The OH radical has remarkable features in aqueous environments. Studies of vibrational properties can uncover more information about this omnipresent radical. However, infrared spectra of the OH radical in water represent a challenging task. This work studies the OH ⋆ stretching vibration from the gas phase for OH ⋆-wn (w = water, n = 0-5) clusters to the bulk phase for OH ⋆-w31 via ab initio molecular dynamics (AIMD) simulations with B3LYP-D3 and the maximally localized Wannier function scheme. The infrared spectrum of pure liquid water reveals from an AIMD simulation with 32 water molecules a characteristic bulk phase. The OH ⋆ stretching vibration is continuously red-shifted from the gas phase to liquid water. This fact is supported by static DFT and RI-MP2 calculations. A comparison of Wannier and radical Voronoi tessellation spectra leads to the same result for all clusters, which implies the absence of delocalized electrons. Despite the use of van der Waals radii, the Voronoi approach is able to distinguish between strong and weak hydrogen bonds, emphasizing the flexibility of this approach toward different hydrogen bond types. The stretching vibration of the OH ⋆ in the gas phase appears as a doublet due to the coupling of rotation and stretching.

In this thesis, complicated solvation phenomena that are impossible to observe via laboratory experiments are comprehensively investigated by molecular dynamics (MD) simulations. The studied system types are the OH radical in aqueous systems and keratin in ionic liquids (ILs), which are both important key contributors to the environment. The OH radical effectively cleanses the atmosphere and is also used in wastewater cleaning processes. Regenerated keratin is a biodegradable material that has been recently used as an ingredient in bioplastics. Its regeneration minimizes environmental pollution and a regeneration process by means of a greener route with ILs underpins the urgency of this research area.Within the last 15 years, only representative ab initio MD (AIMD) simulation studies with the generalized gradient approximation (GGA) functionals can be found for the OH radical in aqueous environments. However, these aforementioned functionals include the self-interaction error (SIE) that leads to artificial delocalization of unpaired electrons. Thus, a comprehensive, representative and accurate Born-Oppenheimer (BO) MD simulation study of OH -wn (w=water, n=1-5) clusters and OH -w31 was performed by employing hybrid functionals and the accurate diffuse basis set DZVP-MOLOPT-SR-GTH. In particular, one important research area was to investigate the existence of the hemibonded structure. This hemibonded structure is a threeelectron two-center interaction between the oxygen atoms of the OH radical and water with a characteristic low O -O distance of around 238 pm and a delocalization of the unpaired electron over these two centers. With the aid of this highly accurate BOMD simulation, the absence of the long-debated hemibonded configuration is shown. This clearly conveys that the hemibonded structure is an artifact from the SIE. Furthermore, this thesis reveals that a less accurate basis set such as the 6-31G basis set and a too low simulation temperature can also lead to the occurrence of the hemibonded structure. Since these two features were also used in recent AIMD simulation studies, this thesis paves the way for a more accurate description of this system type and thus sets a clear milestone within the whole topic. Finally, also the orientation of the OH radical in the gas phase up to bulk liquid water was studied by means of these BOMD simulations. It is shown that the OH radical has a less propensity for the bulk phase and that the highest occurrence is given by the OH -w1 complex in which the OH acts as a hydrogen bond donor toward water and which will therefore be a focal point for future tropospheric reactions.Additionally, a BOMD simulation of pure liquid water, involving 32 water molecules and simulated at the B3LYP-D3 and PBE0-TC-LRC-D3 levels of theory, showed very precise structural features that were in very good agreement with highly accurate experimental data.The former BOMD simulations of the OH radical in aqueous systems by using the B3LYP-D3/DZVP-MOLOPT-SR-GTH level of theory were further used to ...

Regeneration of the hoof keratin from ionic liquids was never successful in the past because the ionic liquids were not strong enough. However, this biomaterial starts to play a central role for the preparation of biofilms in the future. In the present study, hoof keratin was regenerated for the first time from an ionic liquid by experiment and characterized by FTIR spectroscopy, Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM). As 1‐Ethyl‐3‐methylimidazolium acetate is strong enough to dissolve hooves, which have a lot of disulfide bonds, a Molecular Dynamics (MD) simulation was performed with this ionic liquid and diphenyl disulfide. The MD simulation reveals that not only the cation as postulated after experiments were carried out, but also the anion is very important for the dissolution process. This complete picture was and is not accessible via experiments and is therefore valuable for future investigations. The anion always interacts with the disulfide bond, whereas the cation prefers in some situations a strong H−O interaction with the anion. If the cations and the anions are separated from each other so that the cation can not interact with the anion, both interact with the disulfide bond. The high solvation power of this solvent is shown by the fact that the cation interacts from the left and right side and the anion from above and below the disulfide bond.

The floating orbital molecular dynamics approach treats the basis functions' centers in ab initio molecular dynamics simulations variationally optimized in space rather than keeping them strictly fixed on nuclear positions. An implementation of the restricted theory for closed shell systems is already available (Perlt et al., Phys. Chem. Chem. Phys., 2014, 16, 6997-7005). In this article, the extension of the methodology to the unrestricted theory in order to cover open shell systems is introduced. The methyl radical serves as a test system to prove the correctness of the implementation and to demonstrate the scope of this method. The available spin density plots and vibrational spectra are compared to those obtained from atom-centered bases. Finally, more complex systems as well as further properties to be studied in future investigations by floating orbitals are suggested.