Molecules Of Different Sizes Research Articles

Determination of toxin-induced leakage of different-size nucleotides through the plasma membrane of human diploid fibroblasts

Human diploid lung fibroblasts were treated with cytolytic bacterial toxins and the nature of the membrane damage was investigated. [3H] uridine was used for differential labeling of cytoplasmic components of small or large molecular size. Two principal size categories were achieved by labeling the fibroblasts in either early growth phase or stationary phase, a high-molecular weight ribonucleic acid label and a low-molecular-weight nucleotide label. The size of the labeled molecules was determined by perchloric acid precipitation and gel chromatography. Leakage of labeled molecules of different size indicated the size of the "functional pores" in the plasma membrane caused by the test substance. The nonionic detergent Triton X-100 produced large functional pores in the fibroblast membrane as evidenced by rapid leakage of both large and small labeled molecules. Theta-toxin from Clostridium perfringens and the polyene antibiotic filipin both gave rise to considerably small functional pores in the plasma membrane. Although small molecules easily passed the treated membrane, large molecules could not escape from the cells even after prolonged treatment with these substances or by increasing their concentration. By the contrast, the leakage profiles obtained with melittin from bee venom or with delta-toxin from Staphylococcus aureus in each case suggested the formation initially of pores of intermediate size that increased upon prolonged incubation or when higher concentrations were used.

The amplified ribosomal DNA of dytiscid beetles.

During oogenesis in many animals there is a massive extrachromosomal synthesis of the genes for ribosomal RNA. In Dytiscid beetles, as in the toad Xenopus, the amplified ribosomal DNA occurs as circular molecules of different sizes. The circles fall into size classes that are integral multiples of a unit circle. It is probable that the unit circle contains the coding sequence for one precursor ribosomal RNA molecule plus accompanying spacer sequences.

ChemInform Abstract: HEATS OF MIXING OF TETRA‐ALKYLTIN COMPOUNDS WITH NORMAL AND BRANCHED ALKANES. ORDER IN LONG ALKANES

Heats of mixing at 25°C of SnR4(R = CH3, C2H5, C4H10) with seven n-alkanes from C5 to C16, three very branched alkanes 2,2,4-trimethylpentane, 2,2,4,6,6-pentamethylheptane, 2,2,4,4,6,8,8-heptamethylnonane and two lightly branched alkanes 2-methylpentane and 2-methylundecane are reported. Except for SnBu4 with n-C5 and n-C6, and SnR4 with the n-Cn series gives positive Δhm values which increase rapidly with n. In contrast, any SnR4 with the very branched alkanes give small or negative ΔhM values which are independent of the number of carbon atoms in the alkane. Intermediate results are obtained with the lightly branched alkanes. The heats indicate that only the alkane exterior of the SnR4 molecules interacts with the alkane component. We associate the positive contribution in the normal alkane systems with destruction, by the spherical SnR4 molecules, of the orientational order existing in the n-Cn components. The order being absent in the globular branched alkanes, the ΔhM are small and negative as required by the difference in free volumes of the components. A quantitative treatment is given in terms of recent free volume theories coupled with an estimate of the orientational order obtained from depolarized Rayleigh scattering results. It is possible that part of the highly negative heats found with tetrabutyltin and the highly branched alkanes, which are unexplained by free volume differences, reflects preferential packing, an effect observed with spherical molecules of different size.

On the form of adsorption isotherms for substitutional adsorption of molecules of different sizes

Adsorption from solution occurs by solvent displacement in the interphase. When the adsorbate differs appreciably in size from the previously adsorbed solvent, the relative size factor ( x) of adsorbate and solvent determines ( a) the form of the relation for free energy of adsorption and ( b) the form of the configurational function in terms of fractional coverage θ or site fraction X. Various types of isotherms that have been proposed for this situation are critically compared in relation to the statistics of the solvent-lattice replacement process that occurs in adsorption, eg, of organic substances at electrodes. It is concluded that the correct configurational term to be used when x > 1 is θ/ e x−1 (1 −θ) x . Using this term in an equilibrium adsorption isotherm then allows standard free energies of adsorption and derived quantities to be properly calculated from experimental coverage or surface excess measurements. It is shown that it is strictly incorrect to refer to an isotherm containing the configurational term θ/ x(1 −θ) x as the “Flory—Huggins isotherm,” since Flory—Huggins statistics leads to an isotherm having a different form for the configurational term, viz that containing e x−1 , as above. For adsorption of molecules for which x > 1, failure to include the size factor term in the isotherm leads to errors in the evaluation of any interaction effects in the adsorption behaviour.

Determinants of intestinal mucosal uptake of short- and medium-chain fatty acids and alcohols

Uptake rates across the jejunal brush border have been measured for water-soluble fatty acids and alcohols and analyzed to determine the relative roles of the unstirred water layer and the lipid cell membrane as determinants of the intestinal absorptive process. Initial studies involving measurement of time courses of electrical transients developed across the intestine exposed to poorly permeant solute molecules showed no anomalous discrimination of probe molecules of different size or charge. This finding suggests that the diffusion barrier in the intestine can be considered as an unstirred water layer. Next, uptake rates of fatty acid were found to be linear with respect to concentration of the test solute, demonstrated no competitive inhibition or contralateral stimulation, had low temperature dependency, and were insensitive to metabolic inhibition, indicating that uptake proceeds by passive diffusion. Passive permeability coefficients, *P, varied from 22 +/- 1.4 to 395 +/- 9.2 nmoles.min(-1).100 mg(-1).mm(-1) for the saturated fatty acids 2:0 through 12:0 and from 119 +/- 3.3 to 581 +/- 45.2 for the saturated alcohols 6:0 through 10:0. Vigorous stirring of the bulk buffer solution enhanced *P values in direct proportion to chain length while the presence of bile acid micelles depressed apparent permeability coefficients in proportion to fatty acid chain length. These results demonstrate that uptake of short-chain fatty acid monomers is rate limited by the lipid cell membrane but diffusion through the unstirred water layer becomes increasingly rate limiting as the chain length increases. It is also possible to conclude from these data that diffusion through the unstirred water layer becomes totally rate limiting for uptake of long-chain fatty acid monomers of physiological importance.

Characterization of adenovirus DNA in KB cells infected with adenovirus type 12

In KB cells infected with adenovirus type 12, the newly synthesized viral DNA contains molecules of different sizes. Sedimentation studies show that fragments of about 0.5, 0.25 and 0.1 of the whole genome are formed, besides molecules of normal length. The fragments have the same average base composition and hybridization characteristics as parental DNA, which suggest that they represent the whole genome. The degree of degradation of type 12 parental and progeny DNA is not influenced by the multiplicity of infection ranging from 1000 to 5000 physical particles per cell. Coinfection of cells with adenovirus types 5 and 12 reveals that, in contrast to in vitro experiments, type 5 DNA is not affected by type 12 endonuclease. These results indicate that the structural viral components do not freely interact during uncoating and fragmentation.

The effect of varying molecular weight distribution on the properties of binders

Work is reported on the effect of variation of molecular weight distribution on the properties of binder stocks. This work used three prepolymers (polypropylene glycol 1000, 2000, and 4000 and polypropylene glycol 400, 1000, and 2000) of different molecular weight and known molecular weight distribution. The prepolymer of the middle molecular weight was employed as standard, and stocks were prepared from it. To this prepolymer was added some of the high and low molecular weight prepolymers in proportions such that the crosslink density of stocks made from the mixture was the same as that of stocks made from the middle molecular weight prepolymer alone. Two series were prepared with different crosslinking agents. The proportions of high and low molecular weight prepolymer were successively increased until finally none of the middle molecular weight remained. Heterogeneity indexes of the glycols and their mixtures were measured by gel permeation chromatography. Elongation at break, modulus of elasticity, and extent of solvent swelling were determined on the crosslinked stocks. Properties which vary with crosslink density were found to show decreasing values with increasing heterogeneity index even though the stocks were formulated to a constant crosslink density. Narrow-distribution stocks reach the maximum degree of cure faster than the broader-distribution stocks. Infrared and thermal analysis confirm that monodisperse polymer has a greater extent of reaction than heterodisperse polymer. Results showed that the variation in elongation at break to be expected because of lot-to-lot variations in heterogeneity index is probably not greater than the experimental variation in the elongation test below a heterogeneity index of 1.5. Above 1.5, however, if the effects observed are entirely due to variation in heterogeneity index, lot-to-lot variations in molecular weight distribution cannot be ignored. An explanation is presented based on the varying ability of prepolymer molecules of different size to diffuse through uniform mesh openings resulting in lower final extents of reaction for broad distribution material.

Dialysance of molecules of different size.

Dialysance of molecules of different size.

Biosynthesis of proteoglycans in cartilage slices. Fractionation by gel chromatography and equilibrium density-gradient centrifugation.

The kinetics of incorporation of [(35)S]sulphate into slices of pig laryngeal cartilage in vitro was linear with time up to 6h. The specific radioactivities of the extracted proteoglycans (containing about 80% of the uronic acid of the cartilage) and the glycosaminoglycans remaining in the tissue after extraction were measured after various times of continuous and ;pulse-chase' radioactivity incorporation. Radioactivity was present in the isolated chondroitin sulphate after 2 min, but there was a 35min delay in its appearance in the extractable proteoglycan fraction. Fractionation of the proteoglycans by gel chromatography showed that the smallest molecules had the highest specific radioactivity, but ;pulse-chase' experiments over 5h did not demonstrate any precursor-product relationships between fractions of different size. Equilibrium density-gradient centrifugation in 4m-guanidine hydrochloride showed that among the proteoglycan fractions the specific radioactivity increased as the chondroitin sulphate content decreased, but with preparations from ;pulse-chase' experiments there was again no evidence for precursor-product relationships between the different fractions. Differences in radioactive incorporation would seem to reflect metabolic heterogeneity within the proteoglycans extracted from cartilage. This may be due either to a partial separation of different types of proteoglycans or to differences in the rates of degradation of the molecules of different size and composition as a result of the nature and specificity of the normal degrading enzymes. The results suggest that molecules of all sizes were formed at the same time.

Renin induced proteinuria and the effects of adrenalectomy. II. Morphology in relation to function.

Glomerular permeability was investigated by using saccharated ferric oxide (Ferrivenin) as a tracer substance in sham operated and adrenalectomized rats during the infusion of normal saline and of renin and angiotensin. Kidney tissue was examined by electronmicroscopy. A striking increase in the number of the tracer substance particles was noted within the endothelial cells and basement membrane of sham operated rats infused with renin and angiotensin compared with that in adrenalectomized rats similarly treated or in rats infused with physiological saline only. No prominent change in the structure of the capillary wall was noted. More detailed information on the sieving characteristics of the glomerular filter and of the modifications induced by renin and angiotensin and by adrenalectomy was obtained by studying its behaviour in relation to the rates of passage of radioactively labelled PVP molecules of different sizes. In sham operated rats during renin or angiotensin infusion the passage of the higher molecular weight fractions of the polymer through the glomerular membrane was significantly increased, while the filtration of the lower molecular weight fractions was similar to that observed in rats infused with normal saline. One possible explanation could be an increase in intraglomerular pressure resulting in stretching of a small proportion of the total pore area. The absence of a similar response in adrenalectomized rats was attributed to the severe reduction in glomerular filtration rate and renal plasma flow caused in these animals by the infusion of renin and angioten.

Calculation of the interaction energy between two parallel adsorbing planes immersed in a solution composed of molecules of different size

The interaction between parallel planes, immersed in a solution from which r-mer molecules are adsorbed, is treated theoretically using the multilayer lattice model for adsorption from solution. The surface excess of the configurational free energy is calculated as a function of the plane separation. The model is applicable both in dilute and concentrated solutions. Results are presented for solutions composed of monomers plus dimers and monomers plus flexible tetramers. The influence of the following parameters is shown: strength of adsorption, segment interchange energy, and concentration of the solution. Adsorption of r-mers with one end-segment preferentially adsorbed leads to a repulsive energy between the parallel planes at small separations. An increase in the length of the r-mer or in the quantity of r-mer adsorbed increases the repulsive energy at any separation. Adsorption of r-mers with every segment preferentially adsorbed from solution gives an attractive energy which increases as the planes approach.

Base ratios in RNA molecules of different sizes from a Balbiani ring

The base ratios in newly synthesized RNA from a chromosome puff (Balbiani ring 2) in the salivary glands of Chironomus tentans were compared with the corresponding ratios in RNA produced in chromosome I–III and in the nucleoli. Salivary glands were incubated in larval haemolymph supplemented with tritiated cytidine and uridine. Balbiani ring 2, chromosome I–III and nucleoli were isolated from 50 to 70 cells by micromanipulation. The labelled RNA from the two chromosomal samples was fractionated by electrophoresis in agarose. RNA from different parts of the migration path was eluted. Fractionated, as well as unfractionated, RNA was hydrolysed in alkali and the labelled products in the hydrolysate, CMP and UMP, were separated by thin-layer chromatography and their radioactivities determined. The CMP/UMP activity quotients were calculated and the following results obtained: 1. (1) The newly synthesized RNA in Balbiani ring 2 is different from that in chromosome I–III and in the nucleoli. 2. (2) Rapidly labelled, high molecular weight RNA of a given size in Balbiani ring 2 is different from RNA of the same size in chromosome I–III. 3. (3) There is no difference between rapidly labelled, high molecular weight RNA molecules of different sizes within Balbiani ring 2 and within chromosome I–III. The results show a similarity between giant RNA molecules of different sizes produced in a single chromosome puff. This may indicate that this newly synthesized RNA contains repeating sequences; but alternative explanations are possible.

Introductory. Structure and properties of simple liquids and solutions: a review

The structure of a simple liquid is determined primarily by the repulsive forces between the molecules. The effects of the attractive forces can be found by perturbation treatments, of which that of van der Waals is the prototype, and that of Barker and Henderson the most recent. The repulsive forces are equally important in determining the structures of mixtures of spherical molecules of different sizes—structures which are quite different from those found in the unmixed liquids. Recent Monte Carlo calculations by Singer can be used as a standard by which theories of mixtures can be judged, and it is shown that the only adequate theories are those which do justice to this difference in structures. It is suggested that the shape of molecules is often of less importance than their size in determining the free energy, and hence that theories of solutions of n-alkanes or of linear polymers do not, in their results, differ greatly from those of mixtures of spherical molecules of different sizes.

Thermodynamic excess functions of mixtures of molecules of different sizes

Van der Waals's equation of state, with his original rules for relating his a and b to the composition of the mixture, is shown to lead to values of the thermodynamic excess functions for mixtures of spherical (or nearly spherical) molecules, which agree nearly as well with experiment as those obtained even with Leland, Rowlinson and Sather's greatly improved version of the more elaborate “pure-fluid based” theories of Prigogine, Kirkwood, Scott, Brown and others. Guggenheim's equation of state is shown to lead to excess functions which agree more closely with experiment than any previously published version of the more elaborate theories.

Low Temperature Thermodynamics. The excess Gibbs function and the volumes of mixing for the system methane + propane at 90.68K

AbstractThe excess Gibbs function Ge and the excess volumes of mixing Ve have been measured at the methane triple point (90.68 K) for the system methane+propane. They were compared with McGlashan's recent theory for mixtures of molecules of different sizes.

Statistical thermodynamics of two-fluid models of mixtures

An approximation of a type devised by van der Waals has been shown to be superior to the random mixing approximation, and to theories derived from it, when applied to mixtures of molecules of different sizes. In this paper, van der Waals's approximation is extended to a two-fluid model, and so takes into account the departures from a random distribution induced by differences of intermolecular energy. The treatment is further extended to mixtures of molecules of different shapes. The two-fluid van der Waals approximation is compared with the experimental excess thermodynamic functions for ten simple binary mixtures. These yield unambiguous evidence that the intermolecular energy between unlike molecules is less than the geometric mean of that between the like molecules by up to 2 %. Independent and quantitative confirmation of such differences is provided by recent measurements of the second virial coefficients and of the critical temperatures of the same mixtures.

Gas-liquid chromatographic determination of cross-term second virial coefficients using glycerol. Benzene + nitrogen and benzene + carbon dioxide at 50°C

This paper extends the theory of gas-chromatographic elution of a highly dilute solute to the second order in gas-phase imperfection terms, yielding a precise expression for the ideal retention volume in terms of the thermodynamic parameters of the system. The effect of carrier gas dissolution in the solvent is included explicitly; the cross-term second virial coefficient B12 for the system solute + carrier gas cannot be evaluated unambiguously for an appreciably soluble carrier gas. The use in such cases of polar solvents in which non-polar carrier gases are effectively insoluble is discussed with reference to surface adsorption and chromatographic non-ideality, which are important in polar solvents. Extrapolation of observed retention volume to zero flowrate for each of a series of columns covering a range of solvent loadings should give, corresponding to the limit of infinite loading, unambiguous values of bulk-phase solute-in-solvent activity coefficient and of B12. The theory has been applied to measurements on the systems benzene + nitrogen + glycerol, and benzene + carbon dioxide + glycerol, using four columns loaded at 15.7, 25.3, 33.6 and 23.3 % by weight glycerol on Celite, and the system benzene + hydrogen + glycerol using a column loaded at 44.0 %. The flowrate-dependence of the net retention volume is approximately linear on all columns, the gradient correlating well with empirical plate height and with solvent loading, in accordance with theory and with the known facts about the distribution of a polar solvent on Celite. The zero-flowrate B12 values are effectively the same with all columns. These values of B12 at 50°C are, for benzene + nitrogen, –98 ± 9 cm3 mole–1, and for benzene + carbon dioxide, –250 ± 15 cm3 mole–1, both being in fair agreement with theoretical predictions for systems of non-spherical molecules of different sizes. The activity coefficient for benzene at infinite dilution in glycerol at 50°C is logγ∞13= 2.084 ± 0.005.

Gas chromatographic behaviour of C 1C 5 alcohols on carbowax 400

The gas chromatographic behaviour of C 1C 5 alcohols and chloroform on Carbowax 400 was studied in the range 58–88°. The specific retention volumes were determined, and the deviations from the expected order of elution were investigated by calculating the activity coefficients and the thermodynamic excess functions. The F lory-H uggins theory was used to evaluate the statistical contribution made by the mixing of molecules of different sizes, and the results were interpreted on the basis of the theory of associated ideal solutions. The difference between the order of elution of alcohols and the order of their boiling points was found to be due to differences in their molecular volumes. On the other hand, the nature of the association between the alcohols and Carbowax 400 is not very different from that of the associated species in the pure alcohol samples. The relative volatilities may therefore be predicted from the F lory-H uggins theory.

Thermodynamic Properties of Solutions of m-Terphenyl in Benzene. I. The Vapor Pressures and the Related Thermodynamic Functions at 30 and 50°C

Abstract Vapor pressures of solutions of m-terphenyl in benzene were measured for the concentration less than 0.23 in mole fraction x of terphenyl at 30 and 50°C. Vapor pressures P mmHg obtained are represented by log10P(30°)=2.076970–0.4343x–0.06569x2–0.4340x3 and log10P(50°)=2.432100–0.4343x–0.14654x2–0.3412x3. Chemical potentials observed were reproduced by the quasi-lattice theory for mixtures of molecules of different sizes. The Miller-Guggenheim expression (r=3, z=6–8) gives w⁄k=100±5°, and the Flory-Huggins expression (r=molecular volume ratio) gives χ=0.272±0.004 (30°) and χ=0.243±0.006(50°). Partial molar heats of mixing are rather fitted by the regular solution theory similarly to the case for benzene+biphenyl, and the Flory-Huggins expression gives a concentration-dependent enthalpy parameter, χH=(0.772+1.716φ)×102⁄T, where φ means a volume fraction of terphenyl. The average value of χH, 0.39 agreed with a theoretical estimate from solubility parameters.

Statistical thermodynamics of mixtures of molecules of different sizes

The central problem in the theory of mixtures is the calculation of the free energy of mixing of molecules of different sizes. An explicit calculation of this free energy is made for a mixture in which all intermolecular potentials are of the form uαα(r)=(σαα/r)n, where σαα is a distance characteristic of the interaction of two molecules of species α, and where σαβ= 1/2(σαα+σββ) when α≠β. This result follows from a solution of Percus-Yevick integral equation for the pair distribution function of a mixture of hard spheres. The form of the free energy provides a criterion by which existing theories can be judged, and it is shown that an approximation of the type originally suggested by van der Waals is superior to approximations based on the concept of random mixing. Molecules that differ only in size mix with a small and negative excess free-energy. The recommended approximation is confirmed by comparison with experiment.