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Author: search.filters.author.Srepusharawoot, PornjukSubject: search.filters.subject.Antibacterial property

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    Effect of free oxygen radical anions and free electrons in a Ca12Al14O33 cement structure on its optical, electronic and antibacterial properties
    (2019-05-01)
    Phrompet, Chaiwat
    ;
    Sriwong, Chaval
    ;
    Srepusharawoot, Pornjuk
    ;
    Maensiri, Santi
    ;
    Chindaprasirt, Prinya
    The aim of this work was to investigate the effect of free oxygen radicals and free electrons in a Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> (C12A7) cement structure on the optical, electronic and antibacterial activity of this material. Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> was successfully fabricated via rapid heating to high temperatures by high frequency electromagnetic induction. Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> cement samples were characterized using XRD and UV-Vis-DRS spectroscopy. The morphology and chemical composition of the samples were also investigated using SEM and EDS techniques. The presence of free oxygen radicals (O<inf>2</inf> <sup>−</sup>ions) in the insulating structure of Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> was confirmed using Raman spectroscopy showing a spectrum peak at 1067 cm<sup>−1</sup>. The excitation of free electrons in the Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> cement was indicated by UV-Vis absorption spectra at 2.8 eV and an optical energy gap of 3.5 eV, which is consistent with the first-principles calculations for the band energy level. The effects of free oxygen radicals and free electrons in the Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> structure as antibacterial agents against Escherichia Coli (E. coli) and Staphylococcus Aureus (S. aureus) were investigated using an agar disk-diffusion method. The presence of O<inf>2</inf> <sup>−</sup> anions as a reactive oxygen species (ROS) at the surface of Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> caused inhibition of E. coli and S. aureus cells. The free electrons in the conducting C12A7 reacted with O<inf>2</inf> gas to produce ROS, specifically super oxides (O<inf>2</inf> <sup>−</sup>), superoxide radicals (O<inf>2</inf> <sup>•-</sup>), hydroxyl radicals (OH<sup>•</sup>) and hydrogen peroxide (H<inf>2</inf>O<inf>2</inf>), which exhibited antibacterial properties. Both mechanisms were active against bacteria without effects from nano-particle sized materials and photocatalytic activity. The experimental results showed that the production of ROS from free electrons was greater than that of the free O<inf>2</inf> <sup>−</sup> anions in the structure of Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf>. The antibacterial actions for insulating and conducting Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> were different for E. coli and S. aureus. Thus, Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf> cement has antibacterial properties that do not require the presence of nano-particle sizes materials or photocatalysis.