Transition metal ion complexes are involved in chemical, physical and biological properties which make them of remarkable fundamental and technological interest. In view of understanding the chemical reactivity and/or the physical properties of these transition metal ion complexes, their electronic properties are studied by a large number of experimental techniques. Nevertheless, there remain situations in which experimental techniques have failed to fully determine their electronic structure so far. Mangacom addresses such cases. In particular, it will be focused on manganese complexes that are involved in many domains such as biology, catalysis, and materials science. One of the aims of Mangacom is to develop a novel approach for determining the electronic structure of dinuclear Mn complexes, which are weakly magnetically coupled. This approach is mostly based on powerful experimental techniques. Multifrequency EPR spectroscopy, and especially high field EPR, as well as high field and low temperature solid state 55Mn NMR will be used. Unique information on their magnetic/electronic properties will be obtained through the confrontation of EPR and NMR parameters with state-of-the-art theoretical calculations (DFT and ab-initio). This project should be considered as a first step in a long-term strategy for understanding the electronic properties in larger molecular systems. The project is truly multidisciplinary since it involves chemists, physico-chemists and physicists and it makes use of both experimental and theoretical tools. It is interdisciplinary as well, since it particularly aims at transferring methods of condensed matter physics into the chemistry world. One of the major assets of the project is the complementarities between the different skills of the participants and the various techniques used.

This project exploits the capacities of a high cooling power refrigerator for implementing a large dimensions von Karman flow (diameter 80 cm), working as well with liquid or gaseous helium, as with superfluid. Von Karman flow is producted between two parallel contrarotating disks. It is now well documented. Recent progress has been realised on the understanding of the mean flow structures. Depending on the location, it presents either a reasonable example of homogeneous isotropic turbulence, or an interesting case of strong anisotropy. P. Tabeling et al. already used cryogenic helium in a von Karman flow, and obtained the main known results on superfluid turbulence. A traditional weak point of cryogenic turbulence experiments is the small number of available probes. We shall develop an original instrumentation (hot wire, second sound tweezers, acoustic scattering, ...) allowing to probe the flow at any scale, from the mean flow to sub-inertial scales. Comparing the normal and super-fluid behaviours in the same geometry will provide an original way to test some controversed ideas about turbulence. An asset to this ambitious project is that each participant is interested in everything, from the design of the experiment to the results analysis.

This project will focus on a poorly known type of adhesive structures but that have been described to be essential in physiological and pathological cell invasion of cohesive tissues. These structures are named podosomes in osteoclasts and macrophages and invadopodia in metastatic cancer cells. Pososomes/invadopodia exhibits the extraordinary property of self assembling into a donut shaped supra-molecular structure called the rosette, whose diameter increases with time. Rosette self assembly is required for efficient cell invasion of cohesive tissues.The understanding of this function requires not only the knowledge of the enzymes involved but also the supra-molecular properties of this structure. Individual podosomes/invadopodia assembly is initiated by the nucleation of an actin column that is perpendicular relative to the substrate on which the cell spread. This column is able to divide as shown by Evans et al. in 2003. Podosomes/invadopodia assembly is strictly controlled by the non receptor protein kinase Src. Quiescent Src kinase can be activated either by mechanical tensions applied on integrins, (the major receptors enabling cell adhesion on extracellular matrix), or by its interaction with a variety of partners. Src is not only required for podosomes/invadopodia assembly, but it initiates a negative retro control loop that involves the cleavage by the endoprotease calpain 2, and therefore, the inactivation, of podosomes key components (including Src itself) leading to the disassembly of these adhesive structures. On the bases of these experimental results, the aim of this project is to design a minimal predictive model of podosomes/invadopodia rosette assembly and dynamics (task1). This physical model will give trends as parameters vary suggesting a key role of a limited number of regulatory mechanisms. Rosette dynamics can be followed by live cell imaging so that we can hopefully compare with experiments by expressing proteins fused with fluorescent proteins. Thereby, a number of well defined parameters such as the rate of rosette expansion, its width, the spacing between individual podosomes/invadopodia, and the diameter of the actin column, it is possible to carry out quantitative studies. The predictions of the model will be challenges by the experimental data. More precisely, with will measure the Src activation gradient around the rosettes and the absence of Src activity at the rosette center using a FRET based biosensor. In addition, the effect on rosette dynamics of calpain 2 activity modulation by genetically engineered modification of the enzyme itself, or of its substrates such as cortactin, beta 3 integrin chain or Src will be analyzed (Task 2). The activity of Src biosensors will be correlated with 3D force mapping generated by rosettes. Finally we shall study the rosette deformations generated by tension anisotropy within the cell triggered either by local deformations triggered by AFM, or by patterning of the adhesive substrate. According to the experimental data, the preliminary model will be revised and refined.

The project is focused on tyrosinase (Ty), a copper-containing metalloenzyme which to date remains poorly characterized. Ty belongs to the type-3 copper-containing enzymes that contain a coupled binuclear active site. Ty is the key enzyme involved in melanins (protective pigments) biosynthesis. It catalyzes the rate-limiting step, the oxidation of the amino acid tyrosine to 3,4-dihydroxyphenylalanine (Dopa) and subsequently to Dopa-quinone, which is then converted by multi-step reactions to melanin pigments. Ty is widely distributed in nature in many organisms with slightly different forms. In mammals, the final products of Ty activity are melanins, pigments responsible for the skin, eyes and hair color. Melanins are produced in melanocytes, cells located in the basal layer of the dermis after further chemical transformations involving Ty and Ty-related proteins (TRP-1 and TRP-2). This multistep process leads to the formation of eumelanin (the most protective melanins). Accumulation of high levels of melanins causes a variety of disorders as cutaneous hyperpigmentation (melasma, naevi'..) and ocular retinitis pigmentosa. A number of treatments exist for these conditions and the most prominent ones function as inhibitors of Ty activity. Ty inhibition is thus now the well-known approach against increased production and accumulation of melanins. Despite the numbers of Ty inhibitors described in vitro, very few are efficient under clinical trials. Among them the most widely used (1,4-dihydroquinone and kojic acid ) in medical prescriptions to achieve hypopigmentation and skin-whitening agent for cosmetic products, have been proven to be cytotoxic and mutagenic agents. In this context there is an urgent need for new strategies for the rational conception of Ty-inhibitors. In addition to efficiency of inhibition (low KI) others parameters related to cytotoxicity, solubility, skin and cellular penetration parameters should be considered. Therefore the main objectives of this project are to enhance the fundamental knowledge about inhibition of Ty and its related proteins via a novel and rational approach based on bio-inorganic chemistry, combining enzymes and models studies. Understanding the way of action of our targets would allow rationally designed inhibitors to emerge. Such products will be searched among a family of natural compounds recently discovered by one of the partners as potent Ty inhibitors and from design of new compounds. Aware of the health and efficacy concerns related to existing drugs, we consider the present multidisciplinary approach to develop specific and safe inhibitors. The partners involved in the project combine complementary expertise associating enzyme biochemistry, bioinorganic chemistry, computational chemistry and organic synthesis. Iterative feedbacks between partners are of importance to take advantage of all these expertise. The specific aims of the proposed research are as follows: i) From models and enzymes studies (experimental and theoritical), establishment of structural and mechanistic aspects of inhibition in Ty for the rational design of inhibitors, ii) Design and synthesis of new specific inhibitors, iii) Biological evaluation of synthesized inhibitors, including tests on enzymes, cellular tests on human melanocytes and tests to evaluate the cytotoxic effects. There is no doubt that a better understanding at a molecular level will open new fields for future development of potent and specific inhibitors for pharmaceutical and cosmetic industries.

Concerted research of 4 research groups involving chemical synthesis, laser spectroscopy, electrochemistry, and theory will be aimed at demonstrating the suitability of new heteroleptic copper(I) complexes for solar energy conversion schemes. While the area of photochemistry is dominated by ruthenium(II) polypyridine complexes, little attention has been paid to copper(I) complexes. One particularly significant driving force of this program lies in the lower cost, higher abundance and lower toxicity of copper compared to ruthenium. New heteroleptic copper complexes will be prepared and investigated with respect to advancing two areas: (i) novel photo- and electro- active rod-like molecular arrays of the general type Donor-Sensitizer-Acceptor in view of long range photoinduced charge separation and (ii) photo-electrochemical devices based on the sensitization of p-type semiconductor (NiO). Synthesis, characterizations and theoretical research will be twinned aiming at a rational design of the complexes in view of the envisioned function. The expected results are the synthesis and the discovery of new copper(I) complexes with useful photophysical properties, which will in turn lead to new breakthroughs in the rational design of copper complexes for long-range photoinduced charge separation and for photoelectrochemical devices, where traditional ruthenium complexes are used. All this will be of fundamental importance for establishing new materials for solar energy convsersion.