Determination of the Molar Mass and the Radius of Gyration, Together with their Distributions for Methylhydroxyethylcelluloses

Three molar mass series were produced by different methods of degradation (namely ultrasonic (seven samples), oxidation (seven samples) and autoclaving (eight samples)) from a methylhydroxyethylcellulose (MHEC) sample with an average degree of substitution (DS) of 1.3, a molar degree of substitution (MS) of 0.46, a radius of gyration of 67 nm and a weight-average molar mass, M _w, of 318,000 g/mol. The degraded samples were characterized in terms of their molar mass and particle size together with their respective distributions with a hyphenated apparatus consisting of size exclusion chromatography and multi-angle laser light scattering and concentration detector (SEC/MALLS/DRI) at 25 °C in 0.1 M NaNO₃ solution (with 200 ppm NaN₃ as antibactericide). The refractive index increment was determined as dn/dc = 0.135 cm³/g. It was possible to reduce the weight-average molar mass down to approximately 10% of the initial molar mass using all the methods. In a comparison of the three degradation methods it was shown that only ultrasonic degradation retains the monomodal distribution, whereas the other two degradation methods yield a bimodal molar mass distribution. Consequently, only ultrasonic degradation represents a suitable method for producing homologous molar mass series. An R _G–M relationship of R _G = 0.0511 × M ^0.56 was established for the sample used in this case, and from this it was possible to calculate an []–M relationship of [] = 0.3587 × M ^0.68.     

Characterizing a spheroidal nanocage drug delivery vesicle using multi-detector hydrodynamic chromatography

The biological application of nanoparticles has resulted in an increased need for the development of robust, accurate, and precise methods for quality control analysis and characterization. Parameters such as particle size, particle shape, and their distributions affect end-use properties such as chemical reactivity, diffusivity, permeability, and transport. Introduced here is a hydrodynamic chromatography (HDC) method utilizing multi-angle static light scattering, quasi-elastic light scattering, differential viscometry, and differential refractometry detection for characterizing nanoscale vesicles. Quadruple-detector HDC was used to determine multiple sizing parameters and their statistical moments and distributions. Molar mass and molar mass averages were determined in a calibrant-independent fashion. Both the sizing parameters and the molar mass were measured across the HDC elution profile. The shape and structure of the nanoparticle were monitored as a function of HDC elution volume through the dimensionless ratio ??????R _G,z /R _H,z . The HDC results were comparable to those obtained by transmission electron microscopy, but more extensive characterization was possible by HDC, which provided distributions of both particle size and particle shape.

Homogenous synthesis of 3-allyloxy-2-hydroxypropyl-cellulose in NaOH/urea aqueous system

3-Allyloxy-2-hydroxypropylcelluloses (AHP-celluloses), reactive unsaturated cellulose derivatives, were homogeneously synthesized by the reaction of cellulose with allyl glycidyl ether (AGE) in NaOH/urea aqueous solution. Water-soluble AHP-celluloses with DS_NMR = 0.32–0.67 were prepared from microcrystalline cellulose. The degree of substitution (DS) of AHP-celluloses could be controlled by varying the molar ratio of AGE and NaOH to AGU and the reaction conditions. The structure of AHP-cellulose samples were characterized by means of FT-IR, NMR spectroscopy and size exclusion chromatography. The cellulose ether shows thermoreversible flocculation. Bromination reactions were carried out as subsequent functionalization both to illustrate the reactivity of the allyl function and to determine the DS values.     

Synthesis of O‐(2,3‐dihydroxypropyl) cellulose in NaOH/urea aqueous solution: As a precursor for introducing “necklace‐like” structure

O‐(2,3‐dihydroxypropyl) cellulose (DHPC) samples were synthesized by etherification of cellulose with glycidol (GLY) in a NaOH/urea aqueous solution system under different reaction conditions, so that they had different degrees of ether substitution (DS) in both the overall and regional distributions. The characterization was made by NMR spectroscopy in order to clarify the effects of the molar ratio of in‐fed GLY to anhydroglucose unit and of the reaction temperature not only on the total and regional DSs but also on the molar substitution (MS_dhp) for the multireactive dihydroxypropyl group. The evaluation of MS_dhp was performed after complete propionylation of each DHPC sample. Determination of molecular weights was also conducted on the propionylated DHPCs by GPC analysis. As a preliminary extension, butyralization of DHPC was undertaken in aqueous solution by using p‐toluenesulfonic acid as catalyst together with butyraldehyde (BuA). Two‐dimensional NMR (¹H–¹³C gHSQC) spectra measurements revealed that the products contained butyral groups, owing to dehydration‐cyclization between the BuA‐carbonyl and the duplicate hydroxyls in the side chain of DHPC. Such butyral derivatives of cellulose are expected to be a promising functional material parallel or superior to poly(vinyl butyral) available for safety glass interlayers, etc. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3590–3597     

Interactions and stability of silver nanoparticles in the aqueous phase: Influence of natural organic matter (NOM) and ionic strength

The rapid development of nanotechnology and the related production and application of nanosized materials such as engineered nanoparticles (ENP) inevitably lead to the emission of these products into environmental systems. So far, little is known about the occurrence and the behaviour of ENP in environmental aquatic systems. In this contribution, the influence of natural organic matter (NOM) and ionic strength on the stability and the interactions of silver nanoparticles (n-Ag) in aqueous suspensions was investigated using UV–vis spectroscopy and asymmetrical flow field-flow fractionation (AF⁴) coupled with UV–vis detection and mass spectrometry (ICP-MS). n-Ag particles were synthesized by chemical reduction of AgNO₃ with NaBH₄ in the liquid phase at different NOM concentrations. It could be observed that the destabilization effect of increasing ionic strength on n-Ag suspensions was significantly decreased in the presence of NOM, leading to a more stable n-Ag particle suspension. The results indicate that this behaviour is due to the adsorption of NOM molecules onto the surface of n-Ag particles (“coating”) and the resulting steric stabilization of the particle suspension. The application of AF⁴ coupled with highly sensitive detectors turned out to be a powerful method to follow the aggregation of n-Ag particle suspensions at different physical–chemical conditions and to get meaningful information on their chemical composition and particle size distributions. The method described will also open the door to obtain reliable data on the occurrence and the behaviour of other ENP in environmental aquatic systems.     

Phase-transfer reactions catalyzed by polymer-supported crown ethers

Polymer-supported crown ethers were prepared from chloromethylated or ω-bromoalkylated polystyrene resins and hydroxymethylbenzo-18-crown-6 and 15- or 18-membered monoazacrown ethers. Effects of the cavity size of crown ethers, the degree of crosslinking, the degree of ring substitution, particle size, spacer chains, and solvents on the activity of the polymer-supported crown ethers in the reaction of 1-chloro- or 1-bromo-octane with aqueous NaI or KI were investigated and mechanisms of the reaction were discussed in terms of mass transfer, intraparticle diffusion, and intrinsic reactivity.     

Multidimensional analytical protocols for the fractionation and analysis of complex polyolefins

Although produced from simple monomers that contain just carbon and hydrogen, polyolefin have complex molecular structures that are characterized by distributions in molar mass, chemical composition, and branching. Accordingly, a variety of advanced analytical techniques are needed for the comprehensive characterization of the molecular heterogeneity of polyolefins. These include different fractionation, spectroscopic, and thermal analysis methods. Very frequently, method couplings such as two-dimensional liquid chromatography or the coupling of crystallization- and column-based techniques are required. This review presents the current state of the art in multidimensional analysis of complex polyolefins. It discusses methods for bulk analysis as well as different analytical and preparative fractionation protocols. For different types of polyolefins it is shown that a preparative fractionation according to chemical composition/branching or molar mass helps to reduce the molecular complexity of the sample. Sample libraries can be obtained that may have narrow distributions regarding one molecular parameter. A detailed investigation of such library samples regarding other (broadly distributed) molecular parameters helps to fully explore the molecular heterogeneity of a complex sample.     

Studies on the molecular flexibility of novel dendronized carboxymethyl cellulose derivatives

Water-soluble deoxy-azido cellulose derivatives were synthesized by heterogeneous carboxymethylation, applying 2-propanol/aqueous NaOH as slurry medium. The novel, carboxymethyl deoxy-azido cellulose provides a convenient starting material for the selective dendronization of cellulose via the copper-catalyzed Huisgen reaction yielding water-soluble carboxymethyl 6-deoxy-(1-N-[1,2,3-triazolo]-4-polyamidoamine) cellulose derivatives of first (degree of substitution, DS 0.51), second (DS 0.44) and third generation (DS 0.39). The novel biopolymer derivatives were characterized by FT-IR and NMR spectroscopy, intrinsic viscosity, sedimentation coefficient and weight average molar mass. Solution conformation and flexibility were estimated qualitatively using conformation zoning and quantitatively (persistence length) using the combined global method. Sedimentation conformation zoning showed a semi-flexible coil conformation and the global method applied to each carboxymethyl deoxy-azido cellulose and carboxymethyl 6-deoxy-(1-N-[1,2,3-triazolo]-4-polyamidoamine) cellulose derivative yielded persistence length all within the range of 2.8-4.0 nm with no evidence of any change in flexibility with dendronization.     

Pure Cellulose Nanoparticles from Trimethylsilyl Cellulose

Silyl ethers of cellulose are promising derivatives of the biopolymer because they exhibit thermoplastic behavior at higher functionalization, may be applied as intermediate in subsequent reactions and have a high tendency to form defined supramolecular structures. Trimethylsilylation can be carried out by applying ionic liquids (ILs) such as 1-ethyl-3-methylimidazolium acetate (EMIMAc) as reaction medium. Pure trimethylsilyl cellulose (TMSC) can be efficiently synthesized with 1,1,1,3,3,3-hexamethyldisilazane (HMDS) yielding products with degrees of substitution (DS) up to 2.89. During the synthesis of highly functionalized derivatives, precipitation of the TMSC occurred, which simplifies the recycling of the IL. The tendency of TMSC toward the formation of supermolecular structures was exploited for the formation of pure cellulose nanospheres by a simple dialysis process. FTIR spectroscopy confirmed the complete removal of the TMS functions during this process. Scanning electron microscopy, dynamic light scattering, atomic force microscopy, and particle size distribution analysis showed that cellulose particles with a size of 100 to 200 nm are accessible in this simple manner.     

Preparation of new types of temperature-responsive cellulose derivatives

This paper reviews briefly our preliminary results concerning thermoplastic hydrogels and thermotropic aqueous gels from cellulose. Several kinds of thermoplastic hydrogels and thermotropic aqueous gels were prepared from cellulose and their thermal properties were examined. The former aims at preparing water-insoluble cellulose derivatives having a high water absorbency and a thermal flow temperature of approximately 130°C, while the later aims at preparing water-soluble cellulose derivatives which show a solubility behavior similar to that of synthetic polymers with a lower critical solution temperature (LCST) in aqueous solution. The results will be discussed in terms of the chemical structure of the prepared derivatives and their substituent distributions along the cellulose chain.     

Determining the absolute, chemical-heterogeneity-corrected molar mass averages, distribution, and solution conformation of random copolymers

We present a method by which to obtain the absolute, chemical-heterogeneity-corrected molar mass (M) averages and distributions of copolymers and apply the method to a gradient random copolymer of styrene and methyl methacrylate in which the styrene percentage decreases from approximately 30% to 19% as a function of increasing molar mass. The method consists of separation by size-exclusion chromatography (SEC) with detection using multi-angle static light scattering (MALS), differential viscometry (VISC), differential refractometry (DRI), and ultraviolet absorption spectroscopy (UV) and relies on the preferential absorption of styrene over methyl methacrylate at 260 nm. Using this quadruple-detector SEC/MALS/UV/VISC/DRI approach, the percentage of styrene (%St) in each elution slice is determined. This %St is then used to determine the specific refractive index increment, corrected for chemical composition, at each elution slice, which is then used to obtain the molar mass at each slice, corrected for chemical composition. From this corrected molar mass and from the chemical-composition-corrected refractometer response, the absolute, chemical-heterogeneity-corrected molar mass averages and distribution of the copolymer are calculated. The corrected molar mass and intrinsic viscosity at each SEC elution slice are used to construct a chemical-heterogeneity-corrected Mark–Houwink plot. The slice-wise-corrected M data are used, in conjunction with the MALS-determined R _G,z of each slice, to construct a conformation plot corrected for chemical heterogeneity. The corrected molar mass distribution (MMD) of the gradient copolymer extends over an approximately 30,000 g/mol wider range than the uncorrected MMD. Additionally, correction of the Mark–Houwink and conformation plots for the effects of chemical heterogeneity shows that the copolymer adopts a more compact conformation in solution than originally concluded.     

Physicochemical characterisation of different welding aerosols

Physicochemical properties important in exposure characterisation of four different welding aerosols were investigated. Particle number size distributions were determined by scanning mobility particle sizer (SMPS), mass size distributions by separation and weighing the individual size fractions of an 11-stage cascade impactor. The size distribution of the primary particles of agglomerates, chemical composition and morphology of the particles were examined by TEM. There were significant differences in the particle number size distributions of the different welding aerosols according to the SMPS determinations. The particle mass size distributions determined gravimetrically were, however, not really different. The dominant range with respect to mass was between 0.1 and 1 μm, regardless of the welding technique. Most of the primary particles in all different welding aerosols had diameters between 5 and 40 nm. All types of primary particles had a tendency to form chainlike agglomerates. A clear size dependence of the particle chemical composition was encountered in the case of manual metal arc welding aerosol. Small particles with diameters below 50 nm were mostly metal oxides in contrast to larger particles which also contained more volatile elements (e.g. potassium, fluorine, sodium, sulphur).     

Pyrolysis chemical ionization mass spectrometry of cellulose ethers

Pyrolysis ammonia chemical ionization (PyCI) mass spectrometry was performed on hy-droxyethyl-, hydroxypropyl-,methyl-, hydroxypropylmethyl-, and ethylhydroxyethyl cel-luloses. The mass peaks in the PyCI mass spectra of these cellulose ethers could be assigned to the ions of pyrolytic dissociation products which form via the [2 + 2 + 2] cycloreversion and the E_i elimination pyrolysis pathway. Structural information about the residual amount of nonderivatized cellulose, the relative chain length distributions of the substituents in hydroxyalkyl celluloses, and the end-capping of hydroxyalkyl substituents by alkyl groups in the mixed cellulose ethers is obtained. Interference of secondary pyrolysis products in the PyCI mass spectra is found to be of minor importance, especially in the lower mass regions. © 1995 John Wiley & Sons, Inc.     

Uses of Chloromethyldimethylsilyl Ethers as Derivatives for Combined Gas Chromatography-Mass Spectrometry of Steroids

Abstract

Chloromethyldimethylsilyl (CMDMS) ethers are useful derivatives for combined gas chromatography-mass spectrometry. They have characteristically longer retention times than the corresponding trimethylsilyl (TMS) derivatives, and this permits effective fractionation of mono-, di-, and trihydroxy steroids. CMDMS ethers provide mass spectra comparable with those of TMS ethers, but ions containing the CMDMS group are readily recognisable in the former by virtue of the two abundant natural isotopes of chlorine. This facilitates interpretation of spectra and may be expected to aid the location of drug metabolites by selective ion monitoring.     

Characterizing ablation and aerosol generation during elemental fractionation on absorption modified lithium tetraborate glasses using LA-ICP-MS

The influence of sample matrix composition, absorption behavior and laser aerosol particle size distribution on elemental fractionation in laser ablation inductively coupled plasma mass spectrometry was studied for nanosecond laser ablation at a wavelength of 266 nm. To this end, lithium tetraborate glass samples with different iron oxide contents and trace amounts of a group of 11 elements were prepared synthetically. The samples were characterized in terms of optical absorbance, melting points, trace element concentrations and homogeneity. UV/VIS spectra showed that sample absorption rises with increasing Fe₂O₃ content. Crater depths and time-dependent particle size distributions were measured, and ablated and transported sample volumes were estimated. Furthermore, the laser aerosol was filtered using a particle separation device and transient ICP-MS signals were acquired with and without filtering the aerosol. The results demonstrate that the amount of ablated sample is related to the absorption coefficient of the sample and therefore to the optical penetration depth of the laser beam into the sample. The higher energy densities resulting from the shorter penetration depths result in smaller average particle sizes for highly absorbing samples, which allows more efficient transport to and atomization and excitation of the ablated material within the ICP. The particle size distribution changes continuously with ablation time, and larger particle fractions occur mainly at the beginning of the ablation, which leads to particle-related fractionation processes at the beginning of the transient signal. Exceeding a critical depth to diameter ratio, laser-related elemental fractionation processes occur. Changes in the volatile to non-volatile element intensity ratio after the aerosol is filtered indicate that particle size-related enrichment processes contribute to elemental fractionation.     

Synthesis of cyanoethyl ethers of cellulose from flax fiber production waste

Conditions of preparation of cellulose cyanoethyl ethers with different degrees of substitution, based flax fiber production waste were examined. The chemical structure of the resulting cellulose ethers and variation of the structure of the cellulose materials during cyanoethylation were examined by IR-Fourier spectroscopy and X-ray diffraction analysis. The degree of substitution of cellulose ethers was examined in relation to cyanoethylation conditions and chemical composition of the initial cellulose materials.     

Nanofiber cellulose di- and tri-acetate using ferric chloride as a catalyst promoting highly efficient synthesis under microwave irradiation

An efficient method for the generation of cellulose di- and tri-acetate nano-structures is obtained through testing ferric chloride hydrate (FeCl₃·6H₂O) as a valuable Lewis acid catalyst with acetic anhydride under microwave irradiation. Our target was to evaluate the effects of the reaction conditions on the products' properties such as surface area and particle size distribution. It was found that changes in the degree of substitution (DS), the surface area, the degree of polymerization and the particle size distribution of the products correlated with reaction conditions. Cellulose tri-acetate nanofibers with DS of 2.94 with 98.03% yield was prepared using 200 mg of FeCl₃·6H₂O, 25 ml of Ac₂O and 4 minutes of microwave irradiation. Also, cellulose di-acetate nanofibers were prepared with DS values ranged between 2.37 and 2.72 with yield ranged between 78.92 and 90.58%. The percentage of acetyl groups (Ac%) as well as the BET specific surface area, total pore volume, mean pore diameter, mono layer volume and the mean particle size of the products were determined. The maximum specific surface area obtained for the acetylated cellulose was about ten times larger than that measured for the commercial cotton cellulose and about six times larger than that of the commercial cellulose acetate. The lowest mean particle size (34.90 nm) was about eleven times smaller than the mean particle size of the commercial cellulose acetate (394 nm). The present work has proved that FeCl₃·6H₂O was a highly active catalyst for the esterification of cellulose with unexpected yields and for the formation of nanofibers with low molecular weight.     

Thermal stability and degradation of starch derivatives

Thermal behaviour of different starch derivatives, i.e. starch esters and ethers having degree of substitution (DS) in the range of 0.02–0.18 were studied. Potato, maize and wheat starches were used. Measurements were carried out by coupled thermal analysis/ mass spectrometry method (STA-MS) in air atmosphere. The major DTG peak during the investigation for starch derivatives is observed below 300°C. The mass loss up to a temperature of 300°C is about 50%. The most abundant ions found areH₂O⁺ and CO₂ ⁺. For the studied starch derivatives with a low degree of substitution (DS<0.18) no correlation was found between thermal stability and the level of substitution regardless of the nature of substitution.     

Synthesis and characterization of cellulose derivatives prepared in NaOH/urea aqueous solutions

We successfully synthesized hydroxypropylcellulose (HPC) and methylcellulose (MC) in high yields from cellulose in 6 wt % NaOH/4 wt % urea aqueous solutions at 25 °C. The cellulose derivatives were characterized with NMR, size exclusion chromatography/laser light scattering, gas chromatography (GC), ultraviolet, and solubility measurements in different solvents. According to the results of solution ¹³C NMR and GC, the individual degree of substitution (DS; i.e., the average number of substituted hydroxyl groups in the monomer unit) at C‐2 hydroxyl groups was slightly higher than the DS values at C‐3 and C‐6 hydroxyl groups for HPC and MC. In comparison with traditional systems, NaOH/urea aqueous solutions were proved to be a stable and more homogeneous reaction medium for preparing cellulose ether with a more uniform microstructure. The low limits for the average number of moles of the substituent groups per monomer unit and the DS value of water‐soluble HPC were 1.03 and 0.85, respectively. MC (DS = 1.48) had good solubility in both water and organic solvents, and the precipitation point occurred at about 67 °C for a 2% (w/v) aqueous solution. In this way, we could provide a simple, pollution‐free, and homogeneous aqueous solution system for synthesizing cellulose ethers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5911–5920, 2004