Effect of Al substitution on the magnetization reversal and complex magnetic properties of NiCr2O4 ceramics

A series of polycrystalline NiCr_2-xAl_xO₄ (0.1 ≤ x ≤ 0.25) spinel ceramics have been synthesized using a sol-gel method. DC magnetization measurements are carried out at different temperatures and magnetic fields. A novel magnetization reversal has been observed in the field cooling process for the x = 0.2 sample, which can be ascribed to the competition between two magnetic sublattices due to their different temperature dependences. The magnetic interaction evolution, related to the complex magnetic properties, is revealed by exchange constants that have been estimated according to ferrimagnetic Curie-Weiss fitting and mean field theory. The fitting result confirmed the evolution of antiferromagnetic and ferromagnetic components with Al substitution, which is supported by the observations from the isothermal magnetization measurements. The positive and negative values of the magnetic moment can be utilized for storage applications based on the results of magnetic switching effect measurements.

Negative magnetization, complex magnetic ordering and applications of Cr-doped Co2TiO4

Polycrystalline Co2Ti1-xCrxO4 (0 ≤ x ≤ 0.2) inverse spinel ceramics have been synthesized via a sol-gel technique. The dc magnetization measurement in the field-cooled mode shows that negative magnetization could be observed until x reaches 0.2. The exchange constants are calculated using the ferrimagnetic Curie-Weiss fitting and the mean-field theory. This reveals that the strength of the inter sublattice magnetic interaction presents a non-monotonic trend with the increase in Cr content and reaches the minimum at x = 0.1, giving rise to the highest compensation temperature in the x = 0.1 sample. The applicability of the x = 0.1 sample is investigated in light of two prominent magnetic effects: (i) the stable magnetic switching effect indicates the potential applications in magnetic switching and data storage and (ii) the coexistence of normal and inverse magnetocaloric effects suggests a potential application in a constant temperature bath at 54 K.

The crucial role of Mn spiral spin order in stabilizing the Dy–Mn exchange striction in multiferroic DyMnO3

Mn spiral spin ordering can be a prerequisite for the symmetric Dy–Mn exchange striction in DyMnO₃.

Aggregation between Xanthan and Nonyphenyloxypropyl β-Hydroxyltrimethylammonium Bromide in Aqueous Solution: MesoDyn Simulation and Binding Isotherm Measurement

The aggregation behavior of nonyphenyloxypropyl beta-hydroxyltrimethylammonium bromide (C9phNBr) and xanthan (XC) in aqueous solution was investigated by MesoDyn density functional simulation and binding isotherm measurement. The process of aggregate formation and the aggregate morphology are reported. The formation of aggregates includes three stages and the morphology of XC-C9phNBr aggregates is rodlike or ellipsoidal. The effects of temperature and XC concentration on the aggregation are analyzed. Results indicate that the formation of aggregates is an exothermic process, and their formation becomes more difficult and the formation rate decreases with increasing temperature. The formation of aggregates is also related to XC concentration, and it becomes much more difficult when the concentration of XC is higher than 20 vol %. The simulation results agree with binding isotherms of C9phNBr to XC obtained via the potentiometric titration method, which shows a typical cooperative binding between C9phNBr and XC.

Extrapyramidal motor symptoms versus striatal infarction volume after focal ischemia in mongolian gerbils

Few behavioral tests are available to evaluate extrapyramidal dysfunctions after focal cerebral ischemia in rodents, although extrapyramidal motor dysfunctions are often observed clinically in patients with cerebral infarction. We evaluated the methamphetamine (MP)-induced rotation test for the detection and quantification of extrapyramidal motor dysfunction induced by striatal infarction in gerbils after focal cerebral ischemia. Mongolian gerbils (n=79) underwent the left common carotid artery occlusion (CCAO) for 10, 15, or 20 min. Spontaneous and MP-induced rotation tests were repeated postischemia, and the results compared with the extent of ischemic tissue injury. The density of dopaminergic neurons immunostained with a tyrosine hydroxylase antibody in the substantia nigra pars compacta (SNpc) also was measured. Histological examination revealed selective neuronal death of the hippocampal cornu ammonis 1 (CA1) sector in 10-min CCAO animals, infarction confined to the striatum and hippocampal neuronal death in 15-min CCAO animals, and widespread hemispheric infarction in 20-min CCAO animals. Dopaminergic neurons in the SNpc were preserved in 10- and 15-min CCAO animals but were significantly reduced in 20-min CCAO animals. In MP-induced rotation tests, 15-min CCAO animals showed biased rotation ipsilateral to the lesioned side. Biased rotation persisted 4 weeks postischemia, and the number of rotations significantly correlated with the regional infarction volume of the striatum. Twenty-minute CCAO animals showed biased rotation contralateral to the lesioned side; rotation number was not correlated with the infarction volume. Our results show that biased rotation behavior is a sensitive parameter of the extent of striatal injury after focal cerebral ischemia provided the lesion is not extended to the ipsilateral cortex. MP-induced rotation in rodents probably coordinates with the extrapyramidal motor dysfunction after striatal infarction in patients with vascular Parkinsonism.

High-level expression of Amsacta moorei entomopoxvirus spheroidin depends on sequences within the gene

Spheroidin (SPH) is the most highly expressed gene of the entomopoxvirus isolated from Amsacta moorei (AmEPV). The level of expression of poxvirus genes is believed to be governed in large part by the promoter. Poxvirus promoters generally consist of approximately 40 bp which frequently terminate at the 3' end with a translation initiating TAAATG sequence. We have examined the requirements for high levels of SPH gene expression by constructing AmEPV recombinants containing either the SPH promoter or the late vertebrate poxvirus promoter derived from the cowpox virus A-type inclusion (ATI) gene. In addition, we have examined SPH promoter derivatives which extend beyond the 3' TAAATG to include 2 or 20 bp of the 5' coding sequence of the SPH gene. Examination of insect cells infected with these AmEPV ATI-lacZ or SPH-lacZ recombinants suggests that ATI-lacZ expression begins 12 h before and is essentially complete prior to any SPH-lacZ expression, allowing functional distinction between the ATI and SPH promoters and implying that different factors regulate the two promoters within the insect environment. SPH promoter-regulated expression is significantly enhanced within infected insect cells by including the additional 20 bp of the N-terminal SPH coding sequences as part of the promoter. However, when any of the SPH promoter constructs, including those containing the downstream sequences, were inserted into vaccinia virus, only very low levels of beta-galactosidase expression were observed. These results imply that downstream coding sequences within the SPH gene enhance SPH gene expression only within the insect environment.

[Distribution, content and action site of leucine-enkephalin in pulmonary artery wall of rat and rabbit]

Using immunohistochemical method to investigate the distribution of peptidergic fibers in the pulmonary artery wall of SD rat, L-enkephalin immunoreactive (L-ENK ir) fibers were easily demonstrated. The contents of L-ENK in pulmonary artery of rat and rabbit measured by radioimmunoassay were respectively 439.18 +/- 30.52 and 29.9 +/- 1.4 (pg/mg of wct tissue). Contraction of superfused strips of pulmonary artery of rabbit could be evoked by parameter I electric field stimulation. The response was blocked by alpha-receptor antagonist phentolamine. Alpha 2-receptor antagonist Yohimbine enhanced the response in small doses (0.06-0.12 mumol/L), while inhibited in large (3.2 mumol/L). The contraction could also be enhanced when the artery strips were preincubated with naloxone. After the alpha-receptors were blocked with phentolamine, stronger contraction could still be evoked by parameter II electric field stimulation and the response was not affected by naloxone. L-ENK had no effect on the contraction evoked by exogenous NE. The present experiments demonstrate that enkephalin presented in the pulmonary artery wall are released by electric field stimulation. Enkephalin may reduce the release of NE from sympathetic nerve endings via opioid receptors and inhibit the contraction response.

[Effects of diazepam on the rat open field behavior and high K+ induced release of monoamine neurotransmitters from brain slices]

Acute i. p injection of diazepam (3 mg/kg) significantly decreased the open field behaviors (locomotion and rearing) of rats. However, when diazepam (3 mg/kg) was given ip daily for 15 consecutive days, no depressive effect on the open field behaviors was observed. After the open field observation, rats were immediately decapitated and brain slices of cortex, hippocampus, amygdala and brain stem were stimulated by high K+ (65 mmol/L) to cause the release of noradrenaline (NA), dopamine (DA) and serotonin (5-HT). Diazepam (9 mumol/Ls) significantly depressed the release of monoamine neurotransmitters caused by high K+, which were antagonized by Ro 15-1788 (5 mumol/L) in vitro. Acute administration of diazepam (ip 3 mg/kg) also significantly depressed the release of monoamine neurotransmitters caused by high K+ from all regions observed. However, hippocampus showed tolerance to the depressive effects of diazepam on the releases of NA and DA, and amygdala only on the release of DA, caused by high K+, when given ip chronically (3 mg/kg, 15 d). Our results suggest that the depressive effect of benzodiazepines on the release caused by anxiogenic factors of catecholamine in the hippocampus, front cortex and amygdala regions may be one of the mechanisms of sedative and anxiolytic actions of benzodiazepines.

The molecular weight and thiol residues of acetyl-coenzyme A synthetase from ox heart mitochondria

1. A constant molecular weight of 57000 was obtained by gel filtration of highly purified acetyl-CoA synthetase over a 1000-fold range of enzyme concentrations. The amino acid analysis is reported. 2. With native enzyme at 20 degrees C the relatively rapid reaction of four thiol residues with p-hydroxymercuribenzoate caused an immediate inhibition reversible by either CoA or mercaptoethanol. Other substrates did not protect against this rapid inhibition. 3. The much slower reaction of the remaining four thiol residues was independent of the concentration of the mercurial, first-order with respect to enzyme, and had a large energy of activation (+136kJ/mol), suggesting that a conformation change in the protein was rate-limiting. This slow phase of the reaction was accompanied by an irreversible inactivation of the enzyme. 4. The effects of substrates on this irreversible inactivation at pH7.0 in 5 mm-MgCl(2) indicated strong binding of ATP and pyrophosphate by the enzyme (concentrations for half-maximal effects, K((1/2)), were <30mum and <10mum respectively) and weaker binding of acetyl-CoA (K((1/2)) about 1 mm), AMP (K((1/2)) about 2mm) and acetate. In the presence of acetate, MgCl(2) and p-hydroxymercuribenzoate, titration of the enzyme with ATP revealed at least two ATP binding sites/mol. 5. The experiments suggest that reaction of the thiol residues with mercurial causes loss of enzymic activity by altering the structure of the enzyme, rather than that the thiol residues play a direct role in the catalysis.