1,721,044 research outputs found
Cu(II)-binder complexes in azurite and malachite pictorial mixtures: An EPR study
Full text linkDegradation processes of paintings, frescos, illuminations, and painted decorations represent a relevant challenge
in the cultural heritage field for both conservators and scientists dealing with the causes of these processes. It is
very important understanding the molecular origin of colour changes, like fading, yellowing, blackening, as well
as the molecular origin of damages due to degradation, like cracking and fall of pictorial layers. Metal complexes,
often indicated as “metal soaps”, when referred to metal carboxylates, play a relevant role in degradation.
However, their identification is not easy, and the involvement of the metal ions in the degradation mechanisms is
often not clear. Continuous Wave Electron Paramagnetic Resonance (CW-EPR) spectroscopy is a very sensitive
tool towards paramagnetic species (e.g., transition metal ions like Fe(III), Cu(II), Mn(II), radicals, etc.), providing
relevant information on these species, not always well-characterized with other methods. In this paper, we use
CW-EPR to study the formation of Cu(II)-binder complexes in natural malachite and azurite pigments mixed with
several organic binders. We show that CW-EPR technique is able to detect easily Cu(II) complexes with organic
ligands, and can additionally provide information on the pigments themselves. In particular, the first coordi-
nation sphere of the Cu(II) complexes is characterized by applying the Peisach-Blumberg method. Moreover, CW-
EPR shows that binders can affect the structure of the raw pigments
Le analisi spettroscopiche sul Diario spirituale di Sant’Ignazio in occasione del suo restauro
Full text linkIn this work, a step-by-step approach is proposed, where each level of a conservation treatment on Saint Ignatius’ spiritual diary, a valuable XVI c. manuscript, is monitored through non-invasive spectroscopic techniques: UV-VIS reflectance (FORS) and X-Ray fluorescence (XRF). FORS and XRF allowed us to evaluate the potentially dangerous ink or iron migration in each step. The acquisition of many FORS and XRF spectra all over the manuscript allowed us to make considerations about the type and nature of the iron-gall inks. Finally, Raman, FORS and XRF were used also to characterise the materials used to decorate the XVIII c. precious cove
Copper Complexes in Verdigris Painting Mixtures: An Electron Paramagnetic Resonance Characterization
No full textCopper complexes, also called “copper soaps” when referred to carboxylate compounds, have become a concern in the conservation of historical artefacts. These complexes are suspected to play a significant role in degradation processes such as darkening and cracking of painting layers. Here we propose the Continuous Wave Electron Paramagnetic Resonance spectroscopy (CW-EPR) as a tool for the identification of these species. EPR spectroscopy is a micro-invasive and non-destructive technique that is highly sensitive to paramagnetic species, including radicals, crystal defects, and transition metal ions, e.g., Cu(II) and Fe(III). We have selected the verdigris (copper acetate) pigment combined with many organic binders, e.g., egg tempera and gum Arabic, as mock-up systems because of the known degradation tendency of the copper-based pigment. We would like to demonstrate that a precise analysis of the experimental spectra assisted with the calculus of the main magnetic quantities could lead to a good characterization of the copper complexes (or “soaps”)
Spin concentration in a possible ESR dosimeter: An electron spin echo study on X-irradiated ammonium tartrate
No full textSeveral single crystals and powder samples of ammonium tartrate, recently proposed as a possible ESR dosimeter, have been X-irradiated with different doses. The total radical concentration has been determined by quantitative cw ESR, by comparison with a standard. The samples have been studied by electron spin echo spectroscopy. The two-pulse echo decay has been obtained and simulated by a single exponential function for different values of the microwave power of the pulses and for different pulse lengths. The dependence of the phase memory time TM on the microwave power has been exploited to get information on the contribution of the instantaneous diffusion to spin dephasing. At room temperature in the range of radical concentrations of 1E18-1E19 spins/cm3 the instantaneous diffusion is the dominant spin dephasing mechanism. The linear dependence of the instantaneous diffusion on the total concentration of the radicals is in agreement with the theory. From the latter result we conclude that the average radical-radical distance corresponds to a random distribution of the radicals in the matrix. A simple method of measuring the radical concentration by the ESE decays in powder samples of irradiated ammonium tartrate is described
Characterization of ancient and modern papers by CW-EPR spectroscopy
No full textSeveral old (15th to 18th century), new (1900–1950) and recently produced (after 1990) papers have been investigated by X-band continuous-wave electron paramagnetic resonance (EPR) spectroscopy. Signals from Cu(II), Fe(III), Mn(II) and radicals are apparent. A clear-cut distinction is observed between recently produced papers and the other samples: recent papers show just EPR signals from Mn(II) and sometimes small signals from Fe(III) in rhombic site, while the older samples show usually strong signals from Fe(III), Mn(II), Cu(II) and radicals. Furthermore, Mn(II) EPR signals from recent papers are characterized by small zero-field splitting (ZFS) parameters, indicating Mn(II) in high-symmetry sites, while older samples show broader Mn(II) EPR signals, typical for Mn(II) in low-symmetry sites (increased ZFS parameters)
Echo detected EPR as a tool for detecting radiation-induced defect signals in pottery
No full textArchaeological fragments of pottery have been investigated by using CW-EPR and Echo Detected EPR (EDEPR). EDEPR allows to remove the CW-EPR dominant Fe(III) background spectrum, hiding much weaker signals potentially useful for dating purpose. EDEPR spectra attributed to a methyl radical and to feldspar defects have been recorded at room and low temperature for an Iron Age cooking ware (700 B.C.). A study on the dependence of EDEPR intensity over absorbed dose on a series of gamma-irradiated brick samples (estimated age of 562 +/- 140 B.C.) has confirmed the potential efficacy of the proposed method for spotting defect signals out of the strong iron background. (C) 2011 Elsevier Ltd. All rights reserved
Electron Paramagnetic Resonance as a Probe for Metal Ions and Radicals in Paper
No full textElectron Paramagnetic Resonance (EPR) is a technique devoted to the identification and characterization of paramagnetic species, i.e. chemical species with unpaired electrons. Very common paramagnetic species which can be detected through EPR in historic paper are Fe(III), Mn(II), Cu(II) ions and radicals, where Fe(III), Cu(II) and radicals play a relevant role in paper degradation. Specifically, Fe(III) is almost ubiquitous in historic paper. Here we propose an overview of the EPR signals in historic and artificially aged paper, and in particular, we would like to show how a deep analysis of EPR signals from paper could provide useful information about the paper's origin and unique indications of the degradation and oxidation level of the paper
Radical anions of mono- and bis-fulleropyrrolidines: An EPR study
No full textThe radical anions of three C60 derivatives (N-methyl-3,4-fulleropyrrolidine, N-methyl-2-(3,6,9-trioxadecyl)-3,4-fulleropyrrolidine, and bis-N-methyl-3,4-fulleropyrrolidine are respectively MFP-, tegMFP-, and bisMFP-) have been investigated by continuous wave (cw) and pulsed EPR in methyltetrahydrofuran and tetrahydrofuran solutions. The EPR spectra for MFP- and tegMFP- show a 1:1:1 triplet, due to the hyperfine coupling with the pyrrolidine nitrogen. The EPR spectrum of bisMFP- shows a superimposition of two signals, each due to a 1:2:3:2:1 quintet. Each quintet is due to the hyperfine coupling with the two pyrrolidine nitrogen atoms. The two signals are attributed to two different conformers of the radical. A direct transfer of spin density from the sphere to the nitrogen atoms is discussed as arising from the bent conformation of the pyrrolidine rings. All the spectra show several weaker satellite lines, due to the radical anions containing a 13C atom. From their analysis a C2v symmetry for the spin distribution is obtained in the case of MFP- and tegMFP-. The EPR line widths of these latter radicals at room temperature are larger than those expected on the basis of spin relaxation due to rotational diffusion in solution, and the line widths decrease upon decreasing the temperature. Pulsed EPR measurements of T1 in liquid and frozen solutions show that the EPR line widths are determined by the anomalously short lifetimes of the spin states. The temperature dependence of T1 obeys to the Arrhenius law, giving an activation energy of 7 kJ/mol. The latter results are compared with those obtained in the past for the lone . They are attributed to the closeness of the electronic levels, due to the weak perturbation of the pyrrolidine ring on the symmetrical electronic distribution of C60. On the other hand, the spin relaxation properties of bisMFP- are shown those expected for a nonsymmetrical radical. The comparison of cw- and pulsed-EPR spectra of MFP- in frozen solutions of MeTHF and THF indicates the presence of aggregates of interacting radicals in THF
Copper Soaps Formation in Verdigris-Linseed Oil Painting Mixtures: A Multispectroscopic Characterization
No full textCopper acetate (also known as verdigris) is a bimetallic Cu(II) greenish pigment widely used in oil paintings. Since ancient times, this pigment has been known as a degradation-prone compound, especially when combined with lipidic binders. However, the degradation mechanism and the involved species have not yet been disclosed. In this article, we study verdigris interactions with linseed oil in painting mock-ups, stressing out the formation of copper-based complexes and proposing reaction routes. Such complex systems are studied by applying a complementary multispectroscopic approach: a combination of continuous-wave (CW) electron paramagnetic resonance (EPR), electron spin echo envelope modulation (ESEEM), and Raman and attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopies. Based on the experimental evidence, we propose the following mechanism: the neutral copper acetate shifts to a basic verdigris-promoting triglyceride hydrolysis, aided by the coordination of Cu(II) cations toward the carboxylic functions. The increased amount of free fatty acids in the mixtures triggers the formation of monomeric Cu(II) complexes. Afterward, the oil polymerization reaction occurs, and secondary oxidation species, containing OH groups in the alkyl chain, act as further ligands for copper nuclei. This is the first time, to the best of our knowledge, that a comprehensive view is proposed
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