniline inside niosome, a nonionic innocuous polyethylene glycol-based surfactant assembly

Photoinduced electron transfer (ET) reactions between coumarin dyes and N,N-dimethylaniline have been investigated inside niosome, a nonionic innocuous polyethylene glycol (PEG)-based surfactant assembly using steady state and time-resolved fluorescence measurements. The location of coumarin dyes inside the bilayer headgroup region of niosome has been reported and it was verified by determination of the high distribution coefficient of all the dyes inside niosome compared to bulk water. Fluorescence anisotropy parameters of the dyes inside niosome are also in good correlation with the above inference about their location. Bimolecular diffusion guided rates inside niosome were determined by comparing the microviscosities inside niosome and in acetonitrile and butanol solutions and it was found that diffusion of the donor and the acceptor is much slower than the ET rates, implying insignificant role of reactant diffusion in ET reaction inside niosome. We have observed a Marcus inversion region in our restricted media, which shows maxima at lower exergonicity. Such behavior has been demonstrated by the presence of nonequilibrium solvent excited state using two dimensional ET (2DET) theory. Unusually high quenching rates of two coumarins C-152 and C-152A inside niosome were explained by the presence of a stable non-fluorescent twisted intramolecular charge transfer (TICT) state along with an emissive intramolecular charge transfer (ICT) state. Moreover, intermolecular hydrogen bonding between carbonyl oxygens of these two dyes and water in their non-emissive and emissive charge transfer states also plays a key role in their dynamical exchange with each other [G.-J. Zhao and K.-L. Han, Acc. Chem. Res., 2011].     

Quantitative investigation, stability and in vitro release studies of anti-TB drugs in Triton niosomes

The highly stable innocuous niosomes composed of four components (Triton X 100, polyethylene glycol 2000, water, Span 80) have been prepared successfully and characterized using particle size analyzer, transmission and scanning electron microscopy. The mean size has been found to be in the range 200-300 nm. The optimization of niosomes has been carried out using fluorescence spectroscopy. An attempt has been made to incorporate anti-tuberculosis drugs (ATD's) in the prepared niosomes. The stability and encapsulation efficiency of these drugs in the niosome have also been assessed and high encapsulation efficiency is observed. Such high encapsulation efficiency will serve as an advantage to solve the problem of multi-drug resistance in case of tuberculosis. Release studies and kinetics have been carried out to investigate the release behavior of drugs from the prepared niosomes. Fickian or diffusional release has been observed for rifampicin and isoniazid and a non-Fickian release mechanism for pyrazinamide. Fluorescence probe quenching technique has been used to determine the location and distribution coefficient of the ATD's in niosome/water system.     

Effect of addition of hydrophilic ionic liquid 3-methyl-1-pentylimidazolium tetrafluoroborate ([C5mim][BF4]) on an aqueous solution of triton X-100

The effect of addition of 3-methyl-1-pentylimidazolium tetrafluoroborate ([C₅mim][BF₄]) on the micellization of a nonionic surfactant, Triton X-100 (TX-100), has been investigated. The techniques employed to study the aggregation behavior are fluoremetry, dynamic light scattering (DLS), and transmission electron microscopy (TEM) and the concentration range covered is 0–2?wt% [C₅mim][BF₄]. The probes, viz. pyrene and pyrene-1-carboxaldehyde (PyCHO), have been used for fluorescence analysis. According to the findings, the addition of pentyl-chained ionic liquid (IL) to aqueous TX-100 results in a dramatic increase in critical micelle concentration (cmc) decrease in micellar size, and aggregation number pointing toward an overall “unfavorable” aggregation process.     

Solvation dynamics in ionic liquid swollen p123 triblock copolymer micelle: a femtosecond excitation wavelength dependence study

Femtosecond solvation dynamics of coumarin 480 (C480) in a mixed micelle is reported. The mixed micelle consists of a triblock copolymer (PEO)20-(PPO) 70-(PEO)20 (Pluronic P123) and an ionic liquid (IL), 1-pentyl-3-methylimidazolium tetrafluoroborate ([pmim][BF4]). At a low concentration (0.3 M), the sparingly water soluble IL ([pmim][BF4]) penetrates the hydrophobic PPO core of the P123 micelles. Thus emission maximum of C480 in the core (accessed at lambdaex=375 nm) in 0.3 M IL is red-shifted by 8 nm from that in its absence and the red edge excitation shift (REES) is large (19+/-1 nm). At a high concentration (0.9 M), the ionic liquid [pmim][BF4] invades both the core and corona region and the mixed micelle exhibits very small REES (3+/-1 nm). Anisotropy decay and solvation dynamics in different regions of the mixed micelle are studied by variation of excitation wavelength (lambda ex). In P123 micelle, the average rotational time () is 2800 ps in the core (at lambdaex=375 nm) and 1350 ps in the corona region (at lambdaex=435 nm). In 0.3 M [pmim][BF4], tau rot at the core of the mixed micelle decreases to 1950 ps while that in the corona remains unaffected. In 0.9 M IL, both the core and corona (lambda ex=375 and 435 nm) exhibit similar and short approximately 600 ps. In 0.3 M IL, solvation dynamics in the core region (lambdaex=375 nm) of P123 micelle is about 2 times faster than in its absence. In 0.3 M IL, solvation dynamics in the corona region (lambdaex=435 nm) is approximately 100 times faster than that in the core. In 0.9 M IL, the solvation dynamics in the core and in the corona is, respectively, approximately 9 times and 4 times faster than that in 0.3 M IL.     

Study of the Volumetric Properties of the Aqueous Ionic Liquid 1-Methyl-3-pentylimidazolium Tetrafluoroborate

This paper reports the densities of aqueous solutions of the ionic liquid (IL) 1-methyl-3-pentylimidazolium tetrafluoroborate ([pmim][BF₄]) that were measured from 278.15 to 343.15 K, at intervals of 5 K, using an Anton Parr model DMA 4500 oscillating U-tube densitometer. The apparent molar volume, ^φ V _B, and the partial molar volume of [pmim][BF₄], , were calculated. The values of the apparent molar volume, ^φ V _B, were fitted to Pitzer’s model for volumetric properties by the method of least-squares, which allowed the partial molar volume of the IL at infinite dilution, , and Pitzer’s parameters, β _M,X ^(0)V and β _M,X ^(1)V , to be obtained. The small standard deviations of the fits show that Pitzer’s model is also appropriate for representing the volumetric properties of aqueous solutions of the ionic liquid [pmim][BF₄].     

A comprehensive study of {γ-butyrolactone + 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide} binary mixtures

Density, electrical conductivity and viscosity of binary liquid mixtures of γ-butyrolactone, (GBL) with 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide, [pmim][NTf₂], were measured at different temperatures from (293.15 to 323.15) K and at atmospheric pressure (p = 0.1 MPa) over the whole composition range. Excess molar volumes have been calculated from the experimental densities and were fitted with Redlich–Kister’s polynomial equation. Other volumetric properties have been also calculated in order to obtain information about interactions between GBL and selected ionic liquid. All the results are compared with those obtained for binary mixtures of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [bmim][NTf₂], with GBL. From the viscosity measurements, the Angell strength parameter was calculated for pure ionic liquid indicating that [pmim][NTf₂] is a “fragile” liquid. Electrical conductivity results were discussed in the scope of Bahe–Varela theoretical model.     

Surface interaction and self-assembly of cyclodextrins with organic dyes

The interaction of seven novel substituted merocyanine dyes, i.e. 1-methyl-4-[2-(3-methoxy-4-hydroxyphenyl)ethenyl)]pyridinium iodide, 1-methyl-4-[2-(3,5-dimethoxy-4-hydroxyphenyl)ethenyl)]pyridinium iodide, 1-methyl-4-[2-(4-dimethylaminophenyl)ethenyl)]pyridinium iodide, their quinoide forms as well as 1-methyl-4-[2-(3-methoxy-4-oxocyclohexadienilydene)ethylidene]-1,4-dihydropyridine, 1-methyl-4-[2-(3,5-dimethoxy-4-oxocyclohexadienilydene)ethylidene]-1,4-dihydropyridine, with α-CD, γ-CD as well as functionalized γ-cyclodextrin phosphate sodium salt is studied by the methods such as UV–Vis and fluorescence spectroscopy, linear-polarized infrared (IR-LD) spectroscopy of oriented colloids in nematic host, ¹H- and ¹³C-NMR spectroscopy, HPLC ESI tandem mass spectrometry, scanning electron and tunneling microscopy, powder X-ray diffraction as well as thermal methods. A formation of the 1D and 2D “supramolecular polymers” with nanosizes is found. The dyes are adsorbed on the CDs surface and form a hexagonal microcrystalline sub-structures. Remarkable fluorescence properties depending of the type of the substituent in the dyes, in solid-state are observed.     

Preparation of a highly stable niosome and its hydrotrope-solubilization action to drugs

Highly stable niosomes are prepared and investigated in Tween80/PEG6000/Span80/H2O system. The mean radius of the niosomes is 0.15-0.2 microm. The contents of PEG6000 and Span80 and the system temperature affect the size and the stability of the niosome. A certain Span80 can remarkably improve the stability. The niosome is provided distinctly with the hydrotrope-solubilization action to the hydrophilic drug and hydrophobic drug, which affects the niosome membrane. The mechanism of the effects of PEG6000 and Span80 on the niosome is discussed in this paper.     

Local viscosity analysis of triblock copolymer micelle with cyanine dyes as a fluorescent probe

The local viscosity of Pluronic F127 triblock copolymer micelles in water was determined with cyanine dyes as fluorescent probes. These dyes show very weak fluorescence at a low temperature, but show enhanced fluorescence at a temperature higher than the critical micellization temperature (T(cm)). This is because a viscous environment within the micelle suppresses the formation of a nonradiative twisted intramolecular charge transfer (TICT) excited state of the dyes. The good correlation between the fluorescence quantum yields of the dyes and the viscosity and the temperature of the media allows a determination of local viscosity of micelle based on the fluorescence quantum yields. The local viscosity of both core and corona regions of micelles increases at >T(cm) and shows a maximum at a temperature 7-9 °C higher than T(cm), and decreases at higher temperature due to the increased fluidity. The core viscosity is larger than that of the corona, and the corona viscosity increases toward the micelle center. The polymer concentration has different effects on the core and corona viscosity: the corona viscosity increases with a polymer concentration increase at the entire temperature range, whereas the core viscosity increases only at a low temperature. The corona viscosity increase is due to the condensation of a large number of polyethylene oxide (PEO) blocks. In contrast, the dehydration degree of polypropylene oxide (PPO) blocks in the core scarcely changes, and the core has a similar composition regardless of polymer concentration. The larger polymer concentration promotes a micelle formation at lower temperature where the fluidity increase is very weak, resulting in larger core viscosity.     

Synthesis and application of poly(ethylene glycol)-cholesterol (Chol-PEGm) conjugates in physicochemical characterization of nonionic surfactant vesicles

Vesicles possessing poly(ethylene glycol) (PEG) chains on their surface have been described as a blood-persistent drug delivery system with potential applications for intravenous drug administration. In this research with different molecular weights (400–10,000 g/mol) of PEG, a series of Chol–PEG^m conjugates were generated by the DCC (N,N′-dicyclohexylcarbodiimide, DCC)/(4-dimethylaminopyridine, 4-DMAP) esterification method, and confirmed by FT-IR and ¹H NMR spectrum. Then their properties in aqueous solution were studied by electron microscopy images, associative behavioral and systematic tensiometric studies over a wide concentration range. In order to elucidate the application of this Chol–PEG^m in vesicles, conventional nonionic surfactant vesicles (niosomes) composed of span 60 and cholesterol were prepared and the influence of various hydrophilic chains of the Chol–PEG^m conjugates was investigated. Results indicated that all the niosomes prepared, with or without Chol–PEG^m composition were similar in micrograph with diameter between 120 nm and 180 nm. The fixed aqueous layer thickness (FALT) around niosomes increased as Chol–PEG^m chain length increase, particularly in the Chol–PEG^10,000 modified niosomes with 9.33 ± 0.67 nm. In vitro release experiments indicated that release rate of nimodipine from Chol–PEG^m modified niosomes was enhanced. Chol–PEG^m modified niosomes showed greater accumulative release than that of plain niosomes over a period of 24 h. These studies have shed some light on the suitability of Chol–PEG^m containing niosome preparation.     

Femtosecond solvation dynamics in a neat ionic liquid and ionic liquid microemulsion: excitation wavelength dependence

Solvation dynamics in a neat ionic liquid, 1-pentyl-3-methyl-imidazolium tetra-flouroborate ([pmim][BF4]) and its microemulsion in Triton X-100 (TX-100)/benzene is studied using femtosecond up-conversion. In both the neat ionic liquid and the microemulsion, the solvation dynamics is found to depend on excitation wavelength (lambda(ex)). The lambda(ex) dependence is attributed to structural heterogeneity in neat ionic liquid (IL) and in IL microemulsion. In neat IL, the heterogeneity arises from clustering of the pentyl groups which are surrounded by a network of cation and anions. Such a nanostructural organization is predicted in many recent simulations and observed recently in an X-ray diffraction study. In an IL microemulsion, the surfactant (TX-100) molecules aggregate in form of a nonpolar peripheral shell around the polar pool of IL. The micro-environment in such an assembly varies drastically over a short distance. The dynamic solvent shift (and average solvation time) in neat IL as well as in IL microemulsions decreases markedly as lambda(ex) increases from 375 to 435 nm. In a [pmim][BF4]/water/TX-100/benzene quaternary microemulsion, the solvation dynamics is slower than that in a microemulsion without water. This is ascribed to the smaller size of the water containing microemulsion. The anisotropy decay in an IL microemulsion is found to be faster than that in neat IL.     

血红蛋白在Span 80/PEG 400/H2O囊泡体系中的结构性质

通过紫外-可见吸收光谱、荧光光谱、动态光散射、圆二色谱、负染-透射电镜(NS-TEM)和冷冻蚀刻-透射电镜(FE-TEM)等实验方法研究了血红蛋白(Hb)与Span 80/PEG 400/H₂O囊泡间的相互作用及其结构特性. 结果表明: Hb易于吸附在囊泡表面, 使得囊泡的表观半径稍有增大; Hb的肽链在囊泡表面能够逐渐伸开, 特征荧光峰强度显著增强, 部分氨基酸残基进一步暴露, α-螺旋结构含量减少, β-折叠和β-转角结构含量增加, 无规卷曲结构含量基本不变. 囊泡体系中Hb的稳定性与囊泡的稳定性有关.     

Solvatochromic azamethine dyes for probing the polarity of gold-cluster-functionalized silica particles

Azamethine dyes of the merocyanine type [4-(N,N-di-n-butylamino)-2-methylphenyl][2,4-di-keto-3-[N'-(n-hexyl)]-5-cyano-6-methyl-3-pyridinio]-1-azamethine (1) and [4-(N,N-diethylamino)-2-(N'-tert-butylcarboxy)-amidophenyl]-[2,4-diketo-3-[N"-(n-hexyl)]-5-cyano-6-methyl-3-pyridinio]-1-azamethine (2) have been used as surface-polarity indicators for gold-cluster-functionalized silica particles. Their UV/Vis absorption maxima range from about lambda=600 to 700 nm as a function of solvent polarity and are clearly separated from the surface plasmon UV/Vis absorption band of gold (lambda approximately 520-540 nm). Solvatochromism of both dyes has been investigated in 26 solvents of different polarity. The positive solvatochromic band shifts of 1 and 2 can be well expressed in terms of the empirical Kamlet-Taft solvent polarity parameters alpha and pi*. They are mainly sensitive to the dipolarity/polarizability (pi* term; 70-75 %) and HBD (hydrogen-bond donating) acidity (alpha term) of the solvent. Both dyes adsorb readily on functionalized silica samples from solutions in 1,2-dichloroethane or cyclohexane. The surface polarities of gold-cluster-functionalized silica particles, with and without co-adsorbed L-cysteine and poly(ethylenimine), have been investigated by using these solvatochromic dyes. The specific interaction of dye 2 with cysteine has been examined independently by quantum-chemical calculations by using the AM1 and PM3 methods.     

Ionic liquids as silica deactivating agents in gas chromatography for direct analysis of primary amines in water

Analysis of primary amines in aqueous samples remains a challenging analytical issue. The preferred approach by gas chromatography is hampered by interactions of free silanol groups with the highly reactive amine groups, resulting in inconsistent measurements. Here, we report a method for direct analysis of aliphatic amines and diamines in aqueous samples by gas chromatography (GC) with silanol deactivation using ionic liquids (ILs). ILs including trihexyl(tetradecyl)phosphonium bis 2,4,4-(trimethylpentyl)phosphinate (Cyphos IL-104), 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide [pmim][Tf(2)N] and N″-ethyl-N,N,N',N'-tetramethylguanidinium tris(pentafluoroethyl)trifluorophosphate [etmg][FAP] were tested as deactivating media for the GC liner. Solutions of these ILs in methanol were injected in the system prior to the analysis of primary amines. Butane-1,4-diamine (putrescine, BDA) was used as a reference amine. The best results were obtained using the imidazolium IL [pmim][Tf(2)N]. With this deactivator, excellent reproducibility of the analysis was achieved, and the detection limit of BDA was as low as 1mM. The applicability of the method was proven for the analysis of two different primary amines (C4-C5) and pentane-1,5-diamine.     

Catalysis by ionic liquid. A green protocol for the stereoselective debromination of vicinal-dibromides by [pmIm]BF4 under microwave irradiation

An easily accessible ionic liquid, 1-methyl-3-pentylimidazolium fluoroborate, [pmIm]BF4, has been demonstrated to be an efficient catalyst as well as reaction medium for the stereoselective debromination of a variety of structurally diverse vicinal-dibromides to the corresponding (E)-alkenes in high yields under microwave irradiation. This reaction does not require any organic solvent and any metal or any conventional reducing agent, and the ionic liquid is recycled without any appreciable loss of its catalytic efficiency.     

Nanostructural organization and anion effects in the optical Kerr effect spectra of binary ionic liquid mixtures

This article reports a study of the effect of anions on the optical Kerr effect (OKE) spectra of binary ionic liquid mixtures with one mixture comprising the 3-methyl-1-pentylimidazolium ([C 5mim] (+)) cation and the anions PF 6 (-) and CF 3CO 2 (-) (TFA (-)), and another mixture comprising the [C 5mim] (+) cation and the anions Br (-) and bis(trifluomethanesulfonyl)imide (NTf 2 (-)). The spectra were obtained by the use of optical heterodyne-detected Raman-induced Kerr Effect Spectroscopy at 295 K. The OKE spectra of the mixtures are compared with the calculated mole-fraction weighted sum of the normalized OKE spectra of the neat liquids. The OKE spectra are nearly additive for [C 5mim]Br/[C 5mim][NTf 2] mixtures, but nonadditive for [C 5mim][PF 6]/[C 5mim][TFA] mixtures. In the case of the equimolar [C 5mim][PF 6]/[C 5mim][TFA] mixture, the nonadditivity is such that the experimental OKE spectrum is narrower than the calculated OKE spectrum. The additivity or nonadditivity of OKE spectra for IL mixtures can be explained by assuming ionic liquids are nanostructurally organized into nonpolar regions and ionic networks. The ionic networks in mixtures will be characterized by "random co-networks" for anions that are nearly the same in size (PF 6 (-) and TFA (-)) and by "block co-networks" for anions that differ greatly in size (Br (-) and NTf 2 (-)).     

Self-assembling molecular wires of halogen-bridged platinum complexes in organic media. Mesoscopic supramolecular assemblies consisting of a mixed valent Pt(II)/Pt(IV) complex and anionic amphiphiles

A novel class of supramolecular assemblies in organic media consisting of a molecular wire of a halogen-bridged platinum complex [Pt(en)2][PtCl2(en)2]4+ (en = 1,2-diaminoethane) and anionic amphiphiles is developed. When double-chained phosphates or sulfonates are employed, the resultant [Pt(en)2][PtCl2(en)2](4+)-lipid complexes displayed intervalence charge transfer (CT) absorption bands in the crystalline state. They are soluble in organic solvents because of the amphiphilic superstructure, in which the solvophobic one-dimensional platinum complex is surrounded by solvophilic alkyl chains. CT absorption bands of halogen-bridged linear complexes are maintained in organic media, with varied colors that depend on the chemical structure of constituent amphiphiles. Monoalkylated phosphates failed to form colored, halogen-bridged ternary complexes probably because of their coordination to the axial position of PtII(en)2. Formation of mesoscopic supramolecular assemblies in organic media was confirmed for the [Pt(en)2][PtCl2(en)2] complexes by electron microscopy. Interestingly, a supramolecular complex consisting of dihexadecyl sulfosuccinate and [Pt(en)2][PtCl2(en)2]4+ displayed clear, indigo solutions that are distinct from the yellow color observed for those of [Pt(en)2][PtCl2(en)2]/dialkyl phosphate complexes. The indigo color of the former complex disappeared upon heating the solution to 60 degrees C, whereas it reappeared reversibly by cooling the solution to room temperature. In electron microscopy, rodlike nanostructures with a minimum width of 18 nm and lengths of 700-1700 nm were observed after cooling, though not at elevated temperatures. Apparently, the lipid-[Pt(en)2][PtCl2(en)2]4+ complex undergoes reversible dissociation and reassembly processes in chloroform, and it becomes better dispersed after the reassembling process. The present finding opens a general route to solution chemistry of low-dimensional inorganic complexes and enables rational design and control of self-assembling inorganic molecular wires.     

Fluorescence correlation spectroscopy evidence for structural heterogeneity in ionic liquids

In this work, we provide new experimental evidence for chain length-dependent self-aggregation in room temperature ionic liquids (RTILs) using fluorescence correlation spectroscopy (FCS). In studying a homologous series of N-alkyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide, [C(n)MPy][Tf(2)N] RTILs of varying alkyl chain length (n = 3, 4, 6, 8, and 10), biphasic rhodamine 6G solute diffusion dynamics were observed; both the fast and slow diffusion coefficients decreased with increasing alkyl chain length, with the relative contribution from slower diffusion increasing for longer-chain [C(n)MPy][Tf(2)N]. We propose that the biphasic diffusion dynamics originate from self-aggregation of the nonpolar alkyl chains in the cationic [C(n)MPy](+).