PREPARATION OF NANOPARTICLES BY GREEN METHOD
Various methods have been reported for the preparation of different NPs by green methods:
FROM PLANT RESIDUES
Various plant residues have been used for the synthesis of various NPs. These plant residues act as reducing agents and reduce metallic NPs to the zerovalent state.
Gold NPs: The production of gold NPs has been done by the controlled reduction of the Au3+ ion to Au°. Green synthesis of gold NPs was reported by using a variety of plant materials, such as Achillea wilhemsii flowers (Andeani et al., 2011), ethanolic extract of the plant Mirabilis jalapa flowers (Vankar and Bajpai, 2010), Coleus ambouiicus L. leaf extract (Narayanan and Sakthivel, 2010), aqueous extract of cypress leaves (Noruzi et al., 2012),
Barbated Skullcap herb extract (Wang et al., 2009), aqueous extract of rose petals (Noruzi et al., 2011), leaf extracts of two plants Magnolia kobus and Diopyros kaki (Song et al., 2004), oat (Arena sativa) biomass (Annendariz et al., 2004), flower extracts of Ixora coccinea (chetty flower) (Nagaraj et al., 2011), Azadirachta indica plant leaf extract (Thirumurugan et al., 2010), ethanol extract of black tea and its tannin free fraction (Banoee et al.,
2010) , alfalfa plants (Gardea-Torresdey et al., 2002), and coriander leaves (Narayanan and Sakthivel, 2008). Gold NPs were also synthesized using banana peel extract, and their antimicrobial activity toward most of the tested fungal and bacterial cultures was described (Bankar et al., 2010).
Silver NPs: The synthesis of NPs using plant extracts as reducing and capping agents has received special attention. The synthesis of plant- mediated silver NPs by Solanum toman (Govindaraju et al., 2010), papaya fruit extract (Jain et al., 2009), Nicotiana tobaccwn leaf extract (Prasad et al.,
2011) , Elettaria cardanionioni (Jobitha et al., 2012), and onion (Allium сера) (Saxena et al., 2010) and their promising antimicrobial activity are reported. Krishnaraj and co-workers reported the synthesis of silver NPs using Acalypha indica leaf extracts (Krishnaraj et al., 2010). Green synthesis of small silver NPs using Geraniol and their cytotoxicity against Fibrosarcoma-Wehi 164 were evaluated by Safaepour et al. (Safaepour et al., 2009). Ghosh et al. reported the synthesis of silver NPs using Dioscorea bulbifera tuber extract and evaluated their synergistic potential in combination with antimicrobial agents (Ghosh et al., 2012). Green synthesis, antimicrobial, and cytotoxic effects of silver NPs using Eucalyptus Chapmaniana leaves extract are also reported (Sulaiman et al., 2013).
Titanium dioxide NPs: The biosynthesis of titanium dioxide NPs by Nyctanthes leaves extract (Sundrarajan and Gowri, 2011), Eclipta prostrata leaf extract (Rajakumar et al., 2012), and Annona squamosa peel extract (Roopan et al., 2012) was reported. The synthesis of titanium dioxide NPs utilizing aqueous leaf extract of Catharanthus roseus against the adults of hematophagous fly, Hippobosca maculata leach (Diptera: Hippoboscidae), and sheep-biting louse, Bovicola ovis Schrank (Phthiraptera: Trichodectidae), was reported for their antiparasitic activities (Velayutham et al., 2012).
Zinc oxide NPs: Zinc oxide NPs have been synthesized using orange juice (Jha et al., 2011), aloe vera extract (Sangeetha et al., 2011), Citrus auranti- folia extracts (Samat and Nor, 2013), and milky latex of Calotropis procera (Singh et al., 2011).
Copper oxide NPs: Copper oxide NPs have been synthesized using plant leaf extract of Magnolias as a reducing agent, (Lee et al., 2011) latex of
Calotropis procera L. (Наше et al., 2012), soybean (Guajardo-Pacheco et al., 2010), and many more, and their antibacterial activity was assessed.
BACTERIA- AND FUNGUS-MEDIATED SYNTHESIS
Different bacteria species have been successfully used to reduce gold ions to a zerovalent metal. Gold particles of nanoscale dimensions may be readily precipitated within bacterial cells by incubation of the cells with Au3+ ions. Lower pH values and initial concentrations of Au(III) were individually responsible for reductions in nanogold particle size. Gold NPs were synthesized using Magnetospirillum gryphiswaldense MSR-1 (Cai et al., 2011), Bacillus megatherium DO 1 (Wen et al., 2009), mesophilic bacterium Shewanella (Ogi et al., 2010), Rhodopseudomonas capsulata (Shiying et al., 2007), Pseudomonas aeruginosa (Husseiny et al., 2007), Stenotrophomonas maltophilia (Nangia et al., 2009), Escherichia coli and Desulfovibrio desulfuricans (Deplanche and Macaskie, 2008), marine alga Sargassunnvightii Greville (Singaravelu et al., 2007), marine microalga Tetrasehnis suecica (Shakibaie et al., 2010), marine bacterial strain of Marinobacterpelagius (Shanna et al., 2012), aqueous extract of brown algae Laminaria Japonica (Ghodake and Lee, 2011), and alkalotolerant actinomycete (Rhodococcus sp.) (Ahmad et al., 2003). The synthesis of gold NPs using the cell-free filtrate of fungus, Sclerotium rolfsii (Narayanan and Sakthivel, 2011) fungus Verticillium sp. (Mukherjee et al., 2001), fungus Trichoderma harzianum (Singh and Raja, 2011) was reported in the literature. The synthesis of silver NP by eukaryotic organisms like Verticillium sp. is also reported (Mukherjee et al., 2012). Among fungi, Aspergillus sp. is the least expensive and economical biomaterial for the biosynthesis of silver NP. The use of filamentous fungus Phoma sp. 3.2883 (Chen et al., 2003) and white-rot fungus Phanerochaete chrysosporium in the synthesis of silver NP was reported (Vigneshwaran et al., 2006). Penicillium fellutanum isolated from coastal mangrove sediment (Kathiresan et al., 2009) for silver NP production was reported earlier. The biosynthesis of silver NPs using fungi Penicillium diversum and their antimicrobial activity against E. coli, Salmonella typin', Vibrio cholerae, and the clinical isolate of Paratyphia were investigated (Ganachari et al., 2012). Titanium dioxide NP synthesis by using Lactobacillus sp., Saccharomyces cerevisae (Jha et al., 2009), fungus Fusarium oxysporum, and Bacillus subtilis (Bansal et al., 2005) was reported. In another study, the biosynthesis of titanium NPs was achieved by using Aspergillus flams as a reducing and capping agent and assessed to be a good novel antibacterial material (Rajakumar et al., 2012). The manganese and zinc
NPs were successfully synthesized by using Streptomyces sp. HBUM171191 (Waghmare et al.). The biosynthesis of phase-pure metallic copper NPs using a silver-resistant bacterium MorganeUa morganii was investigated (Ramanathan et al., 2013). The biosynthesis of copper oxide NPs using Penicillium aurantiogriseum, Penicillium citrinu, and Penicillium waksmanii was also reported (Honaiy et al., 2012). Biological method for extracellular bacterium belonging to the genus Serratia is known (Hasan et al., 2008).
APPLICATION OF GREEN CHEMISTRY IN SUPRAMOLECULAR CHEMISTRY
The field of supramolecular chemistry concerns the design of molecular entities that are defined by reversible, noncovalent interactions. While each supramolecular interaction is quite weak individually, the effect of many such interactions working in combination can produce strongly associated and structurally well-defined molecular species. Such additive effects are responsible for the spectacular structural complexity found in biomacromolecules such as proteins. Supramolecular chemistry represents a complementary approach toward molecular construction and relies upon noncovalent interactions to provide the primary associative interaction between the catalyst and the substrate, a factor that is responsible for the spectacular selectivity and reactivity of enzymes. Supramolecular interactions can be involved in catalysis in several ways. Supramolecular encapsulation of one or more substrate molecules within a host (which itself is often self-assembled through supramolecular chemistry) can promote or modulate reactivity. Supramolecular binding can enforce substrate- catalyst interactions through molecular recognition processes that function independently of the reactive functional groups. Finally, it is possible to install catalytic moieties within the cavity of a molecular host, which can then bind substrate molecules. The synthesis of supramolecular devices utilize toxic chemicals posing a threat to the environment. Hence, the emphasis has now shifted to the synthesis of supramolecules using green solvents. Solvents account for a large fraction of waste generated in chemical reactions, and switching to environmentally innocuous solvents is one of the 12 principles of green chemistry (Anastas and Werner, 1998). Many studies have been reported for the same. A substantial fraction of self-assembled molecular hosts is soluble in water and possess hydrophobic interiors. When the reactants and/or catalyst of an organic reaction are encapsulated within a hydrophobic cavity, the molecular host can act as a nanometer-sized reaction flask, bringing together reactants that would otherwise be insoluble (Yoshizawa et al., 2009). While many examples of supramolecular catalysis in the water now exist, the most practical and synthetically useful strategy that has emerged is the use of micellar hosts that spontaneously self- assemble in water. The advantages of these systems over other water-soluble hosts include their reliable self-assembly under a wide range of conditions, commercial availability, low cost of many micelle-forming surfactants, and a wide range of hydrophobic molecules that are encapsulated.
Tamiaki and co-workers reported synthetic zinc and magnesium chlorine aggregates as a model for supramolecular antenna complexes of green photosynthetic bacteria (Tamiaki et al., 1996). Alarge-channel supramolecular structure composed entirely of organic molecules was synthesized using a green chemistry approach, combining mechanochemistry and solid-state photodimerization.
