General introduction

Dans le document DNA-copolymers structure formation: beyond self-assembly (Page 8-12)

Nature is a constant topic of wonder and source of inspiration for human kind. This inspiration gave birth to a new branch of chemistry based on Nature principles, called

“biomimetic chemistry”, which is focused on developing ideas by mimicking Nature. Since the 1970s when the biomimetic chemistry was born, the dream of mimicking nature became realistic as it has never been before [1]. The essence of biomimetic chemistry consists in a creative transversal flow between biology and chemistry in order to broaden the breadth of this discipline [2]. The basic motivation of biomimetic chemistry is the understanding of key processes at the molecular level in biological systems, like for example, the molecular recognition of quickly targeting and highly selective artificial enzymes. The discipline which is highly associated with biomimetic chemistry is the field of polymer chemistry [3].

Synthetic polymers can be obtained from a plethora of different monomers in comparison to molecules present in nature which are based on a limited choice of construction units [4].

However, synthetic polymers have no biological activity per se. Taking into consideration the constant advances in polymer science it thus became clear that this discipline cannot just focus on the development of synthetic plastics but needs to expand, especially towards potential applications in biology. In this regard, Helmut Ringsdorf who described the first artificial membranes and who is regarded as the pioneer of this approach has also exploited the possibility of using polymers to simulate cellular processes like surface specific recognition and biomembrane stabilization. This work did set the background for the research at the material level like designing functional artificial biological systems, for example biomimetic photosynthetic systems using peptide nanotubes [5]. The branch of science that

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greatly expanded in the last 20 years along with biomimetic chemistry and which constitutes an integral part of biomimetic chemistry is nanotechnology [6].

Nanotechnology, which has drawn a remarkable attention due to the possibility to generate new materials and devices with outstanding physical and chemical properties [7, 8] is considered as the logical continuity in technological progress [9]. Despite great efforts made in design and development to ensure high performance devices, their implementation in real-application has faced many obstacles like reproducibility or scale feasibility for industrial production. A branch of nanotechnology called macromolecular self-assembly (MSA) appears to be promising and attractive, since it is an easily scalable and low-cost methodology which can overcome some of the obstacles mentioned above [9]. MSA results from the synergy between two major disciplines. The first relies on the organization of molecules by non-covalent interactions into so called supramolecular polymers, and the second one is the self-organization of macromolecules into multicompartment systems. Research on supramolecular polymer assembly is conducted with analogous approaches and tools as supramolecular chemistry. Hydrogen bonding, π- interaction, van der Waals forces, hydrophobic effect, ionic and dipolar interactions are identified as basic non-covalent interactions leading to the formation of supramolecular structures [10]. These interactions together with forces that result from the repulsion between unlike blocks and cohesive interactions between like moieties, drive self-assembly [11]. Production of structures with tailored architecture, size, complexity as well as well-defined localization of functional groups, through a spontaneous bottom-up process of macromolecules organization is the main goal of MSA [12]. Both, top-down approaches through which the bulk material is modified to obtain desired products as well as bottom-up approaches with which materials are obtained from atoms/molecules assembly can provide well-defined nano-sized devices with unique chemical and physical properties [13, 14]. Properties such as mechanical strength and, elasticity as well as function of materials

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achieved by self-assembly result usually from the manipulation of pressure and pH under normal temperature in the liquid phase. However, reaching the suitable balance between repulsive and attractive forces is a fundamental condition of self-organization of various systems like colloidal suspensions, emulsions or biological systems. In order to be able to manipulate the alignment of particles in the desired manner the understanding of the nature and intricacy of these phenomenas is necessary [15]. The net relation between individuals can be isotropic or anisotropic relying on the type of synergy. In general, naturally occurring self-organized structures of non-biological systems are isotropic and result in non-hierarchically organized architectures. On the other hand, biomimetic (artificial amino acids, dendriticc polymers) and aggregating systems found in nature like deoxyribonucleic acid (DNA) or proteins are often remarkably anisotropic and results in well-defined, functional self-assemblies [9].

DNA is the amazing biological macromolecule evolved by Nature for billions of years [16]

encoding the genetic information of the vast majority of living organisms [17]. DNA units/strands are composed of a sequence of the four nucleotides: purines, adenine (A) and guanine (G); and pyrimidines, cytosine (C) and thymidine (T) linked to phosphate–

deoxyribose sugar [18]. The helical structure discovered by Watson and Crick, assembled by two hybridized complementary DNA strands is the simplest example of DNA organization [19]. Since that breakthrough work, interest raised DNA beyond its basic role, i. e. universal carrier of the genetic information. Owing to the highly programmable nature of DNA, current interests focus on the development of DNA based nanostructures [20]. DNA is considered as an ideal material for nanotechnology as its composition enables the production of nanoscale objects, with outstanding precision and intricacy in 1D, 2D and 3D [20, 21].

The versatility of polymers synthesis is the reason why they belong to the popular class of self-assembling building blocks, [12, 22]. In 1960s when the development of synthetic

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techniques allowed the production of well-defined block copolymers (BC) in terms of molecular weight, distribution as well as composition, the studies of self-assembling synthetic macromolecules were initiated. BCs undergo microphase separation into nanoscale periodic domains of chemically distinct covalently linked blocks [23]. The segregation of chemically unlike blocks and the cohesive interactions of like blocks can be considered as the driving force [24].Such a behavior has drawn the attention of the polymer community due to the fact that this phenomenon has never been noticed for any synthetic polymer before. In general block copolymers are depicted as macromolecules composed of at least two blocks of differing monomers with linear and/or radial alignment [25]. The whole family of block copolymers belongs to the wide category of soft condensed matter, which is characterized by fluid-like disorder on the molecular scale and a high degree of organization at wider length scales. The exceptional properties of BCs is a consequence of their complex structure resulting in their implementation in many industrial applications as thermoplastics elastomers, foams and adhesives [26]. Boosted toughness and surface properties for various applications in the microelectronic or biomedical industry can be achieved by selection of proper block copolymers. The highest input in polymer science originates from the development of controlled radical polymerization (CRP) in particular ATRP (Atom Transfer Radical Polymerization) and RAFT (Reversible Addition-Fragmentation chain Transfer) polymerization [27]. Sometimes combination of two or several polymerization strategies is used to achieve desired convoluted copolymers.

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Dans le document DNA-copolymers structure formation: beyond self-assembly (Page 8-12)