Lars Einfeldt

Analysis of side group motion in O-acetyl-starch using regioselective 2-O-acetyl-starches by means of dielectric spectroscopy

The complex dielectric constant of O-acetyl-starches with regioselective and the statistical distribution of substituents at the anhydroglucose unit (AGU) are measured in an extended frequency range from 10 mHz to 2 MHz and in the low temperature range from2120 to 08C. The experimentally determined relaxation spectra are evaluated with the well-known model function of Havriliak‐Negami for relaxation processes. In the case of 2-O-acetyl-starch two significant relaxations are detected which are associated with the orientational motion of the methylolgroup at the AGU and the acetylgroup in position C-2. The activation energies are 48 and 60 kJ/mol, respectively. Owing to that assignment of relaxations at the AGU with acetylation in position C-2 has proved that it is possible to describe further relaxation processes in acetylated amylomaize starch with a statistical substitution pattern. It was found that an additional relaxation process is associated with the dynamics of the acetylgroup at the position C-6 at the AGU and characterized by a lower activation energy of 28 kJ/mol. From the analytical point of view these results of dielectric spectroscopy analysis demonstrate that the mobility of the side groups depend significantly on the position at the AGU and the type of substituent in their frequency and temperature dependence.q 2000 Elsevier Science Ltd. All rights reserved.

Structure design of polysaccharides : Novel concepts, selective syntheses, high value applications

Using protecting silyl groups, catalyzed transesterification, and stereochemically controlled S N 2 mechanisms examples of well-defined 2-, 3-, 6-, and 2,6-ethers, esters, resp. amino derivatives of cellulose, starch, and related polysaccharides have been synthesized and characterized by two-dimensional NMR spectroscopy. Supramolecularly structured polymer matrices useful in biosensors could be developed by immobilization of enzymes like glucose oxidase and aromatic redox-chromogenic structures at 6-deoxy-6-(4-aminophenyl)-aminocellulose. Cellulose tubes grown biotechnologically from D-glucose in the culture medium of Acetobacter xylinum represent novel types of artificial blood vessels because of their unique highly-swollen nanofiber network-structure.

Preparative and 1H NMR Investigation on Regioselective Silylation of Starch Dissolved in Dimethyl Sulfoxide

Reaction of starch 1 dissolved in dimethyl sulfoxide (DMSO) with bulky thexyldimethylchlorosilane (TDSCl) in the presence of pyridine leads to regioselectively functionalized silyl ethers with a degree of substitution (DS) up to 1.8. The control of the DSSi, of the regioselectivity, and of the reaction pathway is described in detail. The reaction proceeds homogeneously up to DSSi of 0.6. With ongoing silylation the polymers form a separate phase incorporating the silylating agent to form TDS-starches with DSSi values higher than 1.0. After peracetylation of the silyl starches, the substitution pattern has been characterized not only in the anhydroglucose repeating units (AGU) but also in the non-reducing terminal end groups (TEG) by means of two-dimensional 1H NMR techniques. Up to DSSi 1.0, a very high regioselective functionalization of the primary 6-OH groups in the AGU as well as in the TEG is detectable. With increasing silylation (DSSi > 1.0), the subsequent silylation takes place at the 2-OH groups of the AGU and at the 3-OH groups of the TEG. These results are compared with our own investigations on the silylation of starch in the reaction system N-methylpyrrolidone (NMP)/ammonia and on the silylation of cellulose in N,N-dimethylacetamide (DMA)/LiCl/pyridine solution.

Acetylated Carbohydrate Derivatives as C-Sources for Acetobacter xylinum

Abstract Fully acetylated carbohydrate derivatives were used as C-sources instead of glucose for cultivation of Acetobacter xylinum. The resulting bacterial celluloses were analysed by IR-spectroscopy for possible incorporation of these substrates into the (1→4)-β-glucan chains. It is established, that acetyl substituents found in the polymer product are due to acetylated derivatives which are associated or intercalated with the produced bacterial cellulose.

The Control of Cellulose Biosynthesis by Acetobacter Xylinum in View of Molecular Weight and Molecular Weight Distribution Part I: Change of Molecular Weight of Bacterial Cellulose by Simple Variation of Culture Conditions 1

Abstract The variation of culture conditions - such as inoculation procedures, cultivation times, subspecies of Acetobacter xylinum and carbon sources - lead to different bacterial cellulose products. After isolation and purification of the bacterial cellulose (BC) from the culture medium the BC was analyzed by subsequent mild trimethylsilylation to silylated cellulose followed by size-exclusion chromatography (SEC). Significant molecular weight shifts of these BCs were shown and discussed for a control of BC formation. The data of SEC from silylated BC are critically compared with a carbanilated BC. 1. Presented at the XVIII th International Carbohydrate Symposium, Milano, Italy, July 20-26, 1996.