Hydrogen bond, electron donor-acceptor dimer, and residence dynamics in supercritical CO2-ethanol mixtures and the effect of hydrogen bonding on single reorientational and translational dynamics: A molecular dynamics simulation study

Abstract

The hydrogen bonding and dynamics in a supercritical mixture of carbon dioxide with ethanol as a cosolvent (X(ethanol) approximately 0.1) were investigated using molecular dynamics simulation techniques. The results obtained reveal that the hydrogen bonds formed between ethanol molecules are significantly more in comparison with those between ethanol-CO(2) molecules and also exhibit much larger lifetimes. Furthermore, the residence dynamics in the solvation shells of ethanol and CO(2) have been calculated, revealing much larger residence times for ethanol molecules in the ethanol solvation shell. These results support strongly the ethanol aggregation effects and the slow local environment reorganization inside the ethanol solvation shell, reported in a previous publication of the authors [Skarmoutsos et al., J. Chem. Phys. 126, 224503 (2007)]. The formation of electron donor-acceptor dimers between the ethanol and CO(2) molecules has been also investigated and the calculated lifetimes of these complexes have been found to be similar to those corresponding to ethanol-CO(2) hydrogen bonds, exhibiting a slightly higher intermittent lifetime. However, the average number of these dimers is larger than the number of ethanol-CO(2) hydrogen bonds in the system. Finally, the effect of the hydrogen bonds formed between the individual ethanol molecules on their reorientational and translational dynamics has been carefully explored showing that the characteristic hydrogen bonding microstructure obtained exhibits sufficiently strong influence upon the behavior of them.

Distinctly Different Glass Transition Behaviors of Trehalose Mixed with Na2HPO4 or NaH2PO4: Evidence for its Molecular Origin

“…The T α profile yields a similar phenomenon: a 12.4 K increase in T α by adding Na 2 HPO 4 from R =0 to R =1 and a 28.1 K decrease when adding NaH 2 PO 4 to trehalose with R rising from 0 to 1. It should be noted that T g and T α should not be considered fully equivalent since the sample is subjected to stresses of a different physical nature (e.g., temperature change in DSC and shearing or compression in DMA) (28). Values that are more closely correlated between methods can be obtained by adjusting the heating rate and oscillation frequency of DMA, but this type of systematic study of scanning rates and frequencies was not of interest for the current study.…”

“…The hydrogen bond time correlation function C HB ( t ) for the pairs i and j is defined as: $$C_{HB}false(tfalse)=\frac{{false\langle h_{ij}false(0false)·h_{ij}false(tfalse)false\rangle }_{t^{*}}}{false\langle h_{ij}{false(0false)}^{2}false\rangle }$$ where h ij (t) equals 1 if the O atom i is hydrogen bonded with O atom j at 0 and t and the bond has not been broken in the meantime for a period longer than t * (28). In this study t *=0.6 ps and the above equation produces the continuous hydrogen bond time correlation function C HB c ( t ).…”

“…In this study t *=0.6 ps and the above equation produces the continuous hydrogen bond time correlation function C HB c ( t ). The hydrogen bond lifetime τ HB can be obtained from the following equation: (28) $${\tau }_{HB}={\int }_0^{\infty }{C_{HB}}^{c}false(tfalse)dt.$$ …”

Hydrogen Bonding and Related Properties in Liquid Water: A Car–Parrinello Molecular Dynamics Simulation Study

“…At this point it has to be mentioned that very similar geometric criteria have been successfully used in the past to predict the HB properties of water and alcohols 9,[31][32][33][34][35][36][37][38][39][40][41][42][43] . Using this simple geometric criterion, the calculated average number of hydrogen bonds per water molecule < n HB > has been estimated to be 3.48, in agreement with the value of 3.58 obtained by reverse modelling of neutron diffraction data 44 .…”

Hydrogen Bonding Analysis of Hydroxyl Groups in Glucose Aqueous Solutions by a Molecular Dynamics Simulation Study

“…Hydrogen Bonding Kinetics Analysis: Hydrogen bonding kinetics has been analyzed by hydrogen bonding lifetimes. In the present study, hydrogen bonding lifetimes have been predicted by autocorrelation functions: 25 where τ is the hydrogen bonding lifetime and C HB (t) is the autocorrelation function. The autocorrelation function can be expressed as: [26][27][28][29] where p ij (t) equals 0 or 1 depending on the hydrogen bond state of a given atoms pair i and j.…”