Biomedical subjects

Sara Richardson

Publications and source records attributed to Sara Richardson.

6 recordsLinked to original sources

PubMed2006

Characterization of chemical substitution of hydroxypropyl cellulose using enzymatic degradation.

The distribution of substituents along the polymer backbone will have a strong influence on the properties of modified cellulose. Endoglucanases were used to degrade a series of hydroxypropyl cellulose (HPC) derivatives with a high degree of substitution. The HPCs were characterized with cloud-point analysis prior to degradation. The extent of enzymatic degradation was determined with size-exclusion chromatography with online multi-angle light scattering and refractive index detection and also with high-pH anion exchange chromatography with pulsed amperometric detection. To further characterize the formed products, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was employed for analysis of short-chained oligosaccharides. The different endoglucanases showed varying degradation capability depending on structure of the active site. The highly substituted HPCs had different susceptibility to degradation by the endoglucanases. The results show a difference in substituent distribution between HPCs, which would explain the differing cloud-point behaviors. Increased number of regions with low substitution could be correlated with lower polymer cloud point. The study shows the usefulness of enzymatic degradation to study the distribution of substituents in soluble biopolymer derivates.

Bacterial Proteins↗

PubMed2006

NMR, cloud-point measurements and enzymatic depolymerization: complementary tools to investigate substituent patterns in modified celluloses.

The substituent patterns of some chemically modified celluloses were characterized as a function of their size distribution, using size-exclusion chromatography coupled to both nuclear magnetic resonance spectroscopy (NMR) and cloud-point measurements. Intact and enzymatically hydrolyzed methyl cellulose (MC) was fractionated according to size, and the level of substitution of the fractions was measured off-line using NMR. Clouding behavior was also measured as a function of size. Clear differences between hydrolyzed and nonhydrolyzed samples were observed using both techniques. For samples that had been selectively hydrolyzed using cellulose-degrading enzymes, NMR data showed a direct link between the degree of degradation and the level of substitution. Differences in the clouding behavior highlighted changes in substituent levels and substituent patterns across the size distribution. The techniques gave valuable and somewhat complementary information on the substituent distributions of the samples before and after enzymatic hydrolysis.

Bacillus↗

PubMed2006

Substituent distribution and clouding behavior of hydroxypropyl methyl cellulose analyzed using enzymatic degradation.

The distribution of substituents along the polymer backbone will have a strong influence on the properties of modified cellulose. Endoglucanases were used to degrade three different batches of hydroxypropyl methyl cellulose (HPMC) derivatives with similar chemical properties. The phase separation of the HPMCs as a function of temperature, i.e., the clouding behavior, was analyzed prior to degradation. The total amount of unsubstituted glucose was determined using total acid hydrolysis followed by high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). The products after enzymatic degradation were analyzed with size-exclusion chromatography with online multiangle light scattering and refractive index detection and also with reducing end determination. To further characterize the formed products, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was employed for analysis of short-chained oligosaccharides. The different endoglucanases showed varying degradation capability of HPMC derivatives, depending on structure of the active site. The investigated HPMCs had different susceptibility to degradation by the endoglucanases. The results showed a difference in substituent distribution between HPMC batches, which could explain the differing clouding behaviors. The batch with the lowest cloud point was shown to contain a higher number of non-degradable, highly substituted regions.

Cellulase↗

PubMed2003

Enzyme-aided investigation of the substituent distribution in cationic potato amylopectin starch.

The distribution of substituents along the polymer chain in cationic potato amylopectin starch, modified in solution, granular slurry, or dry state, was investigated. The starch derivatives were successively hydrolyzed by different enzymes, followed by characterization of the hydrolysis products obtained by means of electrospray mass spectrometry (ESI-MS) and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). ESI-MS and MALDI-MS were proved to be appropriate techniques for identification of the substituted hydrolysis products, for which there are no standard compounds available. No highly substituted oligomers were found in the hydrolysates, which was taken as an indication of a more or less homogeneous distribution of cationic groups in the amylopectin molecules. Furthermore, from the results obtained it was suggested that the enzymes cleave glucosidic linkages only between unsubstituted glucose units and, preferentially, linkages in sequences containing more than two adjacent unsubstituted units. The determination of the amount of unsubstituted glucose produced from every successive hydrolysis step revealed slight differences between the different starch samples with respect to the homogeneity of the substitution pattern. Among the three samples under investigation, starch cationized in solution was found to have the most and dry-cationized starch the least homogeneous distribution of substituents.

Amylopectin↗

PubMed2003

Analytical approaches to improved characterization of substitution in hydroxypropyl cellulose.

Chemical characterization of cellulose derivatives is of high importance as it provides information about the often inhomogeneous substitution that may seriously affect the properties of these polymers in various applications. A detailed mapping of the chemical structure of these derivatives requires several advanced techniques to be employed. In this study, the average substitution and the substitution heterogeneity in two hydroxypropyl cellulose (HPC) samples from different suppliers were studied by means of NMR spectroscopy, MALDI-TOF MS, and HPAEC-PAD. (1)H and (13)C NMR provided information on the molar substitution, a parameter that could be analyzed by MALDI-TOF MS as well. In addition, the latter technique was used for determination of the distribution of the number of hydroxypropyl groups per glucose unit present in the two polymers. The heterogeneity of the substitution was studied by determining the amount of unsubstituted glucose units in the HPC samples, which was accomplished by HPAEC-PAD analysis. The results obtained suggest that the two HPC samples differ in both hydroxypropoxy content and distribution of the hydroxypropyl groups. Further, the benefits and importance of employing several analytical methods when investigating the cellulose ether substitution are demonstrated, as each method provides different kinds of information on the chemical content.

Carbohydrate Sequence↗

PubMedDate not supplied

Initial characterization of ethyl(hydroxyethyl) cellulose using enzymic degradation and chromatographic methods.

Two different ethyl(hydroxyethyl) cellulose (EHEC) samples were characterized by size-exclusion chromatography (SEC) with multiangle light scattering (MALS) detection and high-performance anion-exchange chromatography (HPAEC) with pulsed amperometric detection (PAD). The aim of the study was to investigate the molar mass distribution and the heterogeneity of the substituent distribution, factors that are thought to affect the functional properties of EHEC. The presence of blocks of unsubstituted glucose units was studied by enzymic degradation of EHEC by two different endoglucanases from Trichoderma reesei. The SEC-MALS analysis of the hydrolysis products showed that both enzymes were strongly inhibited by the large number of substituents along the cellulose chain. However, as the weight-average molar mass was reduced from approximately 360,000 to 80,000 g/mol in one of the polymers and from 770,000 to 60,000 g/mol in the other polymer, it was suggested that both samples were composed of some unsubstituted regions where the enzymes got access to the glucosidic bonds. The amount of glucose released upon endoglucanase hydrolysis was determined by HPAEC-PAD, which gave information on the homogeneity of the substituent distribution. The production of unsubstituted glucose units indicated that one of the polymers had a more uneven distribution compared with the other. It was demonstrated that chemical characterization of EHEC is a complex task, which requires an analytical approach involving numerous different methods and techniques.

Cellulase↗