High-performance liquid chromatography (HPLC)-size exclusion chromatography (SEC) for qualitative detection of humic substances and dissolved organic matter in mineral soils and peats in Lithuania

High-performance liquid chromatography (HPLC) with size exclusion (SEC) separation function was used to isolate and examine the molecular mass (MM) distributions and polydispersity of humic substances (HSs) and dissolved organic matter (DOM) from mineral soils and peats. The aim was to improve their detailed characterisation and to inform of their soil carbon (C) sequestration and environmental quality. This is the first study conducted in Lithuania in which HSs and DOM, separated from two soil types, have been used to characterise soil at the molecular level. The HPLC-SEC, as a separation method, was coupled with diode-array detection (DAD), thus enabling the separation of molecular fractions. Results showed that HPLC-SEC can be used to determine the MM of HSs in soil, provided that the relation between retention time and MM is known and a suitable method for fitting the HS peak is available. The UV-spectra analysis showed that DOM has a larger MM (M_w = 2439–3436 Da), which contains more aliphatic C. The HS fraction has a smaller MM (M_w = 2776 Da), with aromatic structures that reflect a higher aromaticity. Separated fractions had characteristic MMs of humic acid (HA) and fulvic acid (FA) and DOM. The HSs separated from peat samples were characterised by higher aromaticity, humification and stability. The HSs extracted from mineral soil samples showed a higher degradability level. The results also show the MM distribution and polydispersity of HS and DOM fractions (M_w/M_n = 1.009–1.252) are relatively homogenous in both soil types. Findings confirm that chromatographic and spectrometric parameters can be used for characterisation of both HSs and DOM, and for detecting changes in organic matter quality. Moreover, they can also be used for a further understanding the C-cycle and could be applied for enhancing soil C-sequestration and informing environmental quality management.     

Evolution of crystal and amorphous fractions of poly[(R)-3-hydroxybutyrate] upon storage

Quantitative thermal analysis of the evolution of crystal and amorphous fractions of poly[(R)-3-hydroxybutyrate] (PHB) upon storage at room temperature is detailed in this contribution. Conventional and temperature-modulated calorimetry were used to quantify the crystallinity, as well as the mobile and rigid amorphous fractions, of an initially partially crystallized PHB, subsequently maintained at 25 °C for various times. PHB undergoes progressive crystallization during storage, with an increase in crystal fraction (w _C) from the initial w _C = 0.35 up to w _C = 0.71 attained after 1 year of storage. Crystallization is accompanied by vitrification of rigid amorphous segments, which leads to a noteworthy increase of the overall fraction of the material that is solid at room temperature, leaving only a mobile amorphous fraction w _A = 0.04 after 1 year at 25 °C. The quantitative thermal analysis allowed to clarify the kinetics of evolution of both the ordered and unordered fractions of PHB upon storage, which leads to a severe deterioration of material’s properties.     

Controlled ring‐opening polymerization of l‐lactide and ε‐caprolactone catalyzed by aluminum‐based Lewis pairs or Lewis acid alone

Ring‐opening polymerization of cyclic esters was studied using catalysts composed of bulky Lewis acids (LA) and Lewis bases (LB). Controlled polymerization of l ‐lactide (l ‐Lac) was proceeded by Al(C₆F₅)₃·THF in combination with trimesitylphosphine (Mes₃P) or triphenylphosphine (Ph₃P) using BnOH as an initiator to produce poly(l ‐Lac) with narrow molecular weight distribution (MWD; M_w/M_n = 1.1). Both the LA and the LB were indispensable to promote the polymerization. The molecular weights of the resulting poly(l ‐Lac)s were controlled by the feed monomer to initiator ratio. ε‐Caprolactone (CL) was rapidly polymerized by Al(C₆F₅)₃·THF with or without Mes₃P, although the resulting polymer had rather broad MWD (M_w/M_n = 1.7). The CL polymerization by Al(C₆F₅)₃·THF alone at r.t. gave poly(CL) with relatively narrow MWD (M_w/M_n = 1.2). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 297–303     

Physicochemical Properties of Calcium Lignosulfonate with Different Molecular Weights as Dispersant in Aqueous Suspension

Five purified calcium lignosulfonate (CL) fractions with different molecular weights were obtained by fractionation using ultrafiltration and dialysis. The influence of molecular weight on their physicochemical properties was investigated by determining the properties of five fractions. TEM and ESEM imaging indicated that CL has a globular structure to form locally regular colloidal assemblies with the diameter of approximately 200 ～ 300 nm. Fraction3 (M _w is 7621) with the molecular weight of 5,000–l0,000 has more sulfonic and carboxyl group, so the highest zeta potential (?36 mV) can be charged on the TiO₂ particles. With the increase of molecular weight, the hydrophobicity and surface activity of CL in aqueous solution increase, so Fraction5 (M _w is 21646) which molecular weight is more than 30000 has the biggest adsorption amount. The adsorption characteristic of CL on solid-water interface have great impact on the dispersive properties of TiO₂ particle in aqueous solution and the higher adsorption capacity is helpful to improve the dispersive ability of CL. On the other hand, the surface charge of TiO₂ particle absorbing CL is another important factor to the dispersive ability of CL. Furthermore, when the CL concentration in TiO₂ suspension is less than 4 mg/mL, Fraction3 has the best dispersive ability because the electrostatic repulsion effect is controlling factor. The dispersive ability of CL increases with the increase of molecular weight when the CL concentration in TiO₂ suspension is more than 4 mg/mL, so Fraction5 has the best dispersive ability owing to the steric hindrance effect.     

Light-scattering characterization of poly(ethylene terephthalate)

By using a closed-circuit filtration system, we have succeeded in clarifying poly(ethylene terephthalate) (PET) dissolved in hexafluoroisopropanol (HFIP). Such static properties as the radius of gyration R_g, the weight-average molecular weight M_w, and the second virial coefficient A₂ and such dynamic properties as the translational diffusion coefficient D, or its equivalent hydrodynamic radius R_h, and the second (diffusion) virial coefficient k_d were determined for several PET samples of different molecular weights by using light-scattering intensity and linewidth measurements. An empirical relation between D_o (or R_h) and M_w was established: R_h = (1.77±0.15)X10^?2 M with R_h and M_w expressed in units of nanometers and grams per mole, respectively. The empirical exponent α_D(ca. 0.58±0.01) is in good agreement with the less precisely determined intrinsic viscosity/molecular weight exponent α_η (ca. 0.71±0.02). Several intensity correlation functions were measured very precisely using long accumulation times. A Laplace inversion was performed using the singular-value decomposition technique. The approximate molecular weight distribution (MWD) determined by light-scattering spectroscopy was in reasonable agreement with a completely independent determination of MWD using gel permeation chromatography (GPC). It was interesting to note, though not surprising, that GPC showed emphasis on lower-molecular-weight fractions, while light-scattering emphasized higher-molecular-weight fractions. The agreement further strengthens some complementary aspects of the two techniques.     

Molecular weight distribution in living polymerization proceeding with reshuffling of polymer segments due to chain transfer to polymer with chain scission, 1. Determination of kp/ktr ratio from DPw/DPn data. Ideal reproduction of polymer chain activities

The molecular weight distribution (MWD) curves for polymerization systems with chain transfer to polymer leading to reshuffling of polymer segments (and broadening of the MWD), but not changing chain functionalities, were simulated by the Monte Carlo method. The bimodality observed in some distributions was explained by different distribution functions of chains which did not undergo reshuffling and of those which underwent the chain transfer reaction. Using this observation, a numerical integration method for computing DP _w/DP _n (and the MWD curves) in the systems under consideration was devised. Plots relating DP _w/DP _n to monomer conversion and k_tr/k_p are presented and a method of determination of k_tr/k_p from the DP _w/DP _n data is proposed.     

Characterization of aquatic dissolved organic matter by asymmetrical flow field-flow fractionation coupled to UV-Visible diode array and excitation emission matrix fluorescence

Flow field-flow fractionation (FlFFF) with on-line UV/Visible diode array detector (DAD) and excitation emission matrix (EEM) fluorescence detector has been developed for the characterization of optical properties of aquatic dissolved organic matter (DOM) collected in the Otonabee River (Ontario, Canada) and Athabasca River (Alberta, Canada). The molecular weight (MW) distribution of DOM was estimated using a series of organic macromolecules ranging from 479 to 66,000 Da. Both the number-average (M_n) and weight-average (M_w) molecular weights of Suwannee River fulvic acid (SRFA) and Suwannee River humic acid (SRHA) determined using these macromolecular standards were comparable to those obtained using polystyrenesulfonate (PSS) standards, suggesting that organic macromolecules can be used to estimate MW of natural organic colloids. The MW of eight river DOM samples determined by this method was found to have an M_n range of 0.8–1.1 kDa, which agrees with available literature estimates. The FlFFF-DAD-EEM system provided insight into the MW components of river DOM including the optical properties by on-line absorbance and fluorescence measurement. A red-shift in emission and excitation wavelength maxima associated with lower spectral slope ratios (S_R = S_275–295:S_350–400) was related to higher MW DOM. However, DOM of different origins at similar MW also showed significant difference in optical properties. A difference of 47 and 40 nm in excitation and emission peak C maxima was found. This supports the hypothesis that river DOM is not uniform in size and optical composition.     

Characterization of oat proteins and aggregates using asymmetric flow field-flow fractionation

The soluble proteins and protein aggregates in Belinda oats were characterized using asymmetric flow field-flow fractionation (AF4) coupled with online UV–vis spectroscopy and multiangle light-scattering detection (MALS). Fractions from the AF4 separation were collected and further characterized by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE). The AF4 fractogram of the oat extracts revealed three peaks which were determined to be monomeric forms of soluble proteins, globulin aggregates, and β-glucan, respectively. The early eluting monomeric proteins ranged in molar mass (MM) between 5 and 90 kg/mol and in hydrodynamic diameter (D _h) from 1.6 to 13 nm. The MM at peak maximum of the globulin aggregate peak was found to be ～300 kg/mol and the D _h was measured to be ～20 nm. SDS-PAGE of the collected fraction across this peak revealed two bands with MM of 37 and 27 kg/mol which correspond to the α and β subunits of globulin indicating the elution of globulin aggregates. A third peak at long retention time was determined to be β-glucan through treatment of the oat extract with β-glucanase and by injection of β-glucan standards. The amount of soluble protein was measured to be 83.1?±?2.3 wt.%, and the amount of albumin proteins was measured to be 17.6?±?5.7 wt.% of the total protein in the oats. The results for Belinda oat extracts show that the AF4-MALS/UV platform is capable of characterizing the physicochemical properties such as MM and hydrodynamic size distribution of proteins and protein aggregates within a complicated food matrix environment and without the need to generate protein isolates.

Polymerization of MMA catalyzed by different novel mixed ligand lanthanocene{(Cp)(Cl) LnSchiff-base (THF)},(COT) -Ln(methoxyethylindenyl)(THF) /Al (i -Bu)_3 systems

This article deals that the rare earth metal complexes along with Al(i'-Bu),can catalyze the polymerization of methyl-methacrylate (MMA) into high molecular weight poly(MMA) along with narrow molecular weight distributions (MWD).A typical example was mentioned in the case of {Cp(Cl) Sm-Schiff-base(THF)} which expresses maximum (conv.% = 55.46 and Mn=354×103) efficiency along with narrow MWD (Mw/Mn<2) at 60℃.The resulting polymer was partially syndiotactic (>60%).The effect of the catalyst,temperature,catalyst/MMA molar ratio,catalyst/Al( i-Bu)3 molar ratio on the polymerization of MMA at 60℃ were also investigated.     

Gel-permeation chromatography: X. Molecular weight detection by low-angle laser light scattering

Effluent from a gel-permeation chromatographic column has been simultaneously and continuously monitored with a differential refractometer and a low-angle laser light-scattering (LALLS) photometer. This provides a true and direct determination of molecular weight distribution rather than through a calibration method as obtained by conventional GPC techniques. Computer assisted data reduction provides a rapid determination of M?_w, M?_n, M?_z, M?_w/M?_n, as well as a plot of molecular weight distribution. Samples of very narrow molecular weight distribution (MWD) polystyrene from Pressure Chemicals Co. and relatively wide MWD samples of poly(methyl methacrylate) in chloroform have been characterized.     

Theoretical evaluation of the nature and strength of the F������F intermolecular interactions present in fluorinated hydrocarbons

The nature, strength and directionality of C?CF···F interactions were theoretically evaluated on all symmetry unique dimers present in the CF₄, C₂F₄ and C₆F₆ crystals and on CF₄, CHF₃, CH₂F₂ and CH₃F model dimers placed in two different geometries. On each dimer, the interaction energy was computed at the MP2/aug-cc-pVDZ level, and also an Atoms in Molecule analysis of the dimer electron density was done to find all intermolecular bonds. The characterization was completed by computing the energy components of the dimer interaction energy, using the SAPT method. The results show that in most dimers found in the CF₄, C₂F₄ and C₆F₆ crystals, there are more than one C?CF···F intermolecular bond and sometimes even a C?CF···?? intermolecular bond. By selecting dimers presenting one C?CF···F bond, the following strength can be estimated for a single C?CF···F bond: ?0.21?kcal/mol in C(sp³) atoms, ?0.25?kcal/mol in C(non-aromatic sp²), ?0.41?kcal/mol in C(aromatic sp²). The interaction energy of the dimer grows almost linearly with the number of C?CF···F bonds present. The relative orientation of the C?CF···F bond affects the bond strength. The SAPT calculations indicate that in collinear dimers, C?CF···F interactions are strongly dominated by the dispersion energetic component, while when in non-collinear conformations the electrostatic component can be as important as the dispersion one.     

Conformations of Alternating Partially Fluorinated Copolymers in Dilute Ethanol Solutions

Equimolar copolymers of N-vinyl pyrrolidone with 1,1,1-3,3,3-hexafluoroisopropyl-α-fluoroacrylate were obtained by reversible addition-fragmentation chain transfer radical (RAFT) polymerization and by conventional radical polymerization (RAD). The copolymer conformation and compositional heterogeneity were analyzed by dynamic and static light scattering. RAFT copolymers of 41,000 ≤ M _w  ≤ 68,000 g/mol were shown to adopt cylindrical all-trans conformation. RAD copolymer of higher molecular mass (M_w = 390,000 g/mol) exhibited less extended conformation, thus indicating that the statistical Kuhn segment is less than RAD copolymer length.     

Randomly branched bisphenol A polycarbonates. I. Molecular weight distribution modeling,interfacial synthesis,and characterization

Randomly branched bisphenol A polycarbonates (PCs) were prepared by interfacial polymerization methods to explore the limits of gel‐free compositions available by the adjustment of various composition and process variables. A molecular weight distribution (MWD) model was devised to predict the MWD, G, and weight‐average molecular weight per arm (M_w /arm) values based on the composition variables. The amounts of the monomer, branching agent, and chain terminator must be adjusted such that the weight‐average functionality of the phenolic monomers (F_OH ) was less than 2 to preclude gel formation in both the long‐ and short‐chain branched (SCB) PCs. Several series of SCB and long‐chain branched PCs were prepared, and those lacking gels showed molecular weights measured by gel permeation chromatography–UV and gel permeation chromatography–LS consistent with model calculations. In SCB PCs, the minimum M_w /arm that could be realized without gel formation depended on both composition (molecular weight, terminator type) and process (terminator addition point, coupling catalyst) variables. The minimum M_w /arm achieved in the low molecular weight series studied ranged from ∼3300 to ∼1000. The use of long chain alkyl phenol terminators gave branched PCs with lower glass‐transition temperatures but a higher gel‐free minimum M_w /arm. SCB PCs where M_w /arm was less than ∼M_c spontaneously cracked after compression molding, a result attributed to their lack of polymer chain entanglements. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 560–570, 2000     

Sonochemical reactions of dissolved organic matter

Property changes of Aldrich and Pahokee peat dissolved organic matter (DOM) at different ultrasonic frequencies and energy densities were systematically investigated. Exposure of DOM to ultrasound resulted in decreases in TOC, Color₄₆₅, specific UV absorbance (SUVA), aromaticity and molecular weight, while DOM acidity increased. Compared to 20 kHz ultrasound, greater sonochemical transformation of DOM occurred at 354 kHz and at higher energy density, due to greater ^·OH radical production. The changes to DOM properties suggest that ultrasound may significantly affect DOM-pollutant interactions (e.g.facilitate desorption of hydrophobic organics from DOM or promote complexation between metallic cations and DOM).     

Cationic polymerization of α-methylstyrene in dichloromethane initiated with system 2,5-dichloro-2,5-dimethylhexene-BCl3. II. Continuous addition of monomer into initiator,quasiliving polymerization

A slow continuous addition of dichloromethana solutions of α-methylstyrene (α-MeSt) into a dichloromethane solution of 2,5-dichloro-2,5-dimethylhexane (DDH) with BCI₃ (initiating system II) prepared in advance resulted, in the temperature range between ?20 and ?40°, in a quasilving polymerization of α-MeSt. At ?20°C and a 100% conversion a polymer with a very narrow molecular weight distribution is formed, M?_w/M?_n - 1.1. Quasiliving polymerization of α-MeSt has not been achieved with freshly prepared dischloromethane solutions of DDH with BC₃ (initiating sytem I), or with solutions of BCI₃ alone (initiating system III). Polarity of the polymerization medium affected molecular weight distribution (MWD) of the polymer, and the polydispersity index decreased with decreasing polarity. MWD of the polymer samples were studied by the GPC method, the structure of poly (α-methylstyrene) (Pα-MeSt) was investigated by the ₁H-NMR analysis     

Effects of the thermal history and concentration on the aggregation of Erwinia gum in an aqueous solution

The aggregation of Erwinia (E) gum in a 0.2 M NaCl aqueous solution was investigated by multi‐angle laser light scattering and gel permeation chromatography (GPC) combined with light scattering. The GPC chromatograms of five fractions contained two peaks; the fractions had the same elution volume but different peak areas, suggesting that aggregates and single chains coexisted in the solution at 25 °C. The apparent weight‐average molecular weights (M_w) of the aggregates and single chains for each fraction were all about 2.1 × 10⁶ and 7.8 × 10⁴, respectively. This indicates that the aggregates were composed of about 27 molecules of E gum in the concentration range used (1.0 × 10⁻⁶ to 5.0 × 10⁻⁴ g/mL). The weight fraction of the aggregates (w_ag) increased with increasing concentration, but the aggregates still existed even in an extremely dilute solution. The fractionation process and polymer concentration hardly affected the apparent aggregation number but significantly changed w_ag. The E‐gum M_w decreased sharply with an increase in temperature. When the E‐gum solution was kept at 100 °C, w_ag decreased sharply for 20 h and leveled off after 100 h. Once the aggregates were decomposed at a higher temperature, no aggregation was observed in the solution at 25 °C, indicating that the aggregation was irreversible. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1352–1358, 2000     

Highly reactive polyisobutylenes via AlCl3OBu2‐coinitiated cationic polymerization of isobutylene: Effect of solvent polarity,temperature, and initiator

The cationic polymerization of isobutylene using 2‐phenyl‐2‐propanol (CumOH)/AlCl₃OBu₂ and H₂O/AlCl₃OBu₂ initiating systems in nonpolar solvents (toluene, n‐hexane) at elevated temperatures (?20 to 30 °C) is reported. With CumOH/AlCl₃OBu₂ initiating system, the reaction proceeded by controlled initiation via CumOH, followed by β‐H abstraction and then irreversible termination, thus, affording polymers (M_n = 1000–2000 g mol^?1) with high content of vinylidene end groups (85–91%), although the monomer conversion was low (≤35%) and polymers exhibited relatively broad molecular weight distribution (MWD; M_w/M_n = 2.3–3.5). H₂O/AlCl₃OBu₂ initiating system induced chain‐transfer dominated cationic polymerization of isobutylene via a selective β‐H abstraction by free base (Bu₂O). Under these conditions, polymers with very high content of desired exo‐olefin terminal groups (89–94%) in high yield (>85%) were obtained in 10 min. It was shown that the molecular weight of polyisobutylenes obtained with H₂O/AlCl₃OBu₂ initiating system could be easily controlled in a range 1000–10,000 g mol^?1 by changing the reaction temperature from ?40 to 30 °C. The MWD was rather broad (M_w/M_n = 2.5–3.5) at low reaction temperatures (from ?40 to 10 °C), but became narrower (M_w/M_n ≤ 2.1) at temperatures higher than 10 °C. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Producing bimodal molecular weight distribution polymers through facile one‐pot/one‐step RAFT polymerization

Well‐defined bimodal molecular weight distribution (MWD) polystyrene and polystyrene‐b‐poly(acrylonitrile) were successfully synthesized using a pair of mono/difunctional trithiocarbonate RAFT agents 1 and 2 via one‐pot RAFT polymerization. The kinetics of RAFT polymerization for styrene in bulk with a molar ratio of [St]₀:[AIBN]₀:[ 1 ]₀:[ 2 ]₀ = 1200:1:2.5:2.5 was studied at 75°C. The results indicated that the system showed excellent controllability and “living” characteristics to both higher and lower molecular weight fractions, providing an efficient and facile way to producing bimodal MWD (co)polymers with both controlled molecular weight (MW) and MWD in molecular level, and the plausible mechanism was discussed in this work. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Mass spectroscopy and SEC of SRM 1487, a low molecular weight poly(methyl methacrylate) standard

Matrix Assisted Laser Desorption Ionization (MALDI) Time of Flight (TOF) Mass Spectrometry (MS) was used to study the molecular weight distribution (MWD) and the number of α-methyl styrene (α-MeSty) repeat units in SRM 1487, a narrow MWD poly(methyl methacrylate) (PMMA) standard reference material of about 6300 g/mol, which was initiated with α-MeSty. It was found that each PMMA polymer chain had from zero to seven α-MeStys per chain. The MWD of the polymer chains containing a fixed number of α-MeStys was obtained. The MWD, M_w, and the average number of α-MeSty at a given molecular weight from MALDI TOF MS compare well with those obtained from more traditional methods such as ultracentrifugation and Size Exclusion Chromatography (SEC). The implications of the number of α-MeStys per chain is discussed in terms of the chemistry of anionic polymerization. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2409–2419, 1997     

Molecular properties and immunomodulatory activities of a water-soluble heteropolysaccharide isolated from Plantago asiatica L. leaves

This study aims at investigating physical–chemical properties of a water-soluble heteropolysaccharide from Plnatago asiatica L. leaves, and its immunomodulatory effects on macrophages RAW264.7 cells. Hot water-extracted crude polysaccharide from the plant leaves (PLLCP) was fractionated into four fractions by DEAE Sepharose Fast Flow eluted with 0.1–0.5 M NaCl solutions. The most abundant fraction (0.3 M NaCl elution), designated PLLP-2, was identified as a heteropolysaccharide with an average molecular weight (M_w) of 3.54 × 10⁴ and composed mainly of Gal (34.4%), GalA (36.5%), Ara (10.1%) and Rha (8.4%). PLLP-2 was an acidic polysaccharide exhibiting inflaky curly aggregation with smooth surface. PLLCP and its main subfraction PLLP-2 displayed immunomodulatory activities by stimulating the production of pro-inflammatory cytokines, including TNF-α and IL-1β in macrophage RAW264.7 cells. These results indicate that the main polysaccharide fraction purified from P. asiatica L. leaves is probably pectin, and have potential immunomodulatory function.