Zhixue Zhu

Sequence-selective assembly of tweezer molecules on linear templates enables frameshift-reading of sequence information

Information storage and processing is carried out at the level of individual macromolecules in biological systems, but there is no reason, in principle, why synthetic copolymers should not be used for the same purpose. Previous work has suggested that monomer sequence information in chain-folding synthetic copolyimides can be recognized by tweezer-type molecules binding to adjacent triplet sequences, and we show here that different tweezer molecules can show different sequence selectivities. This work, based on 1H NMR spectroscopy in solution and on single-crystal X-ray analysis of tweezer–oligomer complexes in the solid state, provides the first clear-cut demonstration of polyimide chain-folding and adjacent-tweezer binding. It also reveals a new and entirely unexpected mechanism for sequence recognition, which, by analogy with a related process in biomolecular information processing, may be termed ‘frameshift-reading’. The ability of one particular tweezer molecule to detect, with exceptionally high sensitivity, long-range sequence information in chain-folding aromatic copolyimides is readily explained by this novel process. Monomer-sequence information in synthetic copolyimides can be recognized by tweezer-type molecules binding to adjacent triplet-sequences through complementary aromatic π–π-stacking, with different tweezer molecules showing different sequence-selectivities. Single-crystal X-ray analysis of tweezer–oligomer complexes confirms the tweezer-binding selectivity, and NMR spectroscopy reveals a new mechanism (‘frameshift-reading’) for tweezer-based sequence recognition in chain-folding copolyimides.

Induced‐Fit Binding of π‐Electron‐Donor Substrates to Macrocyclic Aromatic Ether Imide Sulfones: A Versatile Approach to Molecular Assembly

Novel macrocyclic receptors that bind electron-donor aromatic substrates through pi-stacking donor-acceptor interactions are obtained by cycloimidisation of an amine-functionalised aryl ether sulfone with pyromellitic and 1,4,5,8-naphthalenetetracarboxylic dianhydrides. These macrocycles can form complexes with a wide variety of pi-donor substrates, including tetrathiafulvalene, naphthalene, anthracene, pyrene, perylene and functional derivatives of these polycyclic hydrocarbons. The resulting supramolecular assemblies range from simple 1:1 complexes to [2]- and [3]pseudorotaxanes and even (as a result of crystallographic disorder) an apparent polyrotaxane. Direct five-component self-assembly of a metal-centred [3]pseudorotaxane is also observed on complexation of a macrocyclic ether imide with 8-hydroxyquinoline in the presence of palladium(II) ions. Binding studies in solution were carried out by using (1)H NMR and UV/Vis spectroscopy, and the stoichiometries of binding were confirmed by Job plots based on the charge-transfer absorption bands. The highest association constants were found for strong pi-donor guests with large surface areas, notably perylene and 1-hydroxypyrene, for which K(a) values of 1.4x10(3) and 2.3x10(3) M(-1), respectively, were found. Single-crystal X-ray analyses of the receptors and their derived complexes reveal large induced-fit distortions of the macrocyclic frameworks as a result of complexation. These structures provide compelling evidence for the existence of strong attractive forces between the electronically complementary aromatic pi systems of host and guest.

Microfabrication of high-performance aromatic polymers as nanotubes or fibrils by in situ ring-opening polymerisation of macrocyclic precursors

Melt-phase nucleophilic ring-opening polymerisation of macrocyclic aromatic ethers and thioethers at high temperatures within the cylindrical pores of an anodic-alumina membrane, followed by dissolution of the template, enables replication of the membranes internal pore structure and so affords high-performance aromatic polymers with well-defined fibrillar or tubular morphologies.

Bis(hydroxy-isoindolinone)s: synthesis, stereochemistry, polymer chemistry, and supramolecular assembly.

Pseudoacid chlorides of 2,5-bis(4-fluorobenzoyl) terephthalic acid and 4,6-bis(4-fluorobenzoyl) isophthalic acid condense with primary amines to afford diastereomeric bis(hydroxyindolinone)s in good isolated yields and with diamines to give high molecular weight poly(hydroxyindolinone)s. Bis-N-pyrenemethyl bis(hydroxyindolinone)s assemble, even in dipolar solvents such as DMSO, with macrocyclic diimide-sulfones to give [3]pseudorotaxanes stabilized by electronically complementary aromatic pi-pi-stacking and shape-complementary van der Waals interactions.

Quadruple stacking of macrocyclic viologen radical-cations

Abstract The solid state structures of the di-cationic (1a) and radical mono-cationic (1b) redox forms of a 4,4′-bipyridinium (viologen) containing macrocycle have been established by single crystal X-ray analysis. Formation of the radical cation has a dramatic effect on the molecular structure of the macrocycle. Addition of an electron to 1a both decreases the diameter of the ring cavity (from 8.5 to 7.8 Å) and drastically flattens the torsion angle between the two pyridinium residues in the viologen, reducing it from 48° to either 3° or 9° (two independent molecules). Moreover, a close association of these near-planar radical cation units drives the formation of a tetrameric supramolecular structure in the solid state.

Tweezers and zigzags - models for sequence specific tweezer-polymer interactions

Solid-State Reactivity in Halogen-Bonded CoCrystals. Pierangelo Metrangolo, Serena Biella, Gabriella Cavallo, Tullio Pilati, Giuseppe Resnati, Giancarlo Terraneo. NFMLab D.C.M.I.C. “Giulio Natta”, Politecnico di Milano, Via L. Mancinelli 7, 20131 Milan, Italy. CNST IIT@POLIMI, Politecnico di Milano, Via G. Pascoli 70/3, 20133 Milan, Italy. C.N.R. I.S.T.M., University of Milan, Via C. Golgi 19, 20133 Milan, Italy. E-mail: pierangelo.metrangolo@polimi.it