Halogen bonding-driven formation of supramolecular macrocycles and double helix

Halogen bonding has been used to hold two hydrogen bonded aromatic amide foldamers to form supramolecular macrocycles.     

Exo-coordination-based supramolecular silver(I) complexes of S2O macrocycles: effect of ligand isomerism on the structural diversity

An isomeric series of S2O macrocycles incorporating a xylyl group at the ortho (L1), meta (L2), and para (L3) positions were employed to examine the influence of the ring rigidity on silver(I) coordination modes in resulting supramolecular complexes (1-3); L1 and L3 afforded sandwich (1; Ag:L1 = 1:2) and infinite 1-D (3) complexes, respectively; otherwise, L2 gave the 1-D polymer (2a), 2:3 club sandwich (2b), and unique 2:4 bridged dinuclear complex (2c) complexes, in which their topologies vary with the solvent used.     

Ranging correlated motion (1.5 nm) of two coaxially arranged rotors mediated by helix inversion of a supramolecular transmitter

For a long-range transmission of motion between two movable parts apart from each other, transmitters that can precisely correlate these two motions should be properly incorporated into the system. However, such a motional relay is yet to be realized in artificial systems because of the lack of reliable methodologies for arranging a discrete number of motional parts. Herein, we report a correlated motion of two rotor molecules, which are coaxially arranged at a distance of 1.5 nm, through either Ag (+)- or Hg (2+)-assembled helical transmitters, leading to different frequencies of synchronized motion. A helix inversion in the transmitter was proven to strongly correlate the motions of both terminals. The X-ray analysis of the entity determined a quadruple-decker nonanuclear structure of the metal complex comprising two terminal rotor-like ligands closely attached to a central transmitter moiety. (1)H NMR analysis fully demonstrated the synchronized motion of the two rotors coaxially stacked and connected through the transmitter. Since the transmitter is composed of simple helical repeating units, the principle of helix inversion would be an efficient and widely applicable strategy for the long-range transmission of molecular motion.     

Molecular chairs, zippers, zigzag and helical chains: chemical enumeration of supramolecular isomerism based on a predesigned metal-organic building-block

A predesigned metal-organic building-block [Cu(I)(2-pytz)](2-Hpytz = 3,5-di-2-pyridyl-1,2,4-triazole) has been successfully used to synthesize four genuine supramolecular isomers.     

Solution and solid state studies of a triangle-square equilibrium: anion-induced selective crystallization in supramolecular self-assembly

We report that an equilibrium mixture of triangular and square supramolecular species results when the flexible, ditopic donor unit, trans-bis(4-pyridyl)ethylene, is reacted with the ditopic acceptor unit, cis-(Me(3)P)(2)Pt(OTf)(2), in a one-to-one ratio. Both products are characterized in solution, by way of multinuclear NMR, and in the solid state, via X-ray crystallography. The effects of water and anions, cobalticarborane versus triflate, on the equilibrium are probed. The selective crystallization of either of the two species can be accomplished via the appropriate choice of solvents and ratio of anions present in the system. The dominant species in solution is not always consistent with the most prevalent species in the solid state.     

The supramolecular isomerism based on argentophilic interactions: the construction of helical chains with defined right-handed and left-handed helicity

The reactions of racemic and enantiopure macrocyclic compounds [Ni(alpha-rac-L)](ClO(4))(2) (containing equal amounts of SS and RR enantiomers), [Ni(alpha-SS-L)](ClO(4))(2), and [Ni(alpha-RR-L)](ClO(4))(2) with K[Ag(CN)(2)] in acetonitrile/water afford three 1D helical chains of {[Ni(f-rac-L)][Ag(CN)(2)](2)}(n) (1), {[Ni(f-SS-L)](2)[Ag(CN)(2)](4)}(n) (Delta-2), and {[Ni(f-RR-L)](2)[Ag(CN)(2)](4)}(n) (Lambda-2); one dimer of [Ni(f-rac-L)][Ag(CN)(2)](2) (3); and one trimer of [Ni(f-rac-L)Ag(CN)(2)](3).(ClO(4))(3) (4) (L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane). Compounds 1, Delta-2, Lambda-2, and 3, which are supramolecular isomers, are constructed via argentophilic interactions. In 1, [Ni(f-RR-L)][Ag(CN)(2)](2) enantiomers alternately connect with [Ni(f-SS-L)][Ag(CN)(2)](2) enantiomers through intermolecular argentophilic interactions to form a 1D meso-helical chain, and the 1D chains are further connected through the interchain hydrogen bonds to generate a 2D network. When chiral [Ni(alpha-SS-L)](ClO(4))(2) and [Ni(alpha-RR-L)](ClO(4))(2) were used as building blocks, two supramolecular stereoisomers of Delta-2 and Lambda-2 were obtained, which show the motif of homochiral right-handed and left-handed helical chains, respectively, and the 1D homochiral helical chains are linked by the interchain hydrogen bonds to form a 3D structure. In 3, a pair of enantiomers of [Ni(f-RR-L)][Ag(CN)(2)](2) and [Ni(f-SS-L)][Ag(CN)(2)](2) connect with each other through intermolecular argentophilic interactions to form a dimer. The reaction of [Ni(alpha-rac-L)](ClO(4))(2) with K[Ag(CN)(2)] in acetonitrile gives a trimer of 4; each trimer is chiral with unsymmetrical RR, RR, and SS, or RR, SS, and SS configurations. The homochiral nature of Delta-2 and Lambda-2 was confirmed by the results of solid circular dichroism spectra measurements. The solid samples of 1-4 show strong fluorescent emissions at room temperature.     

Triple-stranded helices and zigzag chains of copper(I) 2-ethylimidazolate: solvent polarity-induced supramolecular isomerism

The solvent effect of different polarities in hydro(solvo)thermal reaction of Cu(II) and 2-ethylimidazole leads to the generation of two supramolecular isomers of triple-stranded helical and zigzag chain-like structures of Cu(I) 2-ethylimidazolate.     

X-ray crystallographic signature of supramolecular triple helix formation from a water soluble synthetic tetrapeptide

Single crystal X-ray diffraction studies on the water soluble, synthetic tetrapeptide Tyr(1)-Aib(2)-Tyr(3)-Val(4) with a non-coded amino acid residue (Aib: [small alpha]-amino isobutyric acid) reveal that the peptide adopts an "S"-shaped molecular structure which self-assembles to form a supramolecular triple helix using various non-covalent interactions including water mediated hydrogen bonds in the solid state.     

Conformational effect of 2,6-bis(imidazol-1-yl)pyridine on the self-assembly of 1D coordination chains: spontaneous resolution, supramolecular isomerism, and structural transformation

The achiral 2,6-bis(imidazol-1-yl)pyridine (L) was used as the ditopic organic tecton for the formation of coordination polymers with Zn(II) ions. Hydrothermal reaction between L and ZnX2 (X=Br, Cl) afforded spontaneous resolved double helical motifs in ZnLCl2.0.5H2O (1) and ZnLBr2.0.25H2O (2). In the homochiral crystals of 1a and 2a, the helices are of M-helicity, whereas, in 1b and 2b, they are of P-helicity. In contrast, solvothermal reaction between L and ZnCl2 in dried DMF afforded achiral ZnLCl2 (3a), which exhibits a zigzag polymeric motif. An achiral polymorph 3b which contains 21 helical chains was obtained in wet DMF. The formation of different 1D motifs was related to the conformations of L. All these compounds were characterized by infrared spectroscopy, elemental analyses, and single-crystal X-ray diffraction. As revealed by thermal gravimetric analysis and powder X-ray diffraction study, the homochiral motif in 1 was stable even upon removal of guest water molecules. Contrastingly, structural transformation from 3a or 3b to 1 is possible upon hydration.     

Conformational isomerism in 1,2-di-o-tolylnaphthalenes: selective rotation of the 2-aryl ring

Two derivatives (X=Cl, CN) of 1,2-ditolylnaphthalene were prepared as models to investigate their conformational behavior that could involve rotation of either of the tolyl rings. The existence of anti and syn atropisomers was evident from their ¹H NMR spectra at room temperature indicating two pairs of well-resolved singlets for the methyl protons. Dynamic ¹H NMR studies estimated the rotation barrier to be about 76-82 kJ mol⁻¹, a value consistent with selective rotation of the 2-tolyl ring in the conformation inter-conversion.     

Inducing effect of additive agents on coordination assembly of silver(I) nitrate with 3,5-bis(2-pyridyl)-4-amino-1,2,4-triazole: supramolecular isomerism and interconversion

By using different organic acids as additive agents, hydrothermal reactions of AgNO(3) with 3,5-bis(2-pyridyl)-4-amino-1,2,4-triazole (2-bpt) lead to formation of two conformational polymorphs of [Ag(2-bpt)](NO(3)) with bimetallocyclic and 1-D helical coordination patterns. Interconversion between the two supramolecular isomers can be achieved under proper conditions, which will pass through the same intermediate state.     

Synthesis and electrogenerated chemiluminescence of donor-substituted phenylquinolinylethynes and phenylisoquinolinylethynes: effect of positional isomerism

In furtherance of our research on the design, synthesis and study of electrogenerated chemiluminescence (ECL) of new donor substituted phenylquinolinylethynes, we report here more new series with the aim of studying the effect of positional isomerism on their overall photophysical properties with a special focus on ECL. For this study we have chosen 2-, 3-, and 4-(p-substituted phenyl)ethynylquinolines, and 1- and 4-(p-substituted phenyl)ethynylisoquinolines. These ethynes were synthesized in good yields by modified Sonogashira coupling of the corresponding terminal alkyne with the respective haloquinolines. The photophysical properties and ECL were studied in acetonitrile solvent and the various results are discussed.     

Synthesis and supramolecular assemblies of bipolar archaeal glycolipid analogues containing a cis-1,3-disubstituted cyclopentane ring

Unsymmetrical archaeal tetraether glycolipid analogues 1-2 incorporating a 1,3-disubstituted cyclopentane ring into the bridging chain have been synthesized. The cyclopentane has been introduced with a totally controlled cis configuration, either into the middle of the aliphatic chain or at three methylene groups from the glycerol unit linked to the bulkier disaccharide residue. Freeze-fracture and cryotransmission electron microscopy experiments clearly demonstrated unprecedented glycolipid supramolecular organizations involving two-by-two monolayer associations coupled with interconnection and fusion phenomena. Furthermore, a significant difference in the hydration properties and in the lyotropic liquid crystalline behavior of bipolar lipids 1-2 was found depending on the position of the cyclopentane residue.     

Novel supramolecular isomerism in coordination polymer synthesis from unsymmetrical bridging ligands: solvent influence on the ligand placement orientation and final network structure

The assembly of Co(NCS)(2) with 1-methyl-1'-(3-pyridyl)-2-(4-pyridyl)ethene (L(1)) exhibits a novel supramolecular isomerism of [Co(L(1))(2)(NCS)(2)](infinity) caused by different placement orientation of L(1) around metal centers. The reaction in MeOH/H(2)O and EtOH/H(2)O resulted in a double chain structure of 1, and that in EtOH/CH(3)NO(2) led to an open framework structure of 2. The reaction in MeOH/CH(3)NO(2) solvent system concomitantly afforded 1 and 2. The assemblies of 1-(3-pyridyl)-2-(4-pyrimidyl)ethene (L(2)) with Co(NCS)(2) created the water-coordinated complexes of Co(L(2))(2)(H(2)O)(2)(NCS)(2) (3 and 4), an MeOH coordinated complex of Co(L(2))(2)(H(2)O)(2)(NCS)(2) (5), and an open framework coordination polymer of [Co(L(1))(2)(NCS)(2)](infinity) (6) depending on the reaction solvent system. From these observations, it is suggested that in the formation of 1, the solvent-coordinated intermediate species would be generated first and its trans coordination configuration should define the placement orientation of L(1) in the resulting polymer of 1. On the other hand, it is presumed that the solvent-coordinated intermediate would not be produced during the formation of 2 due to the weaker coordination ability of EtOH and CH(3)NO(2) molecules. The open framework coordination polymers of 2 and 6 are converted in the solid state into the isomeric coordination polymer of 1 and hydrogen bonded network structure of 3, respectively.