Relation between structural patterns and magnetism in small iron oxide clusters: reentrance of the magnetic moment at high oxidation ratios.

Due to quantum confinement effects, the understanding of iron oxide nanoparticles is a challenge that opens the possibility of designing nanomaterials with new capacities. In this work, we report a theoretical density functional theory study of the structural, electronic, and magnetic properties of neutral and charged iron oxide clusters FenOm0/± (n = 1-6), with m values until oxygen saturation is achieved. We determine the putative ground state configuration and low-energy structural and spin isomers. Based on the total energy differences between the obtained global minimum structure of the parent clusters and their possible fragments, we explore the fragmentation channels for cationic oxides, comparing with experiments. Our results provide fundamental insight on how the structural pattern develops upon oxidation and its connection with the magnetic couplings and net total moment. Upon addition of oxygen, electronic charge transfer from iron to oxygen is found which weakens the iron-iron bond and consequently the direct exchange coupling in Fe. The binding energy increases as the oxygen ratio increases, rising faster at low oxidation rates. When molecular oxygen adsorption starts to take place, the binding energy increases more slowly. The oxygen environment is a crucial factor related to the stabilities and to the magnetic character of iron oxides. We identified certain iron oxide clusters of special relevance in the context of magnetism due to their high stability, expected abundance and parallel magnetic couplings that cause large total magnetic moments even at high oxidation ratios.

Tuning the Magnetic Moment of Small Late 3d-Transition-Metal Oxide Clusters by Selectively Mixing the Transition-Metal Constituents.

Transition-metal oxide nanoparticles are relevant for many applications in different areas where their superparamagnetic behavior and low blocking temperature are required. However, they have low magnetic moments, which does not favor their being turned into active actuators. Here, we report a systematical study, within the framework of the density functional theory, of the possibility of promoting a high-spin state in small late-transition-metal oxide nanoparticles through alloying. We investigated all possible nanoalloys An-xBxOm (A, B = Fe, Co, Ni; n = 2, 3, 4; 0≤x≤n) with different oxidation rates, m, up to saturation. We found that the higher the concentration of Fe, the higher the absolute stability of the oxidized nanoalloy, while the higher the Ni content, the less prone to oxidation. We demonstrate that combining the stronger tendency of Co and Ni toward parallel couplings with the larger spin polarization of Fe is particularly beneficial for certain nanoalloys in order to achieve a high total magnetic moment, and its robustness against oxidation. In particular, at high oxidation rates we found that certain FeCo oxidized nanoalloys outperform both their pure counterparts, and that alloying even promotes the reentrance of magnetism in certain cases at a critical oxygen rate, close to saturation, at which the pure oxidized counterparts exhibit quenched magnetic moments.

Breakdown of magnetism in sub-nanometric Ni clusters embedded in Ag.

Downsizing to the nanoscale has opened up a spectrum of new magnetic phenomena yet to be discovered. In this context, we investigate the magnetic properties of Ni clusters embedded in a metallic Ag matrix. Unlike in Ni free-standing clusters, where the magnetic moment increases towards the atomic value when decreasing the cluster size, we show, by tuning the Ni cluster size down to the sub-nanoscale, that there is a size limit below which the clusters become non-magnetic when embedded in Ag. To this end, we have fabricated by DC-sputtering a system composed of sub-nanometer sized and non interacting Ni clusters embedded into a Ag matrix. A thorough experimental characterization by means of structural techniques (x-ray diffraction, x-ray absorption spectroscopy) and DC-magnetization confirms that the cluster size is in the sub-nanometric range and shows that the magnetization of the system is dramatically reduced, reaching only 38% of the bulk value. The experimental system has been reproduced by density functional theory calculations on Ni m clusters (m = 1-6, 10 and 13) embedded in Ag. The combination of the experimental and theoretical analysis points out that there is a breakdown of magnetism occurring below a cluster size of six atoms. According to our results, the loss of magnetic moment is not due to Ag-Ni hybridization but to charge transfer between the Ni sp and d orbitals, and the reduced magnetization observed experimentally is explained on the basis of the presence of a narrow cluster size-distribution where magnetic and non-magnetic clusters coexist.

Titanium embedded cage structure formation in Al(n)Ti+ clusters and their interaction with Ar.

Recently, Ar physisorption was used as a structural probe for the location of the Ti dopant atom in aluminium cluster cations, Al(n)Ti(+) [Lang et al., J. Am. Soc. Mass Spectrom. 22, 1508 (2011)]. As an experiment result, the lack of Ar complexes for n > nc determines the cluster size for which the Ti atom is located inside of an Al cage. To elucidate the decisive factors for the formation of endohedrally Al(n)Ti(+), experimentalists proposed detailed computational studies as indispensable. In this work, we investigated, using the density functional theory, the structural and electronic properties of singly titanium doped cationic clusters, Al(n)Ti(+) (n = 16-21) as well as the adsorption of an Ar atom on them. The first endohedral doped cluster, with Ti encapsulated in a fcc-like cage skeleton, appears at nc = 21, which is the critical number consistent with the exohedral-endohedral transition experimentally observed. At this critical size the non-crystalline icosahedral growth pattern, related to the pure aluminium clusters, with the Ti atom in the surface, changes into a endohedral fcc-like pattern. The map of structural isomers, relative energy differences, second energy differences, and structural parameters were determined and analyzed. Moreover, we show the critical size depends on the net charge of the cluster, being different for the cationic clusters (nc = 21) and their neutral counterparts (nc = 20). For the Al(n)Ti(+) · Ar complexes, and for n < 21, the preferred Ar adsorption site is on top of the exohedral Ti atom, with adsorption energy in very good agreement with the experimental value. Instead, for n = 21, the Ar adsorption occurs on the top an Al atom with very low absorption energy. For all sizes the geometry of the Al(n)Ti(+) clusters keeps unaltered in the Ar-cluster complexes. This fact indicates that Ar adsorption does not influence the cluster structure, providing support to the experimental technique used. For nc = 21, the smallest size of endohedral Ti doped cationic clusters, the Ar binding energy decreases drastically, whereas the Ar-cluster distance increases substantially, point to Ar physisorption, as assumed by the experimentalists. Calculated Ar adsorption energies agree well with available experimental binding energies.

Structural, electronic, and magnetic properties Of Co(n)Cu(m) nanoalloys (m + n = 12) from first principles calculations.

Using the generalized gradient approximation (GGA) to density functional theory (DFT), we compute the electronic structure and related magnetic properties of free-standing Co(12-x)Cu(x) clusters (x = 0-12) with structures resulting from the optimization of those of the low-lying energy isomers of pure Co(12) and Cu(12) in which Co(Cu) were replaced by Cu(Co) atoms. Structural transitions for the lowest energy homotop are obtained as a function of the concentration, but in all cases, a clear surface segregation of Cu is found in the low concentration regime x < 5. The binding energy decreases monotonically when x increases. The dipole moment changes abruptly from 0.06 D for x = 2 to 0.59 D for x = 3 in coincidence with a structural change. The electronegativity of the lowest energy homotop exhibits minimum (maximum) value for x = 11 (x = 9). The x = 5, 9 clusters show local maxima of the hardness, of the excess energy, and of the second difference in energy, clear indicators of specially stable stoichiometries. The magnetic behavior of Co(12-x)Cu(x) is a monotonous function of the Co concentration, decreasing by steps of ≥2 µ(B) for every Co atom that is replaced by Cu, although for certain concentrations, different spin isomers, sometimes accompanied by structural transitions, are found close to the ground state. Ferromagnetic-like order is obtained as the ground state in all cases, contrary with the trend found in binary clusters of the same elements by other authors who predicted antiferromagnetic order. We analyze in detail the possible spin excitations in Co(12)Cu to demonstrate that local antiferromagnetic couplings can only exist as metastable spin states.

Ab initio study of the adsorption of NO on the Rh6(+) cluster.

The process of NO adsorption on the cationic cluster Rh(6)(+) is investigated using the density-functional theory (DFT) with the generalized gradient approximation (GGA) to exchange and correlation. We determine the geometries, electronic structure, and relevant energies for different structural and spin isomers of Rh(6)(0,±), and we study the consecutive adsorption of two NO molecules on the cationic cluster Rh(6)(+). With regard to the first NO molecule, different adsorption energies are found for the ground state octahedral structure of the bare cationic cluster and for the first isomer, which, having a prism-type structure, undergoes a structural transition to an octahedral symmetry upon dissociative adsorption of NO. Several dissociative NO adsorption processes are analyzed in comparison with molecular adsorption of NO to give support to the first step of the reaction inferred from experiments. With regard to the adsorption of a second NO molecule, the intermediate with lowest energy contains a preformed N(2) molecule. The energy of that complex is about 0.7 eV smaller than the sum of the free N(2) energy plus the lowest energy of the Rh(6)(+)-O(2) complex. This complex is composed of two separated O atoms occupying adjacent 2-fold bridging positions of the nearly undistorted Rh(6)(+) octahedral cluster. These findings are in qualitative agreement with experiments.

Diprosopia em bovino / Bovine diprosopus

This work describes a malformation in one newborn female bovine, with two faces and two skull fused, showing one single head. Duplications of the nasal and oral structures, tetraofthalmy, two brains, one single cerebellum, and pons were observed. The right thyroid was hypertrophic and the other organs had normal morphology. Every change observed in this case was compatibles with diprosopus.

Effects of a homeopathic complex in Nile tilapia (Oreochromis niloticus L.) on performance, sexual proportion and histology.

This study aimed to evaluate the effects of the homeopathic complex Homeopatila RS (REAL Homeopathy, Brazil), in the performance, sexual proportion and gills and liver histology of the Nile tilapia fish (Oreochromis niloticus L.). 4,800 post-larvae were treated for 45 days, in 12 tanks (500 L), in a closed environment, with density of 400 larvae per tank. Three treatments were given: alcohol 30%, negative control (C); hormonal, positive control, 17 alpha-methyltestosterone (H); homeopathic, Homeopatila RS, in ethanol (HH), with four replications. Mean values for length, weight, liver somatic index, condition factor, survival rate, average values of histological alterations and sexual proportion were determined. Analysis revealed significant differences (p<0.05) in growth, survival rate, liver somatic index and average values of hepatic histological alterations between treatments. It was concluded that the addition of Homeopatila RS to the diet of Nile tilapias, during the phase of gonadal differentiation, did not induce any alteration in the sexual proportion. Homeopathically treated fish were significantly smaller, but had significantly greater survival than the other two groups, there was no significant difference in final total biomass. The homeopathically treated fish had a lower liver/somatic index with less hepatic lipid inclusions than the other groups.

Comparison of tacrolimus with microemulsion cyclosporine as primary immunosuppression in hepatitis C patients after liver transplantation.

BACKGROUND: Immunosuppression in patients with hepatitis C virus (HCV) following orthotopic liver transplantation can lead to significant increases in serum viral loads. Our aim was to analyze the effect of a randomized study of two immunosuppressive agents (tacrolimus vs. microemulsion cyclosporine) on the outcome of HCV patients following orthotopic liver transplantation. METHODS: From December 1995 to September 1996, 50 adult patients transplanted for HCV cirrhosis were randomly assigned to receive tacrolimus (Prograf) (group 1, 25 patients) or microemulsion cyclosporine (Neoral) (group 2, 24 patients). All patients received alpha-interferon after transplantation, and the overall steroid doses were no different between the groups. Serum RNA levels were measured by signal amplification of Chiron. Biopsies were taken when transaminases were greater than 2x base line or when there was an inappropriate response to alterations in immunosuppression regimens. RESULTS: There were more episodes of rejection in the Neoral group, but there were no differences in bacterial and viral infections, nor in the rate of HCV recurrence between the two groups. There were seven deaths in group 1 and eight in group 2. Overall patient and graft survival rates in the Prograf and Neoral groups at 18 months were 72 and 68% and 67 and 64%, respectively. CONCLUSIONS: (a) Both immunosuppression regimens had similar HCV recurrence rates; (b) there were no differences in bacterial or opportunistic infections; and (c) patient and graft survival was similar between the two groups.

Redroot pigweed (Amaranthus retroflexus) poisoning of cattle in southern Brazil.

Two outbreaks of Amaranthus retroflexus (redroot pigweed) poisoning occurring in cattle in southern Brazil in late summer and early autumn are described. In both instances too many cattle were held in small paddocks heavily invaded by A retroflexus in its seeding stage. In 1 herd 8/28 heifers and in the other 15/45 adult cows died. Clinical courses ranged from 3 to 7 d. Clinical signs included depression, loss of weight, mild serous nasal discharge, foul smelling liquid feces tinged with blood, subcutaneous dependent edema, and laborious and incoordinated walking. Main necropsy findings were subcutaneous, cavitary and perirenal edemas, renal subcapsular hematomas, and ulcerative lesions in the alimentary tract. The kidneys were swollen and pale. Histopathological findings were in the kidneys and consisted of tubular degeneration, necrosis and regeneration with interstitial fibrosis and tubular proteinosis.

A sandwich ELISA based on anti-apo(a) and anti-apo B monoclonal antibodies for lipoprotein(a) measurement.

Lipoprotein(a) (Lp(a)) is one of the most important independent risk factors for the prediction of premature atherosclerosis. Lp(a) is a low-density lipoprotein (LDL)-like particle which contains a glycoprotein (apoprotein(a)) disulfide linked to apo B-100. We describe a sandwich ELISA based on an anti-apo(a) monoclonal antibody (MAb) and an anti-apo B MAb for the quantitative determination of Lp(a) in human serum. The assay is sensitive, precise and specific. Samples with different apo(a) isoforms had a linear response in a range of 3-70 mg/dl of Lp(a). Correlations between the ELISA and a commercial ELISA, an immunoradiometric assay and electroimmunodiffusion were 0.92, 0.96 and 0.98, respectively. The frequency distribution of Lp(a) concentration in blood donors showed the skew toward the right reported in other populations. Patients with angiographically assessed coronary atherosclerosis had three times higher levels of Lp(a) than those with no signs of coronary atherosclerosis.

Anticuerpos monoclonales para la cuantificación de apolipoproteína A1 / Monoclonal antibodies for quantitation of apolipoprotein A1

Se describe la producción de anticuerpos monoclonales (AcMs) de ratón contra la apolipoproteína A1 (APO A1), a partir de la inmunización de ratones BALB/c con APO A1 purificada de plasma humano. Los anticuerpos obtenidos son de la clase IgG1 y fueron purificados a partir de líquido ascítico mediante cromatografía de afinidad con Proteína A Sepharosa. Dos de ellos, que reconocen sitios diferentes de la molécula de APO A1 en muestras de suero. Los coeficientes de variación intra e interensayo fueron de 3,4 y 10 % respectivamente. Con este sistema se detectaron niveles disminuídos de APO A1 en pacientes con infarto agudo del miocardio entre 45 y 80 años, y en grupo con aterosclerosis periférica entre 40 y 49 años, con relación a sujetos controles de igual rango de edad. En los pacientes con aterosclerosis periférica de mayor edad (entre 60 y 80 años), aunque se encontraron valores de APO A1 más bajos que el grupo control respectivo, esta diferencia no fue estadísticamente significativa