Matthias Schnabelrauch

13C-N.M.R. spectroscopic study of the homogeneous sulphation of cellulose and xylan in the N2O4-DMF system

Abstract By means of 13 C-n.m.r. spectroscopy the substituent distribution within the anhydroglucose and anhydroxylose units, respectively, in the systems N 2 O 4 -DMF-cellulose, and N 2 O 4 -DMF-SO 3 -xylan has been investigated. In the systems containing cellulose, a derivatization exclusively at C-6 is observed on dissolution in N 2 O 4 -DMF and on subsequent reaction with SO 2 , while with SO 3 as the acylating agent some substitution also takes place on the secondary OH groups at higher d.s. The OH groups of xylan are substituted to a rather low d.s. by nitrite ester groups in the system N 2 O 2 -DMF and by sulphate half-ester groups on subsequent reaction with SO 2 or SO 3 . The results are discussed on the basis of a transesterification from the nitrite to the sulphate ester.

Biodegradable polymer networks based on oligolactide macromers: synthesis, properties and biomedical applications.

Novel linear and star-shaped oligolactide macromers were synthesized by ring-opening oligomerization of L-lactide in the presence of suitable initiators (di- and polyols, amino acid esters) and subsequent endgroup-functionalization of the formed oligolactides with methacrylate moities. The obtained liquid macromers are valuable building blocks for the preparation of biocompatible polymer networks. Based on these macromers, the fabrication and the material properties including biodegradation behaviour of highly porous polymer network devices will be described. The application of these materials as resorbable scaffolds in tissue engineering will be discussed.

New synthetic catecholate-type siderophores based on amino acids and dipeptides.

New analogs of bacterial siderophores with one, two or three catecholate moieties were synthesized using various mono- and diamino acid and dipetide scaffolds, respectively. In addition to 2,3-dihydroxybenzoyl siderophore analogs and their acylated derivatives, 3,4-dihydroxybenzoyl derivatives were prepared. Furthermore, the synthesis of a new triscatecholate serving as an intimate model for enterobactin is reported. Most of the new compounds gave a positive CAS-test and were active as siderophores tested by growth promotion assays with a set of siderophore indicator mutants under iron limitation. Structure-activity-correlations have also been studied.

Investigations on synthesis and characterization of carboxy-groups containing cellulose sulfates

SummaryCarboxymethyl cellulose and C-6-carboxy cellulose were treated with SO3 and HSO3CL in DMF yielding the corresponding watersoluble sulfate half-esters. A preferred sulfation of primary hydroxyl groups was found by 13C-n. m.r. spectroscopy. The potentiometric titration of the polyelectrolytes showed significant differences in the titration behaviour which can be explained by the different acidity of the carboxy groups in the two cellulose derivatives.

New artificial siderophores based on a monosaccharide scaffold.

New artificial catecholate siderophores with methyl α-d-glucopyranoside as scaffold were synthesized. The dihydroxy- or di(acetoxy)benzoyl moieties were attached either directly or via aminopropyl spacer groups, to the carbohydrate scaffold. The siderophore activity of the prepared siderophore analogs was examined by a growth promotion assay using various Gram-negative bacteria and mycobacteria and by the CAS-assay.

Evaluation of Madurahydroxylactone as a Slow Release Antibacterial Implant Coating

Madurahydroxylactone (MHL), a secondary metabolite with antibacterial activity was evaluated for its suitability to generate controlled drug release coatings on medical implant materials. A smooth and firmly attached layer could be produced from a precursor solution on various metallic implant materials. In physiological salt solutions these coatings dissolved within a time period up to one week. A combination of MHL with a broad spectrum fluoroquinolone antibiotic was used to create a coating that was active against all bacterial strains tested. The time period during which the coating remained active against Pseudomonas aeruginosa was investigated. The results indicated a delayed drug release from single layer coatings in the course of seven days. MHL was biocompatible in cell culture assays and could after a delay even serve as a cell adhesion substrate for human or murine cells. The findings indicate a potential for MHL for the generation of delayed release antimicrobial implant coatings.

Fabrication and characterization of electrospun polylactide/β-tricalcium phosphate hybrid meshes for potential applications in hard tissue repair

Abstract Non-woven hybrid meshes based on poly(l-lactide-co-d,l-lactide) (dl-PLA) and β-tricalcium phosphate (β-TCP) were fabricated and comprehensively characterized. Stock suspensions of β-TCP powder in dl-PLA acetone solutions were used for the electrospinning process. Structure, morphology and thermal properties of the electrospun samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The electrospun hybrid materials show a micro-composite structure, and a morphology characterized by a three-dimensional porous fibrous mesh with randomly distributed fibers possessing average fiber diameters between 680 and 970 nm, uniform thickness along the fibers and beads structure only for higher β-TCP concentration electrospun samples. Both pure PLA and hybrid non-woven meshes exhibit a good thermal stability and a continuous degradation in simulated body fluid medium. A live/dead staining viability assay using MC3T3-E1 preosteoblasts reveals the excellent cytocompatibility of the fabricated non-wovens. Enhanced alkaline phosphatase (AP) activity of MC3T3-E1 cells during culture on the dl-PLA and the composite non-woven meshes demonstrates their potential for applications in hard tissue repair.

Investigation of Magnetically Active Core Size Distributions Utilizing Magnetic Measurements

In this work, we show how one can convert the energy barrier distribution over temperature, which is the result of temperature dependent magnetorelaxometry, to a distribution of the size of the magnetically active cores of fractioned magnetic solutions by using additional susceptometric measurements.

Synthesis, Characterization, and Preliminary Investigation of Cell Interaction of Magnetic Nanoparticles with Catechol‐Containing Shells

Superparamagnetic iron oxide cores were synthesized by co‐precipitation of Fe(II) and Fe(III) salts and subsequently stabilized by coating with different catechols (levodopa, dopamine, hydrocaffeic acid, dopamine‐containing carboxymethyl dextran) known to act as high‐affinity, bidentate ligands for Fe(III). The prepared stable magnetic fluids were characterized with regard to their chemical composition (content of iron and shell material, Fe(II)/Fe(III) ratio) and their physical properties (size, surface charge, magnetic parameters). The nanoparticles showed no or only slight cytotoxic effects within 1 and 4 days of incubation with 3T3 fibroblast cells. Preliminary experiments were performed to study the interaction of the prepared nanoparticles with human MCF‐7 breast cancer cells and leukocytes. An intense interaction of the MCF‐7 cells with these particles was found whereas the leukocytes showed a lower tendency of interaction. Based on these finding, the novel magnetic nanoparticles possess the potent...