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We show here for the first time that strongly correlated linear relationships exist between equilibrium bond lengths of the sulfonamide group and aqueous pKa values. Models are constructed for three variants of the SO2NHR group: primary benzene sulfonamide derivatives (e.g. diuretic drugs furosemide and hydrochlorothiazide), N-phenyl substituted 4-amino-N-phenylbenzenesulfonamide analogues (e.g. the sulfa antibiotic sulfadiazine) and phenylsulfonylureas (e.g. insulin secretogogue, glimepiride). In the context of these compounds, we present solutions to some of the more complex challenges in pKa prediction: (i) prediction for multiprotic compounds, (ii) predicting macroscopic values for compounds that tautomerize, and (iii) quantum chemical pKa prediction for compounds with more than 50 atoms. Using bond lengths as a powerful descriptor of ionization feasibility, we also identify that literature values for drug compounds celecoxib, glimepiride and glipizide are inaccurate. Our newly measured experimental values match our initial predictions to within 0.26 pKa units, whereas previous values were found to deviate by up to 1.68 pKa units. For glimepiride, our corrected value denotes a percentage of ionization at intracellular pH, which is only now in excellent agreement with its known therapeutic efficacy. We propose that linear relationships between bond lengths and pKa should emerge for any set of congeners, thus providing a powerful method of pKa prediction in instances where pKa data exist for close congeners, thereby obviating the need for thermodynamic cycles.

The aims of this research is the identification of the degradation by-products in ancient papers by means of chemical, spectroscopic and chromatographic analyses and the development of innovative methods of artificial ageing that should be able to simulate the natural degradation in these materials. For many centuries paper has been representing the main writing support for storing human knowledge. Paper is a material prone to degradation, and its conservation is a main concern, due to its obvious wide diffusion. A considerable effort has been dedicated to the paper preservation issue and it is widely recognized that a proper knowledge of the degradation reactions is essential in designing an efficient conservation treatment. To this purpose, a relevant amount of data has been collected about artificially aged paper, but just a few articles deal with naturally aged materials, since generally paper from ancient books has an artistic or historical value, and either non-destructive or micro-destructive spectroscopic techniques can be applied. In the first part of this work, (“Analysis of degradation by-products in ancient papers”, Chapter 4) a new comprehensive protocol is proposed for assessing the degradation of ancient books. The protocol is based on a multi-technique spectroscopic, chemical and analytical study of material obtained by washing leaves of ancient books. Indeed, the conservation treatments on ancient books involve frequently washing the paper leaves with water to remove the acidic by-products, which is considered a safe treatment. If the waters used for washing are collected rather than wasted, the cross-referencing of the analysis results of these “wasted waters” can provide a broad and deep insight into paper degradation by-products, thus furnishing much valuable information on both the conservation state of the books/documents in question and the degradation reactions occurring within their leaves. The proposed protocol is applied here, as a case-of-study, to the “wasted waters” obtained from washing leaves of a 16th-century-printed book, the De Divina Providentia. The widest range of analytical techniques was applied to the degradation by-products extracted from leaves in different conservation state, ranging from not degraded to very degraded. The here-proposed method is meant to become a pilot protocol for the study of ancient/historical paper degradation processes: it represents the starting point of a wider study on ancient and historical papers. Its potential application on a broad range of books and papers of different ages, origins and in different conservation state could allow for the creation of the first database on the natural by-products generated by aging in ancient books. Furthermore, a fruitful comparison with the data collected directly on ancient sheets can represent the basis for the development and the optimization of an innovative method for paper ageing (accelerated or artificial ageing methods, AAMs), able to closely simulate the natural degradation of cellulosic materials, depending on their chemical composition. In the second part of this research (“Artificial ageing by ozonation”, Chapter 5) a method for the artificial ageing of paper is proposed, aiming to reproduce oxidative by-products found in naturally aged paper. In literature, much research has been carried out in the area of paper artificial ageing, especially as regards the simulation of hydrolytic damage of paper leading to the depolymerisation of cellulose. However, other mechanisms that proceed during the natural ageing of paper, such as oxidation and autoxidation reactions, can become predominant in certain cases and therefore render these systems more complex and difficult to reproduce in the laboratory. In the last few years, much work has been performed in order to shed light on this class of reactions and on the reactive species, which promote and catalyze them. Much evidence has been collected on the role of reactive oxygen species (ROS) in the cellulose natural oxidation reactions, on their ability to induce paper radical reactions and to produce radical species in ancient papers. In general, nowadays serious and complete studies of paper radicals and, in particular, of their correlation with the paper oxidation by-products are not present in literature. In this sense, they have been reported here the first steps followed towards the development of a specific method of artificial ageing, which implies the use of ozone as a trigger for the accelerated degradation of paper. A great effort has been dedicated towards the achievement of an ozonation protocol of paper, which could reproduce the formation of both the natural degradation by-products and the open-shell species and allow for a deeper study of their nature and their effect on the writing support. The continuous comparison between the data collected on ancient papers and on artificially aged papers is the only sensible way to develop and optimize new methods for artificial or accelerated ageing of paper, able to simulate the natural degradation in cellulosic materials according to their chemical composition. The third part of this research (“Logwood inks”, Chapter 7) reports the results of the spectroscopic and analytical study on Logwood inks, carried out in cooperation with the Scientific Department of the Metropolitan Museum of Art, NYC. Fe and Cu/Fe - based Logwood inks have been synthesized following late 19threcipes and they have been characterized using UV-VIS, IR, Raman, EPR and ESI-MS analyses. This multi-technique approach is aimed to shed light on the coordination environment of the metallic ions in the colorant matrix, in order to better understand the structure of the complexes responsible for the ink colors. The UV-VIS and FT-IR spectra confirm the complexation of the metallic ions by the coloring Logwood organic matter, the hematein (Hm) macromolecule, while the Raman spectra show that the aromatic rings, composing the molecule, are also involved in the interaction. The high-sensitivity of the EPR technique allows for a deeper study of the ink structure giving information about the coordination environment of the metal ions. It turns out, together with ESI-MS, as the only technique, among the applied ones, that can provide a unique outline for each ink. Unexpected results are obtained by the ESI-MS analyses: for the first time in literature, mass analysis of Logwood inks has demonstrated the breakdown of Hm molecules during the ink preparation, as just complexed cathecols and/or byciclic compounds were identified as the main component of the three inks. These chemical species are very similar to the ones which compose the iron gall inks: the Fe(II)/Fe(III)-pyrogallates.