Deep Eutectic Solvents (DESs): Preliminary Results for Their Use Such as Biocides in the Building Cultural Heritage

Abstract

Biodeterioration is an increasingly widespread process of degradation in the context of the conservation of cultural heritage, which involves a combination of physical and chemical damages together with an aesthetic alteration of materials. For biological damage on monuments caused by pathogens, macro- and microorganisms, chemical treatments are generally used, most of the time dangerous for the environment and for the operator. In this context, new eco-friendly products represent necessary tools for the treatment of biologically deteriorated stone surfaces and represent a new challenge in the field of restoration and conservation of materials of cultural interest. A relatively new class of unconventional green solvents are deep eutectic solvents (DESs), which have peculiar chemical-physical characteristics such as being non-toxic, ecological, biodegradable, non-flammable, and stable in the presence of water. Furthermore, many DESs known in the literature have also been shown to have a biocidal action. All these characteristics make DESs very advantageous and safe, and they could be used as biocidal agents for the treatment of biodegraded surfaces of cultural heritage, being non-toxic for the environment and for the operator. So far, they are used in various fields, but they still represent a novel frontier in the cultural heritage sector. The present research aims at testing five different DESs for the first time in cultural heritage. In particular, DESs are applied to a mosaic located in the Ostia Antica Archaeological Park (Rome), and their efficiency is compared with a biocide product currently used in the restoration field, namely, Preventol RI50, through luminescence, bio-luminometry, and spectrocolorimetry analysis. The preliminary results achieved show the different behaviors of each DESs, highlighting the possibility of employing them in the field of cultural heritage. Further studies have been planned, some of which are already underway, to investigate the properties of DESs and indicate any improvements to make them more effective, both as solvents and as biocides, and easy to apply to various types of materials. The results obtained from this first study are very promising for the use of DES as a new green strategy for cleaning and conservation treatments of materials in the field of cultural heritage.

Iodocyclization of 2‐Methylthiophenylacetylenes to 3‐Iodobenzothiophenes and their coupling Reactions under More Sustainable Conditions

“…Substrates 1 q and 1 r, bearing an electron-donating (Me) or electron-withdrawing (F) on the aromatic ring, also reacted well, with formation of the corresponding 3-iodobenzothiophenes 2 q and 2 r in 68% and 77% yields, respectively (Table 2, entries 17 and 18). The possibility to recycle the DES solvent several times, without appreciable yield loss, was also assessed for representative substrates, as shown in Table 2,entries 2,9,13,and 15. We then verified the possibility to carry out paradigmatic examples of Sonogashira and Suzuki cross-couplings in a ChClbased DES as the solvent, using the synthesized 3-iodobenzothiophenes 2 and different 1-alkynes 3 as coupling partners. We first tested the Sonogashira coupling of 2- (3iodobenzo[b]thiophen-2-yl)propan-2-ol 2 a and 1-hexyne 3 a in the same DES solvent successfully employed for iodocyclizations [ChCl/urea (1/2, mol/mol)].…”

“…Melting points are uncorrected. 1 H NMR and 13 C NMR spectra were recorded at 25 °C on a 300 or 500 Spectrometer in CDCl 3 and DMSO-d 6 with Me 4 Si as internal standard. Chemical shifts (δ) and coupling constants (J) are given in ppm and in Hz, respectively.…”

“…Preparation of DESs and Substrates: DESs [ChClÀ Gly (1 : 2 mol/ mol); ChClÀ Urea (1 : 2 mol/mol); ChClÀ EG (1 : 1 mol/mol)] were prepared as we already reported. [13] Starting materials 1 were prepared as described in the Supporting Information.…”

“…Yield: 78.2 mg, starting from 62.5 mg of 1 a (81%) ( 9, 142.7, 136.8, 125.3, 125.13, 125.08, 122.0, 73.8, 73.1, 29.9; GC-MS (EI, 70 eV): m/z = 318 (M + , 55), 303 (100), 300 (42), 171 (11), 147 (18), 129 (23), 115 (14), 89 (31); HRMS-ESI (m/z): [(MÀ H 2 O + H) + ] cald for (C 11 H 10 IS) + : 300.9542; found: 300.9556. 13 C NMR (CDCl 3 , 125 MHz): δ = 151. 5, 142.7, 137.1, 125.4, 125.0, 124.9, 122.0, 75.8, 73.4, 34.2, 28.3, 8.0; GC-MS (EI, 70 eV): m/z = 332 (M + , 26), 303 (100), 161 (12), 147 (12), 89 ( 14 1- 9, 141.4, 140.8, 138.0, 128.6, 128.3, 126.6, 125.5, 125.3, 125.2, 122.6, 79.3, 74.6 [b] 17 68…”

“…IR (KBr): ν = 1435 (m), 1358 (w), 1242 (m), 1165 (w), 1080 (w), 1018 (w), 910 (w), 849 (m), 779 (s), 748 (s) cm À 1 ; 1 H NMR (CDCl 3 , 500 MHz): δ = 7. 90-7.67 (m, 3 H), 7.57-7.48 (m, 1 H), 7.48-7.27 (m, 3 H); 13 C NMR (CDCl 3 , 125 MHz): δ = 142. 1, 138.2, 137.3, 134.7, 128.4, 126.2, 125.8, 125.5, 125.4, 122.0, 78.6; GC-MS (EI, 70 eV): m/z = 342 (M + , 100), 215 (20), 214 (19), 171 (78), 127 (12), 107 (25); HRMS-ESI (m/z): [(M + H) + ] cald for (C 12 H 8 IS 2 ) + : 342.9107; found: 342.9144.…”