Copper Soaps Formation in Verdigris-Linseed Oil Painting Mixtures: A Multispectroscopic Characterization.

Copper 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.

Application of Multispectral Imaging and Portable Spectroscopic Instruments to the Analysis of an Ancient Persian Illuminated Manuscript.

Illuminated manuscripts are, in general, the final products of a wise and complex interaction of different competencies. In particular, each manuscript reflects uses and techniques rooted in the historical and geographical traditions of the area of realization. Defining the characteristics and the materials in these valuable artefacts is an essential element to reconstruct their history and allow a more precise collocation and a possible comparison with other works in similar periods and areas. Non-invasive methods, mainly using portable instruments, offer undoubtedly good support in these studies. Recent analyses of an ancient Persian illuminated manuscript, combining multispectral imaging and spectroscopic measurements made with portable instruments (XRF, FORS, micro-Raman, IR-ATR) on selected points, provided new data for an improved understanding of this rare book. This study details the possibilities offered by combining these non-invasive methods for an in-depth understanding of the techniques and practices behind the realization of Middle Eastern illuminated manuscripts and provided new perspectives for multidisciplinary approaches to research in this field.

Spotting aged dyes on paper with SERS.

Surface enhanced Raman spectroscopy (SERS) is a highly sensitive technique for the non- or minimally invasive identification of molecules at very low concentrations. In this work, SERS is exploited using naked laser-ablated gold nanoparticles (AuNPs) for the detection of dyes on artificially aged paper inked with a ballpoint pen. Although several studies on inks with SERS are present in the literature, most of them report on the investigations on freshly prepared products, and less information is present on the detection of aged dyes and inks using SERS. Ballpoint inks are commonly used in daily activities, but have also been employed by several contemporary artists. These inks are very sensitive to light, and they discolor rapidly, making their detection demanding. In the present work, the SERS spectra of a ballpoint pen ink on two types of paper were analyzed after light-induced ageing, and the importance of the dye-AuNP interaction is discussed. The results show that the interpretation of the SERS spectra of the aged samples, such as those of interest in the Cultural Heritage field, is a tricky and delicate operation and that the diffusion of the dyes to the hot spot regions of the plasmonic nanoparticles plays a pivotal role in the detection of degraded ink components. Therefore, appropriate evaluation of the factors affecting the molecule-plasmonic nanoparticle interactions and of the history of the artwork to be analyzed is fundamental to avoiding the misinterpretation of the spectra and, consequently, of the original composition of the analyzed artwork.

Synthesis, Characterization and Biological Activity of Novel Cu(II) Complexes of 6-Methyl-2-Oxo-1,2-Dihydroquinoline-3-Carbaldehyde-4n-Substituted Thiosemicarbazones.

Three new 6-methyl-2-oxo-1,2-dihydroquinoline-3-carbaldehyde-thiosemicarbazones-N-4-substituted pro-ligands and their Cu(II) complexes (1, -NH2; 2, -NHMe; 3, -NHEt) have been prepared and characterized. In both the X-ray structures of 1 and 3, two crystallographically independent complex molecules were found that differ either in the nature of weakly metal-binding species (water in 1a and nitrate in 1b) or in the co-ligand (water in 3a and methanol in 3b). Electron Paramagnetic Resonance (EPR) measurements carried out on complexes 1 and 3 confirmed the presence of such different species in the solution. The electrochemical behavior of the pro-ligands and of the complexes was investigated, as well as their biological activity. Complexes 2 and 3 exhibited a high cytotoxicity against human tumor cells and 3D spheroids derived from solid tumors, related to the high cellular uptake. Complexes 2 and 3 also showed a high selectivity towards cancerous cell lines with respect to non-cancerous cell lines and were able to circumvent cisplatin resistance. Via the Transmission Electron Microscopy (TEM) imaging technique, preliminary insights into the biological activity of copper complexes were obtained.

Degradation products from naturally aged paper leaves of a 16th-century-printed book: a spectrochemical study.

In this work, we present a wide-range spectrochemical analysis of the degradation products from naturally aged paper. The samples obtained from wash waters used during the de-acidification treatment of leaves from a 16th-century-printed book were analysed through NMR, IR, Raman UV/Vis, EPR and X-ray fluorescence (XRF) spectroscopy and HPLC-MS and inductively coupled plasma (ICP) analysis. By these methods we also studied some of the previous samples treated by acidification (sample AP) and catalytic hydrogenation (sample HP). Crossing all the data, we obtained precise indications about the main functional groups occurring on the degraded, water-soluble cellulose oligomers. These results point out that the chromophores responsible for browning are conjugated carbonyl and carboxyl compounds. As a whole, we show that the analysis of wash waters, used in the usual conservation treatments of paper de-acidification, gives much valuable information about both the conservation state of the book and the degradation reactions occurring on the leaves, due to the huge amount of cellulose by-products contained in the samples. We propose therefore this procedure as a new very convenient general method to obtain precious and normally unavailable information on the cellulose degradation by-products from naturally aged paper.

Preserving the Ephemeral: A Micro-Invasive Study on a Set of Polyurethane Scenic Objects from the 1960s and 1970s.

Among the innovative materials used by 20th-century artists, polyurethane (PUR) has been shown to be highly unstable, and therefore artworks made of it are now in need of careful conservation strategies. This study presents a multi-analytical investigation of PUR foam scenic objects originally made between the 1960s and 1970s during the Italian Arte Viva movement. The main components in the foam and additives were characterized through micro attenuated total reflectance infrared spectroscopy (µ-ATR-FTIR) and pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC/MS). Painted samples were further investigated through µ-FTIR and Raman spectroscopy to define binders and pigments. The use of µ-ATR-FTIR in combination with evolved gas analysis-mass spectrometry (EGA-MS) allowed the variable conditions of the artworks to be assessed and attained some insights into the chemical processes responsible for aging. At the same time, morphological changes due to the degradation phenomena were recorded through optical (OM) and scanning electron microscopy (SEM). The detailed characterization of the PUR foam and painting materials was helpful in attaining some insights into harmful environmental parameters for the artworks, thus informing preventive conservation.

ENDOR evidence of electron-H2 interaction in a fulleride embedding H2.

An endofulleropyrrolidine, with H2 as a guest, has been reduced to a paramagnetic endofulleride radical anion. The magnetic interaction between the electron delocalized on the fullerene cage and the guest H2 has been probed by pulsed ENDOR. The experimental hyperfine couplings between the electron and the H2 guest were measured, and their values agree very well with DFT calculations. This agreement provides clear evidence of magnetic communication between the electron density of the fullerene host cage and H2 guest. The ortho-H2/para-H2 interconversion is revealed by temperature-dependent ENDOR measurements at low temperature. The conversion of the paramagnetic ortho-H2 to the diamagnetic para-H2 causes the ENDOR signal to decrease as the temperature is lowered due to the spin catalysis by the paramagnetic fullerene cage of the radical anion fulleride.

Highly hydrophilic copolymers of N,N-dimethylacrylamide, acrylamido-2-methylpropanesulfonic acid, and ethylenedimethacrylate: nanoscale morphology in the swollen state and use as exotemplates for synthesis of nanostructured ferric oxide.

The polymer framework of water-swollen copolymers of N,N-dimethylacrylamide, acrylamido-2-methylpropanesulfonic acid, and ethylenedimethacrylate (nominal cross-linking degrees of 4, 8, and 20 mol %) is composed of highly expanded domains, with "pores" not less than 6 nm in diameter. When the 4% cross-linked copolymer (DAE 26-4) is swollen with a 10(-4) M solution of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) in water, MeOH, EtOH, or nBuOH, the molecules of the paramagnetic probe rotate rapidly (τ<1000 ps) and as fast as in the bulk liquid in the case of water. The swelling degree of DAE 26-4 is related to the Hansen solubility parameters of a number of liquids, including linear alcohols up to n-octanol. It is also found that the rotational correlation time of TEMPOL in the copolymer swollen by water and the lightest alcohols increases with decreasing specific absorbed volume. Time-domain NMR spectrometry of water-swollen DAE 26-4 shows that sorption of only 14% of the liquid required for its complete swelling is enough for full hydration of the polymer chains. Accordingly, in fully swollen DAE 26-4 the longitudinal relaxation time of water closely approaches the value of pure water. {(13)C} CP-MAS NMR on partially and fully water swollen samples of DAE 26-4 shows that swelling increases the mobility of the polymer chains, as clearly indicated by the narrowing of the best-resolved peaks. DAE 26-4 was used as an exotemplate for the synthesis of nanocomposites composed of the polymer and nanostructured Fe(2)O(3) through a series of ion-exchange/precipitation cycles. After the first cycle the nanoparticles are 3-4 nm in diameter, with practically unchanged size after subsequent cycles (up to five). In fact, the nanoparticle size never exceeded the diameter of the largest available pores. This suggests that the polymer framework controls the growth of the nanoparticles according to the template-controlled synthesis scheme. Selected-area electron diffraction, TEM, and high-resolution electron microscopy show that the nanostructured inorganic phase is composed of hematite.

Structural characterization of a high affinity mononuclear site in the copper(II)-α-synuclein complex.

Human α-Synuclein (aS), a 140 amino acid protein, is the main constituent of Lewy bodies, the cytoplasmatic deposits found in the brains of Parkinson's disease patients, where it is present in an aggregated, fibrillar form. Recent studies have shown that aS is a metal binding protein. Moreover, heavy metal ions, in particular divalent copper, accelerate the aggregation process of the protein. In this work, we investigated the high affinity binding mode of truncated aS (1-99) (aS99) with Cu(II), in a stoichiometric ratio, to elucidate the residues involved in the binding site and the role of copper ions in the protein oligomerization. We used Electron Paramagnetic Resonance spectroscopy on the Cu(II)-aS99 complex at pH 6.5, performing both multifrequency continuous wave experiments and pulsed experiments at X-band. The comparison of 9.5 and 95 GHz data showed that at this pH only one binding mode is present. To identify the nature of the ligands, we performed Electron Spin Echo Envelope Modulation, Hyperfine Sublevel Correlation Spectroscopy, and pulsed Davies Electron-Nuclear Double Resonance (Davies-ENDOR) experiments. We determined that the EPR parameters are typical of a type-II copper complex, in a slightly distorted square planar geometry. Combining the results from the different pulsed techniques, we obtained that the equatorial coordination is {N(Im), N(-), H(2)O, O}, where N(im) is the imino nitrogen of His50, N(-) a deprotonated amido backbone nitrogen that we attribute to His50, H(2)O an exchangeable water molecule, and O an unidentified oxygen ligand. Moreover, we propose that the free amino terminus (Met1) participates in the complex as an axial ligand. The MXAN analysis of the XAS k-edge absorption data allowed us to independently validate the structural features proposed on the basis of the magnetic parameters of the Cu(II)-aS99 complex and then to further refine the quality of the proposed structural model.

Understanding and controlling the efficiency of Au24M(SR)18 nanoclusters as singlet-oxygen photosensitizers.

Singlet oxygen, 1O2, can be generated by molecules that upon photoexcitation enable the 3O2 → 1O2 transition. We used a series of atomically precise Au24M(SR)18 clusters, with different R groups and doping metal atoms M. Upon nanosecond photoexcitation of the cluster, 1O2 was efficiently generated. Detection was carried out by time-resolved electron paramagnetic resonance (TREPR) spectroscopy. The resulting TREPR transient yielded the 1O2 lifetime as a function of the nature of the cluster. We found that: these clusters indeed generate 1O2 by forming a triplet state; a more positive oxidation potential of the molecular cluster corresponds to a longer 1O2 lifetime; proper design of the cluster yields results analogous to those of a well-known reference photosensitizer, although more effectively. Comprehensive kinetic analysis provided important insights into the mechanism and driving-force dependence of the quenching of 1O2 by gold nanoclusters. Understanding on a molecular basis why these molecules may perform so well in 1O2 photosensitization is instrumental to controlling their performance.

Chemical variability of artificial stone powders in relation to their health effects.

The occurrence of highly severe silica-related diseases among the resin- and silica-based artificial stone workers was claimed, associated to an extremely short latency. High levels of exposure and intrinsic properties of AS are thought to modulate the development of silicosis and auto-immune diseases. This study compares parent materials and processed dusts, to shed light on changes of AS occurring in the manufacturing process, through an XRF, EPR and XAS investigation. We point out the extremely wide variability of the materials, the occurrence of chemical signatures impressed by the processing techniques, and the unprecedented generation of stable radicals associated to the lysis of the Si-O chemical bond inside the resin coated respirable crystalline silica. These results suggest that the AS processing in industrial stone workshops can create respirable dusts with peculiar physical and chemical properties, to be correlated to the observed clinical evidences.

Three different tyrosyl radicals identified in L-tyrosine HCl crystals upon gamma-irradiation: magnetic characterization and temporal evolution.

High-frequency electron paramagnetic resonance (EPR) and X-band electron-nuclear double resonance (ENDOR) spectroscopies were used to investigate the effect of gamma-irradiation on single crystals of L-tyrosine hydrochloride at room temperature. The oxidation product is the tyrosyl radical formed by hydrogen abstraction from the phenolic group; interestingly, on freshly irradiated crystals, two tyrosyl radicals were identified, characterized by slightly different magnetic parameters. In particular, one of the two radicals, with a gxx value of 2.00621, has its phenoxyl oxygen strongly hydrogen-bonded to one or more donors; to our knowledge, this is the lower gxx value reported for tyrosyl radicals. These two oxidation radicals are found to evolve very slowly to a third, single more stable radical conformation. To interpret the experimental data, a possible molecular scenario is presented, where the process of radical formation can be seen as a hydrogen atom transfer or a proton-coupled electron transfer. These processes seem to be controlled by the specific network of hydrogen-bond interactions present in the crystal. The results are discussed in relation to their relevance for the interpretation of EPR spectra of tyrosyl radicals in biological systems.

Synthesis, characterization and cytotoxic activity of novel copper(II) complexes with aroylhydrazone derivatives of 2-Oxo-1,2-dihydrobenzo[h]quinoline-3-carbaldehyde.

Three new 2-oxo-1,2-dihydrobenzo[h]quinoline-3-carbaldehyde terminal substituted aroylhydrazone ligands (2-Oxo-1,2-dihydrobenzo[h]quinoline-3-carbaldehyde(2'-hydroxybenzoyl)hydrazine, H2L1, 1, 2-Oxo-1,2-dihydrobenzo[h]quinoline-3-carbaldehyde(2'-hydroxybenzoyl)hydrazine, H2L2, 2, 2-Oxo-1,2-dihydrobenzo[h]quinoline-3-carbaldehyde(2'-hydroxybenzoyl)hydrazine, H2L3, 3) and the corresponding novel copper(II) complexes [Cu(L)(CH3OH)(NO3)](L = HL1 (4), HL2 (5), HL3 (6-6+), have been synthesized to compare their coordination behaviour and biological activity with respect to the presence of an OH group in different positions of the phenyl ring in the hydrazone moieties. The new ligands and their copper complexes were characterized by elemental analysis and spectroscopic techniques. The molecular structures of the new complexes 4 and 6-6+ were determined by single crystal X-ray diffraction. The interactions of the free ligands and their copper complexes with calf thymus DNA were tested by absorption measurements and ethidium bromide competitive studies which revealed that all compounds may interact with calf thymus DNA through intercalation. Furthermore, a comparative analysis of the cytotoxic effect of the compounds on a panel of human cancer cell lines showed that the copper complexes exhibited in vitro antitumor activity significantly higher than that of the free ligands and also of cisplatin.

Magnetic Ordering in Gold Nanoclusters.

Several research groups have observed magnetism in monolayer-protected gold cluster samples, but the results were often contradictory, and thus, a clear understanding of this phenomenon is still missing. We used Au25(SCH2CH2Ph)18 0, which is a paramagnetic cluster that can be prepared with atomic precision and whose structure is known precisely. Previous magnetometry studies only detected paramagnetism. We used samples representing a range of crystallographic orders and studied their magnetic behaviors using electron paramagnetic resonance (EPR). As a film, Au25(SCH2CH2Ph)18 0 exhibits a paramagnetic behavior, but at low temperature, ferromagnetic interactions are detectable. One or few single crystals undergo physical reorientation with the applied field and exhibit ferromagnetism, as detected through hysteresis experiments. A large collection of microcrystals is magnetic even at room temperature and shows distinct paramagnetic, superparamagnetic, and ferromagnetic behaviors. Simulation of the EPR spectra shows that both spin-orbit (SO) coupling and crystal distortion are important to determine the observed magnetic behaviors. Density functional theory calculations carried out on single cluster and periodic models predict the values of SO coupling and crystal-splitting effects in agreement with the EPR-derived quantities. Magnetism in gold nanoclusters is thus demonstrated to be the outcome of a very delicate balance of factors. To obtain reproducible results, the samples must be (i) controlled for composition and thus be monodisperse with atomic precision, (ii) of known charge state, and (iii) well-defined in terms of crystallinity and experimental conditions.

Correction to "Magnetic Ordering in Gold Nanoclusters".

[This corrects the article DOI: 10.1021/acsomega.7b00472.].

An insight into the metal coordination and spectroscopic properties of artistic Fe and Fe/Cu logwood inks.

Fe- and Fe/Cu-based logwood inks were synthesized following recipes in nineteenth and early twentieth century manuals and were characterized by EPR, ESI-MS, FTIR, and Raman spectroscopies. This multi-technique approach allowed us to shed light on the structures of the complexes responsible for the inks' colors and to obtain vibrational signatures that can be used to identify the different inks in works of art and in historic documents. Information on the nature and chemical properties of the complexes formed between a dye and a mordant is important as these determine, at least in part, their lightfastness. EPR permitted to determine the coordination environment of the metallic ions. The results of the ESI-MS analysis demonstrated, for the first time, the breakdown of the hematein molecule during the ink preparation, and that the colorants are formed by the complexation of the metallic ions by hematein breakdown products, mainly catechol and/or bicyclic compounds. The FTIR spectra obtained were found to be dominated by bands due to the binding medium and sulfates used as reagents. The Raman analysis showed that the characteristic features for the different inks studied depend on the historic recipe used, attesting to the challenges that their identification and characterization in works of art present. In the Raman spectra of the inks applied on paper, broadening of bands in the 750-400 cm(-1) range are observed when compared to the spectra of the inks' powders, possibly due to the interaction of the compounds with the cellulose in the substrate.

A magnetic look into the protecting layer of Au25 clusters.

The field of molecular metal clusters protected by organothiolates is experiencing a very rapid growth. So far, however, a clear understanding of the fine interactions between the cluster core and the capping monolayer has remained elusive, despite the importance of the latter in interfacing the former to the surrounding medium. Here, we describe a very sensitive methodology that enables comprehensive assessment of these interactions. Pulse electron nuclear double resonance (ENDOR) was employed to study the interaction of the unpaired electron with the protons of the alkanethiolate ligands in four structurally related paramagnetic Au25(SR)018 clusters (R = ethyl, propyl, butyl, 2-methylpropyl). Whereas some of these structures were known, we present the first structural description of the highly symmetric Au25(SPr)018 cluster. Through knowledge of the structural data, the ENDOR signals could be successfully related to the types of ligand and the distance of the relevant protons from the central gold core. We found that orbital distribution affects atoms that can be as far as 6 Å from the icosahedral core. Simulations of the spectra provided the values of the hyperfine coupling constants. The resulting information was compared with that provided by 1H NMR spectroscopy, and molecular dynamics calculations provided useful hints to understanding differences between the ENDOR and NMR results. It is shown that the unpaired electron can be used as a very precise probe of the main structural features of the interface between the metal core and the capping ligands.

Physico-chemical properties of quartz from industrial manufacturing and its cytotoxic effects on alveolar macrophages: The case of green sand mould casting for iron production.

Industrial processing of materials containing quartz induces physico-chemical modifications that contribute to the variability of quartz hazard in different plants. Here, modifications affecting a quartz-rich sand during cast iron production, have been investigated. Composition, morphology, presence of radicals associated to quartz and reactivity in free radical generation were studied on a raw sand and on a dust recovered after mould dismantling. Additionally, cytotoxicity of the processed dust and ROS and NO generation were evaluated on MH-S macrophages. Particle morphology and size were marginally affected by casting processing, which caused only a slight increase of the amount of respirable fraction. The raw sand was able to catalyze OH and CO2(-) generation in cell-free test, even if in a lesser extent than the reference quartz (Min-U-Sil), and shows hAl radicals, conventionally found in any quartz-bearing raw materials. Enrichment in iron and extensive coverage with amorphous carbon were observed during processing. They likely contributed, respectively, to increasing the ability of processed dust to release CO2- and to suppressing OH generation respect to the raw sand. Carbon coverage and repeated thermal treatments during industrial processing also caused annealing of radiogenic hAl defects. Finally, no cellular responses were observed with the respirable fraction of the processed powder.

Au25(SEt)18, a nearly naked thiolate-protected Au25 cluster: structural analysis by single crystal X-ray crystallography and electron nuclear double resonance.

X-ray crystallography has been fundamental in discovering fine structural features of ultrasmall gold clusters capped by thiolated ligands. For still unknown structures, however, new tools capable of providing relevant structural information are sought. We prepared a 25-gold atom nanocluster protected by the smallest ligand ever used, ethanethiol. This cluster displays the electrochemistry, mass spectrometry, and UV-vis absorption spectroscopy features of similar Au25 clusters protected by 18 thiolated ligands. The anionic and the neutral form of Au25(SEt)18 were fully characterized by (1)H and (13)C NMR spectroscopy, which confirmed the monolayer's properties and the paramagnetism of neutral Au25(SEt)18(0). X-ray crystallography analysis of the latter provided the first known structure of a gold cluster protected by a simple, linear alkanethiolate. Here, we also report the direct observation by electron nuclear double resonance (ENDOR) of hyperfine interactions between a surface-delocalized unpaired electron and the gold atoms of a nanocluster. The advantages of knowing the exact molecular structure and having used such a small ligand allowed us to compare the experimental values of hyperfine couplings with DFT calculations unaffected by structure's approximations or omissions.

Gold nanowired: a linear (Au25)(n) polymer from Au25 molecular clusters.

Au25(SR)18 has provided fundamental insights into the properties of clusters protected by monolayers of thiolated ligands (SR). Because of its ultrasmall core, 1 nm, Au25(SR)18 displays molecular behavior. We prepared a Au25 cluster capped by n-butanethiolates (SBu), obtained its structure by single-crystal X-ray crystallography, and studied its properties both experimentally and theoretically. Whereas in solution Au25(SBu)18(0) is a paramagnetic molecule, in the crystal it becomes a linear polymer of Au25 clusters connected via single Au-Au bonds and stabilized by proper orientation of clusters and interdigitation of ligands. At low temperature, [Au25(SBu)18(0)]n has a nonmagnetic ground state and can be described as a one-dimensional antiferromagnetic system. These findings provide a breakthrough into the properties and possible solid-state applications of molecular gold nanowires.