Novel Microemulsions with Essential Oils for Environmentally Friendly Cleaning of Copper Cultural Heritage Artifacts

Cleaning represents an important and challenging operation in the conservation of cultural heritage, and at present, a key issue consists in the development of more sustainable, "green" materials and methods to perform it. In the present work, a novel xylene-in-water microemulsion based on nonionic surfactants with low toxicity was obtained, designed as low-impact cleaning agent for metallic historic objects. Phase diagram of the mixtures containing polyoxyethylene-polyoxypropilene triblock copolymer Pluronic P84 and D-alpha-tocopheryl polyethylene glycol 1000 succinate (TPGS) as surfactants, water, ethanol and xylene was studied, and a microemulsion with low surfactant content was selected as suitable cleaning nanosystem. Essential oils (EOs) from thyme and cinnamon leaf were added to the selected microemulsion in order to include other beneficial properties such as anticorrosive and antifungal protection. The microemulsions with or without EOs were characterized by size, size distribution and zeta potential. The cleaning efficacy of the tested microemulsions was assessed based on their ability to remove two types of artificial dirt by using X-ray energy dispersion spectrometry (EDX), scanning electron microscopy (SEM), contact angle measurements and color analysis. Microemulsions exhibit high capacity to remove artificial dirt from model copper coupons in spite of very low content of the organic solvent. Both thyme and cinnamon oil loading microemulsions prove to significantly reduce the corrosion rate of treated metallic plates compared to those of bare copper. The antifungal activity of the novel type of microemulsion was evaluated against Aspergillus niger, reported as main treat in biocorrosion of historic copper artifacts. Application of microemulsion with small amounts of EOs on Cu plates inhibits the growth of fungi, providing a good fungicidal effect.

Luminescence, Paramagnetic, and Electrochemical Properties of Copper Oxides-Decorated TiO2/Graphene Oxide Nanocomposites

The properties of newly synthesized Cu₂O/CuO-decorated TiO₂/graphene oxide (GO) nanocomposites (NC) were analyzed aiming to obtain insight into their photocatalytic behavior and their various applications, including water remediation, self-cleaning surfaces, antibacterial materials, and electrochemical sensors. The physico-chemical methods of research were photoluminescence (PL), electron paramagnetic resonance (EPR) spectroscopy, cyclic voltammetry (CV), and differential pulse voltammetry (DPV). The solid samples evidenced an EPR signal that can be attributed to the oxygen-vacancy defects and copper ions in correlation with PL results. Free radicals generated before and after UV-Vis irradiation of powders and aqueous dispersions of Cu₂O/CuO-decorated TiO₂/GO nanocomposites were studied by EPR spectroscopy using two spin traps, DMPO (5,5-dimethyl-1-pyrroline-N-oxide) and CPH (1-hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine), to highlight the formation of hydroxyl and superoxide reactive oxygen species, respectively. The electrochemical characterization of the NC modified carbon-paste electrodes (CPE) was carried out by CV and DPV. As such, modified carbon-paste electrodes were prepared by mixing carbon paste with copper oxides-decorated TiO₂/GO nanocomposites. We have shown that GO reduces the recombination process in TiO₂ by immediate electron transfer from excited TiO₂ to GO sheets. The results suggest that differences in the PL, respectively, EPR data and electrochemical behavior, are due to the different copper oxides and GO content, presenting new perspectives of materials functionalization.

Synthesis, Characterization, DFT Study and Antifungal Activities of Some Novel 2-(Phenyldiazenyl)phenol Based Azo Dyes

In recent decades, there has been an increased interest in azo compounds with special optical and biological properties. In this work, we report the preparation of novel azo-compounds with two and three -N=N- double bonds, using the classical method of synthesis, diazotization and coupling. The compounds were characterized by ¹H-NMR, ¹³C-NMR, FTIR, UV-VIS and fluorescence spectra. DFT calculations were employed for determining the optical parameters, polarizability α, the total static dipole moment μ_tot, the quadrupole moment Q and the mean first polarizability β_tot. All azo derivatives show strong fluorescence emission in solutions. The antioxidant and antifungal activities were determined and the influence of the number of azo bonds was discussed. The synthesized compounds exhibit remarkable efficiency in the growth reduction of standard and clinical isolated Candida strains, suggesting future applications as novel antifungal.

Design, Synthesis, and Biological Evaluation of New Azulene-Containing Chalcones

Azulene-containing chalcones have been synthesized via Claisen-Schmidt condensation reaction. Their chemical structure has been established by spectroscopic methods where the ¹H-NMR spectra suggested that the title chalcones were geometrically pure and configured trans (J = 15 Hz). The influence of functional groups from azulene-containing chalcones on the biological activity of the 2-propen-1-one unit was investigated for the first time. This study presents optical and fluorescent investigations, QSAR studies, and biological activity of 10 novel compounds. These chalcones were evaluated for their antimicrobial activity against Gram-positive and Gram-negative bacteria. The results revealed that most of the synthesized compounds showed inhibition against Gram-negative microorganisms, independent of the substitution of azulene scaffold. Instead, all azulene-containing chalcones exhibited good antifungal activity against Candida parapsilosis, with MIC values ranging between 0.156 and 0.312 mg/mL. The most active compound was chalcone containing azulene moieties on both sides of the 2-propene-1-one bond, exhibiting good activity against both bacteria-type strains and good antifungal activity. This antifungal activity combined with low toxicity makes azulene-containing chalcones a new class of bioorganic compounds.

Synthesis and properties of fluorescent 4'-azulenyl-functionalized 2,2':6',2″-terpyridines

4′-Azulenyl-substituted terpyridines were efficiently synthesized following the Kröhnke methodology via azulenylchalcone intermediates. These azulenyl-containing terpyridines showed fluorescent emission with a fluorescence quantum yield varying from 0.14, in the case of parent terpyridine, to 0.64 when methyl groups are grafted on the azulenyl seven-membered ring. According to the crystal structures and TDDFT calculations, different twisting of the aromatic constituents is responsible for the observed fluorescent behavior. The electrochemical profile contains one-electron oxidation/reduction steps, which can only be explained on the basis of the redox behavior of the azulene unit. The ability of the 4′-azulenyl 2,2′:6′,2″-terpyridine to bind poisoning metal cations was studied by UV–vis titrations using aqueous solutions of Hg(II) and Cd(II) chlorides as illustrative examples.

Visible-light triggered photoswitching systems based on fluorescent azulenyl-substituted dithienylcyclopentenes

Novel azulenyl functionalized dithienylethenes were synthesized, and their photochromic reactivity, fluorescent and electrochemical properties were investigated.