Reversible covalent bond formation under thermodynamic control adds reactivity to self-assembled supramolecular systems, and is therefore an ideal tool to assess complexity of chemical and biological systems. Dynamic combinatorial/covalent chemistry (DCC) has been used to read structural information by selectively assembling receptors with the optimum molecular fit around a given template from a mixture of reversibly reacting building blocks. This technique allows access to efficient sensing devices and the generation of new biomolecules, such as small molecule receptor binders for drug discovery, but also larger biomimetic polymers and macromolecules with particular three-dimensional structural architectures. Adding a kinetic factor to a thermodynamically controlled equilibrium results in dynamic resolution and in self-sorting and self-replicating systems, all of which are of major importance in biological systems. Furthermore, the temporary modification of bioactive compounds by reversible combinatorial/covalent derivatisation allows control of their release and facilitates their transport across amphiphilic self-assembled systems such as artificial membranes or cell walls. The goal of this review is to give a conceptual overview of how the impact of DCC on supramolecular assemblies at different levels can allow us to understand, predict and modulate the complexity of biological systems.

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A new class of water-soluble, amphiphilic star block copolymers with a large number of arms was prepared by sequential atom transfer radical polymerization (ATRP) of n-butyl methacrylate (BMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA). As the macroinitiator for the ATRP, a 2-bromoisobutyric acid functionalized fourth-generation hyperbranched polyester (Boltorn H40) was used, which allowed the preparation of star polymers that contained on average 20 diblock copolymer arms. The synthetic concept was validated by AFM experiments, which allowed direct visualization of single molecules of the multiarm star block copolymers. DSC and SAXS experiments on bulk samples suggested a microphase-separated structure, in agreement with the core−shell architecture of the polymers. SAXS experiments on aqueous solutions indicated that the star block copolymers can be regarded as unimolecular micelles composed of a PBMA core and a diffuse PPEGMA corona. The ability of the polymers to encapsulate and release hydrophobic guests was evaluated using 1H NMR spectroscopy. In dilute aqueous solution, these polymers act as unimolecular containers that can be loaded with up to 27 wt % hydrophobic guest molecules.

Volatile organic compounds serve in nature as semiochemicals for communication between species, and are often used as flavors and fragrances in our everyday life. The quite limited longevity of olfactive perception has led to the development of pro-perfumes or pro-fragrances--ideally nonvolatile and odorless fragrance precursors which release the active volatiles by bond cleavage. Only a limited amount of reaction conditions, such as hydrolysis, temperature changes, as well as the action of light, oxygen, enzymes, or microorganisms, can be used to liberate the many different chemical functionalities. This Review describes the controlled chemical release of fragrances and discusses additional challenges such as precursor stability during product storage as well as some aspects concerning toxicity and biodegradability. As the same systems can be applied in different areas of research, the scope of this Review covers fragrance delivery as well as the controlled release of volatiles in general.

cAlthough higher fullerenes are not yet of even the larger, more complex carbon the larger carbon cages, it was sofar available in larger amounts, their acces-spheres C,,, CS4, and recently also C,, , mostly explored through their chemistry sibility, like that of C,,, has gradually have been isolated and characterized. and can be related to different structural improved since the early days of From the collected body of data, first characteristics. A recently proposed sysfullerene chemistry. Today, many of the general principles of reactivity and selec-tem allows simple specification by a soluble larger carbon cages can be pur-tivity begin to emerge for these fuller-single descriptor of the configuration of chased either in pure form or as isomeric enes, which are all less symmetric than chiral fullerenes and fullerene derivamixtures. In particular, pure C,, is C,, . Important information is provided tives with a chiral functionaiization patavailable in preparative amounts from by multiple additions to higher fuller-tern, including highly branched carbon fullerene soot without the need for te-enes, in which certain isomers are frameworks with a multitude of possible dious separation by high-performance formed with a remarkable selectivity stereogenic centers. liquid chromatography; this has had a that exceedes that observed for C,,. A major impact on the progress of the particularly attractive aspect is the chi-Keywords: carbon allotropes -chiralichemistry of this higher fullerene. Over rality of certain allotropes and many ty -fullerenes reactivity the last years C,, has been functional-derivatives. Although the chirality of ized in many ways, and pure derivatives fullerene derivatives is not restricted to L

To develop their biological activity, bioactive volatile compounds, such as pheromones or fragrances, have to evaporate from surfaces. Because these surfaces are usually exposed to natural daylight, the preparation of non-volatile precursors using photoremovable protecting groups is an ideal tool to control the release of caged volatile molecules from various surfaces by light-induced covalent bond cleavage. Many photoreactions occur under mild environmental conditions and are highly selective. To break covalent bonds under typical application conditions, the photoreaction has to proceed at ambient daylight, to tolerate the presence of oxygen and to run in polar media (e.g. in water). The amount of volatiles generated from photochemical delivery systems depends on the light intensity to which the systems are exposed. Both photoisomerisations and photofragmentations have successfully been investigated for the slow release of caged pheromones and fragrances from their corresponding precursors.

The pure enantiomers of D -C as well as a third constitutional isomer of this higher fullerene were produced by a retro-Bingel reaction on the first organic derivatives of C (see scheme). These derivatives were synthesized by Bingel cyclopropenation of C , separated, and unambiguously structurally characterized.

in Polyphenylene Dendrimers with an Increasing Number of Peryleneimide Chromophores Maus, M.; Mitra, S.; Lor, M.; Hofkens, J.; Weil, T.; Herrmann, A.; Müllen, K.; Schryver, F.C. DeThe photophysical properties and the excitation energy transfer (EET) process of a series of first generation dendrimers having a rigid tetrahedral core and different numbers of peryleneimide chromophores at the rim were investigated by steady-state and time-resolved fluorescence spectroscopy in toluene. It was shown that the model dendrimer containing only one chromophore decays monoexponentially with a time constant of 4.2 ns. In the multichromophoric compounds an additional long decay time of 7.4 ns assigned to an "excimerlike" state was observed, and its contribution increases with the number of chromophores. The time-resolved polarization measurements resulted in a nanosecond relaxation component due to the rotation of the entire dendritic structure. However, for the compounds having more than one chromophore, an additional fast anisotropy decay time of 100-200 ps was observed which corresponds to Förster type EET among the chromophores. 3965 continuing support. S.M. and J.H. thank KUL and FWO, respectively, for postdoctoral fellowships. M.M. thanks the EC through TMR-Sisitomas for a postdoctoral fellowship.