Molecular Size Parameters Research Articles

Chemically reactive and aging macromolecular mixtures. I. Phase diagrams, spinodals, and gelation

Multicomponent macromolecular mixtures often form higher-order structures, which may display non-ideal mixing and aging behaviors. In this work, we first propose a minimal model of a quaternary system that takes into account the formation of a complex via a chemical reaction involving two macromolecular species; the complex may then phase separate from the buffer and undergo a further transition into a gel-like state. We subsequently investigate how physical parameters such as molecular size, stoichiometric coefficients, equilibrium constants, and interaction parameters affect the phase behavior of the mixture and its propensity to undergo aging via gelation. In addition, we analyze the thermodynamic stability of the system and identify the spinodal regions and their overlap with gelation boundaries. The approach developed in this work can be readily generalized to study systems with an arbitrary number of components. More broadly, it provides a physically based starting point for the investigation of the kinetics of the coupled complex formation, phase separation, and gelation processes in spatially extended systems.

The impact of ultrasonic-assisted extraction on the in vitro hypoglycemic activity of peach gum polysaccharide in relation to its conformational conversion.

Peach gum (PG) is an exudate of the peach tree (Prunus persica of the Rosaceae family), which consists primarily of polysaccharides with a large molecular weight and branching structure. Consequently, PG can only swell in water and does not dissolve easily, which severely limits its application. Current conventional extraction methods for PG polysaccharide (PGPS) are time consuming and inefficient. This study investigated the impact of ultrasonic-assisted extraction (UAE) on PGPS structure and conformation, and their relationship to hypoglycemic activity in vitro. In comparison with conventional aqueous extraction, UAE enhanced PGPS yielded from 28.07-32.83% to 80.37-84.90% (w/w) in 2 h. It drastically decreased the molecular size and conformational parameters of PGPS, including weight-average molecular weight (Mw), number-average molecular weight (Mn), z-average radius of gyration (Rg), hydrodynamic radius (Rh) and instrinsic viscosity ([η]) values. Peach gum polysaccharide conformation converted extended molecules to flexible random coil chains or compact spheres with no obvious primary structure alteration. Furthermore, UAE altered the flow behavior of PGPS solution from that of a non-Newtonian fluid to that of a Newtonian fluid. As a result, PGPS treated with UAE displayed weaker inhibitory activity than untreated PGPS, mostly because UAE weakens the binding strength of PGPS to α-glucosidase. However, this negative effect of UAE on PGPS activity was compensated by the increased solubility of polysaccharide. This enabled PGPS to achieve a wider range of doses. Ultrasonic-assisted extraction is capable of degrading PGPS efficiently while preserving its primary structure, resulting in a Newtonian fluid solution. The degraded PGPS conformations displayed a consistent correlation with their inhibitory effect on α-glucosidase activity. © 2024 Society of Chemical Industry.

QSPR models for enthalpy and entropy of organic compounds based on a set of norm indices

In this study, quantitative structure–property relationship (QSPR) models are developed to predict the standard vapourisation enthalpy (ΔvapH°), enthalpy of fusion (ΔfusH), entropy of fusion (ΔfusS), and standard sublimation enthalpy (ΔsubH°) of organic compounds. Molecular size and shape parameters describing the structural information are introduced to improve the accuracy and robustness of the predictive effect. The correlation coefficients (R2) for ΔvapH°, ΔfusH, ΔfusS, and ΔsubH° are 0.981, 0.851, 0.888, and 0.844, respectively, and these results indicate the high accuracy of models. Because some experimental values of the ΔfusH and ΔfusS are less than average absolute error (AAE) of QSPR models, which leads to negative values by linear models, nonlinear models are proposed to mitigate this problem. Additionally, a comparison with previously published results further demonstrates that these QSPR models can achieve high precision for data set comprising numerous chemical substances. From a holistic perspective, the novel QSPR models can be widely used in multiple domains, such as chemical reaction and predesign prediction.

Deciphering external chain length and cyclodextrin production with starch catalyzed by cyclodextrin glycosyltransferase

Cyclodextrins (CDs) are yielded by cyclodextrin glycosyltransferase (CGTase) using starches or their derivatives as substrates. However, how starch fine structure affects it production is still ambiguous. This study aimed to decipher the relevance between the external chain length (ECL) and CD production. The waxy maize starch was hydrolyzed by β-amylase to prepare starchy substrates with regular gradient ECL for CGTase. The HPAEC results reflected that β-amylolysis lower the starch chain fractions with DP range of 13–24 by 30%, while the fractions with DP < 6 promoted by 30%. The molecular weight distribution and iodine binding results reflected that this process had limited impact on overall starch molecular size parameters. After CGTase conversion, it is interesting to find that the ECL was positively correlated with CD contents, which also has a high consistency among α-CD, β-CD, and γ-CD. This research would provide a favorable perspective for CD production improvement.

Structure, size and aggregated morphology of a β-D-glucan from Lignosus rhinocerotis as affected by ultrasound

The effect of ultrasonic treatment on the structure, size and aggregated morphology of Lignosus rhinocerotis polysaccharide (LRP) was investigated. Ultrasonic treatment for 10 min has demonstrated to improve the aqueous solubility of LRP, leading to a uniform and narrow LRP particle size distribution. Meanwhile, short-time ultrasound was found to obviously decrease the molecular size parameters (Mw, Mn, <S2>z1/2, [η] and Rh) of LRP, and transform the hyperbranched LRP molecules into flexible and extended chains, which would reaggregate to form spherical aggregates under long-time ultrasonication. Additionally, Congo red experiment combined with CD analysis indicated the existence of triple helix structure in LRP, which was still retained after ultrasonic treatment. Furthermore, under short-time ultrasonication, the spherical aggregates with some branched chains in the native LRP solution could disaggregate and form triple helixes that could be further arranged to a dense network structure, but the untangled LRP chains would reaggregate after long-time ultrasonication. Chemical compounds studied in this articleCongo red (PubChem CID: 11313); Sodium hydroxide (PubChem CID: 14798); Potassium bromide (PubChem CID: 253877).

Physico-chemo-rheological characterization of neat and polymer-modified asphalt binders

The physico-chemo-rheological properties of asphalt binder are critical for the long-term performance of asphalt pavement infrastructures. The objectives of this study are to characterize the physico-rheological properties of unmodified neat and polymer-modified asphalt binders with newly developed rheological performance tests, and further investigate the binder chemical properties as well as the possible performance relationship from macroscale to microscale perspective. Three neat asphalt binders and two styrene–butadiene–styrene (SBS) modified asphalt binders are selected in this study. The physical properties of asphalt binder include traditional penetration, softening point and ductility. The saturates, aromatics, resins and asphaltenes (SARA) fractionation test, gel permeation chromatography (GPC) and fourier transform infrared spectroscopy (FTIR) tests are respectively conducted to quantify the chemical composition, molecular weight distribution and structure properties of asphalt binders. The rheological rutting and fatigue resistance are evaluated through the multiple stress creep recovery (MSCR), linear amplitude sweep (LAS) and DSR-based elastic recovery (DSR-ER) tests. Experimental results indicate that the physical properties are only effective to distinguish the rheological performance of neat asphalt binders. The lower aromatics contents improve the binder rutting resistance and an unified relationship between aromatic contents and binder rutting performance is obtained for both neat and modified binders. In addition, increasing the amount of small asphalt molecules decrease the resistance to permanent deformation respectively for neat and modified binders. However, the small asphalt molecule is favorable for improving the binder fatigue performance. The large molecular size (LMS) parameter from GPC test is demonstrated a unified correlation to the fatigue life of both neat and modified binders.

Cyclic trimer of human cystatin C, an amyloidogenic protein - molecular dynamics and experimental studies

Human cystatin C (HCC) is a cysteine protease inhibitor that takes a series of oligomeric forms in solution (e.g., dimers, trimers, tetramers, decamers, dodecamers, and other higher oligomers). The best-known form of cystatin C is the dimer, which arises as a result of a domain swapping mechanism. The formation of the HCC oligomeric forms, which is most likely due to this domain swapping mechanism, is associated with the aggregation of HCC into amyloid fibrils and deposits. To investigate the structure of a specific HCC oligomer, we developed a covalently stabilized trimer of HCC. An atomic model of this HCC trimer was proposed on the basis of molecular docking and molecular dynamics simulations. The most stable model of the HCC trimer obtained from the molecular dynamics simulations is characterized by a well-preserved secondary structure. The molecular size and structural parameters of the HCC trimer in solution were also confirmed by Small Angle Neutron Scattering and Nuclear Magnetic Resonance Diffusometry.

Curing of polyfurfuryl alcohol resin catalyzed by a homologous series of dicarboxylic acid catalysts. II. Swelling behavior and thermal properties

ABSTRACTPolyfurfuryl alcohol (PFA), as a bio‐based resin made from lignocellulosic materials, was crosslinked using a homologous series of dicarboxylic acid catalysts consisting of oxalic, succinic, and adipic acids, which are different in their dissociation constants. Swelling behavior, thermal stability, and non‐oxidative char residue of the resulting networks were characterized as a function of the acids strength and their concentration. Swelling of the networks were investigated at room temperature in eight solvents differing in molecular size and solubility parameter. Using acetonitrile as a solvent, the swelling mechanism was explored by applying kinetic models to the swelling data. Dynamic swelling studies during 16–30 days supported non‐Fickian and anomalous diffusion mechanism in highly crosslinked samples supporting PFA chain rigidity and high crosslinking density of the networks. Polymer–solvent interaction parameter, molecular weight between crosslinks and crosslinking densities were also determined. According to the results, the extent of PFA crosslinking and non‐Fickian behavior of the swelling solvent diffusion through the networks are strongly dependent on the concentration and dissociation characteristics of the catalysts used. Thermal stability studies showed no significant differences between the compositions, up to 900 °C. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45770.

Determination of molecular size parameters and quantification of polyacrylic acid by high performance size-exclusion chromatography with triple detection.

Synthetic polyelectrolytes are a broad class of vaccine adjuvants. Among them, polyacrylic acid (PAA), a polyanionic polymer, is currently evaluated by Sanofi Pasteur. As chain length is considered to be a critical quality attribute for adjuvant properties of PAA, measurement of precise and accurate molecular size parameters is important for these polymers. In the field of synthetic polymer chemistry, methods for determination of molecular size parameters are well defined. Specifically, high performance size-exclusion chromatography (HPSEC) with multi-detection system is a method of choice. This paper describes the development of HPSEC method to well characterize and precisely quantify PAA in different adjuvant formulations. A first set of characterizations were made, with determination of dn/dc coefficient, which enabled the determination of weight- and number-average molecular weight, viscosimetric radius, and intrinsic viscosity. In-depth characterization was also made with branching study through the use of Mark-Houwink parameter determination. The quantification method was also evaluated according to validation method-like criteria: limit of detection and limit of quantification, repeatability, accuracy, and specificity with recombinant surface glycoprotein gB from human cytomegalovirus (CMV-gB) as model antigen.

Water solubility of selected C9–C18 alkanes using a slow-stir technique: Comparison to structure – property models

Aqueous solubility is a fundamental physical-chemical substance property that strongly influences the distribution, fate and effects of chemicals upon release into the environment. Experimental water solubility was determined for 18 selected C9–C18 normal, branched and cyclic alkanes. A slow-stir technique was applied to obviate emulsion formation, which historically has resulted in significant overestimation of the aqueous solubility of such hydrophobic liquid compounds. Sensitive GC–MS based methods coupled with contemporary sample extraction techniques were employed to enable reproducible analysis of low parts-per billion aqueous concentrations. Water solubility measurements for most of the compounds investigated, are reported for the first time expanding available data for branched and cyclic alkanes. Measured water solubilities spanned four orders of magnitude ranging from 0.3 μg/L to 250 μg/L. Good agreement was observed for selected alkanes tested in this work and reported in earlier literature demonstrating the robustness of the slow-stir water solubility technique. Comparisons of measured alkane water solubilities were also made with those predicted by commonly used quantitative structure–property relationship models (e.g. SPARC, EPIWIN, ACD/Labs). Correlations are also presented between alkane measured water solubilities and molecular size parameters (e.g. molar volume, solvent accessible molar volume) affirming a mechanistic description of empirical aqueous solubility results and prediction previously reported for a more limited set of alkanes.

Determination of interfacial tension of binary mixtures from perturbative approaches

We determine the interfacial properties of mixtures of spherical Lennard-Jones molecules from direct simulation of the vapour–liquid interface. We consider mixtures with same molecular size but different dispersive energy parameter values. We use the extensions of the improved version of the inhomogeneous long-range corrections of Janeček, presented recently by MacDowell and Blas and Martínez-Ruiz et al., to deal with the interaction energy and microscopic components of the pressure tensor. We have performed Monte Carlo simulations in the canonical ensemble to obtain the interfacial properties of mixtures of Lennard-Jones molecules with a cut-off distance rc = 3σ in combination with the inhomogeneous long-range corrections. The pressure tensor is obtained using the mechanical (virial) and thermodynamic route. The vapour–liquid interfacial tension is also evaluated using three different procedures, the Irving–Kirkwood method, the difference between the macroscopic components of the pressure tensor, and the test-area methodology. This allows to check the validity of the recent extensions presented to deal with the contributions due to long-range corrections for intermolecular energy and pressure tensor in the case of binary mixtures. In addition to the pressure tensor and the surface tension, we also obtain density profiles, coexistence densities, and interfacial thickness as functions of pressure, at a given temperature. According to our results, the main effect of increasing the ratio between the dispersive energy parameters of the mixture, ε22/ε11, is to sharpen the vapour–liquid interface and to increase the width of the biphasic coexistence region. Particularly interesting is the presence of a relative maximum in the density profiles of the less volatile component at the interface. This maximum is related with adsorption or accumulation of these molecules at the interface, a direct consequence of stronger attractive interactions between these molecules in comparison with the rest of intermolecular interactions. In addition to that, the interfacial thickness decreases, the width of the tangential microscopic component of the pressure tensor profile increases, and the surface tension increases as ε22/ε11 is larger.

Predicting the bioconcentration factor of highly hydrophobic organic chemicals

Bioconcentration refers to the process of uptake and buildup of chemicals in living organisms. Experimental measurement of bioconcentration factor (BCF) is time-consuming and expensive, and is not feasible for a large number of chemicals of regulatory concern. Quantitative structure–activity relationship (QSAR) models are used for estimating BCF values to help in risk assessment of a chemical. This paper presents the results of a QSAR study conducted to address an important problem encountered in the prediction of the BCF of highly hydrophobic chemicals. A new QSAR model is derived using a dataset of diverse organic chemicals previously tested in a United States Environmental Protection Agency laboratory. It is noted that the linear relationship between the BCF and hydrophobic parameter, i.e., calculated octanol–water partition coefficient (ClogP), breaks down for highly hydrophobic chemicals. The parabolic QSAR equation, log BCF=3.036 ClogP−0.197 ClogP2−0.808 MgVol (n=28, r2=0.817, q2=0.761, s=0.558) (experimental log BCF range=0.44–5.29, ClogP range=3.16–11.27), suggests that a non-linear relationship between BCF and the hydrophobic parameter, along with inclusion of additional molecular size, weight and/or volume parameters, should be considered while developing a QSAR model for more reliable prediction of the BCF of highly hydrophobic chemicals.

Development and validation of high-performance size exclusion chromatography methods to determine molecular size parameters of Haemophilus influenzae type b polysaccharides and conjugates

Current vaccines against Haemophilus influenzae type b (Hib) consist of the polyribosyl ribitol phosphate (PRP) capsular polysaccharide chemically conjugated to a carrier protein. Among the various biological and physical analyses to be performed on these vaccines, the determination of the molecular size of the polysaccharide preparations throughout the conjugation process is particularly relevant. Comparison of results from high-performance size exclusion chromatography (HPSEC) with those routinely obtained using conventional gel permeation chromatography (CGPC) methods highlights the correlation between the two methods for determining the values of the chromatographic distribution coefficient (KD) of native and activated polysaccharides. The resulting data showed that the KD value is sufficient to characterize these polysaccharides using an HPSEC method. However, additional molecular size parameters (i.e., molar mass and hydrodynamic radius) are necessary for a reliable characterization of the tetanus conjugate (PRP-T), certainly due to the lattice-like structure of the conjugate. In practice, an absolute detection system in HPSEC composed of a low-angle light scattering detector, a viscometer, and a refractive index (RI) detector was used. As demonstrated, these HPSEC methods are rapid, accurate, and reproducible for the polysaccharides and their glycoconjugates and provide a relevant and more informative alternative to the current CGPC methods.

Anomalocaris: la supervisión del gigante marino del período Cámbrico

Current vaccines against Haemophilus influenzae type b (Hib) consist of the polyribosyl ribitol phosphate (PRP) capsular polysaccharide chemically conjugated to a carrier protein. Among the various biological and physical analyses to be performed on these vaccines, the determination of the molecular size of the polysaccharide preparations throughout the conjugation process is particularly relevant. Comparison of results from high-performance size exclusion chromatography (HPSEC) with those routinely obtained using conventional gel permeation chromatography (CGPC) methods highlights the correlation between the two methods for determining the values of the chromatographic distribution coefficient (KD) of native and activated polysaccharides. The resulting data showed that the KD value is sufficient to characterize these polysaccharides using an HPSEC method. However, additional molecular size parameters (i.e., molar mass and hydrodynamic radius) are necessary for a reliable characterization of the tetanus conjugate (PRP-T), certainly due to the lattice-like structure of the conjugate. In practice, an absolute detection system in HPSEC composed of a low-angle light scattering detector, a viscometer, and a refractive index (RI) detector was used. As demonstrated, these HPSEC methods are rapid, accurate, and reproducible for the polysaccharides and their glycoconjugates and provide a relevant and more informative alternative to the current CGPC methods.

Assessment of phenomena underlying the removal of micropollutants during water treatment by nanofiltration using multivariate statistical analysis

Multivariate statistically-based models were developed for the comprehension of the phenomena underlying the removal of several micropollutants during drinking water treatment. Projection to latent structures (PLS) modeling was used to describe the apparent rejection as well as adsorption using specific descriptors of the molecules (physico-chemical properties and molecular size parameters), descriptors of the membrane used and of the water matrices, and operating related conditions. Multilinear PLS models with good descriptive capability towards rejection were developed. Alkalinity, molecular size descriptors, molecular weight, molar volume, and LogD were found to be the most relevant contributors for the rejection of the selected micropollutants, showing the impact of size exclusion and electrostatic interactions with minor contributions of hydrophobic interactions. The incorporation of molecular size descriptors demonstrated that the geometry of the molecule is important to determine rejection when molecules have very different geometry. Conversely, PLS modeling of adsorption required also the inclusion of quadratic and interaction terms to achieve good description. Adsorption of the selected compounds seems to be mainly determined by polar and electrostatic interactions rather than hydrophobic and may be described by polarizability as well as several specific interactions. Additionally, the incorporation of molecular size descriptors did not improve modeling of adsorption, showing that molecular geometry is not so important to describe this process as for rejection.

GC-PPC-SAFT Equation of State for VLE and LLE of Hydrocarbons and Oxygenated Compounds. Sensitivity Analysis

Group-contribution polar versions of SAFT equations of state are very useful for predictive calculations of mixtures containing diverse polar molecules. In this work, we have evaluated the predictive performance of one such model, the so-called polar perturbed-chain (PPC) SAFT model for phase-equilibrium properties of 290 hydrocarbons and monofunctional oxygenated compounds. Emphasis has been given on carrying out an extensive evaluation considering diverse types of phase behavior (vapor–liquid and liquid–liquid equilibria) and properties/conditions (Henry’s law constant for H2, N2, and CH4; infinite-dilution activity coefficient in water; solubility in water; infinite-dilution n-octanol/water partition coefficient). In general, considering the predictive nature of the calculations, encouraging results were obtained. For pure-component vapor pressures and liquid molar volumes, the deviations are very small, at 20% and 3%, respectively. The deviations in the prediction of the Henry’s law constants are within a factor of 2, with the best results found for the methane and nitrogen solubilities. For solubilities in water and, consequently, for infinite-dilution n-octanol/water partition coefficients, deviations are within a factor of 2 for hydrocarbons and within a factor of 4 for alcohols and aldehydes, but they are large for the other oxygenated families. To identify paths for improvement, a sensitivity analysis was performed, indicating that all of the parameters make large contributions to almost all properties. In addition, the sensitivity of the infinite-dilution activity coefficient in water to the molecular size parameters was extremely high. This suggests that a small change in these parameters might improve the results significantly.

Viscosity of liquid mixtures: The Vesovic-Wakeham method for chain molecules

New expressions for the viscosity of liquid mixtures, consisting of chain-like molecules, are derived by means of Enskog-type analysis. The molecules of the fluid are modelled as chains of equally sized, tangentially joined, and rigid spheres. It is assumed that the collision dynamics in such a fluid can be approximated by instantaneous collisions. We determine the molecular size parameters from the viscosity of each pure species and show how the different effective parameters can be evaluated by extending the Vesovic-Wakeham (VW) method. We propose and implement a number of thermodynamically consistent mixing rules, taking advantage of SAFT-type analysis, in order to develop the VW method for chain molecules. The predictions of the VW-chain model have been compared in the first instance with experimental viscosity data for octane-dodecane and methane-decane mixtures, thus, illustrating that the resulting VW-chain model is capable of accurately representing the viscosity of real liquid mixtures.

落叶松林土壤可溶性碳、氮和官能团特征的时空变化及与土壤理化性质的关系

土壤可溶性有机碳(DOC)、可溶性有机氮(DON)及其官能团特征在土壤碳、氮循环中作用非常重要。对25个不同年龄落叶松林样地、4个深度(0-20、20-40、40-60和60-80 cm)土壤DOC、DON、有机物官能团(芳香性、分子量和疏水性)特征指标(254、260、272 nm和280 nm的单位吸光度值SUVA:吸光度值/DOC含量)和土壤理化指标(土壤全碳SOC、全氮SON、pH值、电导率、容重)进行测定,旨在探究它们的时、空变化特征及与土壤理化指标相关关系。在空间尺度上,与SOC、SON一致,表层土壤DOC、DON多显著高于深层(<em>P</em><0.05),但是4个单位吸光度值SUVA₂₅₄、SUVA₂₆₀、SUVA₂₇₂和 SUVA₂₈₀均不存在差异(<em>P</em>>0.05);在时间尺度上,仅表层土壤DOC、SOC 和SON随落叶松年龄显著线性增长(<em>P</em><0.05),而深层DOC、SOC、SON、不同层土壤DON及各官能团指标均没有显著变化(<em>P</em>>0.05)。可见,土壤可溶性有机物内碳的累积(7 mg kg^-1 a^-1)是SOC累积的一部分(762 mg kg^-1 a^-1),但其DON及可溶性有机物芳香性比例、分子量大小及疏水性容量等官能团特征并未受落叶松生长时间以及土壤深度的显著影响。进一步回归分析表明这些官能团指标随土壤DOC含量增加而指数下降,深层土壤同时受DON显著影响。表层土壤DOC、DON与土壤SOC、SON、土壤电导率显著正相关(<em>P</em><0.05),深层相关不显著(<em>P</em>>0.05),而官能团指标与土壤理化性质的相关性在各个土层均不显著,显示出表层土壤可溶性有机物的量,而不是官能团组成对土壤理化性质影响显著,而深层土壤可溶性有机物量对土壤理化性质不构成显著影响。对于从可溶性组分、官能团角度,分析落叶松人工林成长过程中土壤碳、氮时空变化具有科学意义。;Soil dissolved organic carbon (DOC) and nitrogen (DON), and their composition play key roles in soil carbon sequestration and nutrient cycling. In this paper, DOC, DON and specific ultraviolet absorbance (SUVA at 254 nm, 260 nm, 272 nm and 280 nm, equaling to the measured absorbance divided by the DOC concentration) of dissolved organic matter, as well as soil physical-chemical parameters (soil organic carbon SOC, soil total nitrogen SON, pH value, electrical conductivity and bulk density) were determined in 0-20, 20-40, 40-60 and 60-80cm soil layers of 25 chronosequence larch plantations. The aim of this paper is to explore the temporal-spatial change of DOC, DON, SOC, SON and functional group (aromaticity, apparent molecular size and hydrophobic capacity) parameters, and their influences on soil physical-chemical properties. In the vertical profile, DOC, DON, SOC and SON in surface soil layer were significantly higher than those in the deep soil layers (<em>P</em><0.05), while no significant differences were found in SUVA₂₅₄, SUVA₂₆₀, SUVA₂₇₂ and SUVA₂₈₀ (<em>P</em>>0.05); During of the development larch plantation, DOC, SOC and SON at the surface soil (0-20cm) linearly increased with larch age (<em>P</em><0.05), while no significant changes were observed in deep soils. DON, aromaticity, apparent molecular size and hydrophobic capacity of all testified soil layers did not significantly change with larch age (<em>P</em>>0.05). Thus, DOC accumulation at surface 0-20cm soil (7 mg kg^-1 a^-1) should be a part of the SOC accumulation (762 mg kg^-1 a^-1), while no marked temporal changes were observed in both SON, DON and functional groups. Different from the significant space-temporal changes in total and dissolved C and N, composition of functional group relating to aromaticity, apparent molecular size and hydrophobic capacity were not affected by larch age and soil depth (<em>P</em>>0.05). A further regression analysis showed that these functional groups exponentially decreased with DOC and also significantly related to DON in the deep layer. Pearson correlations showed DOC and DON in surface soil positively correlated with SOC, SON and soil electrical conductivity (<em>P</em><0.05), while no significant relations between SUVA₂₅₄, SUVA₂₆₀, SUVA₂₇₂, SUVA₂₈₀ and soil physical-chemical properties were found in each soil layer. This indicates that quantity, rather than composition of dissolved organic matter could determine soil physical-chemical property, especially in surface soil. Our findings have scientific significance in understanding dynamics processes of soil carbon and nitrogen from the view of soluble components and functional groups during the plantation development.

Mean Span Dimensions of Ideal Polymer Chains Containing Branches and Rings

We present a general method for calculating the mean span dimension of various branched and ringed polymers under the assumption of Gaussian chain statistics. The method allows a routine construction of an integral expression of the mean span dimension based on three base functions, determined for a connector, an arm and a loop, respectively. Applications of our method are shown to a variety of polymer architectures including star, two-branch-point, comb and various cyclic chains (eight-shaped, Θ-shaped and several semicyclic chains). Comparing the mean span dimension with other commonly used molecular size parameters—the radius of gyration and the hydrodynamic radius, it is found that both the mean span dimension and the hydrodynamic radius shrink less than does the radius of gyration when comparing averaged sizes of a branched chain with its linear analogue. Finally, possible use of the mean span dimension in size exclusion chromatography (SEC) experiments is discussed.

Phase Equilibrium Calculations of Ternary Liquid Mixtures with Binary Interaction Parameters and Molecular Size Parameters Determined from Molecular Dynamics

The method presented in this paper was developed to predict liquid-liquid equilibria in ternary liquid mixtures by using a combination of a thermodynamic model and molecular dynamics simulations. In general, common classical thermodynamic models have many parameters which are determined by fitting a model with experimental data. This proposed method, however, provides a simple procedure for calculating liquid-liquid equilibria utilizing binary interaction parameters and molecular size parameters determined from molecular dynamics simulations. This method was applied to mixtures containing water, hydrocarbons, alcohols, chlorides, ketones, acids, and other organic liquids over various temperature ranges. The predicted results agree well with the experimental data without the use of adjustable parameters.