Date Published: February 11, 2019
Author(s): Dhiraj A. Jamdade, Dishantsingh Rajpali, Komal A. Joshi, Rohini Kitture, Anuja S. Kulkarni, Vaishali S. Shinde, Jayesh Bellare, Kaushik R. Babiya, Sougata Ghosh.
Rapid, eco-friendly, and cost-effective one-pot synthesis of copper nanoparticles is reported here using medicinal plants like Gnidia glauca and Plumbago zeylanica. Aqueous extracts of flower, leaf, and stem of G. glauca and leaves of P. zeylanica were prepared which could effectively reduce Cu2+ ions to CuNPs within 5 h at 100°C which were further characterized using UV-visible spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy, energy dispersive spectroscopy, dynamic light scattering, X-ray diffraction, and Fourier-transform infrared spectroscopy. Further, the CuNPs were checked for antidiabetic activity using porcine pancreatic α-amylase and α-glucosidase inhibition followed by evaluation of mechanism using circular dichroism spectroscopy. CuNPs were found to be predominantly spherical in nature with a diameter ranging from 1 to 5 nm. The phenolics and flavonoids in the extracts might play a critical role in the synthesis and stabilization process. Significant change in the peak at ∼1095 cm−1 corresponding to C-O-C bond in ether was observed. CuNPs could inhibit porcine pancreatic α-amylase up to 30% to 50%, while they exhibited a more significant inhibition of α-glucosidase from 70% to 88%. The mechanism of enzyme inhibition was attributed due to the conformational change owing to drastic alteration of secondary structure by CuNPs. This is the first study of its kind that provides a strong scientific rationale that phytogenic CuNPs synthesized using G. glauca and P. zeylanica can be considered to develop candidate antidiabetic nanomedicine.
Nature has an infinite collection of medicinal plants which serve as repository of bioactive principles that are considered as complementary and alternative medicine. Combinatorial chemistry, nanotechnology, and cutting edge research on nutraceuticals have helped to expand the horizons beyond contemporary therapeutics [1, 2]. Interdisciplinary research has enabled to exploit the medicinal plants which are storehouses of diverse groups of phytochemicals for fabrication of novel nanomedicine with broad-spectrum therapeutic applications [2–5]. Numerous medicinal plants like Dioscorea bulbifera, Dioscorea oppositifolia, Gloriosa superba, Barleria prionitis, and Litchi chinensis are used for synthesis of gold, silver, platinum, and palladium nanoparticles with antimicrobial, antibiofilm, and anticancer activities [6–12]. However, there is a lacuna in the area of synthesis of copper nanoparticles (CuNPs) using medicinal plants. Hereby, synthesis of therapeutic CuNPs using medicinal plants has drawn considerable attention recently. Among various nanoparticles, CuNPs have gained wide applications in photothermal ablation, photoacoustic imaging, drug delivery, theranostics, electrical conductors, biochemical sensors, electrocatalysis, photocatalysis, and catalytic organic transformations [13, 14]. Although there are various physical and chemical routes for synthesis of CuNPs, the involvement of hazardous and toxic chemicals poses a threat to the environment and compromises with the biocompatibility . Hence, there is a growing need to develop the green synthesis approach for fabrication of stable CuNPs with therapeutic significance.
Metal nanoparticles have got wide applications in optoelectronics, semiconductors, sensors, and biomedical applications as well. Medicinal plants are widely explored to synthesize metal nanoparticles. In this study, we found that G. glauca and P. zeylanica have tremendous potential to synthesize and stabilize metallic CuNPs. In our previous studies, we have reported G. glauca flower-, leaf-, and stem-mediated synthesis of AuNPs and AgNPs [24–26]. However, there are no reports till date on their potential to synthesize bioactive CuNPs. Hereby, we have used three parts of G. glauca. Similarly, earlier, we could find that only P. zeylanica leaf can synthesize AuNPs, AgNPs, and bimetallic nanoparticles most effectively. But, till date, there are no reports of synthesis of CuNPs using P. zeylanica leaf extract . In our present study, synthesis of CuNPs was found to be rapid and efficient which is well in agreement with our previous reports where AuNPs and AgNPs were synthesized using the aforementioned plants. The parts of the plants used in this study are reported to contain coumarins like seselin, 5-methoxyseselin, suberosin, xanthyletin, and xanthoxyletin apart from alkaloids, glycoside, reducing sugars, simple phenolics, tannins, lignin, saponins, and flavonoids which have a high potential to synthesize and stabilize nanoparticles [16, 17, 19]. Absorption bands of CuNPs are in the range between 550 and 600 nm. However, in our phytogenic approach, no sharp peak attributed to the surface plasmon resonance was observed which is well established by the earlier reports where similar observations were made for CuNPs coated with biomolecules . Intensity of the UV-visible spectra progressively increases similar to the synthesis of CuNPs by hydroxyl ion-assisted alcohol reduction . It can be rationalized by the earlier observations where freshly synthesized CuNPs (size, <5 nm diameter) at lower copper ion concentration demonstrated a featureless Mie scattering profile without the appearance of an apparent surface plasmon band which is in close agreement with our observation in the present study. This featureless broad peak may be attributed to the small size of bioreduced CuNPs . Likewise, CuNPs synthesized using L-ascorbic acid were found to be less than 4 nm in diameter that exhibited a broadened peak and featureless absorbance, which increased monotonically towards higher energies. In our study as well, the bioreduced CuNPs did not show a plasmon peak at around 570 nm but rather displayed a broadened peak indicating the presence of a very small dimension of CuNPs which can be rationalized by the presence of ascorbic acid in the plant extracts that can lead to efficient reduction of Cu2+ to Cu0 and further more effective capping capacity [30–33]. High temperature was found to be suitable for synthesis of CuNPs which was evident from the visible colour change. Enhancement of the rate of synthesis of metal nanoparticles with rise in temperature is in close correlation with previous reports where the rate of synthesis of AgNPs using the Lippia citriodora leaf aqueous extract could be enhanced by increasing the temperature from 25°C to 95°C resulting in average particle size of 15–30 nm . It is important to note that temperature plays a very critical role in the size and shape of the synthesized nanoparticles. Owing to the higher rate of reduction at higher temperatures, the copper ions could be consumed mainly on the formation of nuclei, whereas the secondary reduction process which takes place on the surface of the preformed nuclei might be hindered. This phenomenon is well documented during synthesis of AgNPs and AuNPs using Lippia citriodora and lemon grass, respectively [34, 35]. The rate of synthesis of AgNPs using aqueous extract of the leaves of Mimosa pudica could be effectively enhanced by heating the reaction mixture from ambient (29 ± 3°C) to 70°C. Moreover, increase in the reaction temperature evidently led to the synthesis of larger quantities of nanoparticles and, simultaneously, reduction in the size of the nanoparticles . G. glauca- and P. zeylanica-mediated synthesis of CuNPs may prove to be a novel, rapid, and efficient route to fabricate spherical nanoparicles of smaller dimensions. The extracts rich in diverse phytochemicals not only bioreduce but also stabilize the nanoparticles as well. Elevated temperature was found to be suitable for synthesis. Phenolics and flavonoids might play a key role in the synthesis process. CuNPs could effectively inhibit α-amylase and α-glucosidase. The mechanism of enzyme inhibition was established to be alteration of the secondary structures in the enzyme leading to conformational change. In view of the background, it can be concluded that phytogenic CuNPs reported herein may lead to development of environmentally benign route for rational designing of safe and effective antidiabetic nanomedicine. Source: http://doi.org/10.1155/2019/9080279