Separation and quantification of the linear and cyclic structures of polyamide-6 at the critical point of adsorption

The linear and cyclic structures of polyamide-6 were separated by liquid chromatography at critical conditions (LCCC) and identified with different mass spectrometric (MS) techniques and quantitated by LCCC with evaporative light-scattering detection (ELSD). Electrospray ionization MS was not suitable to identify the higher cyclic structures. For this purpose, matrix-assisted laser desorption ionization time-of-flight MS performed better and cyclic and linear structures were oligomerically resolved and separately identified in the mass spectrometer. The highest cyclic structure present and detected was the cyclic pentacontamer. It could be demonstrated that cyclic and linear oligomers follow different ionization and fragmentation routes/patterns. Quantification with ELSD of the components separated by LCCC using a universal calibration curve or an iterative procedure was developed. An area correction to account for different peak widths of coeluting components improves precision and accuracy of the calibration curve and improves quantitation accuracy for the samples analyzed. With these corrected values, no molecular mass dependency was observed for the cyclic and linear structures. Under critical conditions, the linear and cyclic structures of polyamide-6 were separated, identified and quantified.     

The offline combination of thin-layer chromatography and high-performance liquid chromatography with diode array detection and micrOTOF-Q mass spectrometry for the separation and identification of spinochromes from sea urchin (Strongylocentrotus droebachiensis) shells

Thin-layer chromatography (TLC) with off-line high-performance liquid chromatography coupled to diode array detection and micrOTOF-Q mass spectrometry (HPLC-DAD-MS) resulted in the successful fractionation, separation and identification of spinochrome pigments from sea urchin (Strongylocentrotus droebachiensis) shells. Two fractions of pigments were separated by TLC and eluted with methanol using a TLC-MS interface. HPLC-DAD-MS analysis of the fractions indicated the presence of six sea urchin pigments: spinochrome monomers B and D, three spinochrome dimers (anhydroethylidene-6,6'-bis(2,3,7-trihydroxynaphthazarin) and its isomer and ethylidene-6,6'-bis(2,3,7-trihydroxynaphthazarin)), and one pigment that was preliminary identified as a spinochrome dimer with the structural formula C(22)H(16)O(16).     

Quantitation of functionality of poly(methyl methacrylate) by liquid chromatography under critical conditions followed by evaporative light-scattering detection. Comparison with NMR and titration

Atom transfer radical polymerisation (ATRP) is a versatile 'living' controlled polymerisation technique for the synthesis of well-defined architectures such as block copolymers, gradient copolymers, hyperbranched polymers and telechelic polymers. ATRP provides control over molecular mass and molecular mass distribution and is suitable for the polymerisation of a wide variety of monomers, including methyl methacrylate. A chromatographic method was developed for an endgroup-based separation of low-molecular-mass poly(methyl methacrylate) (PMMA), based on liquid chromatography under critical conditions. With this method the PMMA, irrespective of its low-molecular-mass, is separated according to endgroups (functionality) due to interactions of the polar endgroups with the non-modified silica based stationary phase. The different series were identified using on-line atmospheric pressure ionisation electrospray mass spectrometry and quantified by evaporative light scattering detection. These results were compared with those obtained by NMR and titration.     

Elevation of charring level of polyamide-6,6 films via ionic introduction of phosphoric acid and boric acid esters

Phosphorus and boron containing materials have the feature of increasing char formation, which can be effectively used as flame retardants especially in textiles. This paper discusses the ionic addition of phosphorus and boron esters to polyamide-6,6 (PA66), and its effect on the charring level. A mixture of phosphoric acid–boric acid ester at different degrees of esterification (ED) was prepared and two theoretical mechanisms for the esterification reaction were suggested. Ionically grafted polymer films were prepared by introducing the ester of highest ED to PA66–formic acid solution via three different processes: open air (cold) grafting, ultraviolet irradiation grafting, and hot vacuum oven grafting. Thermogravimetry was conducted for all synthesized esters and films, and the formation of new bonds between the ester and PA66 was verified using Fourier transform infrared spectroscopy.     

Grand canonical ensemble molecular dynamics simulation of water solubility in polyamide-6,6

Grand canonical ensemble molecular dynamics simulation is employed to calculate the solubility of water in polyamide-6,6. It is shown that performing two separate simulations, one in the polymeric phase and one in the gaseous phase, is sufficient to find the phase coexistence point. In this method, the chemical potential of water in the polymer phase is expanded as a first-order Taylor series in terms of pressure. Knowing the chemical potential of water in the polymer phase in terms of pressure, another simulation for water in the gaseous phase, in the grand canonical ensemble, is done in which the target chemical potential is set in terms of pressure in the gas phase. The phase coexistence point can easily be calculated from the results of these two independent simulations. Our calculated sorption isotherms and solubility coefficients of water in polyamide-6,6, over a wide range of temperatures and pressures, agree with experimental data.     

Transferability of coarse-grained force fields: the polymer case

A key question for all coarse-graining methodologies is the degree of transferability of the resulting force field between various systems and thermodynamic conditions. Here we present a detailed study of the transferability over different thermodynamic states of a coarse-grained (CG) force field developed using the iterative Boltzmann inversion method. The force field is optimized against distribution functions obtained from atomistic simulations. We analyze the polymer case by investigating the bulk of polystyrene and polyamide-6,6 whose coarse-grained models differ in the chain length and in the number of atoms lumped in one bead. The effect of temperature and pressure on static, dynamic, and thermodynamic properties is tested by comparing systematically the coarse-grain results with the atomistic ones. We find that the CG model describing the polystyrene is transferable only in a narrow range of temperature and it fails in describing the change of the bulk density when temperature is 80 K lower than the optimization one. Moreover the calculation of the self-diffusion coefficient shows that the CG model is characterized by a faster dynamics than the atomistic one and that it overestimates the isothermal compressibility. On the contrary, the polyamide-6,6 CG model turns out to be fully transferable between different thermodynamic conditions. The transferability is checked by changing either the temperature or the pressure of the simulation. We find that, in this case, the CG model is able to follow all the intra- and interstructural rearrangements caused by the temperature changes. In addition, while at low temperature the difference between the CG and atomistic dynamics is remarkable due to the presence of hydrogen bonds in the atomistic systems, for high temperatures, the speedup of the CG dynamics is strongly reduced, leading to a CG diffusion coefficient only six times bigger than the atomistic one. Moreover, the isothermal compressibility calculated at different temperatures agrees very well with the experimental one. We find that the polymer chain length does not affect the transferability of the force field and we attribute such transferability mainly to the finer model used in describing the polyamide-6,6 than the polystyrene.     

Analysis of polynitrophenols and hexyl by liquid chromatography-mass spectrometry using atmospheric pressure ionisation methods and a volatile ion-pairing reagent

An LC-MS method for the determination of picric acid (2,4,6-trinitrophenol), its reductive transformation products picramic acid (2-amino-4,6-dinitrophenol) and iso-picramic acid (4-amino-2,6-dinitrophenol) and hexyl (2,2',4,4',6,6'-hexanitrodiphenylamine) has been developed. The analytes were separated using ion-pairing chromatography with a volatile ion-pairing reagent suitable for subsequent MS detection. The performance of an atmospheric pressure chemical ionisation (APCI) and an electrospray ionisation (ESI) interface was compared. ESI-MS is more sensitive for the analytes, especially for hexyl and picric acid, APCI-MS delivered more fragments necessary for unequivocal identification. With LC-ESI-MS limits of detection using single ion monitoring (SIM) mode are 4 ng (iso-picramic acid), 800 pg (picramic acid), 400 pg (picric acid) and 80 pg (hexyl). For quantification, 15N-picric acid was used as an internal standard. Using this new method, the degradation of picric acid in soil was monitored in a laboratory study. Furthermore, the presence of picramic acid was for the first time verified in soil samples from a former ammunition plant.     

Separation and characterisation of caprolactam-formaldehyde reaction products

Methylolation and condensation products formed in caprolactam-formaldehyde reaction mixtures have been identified using nuclear magnetic resonance (NMR) and mass spectrometry (MS). Previously unreported side-products were also detected. All of the reaction products were separated by micellar electrokinetic chromatography (MEKC) and high performance liquid chromatography (HPLC), and the separation parameters, such as efficiency and distribution constants, obtained in the two techniques were compared. For quantification, the response factors for the monomers were determined using standard calibration and hydrolysis, whilst those for the condensation products were deduced from the values of the monomers. The accurate determination of the response factors was confirmed by checking the mass balance of a known mixture.     

Synthesis and characterization of covalently linked multilayer films prepared in the absence of solvent

We report the preparation of multilayer organic thin films prepared by sequential vapor-phase coupling of monomers. The reactions were carried out at room temperature and atmospheric pressure. Films prepared using up to six sequential coupling reactions are reported. The following specific vapor-phase reactions were found to be viable: reactions between acid chlorides and both aliphatic and aromatic amine, hydrolysis reactions, anhydride activation, and reactions between anhydrides and primary amines. Homobifunctionalized monomers, such as hexamethylenediamine, react primarily via a single endgroup rather than cross coupling to the reactive surface via both reactive groups. The estimated coverage of the multilayer films is between 36 and 46%. The films were characterized using ellipsometric, contact angle, and spectroscopic measurements.     

Separation and characterization of functional poly(n-butyl acrylate) by critical liquid chromatography

The separation of functional poly(n-butyl acrylate) (PnBA) polymers based on the number of end-groups under critical liquid chromatography (LC) conditions has been studied using a bare-silica column. The (near-) critical solvent compositions for non-, mono-, and difunctional (telechelic) carboxyl-PnBAs were determined in normal-phase LC, using mixtures of acetonitrile, acetic (or formic) acid, and dichloromethane of varying composition. Some formic or acetic acid had to be added to the mobile phase to elute PnBA polymers with carboxyl end-groups. The critical solvent compositions obtained were not exactly the same for non-, mono-, and difunctional PnBA polymers. These were unusual experimental observation, but they were in agreement with theoretic predictions. Nevertheless, low-molecular-mass PnBA samples were successfully separated according to the carboxyl functionality at (near-) critical conditions. With the aid of mass spectrometry (MS), the (near-) critical separation of low-molecular-mass PnBA polymers was confirmed to be mainly based on the carboxyl functionality. Calibration curves for evaporative light-scattering detection (ELSD) were used for quantitative analysis of carboxyl-functional PnBA polymers. The results proved that nearly ideal functionalities (average number of carboxyl end-groups per molecule up to 1.99) were achieved for telechelic PnBAs prepared by one-step reversible addition-fragmentation chain-transfer (RAFT) polymerization of PnBA.     

Surface modification of polyamide-6: graft copolymerization of vinyl monomers onto polyamide-6 and thermal analysis of the graft copolymers

Graft copolymerization of vinyl monomers onto polyamide-6 using radical initiation has been investigated. Two monomers were used: methacrylic acid and acrylic acid. The initiators selected included hydrogen peroxide, benzoyl peroxide and azobisisobutyronitrile. The extent of graft copolymerization depends on the concentrations and identity of the initiator and monomer and the time and temperature of the reaction. The graft copolymers were not soluble in solvents that will dissolve the starting material; definitive proof for the formation of the graft copolymers was obtained from infrared spectroscopy. Thermogravimetric analysis was performed on the graft copolymers and it was found that the presence of the acid invariably accelerated the degradation of the polyamide. © 1998 John Wiley & Sons, Ltd.     

Robust isocratic liquid chromatographic separation of functional poly(methyl methacrylate)

The separation of telechelic poly(methyl methacrylate) (PMMA) prepolymers based on the number of end-groups under critical liquid chromatography (LC) conditions has been studied using a bare-silica column, which can interact with polar functional groups. The critical solvent compositions for non-functional, mono-functional and bi-functional PMMAs were determined in normal-phase LC using mixtures of acetonitrile and dichloromethane (DCM) of varying composition as the mobile phase. The telechelic prepolymers were successfully separated according to hydroxyl (OH) functionality (with zero, one, or two OH groups, respectively) under the critical conditions, in which fast (5 min), base-line separations were obtained independent of molecular weight. Changing the column temperature, flow rate, and mobile-phase composition within a certain range did not affect the functionality separation. Therefore this isocratic LC separation method is quite robust. Evaporative light-scattering detector (ELSD) calibration curves were used for the quantitative analysis of functional PMMA prepolymers.     

Excellent combination of counter-current chromatography and preparative high-performance liquid chromatography to separate galactolipids from pumpkin

Galactolipids in the fruits of Cucurbita moschata (pumpkin) could not be completely separated by high-performance liquid chromatography (HPLC). Preparative HPLC was not available for preparing major galactolipid monomers in pumpkin. In the present paper, a combination of high-speed counter-current chromatography (HSCCC) and preparative HPLC was used for preparing the galactolipids. A fraction containing galactolipids (Fr60) from the purification of the n-butanol extract of pumpkin by macro-porous resin column chromatography was first separated by HSCCC to result in three sub-fractions of each containing two galactolipid monomers. The three sub-fractions were further separated by preparative HPLC respectively to yield six galactolipid monomers with purity more than 96%. The method is a good one for preparing galactolipid monomers from plant materials for the studies of bioactivities.     

An efficient chemical method for separation of corsolic acid from its isomeric maslinic acid

Based on the difference in steric bulk around C12-C13 double bond, the two isomeric dihydroxy pentacyclic triterpenic acids viz: corsolic acid and maslinic acid have been quantitatively separated via their methyl esters by reacting with the bulky m-chloroperbenzoic acid. Corsolic acid methyl ester was obtained in pure form, whereas maslinic acid methyl ester was separated as 12-oxo derivative formed via its epoxide. Alkaline hydrolysis of corsolic acid methyl ester afforded the desired acid. This method was also found to work well with the isomeric amyrin mixture (alpha- and beta-), but not highly selective. The high selectivity of this method with corsolic maslinic acid system can be rationalized in terms of 2alpha-hydroxy functionality, which provides additional crowding around the double bond and completely prevented corsolic acid from its reaction with perbenzoic acid.     

高效液相色谱法分析大豆中磷脂酰胆碱的分子种

用高效液相色谱法（HPLC）在正相半制备硅胶柱上将大豆磷脂酰胆碱与其它组分分离，从柱后收集磷脂酰胆碱（PC），然后在反相C18柱上分析其分子种组成，蒸发光散射检测器检测。在25min内将大豆磷脂酰胆碱分离成11个分子种组分，使用易挥发溶剂，可获得各种分子种的纯物质，供进一步分析。分子种根据HPLC峰的脂肪酸组成分析而确定。     

Investigating Lignin-Derived Monomers and Oligomers in Low-Molecular-Weight Fractions Separated from Depolymerized Black Liquor Retentate by Membrane Filtration

Base-catalyzed depolymerization of black liquor retentate (BLR) from the kraft pulping process, followed by ultrafiltration, has been suggested as a means of obtaining low-molecular-weight (LMW) compounds. The chemical complexity of BLR, which consists of a mixture of softwood and hardwood lignin that has undergone several kinds of treatment, leads to a complex mixture of LMW compounds, making the separation of components for the formation of value-added chemicals more difficult. Identifying the phenolic compounds in the LMW fractions obtained under different depolymerization conditions is essential for the upgrading process. In this study, a state-of-the-art nontargeted analysis method using ultra-high-performance supercritical fluid chromatography coupled to high-resolution multiple-stage tandem mass spectrometry (UHPSFC/HRMSⁿ) combined with a Kendrick mass defect-based classification model was applied to analyze the monomers and oligomers in the LMW fractions separated from BLR samples depolymerized at 170–210 °C. The most common phenolic compound types were dimers, followed by monomers. A second round of depolymerization yielded low amounts of monomers and dimers, while a high number of trimers were formed, thought to be the result of repolymerization.     

Galacturonic acid lactones in the synthesis of all trisaccharide repeating units of the zwitterionic polysaccharide Sp1

A modular approach toward the synthesis of all possible trimer repeating units of the type 1 capsular polysaccharide of Streptococcus pneumonia, Sp1, is described. This zwitterionic polysaccharide is built up from trisaccharide repeats, which in turn are composed of two galacturonic acid monomers and a 2,4,6-trideoxy-4-amino-2-acetamido-D-galactose moiety. All monomeric constituents are linked through cis-glycosidic bonds. To overcome the difficulty associated with the efficient stereoselective introduction of the α-galacturonic acid bonds, we have employed galacturonic acid-[3,6]-lactone building blocks. Not only did these building blocks perform well when used as donor galactosides, they were also shown to be reactive acceptor glycosides when equipped with a free hydroxyl function. All three frame-shifted trimer repeats were constructed via highly stereoselective glycosylation reactions, with one exception. The epimeric mixture of trisaccharides, formed in the nonselective glycosylation event, could be readily separated after global deprotection using high performance anion exchange chromatography (HPEAC).     

Fractionation into Components of a Mixture of Acidic Ninhydrin-Positive Compounds of Mouse Brain Extracts with Thin-Layer and Ion-Exchange Chromatography

Abstract

A mixture of more than ten acidic or highly ionized ninhydrin-positive compounds of mouse brain extracts, occurring in ion-exchange chromatography from the beginning up to aspartic acid, was analyzed using ion-exchange and thin-layer chromatography standardized with known substances. These formed four peak groups in the chromatogram of an automatic amino acid analyzer. The first group contained cysteic acid, cysteine-sulfinic acid and phosphoserine, which could be separated from each others only by thin-layer chromatography. Only phosphoserine could be identified in the brain extract (about 0.14 mmol/kg brain wet weight), however. Taurine (4.1 mmol/kg) and phosphoethanolamine (1.05 mmol/kg) in the second group could be satisfactorily separated from each others after the hydrolysis of glycerylphosphoethanolamine (about 0.6 mmol/kg) and certain acidic peptides with 6 mol/1 HCl. Hypotaurine (0.03 mmol/kg) and urea (6.6 mmol/kg) were completely overlapped in the third peak, but urea was decomposed in the hydrolysis with 6 mol/1 HCl. The fourth group consisted of aspartic acid (2.1 mmol/kg). A number of low-molecular weight peptides also appeared in the chromatograms, above all in the phosphoserine and taurine peaks, but they were eliminated by the hydrolysis. They contained, however, some of the above-mentioned critical amino acids (phosphoserine, taurine and aspartic acid).     

四氢呋喃正离子聚合转为烯类单体负离子嵌段共聚合的研究

本文以癸二酰氯-高氯酸银催化剂在低温引发四氢呋喃正离子聚合,用伯胺终止,制得带有双端仲胺基的聚四氢呋喃遥爪聚合物(PTHF-NHR,R为苄基、正丁基、苯基)。当R为苯基时,PTHF-NHR与萘钠的金属化反应接近完全。以PTHF-NHR的胺钠盐引发烯类单体(甲基丙烯酸甲酯、苯乙烯、丙烯腈)负离子嵌段共聚合。当R为苯基、单体为甲基丙烯酸甲酯时,室温反应可得到转化率为100％的ABA型嵌段共聚物,为热塑性弹性体,其抗张强度为157kg/cm~2,扯断伸长率为700％。