Molecules Of Different Sizes Research Articles

Das gelbe Element und seine erstaunliche Vielseitigkeit

AbstractElemental sulfur ‐ both in the solid, liquid, and gaseous state ‐ shows highly unusual physical and chemical properties not matched by any other element. The reason for this unique behavior is the formation of molecules of different size ‐from S2 to S6, S7, and S8 up to macromolecules („S,”︁) ‐ every size is possible. Which mixture is obtained depends on the temperature and other reaction conditions. These findings are important for the understanding of elemental sulfur produced industrially in huge quantities, certain astonishing observations made with bacteria that oxidize sulfur, the Stretford process for sulfur production, and the sulfur covering Ios surface.

Phase diagrams of perhydrotriphenylene and aromatic compounds

Perhydrotriphenylene (PHTP) forms channel-like adducts with molecules of different size and molecular weight. In the crystal structure of the adduct the included long sequences of molecules are separated from each other by the channel walls. The optical properties of the included molecules differ from those of the bulk molecules. The phase diagram of mixtures of PHTP and trans stylbene and 4H-cyclopenta [2,1-b∶3,4-b′] dithiophene (CPDT) were determined by DSC experiments. Ideality in the liquid phase was observed only in the PHTP/CPDT system.

Experimental Measurement of Aromatic Stacking Affinities in the Context of Duplex DNA

Experimental Measurement of Aromatic Stacking Affinities in the Context of Duplex DNA

Cyclic migration of DNA in gels: DNA stretching and electrophoretic mobility.

Available data from spectroscopic and microscopy studies of electrophoretic orientation of long DNA (above 40 kbp) in agarose gels is analyzed on the basis of the fact that the migration in constant fields is cyclic in nature. Defining a cycle period as the time between two consecutive compact states, a simple model is used to obtain data on the average time period (< T >) and the step length (< L >) of the migration cycle from spectroscopic measurements of the dynamics of helix orientation and center-of-mass velocity. Furthermore, the degree of orientation is used to analyze tube-orientation and DNA stretching contributions to < L > and < T >. Finally, the average electrophoretic velocity v = < L >/< T > is analyzed in terms of < L > and < T > for different DNA sizes (Lc), field strengths (E), and gel concentrations (A). The main results of the analysis are: (i) the increase and saturation of the electrophoretic mobility with increasing E is mainly governed by < L > via the degree of DNA stretching, (ii) DNA molecules of different sizes migrate with the same velocity because < L > and < T > both increase approximately linearly with Lc, and (iii) migration in a denser gel is slower mainly because < T > increases, while the step length is approximately constant. Assuming the charge Q of DNA is the same as in free solution, these results suggest that the reason the fundamental reptation equation for the electrophoretic mobility mu = (Q/zeta) < (hx/Lt)2 > also applies in the presence of strong fluctuations in the tube length Lt, and end-to-end distance hx, is that the friction coefficient zeta for motion along the tube is lower the more stretched the DNA is.

Equilibrium Adsorption and Tension of Binary Surfactant Mixtures at the Air/Water Interface

The nonideal adsorbed solution model (NAS) is extended to the air/water interface for determining the surface tension of aqueous binary surfactant mixtures with molecules of different size, surface activity, and nonideal interactions. The regular solution theory is used for modeling the nonideal interactions between the adsorbed molecules and in the micelles. Two mixing parameters β σ and β m are used for fitting data for premicellar and micellar concentrations. This model can also be extended to account for molar area changes upon mixing in the monolayer or more complex nonideal interactions. Synergism in surface tension reduction efficiency can be predicted with this model. The ranges of mole fractions and concentrations for the existence of synergism can be determined. Tension data of two nonionic binary mixtures, C 12 E 8 /SDS (from the literature) and C 12 E 6 /Triton X-100, fit this model well. New tension data for C 12 E 5 /Triton X-100 are reported, and they are synergistic for a specific range of concentrations. Moreover, the surface coverages and compositions for the two nonionic mixtures are calculated with the NAS model. These calculations show that the larger molecules adsorb at the interface more favorably at low concentrations than at high concentrations.

Sieving Properties of Carbons Obtained by Template Carbonization of Polyfurfuryl Alcohol within Mineral Matrixes

Carbons obtained by carbonization of polyfurfuryl alcohol within the smectite and taeniolite matrices were studied by sorption methods. The sorption of nitrogen at 77 K showed only small differences in the pore structure ofthese materials related to the properties of the inorganic matrix. More specific information about pore structure was obtained from inverse gas chromatography, where molecules of different sizes were used to study sieving properties. Micropore structure was also studied by sorption of methane, carbon tetrafluoride, and sulfur hexafluoride at supercritical temperatures ; at these temperatures they are adsorbed mainly in small pores. Thermodynamic quantities, such as adsorption energy distribution, micropore size distribution, and isosteric heat of adsorption, were calculated assuming the energy distribution is governed by pore size distribution due to adsorption potential enhancement in small pores. The results obtained demonstrate the presence of sieving effects for molecular sizes between 3.6 and 6 A.

Thermodynamically Consistent Equilibrium Adsorption Isotherms for Mixtures of Different-Sized Molecules

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThermodynamically Consistent Equilibrium Adsorption Isotherms for Mixtures of Different-Sized MoleculesElias I. Franses, Faisal A. Siddiqui, Dong June Ahn, Chien-Hsiang Chang, and Nien-Hwa Linda WangCite this: Langmuir 1995, 11, 8, 3177–3183Publication Date (Print):August 1, 1995Publication History Published online1 May 2002Published inissue 1 August 1995https://doi.org/10.1021/la00008a050RIGHTS & PERMISSIONSArticle Views349Altmetric-Citations48LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (657 KB) Get e-Alerts Get e-Alerts

CG and CNG methyltransferases in plants

We have purified two distinct DNA methyltransferases from pea shoot tips and analysed their sequence specificity using synthetic oligodeoxyribonucleotide substrates and chemical sequencing methods. One methylates only CG target sequences, whereas the other methylates only CAG or CTG target sequences. We have found no evidence for methylation of the 5′ cytosine in CCG target sequences either in vivo or in vitro. Using amino-acid sequence data, PCR-amplified fragments from conserved sequences and heterologous probes, we have isolated several cDNA clones that react with mRNA molecules of different sizes.

Activity coefficients of adsorbed mixtures

Experimental and simulated data for adsorption of gas mixtures on energetically heterogeneous surfaces like activated carbon and zeolites exhibit negative deviations from ideality. The deviations are large in some cases, with activity coefficients at infinite dilution equal to 0.1 or less. Similar molecules form ideal mixtures, but molecules of different size or polarity are nonideal. Equations for bulk liquid mixtures (Wilson, Margules, etc.) do not apply to isobars for adsorbed mixtures. A two-constant equation for activity coefficients as a function of composition and spreading pressure is in good agreement with theory, simulation, and experiment.

Immersion Heats of Active Carbons in Water and Organic Substances

The immersion heats of two active carbon (AC) samples in water and organic substances with molecules of different size have been investigated. A molecular sieve effect was established. It has been shown that changes in the immersion heats of the active carbons correspond to pore structure characteristics such as the size distribution of the micropores. The immersion heats of moistened active carbons in liquids have also been investigated, and the heat balance of the process calculated.

Isolation of a dsRNA virus from Dipodascus (Endomyces) magnusii.

Virus-like particles (VLPs) of 40 nm diameter were isolated from the yeast-like fungus Dipodascus magnusii. These VLPs copurify with several linear double-stranded RNA molecules of different size. We have found some polymorphism in both the length and the number of these dsRNAs among six D. magnusii strains. Analysis of CsCl gradient-purified VLPs on PAGE/SDS electrophoresis showed one major protein component with an apparent molecular weight of 75 kDa.

A segment-based local composition model for the gibbs energy of polymer solutions

A segment-based local composition model is presented for the Gibbs energy of polymer solutions. The model represents a synergistic combination of the Flory-Huggins description for the configurational entropy of mixing molecules of different sizes and the Non-Random Two Liquid (NRTL) theory for the local composition contribution from mixing solvents and polymer segments. It reduces to the well-known NRTL equation if polymers are removed from the system. The model provides a most flexible thennodynamic framework to correlate the phase behavior of polymer solutions. The utility of the model was demonstrated with successful representation of vapor-liquid equilibrium and liquid-liquid equilibrium of single solvent, single polymer systems.

Molecular recognition on acoustic wave devices: sorption in chemically anchored zeolite monolayers

Zeolite crystals were attached to the gold electrodes of quartz crystal microbalances (QCM). Monolayers of thiol-alkoxysilanes on the gold surface served as interfacial layers for the subsequent adhesion of the zeolite crystals to the QCM. The process of anchoring the zeolite crystals via the thiol-silane monolayers was studied by reflection adsorption infrared (IR) spectroscopy, contact angle, and scanning electron microscopy (SEM). The siloxane linkages between the microporous zeolite crystals and the terminal cross-linked polysiloxane groups of the interfacial monolayer play an important role in enhancing the packing density of microporous crystals and the thermal stability (up to at least 350 {degrees}C) of the film on the gold surface. Dynamic sorption isotherms of organic vapors and nitrogen as well as the transient sorption behavior of organic vapor pulses were studied to characterize the zeolite-coated QCMs. The resonance frequency response of zeolite-coated QCMs to vapor pulses could be increased up to 500-fold compared to the bare sensor. The regular micropores (0.3-0.75 nm) of the QCM-attached zeolite crystals were found to efficiently control molecular access into the coating. Selectivity of the frequency response in excess of 100:1 toward molecules of different size and/or shape could be demonstrated. The kinetics of vapor desorption frommore » the zeolite layers are strongly dependent on the adsorbate/zeolite combination, thus providing an additional capability for molecular recognition. 33 refs., 11 figs., 2 tabs.« less

APPARENT SELECTIVE NEUTRALITY OF MITOCHONDRIAL DNA SIZE VARIATION: A TEST IN THE DEEP-SEA SCALLOP PLACOPECTEN MAGELLANICUS.

Animal mitochondrial DNA (mtDNA) is believed to have evolved under intense selection for economy of the size of the molecule. Among scallop species mtDNA size may vary by a factor of two and among conspecific individuals by as much as 25%. We have examined the possibility that large mtDNA size differences may be associated with fitness in the deep sea scallop Placopecten magellanicus by comparing shell lengths of individuals with different copy numbers of a large mtDNA repeated sequence. Among juvenile cohorts of same age, shell length is known to be a good index of overall fitness in marine bivalves and it is shown here to be affected by differences in nuclear genotype, expressed as the degree of enzyme heterozygosity. We have observed no correlation between shell length and mtDNA length and interpreted this to mean that variation in the size of animal mtDNA is effectively neutral to the forces of natural selection acting on the individual. This type of mtDNA variation must, therefore, be explained in terms of biases in the molecular mechanisms causing expansion or contraction of the molecule, differential replication rates of mtDNA molecules of different size, and the stochastic assortment of mtDNA size classes among individuals.

Analytical theory of solution of attracting molecules of different size derived from hypernetted-chain equation for radial distribution function

The Flory–Huggins formula of mixing entropy of different size molecules originally proved for polymer solution is generally proved for attracting spherical molecules different in size. The Scatchard formula of the excess energy known for application in the solubility parameter is also proved theoretically. The proof is based on analytical solutions of the radial distribution functions for mixture and does not rely on the lattice model. The hypernetted-chain (HNC) equation is perturbed taking hard-sphere system as reference and the attractive force as perturbation. The obtained equation for the perturbed radial distribution function for mixture is solved analytically under simplifying assumptions, which enabled to give the equation of state in analytical form. In order to give the excess Gibbs free energy in explicit form, the vapor pressure of liquid mixture is obtained by applying a phase equilibrium condition corresponding to the Maxwell’s equal-area rule to mixture. The excess entropy and enthalpy are derived directly.

Systematic investigation of the phase behavior in binary fluid mixtures. II. Calculations based on the Carnahan–Starling–Redlich–Kwong equation of state

Phase diagrams of binary fluid mixtures have been calculated from the Carnahan–Starling–Redlich–Kwong equation of state in connection with standard quadratic mixing rules. The phase diagrams were classified according to the system of van Konynenburg and Scott and then used to construct global phase diagrams showing the extent of the various phase diagram classes in the space of the parameters of the equation of state. For molecules of equal size, the global phase diagram is rather similar to that of the Redlich–Kwong or the van der Waals equation. For molecules of different sizes, however, a new tricritical line appears. Such a behavior is observed for cubic equations of state only if nonadditive covolumes are assumed. Along this new tricritical line, some unusual phase diagrams involving four-phase states and high-density instabilities can be found. The influence of molecular size ratios on the global phase diagrams and the relationship of the equation of state of this work to the ternary symmetric lattice gas and the van der Waals lattice gas are discussed.

Gas transport in halogen‐containing aromatic polycarbonates

AbstractThe gas permeability and permselectivity of a series of halogen‐containing polycarbonates are discussed in terms of the fundamental solubility and diffusivity factors. These materials have structural features that hinder interchain packing and intrachain rotational mobility. Both diffusion and solubility coefficients are higher in materials with higher fractional free volumes. Diffusivity selectivities tend to increase with increasing restriction of intrachain torsional mobility. The materials with four bromine atoms substituted on the phenyl rings ortho to the carbonate linkages display a significantly increased diffusivity selectivity relative to conventional polycarbonate. This improvement in the ability of the polymer matrix to discriminate between gas molecules of different sizes is due to a reduction in intrachain torsional mobility. The reduction in chain mobility is indicated by higher glass transition and higher sub‐Tg transition temperatures in the bromine‐substituted materials. The materials with hexafluoroisopropylidene moieties have high fractional free volumes and exhibit a very significant increase in permeability relative to conventional bisphenol‐A polycarbonate. The material with both the hexafluoro and the tetrabromo substitutions displays significant simultaneous increases in permeability and permselectivity relative to conventional polycarbonate.

Molecular separation by thermosensitive hydrogel membranes

A new method for separation of molecules of different size is presented. The method is a useful addition to conventional separation methods which depend mainly on gel permeation chromatography using size exclusion. In the new method, hydrogel membranes are used which swelling level can be thermally controlled. In this study, a crosslinked poly(N-isopropylacrylamide—co-butylmethacrylate 95:5mol%) membrane is used and three solutes of distinct molecular size: two dextrans with molecular weights of 150,000 and 4,400 g/mol respectively and uranine with a molecular weight of 376 g/mol. The swelling of the membranes as function of temperature was measured as well as the influence of the swelling level on the permeability of the three solutes. the influence of the swelling level and the solute size on the permeability was as expected from the free-volume theory. Based on these permeability phenomena, separation was performed in a continuous way by varying the membrane swelling at the appropriate time. A linear relationship between inverse membrane hydration and solute diffusion was found for uranine and dextran ( MW=4,400), indicating the validity of the free-volume theory.

Group-contribution equation of state for correlating and predicting thermodynamic properties of weakly polar and non-associating mixtures: Binary and multicomponent systems

Abdoul W., Rauzy E. and Péneloux A., 1991. Group-contribution equation of state for correlating and predicting thermodynamic properties of weakly polar and non-associating mixtures. Binary and multicomponent systems. Fluid Phase Equilibria, 68: 47-102. The applicability of the “Guggenheim quasi-lattice excess function equation of state” formalism is tested through a zeroth approximation group-contribution model and a Peng-Robinson-type equation of state. The temperature-dependent correlations of the group-contribution model are derived from low-pressure excess enthalpy ( H E) and vaporliquid equilibrium (VLE) binary data and are then extended to the prediction of high-pressure vapor-liquid equilibria of mixtures of weakly polar and non-associating compounds (i.e. hydrocarbons, CO 2, H 2S, N 2). The numbers of binary systems, data sets and determinations used in the development and testing of the method are 169, 805 and 10634 for low-pressure VLE; 282, 789 and 11308 for H E; and 163, 1329 and 12272 for high-pressure VLE, respectively. The average relative deviation with experiment in bubble-point pressure is 1% and the average absolute deviation in vapor-phase composition is 0.005 for low-pressure VLE data. Heat effects are well reproduced with average deviations of 12 J for 7009 determinations of binaries with H E less than 300 J and 5.5% for 4299 determinations of binaries with higher H E. Owing to a term accounting for chain-length effects, the accuracy of the prediction of high-pressure VLE is not deteriorated by the group-contribution approach (average deviations of 3% in bubble-point pressure, 0.0103 in vapor-phase composition). Thus, in addition to its predictive power, the method is found to be an improvement over the classical Peng-Robinson procedure with constant binary interaction parameters, especially for mixtures of molecules of different sizes.

Lung to blood passage of different-sized molecules during lung inflammation in the rat

The passage of different-sized marker molecules over the lower respiratory tract into the blood circulation during pulmonary inflammation induced by dextran, endotoxin [i.e., lipopolysaccharide from Escherichia coli (LPS)], or ferritin was assessed in the rat. Bovine immunoglobulin G (BIgG, mol wt = 150,000 Da), bovine serum albumin (BSA, mol wt = 67,000 Da), and the nonapeptide 1-deaminocysteine-8-D-arginine vasopressin (dDAVP, mol wt = 1,067 Da) were used as permeability markers after intratracheal instillation. The pathophysiological indexes of a proceeding lung inflammation were increased total cell number, changed leukocyte proportions and increased total protein content obtained in bronchoalveolar lavage, and lung edema formation shown as an increased lung wet-dry weight difference. Intratracheal instillation of dextran induced a moderate neutrophil invasion into the lungs but had no effect on the passage of the different markers over the lungs (BIgG 1.8 +/- 0.6%, BSA 3.5 +/- 1.2%, dDAVP 26.1 +/- 20.7%) compared with control rats instilled with the markers alone (1.8 +/- 0.4%, 4.1 +/- 1.3%, 20.0 +/- 3.8%, respectively). Endotoxin administration resulted in markedly higher lavage cell counts and lung edema concomitantly with an increased lung passage of the markers (3.2 +/- 0.9%, 22.0 +/- 6.1%, 33.3 +/- 12.0%, respectively; P less than 0.01-P less than 0.001). The highest marker passage was obtained when the inflammation was most severe, i.e., after ferritin administration (17.6 +/- 2.3%, 60.0 +/- 6.7%, 41.6 +/- 6.9%, respectively; P less than 0.001), which resulted in markedly elevated lavage cell numbers and protein content as well as edema formation.(ABSTRACT TRUNCATED AT 250 WORDS)