Role of torsional potential in chain conformation, thermodynamics, and glass formation of simulated polybutadiene melts.

For polymer chains, the torsional potential is an important intramolecular energy influencing chain flexibility and segmental dynamics. Through molecular dynamics simulations of an atomistic model for melts of cis-trans-1,4-polybutadiene (PBD), we explore the effect of the torsions on conformational properties (bond vector correlations and mean-square internal distances), fundamental thermodynamic quantities (density, compressibility, internal energy, and specific heat), and glass transition temperature Tg. This is achieved by systematically reducing the strength of the torsional potential, starting from the chemically realistic chain (CRC) model with the full potential toward the freely rotating chain (FRC) model without the torsional potential. For the equilibrium liquid, we find that the effect of the torsions on polymer conformations is very weak. Still weaker is the influence on the monomer density ρ and isothermal compressibility κT of the polymer liquid, both of which can be considered as independent of the torsional potential. We show that a van der Waals-like model proposed by Long and Lequeux [Eur. Phys. J. E 4, 371 (2001)] allows us to describe very well the temperature (T) dependence of ρ and κT. We also find that our data obey the linear relation between 1/kBTρκT and 1/T (with the Boltzmann constant kB) that has recently been predicted and verified on the experiment by Mirigian and Schweizer [J. Chem. Phys. 140, 194507 (2014)]. For the equilibrium liquid, simulations result in a specific heat, at constant pressure and at constant volume, which increases on cooling. This T dependence is opposite to the one found experimentally for many polymer liquids, including PBD. We suggest that this difference between simulation and experiment may be attributed to quantum effects due to hydrogen atoms and backbone vibrations, which, by construction, are not included in the classical united-atom model employed here. Finally, we also determine Tg from the density-temperature curve monitored in a finite-rate cooling process. While the influence of the torsional potential on ρ(T) is vanishingly small in the equilibrium liquid, the effect of the torsions on Tg is large. We find that Tg decreases by about 150 K when going from the CRC to the FRC model.

Theory of length-scale dependent relaxation moduli and stress fluctuations in glass-forming and viscoelastic liquids.

The spatiotemporal correlations of the local stress tensor in supercooled liquids are studied both theoretically and by molecular dynamics simulations of a two-dimensional (2D) polydisperse Lennard-Jones system. Asymptotically exact theoretical equations defining the dynamical structure factor and all components of the stress correlation tensor for low wave-vector q are presented in terms of the generalized (q-dependent) shear and longitudinal relaxation moduli, G(q, t) and K(q, t). We developed a rigorous approach (valid for low q) to calculate K(q, t) in terms of certain bulk correlation functions (for q = 0), the static structure factor S(q), and thermal conductivity κ. The proposed approach takes into account both the thermostatting effect and the effect of polydispersity. The theoretical results for the (q, t)-dependent stress correlation functions are compared with our simulation data, and an excellent agreement is found for qb̄≲0.5 (with b̄ being the mean particle diameter) both above and below the glass transition without any fitting parameters. Our data are consistent with recently predicted (both theoretically and by simulations) long-range correlations of the shear stress quenched in heterogeneous glassy structures.

Composition fluctuations in polydisperse liquids: Glasslike effects well above the glass transition.

We study a two-dimensional glass-forming system of slightly polydisperse (LJ) particles using molecular dynamics simulations and demonstrate that in the liquid regime (well above the vitrification temperature) this model shows a number of features typical of the glass transition: (i) the relation between compressibility and structure factor S(q) is strongly violated; (ii) the dynamical structure factor S(q,t) at low q shows a two-step relaxation; (iii) the time-dependent heat capacity c_{v}(t) shows a long-time power-law tail. We show that these phenomena can be rationalized with the idea of composition fluctuations and provide a quantitative theory for the effects (i) and (ii). It implies that such effects must be inherent in all polydisperse colloidal models, including binary LJ mixtures.

Continuous-time random-walk approach to supercooled liquids: Self-part of the van Hove function and related quantities.

From equilibrium molecular dynamics (MD) simulations of a bead-spring model for short-chain glass-forming polymer melts we calculate several quantities characterizing the single-monomer dynamics near the (extrapolated) critical temperature [Formula: see text] of mode-coupling theory: the mean-square displacement g0(t), the non-Gaussian parameter [Formula: see text] and the self-part of the van Hove function [Formula: see text] which measures the distribution of monomer displacements r in time t. We also determine these quantities from a continuous-time random walk (CTRW) approach. The CTRW is defined in terms of various probability distributions which we know from previous analysis. Utilizing these distributions the CTRW can be solved numerically and compared to the MD data with no adjustable parameter. The MD results reveal the heterogeneous and non-Gaussian single-particle dynamics of the supercooled melt near [Formula: see text]. In the time window of the early [Formula: see text] relaxation [Formula: see text] is large and [Formula: see text] is broad, reflecting the coexistence of monomer displacements that are much smaller ("slow particles") and much larger ("fast particles") than the average at time t, i.e. than [Formula: see text]. For large r the tail of [Formula: see text] is compatible with an exponential decay, as found for many glassy systems. The CTRW can reproduce the spatiotemporal dependence of [Formula: see text] at a qualitative to semiquantitative level. However, it is not quantitatively accurate in the studied temperature regime, although the agreement with the MD data improves upon cooling. In the early [Formula: see text] regime we also analyze the MD results for [Formula: see text] via the space-time factorization theorem predicted by ideal mode-coupling theory. While we find the factorization to be well satisfied for small r, both above and below [Formula: see text] , deviations occur for larger r comprising the tail of [Formula: see text]. The CTRW analysis suggests that single-particle "hops" are a contributing factor for these deviations.

Shear-stress fluctuations and relaxation in polymer glasses.

We investigate by means of molecular dynamics simulation a coarse-grained polymer glass model focusing on (quasistatic and dynamical) shear-stress fluctuations as a function of temperature T and sampling time Δt. The linear response is characterized using (ensemble-averaged) expectation values of the contributions (time averaged for each shear plane) to the stress-fluctuation relation µ_{sf} for the shear modulus and the shear-stress relaxation modulus G(t). Using 100 independent configurations, we pay attention to the respective standard deviations. While the ensemble-averaged modulus µ_{sf}(T) decreases continuously with increasing T for all Δt sampled, its standard deviation δµ_{sf}(T) is nonmonotonic with a striking peak at the glass transition. The question of whether the shear modulus is continuous or has a jump singularity at the glass transition is thus ill posed. Confirming the effective time-translational invariance of our systems, the Δt dependence of µ_{sf} and related quantities can be understood using a weighted integral over G(t).

Numerical determination of shear stress relaxation modulus of polymer glasses.

Focusing on simulated polymer glasses well below the glass transition, we confirm the validity and the efficiency of the recently proposed simple-average expression [Formula: see text] for the computational determination of the shear stress relaxation modulus G(t). Here, [Formula: see text] characterizes the affine shear transformation of the system at t = 0 and h(t) the mean-square displacement of the instantaneous shear stress as a function of time t. This relation is seen to be particulary useful for systems with quenched or sluggish transient shear stresses which necessarily arise below the glass transition. The commonly accepted relation [Formula: see text] using the shear stress auto-correlation function c(t) becomes incorrect in this limit.

Marginally compact hyperbranched polymer trees.

Assuming Gaussian chain statistics along the chain contour, we generate by means of a proper fractal generator hyperbranched polymer trees which are marginally compact. Static and dynamical properties, such as the radial intrachain pair density distribution ρpair(r) or the shear-stress relaxation modulus G(t), are investigated theoretically and by means of computer simulations. We emphasize that albeit the self-contact density diverges logarithmically with the total mass N, this effect becomes rapidly irrelevant with increasing spacer length S. In addition to this it is seen that the standard Rouse analysis must necessarily become inappropriate for compact objects for which the relaxation time τp of mode p must scale as τp ∼ (N/p)5/3 rather than the usual square power law for linear chains.

Molecular dynamics simulations of the chain dynamics in monodisperse oligomer melts and of the oligomer tracer diffusion in an entangled polymer matrix.

The apparent analogy between the self-diffusion of linear oligomers in monodisperse systems, 2 up to 32 monomers, and their tracer diffusion in an entangled polymer matrix of length 256 is investigated by molecular dynamics simulations at constant pressure. Oligomers and polymers are represented by the same coarse-grained (bead-spring) model. An analysis based on the Rouse model is presented. The scaling relationship of the self-diffusion coefficient D with the chain length N written as D proportional, variantN(-alpha) is analyzed for a wide range of temperatures down to the glass transition temperature T(g). Near T(g), the heterogeneous dynamics is explored by the self-part of the van Hove distribution function and various non-Gaussian parameters. For the self-diffusion in a monodisperse system a scaling exponent alpha(T)>1 depending on temperature is found, whereas for the tracer diffusion in an entangled matrix alpha=1 is obtained at all temperatures, regardless of the oligomer length. The different scaling behavior between both systems is explained by a different monomer mobility, which depends on chain length for monodisperse systems, but is constant for all tracers in the polymer matrix.

Expression of an estrogen-induced breast cancer-associated protein (pS2) in benign and malignant human ovarian cysts.

BACKGROUND: In human mammary tumors, pS2 expression is directly controlled by estrogens and restricted to a subclass of breast carcinomas. In addition, recent studies have suggested that this gene is expressed in both the invasive and preinvasive forms of breast cancer. EXPERIMENTAL DESIGN: pS2 gene expression was investigated in benign and malignant ovary tumors and whenever possible, pS2 expression was also studied in cells collected from cystadenoma fluids. In several cases, particularly with cells from cystadenoma fluids, the limited amount of material available prevented the used of the traditional RNA detection methods such slot/dot blots or Northern blots. Therefore, a rapid and sensitive polymerase chain reaction assay of pS2 expression has been developed and used in this study. RESULTS: In human ovarian tumors, data obtained show that pS2 transcripts and proteins are present in all mucinous cystadenomas studied and at a lower frequency in endometrioid cystadenomas. Quantitation of the CA 19-9 mucin concentration in ovarian fluids indicate that pS2 expression is always associated with high mucin concentrations, but mucin-positive and pS2-negative samples are also frequently observed. CONCLUSIONS: These data suggest that pS2 expression is restricted to subclasses of human ovarian cystadenomas.

Specific binding between human neutrophils and heparin.

Heparin binding on polymorphonuclear leucocytes (PMNL) was characterized. Heparin binding was specific, rapid, saturable and reversible. One single class of heparin binding sites was found with a dissociation constant of 1.22 mumol/l and 7.7 x 10(6) sites per PMNL. The binding was independent of the anticoagulant activity of heparin. Heparin affinity chromatography on radio-iodinated cell lysates followed by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulphate revealed a 130 kD heparin binding protein. Heparin binding was inhibited by disodium salt of ethylenediamine tetraacetic acid. Cell surface bound heparin was functionally inactive and did not affect the inactivation of thrombin by antithrombin III. Our study demonstrates that heparin interacts with PMNL by a cell-surface binding protein. These instructions could be consistent with the modifications of some PMNL functional properties in the presence of heparin.

Serum ferritin spectrotypes in patients with heterozygous beta-thalassaemia.

Serum ferritin spectrotypes from patients heterozygous for beta-thalassaemia were determined after agarose isoelectric focusing followed by radio-immunofixation with anti-ferritin antibody. Multivariate analysis demonstrated a specific spectrotype for heterozygous beta-thalassaemia. This spectrotype was shown to be different from those in hereditary spherocytosis and idiopathic haemochromatosis. Statistical discrimination reached 100% of well-classified patients between these pathological conditions.

Radioimmunofixation of human ferritin following serum isoelectric focusing.

Radioimmunofixation of human ferritin following isoelectric focusing of serum was developed to study the microheterogeneity of this protein in native serum without previous purification or concentration. This method requires only 2-10 microliter of serum and can be used with levels of ferritin as low as 10 micrograms/l. In this way, the extensive microheterogeneity of this protein was revealed, since in some cases it produced as many as 35 bands with isoelectric points in a pH range of 4.95-5.9. Very different isoelectric focusing patterns (spectrotypes) of ferritin were observed during the investigation of pathological sera. The high sensitivity of this technique makes it useful for the investigation of serum ferritin in diseases involving modifications of the metabolism of this protein.

A fast silver staining method for protein detection after isoelectric focusing in agarose gels.

A sensitive staining method was developed for detecting proteins in agarose gels after isoelectric focusing. Its sensitivity is about 20 times that of the Coomassie blue R-250 staining technique, and the time required is only 10 min.

[Fibrotic interstitial pneumopathies. Collagenolytic activity of the alveolar fluid]. / Pneumopathies interstitielles fibrosantes. Activité collagénolytique du liquide alvéolaire.

Collagenolytic enzyme release in alveolar structures is probably one of the initial events leading to impaired balance between collagen synthesis and degradation in the connective matrix of the lung, resulting in pulmonary fibrosis. The collagenolytic activity was determined in the bronchoalveolar fluid of 40 normal subjects or patients with miscellaneous pulmonary diseases and was found to be present in seventeen, viz.: 7/7 patients with interstitial fibrosis, irrespective of its origin: 4/4 patients with radiation pneumonitis; 4/15 patients with sarcoidosis and 2/2 patients with transient eosinophilic pneumopathy. There was no evidence of fibrosis in the 23 patients who showed no collagenolytic activity. Thus, collagenolytic enzymes are present in the alveolar structures of patients with interstitial pulmonary diseases of diverse origin capable of leading to fibrosis. Monitoring the release of this enzyme by bronchoalveolar lavage could be useful to evaluate the risk of fibrosis in such patients.

Role of sialic acid in the microheterogeneity of serum thyroxine-binding globulin. Study by two-dimensional isoelectric focusing.

A new technique combining a neuraminidase treatment of thyroxine-binding globulin after serum isoelectric focusing and a second-dimensional isoelectric focusing was developed to study the role of sialic acid in the microheterogeneity of native thyroxine-binding globulin. By showing the change of PI occasioned by the desialylation for each of the bands constituting the thyroxine-binding globulin pattern separately, this procedure clearly demonstrated that the microheterogeneity of the native protein could not be imputed to the varying sialic acid content of the bands only. We suggest that at least three molecules of thyroxine-binding globulin, with probably slight differences in their amino acid composition, are present in the serum, and that different degrees of sialylation ensure greater microheterogeneity of this protein.

A sensitive method for characterization of oligoclonal immunoglobulins in unconcentrated cerebrospinal fluid.

Although isoelectric focusing has been used to demonstrate the presence of oligoclonal IgG in the CSF, the technique has not allowed detection of oligoclonal IgG in unconcentrated CSF. A new technique is reported, by which unconcentrated CSF is separated by isoelectric focusing, and the IgG bands are then detected by radioimmunofixation. Samples as small as 20 microliters may be used.

Microhetero;geneity and polymorphism of human serum thryroxine-binding globulin. Study by isoelectric focusing and radioprint immunofixation.

A new technique of radioprint immunofixation following isoelectric focusing was applied to the study of microheterogeneity of thyroxine-binding globulin without purification, in individual sera; this protein appeared to give rise to at least seven bands with isoelectric points in the range of pI 4.2--5.0. Furthermore, two different distributions of the intensity of these bands were found in the sera investigated, suggesting the existence of thyroxine-binding globulin polymorphism in man.

[Radioimmunofixation: a new technic for characterizing immunoglobulins in unconcentrated cerebrospinal fluid. Preliminary results]. / Radio-immunofixation: une nouvelle technique de caractérisation des immunoglobulines dans le liquide céphalo-rachidien non concentré. Résultats préliminaires.

The restriction of heterogenicity of immunoglobulins G (IgG), or oligoclonal distribution, in the cerebrospinal fluid (CSF) can be observed after electrophoresis or electrofocalization, the IgG nature of each oligoclonal band being confirmed by subsequent immuno-electrophoresis. Using immunofixation, the oligoclonal bands can be visualized and characterized simultaneously, but requires previous concentration of the CSF, which is a source of error. The technique of radioimmunofixation, here described, allows the study of IgG with 20 microliters of non-concentrated CSF. It demonstrates that the oligoclonal characteristic is present in normal CSF and is a more quantitative than qualitative feature. Preliminary results show that the method can be applied to the study of all CSF proteins. By using a viral antigen labelled with I-125, for example, it should be possible to reveal and visualize the antibody activity of each oligoclonal band and to determine whether the quantitative increase in an oligoclonal band corresponds to a definite antigenic stimulation.