Hydrogen Bonding Barrier-Crossing Dynamics at Biomimicking Surfaces
نویسندگان
چکیده
Water has anomalous properties that emanate from its hydrogen-bond-induced structure. Most of the unique properties ofwater are related to the network of strong three-dimensional hydrogen bonds that interconnect the water molecules [1, 2]. According to Stillinger [3], water has a preferential three-dimensional tetrahedral structure containing a few free or single-bonded water molecules. A simulation study [4] challenges this concept and reports some distorted hydrogen-bonded structure in which one hydrogen atom is attached with two oxygen atoms, and these bifurcated bonds play a central role in themolecularmobility in the liquid state by lowering the Gibbs energy barrier of diffusion. In pure water, hydrogen bonds have a lifetime of about 1 ps. Defects in this hydrogen-bonded network seem to produce very short-lived hydrogen bonds (<200 fs) [5]. In biological interfaces, however, certain water molecules in the hydration shell have dynamics very different from that of bulk water, with a residence time of up to 100 ps [6, 7]. In proteins, the internal water molecules exchange with external water molecules typically on a timescale of 0.1–10 ms [8–10]. Hydrogen bonds are in a continuous process of breaking and reformation, with a continuous change in hydrogen bond length and strength. Pure liquid water represents a disordered ensemble of highly polar molecules linked through a fluctuating network of intermolecular hydrogen bonds on femtosecond to picosecond timescales, as shown by the pioneering work by Elsaesser et al. [11–13], Wiersma et al. [14, 15], Voehringer et al. [16], Fayer et al. [17], Tokmakoff et al. [18], using ultrafast vibrational spectroscopy and MD simulation studies, and Bakker et al. [19, 20], using time-resolved pump–probe laser spectroscopy measurements. The slowest component of the fluctuations is associated with the globular structural rearrangement of the hydrogen bond
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