Ultrafast Dynamics in Biological Systems and in Nano-Confined Environments

Abstract

Ultrafast chemical dynamics in a nano-confined system is very different from that in a bulk liquid. In this account, we give an overview on recent femtosecond study on dynamics of ultrafast chemical processes in the nanocavity of a biological system. Dynamics in a biological system crucially depends on the location of the fluorescent probe. We show that one can study solvation dynamics in different regions (i.e. spatially resolve) by variation of the excitation wavelength. We discuss two interesting cases of how structure affects dynamics. First, solvation dynamics of two protein folding intermediates of cytochrome c is found to be differ significantly in the ultrafast initial part (<20 ps). Second, methyl substitution of the OH group in a cyclodextrin is shown to slow down the initial part of solvation dynamics quite dramatically. The most interesting observation is the discovery of the ultraslow component of solvation dynamics which is 100-1000 times slower compared to bulk water. The electron-and proton-transfer processes in a nano-confined system are found to be markedly retarded because of slow solvation and structural constraints. Close proximity of the reactants in a confined system is expected to accelerate dynamics of bi-molecular processes. This is illustrated by ultrafast fluorescence resonance energy transfer (FRET) in %1 ps time scale between a donor and an acceptor in a micelle. Finally, it is demonstrated that the decay of fluorescence anisotropy provides structural information (e.g. size of a cyclodextrin inclusion complex) and may be used to detect formation of a nano-aggregate.

Macro and nano scale modelling of water–water interactions at ambient and low temperature: relaxation and residence times

“…[41][42] However if microscopic data are taken into account, that hydration water dynamics exhibits a slow component neatly smaller than that of bulk water (2-3 orders of magnitude). 38,43 The residence times of water molecules located in the first hydration shell of commonly studied proteins have been recently shown to exhibit multiple time scales with a significant temporal disorder in the system. [43][44][45] The question is if that particular dynamics of biological water is solely due to the presence of the protein or, by the contrary, the dynamics of residence times in free water would also exhibit such heterogeneity of relaxation processes.…”

Ultrafast reaction dynamics of auramine O in a cyclodextrin nanocavity

“…The driving force for this new direction is the number of important chemical reactions that occur in such media. Examples include reactions in porous clays or on particulate surfaces [11], which are important in catalysis or environmental chemistry, reactions in spatially confined or structured media [19][20][21], such as occur in enzyme catalysed reactions in biology, or reactions in nanoconfined water [12,22,23], which is present in inverse micelles and intracellular spaces.…”

Altered relaxation dynamics of excited state reactions by confinement in reverse micelles probed by ultrafast fluorescence up-conversion

“…Both Bhattacharyya and Levinger have provided detailed reviews on this topic. 81,[119][120][121][122] Below the focus is on those results for ultrafast S(t) measurements which overlap with the reaction timescales investigated for AO in micelles.…”