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This study demonstrates the comprehensive investigation on the reversible linear-cyclic topological conversion of hydrophilic and hydrophobic polymers with various molecular weights. The reactions were triggered by light or heat, which reversibly dimerize and cleave the anthryl or coumarinyl end groups of the telechelics. Poly(ethylene oxide) telechelics with anthryl end groups attached through electron-donating (Ant-O-PEO and Ant-CH2-PEO) and electron-withdrawing (Ant-CO2-PEO) linking groups were synthesized. While Ant-O-PEO and Ant-CH2-PEO decomposed upon photoirradiation at 365 nm, Ant-CO2-PEO efficiently cyclized through the photodimerization of the anthryl end groups both in water and in organic solvents shown by NMR, SEC, and MALDI-TOF MS. The lower the molecular weight, the faster the cyclization proceeded. When cyclized Ant-CO2-PEO was heated at 150 °C in bulk, the polymers quantitatively converted back into the original linear topology. Furthermore, repeatable linear-cyclic topological conversion was confirmed. The reversible topological conversion of hydrophobic poly(tetrahydrofuran) telechelics with anthryl end groups (Ant-PTHF) was also successful. In addition, poly(ethylene oxide) telechelics with coumarinyl end groups (Cou-PEO) were also cyclized by irradiation at 365 nm in water. However, the cyclization hardly occurred when performed in methanol likely due to the lack of sufficient hydrophobic interaction of the coumarinyl end groups. Cyclized Cou-PEO was irradiated at 254 nm to test for linearization, finding the linear product and cyclic precursor were likely photoequilibrated. [ABSTRACT FROM AUTHOR]

The coordination-driven self-assembly of four different trigonal prisms from 3 equiv of one of four different tetrapyridyl star connectors and 6 equiv of a platinum linker dication in nitromethane is presented. This face-directed approach affords high yields without template assistance. The prisms have been characterized by multinuclear and DOSY NMR and dual ESI-FT-ICR mass spectrometry. The use of a conformationally chiral star connector leads to a conformationally chiral prism when connector arm ends attached to a vertex have a strongly correlated twist sense and chirality is communicated across polyhedral faces, edges, and vertices. Molecular mechanics results suggest that in the smallest prism 3d collective effects dominate and the all-P and all-M conformers are strongly favored. NMR data prove that the two edges of the pyridine rings in the triflate salts of 3a-3d are distinct. An Eyring plot of rates obtained from line-shape analysis and 1-D EXCHSY NMR yields an activation enthalpy ΔH‡ of ~12 kcal/mol and activation entropy ΔS‡ of ~-15 cal/mol·K for the edge interconversion process, compatible with pyridine rotation around the Pt-N bond. For 3c, this behavior is observed only up to ~318 K. At higher temperatures, the Eyring plot is again linear but follows a very different straight line, with a ΔH‡ of ~35 kcal/mol and ΔS‡ of ~60 cal/mol·K. This highly unusual result is further investigated and discussed in the following companion paper. [ABSTRACT FROM AUTHOR]

Newly designed norbornene-appended hexabenzocoronene 1 self-assembles, upon diffusion of an Et2O vapor into its CH2Cl2 solution, to form either graphitic nanocoils or nanotubes, depending on the self-assembling conditions. The coiled assembly, selectively formed at 15 °C, is a kinetic intermediate for the tubular assembly and transforms into nanotubes on standing at 25 °C. However, post-ring-opening metathesis polymerization of the norbornene pendants of 1 enhances the thermal stability of the coiled assembly as well as the tubular one and disables a thermodynamic coil-to-tube transition. The polymerized nanocoils show an electroconductivity of 1 × 10-4 S cm-1 upon doping with I2, while the nonpolymerized nanocoils are disrupted upon being doped. [ABSTRACT FROM AUTHOR]

A supramolecular dimeric rhomboid and its trimeric counterpart, a hexagon, are generated by design via the directional bonding methodology of self-assembly. The different-sized supramolecular macrocycles formed by Pt-coordination undergo a concentration- and temperature-dependent dynamic equilibrium. The two structures are characterized by multinuclear NMR and ESI-MS. Extensive study of the dynamic equilibrium of the two species in solution is performed to obtain its thermodynamic properties. By varying the ionic strength, μ, of the solutions, the true thermodynamic equilibrium constant, K, is determined at each experimental temperature (K[sub 253] = 36 ± 7, K[sub 273] = 18 ± 6, K[sub 293] = 10 ± 3, K[sub 313] = 9 ± 2, K[sub 333] = 5 ± 2, and K[sub 353] = 3.0 ± 0.2). By applying these values of true K at the respective temperatures to the van't Hoff equation extended with the entropy term, the standard enthalpy and entropy changes are determined for the equilibrium: with ΔH° = -18 ± 1 kJ mol[sup -1] and ΔS° = -43 ± 4 J mol[sup -1] K[sup -1], respectively, for the forward reaction (rhomboid to hexagon) of the equilibrium. The rhomboid is selectively crystallized, and its crystal structure is determined by X-ray diffraction. The structure reveals a significant amount of porosity as well as distortion of the rhomboid from planarity, leading to channels that can be observed from two viewing positions of the packing. [ABSTRACT FROM AUTHOR]

The thermal stability of a self-assembled micelle was remarkably enhanced by a topology effect. Linear poly(butyl acrylate)-block-poly(ethylene oxide)-block-poly(butyl acrylate) (1) and the cyclized product, poly(butyl acrylate)-block-poly(ethylene oxide) (2), were self-assembled to form flower-like micelles. By means of viscometry, the critical micelle concentrations were determined to be 0.13 and 0.14 mg/mL for 1 and 2, respectively. Dynamic light scattering, atomic force microscopy, and transmission electron microscopy studies revealed that both micelles are spherical and approximately 20 nm in diameter. Despite no distinctive change in the chemical composition or structure of the micelle, we found that the cloud point (Tc) was elevated by more than 40 °C through the linear-to-cyclic topological conversion of the polymer amphiphile. Furthermore, the Tc was tuned by coassembly of 1 and 2. [ABSTRACT FROM AUTHOR]

The article discusses the importance of cationic gold in chemistry in the U.S. It states that cationic gold complexes have emerged as powerful acids capable of promoting a diverse range of enyne cycloisomerization reactions. It is discussed that in these reactions, the gold catalyst not only serves to activate the alkyne toward nucleophilic addition, but also plays a role in stabilizing the cationic intermediates produced in the cyclization event.

The article presents a study which reveals the successful formation of a nanotubular precursor bearing reactive surface groups. Researchers used [3 + 2] cycloaddition of azides and alkynes as a means of chemically modifying the graphitic nanotubes. Selective grafting of the G2 dendron on the exterior surface was also conducted to functionalize the interior of the nanotubes.

A tandem alkyne-azide addition, i.e., click, and an olefin metathesis condensation, i.e., clip, reactions in conjunction with an electrostatic self-assembly and covalent fixation (ESA-CF) process, have been demonstrated as effective means to produce constructions of programmed folding of polymers having doubly fused tricyclic and triply fused tetracyclic topologies. Thus, a series of cyclic poly(tetrahydrofuran), poly(THF), precursors having an allyloxy group and an alkyne group (Ia), an allyloxy group and an azide group (Ib), and two alkyne groups (Ic) at the opposite positions was prepared by means of the ESA-CF method. The subsequent click reactions of Ia with a linear telechelic poly(THF) precursor having azide end groups (Id) and of Ib with Ic afforded a bridged dicyclic polymer (IIa) and a tandem spiro tricyclic precursor (IIb), respectively, both having two allyloxy groups at the opposite positions of the ring units. Finally, the intramolecular metathesis condensation reaction of IIa and of IIb in the presence of a Grubbs catalyst was performed to construct effectively a doubly fused tricyclic and a triply fused tetracyclic polymer topologies (III and IV), respectively. [ABSTRACT FROM AUTHOR]

An alkyne-azide addition, i.e., click, reaction in conjunction with an electrostatic self-assembly and covalent fixation (ESA-CF) process has been demonstrated to effectively construct a variety of unprecedented multicyclic polymer topologies. A series of single cyclic poly(tetrahydrofuran), poly(THF), precursors having an alkyne group (Ia), an azide group (Ib), two alkyne groups at the opposite positions (IC), and an alkyne group and an azide group at the opposite positions (Id) have been prepared by the ESA-CF process. Moreover, a bicyclic 8-shaped precursor having two alkyne groups at the opposite positions (le) was synthesized. The subsequent click reaction of la with linear (ha) and three-armed star (llb) telechelic precursors having azide groups has been performed to construct bridged-type two-way (lla) and three-way (llb) paddle-shaped polymer topologies, respectively. Likewise, spiro-type tandem tricyclic (IVa) and tetracyclic (IVb) topologies resulted from lb/lc and lb/le, respectively. Furthermore, three types of multicyclic topologies that are composed of repeating ring (Va), alternating ringllinear (Vb), and alternating ring/star (Vc) units have been synthesized from ld, lc/lla, and lc/llb, respectively. [ABSTRACT FROM AUTHOR]

The syntheses, structures, and N2 adsorption properties of six new supramolecular metallacycles are reported. Flexible ditopic linkers, 1-4, with systematically varied lengths and conformational degrees of freedom were synthesized utilizing ester linkages. They were used in combination with (dppp)M(OTf)2, where M = Pt(II) and Pd(II), and cis-(Me3P)2Pt(OTf)2 to form flexible supramolecular metallacycles 5-10 in 88-98% isolated yields. Their structures were characterized via multinuclear NMR and X-ray crystallography. The metallacycles stack to form porous structures in the crystalline state. The pore dimensions depend on both the phosphorus ligands attached to the metals and the flexible linkers. Adsorption studies on the porous materials show that 5a, 6, 8, and 9 held 11.7, 16.5, 5.7, and 6.8 cm⊃3/g STP of N2 at 77 K, respectively. A guest-exchange study with nitromethane and toluene reveals that the nanopore in 5 is flexible, a property which was transferred from the linker to the supramolecular structure in the solid state. [ABSTRACT FROM AUTHOR]