Synthesis, characterization and effects of citric acid and PVA on magnetic properties of CoFe2O4

Cobalt ferrite (CoFe2O4) particles were synthesized by sol-gel method using metal nitrates, citric acid (CA) and polyvinyl alcohol (PVA). X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), thermogravimetry/differential scanning calorimetry analysis and vibrating sample magnetometer were used to study the structural, thermal and magnetic properties of the CoFe2O4 powder. XRD results indicate that the resultant particles have crystalline, pure single phase spinel structure. From HR-SEM images, a systematic decrease in particle size is observed with an increase in PVA concentration, along with addition of CA. CA at various concentrations of PVA significantly enhance the magnetic properties of the materials

Structure, Dynamics, and Branch Migration of a DNA Holliday Junction: A Single-Molecule Fluorescence and Modeling Study

AbstractThe Holliday junction (HJ) is a central intermediate of various genetic processes, including homologous and site-specific DNA recombination and DNA replication. Elucidating the structure and dynamics of HJs provides the basis for understanding the molecular mechanisms of these genetic processes. Our previous single-molecule fluorescence studies led to a model according to which branch migration is a stepwise process consisting of consecutive migration and folding steps. These data led us to the conclusion that one hop can be more than 1 basepair (bp); moreover, we hypothesized that continuous runs over the entire sequence homology (5 bp) can occur. Direct measurements of the dependence of the fluorescence resonance energy transfer (FRET) value on the donor-acceptor (D-A) distance are required to justify this model and are the major goal of this article. To accomplish this goal, we performed single-molecule FRET experiments with a set of six immobile HJ molecules with varying numbers of bps between fluorescent dyes placed on opposite arms. The designs were made in such a way that the distances between the donor and acceptor were equal to the distances between the dyes formed upon 1-bp migration hops of a HJ having 10-bp homology. Using these designs, we confirmed our previous hypothesis that the migration of the junction can be measured with bp accuracy. Moreover, the FRET values determined for each acceptor-donor separation corresponded very well to the values for the steps on the FRET time trajectories, suggesting that each step corresponds to the migration of the branch at a defined depth. We used the dependence of the FRET value on the D-A distance to measure directly the size for each step on the FRET time trajectories. These data showed that one hop is not necessarily 1 bp. The junction is able to migrate over several bps, detected as one hop and confirming our model. The D-A distances extracted from the FRET properties of the immobile junctions formed the basis for modeling the HJ structures. The composite data fit a partially opened, side-by-side model with adjacent double-helical arms slightly kinked at the four-way junction and the junction as a whole adopting a global X-shaped form that mimics the coaxially stacked-X structure implicated in previous solution studies

The J-elongated conformation of β2-glycoprotein I predominates in solution: implications for our understanding of antiphospholipid syndrome

β2-Glycoprotein I (β2GPI) is an abundant plasma protein displaying phospholipid-binding properties. Because it binds phospholipids, it is a target of antiphospholipid antibodies (aPLs) in antiphospholipid syndrome (APS), a life-threatening autoimmune thrombotic disease. Indeed, aPLs prefer membrane-bound β2GPI to that in solution. β2GPI exists in two almost equally populated redox states: oxidized, in which all the disulfide bonds are formed, and reduced, in which one or more disulfide bonds are broken. Furthermore, β2GPI can adopt multiple conformations (i.e. J-elongated, S-twisted, and O-circular). While strong evidence indicates that the J-form is the structure bound to aPLs, which conformation exists and predominates in solution remains controversial, and so is the conformational pathway leading to the bound state. Here, we report that human recombinant β2GPI purified under native conditions is oxidized. Moreover, under physiological pH and salt concentrations, this oxidized form adopts a J-elongated, flexible conformation, not circular or twisted, in which the N-terminal domain I (DI) and the C-terminal domain V (DV) are exposed to the solvent. Consistent with this model, binding kinetics and mutagenesis experiments revealed that in solution the J-form interacts with negatively charged liposomes and with MBB2, a monoclonal anti-DI antibody that recapitulates most of the features of pathogenic aPLs. We conclude that the preferential binding of aPLs to phospholipid-bound β2GPI arises from the ability of its preexisting J-form to accumulate on the membranes, thereby offering an ideal environment for aPL binding. We propose that targeting the J-form of β2GPI provides a strategy to block pathogenic aPLs in APS

Experimental Analysis and Quasi-Static Numerical Idealization of Dynamic Stresses on a Heavy Truck Chassis Frame Assembly

Abstract. The current trend in automotive design is to optimize components for weight. To achieve this, automotive designers need to have complete understanding of various stresses prevalent in different areas of the component. The chassis frame assembly of a heavy truck used for long distance goods hauling application is chosen for this investigation and dynamic stress-strain response of the component due to braking and cornering maneuvers are experimentally measured and reported. A quasi-static approach that approximates the dynamic maneuvers into number of small processes having static equilibriums is followed to carry out the numerical simulation, approximating the dynamic behavior of frame rail assembly during cornering and braking. With the help of commercial finite element package ANSYS, the quasi-static numerical simulations are carried out and compared with experimental results. This study helps in understanding prevailing stresses in truck frame rails especially during cornering and braking maneuvers and brings out all geometric locations that may be potential failure initiation locations. This study makes a case for further investigation on the effects of residual and assembly stresses on frame rails

Risk factors of tuberculosis (TB) among homeless population in Chennai city

Background: Tuberculosis (TB) is a major concern among high-risk populations such as the homeless. Tuberculosis (TB) is a major public health problem. The Chennai City has a large population of homeless persons and caregivers and is estimated to be the largest TB-endemic area in the intermediate-prevalence country, India. However, there have been few studies of homeless persons and caregivers. The objective of this study to assess the prevalence and risk factors for pulmonary TB among homeless population around Chennai. Methods: We conducted a cross-sectional study for screening TB symptoms using questionnaire. The study participants were recruited from 15 zones, which included 47-night shelters around Chennai under the control of the Chennai City in Tamil Nadu. Data was collected from homeless people who were living in night shelters in the northern, central, and southern regions of Chennai City. Results: Complete responses were available from 484 individuals (263 homeless persons and 173 caregivers). Four active TB cases (1.5%) among homeless persons were found, while there were no cases among caregivers

The J-elongated conformation of b2-glycoprotein I predominates in solution: implications for our understanding of antiphospholipid syndrome

b2-Glycoprotein I (b2GPI) is an abundant plasma protein displaying phospholipid-binding properties. Because it binds phospholipids, it is a target of antiphospholipid antibodies (aPLs) in antiphospholipid syndrome (APS), a life-threatening autoimmune thrombotic disease. Indeed, aPLs prefer membrane-bound b2GPI to that in solution. b2GPI exists in two almost equally populated redox states: oxidized, in which all the disulfide bonds are formed, and reduced, in which one or more disulfide bonds are broken. Furthermore, b2GPI can adopt multiple conformations (i.e. J-elongated, S-twisted, and O-circular). While strong evidence indicates that the J-form is the structure bound to aPLs, which conformation exists and predominates in solution remains controversial, and so is the conformational pathway leading to the bound state. Here, we report that human recombinant b2GPI purified under native conditions is oxidized. Moreover, under physiological pH and salt concentrations, this oxidized form adopts a J-elongated, flexible conformation, not circular or twisted, in which the N-terminal domain I (DI) and the C-terminal domain V (DV) are exposed to the solvent. Consistent with this model, binding kinetics and mutagenesis experiments revealed that in solution the J-form interacts with negatively charged liposomes and with MBB2, a monoclonal anti-DI antibody that recapitulates most of the features of pathogenic aPLs. We conclude that the preferential binding of aPLs to phospholipid-bound b2GPI arises from the ability of its preexisting J-form to accumulate on the membranes, thereby offering an ideal environment for aPL binding. We propose that targeting the J-form of b2GPI provides a strategy to block pathogenic aPLs in APS