Vibrational echo spectroscopy has become a powerful technique to study vibrational spectral diffusion in water and aqueous solutions. The dynamics of vibrational spectral diffusion is intimately related to the hydrogen bond fluctuations in liquid water and other hydrogen bonded liquids. Earlier theoretical calculations of vibrational echo spectroscopy of aqueous systems were based on classical molecular dynamics simulations involving empirical force fields of water. In the current work, we have employed the method of ab initio molecular dynamics simulation to calculate the spectral observables of vibrational echo and two-dimensional infrared (2D-IR) spectroscopy of liquid water at room temperature under Condon and cumulant approximations. The time scales extracted from the temporal decay of the frequency-time correlation function (FTCF), short-time slope of three pulse photon echo (SP3E), dynamic line width (DLW), and the slope of nodal line of 2D-IR spectra are found to be in reasonably close agreement with each other which reinforces the assertion that signatures of FTCF can be captured using three pulse photon echo and 2D-IR spectroscopy.

In the present work, we introduce two new metrics i.e. hydrogen-bond strength and charge-transfer between the donor/acceptor water molecules as a measure of hydrogen-bond rearrangement dynamics. Further, we also employ a simple model based on energy flux through the donor-acceptor water pairs to quantify the extent of the local hydrogen-bond network reorganization. Most importantly, we report a linear relationship between the OH stretch frequency and the charge and energy transfer through donor-acceptor water pairs. We demonstrate that the vibrational frequency fluctuations, which are used to determine third-order non-linear spectroscopic observables like the short-time slope of three pulse photon echo, can be used as an analog of the fluctuations in the hydrogen-bond strength and charge-transfer. The timescales obtained from our hydrogen-bond strength correlation and charge-transfer correlation decay are in excellent agreement with the computed frequency-time correlation function, as well as with recent vibrational echo experiments.

Based on quantum-mechanical path-integral molecular dynamics simulations, the impact of nuclear quantum effects on the vibrational and hydrogen bond dynamics in liquid water is investigated. The instantaneous fluctuations in the frequencies of the O-H stretch modes are calculated using the wavelet method of time-series analysis, while the time scales of the vibrational spectral diffusion are determined from frequency-time correlation functions, joint probability distributions, and the slope of three-pulse photon echo. We find that the inclusion of nuclear quantum effects leads not only to a redshift of the vibrational frequency distribution by around 130 cm but also to an acceleration of the vibrational dynamics by as much as 30%. In addition, quantum fluctuations also entail a significantly faster decay of correlation in the initial diffusive regime, which is in agreement with recent vibrational echo experiments.

Vibrational sum-frequency generation spectroscopy is a powerful method to study the microscopic structure and dynamics of interfacial systems. Here we demonstrate a simple computational approach to calculate the time-dependent, frequency-resolved vibrational sum-frequency generation spectrum (TD-vSFG) of the air-water interface. Using this approach, we show that at the air-water interface, the transition of water molecules with bonded OH modes to free OH modes occurs at a time scale of $3 ps, whereas water molecules with free OH modes rapidly make a transition to a hydrogen-bonded state within $2 ps. Furthermore, we also elucidate the origin of the observed differential dynamics based on the time-dependent evolution of water molecules in the different local solvent environments.

Aqueous solution of a fluoride ion at 300 K is studied using the method of ab initio molecular dynamics simulation. Instantaneous fluctuations in vibrational frequencies of local OD stretch modes of deuterated water are calculated using a time-series analysis of the simulated trajectory. The vibrational spectral diffusion of OD modes in the first and second solvation shells and also in bulk of the aqueous fluoride ionic solution are studied through calculations of the frequency time correlation function (FTCF), joint probability distributions, slope of three pulse photon echo (S3PE) and two dimensional infrared spectrum (2D-IR). The vibrational spectral dynamics in the first solvation shell shows decay with three components which can be correlated with the dynamics of intact ion-water hydrogen bonds, ion-water hydrogen bond lifetime and the escape dynamics of water molecules from the solvation shell. The vibrational spectral diffusion of OD modes in the second solvation shell and in the bulk show very similar decay behavior. The timescales obtained from FTCF, S3PE and the slope of nodal line (SNL) of 2D-IR are found to be in reasonable agreement with each others.

Renovation of host erythrocytes is vital for pathogenesis by Plasmodium falciparum. These changes are mediated by parasite proteins that translocate beyond the parasitophorous vacuolar membrane in an unfolded state, suggesting protein folding by chaperones is imperative for the functionality of exported proteins. We report a type IV P. falciparum heat-shock protein 40, PF11_0034, that localizes to the cytoplasmic side of J-dots and interacts with the erythrocyte cytoskeleton, and therefore named eCiJp (erythrocyte cytoskeleton-interacting J protein). Recombinant eCiJp binds to the human heat-shock protein 70 HsHSPA1 and promotes its ATPase activity. In addition, eCiJp could suppress protein aggregation. Our data suggest that eCiJp recruits HsHSPA1 to the host erythrocyte cytoskeleton, where it may become involved in remodeling of the erythrocyte cytoskeleton and/or folding of exported parasite proteins.

Aqueous solution of urea at a concentration of 4.0 M is studied by using ab initio molecular dynamics simulation. The radial and spatial distribution functions reveal no significant disruption of the local solvent structure by urea even at such a rather high concentration. Although the static structural features are not altered in any significant manner, the translational, rotational, and vibrational dynamics are found to show noticeable slowing down. The diffusion coefficient of urea is found to be three times lower than that of bulk water molecules. Similarly, orientational relaxation of water molecules in the solvation shell of urea is found to be about 5.0 ps which is significantly higher than the average value of 3.8 ps found for all water molecules. The vibrational dynamics is investigated through calculations of frequency-time correlation function (FTCF), joint frequency probability, and frequency–structure correlation functions. The timescale of vibrational spectral diffusion as determined from FTCF is found to be 2.7 ps which is higher than the known calculated timescale of ∼2 ps for spectral diffusion of pure water for similar levels of calculations. The third-order polarization and the corresponding vibrational echo intensity of OD modes are calculated within the Condon and second-order cumulant approximations. The timescales of loss of correlation in the vibrational echo spectrum are calculated from the time dependence of the slope of the 3-pulse photon echo (S3PE) function. The timescales obtained from S3PE are found to be in agreement with the FTCF. The slowing down of vibrational, translational, and rotational dynamics means that urea affects the properties of water from a dynamical perspective.

In the present work, we provide an electronic structure based method for the “on-the-fly” determination of vibrational sum frequency generation (v-SFG) spectra. The predictive power of this scheme is demonstrated at the air-water interface. While the instantaneous fluctuations in dipole moment are obtained using the maximally localized Wannier functions, the fluctuations in polarizability are approximated to be proportional to the second moment of Wannier functions. The spectrum henceforth obtained captures the signatures of hydrogen bond stretching, bending, as well as low-frequency librational modes.