Phase transitions in phospholipid monolayers: Statistical model at the pair approximation.

A Langmuir film, consisting of a phospholipid monolayer at the air-water interface, was modeled as a two-dimensional lattice gas corresponding to a ternary mixture of water molecules (w), ordered-chain lipids (o), and disordered-chain lipids (d). The statistical problem is formulated in terms of a spin-1 model, in which the disordered-chain lipid states possess a high degenerescence ω≫1, and was termed Doniach lattice gas (DLG). Motivated by some open questions in the analysis of the DLG model at the mean-field approximation (MFA) [Phys. Rev. E 90, 052705 (2014)PLEEE81539-375510.1103/PhysRevE.90.052705], we have reconsidered it at the pair-approximation level by solving the model on a Cayley tree of coordination z. The attractors of the corresponding discrete-map problem are associated with the thermodynamic solutions on the Bethe lattice (the central region of an asymptotically infinite Cayley tree). To check the thermodynamic stability of the possible phases, the grand-potential density was obtained by the method proposed by Gujrati [Phys. Rev. Lett. 74, 809 (1995)PRLTAO0031-900710.1103/PhysRevLett.74.809]. In general, the previous MFA results are confirmed at the pair-approximation level, but a novel staggered phase, overlooked in the MFA analysis, was found when the condition ε_{wd}>1/2(ε_{ww}+ε_{dd}) is satisfied, where ε_{xy} represents the nearest-neighbor intermolecular interactions between single-site states x and y. Model parameters obtained by fitting to experimental data for the two most commonly studied zwitterionic phospholipids, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), yield phase diagrams consistent with the phase transitions observed on Langmuir films of the same lipids under isothermal compression, which present a liquid-condensed to a liquid-expanded first-order transition line ending at a critical point.

Phase Transitions in Phospholipid Monolayers: Theory Versus Experiments.

The Doniach lattice gas (DLG) represents a ternary-mixture statistical model, whose components, water molecules (w), ordered-chain lipids (o), and disordered-chain lipids (d)-the latter carrying a high degenerescence ω ≫ 1-are located at each site of a two-dimensional lattice. The DLG model was introduced to describe phospholipid Langmuir films at the air-water interface and can be mapped into a spin-1 model, with the single-site states s i = 0, +1, and -1 representing the three types of molecules in the system (w, o, and d), respectively. The model allows lipid-density fluctuations and has been analyzed at the mean-field approximation (Guidi, H. S.; Henriques, V. B. Phys. Rev. E 2014, 90, 052705) as well as at the pair approximation (de Oliveira, F. O.; Tamashiro, M. N. Phys. Rev. E 2019, 99, 012147). In this work, we focus on performing an explicit comparison of the theoretical predictions obtained for the DLG model at the pair approximation with isothermal monolayer compression experiments (Nielsen, L. K.; Bjørnholm, T.; Mouritsen, O. G. Langmuir 2007, 23, 11684) for the two most commonly studied saturated zwitterionic phospholipids, DMPC (1,2-dimyristoyl- sn-glycero-3-phosphocholine) and DPPC (1,2-dipalmitoyl- sn-glycero-3-phosphocholine). The model parameters obtained by fitting to the experimental data yield phase diagrams that are qualitatively consistent with the observed phase transitions on DMPC and DPPC monolayers, with the absence of a low-density gas phase. Quantitative agreement, however, was less significant partially because of the challenging reproducibility of Langmuir monolayer compression experiments, claimed in the literature to be influenced by kinetic effects.

Multicritical behavior of the ferromagnetic Blume-Emery-Griffiths model with repulsive biquadratic couplings.

The ferromagnetic (J>0) version of the Blume-Emery-Griffiths model in the region of repulsive biquadratic couplings (K<0) is considered on a Cayley tree of coordination z, reducing the statistical problem to the analysis of a two-dimensional nonlinear discrete map. In order to investigate the effect of the coordination z on the system multicritical behavior, we study the particular case K/J=-3.5 with the inclusion of crystal fields (D≠0), but vanishing external magnetic fields (H=0), for two distinct lattice coordinations (z=4 and z=6). The thermodynamic solutions on the Bethe lattice (the central region of a large Cayley tree) are associated with the attractors of the two-dimensional map. The phase diagrams display several thermodynamic phases (paramagnetic, ferromagnetic, ferrimagnetic, and staggered quadrupolar). In some cases, there are regions of numerical costability of two different attractors of the map, associated with discontinuous phase transitions between the corresponding phases. To verify the thermodynamic stability of the phases and to locate the first-order boundaries, the analytical expression of the Gibbs free energy was obtained by the method proposed by Gujrati [Phys. Rev. Lett. 74, 809 (1995)PRLTAO0031-900710.1103/PhysRevLett.74.809]. For lower coordinations (z=4) the transition between the ferrimagnetic and the staggered quadrupolar phases is always continuous, while the transition between the ferromagnetic and the ferrimagnetic phases is discontinuous at low temperatures, turning into continuous for temperatures above a tricritical point. On the other hand, for higher coordinations (z=6), the transition between the ferromagnetic and the ferrimagnetic phases is always continuous. However, the transition between the ferrimagnetic and the staggered quadrupolar phases is continuous for higher temperatures and discontinuous for temperatures below a tricritical point, in agreement with previous results obtained in the mean-field approximation (infinity-coordination limit). In both cases, the occurrence and the thermodynamic stability of the ferrimagnetic phase is confirmed.

Phase transitions and spatially ordered counterion association in ionic-lipid membranes: a statistical model.

We propose a statistical model to account for the gel-fluid anomalous phase transitions in charged bilayer- or lamellae-forming ionic lipids. The model Hamiltonian comprises effective attractive interactions to describe neutral-lipid membranes as well as the effect of electrostatic repulsions of the discrete ionic charges on the lipid headgroups. The latter can be counterion dissociated (charged) or counterion associated (neutral), while the lipid acyl chains may be in gel (low-temperature or high-lateral-pressure) or fluid (high-temperature or low-lateral-pressure) states. The system is modeled as a lattice gas with two distinct particle types--each one associated, respectively, with the polar-headgroup and the acyl-chain states--which can be mapped onto an Ashkin-Teller model with the inclusion of cubic terms. The model displays a rich thermodynamic behavior in terms of the chemical potential of counterions (related to added salt concentration) and lateral pressure. In particular, we show the existence of semidissociated thermodynamic phases related to the onset of charge order in the system. This type of order stems from spatially ordered counterion association to the lipid headgroups, in which charged and neutral lipids alternate in a checkerboard-like order. Within the mean-field approximation, we predict that the acyl-chain order-disorder transition is discontinuous, with the first-order line ending at a critical point, as in the neutral case. Moreover, the charge order gives rise to continuous transitions, with the associated second-order lines joining the aforementioned first-order line at critical end points. We explore the thermodynamic behavior of some physical quantities, like the specific heat at constant lateral pressure and the degree of ionization, associated with the fraction of charged lipid headgroups.

Phase transitions and spatially ordered counterion association in ionic-lipid membranes: theory versus experiment.

Aqueous dispersions of phosphatidylglycerol (PG) lipids may present an anomalous chain-melting transition at low ionic strengths, as seen by different experimental techniques such as calorimetry or light scattering. The anomaly disappears at high ionic strengths or for longer acyl-chain lengths. In this article, we use a statistical model for the bilayer that distinguishes both lipid chain and headgroup states in order to compare model and experimental thermotropic and electrical properties. The effective van der Waals interactions among hydrophobic chains compete with the electrostatic repulsions between polar headgroups, which may be ionized (counterion dissociated) or electrically neutral (associated with counterions). Electric degrees of freedom introduce new thermotropic charge-ordered phases in which headgroup charges may be spatially ordered, depending on the electrolyte ionic strength, introducing a new rationale for experimental data on PGs. The thermal phases presented by the model for different chain lengths, at fixed ionic strength, compare well with an experimental phase diagram constructed on the basis of differential scanning calorimetry profiles. In the case of dispersions of DMPG (dimyristoyl phosphatidylglycerol) with added monovalent salt, the model properties reproduce the main features displayed by data from differential scanning calorimetry as well as the characteristic profile for the degree of ionization of the bilayer surface across the anomalous transition region, obtained from the theoretical interpretation of electrokinetic (conductivity and electrophoretic mobility) measurements.

Ions at the water-vapor interface.

We obtain the electrostatic free energy of finite-sized ions near a dielectric interface within the framework of the classical continuum dielectric theory. The ion is modeled as a dielectric sphere with a fixed uniform surface charge density. In order to avoid the generation of additional induced charges on the ionic surface, it is assumed there is no dielectric contrast between the ion core and the external dielectric medium where it is embedded, which allows an exact solution of the electrostatic problem by the image-charge method. It is shown that earlier results reported in the literature, especially when there is partial ionic penetration into the interface, always underestimate the electrostatic free energy associated with nonpolarizable ions. For an ion modeled as a vacuum cavity at the water-vapor interface, it is estimated that the free energy is an order of magnitude larger than prior predictions.

Rayleigh instability of charged aggregates: Role of the dimensionality, ionic strength, and dielectric contrast.

We extended a previous analysis of the classical Rayleigh instability of spherical charged droplets in the presence of neutralizing monovalent counterions [M. Deserno, Eur. Phys. J. E 6, 163 (2001)], by generalizing the problem for suspensions of aggregates with D-dimensional symmetry, corresponding for D = 2 to infinite (rodlike) cylindrical charged bundles and for D = 3 to spherical charged droplets. In addition, we include the effects of added monovalent salt and of dielectric contrast between the charged aggregate and the surrounding solvent. The electrostatic energy taking the microion screening into account is estimated using uniform profiles within the framework of the cell model. We verify the robustness of these results by also considering Debye-Hückel-type microion profiles that are obtained by the minimization of a linearized Poisson-Boltzmann free-energy functional. In the case when the microions can enter inside the charged aggregates, we confirm the occurrence of a discontinuous phase change between aggregates of finite size and an infinite aggregate, which takes place at a collapse temperature that depends on their volume fraction phi and on the salt content. Decrease of phi shifts the phase-change temperature toward higher values, while salt addition has an opposite effect. We obtain analytical expressions for the phase-separation line in the asymptotic limit of infinite dilution (phi-->0), showing that the collapse temperature depends logarithmically on phi . As an application for D = 3 we discuss the stability of the pearl-necklace structures of flexible polyelectrolytes in poor solvents. The case D = 2 is applied to the problem of finite bundle sizes of stiff polyelectrolytes that attract each other-via, e.g., multivalent counterions-leading to an effective surface tension.

Aqueous suspensions of charged spherical colloids: dependence of the surface charge on ionic strength, acidity, and colloid concentration.

We theoretically investigate the dependence of the surface charge developed on charged spherical colloids upon several environmental parameters: the ionic strength of the monovalent added electrolyte, acidity (stabilized by a pH buffer solution), and colloid concentration. In the framework of the mean-field Poisson-Boltzmann spherical cell model, we include the charged colloid-microion correlations into the buffer equation, and we allow for the specific binding of ions to the ionizable groups on the colloid surface. Theoretical predictions are compared to the results obtained under the planar-symmetry Gouy-Chapman approximation and analyzed for the experimental conditions of an aqueous dispersion of the phospholipid dimyristoyl phosphatidylglycerol (DMPG). Experimental measurements of the partition ratio of an aqueous soluble cationic spin label on buffered dispersions of polyanionic unilamellar vesicles of DMPG in the presence of added monovalent salt are theoretically interpreted in terms of ion partition due to electrostatic interactions. We show that the specific binding of the probe must be admitted to explain the experimental results.

Where the linearized Poisson-Boltzmann cell model fails: the planar case as a prototype study.

The linearized Poisson-Boltzmann (PB) approximation is investigated for the classical problem of two infinite, uniformly charged planes in electrochemical equilibrium with an infinite monovalent salt reservoir. At the nonlinear level, we obtain an explicit expression of the associated electrostatic contribution to the semi-grand-canonical potential. The linearized osmotic-pressure difference between the interplane region and the salt reservoir becomes negative in the low-temperature, large-separation, or high-surface charge limits, in disagreement with the exact (at mean-field level) nonlinear PB solution. We show that these artifacts--although thermodynamically consistent with quadratic expansions of the nonlinear functional--can be traced back to the nonfulfillment of the underlying assumptions of the linearization. Explicit comparison between the analytical expressions of the exact nonlinear solution and the corresponding linearized equations allows us to show that the linearized results are asymptotically exact in the weak-coupling and counterionic ideal-gas limits, but always fail otherwise, predicting negative osmotic-pressure differences. By taking appropriate limits of the full nonlinear PB solution, we provide asymptotic expressions for the semi-grand-canonical potential and the osmotic-pressure difference that involve only elementary functions, which cover the complementary region where the linearized theory breaks down.

Factor XIII en transplante de médula ósea / Factor XIII in Bone Marrow Transplantation

La subunidad A del Factor XIII (FXIII), parte activa del FXIII, es sintetizada casi exclusivamente por megacariocitos y precursores de monocitos-macrófagos. Determinándose la actividad del FXIII en pacientes sometidos a transplante de médula ósea autólogo (TAMO) y alegeneico (TMO). En 52 pacientes, 30 TAMO y 22 TMO, la actividad del FXIII fue estudiada en días fijos (basal, mitad de régimen condicionante, día 0, día +7, día +15 y día +30). Un descenso del FXIII fue encontrado en todos los casos, cuando se comparó con los niveles basales, alcalzando el nadir de la actividad al día +7. La caída del FXIII fué significativamente más pronunciada en TMO que en TAMO. Se demostró correlación entre la actividad del FXIII y el tiempo de recuperación hematopoyética. Siete de los 52 ptes. (13, 4 porciento) tuvieron niveles de actividad del FXIII inferiores al 10 porciento, sólo 3 sufrieron sangrados asociados. En TMO, los niveles de PAI estaban significativamente aumentados en los días +7, +15 y +30. En conclusión, la actividad del FXIII está siempre desminuída post-trasplante y el restablecimiento de los niveles basales se relaciona directamente con la velocidad de reconstitución hematopoyética. Diferencias en los tiempos de "engraftment" podrían explicar las diferencias encontradas entre TAMO y TMO. Finalmente, la ausencia de sangrado en ptes. con actividad del FXIII por debajo de niveles hemostáticos(<10 porciento) podría deberse a hipofibrinolisis concominante asociada a aumento del PAI

Arrhythmogenic right ventricular dysplasia presenting as regression of left ventricular dysfunction: a case report.

Arrhythmogenic right ventricular dysplasia is considered to be a slowly progressive disease in which left ventricular dysfunction and congestive heart failure usually appear at the end stage. The initial clinical presentation of this 56-year-old Japanese woman was left-sided heart failure, and the diagnosis was dilated cardiomyopathy, but her left ventricular size and ejection fraction regressed during 10 years of treatment, whereas her right ventricular parameters showed no change.

Significant association between the progression of coronary artery calcification and dyslipidemia in patients on chronic hemodialysis.

Quantification of coronary artery calcification (CAC) determined by electron-beam computed tomography (EBCT), known as the CAC score (CACS), correlates with total plaque amount and coronary risk factors and strongly associates with maximal stenosis in the epicardial arteries. However, data are limited concerning the CACS in chronic dialysis patients, although atherosclerotic vascular disease is the most frequent complication. We examined the relation between coronary risk factors, metabolic factors of calcium and other minerals, and CACS progression in 24 dialysis patients. The mean patient age was 53 +/- 14 (SD) years, and mean duration of dialysis was 64 +/- 69 months. In each patient, the CACS was measured twice, with a mean interscan period of 17 +/- 3 months. The mean CACS progressed from 449 +/- 605 to 669 +/- 894 overall, and the mean change in CACS (DeltaCACS) was 220 +/- 78. Patients were divided into two groups: slow progressors, with DeltaCACS of 7.5 +/- 31 (n = 12), and rapid progressors, with DeltaCACS of 432 +/- 458 (n = 12). Triglyceride concentrations (198 +/- 65 versus 103 +/- 50 mg/dL; P < 0.001) were high, and high-density lipoprotein cholesterol (HDL-C) concentrations (46 +/- 11 versus 60 +/- 18 mg/dL; P < 0.05) were low in rapid progressors. Rapid progression of CAC was associated with high triglyceride and low HDL-C concentrations. The clinical significance of these observations remains to be determined.

Risk factors for stiffness of the wall of the thoracic aorta in patients with mild atherosis.

Previous studies have suggested that aging is associated with progressive arterial stiffness and widening of the pulse pressure, and pulse pressure has been found to be a risk factor of cardiovascular diseases. However, the effects of age, blood pressure (including pulse pressure) or atherogenic factors on thoracic aortic wall stiffness in patients with mild atherosis are unclear, so the present study used transesophageal echocardiography to examine 103 consecutive patients with various cardiovascular diseases. The extent of atherosis was evaluated in terms of intima-medial thickness (IMT), and 2 indices of wall stiffness in the aorta were calculated: elastic modulus and stiffness parameter (beta). In subjects with mild atherosis (IMT <1.0mm), age, body mass index, systolic blood pressure, pulse pressure, triglyceride level, and hypertension were factors significantly associated with high wall stiffness, and multiple logistic stepwise analysis revealed that age, pulse pressure, and triglyceride level were particularly significant.

Helix-coil transition in homopolypeptides under stretching.

We consider the effect of an external applied force on the alpha-helix-coil transition of a single-stranded homopolypeptide chain. An annealed scenario is assumed, where the building amino acid monomers may interconvert between random-coiled and ordered alpha-helical configurations. By exact evaluation of the partition function of the freely jointed chain with helix-coil internal degrees of freedom in the thermodynamic limit, we obtain the result that the stress-strain characteristic has an asymmetrical sigmoid shape with a prominent pseudoplateau. Because of the one-dimensional nature of this system, fluctuations dominate over the mean-field approximation, which incorrectly predicts a second-order phase transition.

Distribution and localization of cells and collagens in the proliferated intima of arterially implanted autovein grafts.

We examined the microscopic features and distribution of collagens in the hyperplastic intima of arterially implanted autovein bypass grafts under conditions of a reduced blood flow with a poor distal outflow. Vascular anastomosis was made using 7-0 nonabsorbable polypropylene sutures (PP group), or absorbable polydioxanone sutures (PDS group). On the contralateral limb, an autovein bypass graft was performed under normal flow conditions (NF group). The thickness of the intima in the NF group was approximately 50 microm throughout the duration of the study, while in the PP and PDS groups, intimal hyperplasia progressed to 290+/-112 microm and 267+/-123 microm, respectively, at 13 months after grafting. Collagen accumulated significantly in both the PP and PDS groups; types IV and V collagen in particular increased considerably in the deep layer. Regardless of the suture materials, the progression of intimal hyperplasia was considered to be closely related to the poor distal outflow to be and caused by the proliferation of myofibroblasts and active production of collagen. The increase in types IV and V collagen, particularly in the deep layer of the hyperplastic intima, was due to development of numerous vasa vasora in this region.

Electrolytic depletion interactions.

We consider the interactions between two uncharged planar macroscopic surfaces, immersed in an electrolyte solution, which are induced by interfacial selectivity. These forces are taken into account by introducing a depletion free-energy density functional, in addition to the usual mean-field Poisson-Boltzmann functional. The minimization of the total free-energy functional yields the density profiles of the microions and the electrostatic potential. The disjoining pressure is obtained by differentiation of the total free energy with respect to the separation of the surfaces, holding the range and strength of the depletion forces constant. We find that the induced interaction between the two surfaces is always repulsive for sufficiently large separations, and becomes attractive at shorter separations. The nature of the induced interactions changes from attractive to repulsive at a distance corresponding to the range of the depletion forces.

[Thoracoscopic surgery for diagnosis of interstitial pneumonia special reference to medicoeconomical effect].

We compared thoracoscopic surgery (TS) and open thoracotomy for the diagnosis of interstitial pneumonia. Intraoperative blood loss and duration of postoperative chest drainage were significantly less with TS than with thoracotomy. The length of postoperative hospital stay and social insurance costs with TS was significantly less than with thoracotomy. These results show that TS for the diagnosis of interstitial pneumonia is superior to open thoracotomy in terms of surgical stress and cost.