Molecularly imprinted polymers for selective extraction of rosmarinic acid from Rosmarinus officinalis L.
Introduction
A rich plant-based diet has become of substantial importance for human health, as it provides a source for valuable bioactive compounds; among those are phenolic acids, which are present in fruits, vegetables, and spices (Sevgi, Tepe, & Sarikurkcu, 2015), and are reported to have various potential health benefits (Bhuyan & Basu, 2017).
Rosmarinus officinalis L. (rosemary) is one of the most commonly used medicinal plants. It is an edible herb that belongs to family Lamiaceae that is native to the Mediterranean region, and is now cultivated in many other regions all over the world as an ornamental and aromatic plant. Most of the pharmacological effects that were reported for rosemary, are due to its unique phytochemical composition including its phenolic acids pattern that is highly enriched with hydroxycinnamic acids content especially rosmarinic (RA) and its derivatives (Rašković et al., 2014).
Being a potential antioxidant and a promising candidate for alleviating several disorders including diabetes, cancer, cardiac and hepatic diseases (Nadeem et al., 2019), several techniques were reported for RA extraction, such as, flash chromatography techniques or ion‐exchange centrifugal partition chromatography (Akşit et al., 2019, Maciuk et al., 2005), microwave- and ultrasound-assisted extraction (Chatterjee et al., 2014, Zu et al., 2012), and solvent extraction from supercritical fluid (Zibetti, Aydi, Livia, Bolzan, & Barth, 2013). However, the reported methods were often solvent- and time-consuming, obtained inefficient yield, or lacked selectivity towards RA.
Owing to their molecular recognition properties, molecularly imprinted polymers (MIPs) have been increasingly used for selective extraction applications of target compounds from complex sample matrices (Cheng, Pan, Ding, He, & Wang, 2017). This technique enables incorporation of specific molecular recognition sites into polymeric networks to produce polymers with receptor-like properties including a distinctive and predetermined selectivity towards the target molecule (Pan et al., 2018, Zhang and Lei, 2013). Molecularly imprinted solid phase extraction (MISPE) technique has the advantages of using MIP as selective sorbent for a simple, rapid and cost effective SPE method, which consumes significantly small volumes of organic solvents (Jiang et al., 2009).
Bulk polymerization is the most commonly used technique for MIP preparation, and involves the polymerization of solution containing template (T), functional monomer (FM), cross-linker (CL) and initiator, resulting in a solid that needs to be mechanically ground and sieved into the desired size ranges (Huang et al., 2015). Although this technique has high affinity and selectivity, it still has a few limitations including shape irregularity, and heterogeneous binding site distribution. Moreover, grinding and sieving processes could result in destruction of some of the binding sites (Chrzanowska et al., 2015b, Liao et al., 2016, Luo et al., 2008).
Surface imprinting technology based on silica as supporting material is considered as promising alternative method to overcome bulk polymerization associated problems. This is due to the high stability of silica particles, chemical inertness and non-swelling properties. The fundamental strategy is to locate specific binding sites on the polymer surface, to provide larger number of readily accessible binding sites with remarkable specificity and selectivity for target molecules (Chrzanowska et al., 2015b).
The current work emphasizes MIPs as an alternative, selective, reproducible and environmentally compatible extraction technique of RA from rosemary for subsequent usage e.g., in phytopharmaceutical formulations. Polymers with different morphologies, irregular bulk polymers, and spherical surface imprinted (SI) polymers of different composition have been tested to selectively isolate RA from closely related structural analogues. Furthermore, their binding performance and ability to be used as sorbents in SPE have been examined. The isolated compounds using targeted MIPs were characterized using HPLC/PDA/ESI-MS.
Section snippets
Reagents
Standard RA (96%), caffeic acid (CA) (98%) and chlorogenic acid (CLA) (95%), acetonitrile (ACN), methanol, absolute ethanol (EtOH), formic acid, 4-vinylpyridine (4-VP), methacrylic acid (MAA), ethylene glycol dimethacrylate (EGDMA), 2–2′-Azoisobutyronitrile (AIBN), dimethyl sulfoxide (DMSO), (3-aminopropyl)triethoxysilane (APTES), ammonia solution 33%, and glacial acetic acid were obtained from Sigma–Aldrich (Germany). Tetraethyl orthosilicate (TEOS) was purchased from Merck (Germany), ethyl
Template-to-functional monomer molar ratio screening
Computational methods have been adopted to provide a fast alternative approach for the rational design of high affinity MIPs rather than the extensive and time consuming traditional methods (Li, Zhong, Chen, & Whittaker, 2011). In this study, computational modeling was used to optimize the composition of the pre-polymerization complex for bulk polymers. In which, the complex level was only estimated by the number of intermolecular hydrogen H-bonds that could be possibly formed between RA and
Conclusion
The current study has developed the foundation for a simple, rapid and convenient MISPE approach using bulk imprinted polymers to selectively extract RA from a challenging sample complex of rosemary extract. It could be concluded that MISPE is superior to conventional extraction methods with respect to yield and purity; Purified extract fraction with RA content of 49.11 ± 4.58 mg g−1 rosemary (81.96 ± 6.33% recovered) and 80.59 ± 0.30% purity was achieved. After optimization, the developed
CRediT authorship contribution statement
Engy M. Saad: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Writing - original draft. Nesrine Abdelrehim El Gohary: Conceptualization, Supervision, Writing - review & editing. Mohammad Abdel-Halim: Supervision, Validation, Writing - review & editing. Heba Handoussa: Conceptualization, Supervision, Writing - review & editing. Rasha Mohamed El Nashar: Conceptualization, Supervision, Writing - review & editing. Boris Mizaikoff: Conceptualization, Supervision, Writing
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors would like to thank Dr. Basma EL Shenawy, Magy Maged, Nadine Medhat and Marian Magdy- Faculty of Pharmacy and Biotechnology, German University in Cairo -for their valuable assistance.
The Focused Ion Beam Center UUlm is thanked for support with electron microscopy imaging. This work was partially supported by DAAD-BMBF under the initiative “Sustainable research cooperation with the GUC” (project #57128284).
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