Substituent Distribution and Clouding Behavior of Hydroxypropyl Methyl Cellulose Analyzed Using Enzymatic Degradation

Fingerprinting of hydroxy propyl methyl cellulose by comprehensive two-dimensional liquid chromatography-mass spectrometry of monomers resulting from acid hydrolysis

Hydroxypropyl methyl cellulose (HPMC) is a type of cellulose derivative with properties that render it useful in e.g. food, cosmetics, and pharmaceutical industry. The substitution degree and composition of the β-glucose subunits of HPMC affect its physical and functional properties, but HPMC characterization is challenging due to its high structural heterogeneity, including many isomers. In this study, comprehensive two-dimensional liquid chromatography-mass spectrometry was used to examine substituted glucose monomers originating from complete acid hydrolysis of HPMC. Resolution between the different monomers was achieved using a C18 and cyano column in the first and second LC dimension, respectively. The data analysis process was structured to obtain fingerprints of the monomers of interest. The results revealed that isomers of the respective monomers could be selectively separated based on the position of substituents. The examination of two industrial HPMC products revealed differences in overall monomer composition. While both products contained monomers with a similar degree of substitution, they exhibited distinct regioselectivity.

Investigation of Thermal Gel Formation of Methylcellulose in Glycols Using DSC and XRD

Novel compositions of methylcellulose in ethylene, propylene and butylene glycol were investigated for their thermal gel formation. These compositions have previously been found useful for inkjet-printing-based additive manufacturing processes as support materials. Experimental techniques such as viscosity measurements between 20 °C–150 °C–20 °C, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were used and the results showed that the gel formation upon cooling is caused by polymer–polymer association. The results also show that, for methylcellulose, propylene glycol is a better solvent than ethylene glycol and butylene glycol. Since no chemical reaction is involved, these gels can be used as support materials for jetting-based additive manufacturing processes.

Synthesis and Fluorescent Thermoresponsive Properties of Tetraphenylethylene-Labeled Methylcellulose

Functional polymer, especially the one based on renewable and sustainable materials, has attracted increasing attention to satisfy the growing demand for the design of stimuli-responsive devices. Methylcellulose (MC) is a water-soluble derivative of cellulose, which has been widely used in many fields for its biocompatibility and biological inertness. In this work, MC is labeled by tetraphenylethylene (TPE) via azide-alkyne click reaction to obtain a fluorescent cellulose-based derivative of MC-TPE. The degree of substitution of MC-TPE is determined to be 0.074, which can be self-assembled into micelles in water with the size of 42 ± 6 nm. MC-TPE shows thermoresponsivity and thermoreversibility in size, transmittance, and fluorescence, enabling it to work as a fluorescent thermosensor. Moreover, MC-TPE exhibits nontoxicity and biocompatibility, allowing its application in MCF-7 cell imaging. Therefore, this newly functional natural polymer shows promising potentials in the fields of sensing and bioimaging.

Substituent distribution of propyl cellulose studied by nuclear magnetic resonance

A series of propyl cellulose (PC) samples with different degrees of substitution (DS) ranging from 0.34 to 2.02 were prepared by a slurry method using propyl bromide as the etherification reagent. Two-dimensional nuclear magnetic resonance (NMR) studies were performed to identify the ¹H and ¹³C chemical shifts of eight anhydroglucose units (AGUs) in PC chains including un-, 2-mono-, 3-mono-, 6-mono-, 2,3-di-, 2,6-di-, 3,6-di-, and 2,3,6-tri-substituted ones. In addition, the mole fractions (χ) of these AGUs in the studied PC samples and their changes with DS were determined from the quantitative ¹³C NMR spectra. The obtained χ-DS profiles were different from those of methyl and ethyl celluloses prepared by a similar slurry method, indicating that the molecular sizes of the substituent reagents utilized for cellulose ethers strongly affected their substituent distributions.

Size-exclusion chromatography of ultrahigh molecular weight methylcellulose ethers and hydroxypropyl methylcellulose ethers for reliable molecular weight distribution characterization

Size-exclusion chromatography (SEC) coupled with multi-angle laser light scattering (MALLS) and differential refractive index (DRI) detectors was employed for determination of the molecular weight distributions (MWD) of methylcellulose ethers (MC) and hydroxypropyl methylcellulose ethers (HPMC) having weight-average molecular weights (Mw) ranging from 20 to more than 1,000kg/mol. In comparison to previous work involving right-angle light scattering (RALS) and a viscometer for MWD characterization of MC and HPMC, MALLS yields more reliable molecular weight for materials having weight-average molecular weights (Mw) exceeding about 300kg/mol. A non-ideal SEC separation was observed for cellulose ethers with Mw>800kg/mol, and was manifested by upward divergence of logM vs. elution volume (EV) at larger elution volume at typical SEC flow rate such as 1.0mL/min. As such, the number-average molecular weight (Mn) determined for the sample was erroneously large and polydispersity (Mw/Mn) was erroneously small. This non-ideality resulting in the late elution of high molecular weight chains could be due to the elongation of polymer chains when experimental conditions yield Deborah numbers (De) exceeding 0.5. Non-idealities were eliminated when sufficiently low flow rates were used. Thus, using carefully selected experimental conditions, SEC coupled with MALLS and DRI can provide reliable MWD characterization of MC and HPMC covering the entire ranges of compositions and molecular weights of commercial interest.

Characterization of the substitution pattern of cellulose derivatives using carbohydrate-binding modules

BACKGROUND

Derivatized celluloses, such as methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC), are of pharmaceutical importance and extensively employed in tablet matrices. Each batch of derivatized cellulose is thoroughly characterized before utilized in tablet formulations as batch-to-batch differences can affect drug release. The substitution pattern of the derivatized cellulose polymers, i.e. the mode on which the substituent groups are dispersed along the cellulose backbone, can vary from batch-to-batch and is a factor that can influence drug release.

RESULTS

In the present study an analytical approach for the characterization of the substitution pattern of derivatized celluloses is presented, which is based on the use of carbohydrate-binding modules (CBMs) and affinity electrophoresis. CBM4-2 from Rhodothermus marinus xylanase 10A is capable of distinguishing between batches of derivatized cellulose with different substitution patterns. This is demonstrated by a higher migration retardation of the CBM in acrylamide gels containing batches of MC and HPMC with a more heterogeneous distribution pattern.

CONCLUSIONS

We conclude that CBMs have the potential to characterize the substitution pattern of cellulose derivatives and anticipate that with use of CBMs with a very selective recognition capacity it will be possible to more extensively characterize and standardize important carbohydrates used for instance in tablet formulation.

Chemical structure analysis of starch and cellulose derivatives

Starch and cellulose are the most abundant and important representatives of renewable biomass. Since the mid-19th century their properties have been changed by chemical modification for commercial and scientific purposes, and there substituted polymers have found a wide range of applications. However, the inherent polydispersity and supramolecular organization of starch and cellulose cause the products resulting from their modification to display high complexity. Chemical composition analysis of these mixtures is therefore a challenging task. Detailed knowledge on substitution patterns is fundamental for understanding structure-property relationships in modified cellulose and starch, and thus also for the improvement of reproducibility and rational design of properties. Substitution patterns resulting from kinetically or thermodynamically controlled reactions show certain preferences for the three available hydroxyl functions in (1→4)-linked glucans. Spurlin, seventy years ago, was the first to describe this in an idealized model, and nowadays this model has been extended and related to the next hierarchical levels, namely, the substituent distribution in and over the polymer chains. This structural complexity, with its implications for data interpretation, and the analytical approaches developed for its investigation are outlined in this article. Strategies and methods for the determination of the average degree of substitution (DS), monomer composition, and substitution patterns at the polymer level are presented and discussed with respect to their limitations and interpretability. Nuclear magnetic resonance spectroscopy, chromatography, capillary electrophoresis, and modern mass spectrometry (MS), including tandem MS, are the main instrumental techniques employed, in combination with appropriate sample preparation by chemical and enzymatic methods.

Liquid chromatography combined with mass spectrometry for the investigation of endoglucanase selectivity on carboxymethyl cellulose

Endoglucanases are useful tools in the chemical structure analysis of cellulose derivatives. However, knowledge on the endoglucanase selectivity, which is of central importance for data interpretation, is still limited. In this study, new reverse-phase liquid chromatography mass spectrometry (LC-MS) methods were developed to investigate the selectivity of the endoglucanases Cel5A, Cel7B, Cel45A, and Cel74A from the filamentous fungus Trichoderma reesei. The aim was to improve the identification of the regioisomers in the complex mixtures that are obtained after enzymatic hydrolysis. Reduction followed by per-O-methylation was performed in order to improve the separation in reverse-phase LC, increase MS sensitivity, and to facilitate structure analysis by MS/MS of O-carboxymethyl glucose and cellooligosaccharides. The cellulose selective enzymes that were investigated displayed interesting differences in enzyme selectivity on CMC substrates.