Hierarchical communication of chirality for aromatic oligoamide sequences

The communication of chirality at a molecular and supramolecular level is the fundamental feature capable of transmitting and amplifying chirality information. Yet, the limitation of one-step communication mode in many artificial systems has precluded the ability of further processing the chirality information. Here, we report the chirality communication of aromatic oligoamide sequences within the interpenetrated helicate architecture in a hierarchical manner, specifically, the communication is manipulated by three sequential steps: (i) coordination, (ii) concentration, and (iii) ion stimulus. Such approach enables the information to be implemented progressively and reversibly to different levels. Furthermore, the chiral information on the side chains can be accumulated and transferred to the helical backbones of the sequences, resulting in that one of ten possible diastereoisomers of the interpenetrated helicate is finally selected. The circular dichroism experiments with a mixture of chiral and achiral ligands demonstrate a cooperative behavior of these communications, leading to amplification of chiral information.


General methods
All chemicals and solvents were purchased from commercial suppliers and were used without further purification unless otherwise specified. Dichloromethane (DCM) and N,N-diisopropylethylamine (DIEA) was distilled over CaH 2 prior to use. Column chromatography was carried out on Merck GEDURAN Si60 (40-63 µm).
NMR spectra were recorded on Bruker AVANCE 600 (600 MHz), and Bruker AVANCE 400 (400 MHz) spectrometers. The solvent signals were assigned by Fulmer et al. 1  High-resolution electrospray ionization mass spectrometry (ESI-MS) was performed on a micro TOF II instrument featuring a Z spray source with electrospray ionization and modular LockSpray interface.
CD studies were recorded using a 2 mm pathlength cell on a Jasco J-810 spectropolarimeter. were prepared accordingly to Supplementary Reference 3. Compound 6. To a suspension of 2,5-dimethoxy-4-nitrobenzenamine (3.96 g, 20 mmol) and compound 5 (2.83 g, 20 mmol) in dry DCM (60 mL) under nitrogen, dry DIEA (17.47 ml, 100 mmol) were added slowly. The reaction mixture was stirred at room temperature for 2 days. After that time, the reaction mixture was poured into 300ml petroleum ether to effect precipitation, the precipitate was obtained by filtration. And it was then washed with water and ice-cold MeOH, dried and desiccated to yield compound 6 as a pale yellow powder (4.79 g, 79%). 1 3.90 (s, 6 H). 13  Compound 9. Compound 8 (0.63 g, 2.14 mmol) was dissolved in ethanol/H 2 O (10 mL/2 mL), to which KOH (1.20 g, 21.40 mmol) was added in the surrounding atmosphere. The mixture was allowed to stir at room temperature for overnight. Then ethanol was removed in vacuo and the aqueous layer was brought to pH 3 ~ 4 by slow addition of 1 M HCl aqueous solution. The resulting mixture was extracted three times with EtOAc, and the combined organic phases, which washed by saturated NaCl aqueous solution and dried over anhydrous MgSO 4 and evaporated to yield compound 9 as a white solid (0.46 g, 90%), which was directly used in the next step without further purification. 1  Ligand L. Compound 9 (0.15 g, 0.64 mmol), compound 7 (0.37 g, 1.34 mmol) and (benzotriazol-1yloxy)tripyrrolidinophosphonium hexafluorophosphate (0.83 g, 1.60 mmol) was dissolved in dry DMF (10 mL) under nitrogen, dry DIEA (0.55 ml, 3.2 mmol) was added. The reaction mixture was stirred at room temperature for 2 days. Then the reaction mixture was poured into 150ml water to effect precipitation. The precipitate was collected by filtration, which was purified by washing with water, ice-cold MeOH and CH 3 CN, dried and desiccated to yield compound L 1 as a yellow powder (0.33 g, 69%). 1    which NaOH (0.53 g, 13.30 mmol) was added in the surrounding atmosphere. The mixture was allowed to stir at room temperature for overnight. Then ethanol was removed in vacuo and the aqueous layer was brought to pH 5 ~ 6 by slow addition of 1 M HCl aqueous solution. The resulting mixture was extracted three times with DCM, and the combined organic phases, which washed by saturated NaCl aqueous solution and dried over anhydrous MgSO 4 and evaporated to yield compound 13 as a white solid (0.35 g, 89%), which was directly used in the next step without further purification. Ligand L R (or L S ). Compound 13 (0.17 g, 0.58 mmol), compound 7 (0.35 g, 1.28 mmol) and (benzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate (0.76 g, 1.46 mmol) was dissolved in dry DMF (10 mL) under nitrogen, dry DIEA (0.51 ml, 2.90 mmol) was added. The reaction mixture was stirred at room temperature for 2 days. Then the reaction mixture was poured into 150ml water to effect precipitation. The precipitate was collected by filtration, which was purified by washing with water, ice-cold MeOH and CH 3 CN, dried and desiccated to yield compound L R (or L S ) as a yellow powder (0.35 g, 75%). 1     For the equilibrium shown in Eq. 1, the equilibrium constant Ka of the dimer is given by Eq. 2.

Method for definition of P/M helicity
The azimuthal angle θ is commonly used to describe the helicity for M 2 L 4 helicates. 5 A structure is qualified to be a helicate with helicity when the azimuthal angle θ is non zero. This method is based on the torsion angle of coordinating segments with respect to the Pd-Pd axis (i.e., N pyridine -Pd-Pd-N pyridine angle), not just in view of the amide torsion angle.
Although it is convenient to use this parameter to describe the helicity for M 2 L 4 helicates, it has some drawbacks. In our case, the ligands can be subjected to a distortion or twisting in the center and partitioned into two sections, each of which can thus coordinate the metal ion to different chiralities (P and M), leading to a meso complex. The azimuthal angle is equal to zero, but the ligands still show the helical conformation. In order to better assign the helicity in our system, it is necessary to horizontally divide a monomeric helicate into two equal parts and quantify the helicity in a piecewise manner. Therefore, to characterize the helicity, it needs two symbols (XX, X = P or M) for a monomeric helicate, and four symbols (XXXX, X = P or M) for a dimeric helicate, given the consistency of twisting of ligands in the individual helicate. The approach to assign the helicity is presented as follow: 1) Determine the azimuthal angle.
2) If the azimuthal angle is not zero, observe the angle phase. When it is clockwise spin from the topto-down view, the corresponding segment is defined with M helicity, and assigned to P helicity when angle phase is anticlockwise.
3) If the azimuthal angle is zero, observe the rotation direction of the twisted ligand around the metal.
When it is clockwise from the top-to-down view, the corresponding segment is defined with M helicity, and assigned to P helicity when the direction is anticlockwise.
This method for P/M helicity definition is consistent with the description in the main text where helicity is defined by the helical orientation of each Pd 2+ cation with respect to the center of the ligand.    Table   1. The models revealed that the isomers (PPPP, PMMP) are more stable than other isomers. It seems the helicate dimerization prefer occurring between two monomeric helicates with the same helicity rather than with the different helicity. Moreover, the tight packing of the aromatic rings could be observed when the dimeric helicates adopted the same ligand twisting at the intertwined section. These The structures were solved by direct methods using SHELXT 8 and refined against F 2 on all data by full-matrix least squares with SHELXL 9 following established refinement strategies. 10 Most of the non-H atoms were refined with anisotropic temperature parameters, the disordered ones were refined with isotropic temperature parameters. All hydrogen atoms, were included into the model at geometrically calculated positions and refined using a riding model. SHELX ISOR and DELU restraints were used in the refinement strategy in order to reduce the anisotropic displacement parameters of the side chains. DFIX instructions were used to geometrically restraint most of the side chains. The contribution of the electron density associated with disordered solvent molecules, which could not be modelled with discrete atomic positions were handled using the SQUEEZE 11 routine in PLATON. 12,13 Crystallographic data have been deposited with the CCDC, under deposition number CCDC 1893706.   Table 3. The azimuthal angles all show the anticlockwise spin from the top-to-down view, indicating all the ligands have a coincident helicity (i.e., P helicity).   1). Signals of the monomeric helicate are marked with black circles. Signals of 2 and of 4S are marked with empty white circles and black triangles, respectively. And CD spectra of these complexes are showed in Figure 5c.