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Morbidity following major surgery is a growing healthcare problem. Previous studies have shown associations between preoperative lymphopenia and adverse postoperative outcomes, albeit in patient groups with multiple confounding factors. Lymphopenia is also associated with poor outcomes in a range of chronic and acute disease states including cardiac failure and sepsis, where lymphocyte dysfunction and excess lymphocyte apoptosis is observed. Cellular bioenergetic failure has been observed in these disease states and is proposed as a key pathophysiological mediator. The core hypothesis of this thesis is that preoperative lymphopenia is associated with increased morbidity after a standardized physiological insult due to underlying bioenergetic dysfunction. A large observational cohort study in patients undergoing elective lower limb arthroplasty showed preoperative lymphopenia to be a common phenomenon independently associated with increased postoperative morbidity and length of hospital stay. Further analysis of a subset of this cohort showed lymphopenia to be a chronic feature, not associated with common diagnoses known to cause lymphopenia. Immunophenotyping using flow cytometry confirmed lymphopenia affecting all lymphocyte subsets, but with normal monocyte and neutrophil number and function. Lymphocyte function was further explored using ex-vivo culture experiments in normal and lymphopenic subjects. In lymphopenic patients, lymphocyte apoptosis in response to a variety of insults was increased and ex-vivo stimulated lymphocyte proliferation was reduced. A novel experimental model was developed to assess lymphocyte bioenergetic function, using respirometry to assess glycolysis and mitochondrial function in freshly isolated cells. Lymphocytes from lymphopenic patients had global reductions in bioenergetic function and intracellular ATP content. In summary, chronic lymphopenia is common in the elective orthopaedic population and is robustly associated with adverse postoperative outcomes. The data here characterise a patient phenotype at increased perioperative risk. The underlying cellular dysfunction described may have important implications in a range of acute and chronic illnesses.

Molecules pack in accordance with Kitaigorodsky's theory of close packing to minimise empty space between molecules. The mode of packing is dependent on molecular shape, such that the bumps on one molecule fit roughly into the grooves of a neighbouring molecule. It is possible to extend the close packing theory to ask the following question: Is it possible to interchange substituents of similar shape and size, such as chlorine and methyl (Cl-Me interchange), on a molecule without causing it to adopt a different crystalline structure? This thesis summarises attempts to answer this question. Chapter 2 summarises methods for finding the frequency of isostructural Cl-Me interchange by retrieving as many examples as possible from the Bath Information and Data Services and the Cambridge Structural Database (CSD). However, given the large number of crystal data entries within the CSD, the frequency was approximated from that database. Approximately 23% of all examples retrieved from the CSD are isostructural, which illustrates that factors other than the size and shape of interchanged substituents determine crystal structure. Chapter 3 summarises attempts at finding intermolecular and molecular factors that govern isostructural CL-Me interchange and concludes that minimising the intermolecular interactions of Cl and Me can facilitate isostructurality. Chapters 4, 5 and 6 go on to summarise three approaches for reducing the intermolecular contacts of Cl and me with successful examples of forced isostructurality through co-crystallisation. Finally, chapter 7 discusses the formation of supramolecular tapes - common structures formed by crystal engineers, and illustrates how small changes in the size and shape of acid spacers can effect tape structure and crystal structure.