Intrinsic viscosity versus molecular weight relationship of polystyrene in cis-decahydronaphthalene

Intrinsic viscosities [η] and mean-square radii of gyration 〈R〉 of a polymer homologous series of commercially available narrow-molecular-weight-distribution polystyrene (PS) samples in a molecular-weight range of 800 up to 24 · 10⁶ were determined in cis-decahydronaphthalene at 25°C by light-scattering and viscosity measurements. These dilute solution properties were compared with those for PS in the good solvent toluene, in the constitutional isomer trans-decahydronaphthalene both at 25°C and in cyclohexane at 34,5°C as a theta-system.     

Limiting viscosity number—molecular weight relationships for phenol-formaldehyde resin in solution

The effect of molecular structure of phenol-formaldehyde resin on the Mark-Houwink-Sakurada equation for solutions in acetone is systematically studied. Random and high-orthophenol-formaldehyde resins are prepared by conventional, acid-catalyzed and Zn⁺⁺-catalyzed condensations, respectively. The relative contents of 2,2′-, 2,4′- and 4,4′-methylene linkages are determined by ¹³C NMR spectroscopy. From these the detailed distribution of structural isomers is calculated. Several fractions having number-average molecular weights (by vapor pressure osmometry) M?_n≥10⁴ are isolated by a successive solutional fractionation run from whole random polymers. For solutions of random polymer in acetone at 30°C, [η]=0,631 · M? (where [η] is limiting viscosity number) and for high-ortho polymer [η]=0,0813 · M? are established. The former equation can be interpreted in terms of the Zimm-Stockmayer theory of branched polymer solutions.     

Deuteron NMR relaxation and molecular motion of polystyrene in solution

Deuteron relaxation times T₁ of polystyrenes deuterated at the backbone (PS-d₃) and the phenyl ring (PS-d₅), respectively, have been measured in solutions of benzene and diethyl malonate as a function of concentration and temperature. We conclude that the motion of the phenyl ring is faster than that of the backbone, the difference being smallest at high temperatures around 180°C. The temperatures dependence is discussed in relation to the activation energies in polystyrene.     

Change in molecular weight distribution accompanying thermal degradation of isotactic polystyrene

The molecular weight distributions of isotactic polystyrene samples subjected to various degrees of thermal degradation were experimentally determined and compared with those derived theoretically for randoms scission of the polymer chains. Agreement between the theoretical and the experimental results was fairly good. It was found that the molecular weight distributions of the original and the thermally degraded isotactic polystyrene can be represented by the logarithmic normal distribution function. The degree of degradation is nearly linear with time. The scission of the main chains seems to occur at random up to 330°C. The activation energy for the thermal degradation of isotactic polystyrene at 290 to 330°C. was 42 kcal. /mole. The results of thermal degradation of the isotactic polystyrene were compared with those of the atactic polystyrene.     

Phylogeny of low molecular weight immunoglobulins

Because comprehensive studies of antigenic comparison of LMW Igs of non-mammalian vertebrates are lacking, such investigations have been done using double antibody RIA inhibition methods and antisera, produced in rabbits and carps. The dominant 7S Igs of anuran amphibians, reptiles, and birds are highly cross-reactive among one another and therefore belong to one class. They are different from mammalian IgG and IgD. In contrast to the so-called chicken IgA which shows no antigenic cross-reactivity with mammalian IgA and should be named IgB, the dominant 7S Igs of amphibians, reptiles, and birds have a well defined antigenic similarity with mammalian IgA. For that reason they do belong to the IgA class. A phylogenetic tree of Igs is discussed.     

A low molecular weight heparin in hemodialysis

Summary The purpose of our study was to check whether the dosage recommended for the low molecular weight heparin tested here, i.e., 50% of the corresponding unfractionated heparin dose, is adequate to prevent clot formation in the extracorporeal system. Sixteen dialysis treatments of 4–5 h were given to each of six chronic dialysis patients. In dialyses 1, 2, 15 and 16 unfractionated heparin (initial dose 35 IU/kg, continuous dose 20 IU/kg/h) was given, and in dialyses 3–14 low molecular weight heparin (initial dose 17.5 anti-Xa U/kg, continuous dose 10 anti-X U/kg/h). At these dose levels of low molecular weight heparin, clot formation occurred in the extracorporeal system in five of the six patients, despite the fact that the plasma anti-Xa level of 0.5 U/ml recommended by the manufacturer had been attained. For this reason the continuous dose of low molecular weight heparin had to be raised to approx. 80% of the corresponding continuous dose of unfractionated heparin. A plasma anti-Xa level of 0.7 U/ml is necessary to prevent extracorporeal clot formation.Abbreviations anti-Xa U Anti-factor Xa unit - aPTT Activated partial thromboplastin time - AT III Antithrombin III - IU International unit - LMWH Low molecular weight heparin - UFH Unfractionated heparin     

Study on the molecular weight dependence of dilute solution properties of narrowly distributed polystyrene in toluene and in the unperturbed state

Intrinsic viscosities [η], second and third virial coefficients A₂ and A₃, respectively, and mean square radius of gyration 〈R_G²〉 of a polymer homologous series of narrow-molecular-weight-distribution polystyrene samples in a molecular weight range of 2000 up to 24 · 10⁶ were determined in toluene at 25°C by light scattering and viscometry measurements. The results are (3 · 10⁴ < M_w < 24 · 10⁶, M_w/M_n ≤ 1,3): These results were obtained by consideration of the limit of the dilute solution regime, the determination of zero-shear rate intrinsic viscosities, and the molecular weight dependence of the refractive index increment dn/dc. It was found that dn/dc increases slightly up to M_w = 1,8 · 10⁶. A comparison of the [η]?M_w-relationship with literature data is given. In addition the unperturbed (theta) dimension parameters K₀, 〈h²〉₀/M, the characteristic ratio C_∞, the steric factor σ, and the thermodynamic interaction parameter B were calculated from the modified Burchard-Stockmayer-Fixman procedure using polymolecularity correction and the results compared with experimental data from the literature.     

Renal processing of low molecular weight proteins

Previous renal clearance studies provided quantitative data concerning renal reabsorption of proteins while the simultaneous processes of renal accumulation and degradation remain, to a great extent, insufficiently investigated. Thus, it was the aim of this study to measure renal reabsorption of egg-white lysozyme at various lysozyme concentrations and to relate the corresponding accumulation and degradation of lysozyme to the lysozyme transport rates in intact rats and isolated perfused rat kidneys. Lysozyme (with¹²⁵I-lysozyme in certain experiments), was continuously infused i.v. or added to the perfusate to achieve plasma (or perfusate) concentrations of lysozyme (P_LY) of approximately 50, 500 or 1000 mg·l^–1 for periods of time varying between 3 and 120 or 150 min. Clearances of inulin and lysozyme or the total content of radioactivity and the trichloroacetic acid (TCA)-soluble radioactivity in the kidney tissue were determined at the end of clearance or accumulation periods. Additionally the perfusate concentration of the metabolite tyrosine was measured by high performance liquid chromatography (HPLC).The reabsorption rates of lysozyme (T_LY) were concentration-dependent in both intact rats and isolated perfused rat kidney. After 25 min of lysozyme infusion, the lysozyme reabsorption rates amounted to 37, 245 and 331 g·min^–1·g^–1 kidney at the above lysozyme concentrations. After the same infusion time, the accumulation rates of lysozyme were 8, 59 and 118 g·min^–1·g^–1 kidney. The difference between the transport rate and accumulation rate should represent the renal degradation rate of lysozyme. The renal accumulation and degradation of lysozyme appeared to increase in a time- and concentration-dependent manner. The renal lysozyme degradation is of limited capacity as shown by measuring directly the release of the amino acid tyrosine by using HPLC. Renal degradation of lysozyme was almost totally inhibited by gentamicin in the presence of significant transport of lysozyme.The results of this study also demonstrate the ability of the rat kidney to reabsorb and accumulate large amounts of the cationic low molecular weight protein lysozyme without ultrastructural changes at plasma concentrations of lysozyme as high as 500 mg·l^–1. Transmission electron microscopy indicated an increase in the number of endocytic vesicles and lysosomes at 1000 mg·l^–1 plasma concentration of lysozyme after a 30 min infusion.     

How to standardize low molecular weight heparins

Heparin, used in anticoagulant and antithrombotic therapeutic for over fifty years, turns out to mean important side effects and serious haemorrhagic risk. The obtaining, from 1976, of the first low molecular weight heparins (LMWH) preparations is partly allowed to overcome those problems. The LMWH present an identical or greater antithrombotic capacity than the unfractioned heparin and mean a lower haemorrhagic risk. Thus their use in antithrombotic therapy is very interesting. However, the existence of different units for the LMWH sets a standardization problem for their clinical use and for their biological follow up. The first international LMWH standard introduction by the World Health Organisation in 1986 may be useful to give a great homogeneity of the interlaboratory results, to serve as reference to the biologists, as activity standardization for the manufacturers or as security for the clinicians. However, it seems its definition mode and its validity call into question by several authors. The anti Xa activity, advocated in the biological surveillance, does not seem to perfectly fit to the LMWH therapy. The debate about the standardization of the low molecular weight heparins keeps open.     

Synthesis and molecular weight characterization of low molecular weight end-functionalized poly(4-acryloylmorpholine)

New amphiphilic oligomers ending at one side with a reactive function were synthesized by radical polymerization of a vinyl monomer, N-acryloylmorpholine, in the presence of functionalized chain-transfer agents (CTAs). The oligomers were characterized in terms of molecular weight and molecular weight distribution, by means of analytical size-exclusion chromatography (SEC) working in buffered aqueous media. This has been accomplished by determining a calibration curve for a set of SEC columns, with poly(N-acryloylmorpholine) standards purposely obtained by means of preparative SEC. The transfer constant C_T of some CTAs towards N-acryloylmorpholine has been estimated to be approximately 1.     

Osmometry with membrane-permeating solutes of low molecular weight

Experimental osmotic pressure (p)-time (t) curves for several low-molecular weight Solutes in toluene were studied by means of a recording automatic osmometer. The results for a monodisperse solute can be expressed by p = r π exp (?αt), with π the theoretical osmotic pressure. In the case of more than one solute the pressures are additive. for a given set of experimental conditions, the parameters r and α depend on the molecular weight of the solute, but to some extent also on its structure. It is shown how an approximate estimate of molecular weight and concentration of a polymer additive can be made from p versus t plots in the course of a molecular weight determination of the polymer. The results could not be brought in agreement with the equation of HOFFMANN and UNBEHEND . Also, the assumptions underlying the theory of LAIDLER and SHULER do not seem to be adequate in the general case to relate α to r.     

Antigenicity of low molecular weight surfactant species.

The authors tested the antigenicity of human lung surfactant isolated from amniotic fluid. Mice and rabbits were immunized. Rabbit polyclonal antisera to these surfactant preparations were absorbed with normal human plasma proteins. Polyclonal antisera reacted with both high molecular weight (35 kd) surfactant apoprotein and to lower molecular weight species, both 18 kd and 9 kd. Mice were used to generate monoclonal antibodies to surfactant. Enzyme-linked immunosorbant assay was used to identify five monoclonal antibodies that reacted with surfactant. By Western blot analysis, all of these recognized a low molecular weight surfactant species (9 kd) that could be either SP-B or SP-C. One reacted with a 37 kd protein in the surfactant preparation, consistent with SP-A. One monoclonal antibody also recognized a higher molecular weight species (44 kd) of unknown origin. The ability of antisera and monoclonal antibodies to inhibit the functional activity of surfactant was assayed using a pulsating bubble surfactometer. Rabbit polyclonal antisera inhibited initial surface adsorption to equilibrium surface tension and increased the minimum surface tension after 1 and 5 minutes of initiation of pulsations. This inhibitory activity of the antisera was noted in divalent F(ab')2 fragments. Monovalent F(ab) fragments and control normal rabbit sera did not inhibit surfactant function in this assay. Of the anti-surfactant monoclonal antibodies that reacted with surfactant by ELISA and Western blot, three inhibited its capacity to lower surface tension on the pulsating bubble apparatus. The other two monoclonal antibodies showed no functional inhibitory activity. It is concluded that both the 35 kd SP-A and the 9 kd proteins of human surfactant are highly immunogenic and partially crossreactive. Resulting antibodies could alter the ability of surfactant to perform its physiologic function, ie, to lower surface tension.     

Intrinsic viscosity-molecular weight relationship for low molecular weight cellulose and oligosaccharides

The viscosity behaviour of low molecular weight cellulose and oligosaccharides has been investigated. In the high molecular weight region the double-logarithmic plot of intrinsic viscosity vs molecular weight is linear down to approximately DP = 150. On passing to lower molecular weights the slope of the curve at first increases, passes through a maximum and finally decreases to very low values in the oligomere region.     

Application of the FLORY-FOX-SCHAEFGEN intrinsic viscosity molecular weight relation to high polymers

The relationship for the determination of unperturbed dimensions, as proposed by FLORY -FOX -SCHAEFGEN , has been found to be inapplicable to many polymer-solvent systems. However, while plotting [η]^2/3/M^1/3 vs. M/[η] for different solvents a common point of intersection which is not on the ordinate has been observed in all the cases. Unperturbed dimensions obtained from this point have been found to agree with those derived by using other methods.     

Expression of low molecular weight cytokeratin proteins in laryngeal dysplasia

In twenty-three cases of laryngeal dysplasia frozen mucosal strips were examined with four monoclonal and one polyclonal keratin antibody. The expression of specific keratin polypeptides was studied in different degrees of dysplasia with regard to the subunits expressed in normal and carcinomatous laryngeal epithelium in the same patient. An alteration in the expression of the subunits of cytokeratin in favour of low molecular weight polypeptides takes place in the transformation of normal epithelium to squamous cell carcinoma. This alteration seems to occur at an early stage and is present already in mild dysplasia. The results suggest that with a suitable antibody dysplastic laryngeal epithelium can be distinguished from normal epithelium, and also on some cases, mild dysplasia from more severe degrees of dysplasia. CAM 5.2, which identifies lower molecular weight cytokeratin proteins (50, 43 and 38 kD), is such an antibody, and can be a valuable diagnostic aid in the histological interpretation of laryngeal dysplasia.