Staff Publications

Staff Publications

  • external user (warningwarning)
  • Log in as
  • language uk
  • About

    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

    We have a manual that explains all the features 

    Current refinement(s):

    Records 1 - 16 / 16

    • help
    • print

      Print search results

    • export

      Export search results

    Check title to add to marked list
    How much bio is in there? Can stable isotopes be used to determine the bio-based content of products?
    Broek, L.A.M. van den; Veer, G. van der; Zee, M. van der - \ 2015
    Bioplastics Magazine 10 (2015)5. - ISSN 1862-5258 - p. 18 - 22.
    isotopen - stabiele isotopen - biobased economy - materialen uit biologische grondstoffen - samenstelling - analytische methoden - isotopes - stable isotopes - biobased economy - biobased materials - composition - analytical methods
    Can stable isotopes be used to determine the bio-based content of products?
    Studying biosphere-atmosphere exchange of CO2 through Carbon-13 stable isotopes
    Velde, I.R. van der - \ 2015
    Wageningen University. Promotor(en): Maarten Krol; Wouter Peters, co-promotor(en): J.B. Miller. - Wageningen : Wageningen University - ISBN 9789462572935 - 143
    kooldioxide - biosfeer - atmosfeer - isotopen - koolstofcyclus - klimaat - voorspellingen - carbon dioxide - biosphere - atmosphere - isotopes - carbon cycle - climate - forecasts

    Summary Thesis ‘Studying biosphere-atmosphere exchange of CO2 through

    carbon-13 stable isotopes’

    Ivar van der Velde

    Making predictions of future climate is difficult, mainly due to large uncertainties in the carbon cycle. The rate at which carbon is stored in the oceans and terrestrial biosphere is not keeping pace with the rapid increase in fossil fuel combustion and deforestation, resulting in an increase of atmospheric carbon dioxide (CO2). To gain a better understanding of the global carbon cycle we need to combine multiple sources of data into one consistent analysis, such as, forest and agricultural statistics, satellite data, atmospheric and ecological observations, and mechanistic models. This thesis describes fundamental research on some of the key components of the terrestrial carbon cycle, i.e., gross primary production (GPP) and terrestrial ecosystem respiration (TER) of CO2, which forms the key to improved prediction of net exchange. Droughts have been shown to strongly influence this exchange, and to interpret these responses adequately we have turned to a large collection of new atmospheric observations of CO2, and its 13C isotope (13CO2), to constrain key model components.

    In Chapter 2 we studied the global budget of atmospheric CO2 and the ratio of 13CO2/12CO2 (δ13C) and investigated the main terrestrial drivers of interannual variability (IAV) responsible for the observed atmospheric δ13C variations. In this chapter we introduced the SiBCASA biogeochemical model that we provided with a detailed isotopic discrimination scheme (to calculate the natural preference of 12CO2 over 13CO2 in uptake processes), separate 12C and 13C biogeochemical pools, and satellite-observed fire disturbances. This model was able to calculate uptake of 13CO2 and 12CO2 and produced return fluxes from its differently aged carbon pools, contributing to the so-called disequilibrium flux. Our simulated terrestrial isotope processes, plant discrimination and disequilibrium, closely resembled previously published values and similarly suggested that discrimination variations in C3 type plants and year-to-year variations in C3 and C4 productivity are the main drivers of IAV. The year-to-year variability in the terrestrial disequilibrium flux was much lower than required to match variations in atmospheric observations, under the common assumption of low variability in net ocean CO2 exchange, constant discrimination, and a closed CO2 budget. It was unclear how to increase IAV in the terrestrial biosphere, which suggested that SiBCASA missed adequate drought responses resulting in a latent isotope discrimination and variability in C3/C4 plant productivity.

    Implementation of carbon isotope cycling, biomass burning, and SiBCASA’s drought response were closely studied in Chapter 3. Our biomass burning emissions were similar as in CASA-GFED; both in magnitude and spatial patterns, and the implementation of isotope exchange gave a global mean discrimination value of approximately 15 ‰, and varied spatially depending on the photosynthetic pathway in the plant. These values compared well (annually and seasonally) with other published results. Similarly, the size of the terrestrial isotopic disequilibrium was close to that of other studies. As plants experience drought stress, they respond by closing their stomata to prevent the loss of water. This process also inhibits the uptake of CO2 and reduces the isotope discrimination against 13CO2 molecules. We found that the amplitude of drought response in SiBCASA was smaller than suggested by the measured isotope signatures. We also found that a slight increase in stomatal closure for large vapor pressure deficits amplified the variations in the respired isotope signature. Finally, we saw the need for modified starch/sugar storage pools to improve the propagation of isotopic discrimination anomalies to respiration on short-term time scales.

    In Chapter 4 we developed a multi-tracer inversion system to interpret signals in atmospheric CO2 and δ13C observations simultaneously. We wanted to know whether drought stress in plants can induce changes in atmospheric δ13C and whether they are interpretable. Using inverse modeling we were able to refine the discrimination parameter for plants as it reflected detectable variations in atmospheric δ13C. The results showed that the isotope discrimination values were consistently smaller during large severe droughts in the Northern Hemisphere, exceeding the estimates from SiBCASA (i.e., a larger reduction). Decreased discrimination suggested an increase in the regional intrinsic water use efficiency, which was also recorded at a large number of measurement sites. The IAV in net ecosystem exchange was relatively insensitive as we allowed the variability of the discrimination parameter to increase more than 8-fold, but it also allowed significant correlation between annual net exchange and discrimination. This study suggested a larger effect of droughts on discrimination than previously thought and that the treatment of drought response in biosphere models needs to be improved.

    Carbon cycle research is far from complete as many components are still largely uncertain, which prevents us from making better predictions of future climate. This thesis, however, highlights the importance of isotope observations to assess and improve biogeochemical models, especially with regard to the allocation and turnover of carbon, and responses to droughts.

    Environmental and physiological drivers of tree growth : a pan-tropical study of stable isotopes in tree rings
    Sleen, J.P. van der - \ 2014
    Wageningen University. Promotor(en): Pieter Zuidema; Frans Bongers; Niels Anten. - Wageningen : Wageningen University - ISBN 9789461739544 - 174
    bomen - groei - plantenfysiologie - jaarringen - milieueffect - isotopen - tropische bossen - tropen - trees - growth - plant physiology - growth rings - environmental impact - isotopes - tropical forests - tropics

    Forests in the wet tropics harbour an incredible biodiversity, provide many ecosystem services and regulate climatic conditions on regional scales. Tropical forests are also a major component of the global carbon cycle, storing 25% of the total terrestrial carbon and accounting for a third of net primary production. This means that changes in forest structure and forest cover in the wet tropics will not only affect biodiversity and ecosystem services, but also have implications for the global carbon cycle and – as a result – may speed up or slow down global warming. Deforestation rates are still high in the tropics and have profoundly affected the extent of forests in many countries. Additionally, there are indications that undisturbed and pristine tropical forests are changing. The most notable changes found by the monitoring of permanent forest plots are an increase of tree growth and forest biomass per unit of surface area over the last decades. If this is indeed the case, it would entail that the world’s tropical forests are potentially absorbing a significant fraction of human caused CO2emissions and as such are mitigating global warming. However, increased tree growth and forest biomass have not been found in all studies. Furthermore, it is unknown whether the observed changes in intact forests are part of a long-term change, or merely reflect decadal scale fluctuations. These uncertainties lead to an ongoing debate on whether tree growth and forest biomass have increased in tropical forests and – if so – to what extent. In addition, there is also a scientific discussion on the factor(s) that could underlie the potential changes in tree growth and forest biomass. Possibly, they are caused by an internal driver, like the lasting effect of large scale disturbances in the past, or by external drivers. Possible external factors affecting tropical forest dynamics are (1) climate change (temperature and precipitation), (2) increased nutrient depositions and (3) increased atmospheric CO2concentration.

    In this thesis, I investigated the environmental changes that could have formed the basis for changes in tropical tree growth. I used two relatively new tools in tropical forest ecology: tree-ring measurements and stable isotope analyses. Tree-ring widths were measured to obtain long-term information on tree growth. Stable isotopes in the wood of tree rings were analysed to provide information on the environmental and physiological drivers of tree growth changes. This thesis is part of a larger project on the long-term changes in intact forests in the wet tropics (the TroFoClim project, led by Pieter Zuidema) and also includes the PhD theses of Mart Vlam and Peter Groenendijk. In this project, ~1400 trees of 15 species were examined that were collected in three forest sites distributed across the tropics (in Bolivia, Cameroon and Thailand).

    For the assessment of long-term changes in growth and stable isotopes, it is important to understand shorter term fluctuations due to forest dynamics (i.e. gap formation), because these interfere with changes on a longer temporal scale. The formation of a gap in a closed canopy forest, after the death of a tree, can cause considerable environmental changes in the surrounding area, e.g. in light, nutrient and water availability. This can strongly affect the growth rates of the remaining trees. However, in most studies the environmental drivers of changes in tree growth after gap formation are not considered. In CHAPTER 2 I measured carbon isotope discrimination (Δ13C) in annual growth rings of Peltogyne cf.heterophylla, from a moist forest in North-eastern Bolivia, and evaluated the environmental drivers of growth responses after gap formation. Growth and Δ13C was compared between the seven years before and after gap formation. Forty-two trees of different sizes were studied, half of which grew close (<10m) to single tree-fall gaps; the other half grew more than 40 m away from gaps (control trees). I found that increased growth was mainly associated with decreased Δ13C suggesting that this response was driven by increased light availability and not by improved water availability. Interestingly, most small trees did not show a growth stimulation after gap formation. This result was hypothesized to be caused by an increased drought stress. However, the measurement of Δ13C showed that increased water stress is unlikely the cause for the absence of increased growth, but rather suggested that light conditions had not improved after gap formation. These results show that combining growth rates with changes in Δ13Cis a valuable tool to better understand the causes of temporal variation in tree growth.

    An important potential driver of long-term changes in tree growth is climate change, e.g. global warming and altered annual precipitation. To understand the effect of climate change on tree growth, the availability of reliable data on historical climate is off course crucial. For the study areas in Bolivia and Thailand, previous studies have investigated the occurrence of temporal trends in temperature and precipitation. For the study area in Cameroon however, as well as for West and Central Africa in general, the availability of instrumental climate data is very restricted. This limits the possibility to relate past climatic variation to changes in tree growth and calls for proxies that allow reconstruction of past climatic conditions. In CHAPTER 3 I assessed the potential use of stable isotopes of oxygen (δ18O) in tree rings as a tool for the reconstruction of precipitation in tropical Africa. I measured δ18O in tree rings of five large Entandrophragmautiletreesfrom North-western Cameroon. A significant negative correlation was found between annual tree-ring δ18O values (averaged over the five individuals) and annual precipitation amount during 1930-2009 in large areas of West and Central Africa. I also found tree-ring δ18O to track sea surface temperatures (SST) in the Gulf of Guinea (1930-2009). These two results are related because rainfall variabilityin West and Central Africa is profoundly influenced by the SST of the tropical AtlanticOcean. Thus a high SST in the Gulf of Guinea is associated with high precipitation over large parts of West and Central Africa and recorded in tree rings by a relatively low δ18O value. On the other hand, dry years when SST is low, are recorded by relatively high tree-ring δ18O values. I also found a significant long-term increase of tree-ring δ18O values. This trend seems to be caused by lowered precipitation from 1970 to 1990 (the Sahel drought period). From 1860 to 1970, no significant long-term trend was observed in tree-ring δ18O values, suggesting no substantial change in precipitation amount occurred over this period.

    Another potential driver of altered tree growth and biomass in intact tropical forests is the increase of anthropogenic nutrient depositions, especially nitrogen. The deposition of nitrogen has likely risen due to an increased industrialization and use of artificial N fertilizers in most tropical countries. Nitrogen can stimulate plant growth, as is well known from the positive effect of N fertilizer application on crop yields. Previous studies have shown that the stable isotope ratio of nitrogen (δ15N) increased during the last decennia in the wood of trees from Brazil and Thailand as well as in tree leaves from Panama. This increased δ15N has been interpreted as a signal that tropical nitrogen cycles have become more ‘open’ and ‘leaky’ during the last decades in response to increased anthropogenic nitrogen depositions. The underlying mechanism is that high rates of nitrogen deposition and high ambient nitrogen availability lead to an increased nitrification. This process can cause a gradual 15N-enrichment of soil nitrogen. In CHAPTER 4 I analysed changes in tree-ring δ15N values of 400 trees of six species from the three study sites. In the trees from Cameroon no long-term change of tree-ring δ15N values was found (1850-2005), even though NH3and NOxemissions seem to have increased strongly around the study area since 1970. Possibly, the very high precipitation at that site causes the local nitrogen cycle to be already very ‘leaky’, limiting the effect of additional nitrogen input on the δ15N signature of soil nitrogen. Alternatively, nitrogen input in this forest might be much lower than reconstructed NH3and NOxemissions suggest. For the study site in Bolivia, no significant change of tree-ring δ15N values was found (1875-2005), which is in line with the expected result for areas with a low anthropogenic nitrogen input. I found a marginally significant increased of δ15N values since 1950 in trees from Thailand, which confirms previous observations. This points to an effect of increased anthropogenic nitrogen deposition, which could have stimulated photosynthetic rates, if indeed nitrogen was limiting tree growth.

    The most often hypothesized factor to cause a long-term increase of tree growth is the rise of atmospheric CO2. Since the onset of the industrial revolution (~1850) global atmospheric CO2concentration has increased by 40%. Elevated CO2can directly affect plants by increasing the activity, as well as the efficiency, of the CO2fixing enzyme rubisco and thereby increase photosynthetic rates. Potentially more important in plant communities subjected to periods of limited water availability (like a dry season) is that elevated CO2 can cause a reduction of stomatal conductance, which lowers evapo-transpiration and hence reduces water losses.This increases water-use efficiency (i.e. the amount of carbon gained through photosynthesis divided by the amount of water loss through transpiration) and might allow plants to extend their growth season and/or increase their photosynthetic activity during the hottest hours of the day when water-stress might be severe. Elevated atmospheric CO2is thus a very likely candidate to have stimulated tropical tree growth (also referred to as CO2fertilization), provided at least that plant growth was either carbon or water limited. In CHAPTER 5 I tested the CO2fertilization hypothesis by analysing growth-ring data of 1100 trees from the three study sites. The measurement of tree-ring widths allowed an assessment of historical growth rates, whereas stable carbon isotopes (δ13C) in the wood of the trees were used to obtain an estimate of the CO2concentration in the intercellular spaces in leaves (Ci) and of water-use efficiency (intrinsic water-use efficiency; iWUE). I used a sampling method that controls for ontogenetic (i.e. size developmental) changes in growth and δ13C. With this method, trees were compared across a fixed diameter (i.e. same ontogenetic stage). I chose two diameters: 8 cm (referring to small understorey trees) and 27 cm (referring to larger canopy trees). A mixed-effect model revealeda highly significant and exponential increase of Ciat each of the three sites, and in both understorey and canopy trees. Over the last 150 years Ciincreased by 43% and 53% for understorey and canopy trees respectively. Yet, the rate of increase in Ciwas consistently lower than that of atmospheric CO2. This ‘active’ response to elevated atmospheric CO2resulted in a significant and large increase of iWUE. Over the last 150 years, iWUE increased by 30% and 35% for understorey and canopy trees.A long-term increase of iWUE indicates either a proportional increase of net photosynthesis and/or a decrease of stomatal conductance and thus transpiration, both of which could have stimulated biomass growth. However, I found no increase of tree growth over the last 150 years in any of the sites. Although there are several possible explanations for these findings, I argue that it is most likely that tropical tree growth is generally not limited by water and carbon, but by a persistent nutrient limitation (e.g. of phosphates) and that this has prevented tropical trees to use the extra CO2for an acceleration of growth.

    In this thesis I have studied environmental and physiological drivers of tree growth changes. I found evidence of decreased precipitation over the last decades at the study site in Cameroon (CHAPTER 3), a changed nitrogen cycle at the study site in Thailand (CHAPTER 4) and an overall change in the physiology of all tree species studied (increased iWUE; CHAPTER 5). One of the main findings of this thesis is however, that these changes have not led to a net change of tree growth over the last 150 years (CHAPTER 5). This is an important finding that could have two major implications. Firstly, the absence of a long-term growth stimulation suggests that the increase of iWUE is mainly driven by a reduced stomatal conductance, which likely leads to a reduced evaporative water loss. If trees across the tropics are reducing evapo-transpiration, this will change affect hydrological cycles, e.g. leading to a lower humidity, higher air temperatures and a reduced precipitation. Secondly, the absence of a growth stimulation over the last 150 years suggests that the carbon sink capacity of tropical forests is currently overestimated, e.g. by Dynamic Global Vegetation Models, which assume strong CO2fertilization effects and as such a high capacity of tropical forests to mitigate global warming. I anticipate that the planned Free Air Concentration Enrichment (FACE) experiments in the tropics will shed light on the reasons why increased CO2does not stimulate the growth rates of tropical trees. Furthermore, I argue that combining tree-ring measurements and stable isotope analyses together with permanent plot research is the most promising way to increase our understanding of the changes in tropical forests.

    Immunogenetic analysis of natural antibody isotypes in laying hens
    Sun, Y. - \ 2013
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Jan van der Poel; Henk Parmentier. - S.l. : s.n. - ISBN 9789461736796 - 192
    hennen - pluimvee - immunogenetica - genetische analyse - antilichamen - isotopen - overleving - genetische parameters - verenpikken - dierveredeling - hens - poultry - immunogenetics - genetic analysis - antibodies - isotopes - survival - genetic parameters - feather pecking - animal breeding

    Worldwide, especially in Europe, poultry industry is undergoing important changes including ban of the battery housing system and prohibition of beak trimming. The former can facilitate more spread of infectious diseases, and the latter will contribute to higher mortality because of severe feather pecking. Furthermore, given the growing social concern about food safety and human health, abundant use of antibiotics will either be prohibited or restricted. These changes further emphasize the importance of implementing general disease resistance in layers breeding goals next to maintaining high production. The aim of this thesis was to find proper traits which are associated with laying hens survival, and reveal genetic architecture and background underlying the traits. Natural antibody (NAb), which are the antibodies present in normal healthy animals in the absence of a deliberate antigen exposure are an important humoral part of innate immunity. The relationships between survival and NAb isotype titers were firstly investigated by the logistic regression analysis in a population of laying hens from 12 purebred lines. The results indicated that NAb, especially the IgM isotype titers at young age was predictive for survival of a laying period. Genetic parameters of NAb isotypes IgM and IgG titers were estimated in the same population. The estimation showed that both NAb isotypes are moderate to high heritable traits which were possible to breed for. An association study revealed different QTL or SNP markers for NAb isotypes titers. The majority of the commercial laying hens are crossbred. Therefore, the relationships between NAb isotype titers and survival were further investigated in crossbred laying hens. However, a consistent relationship as in the purebred was not found. This confirmed the speculation that non-health-related causes of mortality (severe feather pecking) overruled the anticipated relationships between NAb isotype titers and survival in birds with intact beaks. Overall, the present studies indicate that it is possible to implement NAb especially the IgM isotype titers into the breeding goals of laying hens to improve the health-related survival.

    Assessment of the effect of kinetics on colloid facilitated radionuclide transport in porous media.
    Weerd, H. van de; Leijnse, A. - \ 1997
    Journal of Contaminant Hydrology 26 (1997). - ISSN 0169-7722 - p. 245 - 256.
    grondwaterstroming - hydrodynamica - vloeistoffen (liquids) - vloeistoffen (fluids) - stroming - poreus medium - toepassingen - isotopen - straling - radioactiviteit - modellen - onderzoek - groundwater flow - hydrodynamics - liquids - fluids - flow - porous media - applications - isotopes - radiation - radioactivity - models - research
    Binding of radionuclides to natural colloids can significantly alter their transport behaviour in porous media. Dependent on the interaction between radionuclides, colloids and the solid matrix, radionuclide transport may be enhanced or retarded as a result of the presence of colloids. Often, equilibrium models are used to describe interactions between radionuclides, colloids and the solid matrix. However, experimental results indicate that kinetic processes may be important. In this paper, a model for coupled colloid and radionuclide transport in porous media is presented. Kinetic relationships are incorporated for the interaction between radionuclides, colloids and solid matrix. With this transport model, column experiments have been simulated, and modelling results are compared with experimental data reported in literature. It appears that kinetic interaction relationships are required to adequately model the experimental data.
    Kwantitatieve massaspectrometrie van Clenbuterol met behulp van isotoopverdunning
    Traag, W.A. ; Bennekom, E.O. van; Weseman, J.M. ; Kienhuis, P.G.M. ; Tuinstra, L.G.M.Th. - \ 1989
    Wageningen : RIKILT (Rapport / RIKILT 89.29) - 11
    vleessamenstelling - massaspectrometrie - clenbuterol - isotopen - monsterverwerking - spectrometers - kwantitatieve methoden - doping - meat composition - mass spectrometry - clenbuterol - isotopes - sample processing - spectrometers - quantitative methods - doping
    Om de toepassing van massaspectrometrie met behulp van isotoopverdunning in urine, vlees en lever te onderzoeken is een aantal experimenten uitgevoerd met de 'Hewlett-Packard Hass Selective Detector' (Electron Impact). Ook zijn met Finnigan 4500 aanvullende experimenten (Chemical Ionisation) uitgevoerd om na te gaan of de gelabelde verbinding de bepaling met chemische ionisatie kwalitatief en dus ook kwantitatief zou storen.
    De herhaalbaarheid van het massaspectrum van hexachloorbenzeen
    Kienhuis, P.G.M. ; Traag, W.A. ; Tuinstra, L.G.M.T. - \ 1985
    Wageningen : RIKILT (Rapport / RIKILT 85.29) - 2
    massaspectrometrie - hexachloorbenzeen - isotopen - mass spectrometry - hexachlorobenzene - isotopes
    In verband met de betrouwbaarheid van massaspectrametrische confirmaties is het van belang om de herhaalbaarheid van massaspectrametrische resultaten te bepalen. Gekozen is voor de bepaling van een aantal chloor isotopen van het molecuulion van hexachloorbenzeen (HCB).
    Kwantitatieve massaspectrometrie van stilbeenhormonen (als HFB derivaat) met behulp van isotoopverdunning
    Kienhuis, P. ; Traag, W.A. ; Tuinstra, L.G.M.T. - \ 1984
    Wageningen : RIKILT (Rapport / RIKILT 84.107)
    oestrogenen - hormonen - isotopen - massaspectrometrie - stilbenen - gaschromatografie - analytische scheikunde - oestrogens - hormones - isotopes - mass spectrometry - stilbenes - gas chromatography - analytical chemistry
    The use of ionizing radiation in agriculture : proceedings of a workshop, 22, 23 and 24 March 1976, Wageningen, The Netherlands
    Stichting ITAL, ; Association Euratom, - \ 1977
    Commission of the European Communities (Commission of the European Communities EUR 5815 en) - ISBN 9789282500576 - 566
    agriculture - applications - effects - food irradiation - food preservation - genetic control - insects - isotopes - mutations - plant breeding - radiation - radioactivity - sterile insect release - sterilization - landbouw - toepassingen - effecten - voedselbestraling - voedselbewaring - genetische gewasbescherming - insecten - isotopen - mutaties - plantenveredeling - straling - radioactiviteit - steriele insecten techniek - sterilisatie
    Verslag van het international symposium on nuclear techniques in animal production and health as related to the soil - plant system, Wenen februari 1976
    Metz, S.H.M. - \ 1976
    Hoorn : Unknown Publisher (Intern rapport / Instituut voor veevoedingsonderzoek "Hoorn" no. 90) - 11
    dierfysiologie - toepassingen - isotopen - kernenergie - straling - radioactiviteit - zoötechniek - animal physiology - applications - isotopes - nuclear energy - radiation - radioactivity - zootechny
    Inwerking van kaliumamide op enige 15N-gemerkte 4-halogeenpyrimidinederivaten
    Valk, J. de - \ 1973
    Wageningen University. Promotor(en): H.C. van der Plas. - Wageningen : Landbouwhogeschool - 44
    ammoniak - isotopen - stikstof - kalium - pyrimidines - derivaten - chemische reacties - ammonia - isotopes - nitrogen - potassium - pyrimidines - derivatives - chemical reactions
    Aan de hand van de in de inleiding gegeven voorbeelden is het duidelijk dat tal van gesubstitueerde halogeenpyrimidinen, in reactie gebracht met een geschikt nucleofiel reagens, aanleiding kunnen geven tot het optreden van ringopeningsreacties. De daarbij gevormde, vaak instabiele open-ketenverbindingen kunnen hetzij verder reageren door een ringsluiting dan wel overgaan in meer stabiele open-ketenverbindingen.

    De vorming van (1.31) in de reactie van (1.29) met lithiumpiperidide in piperidine deed ons besluiten de aminering van (1.29) met kaliumamide in vloeibare ammoniak opnieuw aan een onderzoek te onderwerpen. De overweging die hierbij een rol speelt, was de volgende. Het amide-ion zou, op analoge wijze als het lithiumpiperidide in de reactie met (1.29) op de 2-plaats van het pyrimidinemolecuul kunnen aanvallen. Een daaropvolgende verbreking van de C 2 - N 3 band levert dan een open-ketenverbinding (1.33) op, die echter hierin wezenlijk verschilt van de piperidinoverbinding (1.31) dat door additie van de aminogroep in (1.33) over de drievoudige band van de nitrilfunctie ringsluiting kan optreden, waarbij 4-amino-6-fenylpyrimidine (1.34) ontstaat. Daar bij een aminering volgens het zojuist beschreven mechanisme een van de ringstikstofatomen van (1.29) zich na de reactie in de aminogroep buiten de ring zal bevinden, is het mogelijk d.m.v. is N-gemerkte moleculen na te gaan of de aminering van (1.29) via dit mechanisme (geheel dan wel gedeeltelijk) verloopt dan wel via een mechanisme, waarbij de ring niet wordt geopend.

    Het mechanisme, verlopend via een intermediaire open-ketenverbinding, blijkt zowel in de aminering van (1.29) als in de aminering van diverse andere gesubstitueerde 4-halogeenpyrimidinen een belangrijke rol te spelen. Voorgesteld is dit nieuwe substitutie-mechanisme het A(additie)N(nucleofiel)R(ring) O(opening)R(ring)S(sluiting)-mechanisme te noemen (ANRORS- mechanisme).

    In dit proefschrift wordt het onderzoek beschreven naar het voorkomen van het ANRORS-mechanisme in de aminering van diverse gesubstitueerde 4-halogeenpyrimidinen met kaliumamide in vloeibare ammoniak; tevens wordt ook aandacht geschonken aan het optreden van dit mechanisme in de aminering van een halogeen bevattend bicyclisch systeem, n.l. 4-chloorchinazoline.

    De resultaten van de aminering en het voorkomen van het ANRORS-mechanisme in de aminering van de vier 4-halogeen-6-fenylpyrimidinen zal worden beschreven in hoofdstuk II, terwijl in hoofdstuk III de invloed van substituenten op dit ANRORS-mechanisme aan de orde zal komen . In hoofdstuk IV zijn resultaten bijeengebracht van een 14C-onderzoek dat als doel had meer informatie te verkrijgen over de structuur van de in dit basisch milieu niet te isoleren open-ketenverbindingen. Het onderzoek naar het voorkomen van het ANRORS-mechanisme in de aminering van 4-chloorchinazoline staat beschreven in hoofdstuk V. In hoofdstuk VI zullen de in dit proefschrift beschreven resultaten worden besproken en vergeleken worden met analoge, in de literatuur vermelde reactietypen.

    IAEA/FAO international training course on the use of radioisotopes and radiation in soil and plant nutrition studies, 10 August - 25 September 1970
    Zeeuw, D. de; Schuffelen, A.C. - \ 1970
    Wageningen : ITAL - 450
    landbouw - bodemkunde - plantenvoeding - kunstmeststoffen - mest - toepassingen - isotopen - straling - radioactiviteit - tracer technieken - tracers - metabolisme - kernfysica - moleculaire fysica - agriculture - soil science - plant nutrition - fertilizers - manures - applications - isotopes - radiation - radioactivity - tracer techniques - tracers - metabolism - nuclear physics - molecular physics
    Soil moisture measurement by the gamma transmission method
    Ryhiner, A.H. ; Pankow, J. - \ 1969
    Wageningen : [s.n.] (Technical bulletin / Institute for land and water management research 66) - 12
    bodemwater - grondanalyse - toepassingen - isotopen - straling - radioactiviteit - materialen - testen - mechanische eigenschappen - soil water - soil analysis - applications - isotopes - radiation - radioactivity - materials - testing - mechanical properties
    Calcium movement in oat leaves measured by semi - conductor detectors
    Ringoet, A. ; Rechenmann, R.V. ; Veen, H. - \ 1967
    Wageningen : [s.n.] (Publication / Plant physiological research centre no. 60) - 10
    assimilatie - avena sativa - plantkunde - calcium - instrumenten (meters) - isotopen - meting - stikstof - haver - deeltjes - fosfor - zwavel - assimilation - avena sativa - botany - calcium - instruments - isotopes - measurement - nitrogen - oats - particles - phosphorus - sulfur
    Verslag van de cursus over het gebruik van radio-actieve isotopen bij het dierkundig onderzoek en de diergeneeskunde, gehouden op 19 juli tot 11 september 1965 aan de Universiteit van Cornell (Ithaca) U.S.A.
    Grift, J. van der - \ 1965
    Lelystad : Instituut voor Veevoedingsonderzoek "Hoorn" (Intern rapport / Instituut voor Veevoedingsonderzoek "Hoorn" no. 4) - 23
    toepassingen - isotopen - straling - radioactiviteit - diergeneeskunde - applications - isotopes - radiation - radioactivity - veterinary science
    Landbouwtrainingscursus ITAL
    Anonymous, - \ 1960
    Wageningen : ITAL - 139
    landbouw - toepassingen - isotopen - straling - radioactiviteit - agriculture - applications - isotopes - radiation - radioactivity
    Check title to add to marked list

    Show 20 50 100 records per page

    Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.