Odivaldo Cambraia Alves

Magnetoreception in eusocial insects: an update

Behavioural experiments for magnetoreception in eusocial insects in the last decade are reviewed. Ants and bees use the geomagnetic field to orient and navigate in areas around their nests and along migratory paths. Bees show sensitivity to small changes in magnetic fields in conditioning experiments and when exiting the hive. For the first time, the magnetic properties of the nanoparticles found in eusocial insects, obtained by magnetic techniques and electron microscopy, are reviewed. Different magnetic oxide nanoparticles, ranging from superparamagnetic to multi-domain particles, were observed in all body parts, but greater relative concentrations in the abdomens and antennae of honeybees and ants have focused attention on these segments. Theoretical models for how these specific magnetosensory apparatuses function have been proposed. Neuron-rich ant antennae may be the most amenable to discovering a magnetosensor that will greatly assist research into higher order processing of magnetic information. The ferromagnetic hypothesis is believed to apply to eusocial insects, but interest in a light-sensitive mechanism is growing. The diversity of compass mechanisms in animals suggests that multiple compasses may function in insect orientation and navigation. The search for magnetic compasses will continue even after a magnetosensor is discovered in eusocial insects.

Heat denaturation of metHb and HbNO: e.p.r. evidence for the existence of a new hemichrome

Electron paramagnetic resonance was used to follow the time dependence of heat denaturation of met- and nitrosyl-haemoglobin (metHb and HbNO) at 60 degrees C, 70 degrees C and 80 degrees C. The spectral changes of both complexes indicate that conformational changes in the protein manifest themselves in changes of the equilibrium of hemichromes in metHb and of six- and five-coordinated iron in HbNO. The formation of a hemichrome which has not been described before, with g = 2.45, 2.27 and 1.85, is observed. A His-Fe-Cys complex is proposed for its structure.

Ingested and biomineralized magnetic material in the prey Neocapritermes opacus termite: FMR characterization.

The temperature dependence of Ferromagnetic Resonance spectra, from 5K to 280K, was used to study the magnetic material present in Neocapritermes opacus termite, the only prey of the Pachycondyla marginata ant. The analysis of the resonant field and peak-to-peak linewidth allowed estimating the particle diameters and the effective anisotropy energy density, K(EFF), as a sum of the bulk and surface contributions. It allowed to magnetically distinguish the particles of termites as collected in field from those of termites after 3 days under a cellulose diet, introduced to eliminate ingested/digested material. The data also, suggest the presence of oriented magnetite nanoparticles with diameters of 11.6+/-0.3nm in termites as collected in field and (14.0+/-0.4nm) in that under a cellulose diet. Differences between their K(EFF) and its components are also observed. Two transitions are revealed in the resonant field temperature dependence, one at about 50K that was associated to surface effects and the other at about 100K attributed to the Verwey transition.

Caracterização tecnológica e mineralógica dos caulins Belmiro Braga e São Miguel do Anta, Minas Gerais

The study aimed the technological and mineralogical characterization of the kaolins Belmiro Braga (BB) and Sao Miguel do Anta (SMA), through X ray diffraction (XRD), scanning electron microscopy (SEM-EDS), X ray fluorescence and electron spin resonance (ESP) as well as the physical and chemical beneficiation to eliminate the ion Fe+3 and upgrade their whiteness levels. Both kaolins are fine grained; the BB kaolin has kaolinite in its mineralogy, and the SMA kaolin has quartz. After chemical bleaching, the whiteness reached 81.0% ISO to the BB sample, and 71.2% ISO to the SMA sample.

Low temperature photolysis of denatured nitrosyl hemoproteins

Photolysis of denatured HbNO were carried out at temperatures below 26 K. The normalized kinetic curves were fitted using either two exponentials or a conformational substate energy distribution or a fractal model. The parameters are related to the protein structure. The two exponentials model assumes the existence of two fractions of photolysed molecules that rebind with slow and fast reaction rates. Only the slow reaction rate is sensitive to the denaturation process. The pre-exponential factor and the peak energy of the substate distribution values suggest an increase in the entropy and a decrease of the flexibility in the denatured samples, respectively. The fractal model parameters strengthened the functional relevance of the flexibility of the protein chain.