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.

Magnetic material in head, thorax, and abdomen of Solenopsis substituta ants: a ferromagnetic resonance study.

Ferromagnetic resonance temperature dependence is used to study the magnetic material in smashed head, thorax, and abdomen of Solenopsis substituta ants. These three body parts present the five lines previously observed in other social insects. The magnetic material content is slightly higher in heads with antennae than in abdomen with petiole. Isolated nanoparticle diameters were estimated as 12.5 +/- 0.1 and 11.0 +/- 0.2 nm in abdomen with petiole and head with antennae, respectively. The presence of linear chains of these particles or large ellipsoidal particles are suggested. A bulk-like magnetite particle was observed in the thorax. The Curie-Weiss, the structural-electronic and ordering transition temperatures were obtained in good agreement with those proposed for magnetite nanoparticles.

Magnetic material arrangement in oriented termites: a magnetic resonance study.

Temperature dependence of the magnetic resonance is used to study the magnetic material in oriented Neocapritermes opacus (N.o.) termite, the only prey of the migratory ant Pachycondyla marginata (P.m.). A broad line in the g = 2 region, associated to isolated nanoparticles shows that at least 97% of the magnetic material is in the termite's body (abdomen + thorax). From the temperature dependence of the resonant field and from the spectral linewidths, we estimate the existence of magnetic nanoparticles 18.5+/-0.3 nm in diameter and an effective magnetic anisotropy constant, K(eff) between 2.1 and 3.2 x 10(4)erg/cm(3). A sudden change in the double integrated spectra at about 100K for N.o. with the long body axis oriented perpendicular to the magnetic field can be attributed to the Verwey transition, and suggests an organized film-like particle system.

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.

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.

Nitrosyl hemoglobins: EPR above 80 K.

The EPR spectra of nitrosyl hemoglobin and myoglobin in different conditions (native, denatured and lyophilized), as well as of hematin-NO were obtained in the temperature range of 80-280 K. There is a substantial and reversible decrease of the areas of the EPR spectra of all the hemoglobin samples above 150 K. The interpretation of the results implies the existence of two conformational states in thermal equilibrium, only one of which is EPR detectable. Thermodynamical parameters are determined for the hexa- and penta-coordinated cases.

Spin-lattice relaxation of denatured nitrosyl hemoproteins.

The temperature dependence of the spin-lattice relaxation of denatured nitrosyl hemoglobin (HbNO), nitrosyl myoglobin, powdered HbNO, and hematin-NO was studied between 4 and 70 K. The results were fitted with both Tn and e-delta/tau models. In the first model, the relaxation is mediated by tunneling modes of a two-level system. A correlation between the n values and the functional state of the protein was observed. The striking coincidence of the range of the low-lying energy level and the temperature range where EPR spectra change suggests the existence of two conformations of the bound heme. The importance of the presence and structure of the globin is revealed in the difference between relaxation parameters of native proteins, denatured proteins, and hematin.