Influence of Cooling Rate on the Enthalpy Relaxation and Fragility of a Metallic Glass

Structural relaxation behavior of a rapidly quenched (RQ) and a slowly cooled Pd40Cu30Ni10P20 metallic glass was investigated and compared. Differential scanning calorimetry was employed to monitor the relaxation enthalpies at the glass transition temperature, T-g , and the Kolrausch-Williams-Watts (KWW) stretched exponential function was used to describe its variation with annealing time. It was found that the rate of enthalpy recovery is higher in the ribbon, implying that the bulk is more resistant to relaxation at low temperatures of annealing. This was attributed to the possibility of cooling rate affecting the locations where the glasses get trapped within the potential energy landscape. The RQ process traps a larger amount of free volume, resulting in higher fragility, and in turn relaxes at the slightest thermal excitation (annealing). The slowly cooled bulk metallic glass (BMG), on the other hand, entraps lower free volume and has more short-range ordering, hence requiring a large amount of perturbation to access lower energy basins.

Multiple conformational states in crystals and in solution in alpha gamma hybrid peptides. Fragility of the C-12 helix in short sequences

The conformational properties of foldamers generated from alpha gamma hybrid peptide sequences have been probed in the model sequence Boc-Aib-Gpn-Aib-Gpn-NHMe. The choice of alpha-aminoisobutyryl (Aib) and gabapentin (Gpn) residues greatly restricts sterically accessible coil formational space. This model sequence was anticipated to be a short segment of the alpha gamma C-12 helix, stabilized by three successive 4 -> 1 hydrogen bonds, corresponding to a backbone-expanded analogue of the alpha polypeptide 3(10)-helix. Unexpectedly, three distinct crystalline polymorphs were characterized in the solid state by X-ray diffraction. In one form, two successive C-12 hydrogen bonds were obtained at the N-terminus, while a novel C-17 hydrogen-bonded gamma alpha gamma turn was observed at the C-terminus. In the other two polymorphs, isolated C-9 and C-7 hydrogen-bonded turns were observed at Gpn (2) and Gpn (4). Isolated C-12 and C-9 turns were also crystallographically established in the peptides Boc-Aib-Gpn-Aib-OMe and Boc-Gpn-Aib-NHMe, respectively. Selective line broadening of NH resonances and the observation of medium range NH(i)<-> NH(i+2) NOEs established the presence of conformational heterogeneity for the tetrapeptide in CDCl3 solution. The NMR results are consistent with the limited population of the continuous C-12 helix conformation. Lengthening of the (alpha gamma)(n) sequences in the nonapeptides Boc-Aib-Gpn-Aib-Gpn-Aib-Gpn-Aib-Gpn-Xxx (Xxx = Aib, Leu) resulted in the observation of all of the sequential NOEs characteristic of an alpha gamma C-12 helix. These results establish that conformational fragility is manifested in short hybrid alpha gamma sequences despite the choice of conformationally constrained residues, while stable helices are formed on chain extension.

Acute toxicity of methyl isocyanate in rabbit: In vitro and in vivo effects on rabbit erythrocyte membrane

Methyl isocyanate (MIC) interaction with the rabbit erythrocyte membrane increased the fluidity of the membrane and decreased the osmotic fragility of erythrocytes both in vitro and in vivo in rabbits intoxicated with MIC subcutaneously. MIC inhibited both acetylcholinesterase (AChE) and adenosine triphosphatase (ATPase) activities of erythrocytes dose-dependently in vitro, while in vivo a decreased trend in ATPase activity with unaltered AChE activity was observed. MIC also caused significant decrease in plasma sodium level with corresponding increase in potassium level in rabbits. The observed effects are due to MIC, per se, as the hydrolysis products of MIC, methylamine and N,Nprime-dimethylurea did not affect the erythrocyte fluidity and enzymes activities both in vitro and in vivo while they increased the osmotic fragility of erythrocytes in vivo in rabbits administered subcutaneously in equimolar concentration to MIC dosage. Inhibition of Na+-K+-dependent ATPase with altered permeability to cations and also probably water transport of plasma membrane due to MIC interaction are envisaged.

Bufferless lysis of erythrocytes for isolation of hemoglobin using modified cellulose acetate membranes

This paper presents a modified cellulose acetate membrane prepared using a dry casting technique that can be used to perform lysis of erythrocytes and isolation of hemoglobin. Isolation of hemoglobin is thus achieved without the use of lysis buffers. Cellulose acetate (CA) membranes are embedded with ammonium chloride (NH4Cl) and potassium bicarbonate (KHCO3), which act as lysing agents. The presence of embedded salts is confirmed using EDS analysis. The pores in the CA membrane act as filters. The average pore size in these membranes is designed to be 1.5 mu M, as characterized by SEM analysis, so that they allow hemoglobin to pass through and block all other cells and unlysed erythrocytes present in blood. When a drop of blood is added to the membrane, the NH4Cl and KHCO3 embedded in the membrane dissolve in plasma and lyse the erythrocytes. The filtered hemoglobin is characterized using UV-Vis Spectroscopy. The results indicate extraction of higher concentration of hemoglobin compared with conventional methods.

Capillary Electrophoresis of Erythrocytes.

Capillary electrophoresis (CE) of erythrocytes from different sources under various conditions is reported in this paper. It was found that erythrocyte samples from sheep, duck, and human showed characteristic and reproducible elution peaks, and that the retention times of A-, B-, AB-, and O-type erythrocytes from human blood were distinctively different; even subtle differences, among individuals with the same blood type could be detected by CE. A strictly linear correlation was obtained between the peak area and the amount of human erythrocyte over a range of 4.8×102–1.9×104 cells (r=0.999), indicating that CE could be used for rapid and accurate quantification of erythrocytes. Using this CE protocol, the decrease of the surface electrical charge of erythrocyte during storage was confirmed. Therefore, this work demonstrated that CE could be a useful alternative for characterizing and quantifying erythrocytes or other cells.

Fragility of information cascades: an experimental study using elicited beliefs

This paper examines the occurrence and fragility of information cascades in two laboratory experiments. One group of low informed participants sequentially guess which of two states has been randomly chosen. In a matched pairs design, another group of high informed participants make similar guesses after having observed the guesses of the low informed participants. In the second experiment, participants' beliefs about the chosen state are elicited. In equilibrium, low informed players who observe an established pattern of identical guesses herd without regard to their private information whereas high informed players always guess according to their private information. Equilibrium behavior implies that information cascades emerge in the group of low informed participants, the belief based solely on cascade guesses is stationary, and information cascades are systematically broken by high informed participants endowed with private information contradicting the cascade guesses. Experimental results show that the behavior of low informed participants is qualitatively in line with the equilibrium prediction. Information cascades often emerge in our experiments. The tendency of low informed participants to engage in cascade behavior increases with the number of identical guesses. Our main finding is that information cascades are not fragile. The behavior of high informed participants differs markedly from the equilibrium prediction. Only one-third of laboratory cascades are broken by high informed participants endowed with private information contradicting the cascade guesses. The relative frequency of cascade breaks is 15% for the situations where five or more identical guesses are observed. Participants' elicited beliefs are strongly consistent with their own behavior and show that, unlike in equilibrium, the more cascade guesses participants observe the more they believe in the state favored by those guesses.

Fragility of the spin-glass-like collective state to a magnetic field in an interacting Fe-C nanoparticle system

The effect of applied magnetic fields on the collective nonequilibrium dynamics of a strongly interacting Fe-C nanoparticle system has been investigated. It is experimentally shown that the magnetic aging diminishes to finally disappear for fields of moderate strength. The field needed to remove the observable aging behavior increases with decreasing temperature. The same qualitative behavior is observed in an amorphous metallic spin glass (Fe0.15Ni0.85)(75)P16B6Al3.

5-Lipoxygenase plays a role in the control of parasite burden and contributes to oxidative damage of erythrocytes in murine Chagas` disease

Chagas` disease is accompanied by severe anemia and oxidative stress, which may contribute to mortality. In this study, we investigated the role of 5-lipoxygenase (5-LO) in the control of parasitism and anemia associated with oxidative damage of erythrocytes in experimental Trypanosoma cruzi infection. Wild-type C57BL/6, 129Sv mice treated or not with nordihydroguaiaretic acid (NDGA, 5-LO inhibitor), mice lacking the 5-LO enzyme gene (5-LO(-/-)) and inducible nitric oxide synthase gene (iNOS(-/-)) were infected with the Y strain of T cruzi. impairment of 5-LO resulted in increased numbers of trypomastigote forms in the blood and amastigote forms in the heart of infected mice. We assessed oxidative stress in erythrocytes by measuring oxygen uptake, induction time and chemiluminescence following treatment with tert-butyl hydroperoxide (TBH). Our results show that 5-LO metabolites increased lipid peroxidation levels in erythrocytes during the early phase of murine T cruzi infection. NDGA treatment reduced oxidative damage of erythrocytes in C57BL/6 T cruzi-infected mice but not in C57BL/6 iNOS-/- infected mice, showing that the action of NDGA is dependent on endogenous nitric oxide (NO). In addition, our results show that 5-LO metabolites do not participate directly in the development of anemia in infected mice. We conclude that 5-LO products may not only play a major role in controlling heart tissue parasitism, i.e., host resistance to acute infection with T cruzi in vivo, but in the event of an infection also play an important part in erythrocyte oxidative stress, an NO-dependent effect. (C) 2009 Elsevier B.V. All rights reserved.

High gradient magnetic separation (HGMS) of erythrocytes infected with plasmodium falciparum

This thesis was undertaken to explore possible applications of high gradient magnetic separation (HGMS) for the separation of RBCs infected with Plasmodium falciparum, with the dual aim of establishing a novel and superior method for isolating late-stage infected cells, and of obtaining synchronized cell cultures.rnThe presented work presents protocols for HGMS of parasitized RBCs that fulfil these aims. Late-stage parasitized cell can be isolated essentially devoid of contamination with non-infected and ring-stage infected cells. Such an easy method for a highly quantitative and qualitative purification has not yet been reported. Synchronous cultures can be obtained both following depletion of late-stage infected cells, and following isolation of the latter. The quality of synchronization cultures matches that of sorbitol lysis, the current standard method for malaria culture synchronization. An advantage of HGMS is the avoidance of osmotic stress for RBCs. The new methods further have the appeal of high reproducibility, cost-effectiveness, and simple protocol.rnIt should be possible to take the methods beyond Plasmodium infected RBCs. Most magnetic separation techniques in the sector of biomedical research employ columns with a hydrophilic polymer-coated matrix. Our procedure employs an optimized buffer system. Polymer coating becomes unnecessary and uncoated columns are available at a fraction of the cost.

ALTERNATING CURRENT DIELECTROPHORETIC MANIPULATION OF ERYTHROCYTES IN MEDICAL MICRODEVICE TECHNOLOGY

Medical microdevices have gained popularity in the past few decades because they allow the medical laboratory to be taken out into the field and for disease diagnostics to happen with a smaller sample volume, at a lower cost and much faster. Blood is the human body's most readily available and informative diagnostic fluid because of the wealth of information it provides about the body's general health including enzymatic, proteomic and immunological states. The purpose of this project is to optimize operating conditions and study ABO-Rh erythrocytes dielectrophoretic responses to alternating current electric signals. The end goal of this project is the creation of a relatively inexpensive microfluidic device, which can be used for the ABO-Rh typing of a blood sample. This dissertation presents results showing how blood samples of a known ABO- Rh blood type exhibit differing behavior to the same electrical stimulus based on their blood type. The first panel of donors and experiments, presented in Chapter 4 occurred when a sample of known blood type was injected into a microdevice with a T-shaped electrode configuration and the erythorcytes were found to rupture at a rate specific to their ABO-Rh blood type. The second set of experiments, presented in Chapter 5, were originally published in Electrophoresis in 20111. Novel in this work was the discovery that treatment of human erythrocytes with β-galactosidase successfully removed ABO surface antigens such that native A and B blood no longer agglutinated with the proper antibodies. This work was performed in a medium of conductivity 0.9S/m which is close to the measured conductivity of pooled plasma (~1.1S/m). The ability to perform dielectrophoresis experiments at physiological conductivities conditions is advantageous for future portable devices because the device/instrument would not need to store dilution buffers. The final results of this project, presented in Chapter 6, explore the entire dielectrophoretic spectra of the ABO-Rh erythrocytes including the cross-over frequency and the magnitudes of the positive or negative dielectrophoretic response. These were completed at lower medium conductivities of 0.1S/m and 0.01-0.04S/m. These results show that by using the sweep function built into the Agilent alternating current generator it is possible to explore how a single group of blood cells will react to rapid changes in frequency and will provide the user with curve that can be matched the theoretical dielectrophoretic response curves. As a whole this project shows that it is possible to distinguish human erythrocytes by their ABO-Rh blood type via three different dielectrophoretic methods. This work builds on the foundation of that it is possible to distinguish healthy from infected cells2-7, similar cell types1,7-14 and other work regarding the dielectrophoresis of human erythrocytes1,10,11. This work has implications in both medical diagnostics and future dielectrophoretic work because it has shown that ABO-Rh blood type is now a factor, which must be identified when working with a human blood sample. It also shows that the creation of a microfluidic device that subjects human erythrocytes to a dielectrophoretic impulse and then exports an ABO-Rh blood type is a near future possibility.

The fragility of two monetary regimes: The European Monetary System and the Eurozone. National Bank of Belgium Working Paper No. 243, October 2013

The purpose of these working papers is to promote the circulation of research results (Research Series) and analytical studies (Documents Series) made within the National Bank of Belgium or presented by external economists in seminars, conferences and conventions organised by the Bank. The aim is therefore to provide a platform for discussion. The opinions expressed are strictly those of the authors and do not necessarily reflect the views of the National Bank of Belgium.

Hereditary fragility of bone (fragilitas osseus, osteopsathyrosis)

Mode of access: Internet.

Mechanisms involved in the swelling of erythrocytes caused by Pacific and Caribbean ciguatoxins

The mechanisms underlying the swelling of frog red blood cells (RBC), induced by Pacific (P-CTX-1) and Caribbean (C-CTX-1) ciguatoxins (CTXs), were investigated by measuring the length, width and surface of their elliptic shape. P-CTX-1 (0.5 to 5 nM) and C-CTX-1 (1 mu M) induced RBC swelling within 60 min. The CTXs-induced RBC swelling was blocked by apamin (1 mu M) and by Sr2+ (1 mu M). P-CTX-1-induced RBC swelling was prevented and inhibited by H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one(27 mu M), an inhibitor Of Soluble guanylate cyclase (sGC), and NOS blockade by NG methyl-L-arginine (L-NMA; 10 mu M). Cytochalasin D (cytD, 10 mu M) increased RBC surface and mimicked CTX effect but did not prevent the P-CTX-1-induced L-NMA-sensitive extra increase. Calculations revealed that P-CTX-1 and cytD increase RBC total surface envelop and volume. These data strongly suggest that the molecular mechanisms underlying CTXs-induced RBC swelling involve the NO pathway by an activation of the inducible NOS, leading to sGC activation which modulates intracellular cGMP and regulates L-type Ca2+ channels. The resulting increase in intracellular Ca2+ content, in turn, disrupts the actin cytoskeleton, which causes a water influx and triggers a Ca2+-activated K+ current through SK2 isoform channels. (c) 2005 Elsevier Inc. All rights reserved.

An investigation of the effects of antitumour and other drugs on cell morphology and the cytoskeleton of erythrocytes

Human arythrocytes were used as a model system for an investigation of the mechanism of action of the antiproliferative drug Adriamycin. Erythrocytes were induced to undergo a change in morphology by elevation of intracellular calcium. It was revealed that the widely used media employed for the study of morphological change were unsuitable; a new incubation medium was developed so that cells were metabolically replete. In this medium echinocytosis took place both in a calcium concentration- and time-dependent manner. Pretreatment of erythrocytes with Adriamycin (10 M for 10 mins) protected the erythrocytes against calcium-induced echinocytosis at calcium concentrations < 150M. SDS-PAGE analysis of the cytoskeletal proteins prepared from erythrocytes revealed the calcium-induced proteolysis of two main cytoskeletal proteins: band 2:1 and band 4:1. Only the rate of the proteolysis of band 2.1 correlated with the onset of echinocytosis. Adriamycin inhibited the breakdown of band 2.1 even when the cells formed echinocytes; this raises doubts concerning the importance of band 2.1 in the maintenance of discocyte morphology. Adriamycin only marginally inhibited the purified calcium-activated thio protease (calpain). Calcium-loading of human erythrocytes increased the phosphorylation of several major cytoskeletal proteins including pp120, band 3, band 4.1 and band 4.9. The pattern of increase resembled that induced by 12-0-tetradecanoyl-phorbol-13-acetate. Pre-treatment with Adriamycin prior to calcium loading caused a general lowering of basal phosphorylation. Adriamycin had no effect on the activity of the calcium-activated phospholipid-dependent protein kinase (protein kinase C). A hypothesis is put forward that the morphological transition of erythrocytes might be dependent upon the activity of a contractile system.