The CD3epsilon subunit of the T cell receptor (TCR) complex undergoes a conformational change upon ligand binding that is thought to be important for the activation of T cells. To study this process, we built a molecular dynamics model of the transmission of the conformational change within the ectodomains of CD3. The model showed that the CD3 dimers underwent a stiffening effect that was funneled to the base of the CD3epsilon subunit. Mutation of two relevant amino acid residues blocked transmission of the conformational change and the differentiation and activation of T cells. Furthermore, this inhibition occurred even in the presence of excess endogenous CD3epsilon subunits. These results emphasize the importance of the conformational change in CD3epsilon for the activation of T cells and suggest the existence of unforeseen cooperativity between TCR complexes.

Magnetic and NMR relaxivity properties of γ-Fe 2 O 3 nanoparticles embedded into the walls of polyelectrolyte multilayer capsules and freely dispersed in a sodium borate buffer solution have been investigated. The different geometric distribution of both configurations provides the opportunity to study the relationship of water accessibility and magnetic properties of particles on the NMR relaxivity. Changes in their blocking temperature and average dipolar field were modeled as a function of packing fraction in the ensemble of free and entrapped nanoparticles. For free nanoparticles with relatively low concentration, relaxivity values increase with packing fraction according to an increase in the dipolar field and larger water accessibility. However for embedded NPs in the capsule wall, packing fractions should be limited to optimise the efficiency of this system as magnetic resonance imaging (MRI) contrast agent.

Iron oxide nanomaterial is a typical example of a magnetic resonance imaging probe for negative contrast. It has also been shown how this nanomaterial can be synthesized for positive contrast by modification of the composition and size of the core. However, the role of the organic coating in the relaxometric properties is largely unexplored. Here, maghemite nanoparticles with either excellent positive or very good negative contrast performance are obtained by modifying coating thickness while the core is kept unchanged. Different nanoparticles with tailored features as contrast agent according to the coating layer thickness have been obtained in a single-step microwave-driven synthesis by heating at different temperatures. A comprehensive analysis is conducted of how the composition and structure of the coating affects the final magnetic, relaxometric, and imaging performance. These results show how the organic coating plays a fundamental role in the intrinsic relaxometric parameters of iron oxide-based contrast media.