Search PubMed⌕ Search

Biomedical subjects

Jurriaan Huskens

Publications and source records attributed to Jurriaan Huskens.

At least 19 recordsLinked to original sources
PubMed2007

Redox-controlled interaction of biferrocenyl-terminated dendrimers with beta-cyclodextrin molecular printboards.

This paper describes the synthesis and electrochemistry of biferrocenyl-terminated dendrimers and their beta-cyclodextrin (beta-CD) inclusion complexes in aqueous solution and at surfaces. Three generations of poly(propylene imine) (PPI) dendrimers, decorated with 4, 8, and 16 biferrocenyl (BFc) units, respectively, were synthesized. A water-soluble BFc derivative forms stable inclusion complexes with beta-CD. The intrinsic binding constant is K(i)=2.5 x 10(4) M(-1). The BFc dendrimers were solubilized in water by complexation of the end groups with beta-CD, resulting in large water-soluble supramolecular assemblies. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) showed that all the end groups are complexed to beta-CD. Adsorption of the dendrimers at self-assembled monolayers (SAMs) of heptathioether-functionalized beta-CD on gold ("molecular printboards") resulted in stable monolayers of the dendrimers due to the formation of multivalent host-guest interactions between the BFc end groups of the dendrimers and the immobilized beta-CD molecules. The number of interacting end groups is 3, 4, and 4 for dendrimer generations 1, 2, and 3, respectively. The complexation of BFc to beta-CD is sensitive to the oxidation state of the BFc unit. Oxidation of neutral BFc-Fe(2) ((II,II)) to the cationic, mixed-valence biferrocenium BFc-Fe(2) ((II,III)+) resulted in dissociation of the host-guest complexes. Scan-rate-dependent CV and DPV analyses of the dendrimer-beta-CD assemblies immobilized at the beta-CD host surface and in solution revealed that the dendrimers are oxidized in three steps. First, the surface-beta-CD-bound BFc moieties are oxidized to the mixed-valence state, Fe(2) ((II,III)+), followed by the oxidation of the non-surface-interacting BFc groups to the Fe(2) ((II,III)+) state. The third step involves the oxidation of all the BFc moieties to the Fe(2) ((III,III)2+) state.

Dendrimers↗
PubMed2006

Expression of a supramolecular complex at a multivalent interface.

The multivalent binding of a supramolecular complex at a multivalent host surface by combining the orthogonal beta-cyclodextrin (CD) host-guest and metal ion-ethylenediamine coordination motifs is described. As a heterotropic, divalent linker, an adamantyl-functionalized ethylenediamine derivative was used. This was complexed with Cu(II) or Ni(II). The binding of the complexes to a CD self-assembled monolayer (SAM) was studied as a function of pH by means of surface plasmon resonance (SPR) spectroscopy. A heterotropic, multivalent binding model at interfaces was used to quantify the multivalent enhancement at the surface. The Cu(II) complex showed divalent binding to the CD surface with an enhancement factor higher than 100 relative to the formation of the corresponding divalent complex in solution. Similar behavior was observed for the Ni(II) system. Although the Ni(II) system could potentially be trivalent, only divalent binding was observed at the CD SAMs, which was confirmed by desorption experiments.

Copper↗
PubMed2006

Oxidized gold as an ultrathin etch resist applied in microcontact printing.

In this report it is described how a gold surface can be treated with an oxygen plasma to become an effective etch mask, with its etch resistive properties based upon electrostatic repulsion. Such a treated gold layer is only temporarily stable and may therefore be employed as a temporary etch barrier that introduces no contaminating species. Deterioration of the barrier properties can be locally expedited in a scheme that is compatible with microcontact printing. This has been achieved by the microcontact printing of a reductant on a fully oxidized gold substrate.

Journal Article↗
PubMed2006

Controlling the supramolecular assembly of redox-active dendrimers at molecular printboards by scanning electrochemical microscopy.

Redox-active ferrocenyl (Fc)-functionalized poly(propylenimine) (PPI) dendrimers solubilized in aqueous media by complexation of the Fc end groups with beta-cyclodextrin (betaCD) were immobilized at monolayers of betaCD on glass ("molecular printboards") via multiple host-guest interactions. The directed immobilization of the third-generation dendrimer-betaCD assembly G3-PPI-(Fc)16-(betaCD)16 at the printboard was achieved by supramolecular microcontact printing. The redox activity of the patterned dendrimers was mapped by scanning electrochemical microscopy (SECM) in the positive feedback mode using [IrCl(6)](3-) as a mediator. Local oxidation of the Fc-dendrimers by the microelectrode-generated [IrCl(6)](2-) resulted in an effective removal of the Fc-dendrimers from the host surface since the oxidation of Fc to the oxidized form (Fc+) leads to a concomitant loss of affinity for betaCD. Thus, SECM provided a way not only to image the surface, but also to control the binding of the Fc-terminated dendrimers at the molecular printboard. Additionally, the electrochemical desorption process could be monitored in time as the dendrimer patterns were gradually erased upon multiple scans.

Dendrimers↗
PubMed2006

Ferrocenyl-functionalized silica nanoparticles: preparation, characterization, and molecular recognition at interfaces.

Ferrocenyl-functionalized silica nanoparticles (Fc-SiO(2), 6a-6c) of about 60 nm with supramolecular "guest" properties were prepared. Nanoparticles 6a-6c differed by the addition of different molar ratios of starting compounds during the functionalization step, i.e., 1:0, 1:10, and 1:90 of 2-ferrocenyl amidoethoxyethanol and diethylene glycol for 6a,6b, and 6c, respectively. X-ray photoelectron spectroscopy (XPS) proved the presence of ferrocenyl groups on the surfaces of 6a-6c, whereas the elemental analysis revealed an iron content of particles 6a-6c of 0.10-0.16%. Dynamic light scattering (DLS) results showed that, compared with 6a, 6b dispersed well in aqueous media, possibly due to the presence of diethylene glycol at the surfaces of 6b that significantly increases its overall hydrophilicity. Cyclic voltammetry of 6b indicated a totally irreversible system and a "mixed" diffusion-adsorption behavior, which is attributed to sluggish electron transfer. The shifted |I(p,C)/I(p,A*)| ratio showed that the ferrocenyl groups are robustly attached to the nanoparticle surface within the experimental potential range. The supramolecular recognition of Fc-SiO(2) nanoparticles at interfaces was verified by their adsorption on beta-cyclodextrin (beta-CD) self-assembled monolayers, as monitored by surface plasmon resonance (SPR) spectroscopy. The ability of the Fc-SiO(2) nanoparticles to form host-guest interactions was also demonstrated by the attachment of beta-CD-functionalized Au nanoparticles (2.8 nm) on the Fc-SiO(2) surfaces, when mixed in solution.

Journal Article↗
PubMed2006

Multivalent interactions at interfaces.

Multivalency describes the interaction between multivalent receptors and multivalent ligands. It plays a pivotal role in biochemistry, particularly in protein-carbohydrate interactions, both in solution and at interfaces. At interfaces in particular, multivalency is often poorly understood in a quantitative sense. Research on multivalency is currently an interplay of the fields of biochemistry and supramolecular chemistry. On the one hand, the understanding of supramolecular interactions at interfaces provides a tool for the quantitative description of multivalency at interfaces. On the other hand, the multivalent design rules developed in biological chemistry are applied in novel supramolecular nanostructures. The current review focuses on the former perspective (i.e. the use of well defined supramolecular platforms that function as model systems for understanding multivalent phenomena at interfaces).

Cyclodextrins↗
PubMed2006

Heavyweight dendritic inks for positive microcontact printing.

Poly(propylene imine) dendrimers with dialkyl sulfide end groups were prepared and developed as inks for positive microcontact printing ((+)muCP) on gold. Long (C10H21-S-C10H20-), medium (C3H7-S-C4H8-), and short (CH3-S-CH2-) dialkyl sulfide end groups were attached to second- and third-generation PPI dendrimers to create a family of dendritic sulfides. The dendritic inks flatten upon adsorption and form monolayers on gold. (+)muCP was performed on gold using commercially available poly(dimethylsiloxane) as stamp material and n-octadecanethiol as etch resist. The gold beneath the dendrimers was selectively etched away with an acidic Fe(NO3)3/thiourea solution to give the positive copy of the original master pattern. The multivalent sulfide attachment and the relatively high molecular mass of these dendrimers ensured minimal lateral ink spreading and thus optimal feature reproducibility. Contact times were varied to analyze the spreading rates of the dendritic inks. The spreading rates of the dendritic inks were found to be much lower than that of pentaerythritol tetrakis(3-mercaptopropionate). (+)muCP with the new inks was extended to submicrometer features. Optical microscopy, scanning electron microscopy, and atomic force microscopy were used to characterize the etched samples. Lines with a width of 100 nm were faithfully replicated with the third-generation dendrimers bearing medium (C3-S-C4-) end groups.

Journal Article↗
PubMed2006

Molecular printboards: versatile platforms for the creation and positioning of supramolecular assemblies and materials.

This tutorial review describes the development of molecular printboards, which are tailor-made surfaces functionalized with receptor (host) molecules. Such substrates can be used for the binding of complementary ligand (guest) molecules through multivalent interactions. Supramolecular multivalent interactions are ideal to attain a quantitative and fundamental understanding of multivalency at interfaces. Because of their quantitative interpretation, the focus is on (i) the interaction of cyclodextrin host surfaces with multivalent hydrophobic guest molecules, (ii) the vancomycin-oligopeptide system, and (iii) the multivalent binding of histidine-tagged proteins to NiNTA receptor surfaces. The review will be of interest to researchers in the fields of supramolecular chemistry, chemical biology, surface chemistry, and molecular recognition.

Journal Article↗
PubMed2006

Ink dependence of poly(dimethylsiloxane) contamination in microcontact printing.

Poly(dimethylsiloxane) (PDMS) is the most widely used stamp material in microcontact printing. It has excellent properties with respect to versatility, chemical inertness, and mechanical stability. However, it has an inclination to contaminate printed substrates with low molecular weight siloxane fragments. In this study, it is shown, by a combination of lateral force microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, that the extent of the PDMS-induced contamination is dependent on the nature of the ink used. The highest degree of contamination was found for relatively polar inks, whereas apolar alkanethiol inks were found to shield the substrate from contamination. This is interpreted in terms of the contaminating species being polar in nature.

Journal Article↗
PubMed2006

Writing with molecules on molecular printboards.

Nanotechnology aspires to create functional materials with characteristic dimensions of the order 1-100 nm. One requirement to make nanotechnology work is to precisely position molecules and nanoparticles on surfaces, so that they may be addressed and manipulated for bottom-up construction of nanoscale devices. Here we review the concept of a "molecular printboard". A molecular printboard is a monolayer of host molecules on a solid substrate on which guest molecules can be attached with control over position, binding strength, and binding dynamics. To this end, cyclodextrins were immobilized in monomolecular layers on gold, on silicon wafers and on glass. Guest molecules (for example, adamantane and ferrocene derivatives) bind to these host surfaces through supramolecular, hydrophobic inclusion interaction. Multivalent interactions are exploited to tune the binding strength and dynamics of the interaction of guest molecules with the printboard. Molecules can be positioned onto the printboard using supramolecular microcontact printing and supramolecular dip-pen nanolithography due to the specific interaction between the 'ink' and the substrate. In this way, nanoscale patterns can be written and erased on the printboard. Currently, the molecular printboard is exploited for nanofabrication, for example in combination with electroless deposition of metals and by means of supramolecular layer-by-layer deposition.

Journal Article↗
PubMed2006

Attachment of streptavidin to beta-cyclodextrin molecular printboards via orthogonal host-guest and protein-ligand interactions.

Streptavidin (SAv) is attached to beta-cyclodextrin (beta-CD) self-assembled monolayers (SAMs) via orthogonal host-guest and SAv-biotin interactions. The orthogonal linkers consist of a biotin functionality for binding to SAv and adamantyl functionalities for host-guest interactions at beta-CD SAMs. SAv complexed to excess monovalent linker in solution and then attached to a beta-CD SAM could be removed by rinsing with a 10 mM beta-CD solution. When SAv was attached to the beta-CD SAM via the divalent linker, it was impossible to remove SAv from the surface by the same rinsing procedure. This is interpreted by assuming that two SAv binding pockets are oriented towards the beta-CD SAM resulting in (labile) divalent and (stable) tetravalent beta-CD-adamantyl interactions for the mono- and divalent linkers, respectively. This was confirmed by experiments at varying beta-CD concentrations. When the [linker]/[SAv] ratio is reduced, a clear trend in the divalent-linker case is seen: the less linker the more protein could be removed from the surface. It is proven that the orthogonality of the binding motifs and the stability of the divalent linker at the beta-CD SAM allows the stepwise assembly of the complex at the beta-CD SAM by first adsorbing the linker, followed by SAv. This stepwise assembly allows the controlled heterofunctionalization of surface-immobilized SAv.

Adsorption↗
PubMed2006

Edge transfer lithography using alkanethiol inks.

Edge lithographic patterning techniques are based on the utilization of the edges of micrometer-sized template features for the reproduction of submicrometer structures. Edge transfer lithography (ETL) permits local surface modification in a single step by depositing self-assembled monolayers onto a metal substrate selectively along the feature edges of an elastomeric stamp. In this report two stamp designs are described that now allow for the use of alkanethiol inks in ETL and their use as etch resists to reproduce submicrometer structures in gold. Anisotropically modified stamps are shown to combine the potential for very high-resolution patterning with the versatility and simplicity of microcontact printing.

Alkanes↗
PubMed2005

Multivalent dendrimers at molecular printboards: influence of dendrimer structure on binding strength and stoichiometry and their electrochemically induced desorption.

A fundamental understanding of multivalency can have a profound influence on bottom-up nanofabrication. For this purpose, three different types of ferrocenyl (Fc) functionalized dendrimers of generations 1-5 with various spacer groups were adsorbed at self-assembled monolayers (SAMs) of heptathioether-functionalized beta-cyclodextrin (betaCD) on gold. The dendrimers formed kinetically stable supramolecular assemblies at the betaCD host surface having up to eight multivalent supramolecular interactions, but could be efficiently removed from the host surface by electrochemical oxidation of the Fc end groups. Dendrimer desorption and re-adsorption could be repeated a number of times without significant decomposition of the system. The stoichiometries of the dendrimers at the surface were determined using cyclic voltammetry (CV). These were quantitatively confirmed for the lower generations by surface plasmon resonance (SPR) titrations of the dendrimers to the betaCD SAM. Measuring CV and SPR simultaneously gave crucial mechanistic information on the electrochemically induced desorption of the dendrimers from the host surface. The redox-active dendrimers effectively blocked the host surface for binding other molecules, e.g. adamantyl-functionalized dendrimers, but electrochemically induced release of the blocking layer revealed the host surface to which the adamantyl dendrimers could then bind.

Journal Article↗
PubMed2005

Chemically patterned flat stamps for microcontact printing.

Locally oxidized patterns on flat poly(dimethylsiloxane) stamps for microcontact printing were used as a platform for the transfer of a hydrophilic fluorescent ink to a glass substrate. The contrast was found to be limited. These locally oxidized patterns were conversely used as barriers for the transfer of hydrophobic n-octadecanethiol. In this case a good contrast was obtained, but the pattern was found to be susceptible to defects (cracks) in the barrier layer. Local stamp surface oxidation and subsequent modification with 1H,1H,2H,2H-perfluorodecyltrichlorosilane, for use as a barrier in the transfer of n-octadecanethiol, 16-mercaptohexadecanoic acid, and octanethiol, resulted in remarkably good contrast and stable patterns. The improved ink transfer control is ascribed to the reduction of undesired surface spreading and a superior mechanical stability of the stamp pattern. This new approach substantially expands the applicability of microcontact printing and provides a tool for the faithful reproduction of even extremely low filling ratio patterns.

Journal Article↗
PubMed2005

Ionizable (Thia)calix[4]crowns as highly selective 226Ra2+ ionophores.

The 226Ra2+ selectivity of the ionizable (thia)calix[4]crowns 1-4 was determined in the presence of a large excess of the most common alkali and alkaline earth cations. Selective 226Ra2+ (2.9 x 10(-)(8) M) extraction occurs even at extremely high M(n+)/226Ra2+ ratios of 3.5 x 10(7) [M(n+) = Na+, K+, Rb+, Cs+, Mg2+, Ca2+, and Sr2+ (1M)] and an ionophore concentration of 10(-4) M. The selectivity coefficients log(K(Ra)(ex)/K(M)(ex)) are approximately 3.5 for Mg2+, Ca2+, and Sr2+. In the presence of Ba2+, which has very similar chemical properties, only the thiacalix[4]crown-6 derivative 4 showed a selectivity for 226Ra2+. In addition to the remarkable 226Ra2+ selectivities, the effective pH range (pH 8-13) of the thiacalix[4]crown dicarboxylic acids (3 and 4) allows for full regeneration of the ionophores at lower pH values (pH <6).

Journal Article↗
PubMed2005

Supramolecular microcontact printing and dip-pen nanolithography on molecular printboards.

The transfer of functional molecules onto self-assembled monolayers (SAMs) by means of soft and scanning-probe lithographic techniques-microcontact printing (muCP) and dip-pen nanolithography (DPN), respectively-and the stability of the molecular patterns during competitive rinsing conditions were examined. A series of guests with different valencies were transferred onto beta-cyclodextrin- (beta-CD-) terminated SAMs and onto reference hydroxy-terminated SAMs. Although physical contact was sufficient to generate patterns on both types of SAMs, only molecular patterns of multivalent guests transferred onto the beta-CD SAMs were stable under the rinsing conditions that caused the removal of the same guests from the reference SAMs. The formation of kinetically stable molecular patterns by supramolecular DPN with a lateral resolution of 60 nm exemplifies the use of beta-CD-terminated SAMs as molecular printboards for the selective immobilization of printboard-compatible guests on the nanometer scale through the use of specific, multivalent supramolecular interactions. Electroless deposition of copper on the printboard was shown to occur selectively on the areas patterned with dendrimer-stabilized gold nanoparticles.

Journal Article↗
PubMed2005

Supramolecular layer-by-layer assembly: alternating adsorptions of guest- and host-functionalized molecules and particles using multivalent supramolecular interactions.

The stepwise construction of a novel kind of self-assembled organic/inorganic multilayers based on multivalent supramolecular interactions between guest-functionalized dendrimers and host-modified gold nanoparticles has been developed, yielding supramolecular layer-by-layer assembly. The deposition process was monitored by surface plasmon resonance spectroscopy. Further characterization of the multilayer films was performed by means of UV/vis absorption spectroscopy, which showed a linear increase in absorption with the number of bilayers. The growth of the gold nanoparticle plasmon absorption band corresponded to approximately a dense monolayer of gold nanoparticles per bilayer. Ellipsometry and atomic force microscopy (AFM) scratching experiments were used to measure the development of the film thickness with the number of bilayers, confirming linear growth and a thickness increase of approximately 2 nm/bilayer.

Journal Article↗