Refractive Increment Research Articles

Surface Modifying Additives for Improved Device–Blood Compatibility

Copolymers composed of polar and nonpolar blocks, when blended with a base polymer in low concentrations, migrate to the base polymer surface during and after fabrication. Migration of these surface modifying additives (SMAs) dramatically changes the outermost surface molecular layers that comprise the region that determines biocompatibility. The blood compatibility of cardiopulmonary bypass and hemodialysis components have been improved by using SMA blended polymers or SMA coated surfaces. The particular SMAs used were a series of triblock copolymers with a general formulation of polycaprolactone-polydimethylsiloxane-polycaprolactone. X-ray fluorescence (XRF), fourier transform infrared (FTIR), refractive increments (RI), and gel permeation chromatography (GPC) were used to characterize the molecular weight of SMA and the bulk concentration of SMA after blending. Electron spectroscopy for chemical analysis (ESCA) proved that the surface of blended polymers was highly saturated with SMA. Results of in vitro experiments with human blood demonstrated that SMA blended polymers delay contact activation (kallikrein-like activity), reduce coagulation activity (thrombin-antithrombin [TAT] generation), and do not adversely affect complement activation (terminal complement complex [TCC] generation) or mononuclear cells activation (IL-1 beta production). Ex vivo canine AV shunt studies showed improvement of platelet compatibility of SMA blended polymers. Reduction of cellular and protein system activation by using components fabricated with SMA blood contacting surfaces can potentially result in reduced morbidity associated with extracorporeal circulation.

Effect of fluctuations on the refractive indices of some pure liquids

This work describes an indirect experimental method for the determination of the specific refractive increments (∂n/∂T)ϱ. Measurements carried out on water and several organic liquids are reported. Different relations between density and refractive index of pure liquids are used. The results prove the superiority of the relation suggested by us.

What is the lowest refractive index of an organic polymer?

The theoretical lower limit of the refractive index of organic polymers was investigated using the Lorenz-Lorentz equation. Starting from an extended data base, optimized refractive and density increments for functional groups were evaluated.

The refractive increments of bovine alpha-, beta-, and gamma-crystallins.

The refractive increments have been determined for purified bovine alpha-, beta- and gamma-crystallins, using three different light sources. The values obtained were used to predict the refractive index gradient in the rat lens. Excellent agreement was obtained between the predicted and observed gradients.

Analytic ultracentrifuge calibration and determination of lipoprotein-specific refractive increments.

Accurate quantification of the major classes and subfractions of human serum lipoproteins is an important analytical need in the characterization and evaluation of therapy of lipid and lipoprotein abnormalities. For calibrating the analytic ultracentrifuge (AnUC), we routinely use a Beckman calibration wedge cell with parallel scribed lines 1 cm apart. Such a cell gives a rectangular pattern in the schlieren diagram, which determines magnification and also provides an area corresponding to an invariant refractive increment. We have independently validated this wedge calibration cell using a special boundary-forming cell in which 1.174% sucrose is overlayered with distilled water. Comparing wedge cell area with extrapolated zero time boundary area refractive increment gives agreement to within less than 1%, corresponding to a refractive increment error of +/- 0.00002 delta n. Complete calibration for AnUC analysis of lipoproteins also requires accurate determination of the specific refractive increments (SRI) of the major lipoprotein classes, namely low density lipoprotein (LDL) and high density lipoprotein (HDL). These are measured in the density in which they are analyzed, i.e., 1.061 g/ml for LDL and 1.200 g/ml for HDL. Five fresh serum samples were fractionated for total LDL and total HDL and their SRI determined. Total lipoprotein mass was determined using precise CHN elemental analysis and compositional analyses. The results yielded corrected SRI of 0.00142 and 0.00135 delta n/g/100 ml for LDL and HDL. Thus, our current values using 0.00154 and 0.00149 delta n/g/100 ml underestimate LDL and HDL by 9% and 11%. Corrections of all previous LDL and HDL AnUC data can be made using appropriate factors of 1.087 and 1.106.

Excess Polarizability and Volume of Mixing and Their Effect on the Partial Specific Volume and the Refractive Increment of Polymers in Mixed Solvents

Excess Polarizability and Volume of Mixing and Their Effect on the Partial Specific Volume and the Refractive Increment of Polymers in Mixed Solvents

Light-scattering and specific refractive increment behavior of amylose and dextran in methyl sulfoxide-water

Light-scattering measurements on polysaccharides in methyl sulfoxide or methyl sulfoxide-water are most reliable when made on a dialyzed solution-solvent system and when proper technique is used to remove the “micro gel” that seems unavoidably present when dried polysaccharide is dissolved in solvent. Discrepancies in published molecular weight-intrinsic viscosity relationships for amylose in methyl sulfoxide appear to be caused in part by differences the preparation and treatment of samples and possibly by differences in botanical source. The specific refractive increment of dextran is not a linear function of solvent composition in methyl sulfoxide-water. Measurements at osmotic equilibrium indicate that, over a moderate range of composition in methyl sulfoxide-water, dextran preferentially associates with about 2.5 molecules of water per glucopyranosyl residue of the polymer. Effects of long-term storage, sample treatment, and botanical source upon the specific rotation of amylose are examined.

Physical and chemical properties of human plasma alpha2-macroglobulin.

Alpha2-M (alpha2-macroglobulin) was purified from human plasma by two different procedures. As well as having no detectable impurities by the usual criteria for testing the homogeneity of protein preparations, these alpha2M preparations showed a single component, after reduction in urea, of 185000 daltons by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. The molecular weight of the alpha2M was found to be 718000 by sedimentation equilibrium experiments using the gravimetrically determined -v of 0.731 ml/g. The interaction of several proteinases with alpha2M was studied by using a novel discontinuous polyacrylamide-gel system, which showed clear separation of the enzyme-complexed alpha2M from the free alpha2M. These studies indicated that urokinase, as well as trypsin, chymotrypsin, plasmin and thrombin forms complexes with alphaM. The cleavage of the 185000-dalton subunit to a 85000-dalton species on interaction of trypsin with alpha2M was demonstrated by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis after reduction of the alpha2M-trypsin complex in urea. The amino acid composition, carbohydrate content, absorption coefficient at 280 nm, the specific refractive increment and the sedimentation coefficient for these alpha2M preparations were measured. The stability of the trypsin-binding activity of the alpha2M preparations was also studied under several storage situations.

New differential Bottcher-Onsager method used to determine polarizability and apparent radius of tungstosilicate (SiO4(WO3)124-)

A differential form for the Bottcher--Onsager law is derived. Based on this form, a new method is presented for determining the polarizability and apparent radius of the molecules of a solute from measurements of the temperature variation of the density and specific refractive increment of its solutions. The method is particularly applicable to solutes which are only slightly soluble in a given solvent. The density and specific refractive increment of aqueous solutions of tungstosilicic acid have been measured at four temperatures: nominally, 20, 25, 35, and 45/sup 0/C. The densities are found to be linear functions of concentration in the range 0 to 0.03 M. From the density measurements, the apparent molar volume of H/sub 4/SiO/sub 4/(WO/sub 3/)/sub 12/ at each temperature is determined. The specific refractive increment is determined for radiation at 589 m..mu... Using our differential method, we find ..cap alpha../sub 2/ = 50 +- 5 A/sup 3/ and a/sub 2/ = 3.2 +- 0.2 A, where ..cap alpha../sub 2/ and a/sub 2/ are the polarizability and effective radius, respectively, of SiO/sub 4/(WO/sub 3/)/sub 12//sup 4 -/.

Solution Properties of Poly(2-methoxyethyl methacrylate)

Solution properties of poly(2-methoxyethyl methacrylate) (PMEMA) were investigated by light scattering, viscometry, and gel-permeation chromatography (GPC). The refractive and density increments and the apparent partial specific volumes of PMEMA in various solvents were determined. The properties of cosolvent mixtures for PMEMA are discussed. The constants of the Mark—Houwink equation for PMEMA fractions were determined in methyl ethyl ketone and tetrahydrofuran. The steric factor of PMEMA was determined from viscometric data. Comparison of the molecular parameters of PMEMA calculated from the GPC data and measured by an independent method confirmed the validity of the universal calibration. The solution properties of PMEMA and poly(methyl methacrylate) are compared.

The macromolecular properties of blood-group-specific glycoproteins. Characterization of a series of fractions obtained by solvent fractionation.

1. The glycoprotein components of a human ovarian-cyst fluid were isolated by a solvent [95% (w/w) phenol]-extraction procedure; the phenol-insoluble water-soluble glycoprotein was further fractionated by (NH(4))(2)SO(4) and by ethanol to yield eight fractions. 2. The fractions were analysed in terms of amino acids, fucose, galactose, N-acetylglucosamine, N-acetylgalactosamine and sialic acid. Variations occurred, particularly in the proportion of peptide; these were partly correlated with varying extent of serological activity. 3. The fractions were characterized physicochemically in terms of buoyant density and degree of spreading in a density gradient, sedimentation velocity and molecular weight; their partial specific volumes and specific refraction increments were also determined. 4. The fractions showed wide variations in their sedimentation-velocity and density-gradient patterns, and gave evidence of pauci-dispersity in density. The fraction regarded as the most typical blood-group-specific glycoprotein sedimented as a single rapidly spreading peak and was of high molecular weight. 5. Significant correlations were observed between the physical properties of the glycoprotein fractions and the amount of their peptide component. The buoyant densities and sedimentation coefficients varied in a manner that suggested the existence of two families of glycoproteins. 6. It is suggested that variability in the extent of glycosylation, or in the degree of cross-linking, might account for the two families of glycoproteins, and that the extent of cross-linkage might also be a factor determining the solubility of these glycoproteins in hot saturated (NH(4))(2)SO(4).

Dilute solution characterization of a POLA polyester

AbstractSamples of poly(4,4′‐isopropylidenediphenylene 1,1,3‐trimethyl‐3‐phenylindan‐4′,5‐ dicarboxylate) were fractionated by the column‐elution, temperature‐gradient technique. Selected fractions, covering a 10‐fold range of molecular weight, were shown to have narrow molecular weight distributions by gel‐permeation chromatography (GPC), i.e., M̄w/M̄n = 1.15 ± 0.10. The fractions were further characterized by viscometry, light scattering, and membrane osmometry. Characterization of the small samples (ca. 0.3 g) was facilitated by use of a low‐volume light scattering cell. This allows measurements of refractive increment, light scattering, and viscosity to be performed on as little as 50 mg of sample. Molecular weights estimated by the GPC‐viscometry technique were in good agreement with the values obtained by light scattering. Estimates of the perturbed coil dimensions (150–200 Å) were in satisfactory agreement with those observed experimentally. The polydispersities of the fractions, determined by osmometry and light scattering, were in fair agreement with GPC data; the latter are considered subject to less experimental uncertainty.

Temperature dependence of optical properties of aqueous dispersions of phosphatidylcholine

Aqueous dispersions of dipalmitoyl phosphatidyl choline exhibit a sharp decrease in turbidity at the crystal-liquid phase transition temperature of 41°C. The intensity of light scattered at 45°, 90°, and 135° also undergoes a sharp drop at the same temperature. Similarly, the refractive index of such dispersions decreases abruptly with the phase transition. Employing the relationship between light scattering intensity and specific refractive increment, it can be shown that about one half of the change in absorbancy and scattering are accounted for by the change in refractive index. The change in refractive index can be entirely accounted for by the known expansion and corresponding decrease in density of the bilayer. That part of the observed change in scattering and turbidity which is not accounted for by the observed change in average refractive index is apparently due to a decrease in the anisotropy of the bilayer during the melting process. Calculations based on a model which, although oversimplified, is consistent with the known thinning of the bilayer during the melting process, give quantitative agreement with experimental results. Below the phase transition temperature other changes in optical properties are observed; near 32°C, the light scattering envelope changes and the turbidity of dispersions drops markedly. The average refractive index remains constant in this region. For this and other reasons, it is postulated that these pre-transition changes indicate an aggregation-disaggregation phenomenon.

Remarks on Light Scattering from Polymers in Mixed Solvents: Effects of Polymer Molecular Weight, Molecular Weight Distribution, and Solvent Composition

It is known that light-scattering data for a polymer in a mixed solvent together with the refractive-index increment of the polymer evaluated at osmotic equilibrium (i.e., at fixed chemical potentials of solvent components) permit unambiguous determination of the molecular weight of the polymer–irrespective of preferential interactions between polymer and solvent. However, the analysis presumes either of two conditions; the polymer is homogeneous in molecular weight or the “osmotic” refractive increment does not depend on molecular weight. When both conditions are violated, the apparent molecular weight obtained may differ from the true weight average. This problem is examined with the aid of parameters derived from light-scattering data of Dondos and Benoit. The error in typical cases is shown to be less than uncertainty in scattering measurements if polymer heterogeneity is not extreme (say Mw/Mn≤2); but the behavior of each scattering system must be assessed individually. The data also afford material for some observations on the dependence of preferential interactions on composition of a binary solvent.

Solution properties of poly(trimethylsiloxanotitanoxanes) (titanium oxide trimethylsilyloxides)

To obtain more information on the structure of the polymeric hydrolysis products of Ti(OSiMe 3) 4, (the titanium oxide trimethylsilyloxides), measurements were made of the degrees of polymerization and hydrolysis, sedimentation, viscosity, specific volume, refractive index increment and turbidity of five hydrolysis products in cyclohexane solution. Refractive increments and turbidities were also measured for two products in carbon tetrachloride, benzene, chlorobenzene and bromobenzene. A self-consistent description of the properties of these polymers is based on repeating units containing a cube-shaped Ti 8O 12 structure. These units undergo condensation to give two types of chains having one and two bridging oxygens, respectively, between successive repeating units. Evidence for this model is obtained from the interdependence of degrees of polymerization and hydrolysis, from sedimentation, and from the dependence of turbidity on the refractive index of the solvent. Specific volumes calculated from the model agree well with experiment. Refractions for the Ti-1bO bonds in metalloxane chains, calculated from the refractive index increments, indicate that formation of longer chains causes an increase in refraction towards the value for TiO 2. The distribution of metalloxane links and the high polydispersity of the products presumably arise. from labile intermolecular condensation during hydrolysis.

Refractive index increments of polymers in solution: 2. Refractive index increments and light-scattering in polydisperse systems of low molecular weight

Theoretical equations are deduced which predict that the specific refractive index of a polymer in solution is v = v ∞ + v 0 M ̄ n , where M ̄ n is the number average molecular weight, and v ∞ and v 0 depend on the refractive index, n 1, of the solvent, on the specific refractivity of the pure polymer, and on the specific volume of the polymer in solution. These equations are used to show that the true weight average molecular weight and second virial coefficient, as obtained from light scattering, can be obtained from the observed values of these quantities only if M ̄ n and the dependence of v on M ̄ n are known. The difference between the true and observed values can be very pronounced for values of M ̄ n less than about 10 3. Mixtures of two polymers whose refractive increments depend on molecular weight are also considered. Methods of distinguishing the effects of polydispersity of composition from effects due to the dependence of the average v on the average molecular weight are discussed for mixtures of components whose individual properties are unknown.

Refractive index increments of polymers in solution: 1. General theory

Methods for calculation of refractive index increments of polymers in solution from the properties of the pure polymer and solvent and a suitable theory of polarization are developed. Volume changes on mixing the components, the effects of polydispersity, and the value of partial specific refractions are discussed rigorously. The general methods are used to derive a new equation for the refractive index increment from the polarization theory of Onsager and Böttcher. Errors in the Lorenz-Lorentz equation for the refractive increment are predicted to depend on the refractive index of the solvent, in agreement with experiment. Tests of the new equation, using existing experimental data, show that its accuracy is greater than the Lorenz-Lorentz equation, but is limited by a lack of knowledge of molecular parameters for the solvent and polymer.

Effect of molecular weight on the refractive increment of polyethylene and n‐alkanes

AbstractAs in the case with other polymers previously reported, the values of the refractive index increment dn/dc of polyethylene and the n‐alkanes change with molecular weight. Most of the variation may be understood by examination of the role of density in the Lorentz‐Lorenz mixing equation for specific refractivity, R12 = p1R1 + P2R2 used to calculate dn/dc. It may also be shown that as the absolute refractive index difference between solute and solvent becomes smaller, dn/dc becomes more sensitive to density change of the solute.

Sedimentation equilibrium in nonideal heterogeneous systems. I. Fundamental equations for heterogeneous solute systems and some preliminary results

AbstractThe sedimentation‐equilibrium method is extended to treat nonideal solutions of heterogeneous macromolecules. The solute is assumed to be heterogeneous not only in molecular weight but also in other quantities such as partial specific volume, second virial coefficient and specific refractive increment. General expressions for various observable molecular weights, especially for weight‐average, z‐average, and number‐average molecular weights, are derived. Their dependences on sedimentation parameter and solute concentration are discussed in detail. For the extrapolation of observable molecular weights, giving a type of weight‐average, and z‐average, to infinite dilution to estimate the molecular weight and the second virial coefficient, average concentration is superior as a concentration variable to original concentration. The plots of observable molecular weight versus average concentration are usually less influenced by the choice of the sedimentation parameter, especially of rotor speed. The general expressions are applied to a few special cases; monodisperse polymer, polydisperse homologous polymer, and polymer blend. The results are compared with experiments on a monodisperse, polystyrene, a polydisperse poly(methyl methacrylate), and a mixture of the two polymers, all in 2‐butanone at 25°C. The agreement between the theory and experiments is satisfactory.

Dipole moments and conformation of sulphinic acid esters

The electric dipole moments of some simple sulphinic acid esters have been measured in benzene. Conformations have been determined by a graphical method. The approximate conformation of the functional group is gauche as is supposed for the conformation of free sulphinic acid. These results can be explained on the assumption that one of the free electron pairs on oxygen is localized in an essentially unhybridized p orbital. The group refraction increment 10·02 cm.3 for –SO·O– was determined.