UNCORRECTED PROOF ARTICLE INFO Article history: Received 1 February 2016 Received in revised form 21 April 2016 Accepted 22 April 2016 Available online xxx Keywords: Bio-membranes Small angle neutron scattering Small angle X-ray scattering Lipids and phospholipids Liposomes ABSTRACT Lipids membranes, the primary component of the living cell, involve collective behaviour of numerous interacting mol- ecules. The rich morphology and complex phase diagram of the lipid systems require different strategies in describing bio-membranes in order to capture the essential properties of self-assembly processes as well as the underling molecular collective phenomena involved in biological functions. Among the experimental methods used, the scattering techniques such as small angle neutrons and X-rays scattering (SANS and SAXS) are probably the most important experimental ap- proach for the structural investigation of bio-membranes and mixed lipids complex systems. In this tutorial review we describe the main approaches employed in the investigation of lipid bio-membranes by means of the neutron and x-ray scattering techniques. While introducing the main structural properties of lipid bio-membranes we highlight the impor- tant role of lipid components in different biological functions of living organisms. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo. © 2016 Published by Elsevier Ltd. BBA - General Subjects xxx (2016) xxx-xxx Contents lists available at ScienceDirect BBA - General Subjects journal homepage: www.elsevier.com Structural characterization in mixed lipid membrane systems by neutron and X-ray scattering ☆ Mikhail A. Kiselev, a Domenico Lombardo b a Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, Ulica Joliot-Curie 6, Dubna, Moscow 141980, Russia b CNR-IPCF, Consiglio Nazionale delle Ricerche. Istituto per i Processi Chimico Fisici, Viale F.S. D'Alcontres, No. 37, 98158 Messina, Italy 1. Introduction The study of the self-assembly processes of lipid bio-membrane in water environment represents a central topic for the understand- ing the physical and chemical bases of the biological functions in liv- ing organism [1–3]. In basic research, mixed lipid bilayers serve as models for the investigation of cell membranes and their interaction with membrane proteins [4–7]. They also serve as delivery agents for drugs, genetic material and enzymes through living cell membranes and other hydrophobic barriers in food industry, cosmetic, biotech- nology and medicine [8–10]. For these reasons self-assembly prop- erties of lipid membranes has been the object of intensive research for many decades both from the theoretical as well as experimental point of view. In both case molecular level investigation of lipid bi- layers bio-membranes involve collective behavior of numberous in- teracting molecules, while their full description require simultaneous calculation (and simulation) of a large number of parameters due to the number of conformations present and the variety of interactions involved [11–17]. From the experimental point of view a large va- riety of methods were applied to study the self-assembly properties of lipid bio-membranes as well as their interaction and complex be- havior in mixed systems [18–24]. Among the experimental methods used, the scattering techniques such as small angle neutrons and X- rays scattering (SANS and SAXS) are probably the most important non–destructive and widely utilized experimental approach for the structural investigation of bio-membranes, and mixed lipids systems. More specifically the formation of different structures with different ☆ This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo. Email address: lombardo@ipcf.cnr.it (D. Lombardo) topologies can be efficiently evidenced by scattering experiments thus highlighting the important role of relevant molecular conformations in many different processes of life science [24–31]. Herein, we describe the main approaches employed in the inves- tigation of lipid bilayers by means of the neutron and x-ray scatter- ing techniques. In the first section, we introduce the main properties of lipid bio-membranes, highlighting the important role of lipid com- ponents in different biological functions of living organisms. We then introduce the fundamental principles of scattering of neutrons and X- rays and their application in structural characterization of bio-mem- branes. Within each section we will present some relevant and recent examples of the efficient use of scattering techniques in the study of lipid self-assembly with emphasis on modern approaches of scattering techniques in the characterization of bio-membranes and in advanced bio-nanotechnology research. 2. Structural properties and main components of bio-membranes 2.1. Fluid mosaic model of bio-membranes Bio-membranes, which are mainly composed by different am- phiphilic molecules, contain also proteins, sugars, cholesterol, and a number of other fundamental components that control important func- tional processes inside the cells such as DNA synthesis, antigen–an- tibody recognition or metabolic processes. According to the fluid mo- saic model of Singer and Nicolson [32], the bio-membranes in living organism can be represented as an highly flexible, mosaic of fluid bi- layer structures of lipids were membrane protein are embedded. To- gether with the integral protein, which has at least one segment an- chored within the lipid bilayer, the fluid bilayer contains also pe- ripheral proteins, which are bound to integral proteins or to the po- lar headgroups of membrane lipids. Finally, the transmembrane pro http://dx.doi.org/10.1016/j.bbagen.2016.04.022 0304-4165/© 2016 Published by Elsevier Ltd.