Mendeleev Commun., 2020, 30, 768–769 – 768 – Mendeleev Communications © 2020 Mendeleev Communications. Published by ELSEVIER B.V. on behalf of the N. D. Zelinsky Institute of Organic Chemistry of the Russian Academy of Sciences. Composite materials based on polymers and metal nanoparticles are of biomedical interest. 1,2 A polymer matrix provides strength, mechanical and adhesive properties of the material, while nanoparticles give additional biocide, catalytic and magnetic properties. 3–5 In creating these materials, it is important to obtain a uniform distribution of nanoparticles in the matrix. First, the mechanical dispersion of prepared nanoparticles in the polymer matrix can be used. 6,7 This process can be accompanied by the mechanical damaging of polymers, additional aggregation of nanoparticles, uncontrollable distribution of the nanoparticles in the volume of polymers, etc. Second, the direct synthesis of nanoparticles in the presence of a polymer matrix can be performed. 8,9 Polymers can organize centers for the growth of nanoparticles, sterically restrict it, and stabilize nanoparticles with charged groups. It was found earlier that carboxymethylcellulose (CMC) can serve as a matrix for g-Fe 2 O 3 (maghemite) nanoparticles in one-pot synthesis. 10 The magnetic nanoparticles of magnetite and maghemite are the most widespread forms of iron oxides. 11 The aim of this work was to study the distribution of g-Fe 2 O 3 nanoparticles upon synthesis in a CMC polymer matrix depending on the fraction of iron in an initial mixture and the physicochemical properties of the resulting nanocomposites. The composites were prepared by synthesizing iron oxide nanoparticles in a solution of CMC sodium salt (Na–CMC) with a molecular weight of 90000 using Mohr’s salt as a precursor. 10 The nanocomposites were obtained by the treatment of an alkaline solution of Mohr’s salt with sodium hypophosphite in the presence of Na–CMC at room temperature. The reaction was carried out in air since oxygen is required to produce the oxidized form of iron. The obtained samples and Na–CMC were dialyzed against twice distilled water. The molar ratio (m) between the monomer units of the poly- saccharide and Fe 2+ ions in the synthesis was varied from 0.04 to 1. The polysaccharide concentration was 2 wt%. Note that only water-soluble products were formed with the above concentrations and amounts of reagents. As a result, three g-Fe 2 O 3 /Na–CMC nanocomposites, in which the brown color intensity increased with the iron content of the system, were obtained (see details in Online Supplementary Materials). The sizes of the nanocomposites were evaluated by quasi- elastic laser light scattering. The diameter of pure Na–CMC in a Tris buffer with pH 7 was 285 nm. Incorporation of g-Fe 2 O 3 nanoparticles in a Na–CMC matrix with m = 0.04 (composite I) resulted in a decrease of the mean diameter to 115 nm. A further increase in the fraction of nanoparticles in a Na–CMC matrix with m = 0.25 (composite II) resulted in a decrease of the mean size to 95 nm. Finally, for the nanocomposite with m = 1 (composite III), the mean diameter was 85 nm. This contraction can be attributed to the action of g-Fe 2 O 3 nanoparticles as inter-macromolecular cross-linking agents. Nevertheless, this size measurement cannot elucidate the overall distribution of nanoparticles within Na–CMC macromolecules. The electrophoretic mobility (EPM) of the nanocomposites was measured to evaluate the surface charges of particles (Figure 1). The EPM value of composite I was –1.5 mm cm s –1 V –1 , which is equal to the value for pure Na–CMC. An increase in the fraction of nanoparticles in the nanocomposites raised the overall negative EPM values to –2.5 mm cm s –1 V –1 for composite II and Composition-dependent mechanism of formation of g -Fe 2 O 3 /carboxymethylcellulose nanocomposites Ekaterina E. Yurmanova, Irina M. Le-Deygen, Vasily V. Spiridonov and Andrey V. Sybachin* Department of Chemistry, M. V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation. Fax: +7 495 939 0174; e-mail: sybatchin@mail.ru DOI: 10.1016/j.mencom.2020.11.026 From center to periphery filling of CMC with nanoparticles Decrease of size of the nanocomposite Increase of the surface charge Increase of the nanoparticles’ fraction The distribution of nanoparticles in the volume of the composite is determined by a ratio between reagents at the stage of synthesis. At low molar fractions of iron in the system, nanoparticles are formed inside the coils of macromolecules, and nanoparticles expand their formation closer to the surface with an increase in the iron fraction. The size of the nanoparticles remains independent of the polymer/iron ratio in the reaction mixture. Keywords: nanocomposite, iron oxide, maghemite, carboxymethylcellulose, nanoparticles. 0 –1 –2 –3 –4 III II I CMC EPM/mm cm s –1 V –1 Figure 1 EPM of pure Na–CMC and composites I–III (Tris buffer solution with pH 7.0; concentration of macromolecules, 0.5 mg ml –1 ).