XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
31
I–13
Solvent effects on the vibrational spectra of dioxane
– theory vs. experiment
Piotr Borowski
1
, Wojciech Gac
2
, Peter Pulay
3
, and Krzysztof Woliński
4
1
Department of Chromatographic Methods, Faculty of Chemistry, MCS University,
Maria Curie-Skłodowska Sq. 3, 20-031 Lublin, Poland, e-mail: piotr.borowski@umcs.lublin.pl
2
Department of Chemical Technology, Faculty of Chemistry, MCS University,
Maria Curie-Skłodowska Sq. 3, 20-031 Lublin, Poland
3
Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville 72701, USA
4
Department of Theoretical Chemistry, Faculty of Chemistry, MCS University,
Maria Curie-Skłodowska Sq. 3, 20-031 Lublin, Poland
A polar solvent like water has a significant effect on the solute and its spectroscopic
properties. It is particularly important for molecules which exhibit specific interactions like
hydrogen bonding with solvent. Accurate modeling of solvent effects is very time-consuming,
and it is often replaced by continuum solvation models, the conductor-like screening model
(COSMO) [1–5] being the representative one. The simplified treatment of solvent-solute
interactions may in this case lead to significant errors in some of the calculated properties. The
present work focuses on comparison between COSMO and explicit solvation model (ESM).
Vibrational spectroscopy is a sensitive test of these models. Their performance for reproducing
vibrational frequency shifts of 1,4-dioxane dissolved in water is examined by comparison of the
calculated harmonic frequency changes with our experimental results. COSMO reproduces the
frequency shifts only in the CH stretching vibrations region indicating that the dominant effect
in this case is electrostatic interaction with a dielectric environment. However, it fails in the
lower frequency range dominated by CC and CO stretchings and deformations. It often predicts
wrong signs for the frequency shifts and the root-mean-square (RMS) deviation between the
calculated and observed shifts is large (nearly 9 cm
–1
). On the other hand our ESM model, in
which one or two water molecules are directly attached to dioxane and form the first
coordination sphere, turned out to be very successful. It provides accurate solvent frequency
shifts, with the proper sign in the overwhelming majority of cases. In addition, the RMS
deviation is below 2 cm
–1
in the low-frequency range. However, it performs slightly worse than
COSMO for CH stretchings. It was also found that the combined COSMO+ESM model
performs worst of all three models considered here.
Keywords: dioxane; water solution; B3LYP calculations; harmonic approximation; ESM; COSMO
References
[1] A. Klamt, G. Schüürmann, J. Chem. Soc. Perkin Trans. 2 (1993) 799.
[2] J. Andzelm, C. Kölmel, A. Klamt, J. Chem. Phys. 103 (1995) 9312.
[3] A. Klamt, J. Phys. Chem. 99 (1995) 2224.
[4] A. Klamt, V. Jonas, J. Chem. Phys. 105 (1996) 9972.
[5] K. Baldridge, A. Klamt, J. Chem. Phys. 106 (1997) 6622.
XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
32
I–14
Different cationic forms of (-)cytisinium
in the crystal structures of its simple salts
Maciej Kubicki
1
, Agata Owczarzak
1
, and Anna K. Przybył
1
1
Faculty of Chemistry, Adam Mickiewicz University in Poznań, Umultowska 89b, Poznań, Poland,
e-mail: mkubicki@amu.edu.pl
(-)-Cytisine belongs to quinolizidine alkaloids naturally occurring in legumes
(Leguminosae). Beneficial properties of cytisine have been recognised for many centuries and
cytisine extracted mainly from Laburnum anagyroides had been used in traditional medicine e.g.
for the treatment of alimentary tract conditions, migraine, insomnia, asthma, and as a substitute
of tobacco [1]. It has been found that cytisine, similarly as nicotine, shows high affinity and
selectivity to nicotine acetylcholine receptors (nAChR), and it has been used as the model
compound in the investigation for alleviation of symptoms of neurological diseases [2].
Moreover, cytisine as the agonist of nAChRs and smoking cessation drug have been employed
in antinicotine therapy [3].
In the course of our studies on this alkaloid, its derivatives and salts, we have prepared,
characterized by means of spectroscopic methods and determined the solid-state crystal
structures of a series of simple salts of ( )-cytisine. The (-)-cytisinium cation was found in three
different forms: as a monocation (protonation at N12 atom, cf. Figure 1), dication (protonation
at N12 and O2 atoms) and in a form of a (3+) charged dimer, connected by a strong O···H···O
hydrogen bond. The intermolecular interactions (strong and weak like common NH···O,
CH···O, CH···X and rare like symmetric H bond, anion-π) will be discussed in detail, including
the comparison of appropriate Hirshfeld surfaces. This method has been widely used for
visualization, understanding and quantify various types of intermolecular interactions in
molecular crystals. Additionally, the fine interplay between different factors, important for
crystal packing modes, caused the occurrence of interesting structural phenomena:
polymorphism and isostructuralism; this will be also shown in a presentation.
Fig. 1. Three different (-)cytisinium cations: mono- (left), di-cation (middle)
and hydrogen-bonded 3+-dimer (right).
Keywords: (-)-cytisine; intermolecular interactions; Hirshfeld surfaces
Acknowledgment
This research was carried out as a part of a National Science Center project (Grant No.
2013/11/B/ST5/01681).
References
[1] K. Fagerström, D. J. Balfour. Expert Opin Investig Drugs 15 (2006) 107.
[2] J. Rouden, M.-C. Lasne, J. Blanchet, J. Baudoux. Chem. Rev. 114 (2014) 712.
[3] P. Tutka Expert Opin. Investig. Drugs 17 (2008) 1473.
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