Electron‐Transfer Rate Enhancements in Nanosized Waterpools

Lorenz, Bret B.; Crans, Debbie C.; Johnson, Michael D.

doi:10.1002/ejic.201402307

Cited by 9 publications

(4 citation statements)

References 25 publications

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“…The dynamic light scattering (DLS) measurements : Dynamic light scattering experiments were performed using a Malvern Instrument (Malvern Instruments Limited, UK) MAN0486. DLS and the autocorrelation method of analyzing scattering were used to measure hydrodynamic radius of AOT reversed micelles at 25.0 °C . A minimum of ten measurements were made for every solution with and without aniline at different pH values (pH 3.00, 6.30, and 9.30) for each w 0 value.…”

Section: Methodsmentioning

confidence: 99%

How Interfaces Affect the Acidity of the Anilinium Ion

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Miller

Johnson

et al. 2016

Chemistry A European J

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The acidity of a compound is a fundamental property that dictates molecular speciation and reactivity in solution. Measurements of acidity of simple molecules in interfacial environments are rarely carried out but assumptions often are made that the difference is sufficiently small that the change can be ignored. The effect of oil-surfactant-water interfaces in reverse micellar systems on the pKa value of the anilinium ion was measured using titrations by NMR spectroscopy as the size of the bis(2-ethylhexyl)sulfosuccinate (AOT)/isooctane reverse micelles decreased. The pKa was observed to drop from 4.85±0.02 to 4.62±0.02 in water as the reverse micelle decreased from w(0) 10 to 4 (that is down to a reverse micellar radius of about 2 nm). NOSEY experiments demonstrated that the aniline moiety resides within the surfactant interface with the amine/ammonium moiety protruding into the waterpool bridging the interface. The presence of the aniline was found to have modest and variable effect on the size of the reverse micelles as observed using dynamic light scattering. Our experimental results provide information important to theoretical studies, which explore interface phenomena and provide a framework for information on such simple molecules. These studies quantitate the small but significant effect on the pKa values upon placement of an aromatic amine molecule at a hydrophilic-hydrophobic interface.

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Section: Methodsmentioning

confidence: 99%

How Interfaces Affect the Acidity of the Anilinium Ion

Sripradite

Miller

Johnson

et al. 2016

Chemistry A European J

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“…As both ΔpH and κ(i) depend on the specific interfacial depth, temperature-dependent 1 H NMR and transient fluorescence anisotropy measurements in the presence of TX-100/SDS (4:1) micelles were performed to identify the temperature-induced change in the probe location within the micellar interface (Figure S5). − The unaffected upfield δ value for the imine proton in s-RHG (2.0 mM) and the τ c value for s-RHG/PMP for the change in the TX-100/SDS (4:1) (5.0 mM)-micelle-containing buffer temperature (15–50 °C) indicate that the interfacial probe location depths are similar among different micelle radii (Figures S5–S7, Table S1). Nearly unchanged optical intensities for s-RHG/PMP (1.0/2.0 μM) between the presence and absence of TX-100/SDS (4:1) (5.0 mM) at bulk pH 5.0 for the increase in temperature from 15 to 50 °C suggest that ΔpH/κ(i) is independent of size and the micellar curvature radius (Table , Figures and A,B).…”

Section: Resultsmentioning

confidence: 97%

“…46 To identify the precise probe-localized depth within the anionic water/oil interface, the local environment of the imine proton in s-RHG during its interaction with the self-assembled systems was monitored by 1 H NMR studies. 51,52 That the anionic self-assembled system induced a considerable amount of upfield chemical shift from ∼7.86 to 7.74 (SDS micelle) or 7.76 (DMPG/DMPC (2:1) LUV) or 7.80 ppm (mixed TX-100/SDS (4:1) micelle) indicates that the s-RHG is located in its opposite charge environment (Figures S2−S5). As s-RHG exists mostly as cationic so-RHG species in acidic pH, it involves an electrostatic interaction with anionic self-assembled headgroups located in the interfacial Stern layer.…”

Section: ■ Resultsmentioning

confidence: 99%

Detection of Curvature-Radius-Dependent Interfacial pH/Polarity for Amphiphilic Self-Assemblies: Positive versus Negative Curvature

et al. 2017

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It is possible that a defined curvature at the membrane interface controls its pH/polarity to exhibit specific bioactivity. By utilizing an interface-interacting spiro-rhodamine pH probe and the Schiff base polarity probe, we have shown that the pH deviation from the bulk phase to the interface (ΔpH)/interfacial dielectric constant (κ(i)) for amphiphilic self-assemblies can be regulated by the curvature geometry (positive/negative) and its radius. According to H NMR and fluorescence anisotropy investigations, the probes selectively interact with an anionic interfacial Stern layer. The ΔpH/κ(i) values for the Stern layer are estimated by UV-vis absorption and fluorescence studies. For the anionic sodium bis-2-ethylhexyl-sulfosuccinate (AOT) inverted micellar (IM) negative interface, the highly restricted water and proton penetration into the Stern layer owing to tight surfactant packing or a reduced water-exposed headgroup area may be responsible for the much lower ΔpH ≈ -0.45 and κ(i) ≈ 28 in comparison to ∼-2.35 and ∼44, respectively, for the anionic sodium dodecyl sulfate (SDS) micellar positive interface with a close similar Stern layer. With increasing AOT IM water-pool radius (1.7-9.5 nm) or [water]/[AOT] ratio ( w) (8.0-43.0), the ΔpH and κ(i) increase maximally up to ∼-1.22 and ∼45, respectively, due to a greater water-exposed headgroup area. However, the unchanged ΔpH ≈ -0.65 and κ(i) ≈ 53.0 within radii ∼3.5-8.0 nm for the positive interface of a mixed Triton X-100 (TX-100)/SDS (4:1) micelle justify its packing flexibility. Interestingly, the continuously increasing ΔpH trend for IM up to its largest possible water-pool radius of ∼9.5 nm may rationalize the increase in ΔpH (∼-1.4 to -1.6) with the change in the curvature radii (∼15 to 50 nm) for sodium 1,2-dimyristoyl- sn-glycero-3-phosphorylglycerol (DMPG)/1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) (2:1) large unilamellar vesicles (LUV) owing to its negative interface. Whereas, similar to the micellar positive interface, the unchanged ΔpH at the positive LUV interface was confirmed by fluorescence microscopic studies with giant unilamellar vesicles of identical lipids composition. The present study offers a unique and simple method of monitoring the curvature-radius-dependent interfacial pH/polarity for biologically related membranes.

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“…[11][12][13][14][15][16][17][18][19][20][21] We have previously found in simple models that the position distributions of a proton transfer reactant complex and product complex differ and that this difference can play a role in the reaction mechanism. 14,15 Interestingly, Sedgwick et al have observed different locations of a photoacid in reverse micelles constructed with different surfactant molecules; 18 in reverse micelles, a solute can move not only within the water pool but also intercalate into the surfactant layer that represents the confining framework.…”

Section: Introductionmentioning

confidence: 99%

Solute location in a nanoconfined liquid depends on charge distribution

Harvey

Thompson

2015

The Journal of Chemical Physics

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Nanostructured materials that can confine liquids have attracted increasing attention for their diverse properties and potential applications. Yet, significant gaps remain in our fundamental understanding of such nanoconfined liquids. Using replica exchange molecular dynamics simulations of a nanoscale, hydroxyl-terminated silica pore system, we determine how the locations explored by a coumarin 153 (C153) solute in ethanol depend on its charge distribution, which can be changed through a charge transfer electronic excitation. The solute position change is driven by the internal energy, which favors C153 at the pore surface compared to the pore interior, but less so for the more polar, excited-state molecule. This is attributed to more favorable non-specific solvation of the large dipole moment excited-state C153 by ethanol at the expense of hydrogen-bonding with the pore. It is shown that a change in molecule location resulting from shifts in the charge distribution is a general result, though how the solute position changes will depend upon the specific system. This has important implications for interpreting measurements and designing applications of mesoporous materials. C 2015 AIP Publishing LLC. [http://dx

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Electron‐Transfer Rate Enhancements in Nanosized Waterpools

Abstract: An enhancement in the electron-transfer rates of metal complexes confined to a nanoscale environment within a sodium bis(2-ethylhexyl)sulfosuccinate/water/isooctane reverse micelle (RM) are reported. The rate constants increase up to

Cited by 9 publications

References 25 publications

How Interfaces Affect the Acidity of the Anilinium Ion

How Interfaces Affect the Acidity of the Anilinium Ion

Detection of Curvature-Radius-Dependent Interfacial pH/Polarity for Amphiphilic Self-Assemblies: Positive versus Negative Curvature

Solute location in a nanoconfined liquid depends on charge distribution

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