Femtosecond water dynamics in reverse-micellar nanodroplets

Ultrafast anisotropy dynamics of water molecules dissolved in acetonitrile

“…10,35,63 This has been conventionally ascribed to energy transfer from the initially excited to randomly oriented OH oscillators due to their high density in liquid H 2 O. Even putting aside numerous complications which arise from the strong isotropic thermal components to the pump-probe signal, 11,12,24,27,47 the possibility of the intramolecular mechanism of the anisotropy decay has never been thoroughly considered. Our results demonstrate that purely intramolecular processes in the hydrogen-bonded H 2 O molecule cause similar effects on the spectroscopic observables as the intermolecular interactions.…”

“…One direction that has been conventionally pursued is the removal of the complications related to the intra-and intermolecular couplings between the OH oscillators by substitution H 2 O with its deuterated isotope HDO. [11][12][13]16 Another possibility, which also mimics biological situations, 17 is to alter the complexity of the hydrogen bond network by studying water at interfaces, 18,19 in reverse micelles, [20][21][22][23][24][25][26][27] or in mixtures with various solvents. 11,28,29 The last setting is particularly advantageous because it allows investigating spatially separated water molecules and, thus, provides a unique opportunity to study purely intramolecular properties, which are not screened by interactions with other water molecules.…”

Reduced coupling of water molecules near the surface of reverse micelles

“…the extent of probed distances from the interface) at charged interfaces is still under debate. 37 On the other hand, ultrafast vibrational spectroscopy studies also evidenced a substantial deceleration of population relaxation rates 38 and a decrease in the induced anisotropy decay [39][40][41][42] of water vibrations in the lipid hydration layer. This implies completely different hydrogen-bond dynamics and effect of intermolecular couplings at the water-lipid interface.…”

“…The previous studies 38,39,[46][47][48][49][50][51] indicated the existence of a layered structure of the nano-droplet interior, consisting of bulk-like water in the micelle ''core'' and a fraction of ''shell'' water near the interface. This partitioning of water molecules into two sub-ensembles makes the reverse micelle an excellent model for interfacial water (in small, d = 1 nm micelles the fraction of border-effected water is more than 80%) and almost bulk-like water (in large d = 10 nm diameter micelles the fraction of core water approaches 90%).…”

Multicolor IR Spectroscopy of Pure Liquid Water

“…The stretchstretch transient first decays and then recovers with time constants of 0.24 ps and 0.26 ps, respectively. While the rapid decay can be assigned to the depopulation of the initially-excited stretching mode [4][5][6][7], the subsequent recovery requires further clarification. The stretch-bend transient peaks with a noticeable retardation of -0.25 ps and then decays with the time constant of -0.26 ps already seen in the stretch-stretch experiment.…”