The research project of the I2M team aims for a better understanding of the relationship between composition - structure - functionality of the so-called complex and sensitive matter based on biopolymers.

Targeted systems include wheat reserve proteins (glutenins and gliadins) and sorghum (kafirins), various vegetable proteins (peas, rapeseed, potatoes, soya etc.) and hyperbranched glycoproteins of plant exudates (arabinogalactan-proteins or AGP). The team deals through the characterization of these systems with transversal scientific questions in order to find generic concepts allowing to explain the effect of external constraints on the mechanisms and dynamics of organization / disorganization of matter.

The approaches developed within the team allow to go up to the control of the functionality of generated systems. Fundamentally, the team seeks to establish the links between the intrinsic properties of the biopolymers studied, their ability to interact in a controlled or variable physicochemical and physical environment, and the properties of use of the assemblies and matrices induced.

The research activities of the I2M team can be divided into 3 main themes:

Intrinsic (molecular) properties of biopolymers

• The topological and conformational complexity of the objects we are working on makes their structural characterization at the molecular level very difficult. The coupled use of classical methods (CD, FTIR) and other instruments (SAXS, SANS) allowed us to elucidate the subject by setting up a methodology for SAXS or SANS data treatment with in particular a simulated annealing modeling.
• The main obstacle to obtaining physically realistic conformations is the heterogeneity of objects, having flexible or rigid zones, but also a heterogeneous distribution of the density of material and its intrinsic properties (polarity, charge, dipole moment, dielectric constant, anisotropy), which guide their interaction and assembly dynamics.
• One of the strategies we intend to develop in the coming years, inspired by the "structural biology" approaches, would be to fragment the macromolecules into subunits or to express them heterologously in the form of recombinant proteins whose structure would be determined, then reconstitute the overall conformation of macromolecules by combining each of the subunits.

Mechanisms of Assembly / Disorganization

• The assembling / destructuring mechanisms we are studying are essentially phase separation mechanisms (simple and complex coacervation, segregation), aggregation / fibrillation / gelation, formation of dispersed systems (emulsions) and dissolution / dispersion of network of biopolymers.
• One of our major ambitions is to better understand the effect of the application of external constraints (temperature, pressure, pH, ionic strength, presence of co-solutes, ...) on the coupling / decoupling of the (non-linear) dynamics of the assembly / destructuration of the material as function of the (non-linear) dynamics of changes in interactions between the biopolymers and the solvents and within the solvent itself.
• These different processes seem to depend on the existence of critical equilibrium of hydration / dehydration - biopolymer chain fluctuations (volumetric properties), defining their stability and functionality. This equilibrium would depend on one hand on the polarizability and the dielectric properties of biopolymers and water, which define a set of repulsive or attractive electrodynamic forces, and on the other hand on the adiabatic compressibility of interacting molecules with respect to that of solvent.
• The study of these mechanisms is carried out by the implementation of adapted methods with in particular the development of coupled systems allowing to analyze the systems while disturbing them in situ in a controlled way along with extreme conditions of temperature or pressure.

Physico-chemical properties and stability

• The conceptual framework of our project is likely to better understand and guide the desired functionality of biopolymers and matrices.
• For example, the differences in the stabilizing, emulsifying and film-forming properties of Acacia senegal and seyal AGPs are related to their hyperbranched structures and volumetric properties, which are directly dependent on the composition of polar and apolar residues and volume fluctuations of objects. Thus, the most compressible AGPs and giving the highest viscosity (so of high mass), are clearly more efficient to stabilize the limonene emulsions. On the other hand, the effect of the nature and the physicochemical properties of aroma compounds has been little studied and could strongly impact the final stability of the emulsified essential oils.
• The effect of the organizational state of biopolymer assemblies and their interactions with solvents affect their degradation properties, for example the hydrolysis of grain storage proteins during digestion or the degradation in natural environment of biopolymers in which amorphous and crystalline phases coexist.
• The effectiveness of insecticidal matrices based on essential oils depends on low energy interactions between the essential oil molecules and the biopolymeric matrix that can be multifactorial and that strongly affect the retention and release of aroma compounds