Current Organic Chemistry - Volume 15, Issue 1, 2011

Supramolecular chemistry, coined as “beyond molecular” chemistry and based on the pioneering work of Donald J. Cram, Jean-Marie Lehn, and Charles J. Pedersen, aims to create novel structures and materials, fabricate nanomachines and small devices, mimic the functions of biomacromolecules and biosystems, and to illuminate the archebiont and make life ultimately. Generally, supramolecular chemistry includes two main subbranches: supramolecular self-assembly and host-guest chemistry. The former gives more emphasis to build beyond structures by repeated noncovalent binding of a same sort of molecules which are normally amphiphilic; the latter always focuses on inclusion complex formed from a “hollow” molecule (i.e., host) and smaller molecules, ions and atoms (i.e., guests). This special issue will concentrate on host-guest supramolecular chemistry, particularlly on the organic inclusion complex systems. Organic inclusion chemistry roots in classic organic chemistry which concerns the covalent bonds of C-X, opens to polymer science, material science, physics, biology, biomedicine, nanoscience and nanotechnology, and theoretics, and has unlimited potential in the industrial applications. Even though there is no unified theory on strong interactions of chemical bonds and weak interactions such as van der Waals' forces, mechanical inclusion, encapsulation, π-π stacking, entropy force, and hydrophobic effect, etc., numerous united host-guest supermolecules perfectly conctructed by both covalent bonds and noncovalent forces widely exist in nature and have been created by scientists in the past decades. This special issue will summarize, comment and highlight the recent advancements of organic inclusion chemistry, and prospects the possible new directions and areas. Typically, cucurbiturils, calixarenes, catenanes, rotaxanes, cyclodextrins, and dendritic macromolecules are selected as the main hosts due to their uniqe structure and properties, and great potential applications. Expect synthesis, characterization, and property of the relevant host-guest supermolecules, utilization of host-guest chemistry to tune surface properties such as hydrophobicity/hydrophilicity, prepare supramolecular polymer of polyrotaxanes, fabricate supramolecular machines, and to direct supramolecular self-assembly is also accounted in this issue. It is a great pleasure for me to be involved as a Guest Editor of this issue of Current Organic Chemistry. I wish to express my sincere gratefulness to all of the authors contributing to this special issue for their valuable work and their support. I am sure that their contributions will broaden the view sights of readers and further the faster development of supramolecular chemistry.

Dendritic macromolecules are three-dimentional polymers with branch-on-branch topology of which dendrimers and hyperbranched polymers (HPs) are the two most researched subclasses. This paper reviews the recent progress of host-guest supramolecular chemistry in terms of various HPs and dendrimers. Because of the highly branched structure and the presence of internal space and binding sites, dendritic macromolecule can serve as host to encapsulate multiple guests, just like a highly branched “tree” accommodating multiple “bird's nests”. Core-shell structure made by functionalization of dendritic polymer core with shielding shell of opposite polarity is usually needed to obtain a stable host-guest complex. Their encapsulation capacities are dependent on various factors, such as core size or molecular weight, polarity difference between core and shell, interaction strength between core and guests, shell density, and so on. Dendritic polymer-based host-guest encapsulation can be applied in many fields including phase-transfer, noncovalent functionalization, metal nanoparticle growth, and biological imaging.

This review summarizes recent work on the chemistry of inclusion complexes formed between redox active guests and cucurbit [n]uril hosts. The large majority of the surveyed research concerns the hosts cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8), while the guests are 4,4'-bipyridinium (viologen) and ferrocene derivatives. The work includes dendronized guests, in which a guest residue is attached to a dendron in such a way that host-guest binding interactions are still possible. The main focus of the review is on the electrochemical behavior of the included guests. In general terms complexation by CB7 has a more pronounced effect on the ferrocene derivatives, giving rise to a measurable attenuation of the electrochemical kinetics. In contrast to this, the electrochemical kinetics of the viologen derivatives remains fast (in the voltammetric time scale, with scan rates up to 2 V s-1) upon inclusion complexation by CB7. The larger cavity host CB8 is extremely effective at mediating the redox-driven self-assembly of dendronized viologens.

The use of calixarenes in asymmetric catalysis was described. The current progress of asymmetric catalysts based on calixarene scaffold for the enantioselective reactions including allylation, alkylation, addition of diethylzinc to benzaldehyde, Micheal-type addition, aldol reaction, hydrogenation, Friedal Crafts reaction, epoxidation, hydroformylation, and Biginelli reaction was illustrated. In these cases, calixarenes were used as organocatalysts or ligands in metal-catalyzed asymmetric reactions.

Regioisomers of calixarenes can be either produced in the reaction process with the same reactants or derived from the isomeric nucleophilic reagents. This article reviews the syntheses, different complexation abilities and self-assembly behaviors of the regioisomers in calixarenes.

Recently, separation science in the presence of cyclodextrins (CDs) has been paid more and more attention. Two important technologies based on CDs, molecularly imprinted polymers (MIPs) and ionic liquid (IL) cooperating approach, have been studied extensively and not been reviewed. MIPs are significant and important in separation processes. MIPs based on cyclodextrins (CD-MIPs) take advantage of unique properties of cyclodextrins and are applied in the separation of various molecules. Different methods for preparation CD-MIPs and supramolecular interactions in the systems are reviewed. Furthermore, ILs have been also widely used in separation science. Cooperative effect of CDs and ILs together for separation usage is discussed in this paper. The related separation techniques are mainly capillary electrophoresis (CE) and gas chromatography (GC). CD-MIPs and cooperative effect of ILs in separation methods, which are two important aspects in cyclodextrins separation science, are summarized here. It is hoped that the discussion on the above two topics will stimulate further research.

The controllable functional encapsulation of cucurbit[n]urils (Q[n]s) to form supramolecular catalysts is reviewed. The relationship of the supramolecular catalytic activity with the structure of included guests and cucurbit[n]urils is documented and discussed. The controllable functional encapsulation is attributed to overall interactions of hydrophobic, ion-dipole and size effects of the cucurbit [n]urils. The accelerated and stereochemical aspects of chemical reactions result from overcoming the hindrance of decreased entropy, the hydrophobic effect and the encapsulation model induced by hosts. The stability of drugs and chemical intermediates of the inclusion complexes depends on the environment within the hydrophobic cavity; the enhanced charge-transfer process of the included electron donor and acceptor guests depends on the compressed distance between guests, the electron donors, and acceptors within the limited space.

The aim of this article is to explore the molecular design, synthesis and construction of molecular shuttles based on conjugated organic molecules with photo-electronic activity by self-assembly techniques. The new functions of molecular shuttles, such as switching surface properties, protecting dyes and insulating molecular wires, controlling the energy transfer, controlling nanostructural morphologies, molecular transporting and multilevel fluorescence switching, are also discussed.

Type 2 diabetes mellitus is a growing health problem across the world. Thiazolidinediones, a new class of oral antidiabetic agents, appear to be ideally suited for the treatment of this disease. The examination of the clinical efficacy of different thiazolidinediones has been extensive. This review summarizes the current state of the cut concerning the clinical use of different thiazolidinediones, starting from the first synthetic thiazolidinediones to the recently developed glitazones. A main focus of this review is the description of the chemistry of these compounds including their synthesis.

C-Glycosylphenols and -polyphenols occur widely in nature and present a variety of biological properties, namely antitumor, antibacterial and antidiabetic activities. Synthetic access to such structures relies mainly on efficient methodologies for phenols C-glycosylation. In the past few years major advances have been described addressing the use of Fries rearrangement to obtain a diversity of C-glycosyl compounds. Herein we survey the glycosyl donors and the activators used for this reaction, covering both early work and recent developments in the area. Reaction mechanism and reaction outcome control, aiming at regio- and stereoselectivity are also discussed.