Aqueous Self-Assembly of Multifunctional Metal-Carbonyl Nanovesicles a

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1 Aqueous Self-Assembly of Multifunctional Metal-Carbonyl Nanovesicles a Nimer Murshid and Xiaosong Wang * * Department of Chemistry and Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, N2L 3G1, Canada Introduction Due to their strong vibrational stretching of the CO groups within a biological transparency window of wavenumber ( cm -1 ), 1,2 MCCs are widely used in cell imaging and bioassay applications. However, MCCs are usually hydrophobic and have low stability in aqueous solutions. 3 To overcome these drawbacks, MCCs are usually incorporated with colloids by integrating of the hydrophobic MC molecules within amphiphilic systems like block copolymers. 4 However, resulting amphiphilic structures are surface active and can self-assemble just above certain concentrations (critical micelle concentration, CMC), with low structural integration upon dilution. 5 On the other hand, due to the weak CO vibrational signal in diluted solution, surface-enhanced IR absorption (SEIRA) is normally reported by adsorption of MCCs at the surface of plasmonic or dielectric nanoparticles. 6 We have recently discovered that the hydrophobic Fp- acyl derivatives (Fp: CpFe(CO)2) 7 including small and macromolecules can selfassemble in water driven and stabilized by water carbonyl interactions (WCI) between the highly polarized carbonyl groups and water molecules. 8,9 For example, FpC6 8 is able to self-assemble in water into highly integrated nanovesicles with induced local electric field that enhanced the IR absorption signal of the CO groups by more than 100-fold. 8 However, optically manipulable aqueous assembles with multiple sensing characteristics, including vibrational and fluorescence, are desirable in diverse biomedical applications. In this extended abstract, 10 we present uniform and highly integrated metal carbonyl vesicles (MCsomes), prepared from aqueous self-assembly of bithiophene tethered Fp-acyl derivatives, with multiple functions including aggregation enhanced IR absorption (AEIRA), aggregation induced emission (AIE) and optical laser trapping. a Optical trapping and SAXS experiments were performed by our collaborators from National Chiao Tung University in Taiwan Ken-ichi Yuyama, San Lien Wu, Kuan-Yi Wu, Hiroshi Masuhara and Chien Lung Wang.

2 Results and discussions The aqueous solution of the bithiophene tethered Fp-acyl building block (FpC3-Bt or 1) is prepared by fast addition of water into a THF solution of 1. Subsequently THF was removed by N2 bubbling for 90 minutes (Figure 1 a). Dynamic light scattering (DLS) analysis reveals that the prepared colloids are monodisperse (PDI = 0.05) with hydrodynamic diameter of ca. 170 nm. As shown in Figure 1a, upon dilution, the obtained colloids remain highly integrated with almost no change in their size or polydispersity. As revealed from surface tension measurements (Figure 1b), no drop in surface tension is observed for all measured concentrations suggesting that 1 is non surface active. Therefore, to measure the critical micelle concentration (CMC), DLS count rates of as a function of the colloids concentration were plotted in Figure 1c. Similar to surface tension measurements, no CMC was detected suggesting that 1 cannot be classified as conventional amphiphile. Moreover, the prepared colloids show a highly negative surface charge (ζ = mv) with colloidal stability over several months. Figure 1. (a) Chemical structure and solution preparation of 1. (b) Surface tensions and (c) DLS count rates of the aqueous solution of 1 as a function of concentration. 10 The morphology of the prepared colloids is first investigated using static and dynamic light scattering (SLS/DLS). The shape factor (Rg/Rh = 0.96) suggests that the MC molecules of 1 are able to self-assemble in water into vesicles (MCsomes) (Figure 2). The vesicle s morphology were

3 further investigated and confirmed by transmission electron microscopy (TEM), atomic force microscopy (AFM), and small-angel X-ray scattering (SAXS). These experiments along with zetapotential and cyclic voltammetry results suggest that the vesicles have a bilayer membrane structure with bithiophene groups are interdigitated within the membrane and the metal carbonyl centers are oriented at the surfaces toward water (Figure 2a). This designed structure with organic bithiophene units and organometallic MC units should provide a multifunctional materials. It is reported that restriction of the intramolecular rotations (RIR) in conjugated structures resulting in aggregation induced emission (AEI). 11 Therefore, the association of the interdigitated bithiophene unites within the membrane of the bilayer MCsome 1 is expected to induce a RIR of the thiophene units and AIE properties. As shown in Figure 2b, no emission is observed for the THF solution of 1 (molecular state); whereas the MCsome in water emits blue FL at ca. 450 nm when exposed to excitation wavelengths between nm. The correlation between the aggregation induced RIR and AEI is investigated by studying the correlation between DLS and FL measurements at different water contents. This investigations reveals that as water content increases the aggregates shrinks and their size decrease. Whereas, the FL intensities increase with increasing of the water contents suggesting that the FL is aggregation induced. Figure 2. (a) Illustration for the bilayer membrane structure for the MCsome 1. (b) FL emission spectra for the solutions of 1 in THF and water. 10 Taking the advantage of the highly polarized carbonyl groups decorated at the surfaces of the MCsome, vibrational properties of the CO groups are investigated. It is known that when an incident light is irradiated at the surface of polarized nanoparticles, a local electromagnetic

4 field, stronger than the field, induces and provides a surface enhanced IR absorption (SEIRA) phenomena. ATR-FTIR measurements were performed for the MCsome solutions in THF/water with varied water contents. As shown in Figure 3, IR absorptions of the terminal CO group for the aggregates (60 vol% of water) is stronger than that for the molecules in THF(no aggregates) with more than 100 times. This AEIRA is also observed and reported by our group for the MCsomes assembled from other Fp-acyl derivatives, suggesting that this feature results from the presence of the highly polarized MC units. 8 Figure 3. ATR-FTIR spectra (terminal CO group) for 1 in THF (molecules) and THF/water (aggregates) solutions. 10 Laser trapping (gradient) force for particles with the size much smaller than the wavelength of the trapping laser depends on the deference in refractive index (RI) between the nanoparticle and the surrounding medium. 12 Therefore, due to the similarities in both interior and exterior environment, laser trapping of nanovesicles (including liposomes) is challenging. 13,14 However, the RI of the building block 1 is 1.71 (at = 633 nm) is significantly higher than water (1.33). Although, the thickness of the membrane is only ca. 3.7 nm, the high contrast in RI between the membrane and water induces gradient force strong enough to trap the MCsome without any modification to the environment. Figure 4 presents the laser trapping progress during the irradiation time. Upon irradiation with a focused continuous-wave near-ir (NIR) laser beam for 1 second, the nanovesicles start aggregate in the focal point. After irradiation for 6 seconds the focal volume becomes fully occupied and he laser trapping reaches the equilibrium state. The trapping and manipulating of the MCsomes position verify the success of the laser trapping experiments.

5 Figure 4. Schematic illustration and the CCD transmission images of the trapped MCsome. 10 Conclusion Uniform aqueous MCsomes, self-assembled from hydrophobic bithiophene tethered Fp-acyl building blocks have been prepared with highly integrated structure. The aggregation of the bithiophene unites provides an AIE characteristics and the association of the highly polarized MC unites at the surfaces endows with an AEIRA functions. Unlike previously reported laser trapping attempts, the MCsome 1 has been successfully laser trapped without using additives. References [1] Meister, K.; Niesel, J.; Schatzschneider, U.; Metzler-Nolte, N.; Schmidt, D. A.; Havenith, M. Angew. Chem. Int. Ed. 2010, 49, [2] S. Clède, C. Policar, Chem. Eur. J. 2015, 21, [3] (a) Fischer-Durand, N.; Salmain, M.; Rudolf, B.; Dai L.; Jugé, L.; Guérineaud, V.; Laprévote, O.; Vessières, A.; Jaouen, G. Anal. Biochem. 2010, 407, (b) Policar, C.; Waern, J. B.; Plamont, M.-A.; Clède, S.; Mayet, C.; Prazeres, R.; Ortega, J.-M.; Vessières, A.; Dazzi, A. Angew. Chem. Int. Ed. 2011, 50, [4] Hasegawa, U.; van der Vlies, A. J.; Simeoni, E.; Wandrey, C.; Hubbell, J. A. J. Am. Chem. Soc. 2010, 132, [5] (a) Maia Y.; Eisenberg A. Chem. Soc. Rev. 2012,41, (b) Owena S. C.; Chana D. P.Y.; Shoichet M. S. Nano Today 2012, 7, [6] Aroca, R. F.; Ross, D. J.; Domingo, C. Applied Spectroscopy 2004, 58, 324A-338A [7] Lanigan, N.; Assoud, A.; Wang, X. ACS Macro Lett. 2014, 3, [8] Murshid, N.; Wang, X. Chem. Eur. J. 2015, 21, [9] Cao, K.; Murshid, N.; Li, L.; Lopez, A.; Tam, K. C.; Wang X. Macromolecules 2015, 48, [10] Murshid, N.; Yuyama, K.-I.; Wu, S. L.; Wu, K. Y; Masuhara, H.; Wang, C. L.; Wang, X. J. Mat. Chem C. 2016, DOI: /C6TC01222A [11] (a) Chang, Z.; Jiang, Y.; He, B.; Chen, J.; Yang, Z.; Lu, P.; Kwok, H. S.; Zhao, Z.; Qiua, H.; Tang, B. Z. Chem. Commun. 2013, 49, (b) Luo, J.; Xie, Z.; Lam, J. W. Y.; Cheng, L.; Chen, H.; Qiu, C.; Kwok, H. S.; Zhan, X.; Liu, Y.; Zhuc, D.; Tang, B. Z. Chem. Commun. 2001, [12] Sugiyama, T.; Yuyama, K.-I.; Masuhara H. Acc Chem Res, 2012, 45, [13] Kitamura, N.; Sekiguchi, N.; Kim, H.-B J. Am. Chem. Soc. 1998, 120, [14] Hotta, J.; Sasaki, K.; Masuhara, H. J. Am. Chem. Soc. 1996, 118,