The number, size, and function of peripheral groups of dendritic macromolecules determine many of the typical dendrimer properties, such as dense-shell packing, overall shape, and multivalency. [1] Properties related to solubility or physical stateÐsemi-crystalline, glass, liquid crystalline, or liquidÐare also strongly dependent on the nature of the dendritic end group. [2] Finally, specific interactions of guest molecules with the dendritic hosts rely on both the core and the shell of the dendrimer. [3±11] Most of the end-group modifications are based on covalent bonding, while the use of supramolecular interactions to obtain new dendritic peripheries is limited. Chechik and Crooks showed that ionic bonding between an amine-terminated poly(aminoamine) (PAMAM) and a fatty acid resulted in similar host ± guest properties as those of the corresponding covalent amide analogues, while Tomalia and co-workers recently used ionic interactions to assemble dendrimers into higher aggregates. [12] We anticipated that the combination of a dense packing of the shell with the possibility of tuning the functionality of the periphery is of great importance in making dendrimers that can be used as shape-persistent building blocks in nanotechnology. Herein we disclose a general methodology to modify the periphery of poly(propyleneimine) dendrimers using such a supramolecular approach. The covalently attached adamantylurea end groups of the dendrimer are used as a scaffold to reversibly bind glycinylurea building blocks through strong and directional multiple interactions (Scheme 1).The design of the modification is given in Scheme 1 and the scaffold is based upon DAB-dendr-(NHCONH-Ad) n (1, with n 4, 8, 16, 32, and 64 for 1 a ± e, respectively). These dendrimers were selected after studying DAB-dendr-(NHCO-Ad) n (2 a ± e), DAB-dendr-(NHCONH-C 12 H 25 ) n , and DAB-dendr-(NHCO-C 12 H 25 ) n as well. All dendrimers were synthesized in quantitative yield from DAB-dendr-(NH 2 ) n and the corresponding isocyanate or acid chloride and were fully characterized. [13a] The concept of the supramolec-pH measurements were made with a Corning 440 pH meter equipped with an Aldrich micro-combination electrode calibrated with standard buffer solutions of pH 4, 7, and 10.Electrospray mass spectrometry (ESI-MS) was performed on a LCQ spectrometer (Finnigan Corporation). The sample was infused at 3 mL min À1 , and the ions were produced in an atmospheric-pressure ionization (API)/ESI ion source. The source temperature was 453 ± 473 K, and the flow rate of the drying gas was 0.9 L min À1 . A potential of 3.5 kV was applied to the probe tip, and a cone voltage of 5 ± 10 V over 200 ± 2000 Da was used. The quadrupole was scanned at 100 amu s À1 . The mass accuracy of all measurements was within 0.5 m/z units. Data acquisition and processing were performed with the Microsoft Windows NT operating system. The mass spectrum was simulated on a PC with IsoPro 3.0. Molecular modeling was performed by using INSIGHT II (95.0, Biosym-MSI software) with the E...