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Aerosol-OT reverse micelles represent a chemical construct where surfactant molecules self-assemble to stabilize water nanodroplets ~1-10 nm in diameter. Although commonly assumed to adopt a spherical shape, all-atom molecular dynamics simulations and some experimental studies predict a non-spherical shape. If these aggregates are not spherical, then what shape do they take? Because the tools needed to evaluate the shape of something that lacks regular structure, order, or symmetry are not well developed, we present a set of three intuitive metrics- coordinate-pair eccentricity, convexity, and the curvature distribution- that estimate the shape of an amorphous object and we demonstrate their use on a simulated Aerosol-OT reverse micelle. These metrics are all well-established methods and principles in mathematics, and each provides unique information about the shape. Together, these metrics provide intuitive descriptions of amorphous shapes, facilitate ways to quantify those shapes, and follow their changes over time.

In bulk aqueous environments, the exchange of protons between labile hydroxyl groups typically occurs easily and quickly. Nanoconfinement can dramatically change this normally facile process. Through exchange spectroscopy (EXSY) NMR measurements, we observe that nanoconfinement of glucose and water within AOT (sodium bis(2-ethylhexyl) sulfosuccinate) reverse micelles raises the energy barrier to labile hydrogen exchange, which suggests a disruption of the hydrogen bond network. Near room temperature, we measure barriers high enough to slow the process by as much as 2 orders of magnitude. Although exchange rates slow with decreasing temperatures in these nanoconfined environments, the barrier we measure below ∼285 K is 3-5 times lower than the barrier measured at room temperature, indicating a change in mechanism for the process. These findings suggest the possibility of hydrogen tunneling at a surprisingly high-temperature threshold. Furthermore, differences in exchange rates depend on the hydroxyl group position on the glucose pyranose ring and suggest a net orientation of glucose at the reverse micelle interface.

The research presented here reports the surprising observation that adding glucose and other carbohydrate osmolytes to the polar phase of water-containing reverse micelles causes the particles to shrink. This apparent change in reverse micelle size is attributed to two factors: an increase in the surface area per surfactant molecule induced by the presence of carbohydrate and changes in the particle shape eccentricity. The studies reported here not only focus on glucose but also explore other carbohydrate osmolytes, specifically ethylene glycol, glycerol, erythritol, xylitol, sorbitol, myo-inositol, and trehalose, in the nanoconfined environments of reverse micelles. Through two-dimensional proton nuclear Overhauser enhancement nuclear magnetic resonance spectroscopy, the osmolytes were determined to reside solvated in the aqueous interior of the reverse micelles. This paper reports the loading limit of carbohydrates into AOT [sodium bis(2-ethylhexyl)sulfosuccinate] reverse micelles, demonstrates the location of the carbohydrates in the reverse micelles, and shows an unexpected effect where the carbohydrates add to the reverse micelle volume without causing an apparent increase in the reverse micelle diameter.

Cryoprotectants allow cells to be frozen in liquid nitrogen and cryopreserved for years by minimizing the damage that occurs in cooling and warming processes. Unfortunately, how the specific cryoprotectants keep the cells viable through the cryopreservation process is not entirely evident. This contributes to the arduous process of optimizing cryoprotectant formulations for each new cell line or species that is conserved. Coherent anti-Stokes Raman scattering microscopy facilitates the visualization of deuterated cryoprotectants within living cells. Using this technique, we directly imaged the location of fully deuterated dimethyl sulfoxide (d6-DMSO), the deuterated form of a commonly used cryoprotectant, DMSO, within rice suspension cells. This work showed that d6-DMSO does not uniformly distribute throughout the cells, rather it enters the cell and sequesters within organelles, changing our understanding of how DMSO concentration varies within the cellular compartments. Variations in cryoprotectant concentration within different cells and tissues will likely lead to differing protection from liquid nitrogen exposure. Expanding this work to include different cryoprotectants and mixtures of cryoprotectants is vital to create a robust understanding of how the distributions of these molecules change when different cryoprotectants are used.

Many students have misconceptions about how chemistry knowledge is generated. These misconceptions can be addressed by highlighting how chemistry knowledge has developed over time. To effectively accomplish this, science educators must be well-versed in the history of chemistry. In this paper, we describe topics that could be covered in a continuing education course for secondary level science educators that centers on the history of chemistry. We hope to stimulate discussions across chemistry departments to encourage our colleagues to offer such courses to in-service secondary science teachers. A history of chemistry course will allow teachers to meet the learning needs of their students. When teachers can explain how chemists made discoveries, overcame obstacles, collaborated with colleagues to answer complex questions, and built upon one another’s ideas, students are presented with a realistic picture of scientific research, hence strengthening their understanding of the nature of science.

To succeed in physical chemistry courses, students need competence with a significant amount of mathematics, including ordinary and partial differential equations and linear operators. This can present a barrier to student success because many of these topics are not taught in the traditional prerequisite calculus sequence. Through a collaboration of the Departments of Chemistry and Mathematics, Colorado State University has developed and implemented a two-semester sequence of courses, Applied Mathematics for Chemists, aimed specifically at providing students with the mathematical tools necessary for success in physical chemistry. This report summarizes one of the invited papers to the ConfChem online conference on Mathematics in Undergraduate Chemistry Instruction, held from October 23 to November 27, 2017, and hosted by the ACS DivCHED Committee on Computers in Chemical Education (CCCE).

Cyanine-3 (Cy3) fluorescent dye molecules confined in sodium di-2-ethylhexyl sulfosuccinate (AOT) reverse micelles were examined using steady-state absorption and emission as well as time-resolved fluorescence spectroscopy to understand the effect of confinement on the spectroscopic properties of the dye. This study explored a wide range of reverse micelle sizes, with hydrodynamic radii ranging from ∼1.7 to ∼5 nm. The relative concentrations of Cy3 and AOT reverse micelles were such that, on average, one dye molecule was present for every 2 × 10(4) to 9 × 10(5) reverse micelles. In the smallest reverse micelles examined, observed changes in the absorption and emission spectra and fluorescence lifetime of the dye molecules indicated H-aggregation of Cy3 into side-by-side dimers. It is hypothesized that this dimerization is governed by the high local concentrations that result from the confinement of the Cy3 in the reverse micelles. What is notable about this study is that this dimer occurs even at overall dye concentrations in the nanomolar range. Such concentrations are too low for aggregation to occur in bulk solution. Hence, the reverse micelles serve as nanocatalysts for this aggregation process.

Recent advances in ultrafast laser technology have spurred investigations of microheterogeneous solutions. In particular, researchers have explored details of reverse micelles (RMs), which present isolated droplets of polar solvent sequestered from a continuous nonpolar phase by a surfactant layer. This review explores recent studies utilizing a variety of ultrafast laser techniques to uncover details about structure and dynamics in various RMs. Using ultrafast vibrational spectroscopy, researchers have probed hydrogen-bond dynamics and vibrational energy relaxation in RMs. These studies have developed our understanding of reverse micellar structure, identifying varying water environments in the RMs. In a plethora of experiments employing probe molecules, researchers have explored the confined environment presented by RMs and their impact on a range of chemical reactions. These studies have shown that confinement, rather than the specific interactions with surfactants, is an important factor determining the impact of the reverse micellar environment on the chemistry.

The dynamics of water confined in two different types of reverse micelles are studied using ultrafast infrared pump-probe spectroscopy of the hydroxyl OD stretch of HOD in H2O. Reverse micelles of the surfactant Aerosol-OT (ionic head group) in isooctane and the surfactant Igepal CO 520 (non-ionic head group) in 50/50 weight percent cyclohexane/hexane are prepared to have the same diameter water nanopools. Measurements of the IR spectra and vibrational lifetimes show that the identity of the surfactant head groups affects the local environment experienced by the water molecules inside the reverse micelles. The orientational dynamics (time dependent anisotropy), which is a measure of the hydrogen bond network rearrangement, is very similar for the confined water in the two types of reverse micelles. The results demonstrate that confinement by an interface to form a nanoscopic water pool is a primary factor governing the dynamics of nanoscopic water rather than the presence of charged groups at the interface.

A wide variety of probe molecules have been used to characterize the environment found within reverse micelles. This manuscript reports on results from steady-state and time-resolved spectroscopies of the probe molecule Coumarin 343. The steady-state spectra for the probe molecule in ternary and quaternary systems are nearly identical. However, the time-resolved studies clearly indicate substantial differences in the probe sensed by the probe molecule. Implications of these results for the interpretation of spectroscopy of probe molecules in confined media are discussed.

Vibrational relaxation and hydrogen bond dynamics in methanol-d dissolved in CCl4 have been measured with ultrafast infrared pump−probe spectroscopy. We excited the subensemble of methanol-d molecules both accepting and donating hydrogen bonds at ∼2500 cm-1. Following vibrational relaxation with a ∼500 fs lifetime, the signal does not decay to zero. Rather, the signal increases to a second maximum at ∼4 ps. The decay from the second maximum occurs on two time scales. We propose a model in which hydrogen bond dissociation, following vibrational relaxation, decreases the concentration of methanol-d molecules that accept and donate hydrogen bonds and produce the observed long-lived bleach of the absorption signal. Using a set of coupled kinetic equations, the time constants for hydrogen bond dissociation and reformation have been determined. Hydrogen bond breaking occurs with ∼200 fs and ∼2 ps time constants. We attribute the fast rate to a direct breaking mechanism wherein the excited hydroxyl stretch decay...

The continuous nonpolar phase can change the morphology of lecithin reverse micelles dramatically. In alkane solvents, increasing the hydration leads to gelation as isolated water droplets transform into an entangled tube network. In contrast, increasing the hydration for lecithin in benzene maintains isolated, largely spherical traditional reverse micelles. Solvation dynamics experiments have been carried out in the two different micellar environments. These measurements show that solvation dynamics are considerably more restricted in the tubular micelles than in the spherical droplets. This is interpreted as evidence for water pool formation and disorder at the interface in the spherical micelles and supports the hypothesis of substantial water incorporation into the tubular micelles. To perform solvation dynamics experiments in the benzene/lecithin/water reverse micelles, we have synthesized a new headgroup-labeled probe molecule. This synthesis, coupling the standard solvation dynamics probe, coumarin...

Time-resolved fluorescence-upconversion spectroscopy has been used to study the polar solvation dynamics of H{sub 2}O and D{sub 2}O at the surface of zirconia (ZrO{sub 2}) nanoparticles. While an isotope effect is observed for the solvation dynamics of bulk D{sub 2}O, there is no isotope effect on the interfacial solvation dynamics. The interfacial solvation dynamics are the same for H{sub 2}O and D{sub 2}O and are faster than the bulk solutions. The bulk isotope effect is due to stronger hydrogen bonding in D{sub 2}O compared to H{sub 2}O, slowing the reorientation of the excited-state dipoles in the bulk D{sub 2}O. The lack of isotope effect for the interfacial dynamics is explained in terms of the solvent interacting with the ZrO{sub 2} surface.

The mobility of water in water/Aerosol OT (AOT)/isooctane reverse micelles has been investigated via polar solvation dynamics measurements using ultrafast, time-resolved fluorescence-upconversion spectroscopy. For the smallest reverse micelles studied, w0 = 1.1, no solvation dynamics are observed on the time scale of the instrument, suggesting that the water is essentially frozen. As w0 increases, the mobility of water increases, and the time-correlation functions exhibit multiexponential decays. A subpicosecond component is observed on a time scale similar to that of diffusive bulk-water motion.1 The other components decay on time scales of a few picoseconds to hundreds of picoseconds. The amplitude of the solvent response increases as w0 increases, which is attributed to increased mobility of the water inside the reverse micelles. Because the micellar interior is highly ionic, the solvation dynamics of coumarin 343 in a 1 M Na+ (Na2SO4) solution were also investigated to compare the dynamics of water in...

Reverse microemulsions have been characterized in isooctane and decane using the surfactant Aerosol-OT (AOT) and the polar solvents formamide, ethylene glycol, acetonitrile, methanol, N,N-dimethylformamide, and 1,2-propanediol. Dynamic light scattering (DLS) experiments show that reverse micelles form in these solutions. The DLS data and steady-state absorption spectra of Coumarin 343 in these solutions reveal that the character of these reverse micelles depends partially upon the solubility of the polar solvent in the hydrocarbon. For formamide and ethylene glycol, which are highly immiscible in the hydrocarbon solvents, changes in micellar size occur for variations in the volume fraction φ of the polar solvent and surfactant in the continuous phase as well as for the traditional changes in w. These reverse micelles with w = 1.1 and φ = 0.006−0.051 exhibit diameters ranging from 5.0 to 26.1 nm. For the solvents acetonitrile, methanol, N,N-dimethylformamide, and 1,2-propanediol, which are slightly miscibl...

Ultrafast dynamics of OH stretching excitations of H2O confined in dioleoylphosphatidylcholine (DOPC) reverse micelles, a phospholipid model system, are studied in femtosecond pump–probe experiments. Measurements in a wide range of hydration show that spectral diffusion within the OH stretching band accelerates substantially with increasing water content. Concomitantly, the OH stretching lifetime decreases from approximately 500 fs at a 1:1 ratio of water and DOPC molecules (w0 = 1) to 300 fs for large water pools (ratio 16:1, w0 = 16). Two-color pump–probe studies mapping the ultrafast OH bending response after OH stretch excitation demonstrate that the relaxation pathway of the OH stretch vibration involves the OH bending mode. After OH stretch relaxation at high hydration levels, vibrational excess energy is randomized within the water pool and then transferred to the surrounding solvent.

Phospholipids self-assembled into reverse micelles in benzene are introduced as a new model system to study elementary processes relevant for energy transport in hydrated biological membranes. Femtosecond vibrational spectroscopy gives insight into the dynamics of the antisymmetric phosphate stretching vibration ν(AS)(PO(2))(-), a sensitive probe of local phosphate-water interactions and energy transport. The decay of the ν(AS)(PO(2))(-) mode with a 300-fs lifetime transfers excess energy to a subgroup of phospholipid low-frequency modes, followed by redistribution among phospholipid vibrations within a few picoseconds. The latter relaxation is accelerated by adding a confined water pool, an efficient heat sink in which the excess energy induces weakening or breaking of water-water and water-phospholipid hydrogen bonds. In parallel to vibrational relaxation, resonant energy transfer between ν(AS)(PO(2))(-) oscillators delocalizes the initial excitation.

Cyanine-3 (Cy3) fluorescent dye molecules confined in sodium di-2-ethylhexyl sulfosuccinate (AOT) reverse micelles were examined using dynamic light scattering and fluorescence correlation spectroscopy to probe the kinetics of Cy3 dye and reverse micelle aggregation. This study explored a range of reverse micelle sizes, defined as w(0) = [H(2)O]/[AOT], in which the occupation number ranged from one Cy3 molecule per ∼10(5) to ∼10(6) reverse micelles. These measurements reveal that in the smallest reverse micelle, w(0) = 1, the Cy3 molecules aggregate to form H-aggregate dimers, and the Cy3 dimerization is accompanied by the formation of a transient dimer between reverse micelles. Transient reverse micelle dimer particles are only observed in the small fraction of Cy3-labeled reverse micelles probed by fluorescence correlation spectroscopy and are not observed in the bulk solution probed by dynamic light scattering. Furthermore, fluorescence correlation spectroscopy makes it possible to probe the size and shape of these dimers, revealing prolate ellipsoid-shaped particles with twice the volume and surface area of a single reverse micelle.

The role of vibrational modes in ultrafast photoinduced intramolecular electron transfer reactions is explored. Femtosecond resolved experiments on two chemical classes will be described, namely, metalmetal intervalence electron transfer in mixed valence compounds and intramolecular charge recombinatiodseparation in organic donor/acceptor compound class, the betaines. The results have been analyzed to reveal the complex interactions of intramolecular and intermolecular modes in electron transfer reactions. I. INTRODUCTION The study of charge transfer processes, and in particular homogeneous electron transfer (ET) in solution, is at the forefront of the study of the molecular details of chemical reactions in liquids. The last decade has brought progress to many central problems in ET research, including the role of the solvent in these reactions, the involvement of vibrational degrees of freedom, the role of nuclear tunneling of the solvent and solute (and related quantum mechanical effects), the pathway and "mechanism" of electronic interactions, including long range ET, and other aspects of biological and heterogeneous ET. Recent reviews of the foundations of ET theories have been given by Newton and Sutinl and Marcus and Sutin.* Theories of ET reactions in solution are formulated in terms of a model in which the transferring electron is localized at a hmr molecular site in the reactant arid at a different acceptor molecular site in theproduct. Figure 1A portrays the usual curves for an ET reaction with no nuclear degrees of freedom other than the solvent coordinate. The coupling of the solvent coordinate to the ET is quantified by h, the solvent reorganization energy. AGO is the reaction free energy (driving force) for the ET. A central expression in ET theozv due to Marcus is as follows (h+AG")2 AG*= 4h where AG* is the activation energy for the ET reaction.

Poly(ethylene) oxide (PEO) is a technologically important polymer with a wide range of applications including ion-exchange membranes, protein crystallization, and medical devices. PEO's versatility arises from its special interactions with water. Water molecules may form hydrogen-bond bridges between the ether oxygens of the backbone. While steady-state measurements and theoretical studies of PEO's interactions with water abound, experiments measuring dynamic observables are quite sparse. A major question is the nature of the interactions of water with the ether oxygens as opposed to the highly hydrophilic PEO terminal hydroxyls. Here, we examine a wide range of mixtures of water and tetraethylene glycol dimethyl ether (TEGDE), a methyl-terminated derivative of PEO with 4 repeat units (5 ether oxygens), using ultrafast infrared polarization selective pump-probe measurements on water's hydroxyl stretching mode to determine vibrational relaxation and orientational relaxation dynamics. The experiments focus on the dynamical interactions of water with the ether backbone because TEGDE does not have the PEO terminal hydroxyls. The experiments observe two distinct subensembles of water molecules: those that are hydrogen bonded to other waters and those that are associated with TEGDE molecules. The water orientational relaxation has a fast component of a few picoseconds (water-like) followed by much slower decay of approximately 20 ps (TEGDE associated). The two decay times vary only mildly with the water concentration. The two subensembles are evident even in very low water content samples, indicating pooling of water molecules. Structural change as water content is lowered through either conformational changes in the backbone or increasing hydrophobic interactions is discussed.

The possibility that a negatively charged organic molecule penetrates the lipid interface in a reverse micellar system is examined using UV-vis absorption and NMR spectroscopy. The hypothesis that deprotonated forms of dipicolinic acid, H(2)dipic, such as Hdipic(-) and dipic(2-), can penetrate the lipid interface in a microemulsion is based on our previous finding that the insulin-enhancing anionic [VO(2)dipic](-) complex was found to reside in the hydrophobic layer of the reverse micelle (Crans et al. J. Am. Chem. Soc. 2006, 128, 4437-4445). Penetration of a polar and charged compound, namely Hdipic(-) or dipic(2-), into a hydrophobic environment is perhaps unexpected given the established rules regarding the fundamental properties of compound solubility. As such, this work has broad implications in organic chemistry and other disciplines of science. These studies required a comprehensive investigation of the different dipic species and their association in aqueous solutions at varying pH values. Combining the aqueous studies using absorption and NMR spectroscopy with those in microemulsions defines the differences observed in the heterogeneous environment. Despite the expected repulsion between the surfactant head groups and the dianionic probe molecule, these studies demonstrate that dipic resides deep in the hydrophobic portion of the reverse micellar interface. In summary, these results provide evidence that ionic molecules can reside in nonpolar locations in microheterogeneous environments. This suggests that additional factors such as solvation are important to molecule location. Documented ability to penetrate lipid surfaces of similar charge provides a rationale for why specific drugs with less than optimal hydrophobicity are successful even though they violate Lipinski's rules.

There is increasing evidence for the involvement of plasma membrane microdomains in insulin receptor function. Moreover, disruption of these structures, which are typically enriched in sphingomyelin and cholesterol, results in insulin resistance. Treatment strategies for insulin resistance include the use of vanadium compounds which have been shown in animal models to enhance insulin responsiveness. One possible mechanism for insulin-enhancing effects might involve direct effects of vanadium compounds on membrane lipid organization. These changes in lipid organization promote the partitioning of insulin receptors and other receptors into membrane microdomains where receptors are optimally functional. To explore this possibility, we have used several strategies involving vanadium complexes such as [VO2dipic]− (pyridin-2,6-dicarboxylatodioxovanadium(V)), decavanadate (V10O286−, V10), BMOV (bis(maltolato)oxovanadium(IV)) and [VO(saltris)]2 (2-salicylideniminato-2-(hydroxymethyl)-1,3-dihydroxypropane-oxovanadium(V)). Our strategies include an evaluation of interactions between vanadium-containing compounds and model lipid systems, an evaluation of the effects of vanadium compounds on lipid fluidity in erythrocyte membranes, and studies of the effects of vanadium-containing compounds on signaling events initiated by receptors known to use membrane microdomains as signaling platforms.

The water inside reverse micelles can differ dramatically from bulk water. Some changes in properties can be attributed to the interaction of water molecules with the micellar interface, forming a layer of shell water inside the reverse micelle. The work reported here monitors changes in intramicellar water through chemical shifts and signal line widths in 51V NMR spectra of a large polyoxometalate probe, decavanadate, and from infrared spectroscopy of isotopically labeled water, to obtain information on the water in the water pool in AOT reverse micelles formed in isooctane. The studies reveal several things about the reverse micellar water pool. First, in agreement with our previous measurements, the proton equilibrium of the decavanadate solubilized within the reverse micelles differs from that in bulk aqueous solution, indicating a more basic environment compared to the starting stock solutions from which the reverse micelles were formed. Below a certain size, reverse micelles do not form when the polyoxometalate is present; this indicates that the polyanionic probe requires a layer of water to solvate it in addition to the water that solvates the surfactant headgroups. Finally, the polyoxometalate probe appears to perturb the water hydrogen-bonding network in a fashion similar to that in the interior surface of the reverse micelles. These measurements demonstrate the dramatic differences possible for water environments in confined spaces.

The motion of water molecules in mixtures of water and d6-dimethyl sulfoxide (DMSO) has been explored through molecular dynamics (MD) simulations using the SPC/E water model (J. Chem. Phys. 1987, 91, 6269) and the P2 DMSO model (J. Chem. Phys. 1993, 98, 8160). We evaluate the self-intermediate scattering functions, FS(Q,t), which are related by a Fourier transform to the incoherent structure factors, S(Q,omega), measured in quasielastic neutron scattering (QNS) experiments. We compare our results to recent QNS experiments on these mixtures reported by Bordallo et al. (J. Chem. Phys. 2004, 121, 12457). In addition to comparing the MD data to the experimental signals, which correspond to a convolution of S(Q,omega) with a resolution function, we examine the rotational and translational components of FS(Q,t) and investigate to what extent simulation results for the single-molecule dynamics follow the dynamical models that are used in the analysis of the experimental data. We find that the agreement between the experimental signal and the MD data is quite good and that the portion of FS(Q,t) due to translational dynamics is well represented by the jump-diffusion model. The model parameters and their composition dependence are in reasonable agreement with experiment, exhibiting similar trends in water mobility with composition. Specifically, we find that water motion is less hindered in water-rich and water-poor mixtures than it is near equimolar composition. We find that the extent of coupling between rotational and translational motion contributing to FS(Q,t) increases as the equimolar composition of the mixture is approached. Thus, the decoupling approximation, which is used to extract information on rotational relaxation from QNS spectra at higher momentum transfer (Q) values, becomes less accurate than that in water-rich or DMSO-rich mixtures. We also find that rotational relaxation deviates quite strongly from the isotropic rotational diffusion model. We explore this issue further by investigating the behavior of orientational time correlations for different unit vectors and corresponding to Legendre polynomials of orders 1-4. We find that the rotational time correlations of water molecules behave in a way that is more consistent with the extended jump rotation model recently proposed by Laage and Hynes (Science 2006, 311, 832).

In this study, mobility and structure of water molecules in Aerosol OT (bis(2-ethylhexyl) sulfosuccinate, AOT) reverse micelles with water content w0 = 5 and Na+, K+, Cs+ counterions have been explored with molecular dynamics (MD) simulations. Using the Faeder/Ladanyi model (J. Phys. Chem. B, 2000, 104, 1033) of the reverse micelle interior, MD simulations were performed to calculate the self-intermediate scattering function, FS(Q,t), for water hydrogen atoms that could be measured in a quasielastic neutron scattering experiment. Separate intermediate scattering functions FRS(Q,t) and FCMS(Q,t) were determined for rotational and translational motion. We find that the decay of FCMS(Q,t) is nonexponential and our analysis of the MD data indicates that this behavior arises from decreased water mobility for molecules close to the interface and from confinement-induced restrictions on the range of translational displacements. Rotational relaxation also exhibits nonexponential decay, which is consistent with relatively rapid restricted rotation and slower rotational relaxation over the full angular range. Rotational relaxation is anisotropic, with the O-H bond short-time rotational mobility considerably higher than that of the molecular dipole. This behavior is related to the decreased density of water-water hydrogen bonds in the vicinity of the interface compared to core or bulk water. We find that the interfacial mobility of water molecules is quite different for the three counterion types, but that the core mobility exhibits weak counterion dependence. Differences in interfacial mobility are strongly correlated with structural features, especially ion-water coordination, and the extent of disruption by the counterions of the water hydrogen bond network.

The behavior of C343, a common molecular probe utilized in solvation dynamics experiments, was studied in homogeneous media and in aqueous and nonaqueous reverse micelles (RMs). In homogeneous media, the Kamlet and Taft solvatochromic comparison method quantified solute-solvent interactions from the absorption and emission bands showing that the solvatochromic behavior of the dye depends not only on the polarity of the medium but also on the hydrogen-bonding properties of the solvent. Specifically, in the ground state the molecule displays a bathochromic shift with the polarity polarizability (pi) and the H-bond acceptor (beta) ability of the solvents and a hypsochromic shift with the hydrogen donor ability (alpha) of the media. The carboxylic acid group causes C343 to display greater sensitivity to the beta than to the pi polarity parameter; this sensitivity increases in the excited state, while the dependence on alpha vanishes. This demonstrates that C343 forms a stable H-bond complex with solvents with high H-bond acceptor ability (high beta) and low H-bond donor character (low alpha). Spectroscopy in nonpolar solvents reveals J-aggregate formation. With information from the Kamlet-Taft analysis, C343 was used to explore RMs composed of water or polar solvents/sodium 1,4-bis-2-ethylhexylsulfosuccinate (AOT)/isooctane using absorption, emission, and time-resolved spectroscopies. Sequestered polar solvents included ethylene glycol (EG), formamide (FA), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMA). Dissolved in the AOT RM systems at low concentration, C343 exists as a monomer, and when introduced to the RM samples in its protonated form, C343 remains protonated driving it to reside in the interface rather than the water pool. The solvathochromic behavior of the dye depends the specific polar solvent encapsulated in the RMs, revealing different types of interactions between the solvents and the surfactant. EG and water H-bond with the AOT sulfonate group destroying their bulk H-bonded structures. While water remains well segregated from the nonpolar regions, EG appears to penetrate into the oil side of the interface. In aqueous AOT RMs, C343 interacts with neither the sulfonate group nor the water, perhaps because of intramolecular H-bonding in the dye. DMF and DMA interact primarily through dipole-dipole forces, and the strong interactions with AOT sodium counterions destroy their bulk structure. FA also interacts with the Na+ counterions but retains its H-bond network present in bulk solvent. Surprisingly, FA appears to be the only polar solvent other than water forming a "polar-solvent pool" with macroscopic properties similar to the bulk.

A core/shell model has often been used to describe water confined to the interior of reverse micelles. The validity of this model for water encapsulated in AOT/isooctane reverse micelles ranging in diameter from 1.7 to 28 nm (w0 = 2-60) and bulk water is investigated using four experimental observables: the hydroxyl stretch absorption spectra, vibrational population relaxation times, orientational relaxation rates, and spectral diffusion dynamics. The time dependent observables are measured with ultrafast infrared spectrally resolved pump-probe and vibrational echo spectroscopies. Major progressive changes appear in all observables as the system moves from bulk water to the smallest water nanopool, w0 = 2. The dynamics are readily distinguishable for reverse micelle sizes smaller than 7 nm in diameter (w0 = 20) compared to the response of bulk water. The results also demonstrate that the size dependent absorption spectra and population relaxation times can be quantitatively predicted using a core-shell model in which the properties of the core (interior of the nanopool) are taken to be those of bulk water and the properties of the shell (water associated with the headgroups) are taken to be those of w0 = 2. A weighted sum of the core and shell components reproduces the size dependent spectra and the nonexponential population relaxation dynamics. However, the same model does not reproduce the spectral diffusion and the orientational relaxation experiments. It is proposed that, when hydrogen bond structural rearrangement is involved (orientational relaxation and spectral diffusion), dynamical coupling between the shell and the core cause the water nanopool to display more homogeneous dynamics. Therefore, the absorption spectra and vibrational lifetime decays can discern different hydrogen bonding environments whereas orientational and spectral diffusion correlation functions predict that the dynamics are size dependent but not as strongly spatially dependent within a reverse micelle.

How water, metabolites and proteins associate and traverse the lipid interface is generally investigated by using probes with spectroscopic handles. Cellular confinement limits the tools of investigation to indirect approaches. Studies of a variety of different probes become important to understand the effects of confinement on chemical reactions and biological function. Confinement of water affects the properties of water and this effect is important for cellular systems. A versatile model system for studying the effect of water confinement on biological processes uses reverse micelles (RMs). Molecular probes are also used to investigate environments that are not readily accessible to direct measurements. Most of the dyes in use contain large hydrophobic chromophores and do not have size and structural flexibility to probe a surface that is both hydrophobic and hydrophilic as common in biological systems. We present the use of vanadium-containing probes for exploration of the fundamental properties of restricted water and lipid interfaces in RMs. The presence of a vanadium atom in these probes provides multiple handles such as chemical shifts, signal linewidth and lifetime experiments in the quadrupolar 51V nuclei as well in 1H and 13C nuclei for investigations. The quadrupolar nuclei have a greater battery of useful spectroscopic parameters and combined with the conventional methods provide multiple handles in one probe. Furthermore, the vanadium-containing probe structure, charge and polarity can be modified for use in various biological settings. Here we introduce the concept and describe a few applications of this approach.

The News of the Week story “A Dark tale behind two retractions” (R. F. Service, 18 December 2009, p. [1610][1]) omitted important issues regarding the training of young scientists. Students and postdocs involved in this debacle may have learned excellent experimental protocols and techniques, but did any of them have training in responsible conduct of research? And if so, how did that training influence their actions? When co-workers present research results, we trust them to be open, honest, and forthright. The high stakes of losing two papers in top-tier journals for all involved, including a pretenure faculty member whose tenure decision may have been affected by the retractions, remind us that we should pursue science for the sake of discovery and self-actualization rather than less savory goals such as power, financial gain, and prestige. Disappointingly, the News story did not discuss subsequent action that could preclude this type of situation from arising again. Challenging results that cannot be reproduced requires substantial courage. At what point do we draw the line between results that “have not yet been reproduced” and those that “cannot be reproduced”? Without guidance about responsible conduct of research, students lack the tools and experience to question protocols or recognize potentially risky situations. Both the National Institutes of Health ([ 1 ][2]) and the National Science Foundation ([ 2 ][3]) have written new guidelines for required training in responsible conduct of research. These changes suggest that the scientific community now acknowledges that training young scientists means more than teaching them how to design and perform experiments and interpret data. We hope that high-profile laboratories, such as Peter Schultz's, will lead by example and will endorse the concept that real-time, face-to-face, responsible-conduct training by qualified professionals is not only desirable but necessary to help avert horror stories like this in the future. 1. [↵][4] NIH, “Update on the Requirement for Instruction in the Responsible Conduct of Research” ( ). 2. [↵][5] NSF, Responsible Conduct of Research ( ). [1]: /lookup/doi/10.1126/science.326.5960.1610 [2]: #ref-1 [3]: #ref-2 [4]: #xref-ref-1-1 "View reference 1 in text" [5]: #xref-ref-2-1 "View reference 2 in text"

We study the ultrafast dynamics of OH stretching and bending vibrations of water inside dioleoylphosphatidylcholine (DOPC) reverse micelles in a wide range of hydration. A strong hydration level dependence for the spectral diffusion rates is found and explained by the distinctly different environment for single water molecules bound to the anionic phosphate group. We show that the energy relaxation pathway of the OH stretching vibration at low hydration level involves the OH bending.

Reverse micelles--isolated, surfactant-coated water droplets--are useful model systems for confined water in biology and materials science. In her Perspective, Levinger reviews recent advances in the study of reverse micelles, which have shown that the properties of confined water differ substantially from those of bulk water. The collective motion of the water molecules is shown to depend strongly on the confinement in the reverse micelles. Such effects are also likely to occur in cells and porous materials and may be exploited in nanometer-scale synthesis.

Popular cultural themes or fads can provide an effective vehicle to enthuse students about science. The program described here uses current children's literature in a versatile chemical education activity. This activity generates excitement in elementary school students because of the integration of the popular Harry Potter literature series with hands-on experiments. Elementary school student participants are prompted to explore three main scientific topics during this activity: properties of solids, liquids, and gases; scientific ethics; and the scientific method. Undergraduate and high school student volunteer mentors are readily trained to conduct the activity at elementary schools via an introduction to the philosophy of the exercise in conjunction with working through the activity themselves. As an outreach activity it serves to connect undergraduate and high school students both with faculty and their local communities.