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. 2023 Jul 30;28(15):5768.
doi: 10.3390/molecules28155768.

Ammonium N-(pyridin-2-ylmethyl)oxamate (AmPicOxam): A Novel Precursor of Calcium Oxalate Coating for Carbonate Stone Substrates

Anna Pintus  1 , M Carla Aragoni  1 , Gianfranco Carcangiu  2 , Veronica Caria  1 , Simon J Coles  3 , Eleanor Dodd  3 , Laura Giacopetti  1 , Domingo Gimeno  4 , Vito Lippolis  1 , Paola Meloni  5   6 , Simone Murgia  1 , Antonia Navarro Ezquerra  7 , Enrico Podda  1   8 , Claudia Urru  1 , Massimiliano Arca  1
Affiliations

Ammonium N-(pyridin-2-ylmethyl)oxamate (AmPicOxam): A Novel Precursor of Calcium Oxalate Coating for Carbonate Stone Substrates

Anna Pintus et al. Molecules. .

Abstract

Ammonium N-(pyridin-2-ylmethyl)oxamate (AmPicOxam), synthesized from O-methyl-N-(pyridin-2-ylmethyl)oxamate, was spectroscopically and structurally characterized and assayed as a novel precursor for the protection and consolidation of carbonate stone substrates. An in-depth characterization of treated and untreated biomicritic limestone and white Carrara marble samples was carried out by means of SEM microscopy, X-ray powder diffraction, helium pycnometry, determination of water transport properties, and pull-off tests. The improved solubility (1.00 M, 16.5% w/w) of the title compound with respect to ammonium oxalate (0.4 M, 5% w/w) results in the formation of a thicker protective coating of calcium oxalate (CaOx) dihydrate (weddellite) on marble and biomicrite samples after the treatment with 5% and 12% w/w water solutions, producing a reduction in the stone porosity and increased cohesion. Theoretical calculations were carried out at the DFT level to investigate both the electronic structure of the N-(pyridin-2-ylmethyl)oxamate anion and the hydrolysis reaction leading from AmPicOxam to CaOx.

Keywords: DFT; calcite; conservation; cultural heritage; limestone; marble; oxamate.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Synthesis of compounds 1–3.
Figure 1
Figure 1
Molecular structure and atom numbering scheme for 2·1/2H2O. Thermal ellipsoids were drawn at a 50% probability level.
Scheme 2
Scheme 2
Reaction of compound 2 with CaCO3 in water.
Figure 2
Figure 2
SEM images of weathered Carrara marble treated with a 5% (a,b) and 12% w/w (c,d) solution of compound 2.
Figure 3
Figure 3
SEM images of biomicrite limestone treated with a 5% (a,b) and 12% w/w (c,d) solution of compound 2.
Figure 4
Figure 4
Isosurfaces of KS-HOMO (left) and KS-LUMO (right) calculated for the PicOxam− anion at B3LYP/def2-TZVP level. Cutoff value = 0.05 |e|.
See this image and copyright information in PMC

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