Draft · 2019-02-27 · Draft 3 atropisomer pairs will undergo physical and transport processes undifferentiated. In contrast, biological processes are predominantly chiral in nature

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Identifying absolute configurations of PCB atropisomers by comparison of their experimental specific rotations

with their DFT calculated values

Journal: Canadian Journal of Chemistry

Manuscript ID cjc-2018-0458.R1

Manuscript Type: Article

Date Submitted by the Author: 14-Dec-2018

Complete List of Authors: Daramola, Oluwadamilola; University of Manitoba, ChemistryCullen, John; University of Manitoba, Chemistry

Is the invited manuscript for consideration in a Special

Issue?:Not applicable (regular submission)

Keyword: PCB atropisomers, optical rotation, absolute configuration, DFT

https://mc06.manuscriptcentral.com/cjc-pubs

Canadian Journal of Chemistry

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Identifying absolute configurations of PCB atropisomers

by comparison of their experimental specific rotations

with their DFT calculated values

Oluwadamilola Daramola

Department of Chemistry, University of Manitoba,

144 Dysart Road, Winnipeg MB R3T-2N2, Canada

and John Cullen

Department of Chemistry, University of Manitoba,

144 Dysart Road, Winnipeg MB R3T-2N2, Canada

Corresponding author: John Cullen (phone: 1-204-474-6441, fax: 1-204-474-7608,email: [email protected])

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mailto:[email protected]

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Abstract

Nineteen enantiomer pairs of polychlorinated biphenyls (PCBs) with three or four chloro

substituents about the central carbon-carbon bond form a stable subclass of compounds whose

biological effects vary with their chirality. Optical rotations for this group of PCBs were determined

from density functional calculations employing extended atomic orbital gauge invariant basis sets. A

comparison of these results with the experimental ones found from the literature for nine of the pairs

enabled the identification of their absolute configurations as analytes in gas chromatography studies.

Keywords: PCB atropisomers, optical rotation, absolute configuration, DFT

Introduction

Polychlorinated biphenyls (PCB) are a class of well documented environmental pollutants1.

Because of their carcinogenic, neurotoxic and endocrine disruption properties their persistence and

bioaccumulation pose a serious threat to both aquatic and terrestrial environments. Of the 209 possible

PCB congeners, 78 are chiral due to the asymmetric distribution of the chlorines on the two phenyl

rings. However, only 19 of these have their chirality locked in under ambient conditions2. With phenyl

rings perpendicular to each other, free energy rotation barriers3 ranging from 177 kJ/mol to 246 kJ/mol,

prevent racemization, even at the relatively high temperatures used for gas chromatographic

separations. These axial enantiomers, called atropisomers, constitute 6 percent by weight of the total

PCBs released into the environment and have been found to undergo considerable atropisomeric

enrichment in wildlife, laboratory animals and humans4. Animal and epidemiological studies have

shown that the environmental effects of this subclass of PCBs is implicated in a range of developmental

neurological disorders such as learning deficits and impaired motor coordination5.

The chirality of these compounds brings about new challenges in their analytical identifications

and environmental effects. Manufactured in a batch chlorination process, PCB atropisomers enter the

environment as racemic mixtures. Having identical physicochemical properties, mixtures of PCB

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atropisomer pairs will undergo physical and transport processes undifferentiated. In contrast, biological

processes are predominantly chiral in nature. For example, a racemic mixture of PCB 846 is found to be

significantly more toxic than either purified atropisomer7. In order to experimentally ascertain and gain

an understanding of the myriad biochemical reactions occurring at the molecular level the separation

and identification of the absolute configuration of each occurring PCB congener is a prerequisite. To

date this has only been accomplished for a few atropisomers, by use of high pressure liquid

chromatography (HPLC) with an enantioselective stationary phase to separate out the pairs followed by

either crystallization/x-ray diffraction on the analytes8 or the application of experimental circular

dichroism (CD) combined with ab initio calculations9. At higher coarse grain levels, the gas

chromatography (GC) elution order of fourteen of the PCB enantiomer pairs has been standardized on

six commonly used enantioselective columns10, while in separate studies the specific rotation of each

analyte for nine enantiomer pairs has been correlated with both their HPLC11 and GC elution order13.

Specific rotation, is an intensive property defined as the change in orientation of [𝛼]𝜈,

monochromatic plane-polarized light, at a given frequency or equivalent wavelength, per unit

distance–concentration product, as the light passes through a sample of a compound in solution.

Quantum mechanically can be calculated from the trace of a frequency-dependent tensor, , [𝛼]𝜈 𝛽𝑥𝑦

which is composed of a sum of products of electric and magnetic transition dipoles between ground and

excited states.14 can be reexpressed within the framework of time-dependent linear-response 𝛽𝑥𝑦

theory15 and in the case of DFT, the tensor is found through a set of time-dependent coupled-perturbed

Kohn-Sham equations.16 Once a PCB atropisomer is identified by its chromatographic eluting order

one may identify its chirality and corresponding absolute configuration by measuring its specific

rotation, and matching the result with the quantum chemical computed values for the two possible [𝛼]𝜈

absolute configurations of the enantiomer. In this paper using density functional calculations we

present the results for all 19 PCB atropisomer pairs and determine the chirality for those PCB

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https://en.wikipedia.org/wiki/Spectral_color

https://en.wikipedia.org/wiki/Linear_polarization

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atropisomers whose specific rotations been previously reported11,12. These results also provide

benchmarks that with future experimental measurements will enable the resolution of the absolute

configurations of the remaining pairs.

Computational Method

All calculations were performed using the Gaussian 16 package17. The geometry for each PCB pair

was fully optimized in vacuum using density functional theory (DFT) with the combination of Becke’s

three-parameter (B3) hybrid exchange functional18 and the Lee–Yang–Parr (LYP) correlation

functional19 in conjunction with a 6-31G(d) basis set. Traditionally, the DFT B3LYP/6-31G(d) is used

due to its low trade off of speed, and accuracy20. The specific optical rotations for wavelengths 436,

546 and 578 nm were then computed for all nineteen atropisomeric PCB pairs using time-dependent

DFT B3LYP. To capture polarizability effects an extended aug-cc-pVDZ basis set is employed in a

gauge invariant atomic orbital (GIAO) form to insure final computed values are independent of the

choice of the origin of the coordinate system used in the calculation16. This method produces similar

results as state of the art but much more computationally demanding coupled cluster calculations21 with

average deviations from experimental values of approximately 20 degrees [dm(g/cm3)]-1.

To compare with experimental optical rotation data measured in ethanol11,12, calculations were

repeated for ten of the enantiomer PCB pairs. Solvent effects were incorporated22 using the integral

equation formalism version of the polarizable continuum dynamic/nonequilibrium model (PCM). To

better take into account polarization effects of the continuum, PCB geometries were optimized with an

aug-cc-pVDZ basis set. Finally, we used these results to identify the absolute configurations of the

analytes whose elution sequences were mapped over 6 commonly used gas chromatography

enantioselective columns by Kania-Korwel and Lehmler10 .

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Results and Discussion

The 19 possible PCB atropisomer structures are shown in Figure 1. The stereochemistry

classification23 starts by arbitrarily selecting one phenyl ring to have precedence over the other. The

priorities of the first two groups or substituents on this ring bordering the axial carbon are then

determined. The third priority needed to complete the R or S designation is resolved by choosing the

highest priority group or substituent found bordering the axial carbon on the opposite perpendicular

ring. For an unsubstituted biphenyl with rings perfectly perpendicular to each other no optical rotation

would be observed. This can be derived from Rosenfeld’s perturbation treatment24,14 of the optical

rotatory strength for an electronic excitation from the ground state, , to the excited state, 𝑅𝑘 𝜓0 𝜓𝑘

where

[1]𝑅𝑘 = 𝐼𝑚{⟨𝜓0│𝜇𝑒│𝜓𝑘⟩ ∙ ⟨𝜓𝑘│𝜇𝑚│𝜓0⟩}

Here is the imaginary component of a dot product of transition matrix elements of and , the 𝑅𝑘 𝜇𝑒 𝜇𝑚

electric and magnetic dipole vectors respectively. With respect to any given symmetry element the

unsubstituted biphenyl states can be classified as even or odd. In turn and will have selection 𝜇𝑒 𝜇𝑚

rules25 opposite to each other for the transition resulting in either or ⟨𝜓0│𝜇𝑒│𝜓𝑘⟩ ⟨𝜓𝑘│𝜇𝑚│𝜓0⟩

equalling zero. will only become nonzero when chlorination of the biphenyl results in the loss of 𝑅𝑘

total symmetry. This is the case when each PCB has either a 2,3,6 or 2,3,4,6 chlorinated primary ring

and a chlorination pattern on the secondary phenyl ring. PCBs sharing a common 2,3,6 chlorinated ring

or 2,3,4,6 chlorinated ring are denoted here as belonging to the 236 PCB set or 2346 PCB set

respectively. In Table 1 members within each set are listed and classified according to the chlorination

pattern found on their secondary phenyl ring. PCB 176 (2,2´,3,3´,4,6,6´ heptachlorobiphenyl),

depending on choice taken for the primary phenyl ring, is a member of both sets. The computed [𝛼]𝜈

results at 436 nm for the PCB R-enantiomers are graphically shown in Figure 2. Specific rotations for

236 PCB set are seen to lie lower and are roughly parallel to those found in the 2346 PCB set.

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Complete results at wavelengths 436, 546 and 578 nm for all enantiomers in the two sets are

presented in Table 2. In principle, should be computed from the thermodynamic average of all [𝛼]𝜈

possible conformer geometries, in practice because of the high rotational barriers3 between the rings

only the most stable equilibrium geometry is used here. The variance of in Table 2 between R and [𝛼]𝜈

S enantiomers of each PCB which theoretically should not exist can be traced to numerical errors in the

convergence of the initial geometry optimization performed for each enantiomer. For example, in the

case of PCB 144, the difference in the nuclear repulsion energy between the two optimized enantiomer

structures is 1.218 millihartrees when in theory it should be exactly zero. The corresponding increase in

magnitude of with shortening wavelengths observed in Table 2 can be empirically fitted to [𝛼]𝜈

[2][𝛼]𝜈 = ∑𝑗

𝐴𝑗

𝜆2 ― 𝜆2𝑗

This is known as the Drude equation26, where the and are constants, and is valid in spectral 𝐴𝑗𝑠 𝜆𝑗𝑠

regions far from absorption bands. Experimental absorption spectra27 of all 209 PCB congeners show

that lowest excited states lie in the 245-265 nm region confirming the validity of equation [2] for the

visible region. This also confirms the validity of the methodology used in the calculations, based on the

Rosenfeld’s perturbation treatment24, which becomes inadequate in absorption regions where Cotton

effects28 occur.

Results in Table 2 for the PCBs 171, 132 and 183 correctly predict the absolute configurations

deduced previously9. Here the corresponding experimental optical rotations at 589 nm reported in

hexane for the S enantiomers9 were 44 ± 6, 39 ± 15 and -15 ± 3 degrees [dm(g/cm3)]-1. This compares

with our 43.17, 56.19 and -8.72 values computed at 578 nm. In general, sources of computational errors

arise from using B3LYP, an approximate DFT functional, a finite basis set, an incomplete PCM solvent

model, ignoring vibrational effects29, geometry optimization and lack of thermal averaging over other

less probable geometries. Stephens and coworkers30 examined the reliability of predicting absolute

configurations by calculating for a set of 65 rigid molecules their specific rotations in the gas phase and

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comparing these results to their experimental values determined in a variety of solvents. For the subset

of the several molecules with one chiral centre there is 100% agreement, for molecules having two or

more chiral centres there was a 12-13% failure rate. However, the methodology employed in this paper

selected rigid molecules based on a gas phase lowest energy conformation which is 2 kcal/mol below

or lower than other stable conformers present. This can be experimentally incorrect due to errors in the

B3LYP method as well as lack of consideration of solvation effects. Optical rotations of different

conformers can differ greatly in sign and magnitude, and the conformer whose computed optical

rotation matches experiment may not be the lowest energy one found in the gas phase31. This source of

error does not arise in our study where there is only one possible stable conformation with one chiral

centre for each PCB.

Table 3 presents a comparison of our calculated results in ethanol and the experimental work [𝛼]𝜈

on the optical rotation11,12 and gas chromatographic retention times13 of 10 PCBs. There is close

agreement between predicted and experimentally measured specific rotations, with the exception of

PCB 84. Despite the large deviations found here, when signs of experimental and computed optical

rotations are matched, the corresponding absolute configurations are in complete agreement with the

recent X-ray study from Lehmler’s group8. The experimental points for the R enantiomers at 436 nm

are also plotted in Figure 2. From Table 1, PCBs having matching chlorination patterns on their

secondary rings are PCBs 84, 131 at carbons 2,3; PCBs 136, 176 at carbons 2,3,6; PCBs 176, 197 at

carbons 2,3,4,6; PCBs 135, 175 at carbons 2,3,5 and PCBs 174, 196 at carbons 2,3,4,5. The specific

rotations found in each of the last 4 pairs lie close in value and follow the parallel trend of the

computed gas phase results of the 236 and 2346 PCB sets seen in Figure 2. In contrast, the

experimental point for PCB 84 at 110 degrees [dm(g/cm3)]-1 below that of PCB 131 lies outside the

range of the graph suggesting possibly an experimental error here.

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The retention time, r, the amount of time a compound spends in the chromatographic column after

it has been injected is a measure of the compound’s relative binding strength to the stationary phase.

Here the stationary phase, Chirasil-Dex, schematically depicted in Figure 3 is composed of 2,3,6-tri-O-

methyl--cyclodextrins linked via a octamethylene spacer to polydimethylsiloxane. Seven glucosidic

units link together to form a truncated cone architecture with a hydrophobic cavity and a bottom

hydrophilic rim. Methylation of the larger top rim distorts the structure32 improving

enantioseparations33. NMR experiments show these cyclodextrins are dynamically very flexible

enabling the selective formation of guest-host inclusion complexes for a wide range of molecules34.

The small Gibbs free binding energy differences between enantiomers which can be as little as 0.1

kJ/mol results in a pairing pattern of retention times seen in Table 3 which facilitates atropisomer

identification. Here the R enantiomer elutes first before the S enantiomer except for PCB 135 and PCB

174. The very small binding energy differences and complexity of the dynamics of the host system

preclude modelling the interplay of intermolecular forces, hydrophobic interactions and cyclodextrin

strain energy driving complex formation with any degree of certainty.

Because no single type of enantioselective gas chromatography column can resolve the

atropisomers of all chiral PCBs, Kania-Korwel and Lehmler10 have conducted a study to standardize

the relative elution orders of twelve of the PCB atropisomers over six commonly used gas

chromatography columns taken as a group. Table 3 from their paper lists the relative elution orders for

seven atropisomers whose optical rotations are experimentally known. In our Table 4, we have repeated

this table replacing optical rotation signs with the corresponding absolute configuration designations

deduced from our calculations.

Conclusion

Due to small binding energy differences to the stationary phase between enantiomer pairs, mixtures

of chiral PCBs produce a pairing pattern in their retention times both in gas or high pressure liquid

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chromatography. This allows one to isolate each enantiomer pair and experimentally determine the

optical rotation and order of elution. By comparing literature results10-12 with our theoretical

calculations the absolute configuration of each PCB enantiomer was ascertained.

Acknowledgements

We thank the University of Manitoba and WestGrid for computing support and the Canada Summer

Jobs program for financial support. O.D. would also like to thanks Dr. James Xidos for his helpful

discussions.

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References

(1) International Agency for Research on Cancer (IARC) 2016, Polychlorinated Biphenyls and Polybrominated Biphenyls, IARC Mongraphs on the Evaluation of Carcinogenic Risks,Vol 107, https://monographs.iarc.fr/wp-content/uploads/2018/08/mono107.

(2) Kaiser, K.L.E. Environ. Pollut. 1974, 7, 93-101

(3) Harju, M.T.; Haglund, P. Fresenius J. Anal. Chem. 1999, 364, 219–22

(4) Kania-Korwel. I.; Lehmler. H.-J. Environ Sci. Pollut. Res. 2016 23, 2042–2057

(5) Schantz, S.L.;Widholm, J.J.; Rice, D.C. Environ. Health Perspect. 2003, 111, 357–376;

Kodavanti, P.R.S.; Zawia, N.H. (Ed.), Molecular Neurotoxicology:Environmental Agents and Transcription–Transduction Coupling. 2004, pp. 151–182, CRC Press, Boca Roton, FL

(6) For details of PCB nomenclature see Ballschmiter, K.; Zell, M. Z. Anal. Chem. 1980, 302, 20-31; Mills III, S.A., Thal, D.I.; Barney, J. Chemosphere 2007, 68, 1603–1612

(7) Lehmler, H.-J.; Robertson, L.W.; Garrison, A.W.; Kodavanti, P.R.S. Toxicology Letters, 2005, 156, 391–400

(8) Li, X.; Parkin, S.R.; Lehmler, H.-J. Environ Sci. Pollut. Res. 2018, 25, 16402–16410

(9) Toda, M; Matsumura, C.; Tsurukawa, M.; Okuno, T.; Nakano, T.; Inoue Y.; Mori,T. J. Phys. Chem. A 2012, 116, 9340-9346

(10) Kania-Korwel, I.; Lehmler, H-J. J. Chromatogr. A 2013, 1278, 133-144

(11) Haglund, P. Chemosphere 1996, 32, 2133-2140

(12) Puttman, M.; Oesch, F.; Robertson, L.W.; Mannschreck, A. Chemosphere 1986, 15, 2061-2064

(13) Haglund, P.; Wiberg, K. J. High Resol. Chromatogr. 1996, 19, 373-376

(14) Crawford, T.D. Theor. Chem. Acc. 2006, 115, 227–245

(15) Autschbach, J.; Ziegler, T. J. Chem. Phys. 2002, 116, 891

(16) Stephens, P. J.; Devlin, F. J; Cheeseman, J. R.; Frisch, M. J. J. Phys. Chem. A. 2001, 105, 5356-5371; Cheeseman, J. R.; Frisch, M. J.; Devlin, F. J.; Stephens, P. J. J. Phys. Chem. A. 2000, 104, 1039-1046

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https://monographs.iarc.fr/wp-content/uploads/2018/08/mono107

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(17) Gaussian 16, Revision B.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, G. A. Petersson, H. Nakatsuji, X. Li, M. Caricato, A. V. Marenich, J. Bloino, B. G. Janesko, R. Gomperts, B. Mennucci, H. P. Hratchian, J. V. Ortiz, A. F. Izmaylov, J. L. Sonnenberg, D. Williams-Young, F. Ding, F. Lipparini, F. Egidi, J. Goings, B. Peng, A. Petrone, T. Henderson, D. Ranasinghe, V. G. Zakrzewski, J. Gao, N. Rega, G. Zheng, W. Liang, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, K. Throssell, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. J. Bearpark, J. J. Heyd, E. N. Brothers, K. N. Kudin, V. N. Staroverov, T. A. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. P. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, J. M. Millam, M. Klene, C. Adamo, R. Cammi, J. W. Ochterski, R. L. Martin, K. Morokuma, O. Farkas, J. B. Foresman, and D. J. Fox, Gaussian, Inc., Wallingford CT, 2016.

(18) Becke, A. D. J. Chem. Phys. 1993, 98, 1372.

(19) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785

(20) Frisch, M. J.; Trucks, G. W.; Cheeseman, J. R. in Recent Developments and Applications of Modern Density Functional Theory: Seminario, J. M.; Ed.; Theoretical and Computational Chemistry; Elsevier Science: Amsterdam, 1996, 4, 679-707.

(21) Ruud, K.; Stephens, P. J.; Devlin, F. J; Taylor, P.R.; Cheeseman, J. R.; Frisch, M. J. Chem. Phys. Lett. 2003, 373, 606-614

(22) Mennucci, B.; Tomasi, J.; Cammi, R.; Cheeseman, J. R.; Frisch, M. J.; Devlin, F. J.; Gabriel, S.; Stephens, P. J. J. Phys. Chem. A. 2002, 106, 6102-6113

(23) Wolf, C. Principles of Chirality and Dynamic Stereochemistry 2008, Chapter 2, 9-11, Royal Society of Chemistry eBook Collection 2007

(24) Rosenfeld, von L. Z. f r Physik 1928, 52, 161-174𝑢

(25) Condon, E.U.; Altar, W.; Eyring, H. J. Chem. Phys. 1937, 5, 753-775

(26) Drude, P. The Theory of Optics 1902, Longmans, London; reprinted 1959, Dover, New York

(27) Andersson, P.L.; Haglund, P.; Tysklind, M. Fresenius J Anal Chem 1997, 357, 1088–1092

(28) Cotton, A. Compt. Rend. 1895, 120, 989 and 1044

(29) Bishop, D. M. Rev. Mod. Phys. 1990, 62, 251-374

(30) Stephens, P. J.; McCann, D.M.; P.R.; Cheeseman, J. R.; Frisch, M. J. Chirality 2005, 17, S52-S64

(31) Haghdani, S.; Hoff, B.H.; Koch, H.; Astrand, P-O. J. Phys. Chem. A 2016, 120, 7973-7986

(32) Schonbeck, C.; Westh, P.; Holm, R. J. Phys. Chem. B 2014, 10120-10129

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(33) Juvancz, Z.; Alexander, G.; Szeitli, J. J. High Resol. Chromatogr. 1987, 10, 105–107; Dai,Y.; Hai, J.; Tang, W.; Ng, S-C. in Modified Cyclodextrins for Chiral Separations, Ed. Tang, W.; Ng, S-C.; Sun, D., Springer Heidelberg New York Dordrecht London, 2013

(34) Dodziuk, H., Ed. in Cyclodextrins and Their Complexes 2006, 1-26, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Table and Figure Captions

Table 1. A classification of the PCB members belonging the 236 and 2346 PBC sets according to the chlorination pattern on their secondary rings

Table 2. Calculated specific rotations in degrees [dm(g/cm3)]-1and predicted R or S chirality for the 19 atropisomers

Table 3. GC retention times, r, specific rotations, , calculated and experimental (in blue) for 10 [𝛼]𝜈PCB atropsiomers

Table 4. Elution order, i.e. 1st/2nd , for the absolute configurations of 7 PCB atropisomers over 6 common used gas chromatograph columns

Figure 1a. PCB atropisomers which have R chiralities for [𝛼]𝜈 > 0

Figure 1b. PCB atropisomers which have S chiralities for [𝛼]𝜈 > 0

Figure 2. Specific Rotations of PCB R Atropisomers at 436 nm

Figure 3. Schematic depiction of Chirasil-Dex

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Table 1. A classification of the PCB members belonging the 236 and 2346 PBC sets according to the chlorination pattern on their secondary rings

Cl positions on Secondary Ring

2,3 2,3,4 2 2,3,6 2,4 2,3,4,6 2,3,5 2,3,4,5 2,5 2,4,5

236 PBC set PCB 84

PCB 132

PCB 45

PCB 136

PCB 91

PCB 176

PCB 135

PCB 174

PCB 95

PCB 149

2346 PBC set PCB 131

PCB 171

PCB 88

PCB 176

PCB 139

PCB 197

PCB 175

PCB 196

PCB 144

PCB 183

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Table 2. Calculated specific rotations in degrees [dm(g/cm3)]-1and predicted R or S chirality for the 19 atropisomers

436 nm 546 nm 578 nm

Compound R S R S R S

PCB 84 -145.41 +146.27 -81.05 +81.53 -70.58 +71.00

PCB 132 -115.38 +115.12 -64.62 +64.47 -56.31 +56.19

PCB 45 -74.06 +72.80 -41.29 +40.57 -35.95 +35.33

PCB 136 -67.55 +68.06 -37.84 +38.11 -32.97 +33.21

PCB 91 -63.82 +63.34 -35.39 +35.42 -31.12 +30.86

PCB 176 -54.87 +55.67 -30.75 +31.19 -26.80 +27.17

PCB 135 -41.61 +41.76 -23.21 +23.30 -20.22 +16.41

PCB 174 -29.50 +29.53 -16.53 +16.54 -14.40 +14.41

PCB 95 +36.96 -37.83 +20.66 -21.14 +18.00 -18.42

PCB 149 +25.86 -25.49 +14.39 -14.18 +12.52 -12.34

PCB 131 -122.07 +122.03 -68.76 +68.74 -59.98 +59.96

PCB 171 -87.63 +87.60 -49.51 +49.48 -43.20 +43.17

PCB 88 -58.72 +60.83 -33.20 +34.42 -28.97 +30.04

PCB 176 -54.87 +55.67 -30.75 +31.19 -26.80 +27.17

PCB 139 -48.89 +50.73 -27.74 +28.86 -24.22 +25.21

PCB 197 -38.12 +39.28 -21.56 +22.21 -18.81 +19.38

PCB 175 -30.10 +30.18 -17.09 +17.13 -14.91 +14.96

PCB 196 -21.84 +21.79 -12.58 +12.54 -11.00 +10.97

PCB 144 +25.72 -23.83 +14.01 -12.94 +12.16 -11.22

PCB 183 +18.72 -18.56 +10.15 -10.06 +8.80 -8.72

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Table 3. GC retention times, r, specific rotations, , calculated and experimental (in blue) for [𝛼]𝜈10 PCB atropsiomers

Compound R-Enantiomer S-Enantiomer

r (min) 436 nm 546 nm 578 nm r (min) 436 nm 546 nm 578 nm

61.13 -153.43 -85.14 -74.07 61.32 +153.45 +85.13 +74.08

PCB 84

-242 -135 -115 +241 +138 +125

-120.52 -67.49 -58.80 +120.34 +67.38 +58.70

PCB 131

-110 -63 -52 +111 +63 +60

77.29 -114.98 -64.19 -55.91 78.02 +115.00 +64.20 +55.91

PCB 132

-111 -62 -51 +110 +61 +54

65.41 -73.25 -40.71 -35.42 65.66 +73.27 +40.71 +35.42

PCB 136

-70 -41 -35 +73 +43 +37

76.80 -43.49 -24.19 -21.03 77.13 +45.46 +25.27 +21.97

PCB 176

-66 -39 -33 +63 +35 +31

68.47 -52.64 -29.46 -25.68 68.22 +52.60 +29.44 +25.66

PCB 135

-42 -22 -21 +31 +18 +17

-43.89 -24.82 -21.65 +43.18 +24.42 +21.31

PCB 197

-32 -18 -16 +32 +18 +16

-35.91 -20.36 -17.78 +35.92 +20.37 +17.78

PCB 175

-34 -20 -17 +34 +20 +16

92.13 -32.37 -18.18 -15.85 91.63 +32.33 +18.15 +15.83

PCB 174

-30 -21 -15 +31 +20 +16

-31.74 -18.28 -16.00 +31.63 +18.22 +15.95

PCB 196

-29 -24 -22 +30 +26 +21

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Table 4. Elution order, i.e. 1st/2nd , for the absolute configurations of 7 PCB atropisomers over 6 common used gas chromatograph columns

Compound 20B BDM BGB BPM CB CD

PCB 84 R/S S/R R/S

PCB 132 R/S R/S R/S R/S

PCB 136 R/S R/S R/S

PCB 176 R/S R/S R/S

PCB 174 R/S S/R R/S S/R

PCB 183 R/S

PCB 149 S/R S/R S/R 20B: 20% -cyclodextrin (in 35%-phenyl)-methylpolysiloxane CB: 30% hepatkis (2,3-di-O-methyl-6-O-tert-butyldimethyl-silyl)--cyclodextrin CD: Chirasil-Dex (2,3,6-tri-O-methyl--cyclodextrin) BGB: 20% tertbutyldimethyl-silyl--cyclodextrin BDM: ChiralDex B-DM (2,3-di-O-methyl-6-tert-butyl-silyl--cyclodextrin) BPM: ChiralDex B-PM (2,3,6-tri-O-methyl-silyl--cyclodextrin)

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Figure 1a. PCB atropisomers which have R chiralities for [𝛼]𝜈 > 0

PCB 95 PCB 144 PCB 149 PCB 183

Figure 1b. PCB atropisomers which have S chiralities for [𝛼]𝜈 > 0




PCB 174 PCB 196 PCB 197

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Figure 2. Specific Rotations of PCB R Atropisomers at 436 nm

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Figure 3. Schematic depiction of Chirasil-Dex

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Draft · 2019-02-27 · Draft 3 atropisomer pairs will undergo physical and transport processes undifferentiated. In contrast, biological processes are predominantly chiral in nature