Petra Mischnick

Synthesis, control of substitution pattern and phase transitions of 2,3-di-O-methylcellulose.

An improved heterogeneous procedure has been found for the regioselective introduction of trityl and 4-methoxytrityl groups at the primary positions of cellulose. The 6-O-tritylcelluloses produced were completely methylated by MeI-NaOH in Me2SO solution. The trityl groups were then completely removed to afford 2,3-di-O-methylcellulose without significant degradation of the polymer. 1H and 13C NMR spectroscopy and degradation analysis showed less than 5% deviation from the regular substitution pattern. Under optimum reaction conditions, almost perfectly regular cellulose derivatives could be obtained. Small changes in the substitution pattern had a strong effect on the phase transitions of the O-methylcelluloses in water. It was shown by DSC for the first time that perfect 2,3-di-O-methylcellulose does not undergo phase separation at elevated temperatures.

Thermal degradation behavior and kinetic analysis of spruce glucomannan and its methylated derivatives

The thermal degradation behavior and kinetics of spruce glucomannan (SGM) and its methylated derivatives were investigated using thermogravimetric analysis to characterize its temperature-dependent changes for use in specific applications. The results were compared with those obtained for commercial konjac glucomannan (KGM). The SGM and the KGM exhibited two overlapping peaks from 200 to 375°C, which correspond to the intensive devolatilization of more than 59% of the total weight. Differences in the pyrolysis-product distributions and thermal stabilities appeared as a result of the different chemical compositions and molecular weights of the two GMs. The Friedman and Flynn-Wall-Ozawa isoconversional methods and the Coats-Redfern were adopted to determine the kinetic triplet of the intensive devolatilization region. Both GMs can be modeled using a complex mechanism that involves both a Dn-type and an Fn-type reaction. The comparative study of partially methylated GM indicated higher homogeneity and thermal resistance for the material with the higher degree of substitution.

Preparation and structural characterisation of O-aminopropyl starch and amylose

O-aminopropyl starch was prepared by Michael addition of acrylonitrile and subsequent reduction with freshly prepared cobalt boride and sodium borohydride. In a second approach, the aminopropyl group was introduced via Williamson etherification with N-phthalyl-protected 3-bromo-1-propylamine. The protecting group was removed by borohydride reduction and subsequent hydrolysis in acetic acid. The DS of all samples and the degree of reduction of the cyanoethyl groups were estimated from the 1H NMR spectra. Total monomer composition was determined after methanolysis or hydrolysis and trimethylsilylation by GLC and GCMS. While the regioselectivity in the thermodynamically controlled reaction was O-6 > O-2 > O-3 (50:37:13), the kinetically controlled process showed strongly preferred O-2-etherification (up to 94%) followed by O-6- and O-3-substitution. It could be influenced by choice of solvent (water, Me(2)SO) and base (NaOH, Li-dimsyl).

Challenges in structure analysis of polysaccharide derivatives

In this paper the state of the art in structure analysis of cellulose and starchderivatives is considered, with special focus on the substituent distribution on differentstructural levels. Monomer composition, substituentdistribution in the polymer chain, and approaches to investigate thetopochemical influence of starch granule and cellulose fibre supramolecularstructure are discussed. Current developments and challenges for futureresearch are outlined, especially the requirement to develop refined models for theinterpretation of analytical data.

Specificity of Microbial α-Amylase and Amyloglucosidase Hydrolysis of Methyl Amyloses

Methyl amyloses prepared under various conditions were exhaustively digested by means of α-amylase (B. licheniformis) and amyloglucosidase (A. niger). The amount of glucose that was released by the action of the enzymes was determined. Degradation products were further investigated as their O-methyl-O-deuteromethyl derivatives by mass spectrometry. The substituent distribution in the reduced and O-methylated-O-ethylated oligosaccharides was determined, differentiating between non-reducing terminal glucosyl residues, 1→4-linked inner glucosyl units and reducing glucose end groups. The portion of glucose that could be liberated by the enzymes decreased with increasing degree of substitution (DS) but at the same DS it was considerably higher for heterogeneously prepared amylose ethers than for those prepared under homogeneous conditions. Mass spectrometry (fast atom bombardment, FAB- and matrix-assisted laser desorption ionisation, MALDI-MS) gave evidence of different oligomer patterns and average values of degree of substituent/degree of polymerisation (DS/DP) in dependence on the methylation conditions applied. More detailed analysis of the O-methylated positions of the oligosaccharides showed that the reducing glucose end group was usually unsubstituted, while the non-reducing glucosyl residues could be 2-, 6- or even 2,6-di-O-substituted. In contrast, all 3-O-methyl groups were located in the inner 1,4-linked glucosyl units, indicating inhibition of both enzymes. The results of this selective partial degradation are compared with those obtained after chemical random degradation and mass spectrometry.

Determination of the DS and substituent distribution of cationic alkyl polyglycosides and cationic starch ethers by GLC after dealkylation with morpholine

The total DS and substituent distribution of starch and alkyl polyglycosides functionalised as O-(2-hydroxy-3-trimethylammonium)propyl ethers were determined by GLC. To achieve volatile analytes, the samples were submitted to methanolysis, N-demethylation and O-trimethylsilylation. Alternatively hydrolysis, reduction with NaBH(4) and subsequent O-acetylation were performed, but suffered from intramolecular acetal formation of 2-O-substituted residues, preventing reduction. Morpholine as nucleophile was superior to thiophenolate with regard to quantitative dealkylation and side product formation. The ratio of un-, mono-, di-, tri-, and tetrasubstituted compounds was determined. The total DS values calculated from these mole fractions were in good agreement with those obtained from elemental analysis or NMR from standards. Regioselectivity of the cationisation reaction was determined after methanolysis, permethylation and Hofmann elimination by GLC.

Formation of unexpected substitution patterns in sulfonylbutylation of cyclomaltoheptaose promoted by host–guest interaction

The distribution of substituents in sulfonylbutylethers of cyclomaltoheptaose (beta-cyclodextrin) formed in aqueous medium has been determined by gas chromatography after hydrolysis and formation of the permethylated sulfonylfluoride derivatives. In contrast to other etherification reactions of beta-cyclodextrin, preferred substitution in position 3 of the glucose units has been detected. From 1H NMR and microcalorimetric experiments, the formation of host-guest complexes by beta-cyclodextrin and the reagent 1,4-butane sultone in water became evident. This spatial preorganization presumably favors the reaction with the O-3. In contrast, in methyl sulfoxide preferred 2-O-alkylation was obtained, indicating that host-guest interaction does not influence regioselectivity in this solvent.

Determination of the substituent distribution in O-sulfonylbutyl-(1-->4)-glucans.

A method has been developed to determine the distribution of substituents in the glucose units of sulfonylbutylethers of cyclomaltoheptaose (beta-cyclodextrin). This method involves hydrolysis of the glucosidic linkages, permethylation, formation of sulfonylchlorides and subsequent transformation to the permethylated sulfonylfluoride derivatives. The latter were thermostable and could be analyzed by GLC and identified by EI and CIMS. For confirmation, the 2-, 3-, and 6-O-substituted standard compounds were independently synthesized and characterized by NMR and GLC-MS.

Biomacromolecules as tools and objects in nanometrology—current challenges and perspectives

AbstractNucleic acids, proteins, and polysaccharides are the most important classes of biopolymers. The inherent properties of biomacromolecules are contrary to those of well-defined small molecules consequently raising a number of specific challenges which become particularly apparent if biomacromolecules are treated as objects in quantitative analysis. At the same time, their specific functional ability of molecular recognition and self-organization (e.g., enzymes, antibodies, DNA) enables us to make biomacromolecules serving as molecular tools in biochemistry and molecular biology, or as precisely controllable dimensional platforms for nanometrological applications. Given the complexity of biomacromolecules, quantitative analysis is not limited to the measurement of their concentration but also involves the determination of numerous descriptors related to structure, interaction, activity, and function. Among the biomacromolecules, glycans set examples that quantitative characterization is not necessarily directed to the measurement of amount-of-substance concentration but instead involves the determination of relative proportions (molar ratios) of structural features for comparison with theoretical models. This article addresses current activities to combine optical techniques such as Raman spectroscopy with isotope dilution approaches to realize reference measurement procedures for the quantification of protein biomarkers as an alternative to mass spectrometry-based techniques. Furthermore, it is explored how established ID-MS protocols are being modified to make them applicable for quantifying virus proteins to measure the HIV viral load in blood samples. As an example from the class of carbohydrates, the challenges in accurate determination of substitution patterns are outlined and discussed. Finally, it is presented that biomacromolecules can also serve as tools in quantitative measurements of dimensions with an example of DNA origami to generate defined dimensional standards to be used for calibration in super-resolution fluorescence microscopy. Graphical abstractQuantitative analysis of biomacromolecules is accompanied with special challenges different from low molecular weight compounds. In addition, they are not only objects but also tools applicable for quantitative measurements

Potential of dibutyltin oxide for the manno/gluco- and regioselective methylation of Konjac glucomannan

Konjac glucomannan, built of β-1,4-linked mannose and glucose, was methylated after treatment with dibutyltin oxide/MeOH in pyridine. Best results were obtained in acetonitrile/DMF in the presence of TBAB and K2CO3. While total DS was only 0.1–0.15 and not significantly enhanced in the tin-promoted reaction, the manno-/gluco- (cis-/trans-diol) and the regioselectivity was completely changed with DSMan/DSGlc increasing from 0.9 to 1.8, a strong preference for secondary over primary OH, and a total order of reactivity being M3 > M2 ≥ G2 > G6 ≥ M6 ≥ G3. The influence of the amount of K2CO3, Bu2SnO, and temperature was studied. By repeated reaction a DS of 0.28 was gained without loss in selectivity. In a solvent-free one-pot stannylation/methylation reaction, a DS up to 0.3 was achieved. Surprisingly, any differences between the two stereoisomeric sugar constituents were leveled under these conditions, and regioselectivity was changed to the order M6 ≈ G6 ≫ M3 ≈ G3 > M2 ≈ G2.Graphical abstract