XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
114
T8: O–3
Chiroptical analysis of supramolecular xanthophyll aggregates
Grzegorz Zając
1
, Monika Dudek
1
, Ewa Machalska
1
, Agnieszka Kaczor
1,2
,
Jiří Kessler
3
, Petr Bouř
3
, and Malgorzata Barańska
1,2
1
Faculty of Chemistry Jagiellonian University, 3 Ingardena 30-060 Krakow, Poland,
e-mail: zajac@chemia.uj.edu.pl
2
Jagiellonian Centre of Experimental Therapeutics, Jagiellonian University, 14 Bobrzynskiego, 30-
348 Krakow, Poland
3
Institute of Organic Chemistry and Biochemistry, Academy of Sciences, Flemingovo náměstí 2,
Prague, 16610, Czech Republic
Xanthophylls (oxygenated carotenes) are red pigments used as animal feed additives and
dietary supplements. They possess high antioxidant activity due to the presence of a polyene
chain in their structure that acts against reactive oxygen species. In some conditions (e.g. water-
organic media) xanthophylls aggregate into chiral, supramolecular structures. Generally, there
are two types of carotenoid arrangements: loose “head-to-tail” J-aggregates, characterized by a
red-shifted absorption band in comparison to the monomer spectrum, and tight “card-pack” H-
aggregates exhibiting blue-shifted absorption [1].
Raman Optical Activity (ROA) spectroscopy, a method used here, is based on observation of
small difference between intensity of Raman scattering from chiral molecules for right- and left-
circularly polarized incident light. ROA provides information about the absolute configuration
and conformational equilibrium of chiral compounds (spectra of two enantiomers are mirror
images of each other). ROA can also be used to study secondary structure of biomolecules. As
the ROA effect is extremely weak, it usually requires long spectral accumulation times and
highly concentrated samples. Therefore possibilities of ROA signal enhancement are of interest.
One approach is to measure ROA in resonance. The theory of Resonance Raman Optical
Activity (RROA) in single electronic state (SES) limit predicts that each band in RROA
spectrum exhibits the same sign. Furthermore, the sign should be opposite to the sign of related
Electronic Circular Dichroism (ECD) bands [2]. Xanthophyll aggregates in contrast to
monomers exhibit a strong rotational strength of the main electronic absorption band. If Cotton
effect occurs close to the excitation laser line (e.g. 532 nm), AIRROA (Aggregation-Induced
Resonance Raman Optical Activity) can be observed [3].
This work reports experimental observation of Aggregation-Induced Resonance Raman
Optical Activity (AIRROA) effect from chiral, supramolecular astaxanthin (AXT), zeaxanthin
(ZXT) and lutein (LUT) assemblies, obtained from various organic solvent-water solutions.
AIRROA spectra were measured using the ChiralRAMAN-2X spectrometer (BioTools Inc.)
with 532 nm excitation. Additionally, spectroscopic properties of obtained aggregates were
studied using Electronic Circular Dichroism (ECD), UV-Vis and resonance Raman
spectroscopy. To better understand obtained experimental spectra, we performed molecular
dynamics (MD) simulations of astaxanthin dimers and decamers in mixed solvents
(acetone/water, e.g. 1:9 and 3:7 ratios) and quantum chemical calculations of ECD spectra of
MD snapshots.
Keywords: self-assembly; chirality; Raman optical activity; xanthophylls
Acknowledgment
This work was supported by National Science Centre (2013/08/A/ST4/00308 and 2015/19/N/ST4/00185).
References
[1] S. Köhn, et al. in Carotenoids SE-5 (eds. G. Britton, S. Liaaen-Jensen, H. Pfander) 4 (2008) 53.
[2] L.A. Nafie, Vibrational Optical Activity: Principles and Applications, John Wiley&Sons, UK 2011.
[3] M. Dudek, G. Zajac, A. Kaczor, M. Baranska, J. Phys. Chem. B, 120 (2016) 7807.
XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
115
T8: O–4
Concentration fluctuation study of benzyl acetone in chemical and
deuterated solvents using Raman and density functional theory
Gomti Devi Thongam
1
1
Department of Physics, North-Eastern Regional Institute of Science and Technology, Nirjuli, India,
e-mail:
tgdevi26@gmail.com
Benzylacetone or 4-phenyl-2-butanone is a liquid with a sweet, flowery smell that is
considered to be the most abundant attractant compound in flowers. Study of this molecule shall
bring the insight of its properties and its interacting environment with different solvents. In this
paper, Raman spectroscopic technique has been used to study the intermolecular interactions
and dynamics of C–H stretching modes of Benzyl Acetone (BA) in binary mixtures using
Chloroform (CLF) and deuterated Chloroform (CLFd) solvents. The Raman band of C=O
stretching mode has been deconvoluted into three distinct bands for neat BA as well as in binary
mixtures. Deconvoluted bands of C–H stretching vibration in neat BA were assigned as chain
dimer, cyclic dimer and monomer having peak wavenumbers 3064.59, 3053.85 and 3035.06 cm
–
1
respectively (Fig. 1). The highest peak frequency has been assigned for monomer as it is the
free molecule in comparison with other associate ones.
The variation peak wavenumbers with the solvent concentration has been plotted with the
solvent concentration (not shown). The peak wavenumbers of C–H stretching mode shows blue
shift with the increase in solvent concentration for both the solvents in the three deconvoluted
peak wavenumbers. The charge transfer from solvents to solute through hydrogen bonding may
lead to blue shift in interacting environment [1–3]. The peak wavenumbers are compared with
the theoretical data using density functional theory (DFT) with basis set b3lyp/6-31+g(d,p)
(Table not shown). We are getting in good agreement with the theoretical data.
The variation in bandwidths with the solvent concentrations has been studied. Diffusion
phenomena and resonant energy transfer are found playing important roles for such variation of
the bandwidth. Furthermore, other molecular parameters such as HOMO-LUMO energy gap,
NBO analysis are also carried out using DFT method.
2960 2980 3000 3020 3040 3060 3080 3100 3120 3140 3160
-50
0
50
100
150
200
250
300
350
I
n
te
n
s
it
y
(a
rb
u
n
it
)
Wavenumber(cm-1)
C-H vibration
3035.06
3053.85
3064.59
Fig. 1. Deconvoluted Raman bands of C–H stretching vibration in neat BA.
Keywords: peak frequency; bandwidth; DFT
Acknowledgment
The author is thankful to DST India for the FIST facility provided to Physics Department, NERIST.
References
[1] T.G. Devi, Vib. Spectrosc. 75 (2014) 65.
[2] T.G. Devi, G. Upadhayay, Spectrochim. Acta A 92 (2012) 106.
[3] G. Upadhyay, T.G. Devi, Spectrochim. Acta A 133 (2014) 250.
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