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Models of four-ring polyamide subunits calculated by density functional theory. Angles indicate the dihedral angles between each Py or Im and the contiguous amide (N1-C2-CO-O). (A) Py-Py-Py-Py. Dotted line indicates the N-to-N distance at both ends of the four-ring polyamide. (B) Im-Py-Py-Py, (C) Py-Py-Im-Py, (D) Im-Py-Im-Py and (E) Im-Im-Im-Im.
