NMR Studies on Silver(I) Ion Complex of G2-PAMAM Dendrimer

1. NMR Studies on Silver(I) Ion Complex of G2-PAMAM Dendrimer Scholar: Charmane Thurmand Mentor: Dr. Minghui Chai Department of Chemistry Central Michigan University

2. Background • PAMAM Dendrimers Dendrimers --- polymers Poly(amidoamine)--- PAMAM Exterior Dendrimer Interior Core cascade symmetrical spherical G0 dendritic-voids multi-functionality monodispersity G1 G2 G2 PAMAM Dendrimer

3. Potential Applications for Dendrimers • Based on the dendrimer’s multifunctionality, dendrimers can form complex with metal ions. • In this project: G2-PAMAM + Ag(I) ions  complex (nanocomposite) • In literature, an interesting finding was reported. • Potential applications: antimicrobial filter for water purification • antifouling coating for ships Ref: Balogh, L.; Swanson, D. R.; Tomalia, D. A.; Hagnauer, G. L.; McManus, A. T. Nano Letters 2001, 1(1), 18-21.

4. Problem Statement In order to understand the properties of the complexes for applications, the following questions need to be answered: (1) How stable are the Ag(I)-PAMAM complexes in aqueous solutions? (the filter or coating has to be stable in water) (2) Where do Ag(I) ions bind with PAMAM dendrimers (binding sites): exterior (i.e. surface), interior (may including core), or both parts? (important to know this information to understand the antimicrobial property of the complex for applications)

5. Background NMR Spectroscopy NMR --- nuclear magnetic resonance spin --- nucleus of the atoms in the chemical materials for the NMR test Spectroscopy --- correlates the molecular structure with the energy (ΔE ) absorbed or emitted by the chemical materials NMR spectrum --- the data collected from the NMR test (shown on the right)

6. Methodology • Investigation on the Stability of the Ag(I)-G2-PAMAM Complexes Method: 1H 1D NMR is used to monitor the Ag(I)-PAMAM complex sample in water for several months. Rationale: If unstable, there will be changes in 1H NMR signals in the spectra; otherwise, no change will be observed. • Investigation on Binding Sites of G2-PAMAM Dendrimers with Ag(I) Ions • Method: 2D NMR 1H- 1H (homonuclear) COSY technique will be used to probe Ag(I)-G2-PAMAM complex system in comparison with PAMAM alone system. • Rationale: Where Ag(I) ions bind with PAMAM, there will be changes observed in 1H signals. In comparison to 1D NMR, 2D NMR can provide three-bond 1H-1H proton connections in the PAMAM dendrimer structure.

7. 2,6,10 13 12 3,7,11 Results 4,8 5,9 * 102 Days 13 2,6,10 12 3,7,11 4,8 5,9 * 41 Days 13 12 2,6,10 3,7,11 4,8 5,9 * 6.5 Days 12 13 2,6,10 3,7,11 4,8 5,9 * 3.5 Days 12 13 2,6,10 3,7,11 4,8 5,9 * 1 Day Stack Plot of 1H NMR Spectra of the 12-run G2-PAMAM and Ag (I) ion complex sample over a period of 102 days

8. Results 2D COSY NMR spectrum of1:16 G2-PAMAM-Ag(I) ion complex with a partial structure of G2-PAMAM dendrimer labeled in color numbers

9. Results 1D 1H NMR stack plot with peaks labeled in color numbers for G2-PAMAM and Ag(I) ion complexes at different ratios.

10. Conclusion • 1D 1H NMR study shows that the Ag(I) ion complex of G2-PAMAM is stable in water . • The results from the NMR studies clearly show that the Ag(I) ions bind to the primary amino groups on the outermost layer of the dendrimer first then proceed to the interior and the core. • 2D COSY NMR experiment can provide adequate resolution for the proton NMR signal assignments of the G2-PAMAM entity in the complex. • With these findings, the antimicrobial properties of Ag(I) ion complexes of PAMAM dendrimers can be understood and explained

11. Acknowledgement CMU Chemistry Department for hosting the project MMI for supplying the materials used in the project Dr. Minghui Chai (research project mentor) Dr. Abhijit Sarkar (collaborator, MMI) Ms. Tracy Z. Zhang (collaborator, MMI) Questions?