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International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
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L-theanine – structural phase transitions
and its vibrational characteristics
Iwona Bryndal1
1
, Lucyna Dymińska
1
, Jadwiga Lorenc
1
, Wojciech Sąsiadek
1
,
Maciej Ptak
2
, and Jerzy Hanuza
2
1
Department of Bioorganic Chemistry, Institute of Chemistry and Food Technology, Faculty of
Engineering and Economy, University of Economics, Komandorska 118/120, 53-345 Wrocław,
Poland, e-mail: lucyna.dyminska@ue.wroc.pl
2
Division of Optical Spectroscopy, Institute of Low Temperature and Structure Research, Polish
Academy of Sciences, Okólna 2, 50-950 Wrocław, Poland
The L-theanine (N
5
-ethyl-L-glutamine) is a non-protein derived amino acid found in tea
(Camellia sinensis) leaves [1]. In addition to the graceful taste, L-theanine can modulate
peripheral physiological parameters such as reducing blood pressure and helping to manage
allergic disorders [2]. Theanine has also recently been linked to cancer prevention [3].
The L-theanine has been characterized by means of FT-IR, FT-Raman, DSC and single
crystal X-ray diffraction studies. The temperature dependence of the IR and Raman spectra has
been studied in the range 80–300 K. The reversible single-crystal-to-single-crystal phase
transition has been examined and the room- (295 K) and low-temperature (100 K) phases have
been structurally determined. The L-theanine crystallizes from water-methanol (3:1) mixtures at
room-temperature in noncentrosymmetric monoclinic space group P2
1
(Z = 4) with one
zwitterion in the asymmetric unit. The low-temperature phase is monoclinic, space group C2 (Z
= 4), with two zwitterions (denoted as A and B) in the asymmetric unit (Fig. 1).
Fig. 1. The asymmetric unit of L-theanine in the low-temperature phase, with atom-numbering scheme.
Displacement ellipsoids are drawn at 50% probability level and H atoms are shown as small spheres
of arbitrary radii. Dotted lines indicate N-H
…
O hydrogen bonds.
The IR and Raman spectra have been measured and interpreted in details with the DFT
calculations (based on the X-ray diffraction) and compared to previously reported data [4-5].
Normal modes of skeleton and functional groups have been identified together with the PED
values. Further to evaluate the strength of the intermolecular interactions, NBO analyses were
also performed.
Keywords: L-Theanine; X-ray structure; FT-IR and Raman spectroscopy
References
[1] Q.V. Vuong, M.C. Bowyer, P.D. Roach, J. Sci. Food Agric. 91 (2011) 1931.
[2] N.H. Kim, H.J. Jeong, H.M. Kim, Amino Acids 42 (2012) 1609.
[3] Q. Liu, H. Duan, J. Luan, K. Yagasaki, G. Zhang, Cytotechnology 59 (2009) 211.
[4] Y. Chen, G. Xi, R. Chen, Y. Li, S. Feng, J. Lei, H. Lin, J. Mol. Struct. 1006 (2011) 559.
[5] S.K. Kang, Y.H. Chen, S.S. Qian, H. Hu, Acta Cryst. E67 (2011) o82.
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International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
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Structure and photochemistry of 5-hydroxyquinoline
isolated in solid nitrogen
Nihal Kuş
1,2
, and Rui Fausto
1
1
CQC, Department of Chemistry, University of Coimbra, P3004-535 Coimbra, Portugal
2
Department of Physics, Anadolu University, 26470 Eskişehir, Turkey, e-mail: nkus@anadolu.edu.tr
Quinoline derivatives are prevalent in a variety of pharmacologically active synthetic and
natural drugs. Among the quinoline derivatives, the hydroxy-substituted quinolines (HQs) have
received particular attention in the last decades because they also exhibit especially appealing
chemical and physical properties: they are excellent chelating agents, catalysts for
polymerization, fungicides (or direct precursors to fungicides), and promising materials for
photoluminescent-based optical devices. In this study, 5-hydroxyquinoline (5HQ; 1) was
isolated in a low temperature nitrogen matrix at 10 K and its structure and photochemistry were
investigated by infrared spectroscopy, complemented by DFT(B3LYP)/6-311++G (d,p)
calculations.
According to the calculations, the trans conformer (with the OH group pointing to the
opposite direction of the pyridine ring of the molecule) is more stable than the cis form by ~8.8
kJ mol
−1
, and was observed in the cryogenic matrix as the sole species. Broadband in-situ UV
irradiation of 5HQ (λ ≥ 288 nm; S
1
) led to its isomerization to both quinolin-5(6H)-one 3 and
quinolin-5(8H)-one 4, which are produced via the quinolinyl radical 2. In addition, a ring
opening photoreaction of quinolin-5(6H)-one 3 was also observed. This reaction was found to be
particularly efficient when the irradiation was performed at higher energy (λ ≥ 235 nm), due to
the opening of an additional reaction channel which, according to results of TD-DFT
calculations, shall involve the S
5
state of the molecule.
Fig. 1. Observed photochemical reactions resulting from UV irradiation of 5HQ (1) isolated in a nitrogen matrix.
(2), quinolinyl radical; (3), quinolin-5(6H)-one; (4), quinolin-5(8H)-one; (5), open-ring isomeric ketenes
(structure has four possible forms).
Keywords: 5-hydroxyquinoline; matrix isolation spectroscopy; photochemistry
Acknowledgments
This investigation has been performed within the Project PTDC/QEQ-QFI/3284/2014 – POCI-01-0145-
FEDER- 016617, funded by the Portuguese “Fundação para a Ciência e a Tecnologia” (FCT) and
FEDER/COMPETE 2020-EU. The Coimbra Chemistry Centre (CQC) is supported by FCT, through the
Project No. UI0313/QUI/2013, also co-funded by FEDER/COMPETE 2020-EU. N. Kuş¸ thanks FCT for
the post-doctoral Grant Ref. No. SFRH/BPD/88372/2012
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