Hydrobiologisch onderzoek in twee tichelgaten van het C.R.M.-reservaat De Mijntjes (Terwolde) : plankton, macrofauna en fysisch-chemische factoren

In het tichelgatencomplex 'de Mijntjes'. iets ten noorden van het dorpje Terwolde in de gemeente Voorst, werd een hydrobiologisch onderzoek verricht om de verschillen in ontwikkeling tussen een recent gegraven plas en een in het begin van deze eeuw gegraven plas te kunnen vaststellen. Hiertoe werden gedurende een jaar maandelijks macrofauna-, bezinkingsplankton- en chemische monsters verzameld om de verschillende levensgemeenschappen te kunnen beschrijven

Uncertainty in diatom assessment: sampling, identification and counting variation

Despite the widespread application of periphytic diatoms to water quality assessment at a regional level, there is no standard European sampling protocol or associated assessment metrics. Furthermore, relatively little is known about the uncertainty in the results of such assessments. One of the objectives of the European project for the Standardisation of River Classifications (STAR) is to improve and standardise diatom assessment methods. An extensive diatom ring test, together with an audit of the project results, provided a better understanding and quantification of the uncertainty in quality assessment of running waters using diatoms. The variation in multimetric analysis shows that the choice of site and substrate for sampling, the inter-operator differences in diatom taxonomy and the counting techniques are the primary sources of uncertainty. To some extent, this variation also reveals the robustness of specific metrics in relation to the sources of uncertainty. Of the three most common substrate types tested (stone, macrophyte and sediment), macrophytes emerge as the most preferred substrate for diatom sampling when performing multimetric water quality assessment

Pentacyclic adenine: a versatile and exceptionally bright fluorescent DNA base analogue

Emissive base analogs are powerful tools for probing nucleic acids at the molecular level. Herein we describe the development and thorough characterization of pentacyclic adenine (pA), a versatile base analog with exceptional fluorescence properties. When incorporated into DNA, pA pairs selectively with thymine without perturbing the B-form structure and is among the brightest nucleobase analogs reported so far. Together with the recently established base analog acceptor qAnitro, pA allows accurate distance and orientation determination via Förster resonance energy transfer (FRET) measurements. The high brightness of its emission at wavelengths above 400 nm also makes it suitable for fluorescence microscopy, as demonstrated by imaging of single liposomal constructs coated with cholesterol-anchored pA-dsDNA, using total internal reflection fluorescence microscopy. Finally, pA is also highly promising for two-photon excitation at 780 nm, with a brightness (5.3 GM) that is unprecedented for a base analog

N-(Di)icosyl-substituted benzo[a]phenoxazinium chlorides : synthesis and evaluation as near-infrared membrane probes

Five benzo[a]phenoxazinium chlorides containing alkyl chains with twenty carbon atoms on 5- or 9-positions of the tetracyclic ring were efficiently synthesised and characterised by UV/Vis/NIR spectroscopy. The absorption and emission maxima in ethanol lie in the range 627-641 nm and 645-676 nm, respectively, with quantum yields varying from 0.14 to 0.38. Preliminary photophysical studies with these fluorochromophores in zwitterionic (2,3- bis(palmitoyl-oxy)propyl-2-(trimethylammonio)ethyl phosphate, DPPC) and cationic (N,N-dimethyl-N-octadecyloctadecan-1-aminium bromide, DODAB) vesicles were carried out. The results showed that the new benzo[a]phenoxazinium derivatives are able to detect the gel to liquid-crystalline lipid phase transition through variations, either in the H-aggregation extent or in an acid-base equilibrium.Fundação para a Ciência e Tecnologia (FCT) - REDE/1517/RMN/2005Fundo Europeu de Desenvolvimento Regional (FEDER) - POCI 201

How good are rodent models of carcinogenesis in predicting efficacy in humans? A systematic review and meta-analysis of colon chemoprevention in rats, mice and men

Tumours in rodent and human colon share many histological and genetic features. To know if rodent models of colon carcinogenesis are good predictors of chemopreventive efficacy in humans, we made a meta-analysis of aspirin, beta-carotene, calcium, and wheat bran studies. Controlled intervention studies of adenoma recurrence in human volunteers were compared with chemoprevention studies of carcinogen-induced tumours in rats, and of polyps in Min (Apc(+/-)) mice: 6714 volunteers, 3911 rats and 458 mice were included in the meta-analyses. Difference between models was small since most global relative risks were between 0.76 and 1.00. A closer look showed that carcinogen-induced rat studies matched human trials for aspirin, calcium, carotene, and were compatible for wheat bran. Min mice results were compatible with human results for aspirin, but discordant for calcium and wheat bran (no carotene study). These few results suggest that rodent models roughly predict effect in humans, but the prediction is not accurate for all agents. Based on three cases only, the carcinogen-induced rat model seems better than the Min mouse model. However, rodent studies are useful to screen potential chemopreventive agents, and to study mechanisms of carcinogenesis and chemoprevention