Oxalyl chloride

A mixture of 120 mg of previously prepared oxidized MWCNT and 80 ml of DMF was sonicated for 20 minutes, then that can be used in different pharmaceutical applications. Liquid oxidation of MWCNT produces functional groups (hydroxyl and carboxyl) on the surface of MWCNT [1, 9] . These functional groups could be used as extra sites for further functionalization or addition reaction [9, 10] . Liquid phase oxidation allows the introduction of oxygenated functional groups on MWCNTs' surface, which is performed using hydrogen peroxide (H ) [11] .
They enhance the decrement of long-range van der Waals attraction forces and the increment of MWCNT-matrix/ solvent interaction which results in homogenous dispersion [12] . Therefore, MWCNT functionalization causes reactivity enhancement, and solubility improvement, and provides a path for further MWCNT chemical modifications such as metal deposition, ion adsorption, and grafting reactions. Furthermore, the functional groups work as anchor groups for two moieties connection and are more deriving by chemical reactions with other functional groups [13] [14] [15] . Functionalization of MWCNT renders them more compatible with organic solvents to prevent aggregation and permit better dispersion and solubilization within the polymer matrix. MWCNTs can be also modified through noncovalent interaction between polymers and CNTs to form polymer/CNT nanocomposites. Chitosan is one of the widespread polymers that is used in CNT modification and in medical applications due to its suitable bioactivity and biological properties [3, 5, [16] [17] [18] . Curcumin is a natural lipophilic polyphenol derived from rhizomes of the Curcuma longa, a perennial plant that belongs to the ginger family Zingiberaceae. , with 368.38 Da. Curcumin has many pharmacological and therapeutic activities, including antitumor, antiproliferative, antioxidant, antimicrobial, antiinflammatory, anti-obesity, anti-metastasis, dietary agent, proapoptotic, neuroprotective, and hepatoprotective activities [19] [20] [21] [22] [23] [24] [25] . The poor bioavailability of curcumin is a crucial challenge in its applications due to its chemical instability, low water solubility, poor absorption, and rapid metabolism [26] . Due to its hydrophobic properties, most of the orally consumed curcumin does not get absorbed into the small intestine epithelium cells [27] . Furthermore, due to the rapid metabolism of curcumin after oral administration, most of it is degraded in tissues such as the liver and small intestine before entering systemic circulation [26] .
In this study, MWCNT was synthesized to improve the water-solubility of hydrophobic curcumin. Depending on the simple conjugation between curcumin's hydroxyl group and MWCNT's carboxyl group via a hydrogen bond, curcumin will be activated to inhibit cell growth. To the best of our knowledge, there are no previous studies about linking curcumin with MWCNTs to test the improved curcumin's antioxidant activity and cytotoxicity against the liver HepG-2 cancer cell line.

MWCNTwith (95% purity, 30-50 nm outside diameter, and 10-20 μm length) were purchased from US Research Nanomaterials, Inc. USA. Nitric acid (70 wt.%) was obtained from (CARLO ERBA, France). Sulfuric acid (98 wt.%), Anhydrous 1 ml oxalyl chloride was added drop-wise to the suspension under nitrogen gas. This mixture was stirred at 350 rpm in an ice bath for 2 hours, then it was stirred at room temperature for another 2 hours, followed by overnight stirring at 70°C to remove excess oxalyl chloride.
After that, a mixture composed of 490 mg of low molecular weight chitosan and 40 ml of DMF was sonicated for 20 minutes, then added to the previous mixture (MWCNT, DMF, and oxalyl chloride) and stirred for 48 hours at 110°C. The resulting mixture was then filtrated and washed until no chitosan residues remained in the filtrate; finally, the particles were vacuum dried for 4 hours [28] .