Next Article in Journal
Mixing Matrix Estimation of Underdetermined Blind Source Separation Based on Data Field and Improved FCM Clustering
Next Article in Special Issue
Chiral Heterocycle-Based Receptors for Enantioselective Recognition
Previous Article in Journal
WPCB-Tree: A Novel Flash-Aware B-Tree Index Using a Write Pattern Converter
Previous Article in Special Issue
Helicene-Based Chiral Auxiliaries and Chirogenesis
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Symmetry
Volume 10
Issue 1
10.3390/sym10010020
symmetry-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

The Asymmetry is Derived from Mechanical Interlocking of Achiral Axle and Achiral Ring Components –Syntheses and Properties of Optically Pure [2]Rotaxanes–

by
Keiji Hirose
1,*,
Masaya Ukimi
1,
Shota Ueda
1,
Chie Onoda
1,
Ryohei Kano
1,
Kyosuke Tsuda
1,
Yuko Hinohara
1 and
Yoshito Tobe
2
1
Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan
2
The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan
*
Author to whom correspondence should be addressed.
Symmetry 2018, 10(1), 20; https://doi.org/10.3390/sym10010020
Submission received: 25 November 2017 / Revised: 20 December 2017 / Accepted: 27 December 2017 / Published: 9 January 2018
(This article belongs to the Special Issue Chiral Auxiliaries and Chirogenesis)
Browse Figures
Versions Notes

Abstract

:
Rotaxanes consisting of achiral axle and achiral ring components can possess supramolecular chirality due to their unique geometrical architectures. To synthesize such chiral rotaxanes, we adapted a prerotaxane method based on aminolysis of a metacyclophane type prerotaxane that had planar chirality, which is composed of an achiral stopper unit and a crown ether type ring component. The prerotaxanes were well resolved using chiral HPLC into a pair of enantiomerically pure prerotaxanes, which were transferred into corresponding chiral rotaxanes, respectively. Obtained chiral rotaxanes were revealed to have considerable enantioselectivity.

1. Introduction

The discoveries of a crown ether and a very stable complex formation with a metal cation by C. J. Pedersen [1] in 1967, following neologisms of the “Host-guest chemistry” by D. J. Cram [2], and that of the “Supramolecular chemistry” by J. M. Lehn [3], showed the importance of interaction between molecules, were tremendously influential and initiated a huge amount of researches. Nobel prize of chemistry was awarded to these researchers in 1987. Many crops from this field of chemistry were industrialized such as ion sensors, ion selective membranes, and electrodes [4,5,6,7,8,9], which were contributed by ion recognition initiated by C. J. Pedersen and chiral selectors for chromatography [10,11,12,13,14,15] initiated by the contribution of D. J. Cram’s chirality recognition technology [16,17]. Research topics such as chiral shift reagents for the determination of enantiomeric excess of chiral substance [18], besides the reagents for the determination of absolute configuration [19,20], chiral indicators [19,21,22,23,24], and rapid chirality detection method using chiral hosts by means of mass spectrometry [25,26], as well as other well established methods [27,28,29] have long fascinated many researchers.
In the late 1980s, fabrications of molecular assemblies using inter- and/or intramolecular interactions of molecular components came under the spotlight. Typical examples are the syntheses of catenanes, rotaxanes, and molecular knots [30]. The emergence and excellent development of supramolecular methods make the syntheses of supramolecules much more effective, with a higher chemical yield [31,32,33,34,35] than before [36]. Covalent methods [37], which were not thought to be versatile for the synthesis of interlocked molecules, were also well developed [38,39]. One of the applications in this field of chemistry is to make the smallest machines at molecular level using fabrications of molecular components. The Nobel prize in chemistry was awarded to three researchers working in this field: J.-P. Sauvage [40], Sir J. F. Stoddart [41], and B. L. Feringa [42] in 2016.
Chiral interlocked molecules provide unique three-dimensional, valuable-binding circumstances capable of chirality recognition of guests. However, the application of interlocked hosts for chirality recognition has been largely overlooked, especially the recognition by hosts with mechanical chirality. A rotaxane has a mechanically interlocked architecture consisting of a dumbbell-shaped axle component that is threaded through a ring component. Rotaxanes consisting of achiral axle components that have C∞v symmetry and achiral ring components that have Cs symmetry can be chiral, caused by their geometrically specific architectures. In Figure 1, an enantiomeric pair of rotaxanes with the specific chirality composed of a C∞v axle and a Cs ring components is shown. Rotaxanes with the specific chirality can be expected as new molecular platforms [43,44,45] for asymmetric catalysts, chiral sensors [27,28,29], etc. However, it is difficult to synthesize such rotaxanes as optically pure forms [46]. In order to synthesize such rotaxanes with the rotaxane-specific chirality in an optically pure form, we applied our prerotaxane method [39], in which a rotaxane can be synthesized via backside attack of a stopper unit to a prerotaxane with planar chirality composed of an achiral stopper unit and a Cs ring component (Scheme 1). In order to investigate binding properties of the rotaxanes that have a mechanically interlocked chirality as host compounds, precise evaluation of the enantioselective complexation ability of the rotaxanes with chiral guests were carried out.

2. Materials and Methods

Compound 1 prepared using hydroquinone mono-methoxymethyl ether as starting material according to previously reported procedures [47,48,49] was used. All other compounds and reagents were obtained from commercial suppliers and used as received. CH2Cl2 and THF were dried by a Glass Contour solvent purification system prior to use. Melting points were measured with a hot-stage apparatus equipped with a thermometer. 1H NMR spectra were recorded with a JEOL GSX-270, a Varian Mercury 300, or a JEOL AL-400 spectrometer for solutions in CDCl3 or C6D6 with SiMe4 as an internal standard and J values given in Hz. 13C NMR spectra were recorded at 75.5 MHz with a JEOL GSX-270 spectrometer, and chloroform (δ C 77.0) was used as a chemical shift reference. Multiplicities for 1H NMR spectra are as follows: singlet (s), doublet (d), triplet (t), quartet (q), and multiplet (m). Multiplicities for 13C NMR spectra are as follows: primary (1°), secondary (2°), tertiary (3°), and quaternary (4°). IR spectra were measured on a JASCO FT/IR–410 spectrophotometer. Circular dichroism spectra were measured using a JASCO J–805 spectropolarimeter, and θ values are given in units of mdeg. MS spectra were recorded with a JEOL JMS-700 spectrometer. Preparative GPLC was performed with JAI LC-908 on JAIGEL 1H and 2H columns with CHCl3 as a solvent. Elemental analyses were carried out by using a Perkin–Elmer 2400II analyser. Analytical thin layer chromatography (TLC) was performed using precoated silica gel plates (Merck Kieselgel 60 F254). Preparative column chromatography was carried out using Fuji Silysia BW-300 silica gel (SiO2; 0.038–0.075 mm) with the indicated solvents, which were mixed v/v as specified.
2-1 Synthetic Procedures and Characterization of Racemic Prerotaxanes (rac)-3
Into a solution of 1 (98.9 mg, 142 μmol) in dry THF (3.5 mL) and KOtBu (55.6 mg, 495 μmol), 3,5-dinitrobenzoyl chloride (131 mg, 568 μmol) was added with stirring under a nitrogen atmosphere. After 2 h stirring at room temperature, the solvent was evaporated under reduced pressure. The residue was extracted with chloroform. The organic layer was washed with brine. After being dried over anhydrous MgSO4, the solvent was removed under reduced pressure. The residue was purified by preparative GPLC to give (rac)-3 (74.8 mg, 84.4 μmol, 60%) as an orange powder: 1H NMR (400 MHz, CDCl3, 30 °C) δ 9.02 (d, 2H, J = 1.9 Hz), 8.86 (d, 1H, J = 2.5 Hz), 8.81 (t, 1H, J = 1.9 Hz), 8.58 (dd, 1H, J = 2.5, 8.8 Hz), 8.28 (d, 1H, J = 2.5 Hz), 8.16 (d, 1H, J = 2.5 Hz), 7.85 (d, 1H, J = 8.8 Hz), 7.45 (d, 2H, J = 8.5 Hz), 7.18–7.30 (m, 2H), 7.09 (s, 1H), 6.85 (s, 1H), 5.45 (d, 1H, J = 12 Hz), 5.15 (d, 1H, J = 12 Hz), 4.83 (d, 1H, J = 13 Hz), 4.70 (d, 1H, J = 13 Hz), 4.08–4.18 (m, 2H), 3.92 (t, 2H, J = 4.2 Hz), 3.48–3.78 (m, 16H); 13C NMR (100 MHz, CDCl3, 30 °C) δ 159.9 (4°), 151.2 (4°), 150.3 (4°), 148.9 (4°), 148.7 (4°), 147.84 (4°), 147.77 (4°), 146.5 (4°), 134.2 (4°), 131.3 (4°), 129.5 (3°), 129.2 (4°), 128.5 (4°), 127.9 (3°), 126.4 (3°), 126.0 (3°), 125.9 (3°), 125.1 (3°), 124.8 (3°), 124.4 (3°), 122.0 (3°), 120.19 (3°), 122.16 (3°), 109.2 (3°), 107.7 (3°), 71.3 (2°), 71.0 (2°), 70.8 (2°), 70.71 (2°), 70.65 (2°), 70.6 (2°), 70.1 (2°), 69.4 (2°), 69.0 (2°), 68.5 (2°), 67.7 (2°); IR (KBr) 3093, 2922, 2866, 1770, 1543, 1345, 1261, 1137, 1114, 920, 717 cm−1; HRMS (FAB) m/z calcd for C41H39N6O17 ([M + H+]): 887.2372, found: 887.2379.
2-2 Characterization of Resolved Prerotaxane 31st
31st: m.p. 88.8–90.1 °C; 1H NMR (400 MHz, CDCl3, 30 °C) δ 9.02 (d, 2H, J = 1.9 Hz), 8.86 (d, 1H, J = 2.5 Hz), 8.81 (t, 1H, J = 1.9 Hz), 8.58 (dd, 1H, J = 2.5, 8.8 Hz), 8.28 (d, 1H, J = 2.5 Hz), 8.16 (d, 1H, J = 2.5 Hz), 7.85 (d, 1H, J = 8.8 Hz), 7.45 (d, 2H, J = 8.5 Hz), 7.18–7.30 (m, 2H), 7.09 (s, 1H), 6.85 (s, 1H), 5.45 (d, 1H, J = 12 Hz), 5.15 (d, 1H, J = 12 Hz), 4.83 (d, 1H, J = 13 Hz), 4.70 (d, 1H, J = 13 Hz), 4.08–4.18 (m, 2H), 3.92 (t, 2H, J = 4.2 Hz), 3.48–3.78 (m, 16H); 13C NMR (100 MHz, CDCl3, 30 °C) δ 160.0 (4°), 151.3 (4°), 150.4 (4°), 149.0 (4°), 148.8 (4°), 147.94 (4°), 147.89 (4°), 146.6 (4°), 134.2 (4°), 131.4 (4°), 129.6 (3°), 129.2 (4°), 128.6 (4°), 128.0 (3°), 126.5 (3°), 126.1 (3°), 126.0 (3°), 125.2 (3°), 124.9 (3°), 124.5 (3°), 122.1 (3°), 120.29 (3°), 120.25 (3°), 109.2 (3°), 107.7 (3°), 71.3 (2°), 71.0 (2°), 70.77 (2°), 70.75 (2°), 70.73 (2°), 70.66 (2°), 70.63 (2°), 70.1 (2°), 69.5 (2°), 69.0 (2°), 68.5 (2°), 67.7 (2°) (1 tertiary carbon and 1 quaternary carbon could not be seen); IR (KBr) 3101, 2869, 1752, 1543, 1344, 1261, 1137, 1114, 922, 717 cm−1; UV/Vis (CHCl3, 22 °C) λmax (log ε) 342 (4.3); MS (LDI) m/z 909.3 ([M + Na+]). HRMS (ESI) m/z Calcd for C41H38N6NaO17: 909.2191, Found: 909.2200 ([M + Na+]). Anal. Calcd for C41H38N6O17: C, 55.53; H, 4.32; N, 9.48. Found: C, 55.25; H, 4.22; N, 9.35.
2-3 Characterization of Resolved Prerotaxane 32nd
32nd: m.p. 88.9–90.0 °C; 1H NMR (400 MHz, CDCl3, 30 °C) δ 9.02 (d, 2H, J = 1.9 Hz), 8.86 (d, 1H, J = 2.5 Hz), 8.81 (t, 1H, J = 1.9 Hz), 8.58 (dd, 1H, J = 2.5, 8.8 Hz), 8.28 (d, 1H, J = 2.5 Hz), 8.16 (d, 1H, J = 2.5 Hz), 7.85 (d, 1H, J = 8.8 Hz), 7.45 (d, 2H, J = 8.5 Hz), 7.18–7.30 (m, 2H), 7.09 (s, 1H), 6.85 (s, 1H), 5.45 (d, 1H, J = 12 Hz), 5.15 (d, 1H, J = 12 Hz), 4.83 (d, 1H, J = 13 Hz), 4.70 (d, 1H, J = 13 Hz), 4.08–4.18 (m, 2H), 3.92 (t, 2H, J = 4.2 Hz), 3.48–3.78 (m, 16H); 13C NMR (100 MHz, CDCl3, 30 °C) δ 160.0, 151.3, 150.4, 149.0, 148.8, 147.94, 147.89, 146.6, 134.2, 131.4, 129.6, 129.2, 128.6, 128.0, 126.5, 126.1, 126.0, 125.2, 124.9, 124.5, 122.1, 120.3, 109.2, 107.7, 71.3, 71.1, 70.79, 70.77, 70.74, 70.69, 70.64, 70.2, 69.5, 69.0, 68.5, 67.8 (2 carbons couldn’t be seen); IR (KBr) 3101, 2870, 1752, 1543, 1345, 1261, 1138, 1114, 922, 718 cm−1; MS (LDI) m/z 909.2 ([M + Na+]). HRMS (ESI) m/z Calcd for C41H38N6NaO17: 909.2191, Found: 909.2185 ([M + Na+]). Anal. Calcd for C41H38N6O17: C, 55.53; H, 4.32; N, 9.48. Found: C, 55.70; H, 4.46; N, 9.35.
2-4 Synthetic Procedures and Characterization of Rotaxanes 51st
Into a solution of 31st (2.99 mg, 3.37 µmol) in C6D6 (660 µL), 3,5-bis(trifluoromethyl)benzylamine 4 (1.63 mg, 6.71 µmol) in C6D6 (22 µL) was added. The aminolysis was monitored by 1H NMR (270 MHz) at 30 °C. After the reaction was completed, the solvent was removed under reduced pressure. The residue was purified by preparative GPLC. Following precipitation from CH2Cl2 and hexane afforded 51st (2.93 mg, 2.59 µmol, 77%) as an orange solid. m.p. 115.1–116.8 °C; 1H NMR (270 MHz, C6D6, 30 °C) δ 8.69 (d, 2H, J = 1.7 Hz), 8.40 (t, 1H, J = 1.7 Hz), 8.27–8.24 (m, 1H), 8.20 (s, 2H), 8.07 (d, 1H, J = 2.2 Hz), 8.05 (d, 1H, J = 2.4 Hz), 7.66 (s, 1H), 7.62 (dd, 1H, J = 8.3, 2.4 Hz), 7.60 (d, 1H, J = 2.4 Hz), 7.37 (d, 1H, J = 9.0 Hz), 7.45–7.33 (m, 4H), 6.96 (s, 1H), 6.03 (s, 1H), 5.34 (dd, 1H, J = 16.2, 8.0 Hz), 5.20 (d, 1H, J = 8.8 Hz), 4.89 (dd, 1H, J = 16.2, 2.3 Hz), 4.71 (d, 1H, J = 10.6 Hz), 4.37 (d, 1H, J = 9.1 Hz), 3.78 (d, 1H, J = 10.6 Hz), 3.61–2.91 (m, 16H), 2.69 (t, 2H, J = 10.2 Hz), 2.43 (d, 1H, J = 10.7 Hz), 2.12 (t, 1H, J = 10.1 Hz); 13C NMR (100 MHz, CDCl3, 30 °C) δ 163.0 (4°), 160.2 (4°), 148.7 (4°),147.6 (4°), 147.4 (4°), 147.2 (4°), 146.8 (4°), 146.0 (4°), 140.7 (4°), 137.2 (4°), 132.0 (3°), 130.3 (3°), 130.2 (q, JCF = 33 Hz, 4°), 128.9 (4°), 128.4 (4°), 127.8 (3°), 127.65 (3°), 127.59 (4°), 126.5 (3°), 125.6 (3°), 124.92 (4°), 124.90 (3°), 124.86 (3°), 124.7 (3°), 122.1 (4°), 120.4 (q, JCF = 4.4 Hz, 3°), 120.0 (3°), 119.8 (3°), 119.7 (3°), 107.3 (3°), 105.8 (3°), 71.20 (2°), 71.15 (2°), 70.9 (2°), 70.6 (2°), 70.5 (2°), 70.4 (2°), 70.2 (2°), 70.1 (2°), 69.8 (2°), 69.4 (2°), 67.6 (2°), 65.1 (2°), 43.7 (2°) (2 tertiary carbon and 3 quaternary carbon could not be seen); IR (KBr) 3346, 3096, 2880, 1601, 1540, 1345, 1278, 1130, 850 cm−1; UV/Vis (CHCl3, 20 °C) λmax (log ε) 390 (4.3); MS (MALDI) m/z 1152.4 ([M + Na+]); HRMS (FAB) m/z Calcd for C51H45F6N7O17: 1130.2854, Found: 1130.2885 ([M + H+]).
2-5 Synthetic Procedures and Characterization of Rotaxanes 52nd
Into a solution of 32nd (3.15 mg, 3.54 μmol) in C6D6 (660 μL), amine 4 (1.72 mg, 7.07 μmol) in C6D6 (22 μL) was added. The aminolysis was monitored by 1H NMR (270 MHz) at 30 °C. After the reaction was completed, the solvent was removed under reduced pressure. The residue was purified by preparative GPLC. Following precipitation from CH2Cl2 and hexane afforded 52nd (3.35 mg, 2.96 μmol, 84%) as an orange solid. m.p. 115.2–116.7 °C; 1H NMR (400 MHz, C6D6, 30 °C) δ 8.69 (d, 2H, J = 1.7 Hz), 8.40 (t, 1H, J = 1.7 Hz), 8.26–8.25 (m, 1H), 8.20 (s, 2H), 8.07 (d, 1H, J = 2.0 Hz), 8.05 (d, 1H, J = 2.5 Hz), 7.66 (s, 1H), 7.62 (dd, 1H, J = 8.3, 2.4 Hz), 7.60 (d, 1H, J = 2.4 Hz), 7.37 (d, 1H, J = 9.0 Hz), 7.45–7.33 (m, 4H), 6.96 (s, 1H), 6.03 (s, 1H), 5.34 (dd, 1H, J = 16.2, 8.0 Hz), 5.20 (d, 1H, J = 9.5 Hz), 4.89 (dd, 1H, J = 14.3, 2.3 Hz), 4.71 (d, 1H, J = 10.3 Hz), 4.37 (d, 1H, J = 9.5 Hz), 3.79 (d, 1H, J = 10.5 Hz), 3.60–2.91 (m, 16H), 2.68 (t, 2H, J = 10.2 Hz), 2.43 (d, 1H, J = 10.7 Hz), 2.13 (t, 1H, J = 10.1 Hz); 13C NMR (100 MHz, CDCl3, 30 °C) δ 163.0, 160.2, 148.7, 147.6, 147.4, 147.2, 146.8, 146.0, 140.7, 137.2, 132.0, 130.3, 130.2 (q, JCF = 33 Hz), 128.9, 128.4, 127.8, 127.65, 127.59, 126.5, 125.6, 124.92, 124.90, 124.86, 124.7, 122.1, 120.4 (q, JCF = 4.4 Hz), 120.0, 119.8, 119.7, 107.3, 105.8, 71.20, 71.15, 70.9, 70.6, 70.5, 70.4, 70.2, 70.1, 69.8, 69.4, 67.6, 65.1, 43.7 (2 tertiary carbon and 3 quaternary carbon could not be seen); IR (KBr) 3351, 3101, 2880, 1601, 1540, 1345, 1278, 1131, 850 cm−1; MS (MALDI) m/z 1152.3 ([M + Na+]); HRMS (FAB) m/z Calcd for C51H45F6N7O17: 1130.2854, Found: 1130.2852 ([M + H+]).

3. Results and Discussion

We planned to synthesize rotaxanes 5 and the enantiomer as target chiral rotaxanes by way of prerotaxanes 3 with planar chirality followed by aminolysis with bulky amine 4 as shown in Scheme 2. This versatile covalent method to synthesize rotaxane consists of two steps: first, esterification of a phenolic crown ether with an acid chloride; second, aminolysis with an amine compound having a bulky group.
Prerotaxanes 3 were prepared from a phenolic pseudo-crown ether 1 and a 3,5-dinitrobenzoyl chloride in the presence of KOtBu in THF. Optical resolution of obtained racemic prerotaxane (rac)-3 was performed by preparative chiral HPLC on Daicel CHIRALFLASH IA. Chromatograms of (rac)-3, resolved 31st, and 32nd were shown in Figure 2. (rac)-3 was well resolved into 31st and 32nd. In Figure 3, CD (a) and UV-visible (b) spectra of 31st and 32nd are shown. The CD spectra of 31st and 32nd are mirror images each other. In general, chirality that appeared in mechanically interlocked systems is attractive due to its unique structure having large and flexible asymmetric field owing to the high mobility of the components. However, the determination of the absolute configuration is therefore difficult when applying chromophore sector rules on CD spectal data [50,51]. Because absolute structures of these enantiomers 3 were not determined in this stage, resolved prerotaxanes were denoted as 31st and 32nd according to the eluted order in this condition.
For preparation of optically pure rotaxane 5, aminolyses of corresponding enantiomeric pure prerotaxanes 3 were carried out. A mixture of a prerotaxane 3 and amine 4 in benzene was stirred at room temperature. Because the aminolysis proceeds via the nucleophilic attack of amino group of 4 from the backside of the crown ether ring of prerotaxanes 3 as shown with dotted arrow in Scheme 2, the corresponding rotaxanes 5 were afforded from a pair of enantiomerically pure prerotaxanes 3, respectively. The reactions of the resolved prerotaxanes 31st and 32nd with amine 4 proceeded quantitatively in C6D6 to give corresponding rotaxanes 51st and 52nd, respectively. The residue after removal of the solvent in the reaction mixture was subjected to GPLC and/or column chromatography on silica gel to give rotaxane 51st and 52nd without producing any dumbbell compound 6 and crown ether 1. The efficiency of the reaction was easily monitored by 1H NMR. The aminolysis by the backside attack of amine 4 took place selectively. 1H NMR spectra of a reaction mixture of aminolysis of 3 are shown in Figure 4. HA signal of prerotaxane 3 (HA(3)) at 9.02 ppm decreased with increasing HA signal of rotaxane 5 (HA(5)) at 8.69 ppm without producing any ring compound 1, e.g., Ha and Hb signals at 5.02 and 4.60 ppm were not observed. Reaction proceeded fast (t1/2: 20 min) and selectively (rotaxane selectivity: >99%). Actually, 5 was obtained in high isolated yield (84%).
The structures of rotaxanes 5 were characterized by spectral data. 1H NMR spectra of rotaxane 5 and the corresponding dumbbell 6 are shown in Figure 5. Significant downfield shift of the signal of the amide proton NH of the axle in rotaxanes 5 was observed relative to the corresponding signal of dumbbell 6 (δ 6.83 to 8.25), indicating the formation of hydrogen bonding between the amide hydrogen with the oxygen atoms of the crown ether moiety of 5. Two singlets assigned to the benzylic protons Ha and Hb of the crown ether became double double-doublets (Ha, Ha’, Hb, and Hb’), evidencing that the ring components are threaded and interlocked by the dumbbell component 6 with different stoppers. More importantly, signals of homotopic methylene protons HC on the axle component became multiplet, because the methylene protons HC became diastereotopic in the chiral circumstance of the rotaxane structure-specific chirality generated by interlocking with Cs ring component as shown in Figure 5.
HPLC Chromatograms on Daicel CHIRALPAK IA shown in Figure 6 with the mirror images of the CD spectra shown in Figure 7a evidenced that obtained 51st and 52nd are pure enantiomers.
In order to evaluate the enantioselective complexation ability of the rotaxane, titration experiments of rotaxane 52nd with (R)-phenylglycinol (PGO) and (S)-PGO were carried out. Because chiral host molecules with 2,4-dinitrophenylazophenol moiety produce ammonium phenolate salts in complexation with PGO accompanying large spectral change in UV-visible region with clear color change [22], there is a considerable chemical shift change of 1H NNR signals assigned to the aromatic protons at low magnetic field.
As shown in Figure 8, spectral and color changes of CHCl3 solution of 52nd and (R)-PGO were observed. This observation shows that the extent of color change is clear enough as a sensor for naked eyes, and that the obtained rough extent of binding constant was around 100 L mol−1. Then, 1H NMR titration was revealed to be suitable for precise evaluation [52,53] of complexation ability of host 5 with PGO. The 1H NMR titration was carried out with 52nd and enantiomeric pair of amines (S)- and (R)-PGO in chloroform. Experimental details are filed in Supplementary Materials and Appendix A, Appendix B, Appendix C and Appendix D. As shown in Table 1, the determined binding constants of 52nd were (8.47 ± 0.40) × 101 L mol−1 for (S)-PGO and (1.25 ± 0.03) × 102 L mol−1 for (R)-PGO, respectively. The ratio of binding constants KR/KS was 1.48. Generally speaking, as perspectives with the ratio of binding constant, it is not enough for application as chirality indicator [19,53], but is promising for application as a chiral selector of a stationary phase for a chiral chromatography [54].

4. Conclusions

We developed an efficient method of rotaxane synthesis based on an aminolysis of a prerotaxane, which proceeded with excellent selectivities and chemical yields. We also found that the rotaxane with mechanical chirality has complexation ability against chiral amine PGO, with high enough enantioselectivity to be applied as a chiral selector of the chiral stationary phase for chiral chromatography.

Supplementary Materials

The followings are available online at www.mdpi.com/2073-8994/10/1/20/s1, Table S1: Tabulated 1H NMR titration data of Rotaxane 52nd with (R)-PGO in CDCl3 at 30 °C, Figure S1: 1H NMR titration curve for the complexation of Rotaxane 52nd with (R)-PGO at 30 °C, Table S2: Tabulated 1H NMR titration data of Rotaxane 52nd with (S)-PGO in CDCl3 at 30 °C, Figure S2. 1H NMR titration curve for the complexation of Rotaxane 52nd with (S)-PGO at 30 °C.

Acknowledgments

This work was partly supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.

Author Contributions

Keiji Hirose conceived and designed the experiments; Masaya Ukimi, Shota Ueda, Chie Onoda, Ryohei Kano, Kyosuke Tsuda and Yuko Hinohara performed the experiments; Yoshito Tobe contributed for scientific guide; Masaya Ukimi, Shota Ueda, and Ryohei Kano analyzed the data; Keiji Hirose, Masaya Ukimi and Chie Onoda wrote the paper.

Conflicts of Interest

The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

Appendix A. General

1H NMR and 13C NMR charts are filed here. Details of each chart are mentioned in Materials and Methods.

Appendix B. 1H-and 13C-NMR Spectra of Ring 1

Symmetry 10 00020 i0a1
Symmetry 10 00020 i0a2

Appendix C. 1H-and 13C-NMR Spectra of Prerotaxanes 3

Symmetry 10 00020 i0a3
Symmetry 10 00020 i0a4

Appendix D. 1H-and 13C-NMR Spectra of Rotaxanes 5

Symmetry 10 00020 i0a5
Symmetry 10 00020 i0a6
Symmetry 10 00020 i0a7
Symmetry 10 00020 i0a8
Symmetry 10 00020 i0a9

References and Note

  1. Pedersen, C.J. The discovery of crown ethers. Science 1988, 241, 536–540. [Google Scholar] [CrossRef] [PubMed]
  2. Cram, D.J. The design of molecular hosts, guests, and their complexes. J. Incl. Phenom. 1988, 6, 397–413. [Google Scholar] [CrossRef]
  3. Lehn, J.M. Supramolecular chemistry—Scope and perspectives molecules, supermolecules, and molecular devices. Angew. Chem. Int. Ed. 1988, 27, 89–112. [Google Scholar] [CrossRef]
  4. Takagi, M.; Nakamura, H. Analytical application of functionalized crown ether-metal complexes. J. Coord. Chem. 1986, 15, 53–82. [Google Scholar] [CrossRef]
  5. Nakashima, K.; Nagaoka, Y.; Nakatsuji, S.I.; Kaneda, T.; Tanigawa, I.; Hirose, K.; Misumi, S.; Akiyama, S. Fluorescence reactions of “crowned” benzothiazolylphenols with alkali and alkaline earth metal ions and their analytical applications. Bull. Chem. Soc. Jpn. 1987, 60, 3219–3223. [Google Scholar] [CrossRef]
  6. Desilva, A.P.; Gunaratne, H.Q.N.; Gunnlaugsson, T.; Huxley, A.J.M.; Mccoy, C.P.; Rademacher, J.T.; Rice, T.E. Signaling recognition events with fluorescent sensors and switches. Chem. Rev. 1997, 97, 1515–1566. [Google Scholar] [CrossRef]
  7. Hisamoto, H. Ion-selective optodes: Current developments and future prospects. Trac-Trends Anal. Chem. 1999, 18, 513–524. [Google Scholar] [CrossRef]
  8. Stradiotto, N.R.; Yamanaka, H.; Zanoni, M.V.B. Electrochemical sensors: A powerful tool in analytical chemistry. J. Braz. Chem. Soc. 2003, 14, 159–173. [Google Scholar] [CrossRef]
  9. Faridbod, F.; Ganjali, M.R.; Dinarvand, R.; Norouzi, P.; Riahi, S. Schiff’s bases and crown ethers as supramolecular sensing materials in the construction of potentiometric membrane sensors. Sensors 2008, 8, 1645–1703. [Google Scholar] [CrossRef] [PubMed]
  10. Sogah, G.D.Y.; Cram, D.J. Total chromatographic optical resolutions of alpha-amino acid and ester salts through chiral recognition by a host covalently bound to polystyrene resin. J. Am. Chem. Soc. 1976, 98, 3038–3041. [Google Scholar] [PubMed]
  11. Machida, Y.; Nishi, H.; Nakamura, K.; Nakai, H.; Sato, T. Enantiomer separation of amino compounds by a novel chiral stationary phase derived from crown ether. J. Chromatogr. A 1998, 805, 85–92. [Google Scholar] [CrossRef]
  12. Hyun, M.H.; Jin, J.S.; Lee, W.J. Liquid chromatographic resolution of racemic amino acids and their derivatives on a new chiral stationary phase based on crown ether. J. Chromatogr. A 1998, 822, 155–161. [Google Scholar] [CrossRef]
  13. Maier, N.M.; Franco, P.; Lindner, W. Separation of enantiomers: Needs, challenges, perspectives. J. Chromatogr. A 2001, 906, 3–33. [Google Scholar] [CrossRef]
  14. Hirose, K.; Nakamura, T.; Nishioka, R.; Ueshige, T.; Tobe, Y. Preparation and evaluation of novel chiral stationary phases covalently bound with chiral pseudo-18-crown-6 ethers. Tetrahedron Lett. 2003, 44, 1549–1551. [Google Scholar] [CrossRef]
  15. Hirose, K.; Jin, Y.; Nakamura, T.; Nishioka, R.; Ueshige, T.; Tobe, Y. Chiral stationary phase covalently bound with a chiral pseudo-18-crown-6 ether for enantiomer separation of amino compounds using a normal mobile phase. Chirality 2005, 17, 142–148. [Google Scholar] [CrossRef] [PubMed]
  16. Cram, D.J.; Cram, J.M. Design of complexes between synthetic hosts and organic guests. Acc. Chem. Res. 1978, 11, 8–14. [Google Scholar] [CrossRef]
  17. Cram, D.J.; Trueblood, K.N. Concept, structure, and binding in complexation. Top. Curr. Chem. 1981, 98, 43–106. [Google Scholar]
  18. Wenzel, T.J.; Freeman, B.E.; Sek, D.C.; Zopf, J.J.; Nakamura, T.; Jin, Y.; Hirose, K.; Tobe, Y. Chiral recognition in NMR spectroscopy using crown ethers and theirYtterbium(III) complexes. Anal. Bioanal. Chem. 2004, 378, 1536–1547. [Google Scholar] [CrossRef] [PubMed]
  19. Kaneda, T.; Hirose, K.; Misumi, S. Chiral azophenolic acerands: Color indicator to judge the absolute configuration of chiral amines. J. Am. Chem. Soc. 1989, 111, 742–743. [Google Scholar] [CrossRef]
  20. Hirose, K.; Goshima, Y.; Wakebe, T.; Tobe, Y.; Naemura, K. Supramolecular method for the determination of absolute configuration of chiral compounds: Theoretical derivatization and a demonstration for phenolic crown ether—2-amino-1-ethanol system. Anal. Chem. 2007, 79, 6295–6302. [Google Scholar] [CrossRef] [PubMed]
  21. Kubo, Y.; Maeda, S.; Tokita, S.; Kubo, M. Colorimetric chiral recognition by a molecular sensor. Nature 1996, 382, 522–524. [Google Scholar] [CrossRef]
  22. Naemura, K.; Takeuchi, S.; Hirose, K.; Tobe, Y.; Kaneda, T.; Sakata, Y. Preparation and enantiomer recognition behaviour of azophenolic crown ethers containing cis-cyclohexane-1,2-diol as the chiral centre. J. Chem. Soc. Perkin Trans. 1995, 213–219. [Google Scholar] [CrossRef]
  23. Van Delden, R.A.; Feringa, B.L. Color indicators of molecular chirality based on doped liquid crystals. Angew. Chem. Int. Ed. 2001, 40, 3198–3200. [Google Scholar] [CrossRef]
  24. Kim, H.N.; Guo, Z.; Zhu, W.; Yoon, J.; Tian, H. Recent progress on polymer-based fluorescent and colorimetric chemosensors. Chem. Soc. Rev. 2011, 40, 79–93. [Google Scholar] [CrossRef] [PubMed]
  25. Sawada, M.; Takai, Y.; Yamada, H.; Hirayama, S.; Kaneda, T.; Tanaka, T.; Kamada, K.; Mizooku, T.; Takeuchi, S.; Ueno, K.; et al. Chiral recognition in host-guest complexation determined by the enantiomer-labeled guest method using fast atom bombardment mass spectrometry. J. Am. Chem. Soc. 1995, 117, 7726–7736. [Google Scholar] [CrossRef]
  26. Sawada, M.; Takai, Y.; Yamada, H.; Nishida, J.; Kaneda, T.; Arakawa, R.; Okamoto, M.; Hirose, K.; Tanaka, T.; Naemura, K. Chiral amino acid recognition detected by electrospray ionization (ESI) and fast atom bombardment (FAB) mass spectrometry (MS) coupled with the enantiomer labelled (EL) guest method. J. Chem. Soc. Perkin Trans. 1998, 2, 701–710. [Google Scholar] [CrossRef]
  27. Finn, M.G. Emerging methods for the rapid determination of enantiomeric excess. Chirality 2002, 14, 534–540. [Google Scholar] [CrossRef] [PubMed]
  28. Hembury, G.A.; Borovkov, V.V.; Inoue, Y. Chirality-sensing supramolecular systems. Chem. Rev. 2008, 108, 1–73. [Google Scholar] [CrossRef] [PubMed]
  29. Jo, H.H.; Lin, C.-Y.; Anslyn, E.V. Rapid optical methods for enantiomeric excess analysis: From enantioselective indicator displacement assays to exciton-coupled circular dichroism. Acc. Chem. Res. 2014, 47, 2212–2221. [Google Scholar] [CrossRef] [PubMed]
  30. Sauvage, J.P. Interlacing molecular threads on transition-metals: Catenands, catenates, and knots. Acc. Chem. Res. 1990, 23, 319–327. [Google Scholar] [CrossRef]
  31. Blanco, M.J.; Jimenez, M.C.; Chambron, J.C.; Heitz, V.; Linke, M.; Sauvage, J.P. Rotaxanes as new architectures for photoinduced electron transfer and molecular motions. Chem. Soc. Rev. 1999, 28, 293–305. [Google Scholar] [CrossRef]
  32. Kawasaki, H.; Kihara, N.; Takata, T. High yielding and practical synthesis of rotaxanes by acylative end-capping catalyzed by tributylphosphine. Chem. Lett. 1999, 10, 1015–1016. [Google Scholar] [CrossRef]
  33. Schalley, C.A.; Weilandt, T.; Bruggemann, J.; Vögtle, F. Hydrogen-bond-mediated template synthesis of rotaxanes, catenanes, and knotanes. In Templates in Chemistry I; Springer: Berlin/Heidelberg, Germany, 2004; pp. 141–200. [Google Scholar] [CrossRef]
  34. Arico, F.; Badjic, J.D.; Cantrill, S.J.; Flood, A.H.; Leung, K.C.F.; Liu, Y.; Stoddart, J.F. Templated synthesis of interlocked molecules. In Templates in Chemistry II; Springer: Berlin/Heidelberg, Germany, 2005; pp. 203–259. [Google Scholar]
  35. Narita, M.; Yoon, I.; Aoyagi, M.; Goto, M.; Shimizu, T.; Asakawa, M. Transition metal(II)-salen and -salophen macrocyclic complexes for rotaxane formation: Syntheses and crystal structures. Eur. J. Inorg. Chem. 2007, 4229–4237. [Google Scholar] [CrossRef]
  36. Harrison, I.T.; Harrison, S. Synthesis of a stable complex of a macrocycle and a threaded chain. J. Am. Chem. Soc. 1967, 89, 5723–5724. [Google Scholar] [CrossRef]
  37. Schill, G.; Zollenko, H. Rotaxane compounds 1. Liebigs Ann. Chem. 1969, 721, 53–74. [Google Scholar] [CrossRef]
  38. Hiratani, K.; Suga, J.; Nagawa, Y.; Houjou, H.; Tokuhisa, H.; Numata, M.; Watanabe, K. A new synthetic method for rotaxanes via tandem claisen rearrangement, diesterification, and aminolysis. Tetrahedron Lett. 2002, 43, 5747–5750. [Google Scholar] [CrossRef]
  39. Hirose, K.; Nishihara, K.; Harada, N.; Nakamura, Y.; Masuda, D.; Araki, M.; Tobe, Y. Highly selective and high-yielding rotaxane synthesis via aminolysis of prerotaxanes consisting of a ring component and a stopper unit. Org. Lett. 2007, 9, 2969–2972. [Google Scholar] [CrossRef] [PubMed]
  40. Sauvage, J.P. From chemical topology to molecular machines (nobel lecture). Angew. Chem. Int. Ed. 2017, 56, 11080–11093. [Google Scholar] [CrossRef] [PubMed]
  41. Stoddart, J.F. Mechanically interlocked molecules (MIMS)-molecular shuttles, switches, and machines (nobel lecture). Angew. Chem. Int. Ed. 2017, 56, 11094–11125. [Google Scholar] [CrossRef] [PubMed]
  42. Feringa, B.L. The art of building small: From molecular switches to motors (nobel lecture). Angew. Chem. Int. Ed. 2017, 56, 11059–11078. [Google Scholar] [CrossRef] [PubMed]
  43. Bordoli, R.J.; Goldup, S.M. An efficient approach to mechanically planar chiral rotaxanes. J. Am. Chem. Soc. 2014, 136, 4817–4820. [Google Scholar] [CrossRef] [PubMed]
  44. Goldup, S.M. Mechanical chirality a chiral catalyst with a ring to it. Nat. Chem. 2016, 8, 404–406. [Google Scholar] [CrossRef] [PubMed]
  45. Nakazono, K.; Takata, T. Chiral interlocked molecule: Synthesis and function. J. Synth. Organ. Chem. Jpn. 2017, 75, 491–502. [Google Scholar] [CrossRef]
  46. Bruns, C.J.; Stoddart, J.F.; Sauvage, J.-P.; Fujita, M. The Nature of the Mechanical Bond: From Molecules to Machines; Wiley: Hoboken, NJ, USA, 2017; pp. 471–554. ISBN 9781119044000. [Google Scholar]
  47. Borsche, W. Ueber die beziehungen zwischen chinonhydrazonen und p-oxyazoverbindungen. (vierte abhandlung): Ueber die condensation von nitroderivaten des phenylhydrazins mit chinonen und chinonoximen der benzolreihe. Liebigs Ann. Chem. 1907, 357, 171–191. [Google Scholar] [CrossRef]
  48. Naemura, K.; Asada, M.; Hirose, K.; Tobe, Y. Preparation and enantiomer recognition of chiral azophenolic crown ethers having three chiral barriers on each of the homotopic faces. Tetrahedron Asymmetry 1995, 6, 1873–1876. [Google Scholar] [CrossRef]
  49. Naemura, K.; Takeuchi, S.; Sawada, M.; Ueno, K.; Hirose, K.; Tobe, Y.; Kaneda, T.; Sakata, Y. Synthesis of azophenolic crown ethers of cs symmetry incorporating cis-1-phenylcyclohexane-1,2-diol residues as a steric barrier and diastereotopic face selectivity in complexation of amines by their diastereotopic faces. J. Chem. Soc. Perkin Trans. 1995, 1, 1429–1435. [Google Scholar] [CrossRef]
  50. Berova, N.; Di Bari, L.; Pescitelli, G. Application of electronic circular dichroism in configurational and conformational analysis of organic compounds. Chem. Soc. Rev. 2007, 36, 914–931. [Google Scholar] [CrossRef] [PubMed]
  51. Stoncius, S.; Bagdziunas, G.; Malinauskiene, J.; Butkus, E. A study of planar chromophores in dichromophoric molecules by circular dichroism spectroscopy. Chirality 2008, 20, 337–343. [Google Scholar] [CrossRef] [PubMed]
  52. Hirose, K. A practical guide for the determination of binding constants. J. Incl. Phenom. 2001, 39, 193–209. [Google Scholar] [CrossRef]
  53. Hirose, K. Quantitative analysis of binding properties. In Analytical Methods in Supramolecular Chemistry; Schalley, C.A., Ed.; John Wiley & Sons: Weinheim, Germany, 2012; pp. 27–66. ISBN 9783527644131. [Google Scholar]
  54. Requirements for an application to a chromatography: Resolution factor (α) for baseline separation (Resolution (R) > 1.25, 99.4% separation) through normal size column (Number of theoretical plates (N) = 5000) is around 1.10 (Retention factor (k’2) = 10) where ratio of binding constant corresponds to resolution factor (α) of HPLC separation on chiral column.
Symmetry 10 00020 g001 550
Figure 1. Rotaxane specific chirality by a combination of C∞v axle component and Cs ring component.
Figure 1. Rotaxane specific chirality by a combination of C∞v axle component and Cs ring component.
Symmetry 10 00020 g001
Symmetry 10 00020 sch001 550
Scheme 1. Key step of our rotaxane synthesis of covalent method via SN2 reaction with a prerotaxane with planar chirality and stopper unit.
Scheme 1. Key step of our rotaxane synthesis of covalent method via SN2 reaction with a prerotaxane with planar chirality and stopper unit.
Symmetry 10 00020 sch001
Symmetry 10 00020 sch002 550
Scheme 2. Synthetic scheme of 5 via aminolysis of prerotaxane 3.
Scheme 2. Synthetic scheme of 5 via aminolysis of prerotaxane 3.
Symmetry 10 00020 sch002
Symmetry 10 00020 g002 550
Figure 2. HPLC chromatogram of prerotaxane (rac)-3, and resolved 31st and 32nd, detected by UV at 330 nm. (Conditions; Column: DAICEL CHIRALPAK IA (10 mmφ × 250 mm); mobile phase: hexane/dichloromethane = 50/50; flow rate = 1.0 mL/min; temperature: 30 °C).
Figure 2. HPLC chromatogram of prerotaxane (rac)-3, and resolved 31st and 32nd, detected by UV at 330 nm. (Conditions; Column: DAICEL CHIRALPAK IA (10 mmφ × 250 mm); mobile phase: hexane/dichloromethane = 50/50; flow rate = 1.0 mL/min; temperature: 30 °C).
Symmetry 10 00020 g002
Symmetry 10 00020 g003 550
Figure 3. (a) Circular dichroism spectra of enantiomerically pure prerotaxanes 31st (red) and 32nd (blue) in CHCl3 at room temperature ([31st] = 65.9 µM, [32nd] = 76.1 µM, cell length = 1.0 cm); (b) Uv-visible spectrum of 32nd under same condition.
Figure 3. (a) Circular dichroism spectra of enantiomerically pure prerotaxanes 31st (red) and 32nd (blue) in CHCl3 at room temperature ([31st] = 65.9 µM, [32nd] = 76.1 µM, cell length = 1.0 cm); (b) Uv-visible spectrum of 32nd under same condition.
Symmetry 10 00020 g003
Symmetry 10 00020 g004 550
Figure 4. 1H NMR (270 MHz, C6D6) spectra of (a) reaction mixture at 0 min (prerotaxane 32nd), (b) 32 min, (c) 92 min, and (d) ring 1 for reference. The descriptors refer to the signals representing rotaxane (HA(5)), dumbbell (HA(6)), and ring1 (Ha and Hb) protons are shown in Scheme 1.
Figure 4. 1H NMR (270 MHz, C6D6) spectra of (a) reaction mixture at 0 min (prerotaxane 32nd), (b) 32 min, (c) 92 min, and (d) ring 1 for reference. The descriptors refer to the signals representing rotaxane (HA(5)), dumbbell (HA(6)), and ring1 (Ha and Hb) protons are shown in Scheme 1.
Symmetry 10 00020 g004
Symmetry 10 00020 g005 550
Figure 5. 1H NMR spectra of dumbbell 6 (a), chiral rotaxane 5 (b), and ring 1 (c) in CDCl3 at 30 °C (400 MHz).
Figure 5. 1H NMR spectra of dumbbell 6 (a), chiral rotaxane 5 (b), and ring 1 (c) in CDCl3 at 30 °C (400 MHz).
Symmetry 10 00020 g005
Symmetry 10 00020 g006 550
Figure 6. HPLC chromatograms of rotaxanes 51st (red), 52nd (blue) detected by UV at 254 nm. (Column: CHIRALPAK IA (4.6 mmφ × 150 mm); mobile phase: hexane/dichloromethane /trifluoroacetic acid = 80/20/0.1; flow rate = 0.8 mL/min; temperature: 30 °C).
Figure 6. HPLC chromatograms of rotaxanes 51st (red), 52nd (blue) detected by UV at 254 nm. (Column: CHIRALPAK IA (4.6 mmφ × 150 mm); mobile phase: hexane/dichloromethane /trifluoroacetic acid = 80/20/0.1; flow rate = 0.8 mL/min; temperature: 30 °C).
Symmetry 10 00020 g006
Symmetry 10 00020 g007 550
Figure 7. (a) Circular dichroism spectra of enantiomerically pure rotaxanes 51st (red) and 52nd (blue) in CHCl3 at room temperature ([51st] = 90.7 µM, [52nd] = 94.6 µM, cell length = 1.0 cm); (b) Uv-visible spectrum of 52nd under same condition.
Figure 7. (a) Circular dichroism spectra of enantiomerically pure rotaxanes 51st (red) and 52nd (blue) in CHCl3 at room temperature ([51st] = 90.7 µM, [52nd] = 94.6 µM, cell length = 1.0 cm); (b) Uv-visible spectrum of 52nd under same condition.
Symmetry 10 00020 g007
Symmetry 10 00020 g008 550
Figure 8. UV-Vis spectral and color changes of rotaxane 52nd with (R)-PGO in CHCl3: (a) UV-Vis spectra and (b) corresponding pictures: rotaxane 5 (41.5 µM) ((a) yellow line and (b) yellow solution) and same solutions containing different (R)-PGO concentration 899 µM, 1.35, 1.87, 2.62, 3.75, 5.99, 8.99, and 12.7 mM in order shown by arrows at 17 °C.
Figure 8. UV-Vis spectral and color changes of rotaxane 52nd with (R)-PGO in CHCl3: (a) UV-Vis spectra and (b) corresponding pictures: rotaxane 5 (41.5 µM) ((a) yellow line and (b) yellow solution) and same solutions containing different (R)-PGO concentration 899 µM, 1.35, 1.87, 2.62, 3.75, 5.99, 8.99, and 12.7 mM in order shown by arrows at 17 °C.
Symmetry 10 00020 g008
Table
Table 1. Binding constants of 52nd for PGO obtained by 1H NMR titration experiments.
Table 1. Binding constants of 52nd for PGO obtained by 1H NMR titration experiments.
GuestsK/L mol−1KR/KS
(R)-PGO(1.25 ± 0.03) × 1021.48
(S)-PGO(8.47 ± 0.40) × 101
In CDCl3 at 30 °C, 400 MHz.

Share and Cite

MDPI and ACS Style

Hirose, K.; Ukimi, M.; Ueda, S.; Onoda, C.; Kano, R.; Tsuda, K.; Hinohara, Y.; Tobe, Y. The Asymmetry is Derived from Mechanical Interlocking of Achiral Axle and Achiral Ring Components –Syntheses and Properties of Optically Pure [2]Rotaxanes–. Symmetry 2018, 10, 20. https://doi.org/10.3390/sym10010020

AMA Style

Hirose K, Ukimi M, Ueda S, Onoda C, Kano R, Tsuda K, Hinohara Y, Tobe Y. The Asymmetry is Derived from Mechanical Interlocking of Achiral Axle and Achiral Ring Components –Syntheses and Properties of Optically Pure [2]Rotaxanes–. Symmetry. 2018; 10(1):20. https://doi.org/10.3390/sym10010020

Chicago/Turabian Style

Hirose, Keiji, Masaya Ukimi, Shota Ueda, Chie Onoda, Ryohei Kano, Kyosuke Tsuda, Yuko Hinohara, and Yoshito Tobe. 2018. "The Asymmetry is Derived from Mechanical Interlocking of Achiral Axle and Achiral Ring Components –Syntheses and Properties of Optically Pure [2]Rotaxanes–" Symmetry 10, no. 1: 20. https://doi.org/10.3390/sym10010020

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop