Correlating Proton Transfer Dynamics To Probe Location in Confined Environments

Abstract

The dramatic impact of differing environments on proton transfer dynamics of the photoacid HPTS prompted us to investigate these systems with two highly complementary methods: ultrafast time-resolved transient absorption and two-dimensional NMR spectroscopies. Both ultrafast time-resolved transient absorption spectroscopy and time-resolved anisotropy decays demonstrate the proton transfer dynamics depend intimately on the specific reverse micellar system. For w(0) = 10 reverse micelles formed with anionic AOT surfactant, the HPTS proton transfer dynamics are similar to dynamics in bulk aqueous solution, and the corresponding (1)H 2D NOESY NMR spectra display no cross peaks between HPTS and AOT consistent with the HPTS residing well hydrated by water in the interior of the reverse micelle water pool. In contrast, ultrafast transient absorption experiments show no evidence for HPTS photoinduced proton transfer reaction in reverse micelles formed with the cationic CTAB surfactant. In CTAB reverse micelles, clear cross peaks between HPTS and CTAB in the 2D NMR spectra show that HPTS embeds in the interface. These results indicate that the environment strongly impacts the proton transfer reaction and that complementary experimental techniques develop understanding of how location critically affects molecular responses.

Solute location in a nanoconfined liquid depends on charge distribution

“…In addition, an improved understanding of dynamical properties that elucidates the mass transport limitations and rate processes in mesoporous materials is still needed. Experimental efforts, including additional [17][18][19] complementary measurements that provide insight into solute location in nanoconfined solvents will, along with theoretical and simulation work, be critical to such efforts.…”

“…[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. However, we are unaware of any measurements that probe the relative positions before and after acid ionization of a proton transfer complex (or photoacid).…”

Insights into the Partitioning Behavior of Secondary Surfactants in a Microemulsion-Based Synthesis of Metal Nanoparticles: A DLS and 2D NMR Spectroscopic Investigation

“…For NOESY experiments, data were obtained using a 90°pulse width of 7.6 μs, 1 H spectral width of 3491 Hz with an acquisition time of 0.250 s, and a relaxation delay of 1.5 s. 200 t 1 increments were used (64 scans per increment), and a 300 ms NOE mixing time was used. 20 Transmission Electron Microscopy. Details of TEM analysis of metal NP-containing samples are provided in the Supporting Information.…”

“…As expected, DDT and DDAm diffuse faster than OAm, as a result of the shorter length of their hydrocarbon chains.2D NMR Experiments: Empty AOT RMs upon Addition of Secondary Surfactants. Once the diffusion coefficients were established for the individual components, 2D DOSY NMR experiments were performed on empty AOT RM systems following addition of each individual secondary surfactant at seven different concentrations(1,5,20, 40, 125, 260, and 400 mM). The dependence of D AOT and D ss on secondary surfactant concentration was investigated.…”

“…The dependence of D AOT and D ss on secondary surfactant concentration was investigated. A selection of the DOSY spectra obtained at 3 of the 7 secondary surfactant concentrations studied(20, 40, and 260 mM) are shown inFigure 3; the remaining results are shown in the Supporting Information(Figures S6 and S7), in the interest of space.D values for each secondary surfactant were determined from DOSY results of the mixtures at each secondary surfactant concentration, and values are reported in…”