State of water in inverse micelles of Aerosol OT, according to IR spectroscopic data

Zhukovskii, A. P.; Petrov, L. N.; Rovnov, N. V.

doi:10.1007/bf00753032

Cited by 4 publications

(16 citation statements)

References 2 publications

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“…These components can be assigned to strongly and weakly hydrogen-bonded OD moieties, respectively . This is consistent with reports in the literature. − , …”

Section: Resultssupporting

confidence: 93%

“…One method that has been used to characterize the AOT reverse micelles is vibrational spectroscopy. − From spectral shifting of bands in IR and Raman spectra, researchers have described the intramicellar water having two different forms: molecules that interact strongly with the surfactant polar headgroups, or bound water, and water that appears to possess similar hydrogen-bonding characteristics to the bulk phase, or free water. This is evident both from studies of the water vibrational modes and from the AOT functional group modes, such as the sulfonate and carbonyl.…”

Section: Introductionmentioning

confidence: 99%

“…In comparison with the extensive information available about water in AOT reverse micelles, there are only a few references to reverse microemulsions where the polar phase is anything other than water. − And, while the water sequestered in reverse micelles has been well characterized via a plethora of experimental techniques, ,− , the properties of other polar solvents present in reverse microemulsions are relatively unknown. Recently, we have begun probing the formation of AOT reverse micelles solubilizing nonaqueous polar solvents …”

Section: Introductionmentioning

confidence: 99%

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Formamide in Reverse Micelles: Restricted Environment Effects on Molecular Motion

et al. 1998

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Novel Aerosol OT (AOT) reverse micelles solubilizing formamide rather than water have been created and studied. In contrast to water sequestered in the interior of AOT reverse micelles, the vibrational spectra indicate that the intramicellar formamide retains a large degree of hydrogen bonding character and its structure appears significantly less perturbed by the restricted environment than water. However, solvation dynamics measurements show that the intramicellar formamide is nearly completely immobilized, a dramatic departure from bulk solvation dynamics. These results show that structural aspects derived from the characteristic vibrational motion does not necessarily provide insight into other dynamical solvent behavior.

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“…These components can be assigned to strongly and weakly hydrogen-bonded OD moieties, respectively . This is consistent with reports in the literature. − , …”

Section: Resultssupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Formamide in Reverse Micelles: Restricted Environment Effects on Molecular Motion

et al. 1998

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“…The water pools inside the AOT reverse micelles possess some interesting properties. For example, IR absorption spectroscopy shows that water molecules solubilized inside small micelles are in contact with and bound to the polar head group of the AOT molecules. − This inhibits their ability to form the normal hydrogen bonds found in bulk water. As w 0 increases, the IR spectrum shifts toward that of bulk water indicating the water molecules in the inner pool form bulklike hydrogen bonds.…”

Section: Introductionmentioning

confidence: 99%

“…The water dynamics in the smallest sized AOT micelles, w 0 < 7, have been shown to differ significantly from bulk water. − ,− While the mobility of the water molecules is reduced inside the reverse micelles, the source of this reduction is not clear. Possible perturbations could arise from the size restriction of the water pool in the micelles or interactions of water molecules with various parts of the surfactant molecules.…”

Section: Introductionmentioning

confidence: 99%

Impact of Counterion on Water Motion in Aerosol OT Reverse Micelles

1998

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We have measured the dynamics of water solvation in two different reverse micellar environments with low water content, w 0 = 1.7. In the water/Aerosol OT (AOT)/isooctane reverse micelles, the characteristic ultrafast bulk water motion is completely absent. In contrast, when the sodium cation normally complexed to the AOT surfactant head group is exchanged for an ammonium cation, solvation dynamics measurements reveal that the water is significantly more mobile. However, the water present in these modified reverse micelles is still less mobile than bulk water. These studies reveal that the Na+ ion in normal AOT reverse micelles is responsible for reducing a large fraction but not all of the water motion in these environments.

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Photoprocesses in AOT Reverse Micelles Containing Metalloporphyrins and Oligopeptides

Aoudia

Rodgers

2003

J. Phys. Chem. B

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Steady-state and time-resolved spectroscopy of two cationic metalloporphyrinsstetrakis(N-methyl-4-pyridyl)porphyrin (Pd(II)TMPyP 4+ and Zn(II)TMPy 4+ )swere studied in reverse micelles of AOT-heptane-H 2 O in the absence, and presence, of oligopeptides containing tyrosine and tryptophan residues (K 2 YL 2 and K 2 WL 2 ). Ground-state absorption spectra for both porphyrins in reverse micelles at different water-to-surfactant molar ratio (w 0 ) values revealed a critical micellar water composition of w 0 ≈ 10. Above this critical value, a w 0independent red shift (∆λ ) 3.1 nm) was observed, suggesting a similar aqueous porphyrin environment. Below w 0 ≈ 10, a w 0 -dependent blue shift was observed, indicating a porphyrin aqueous environment that is strongly related to the micellar size. At high micelle-water composition, the ground-state spectra never approached those observed in aqueous solution, strongly indicating that the porphyrin is preferentially solubilized in close vicinity of the H 2 O-AOT molecular interface. Fluorescence emission from ZnTMPyP 4+ in reverse micelles showed characteristics that were similar to those observed from ground-state absorption. Fluorescence emission from the single tryptophan residues of K 2 WL 2 in aqueous solution and in reverse micelles suggested a solubilization site of the peptide near the micellar oil-water interface. This solubilization site was found to be dependent on w 0 below w 0 values of ∼10 (reflecting a different peptide microenvironment) and independent of w 0 above ∼10 (reflecting a similar peptide microenvironment). Flash photolysis experiments showed that, in the presence of a peptide in reverse micelles, Pd(II)TMPy 4+ triplet decay was described by the sum of two exponential terms. The fast decay component for both oligopeptides was found to be independent of the peptide concentration and dependent on w 0 . The slow decay component showed a linearly dependent increase in value, relative to increases in the peptide concentration. The fast contribution to the porphyrin triplet state T 1 decay was associated with electron transfer in a discrete micelle between the target moiety (tyrosine or tryptophan) and the photoexcited porphyrin molecule. The slow contribution of the decay was associated to molecular quenching during the micellar exchange process. The fast decay component was found to be independent of pH, suggesting a solubilization of the peptide molecule in a pH-independent environment near the oil-AOT molecular interface, where a portion of the heptane chain may extend into the water phase.

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State of water in inverse micelles of Aerosol OT, according to IR spectroscopic data

Cited by 4 publications

References 2 publications

Formamide in Reverse Micelles: Restricted Environment Effects on Molecular Motion

Formamide in Reverse Micelles: Restricted Environment Effects on Molecular Motion

Impact of Counterion on Water Motion in Aerosol OT Reverse Micelles

Photoprocesses in AOT Reverse Micelles Containing Metalloporphyrins and Oligopeptides

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