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 

    Records 1 - 20 / 60

    • help
    • print

      Print search results

    • export

      Export search results

    Check title to add to marked list
    Hedgehog signaling via a calcitonin receptor-like receptor can induce arterial differentiation independently of VEGF signaling in zebrafish
    Wilkinson, R.N. ; Koudijs, M.J. ; Patient, R.K. ; Ingham, P.W. ; Schulte-Merker, S. ; Eeden, F.J.M. van - \ 2012
    Blood : journal of the American Society of Hematology 120 (2012)2. - ISSN 0006-4971 - p. 477 - 488.
    endothelial-growth-factor - embryonic vascular development - hematopoietic stem-cells - aortic endothelium - sonic-hedgehog - pathway - notch - blood - gene - kinase
    Multiple signaling pathways control the specification of endothelial cells (ECs) to become arteries or veins during vertebrate embryogenesis. Current models propose that a cascade of Hedgehog (Hh), vascular endothelial growth factor (VEGF), and Notch signaling acts instructively on ECs to control the choice between arterial or venous fate. Differences in the pheno-types induced by Hh, VEGF, or Notch inhibition suggest that not all of the effects of Hh on arteriovenous specification are mediated by VEGF. We establish that full derepression of the Hh pathway in ptc1;ptc2 mutants converts the posterior cardinal vein into a second arterial vessel that manifests intact arterial gene expression, intersegmental vessel sprouting, and HSC gene expression. Importantly, although VEGF was thought to be absolutely essential for arterial fates, we find that normal and ectopic arterial differentiation can occur without VEGF signaling in ptc1; ptc2 mutants. Furthermore, Hh is able to bypass VEGF to induce arterial differentiation in ECs via the calcitonin receptor-like receptor, thus revealing a surprising complexity in the interplay between Hh and VEGF signaling during arteriovenous specification. Finally, our experiments establish a dual function of Hh during induction of runx1(+) HSCs. (Blood. 2012;120(2):477-488)
    Dimer Biphenyl Liquid Crystals with Trisiloxane-Containing Spacers
    Achten, R. ; Koudijs, A. ; Giesbers, M. ; Marcelis, A.T.M. ; Sudhölter, E.J.R. - \ 2007
    Molecular Crystals and Liquid Crystals 477 (2007)1. - ISSN 1542-1406 - p. 169 - 176.
    mesogenic fluorinated organosiloxanes - polar order - phase - chirality - systems - series
    Dimeric biphenyl liquid crystals with trisiloxane containing spacers were studied. Both the tail lengths and the spacer lengths to a central hexamethyltrisiloxane group were varied. In most cases a SmC-phase was found with an anticlinic interlayer relation. One of the compounds appears to have a SmA-phase, which could be a de Vries SmA-phase. A few other compounds show liquid crystalline polymorphism. X-ray diffraction experiments show that the smectic layers are strongly interdigitated. The thickness of the layers is mainly dependent on the length of the spacers. The length of the terminal alkyl chains hardly influences the smectic layer thickness.
    Spacer length dependence of TGBC* and SmA phases in cholesteryl and dihydrocholesteryl-containing trimer liquid crystals
    Marcelis, A.T.M. ; Giesbers, M. ; Koudijs, A. - \ 2007
    Liquid Crystals 34 (2007)7. - ISSN 0267-8292 - p. 811 - 817.
    twist grain-boundary - smectic-c-phase - dimesogenic compounds - mesomorphic behavior - optical-properties - mesogenic units - terminal group - dimers - moiety - series
    Two series of trimer liquid crystals were investigated that contain a biphenylyl central group and two cholesteryl or dihydrocholesteryl terminal mesogenic groups. Only compounds with even spacers were investigated. The dihydrocholesteryl-containing trimers show a triply intercalated smectic A (SmA) phase when the spacer lengths are greater than 8, whereas the cholesteryl-containing trimers exhibit this triply intercalated SmA phase when the spacer lengths are more than 6. With shorter spacers, a twist grain boundary C* (TGBC*) phase was found. This is revealed by the formation of a typical dotted square grid pattern upon cooling from the chiral nematic (N*) phase in the planar texture. The dots are spaced by a distance of about 1.5-1.8 µm. Upon cooling from the N* phase in the focal conic texture a striped pattern is observed with the same spacing. X-ray diffraction revealed a repeat distance for the TGBC* phase that corresponds with a monolayer ordering. The results show that the weaker interaction between the dihydrocholesteryl groups compared with cholesteryl groups or longer spacers destabilize the monolayer TGBC* phase.
    Liquid crystalline dimers with bent-core mesogenic units
    Achten, R. ; Koudijs, A. ; Giesbers, M. ; Marcelis, A.T.M. ; Sudhölter, E.J.R. ; Schroeder, M.W. ; Weissflog, W. - \ 2007
    Liquid Crystals 34 (2007)1. - ISSN 0267-8292 - p. 59 - 64.
    polar order - achiral molecules - chirality - antiferroelectricity - ferroelectricity - mesophases - spacer - phase
    Two series of dimers, in which two identical aromatic bent core mesogenic units are connected via an organosiloxane or an alkylene spacer, have been investigated. The dimers with a spacer consisting of a trisiloxane central group and relatively long alkylene groups show an intercalated tilted smectic structure. The layer spacings appear to be very weakly dependent on the terminal chain lengths. In these dimers the smectic phase is stabilized for the compounds with a short terminal chain. Dimers with an aliphatic alkylene spacer are liquid crystalline only when the spacer is relatively short and the terminal chains are long. For these dimers a monolayer tilted smectic phase is observed.
    Banana-shaped side chain liquid crystalline siloxanes
    Achten, R. ; Koudijs, A. ; Giesbers, M. ; Reddy, R.A. ; Verhulst, T. ; Tschierske, C. ; Marcelis, A.T.M. ; Sudhölter, E.J.R. - \ 2006
    Liquid Crystals 33 (2006)6. - ISSN 0267-8292 - p. 681 - 688.
    bent-core mesogens - mesomorphic properties - achiral molecules - polar order - chirality - phases - units - polymers - design - field
    Eight banana-shaped side chain liquid crystalline oligomers and polymers have been synthesized by hydrosilylation of vinyl-terminated bent-core mesogens with trimethylsilyl-terminated siloxanes. The synthesized oligomers and polymers, and their olefinic precursors, were investigated by polarizing optical microscopy (POM), differential scanning calorimetry, X-ray diffraction (XRD), electro-optical experiments and Maldi-Tof. The short-tailed olefins form a Colr mesophase, whereas those with longer chains exhibit the SmCPA mesophase. All the oligomers and polymers studied show liquid crystalline properties and do not crystallize upon cooling. Most oligomers with around four repeating siloxane units, show a lamellar (layer) structure and antiferroelectric switching properties, the SmCPA phase. XRD shows that the layer spacings are hardly influenced by the length of the terminal tails. The oligomer prepared from the smallest olefinic precursor, having the shortest alkyl tail, shows an XRD pattern reminiscent of a columnar phase, although POM displays domains of opposite chirality, and no switching behaviour could be detected. The polymers with around 35 repeating siloxane units are liquid crystalline, but due to their high viscosity a thorough characterization of the liquid crystalline phases was impossible
    Determination of free fatty acids in cooking oil: traditional spectrophotometry and optothermal window assay
    Goyrik, M. ; Ajtony, Z. ; Doka, O. ; Alebic-Juretic, A. ; Bicanic, D.D. ; Koudijs, A. - \ 2006
    Instrumentation Science and Technology 34 (2006)1-2. - ISSN 1073-9149 - p. 119 - 128.
    transform infrared-spectroscopy - olive oil - lipase - extraction
    The concept of optothermal window (OW) (with 632.8 nm He-Ne laser used as a radiation source), combined with copper soap based colorimetry, was proposed as a new analytical tool to determine total free fatty acid (FFA) content in thermally treated cooking oil. The results obtained were compared to those acquired by conventional spectroscopy; the correlation between the two methods is high for FFA concentrations exceeding 2 µmol/mL
    AKK-Witte Motor op Groene Brandstof
    Jeddens, M. ; Elgersma, A. ; Boschma, S. - \ 2005
    Den Bosch / Wageningen : AKK - 14
    zuivelonderzoek - kazen - melk - melkvet - onverzadigde vetzuren - kaaskwaliteit - begrazing - veevoeder - productontwikkeling - innovaties - duurzame ontwikkeling - agro-industriële ketens - voeding en gezondheid - dairy research - cheeses - milk - milk fat - unsaturated fatty acids - cheese quality - grazing - fodder - product development - innovations - sustainable development - agro-industrial chains - nutrition and health
    CONO Kaasmakers (zuivelproducent), De Heus Brokking Koudijs (diervoederproducent) en Barenbrug Holland BV (grassenveredelingsbedrijf) willen gezamenlijk duurzame melk met een betere vetzuursamenstelling produceren om gezondere kaas te ontwikkelen en in de markt te introduceren. Dit doen zij vanuit een eigen duurzaamheidsvisie en een marktgerichte oriëntatie. Er vindt wetenschappelijk onderzoek plaats naar een optimale samenstelling van voer om jaarrond melk te produceren met voldoende en de juiste onverzadigde vetzuren. Op het onderzoek volgt het selecteren en beproeven van maatregelen om de optimale kwaliteit te realiseren. Tenslotte wordt een marktconcept ontwikkeld om de verbeterde producten in de markt te positioneren. Een belangrijk resultaat is verbetering van de kwaliteit en het imago van melkvet wat gunstig kan uitwerken voor de melkveehouderij en de zuivelindustrie. Verbetering van de kaaskwaliteit (smaak, gezondheid, duurzame productie) is relevant voor de internationale concurrentiepositie
    Non-symmetric bent-core mesogens with one terminal vinyl group
    Achten, R. ; Koudijs, A. ; Giesbers, M. ; Marcelis, A.T.M. ; Sudhölter, E.J.R. - \ 2005
    Liquid Crystals 32 (2005)3. - ISSN 0267-8292 - p. 277 - 285.
    banana-shaped molecules - ferroelectric liquid-crystals - smectic-a phase - azo-compounds - achiral molecules - clearing temperature - mesophase behavior - homologous series - chiral domains - field
    Two series of non-symmetric banana-shaped compounds, both with one alkyl and one alkenyl terminal tail, have been synthesized and studied. Both series were compared with the corresponding series with two saturated terminal alkyl tails. All the compounds have a bent central 1,3-phenylene bis(4-benzoyloxy) benzoate core; their mesophases were characterized by polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and switching current response experiments. In all four series one of the terminal tails is varied from OC8H17 to OC16H33. The other terminal tails are OC11H23, O(CH2) 9CH=CH2, OC10H21 and O(CH 2)8CH=CH2. The short-tailed compounds show monotropic or enantiotropic B1 phases and the long-tailed compounds the B2 phase. The introduction of one terminal vinyl group slightly lowers the transition temperatures. The introduction of a second terminal vinyl group further suppresses the liquid crystalline properties. All compounds with B2 phases have layer spacings that suggest a tilt of ~45° of the bent molecules in the layers, and their switching behaviour is antiferroelectric
    Non-symmetric banana-shaped liquid crystals with two different terminal alkoxy tails
    Achten, R. ; Cuypers, R. ; Giesbers, M. ; Koudijs, A. ; Marcelis, A.T.M. ; Sudhölter, E.J.R. - \ 2004
    Speciaal hanenvoer tijdens de legperiode
    Emous, R.A. van; Harn, J. van; Lourens, A. - \ 2004
    De Pluimveehouderij 34 (2004)32. - ISSN 0166-8250 - p. 16 - 17.
    pluimveevoeding - hanen - bevruchting - voersamenstelling - paringsgedrag - lichaamsgewicht - voedingsstoffengehalte - poultry feeding - cocks - fertilization - feed formulation - mating behaviour - body weight - nutrient content
    Het gebruik, tijdens de legperiode, van een speciaal hanenvoer met minder eiwit, aminozuren en calcium zou mogelijk een effect hebben op de bevruchting. Praktijkonderzoek komt tot de conclusie dat bij gelijke voergift van het speciale hanenvoer het lichaamsgewicht lager is, er geen verschil is in bevruchting, in het aantal gelukte paringen en in uitval. Een proef bij De Heus Brokking Koudijs bevestigt deze conclusies
    Asymmetric banana-shaped liquid crystals with two different terminal alkoxy tails
    Achten, R. ; Cuypers, R. ; Giesbers, M. ; Koudijs, A. ; Marcelis, A.T.M. ; Sudhölter, E.J.R. - \ 2004
    Liquid Crystals 31 (2004)8. - ISSN 0267-8292 - p. 1167 - 1174.
    lateral substituents - mesophase behavior - distinct formation - achiral molecules - dimeric compounds - smectic phase - chirality - mesogens - field
    Two series of asymmetric banana-shaped compounds have been synthesized and studied. In the 1,3-phenylene bis[4-(4'-alkoxybenzoyloxy)]benzoate series the lack of symmetry was derived solely from the difference in length of the two terminal alkoxy chains. In the 3,4'-biphenylene bis[4-(4'-alkoxybenzoyloxy)]benzoate series the asymmetric nature originates from the 3,4'-substitution of the central biphenyl group and from the difference in length of the two terminal chains. All the melting points of the asymmetrical compounds in the series with the central phenyl unit are lower than those of the symmetrical compounds. The liquid crystalline B-1 or B-2 phase was retained in all cases. In the series with the central biphenyl unit the compounds with the shortest chain attached to the para -position of the central biphenyl unit have the lowest melting points. A significant lowering of the melting points in comparison with the symmetrically substituted compounds, however, could not be achieved. All the compounds of both series show a layer spacing which is comparable to those of the symmetrically substituted parent compounds. The observed switching behaviour of both the symmetric and asymmetric compounds with a B-2 phase was antiferroelectric.
    Smectic C phases and reentrant behavior in cholesterol containing dimer liquid crystals
    Marcelis, A.T.M. ; Koudijs, A. ; Sudhölter, E.J.R. - \ 2004
    Molecular Crystals and Liquid Crystals 411 (2004)1. - ISSN 1542-1406 - p. 193 - 200.
    dimesogenic compounds - terminal group
    A series of dodecyloxybiphenylyl and cholesteryl group containing dimers with ethers as spacers have been prepared and their liquid crystalline properties were investigated as a function of spacer length. For short spacers SmA and SmC phases were observed with monolayer ordering. This is aparent from. polarization microscopy and temperature dependent X-ray measurements. With increasing spacer length a N*-phase gradually appears whose liquid crystalline range increases. For the dodecyl spacer no smectic phase is observed anymore. For the nonyl spacer reentrant behavior is found (N*-TGB-SmA-TGB-N*). Reentrant behavior, probably N*-TGB-N*, is also observed for a related compound with an ester spacer.
    Liquid crystalline properties of salicylaldiminie-based dimers: influence of terminal alkyl chain length and central part
    Achten, R. ; Koudijs, A. ; Karczmarzyk, Z. ; Marcelis, A.T.M. ; Sudhölter, E.J.R. - \ 2004
    Liquid Crystals 31 (2004)2. - ISSN 0267-8292 - p. 215 - 227.
    banana-shaped molecules - smectic mesophase properties - substituted central core - helical superstructures - mesomorphic properties - lateral substituents - phases - mesogens - spacer - behavior
    The synthesis and thermotropic properties of four homologous series of salicylaldimine-based dimer liquid crystals are reported. Two 4-(4-alkoxy-2-hydroxybenzylideneamino) benzoyloxy groups are connected to a central part consisting of a 1,3-phenylene, 1,5-pentylene, 2,2-dimethyl- 1,5-pentylene or 3,3-dimethyl-1,5-pentylene unit. The terminal alkoxy chains have been varied from 4 to 16 carbon atoms in length. All the compounds exhibit liquid crystalline phases whose behaviour depends on the nature of the central part and the length of the alkoxy terminal chains. All compounds of the series with the central phenyl part exhibit enantiotropic B-phases, and the sequence B-6 - B-1 - B-2 on increasing terminal chain length was observed. Replacement of the phenyl group with a pentyl central group partly suppresses the formation of B-phases. The longer homologues of this series show the B1 phase, while the shorter exhibit an intercalated SmCc mesophase. The introduction of methyl substituents to the pentyl spacer causes the melting points to fall dramatically and the formation of B-phases is totally suppressed. The compounds with the long tails show intercalated SmA(c) phases and those with short tails show intercalated SmCc phases.
    Symmetrical dimer liquid crystals with tilted smectic phases
    Achten, R. ; Marcelis, A.T.M. ; Koudijs, A. ; Sudhölter, E.J.R. - \ 2004
    Molecular Crystals and Liquid Crystals 411 (2004)1. - ISSN 1542-1406 - p. 177 - 184.
    alkylene spacer
    Three series of symmetrical dimer liquid crystals, i.e. bis(dodecyloxybenzoyloxybenzoyloxy)alkanes (BC12) and bis(dodecyloxy- and hexadecyloxybenzoyloxyphenyl) alkanedicarboxylates (QC12 and QC16) with a spacer ranging from, two to eight methylene units, have been synthesized and their thermotropic properties were characterized. The isotropization temperatures show a pronounced odd - even effect as a function of the parity of the spacers. Most compounds exhibit a SmC mesophase. The QC12 and QC16 compounds, with on eight methylene spacer, possess an additional low temperature tilled SmI or SmF mesophase. Changing the orientation of the ester group as in the BC12 series results in a dramatic change of the thermotropic behavior.
    Cholesterol-containing liquid crystal dimmers with ether linkages between the spacer and mesogenic units
    Marcelis, A.T.M. ; Koudijs, A. ; Karczmarzyk, Z. ; Sudhölter, E.J.R. - \ 2003
    Liquid Crystals 30 (2003)11. - ISSN 0267-8292 - p. 1357 - 1364.
    twist grain-boundary - dimesogenic compounds - optical-properties - mesomorphic behavior - smectic phases - terminal group - oligomers - lengths - moiety - series
    Three series of chiral liquid crystalline dimers were investigated, having a cholesteryl and a cyanobiphenylyl, butoxybiphenylyl or hexyloxybiphenylyl group connected to a variable alkyl spacer through ether linkages. Their properties were compared with those of the corresponding ester derivatives. The phase behaviour of compounds with ether and ester linkages is comparable, showing N* and SmA phases. The melting points of the compounds with ether linkages are in the same range as those of the ester compounds, but the liquid crystal transition temperatures are lower. The smectic layer spacings and smectic ordering properties are also similar. The cyanobiphenylyl compounds have an interdigitated SmA layer structure, which shows a small odd - even effect with spacer parity. The alkoxybiphenylyl compounds have a monolayer SmA phase for short spacers and an intercalated SmA phase for longer spacers. The selective reflection wavelengths of the chiral nematic phase of the ether compounds are lower than those of the corresponding ester compounds. The transition from N* to interdigitated or monolayer SmA is accompanied by a strong increase in the selective reflection wavelength, indicative of an intermediate TGB phase. This is absent for the transition from N* to intercalated SmA.
    Aggregation of different amino acid conjugates of cholic acid in aqueous solution
    Willemen, H.M. ; Vermonden, T. ; Koudijs, A. ; Marcelis, A.T.M. ; Sudhölter, E.J.R. - \ 2003
    Colloids and Surfaces. A: Physicochemical and Engineering Aspects 218 (2003). - ISSN 0927-7757 - p. 59 - 64.
    bile-acids - glycine - salts
    A series of cholic acid derivatives was synthesized with a variety of alpha-amino acids coupled via an amide bond. These conjugates form aggregates in aqueous solutions. Cryo-transmission electron microscopy (TEM) images show the presence of small micelles with a size of about 5 nm for all compounds. Critical micelle concentration (CMC) values vary slightly with the molecular structure. A small decrease in CMC was found upon increasing the hydrophobicity of the amino acid. The CMC of the tyrosine conjugate showed a small pH-effect, increasing at high pH. (C) 2003 Elsevier Science B.V. All rights reserved.
    Micelle formation antimicrobial activity of cholic acid derivates with three permanent ionic head groups
    Willemen, H.M. ; Smet, L.C.P.M. de; Koudijs, A. ; Cohen-Stuart, M.A. ; Heikamp-de Jong, I.G.A.M. ; Marcelis, A.T.M. ; Sudhölter, E.J.R. - \ 2002
    Angewandte Chemie-International Edition 41 (2002). - ISSN 1433-7851 - p. 4275 - 4277.
    New living polymers in aqueous solutions and colloidal systems
    Vermonden, T. ; Koudijs, A. ; Marcelis, A.T.M. ; Sudhölter, E.J.R. - \ 2001
    In: Book of abstracts : SAFIN 2001, Euroconference on self-assembled fibrillar networks, Autran, France, 24-28 november 2001 - p. 94 - 94.
    Influence of spacer and terminal group lengths on the smectic ordering of cholesterol-containing dimer liquid crystals
    Marcelis, A.T.M. ; Koudijs, A. ; Klop, E.A. ; Sudhölter, E.J.R. - \ 2001
    Liquid Crystals 28 (2001)6. - ISSN 0267-8292 - p. 881 - 887.
    The smectic properties of four series of dimer liquid crystals containing cholesteryl and biphenylyl groups were investigated by polarization microscopy, DSC and X-ray diffraction. Compounds that contain the strongly dipolar cyanobiphenylyl group exhibit a smectic layer spacing that is about 1.7 times the length of the molecule. Three series of alkoxybiphenylylcontaining dimers exhibit two other smectic modifications. For short spacers, a smectic layer spacing is observed that is about the same length as the molecule and for long spacers the smectic layer spacing is about half the length of the molecule. In the latter cases the entropy change at the SmA-N* transition is clearly larger than for the compounds with the other smectic modifications. One or two compounds in each alkoxybiphenylyl-containing series, that have similar spacer length and terminal group length and have an odd number of flexible units in the spacer, exhibit only a chiral nematic phase, and no smectic phase.
    New Living polymers in aqueous solutions and colloid systems
    Vermonden, T. ; Gucht, J. van der; Koudijs, A. ; Marcelis, T. ; Besseling, K. ; Sudh"lter, E. ; Fleer, G. ; Cohen Stuart, M. - \ 2000
    In: Dutch-Israël Symposium on Molecular Avenues In Material And Surface Science, University of Twente, Enschede, ICSC Drienerburght, 23-25 October, 2000 - p. P28 - P28.
    Check title to add to marked list
    << previous | next >>

    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.