Absolute configuration determination through the unique intramolecular excitonic coupling in the circular dichroisms of o,p′-DDT and o,p′-DDD. A combined experimental and theoretical study

Article abstract of DOI:10.1039/c6pp00438e

Circular dichroisms (CDs) of the o,p′-isomers of 1,1,1-trichloro- and 1,1-dichloro-2,2-bis(chlorophenyl)ethanes (DDT and DDD) were investigated experimentally and theoretically. A series of strong Cotton effect peaks in a characteristic negative-negative-positive-negative, or its mirror-imaged, pattern were observed in the CD spectra of these persistent organic pollutants. The theoretical CD spectra at the SAC-CI/B95(d) and RI-CC2/def2-TZVPP levels well reproduced the experimental ones, enabling us to unambiguously assign the absolute configuration of (+)-DDT and (-)-DDD as S.

Full text of DOI:10.1039/c6pp00438e

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Absolute configuration determination through the
unique intramolecular excitonic coupling in the
circular dichroisms of o,p’-DDT and o,p’-DDD.
A combined experimental and theoretical study†
Cite this: DOI: 10.1039/c6pp00438e
a
a
b
a
Hiroki Tanaka, Yoshihisa Inoue, Takeshi Nakano and Tadashi Mori*
Circular dichroisms (CDs) of the o,p’-isomers of 1,1,1-trichloro- and 1,1-dichloro-2,2-bis(chlorophenyl)
ethanes (DDT and DDD) were investigated experimentally and theoretically. A series of strong Cotton
effect peaks in a characteristic negative–negative–positive–negative, or its mirror-imaged, pattern were
observed in the CD spectra of these persistent organic pollutants. The theoretical CD spectra at the
SAC-CI/B95(d) and RI-CC2/def2-TZVPP levels well reproduced the experimental ones, enabling us to
unambiguously assign the absolute configuration of (+)-DDT and (−)-DDD as S.
Received 8th December 2016,
Accepted 1st February 2017
DOI: 10.1039/c6pp00438e
rsc.li/pps
Introduction
Polychlorinated hydrocarbons such as hexachlorocyclohexane,
hexachlorobenzene, heptachlor and chlorodane have long
been known as effective and durable pesticides.
Dichlorodiphenyltrichloroethane (or 1,1,1-trichloro-2,2-bis
(chlorophenyl)ethane, DDT) has also been used widely (and is
still used in a few countries) to control malaria and typhus
1
vectors. Less chlorinated DDD (1,1-dichloro-2,2-bis(chloro-
phenyl)ethane) and DDE (1,1-dichloro-2,2-bis(chlorophenyl) Chart 1 Chirality in o,p’-DDT and o,p’-DDD.
ethene) are metabolites of DDT and contaminants in techni-
cal-grade DDT. Interestingly, o,p′-DDD has been used medically
to treat adrenal gland cancer, while the exposure to p,p′-DDT the pesticidal activity and toxicity, i.e., (−)-o,p′-DDT and
2
5
increases the risk of breast cancer. For this reason, it is (+)-o,p′-DDD are more cytotoxic than the antipodes. Moreover,
imperative to monitor the uptake and degradation of these o,p′-DDT shows enantioselective oestrogenicity and biodegrad-
6
legacy persistent organic pollutants (POPs) in biological and ability. As such, monitoring degradation profiles of the
3
environmental samples.
enantiomers of o,p′-DDT to o,p′-DDD offers a special advantage
Crucially, o,p′-DDT and o,p′-DDD (Chart 1) are chiral and for tracking the transport and fate of POPs in the environment,
7
the enantioisomerism leads in general to distinctly different differentiating biological from physical/chemical degradations.
biological consequences, such as unequal microbial uptake
In this context, knowing the absolute configurations of
and degradation. Thus, a pair of enantiomers are known to DDT and DDD is unquestionably a key issue for elucidating
behave quite differently in ecotoxicology, e.g., the (S)-forms of their biological and ecotoxicological behaviours. The absolute
4
acetofenate and fipronil are more toxic than the antipodes.
configuration of (−)-o,p′-DDT has been tentatively assigned as
Likewise, the absolute configuration of DDT and DDD controls R by single-crystal X-ray diffraction studies with superior
refinement parameters on one of the enantiomers (but
8
without using the anomalous dispersion). The same absolute
a
Department of Applied Chemistry, Graduate School of Engineering,
Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan.
E-mail: tmori@chem.eng.osaka-u.ac.jp
configuration was deduced for (+)-o,p′-DDD derived from
−)-o,p′-DDT, assuming stereoretention in reductive dechlori-
(
9
nation. In general, chiral compounds not possessing heavy
atom(s), however, are not suitable for directly determining the
absolute configuration by X-ray diffraction studies due to the
b
Research Center for Environmental Preservation, Osaka University, 2-4,
Yamada-oka, Suita, Osaka 565-0871, Japan
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
1
0
c6pp00438e
too large uncertainty in the Flack parameter. Recently,
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the absolute configuration determination using chiroptical
properties has been widely recognised as an alternative and/or
complementary method. By direct comparison of the theoretical
versus experimental chiroptical properties such as circular
dichroism, the absolute configurations have been determined
1
1
for a number of natural and synthetic chiral molecules. More
recently, the chiroptical methods have been applied to more
12
complex molecular and supramolecular systems. We have also
demonstrated that the absolute configurations of axially chiral
1
3
PCB congeners can be determined by a chiroptical method.
In this study, we experimentally and theoretically investi-
gated the CD spectra of o,p′-DDT and o,p′-DDD to unambigu-
ously assign their absolute configurations. Applying a chiropti-
cal method to DDT and DDD was thought to be a challenge, as
the Cotton effects reported for point-chiral molecules are
much weaker in general than those for axially chiral ones. It
turned out, however, that DDT and DDD enantiomers exhibit
intense Cotton effects arising from the excitonic coupling of
o- and p-chlorophenyl chromophores, facilitating the absolute
configuration determination.
Fig. 1 Experimental CD spectra of the 1st elutes of o,p’-DDT (red) and
o,p’-DDD (blue) in hexane from a chiral HPLC column (Daicel OJ-H)
at 25 °C.
1
4
p-chlorophenyl chromophores which are conformationally
locked due to the chlorine atom at the ortho position. The CE
intensities of the first and third bands are appreciably larger for
DDT than for DDD, which is also ascribed to the reduced con-
formational freedoms in the relevant chromophores (vide infra).
In a given enantiomer of DDT or DDD, two conformations
Results and discussion
(
labelled r and s) are possible due to the limited bond rotation
Racemic o,p′-DDT and o,p′-DDD are commercially available
of the o-chlorophenyl ring (Chart 2, indicated in blue). The
(Wako Pure Chemicals). Enantiomers of o,p′-DDT and
theoretical investigations at the SCS-MP2/def2-TZVPP//DFT-D3-
o,p′-DDD, on their analytical scales, have been separated by
1
6
9
,15
TPSS/def2-TZVP level have revealed, however, that the former
chiral GC or chiral reverse-phase HPLC.
In the present
−
1
conformation of DDT is highly disfavoured by 3.7 kcal mol
leading to a >99.8% Boltzmann distribution to the latter at
5 °C. Hence, the theoretical CD prediction was performed
,
study, we performed normal-phase HPLC on a Daicel Chiralcel
OJ-H column eluted with a 9 : 1 mixture of hexane/2-propanol
to obtain the enantiopure samples in larger quantities for
precise chiroptical measurements (Fig. S1 in the ESI†). The
specific rotations at the sodium-D line (589 nm) of the first
and second fractions obtained from a racemic mixture of
o,p′-DDT were determined to be [α]D = +23 (±3) and −21 (±3)
deg cm g dm (c 0.010 in hexane at 25 °C), respectively. Similarly,
2
only for the r conformer of o,p′-DDT.
Although the TD-DFT method (with an appropriate choice
of functionals) is nowadays recognized as a fast robust method
to predict various properties, including electronic transitions
such as UV-vis and CD spectra of medium to large-sized mole-
1
7
cules, our investigations and others have occasionally posed
a question to the use of the method without knowing
the detailed electronic nature associated with the relevant
those for o,p′-DDD were found to be [α] = −57 (±3) and +61 (±3)
D
deg cm g dm. For the sake of clarity, we will discuss hereafter
the chiroptical properties and absolute configurations of the
first eluted enantiomers of DDT and DDD, the former of which
was dextrorotatory while the latter was levorotatory.
As anticipated, the enantiomer pairs of o,p′-DDT and
o,p′-DDD exhibited entirely mirror-imaged CD spectra in
hexane at 25 °C (Fig. S2 in the ESI†). Despite the oppositely
signed [α]
D
values (vide supra), the first elutes of both
o,p′-DDT and o,p′-DDD exhibited quite similar negative–nega-
tive–positive–negative CD patterns (Fig. 1), suggesting that
both share the same electronic transition moment and absol-
ute configuration. The Cotton effect (CE) is much weaker for
the lowest energy transition than for the other three higher-
energy transitions, but still keeps the intensity comparable to
(
or even slightly stronger than) those reported for point-chiral
compounds with a chirogenic centre adjacent to the chromo-
1
4
phore. More interestingly, a series of strong sign-alternating
CEs are seen in the high energy region (200–250 nm). This
Chart 2 Conformational considerations for o,p’-DDT and o,p’-DDD.
is ascribed to the excitonic coupling between the o- and Only the (S)-enantiomers are shown for simplicity.
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1
8
transitions. In the present study, we therefore chose more correctly predicted the CE signs of all the transitions, includ-
sophisticated approximate coupled cluster calculations to ing the lowest-energy one, but with an underestimation of the
predict the CD spectra of o,p′-DDT and o,p′-DDD enantiomers. excitation energy, presumably due to the overestimation of the
For this purpose, the SAC-CI (symmetry adapted cluster– negative hyperconjugation effect.
+
−
configuration interaction) and RI-CC2 (resolution-of-identity
approximate coupled cluster) methods were employed. The conceivable with respect to the C
In the case of o,p′-DDD, three conformations (t/g /g ) are
–C bond for each of the s/r
α
β
two methods are slightly different in approximation but conformers (Chart 2, red) to afford six possible conformations
equivalent in theoretical hierarchy, and hence are expected to in total (see the ESI† for details). It turned out, however, that
+
−
provide similar estimates for a given property. Both methods the g and g conformers in the s conformation can be
have been recently demonstrated to accurately reproduce the excluded, as they are less stable than the t conformer by
1
9
−1
CD spectra for a variety of complex molecular systems.
4 kcal mol . As such, we calculated the CD spectra for the
By and large, both the methods are more reliable than the remaining four conformers at the SAC-CI/D95(d) and RI-CC2/
TD-DFT method in predicting the absolute configuration and def2-TZVPP levels.
in reproducing the spectral features of chiral molecules with
complicated transitions (vide infra).
The CE pattern of each conformer differed in sign, shape
and intensity (Fig. S3 in the ESI†), and hence the CEs were
Fig. 2 compares the experimental CD spectrum of the first often mutually cancelled out or augmented upon weight-
eluted dextrorotatory enantiomer of o,p′-DDT with the theore- averaging (based on the Boltzmann distribution using the
tical ones calculated for (S)-o,p′-DDT at the SAC-CI/D95(d) and SCS-MP2/def2-TZVPP level) to afford the theoretical CD spec-
RI-CC2/def2-TZVPP levels. Clearly, the CE pattern in the region trum of o,p′-DDD, which nicely reproduced the overall features
2
00–250 nm, where three strong CEs are found, was satisfac- of the experimental spectrum (Fig. 3). As was the case with
torily reproduced by both methods. Accordingly, the enantio- o,p′-DDT, the CE pattern predicted for o,p′-DDD at 200–250 nm
mer that eluted first from the chiral HPLC column employed was well reproduced (albeit with an overestimation of the rota-
was assigned the (S)-(+)-configuration, reaffirming the previous tory strength of the highest energy band). This agreement
8
estimation by the X-ray crystallographic study. It is noteworthy enabled us to assign the first elute of o,p′-DDD to the
9
that the CE intensities were not well reproduced (especially in (S)-(−)-enantiomer, consistent with the previous prediction. It
the high energy region), due, at least in part, to our failure to is also noteworthy that the SAC-CI, rather than RI-CC2,
include sufficient amounts of diffuse functions and higher- method better reproduced the CD spectrum of o,p′-DDD, in
energy transitions. Of the two methods, the SAC-CI method particular the sign of the lowest energy band.
performed better than the RI-CC2 method in predicting the
whole spectral features of DDT. The RI-CC2/def2-TZVPP
method overestimated all of the transition energies (note that
the theoretical spectrum calculated by this method, shown in
Fig. 2, was red-shifted by 0.3 eV for a better matching with the
experimental one). Moreover, the lowest-energy transition
observed at around 270 nm was incorrectly predicted by this
method, mostly due to the underestimation of the negative
CE for the t/r conformation. In contrast, the SAC-CI method
Fig. 3 Comparison of experimental (first elute from the chiral HPLC
column, red) and theoretical CD spectra of o,p’-DDD. The theoretical
spectra were obtained by weight-averaging all the theoretical spectra
Fig. 2 Comparison of experimental (first elute from the chiral HPLC
column, red) and theoretical CD spectra of o,p’-DDT. The theoretical
spectra were calculated for the (S)-enantiomer by SAC-CI (blue) and
RI-CC2 (0.3 eV red-shifted, green) methods.
calculated for the appreciably populated conformers (top) by SAC-CI
(blue) and RI-CC2 (0.3 eV red-shifted, green) methods. The relative con-
tribution (Boltzmann distribution) of each conformer was estimated by
the energies calculated at the SCS-MP2/def2-TZVPP level.
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Table 1 Experimental and theoretical specific rotations for o,p’-DDT
and o,p’-DDD
Acknowledgements
a
Financial support from the Grant-in-Aids for Scientific
Research, Challenging Exploratory Research, and Innovative
Area “Photosynergetics” (no. JP15H03779, JP15K13642, and
JP15H01087) from JSPS, the Matching Planner Program from
JST (Grant Number MP27215667549), and Cosmetology
Research Foundation, are gratefully acknowledged.
Compound
Method
[α]
D
o,p′-DDT
Experimental (1st elute)
Experimental (2nd elute)
BH-LYP/aug-cc-pVTZ
BH-LYP/aug-cc-pVDZ
B3-LYP/aug-cc-pVTZ
CAM-B3-LYP/aug-cc-pVTZ
Experimental (1st elute)
Experimental (2nd elute)
BH-LYP/aug-cc-pVTZ
+23 ± 3
−21 ± 3
−195
−192
−223
−166 (−176 )
−57 ± 3
+61 ± 3
b
o,p′-DDD
c
d
−175 (−197 )
Notes and references
a
Theoretical calculations were carried out for the (S)-enantiomers.
Experimental values are obtained in hexane at 25 °C (c 0.010) for the
1 R. Weber, A. Watson, M. Forter and F. Oliaei, Review
article: persistent organic pollutants and landfills – a
review of past experiences and future challenges, Waste
Manage. Res., 2011, 29, 107–121.
b
first and second elutes from a Daicel Chiralcel OJ-H column. Value
obtained by incorporating the COSMO solvation model for hexane.
c
Weight-average of the values calculated for the appreciably populated
d
four conformers. Value for the most abundant t/r conformer.
2
B. A. Cohn, M. S. Wolff, P. M. Cirillo and R. I. Sholtz, DDT
and breast cancer in young women: new data on the signifi-
cance of age at exposure, Environ. Health Perspect., 2007,
On the other hand, the theoretical prediction of the
specific rotation by the TD-DFT method failed to supplement
1
15, 1406–1414.
2
0
3 I. Kania-Korwel and H.-J. Lehmler, Chiral polychlorinated
biphenyls: absorption, metabolism and excretion - a
review, Environ. Sci. Pollut. Res., 2016, 23, 2042–2057;
H.-J. Lehmler, S. J. Harrad, H. Hühnerfuss, I. Kania-Korwel,
C. M. Lee, Z. Lu and C. S. Wong, Chiral polychlorinated
biphenyl transport, metabolism, and distribution: a review,
Environ. Sci. Technol., 2010, 44, 2757–2766.
4 M. Zhao and W. Liu, Enantioselectivity in the immunotoxi-
city of the insecticide acetofenate in an in vitro model,
Environ. Toxicol. Chem., 2009, 28, 578–585; J. Ye, M. Zhao,
J. Liu and W. Liu, Enantioselectivity in environmental risk
assessment of modern chiral pesticides, Environ. Pollut.,
the absolute configuration determination of DDT. Table 1
summarizes the experimental and theoretical [α] values. The
D
sign was correctly predicted in the case of DDD, but the oppo-
site sign was predicted for DDT by any of the chosen methods
(
functionals and basis-sets), for reasons not clear at this
moment. Advantages of the coupled cluster methods over the
conventional DFT method in the calculation of optical
2
1
rotations have extensively been discussed recently, but the
use of the former methods is still limited to the relatively
small molecule due to the computational cost. Further
studies in this line on DDD and DDT are remained to be
elucidated.
2
010, 158, 2371–2383.
5
C. Wang, Z. Li, Q. Zhang, M. Zhao and W. Liu,
Enantioselective induction of cytotoxicity by o,p′-DDD in
PC12 cells: implications of chirality in risk assessment of
POPs metabolites, Environ. Sci. Technol., 2013, 47, 3909–
3917.
Conclusions
In summary, the circular dichroisms of enantiomeric o,p′-DDT
and o,p′-DDD separated by chiral HPLC were investigated
experimentally and theoretically. The first-eluted enantiomers
of both DDT and DDD exhibited a weak negative Cotton effect
for the lowest energy transition. Interestingly, much stronger
exciton coupled CEs with a characteristic negative–positive–
negative pattern were also observed in the high energy region
6 A. W. Garrison, V. A. Nzengung, J. K. Avants, J. J. Ellington,
W. J. Jones, D. Rennels and N. L. Wolfe, Phytodegradation
of p,p′-DDT and the rnantiomers of o,p′-DDT, Environ. Sci.
Technol., 2000, 34, 1663–1670.
7 P. Wang, Q. Zhang, Y. Li, C. Zhu, Z. Chen, S. Zheng,
H. Sun, Y. Liang and G. Jiang, Occurrence of chiral organo-
chlorine compounds in the environmental matrices from
King George Island and Ardley Island, west Antarctica, Sci.
Rep., 2015, 5, 13913; X. He, X. Dong, D. Zou, Y. Yu, Q. Fang,
Q. Zhang and M. Zhao, Enantioselective effects of o,p′-DDT
on cell invasion and adhesion of breast cancer cells:
chirality in cancer development, Environ. Sci. Technol.,
2015, 49, 10028–10037.
(200–250 nm), which allowed us to unambiguously determine
the absolute configurations of DDT and DDD by comparison
with the results of theoretical calculations. Thus, the theore-
tical CD spectra obtained at the SAC-CI/B95(d) and RI-CC2/
def2-TZVP levels well reproduced the experimental CE pattern.
The former method performed better in predicting the exci-
tation energies and the CE signs of all relevant transitions
including the lowest one. Accordingly, the enantiomers of
o,p′-DDT and o,p′-DDD that elute earlier from a Chiralcel OJ-H
column were assigned (S)-(+)-DDT and (S)-(−)-DDD, reaffirming
the previous tentative assignments, which will contribute to
reliable monitoring of the biodegradation processes of these
legacy POPs.
8 R. A. Smith and M. J. Bennett, Insecticides. I. The crystal
structure and absolute configuration of (-)-1-(o-chloro-
phenyl)-1-(p-chlorophenyl)-2,2,2-trichloroethane, (-)-o,p′-DDT,
Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem.,
1977, 33, 1126–1128.
Photochem. Photobiol. Sci.
This journal is © The Royal Society of Chemistry and Owner Societies 2017

View Article Online
Photochemical & Photobiological Sciences
Paper
9
H.-R. Buser and M. D. Muller, Isomer-selective and 17 A. E. Nugroho and H. Morita, Circular dichroism calcu-
enantiomerselective determination of DDT and related
compounds using chiral high-resolution gas chromato-
graphy/mass spectrometry and chiral high- performance
liquid chromatography, Anal. Chem., 1995, 67, 2691–2698.
0 H. D. Flack and G. Bernardinelli, The use of X-ray crystallo-
graphy to determine absolute configuration, Chirality,
lation for natural products, J. Nat. Med., 2014, 68, 1–10;
J. Autschbach, L. Nitsch-Velasquez and M. Rudolph,
Time- dependent density functional response theory for
electronic chiroptical properties of chiral molecules, Top.
Curr. Chem., 2011, 298, 1–98; X.-C. Li, D. Ferreira and
Y. Ding, Determination of absolute configuration of natural
products: theoretical calculation of electronic circular
dichroism as a tool, Curr. Org. Chem., 2010, 14, 1678–1697;
M. Seth and T. Ziegler, Calculation of magnetic circular
dichroism spectra with time-dependent density functional
theory, Adv. Inorg. Chem., 2010, 62, 41–109; J. Autschbach,
Density functional theory applied to calculating optical and
spectroscopic properties of metal complexes: NMR and
optical activity, Coord. Chem. Rev., 2007, 251, 1796–1821.
1
1
2
008, 20, 681–690.
1 T. D. Crawford, M. C. Tam and M. L. Abrams, The current
state of ab initio, calculations of optical rotation and elec-
tronic circular dichroism spectra, J. Phys. Chem. A, 2007,
1
11, 12057–12068; P. L. Polavarapu, Renaissance in chirop-
tical spectroscopic methods for molecular structure deter-
mination, Chem. Rec., 2007, 7, 125–136; T. D. Crawford,
Ab initio, calculation of molecular chiroptical properties,
Theor. Chem. Acc., 2006, 115, 227–245; X.-C. Li, D. Ferreira 18 S. Manzhos, H. Segawa and K. Yamashita, Computational
and Y. Ding, Determination of absolute configuration of
natural products: theoretical calculation of electronic
circular dichroism as a tool, Curr. Org. Chem., 2010, 14,
dye design by changing the conjugation order: Failure of
LR-TDDFT to predict relative excitation energies in organic
dyes differing by the position of the methine unit, Chem. Phys.
Lett., 2012, 527, 51–56; M. Nishizaka, T. Mori and Y. Inoue,
Axial chirality of donor-donor, donor-acceptor, and tethered
1,1’-binaphthyls: a theoretical revisit with dynamics trajec-
tories, J. Phys. Chem. A, 2011, 115, 5488–5495; T. Mori,
Y. Inoue and S. Grimme, Quantum chemical study on the
circular dichroism spectra and specific rotation of donor-
acceptor cyclophanes, J. Phys. Chem. A, 2007, 111, 7995–8006.
1
678–1697.
1
2 T. Mori, T. Tanaka, T. Higashino, K. Yoshida and A. Osuka,
Combined experimental and theoretical investigations on
optical activities of Möbius aromatic and Möbius antiaro-
matic hexaphyrin phosphorus complexes, J. Phys. Chem. A,
2
016, 120, 4241–4248; T. Kosaka, Y. Inoue and T. Mori,
Toroidal interaction and propeller chirality of hexaarylben-
zenes. dynamic domino inversion revealed by combined 19 A. Wakai, H. Fukasawa, Y. Cheng, T. Mori and Y. Inoue,
experimental and theoretical circular dichroism studies,
J. Phys. Chem. Lett., 2016, 7, 783–788; J. Kang, D. Miyajima,
T. Mori, Y. Inoue, Y. Itoh and T. Aida, A rational strategy for
the realization of chain-growth supramolecular polymer-
ization, Science, 2015, 347, 646–651.
3 M. Toda, C. Matsumura, M. Tsurukawa, T. Okuno,
T. Nakano, Y. Inoue and T. Mori, Absolute configuration of
atropisomeric polychlorinated biphenyl 183 enantiomeri-
cally enriched in human samples, J. Phys. Chem. A, 2012,
Theoretical and experimental investigations of circular
dichroism and absolute configuration determination of
chiral anthracene photodimers, J. Am. Chem. Soc., 2012,
134, 4990–4997; Y. Nakai, T. Mori, K. Sato and Y. Inoue,
Theoretical and experimental studies of circular dichroism
of mono- and diazonia[6]helicenes, J. Phys. Chem. A, 2013,
117, 5082–5092; Y. Nakai, T. Mori and Y. Inoue,
Circular dichroism of (di)methyl- and diaza[6]helicenes.
A combined theoretical and experimental study, J. Phys.
Chem. A, 2013, 117, 83–93; T. Miyahara, H. Nakatsuji and
H. Sugiyama, Helical structure and circular dichroism
spectra of DNA: a theoretical study, J. Phys. Chem. A, 2013,
117, 42–55; J. Seino, Y. Honda, M. Hada and H. Nakatsuji,
SAC and SAC-CI calculations of excitation and circular
dichroism spectra of straight-chain and cyclic dichalco-
gens, J. Phys. Chem. A, 2006, 110, 10053–10062.
1
1
16, 9340–9346.
1
4 T. Mori, Y. Inoue and S. Grimme, Experimental and theore-
tical study of the cd spectra and conformational properties
of axially chiral 2,2’-, 3,3’-, and 4,4’-biphenol ethers, J. Phys.
Chem. A, 2007, 111, 4222–4234.
5 J. Zhan, J. Li, D. Liu, C. Liu, G. Yang, Z. Zhou and P. Wang,
A simple method for the determination of organochlorine
1
pollutants and the enantiomers in oil seeds based on 20 M. Srebro, N. Govind, W. A. de Jong and J. Autschbach,
matrix solid-phase dispersion, Food Chem., 2016, 194,
19–324; I. Ali and H. Y. Aboul-Enein, Determination of
chiral ratio of o,p-DDT and o,p-DDD pesticides on poly-
saccharides chiral stationary phases by HPLC under
reversed-phase mode, Environ. Toxicol., 2002, 17, 329–333.
6 S. Grimme, Accurate calculation of the heats of formation
Optical rotation calculated with time-dependent density
functional theory: the OR45 benchmark, J. Phys. Chem. A,
2011, 115, 10930; P. J. Stephens, J. J. Pan, F. J. Devlin and
J. R. Cheeseman, Determination of the absolute configur-
ations of natural products using TDDFT optical rotation
calculations: the iridoid oruwacin, J. Nat. Prod., 2008, 71, 285.
3
1
for large main group compounds with spin-component 21 S. Haghdani, O. R. Gautun, H. Koch and P.-O. Åstrand,
scaled MP2 methods, J. Phys. Chem. A, 2005, 109, 3067–
077; S. Grimme, Improved second-order Møller–Plesset
perturbation theory by separate scaling of parallel- and
Optical rotation calculations for a set of pyrrole com-
pounds, J. Phys. Chem. A, 2016, 120, 7351–7360;
S. Haghdani, B. Helge, H. Koch and P.-O. Åstrand, Optical
rotation calculations for fluorinated alcohols, amines,
amides, and esters, J. Phys. Chem. A, 2016, 120, 7973–7986.
3
antiparallel-spin pair correlation energies, J. Chem. Phys.,
2
003, 118, 9095–9102.
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