Biomedical subjects

H R Kricheldorf

Publications and source records attributed to H R Kricheldorf.

10 recordsLinked to original sources

PubMed2001

Syntheses and application of polylactides.

Polylactides can be prepared by direct polycondensation of lactic acid, or better, by ring-opening polymerization of cyclic dilactides (usually called lactides). These lactides exist in the form of four stereoisomers two of which (L,L- and rac. -D,L-) are technically produced in large quantities. These lactides can by polymerized via four different classes of initiators and reaction mechanisms. The characteristics mechanistic and preparative features of the cationic polymerization, anionic polymerization and of the coordination-insertion mechanism are described. Furthermore, copolymerizations of lactides with glycolide or epsilon-caprolactone and their analytical problems are discussed. Finally, a new type of wound dressing based on transparent are resorbable films of copolylactides is mentioned.

Bandages↗

PubMed2001

Polylactones. 55. A-B-A triblock copolymers of various polypeptides. Syntheses involving 4-aminobenzoyl-terminated poly(epsilon-caprolactone) as B block.

A telechelic poly(epsilon-caprolactone) having a degree of polymerization (DP) around 25 and two 4-aminobenzoyl chain ends was used as a macroinitiator for the ring-opening polymerization of various alpha-amino acid N-carboxyanhydrides (NCAs). Glycine-NCA, L-alanine-NCA, L-phenylalanine-NCA, and gamma-benzyl-L-glutamate-NCA served as monomers and the NCA/macroinitiator ratio was varied between 20:1, 40:1, and 100:1. In the case of L-Phe-NCA, a ratio of 200:1 was also used. It was demonstrated by means of model studies, that the NCAs may react almost quantitatively with the 4-aminobenzoyl end groups despite their relatively low nucleophilicity. The isolated triblock copolymers were characterized by viscosity measurements and by (1)H NMR spectroscopy with regard to their composition (which in most cases paralleled the feed ratios). However, in the case of gamma-Bzl-Glu-NCA mixtures of di- and triblock copolymer were obtained. The secondary structures of the solid copolymers were examined by IR spectroscopy and (13)C NMR CP/MAS spectroscopy. It was found that the alpha-helix/beta-sheet ratio of the poly(L-Ala) and poly(L-Phe) blocks increases with their average length, according to the NCA/macroinitiator ratio.

4-Aminobenzoic Acid↗

PubMed1995

[Development and characterization of an absorbable temporary wound dressing].

Most of the temporary dressings used in the treatment of burns do not meet the objectives of a skin substitute concerning application, safety and comfort. Removal is often painful and traumatic and increases the risk of infection. Biodegradable polymers of lactic and caproic acid were developed as part of a research programme (BMFT/FRG 01 KG 8809/7), and chemical and physical properties were investigated. Films made of the copolymer material were characterized by structure, transparency, permeability, tensile strength, flexibility and degradation. The transparent films appeared increasingly opaque during hydrolysis. The water vapour permeance could be varied between 40 and 250 (40-136) ml/m2 per h (according to the method of measurement). The mechanical properties are characterized by a maximum elongation of > 2000% at 37 degrees C and a very low elastically modulus. When the results were compared with those of three established film dressings, no restriction was found in the aptitude of the material as a wound dressing.

Animals↗

PubMed1985

Models of molecular evolution. 2. Stereospecificity of dipeptide syntheses by means of cyanamides and carbodiimides.

Acetyl, benzyloxycarbonyl and tosyl protected DL-alanine, DL-leucine, DL-methionine, DL-phenylalanine, and DL-valine were condensed with DL-amino acid methyl esters. Cyanamide, diethylcyanamide, diisopropyl carbodiimide, dicyclohexyl carbodiimide, and N-cyclohexyl-N'-(2-morpholino ethyl) carbodiimide-N''-methotosylate served as condensing reagents. Water, methanol, and dimethylformamide were used as reaction media. The stereochemical course of these dipeptide syntheses was elucidated by means of 13C-n.m.r. spectroscopy. The formation of L-L and D-D bonds (isotactic sequences) was favoured in ca. 80% of all condensations. L-L/L-D (D-D/D-L) ratios of up to 6:1 were found.

Dipeptides↗

PubMed1977