Relaxation dynamics of deeply supercooled confined water in l,l-diphenylalanine micro/nanotubes

Abstract

The temperature dependence (10 − 290 K) of the low-frequency (20 − 150 cm −1 ) Raman-active phonon modes of supercooled confined water in L,L-diphenylalanine micro/nanotubes was analysed. The isolated dynamics of a specific geometry of water cluster (pentamer) in supercooled confined regime was studied in detail. A particular mode concerning water-nanotube interaction was also probed. A fragile-to-strong transition at 204 K was observed and related to the crossing of the Widom line. The critical exponent analyses of the relaxation rate data based on mode-coupling theory indicated perfect agreement among experimental data and theory. Our results are consistent with the existence of a second critical point of water.The distinction between gas and liquid disappears above its critical point. At pressure and temperature above this point, the system is said to be in a fluid state (supercritical fluid) [1]. Supercritical fluids are recognized as possessing unique solvation properties that make them important technological materials [1]. Of particular interest is the behavior of water in confined spaces since it plays a key role in protein hydration since nanoscale fluctuations associated with the so-called Widom line can influence biological processes [2,3].Poole et al.[4] presented a thermodynamically consistent molecular dynamical simulation study view regarding the global phase behavior of supercooled water. According to these authors, in the supercooled region just below the line of homogeneous ice nucleation, a critical point of liquid-liquid coexistence (LLCP) could exist that would eliminate the first-order transition line between low-density liquid (LDL) and high-density liquid (HDL) aqueous phases. Thus, liquid-liquid phase separation and the existence of the LLCP in water remains as a plausible hypothesis and requires further verification [5]. The Widom line temperature T W corresponds to the loci of maxima of thermodynamic response function in the one-phase region beyond the LLCP proposed to exist in supercooled liquid water [4].Molecular dynamics simulations of the TIP4P/2005 model of water performed by Kumar et al. [6] indicated that the onset of the Boson peak in supercooled bulk water coincides with the crossover to a predominantly LDL-like below T W . Gallo, Corradini and Roveri [7] studied the dynamical properties of aqueous solution of NaCl upon supercooling by molecular simulations. They found a crossover from a fragile (super-Arrhenius) to a strong (Arrhenius) behavior upon crossing the T W by both ionic solution and bulk water.Experiments in the supercooling region are extremely difficult due to crystal nucleation processes. Thus exper- * herculano.martinho@ufabc.edu.br imental pieces of evidence concerning the different hypotheses supporting the existence of LLCP are hard to test [8].In confinement water can be more easily supercooled and studied in region of phase space where crystallization of bulk water cannot be avoided. Confined water in nanoporous silica have been extensively studied [9][10]...

Superconductivity and fast proton transport in nanoconfined water

“…Water can be rapidly supercooled to -43 degC (230 degK)the upper limit to superconducting Tc according to the present theoryor lower by confining water at nanoscale, e.g. in nanotubes 13. Recent x-ray studies of water supercooled to -15 degC in a quartz capillary have revealed the presence of pentagonal dodecahedral and other pentagonal water clathrate nanoclusters similar to those shown in Figs.…”

“…14 Therefore, it is expected that this trend would continue at even lower temperatures in a nanoscale environment. Pentagonal water clusters have been shown to be present in nanotubes13 and proteins near hydrophobic amino acids,15 where the hydrophobicity promotes the pentagonal clustering of water molecules. THz vibrations of water nanoclusters have been argued to be key to biomolecular function such as protein folding.…”

Raman study of structural transformations in self‐assembled diphenylalanine nanotubes at elevated temperatures

“…The detailed analysis of this region is hampered by the complicated tube's structure and overlapping spectral lines. Even the deconvolution of this region into separate lines provides little information about the tube's structure, in spite of the partial lines assignment was performed recently …”

“…Even the deconvolution of this region into separate lines provides little information about the tube's structure, in spite of the partial lines assignment was performed recently. [35,43] Nevertheless, a lot of important information about the crystal structure and its behavior can be obtained from this region using an integrated approach based on the calculation of the effective frequency of the nanotubes' lattice vibrations. [41] Such frequency allows characterizing structural modifications and phase transitions in the tubes under the action of external forces.…”

Raman Spectra of Diphenylalanine Microtubes: Polarisation and Temperature Effects

“…Figure 3 represents the full Raman spectra at 14 and 345 K. The spectrum can be subdivided into three distinct regions, corresponding to the vibrations of constituting structural elements: (i) 10-280 cm −1 that is due to lattice vibrations, (ii) 280-1800 cm −1 vibrations of molecules' functional groups: lines at 1002 and 1032 cm −1 due to phenyl rings vibration, (iii) 2800-3350 cm −1 is a region of C−H, and N−H vibrational modes ( Figure 3). [21][22][23][24][25][26][27][28], and the interpretation of vibrations is also included. Table 1.…”