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At least 1,369 records · Page 76Linked to original sources
PubMed2006

Polymorphic behavior in protein-surfactant mixtures: the water-bovine serum albumin-sodium taurodeoxycholate system.

Mixtures containing water, bovine serum albumin (BSA), and sodium taurodeoxycholate (NaTDC), a component of the bile in mammals, have been investigated in a wide range of composition and pH. Depending on the concentration of both solutes and the pH, solutions, precipitates, and gels are formed. Under spontaneous pH conditions, the transport properties in dilute solutions indicate the occurrence of significant interactions between BSA and the surfactant. Conversely, acidic media favor the formation of nonsoluble protein-surfactant complexes, with subsequent precipitation. The nucleation kinetics of the protein-surfactant complexes in solid form and the related precipitation processes can be slow or fast, depending on the overall solute content and the mole ratio. At high concentrations, a gel, extending on both sides of the charge neutralization line, and two-phase regions are observed. Gels shrink in open air and swell in the presence of excess water. Depending on concentration and temperature, the gels transform from an essentially liquidlike behavior to that peculiar to true gels (when G' > or = G''). The thermal gelation threshold, the temperature above which G' > or = G'', depends on BSA and NaTDC content and is concomitant to moderate heat effects, inferred by differential scanning calorimetry (DSC). The above data also indicate that the protein thermal denaturation in the gel is shifted to higher temperatures compared to water. Such a stabilizing effect is presumably related to the occurrence of both electrostatic and hydrophobic interactions with NaTDC. Water self-diffusion in the gels is slightly slower than that in the bulk and poorly sensitive to composition: it is about 65% the value of neat H2O in a wide concentration range, irrespective of the BSA, or NaTDC, concentration. A peculiar behavior is also observed in 23Na longitudinal and transverse relaxation rates. The T1 and T2 values, measured at 105.75 MHz on BSA-NaTDC gels, indicate that the motions determining the NMR relaxation of the sodium ions in the hydration layer of the protein-surfactant aggregates are not slow, having frequencies comparable with the Larmor one. The above properties, especially the rheological and the spectroscopic ones, are important for understanding the behavior of gels based on protein-surfactant mixtures.

Calorimetry, Differential Scanning↗
PubMed2005

Precipitative growth templated by a fluid jet.

Tubular growth by chemical precipitation at the interface between two fluids, a jet and its surroundings, underlies the development of such important structures as chimneys at hydrothermal vents. This growth is associated with strong thermal and/or solute gradients localized at those interfaces, and these gradients, in turn, often produce radial compositional stratification of the resulting tube wall. A fundamental question underlying these processes is how the interplay between diffusion, advection, and precipitation determines the elongation rate of the tubes. Here we report experimental and theoretical results that reveal a regime in which there exists a new scaling law for tube growth. The model system studied consists of a jet of aqueous ammonia injected into a ferrous sulfate solution, precipitating iron hydroxides with varying oxidation states at the jet boundary. Despite the complex chemistry and dynamics underlying the precipitation, the tube growth exhibits a strikingly simple scaling form, with characteristic lengths and times increasing linearly with the mean velocity of the jet. These observations follow from a kinetic model of advection-dominated flows.

Letter↗
PubMed2003

Transport properties of dense fluid argon.

We calculate using molecular dynamics simulations the transport properties of realistically modeled fluid argon at pressures up to approximately 50 GPa and temperatures up to 3000 K. In this context, we provide a critique of some newer theoretical predictions for the diffusion coefficients of liquids and a discussion of the Enskog theory relevance under two different adaptations: modified Enskog theory and effective diameter Enskog theory. We also analyze a number of experimental data for the thermal conductivity of monoatomic and small diatomic dense fluids.

Journal Article↗
PubMed1992

[Anti-Pr2 cold agglutinin disease with polyneuropathy evolving to malignant lymphoma].

A 53-year-old male was diagnosed as having ataxic polyneuropathy associated with IgM-kappa monoclonal gammopathy in January 1988. Plasmapheresis and chemotherapy with chlorambucil and Melphalan-Prednisolone were effective for his neuropathy, but hemolytic anemia appeared in February 1989. The diagnosis of low-titer cold agglutinin disease (IgM-kappa) with anti-Pr2 specificity was made. Hemolytic anemia became refractory to high-dose corticosteroids, and fever, hepatosplenomegaly and severe pancytopenia appeared in January 1990. Bone marrow involvement of malignant lymphoma (mu, kappa) was found, and he died of pneumonia and gastrointestinal bleeding after the start of chemotherapy. Postmortem examination revealed a widespread infiltration of malignant lymphoma, diffuse, large cell (B-cell) type. Erythrophagocytic histiocytes also increased in bone marrow, liver, spleen and lymph nodes, as if there were hemophagocytic syndrome associated with lymphoma present. In addition to the high thermal amplitude of cold agglutinin in this case, the systemic activation of histiocytes induced by the development of malignant lymphoma may be responsible for progressive hemolysis and severe pancytopenia.

Anemia, Hemolytic, Autoimmune↗
PubMed1998

Multiple time step diffusive Langevin dynamics for proteins.

We present an algorithm for simulating the long time scale dynamics of proteins and other macromolecules. Our method applies the concept of multiple time step integration to the diffusive Langevin equation, in which short time scale dynamics are replaced by friction and noise. The macromolecular force field is represented at atomic resolution. Slow motions are modeled by constrained Langevin dynamics with very large time steps, while faster degrees of freedom are kept in local thermal equilibrium. In the limit of a sufficiently large molecule, our algorithm is shown to reduce the CPU time required by two orders of magnitude. We test the algorithm on two systems, alanine dipeptide and bovine pancreatic trypsin inhibitor (BPTI), and find that it accurately calculates a variety of equilibrium and dynamical properties. In the case of BPTI, the CPU time required is reduced by nearly a factor of 60 compared to a conventional, unconstrained Langevin simulation using the same force field.

Algorithms↗
PubMed1995

Preparation and characterization of poly(epsilon-caprolactone) polymer blends for the delivery of proteins.

A series of ternary blend matrices, based on high- and low-molecular-weight poly(epsilon-caprolactone) (PCL) and a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer (Synperonic L61), has been developed for the delivery of proteins. The inclusion of Synperonic L61 served to enhance the water content of the matrix available for protein diffusion. Blends comprising high-molecular-weight PCL (PCLH) and Synperonic L61 alone were found by scanning electron microscopy to be incompatible over a wide composition range. The addition of a low-molecular-weight PCL (PCLL) enhanced compatibility of the polymeric components. Analysis of the dynamic mechanical and thermal properties of these blends showed a significant shift in the glass transition temperature of the material (-38 to -55 degrees C), as the weight fraction of Synperonic L61 increased to 30 wt%, indicative of limited miscibility of the components in the non-crystalline phase. All ternary blended matrices showed a higher degree of hydration relative to homogeneous PCLH. The maximum water content could be modified by adjusting the weight fraction of Synperonic L61 in the blend. The rate of release of a model protein, bovine serum albumin (BSA), from matrices containing Synperonic L61 was considerably higher than that from PCLH and PCLH/PCLL alone. Analysis of the release mechanisms of BSA from these matrices suggested that, whilst diffusion was the predominant mode of protein transport, the elution of Synperonic L61 from blended matrices during the dissolution caused a notable deviation from Fickian control.

Biocompatible Materials↗
PubMedDate not supplied

Correlation of thermal parameters with outcome in combined radiation therapy-hyperthermia trials.

Many studies utilizing combined hyperthermia (HT) and radiation therapy (XRT) in the treatment of advanced or recurrent malignancies have reported a correlation between some measure of the minimum temperature achieved and outcome. Previous reported studies at Stanford have demonstrated a statistically significant correlation between the duration of local control and Tmin, the mean over treatments of the minima of (a) measured intratumoral temperatures in fields which contained diffuse or nodular tumours, or (b) measured interstitial temperatures in fields treated for microscopic residual disease. Recently, T90, the mean of the temperatures above which 90% of all measured intratumoral temperatures fall, has been proposed as an alternative characterization of the efficacy of the HT treatment that reportedly has a superior correlation with outcome. To test this hypothesis, T90 was computed by two different methods for three groups of patients treated at Stanford with XRT-HT for superficially located tumor recurrences. Tmin was found to be strongly correlated with T90 calculated by both methods. All three thermal parameters correlated with complete response at 3 weeks and with local control, although Tmin usually demonstrated the strongest correlation.

Adenocarcinoma↗
PubMedDate not supplied

Theory of band broadening for DNA gel electrophoresis and sequencing.

The problem of (thermal) band broadening during DNA gel electrophoresis is studied analytically and numerically using the reptation model. It is shown that the orientation of the end-to-end vector of the molecules leads to increased diffusion and even to molecular size-independent band broadening. Thus, the Einstein relation between mobility and diffusion holds for only very small molecules. Also, "self-trapped" molecules are predicted to give fuzzy bands, as observed experimentally. Finally, megabase molecules are discussed and the consequences of our predictions for the improvement of sequencing are considered.

Chemical Phenomena↗
PubMedDate not supplied

Evolution of the unsaturated zone testing at Yucca Mountain.

The evaluation of the Yucca Mountain site has evolved from intensive surface-based investigations in the early 1980s to current focus on testing in underground drifts. Different periods of site characterization activities and prominent issues concerning the unsaturated zone (UZ) are summarized. Data collection activities have evolved from mapping of faults and fractures to estimation of percolation through tuff layers, and to quantification of seepage into drifts. Evaluation of discrete flow paths in drifts has led to fracture-matrix interaction and matrix diffusion tests over different scales. The effects of tuff interfaces and local faults are evaluated in fractured-welded and porous-nonwelded units. Mobilization of matrix water and redistribution of moisture are measured in thermal tests. Lessons learned from underground tests are used to focus on processes needed for additional quantification. Migration through the drift shadow zone and liquid flow through faults are two important issues that have evolved from current knowledge.

Environmental Monitoring↗
PubMed2005

Permeable environmental leaching capsules (PELCAPs) for in situ evaluation of contaminant immobilization in soil.

We encapsulated radioisotope-spiked soil within a water-permeable polyacrylamide matrix cast in a small cylindrical geometry (approximately to 5 cm3) to measure the persistence of immobilized soil contaminants. As a proof-of-principle, soils contained within these permeable environmental leaching capsules (PELCAPs) were labeled with either 85Sr or 134Cs and were leached in both laboratory tests and continuously in situ with ground and streamwaters at two field sites on the Oak Ridge reservation. Groups of PELCAPs were retrieved, assayed nondestructively for radioisotopes via gamma spectroscopy, and then replaced in ground and surface water repeatedly over a 6-month period. PELCAPs that contained no soil readily and quantitatively leached either 85Sr or 134Cs into laboratory extractants or ground or surface water with effective diffusion coefficients (D(eff)) of (1.14 +/- 0.06) and (4.8 +/- 0.2) x 10(-6) cm2/s, respectively. PELCAPs containing untreated soil readily leached > 90% of 85Sr but < 1% of 134Cs during field leaching at both sites, whereas thermally treated soils quantitatively retained both isotopes under all conditions. Permeable polymer encapsulation methods, such as PELCAPs, offer the potential capability to conveniently test large numbers of soils and soil treatments for contaminant release and uptake under actual field environmental conditions.

Cesium Radioisotopes↗
PubMed2005

Effects of precursor and support variation in the genesis of uranium oxide catalysts for CO oxidation and selective reduction of NO: Synthesis and characterization.

A range of uranium oxide-based catalysts, derived from UO2(NO3)2.6H2O and UCl4 precursors, and supported on gamma-Al2O3, SiO2 and mesoporous H1SiO2, have been synthesized and then characterized using the following methods: isothermal nitrogen adsorption/desorption measurements, diffuse reflectance infrared spectroscopy (DRIFTS), gas titration of surface hydroxyl groups using Grignard reagents, U L(III) extended X-ray absorption fine structure (EXAFS), powder X-ray diffraction (PXRD), and thermogravimetric and differential thermal analysis. Brij76-templated H1SiO2 mesoporous silicas are found to be essentially stable under flowing oxygen after 16 h at 1073 K. At temperatures above this, however, extensive structural collapse, together with extensive dehydroxylation, ensues. Titration of the accessible hydroxyl group concentrations shows that in these materials the density of OH groups is considerably lower than in their amorphous counterparts. The adsorption of uranyl nitrate onto these dispersants results in a supported, and partially dehydrated, phase of the parent molecule with little obvious structural distortion; however, the adsorption of UCl4 leads to a complex adstructure which may best be described as U(O)2Cl2. The subsequent formation of the uranium oxide phase, nominally active for the oxidation of CO and selective reduction of NO (generally accepted to be U3O8), is found to be a considerable function of both the precursor and support system employed. Calcination of such systems to 1073 K results in extensive extrusion of the supported uranium phase from mesoporous supports, resulting in the formation of very large orthorhombic U3O8 domains. PXRD, however, shows that on amorphous SiO2 and gamma-Al2O3 similar treatment results in the formation of a hexagonal phase of U3O8. The formation of U3O8 is found to be promoted in mesoporous systems and by the presence of Cl in the catalyst make up. Some evidence is also found that suggests that a persistence of Cl limits the growth of U3O8 domains.

Journal Article↗
PubMed2005

An adiabatic linearized path integral approach for quantum time correlation functions: electronic transport in metal-molten salt solutions.

We generalize the linearized path integral approach to evaluate quantum time correlation functions for systems best described by a set of nuclear and electronic degrees of freedom, restricting ourselves to the adiabatic approximation. If the operators in the correlation function are nondiagonal in the electronic states, then this adiabatic linearized path integral approximation for the thermal averaged quantum dynamics presents interesting and distinctive features, which we derive and explore in this paper. The capability of these approximations to accurately reproduce the behavior of physical systems is demonstrated by calculating the diffusion constant for an excess electron in a metal-molten salt solution.

Journal Article↗
PubMed2000

Electromagnetic and heat transfer computations for non-ionizing radiation dosimetry.

Reliable information on the heat distribution inside biological tissues is essential for the planning and optimization of experiments which aim to study the effects of non-ionizing radiation (NIR). In electrodynamics, the finite-difference time-domain (FDTD) technique has become the dominant technique for radiofrequency dosimetry. In order to obtain the electromagnetic field and heat distributions within the same simulation run without changing discretization, a heat diffusion solver has been directly integrated into an advanced electrodynamic FDTD kernel. The implementation enables both coupled and sequential simulations. It also includes the ability to work with complex bodies and to accelerate heat diffusion. This paper emphasizes the importance of this combination in the field of NIR dosimetry. Two examples from this area are given: the validation of dosimetry with temperature probes and the estimation of the highest thermal load during bioexperiments.

Animals↗
PubMed1992

Comparative histochemistry of port-wine stains after copper vapor laser (578 nm) and argon laser treatment.

The present study compared the histologic changes occurring 15 min after copper vapor laser (CVL; operating at 578 nm) and argon laser (488/514 nm) treatment of port-wine stains (PWS) over a range of energy densities (8-32 J/cm2) with corresponding pulse widths of 50-200 ms. Frozen tissue sections were stained with nitroblue tetrazolium chloride (NBTC). This histochemical method permits an accurate color differentiation between blue-stained viable and unstained thermally damaged cells. At 8, 10, and 12 J/cm2 the argon-laser injury was confined to epidermal cell layers; none to superficial dermal effects were found. Fluences of at least 15 J/cm2 produced a diffuse NBTC-negative coagulation necrosis. Exposure of PWS skin to 8-12 J/cm2 at 578 nm did not alter the integrity of epidermal cells. In the dermis, damage was confined to blood vessels and surrounding collagen, showing a clear demarcation from adjacent viable structures. The maximum penetration depth achieved with these vessel selective energy densities was 0.44 mm. At 15 J/cm2, besides vascular injury, damage to the basal cell layer also occurred. At fluences of 17-20 J/cm2 a diffuse necrosis similar to that induced by the argon laser was found. Vessel selectivity of the 578 nm wave band was achieved with pulse widths from 50-74 ms, exceeding the estimated "ideal" exposure time (0.1-10.0 ms) for a vascular selective laser effect. The NBTC method allowed identification of subtle laser-induced tissue changes providing accurate quantitative data relating to the extent of vascular injury.

Adult↗
PubMedDate not supplied

[Study of dynamic properties of water in poly(A) and poly(U) solutions by proton magnetic resonance].

Proton magnetic relaxation in aqueous solutions of polyadenylic and polyuridylic acids in the temperature range (10-80 degrees C) and acidities (pH 3-9.7) has been investigated. Activation energies of water molecule diffusion and proton exchange, as well as the velocities of these processes have been determined. It is established that from the point of view of magnetic relaxation, the state of single helices resulted from the thermal conformation transition, are not equal to the state obtained by the change of the pH of solution; it refers both to the secondary structure of the chains and the dynamical behaviour of the biopolymer hydrate layers.

Chemical Phenomena↗
PubMed1983

The effect of calcium on the thermotropic properties of bovine blood coagulation factors IX and X and their activation intermediates and products.

The thermotropic properties of bovine blood coagulation Factors IX and X, as well as the activation intermediates and products of these proteins, have been investigated by differential scanning microcalorimetry in the presence and absence of Ca2+. Bovine Factor IX displays a single thermal-denaturation transition characterized by a temperature midpoint (TM) of 54.5 +/- 0.5 degrees C and a calorimetric enthalpy (delta Hc) of 105 +/- 15 kcal/mol, in the absence of Ca2+. In the presence of Ca2+ concentrations sufficient to saturate its sites on Factor IX, the Tm value is increased to 57.0 +/- 0.5 degrees C and the delta Hc is virtually unchanged. When the activation intermediate, Factor IX alpha, is similarly analyzed in the absence of Ca2+, a broad, diffuse thermogram was obtained which did not lend itself to calculation of thermodynamic parameters. In the presence of Ca2+, Factor IX alpha displayed thermograms characterized by a TM of 51.0 +/- 0.5 degrees C and a delta Hc of 109 +/- 10 kcal/mol. The activated product, Factor IXa alpha, in the absence of Ca2+ (the values in the presence of saturating Ca2+ are given in parentheses), undergoes thermal denaturation with a TM of 54.5 +/- 0.5 degrees C (57.0 +/- 0.5 degrees C) and a delta Hc of 158 +/- 10 kcal/mol (156 +/- 10 kcal/mol). Similarly, the terminal-activation product, Factor IXa beta, displays a TM of 51.5 +/- 0.5 degrees C (54.0 +/- 0.5 degrees C) and a delta Hc of 85 +/- 5 kcal/mol (126 +/- 10 kcal/mol). Bovine blood coagulation Factor X has been analyzed in this same fashion, and shows very similar thermal properties to Factor IX. The thermal denaturation of Factor X is represented by a TM of 54.0 +/- 0.5 degrees C (55.0 +/- 0.5 degrees C) and a delta Hc of 102 +/- 10 kcal/mol (118 +/- 10 kcal/mol), whereas its activated form, Factor Xa beta, possesses a TM of 55.0 +/- 0.5 degrees C (55.0 +/- 0.5 degrees C) and a delta Hc of 92.0 +/- 5 kcal/mol (136 +/- 10 kcal/mol). These studies indicate that, for many of these proteins, Ca2+ induces a conformational alteration to a more thermally stable form, which also requires the absorption of greater amounts of heat for thermal denaturation.

Animals↗
PubMed2004

Methemoglobin formation during laser induced photothermolysis of vascular skin lesions.

BACKGROUND AND OBJECTIVE: Monitoring dynamic changes during laser induced photothermolysis of vascular skin lesions is essential for obtaining an optimal therapeutic result. Rapid photoinduced thermal damage occurs at a threshold temperature of about 70 degrees C. It is therefore, relevant to identify markers to indicate if this threshold temperature has been reached. Methemoglobin, which is formed by a photo-induced oxidation of hemoglobin, indicates that the temperature has reached this threshold value. This study presents a proof of concept of a method for monitoring the in vivo presence of methemoglobin immediately after laser exposure. STUDY DESIGN/MATERIALS AND METHODS: The present study was designed to investigate the in vivo temperature dependence of hemoglobin absorption in the 450-800 nm spectrum range. In vivo diffuse reflectance measurements of port-wine stain (PWS) and telangiectasia were performed prior to, and immediately after, laser treatment with a pulsed dye laser (PDL) at 585 nm wavelength. RESULTS: In vivo measurements following laser treatment of vascular skin lesions showed an immediate increase in the optical absorption of blood. This effect, caused by thermal stress, is a result of an increased dermal blood volume fraction and methemoglobin formation. The effect is light dose dependent, and reflectance spectra revealed methemoglobin formation in patients treated with fluences above 5 J/cm2 at 585 nm wavelength. CONCLUSIONS: It was proved that methemoglobin can be measured in vivo by reflectance spectroscopy. Measurements of the average methemoglobin concentrations immediately after laser exposure may be a valuable diagnostic tool to verify that the blood temperature has been sufficiently high to induce thermal damage to the vessel wall.

Adolescent↗
PubMed2003

ZO-1 redistribution and F-actin stress fiber formation in pulmonary endothelial cells after thermal injury.

BACKGROUND: In response to isolated inflammatory stimuli, changes in endothelial cell morphology that enhance paracellular flow of solutes result from F-actin stress fiber formation, myosin phosphorylation, and actin anchoring protein (ZO-1) modifications. We hypothesized that myosin light chain kinase inhibition would diminish burn-enhanced endothelial monolayer permeability by secondarily preventing F-actin and actin anchoring protein rearrangements. METHODS: Human pulmonary microvascular endothelial cells were treated for 4 hours with 20% human burn serum (isolated from patients with > 45% total body surface area thermal injury or healthy volunteers). Select cultures were pretreated with myosin light chain kinase inhibitors (ML-9). Permeability was assessed by migration of bovine serum albumin across cell monolayers. Cells were stained with rhodamine-phalloidin and anti-ZO-1 antisera and examined by means of confocal microscopy. RESULTS: Burn serum significantly enhanced monolayer permeability to albumin, whereas pretreatment with ML-9 limited this effect. Control cells maintained cortical F-actin and peripheral ZO-1 distributions (1a, b), whereas burn serum induced transcellular F-actin stress fiber formation and a diffuse ZO-1 staining (2a, b). ML-9 prevented burn-induced actin rearrangements, but not the diffuse redistribution of ZO-1. CONCLUSION: These data demonstrate that endothelial F-actin stress fiber formation and ZO-1 redistribution contribute to postburn loss of pulmonary endothelial monolayer integrity. Although myosin phosphorylation appears to be required for endothelial F-actin stress fiber formation, redistribution of actin-membrane anchoring proteins appears to be regulated independently after thermal injury.

Actins↗