Supramolecular Modification of the Periphery of Dendrimers Resulting in Rigidity and Functionality

Abstract

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...

Phase Transfer of CdS Nanocrystals Mediated by Heptamine β-Cyclodextrin

“…β-cyclodextrin (βCD) and αcyclodextrin (≥98%, αCD) were purchased from Fluka. Adamantylterminated poly(propylene imine) (PPI) dendrimer (with 16 adamantyl groups, G3-PPI-(Ad) 16 ), 27 βCD heptathioether, 28 and heptamine β-cyclodextrin ((NH 2 ) 7 βCD) 29 were synthesized according to previously reported procedures. 2,2″([1,1′-Biphenyl]-4.4′-diyldi-2,1ethenediyl)bis-benzenesulfonic acid disodium salt (Stilbene 3) was purchased from Lambda Physik.…”