A gas-phase approach to the study of reaction mechanisms of biological and industrial sustainable processes

The quality of life was over time enhanced by a number of economic activities that require a massive consumption of energy. The population growth and the expansion of the global infrastructure have driven the increase of the world energetic needs and the improvement of the living standards. Actually, the demand for energy is predominantly satisfied by the use of non-renewable fossil fuels representing the main responsibles for a series of environmental problems, such as pollution and climate change. Considering also the progressive depletion of the petroleum supply, the employment of renewable resources is becoming extremely urgent. The search for alternative source of energy was first promoted by the serious increase of the petroleum price that followed the oil embargo proclaimed by the OPEC (Organization of the Petroleum Exporting Countries) in 1973. During the years of the energy crisis, natural gas (methane) played a significant role in solving the diminishing availability of crude oil still continuing to do so in combination with the use of renewable bio-resources, such as lignocellulosic biomass and solar energy. Lignocellulosic biomass represents a good candidate for supporting the energy request of the worldwide population. In particular, carbohydrates extracted from wood biomass can be converted into organic compounds and platform molecules, such as 5-hydroxymethylfuraldehyde (5-HMF), 2-furaldehyde (2-FA) and levulinic acid, that can be used directly as fuels or fuel precursors. These furan-type compounds are obtained from the thermal acid-catalysed dehydration of hexose (D-glucose) and pentose (D-xylose) sugars arising from the hydrolysis of the main components of biomass, cellulose and hemicellulose. Owing to the short lifetimes and low concentration of the intermediate species characterized by high reactivity, the achievement of a consistent reaction picture for the conversion of sugars to platform molecules is really challenging, but extremely difficult on the basis of the experimental data available in solution. Theoretical studies point to predict kinetics and thermodynamics of sugar dehydration, but the mechanistic details are still elusive and the proposed conversion pathways are the subject of a flourishing debate. For these reasons, the main focus of the present thesis has been the investigation of the reaction mechanisms concerning the processes that allow the utilization of lignocellulosic biomass and its conversion to green fuels. Taking into account the ionic or radical nature of most transient species, mass spectrometry represents an useful technique to reproduce the reactions in the gas-phase and to study structure and reactivity of ions in the absence of solvent molecules and counter-ions. Owing to the advantages of a gas-phase approach, this method was exploited in this work to investigate the reaction mechanisms of carbohydrate dehydration to platform chemicals. To this end, a crucial step was represented by the characterization of the ionic intermediates and products of the dehydration reactions involving D-hexose (glucose and fructose) and D-pentose (xylose, ribose and arabinose) sugars arising from biomass decomposition. Understanding reaction mechanisms on a molecular level is a pivotal step in order to effectively control the reaction outcome, optimize product yields and reduce the formation of side compounds. As a consequence, the deep knowledge of the sugar decomposition pathways aims at the design of new reagents and catalysts that can increase the selectivity towards the formation of 5-HMF and 2-FA. The same experimental method was also applied to the study of processes involving other sugar substrates or molecules structurally correlated to carbohydrates (L-ascorbic acid) and to the investigation of model reactions that lead to the activation of intrinsically inert bonds

Charge-tagged N-heterocyclic carbenes (NHCs): revealing the hidden side of NHC-catalysed reactions through electrospray ionization mass spectrometry

N‐heterocyclic carbenes (NHCs) are key intermediates in a variety of chemical reactions. Owing to their transient nature, the interception and characterization of these reactive species have always been challenging. Similarly, the study of reaction mechanisms in which carbenes act as catalysts is still an active research field. This Minireview describes the contribution of electrospray ionization mass spectrometry (ESI‐MS) to the detection of charge‐tagged NHCs resulting from the insertion of an ionic group into the molecular scaffold. The use of different mass spectrometric techniques, combined with the charge‐tagging strategy, allowed clarification of the involvement of NHCs in archetypal reactions and the study of their intrinsic chemistry

The Peroxymonocarbonate anion HCO4- as an effective oxidant in the gas phase: A mass spectrometric and theoretical study on the reaction with SO2

The peroxymonocarbonate anion, HCO4-, the covalent adduct between the carbon dioxideand hydrogen peroxide anion, effectively reacts with SO2 in the gas phase following three oxidative routes. Mass spectrometric and electronic structure calculations show that sulphur dioxide is oxidised through a common intermediate to the hydrogen sulphate anion, sulphur trioxide, and sulphur trioxide anion as primary products through formal HO2-, oxygen atom, and oxygen ion transfers. The hydrogen sulphite anion is also formed as a secondary product from the oxygen atom transfer path. The uncommon nucleophilic behaviour of HCO4- is disclosed by the Lewis acidic properties of SO2, an amphiphilic molecule that forms intermediates with characteristic and diagnostic geometries with peroxymonocarbonate

Designing greenhouse subsystems for a lunar mission: the LOOPS - M Project

The 2020s is a very important decade in the space sector, where international cooperation is moving towards the exploration of the Moon and will lead to stable lunar settlements, which will require new, innovative, and efficient technologies. In this context, the project LOOPS–M (Lunar Operative Outpost for the Production and Storage of Microgreens) was created by students from Sapienza University of Rome with the objective of designing some of the main features of a lunar greenhouse. The project was developed for the IGLUNA 2021 campaign, an interdisciplinary platform coordinated by Space Innovation as part of the ESA Lab@ initiative. The LOOPS-M mission was successfully concluded during the Virtual Field Campaign that took place in July 2021. This project is a follow-up of the V-GELM Project, which took part in IGLUNA 2020 with the realization in Virtual Reality of a Lunar Greenhouse: a simulation of the main operations connected to the cultivation module, the HORT3 , which was already developed by ENEA (Italian National Agency for New Technologies, Energy and Sustainable Economic Development) during the AMADEE-18 mission inside the HORTSPACE project. This paper will briefly describe the main features designed and developed for the lunar greenhouse and their simulation in a VR environment: an autonomous cultivation system able to handle the main cultivation tasks of the previous cultivation system, a bioconversion system that can recycle into new resources the cultivation waste with the use of insects as a biodegradation system, and a shield able of withstanding hypervelocity impacts and the harsh lunar environment. A wide overview of the main challenges faced, and lessons learned by the team to obtain these results, will be given. The first challenge was the initial inexperience that characterized all the team members, being for most the first experience with an activity structured as a space mission, starting with little to no know-how regarding the software and hardware needed for the project, and how to structure documentation and tasks, which was acquired throughout the year. An added difficulty was the nature of LOOPS-M, which included very different objectives that required different fields of expertise, ranging from various engineering sectors to biology and entomology. During the year, the team managed to learn how to handle all these hurdles and the organizational standpoint, working as a group, even if remotely due to the Covid-19 pandemic. Through careful planning, hard work and the help of supervisors, the activity was carried out through reviews, up to the prototyping phase and the test campaign with a successful outcome in each aspect of the project. By the end of the year everyone involved had acquired new knowledge, both practical and theoretical, and learned how to reach out and present their work to sponsors and to the scientific community

Intracluster Sulphur Dioxide Oxidation by Sodium Chlorite Anions: A Mass Spectrometric Study

The reactivity of [NaL·ClO2]− cluster anions (L = ClOx−; x = 0–3) with sulphur dioxide has been investigated in the gas phase by ion–molecule reaction experiments (IMR) performed in an in-house modified Ion Trap mass spectrometer (IT-MS). The kinetic analysis revealed that SO2 is efficiently oxidised by oxygen-atom (OAT), oxygen-ion (OIT) and double oxygen transfer (DOT) reactions. The main difference from the previously investigated free reactive ClO2− is the occurrence of intracluster OIT and DOT processes, which are mediated by the different ligands of the chlorite anion. This gas-phase study highlights the importance of studying the intrinsic properties of simple reacting species, with the aim of elucidating the elementary steps of complex processes occurring in solution, such as the oxidation of sulphur dioxide

Accelerated dehydration of D-fructose performed in microdroplets by a commercial ESI Z-spray source

Besides its use as an analytical tool, mass spectrometry (MS) has long been employed in reaction monitoring to intercept elusive intermediates and highlight the mechanistic details of a chemical transformation. The introduction of electrospray ionization (ESI) by Fenn et al. [1] enables one to directly generate from a diluted aliquot of a reaction mixture a plume of charged droplets showing a diameter less than 1,0 μm. Once desolvated, the microdroplets release isolated ionic species that provide an accurate picture of the reaction progress in solution. Interestingly, the desolvation time of the charged droplets can be easily increased in the air by increasing the distance between the ESI source and the MS inlet. Such a dramatic change of the reaction conditions can indeed accelerate the reaction rate up to 105 times compared to the same process occurring in bulk [2]. As a consequence, the ionized reagents, typically detected by MS at short distances, are promptly replaced by the reaction intermediates or even by the ionized products. Since several milestone reactions of organic chemistry have recently benefited from acceleration in confined volumes [3], we studied the dehydration reaction of D-fructose in microdroplets under ambient conditions. Furan derivatives, such as 5-hydromethylfuraldehyde (5-HMF), are indeed produced by the acid-catalysed dehydration of hexoses, thus obtaining key-building block molecules from “green” resources [4]. To this end, we used a commercial ESI Z-spray source of a Q-TOF Ultima mass spectrometer already employed in our laboratory to successfully modify electrode surfaces by ambient ion soft landing experiments [5]. High conversion ratios of D-fructose into 5-HMF were obtained by using KHSO4 metal-free and green catalyst in millimolar concentrations. Nonetheless, the reaction outcome was found to be highly sensitive to the catalyst and solvents employed, as well as to the ionization and desolvation parameters of the ESI source. Further attempts to scale up the reaction for potential industrial application are actually in progress in our laboratory

Gas-phase reactivity of carbonate ions with sulfur dioxide: an experimental study of clusters reactions

Abstract. The reactivity of carbonate cluster ions with sulfur dioxide has been investigated in the gas phase by mass spectrometric techniques. SO2 promotes the displacement of carbon dioxide from carbonate clusters through a stepwise mechanism, leading to the quantitative conversion of the carbonate aggregates into the corresponding sulfite cluster ions. The kinetic study of the reactions of positive, negative, singly, and doubly charged ions reveals very fast and efficient processes for all the carbonate ions

Sulfur dioxide uptake by sodium carbonate cluster anions in the gas phase

Carbonate (CO3 2-) and sulfate (SO4 2-) species are reactive inorganic components of the fine particulate matter (PM) implicated in several environmental and human health issues. Sulfate aerosols usually arise from the atmospheric oxidation of SO2, contributing to acid rain and climate change. [1] In this study the reactivity of [(Na2CO3)n NaCO3]- cluster ions (n≥1) was probed towards SO2 and 13CO2, as a model of processes occurring at the liquid/gas phase interface. The experiments were performed on a LTQ XL linear ion trap (Thermo Fisher Scientific) equipped with an electrospray ionization (ESI) source in negative ion mode. The instrument was in-house modified [2] to allow the introduction of neutral reagent gases (SO2, 13CO2) into the ion trap and measure the kinetic rate constants of the observed ion-molecule reactions. [(Na2CO3)n NaCO3]- cluster ions were generated by spraying a 10^-3 M solution of Na2CO3 in H2O/CH3CN 1:3. Cluster ions with the general formula [(Na2CO3)n NaCO3]- were observed in the gas-phase with n≥1. In the presence of SO2 these carbonate species were quantitatively converted into the corresponding sulfite cluster ions [(Na2SO3)n NaSO3]- through a sequential replacement of each CO2 moiety with a SO2 molecule. The SO2→CO2 conversion may occur through the direct transfer of O 2- from CO3 2- to a SO2 molecule, as reported in a previous study identifying the reactions of SO2 at the surface of a molten carbonate eutectic. [3] The rate constants related to the SO2 adsorption and CO2 release were measured by monitoring the signal of the selected carbonate cluster ion as a function of SO2 concentration. The obtained values were investigated on the basis of n. All the reactions are very fast and efficient. The same experiments were performed also in the presence of 13CO2. As in the case of SO2, 13CO2 is incorporated into the cluster ion structures by replacing CO2 and leading to [(Na2 13CO3)n Na 13CO3]- ions with rate constants lower than those obtained for SO2. SO2 molecules were converted into gaseous CO2 via the reaction of carbonate cluster ions and the consequent formation of sulfite cluster species. Although varying the number n of (Na2CO3) moiety of the reactant ion, CO2 is always efficiently replaced and SO2 entrapped. The same reactions were observed also in the presence of labeled 13CO2, but showing rate constants lower than those measured for SO2. A liquid/gas phase model has been reported to describe the processes involved in the maintenance of the atmospheric SO2/CO2 balance or in the SO2 removal from flue gases

Free N-heterocyclic carbenes from Bronsted Acidic Ionic Liquids: Direct detection by electrospray ionization mass spectrometry and study of their speciation

In recent years, task-specific Brønsted acidic ionic liquids (BAILs) have become increasingly popular and widely used in industrial processes since, as non-volatile materials, they are considered less harmful and corrosive than traditional liquid acids.1 The presence of carboxylic acid groups into the cation scaffold of BAILs represents indeed an important opportunity for the discovery of novel applications and new materials. In situ formation of free N-heterocyclic carbenes (NHC) from Brønsted acidic ionic liquids will be studied, highlighting the crucial role of the anion basicity in promoting the C2-H proton abstraction from imidazolium cations with a carboxylic side chain. The question of the presence of free NHC in the reaction medium is current and of utmost importance being related to the interest in NHC in synthetic chemistry and catalysis, which remains as high as ever.2 The acidic carboxylic group inserted on the N-side chains of the cation can act as a “charge tag” for the direct detection of NHCs in ILs by mass spectrometry (MS). The coupling of MS techniques with soft ionization methods, such as electrospray ionization (ESI), allows one to intercept elusive intermediates, and gently transfer them from the solution to the gas-phase environment for structural and reactivity investigations.3 This experimental study can prove the possibility of using BAILs to furnish proper amounts of stable NHCs. The results can pave the way to the use of the novel compounds as MAIAc (see Fig. 1) and other customized BAILs as catalysts in carbene-mediated reactions, avoiding the use of other bases, generally added to the reaction bulk, with high benefits for organic synthesis. References [1] a) Sarma, P., Dutta, A. K., Borah, R. Catal. Surv. Asia, 2017, 21, 70-93; b) J. S. Wilkes, J. Mol. Catal. A: Chem., 2004, 214, 11-17. [2] Chiarotto, I., Mattiello, L., Pandolfi, F., Rocco, D., Feroci, M. Front. Chem., 2018, 6, 355. [3] a) Troiani, A., de Petris, G., Pepi, F., Garzoli, S., Salvitti, C., Rosi, M. Ricci, A. ChemistryOpen, 2019, 8, 1190-1198; b) Salvitti, C., Chiarotto,I., Pepi, F., Troiani, A. ChemPlusChem, 2021, 86, 209-223

The oxidation of sulfur dioxide by single and double oxygen transfer paths

The oxidation of SO2 by nonmetal oxoanions in the gas phase is investigated in an experimental and theoretical study of the structure of the species involved and the reaction kinetics and mechanism. SO3, SO3.− and SO4.− are efficiently produced by reaction of OnXO− anions (X=Cl, Br, and I; n=0 and 1) with SO2; XO− ions mainly react to give SO3 by oxygen-atom transfer, whereas OXO− ions mainly give SO3.− by oxygen-anion transfer. On descending the halogen group from chlorine to iodine, the SO3/SO3.− ratio decreases and increases for reactions involving XO− and OXO− anions, respectively, whereas the formation of SO4.− is particularly significant with OIO−. Kinetic factors play a major role in the reactions of OnXO−, depending on the halogen atom and its oxidation state