Hydrogen-bonded benzylidenebenzohydrazide macrocycles and oligomers: testing the robust capacity of an amide chain in promoting the formation of vesicles

This Letter describes 2-(2-(dioctylamino)-2-oxoethyl-amino)-2-oxoethoxyl (DOAOE)-tuned self-assembly of vesicles from rigid macrocycles and foldamer-like oligomers. The molecules are prepared through the formation of reversible hydrazone bonds from aldehyde and benzo-hydrazide precursors, which are further facilitated by intramolecular N?H-O hydrogen bonding. SEM, AFM, and fluorescent encapsulation studies reveal that the molecules all self-assemble into vesicular structures in methanol, while similar molecules bearing the triethylene glycol or n-decyl chains do not. The results illustrate that DOAOE is robust in promoting the formation of vesicles for aromatic systems in polar solvents.     

Wraparound hosts for fullerenes: tailored macrocycles and cages

Custom-made macrocyclic receptors for fullerenes are proving a valuable alternative to achieve the affinity and selectivity required to meet challenges such as the selective extraction of higher fullerenes, their chiral resolution, or the self-assembly of functional molecular materials. In this Minireview, we highlight some of the important breakthroughs that this class of fullerene hosts has already produced.     

Controllable synthesis, structures of amidecrownophane-type macrocycles and their binding ability toward anions

Amidecrownophane-type macrocycles with different number of hydroxy groups were prepared in quantitative yields by control of the conditions of thermal reaction with the aim to examine the role of hydroxy groups in anion recognition. It was proved that the hydroxy group played a critical role in anion binding for this type of macrocycles and the anion binding affinity could be tuned by different number of hydroxy groups. Further exploration clarified the presence of intramolecular hydrogen-bonding and exhibited the major effect on their anion binding potential.     

Heptametallic bowl-shaped complexes derived from conjugated Schiff-base macrocycles: synthesis, characterization, and X-ray crystal structures

The reaction of chelating conjugated macrocycles 1a-c with Zn(OAc)2 gives bowl-shaped heptanuclear Zn complexes featuring Zn in tetrahedral, octahedral, and square-pyramidal geometries. Crystallographic and NMR results indicate that vacant Zn coordination sites within the bowl may be accessed, suggesting that these coordination complexes may be used as mimics for Zn fingers and carbonic anhydrase.     

Phosphorylated methano[60]fullerenes containing nitroxyl radicals: synthesis,structures, and electrochemical behavior

Phosphorylated methano[60]fullerenes containing one or two nitroxyl radicals were synthesized for the first time. Their structures were established from spectroscopic data and their compositions, by MALDI-TOF mass spectrometry. Their electrochemical reduction in a system o-dichlorobenzene-DMF/0.1 M Bu₄NBF₄ was studied by cyclic voltammetry, preparative electrolysis, and ESR spectroscopy in combination with in situ electrolysis. Both compounds were found to undergo four-step reduction of the fullerene sphere, reduction of nitroxyl, opening of the three-membered ring, and elimination of addends as carbanions stabilized by protonation and rearrangement into phosphate ions and substituted acetylene, which are accompanied by the formation of free fullerene and dihydrofuranofullerene. The rates of the ring opening and the addend elimination increased with an increase in the negative charge on the fullerene sphere. These reactions are fast in the case of transfer of three electrons. With the use of model compounds, heterogeneous electron transfer to the nitroxyl radical at the potentials of the transfer of the third electron to the fullerene sphere and homogeneous intramolecular electron transfer from the dianion of the fullerene sphere were revealed. The mechanisms of the observed transformations are discussed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1594–1607, July, 2005.     

Phosphorylated macrocycles: structures,complexing properties,and molecular recognition

Procedures were developed for functionalization of macrocycles by introducing a phosphonic group either directly linked to the aromatic rings (in the case of cyclophanes or calixarenes) or as a pendant arm. For these compounds to be used as artificial receptors for amino alcohols and amino acids, the host molecule must possess not only negative charges arising from the phosphonate moieties but also a hydrophobic binding site, such as electron-rich aromatic residues. We designed inter alia new dissymmetric macrocycles capable of being involved in three binding modes with guest molecules, viz., hydrogen bonding, electrostatic attraction, and π-cation interactions. The NMR characterization of the macrocycles, their stereochemistry in solution and in the solid state, and the use as chiral receptors for biologically relevant molecules are described. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1313–1330, June, 2005.     

A simple and efficient synthesis of boron-imidazole macrocycles and their crystal structures

A simple and selective method for the synthesis of boron-imidazole macrocycles is described and their X-ray structures are presented.     

One-step synthesis of amine-functionalized thermo-responsive magnetite nanoparticles and single-crystal hollow structures

A high-temperature solution phase hydrolysis has been developed for the synthesis of amine-functionalized Fe₃O₄ nanostructures. The concentrations of the reagents and the reaction time have great influence on the morphologies of the products. Increasing the amounts of poly (propylene glycol) bis (2-aminopropyl ether) transformed the product morphology from hollow nanostructures to magnetite nanoparticles. Single-crystal solid spherical aggregates, hollow spheres, loose nanoclusters and polyhedral-like magnetite particles can be selectively synthesized by varying the synthesis parameters, including the reaction time or the weight ratio of iron precursors to polyetheramine. The morphological transformation could be attributed to the cooperation of oriented aggregation and Ostwald ripening mechanisms. By using poly (propylene glycol) bis (2-aminopropyl ether) as the capping agent, the amine-functionalized nanoparticles show high water dispersibility and thermo-responsive. In addition, the Pickering emulsion stabilized by amine-functionalized nanoparticles was fabricated. One of the most promising applications of the as-prepared single-crystal hollow structures is as support materials for biological testing, catalysis and targeted drug delivery.     

Shape-persistant macrocycles with terpyridine units: synthesis,characterization, and structure in the crystal

The synthesis of a variety of shape-persistent macrocycles with either one (1a-d, 2) or two (opposing) terpyridine units (3, 4, 5a-c) and inner diameters of up to 2 nm is described. The sequences are mainly based on transition metal cross-coupling reactions and, whenever appropriate, compared with one another regarding their respective efficiency. Typical overall yields and amounts prepared range from 8% (4) to 27% (3) and 25 mg (1a) to 290 mg (1b), respectively. For solubility and processing of the targeted cycles, all precursors have already been decorated with flexible side chains (hexyloxy or hexyloxymethyl). The cycles' characterization is based on MALDI-TOF mass spectrometry, 2D NMR spectroscopy, and/or low-temperature single-crystal X-ray diffraction. Their packing in the crystal is discussed in terms of both number and length of side chains. Cycle 1d was physisorbed into an ordered structure at the solution-HOPG interface and investigated by scanning tunneling microscopy (STM).     

Bis-imine-cyclometalated macrocycles: synthesis, characterization and observation of solution behaviour

A novel class of cyclometalated macrocycles [(Cp*Ir)(2)(R-N=C-C(6)H(2)-C=N-R)(2)](2)(pyrazine)(2)·(OTf)(4) [R = Ph (4a), p-MeOC(6)H(4) (4b), p-MeC(6)H(4) (4c), p-ClC(6)H(4) (4d), Me (4e)]; [(Cp*Rh)(2)(R-N=C-C(6)H(2)-C=N-R)(2)](2)(pyrazine)(2)·(OTf)(4) [R = Ph (4a'), p-MeOC(6)H(4) (4b'), p-MeC(6)H(4) (4c')] and [(Cp*Ir)(2)(R-C=N-C(6)H(4)-N=C-R)(2)](2)(pyrazine)(2)·(OTf)(4) [R = Ph (5a), p-MeOC(6)H(4) (5b)] was stepwise constructed through the double-site C-H activation of aromatic bis-imine substrates. The structures of binuclear complexes and tetranuclear macrocycles were confirmed by single-crystal X-ray diffraction. Isomers were found both in binuclear species and macrocyclic complexes. Flexible substrates led to the existence of isomers for binuclear species, yet gave no isomers after macrocyclic constructions; rigid ones, in contrast, led to isomers only for macrocyclic species. The isomers of tetranuclear macrocycles were thermodynamically stable to reversible transformation on a scale of days. Robust bonding and a certain degree of rigidity were invoked to explain the existence of isomers. This is the first example, to our knowledge, in which coordinated macrocycles containing half-sandwich Cp*M (M = Ir, Rh) fragments have been constructed, without a dynamic reversible process.     

Hydrogen-bonded perylene/terthiophene-materials: synthesis and spectroscopic properties

The synthesis of layered donor/acceptor-materials based on perylenes (1a–c) and ter(thiophen)es (2a, 2b), ordered by hydrogen bonding moieties is reported. Based on the successful (selective) chlorination of 3,4:9,10-perylene tetracarboxylic dianhydride (3) to obtain a perylene derivative with only four chlorine atoms, subsequent functionalization with different hydrogen-bonding moieties is achieved via the azide/alkyne click reaction as proven by extensive ESI-TOF measurements. The perylene- (1a–c) and terthiophene- (2a, 2b) compounds are useful as acceptor and donor parts, respectively, in organic solar cells as proven via UV–vis and fluorescence measurements. Charge transfer between donor and acceptor parts (2a/1b) was determined as 41% via fluorescence resonance energy transfer (FRET), proving the association of the two components via the attached hydrogen bonding moieties. These measurements indicate that the mixture 2a/1b displays large potential for use as a layered ordered material with controlled spacings for organic solar cells based on a thereby facilitated charge-transfer.     

Crystal structures of dicarboxy-2,2'-bipyridyl complexes: the role of hydrogen bonding and stacking interactions

The crystal structures of three complexes of dicarboxy-2,2'-bipyridyl ligands, 5,5'-dicarboxy-2,2'-bipyridyl (1) and 4,4'-dicarboxy-2,2'-bipyridyl (2) are reported. [Rh(1H)3] shows two interpenetrating, homochiral rhombohedral networks linked by short carboxylate-carboxylic acid hydrogen bonds, in which each complex acts as a node for six hydrogen bonds. [Ru(1H2)(1H)2] forms only four such hydrogen bonds, leading to the formation of heterochiral chains held together by stacking between bipyridyls. [Co(2H)3] can in principle form six hydrogen bonds, but in practice forms only four in a layer structure where stacking interactions are important. This is attributed to differences in molecular shape.     

Palladium-catalyzed coupling of ammonia and lithium amide with aryl halides

A mild, palladium-catalyzed coupling of aryl halides with ammonia or lithium amide to form primary arylamines as the major product is described. These reactions occurred with excellent selectivity for formation of the primary arylamine over formation of the diarylamine (9.5:1 to over 50:1 ratios of arylamine to diarylamine). In addition, the first organopalladium complex with a terminal -NH2 ligand has been isolated. This complex reductively eliminates to form arylamines.     

Shape-persistent macrocycles with intraannular polar groups: synthesis, liquid crystallinity, and 2D organization

The synthesis of macrocycles with intraannular polar ester groups and extraannular oligo-alkyl groups is described. The compounds exhibit stable liquid crystalline phases showing fan-shaped textures under the polarizing microscope, typical for a columnar order of the molecules. X-ray powder diffraction data of the LC phase indicate that the unit cell contains two symmetry-related units, a feature pointing most probably to a restricted rotation of the macrocycles within a stack. The X-ray data were further supported by solid-state NMR experiments, showing that the rigid core of the compounds does not rotate with kHz or higher frequencies within the column in the LC phase. Apart from the organization of the molecules in the LC phase, the 2D organization of the macrocycles at the solvent-highly oriented pyrolytic graphite (HOPG) interface was investigated and showed that these compounds are capable of nanofunctionalizing the HOPG surface in the multinanometer regime.     

Novel diethynylcarbazole macrocycles: synthesis and optoelectronic properties

Diethynylcarbazole macrocycles 1b and 2b have been synthesized by oxidative coupling of appropriate precursors. In particular, macrocycle 2b was prepared by bimolecular Pd-catalyzed oxidative coupling in 35% isolated yield. The spectroscopic properties of these macrocycles and their precursors were measured in detail. The films of these macrocycles by the dipping method and the Langmuir-Blodgett technique were fabricated to study their photoinduced charge-transfer properties. A rapid and steady cathodic photocurrent of these films was produced in a three-electrode cell when irradiated with white light. A possible mechanism of the photoinduced electron-transfer pathway was suggested.     

Structurally isomeric two pyridino macrocycles: complexation and structures

Pyridine-based, structurally isomeric two macrocyclic compounds displayed a remarkably different complexation nature. The cage-type compound has an ideal structure for spherical cations, especially for the NH₄⁺ ion, but the reaction with some transition metals and Ln³⁺ produced its protonated species. On the other hand, its isomer formed complexes with alkali metals and lanthanides (1:1) and also with transition metals. Some structures of the complexes were clarified by crystallographic analyses.     

Novel fluorene-containing fullerenes C<Subscript>60</Subscript>: synthesis and structures

Reactions of fullerene C₆₀ with fluorene-2-carbaldehyde or 2,7-diacetylfluorene in toluene gave novel spiromethanofullerenes containing a reactive free formyl group. A novel fluorene-containing fullerenopyrrolidine was obtained by the Prato reaction. The purity and compositions of the compounds obtained were confirmed by MALDI TOF mass spectrometry and HPLC. Their structures were confirmed by 2D homo-and heterocorrelation NMR techniques. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1780–1785, September, 2007.     

Synthesis,characterization and fluorescent properties of lanthanide complexes with two aryl amide ligands

Two aryl amide ligands, N-(p-tolyl)-2-(quinolin-8-yloxy)acetamide (L¹ ) and N-(4-chlorophenyl)-2-(quinolin-8-yloxy)acetamide (L² ), were synthesized. With these ligands, two series of lanthanide(III) complexes were prepared, Ln(L ⁿ )₂(NO₃)₃ (n = 1, 2; Ln = La, Sm, Eu, Gd, Dy), and characterized by the elemental analyses, molar conductivity, ¹H NMR spectra, IR spectra and TG-DTA. The fluorescence properties of the complexes and the triplet state energies of the ligands were studied in detail. In addition, the quantum yields of both Eu(III) complexes and Eu(L⁰)₂(NO₃)₃ [where L⁰ is N-(phenyl)-2-(quinolin-8-yloxy)acetamide] 1 Wu, WN, Yuan, WB, Tang, N, Yang, RD, Yan, L and Xu, ZH. 2006. Spectrochim. Acta A, 65: 912[Crossref], [Web of Science ®] , [Google Scholar] were calculated. The results indicate that among the lowest triplet energies (T) of the three ligands, that of L² is most suitable to the resonance level (⁵D₁) of Eu(III) ion. Furthermore, Eu(L²)₂(NO₃)₃ has the highest fluorescence intensity and quantum yield of the three Eu(III) complexes.     

Copper/iron-catalyzed Ullmann coupling of diiodo- and dibromoarenes and diphenols for the synthesis of aryl ether macrocycles

Diiodoarenes (or dibromoarenes) reacted with diphenols, catalyzed by CuI/Fe(acac)₃ in the presence of K₂CO₃ in anhydrous DMSO at 110 °C for 7 days under nitrogen atmosphere, to afford macrocyclic aryl ethers effectively. To expand this methodology, a cyclic hepta(p-phenylene oxide) and cyclic deca(p-phenylene oxide) were synthesized in one pot. Some macrocyclic aryl ethers showed strong fluorescence in acetone at 25 °C.     

Naphthyridine-based helical foldamers and macrocycles: synthesis, cation binding, and supramolecular assemblies

Unraveling the factors that control the conformation of molecular chains is of great interest both for understanding the shape of biological molecular strands and for designing artificial ones that adopt desired forms. Thus, a variety of artificial folding codons have been identified that enforce the formation, among others, of helices, strands, and loops, the major emphasis being on the shape of the foldamer. We report herein the synthesis and study of a family of foldamers and macrocycles based on the 1,8-naphthyridine and pyrimidine units, whose internal cavity is large enough to accommodate ionic substrates, and focus on the impact of guest binding within a cylindrical environment. Interestingly, the binding event within these large oligomers is translated to the outside of the receptors and affects the interaction of the overall complexes with the outside world. For instance, alkali cations bind to the one-turn helices and macrocycles to promote fibril formation and aggregation. Also, polyammonium substrates are able to tune the length of the overall helix assemblies and the rigidity of long oligomers. The reported data on one-turn, two-turn helices and macrocycles not only allows one to devise a model for the ion-controlled supramolecular assembly of such systems but also provides evidence that such controlled scaffolds bear promise in the design of complex systems.