Elucidating the stability of bolaamphiphilic polypeptide nanosheets using atomistic molecular dynamics.

Atomistic molecular dynamics was employed to characterize the stability of nanosheets formed by bolaamphiphilic polypeptides. Two different nanosheets (based on RFL4FR and EFL4FE peptide sequences) were simulated to quantify the impact of the bolaamphiphilic nature of the peptides on the structure and energetics of the formed nanostructures. Our results corroborate the structural results obtained experimentally, indicating consistent values for the separation between the peptide planes as well as for nanosheet thickness. Energy analysis indicates that in general the stability of the nanosheets is dominated by electrostatic interactions and nanosheet-water environment interactions contribute considerably to stability. In general, the nanosheets were found to be very stable especially the EFL4FE system that presents a greater energy of interaction between the components of the system. PMF calculations indicate that the free energy required to remove a peptide from the nanosheet is greater than 250 kJ mol-1 reaching the highest value of 310 kJ mol-1 for the extraction of the peptide in the EFL4FE nanosheet.

Ab initio study of the isomeric equilibrium of the HCN...H2O and H2O...HCN hydrogen-bonded clusters.

An ab initio study of the stability, spectroscopic properties, and isomeric equilibrium of the hydrogen-bonded HCN...H2O and H2O...HCN isomers is presented. Density functional theory and perturbative second-order MP2 and coupled-cluster CCSD(T) calculations were carried out and binding energies obtained with correlation-consistent basis sets including extrapolation to the infinity basis set level. At the best theoretical level, CCSD(T), the H2O...HCN complex is more stable than the HCN...H2O complex by ca. 6.3 kJ mol(-1). Rotational and vibrational spectra, including anharmonic corrections, are calculated. These calculated spectroscopic data are used to obtain thermochemical contributions to the thermodynamic functions and hence the Gibbs free energy. The relative free energies are used to estimate the equilibrium constant for isomerism. We find that under typical conditions of supersonic expansion experiments (T < 150 K) H2O...HCN is essentially the only isomer present. Furthermore, our calculations indicate that the hydrogen-bonded cluster becomes favorable over the separated moieties at temperatures below 200 K.