Synthesis, characterization and DFT-modeling of novel agents for the protection and restoration of historical calcareous stone substrates.
The ammonium salts of oxamate (AmOxam) and monomethyloxalate (AmMeox), structurally related to ammonium oxalate (AmOx), were synthesized and characterized as protecting agents/filler for calcareous stone substrates. Both compounds featured an improved solubility in water and alcoholic-water mixtures with respect to AmOx. While AmOxam is stable in aqueous solution and reacts with calcite to afford the corresponding insoluble calcium oxamate (CaOxam), AmMeox spontaneously undergoes hydrolysis to give ammonium monohydrogen oxalate hemihydrate (AmBiox) and calcium oxalate (CaOx). Both compounds have been tested for the restoration of naturally weathered marble and biomicritic limestone. The formation of a superficial layer of CaOxam and CaOx was observed on stone samples treated with AmOxam and AmMeox, respectively, depending on the solvent mixture. A quantum-mechanical study was carried out at DFT level in order to investigate the nature of the interactions occurring between the lithic substrate (calcite) and the passivating agents, showing how the structural modifications on oxalic acid derivatives can be exploited to fine-tune their interaction with the calcite surface.
Dipartimento di Scienze Chimiche e Geologiche, S.S. 554 bivio per Sestu, 09042 Monserrato (Cagliari), Italy.
Laura
L
Maiore
Dipartimento di Scienze Chimiche e Geologiche, S.S. 554 bivio per Sestu, 09042 Monserrato (Cagliari), Italy.
M Carla
MC
Aragoni
Consiglio Nazionale delle Ricerche (CNR) Istituto di Scienze dell'Atmosfera e del Clima (ISAC) UOS di Cagliari c/o Dipartimento di Fisica, Università degli Studi di Cagliari, S.S. 554 bivio per Sestu, 09042 Monserrato (Cagliari), Italy.
Gianfranco
G
Carcangiu
Dipartimento di Ingegneria Meccanica, Chimica e dei Materiali, via Marengo 2, 09123 Cagliari, Italy.
Ombretta
O
Cocco
Dipartimento di Scienze Chimiche e Geologiche, S.S. 554 bivio per Sestu, 09042 Monserrato (Cagliari), Italy.
Francesco
F
Isaia
Dipartimento di Scienze Chimiche e Geologiche, S.S. 554 bivio per Sestu, 09042 Monserrato (Cagliari), Italy.
Vito
V
Lippolis
Dipartimento di Ingegneria Meccanica, Chimica e dei Materiali, via Marengo 2, 09123 Cagliari, Italy.
Paola
P
Meloni
Dipartimento di Ingegneria Civile, Ambientale e Architettura, via Marengo 2, 09123 Cagliari, Italy.
Arianna
A
Murru
Dipartimento di Scienze Chimiche e Geologiche, S.S. 554 bivio per Sestu, 09042 Monserrato (Cagliari), Italy.
Enrica
E
Tuveri
Dipartimento di Scienze Chimiche e Geologiche, S.S. 554 bivio per Sestu, 09042 Monserrato (Cagliari), Italy. Electronic address: marca@unica.it.
Massimiliano
M
Arca
DFT; Marble; Oxalate derivatives; Protection