Viscometric properties of dilute polystyrene/dioctyl phthalate solutions

We report viscometric data collected in a Couette rheometry on dilute, single‐solvent polystyrene (PS)/dioctyl phthalate (DOP) solutions over a variety of polymer molecular weights (5.5 × 10⁵ ≤ M_w ≤ 3.0 × 10⁶ Da) and system temperatures (288 K ≤ T ≤ 318 K). In view of the essential viscometric features, the current data may be classified into three categories: The first concerns all the investigated solutions at low shear rates, where the solution properties are found to agree excellently with the Zimm model predictions. The second includes all sample solutions, except for high‐molecular‐weight PS samples (M_w ≥ 2.0 × 10⁶ Da), where excellent time–temperature superposition is observed for the steady‐state polymer viscosity at constant polymer molecular weights. No similar superposition applies at a constant temperature but varied polymer molecular weights, however. The third appears to be characteristic of dilute high‐molecular‐weight polymer solutions, for which the effects of temperature on the viscosity curve are further complicated at high shear rates. The implications concerning the relative importance of hydrodynamic interactions, segmental interactions, and chain extensibility with increasing polymer molecular weight, system temperature, and shear rate are discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 787–794, 2006     

The AMO method at small internuclear distances

The AMO function of the hydrogen molecule ψ = ψ_c + η ψ_i, where ψ_c is the covalent part and ψ_i the ionic part, is investigated for small internuclear distances R. We found η → ?1 as R →,?1 as R → 0, contrary to the intuitively expected limit η → 1. However, near R = 0 an analytical expression of ψ is derived, showing that ψ reduces to the helium ground state as R → 0. We have proved that the empirical concept ?covalent and ionic character”? should be replaced by the symmetry argument in the case of small R.     

Melting temperatures of poly(2,6-dimethyl-1,4-phenylene oxide) in methylene chloride solutions: Thermodynamic analysis

Melting temperatures were observed visually for poly-(2,6-dimethyl-1,4-phenylene oxide) in methylene chloride at nine concentrations (polymer weight fractions ranging from 0.0042 to 0.2362). The data were analyzed upon the assumptions that ΔH_u and ΔS_u, the molar heat and entropy of fusion per polymer unit, are constant over the temperature range studied, and that a Flory-Huggins chemical potential expression with a concentration-independent pair interaction parameter, χ₁ = (0.5 + ψ₁) + ψ₁Φ/T, satisfactorily describes the polymer unit activity in the binary solutions. Computation gave ΔH_u = 1404 cal/mole of units (therefore Δh = 11.7 cal/g), ψ₁ = ?0.569₁, and Φ = 342.₄°K. The effect of using various combinations of data points upon the values of these three parameters, as determined by least-squares linear regression treatment of the melting temperature expression, is indicated.     

Interaction of segmented polyurethanes and polyurethane-ureas with water

Sorption of water vapor by oligomeric homopolymers and triblock copolymers of ethylene oxide and propylene oxide, and by polyurethanes and polyurethane - ureas derived from them is discussed. While the sorption isotherms (plots of ψ₁ vs a₁, where ψ is he volume fraction of sorbed water and a₁ is activity) for most polymers investigated here are smooth and convex towards the abscissa, those found with polyurethane-ureas containing long hard blocks have a “toe” at low activities. The plots of a₁/ψ₁ vs a₁ are shown to facilitate the analysis of data and the interpretation in terms of the D'Arcy-Watt theory. Smooth isotherms are fitted by a simple equation with two parameters. The first is related to the limiting value, χ₀, (at ψ₁ → 0) of the χ parameter characterizing the polymer-water interaction. The dependences of χ₀ on the polymer composition (content of hard segments or oxyethylene units) can provide information on the interaction between hard and soft segments. The second parameter is used in the computation of parameters characterizing the clustering tendency of water molecules. This tendency depends mainly on the content of oxypropylene units but is also raised by urethane or urea groups, though not so much as by oxypropylene groups.     

NMR chemical shielding surface of N-Acetyl-N′-Methylalaninamide: A density functional study

The five energetically lowest minima on the potential energy surface of N-acetyl-N′-methylalaninamide were optimized at the Becke3LYP/DZd level of theory to compare these density functional theory results with the literature findings at restricted Hartree-Fock/3-21G. While the relative energies are very similar, the amide moiety is predicted to be much more flexible at Becke3LYP/DZd. As a consequence, the three minima that favor a nonplanar amide group differ by up to 14° in their ϕ and ψ values between the two levels. To compare the change in the density functional NMR chemical shifts with respect to ϕ and ψ with experimental results, Becke3LYP/DZd was employed to optimize a structure for N-acetyl-N′-methylalaninamide at each 30° interval on the (ϕ, ψ) surface in the regions that correspond to the α helix and the β-pleated sheet and at each 60° interval elsewhere. The corresponding NMR chemical shielding surface was computed with the density functional program deMon. The resultant NMR chemical shielding surfaces for N and C^β are in good agreement with the experiment, while the change in the NMR chemical shielding of C′ and C^α cannot be described only in terms of ϕ and ψ. The chemical shifts for those atoms also depend on the nonplanarity of the amide moiety. We evaluated this dependence for N-methylacetamide as a model system. Estimates of the parameters derived from N-methyl-acetamide allowed the NMR-shielding surfaces of C′ and C^α to be corrected for the nonplanar nitrogen influence. Although the effect is less pronounced with lower level theoretical geometries, due to the smaller degree of pyramidalization of the amide nitrogen, the (ϕ, ψ) NMR chemical shielding surfaces will need to be corrected. The agreement with the experiment was much better for the corrected surface of C′ when the nitrogen in the α helix had a nonplanar environment. © 1997 by John Wiley & Sons, Inc.     

Rapid characterization of triterpene saponins from Conyza blinii by liquid chromatography coupled with mass spectrometry

Conyza blinii Le'vl is a medicinal herb used for the treatment of inflammation in Chinese folk medicine. Its major bioactive constituents are triterpene saponins, most of which contain 6–8 sugar residues. In this report, electrospray ionization tandem mass spectrometry fragmentation behaviors of bisdesmosidic triterpene saponins (conyzasaponin A, B, and C) were studied in both positive and negative ion modes with an ion‐trap mass spectrometer. In full scan mass spectrometry, these saponins gave predominant [M–H]^? and [M+Na]⁺ ions, which determined the molecular weights. In tandem mass spectrometry (MSⁿ, n = 2–4), the [M–H]^? and [M+Na]⁺ ions yielded fragments [Y_0α–H]^? and [B_α+Na]⁺, which were diagnostic for the structures of the triterpene skeleton and sugar chains. The structural elucidation was approved by accurate mass data using IT‐TOF‐MS. An interpretation guideline based on MSⁿ (n = 2–4) diagnostic ions was proposed in order to elucidate the chemical structures of unknown triterpene saponins in C. blinii extract. The saponins in C. blinii were separated by liquid chromatography with a methanol/acetonitrile/water solvent system, and then analyzed by ion‐trap and IT‐TOF mass spectrometers. Based on the interpretation guideline, a total of 35 triterpenoid saponins were tentatively identified. Among them, 15 saponins had been previously reported, and the other 20 saponins were reported from Conyza species for the first time. This study indicates that LC/MS is a powerful technology for the rapid characterization of complicated saponins in herbal extracts. Copyright © 2010 John Wiley & Sons, Ltd.     

Variation of polymer chain dimensions with temperature below the theta point

The temperature dependence of the intrinsic viscosity [η] for the system polystyrene-cyclohexane in the interval ?20 < (T ? ψ) ≤ 0 near the ideal temperature ψ has been investigated. The observed diminution in size of the molecular coil with decreasing temperature is attributable to attractive net polymer-solvent interactions, denoted by negative values for the excluded volume parameter z. The data thus comprise an interesting selection for comparison with the predictions of various excluded volume theories. Among the approximate, closed-form expressions the functional relationship of Flory (x⁵ ? α³ ～ z) appears to describe best the variation of [η] with temperature in the region examined. The behavior of the Huggins constant k′ derived from the intrinsic viscosity plots is also examined, in accordance with the Peterson-Fixman model, suitably extended to the temperature region below ψ.     

Regioisomer characterization of triacylglycerols by non‐aqueous reversed‐phase liquid chromatography/electrospray ionization mass spectrometry using silver nitrate as a postcolumn reagent

Triacylglycerols (TAGs) provide a challenge for mass spectrometry (MS) analysis because of their complexity. In particular, for dietary, nutritional and metabolic purposes, the positional placement of fatty acids on the glycerol backbone of TAGs is a crucial aspect. To solve this problem, we have investigated the TAGs' fragmentation patterns using an ion trap mass spectrometer. A series of pure regioisomeric pairs of TAGs (POP/PPO, POO/OPO and OSO/SOO) were cationized by Ag⁺ after their separation by non‐aqueous reversed‐phase liquid chromatography (NARP‐LC) before MS to improve MS sensitivity. Electrospray ionization–MS (ESI‐MS) conditions were optimized in order to produce characteristic [M + Ag + AgNO₃]⁺ ions from each TAG, which were then fragmented to produce MS/MS spectra and then fragmented further to produce up to MS⁵ spectra. The observation of ions produced by LC‐MS⁵ of on‐line Ag⁺‐cationized TAG provided unambiguous information on the fatty acid distribution on the glycerol backbone. These strategies of MS to MS⁵ experiments were applied to identify components and to determine the regiospecificity of TAG within a complex mixture of lipids in natural oils. Copyright © 2010 John Wiley & Sons, Ltd.     

Tandem mass spectrometry study of p38α kinase inhibitors and related substances

The p38 mitogen‐activated protein kinase α (p38α) is an important drug target widely investigated for therapy of chronic inflammatory diseases. Its inhibitors are rather lipophilic and as such not very favourable lead compounds in drug discovery. Therefore, we explored various approaches to access new chemical space, create diversity, and generate lead libraries with improved solubility and reduced lipophilicity, based on known p38α inhibitors, e.g., BIRB796 and TAK‐715. Compound modification strategies include incubation with human liver microsomes and bacterial cytochrome P450 mutants from Bacillus megaterium and treatment by electrochemical oxidation, H₂O₂, and intense light irradiation. The MS/MS fragmentation pathways of p38α inhibitors and their conversion products have been studied in an ion‐trap–time‐of‐flight MSⁿ instrument. Interpretation of accurate mass MSⁿ data for four sets of related compounds revealed unexpected and peculiar fragmentation pathways that are discussed in detail. Emphasis is put on the usefulness of HRMSⁿ‐based structure elucidation in a screening setting and on peculiarities of the fragmentation with regard to the analytes and the MS instrument. In one example, an intramolecular rearrangement reaction accompanied by the loss of a bulky group is observed. For BIRB796, the double‐charge precursor ion is used in MS², providing a wider range of fragment ions in our instrument. For TAK‐715, a number of related compounds could be produced in a large‐scale incubation with a Bacillus megaterium mutant, thus enabling comparison of the structure elucidation by ¹H NMR and MSⁿ. A surprisingly large number of homolytic cleavages are observed. Competition between two fragmentation pathways involving either the loss of CH₃^? or OH^? radicals was observed for SB203580 and its conversion products. Copyright © 2013 John Wiley & Sons, Ltd.     

Silicotungstic acid modified Ce‐Fe‐Ox catalyst for selective catalytic reduction of NOx with NH3: Effect of the amount of HSiW

The HSiW(x)/Ce‐Fe catalysts were used to research the effect of silicotungstic acid contents on the catalytic activity in the selective catalytic reduction of NO_x with NH₃. Doping different contents of silicotungstic acid affected surface species and redox property as well as the catalytic activity. With the increasing amount of HSiW (x = 5%, 10% and 20%), the redox reaction between Fe³⁺/Fe²⁺ and Ce⁴⁺/Ce³⁺ enhanced, which could improve the ratio of Ce³⁺ and Fe³⁺. And then, more Ce³⁺ increased the ratio of chemisorbed oxygen (O_α). Besides, the type and strength of acid sites over HSiW(_x)/Ce‐Fe was affected by the HSiW contents. These factors facilitated the catalytic performance. Thus, the NO_x conversion of HSiW(x)/Ce‐Fe(x = 20%) was higher than 90%, which maintained in a wide temperature range between 200 and 400 °C.     

Self-bonding in an amorphous polymer below the glass transition: A T-peel test investigation

Films of amorphous polystyrene (PS) with a weight-average molecular weight (M_w) of 225 × 10³ g/mol were bonded in a T-peel test geometry, and the fracture energy (G) of a PS/PS interface was measured at the ambient temperature as a function of the healing time (t_h) and healing temperature (T_h). G was found to develop with (t_h)^1/2 at T_h = T_g-bulk − 33 °C (where T_g-bulk is the glass-transition temperature of the bulk sample), and log G was found to develop with 1/T_h at T_g-bulk − 43 °C ≤ T_h ≤ T_g-bulk − 23 °C. The smallest measured value of G = 1.4 J/m² was at least one order of magnitude larger than the work of adhesion required to reversibly separate the PS surfaces. These three observations indicated that the development of G at the PS/PS interface in the temperature range investigated (<T_g-bulk) was controlled by the diffusion of chain segments feasible above the glass-transition temperature of the interfacial layer, in agreement with our previous findings for fracture stress development at several polymer/polymer interfaces well below T_g-bulk. Close values of G = 8–9 J/m² were measured for the symmetric interfaces of polydisperse PS [M_w = 225 × 10³, weight-average molecular weight/number-average molecular weight (M_w/M_n) = 3] and monodisperse PS (M_w = 200 × 10³, M_w/M_n = 1.04) after healing at T_h = T_g-bulk − 33 °C for 24 h. This implies that the self-bonding of high-molecular-weight PS at such relatively low temperatures is not governed by polydispersity. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1861–1867, 2004     

Use of Auxiliary Functions for Construction of Series Expansion Relations of Noninteger Slater Functions in Standard Convention

Using complete orthonormal sets of ψ ^(α*) ‐self‐frictional exponential type orbitals (ψ ^(α*) ‐SFETOs) and Q^q‐noninteger auxiliary functions (Q^q‐NIAFs) introduced by the author, the combined formulas for the one‐ and two‐center one‐range addition theorems of χ‐noninteger Slater type orbitals (χ‐NISTOs) with arbitrary values of distances between centers R_ab (for R_ab = 0 and R_ab ≠ 0), and of integer (for α* = α, –∞ < α ≤ 2) and noninteger (for α* ≠ α, –∞ < α* < 3) self‐frictional (SF) quantum numbers are suggested. The presented relations for the one‐range addition theorems can be useful tools especially in the electronic structure studies of atoms, molecules and solids when χ‐NISTOs are employed as basis functions.     

Density and Volume Properties of the 2-Methoxyethanol + 1,2-Dimethoxyethane + Water Ternary Solvent System at Various Temperatures

Abstract

Densities (ρ) of the ternary mixtures 2-methoxyethanol +1,2-dimethoxyethane + water have been measured at 19 temperatures in the range - 263.15 ≤ T/K ≤ 353.15. The experimental data were processed by empirical relations accounting for the dependence of ρ on temperature and ternary composition expressed as mole fraction of the components (0≤x_i ≤1). All checked equations seem to be suitable for correlation purposes, in order to obtain interpolated values in correspondence to experimental data gaps. Furthermore, the excess molar volume (V^E ) has been investigated to make evident the possibility of forming stable solvent-cosolvent adducts. The excess property has been interpreted on the basis of specific intermolecular interactions between the components.     

Characterization of N‐Boc/Fmoc/Z‐N′‐formyl‐gem‐diaminoalkyl derivatives using electrospray ionization multi‐stage mass spectrometry

N‐Boc/Fmoc/Z‐N′‐formyl‐gem‐diaminoalkyl derivatives, intermediates particularly useful in the synthesis of partially modified retro‐inverso peptides, have been characterized by both positive and negative ion electrospray ionization (ESI) ion‐trap multi‐stage mass spectrometry (MSⁿ). The MS² collision induced dissociation (CID) spectra of the sodium adduct of the formamides derived from the corresponding N‐Fmoc/Z‐amino acids, dipeptide and tripeptide acids show the [M + Na‐NH₂CHO]⁺ ion, arising from the loss of formamide, as the base peak. Differently, the MS² CID spectra of [M + Na]⁺ ion of all the N‐Boc derivatives yield the abundant [M + Na‐C₄H₈]⁺ and [M + Na‐Boc + H]⁺ ions because of the loss of isobutylene and CO₂ from the Boc protecting function. Useful information on the type of amino acids and their sequence in the N‐protected dipeptidyl and tripeptidyl‐N′‐formamides is provided by MS² and subsequent MSⁿ experiments on the respective precursor ions. The negative ion ESI mass spectra of these oligomers show, in addition to [M‐H]^?, [M + HCOO]^? and [M + Cl]^? ions, the presence of in‐source CID fragment ions deriving from the involvement of the N‐protecting group. Furthermore, MSⁿ spectra of [M + Cl]^? ion of N‐protected dipeptide and tripeptide derivatives show characteristic fragmentations that are useful for determining the nature of the C‐terminal gem‐diamino residue. The present paper represents an initial attempt to study the ESI‐MS behavior of these important intermediates and lays the groundwork for structural‐based studies on more complex partially modified retro‐inverso peptides. Copyright © 2013 John Wiley & Sons, Ltd.     

Identification and quantification of atractylenolide I and atractylenolide III in Rhizoma Atractylodes Macrocephala by liquid chromatography–ion trap mass spectrometry

Rhizoma Atractylodes Macrocephala (RAM) is an important traditional Chinese medicinal herb that is used for treatment of dyspepsia and anorexia. The active ingredients, atractylenolide I (AO‐I) and atractylenolide III (AO‐III), were identified by direct‐injection ion trap‐mass spectrometry (IT‐MS) for collecting MSⁿ spectra. The major fragment ions of AO‐I and AO‐III were confirmed by MSⁿ both in negative ion mode and in positive ion mode. The possible main cleavage pathway of fragment ions was studied. The determinations of AO‐I and AO‐III were accomplished by liquid chromatography (LC) with UV and MS. The analytes provided good signals corresponding to the protonated molecular ions [M + H]⁺ and product ions. The precursor ions and product ions for quantification of AO‐III and AO‐I were m/z 249 → 231 and m/z 233 → 215, respectively, using selected ion monitoring by LC‐IT‐MS. Two methods were evaluated for a number of validation characteristics (repeatability, limit of detection, calibration range, and recovery). MS provides a high selectivity and sensitivity for determination of AO‐III and AO‐I in positive mode. After optimization of the methods, separation, identification and quantification of the two components in RAM were comprehensively tested by HPLC with UV and MS. Copyright © 2012 John Wiley & Sons, Ltd.     

The onset of three-phase separation in ternary polymer solutions

A theoretical study is made of three-phase separation in a ternary solution consisting of a pure solvent and two homologous monodisperse polymers with relative chain lengths P₁ and P₂. The Flory—Huggins interaction parameter X is assumed to depend linearly on the volume fraction ? of the polymer mixture: χ = χ₀(T) + k(T)_?. For a given P₁ the ratio of P₂ to P₁ for the onset of three-phase separation increases with an increase in k, first gradually and then sharply. Loci of critical points for this condition on the χ₀ vs. ? diagram are determined for a series of fixed values of P₁ and their significance is discussed.     

LC-MS<Superscript><Emphasis Type="BoldItalic">n</Emphasis></Superscript> Analysis of Isomeric Chondroitin Sulfate Oligosaccharides Using a Chemical Derivatization Strategy

Improved methods for structural analyses of glycosaminoglycans (GAGs) are required to understand their functional roles in various biological processes. Major challenges in structural characterization of complex GAG oligosaccharides using liquid chromatography-mass spectrometry (LC-MS) include the accurate determination of the patterns of sulfation due to gas-phase losses of the sulfate groups upon collisional activation and inefficient on-line separation of positional sulfation isomers prior to MS/MS analyses. Here, a sequential chemical derivatization procedure including permethylation, desulfation, and acetylation was demonstrated to enable both on-line LC separation of isomeric mixtures of chondroitin sulfate (CS) oligosaccharides and accurate determination of sites of sulfation by MS ⁿ . The derivatized oligosaccharides have sulfate groups replaced with acetyl groups, which are sufficiently stable to survive MS ⁿ fragmentation and reflect the original sulfation patterns. A standard reversed-phase LC-MS system with a capillary C18 column was used for separation, and MS ⁿ experiments using collision-induced dissociation (CID) were performed. Our results indicate that the combination of this derivatization strategy and MS ⁿ methodology enables accurate identification of the sulfation isomers of CS hexasaccharides with either saturated or unsaturated nonreducing ends. Moreover, derivatized CS hexasaccharide isomer mixtures become separable by LC-MS method due to different positions of acetyl modifications.     

Determination of lipoic acid, Trolox methyl ether and tocopherols in human plasma by liquid-chromatography and ion-trap tandem mass spectrometry

A method for the simultaneous determination of lipoic acid and/or Trolox methyl ether, along with α‐, γ‐ and δ‐tocopherol was developed using liquid chromatography–tandem mass spectrometry with negative electrospray ionization (HPLC‐ESI‐MS/MS) in an ion‐trap mass spectrometer. Detection and quantification were accomplished by a multiple reaction monitoring method, using specific transitions from precursor ion to product ion for each analyte. Chromatographic separation was achieved in a 12 min run using a C₁₈‐bonded phase and methanol–aqueous ammonium acetate elution gradient. Linear correlations of the chromatographic peak area (r.u. × s^?1) to the injected amount (ng) gave the slope values (r.u. × s^?1 × ng^?1) 2.34 × 10⁴ for α‐tocopherol, 5.05 × 10⁴ for γ‐tocopherol, 1.27 × 10⁵ for δ‐tocopherol, 8.86 × 10⁵ for lipoic acid and 1.23 × 10⁵ for Trolox methyl ether. The lower limit of quantification ranged between 0.02 and 1.22 ng for Trolox methyl ether and lipoic acid. MS³ experiments of γ‐ and δ‐tocopherol suggest ion‐radical reactions and dependence of the tocopherol fragmentation pattern on the phenolic ring methylation degree. The method is shown to be applicable to measurement of these metabolites in human serum after extraction. Copyright © 2012 John Wiley & Sons, Ltd.     

Excluded volume effect of linear polymer molecules

An approximate closed expression for the excluded volume effect of linear polymer molecules is developed with the aid of a uniform expansion model of perturbed chains. The linear expansion factor α for the end-to-end distance is given by (α³ ? 1) + (3/8) (α⁵ ? α³) = (5/2)z where z is the excluded volume parameter. This equation is numerically close to the Ptitsyn equation in the ordinary range of α; i.e., for 1 ≤ α ≤ 2.     

Toward total structural analysis of cardiolipins: multiple-stage linear ion-trap mass spectrometry on the [M − 2H + 3Li]<Superscript>+</Superscript> ions

ESI multiple-stage linear ion-trap (LIT) mass spectrometric approaches for a near-complete structural characterization of cardiolipins (CLs), including identification of the fatty acyl substituents, assignment of the fatty acid substituents on the glycerol backbone, and location of the double-bond(s) or cyclopropyl group along the fatty acid chain are described. Upon collisionally activated dissociation (CAD) on the [M − 2H + 3Li]⁺ ions of CL in an ion-trap (MS²), two sets of fragment ions (designated as (a + 136) and (b + 136) ions) analogous to those previously reported for the [M − 2H + 3Na]⁺ ions were observed, leading to assignment of the phosphatidyl moieties attached to 1′- or 3′-position of the central glycerol. Further dissociation of the (a + 136) (or (b + 136)) ions (MS³) gives rise to the (a + 136 − R_{1(or 2)}CO₂Li) (or b + 136 − R_{1(or 2)}CO₂Li) ion pairs that identify the fatty acid moieties and their position on the glycerol backbone. This is followed by MS⁴ on the (a + 136 − R_{1(or 2)}CO₂Li) (or b + 136 − R_{1(or 2)}CO₂Li) ion to eliminate a tricylic glycerophosphate ester residue (136 Da) to yield the (a − R_{1(or 2)}CO₂Li) ion, which is then subjected to MS⁵. The MS5 spectrum contains the structural information that locates the double-bond(s) or cyclopropyl group of the fatty acid substituents. Finally, the subsequent MS⁶ on the dilithiated fatty acid ions generated from MS⁵ also yields feature ions that confirm the assignment.