Formation of an imine—from an amine and an aldehyde—is a reversible reaction which operates under thermodynamic control such that the formation of kinetically competitive intermediates are, in the fullness of time, replaced by the thermodynamically most stable product(s). For this fundamental reason, the imine bond has emerged as an extraordinarily diverse and useful one in the hands of synthetic chemists. Imine bond formation is one of a handful of reactions which define a discipline known as dynamic covalent chemistry (DCC), which is now employed widely in the construction of exotic molecules and extended structures on account of the inherent ‘proof-reading’ and ‘error-checking’ associated with these reversible reactions. While both supramolecular chemistry and DCC operate under the regime of reversibility, DCC has the added advantage of constructing robust molecules on account of the formation of covalent bonds rather than fragile supermolecules resulting from noncovalent bonding interactions. On the other hand, these products tend to require more time to form—sometimes days or even months—but their formation can often be catalysed. In this manner, highly symmetrical molecules and extended structures can be prepared from relatively simple precursors. When DCC is utilised in conjunction with template-directed protocols—which rely on the use of noncovalent bonding interactions between molecular building blocks in order to preorganise them into certain relative geometries as a prelude to the formation of covalent bonds under equilibrium control—an additional level of control of structure and topology arises which offers a disarmingly simple way of constructing mechanically-interlocked molecules, such as rotaxanes, catenanes, Borromean rings, and Solomon knots. This tutorial review focuses on the use of dynamic imine bonds in the construction of compounds and products formed with and without the aid of additional templates. While synthesis under thermodynamic control is giving the field of chemical topology a new lease of life, it is also providing access to an endless array of new materials that are, in many circumstances, simply not accessible using more traditional synthetic methodologies where kinetic control rules the roost. One of the most endearing qualities of chemistry is its ability to reinvent itself in order to create its own object, as Berthelot first pointed out a century and a half ago.

Dynamic imine chemistry.

Nanotechnology has recently gained increased attention for its capability to effectively diagnose and treat various tumors. Nanocarriers have been used to circumvent the problems associated with conventional antitumor drug delivery systems, including their nonspecificity, severe side effects, burst release and damaging the normal cells. Nanocarriers improve the bioavailability and therapeutic efficiency of antitumor drugs, while providing preferential accumulation at the target site. A number of nanocarriers have been developed; however, only a few of them are clinically approved for the delivery of antitumor drugs for their intended actions at the targeted sites. The present review is divided into three main parts: first part presents introduction of various nanocarriers and their relevance in the delivery of anticancer drugs, second part encompasses targeting mechanisms and surface functionalization on nanocarriers and third part covers the description of selected tumors, including breast, lungs, colorectal and pancreatic tumors, and applications of relative nanocarriers in these tumors. This review increases the understanding of tumor treatment with the promising use of nanotechnology.

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Effective use of nanocarriers as drug delivery systems for the treatment of selected tumors.

Post-polymerization modification is based on the direct polymerization or copolymerization of monomers bearing chemoselective handles that are inert towards the polymerization conditions but can be quantitatively converted in a subsequent step into a broad range of other functional groups. The success of this method is based on the excellent conversions achievable under mild conditions, the excellent functional-group tolerance, and the orthogonality of the post-polymerization modification reactions. This Review surveys different classes of reactive polymer precursors bearing chemoselective handles and discusses issues related to the preparation of these reactive polymers by direct polymerization of appropriately functionalized monomers as well as the post-polymerization modification of these precursors into functional polymers.

Synthesis of functional polymers by post-polymerization modification.

Chemical Topology: Complex Molecular Knots, Links, and Entanglements

Mono- and di-quaternized 4,4'-bipyridine derivatives constitute a family of heterocyclic compounds, which in recent years have been employed in numerous applications. These applications correspond to various disciplines of research and technology. In their majority, two key features of these 4,4'-bipyridine-based derivatives are exploited: their redox activity and their electrochromic aptitude. Contemporary materials and compounds encompassing these skeletons as building blocks are often characterized as multifunctional, as their presence often gives rise to interesting phenomena, e.g., various types of chromism. This research trend is acknowledged, and, in this review article, recent examples of multifunctional chromic materials/compounds of this class are presented. Emphasis is placed on solvent-/medium- and environment-responsive 4,4'-bipyridine derivatives. Two important classes of 4,4'-bipyridine-based products with solvatochromic and/or environment-responsive character are reviewed: viologens (i.e., N,N'-disubstituted derivatives) and monoquats (i.e., monosubstituted 4,4'-bipyridine derivatives). The multifunctional nature of these derivatives is analyzed and structure-property relations are discussed in connection to the role of these derivatives in various novel applications.

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Mono- and Di-Quaternized 4,4'-Bipyridine Derivatives as Key Building Blocks for Medium- and Environment-Responsive Compounds and Materials

Simultaneous and Reversible Functionalization of Copolymers for Biological Applications

Stimuli-responsive polymers and assemblies are viable candidates for the so-called “smart” materials. In this communication, we report a new class of amphiphilic homopolymers that forms micelle-like structures in polar solvents and inverted micelle-like structures in apolar solvents. We demonstrate that these superstructures are the result of the changes in the molecular-level conformations in the monomer.

Invertible amphiphilic homopolymers.

Mechanically interlocked molecules (MIMs), in the form of donor–acceptor [2]catenane-containing struts of exceptional length, have been incorporated into a three-dimensional catenated metal–organic framework (MOF) at precise locations and with uniform relative orientations. Catenation is expressed simultaneously within the struts and the framework.

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A Catenated Strut in a Catenated Metal-Organic Framework

Amphiphilic dendrimers with a custom-designed biaryl repeat unit have been synthesized. These dendrimers afford hydrophobic nanocontainers in polar solvents and hydrophilic nanocontainers in apolar solvents. These container properties were investigated using dye incorporation studies. The aggregation states of these dendrimers are also reported using DLS studies.

Dendrimers with both polar and apolar nanocontainer characteristics.

Amphiphilic homopolymers containing a hydrophilic and a hydrophobic functionality in each monomer unit have been shown to form polar or apolar containers depending on the solvent environment. When presented with a mixture of solvents, these polymeric containers are capable of releasing certain guest molecules. The fundamental mechanism behind these properties is investigated, and the utility of these assemblies in separations has been demonstrated with an example.

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Subhadeep Basu

Papers

Simultaneous and Reversible Functionalization of Copolymers for Biological Applications

Invertible amphiphilic homopolymers.

A Catenated Strut in a Catenated Metal-Organic Framework

Dendrimers with both polar and apolar nanocontainer characteristics.

Homopolymer micelles in heterogeneous solvent mixtures.