Metalloporphyrin hosts for supramolecular chemistry of fullerenes

This paper is a tutorial review of the host-guest chemistry of fullerenes and metalloporphyrin. Among various host molecules for fullerenes, cyclic hosts composed of metalloporphyrin moieties possess one of the highest affinities toward fullerenes, which can be widely tuned simply by changing the central metal ions of the porphyrin moieties. Inclusion of fullerenes occurs not only by van der Waals interactions but also, in some cases, via pi-electronic charge-transfer from the host metalloporphyrin moieties to the guest fullerenes. Fullerenes such as C(120), upon inclusion with cyclic metalloporphyrin dimers, show an oscillatory motion within the host cavity, whose frequency reflects the solvation/desolvation dynamics of the fullerenes. A molecularly engineered metalloporphyrin host with a self-assembling capability allows a guest-directed formation of a supramolecular peapod, where included fullerenes, as peas, are aligned along the self-assembled metalloporphyrin nanotube, as a pod. Furthermore, certain metalloporphyrin hosts are applicable to the selective extraction of low-abundance higher fullerenes from an industrial production source and also allow spectroscopic discrimination of chiral fullerenes.     

The synthesis of benzoxaboroles and their applications in medicinal chemistry

Benzoxaborole, as a versatile scaffold, plays important roles in organic synthesis, molecular recognition and supramolecular chemistry. It is also a privileged structure in medicinal chemistry due to its desirable physicochemical and drug-like properties. Recently, benzoxaboroles were widely applied as antifungal, antibacterial, antiviral, anti-parasite, and anti-inflammatory agents. This review covers the properties, synthetic methods and applications of benzoxaboroles in medicinal chemistry.     

Solid-state molecular folding and supramolecular structures of triptycene-derived secondary dicarboxamides

The synthesis and X-ray crystal structures of triptycene-derived secondary dicarboxamides 1 and 4-7 and reference compounds 2, 3, and 8 are reported. For comparison, molecular conformations of 1-8 in the gas phase and those of 1 and 3-6 in CD2Cl2 investigated by AM1 modeling and 1H NMR spectroscopy, respectively, are also included. The solid-state conformations of 1 and 5-8 are folded and compact, resulting from the cooperative effects of intramolecular amide-amide hydrogen bonding and edge-to-face arene-arene interactions between the triptycene and the N-acetylsulfanilyl groups. The sulfonyl ester groups are also essential in the folding of 1 and 5-8 and function as structural turn units. In contrast, the conformations of 2-4 are unfolded due to the lack of one of these three essentials. The extended triptycene ring systems in 6 and 7 provide an arene-arene contact mode that is different from that for 1 and 5. While AM1 calculations suggest that the two possible arene-arene contact modes in 6 and 7 have similar conformational energies, the one observed in the solid state is also favored in solutions. To achieve a more regular shape for compact crystal packing, the bulky triptycene groups tend to pack in pairs. As a result, the intermolecular amide-amide hydrogen bonding is perturbed and modified with the participation of either the sulfonyl groups or the methanol solvent molecules, leading to various hydrogen-bonding motifs for these triptycene diamides.     

Emergences of supramolecular chemistry: from supramolecular chemistry to supramolecular science

We describe the field of supramolecular chemistry as a consequence of the progress of chemistry from its premises to recent achievements. Supramolecular chemistry has been claimed to be an emergent field of research taking its roots in chemistry. According to the definitions of emergences related to hierarchy or more recently to scope, supramolecular chemistry is shown to have bottom-up or top-down emergences. The bottom-up emergence, directly related to hierarchy by definition, opens up the world of nanochemistry and nanomaterials while the top-down one, attributable to scope due to the implication of supramolecular chemistry in other fields of research, open the world of supramolecular biochemistry. Both emergences lead supramolecular chemistry to become a supramolecular science. Combining supramolecular chemistry with biology opens new direction in the study of life and it origin.     

Nitroxides: applications in synthesis and in polymer chemistry

This Review describes the application of nitroxides to synthesis and polymer chemistry. The synthesis and physical properties of nitroxides are discussed first. The largest section focuses on their application as stoichiometric and catalytic oxidants in organic synthesis. The oxidation of alcohols and carbanions, as well as oxidative C-C bond-forming reactions are presented along with other typical oxidative transformations. A section is also dedicated to the extensive use of nitroxides as trapping reagents for C-centered radicals in radical chemistry. Alkoxyamines derived from nitroxides are shown to be highly useful precursors of C-centered radicals in synthesis and also in polymer chemistry. The last section discusses the basics of nitroxide-mediated radical polymerization (NMP) and also highlights new developments in the synthesis of complex polymer architectures.     

Bile acid scaffolds in supramolecular chemistry: the interplay of design and synthesis

Since early work in the 1980s, the bile acids have become well established as building blocks for supramolecular chemistry. The author's laboratory has specialised in converting cholic acid, the archetypal bile acid, into macrocyclic and acyclic receptors for anions and carbohydrates. This review highlights the synthetic aspects of this work, especially the use of modern synthetic methodology to perform less obvious structural transformations.     

Microwave-assisted reactions in heterocyclic compounds with applications in medicinal and supramolecular chemistry

Microwave irradiation has been successfully applied in organic chemistry. Spectacular accelerations, higher yields under milder reaction conditions and higher product purities have all been reported. Indeed, a number of authors have described success in reactions that do not occur under conventional heating and modifications in selectivity (chemo-, regio- and stereoselectivity) have even been reported. Recent advances in microwave-assisted combinatorial chemistry include high-speed solid-phase and polymer-supported organic synthesis, rapid parallel synthesis of compound libraries, and library generation by automated sequential microwave irradiation. In addition, new instrumentation for high-throughput microwave-assisted synthesis continues to be developed at a steady pace. The impressive speed combined with the unmatched control over reaction parameters justifies the growing interest in this application of microwave heating. In this review we highlight our recent advances in this area, with a particular emphasis on cycloaddition reactions of heterocyclic compounds both with and without supports, applications in supramolecular chemistry and the reproducibility and scalability of organic reactions involving the use of microwave irradiation techniques.     

Cup-shaped E,E-stilbenophane: synthesis,crystal structure and supramolecular chemistry

A new E,E-stilbenophane was synthesised and characterised. The crystal structure of this cyclophane shows that this molecule has a cup-shaped structure, which hosts a phenyl ring of neighbouring molecule as guest in its cavity with a π–π distance of about 3.7 Å. Moreover, the NMR spectra and theoretical analysis (gauge-independent atomic orbitals (GIAO) and quantum theory of atoms in molecules (QTAIM)) suggest that the silver recognition by E,E-stilbenophane host molecules is based on cation–π interactions in which the π-electrons of the double bonds play a major role.     

Fullerodendrimers: a new class of compounds for supramolecular chemistry and materials science applications

Encapsulation of a fullerene sphere in the middle of a dendritic structure prevents unfavorable effects of the C60 unit, such as aggregation or steric hindering. Such fullerodendrimers appear to be promising compounds for materials science applications. On the other hand, fullerodendrons with peripheral C60 subunits or containing a C60 sphere at each branching unit appear to be versatile building blocks for the preparation of fullerene-rich macromolecules with intriguing properties.     

Alpha-arylsulfanyl-alpha-fluoro carbenoids: their novel chemistry and synthetic applications

The bromine-magnesium exchange reactions of arylthiobromodifluoromethanes with Grignard reagents have been studied. Upon trapping with electrophiles, alkyl aryl sulfides and ketenedithioacetals are obtained. The reaction is proposed to occur via novel alpha-arylsulfanyl-alpha-fluoro carbenoids. The first examples of arylthiomethane multipole synthons are also reported. [reaction: see text]     

Synthesis of a redox-responsive quadruple hydrogen-bonding unit for applications in supramolecular chemistry

A redox-responsive quadruple hydrogen-bonding module (eDAN) has been developed. The strong binding between the reduced form and its partner (DeUG) can be significantly decreased upon oxidation but restored upon subsequent reduction. This on-off switch was successfully applied to provide reversible control of macroscopic supramolecular polymer networks.     

Transition metal based supramolecular systems: synthesis, photophysics, photochemistry and their potential applications as luminescent anion chemosensors

This review describes our recent research results on several transition-metal based supramolecular systems. A number of self-assembly metallocyclophanes and cages have been prepared. We have found that the photophysical properties of these systems are highly dependent on the nature of the bridging ligands and that many of these metallocyclophanes and cages are capable of binding different guest molecules such as inorganic anions and a variety of aromatic compounds. Moreover, trinuclear (diimine) rhenium(I) tricarbonyl complexes linked by a stilbene-like ligand exhibit most interesting photoswitching features, where the luminescence from the complexes can be switched on and off by photoinduced ligand isomerization. In addition, a structurally simple and easily synthesized luminescent anion receptor has been recently developed and it displays outstanding sensitivity and selectivity toward anionic species. We also review the synthesis of two shape-persistent hexagonal phenylacetylenes and their use as ligands to synthesize dinuclear transition-metal complexes. The photophysical properties of both phenylacetylenic ligands and their corresponding metal complexes are summarized.     

CO2 in supramolecular chemistry: preparation of switchable supramolecular polymers

CO2 gas was used to construct novel types of supramolecular polymers. Self-assembling nanostructures 11 and 13 were prepared, which employ both hydrogen bonding and dynamic, thermally reversible carbamate bonds. As precursors, calixarene ureas 1 and 2 were synthesized, which strongly aggregate/dimerize (K(D)>/=10(6) M(-1) per capsule) in apolar solution with the formation of self-assembling capsules 7 and linear polymeric chains 8, respectively, and also possess "CO2-philic" primary amino groups on the periphery. CO2 effectively reacts with molecules 7 and 8 in apolar solvents and cross-links them with the formation of multiple carbamate salt bridges. Oligomeric aggregate 11 and three-dimensional polymeric network 13 were prepared and characterized by 1H and 13C NMR spectroscopy. The morphology of supramolecular gel 13 was studied by scanning electron microscopy. Addition of a competitive solvent destroyed the hydrogen bonding in assembling structures 11 and 13, but did not influence the carbamate linkers; carbamate salts 12 and 14, respectively, were obtained. On the other hand, thermal release of CO2 from 11 and 13 was easily accomplished (1 h, 100 degrees C) while retaining the hydrogen-bonding capsules. Thus, three-dimensional polymeric network 13 was transformed back to linear polymeric chain 8 without breaking up. Encapsulation and storage of solvent molecules by 11 and 13 was demonstrated. This opens the way for switchable materials, which reversibly trap, store, and then release guest molecules. A two-parameter switch and control over hydrogen bonding and CO2-amine adducts was established.     

Multivalency in supramolecular chemistry and nanofabrication

Multivalency is a powerful and versatile self-assembly pathway that confers unique thermodynamic and kinetic behavior onto supramolecular complexes. The diversity of the examples of supramolecular multivalent systems discussed in this perspective shows that the concept of multivalency is a general phenomenon, and that any supramolecular interaction can be employed in multivalent displays to attain the attractive aspects characteristic of multivalent interactions. After a general introduction reviewing the general aspects of multivalency, a number of different supramolecular multivalent complexes are discussed that highlight the different features of multivalent interactions. In contrast to the many biochemical multivalent interactions, supramolecular multivalent interactions are ideal to attain a quantitative and fundamental understanding of multivalency. Several examples in which multivalency has been utilized in supramolecular nanofabrication schemes are described in detail.     

Novel chemistry of alpha-tosyloxy ketones: applications to the solution- and solid-phase synthesis of privileged heterocycle and enediyne libraries

New synthetic technologies for the preparation and elaboration of alpha-tosyloxy ketones in solution- and on solid-phase are described. Both olefins and ketones serve as precursors to these relatively stable chemical entities: olefins via a novel one-pot epoxidation, arylsulfonic acid displacement, and oxidation sequence, and ketones by direct exposure to arylsulfonic acids in the presence of diacetoxy iodobenzene. Reaction of these substrates with O-, S-, or N-centered nucleophiles leads to incorporation of the nucleophile with concomitant expulsion of the sulfonate, while exposure to bis-functional nucleophiles furnishes annulated heterocyclic systems. In addition, the reactions of carbon-centered nucleophiles with alpha-tosylyloxy ketones are also explored. The collated data for all these nucleophiles provide compelling evidence for the proposal that different reaction pathways are followed when alpha-tosyloxy ketones are engaged by "hard" versus "soft" nucleophiles. The accessibility and site-selectivity of the chemistry demonstrated herein offer the promise of an expanded use for this moiety in solid-phase library construction, in particular, and in the field of organic synthesis, in general.     

Carbon dioxide and supramolecular chemistry

Concepts and techniques of supramolecular chemistry are applied to the century-old chemistry between CO2 and amines to design novel sensing systems and nanoscale, self-assembling polymeric materials and networks.     

Halogen bonding in supramolecular chemistry

Halogen bonding is the noncovalent interaction where halogen atoms function as electrophilic species. The energetic and geometrical features of the interaction are described along with the atomic characteristics that confer molecules with the specific ability to interact through this interaction. Halogen bonding has an impact on all research fields where the control of intermolecular recognition and self-assembly processes plays a key role. Some principles are presented for crystal engineering based on halogen-bonding interactions. The potential of the interaction is also shown by applications in liquid crystals, magnetic and conducting materials, and biological systems.     

Novel supramolecular catalysis in the controlled synthesis of polymers and block copolymers

Novel carbanionic polymerization of vinyl monomers as styrene, methyl methacrylate, as well as ring opening polymerization of oxiranes and lactones mediated by supramolecular complexes of alkali metals is demonstrated.     

From supramolecular chemistry towards constitutional dynamic chemistry and adaptive chemistry

Supramolecular chemistry has developed over the last forty years as chemistry beyond the molecule. Starting with the investigation of the basis of molecular recognition, it has explored the implementation of molecular information in the programming of chemical systems towards self-organisation processes, that may occur either on the basis of design or with selection of their components. Supramolecular entities are by nature constitutionally dynamic by virtue of the lability of non-covalent interactions. Importing such features into molecular chemistry, through the introduction of reversible bonds into molecules, leads to the emergence of a constitutional dynamic chemistry, covering both the molecular and supramolecular levels. It considers chemical objects and systems capable of responding to external solicitations by modification of their constitution through component exchange or reorganisation. It thus opens the way towards an adaptive and evolutive chemistry, a further step towards the chemistry of complex matter.