It has been observed in previous works that charges can exert an effect on hydrogen bonding. This can have important consequences given that hydrogen bonds are present in several systems, for instance, hydrogen bonding contributes significantly to the structure of proteins and DNA, which is crucial to their functionality. In order to determine the effect of the charge’s presence and understand it, two approaches were proposed. First, use simulated IR spectra to quantify the effect of charges in hydrogen bonding and second, analyze the orbitals involved in hydrogen bonding and its response to the presence of a charge.<br/>For the first part, small systems of organic molecules with intra and intermolecular hydrogen bonding were selected. DFT was used to optimize the geometry of each system and to obtain its simulated IR spectra. In order to simulate the charge, a Lithium ion was added to each system in different positions near the hydrogen bond. The simulated IR spectra were obtained for the optimized structures. For the second part, the orbitals involved in hydrogen bonding were calculated using post Hartree-Fock.<br/>The DFT optimization calculations showed that the hydrogen bond is broken and/or maintained depending on the system. For both cases the simulated IR spectra showed a shift in the band corresponding to the stretching vibration of the O-H bond to lower and higher frequencies when the hydrogen bond is maintained or broken respectively. Also, a change in the bond length and angle is observed. In addition, the post Hartree-Fock calculations showed that orbitals involved in hydrogen bonding are also affected by the charge.

How charges can affect hydrogen bonding: A theoretical study

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