XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
325
T8: P–4
Induced circular dichroism spectroscopy for the study
of protein-ligand molecular interactions
Robert Dec
1
, and Wojciech Dzwolak
1
1
Department of Chemistry, Biological and Chemical Research Centre, University of Warsaw,
Pasteura 1, 02-093 Warsaw, Poland, e-mail: rdec@chem.uw.edu.pl
Amyloids are examples of highly structured protein aggregates. So far, dozens of human
disorders, including Alzheimer’s disease and Parkinson’s disease, have been linked to in vivo
amyloid deposits assembled from sequentially unrelated protein precursors [1]. There are no
known medications for these disorders.
Some dye such as Congo red (CR), Thioflavin T and Nile red have a strong binding affinity
to amyloid fibrils. Some of these small planar molecules are seen as potential amyloid-inhibiting
drugs. Despite this fact the current understanding of underlying docking interactions between
amyloid fibrils and such ligands remains unsatisfactory. Here, we present a new approach to
study molecular interactions of small ligands with amyloid aggregates.
Our approach uses induced circular dichroism (ICD). Unbounded CR does not give a
circular dichroism (CD) signal. However, when CR is associated with chiral amyloid, it is
possible to record the ICD spectrum of CR. This spectrum can be positive or negative depending
on chosen amyloid (amyloids with different signs of Cotton effect). We measured, for different
temperatures, kinetics of “hopping” CR molecules between two chiral variants of fibrils [Fig. 1].
Fig. 1. Sample stacked time-lapse CD spectra of pre-incubated and equilibrated +ICD
.
CR complexes
mixed with stoichiometric portions of −ICD (top row) and vice versa (bottom row).
Registered kinetics allowed us to determine the rate constants (for different temperatures)
related to the dissociation of complexes amyloid-CR (+ICD
.
CR and –ICD
.
CR). We then
adjusted this rate constants to the Arrhnenius equation, which ultimately allowed us do
determinate CR-amyloid binding energies in the reange of 40–50 kJ mol
–1
[2].
Keywords: Amyloid; Congo red; induced circular dichroism
Acknowledgment
This work was in part supported by University of Warsaw (DSM project).
References
[1] T.P.J. Knowles, M. Vendruscolo, C.M. Dobson, 15 (2014) 384.
[2] R. Dec, V. Babenko, W. Dzwolak, 6 (2016) 97331.
XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
326
T8: P–5
Interplay between intrachain and interchain exciton interactions
involving hydrogen bonds in the crystals of oximes
studied by IR spectroscopy
Barbara Hachuła
1
, Aleksandra Garbacz
1
, and Anna Polasz
1
1
Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland,
e-mail: barbara.hachula@us.edu.pl
Oximes (RR'C=N-OH) represent an important class of organic compounds with a wide range of
practical applications in both research laboratories and in large-scale production [1]. Oximes are also
a very effective antifungal agent so they became a matter of interest [2]. The most interesting
structural feature of oximes is the system of hydrogen bonds. Oximes can act as both hydrogen-bond
donors (via the –O-H moiety) and as hydrogen-bond acceptors (via the –C=N and the –OH moieties).
Thus the oximes can form dimeric, R
2
2
(6), structures as well as catemeric, (C(2), C(3) or C(6)),
chains via O-H
…
O and O-H
…
N hydrogen bonds in the solid-state [1–3]. The R
3
3
(9) and R
4
4
(12)
hydrogen
-
bond patterns in the crystalline oximes were also found [3].
IR spectroscopy has been used in connection with the H/D exchange technique to characterize the
inter-hydrogen bond interaction nature in the crystals of oximes, i.e., cyclohexanone oxime, indan-1-
one oxime and (E)-benzaldehyde oxime (R
3
3
(9), R
4
4
(12) and R
4
4
(12) ring arrangements, respectively).
Thus far, the result of such intrachain/interchain exciton coupling has been analyzed experimentally
for the other types of organic compounds, i.e., carboxylic acids, amides or azoles [4, 5]. In this work,
we show that the interplay of intrachain (through-bond) and interchain (through-space) exciton
couplings between hydrogen bonds within the O-H
…
N ring is dependent on the electronic structure of
the individual molecular system. In the crystals of cyclohexanone oxime and indan-1-one oxime, the
intrachain exciton interactions, involving the vibrationally excited hydrogen bonds in the rings, are
noticeably stronger than in (E)-benzaldehyde oxime. As a result, the lower-frequency branch of the
ν
O-H
band of cyclohexanone oxime and indan-1-one oxime, recorded in the wide temperature range, is
more intense in relation to the intensity of the higher-frequency band branch. On the other hand, the
higher-frequency branch of the ν
O-H
band of (E)-benzaldehyde oxime is the most intense fragment of
the spectrum at 293 K and 77 K. In cyclic ketoximes (cyclohexanone oxime, indan-1-one oxime), the
intrachain exciton interactions, transferred in the O−H
…
N cycles, dominate due to their electronic
molecular structure. In aldoximes ((E)-benzaldehyde oxime), a weak through-space coupling of a van
der Waals type is responsible for the interchain exciton coupling. In this case, the hydrogen bonds are
separated from aromatic rings by methine groups. A non-random distribution of protons and
deuterons in neighbouring hydrogen bonds within a ring occurs in the partially deuterated samples of
selected crystalline systems. The origin of this anomalous arrangement of protons and deuterons
between the hydrogen bonds was assigned to the new kind of co-operative interactions involving
hydrogen bonds (i.e., the dynamical cooperative interactions).
Keywords: oxime; hydrogen bond; IR spectroscopy
References
[1] C. B. Aakeröy, A. S. Sinha, K. N. Epa, P. D. Chopade, M. M. Smith, J. Desper, Crys. Growth Des. 13 (2013)
2687.
[2] G. Yakali, E. Barim, C. Kirilmiş, M. Aygün, J. Chil. Chem. Soc. 61 (2016) 3140.
[3] J. N. Low, L. M. N. B. F. Santos, C. F. R. A. C. Lima, P. Brandão, L. R. Gomes, Eur. J. Chem. 1 (2010) 61.
[4] B. Hachuła B., M. Jabłońska-Czapla, H. T. Flakus., M. Nowak, J. Kusz., Spectrochim. Acta A 134 (2015)
592.
[5] H. T. Flakus, B. Hachuła, E. Turek, A. Michta, W. Śmiszek-Lindert, P. Lodowski, Chem. Phys. Lett. 634
(2015) 113.
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