201 research outputs found
Residual dipolar coupling investigation of a heparin tetrasaccharide confirms the limited effect of flexibility of the iduronic acid on the molecular shape of heparin
The solution conformation of a fully sulfated heparin-derived tetrasaccharide, I, was studied in the presence of a 4-fold excess of Ca2+. Protonâproton and protonâcarbon residual dipolar couplings (RDCs) were measured in a neutral aligning medium. The order parameters of two rigid hexosamine rings of I were determined separately using singular value decomposition and ab initio structures of disaccharide fragments of I. The order parameters were very similar implying that a common order tensor can be used to analyze the structure of I. Using one order tensor, RDCs of both hexosamine rings were used as restraints in molecular dynamics simulations. RDCs of the inner iduronic acid were calculated for every point of the molecular dynamics trajectory. The fitting of the calculated RDCs of the two forms of the iduronic acid to the experimental values yielded a population of 1C4 and 2So conformers of iduronic acid that agreed well with the analysis based on protonâproton scalar coupling constants. The glycosidic linkage torsion angles in RDC-restrained molecular dynamics (MD) structures of I are consistent with the interglycosidic three-bond protonâcarbon coupling constants. These structures also show that the shape of heparin is not affected dramatically by the conformational flexibility of the iduronic acid ring. This is in line with conclusions of previous studies based on MD simulations and the analysis of 1H-1H NOEs. Our work therefore demonstrates the effectiveness of RDCs in the conformational analysis of glycosaminoglycans
The electronic structure of LaSrMnO thin films and its dependence as studied by angle-resolved photoemission
We present angle-resolved photoemission spectroscopy results for thin films
of the three-dimensional manganese perovskite LaSrMnO. We
show that the transition temperature () from the paramagnetic insulating
to ferromagnetic metallic state is closely related to details of the electronic
structure, particularly to the spectral weight at the -point, where
the sharpest step at the Fermi level was observed. We found that this -point is the same for all the samples, despite their different . The
change of is discussed in terms of kinetic energy optimization. Our ARPES
results suggest that the change of the electronic structure for the samples
having different transition temperatures is different from the rigid band
shift.Comment: Accepted by Journal of Physics: Condensed Matte
Momentum resolved spin dynamics of bulk and surface excited states in the topological insulator
The prospective of optically inducing a spin polarized current for spintronic
devices has generated a vast interest in the out-of-equilibrium electronic and
spin structure of topological insulators (TIs). In this Letter we prove that
only by measuring the spin intensity signal over several order of magnitude in
spin, time and angle resolved photoemission spectroscopy (STAR-PES) experiments
is it possible to comprehensively describe the optically excited electronic
states in TIs materials. The experiments performed on
reveal the existence of a Surface-Resonance-State in the 2nd bulk band gap
interpreted on the basis of fully relativistic ab-initio spin resolved
photoemission calculations. Remarkably, the spin dependent relaxation of the
hot carriers is well reproduced by a spin dynamics model considering two
non-interacting electronic systems, derived from the excited surface and bulk
states, with different electronic temperatures.Comment: 5 pages and 4 figure
Nature of the metallic and in-gap states in Ni-doped SrTiO
Epitaxial thin films of SrTiO(100) doped with 6% and 12% Ni are studied
with resonant angle-resolved photoelectron spectroscopy (ARPES) at the Ti and
Ni L2,3-edges. We find that the Ni doping shifts the valence band (VB) of
pristine SrTiO towards the Fermi level (p-doping) and reduces its band gap.
This is accompanied by an upward energy shift of the Ti t2g-derived mobile
electron system (MES). Thereby, the in-plane dxy-derived bands reduce the
embedded electron density, as evidenced by progressive reduction of their Fermi
momentum with the Ni concentration, and the out-of-plane dxz/yz-derived bands
depopulate, making the MES purely two-dimensional. Furthermore, the Ti and Ni
L2,3-edge resonant photoemission is used to identify the Ni 3d impurity state
in the vicinity of the valence-band maximum, and decipher the full spectrum of
the VO-induced in-gap states originating from the Ni atoms, Ti atoms, and from
their hybridized orbitals. Our experimental information about the dependence of
the valence bands, MES and in-gap states in Ni-doped SrTiO may help
development of this material towards its device applications associated with
the reduced optical band gap
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