Van t Hoff Institute for Molecular science

Amsterdam, Netherlands

Van t Hoff Institute for Molecular science

Amsterdam, Netherlands
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Gunbas D.D.,Van T Hoff Institute for Molecular science | Zalewski L.,Van T Hoff Institute for Molecular science | Zalewski L.,Reckitt Benckiser | Brouwer A.M.,Van T Hoff Institute for Molecular science
Chemical Communications | Year: 2010

In rotaxane 1, two co-conformations are populated in CDCl3 at temperatures between 250 and 330 K. The thermodynamic parameters show strong enthalpy-entropy compensation, and a non-negligible heat capacity difference between the two forms. © The Royal Society of Chemistry.

Navarro J.R.G.,CNRS Systems and Applications of Information Technologies and Energy Laboratory | Plugge M.,Van T Hoff Institute for Molecular science | Loumaigne M.,University Paris - Sud | Sanchez-Gonzalez A.,University of Pisa | And 4 more authors.
Photochemical and Photobiological Sciences | Year: 2010

The binding of disulfides to gold nanoparticles was investigated using fluorescence spectroscopy and a perylene-monoimide dye coupled to a dissymmetric disulfide via a tetraethyleneglycolalkyl chain (PMImSS). Quantum chemical calculations using the polarizable continuum model (PCM) predict a strong quenching of perylene-monoimide fluorescence by gold nanoparticles as a result of efficient excitation energy transfer from the dye to the particle. Such quenching is indeed observed when unfunctionalised gold nanoparticles are added to a solution of PMImSS. The fluorimetric titration curves show behaviour indicative of the existence of an equilibrium between free and bound ligands (association constant 5 × 105 M-1), whereas the affinity of thiols and disulfide for gold surfaces is in general assumed to be much higher. Gold nanoparticles fully functionalised with PMImSS were synthesised and purified. Fluorescence correlation spectroscopy shows the appearance of free PMImSS ligands in dilute (approx. pM) suspensions of these PMImSS-functionalised nanoparticles over a period of several days. © 2010 The Royal Society of Chemistry and Owner Societies.

Gargano A.F.G.,University of Vienna | Gargano A.F.G.,Van t Hoff Institute for Molecular science | Lammerhofer M.,University of Tübingen | Lonn H.,Astrazeneca | And 2 more authors.
Journal of Chromatography A | Year: 2014

Mucin glycoproteins belong to a class of high molecular weight, heavy glycosylated, proteins that together with water, salts and lipids constitute mucous secretions. Particular disease states (e.g. obstructive chronic bronchitis and ovarian tumor) are known to modify the composition and the thickness of those barriers. Therefore, it is important to address whether the absorption of potential drug candidates to be administered is influenced by the presence of interaction with this class of proteins. Typically, the methods adopted to characterize drug-protein interaction are dialysis, ultrafiltration and gel filtration. Besides these, bio-affinity chromatographic methods have demonstrated to be valuable tools offering the advantageous characteristics such as simplicity, efficiency, high-throughput capability and robustness. The present contribution reports on the synthesis and analytical characterization of a new chromatographic stationary phase based on covalently immobilized mucin and explores the use of LC-UV affinity zonal chromatography as a tool to screen drugs for their affinity to mucin. A series of different binding chemistries for the covalent linkage of mucin to silica-based supports as well as distinct immobilization protocols (static and dynamic) have been evaluated in order to optimize surface coverage. Resultant stationary phases have been characterized chromatographically by studying the effect of mobile phase and analyte structure on the distribution and retention of test compounds. As conclusive study, we report the evaluation of the retention characteristics of 41 drug-like compounds (having heterogeneous chemical properties) for their interaction with this novel stationary phase. © 2014 Elsevier B.V.

Meeuwissen J.,Van T Hoff Institute for Molecular science | Reek J.N.H.,Van T Hoff Institute for Molecular science
Nature Chemistry | Year: 2010

Supramolecular catalysis - the assembly of catalyst species by harnessing multiple weak intramolecular interactions - has, until recently, been dominated by enzyme-inspired approaches. Such approaches often attempt to create an enzyme-like 'active site' and have concentrated on reactions similar o those catalysed by enzymes themselves. Here, we discuss the application of supramolecular assembly to the more traditional transition metal catalysis and to small-molecule organocatalysis. The modularity of self-assembled multicomponent catalysts means that a relatively small pool of catalyst components can provide rapid access to a large number of catalysts that can be evaluated for industrially relevant reactions. In addition, we discuss how catalyst-substrate interactions can be tailored to direct substrates along particular reaction paths and selectivities. © 2010 Macmillan Publishers Limited. All rights reserved.

Lechner W.,Van T Hoff Institute for Molecular science | Dellago C.,University of Vienna | Bolhuis P.G.,Van T Hoff Institute for Molecular science
Journal of Chemical Physics | Year: 2011

We study the mechanisms of the homogeneous crystal nucleation from the supercooled liquid to the crystal phase in the Gaussian core model for colloidal suspensions with the aim to find optimal reaction coordinates. We introduce a set of novel collective variables based on the local structure of particles. By applying likelihood maximization of the committor function for the reweighted path ensemble constructed by replica exchange transition interface sampling, we select the optimal reaction coordinates from the set of collective variables. We find that the size of the cloud of prestructured particles surrounding the crystalline nucleus enhances the description of the transition. Further, we show that the rearrangement of the inner core of the nucleus according to Ostwalds step rule is a separate process, independent of the growth of the nucleus. © 2011 American Institute of Physics.

Veguillas M.,Manchester Metropolitan University | Sola R.,Manchester Metropolitan University | Fernandez-Ibanez M.A.,Van T Hoff Institute For Molecular Science | Macia B.,Manchester Metropolitan University
Tetrahedron Asymmetry | Year: 2016

An efficient catalyst for the enantioselective synthesis of chiral methyl carbinols from aldehydes is presented. The system uses methyltriisopropoxytitanium as a nucleophile and a readily available binaphthyl derivative as a chiral ligand. The enantioselective methylation of both aromatic and aliphatic aldehydes proceeds with good yields and high enantioselectivities under mild conditions. © 2016 Elsevier Ltd

Lechner W.,Van T Hoff Institute for Molecular science | Dellago C.,University of Vienna | Bolhuis P.G.,Van T Hoff Institute for Molecular science
Physical Review Letters | Year: 2011

For the homogeneous crystal nucleation process in a soft-core colloid model, we identify optimal reaction coordinates from a set of novel order parameters based on the local structure within the nucleus, by employing transition path sampling techniques combined with a likelihood maximization of the committor function. We find that nucleation is governed by solid clusters that consist of an hcp core embedded within a cloud of surface particles that are highly correlated with their nearest neighbors but not ordered in a high-symmetry crystal structure. The results shed new light on the interpretation of the surface and volume terms in classical nucleation theory. © 2011 American Physical Society.

Detz R.J.,Van T Hoff Institute for Molecular science | Abiri Z.,Van T Hoff Institute for Molecular science | Le Griel R.,Van T Hoff Institute for Molecular science | Hiemstra H.,Van T Hoff Institute for Molecular science | Van Maarseveen J.H.,Van T Hoff Institute for Molecular science
Chemistry - A European Journal | Year: 2011

A copper catalyst with a chiral pyridine-2,6-bisoxazoline (pybox) ligand was used to convert a variety of propargylic esters with different side chains (R=Ar, Bn, alkyl) into their amine counterparts in very high yields and with good enantioselectivities (up to 90% enantiomeric excess (ee)). Different amine nucleophiles were applied in the reactions and the highest enantioselectivities were obtained for aniline and its analogues. Interestingly, some carbon nucleophiles could also be used and with indoles excellent ee values were obtained (up to 98% ee). The versatility of the propargylic amines obtained was demonstrated by their further elaboration to formal total syntheses of the antibiotic (+)-anisomycin and the cytokine modulator (-)-cytoxazone. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kerschgens I.P.,Van T Hoff Institute for Molecular science | Claveau E.,Van T Hoff Institute for Molecular science | Wanner M.J.,Van T Hoff Institute for Molecular science | Ingemann S.,Van T Hoff Institute for Molecular science | And 2 more authors.
Chemical Communications | Year: 2012

The pharmacologically interesting indole alkaloids (-)-mitragynine, (+)-paynantheine and (+)-speciogynine were synthesised in nine steps from 4-methoxytryptamine by a route featuring (i) an enantioselective thiourea-catalysed Pictet-Spengler reaction, providing the tetrahydro-β- carboline ring and (ii) a Pd-catalysed Tsuji-Trost allylic alkylation, closing the D-ring. This journal is © The Royal Society of Chemistry 2012..

PubMed | Van t Hoff Institute for Molecular science and Hill International
Type: Journal Article | Journal: Analytical chemistry | Year: 2016

Online comprehensive two-dimensional liquid chromatography (LC LC) offers ways to achieve high-performance separations in terms of peak capacity (exceeding 1000) and additional selectivity to realize applications that cannot be addressed with one-dimensional chromatography (1D-LC). However, the greater resolving power of LC LC comes at the price of higher dilutions (thus, reduced sensitivity) and, often, long analysis times (>100 min). The need to preserve the separation attained in the first dimension ((1)D) causes greater dilution for LC LC, in comparison with 1D-LC, and long analysis times to sample the (1)D with an adequate number of second dimension separations. A way to significantly reduce these downsides is to introduce a concentration step between the two chromatographic dimensions. In this work we present a possible active-modulation approach to concentrate the fractions of (1)D effluent. A typical LC LC system is used with the addition of a dilution flow to decrease the strength of the (1)D effluent and a modulation unit that uses trap columns. The potential of this approach is demonstrated for the separation of tristyrylphenol ethoxylate phosphate surfactants, using a combination of hydrophilic interaction and reversed-phase liquid chromatography. The modified LC LC system enabled us to halve the analysis time necessary to obtain a similar degree of separation efficiency with respect to UHPLC based LC LC and of 5 times with respect to HPLC instrumentation (40 compared with 80 and 200 min, respectively), while at the same time reducing dilution (DF of 142, 299, and 1529, respectively) and solvent consumption per analysis (78, 120, and 800 mL, respectively).

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