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476 D. PATRA AND R. EL KURDI Initially, curcumin was isolated from turmeric by solvent extraction, followed by column chromatography (22). Among solvent extraction, soxhlet, ultrasonic, and microwave extraction were useful in the purpose of extracting curcumin (23). Later on, it was characterized by Milobedeska in 1910, where he found that curcumin is a diferuloylmethane compound, where its IUPAC name is (1,7-bis (4- hydroxy-3-methoxyphenyl)-1,6-hepadiene-3,5-dione). Finally, it was synthesized and proved by Lamp in 1913 (24,25). The synthesis of curcumin involves five consecu- tive steps. The raw materials are carbomethoxyferuloyl chloride and ethyl acetoacetate. Pabon et al. have developed a new method to prepare curcumin using acetylacetone in the presence of boron trioxide, with different substituted aromatic aldehydes, trialkyl borate, and n-butylamine (26) (see Figure 2). Curcumin was introduced in the 14th century to the western world, and till now is still being used (27). Curcu- min in its powdered and roasted form has been used continuously, either consumed with hot milk or adminis- tered as anti-dysenteric agent, respectively (28). The importance of curcumin is very clear since more than 400 000 publications were found when searching for the term ‘Curcumin.’ The crystal structure of curcumin has shown some differences in the electron delocalization and intramole- cular hydrogen bonding in the fragment –CO– HC=COH–. In addition, an electron delocalization has found also in intermolecular hydrogen bonding. However, it was established that no remarkable differ- ences in the lengths of the C–C and C–O bonds present in the enol form (29). Moreover, it was given that the stability of curcumin is pH dependent. This fact was proven by the change of curcumin color while varying the pH. Hence, in acid media, curcumin has a medium solubility with a yellow color, although, in neutral media, curcumin stands in suspension where it is not completely soluble, with a pale yellow solution’s color. However, at alkaline conditions, curcumin pre- sents high solubility at pH > 8, where the solution color turns dark orange (30,31). Curcumin has been used worldwide in different ways, regarding its principal health benefits. In India, curcumin has been used in curries. In Japan and Korea, it is mixed with tea and other drinks. In Thailand, it is added as an essential component to cosmetics products. Moreover, in China, it is used as a colorant. In Lebanon, it is used in sweets and cakes. In Malaysia and Pakistan, it founds its benefits as an antiseptic and as an anti-inflam- matory reagent, respectively. In addition, in the United States, curcumin is considered a primary ingredient in mustard sauce, it is used as a preservative for various compounds (32,33). Mainly, the effect of curcumin as anti-cancer (34–36), anti-oxidant (37–39), anti-inflammatory (40–42), anti- bacterial (43–45), etc., agent in the biomedical field has been extremely developed and established (46–48). Therefore, a large number of reviews have adopted this topic and elaborated. However, curcumin shows very poor bioavailability where several studies have showed undetectable concentrations in blood and extra-intestinal tissue. These limitations are initially due to its low absorption, fast metabolism, chemical instabil- ity, and very high systemic elimination (49,50). Therefore, to overcome these drawbacks, many methods have been tested to surge its bioavailability. Some of these techniques include the use of curcumin with nanoparti- cles, the use of adjuvants such as piperine, formulating liposomal curcumin, etc (51). Consequently, curcumin in nanoparticle formation has been introduced (52). Indeed, a new role of curcumin is being investigated. This role resumes the efficiency of curcumin as a redu- cing agent. In this area, the use of curcumin in the pro- duction of metallic nanoparticles has been developed as a new eco-friendly reducing agent. Generally, the estab- lishment of curcumin functionalized metallic nanoparti- cles comprises six consecutive steps. The reduction potential starts with the deprotonation of the metal ion, followed by its reduction, moving to the nucleation and growth, afterward cleavage occurs, ending up with the maturation of the nanoparticles (see Figure 3) (53,54). Thus, in this review, we will highlight the role of curcumin as a reducing agent for different nanoparticle preparation by assembling the work presented in the literature. To the best of our knowledge, till now no review has focused on the application of curcumin as a reducing agent though many of the reviews focus on the application of curcumin in biology and medicine. 2. Synthesis of metallic nanoparticles Nanoparticles including, gold, silver, and iron oxide have gained too much attention, due to their extreme impor- tance and usage in medicine and the biomedical field (55,56). Therefore, it was necessary to develop green syn- thesis to minimize the toxic waste from the chemical reduction reaction. Lately, researchers have started to replace toxic reducing agents like sodium borohydride and hydrazine by using curcumin as a starting up material to reduce bulk material in the formation of the nanoparticle.PDF Image | Curcumin as a novel agent for metallic nanoparticles
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