Molecular Size Parameters Research Articles

Adsorption of Local Anesthetics on Activated Carbon: Freundlich Adsorption Isotherms

We have shown that adsorbability of local anesthetics onto activated carbon, expressed by the partition coefficients at infinite dilution, correlated well with the pharmacological activity. However, there is no parameter that can singly express the tendency to be adsorbed. Adsorbability is a loosely defined term and its meaning varies with the adsorption model. This study showed that the logarithm of the adsorbed amount of drugs was linearly related to the logarithm of the free drug concentration, in conformity to the Freundlich adsorption isotherms. The slope of the double logarithmic plot is expressed by 1/N in the Freundlich equation and is considered to be inversely related to the drug affinity to the adsorbent. The slope was used to evaluate the tendency to be adsorbed, or “adsorbability” of seven aromatic amine local anesthetics. Phenobarbital was included to compare anionic drugs in contrast to the cationic local anesthetics. The slopes were nearly equal between the cationic and neutral local anesthetics. Apparently, the lower hydrophobicity of the cationic forms is compensated by the electrostatic attraction from the negative charges present on the activated carbon surface. With phenobarbital, the slope value of the anionic form was larger than the neutral form. The lower affinity of the anionic form may be caused by the electrostatic repulsion. The molecular size parameters (i.e., molecular weight, molar refraction, and parachor) showed a linear relationship to the slope values. It may be possible to estimate the affinity-related slope values from these parameters.

On the determination of effective hard convex body parameters for liquid mixtures

We derive a systematic method for determining effective molecular size parameters for use in perturbation theories of dense fluid mixtures using non-spherical reference systems of hard convex bodies. The method is based on the compressibility theorem. For the case of mixtures of atomic fluids, the method reduces to a prescription suggested earlier by one of the authors. For molecular fluid mixtures where a reference system of hard ellipsoids is employed, a sufficient set of equations to determine the size and shape of the equivalent ellipsoids is derived. The method is applied to the benchmark system of an equimolar mixture of Ar/Kr at 115·8 K.

A rapid method for the structural characterization of sulphated phlorotannins by negative ion fast atom bombardment mass spectrometry and acetylation on the target

A method for a rapid and direct structural determination of sulphated phlorotannins has been developed by using a combination of negative ion fast atom bombardment mass spectrometry and acetylation on the target. The structural variations of sulphated phlorotannins include: (i) the number of monomeric phloroglucinol units involved; (ii) the mode of their connectivity; (iii) the orientation of hydroxy groups on aromatic carbon atoms; (iv) the presence of the substituents other than hydroxy groups on aromatic carbon atoms; and (v) the number of sulphate esters on the hydroxy groups. Additionally, the acidic protons on the sulphate groups can be easily substituted by sodium or potassium cations, depending on the mode of isolation. In the negative ion mode, several ions were observed and a determination of molecular size and molecular parameters (i)–(v) appeared to be rather speculative. After adding diluted hydrochloric acid to the sample in order to substitute alkali ions for protons, the hydrolysis of sulphate groups has been observed. The acetylation on the target, however, represents a rapid method to observe the molecular ions, and from the mass differences the molecular parameters can be easily calculated. This procedure also demonstrates the general possibility of studying rapid chemical reactions by fast atom bombardment mass spectrometry.

A rotational equation of state for normal paraffins

The hard convex body and hard sphere equations of state are used to derive a partition function that considers the effect of density on ratational motion in addition to translation. The inclusion of the rotational contribution in the perturbation theory gives rise to a more general principle of corresponding states for thermodynamic properties of polyatomic fluids. The argon equation of state developed by Twu—Lee—Starling is used to calculate the properties of a reference system in the perturbation expansion. In addition to adding the rotational pressure to the argon equation of state, the size of the reference system is also scaled up to that of real systems of interest to describe the properties of systems with either small or large molecules. The equation of state contains a structure parameter which acts as a third parameter in addition to molecular size and energy parameters. The size parameter can be calculated from the critical volume, the energy parameter from the critical temperature, and the structure parameter from the normal boiling-point temperature. Furthermore, the generalized equation of state for normal alkanes can be reduced to a function only of normal boiling-point temperature. The rotational equation of state represents accurately the vapor pressures, densities and enthalpy departures of the vapor, liquid and fluid states over the entire range of practical interest for the normal paraffins. For normal-paraffins, methane through n-eicosane, the average absolute deviation percent for all properties is less than 1% for 1541 points.

Mark–Houwink–Sakurada constants and dilute solution behavior of heterodisperse poly(acrylamide-co-sodium acrylate) in 0.5M and 1M NaCl

Mark Houwink coefficients and molecular size parameters are presented for 31 unfractionated samples of polyacrylamide and hydrolyzed polyacrylamide in 0.5M and 1M aqueous NaCl. Polymers investigated include polyacrylamide, plus 10, 20, 50, 70, and 100 mol % poly(sodium acrylate). Their solution characteristics were studied by gel permeation chromatography, intrinsic viscosity, and light scattering techniques. A density function and heterodispersity index was assigned to each polymer sample due to the polydispersity of the molecular weight distributions. This technique improves the intrinsic viscosity–molecular weight correlation for heterodisperse commercially synthesized polymer systems. The intrinsic viscosity of these commercial compounds will yield useful estimates of their molecular weight, in spite of their obvious heterogeneity.

SANS studies of concentrated protein solutions. I. Bovine serum albumin.

AbstractSmall‐angle neutron scattering (SANS) was used to examine concentrated bovine serum albumin solutions of up to 20% protein w/v. At higher protein concentrations, scattering data show distinct features that can be ascribed to strong intermolecular interactions. Differential scattering cross‐sections are fitted to a theoretical model of interparticle potential consisting of a hard core plus an exponentially decaying “tail.” For moderate ionic strength (0.03M K Acetate, pH 5.9), the intermolecular interaction agrees with the double‐layer repulsive part of the well‐known DLVO (Derjaguin, Landau, Verwey, Overbeek) theory for interacting colloidal particles. We thus demonstrate that it is possible to determine size parameters and the surface charge of protein molecules in dense solutions. At high salt concentrations (≥0.2M NaCl) data can be fitted by the same potential model, although interpretation in terms of DLVO theory is not possible. Even in this case, however, “effective” molecular size and potential parameters can be determined.

COMMENTS CONCERNING A SIMPLE EQUATION OF STATE OF THE VAN DER WAALS FORM

When the Carnahan-Starling equation of state for hard spheres is combined with a simple attractive term, the molecular size parameter b for argon (as obtained from critical data) is much closer to the “correct” value than that obtained from the empirical Redlich-Kwong equation For the critical isotherm for argon, the best simple form of the attractive term lies between the two common forms, proposed by van der Waals and by Redlich. At constant temperature, the attractive contribution to the compressibility factor is proportional to (v + 0.2b)−1 where v is the molar volume. This proportionality is in agreement with results for a square-well fluid recently reported by Sandier.

Heat-stable low molecular weight form of phosphodiesterases from bovine pineal gland.

The 105,000 X g supernatant fraction of bovine pineal gland contains a phosphodiesterase activity that hydrolyzes both cyclic AMP and cyclic GMP. The rate of hydrolysis is 4-5 times greater with cyclic GMP as substrate than with cyclic AMP. Chromatography of supernatant fraction on Sephadex G-150 resolves phosphodiesterase activity into two fractions designated PDE I and PDE II. These are distinguishable on the basis of their molecular size, substrate specificity, and kinetic parameters. PDE I hydrolyzes cyclic GMP at a faster rate than cyclic AMP and has a molecular weight of 163,000. PDE II appears to be a smaller protein with a molecular weight of 24,400 and is specific for cyclic AMP. PDE I has apparent Km values of 83 and 53 micron for cyclic AMP and cyclic GMP, respectively, whereas PDE II exhibits an apparent Km value of 330 micron for cyclic AMP. With subsaturating concentrations of cyclic AMP as substrate, the phosphodiesterase activity of PDE I is inhibited by the addition of cyclic GMP. However, PDE II activity remains unaffected by cyclic GMP even at concentrations up to 125 micron. PDE II appears to be thermostable, losing only 20% of its activity on heating at 80 degrees for 2 min. Similar treatment completely abolishes the enzyme activity of PDE I.

Correlations between retention volume and molecular size parameters in gel permeation chromatography of small molecules

Gel permeation columns of Bio Beads S-X8 have been used to provide separation of oligomers and other small organic molecules. Results show successful separations up to molecular weight c. 600. The retention times of compounds have been correlated with the largest molecular dimension of the molecules and also with molar volumes.

An improved treatment of data for estimation of molecular weights by sephadex gel filtration

A method for analysis of elution data of proteins, obtained from Sephadex gel filtration experiments, is described. The relevant elution data from seven different proteins, with known molecular weights and Stoke's radii, were fitted into various equations relating elution parameters and molecular size parameters. It was observed that polynomial relationships represented elution data for proteins with a much greater degree of precision than linear equations. The validity of this procedure was also checked by analysing gel filtration data available in the literature and it was concluded that a better fit was obtained using polynomial relationships, provided a sufficiently large number of experimental points were available for numerical analysis. Using this method, values of 320,000 ± 7000 for the molecular weight, and (60 ± 0.4) × 10 −8 cm for the Stoke's radius of Neurospora NAD-specific glutamate dehydrogenase were calculated.

Effect of temperature on molecular weight measurements in polyethylene

AbstractLight‐scattering evaluations of molecular weight and gyration radii have been carried out over a range of temperatures for linear and branched polyethylenes in α‐chloronaphthalene solutions. In a number of cases the molecular size parameters have been found to depend on the solution temperature. When observed, the temperature dependence can change molecular weight values by as much as 50%. The temperature dependence tends to be more pronounced at higher molecular weights, in linear than in branched polyethylenes, and is particularly noticeable at solution temperatures below that of the normal crystalline melting temperature of the polymer. It is suggested that the temperature dependence of molecular weight parameters may be due to a gradual dissociation in solution of polymer aggregates arising from persisting interchain entanglements. A relationship was established between intrinsic viscosity and molecular weight for selected fractionated polyethylenes by using molecular weight data obtained under conditions unfavorable to the persistence of polymer aggregates. A number of published viscosity–molecular weight functions for polyethylenes was compared with the calibrated relationship. Some of the published equations gave results in good agreement with the present function, but a number of others resulted in gross overestimates of molecular weight. Polymer aggregation problems may have been encountered in the derivation of some of these viscosity–molecular weight functions. The comparison indicates the danger of indiscriminate choice of viscosity–molecular weight functions for use in rapid estimates of polymer molecular weight.