2+ Ion with Ligands in a Range of Solvent Systems

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An Investigation of Beryllium Coordination Chemistry Using Electrospray Ionisation Mass Spectrometry A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry at The University of Waikato by ONYEKACHI RAYMOND 2018 Abstract The electrospray ionisation mass spectrometric behaviour of various complexes of beryllium have been investigated in this thesis. These beryllium complexes were prepared in situ on a small scale by preparing appropriate molar mixtures of the Be2+ ion with ligands in a range of solvent systems. In view of the toxicity of beryllium compounds, this combinatorial type screening, involving miniscule amounts of material in solution, proved to be a safe strategy to pursue the coordination chemistry of beryllium. Starting from simple beryllium compounds which includes the metal salts (Chapter 2), the speciation and hydrolysis of beryllium ions in aqueous solution has been studied over a pH range of 2.5-6.0 using electrospray ionisation mass spectrometry (ESI-MS). Ions observed by ESI-MS revealed that the speciation of beryllium with hydroxide ligands in solution was preserved into the gas phase via charge reduction by ion pairing with the salt anion. The pH-dependent hydrolytic tendencies of the Be2+ cation presented as an ESI-MS speciation diagram for beryllium hydrolysis is in good agreement with previous speciation data which vindicates the ability of ESI-MS as a quick, sensitive and safe screening technique for observing beryllium speciation with ligands of interest at low concentrations. Collision induced dissociation patterns further confirmed that the trimer 3+ [Be3(OH)3] is the most stable beryllium hydroxido-aggregate arrangement while the pronounced ion pairing of the beryllium cation with the sulfato ligand yielded additional beryllium ion cluster arrangements such as Be3(μ3-O) aggregate and mixed sulfato-/hydroxido- species. These ions were further investigated using computational techniques simulated in the gas and aqueous environment which allowed for the first time, the molecular dynamics simulations of the ligand exchange processes of the Be2+ cation (Chapter 3). A major finding from the ab initio molecular simulations was that hydrogen bonding was relevant in stabilis ing the tetraaquaberyllium complex in beryllium solutions. Therefore, in the gas phase where the solvation shell of such beryllium species is very much compromised, the formation of inner sphere complexes is commonplace as observed from the ion signal assignment in the ESI mass spectra. While these extraneous species may not be an exact representation of the solution state, these ions provided insight into plausible modes of beryllium aggregation that are not otherwise easily investigated. i Building on these results, a variety of beryllium complexes was generated with various ligands in solutions and subjected to detailed characterisation by ESI- MS. These ligands containing functional groups or architecture of interest, varied from simple monodentate ligands such as the acetate ion to more common beryllium chelators including 1,3-diketone, hydroxy keto, malonic acid, chromotropic acid and crown ethers (Chapter 4). Generally, there was excellent correlation between the species observed in the mass spectrum and those confirmed to exist in solution by other techniques. This lent strong credence to the ESI-MS methodology used as an efficient analytical technique for the easy screening of a diverse range of potential ligands for the divalent beryllium ion. A fundamental issue in beryllium research is the search for suitable chelating ligands for environmental and biomedical application. Therefore, the ESI- MS methodology was further employed to investigate several multidentate aminopolycarboxylic acids which are well-known commercial and biomedical chelating agents (Chapter 5). Notable among these are the nitrilotripropionic acid (NTP) and related tetradentate ligands designed towards the full encapsulation of the Be2+ cation. Stoichiometric information which was readily obtained from the ESI mass spectra was found to be effective for the preliminary screening of potential encapsulation by tetradentate coordination from a single ligand. Lastly, to corroborate ESI-MS speciation results, beryllium complexes with these class of ligands were synthesised on a larger scale and characterised by 9Be NMR and single-crystal X-ray crystallography. ii Acknowledgements Getting straight to the point: I would like to appreciate all the academics who contributed to the development of the ideas and concepts in this thesis. Firstly, I acknowledge my chief supervisor Prof. Bill Henderson who for his immeasurable support, excellent communication and for offering me a Postgraduate study award. At this point, I will also mention Assoc. Prof. Paul Plieger (Massey University) who was the principal investigator on Marsden Fund Grant (contract MAU1204, administered by the Royal Society of New Zealand) which sponsored this research and associate investigator Prof. Penny Brothers as well as my fellow PhD students on the project Lakshika Perera and David Nixon. Furthermore, many thanks to Assoc. Prof. Michael Mucalo and Dr Jo Lane - my co-supervisors at the University of Waikato. My immense gratitude also goes to Prof. Michael Bühl (University of St Andrews, Scotland) for introducing and training me on the technique of ab initio molecular dynamics as well as a generous computer allocation. Special thanks to Prof. Florian Kraus and Dr Magnus Buchner who were my hosts during a research visit to Philipps Universität Marburg, Germany. Lastly, a big thank you to my numerous officemates especially here at the University of Waikato and other laboratories I visited. I would also like to thank the support of Cheryl Ward (Science Librarian) and the library team (especially the Interloan services). Other teams whose support and services helped progress this research include the postgraduate team, the university research office, the scholarship office and the school of science administration (especially Vicki and Gloria). Many thanks as well to the technical staff of Chemistry, School of Science, University of Waikato and other universities I visited including Dr Herbert Früchtl (University of St Andrews, Scotland), who kept me connected to the University of St Andrews High performance computing (HPC) facilities. Outside the laboratories, the first person whom I want to thank is my fiancée whose contributions to this thesis are so convoluted to be delved into. The support of my parent and siblings was the bed rock which my survival rested. “Family is everything” and though I had put it second at one point or the other, I want to say a big thank for their understanding and love. Thank you as well to my church family at Freedom Christian Church, Hamilton as well as to my music team. iii Finally, I would like to say thank you to all my flatmates, friends and countrymen whom I have mingled with here in New Zealand and overseas. iv Table of Contents Abstract .....................................................................................................................i Acknowledgements ................................................................................................. iii Table of Contents ......................................................................................................i List of Figures ......................................................................................................... vi List of Tables......................................................................................................... xiii List of Abbreviations.............................................................................................. xv 1 Chapter One............................................................................................... 16 The chemistry and metallurgy of beryllium .......................................................... 16 1.1 Introduction ............................................................................................ 16 1.2 Sources and production of beryllium ..................................................... 18 1.3 Properties and uses ................................................................................. 19 1.4 Toxicity................................................................................................... 20 1.5 Beryllium in New Zealand ..................................................................... 21 1.6 Aqueous chemistry of the Be2+ cation .................................................... 22 1.7 Coordination by O-donor ligands ........................................................... 25 1.8 Coordination by N-donor ligands ..........................................................

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