Electrospun complexes - functionalised nanofibres

Transcription

1 Hyperfine Interact (2016) 237:89 DOI /s y Electrospun complexes - functionalised nanofibres T. Meyer 1 M. Wolf 1 B. Dreyer 1,2 D. Unruh 1 C. Krüger 1 M. Menze 1 R. Sindelar 2 G. Klingelhöfer 3 F. Renz 1 Springer International Publishing Switzerland 2016 Abstract Here we present a new approach of using iron-complexes in electro-spun fibres. We modify poly(methyl methacrylate) (PMMA) by replacing the methoxy group with Diaminopropane or Ethylenediamine. The complex is bound covalently via an imine-bridge or an amide. The resulting polymer can be used in the electrospinning process without any further modifications in method either as pure reagent or mixed with small amounts of not functionalised polymer resulting in fibres of different qualities (Fig. 1). Keywords Polymer fibres Iron complexes Electrospinning 1 Introduction Complexes exhibit a broad range of properties based on their structures and contained elements. Nowadays the focus has shifted from simply developing new complexes of distinct properties to specifically considering their future applicability for technical devices or medical treatment. Therefore we illustrate a way to easily attach these complexes to surfaces via the electrospinning process. This article is part of the Topical Collection on Proceedings of the International Conference on the Applications of the Mössbauer Effect (ICAME 2015), Hamburg, Germany, September 2015 F. Renz renz@acd.uni-hannover.de 1 Institute of Inorganic Chemistry, Leibniz University Hannover, Callinstr. 9, Hannover, Germany 2 Faculty II, University of Applied Science Hannover, Ricklinger Stadtweg 120, Hannover, Germany 3 Institute of Inorganic and Analytic Chemistry, Gutenberg-University, Duesbergweg 10-14, Mainz, Germany

2 89 Page 2 of 11 Hyperfine Interact (2016) 237:89 Fig. 1 Model of functionalised fibres with pyridin-carbaldehyde and diaminopropane The electrospinning process is based on charging a polymer solution with high voltage. This results in an acceleration of the polymer solution to a counter electrode [1]. Due to the extreme high voltage at the very top of the polymer droplet, thin polymer fibres are created which can serve as coatings or membranes. Most of the time the material for polymer fibres can be chosen based on its properties. The number of spinnable polymers is countless and the resulting fibres differ in their thickness, durability and length. Aside from the polymer and other things, temperature, viscosity, concentration, molecular weight and process parameters play a key role in the electrospinning process [2]. Typically the polymer fibres are modified by different types of additives or used as templates. These additives are dispersed within the polymer solution and can lower the quality of the prepared fibres or can alternatively be rinsed by solvents. A different approach is the covalent connection between fibre and a reactive centre. Therefore the polymer fibre has to possess a functional group, which can be either directly used as a linker or can be changed

3 Hyperfine Interact (2016) 237:89 Page 3 of Fig. 2 Used compounds to functionalise Poly(methyl methacrylate). I and II were used as bridges between ligand and PMMA. I diaminopropane II ethylenediamine III 2-pyridinecarboxaldehyde IV pyrrole-2- carboxaldehyde V thiophene VI 6-bromo-2-pyridinecarboxaldehyde Fig. 3 Reactionschema of the functionalisation into such. A promising polymer seems to be poly(methyl methacrylate) (PMMA). PMMA consists of a repeating unit with a methoxy ester. From different publications [3 5] in the biomedical field, the methoxy group is known for being easily replaceable. It is activated by different diamine (Fig. 2. I and II) and then functionalised by various numbers of aldehydes (Fig. 2. III-VI).

4 89 Page 4 of 11 Hyperfine Interact (2016) 237:89 Fig. 4 Experimental setup of the electrospinning process Fig. 5 IR-Spectrum showing the difference between unfunctionalised PMMA containing methoxy group and functionalised PMMA with peptide bond 2 Experimental If not mentioned, all chemicals are used as purchased and the products are synthesised without any further purification. The synthesis was divided into a two step procedure (Fig. 3). In the first step, the PMMA was activated with the diamine and in the second step, the ligand was coupled to the PMMA and the complex was synthesised. In a two-necked flask, toluene was cooled to 78 C under nitrogen atmosphere. First 3.75 mmol n-buli was added to the toluene and second, with heavy stirring, 2.5 mmol

5 Hyperfine Interact (2016) 237:89 Page 5 of Fig. 6 Mössbauer spectrum of compound II+VI Is (relative to α -Fe) 0.33 mm/s Qs 0.66 mm/s Fig. 7 Mössbauer spectrum of compound I+III Is (relative to α -Fe) 0.24 mm/s Qs 0.89 mm/s Fig. 8 Mössbauer spectrum of compound II+V Is (relative to α -Fe) 0.27 mm/s Qs 0.65 mm/s

6 89 Page 6 of 11 Hyperfine Interact (2016) 237:89 Fig. 9 Mössbauer spectrum of compound II+III Is (relative to α-fe) 0.35 mm/s Qs 0.89 mm/s Table 1 Least square fitted Mössbauer parameter of Isomericshift (Is) and Quadrupole splitting (QS) Functionalisation Qs (mm/s) Is(mm/s) Spin-State I+III Fe(III)-HS II+III Fe(III)-HS II+V Fe(III)-HS II+VI Fe(III)-HS diamine. After 3 hours 1 g poly(methyl methacrylate) was added to the solution and the mixture was stirred for additional 24h at room temperature. Then the reaction was stopped by quenching with cooled methanol. A solid was obtained by filtrating the solution, which was washed with methanol, water and again methanol. It was dried under decreased pressure. In the second step, the activated PMMA was dissolved in toluene and heated under reflux mmol of the carboxaldehyde was added and stirred for 2 h. Finally 0.25Äq iron(iii)-chloride were added and the solution was heated for another hour. The product was obtained in a coloured powder. For characterisation Mössbauer spectroscopy and infrared spectroscopy were used. Functionalised PMMA : IR (KBr) : v(n H) = 1720cm 1, v(c = N) = 1672, 1587cm 1, v(c N R.) = 1523cm 1 The Mössbauer spectra have been collected on a MIMOSIIa. It uses a 57Co/Rh source and the isomer shifts are given relative to α-iron. The IR-Spectra have been collected on a Tensor27 from Bruker. The SEM measurements have been collected on a Zeiss Leo 1455VP. The complexes were dissolved in different types of solvents (eg.: trifluoroethanol). Therefore the samples were carefully pestled and stirred at room temperature in a closed glass. For a faster procedure they were also treated with supersonic. The polymer solutions were filled into a syringe and spun with 20 kv at an electrode-distance of cm (Fig. 4).

7 Hyperfine Interact (2016) 237:89 Page 7 of Fig. 10 SEM-picture of sample I + IV (right) and the distribution of iron (functionalisation degree: 15.9 %) within the sample (left) Fig. 11 SEM-picture of sample I+V (right) and the distribution of iron (functionalisation degree: 9.7 %) within the sample (left) 3 Results and discussions Figure 5 shows the infrared spectrum of the PMMA and the functionalised complexes. The curves of the functionalised PMMA clearly show an additional signal at 1650 cm 1, which indicates a successful coupling between the diamine and the polymer. This is caused by the insertion of the peptide- and imine bonde during the functionalisation (Fig. 3). To verify that the functionalisation was successful, the complex formation has to be proofed. The educts, except for the PMMA, were solubilized or liquid. Therefore only PMMA or substances connected to the PMMA were isolated. The samples were investigated with Mössbauer spectroscopy to show the presence of iron. In Figs. 6, 7, 8 and 9 these measurements are shown. The spectra show one doublet with an isomer shift of 0.24 mm/s to 0.33 mm/s and a quadrupole splitting of 0.65 mm/s to 0.89 mm/s which differ distinctly from the used iron(iii)chloride (Ls 0.442mm/s) [6].

8 89 Page 8 of 11 Hyperfine Interact (2016) 237:89 Fig. 12 SEM-picture of sample I+V (right) and the distribution of iron (functionalisation degree: 11.4 %) within the sample (left) Fig. 13 SEM-picture of sample I+V (right) and the distribution of iron (functionalisation degree: 19.9 %) within the sample (left) All measurements of the functionalised PMMA are shown in Table 1. Besides to different ligands, which obviously affect the energy of the centred iron-atoms directly, the chain length of the diamine was varied. Mössbauer spectroscopy shows significant differences in the results, indicating, that the chain length presumably affect the geometry of the complex. Compared to the non PMMA connected complexes [7] consisting of the diamine and a carbaldehyde the Mössbauer spectrum shows virtually no difference. It is not surprising due to the small differences in structure. To determine the degree of functionalisation EDX measurements were made which are shown in Figs. 10, 11, 12, 13 and 14. The degree of functionalisation fluctuates between 9.7 % and 19.9 %. Based on the experimental setup a maxium of 25 % would have been possible. Since the diamine can connecting two PMMA repeating units a functionalisation degree close to 25 % would have been surprising. In the last and most important step, the functionalised PMMA was used in the electrospinning process. In order to use the PMMA as a surface cover, the obtaining fibres have to

9 Hyperfine Interact (2016) 237:89 Page 9 of Fig bromo SEM-picture of sample I+VI (right) and the distribution of iron (functionalisation degree: 14.5 %) within the sample (left) Fig. 15 Functionalised PMMA dissolved in acetone for 24 h. No fibres are created. Spinning distance: cm; Voltage: 20 kv be of constant thickness and with few impurities. Due to the functionalisation the solubility of the samples decreases significantly compared to pure PMMA. Especially very high degrees of functionalisation lead to insolubility. The PMMA was dissolved in different solvents (trifluoroethanol, acetone, methanol, toluene, dichloromethane) for various periods of time to prepare them for the spinning process. The impact of the right solvent and adequate amount of time cannot be overrated. It was not possible to obtain fibres by using methanol, toluene, or dichloromethane. Figure 15 shows fibres made from an acetone/pmma solution. The qualities of these fibres are very

10 89 Page 10 of 11 Hyperfine Interact (2016) 237:89 Fig. 16 Functionalised PMMA dissolved in TFE for 24 h. Spinning distance: cm; Voltage: 20 kv Fig. 17 Functionalised PMMA-Fibres. The PMMA was dissolved in TFE for 1 week. Spinning distance: cm; Voltage: kv poor due to their thickness of over 10 μ m and their general appearance. Using trifluoroethanol leads to better results (Fig. 16). Figure 17 shows fibres prepared from the same sample with different periods of time for solubility.

11 Hyperfine Interact (2016) 237:89 Page 11 of It is noticeable that Fig. 16 shows a worse quality compared to the sample of Fig. 17. There are particles many times larger than the fibres. These particles cannot only decrease the quality of the surface but can also lead to problems within the electrospinning process by plugging the syringe. Figure 17 was made after dissolving the sample for 7 days and shows nearly no impurity. 4 Conclusion The results show that functionalising poly(methyl methacrylate) with coordinating compounds is a good way to create spinnable chemical formulations. The PMMA is activated by replacing the methoxy group and modified by various numbers of ligands. IR- and Mössbauer spectroscopy proofed the formation of iron-complexes. The compounds were successfully dissolved in trifluoroethanol and used in the electrospinning process. Thereby new possibilities in respect to surface functionalisation arise. The microscopy pictures show a homogeneous distribution in thickness and in general high quality of the fibres. Due to their low solubility the PMMA samples have to be dissolved for a long period to guarantee such fibres of high quality. This property could be manipulated by changing the functionalisation degree or change of ligands. Acknowledgments We like to thank the MARIO graduate school programme as well as the Laboratory of Nano and Quantum Engineering (LNQE), the University of Applied Science Hannover and the Leibniz University Hannover (LUH). References 1. Greiner, A., et al.: Angewandte Chemie 119(30), (2007) 2. Wang, C., et al.: Springer, Berlin pp (2013) 3. Henry, A.C., et al.: Anal. Chem. 72, (2000) 4. Sadhu, V.B., et al.: Macromol. Chem. Phys. 205, (2004) 5. Fixe, A.F., et al.: Nucleic Acids Res. 32(1), e9., 10 (2004) 6. Greenwood, N.N., Gibb, T.C.: Mössbauer spectroscopy. Chapman and Hall, London (1971) 7. Paoli, M.A.D.: Inorg. Chem. Acta 27, (1978)