Chiral supramolecular compounds comprising naphthalene-1,5-disulfonic acid and various α-amino acids: influence of substituents of α-amino acids on the structures, circular dichroism and luminescent properties

Self assembly of naphthalene-1,5-disulfonic acid (1,5-H2NDS) and 11 chiral α-l-amino acids generates 12 chiral supramolecular compounds, namely, 2(HAla)+·(NDS)2− (1), 4(HSer)+·2(NDS)2−·2(H2O) (2), 2(HPhe)+·(NDS)2− (3), 2(HTyr)+·(NDS)2− (4), 2(H2Cys)2+·2(NDS)2−·2(H2O) (5), 2(HVal)+·(NDS)2−·2(Val)·4(H2O) (6), 2(HThr)+·(NDS)2− (7), 2(HLeu)+·(NDS)2−·2(H2O) (8), 2(HLle)+·(NDS)2−·(H2O) (9), 2(HArg)+·(NDS)2−·3(H2O) (10), (H2His)2+·(NDS)2−·2(H2O) (11), and 2(H2His)2+·2(NDS)2−·6(H2O) (12), which have been characterized by elemental analysis, IR, TG, PL, circular dichroism (CD), powder and single-crystal X-ray diffraction. Structural analyses indicate that substituents of α-amino acids influence the supramolecular patterns formed by –SO3 and –NH3 groups and supramolecular networks. Compounds 1–12 crystallize in different chiral P1, P212121, P32 and P21 space groups, respectively. The patterns formed by –SO3 and –NH3 groups are more abundant, such as 1D double chain in 1, 3 and 4, [(SO3)4(NH3)4] cage in 2, [(SO3)4(NH3)4] motif in 5, [(SO3)2(NH3)4] motif in 6, 1D cylinder in 7, [(SO3)(NH3)] motif in 8, 11 and 12, 1D single and double chain in 9, as well as [(SO3)2(NH3)2] motif in 10. Compounds 1–9 exhibit different pillared layered networks, in which weak π⋯π and C–H⋯π interactions are detected except for compounds 4, 6, 8 and 9. Compound 11 presents an interesting network constructed from the interconnection of two types of DNA shaped double helixes. It should be indicated that exposure of 12 under atmosphere can transform into compound 11, in which the configuration of H2His2+ cations varies from R to S. CD spectra indicate that the solid samples of compounds 3, 4 and 6–11 display dichroic signals in their CD spectra. Luminescent investigation reveals that compounds 1–11 exhibit stronger emission than the 1,5-H2NDS with the emission maximum varying from 342 to 413 nm.

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