Abstract
Research in the field of natural dyes has constantly focused on methods of conditioning curcumin and diversifying their fields of use. In this study, hybrid materials were obtained from modified silica structures, as host matrices, in which curcumin dyes were embedded. The influence of the silica network structure on the optical properties and the antimicrobial activity of the hybrid materials was monitored. By modifying the ratio between phenyltriethoxysilane:diphenyldimethoxysilane (PTES:DPDMES), it was possible to evaluate the influence the organosilane network modifiers had on the morphostructural characteristics of nanocomposites. The nanosols were obtained by the sol–gel method, in acid catalysis. The nanocomposites obtained were deposited as films on a glass support and showed a transmittance value (T measured at 550 nm) of around 90% and reflectance of about 11%, comparable to the properties of the uncovered support. For the coatings deposited on PET (polyethylene terephthalate) films, these properties remained at average values of T550 = 85% and R550 = 11% without significantly modifying the optical properties of the support. The sequestration of the dye in silica networks reduced the antimicrobial activity of the nanocomposites obtained, by comparison to native dyes. Tests performed on Candida albicans fungi showed good results for the two curcumin derivatives embedded in silica networks (11–18 mm) by using the spot inoculation method; in comparison, the alcoholic dye solution has a spot diameter of 20–23 mm. In addition, hybrids with the CA derivative were the most effective (halo diameter of 17–18 mm) in inhibiting the growth of Gram-positive bacteria, compared to the curcumin derivative in alcoholic solution (halo diameter of 21 mm). The results of the study showed that the presence of 20–40% by weight DPDMES in the composition of nanosols is the optimal range for obtaining hybrid films that host curcumin derivatives, with potential uses in the field of optical films or bioactive coatings.
Highlights
Curcumin is the main compound extracted from Curcuma longa
We looked at the influence of the characteristics of the siloxane host matrix on the optical and antimicrobial properties of curcumin derivatives
Four types of host matrices were obtained by modifying the ratio of alkoxysilanes (PTES:DPDMES)
Summary
Curcumin is the main compound extracted from Curcuma longa. Among the classic uses of curcumin, we can mention its frequent presence in our diet, as a spice or food preservative, and it is often used in Ayurvedic medicine or traditional Chinese medicine in the treatment of various diseases. Depending on the field of use, curcumin studies have been directed on methods to increase solubility for biomedical applications [4,5,6,7,8] or aimed at improving light or temperature stability properties for unconventional applications, such as sensors [9,10,11], pH indicators [12,13], dyes for solar cells [14,15,16,17], (bio) active coatings [18,19,20,21,22,23,24,25,26] In this regard, the dye was used in its natural form, or it was chemically modified either on β-diketone or peripheral aromatic groups. Anticorrosive coatings must have barrier properties and usually contain metal oxides; photoactive coatings used in solar applications must have good anti-reflection and transmitting properties and usually contain dyes, or metal complexes, while anti-biofilm coatings frequently host metallic nanoparticles, natural compounds, or antibiotics and have antimicrobial activity [56,57,58,59,60,61,62]
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