Research

Research

magnetiteMagnetite is the material used to track the history of the Earth magnetic field. Thus its magnetism, and especially its changes with temperature, have attracted a long-standing interest. Magnetite undergoes several phase transitions, some purely magnetic, like the spin-reorientation transition (typically at 130-140K) where the magnetization changes direction, and others, like the Verwey transition, a metal-insulator transition due to a change in the crystal structure, from cubic to monoclinic. We have recently employed novel microscopy techniques to observe the changes of magnetic domains due to these transitions: one, spin-polarized low-energy electron microscopy (SPLEEM), of which there are four instruments in the world, in collaboration with Andreas K. Schmid and coworkers from the Berkeley National Laboratory, and the other, spin-resolved photoemission electron microscopy (spin-PEEM), of which there is currently only one instrument, at the Max Planck Insitute for Microstructure Physics (Halle), in collaboration with Christian Tusche. Upper left-hand figure: SPLEEM image of the magnetic domains below the Verwey temperature, color-coded for the orientation of the magnetization as shown in the circle below (1). Right-hand figure: spin-PEEM image (2) of the magnetization above (upper image) and below (lower image) the Verwey temperature. These techniques allowed us to obtain images with nm resolution of the magnetic domains below and above the transition temperature.

(1) Laura Martín-García, Arantzazu Mascaraque, Beatriz M. Pabón, Roland Bliem, Gareth S. Parkinson, Gong Chen (陈宫), Andreas K. Schmid, and Juan de la Figuera, "Spin reorientation transition on magnetite (001)", Phys. Rev. B 93 (2016) 134419, DOI:10.1103/PhysRevB.93.134419

(2) J. de la Figuera and C. Tusche, "The Verwey transition observed by spin-resolved photoemission electron microscopy", App. Surf. Sci. (2016), DOI:10.1016/j.apsusc.2016.05.140

 

HBC revised-MMRThe discovery of stable amyloids composed solely of polar residues surprised scholars who believed that protein conformational stability is chiefly due to the hydrophobic effect. These amyloids, rich in Asn and Gln residues, form extensive hydrogen bonding networks. When aligned, hydrogen bond networks are strengthened due to cooperative effects arising from hyperpolarization. In this work, Density Functional Theory and Natural Bonding Orbital analysis were applied to study a series of polar and hydrophobic peptides in amyloid-like oligomers of different sizes and revealed that hydrogen bond networks formed by Asn and Gln side chains experience a distinct class of cooperativity that strengthens them significantly relative to main chain hydrogen bond networks. These computational results were corroborated experimentally utilizing recognition by amyloid specific molecular probes, nuclear magnetic resonance spectroscopy and experimental electric conductivity measurements on Asn/Gln-rich and hydrophobic peptides. On the basis of these findings, approaches to selectively inhibit the formation of polar versus hydrophobic amyloids can now be devised.

The figure shows a schematic representation of the delocalized electron density (blue shading) in the H-bond networks formed by Asn side chains (left) and the peptide backbone (right).

Miguel Mompeán, Aurora Nogales, Tiberio A. Ezquerra & Douglas V. Laurents ( "Complex System Assembly Underlies a Two-Tiered Model of Highly Delocalized Electrons" J. Phys. Chem. Lett. (2016) 7(10): 1859-1864.
(doi:10.1021/acs.jpclett.6b00699)

 

imanes-molecularesA scientific collaboration between the Institute of Physical Chemistry "Rocasolano" (CSIC), the University of Buenos Aires (Argentina), the National University of La Plata (Argentina) and the University of the Basque Country has been front cover of the journal Molecular Physics, as an invited article of a special volume on the Proceedings of the 55th Sanibel Symposium on theoretical and computational chemistry. These Symposia were initiated in 1961 by Per-Olov Löwdin, a former member of the Nobel Committee. Molecular magnetism manifests itself macroscopically through the magnetic moment (total spin, S) of a molecule, and is due to the presence of unpaired electrons – (poly)radicals – in the ground state of the system. The main conclusion of the article is the prediction of a system with a maximum spin Smax = 6 in its ground state (high-spin state), constructed by connecting twelve NB11H11 radical type (S = ½) icosahedra, forming a magnetic supericosahedron (first iteration). This prediction opens the door towards the design of molecular magnets based on boron molecules (boranes), since the system can be extended in three dimensions, thereby maximizing the total spin Smax in the series Smax(n) = {1/2, 6, 72, ..., 12n/2}.

Diego R. Alcoba, Ofelia B. Oña, Gustavo E. Massaccesi, Alicia Torre, Luis Lain, Rafael Notario, Josep M. Oliva
"Molecular magnetism in closo-azadodecaborane supericosahedrons", Molecular Physics (2016) 114, 3-4, 400-406.
doi:10.1080/00268976.2015.1076900

TDP-43TDP-43 is a protein which acts in part like an editor and in part like a postman; he modifies his "messages" written in RNA, before delivering them to the cytoplasm. Under certain "bad weather" conditions, part of the TDP-43 protein acts like an "umbrella" (really a hydrogel or functional amyloid) to protect the messages. But sometimes these "umbrellas" can break and become tangled together, forming a "net" (harmful amyloid aggregates) that disrupts the message editing and delivery system, and putatively leads to cell death. In fact, TDP-43 aggregates are linked to amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease that kills 4000 Spaniards per year. The elucidation by NMR of the structure, dynamics and stability of the first quarter, or N-terminal domain, of the TDP-43 protein's structure, dynamics and stability by NMR methods provides the keys to better understand the function and malfunction of this important protein.

Mompeán M, Romano V, Pantoja-Uceda D, Stuani C, Baralle FE, Buratti E and Laurents DV "The TDP-43 N-Terminal Domain Structure at High Resolution." FEBS J. Jan 12th, 2016
doi: 10.1111/febs.13651

 

Orrego-et-alA new method for connecting the dynamics and function of proteins immobilized on agarose beads is demonstrated. The mobility of proteins was quantified in any location of agarose beads, at different depths (0-100 microns; 500-600 nm spatial resolution), from fluorescence anisotropy optical sections of the beads. Protein fluorescence anisotropy informs about restriction of the global rotation of the immobilized proteins onto a solid surface. A general protein mobility scale was defined, which is independent of instrumental settings and fluorescent probes. Protein mobility is very sensitive to the chemistry of immobilization, as well as to the hydrogel porous microstructure resulting from the immobilization reactions. In this way better immobilization processes may be designed, leading to more stable heterogeneous biocatalysts with interest for the biodiesel and food industries.

Orrego AH, García C, Mancheño JM, Guisán JM, Lillo MP, López-Gallego F
"Two-Photon Fluorescence Anisotropy Imaging to Elucidate the Dynamics and the Stability of Immobilized Proteins" J Phys Chem B (2016) 120, 485-491.
DOI: 10.1021/acs.jpcb.5b12385