Substitution patterns in methylated starch as studied by enzymic degradation

Analysis of the Heterogeneities of First and Second Order of Cellulose Derivatives: A Complex Challenge

The complexity of the substituent distribution in polysaccharide derivatives is discussed and defined. The challenges regarding analytical characterization that results from various interrelated categories of distributions, including molecular weight, chemical composition, and microstructure, are outlined. Due to these convoluted levels of complexity, results should always be interpreted with carefulness. Various analytical approaches which have been applied to starch and cellulose derivatives are recapped, including enzymatic, mass spectrometric, and chromatographic methods. The relation of heterogeneities of first and second order among and along the polysaccharide chains is addressed. Finally, examples of own analytical work on cellulose ethers are presented, including the MS analysis of methyl cellulose (MC) blends and fractionation studies of fully esterified MC, especially its 4-methoxybenzoates by gradient HPLC on normal phase. Preparative fractionation according to the degree of substitution (DS) allows follow-up analysis in order to get more detailed information on the substituent distribution in such sub-fractions.

Effects of microwaves on molecular arrangements in potato starch

The effects of microwave heating on the molecular arrangements in potato starch, including single and double helices and amorphous structures, were studied using a ¹³C CP/MAS NMR method combined with X-ray diffraction.

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–mass spectrometry analysis of enzyme-hydrolysed carboxymethylcellulose for investigation of enzyme selectivity and substituent pattern

A series of celloendoglucanases: Bacillus agaradhaerens Cel 5a, Humicola insolens Cel 5a, H. insolens Cel 7b, H. insolens Cel 45a, Trichoderma reesei Cel 7b, and T. reesei Cel 45a were used to hydrolyse carboxymethylcellulose (CMC) and the hydrolysis products were investigated with a novel liquid chromatography-mass spectrometry (LC-MS) method. Separation was achieved using a graphitised carbon chromatographic column which allowed the use of electrospay compatible eluents. Analysis of the compounds produced during enzyme hydrolysis of CMC is used to understand enzyme selectivities and substitution pattern of CMC. Conventional high-performance anion-exchange chromatography (HPAEC)-pulsed amperometric detection (PAD), size-exclusion chromatography (SEC)-refractive index (RI) detection, and reducing end analysis are also used to analyse enzyme-hydrolysed CMC. The LC-MS method presented allows for a more detailed investigation of hydrolysis products, which facilitates characterisation of both enzymes and substrates.

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.

Enzymatic degradation of hydroxypropyltrimethylammonium wheat starches

The enzymatic degradation of hydroxypropyltrimethylammonium modified starches synthesised by dry process was compared with that of hydroxypropyltrimethylammonium modified starches synthesised in glycerol-water plasticised molten medium. The enzymatic degradation rate of products from both origins decreased as the degree of substitution increased. However, two distinct enzymatic degradation profiles were obtained. Dry process products displayed a regular decrease pattern as DS increased. Molten medium synthesised cationic starches displayed a constant degradation level on a wide DS range with alpha,beta-amylase and amyloglucosidase, whereas isoamylase degradation rapidly reached its degradation limit at DSs 0.05. The various plasticising conditions used to synthesise cationic starch in molten medium show no influence on the enzymatic degradation. By measuring the affinity of alpha-amylase, beta-amylase and isoamylase for native, extruded non-modified and hydroxypropyltrimethylammonium-modified starches. It was evident that the enzymes' affinity for the substrate diminishes with increasing chemical modification, particularly in the case of alpha-amylase, suggesting that the location of cationic groups impairs the enzyme's recognition of the substrate. Structural elements of limit dextrins were analysed by (1)H NMR.

A new model for the substitution patterns in the polymer chain of polysaccharide derivatives

A new mathematical model is presented for the analysis of the substituent distribution in the polymer chain of polysaccharide derivatives. For the first time, the influence of substitution on the reactivity of neighbored monomer units is taken into account. The model was applied to various cellulose and amylose ethers and esters and excellently fits the experimental data.

Regioselectively substituted 6-O- and 2,3-di-O-acetyl-6-O-triphenylmethylcellulose: its chain dynamics and hydrophobic association in polar solvents

Two kinds of regioselectively substituted cellulose derivatives, i.e., 6-O-triphenylmethylcellulose (6TC) and 2,3-di-O-acetyl-6-O-triphenylmethylcellulose (2,3Ac6TC), were prepared via cellulose. In these samples, C-6 position hydroxyls in the anhydroglucose units (AGU) along the cellulose chain were selectively substituted by the hydrophobic triphenylmethyl groups, but C-2 and -3 position hydroxyls remained in 6TC or were substituted completely by O-acetyls in 2,3Ac6TC. Their chain dynamics in polar solvents, dimethyl sulfoxide (DMSO) and N,N-dimethylacetamide (DMAc), in dilute solution were investigated by dynamic light scattering in the viewpoint of cluster formation. The results were compared with those of cellulose diacetates (CDA) in DMAc where three hydroxyls in the AGU were statistically substituted up to 2.44 by O-acetyls but hydroxyls at C-6 positions remained predominantly. It was found that 6TC and 2,3Ac6TC formed a dynamic structure about 10 times larger than single chains and that the structure would be a temporary and local association due to concentration fluctuations (dynamic structures) which were originated from the hydrophobic interactions between intermolecular triphenylmethyl groups. The dynamics and structures were in clear contrast to those of CDA where a solvent-mediated hydrogen bonding between intermolecular C-6 position hydroxyls was essential to cluster formation. The present structures were so weak as to dissipate easily under low shear field.

High-performance anion-exchange chromatography-electrospray mass spectrometry for investigation of the substituent distribution in hydroxypropylated potato amylopectin starch

The use of high-performance anion-exchange chromatography (HPAEC) with pulsed amperometric detection (PAD) coupled on-line with electrospray mass spectrometry (ESI-MS) for analysis of the substitution pattern in chemically modified starch, has been investigated. In order to characterise the distribution of substitution groups along the polymer chain, hydroxypropylated potato amylopectin starch (HPPAP) was subjected to enzymic hydrolysis, followed by analysis of the degradation products by HPAEC-PAD-MS. When using conventional chromatographic techniques for characterisation of enzymic hydrolysates, standard compounds are required for identification of the hydrolysis products. However, the on-line coupling with ESI-MS allowed identification of all products obtained, substituted as well as unsubstituted, and also of those compounds that co-eluted, without the need for standards. Further, HPAEC-PAD-MS was shown to be useful for analysis of the substitution pattern in modified starch; from results obtained it was suggested that the hydroxypropyl groups were homogeneously distributed in the amylopectin molecule. It was also shown that the starch hydrolysing enzymes were hindered by the hydroxypropyl groups and preferentially cleaved glucosidic linkages between unsubstituted glucose units.

Synthesis, analysis and reduction of 2-nitropropyl starch

Granular 2-nitropropyl potato starch was synthesized by reaction with 2-nitropropyl acetate in an aqueous suspension. Nitroalkylation occurs preferentially with the amylose fraction of potato starch, as was confirmed by leaching experiments and digestion of the modified starch with alpha-amylase. The 2-nitropropyl substituent is a mixture of the nitroalkane and nitronic acid tautomer. Some grafting occurs and to a lesser extent additional reactions (formation of carbonyls and oximes) of the nitro group take place. After catalytic hydrogenation of water soluble 2-nitropropyl starch only a small amount of the nitro functionality was reduced to the corresponding amine. Reduction of granular 2-nitropropyl starch with sodium dithionite did not go to completion and led to a complex mixture of starting material, several intermediates and side products (for example sulfamates).

The substitution pattern in cationised and oxidised potato starch granules

The distribution pattern of substituents within the granules and the components of two cationised and two oxidised potato starches was studied. The level of crystallinity in wet-cationised (WC) and hypochlorite oxidised (HO) starch granules was similar to that of native starch granules but lower in dry-cationised (DC) and peroxide oxidised (PO) granules. However, the melting temperature of DC granules remained similar to native granules but was decreased in the other samples. With all modified starches, the initial rate of acid hydrolysis (lintnerisation) was increased compared to native granules. The degree of substitution decreased only slightly in WC granules after the lintnerisation, whereas virtually all the substituted glucosyl units in DC starch were hydrolysed already at initial stages. The decrease of substituents in the HO and PO starches was intermediate. The starches were partly resistant to the action of isoamylase and the successive beta-amylolysis, suggesting that substituents were found both close to the branches and near the nonreducing ends in the amylopectin component. It is suggested that the DC starch was preferentially cationised at the surface of the granules, whereas WC and oxidised starches were modified throughout the granules.

FAB CIDMS/MS analysis of partially methylated maltotrioses derived from methylated amylose: a study of the substituent distribution

Amylose was methylated with CH3I in alkaline aqueous suspension, yielding methylated amylose (MeAl) with a degree of substitution of 1.44 (s < 0.01). Determination of the monomer composition showed that HO-6 and HO-2 were highly substituted in contrast to HO-3 (7:2:5.5, HO-2:HO-3:HO-6). By using partial acid hydrolysis, oligomers were prepared that varied both in degree of polymerisation and in methyl-content. Studies on the distribution of substituents in trimers showed large deviations from random distributions. By using CID tandem mass spectrometry, the substituent distribution in these trimers was determined in more detail. Various sets of trimers with equal amounts of methyl-groups but differing in substituted positions were quantified. From the monomer composition of MeAl, the probability of each trimer was calculated and compared to the outcome of the measured distributions. It was concluded that trimers with terminal tri- or non-substituted glucose monomers at the non-reducing end were formed preferentially during partial hydrolysis and that partial hydrolysis of MeAl yielded oligomers in a non-random way. This is the first study that describes the partial hydrolysis of MeAl in such detail.

Characterisation of the substituent distribution in hydroxypropylated potato amylopectin starch

The distribution of substituents in hydroxypropylated potato amylopectin starch (amylose deficient) modified in a slurry of granular starch (HPPAPg) or in a polymer 'solution' of dissolved starch (HPPAPs), was investigated. The molar substitution (MS) was determined by three different methods: proton nuclear magnetic resonance (1H NMR) spectroscopy, gas-liquid chromatography (GLC) with mass spectrometry, and a colourimetric method. The MS values obtained by 1H NMR spectroscopy were higher than those obtained by GLC-mass spectrometry analysis and colourimetry. The relative ratio of 2-, 3-, and 6-substitution, as well as un-, mono-, and disubstitution in the anhydroglucose unit (AGU) were determined by GLC-mass spectrometry analysis. Results obtained showed no significant difference in molar distribution of hydroxypropyl groups in the AGU between the two derivatives. For analysis of the distribution pattern along the polymer chain, the starch derivatives were hydrolysed by enzymes with different selectivities. Debranching of the polymers indicated that more substituents were located in close vicinity to branching points in HPPAPg than in HPPAPs. Simultaneous alpha-amylase and amyloglucosidase hydrolysis of HPPAPg liberated more unsubstituted glucose units than the hydrolysis of HPPAPs, indicating a more heterogeneous distribution of substituents in HPPAPg.

Distribution of methyl substituents in amylose and amylopectin from methylated potato starches

Granular potato starches were methylated in aqueous suspension with dimethyl sulfate to molar substitution (MS) values up to 0.29. Fractions containing mainly amylose or amylopectin were obtained after aqueous leaching of the derivatised starch granules. Amylopectin in these fractions was precipitated with Concanavalin A to separate it from amylose. Amylose remained in solution and was enzymatically converted into D-glucose for quantification, thereby taking into account the decreased digestibility due to the presence of methyl substituents. It was found that the MS of amylose was 1.6-1.9 times higher than that of amylopectin in methylated starch granules. The distributions of methyl substituents in trimers and tetramers, prepared from amylose- or amylopectin-enriched fractions, were determined by FAB mass spectrometry and compared with the outcome of a statistically random distribution. It turned out that substituents in amylopectin were distributed heterogeneously, whereas substitution of amylose was almost random. The results are rationalised on the basis of an organised framework that is built up from amylopectin side chains. The crystalline lamellae are less accessible for substitution than amorphous branching points and amylose.

Enzymic analysis of the structure of oxidized potato starches

The possibility to use enzymic methods for the analysis of the positions of carboxyl and carbonyl groups in sodium hypochlorite oxidized (HO) and hydrogen peroxide oxidized (PO) potato starches was investigated. The HO-starch, that contained more modified glucosyl residues, possessed a lower beta-amylolysis limit and all of the polymer components were resistant to complete hydrolysis as judged from gel-permeation chromatograms. In contrast, the PO-starch contained 24% of apparently unmodified, linear chains that were hydrolysed by beta-amylase. After debranching, approximately 30% of the chains in the HO-sample and approximately 20% in the PO-sample remained partly resistant to successive beta-amylolysis.