Synthesis and Properties of New Thiourea-Functionalized Poly(propylene imine) Dendrimers and Their Role as Hosts for Urea Functionalized Guests

Abstract

Five generations of poly(propylene imine) dendrimers have been modified by palmityl and adamantyl endgroups via a thiourea linkage. The synthesis of the thiourea dendrimers DAB-dendr-(NHCSNHAd)(n) and DAB-dendr-(NHCSNHC(16)H(33))(n) (n = 4, 8, 16, 32, 64) proceeds smoothly via the amino-terminated DAB dendrimer and the adamantyl and palmityl isothiocyanates, respectively. The properties of the thiourea dendrimers have been studied by IR and (1)H NMR, including relaxation (T1, T2) measurements. The thiourea dendrimers are used as multivalent hosts for a number of guest molecules containing a terminal urea-glycine unit in organic solvents. The host-guest interactions have been investigated using 1D- and NOESY-NMR. These investigations show that the guest molecules bind to the dendritic host via thiourea (host)-urea (guest) hydrogen bonding, and ionic bonding between the terminal guest carboxylate moiety and the outer shell tertiary amines of the dendrimer. The ability to bind guest molecules of the adamantyl- and palmitylthiourea dendrimers has been compared with their respective urea containing dendrimer analogues, by NMR-titration, and competition experiments. Upon complexation, the thiourea dendrimer hosts show a larger downfield NH shift than the corresponding urea dendrimer hosts, indicative of stronger hydrogen bonding in the complexed state. Furthermore, microcalorimetry has been used to determine binding constants for formation of the host-guest complexes; the binding constants are typically in the order of 10(4) M(-1). Both NMR and microcalorimetric studies show that the thiourea dendrimers bind the urea containing guests with somewhat higher affinity than the corresponding urea dendrimers.

Dendrimer Effects on Peptide and Protein Fibrillation

“…This was later obtained through non-covalent bonding of surface groups. [9,10] (1992). He has since worked with immunology and protein chemistry in various projects at the borderline between bioorganic chemistry and infection biology at the University of Copenhagen, in the private sector, and, presently, at the National Veterinary Institute (Technical University of Denmark) in Copenhagen.…”

Dendrimer‐Based Sensors

“…The generation-5 PPI dendrimer 59 containing 64 thiourea end functional groups, that is 32 of the bisthiourea pincer, was prepared by Meijer (Scheme 8.8) [103]. The interaction of 59 with the glycine-urea guest molecule 60 was studied.…”

New-generation biomedical materials: Peptide dendrimers and their application in biomedicine

“…Meijer et al [107] used modified PPI dendrimer as a host to encapsulate glycin (Figure 25(a)). Both hydrogen bond and static elec- Figure 25 (a) The interaction between the dendrimer and urea-glycine [107]. (b) The interaction between the dendrimer and Boc protected peptide [108].…”