Impacts of Conformational Geometries in Fluorinated Alkanes (original) (raw)

Research of blood substitute formulations and their base materials is of high scientific interest. Especially fluorinated microemulsions based on perfluorocarbons, with their interesting chemical properties, offer opportunities for applications in biomedicine and physical chemistry. In this work, carbon K-edge absorption spectra of liquid perfluoroalkanes and their parent hydrocarbons are presented and compared. Based on soft X-ray absorption, a comprehensive picture of the electronic structure is provided with the aid of time dependent density functional theory. We have observed that conformational geometries mainly influence the chemical and electronic interactions in the presented liquid materials, leading to a direct association of conformational geometries to the dissolving capacity of the presented perfluorocarbons with other solvents like water and possibly gases like oxygen. Research in blood substitute formulations is gaining more attention in the scientific community in recent years 1-9 as more pharmaceutical companies start clinical trials on various artificial blood approaches 7,10-12. In general, artificial blood consists of emulsions of different liquid or protein compounds to increase oxygen solubility and transport capabilities as well as to decrease toxicity to biological tissue 7,10. Two of the more promising approaches center themselves around hemoglobin-based carriers 11 and fluorinated microemulsions 6,9. Despite setbacks regarding clinical tests and medicinal approval of recent formulations 5,13 , an emulsion containing perfluorodecalin named Fluosol 12 was successfully approved by the U.S. Food and Drug Administration in 1989 (New Drug Application N860909). The main oxygen carrier in Fluosol, perfluorodecalin, is part of the family of perfluorocarbons. They have a wide range of applications ranging from tissue oxygenation 1,14,15 to post-operative treatment 16,17. Their wide range of extraordinary properties-high density, high viscosity, high biological and chemical inertness, high gas solubility 18,19-offer opportunities for applications in biomedicine and physical chemistry 20,21 , therefore leading to a high interest in scientific development 2,18,19,22-25. An inherent feature to all perfluorocarbons is the so called "perfluoro effect", which describes the energy shifts of the spectral features due to the stabilization effect of fluorine in the fluorination process 24-27. The magnitude of the energy shift can subsequently be used for a classification of a molecular orbital (MO) to either bear σ-or π-character 24,25 delivering an experimental method for the orbital classification. Some experimental studies based on photoelectron and X-ray absorption (XA) spectroscopy have already been performed 24-28 , but the development of more complex theoretical models 29 and new experimental techniques 30-32 gives opportunities for further investigation of perfluorocarbons. In liquid emulsions several effects need to be accounted for. Two of the more prominent are the conformation effect 33 and the van der Waals force 34. The conformation effect affects peak broadenings and is a result of excited orbital interactions with surrounding molecules of different conformations 33,35. In the case of nonpolar systems, the acting van der Waals force is the London dispersion force, that is, an attractive force resulting from induced dipoles 34. The objective of the present work is to provide experimental and theoretical information on the electronic structure of liquid fluoroalkanes and their respective hydrocarbons, which are subject to weak van der Waals forces and have a high amount of different conformational geometries 18,36 , through element specific XA spectroscopy. A discussion of experimental XA and theoretically calculated spectra is presented revealing a strong involvement of the conformation effect with the local electronic structure and relative inertness of liquid