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عنوان فارسی مقاله:
camphorquinone کربوکسیله به عنوان آغازگر نوری نور مرئی برای استفاده پزشکی
عنوان انگلیسی مقاله:
Carboxylated camphorquinone as visible-light photoinitiator for biomedical application: Synthesis, characterization, and application
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
In recent years, photopolymerization has emerged as a valuable tool in biomedical applications because of its ability to rapidly convert a liquid monomer or macromer into 3D polymer networks under physiological conditions with temporal and spatial control. In this way biodegradable polymer hydrogels were prepared which can be used as drug delivery systems (Bertz et al., 2013; Lu and Anseth, 1999; Scott and Peppas, 1999; Wo¨hl-Bruhn et al., 2012a). However, for applications for example in dental surgery with direct preparation of hydrogels in situ the photopolymerization has to be carried out with visible light lamps as commonly used by dentists (Kamoun and Menzel, 2010). Photopolymerization uses light to dissociate initiator molecules into free radicals, which react with double bonds in the monomers or pre-polymers and thus crosslinking can occur. Camphorquinone (1,7,7-trimethylbicyclo[2.2.1]heptane-2,3- dione, CQ) belongs to the aliphatic a-diketones (Fig. 1) and is utilized as a photoinitiator for visible-light photocrosslinking. It is most frequently applied among the commercial photoinitiators (Alvim et al., 2007). The efficiency of this photoinitiator alone is insufficient. However, addition of e.g. tertiary amines as an electron/proton donor or as a reducing agent, gives an effective photoinitiating system (Cook, 1992; Jakubiak et al., 2003; Kamoun and Menzel, 2010). Such combinations are widely used for the crosslinking of methacrylate-based dental restorative polymers. CQ absorbs light in the UV-region at 200–300 nm and in the visible light region at 467 nm (responsible for its yellow color) (Cook, 1992; Kamoun and Menzel, 2010). Actually many publications have been devoted to the investigation of the mechanism of CQ-amine photoinitiating system. Absorption of light by CQ typically leads to the formation of two excited states: (i) the ‘‘singlet state’’, which does not involve reversal of electron spin, and (ii) the ‘‘triplet state’’ which is the one relevant to free radical formation and which has a very short half-life (Tsai and Charney, 1969). While in the triplet state, the CQ molecule may interact with an amine molecule to generate an excited state complex, the ‘‘exciplex’’ (Fig. 2) (Cook, 1992; Kamoun and Menzel, 2010). In the exciplex the CQ abstracts a hydrogen atom from the tertiary amine resulting in the formation of free radicals (Stansbury, 2000). The hydrogen abstraction by triplet 3 CQ* from amines, proceeds much faster compared to the reaction with the pure monomer. This is since the amines have a much lower oxidation potential compared with other hydrogen donors (Cook and Chen, 2011). Therefore, it is assumed that the CQ-amine system reaction is facilitated by the electron– proton transfer (Cook, 1992; Kamoun and Menzel, 2010; Pyszka et al., 2004). Addition of diphenyliodonium chloride DPIC (Kamoun and Menzel, 2010, 2012; Kim and Scranton, 2004; Wang et al., 2006), or diphenyliodonium hexafloro-phosphate (DPIHP) (Guo et al., 2008) further accelerates photopolymerization, because they regenerate the dye, and produce additional active radicals (Fig. 2). There are some disadvantages associated with the use of CQ as a visible-light photoinitiator (Yoshida and Greener, 1994; Jakubiak et al., 2001). A yellow shade of the photoinitiator (Park et al., 1999) results in a more intense color of unpolymerized filling composite and complicates the production of high-esthetic tooth colored restorations. Furthermore, an inner shielding effect (Jakubiak et al., 2001) of the colored CQ may result in unreacted photoinitiator (Janda et al., 2004). A significant lower photoreactivity of CQ was observed at higher concentrations (Schneider et al., 2008). To address these disadvantages of CQ, alternative photoinitiators such as phenyl propane-dione (PPD) or acrylphosphine dioxides (APO), which absorb light at lower wavelengths than CQ have been studied (Schneider et al., 2008; Schroeder et al., 2008; Sun and Chae, 2000). PPD showed a lower rate of polymerization without affecting the final degree of conversion compared to CQ (Ogunyinka et al., 2007). The poor solubility of CQ in water restricts its utilization for crosslinking polymers for hydrogel formation. Thus, it is mandatory to use polar solvents e.g. DMSO or DMF mixed with water dissolve the CQ (Kamoun and Menzel, 2010). Magoshi and Matsuda (2002), Matsuda and Magoshi (2002), Nakayama et al. (2001) and Okino et al. (2002) have reported for the first time the water soluble carboxylated camphorquinone (CQCOOH) as a visible light photoinitiator, which might be
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