Nature-based solutions for monitoring the impact of vehicular particulate matter and for the preventive conservation of the Palatine Hill archaeological site in Rome, Italy.

Magnetic and chemical biomonitoring methodologies were applied to the southern slopes of the Palatine Hill archaeological area in Rome, Italy. Plant leaves and lichen transplants were respectively sampled and exposed between July 2022 and June 2023 to assess the impact of vehicular particulate matter from Via dei Cerchi, a trafficked road coasting Circus Maximus, towards the archaeological area upon the Palatine Hill. The magnetic properties of leaves and lichens, inferred from magnetic susceptibility, hysteresis loops and first order reversal curves, were combined with the concentration of trace elements. It was demonstrated that the bioaccumulation of magnetite-like particles, associated with tracers of vehicular emissions, such as Ba and Sb, decreased with longitudinal distance from the road, without any important influence of elevation from the ground. Lichens demonstrated to be more efficient biomonitors of airborne PM than leaves, irrespective of the plant species. Conversely, leaves intercepted and accumulated all PM fractions, including road dusts and resuspended soil particles. Thus, plant leaves are suitable for providing preventive conservation services that limit the impact of particulate pollution on cultural heritage sites within busy metropolitan contexts.

Assessing the impact of vehicular particulate matter on cultural heritage by magnetic biomonitoring at Villa Farnesina in Rome, Italy.

Magnetic biomonitoring methodologies were applied at Villa Farnesina, Rome, a masterpiece of the Italian Renaissance, with loggias frescoed by renowned artists such as Raffaello Sanzio. Plant leaves were sampled in September and December 2020 and lichen transplants were exposed from October 2020 to early January 2021 at increasing distances from the main trafficked road, Lungotevere Farnesina, introducing an outdoor vs. indoor mixed sampling design aimed at assessing the impact of vehicular particulate matter (PM) on the Villa Loggias. The magnetic properties of leaves and lichens - inferred from magnetic susceptibility values, hysteresis loops and first order reversal curves - showed that the bioaccumulation of magnetite-like particles, associated with trace metals such as Cu, Ba and Sb, decreased exponentially with the distance from the road, and was mainly linked to metallic emission from vehicle brake abrasion. For the frescoed Halls, ca. 30 m from the road, the exposure to traffic-related emissions was very limited or negligible. Tree and shrub leaves of the Lungotevere and of the Villa's Gardens intercepted much traffic-derived PM, thus being able to protect the indoor cultural heritage and providing an essential conservation service. It is concluded that the joint use of magnetic and chemical analyses can profitably be used for evaluating the impact of particulate pollution on cultural heritage within complex metropolitan contexts as a preventive conservation measure.

Computational chemistry meets cultural heritage: challenges and perspectives.

Chemistry is central to addressing topics of interest in the cultural heritage field, offering particular insight into the nature and composition of the original materials, the degradation processes that have occurred over the years, and the attendant physical and chemical changes. On the one hand, the chemical characterization of the constituting materials allows researchers to unravel the rich information enclosed in a work of art, providing insight into the manufacturing techniques and revealing aspects of artistic, chronological, historical, and sociocultural significance. On the other hand, despite the recognized contribution of computational chemistry in many branches of materials science, this tool has only recently been applied to cultural heritage, largely because of the inherent complexity of art materials. In this Account, we present a brief overview of the available computational methods, classified on the basis of accuracy level and dimension of the system to be simulated. Among the discussed methodologies, density functional theory (DFT) and time-dependent DFT represent a good compromise between accuracy and computational cost, allowing researchers to model the structural, electronic, and spectroscopic properties of complex extended systems in condensed phase. We then discuss the results of recent research devoted to the computer simulation of prototypical systems in cultural heritage, namely, indigo and Maya Blue, weld and weld lake, and the pigment minium (red lead). These studies provide insight into the basic interactions underlying the materials properties and, in some cases, permit the assignment of the material composition. We discuss properties of interest in the cultural heritage field, ranging from structural geometries and acid-base properties to IR-Raman vibrational spectra and UV-vis absorption-emission spectra (including excited-state deactivation pathways). We particularly highlight how computational chemistry applications in cultural heritage can complement experimental investigations by establishing or rationalizing structure-property relations of the fundamental artwork components. These insights allow researchers to understand the interdependence of such components and eventually the composition of the artwork materials. As a perspective, we aim to extend the simulations to systems of increasing complexity that are similar to the realistic materials encountered in works of art. A challenge is the computational investigation of materials degradation and their associated reactive pathways; here the possible initial components, intermediates, final materials, and various deterioration mechanisms must all be simulated.

In situ noninvasive study of artworks: the MOLAB multitechnique approach.

Driven by the need to study precious and irreplaceable artworks without compromising their integrity, researchers have undertaken numerous efforts to develop noninvasive analytical tools and methodologies that can provide a chemical description of cultural heritage materials without any contact with the object. The challenge is that artworks are made of complex mixtures, often with heterogeneous and unknown layered materials. Their components must be identified over a range of size scales, from the molecular identification of constituent compounds to the mapping of alteration phases. In this Account, we review recent research in spectroscopic techniques accessible from the mobile laboratory (MOLAB). The lab is equipped with an array of state-of-the-art, portable, and noninvasive instruments specifically tailored to tackle the different issues confronted by archaeologists, curators, and conservators. The MOLAB approach is suitable for studying a variety of objects, from ceramics to manuscripts or from historical wall paintings to contemporary canvases. We begin by discussing issues related to the acquisition and interpretation of reflectance or backscattered spectra from the surface of heterogeneous materials. Then we show how the selectivity needed for the noninvasive identification of pigments in paintings, even in mixtures or in layered matrices, can be acquired by combining elemental information from X-ray fluorescence with molecular and structural insights from electronic and vibrational spectroscopies. Discriminating between original pigments and restoration retouches is possible, even when both comprise similar chromophores, as highlighted in the study of paintings by Jordaens and Raphael. The noninvasive approach permits the examination of a very large number of artworks with a virtually limitless number of measurements. Thus, unexpected and uncommon features may be uncovered, as in the case of a lead pyroantimonate yellow doped with zinc that was discovered by micro-Raman and X-ray fluorescence on an Italian Renaissance majolica. For characterizing binding media, we discuss the strengths and limitations of using mid- and near-FTIR (Fourier transform infrared) spectroscopies supported by a multivariate statistical analysis, detailing the study of organic materials in a wall painting by Perugino and a survey of the painting technique on 18 contemporary paintings by Burri. In Michelangelo's David, we show how the noninvasive mapping of contaminants and alteration phases might inform decisions on preventive conservation plans. The multitechnique MOLAB approach overcomes the intrinsic limitation of individual spectroscopic methods. Moreover, the ability to analyze artworks without the need to move them is an invaluable asset in the study and preservation of cultural heritage.

Multivariate chemical mapping of pigments and binders in easel painting cross-sections by micro IR reflection spectroscopy.

Paintings are composed of superimposed layers of inorganic and organic materials (pigments and binders). Knowledge of the stratigraphic sequence of these heterogeneous layers is fundamental for understanding the artist's painting technique and for conservation issues. In this study, micro-IR mapping experiments in reflection mode have been carried out on cross-sections taken from simulations of ancient easel paintings. The objective was to locate both organic binders and inorganic pigments. Chemical maps have been re-constructed using the common approach based on the integration of specific infrared bands. However, owing to the complexity of painting materials, this approach is not always applicable when dealing with broad and superimposed spectral features and with reststrahlen or derivative-like bands resulting from acquisition in reflection mode. To overcome these limitations, principal-component analysis has been successfully used for the re-construction of the image, extracting the relevant information from the complex full spectral data sets and obtaining reliable chemical distributions of the stratigraphy materials. Different pigment-binder combinations have been evaluated in order to understand limitations and strengths of the approach. Finally, the method has been applied for stratigraphic characterization of a cross-section from a 17th century wooden sculpture identifying both the original paint layer and the several overpaintings constituting the complex stratigraphy.

Cyclometalated Ir(III) complexes with substituted 1,10-phenanthrolines: a new class of efficient cationic organometallic second-order NLO chromophores.

Cyclometalated cationic Ir(III) complexes with substituted 1,10-phenanthrolines (1,10-phen), such as [Ir(ppy)(2)(5-R-1,10-phen)]Y (ppy=cyclometalated 2-phenylpyridine; R=NO(2), H, Me, NMe(2); Y(-)=PF(6) (-), C(12)H(25)SO(3) (-), I(-)) and [Ir(ppy)(2)(4-R,7-R-1,10-phen)]Y (R=Me, Ph) are characterized by a significant second-order optical non linearity (measured by the electrical field induced second harmonic generation (EFISH) technique). This nonlinearity is controlled by MLCT processes from the cyclometalated Ir(III), acting as a donor push system, to pi* orbitals of the phenanthroline, acting as an acceptor pull system. Substitution of cyclometalated 2-phenylpyridine by the more pi delocalized 2-phenylquinoline (pq) or benzo[h]quinoline (bzq) or by the sulfur-containing 4,5-diphenyl-2-methyl-thiazole (dpmf) does not significantly affect the mubeta absolute value, which instead is affected by the nature of the R substituents on the phenanthroline, the higher value being associated with the electron-withdrawing NO(2) group. By using a combined experimental (the EFISH technique and (1)H and (19)F PGSE NMR spectroscopy) and theoretical (DFT, time-dependent-DFT (TDDFT), sum over states (SOS) approach) investigation, evidence is obtained that ion pairing, which is controlled by the nature of the counterion and by the concentration, may significantly affect the mubeta values of these cationic NLO chromophores. In CH(2)Cl(2), concentration-dependent high absolute values of mubeta are obtained for [Ir(ppy)(2)(5-NO(2)-1,10-phen)]Y if Y is a weakly interacting anion, such as PF(6) (-), whereas with a counterion, such as C(12)H(25)SO(3) (-) or I(-), which form tight ion-pairs, the absolute value of mubeta is lower and quite independent of the concentration. This mubeta trend is partially due to the perturbation of the counterion on the LUMO pi* levels of the phenanthroline. The correlation between the mubeta value and dilution shows that the effect of concentration is a factor that must be taken into careful consideration.

Complexation of apigenin and luteolin in weld lake: a DFT/TDDFT investigation.

A DFT-TDDFT investigation on the aluminium complexation of apigenin and luteolin has been carried out. We have focused our attention on these hydroxyflavonoids, which are the main components of weld, one of the earliest natural dyestuff used in art. In particular, weld, upon complexation with Al(iii) forms a highly prized lake which has been widely used in medieval manuscripts and easel paintings for its rich yellow colour and transparency. The experimental spectra of apigenin and luteolin upon addition of increasing [Al(3+)] show a general red-shift of the lowest absorption bands of both flavonoids spectra, associated with the presence of two and three isosbestic points for apigenin and luteolin, respectively. The molecular geometries of all the Al-apigenin and -luteolin complexes have been optimized, followed by calculation of the formation Gibbs free energies and UV-vis absorption spectra. The comparison between the computed absorption spectra of the Al-flavonoid complexes and the experimental ones corresponding to various limit [Al(3+)] concentrations has been used to discriminate between the possible complexation modes as well as the stoichiometry ratio. We have thus been able to associate specific Al-apigenin (-luteolin) complexes with the experimental absorption spectra as a function of the [Al(3+)] concentration, thus providing insights into the aluminium complexation of these hydroxyflavonoids and most importantly into the weld lake composition.

Cr(CO)3-activated Diels-Alder reaction on single-wall carbon nanotubes: a DFT investigation.

Breaking barriers: In agreement with experimental evidence, it was found by means of high-level DFT calculations that the Cr(CO)(3) metal fragment considerably reduces the reaction energy barrier-for both the concerted and stepwise reaction mechanisms (see graphic)-of the Diels-Alder reaction of butadiene on (5,5) carbon nanotubes.The reaction mechanism and the effect of Cr(CO)(3) on the Diels-Alder reaction of butadiene on (5,5) carbon nanotube sidewalls have been investigated by high-level DFT calculations. We investigated both concerted and stepwise reaction pathways on closed-shell and open-shell potential-energy surfaces. In agreement with recent experimental evidence, we found the Cr(CO)(3) metal fragment to considerably reduce the reaction energy barrier, both for the concerted and stepwise reaction mechanisms. The latter mechanism, previously found to be higher in energy with traditional substrates, appears to compete with the concerted mechanism on the carbon nanotube sidewalls. An analysis of the frontier molecular orbitals on the pristine and Cr(CO)(3)-complexed carbon nanotubes allowed us to identify the reason for this inverted reactivity pattern and the role of the transition metal on the addition of the diene.

Proteomic strategies for the identification of proteinaceous binders in paintings.

The identification of proteinaceous components in paintings remains a challenging task for several reasons. In addition to the minute amount of sample available, complex and variable chemical composition of the paints themselves, possible simultaneous presence of several binders and contaminants, and degradation of the original materials due to aging and pollution are complicating factors. We proposed proteomic strategies for the identification of proteins in binders of paintings that can be adapted to overcome the requirements and difficulties presented by specific samples. In particular, we worked on (1) the development of a minimally invasive method based on the direct tryptic cleavage of the sample without protein extraction; (2) the use of microwave to enhance the enzymatic digestion yield, followed by the analysis of the peptide mixtures by nanoLC-MS/MS with electrospray ionization (ESI). Moreover, as an additional tool to tackle the problem of contaminating proteins, we exploited the possibility of generating an exclusion list of the mass signals that in a first run had been fragmented and that the mass spectrometer had to ignore for fragmentation in a subsequent run. The methods, tested on model samples, allowed the identification of milk proteins in a sample from paintings attributed to Cimabue and Giotto, thirteenth-century Italian masters, decorating the vaults of the upper church in the Basilica of St. Francis in Assisi, Italy.

Absorption and emission of the apigenin and luteolin flavonoids: a TDDFT investigation.

The absorption and emission properties of the two components of the yellow color extracted from weld (Reseda luteola L.), apigenin and luteolin, have been extensively investigated by means of DFT and TDDFT calculations. Our calculations reproduce the absorption spectra of both flavonoids in good agreement with the experimental data and allow us to assign the transitions giving rise to the main spectral features. For apigenin, we have also computed the electronic spectrum of the monodeprotonated species, providing a rationale for the red-shift of the experimental spectrum with increasing pH. The fluorescence emission of both apigenin and luteolin has then been investigated. Excited-state TDDFT geometry optimizations have highlighted an excited-state intramolecular proton transfer (ESIPT) from the 5-hydroxyl to the 4-carbonyl oxygen of the substituted benzopyrone moiety. By computing the potential energy curves at the ground and excited states as a function of an approximate proton transfer coordinate for apigenin, we have been able to trace an ESIPT pathway and thus explain the double emission observed experimentally.

A non-invasive XRF study supported by multivariate statistical analysis and reflectance FTIR to assess the composition of modern painting materials.

The palette used in two paintings by Paul Cézanne, L'étang des soeurs dated c. 1875 and La route tournante, made in the last year of his life (1902), were analyzed using non-invasive spectroscopic methods. X-ray fluorescence combined with principal components analysis (PCA) and supported by reflectance near- and mid-FTIR was shown to be a powerful analytical tool to draw conclusions about the chemical identification of inorganic materials in paintings. Pigments and fillers such us Thénard's blue, Prussian blue, red ochre, kaolin, vermilion, lead white, zinc white and barium sulphate, were identified. Evidence for three different pigments, namely a copper arsenite pigment, chrome green (a mixture of chrome yellow and Prussian blue) and viridian has been obtained by the PCA analysis of elemental compositions of green hues.

Cyclometallated iridium(III) complexes with substituted 1,10-phenanthrolines: a new class of highly active organometallic second order NLO-phores with excellent transparency with respect to second harmonic emission.

[Ir(ppy)(2)(5-R-1,10-phen)][PF(6)] (ppy = cyclometallated 2-phenylpyridine, phen = phenanthroline, R = H, Me, NMe(2), NO(2)) and [Ir(ppy)(2)(4-R',7-R'-1,10-phen)][PF(6)] (R' = Me, Ph) complexes are characterized by one of the highest second order NLO response (measured by the EFISH technique) reported for a metal complex, mainly due (as suggested by a theoretical SOS-TDDFT investigation) to MLCT processes from the ppy-Ir based moiety acting as donor push system to pi* orbitals of phen, acting as an acceptor pull system; the good transparency to the second harmonic emission renders these NLO-phores appealing as building blocks for molecular materials with second harmonic generation.

Functionalization of carbon nanotubes with Vaska's complex: a theoretical approach.

The functionalization of single-walled carbon nanotubes (CNTs) with Vaska's complex trans-Ir(CO)Br(PPh(3))(2) has been investigated by means of hybrid quantum mechanics/molecular mechanics (QM/MM) calculations. The formation of a stable adduct has been experimentally evidenced by Wong et al. (Nano Lett. 2002, 2, 49), but microscopical details on the metal-nanotube interaction are still unclear. Our calculations show a low propensity to eta(2) coordination of Vaska's complex with the perfect hexagonal network of CNTs. Rather, a stronger interaction takes place when the transition metal center coordinates to carbon atoms belonging to pentagonal rings, as in topological defects or end-caps.

Selective functionalization of the Si(100) surface by a bifunctional alkynylamine molecule: density functional study of the switching adsorption linkage. 2.

The reaction of the bifunctional organic molecule 1-(dimethylamino)-2-propyne (DMAP) on the Si(100) surface has been investigated by density functional calculations employing a two-dimer cluster model. We found that, once in the physisorbed dative bonded well (-20.0 kcal mol(-1)), DMAP can proceed via a number of pathways, involving the formation of Si-C sigma bonds, which lead to thermodynamically more stable configurations. We first considered the cycloaddition of the CC triple bond, leading to a Si-C di-sigma bonded product (-58.7 kcal mol(-1)), for which we computed an energy barrier of only 12.5 kcal mol(-1), consistently with the observed switching of DMAP adsorption linkage at 300 K. We also explored the dissociative pathway involving the methylene C-H bond cleavage on the dative bonded DMAP, leading to three adsorption products with one (-57.3 kcal mol(-1)) and three Si-C sigma bonds (-58.7 and -60.6 kcal mol(-1)). The energy barrier for this pathway is computed 24.7 kcal mol(-1) and may therefore compete at temperature above 300 K with the reaction pathway involving the addition of the alkyne unit.

Vacancy-induced chemisorption of NO2 on carbon nanotubes: a combined theoretical and experimental study.

The role of structural defects on the adsorption of NO2 on carbon nanotubes (CNTs) is analyzed here by means of both statical density functional theory calculations and Car-Parrinello molecular dynamics and further confirmed by X-ray photoelectron spectroscopy measurements. The interaction of a NO2 molecule with an active site produced by a single vacancy on the sidewall follows two possible reaction routes, leading to the formation of a C-N bond or to dissociation of NO2. Accounting for defective adsorption sites allows a better understanding of microscopic mechanisms involved in technological applications of CNTs, e.g., gas-sensing devices.

Electron paramagnetic resonance, scanning electron microscopy with energy dispersion X-ray spectrometry, X-ray powder diffraction, and NMR characterization of iron-rich fired clays.

The aim of this study is to clarify the structure of an iron-rich clay and the structural changes involved in the firing process as a preliminary step to get information on ancient ceramic technology. To this purpose, illite-rich clay samples fired at different temperatures were characterized using a multitechnique approach, i.e., by electron paramagnetic resonance, scanning electron microscopy with electron dispersion X-ray spectrometry, X-ray powder diffraction, magic angle spinning and multiple quantum magic angle spinning NMR. During firing, four main reaction processes occur: dehydration, dehydroxylation, structural breakdown, and recrystallization. When the results are combined from all characterization methods, the following conclusions could be obtained. Interlayer H2O is located close to aluminum in octahedral sites and is driven off at temperatures lower than 600 degrees C. Between 600 and 700 degrees C dehydroxylation occurs whereas, between 800 and 900 degrees C, the aluminum in octahedral sites disappears, due to the breakdown of the illite structure, and all iron present is oxidized to Fe3+. In samples fired at 1000 and 1100 degrees C iron clustering was observed as well as large single crystals of iron with the occurrence of ferro- or ferrimagnetic effects. Below 900 degrees C the aluminum in octahedral sites presents a continuous distribution of chemical shift, suggesting the presence of slightly distorted sites. Finally, over the whole temperature range, the presence of at least two tetrahedral aluminum sites was revealed, characterized by different values of the quadrupolar coupling constant.

Oligomerization of the PH(3)CuC&tbd1;CCuPH(3) Acetylide toward the Formation of (PH(3)CuC)(n)() (n = 4, 6, 8) Metal Carbides: A Theoretical Study Based on Density Functional Theory.

Density functional calculations were performed on a series of Cu(PH(3))-substituted cyclopolyenes as simple models of molecular metal carbides. We studied the oligomerization of the copper acetylide PH(3)CuC&tbd1;CCuPH(3) as a possible precursor of these (PH(3)CuC)(n)() (n = 4, 6, 8) hypothetical species. Special emphasis was placed on the comparison of the main properties of these metal-substituted cyclopolyenes with those of the corresponding cyclopolyenes in an attempt to study the effects of metal substituents on the organic C(4), C(6), and C(8) cyclic moieties. We found comparable geometries of the C(n)() units and, for n = 3, a thermodynamically stable species with respect to dissociation toward dinuclear copper acetylides.

Isotope Exchange in Ionized O(3)/O(2) Mixtures: The Role of O(5)(+), a Unique O(n)()(+) Complex.

A hitherto unknown reaction, the isotope exchange between oxygen and ozone, accompanies formation of the latter upon ionization of O(2) or air, a long-known process widely utilized for the production of ozone and of great relevance to atmospheric chemistry. The isotope exchange was demonstrated and its mechanism established by mass spectrometric techniques that allowed identification of the charged intermediate, the O(5)(+) ion, characterized by the joint application of theoretical and experimental methods as truly unique among all known O(n)()(+) complexes. The results are of interest to atmospheric chemistry, bearing on the problem related to the widely different extent of (18)O enrichment of ozone in the stratosphere and in the troposphere.