Matthias Findeisen

Preparation of scratch and abrasion resistant polymeric nanocomposites by monomer grafting onto nanoparticles, 1 FTIR and multi‐nuclear NMR spectroscopy to the characterization of methacryl grafting

Nano-sized silica and alumina particles were used as fillers for polymer reinforcement and scratch resistant coatings. For favorable embedding within the polyacrylate matrix the surface of the fillers was chemically modified by reaction with methacroyloxy (propyl)-trimethoxysilane. The formation of covalent Si(Al)-O-Si-C bonds between functional groups from silane and OH groups on silica and alumina was demonstrated by means of FTIR and MAS NMR spectroscopy. The reactivity of the various surface silanols towards the coupling agent and the yield of surface Si-O-Si bonds were estimated by 29 Si CP MAS NMR data.

Preparation of Scratch and Abrasion Resistant Polymeric Nanocomposites by Monomer Grafting onto Nanoparticles, 3. Effect of Filler Particles and Grafting Agents

After modification with different trialkoxysilanes, nano-sized silica and alumina particles were used as fillers in transparent UV/EB curable acrylates for polymer reinforcement, particularly to attain scratch and abrasion resistant coatings. The acid catalyzed condensation of the organosilanes forms a polysiloxane shell which covers the nanoparticle like a nanocapsule. CP MAS NMR spectroscopy and MALDI-TOF mass spectrometry proved to be useful for the characterization of the polysiloxane structures. Grafter oligomers with more than 20 monomeric units were observed. Nanoparticles modified by methacroyloxy(propyl)trimethoxysilane and vinyltri-methoxysilane can copolymerize with acrylates. Compared with the pure polymers, these crosslinked polyacrylate nanocomposites, containing up to 35 wt.-% silica, exhibit markedly improved surface mechanical properties. Promising scratch and abrasion resistance of radiation-cured nanocomposite materials were also obtained by propyltrimethoxysilane grafting which results in an organo-philation of pyrogenic silica. Both colloidal and pyrogenic nano-sized silica nanopowders were used as fillers in polyacrylate films. The concentration of colloidal SiO 2 in commercial acrylate formulations amounts up to 50 wt.-%, whereas pyrogenic silica, notwhithstanding their surface modification by silanes, results in a thickening effect which limits its content to about 35 wt.-%. Never-theless, a comparison showed a distinct improvement in the surface mechanical properties such as haze and diamond microscratch hardness for surface-modified pyrogenic silica.

Preparation of scratch and abrasion resistant polymeric nanocomposites by monomer grafting onto nanoparticles, 2 Characterization of radiation‐cured polymeric nanocomposites

By in situ grafting methacroyloxy functionalized-silanes on commercial nanoglobular silica polymerization-active silico-organic nanoparticles were prepared. In radiation (UV, EB) induced polymerization reactions these modified nanoparticles form covalent crosslinks to acrylate substrates, thus efficiently modifying their viscoelastic properties. The transparent nanopowder composites can be used as scratch resistants coatings. The composite films show excellent adhesion on PC and PVC and good abrasion resistance after the Taber abraser test with haze values of about 6% after 500 cycles.

Moenomycin A: The role of the methyl group in the moenuronamide unit and a general discussion of structure-activity relationships

Abstract Two disaccharide analogues 1b and 17a of moenomycin A have been synthesized and their antibiotic and transglycosylase-inhibiting properties have been determined. The results permit for the first time to arrive at a general view of the structural requirements in this class of compounds necessary to elicit antibiotic activity.

Synthesis of a trisaccharide analogue of moenomycin A12 Implications of new moenomycin structure-activity relationships

Abstract A trisaccharide analogue of moenomycin A, 9a, has been synthesized and has found to be antibiotically inactive. This compound differs from an active compound, 9b, solely by the exchange NHAc→OH in unit C. A binding model for moenomycin-type transglycosylase inhibitors at the enzyme penicillin binding protein is proposed.

Studies on the interaction of the antibiotic moenomycin A with the enzyme penicillin-binding protein 1b

The interaction of a moenomycin derivative with the enzyme penicillin binding protein 1b (PBP 1b) has been studied by means of STD NMR. The results obtained initiated the synthesis of a number of moenomycin derivatives modified in unit A including a moenomycin-ampicillin conjugate and determination of their antibiotic activities. A protocol is described that allows studying the interaction of moenomycin analogues with PBP 1b by fluorescence correlation spectroscopy.

Moenomycin analogues with modified lipid side chains from indium-mediated Barbier-type reactions

Abstract From moenomycin A both the chromophore part and the lipid side chain were degraded by ozonolysis to give an analogue with a glycolaldehyde unit in 2-position of the glyceric acid moiety. The aldehyde was converted to a number of homoallylic alcohols by indium-mediated Barbier-type reactions with allylic and benzylic halides. With exception of the phytyl bromide-derived reaction product all compounds were antibiotically inactive.

Moenomycin analogues with long-chain amine lipid parts from reductive aminations

Abstract From a moenomycin A glycolic aldehyde degradation product lacking the chromophore unit and most of the lipid part, a number of amines were prepared by reductive amination. Their interaction with artificial membranes as well as their transglycosylase inhibiting and antibiotic properties were studied.

Use of Winterfeldt's template to control the C-2′ configuration in the synthesis of strigol-type compounds

Abstract A route comprising (i) a cycloaddition reaction of citraconic anhydride with the Winterfeldt auxiliary, (ii) hydride reduction of the cycloadduct, (iii) a (formal) ether formation, and (iv) a cycloreversion reaction allows efficient stereocontrol at C-2′ in the synthesis of strigol and its structural analogues.

Mechanistic and Kinetic Insights into the Thermally Induced Rearrangement of α-Pinene

The thermal rearrangement of alpha-pinene (1) is interesting from mechanistic as well as kinetic point of view. Carrier gas pyrolyses with 1 and its acyclic isomers ocimene (2) and alloocimene (3) were performed to investigate the thermal network of these hydrocarbons. Kinetic analysis of the major reaction steps allows for a deeper insight in the reaction mechanism. Thus it was possible to explain the racemization of 1, the formation of racemic limonene (4), and the absence of the primary pyrolysis product 2 in the reaction mixture resulting from thermal rearrangement of 1. Results supported the conclusion that the reactions starting with 1 involve biradical transition states.