TY - JOUR
T1 - To be or not to be an azo pigment: Chemistry for the preservation of historical β-naphthol reds in cultural heritage
AU - Angelin, Eva Mariasole
AU - Oliveira, M. Conceição
AU - Nevin, Austin
AU - Picollo, Marcello
AU - Melo, Maria J.
N1 - Funding Information:
info:eu-repo/grantAgreement/FCT/6817 - DCRRNI ID/UIDB%2F50006%2F2020/PT#
info:eu-repo/grantAgreement/FCT/6817 - DCRRNI ID/UIDP%2F50006%2F2020/PT#
This work was supported by Funda??o para a Ci?ncia e Tecnologia, Minist?rio da Educa??o e da Ci?ncia (FCT/MCTES), Portugal, through doctoral programme CORES-PD/00253/2012, PhD grant PB/BD/114412/2016 (Eva Mariasole Angelin), Associate Laboratory for Green Chemistry- LAQV financed by national and LISBOA-01-0145-FEDER-022125-IST/RNEM.
Funding Information:
info:eu-repo/grantAgreement/FCT/6817 - DCRRNI ID/UIDB%2F50006%2F2020/PT#
info:eu-repo/grantAgreement/FCT/6817 - DCRRNI ID/UIDP%2F50006%2F2020/PT#_
This work was supported by Fundação para a Ciência e Tecnologia, Ministério da Educação e da Ciência (FCT/MCTES), Portugal , through doctoral programme CORES-PD/00253/2012 , PhD grant PB/BD/114412/2016 (Eva Mariasole Angelin), and LISBOA-01-0145-FEDER-022125-IST/RNEM .
Publisher Copyright:
© 2021 Elsevier Ltd
PY - 2021/6
Y1 - 2021/6
N2 - Naphthol reds are historical pigments widely found in cultural heritage, characterized by 1-arylhydrazone-2-naphthol basic skeleton. Little is known about their degradation mechanisms, and this knowledge is essential for their long-term preservation. In this research, for the first time, the photodegradation quantum yields (ΦR) were calculated for a series of pigment reds selected based on published literature, in order to evaluate the effects of the electron-withdrawing and donating groups present in C(4′), in particular the effect of sulfonate groups on the stability of these compounds. ΦR values in homogeneous media, ranging from 3 × 10−6 to 4 × 10−5, are difficult to obtain in these systems, but provide the quantification of the stability of naphthol reds. One of the main conclusions is that the sulfonate groups have a stabilizing effect and that the keto forms are generally more stable. Another important piece of information is that the solvent, and as such the medium predictably, has a major impact on stability. For Sudan I and Orange II irradiation was also carried with a xenon source (λirr ≥ 300 nm), allowing characterizing the main degradation products by HPLC-DAD-MS and UHPLC-HRMS. For the dyes characterized by higher ΦR, extensive degradation was observed with the formation of volatile compounds as phthalates.
AB - Naphthol reds are historical pigments widely found in cultural heritage, characterized by 1-arylhydrazone-2-naphthol basic skeleton. Little is known about their degradation mechanisms, and this knowledge is essential for their long-term preservation. In this research, for the first time, the photodegradation quantum yields (ΦR) were calculated for a series of pigment reds selected based on published literature, in order to evaluate the effects of the electron-withdrawing and donating groups present in C(4′), in particular the effect of sulfonate groups on the stability of these compounds. ΦR values in homogeneous media, ranging from 3 × 10−6 to 4 × 10−5, are difficult to obtain in these systems, but provide the quantification of the stability of naphthol reds. One of the main conclusions is that the sulfonate groups have a stabilizing effect and that the keto forms are generally more stable. Another important piece of information is that the solvent, and as such the medium predictably, has a major impact on stability. For Sudan I and Orange II irradiation was also carried with a xenon source (λirr ≥ 300 nm), allowing characterizing the main degradation products by HPLC-DAD-MS and UHPLC-HRMS. For the dyes characterized by higher ΦR, extensive degradation was observed with the formation of volatile compounds as phthalates.
KW - Art conservation
KW - Azo pigments
KW - Photodegradation
KW - Photophysics
KW - β-Naphthols hydrazone pigments
UR - http://www.scopus.com/inward/record.url?scp=85103967473&partnerID=8YFLogxK
U2 - 10.1016/j.dyepig.2021.109244
DO - 10.1016/j.dyepig.2021.109244
M3 - Article
AN - SCOPUS:85103967473
VL - 190
JO - Dyes And Pigments
JF - Dyes And Pigments
SN - 0143-7208
M1 - 109244
ER -