Influence of halogen-halogen interactions in the self-assembly of pillar[5]arene-based supramolecular polymers.

Halogen-halogen interactions play a pivotal role in the formation and stability of supramolecular assemblies. Herein, we investigate the assembly dynamics and dissociation pathways of linear supramolecular polymers based on pillar[5]arene-mediated by guest halogen-halogen interactions (C-X × X-C) in both the solution and solid states. The structure of the solid-state supramolecular assembly was determined by single-crystal X-ray diffraction analysis. The binding affinities of four different 1,4-dihalobutane guests with pillar[5]arene were investigated by 1H NMR spectroscopic titration and isothermal titration calorimetry (ITC). The formation of the halogen-bonded linear supramolecular polymer in solution was demonstrated using diffusion-ordered spectroscopy (DOSY) and ITC. Our findings highlight the dependence of the dissociation process on halogen nature within the encapsulated guest, revealing that the process is entropically driven (TΔS = 27.12 kJ mol-1) and enthalpically disfavored (ΔH = 9.99 kJ mol-1). Moreover, the disassembly of supramolecular polymers promoted by N-containing compounds was investigated using 1H NMR spectroscopy and ITC, revealing that the process is driven both enthalpically (ΔH = -2.64 kJ mol-1) and entropically (TΔS = 15.70 kJ mol-1). Notably, the data suggest the formation of N⋯I bonding interactions at both ends of the inclusion guest, elucidating the intricate interplay of halogen interactions and host-guest chemistry in supramolecular polymer systems.

Crystal structure and supra-molecular features of a bis-urea-functionalized pillar[5]arene.

The crystal structure of a bis-urea derivative based on A1/A2-functionalized pillar[5]arene (DUP) that encapsulates dimethyl formamide (DMF) inside the macrocyclic cavity is reported. The crystal structure of DUP·DMF, C63H70N4O12·C3H7NO, reveals that out of two urea functionalized spacers, one arm is oriented above the macrocyclic cavity with strong hydrogen-bonding inter-actions between the urea H atoms and DMF guest, whereas, the other arm is positioned away from the macrocycle, leading to inter-molecular hydrogen-bonding inter-actions between the urea H atoms of two adjacent pillar[5]arene macrocycles, resulting in the formation of a supra-molecular dimer.

1-[1,4-Bis(but-3-en-1-yl-oxy)]-2,3,4,5-(1,4-dimeth-oxy)pillar[5]arene-1,4-di-bromo-butane 1:1 inclusion complex.

In the title compound, C51H58O10·C4H8Br2, both the host and guest are completed by crystallographic twofold symmetry (one carbon atom of the host lies on the rotation axis). The penta-gonal-shaped macrocycle has a pair of butene-oxy substituents on one of its faces and one mol-ecule of 1,4-di-bromo-butane is encapsulated within the cavity of the pillararene, forming a 1:1 inclusion complex. The terminal alkene parts, which project outwards from the pillararene ring, exhibit positional disorder over two sets of sites in a 0.52 (2): 0.48 (2) ratio. The host and guest inter-act via C-H⋯O, C-H⋯Br and C-H⋯π inter-actions and adjacent host mol-ecules inter-act via C-H⋯O and C-H⋯π bonds.

Spatially Designed Supramolecular Anion Receptors Based on Pillar[5]arene Scaffolds: Synthesis and Halide Anion Binding Properties.

Urea-functionalized anion receptors based on brominated functionalized pillar[5]arenes were prepared. The binding affinity toward halide anions was investigated and probed using 1H NMR titration and isothermal titration calorimetry (ITC). The complexation behavior was affected by the structure of the receptor and the nature of the anionic guest. The synthesized receptors are highly selective toward fluoride resulting in the formation of a 1:2 host-to-guest complex. The anion receptor based on the 1,3-alternate pillar[5]arene regioisomer shows the highest affinity toward fluorine anions. No significant interactions were observed with larger bromine anions. The formation of a self-assembled supramolecular polymer driven by hydrogen bonds in solution was demonstrated by diffusion-ordered spectroscopy (DOSY), ITC, and dynamic light scattering (DLS) measurements. From ITC dilution experiments, we found that the supramolecular polymer self-assembly at higher concentrations is a spontaneous process as indicated by the positive value of Gibbs free energy (ΔG = 12.04 kJ mol-1).

External-stimulus-triggered conformational inversion of mechanically self-locked pseudo[1]catenane and gemini-catenanes based on A1/A2-alkyne-azide-difunctionalized pillar[5]arenes.

Herein, we report a methodology for constructing mechanically self-locked molecules (MSMs) through the efficient intramolecular copper(i)-catalyzed alkyne-azide cycloaddition (CuAAC) of self-threaded A1/A2-azido-propargyl-difunctionalized pillar[5]arenes. The obtained monomeric "pseudo[1]catenane" and dimeric "gemini-catenane" were isolated and fully characterized using mass spectrometry, nuclear magnetic resonance (NMR) spectroscopy, and X-ray crystallography. Upon investigation by 1H NMR spectroscopy in chloroform, the observed motion for the threaded ring in the pseudo[1]catenane was reversibly controlled by the temperature, as demonstrated by variable-temperature 1H NMR studies. Two gemini-catenane stereoisomers were also isolated in which the two pillar[5]arene moieties threaded by two decyl chains were aligned in different topologies. Furthermore, the conformational inversion of pseudo[1]catenane and the gemini-catenanes triggered by solvents and guests was investigated and probed using 1H NMR spectroscopy, isothermal titration calorimetry, and single-crystal X-ray analysis.

Concentration-dependent supramolecular self-assembly of A1/A2-asymmetric-difunctionalized pillar[5]arene.

A series of A1/A2-bromoalkoxy-and-hydroxy-difunctionalized pillar[5]arenes were synthesized by the removal of the pillar[5]arene-bearing benzyl group using catalytic hydrogenation. The difunctionalized pillar[5]arene bearing 8-bromooctoxy and benzyloxy substituents at the A1/A2 positions formed pseudo[1]rotaxane at low concentration and double-threaded supramolecular dimer at high concentration. The supramolecular self-assembly behavior has been probed with multiple methods including varying (variable) concentration 1H NMR spectroscopy, diffusion-ordered spectroscopy (DOSY), dynamic light scattering (DLS) measurements, isothermal titration calorimetry (ITC), and single-crystal X-ray analysis.

Synthesis, functionalization, and isolation of planar-chiral pillar[5]arenes with bulky substituents using a chiral derivatization agent.

Bulky perneopentyloxy-pillar[5]arene (Pillar-1) was synthesized and its conformational mobility was investigated using variable-temperature 1H NMR spectroscopy. The host-guest interactions between Pillar-1 and n-octyltrimethylammonium hexafluorophosphate (OMA) were investigated, and the formation of a 1 : 1 complex was revealed via 1H NMR. Planar-chiral isomers were synthesized via the reaction of a hydroxy-functionalized pillar[5]arene with chiral derivatization agent (S)-(+)-MTPA-Cl. The (Sp, R)-and (Rp, R)-forms of the pillar[5]arene diastereomers were isolated by HPLC, and their structures were analyzed by 19F NMR. HPLC measurements indicated that racemization did not take place at 40 °C for 72 h.

Constitutional isomers of brominated-functionalized copillar[5]arenes: synthesis, characterization, and crystal structures.

We herein report the preparation of constitutional isomers of brominated-functionalized pillar[5]arenes via co-condensation of 1,4-bis(2-bromoethoxy)benzene and 1,4-dimethoxybenzene. The structures of the obtained isomers were then established using single crystal X-ray diffraction. We also found that the isomeric yield distribution of the different constitutional isomers was independent of the monomer's mole feed ratio, as revealed by HPLC analysis of the crude mixture. Finally, further characterization of the separated constitutional isomers indicated that they possess different melting points, NMR spectra, crystal structures, binding constants and stacking patterns in the solid state.

Encapsulated di-chloro-ethane-mediated inter-locked supra-molecular polymeric assembly of A1/A2-dihydroxy-oct-yloxy pillar[5]arene 1,2-di-chloro-ethane monosolvate.

Crystals of 1-(1,4-dihy-droxy)-2,3,4,5-(1,4-dioct-yloxy)-pillar[5]arene, C99H158O10·C2H4Cl2, were grown from a 1,2-dicholoro-ethane/n-hexane solvent system. In the crystal, the encapsulated 1,2-di-chloro-ethane solvent is stabilized by C-H⋯π inter-actions and mediates the formation of an inter-locked supra-molecular polymer via C-H⋯Cl inter-actions.

An alternative route for the synthesis of hydroxylated pillar[5]arene-based amphiphiles.

Conformational mobilities of the units and host-guest complexation with n-octyltrimethylammonium hexafluorophosphate of the synthesized perbenzylated pillar[5]arenes were studied. The formed complex was confirmed by proton nuclear magnetic resonance spectroscopy and mass spectral analysis. Hydroxylated pillar[5]arene-based amphiphiles were synthesized by a co-cyclization strategy followed by catalytic hydrogenation. This approach unlocks the synthesis and the design of a wide range of structural manipulations to these amphiphilic pillararenes.

Single-crystal X-ray diffraction study of a host-guest system comprising monofunctionalized-hydroxy pillar[5]arene and 1-octa-namine.

Co-crystallization of a monofunctionalized hy-droxy pillar[5]arene with 1-octa-namine resulted in the formation of an inclusion complex where the alkyl chain is threaded in the macrocycle cavity, namely 1,2,3,4-(1,4-dimeth-oxy)-5-(1-hy-droxy-4-meth-oxy)-pillar[5]arene-1-octa-namine-water (1/1/1), C44H48O10·C8H19N·H2O. The guest compound is stabilized inside the cavity by hydrogen-bonding and C-H⋯π inter-actions. The water mol-ecule in the asymmetric unit mediates the formation of a supra-molecular dimer by hydrogen-bonding inter-actions. These functionalized-pillararene hosts expand the possibility of exploring more supra-molecular inter-actions with various guest species.

Constitutional Isomers of Pentahydroxy-Functionalized Pillar[5]arenes: Synthesis, Characterization, and Crystal Structures.

We herein report the preparation of constitutional isomers of pentahydroxy-functionalized pillar[5]arenes via the deprotection of their benzylated derivatives by catalytic hydrogenation. The structures of the obtained isomers were then established using single crystal X-ray diffraction. We also found that the yield distribution of the different constitutional isomers was dependent on the nature of the substitution, as revealed by HPLC analysis of the crude mixture. Finally, further characterization of the separated constitutional isomers indicated that they possess different melting points, NMR spectra, crystal structures, and stacking patterns in the solid state.

Molecular assemblies of porphyrins and macrocyclic receptors: recent developments in their synthesis and applications.

Metalloporphyrins which form the core of many bioenzymes and natural light harvesting or electron transport systems, exhibit a variety of selective functional properties depending on the state and surroundings with which they exist in biological systems. The specificity and ease with which they function in each of their bio-functions appear to be largely governed by the nature and disposition of the protein globule around the porphyrin reaction center. Synthetic porphyrin frameworks confined within or around a pre-organized molecular entity like the protein network in natural systems have attracted considerable attraction, especially in the field of biomimetic reactions. At the same time a large number of macrocyclic oligomers such as calixarenes, resorcinarenes, spherands, cyclodextrins and crown ethers have been investigated in detail as efficient molecular receptors. These molecular receptors are synthetic host molecules with enclosed interiors, which are designed three dimensionally to ensure strong and precise molecular encapsulation/recognition. Due to their complex structures, enclosed guest molecules reside in an environment isolated from the outside and as a consequence, physical properties and chemical reactions specific to that environment in these guest species can be identified. The facile incorporation of such molecular receptors into the highly photoactive and catalytically efficient porphyrin framework allows for convenient design of useful molecular systems with unique structural and functional properties. Such systems have provided over the years attractive model systems for the study of various biological and chemical processes, and the design of new materials and molecular devices. This review focuses on the recent developments in the synthesis of porphyrin assemblies associated with cyclodextrins, calixarenes and resorcinarenes and their potential applications in the fields of molecular encapsulation/recognition, and chemical catalysis.

Sequential Staudinger ketene-imine cycloaddition, RCM approach to highly rigid macrocrocyclic bisazetidinones.

An efficient approach to highly rigid macrocyclic bisazetidinones with interesting structural feature was achieved via sequential Staudinger ketene-imine cycloaddition of o-allyloxyphenoxyketene and bis-arylidenediamines followed by RCM. The ketene-imine cycloaddition afforded the corresponding bis-o-allyloxyphenoxyazetidinones as the cis-cis diastereomers, exclusively obtained as a mixture of cis-syn-cis and cis-anti-cis. RCM of the latter using Grubbs' catalysts afforded good yields of the corresponding novel macrocyclic bisazetidinones. The cis-anti-cis bisazetidinones are readily identified by (1)H NMR using Eu(hfc)(3) chiral shift reagent. (1)H NMR indicated the high shielding effect of the aryl substituents on one of the ortho-H's of the condensed phenylene ring, and VT (1)H NMR indicates the highly restricted rotation of the aryl groups, thus offering a highly rigid system.

Staudinger ketene-imine cycloaddition, RCM approach to macrocrocyclic bisazetidinones.

Application of Staudinger ketene-imine cycloaddition reaction to bis-o-allyloxyarylideneamines afforded the corresponding bisallyloxyazetidinones as the cis-cis diastereomers, exclusively obtained as a mixture of cis-syn-cis and cis-anti-cis. RCM of the latter using Grubbs' catalysts afforded the corresponding macrocyclic bisazetidinones in good yields. The cis-anti-cis bisazetidinones are readily identified by (1)H NMR using Eu(hfc)(3) chiral shift reagent.

Spatially directional multiarm poly(epsilon-caprolactone) based on resorcin[4]arene cavitand core.

Highly crystalline directional poly(epsilon-caprolactone) based on a tetrahydroxymethyl resorcin[4]arene initiator core was synthesized by a "core first" method via ring-opening polymerization catalyzed by Sn(Oct)(2) in bulk at 120 degrees C.

Functionalized polycarbonate derived from tartaric acid: enzymatic ring-opening polymerization of a seven-membered cyclic carbonate.

Enantiomerically pure functional polycarbonate was synthesized from a novel seven-membered cyclic carbonate monomer derived from naturally occurring L-tartaric acid. The monomer was synthesized in three steps and screened for polymerization with four commercially available lipases from different sources at 80 degrees C, in bulk. The ring-opening polymerization (ROP) was affected by the source of the enzyme; the highest number-average molecular weight, M(n) = 15500 g/mol (PDI = 1.7; [alpha]D(20) = +77.8, T(m) = 58.8 degrees C) optically active polycarbonate was obtained with lipase Novozyme-435. The relationship between monomer conversion, reaction time, molecular weight, and molecular weight distribution were investigated for Novozyme-435 catalyzed ROP. Deprotection of the ketal groups was achieved with minimal polymer chain cleavage (M(n) = 10000 g/mol, PDI = 2.0) and resulted in optically pure polycarbonate ([alpha]D(20) = +56) bearing hydroxy functional groups. Deprotected poly(ITC) shows T(m) of 60.2 degrees C and DeltaH(f) = 69.56 J/g and similar to that of the poly(ITC), a glass transition temperature was not found. The availability of the pendant hydroxyl group is expected to enhance the biodegradability of the polymer and serves in a variety of potential biomedical applications such as polymeric drug delivery systems.