From H-bonded dimer to the H-bond network around protein
Imre Bakó
Research Centre for Natural Sciences, H-1117 Budapest, Magyar tudósok körútja 2., Hungary
The significant cooperative effect between water molecules substantially affects theproperties of liquid water. The cooperativity of hydrogen bonds means that the hydrogen bondstrength is influenced by the neighboring water molecules. The introduction of an external ion
into bulk water also causes a strong perturbation of the water structure in the neighbourhoodof the ion in question. The effects of the environment (mainly asymmetric) on the electronic,
structural and energetic properties of a water molecule are in focus in this lectrure fom different
point of view. We showed that some quantum chemical descriptor ( dipole moment, intra- andintermolecular bond order) can be used to characterise the collective electrostatic and quntum
mechanical effects caused by non-immediate environment of water molecules.
These longer-range effects may be basically attributed to the properties of water as apolarizable medium, but the peculiarities of the wave functions of the actual systems do alsohave some measurable role even for the farther environment.
We performed a detailed analysis of the two- and three-body interaction energies inwater clusters containing up to 30 water molecules using the “hierarchical” basis set
superposition error (BSSE)-corrected energy decomposition scheme. In this work we showedthat the average two and three body interaction energy terms are about 74 to 80 and 20 to 26
percent, respectively, of the total BSSE corrected interaction energy for all investigated clusters.
We observed that the three-body interaction energy component is significantly
negative/positive if there are two H-bonds and one attraction/repulsion interaction energy in thecorresponding trimer, respectively.
I will show based on AIMD calculation that the electronic DOS, XES spectrum andthe net charge depend on hydrogen bonding environment in liquid phase too.
We showed in our calculations that the dipole moment of water molecules in aneighborhood of a cation is primarily increased by polarization from the bare electrostatic
charge of the cation, although the effective value of the latter is somewhat reduced by “backdonation” of electrons from the water. A further important factor is the collective effect of thewater molecules: their mutual arrangement and polarization counteract the polarizing effect of
the cation, resulting in less increased values of the dipole moments.
Additionally, I will analyze from network science how can we calculated thecooperative effect and several topological descriptor in liquid water, water-alcohol mixture andsurface of protein surface using knowledges from network science.
I will discuss a method for the determination of the optimal set of H/D compositions(isotopic substitution method, neutron diffraction) with or without taking into account theexperimental error. I make some outline for the effect of nuclear quantum effect too.

Changes of H-bond network on cooling in 2-propanol-water liquid mixtures
over the entire concentration range
1Sz. Pothoczki, 1I. Pethes, 1L. Temleitner, 1,3L. Pusztai, 2I. Bakó

1

Institute for Solid State Physics and Optics, Wigner RCP of HAS, Konkoly-Thege M. Út 2933, H-1121, Budapest, Hungary, pothoczki.szilvia@wigner.mta.hu
2Institute of Organic Chemistry Research Centre for Natural Sciences, HAS, Magyar tudósok
körútja 2, H-1117, Budapest, Hungary, bako.imre@ttk.mta.hu3
International Research Organization for Advanced Science and Technology (IROAST),
Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto, 860-8555, JapanDue to the fact that 2-propanol molecules show both hydrophobic and hydrophiliccharacters, its aqueous mixtures provide a good opportunity for studying effects of temperatureand composition on the variations of the hydrogen-bonded (H-bonded) network. Understanding
these changes at a microscopic level can be a substantial step toward a better understanding thebehaviour of aqueous solutions of more complex amphiphilic molecules.
A series of Molecular Dynamics (MD) simulations were performed for 2-propanol—watermixtures over the entire concentration range, between room temperature and the freezing pointsof the liquids. All-Atom Optimized Potential for Liquid Simulations (OPLS-AA) [1] was usedfor isopropanol molecules. For water molecules the improved Transferable Intermolecular
Potential with four Particles (TIP4P-2005) [2] was applied. The goodness of our models wasassessed by the goodness of agreement between total scattering structure factors from the MD
models and measured X-ray diffraction data [3,4].
Percolation was monitored by comparing the calculated cluster size distribution functions
for the present systems with that obtained for random percolation on a 3D cubic lattice. In
percolating systems the cluster size distribution exceeds this predicted function at large cluster
size values. It was found that the size of the percolated clusters is decreasing with the increasing
ratio of 2-propanol molecules in the mixtures.
Observable trends on varying the temperature and the composition were revealed in termsof the average H-bond number, the fraction of 2-propanol molecules as H-acceptors and as Hdonors in the H-bonds, as well as in terms of size distributions of cyclic entities [6].

[1] W. L. Jorgensen; D. Maxwell, S. Tirado-Rives, J. Am. Chem. Soc., 118, 11225−11236(1996).
[2] J. L. F. Abascal, C. Vega, J. Chem. Phys., 123, 234505/1−12 (2005).
[3] T. Takamuku, K. Saisho, S. Nozawa, T. Yamaguchi, J. Mol. Liq., 119, 133– 146 (2005).
[4] I. Pethes, L. Temleitner, L. Pusztai, unpublished results[5] I. Bakó, J. Oláh, A. Lábas, Sz. Bálint, L. Pusztai, M.C. Bellissent Funel, J. Mol. Liq., 228,25-31 (2017).
[6] Sz. Pothoczki, L. Pusztai, I. Bakó, J. Phys. Chem. B 122, 6790−6800 (2018).