Influence of Magnetic Field on the Mobility of Aromatic Chiral

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Influence of the Magnetic Field on the Mobility of Aromatic Chiral Molecules Svetlana G. Kozlova, Maxim R. Ryzhikov, Nikolay B. Kompankov, and Marina S. Zavakhina J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.6b05572 • Publication Date (Web): 12 Jul 2016 Downloaded from http://pubs.acs.org on July 17, 2016

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The Journal of Physical Chemistry

Influence of the Magnetic Field on the Mobility of Aromatic Chiral Molecules S. G. Kozlova,*†‡ M. R. Ryzhikov,†‡ N. B. Kompankov,† M. S. Zavakhina† † Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, 3, Akad. Lavrentiev Ave., Novosibirsk 630090, Russian Federation ‡ Novosibirsk State University, 2, Pirogova st., 630090, Russian Federation KEYWORDS. Aromatic enantiomers, mobility, magnetic field, 1H NMR

ABSTRACT. The influence of magnetic fields on the properties of chiral molecules is of great interest nowadays. The work presents an 1H NMR study of the mobility of 1-phenylethanol and 1-phenyl-1-propanol molecules in pure forms and chirally polarized mixtures in external magnetic fields. Molecular mobility is shown to be dependent on the strength of the external magnetic field and chiral mixing. It could be assumed that the mobility changes are caused by rotational interactions and magnetic interactions between induced magnetic moments of the aromatic molecules and the external magnetic field; intermolecular interactions are also essential. The results are important for the tasks related to enantiomer separation.

Introduction. The influence of magnetic fields on the properties of chiral molecules has been subject to great interest lately [1-13]. Recently, the influence of magnetic field on the mobility of

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chirally polarized mixtures of 1-phenylethanol was studied with the method of nuclear magnetic resonance on the hydrogen nucleus (1H NMR) [14]. It was shown that the diffusion coefficients in the pure form and in the chirally polarized mixture of 1-phenylethanol molecules tend to be equalized when the magnetic field is increased. However, the mechanism of enantiomer interactions in the magnetic field, e.g., the dependence of the effect on the type of molecules, degree of chiral polarization, temperature, pressure, and other impacts has not yet been studied in detail. Below we present the results of 1H NMR mobility study for two types of molecules with aromatic properties in external magnetic fields. We chose 1-phenylethanol and 1-phenyl-1propanol molecules in their chiral pure (R-) form and chirally polarized (RS-) mixtures. 1phenylethanol and 1-phenyl-1-propanol molecules were chosen due to similar induced currents (Fig. 1) and similar magnetic isotropic shielding tensors σizo = 7.895 and 7.900 ppm in the center of phenyl rings [14]. It was expected that similarity of induced currents should lead to similarity of diffusion coefficients in the external magnetic fields.

Figure 1. Structure and induced currents in 1-phenylethanol (a) and 1-phenyl-1-propanol (b) molecules. The strongest induced currents among carbon atoms were found on the chiral center (marked blue). Aromatic ring currents are marked with black circles.


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Experimental and Theoretical Methods. For the experiment, R- and S-(+ / −)-1phenylethanol, R- and S-(+ / −)-1-phenyl-1-propanol and their racemic mixtures were purchased from Aldrich and Fluka. Molecular weights of 1-phenylethanol and 1-phenyl-1-propanol are 122.17 and 136.19 g/mol; racemate densities are 1.012 and 0.994 g/mL (25°С) [15] and viscosities are 8.49 и 13.49 mPa s (25°С) [16], respectively. Chirally polarized mixtures were prepared by the addition of corresponding enantiomers to its racemates. Chiral polarization of the solution was described with the Enantiomeric Excess parameter ee = (xR-xS)/ (xR+xS), where xR and xS are the concentrations of R- and S- molecules in the solution. Parameter ee had values 1, 0.6, 0.2, and 0. The PBE [17] density functional and PAW [18] pseudopotentials were used for 1phenylethanol and 1-phenyl-1-propanol relaxation in QuantumEspresso-5.1.1 [19] program suite. The energy cutoff was set to 2721 eV. Induced currents were calculated for relaxed molecules with GIPAW method in QE-GIPAW-5.1.1 [20, 21] module. The 1H NMR studies were done using Bruker Avance NMR 500 and 600 spectrometers with magnetic fields (H0) 11.7 T and 14.1 T, respectively. A pulse method of NMR Diffusion Ordered Spectroscopy (DOSY) was used with a bipolar longitudinal-eddy-current delay sequence to determine diffusion coefficients [22-24] (see the details in Supplementary). To exclude uncontrolled technical influence associated with the design of different spectrometers [25], DRS/DR ratios were studied rather than absolute values of diffusion coefficients (DR and DRS are diffusion coefficients in the pure forms and chirally polarized mixtures, respectively). The justification of the approach was described in [14].


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Figure 2. 1H NMR spectrum (top) and diffusion coefficients (bottom) for RS-mixtures of 1phenylethanol (a,c) and 1-phenyl-1-propanol (b,d) molecules at ee = 0.2; H0 = 11.7 T and 303K. Results. Typical 1H NMR spectra for chirally polarized RS-mixtures of 1-phenylethanol and 1-phenyl-1-propanol with enantiomeric excess parameters ee = 0.2 at 11.7 T magnetic field have been shown on Fig. 2. 1H NMR spectra for other chirally polarized mixtures and another magnetic field (14.1T) are characterized by the same set of spectral lines without additional peaks. The maps of diffusion coefficients are shown in Fig.2. It is seen that hydrogen diffusion coefficients for -C6H5, -CH, -CH3 (Fig. 2a , lines 1, 3, 4) groups of 1-phenylethanol and for C6H5, -CH-, -CH2-, -CH3 (Fig. 2b, lines 1, 3, 4, 5) groups of 1-phenyl-1-propanol are characterized by almost equal values for each molecule, whereas the diffusion coefficients for OH group differ from those for the rest groups of molecules (Figs. 2c and 2d, line 2). Thus, the average values of diffusion coefficients indicate two different diffusion processes (Table 1, all values are cited in Tables 1S and 2S in Supplementary materials). The first one is


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related to the diffusion of C6H5CH(O*)CH3 and C6H5CH(O*)CH2CH3 molecular fragments with hydrogen vacancy (*) and the second one is the diffusion of hydroxy group hydrogen (H*) [14]. However, the diffusion tendency is the same for both processes and we present results only for the molecular fragments (Fig.3 and Fig.4).

Table 1. Mean values of diffusion coefficients (10–10 m2/s) for 1-phenylethanol and 1-phenyl-1propanol molecules in chirally polarized mixtures (ee) at different magnetic field (H0) values and at temperature (T=303K). Molecule

C6H5CH(OH)CH3

C6H5CH(OH)CH2CH3

Fragment

ee (H0 = 11.7 T)

ee (H0 = 14.1 T)

1.0

0.6

0.2

0.0

1.0

0.6

0.2

0.0

C6H5CH(O*)CH3

1.64

1.66

1.73 1.70 2.14 2.31 2.46 2.66

H*

1.69

1.71

1.75 1.72 2.20 2.35 2.49 2.68

C6H5CH(O*)CH2CH3

1.15

1.14

1.12 1.11 1.50 1.42 1.49 1.54

H*

1.20

1.17

1.15 1.14 1.55 1.45 1.52 1.56

The dependences of diffusion coefficient ratios (DRS/DR) for molecular fragments of 1phenylethanol and 1-phenyl-1-propanol are shown in Fig 3 and in Table 3S. DRS/DR ratios at 11.7 T are characterized by close values and their differences are ∆1 ≤ 0.05 and ∆2 ≤ 0.04 for 1phenylethanol and 1-phenyl-1-propanol, respectively. Differences in DRS/DR values grow up to ∆1 ≈ 0.18 and ∆2 ≈ 0.08 for 1-phenylethanol and 1-phenyl-1-propanol, respectively, together with the magnetic field ( H0=14.1T).


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Figure 3. Diffusion coefficient ratios (DRS/DR) as functions of magnetic field for molecular fragment of 1-phenylethanol (a) and 1-phenyl-1-propanol (b) molecules; ee - enantiomeric excess parameter.

Figure 4. Diffusion coefficient ratios (DRS/DR) as functions of magnetic field for H* of 1phenylethanol (a) and 1-phenyl-1-propanol (b) molecules; ee - enantiomeric excess parameter. Thus, in most cases the growth of DRS/DR induced by an increase of the strength of magnetic field is discovered. The maximum increase of DRS/DR ratio together with the magnetic field growth is found for ee = 0.0 (racemate) both for 1-phenylethanol and 1-phenyl-1-propanol. However there is an exception from the growth rule. For 1-phenyl-1-propanol at ee = 0.6 the DRS/DR ratio decreases when the magnetic field grows.


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Discussion. The effect of magnetic field on the diffusion, viscosity and thermal conductivity in rarefied molecular gases (Senftleben effect) was described in [26]. External magnetic field induces the precession of molecular magnetic moment (µ) of molecules around magnetic field direction and leads to changes in frequency and cross section of molecular collisions. In liquids the diffusion processes are much more complicated in comparison with gases due to decrease of mean free path and time between molecules collisions. However the external magnetic field influence would appear. The influence must be the strongest for aromatic molecules with induced magnetic moment µ ≈ χH0 [4]. In the external magnetic field induced magnetic moments of molecules interact with H0 according to ~χH02 law, and with each other according to ~(χH0)2 law. H0 could influence intermolecular interactions related to electronic correlations as well [10, 27]. In our case the second rank tensor of magnetic susceptibility (χ) can be approximated by an ellipsoid with only two different diagonal components along the long (χ॥) and the short (χ⊥) ellipsoidal axis. The calculated anisotropy ∆χ = χ॥ − χ⊥ is diamagnetic and notable. ∆χ is – 53.1·10–6 cm3/mol and –53.6·10–6 cm3/mol for 1-phenylethanol and 1-phenyl-1-propanol respectively (Table 4S). The external magnetic field excites additional currents (Fig. 1, black circle) in the aromatic ring which results in an induced magnetic moment normal to the plane of phenyl group. This leads to an orientational force, tending to minimize the energy of interaction between µ and H0, and causes a dependency of diffusion coefficients from field. Due to the character of intermolecular interactions described above, the dependency must be nonlinear. Conclusion. So, it was found that molecular mobility in R-forms and RS- mixtures is similar and orientational effect does not appear in a relatively weak field (11.7 T) for either 1-


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phenylethanol (DRS/DR = 1.03±0.03) or 1-phenyl-1-propanol (DRS/DR = 0.97±0.02). Stronger magnetic fields change the mobility of the molecules. The molecular mobility in RS-mixtures of 1-phenylethanol is always higher than in R-form at H0 = 14.1 T. The mobility of the 1-phenyl-1propanol molecules in RS-mixtures depends on the degree of chiral polarization. For example, DRS/DR dependencies as functions of the magnetic field for 1-phenylethanol and 1-phenyl-1propanol molecules are opposite at ee = 0.6. We hypothesize that for 1-phenyl-1-propanol molecules some features of intermolecular interactions dependent on the external magnetic field become visible at this value. Apparently the mechanism of the enantiomer interactions could be related to rotational interactions and induced magnetic interactions. These effects could be eliminated by molecular collisions which grow in number together with the temperature. For example, DRS/DR values for 1-phenylethanol chiral molecules grow together with H0 at ee = 0.6 both at 303 K and at 298 K but differ in their magnitudes [14]. It can be assumed that this is due to the influence of temperature on molecular mobility in the external magnetic field. Studies at other temperatures and pressures are to be carried out to understand the interactions of molecules with conjugated bonds in more detail.

Supporting Information. Additional Materials are available for this paper to present the Tables with the results and the details of NMR experiments. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author


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*[email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interests. ACKNOWLEDGMENT This work was supported by the RFBR Grant # 15-03-04905. REFERENCES 1. Choi, H.J.; Hyun, M.H Separation of Enantiomers with Magnetic Silica Nanoparticles Modified by a Chiral Selector: Enantioselective Fishing. Chem. Commun. 2009, 42, 6454–6456; 2. Wei, Y.; Tian, A.; Li, Y.; Wang, X.; Cao, B. A General Chiral Selector Immobilized on Silica Magnetic Microspheres for Direct Separation of Racemates. J. Mater. Chem. 2012, 22, 8499–8504. 3. Rosenberg, R.A.; Abu Haija, M.; Ryan, P.J. Chiral-Selective Chemistry Induced by SpinPolarized Secondary Electrons from a Magnetic Substrate. Phys. Rev. Lett. 2008, 101, 178301(1– 4). 4. Micali, N.; Engelkamp, H.; vanRhee, P.G.; Christianen, P.C.M.; Monsù Scolaro, L.; Maan, J.C. Selection of Supramolecular Chirality by Application of Rotational and Magnetic Forces. Nature Chem. 2012, 4, 201–207.


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5. Buckingham, A. D. Permanent Dipoles Contribute to Electric Polarization in Chiral NMR Spectra. J. Chem. Phys. 2014, 140, 011103 (1–3). 6. Buckingham, A.D. Chiral Discrimination in NMR Spectroscopy. Q. Rev. Biophys. 2015, 48, 421–423. 7. Provasi, P.F.; Pagola, G.I.; Ferraro, M.B.; Pelloni, S.; Lazzeretti, P. Magnetizabilities of Diatomic and Linear Triatomic Molecules in a Time-Independent Nonuniform Magnetic Field. J. Phys. Chem. A. 2014, 118, 6333−6342. 8. Pelloni, S.; Faglioni, F.; Soncini, A.; Ligabue, A.; Lazzeretti, P. Magnetic Response of Dithiin Molecules: is There Anti-Aromaticity in Nature. Chem. Phys. Lett. 2003, 375, 583–590. 9. Fukuyama, T.; Momose, T.; Nomura, D. Anapole Moment of a Chiral Molecule Revisited. Eur. Phys. J. D. 2015, 69, 264 (1–10). 10. Zarycz, N.; Provasi, P.F.; Pagola, G.I.; Ferraro, M.B.; Pelloni, S.; Lazzeretti, P. Computational Study of Basis Set and Electron Correlation Effects on Anapole Magnetizabilities of Chiral Molecules. J Comput Chem. 2016, 37, 1552–1558. 11. Gabuda, S.P.; Kozlova, S.G.; Samsonenko, D.G.; Dybtsev, D.N.; Fedin, V.P. Quantum Rotations and Chiral Polarization of Qubit Prototype Molecules in a Highly Porous Metal_Organic Framework: 1H NMR T1 Study. J. Phys. Chem. C. 2011, 115, 20460–20465. 12. Gabuda, S.P.; Kozlova, S.G. Abnormal Difference Between the Mobilities of Left- and Right-Twisted Conformations of C6H12N2 Roto-Symmetrical Molecules at Very Low Temperatures. J.Chem. Phys. 2015, 142, 2 (1–6).


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


13. Gabuda, S.P.; Kozlova, S.G. Chirality-Related Interactions and a Mirror Symmetry Violation in Handed Nano Structures. J.Chem. Phys. 2014, 141, 044701(1–5). 14. Kozlova, S.G.; Kompankov, N.B.; Ryzhikov, M.R.; Slepkov, V.A. Mobility Inhibition of 1-phenylethanol Chiral Molecules in Strong Magnetic Fields. Chem. Phys. Letters. 2015, 642, 14. 15. Yaws, C.L. The Yaws Handbook of Physical Properties for Hydrocarbons and Chemicals; 2nd Edition, Gulf Professional Publishing, 2015. 16. Wohlfarth C.; Wohlfarth B. Pure Organic Liquids, Lechner M.D. Ed.; Springer-Verlag Berlin Heidelberg, 2002. 17. Perdew, J.P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple, Phys. Rev. Lett. 1996, 77, 3865–3868. 18. THEOS Group Pseudopotential Data Base. http://theossrv1.epfl.ch/Main/Pseudopotentials. (We used the pseudopotentials C.pbe-n-kjpaw_psl.0.1.UPF, O.pbe-n-kjpaw_psl.0.1.UPF and H.pbe-kjpaw_psl.0.1.UPF) [Accessed 30 May 2016]. 19. Giannozzi, P.; Baroni, S.; Bonini, N.; etc. QUANTUM ESPRESSO: a Modular and OpenSource Software Project for Quantum Simulations of Material J. Phys. Condens. Matter. 2009, 21, 395502 (1–19). 20. Pickard, C. J.; Mauri, F. All-Electron Magnetic Response with Pseudopotentials: NMR Chemical Shifts. Phys. Rev. B. 2001, 63, 2451001 (1–13). 21. Yates, J.R.; Pickard C.J.; Mauri, F. Calculation of NMR Chemical Shifts for Extended Systems Using Ultrasoft Pseudopotentials. Phys. Rev. B. 2007, 76, 024401(1–11).


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22. Morris, K.F.; Johnson, C.S. The Resolution of Discrete and Continuous Molecular Size Distributions by Means of Diffusion Ordered 2D-NMR Spectroscopy. J. Am. Chem. Soc. 1993, 115, 4291–4299. 23. Wu, D.;

Chen, A.; Johnson C.S.

An Improved Diffusion-Ordered Spectroscopy

Experiment Incorporating Bipolar-Gradient Pulses. J. Magn. Reson. A, 1995, 115, 260–264. 24. Johnson, C. S. Diffusion Ordered Nuclear Magnetic Resonance Spectroscopy: Principles and Applications. Prog. Nucl .Magn. Reson. Spectrosc. 1999, 34, 203–256. 25. Holz, M.; Heil, S. R.; Sacco, A. Temperature-Dependent Self-Diffusion Coefficients of Water and Six Selected Molecular Liquids for Calibration in Accurate

1

H NMR PFG

Measurements. Phys. Chem. Chem. Phys. 2000, 2, 4740–4742. 26. Beenakker, J.J.M., The Boltzmann Equation, Theory and Applications, E.G.D.; Springer, Wien, 1973. 27. Gabuda, S.P.; Kozlova, S.G. Correlation and Relativistic Effects on Coordinate Bonding in Hexafluorides and Hexafluoro Complexes. Russ. J. Inorg. Chem. 2001, 46, S171-S186.


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Induced currents in 1-phenylethanol and 1-phenil-1-propanol molecules. Insert Table of Contents Graphic and Synopsis Here


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Influence of Magnetic Field on the Mobility of Aromatic Chiral

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