Publications

Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Abstract Dideoxycytidine analogues with a trideoxy-D-hexopyranosyl or hexenopyranosyl moiety were synthesized starting from 2-deoxyglucosyl bromide or tri-O-acetyl-D-glucal.

To decrease the toxicity of potent anti-HIV nucleosides 3'-azido-2',3'-dideoxythymidine (AZT) and 2',3'-dideoxy-3'-fluorothymidine (3'-FddThd, FLT), their new analogues, 3'-azido-2',3'-dideoxy-5-hydroxymethyluridine (3'-Az5HmddUrd) and 2',3'-dideoxy-3'-fluoro-5-hydroxymethyluridine (3'-F5HmddUrd), were synthesized. The reaction of 3'-azido-2',3'-dideoxyuridine (3'-AzddUrd) and 2',3'-dideoxy-3'-fluorouridine (3'-FddUrd) with formaldehyde, under strongly alkaline conditions and at elevated temperature, proceeded after 4 days to completion to afford the corresponding 5-hydroxymethyl derivatives 3'-Az5HmddUrd and 3'-F5HmddUrd in good yield. These compounds were also prepared by oxidation of AZT and FLT with the use of K2S2O8. 1H NMR analyses were subjected to the series of 3', 4 and 5-substituted pyrimidine 2'-deoxy- and 2',3'-dideoxynucleosides involving 3'-Az5HmddUrd and 3'-F5HmddUrd. Analysis of the sugar furanose ring puckering demonstrated that all 3'-fluorine derivatives exhibited strong domination of the S conformation (approximately 100%) while 3'-substitution by electron-donating groups, such as NH2, increased population of the N conformation. Experimentally observed substituent effect on the furanose ring puckering equilibrium was reconstructed in the 100 ps molecular dynamic trajectories obtained for AZT, FLT, dThd, 2',3'-ddThd and 3'-amino-2',3'-ddThd. It may be concluded that anti-HIV activity is linked to a direct interaction of the 3'-substituent with reverse transcriptase (RT) binding site. Anti-HIV activities of 3'-Az5HmddUrd and 3'-F5HmddUrd are lower than activity of AZT and FLT; however, 3'-Az5HmddUrd and 3'-F5HmddUrd are less toxic than AZT and FLT.

Maraging steel is an iron-nickel steel alloy which achieves its superior strength, hardness and toughness by aging the martensite phase.In earlier investigations, however, the toughness of selective laser melted (SLM) and subsequent aged maraging steel was found to be low.Several authors attribute this to the large oxides present in the finished product.In this work, the origin for these oxides is investigated by using microscopy and spectroscopy.The analysis is done on specimens produced under different processing conditions and the most important characteristics of the inclusions are discussed.It is found that during the SLM process, an oxide layer containing Al and Ti is created on top of each layer.Upon melting the next layer, the oxide layer is broken and dragged further.Therefore, accumulations of oxide material are found in the final product as large, irregularly shaped inclusions.

Abstract Review: 51 refs.

Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Porosity is a key parameter determining the functional application limits of polymeric parts produced by laser sintering (LS). In this paper, X-ray computed tomography (CT) is used to investigate the influence of the LS scanning parameters (laser power, hatch spacing, and scan speed) and part or feature size on the distribution and size of pores within polyamide-12 (PA12) laser sintered parts. CT model slices are created parallel to the original LS manufacturing layers in order to determine the porosity distribution and variation within each layer as well as along subsequent layers. Mapping the porosity distribution within these slices onto the laser scanning trajectory moreover allows investigating the influence of LS scanning parameters. Correlation of these porosity data with results from mechanical testing allows identifying optimal LS scanning parameters.

Abstract A number of oligodeoxynucleotides containing thymine bases linked to the deoxyribose in the α-configuration have been synthesized. In view of the possible activity of α-origomers as antisense compounds against HIV replication, the effects of α-thymidylate oligomers (α-dTn, n=1-1-16) in a poly (A)-directed HIV reverse transcriptase (RT) reaction were investigated. No priming activity could be detected with the α-dT oligomers at concentrations up to 100 μM. However, in the presence of the natural β-dT12-18 primer, 50% inhibition of RT activity was achieved at a concentration of about 1 μM with the α-dT oligomers containing ≥ 10 monomer units. The kinetics of RT inhibition by the α-decamer was found to be competitive with respect to the natural primer, β-dT10.

The specific aim of this study was to gain insight into the influence of scaffold pore size, pore shape and permeability on the in vitro proliferation and differentiation of three-dimensional (3-D) human periosteum-derived cell (hPDC) cultures. Selective laser melting (SLM) was used to produce six distinct designed geometries of Ti6Al4V scaffolds in three different pore shapes (triangular, hexagonal and rectangular) and two different pore sizes (500μm and 1000μm). All scaffolds were characterized by means of two-dimensional optical microscopy, 3-D microfocus X-ray computed tomography (micro-CT) image analysis, mechanical compression testing and computational fluid dynamical analysis. The results showed that SLM was capable of producing Ti6Al4V scaffolds with a broad range of morphological and mechanical properties. The in vitro study showed that scaffolds with a lower permeability gave rise to a significantly higher number of cells attached to the scaffolds after seeding. Qualitative analysis by means of live/dead staining and scanning electron micrography showed a circular cell growth pattern which was independent of the pore size and shape. This resulted in pore occlusion which was found to be the highest on scaffolds with 500μm hexagonal pores. Interestingly, pore size but not pore shape was found to significantly influence the growth of hPDC on the scaffolds, whereas the differentiation of hPDC was dependent on both pore shape and pore size. The results showed that, for SLM-produced Ti6Al4V scaffolds with specific morphological and mechanical properties, a functional graded scaffold will contribute to enhanced cell seeding and at the same time can maintain nutrient transport throughout the whole scaffold during in vitro culturing by avoiding pore occlusion.