I. Introduction 4071 II. The Term Supramolecular Polymers 4071 III. General Aspects of Supramolecular Polymers 4073 IV. Supramolecular Polymers Based on Hydrogen Bonding 4073 A. Strength of Hydrogen Bonds 4073 B. Hydrogen Bonding Enforced by Liquid Crystallinity 4075 C. Hydrogen Bonding Enforced by Phase Separation 4076 D. Strong Dimerization of Multiple Hydrogen-Bonding Units 4077 E. Ureidopyrimidinone-Based Polymers 4079 V. Supramolecular Polymers Based on Discotic Molecules 4081 A. Arene−Arene Interactions 4082 1. Triphenylenes 4082 2. Phthalocyanines and Porphyrins 4083 3. Helicenes 4084 4. m-Phenylene Ethynylene Oligomers 4084 5. Other Systems 4085 6. Chromonics 4086 B. Hydrogen Bonding 4086 C. Arene−Arene Interactions and Hydrogen Bonding 4087 1. Guanine and Pterine Derivatives 4087 2. Hydrogen-Bonded Pairs 4089 3. Complexation of Tetrazoles with 1,3,5-Tris (4,5-dihydroimidazol-2-yl)benzene 4089 4. C 3 -Symmetrical Discotic Molecules 4090 VI. Supramolecular Coordination Polymers and Miscellaneous Systems 4091 VII. Conclusions and Outlook 4094 VIII. Acknowledgments 4094 IX. References and Notes 4094

Units of 2-ureido-4-pyrimidone that dimerize strongly in a self-complementary array of four cooperative hydrogen bonds were used as the associating end group in reversible self-assembling polymer systems. The unidirectional design of the binding sites prevents uncontrolled multidirectional association or gelation. Linear polymers and reversible networks were formed from monomers with two and three binding sites, respectively. The thermal and environmental control over lifetime and bond strength makes many properties, such as viscosity, chain length, and composition, tunable in a way not accessible to traditional polymers. Hence, polymer networks with thermodynamically controlled architectures can be formed, for use in, for example, coatings and hot melts, where a reversible, strongly temperature-dependent rheology is highly advantageous.

Reversible S-palmitoylation of cysteine residues critically controls transient membrane tethering of peripheral membrane proteins. Little is known about how the palmitoylation machinery governs their defined localization and function. We monitored the spatially resolved reaction dynamics and substrate specificity of the core mammalian palmitoylation machinery using semisynthetic substrates. Palmitoylation is detectable only on the Golgi, whereas depalmitoylation occurs everywhere in the cell. The reactions are not stereoselective and lack any primary consensus sequence, demonstrating that substrate specificity is not essential for de-/repalmitoylation. Both palmitate attachment and removal require seconds to accomplish. This reaction topography and rapid kinetics allows the continuous redirection of mislocalized proteins via the post-Golgi sorting apparatus. Unidirectional secretion ensures the maintenance of a proper steady-state protein distribution between the Golgi and the plasma membrane, which are continuous with endosomes. This generic spatially organizing system differs from conventional receptor-mediated targeting mechanisms and efficiently counteracts entropy-driven redistribution of palmitoylated peripheral membrane proteins over all membranes.