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61.
Equation of state modeling of the phase equilibria of ionic liquid mixtures at low and high pressure
Karakatsani EK Economou IG Kroon MC Bermejo MD Peters CJ Witkamp GJ 《Physical chemistry chemical physics : PCCP》2008,10(40):6160-6168
Accurate design of processes based on ionic liquids (ILs) requires knowledge of the phase behavior of the systems involved. In this work, the truncated perturbed chain polar statistical associating fluid theory (tPC-PSAFT) is used to correlate the phase behavior of binary and ternary IL mixtures. Both non-polar and polar solvents are examined, while methyl imidazolium ILs are used in all cases. tPC-PSAFT accounts explicitly for weak dispersion interactions, highly directive polar interactions between permanent dipolar and quadrupolar molecules and association between hydrogen bonding molecules. For mixtures of non-polar solvents, tPC-PSAFT predicts accurately the binary mixture data. For the case of polar solvents, a binary interaction parameter is fitted to the experimental data and the agreement between experiment and correlation is very good in all cases. 相似文献
62.
Combining triflic acid-promoted glycosylations of trichloroacetimidates with reductive opening of benzylidene acetals with triflic acid and triethylsilane as one-pot procedures provides access to a wide range of disaccharides and 2,4- and 3,4-branched trisaccharides. 相似文献
63.
C Clarke R J Woods J Gluska A Cooper M A Nutley G J Boons 《Journal of the American Chemical Society》2001,123(49):12238-12247
The interactions of trimannosides 1 and 2 with Con A were studied to reveal the effects of displacement of well-ordered water molecules on the thermodynamic parameters of protein-ligand complexation. Trisaccharide 2 is a derivative of 1, in which the hydroxyl at C-2 of the central mannose unit is replaced by a hydroxyethyl moiety. Upon binding, this moiety displaces a conserved water molecule present in the Con A binding site. Structural studies by NMR spectroscopy and MD simulations showed that the two compounds have very similar solution conformational properties. MD simulations of the complexes of Con A with 1 and 2 demonstrated that the hydroxyethyl side chain of 2 can establish the same hydrogen bonds in a low energy conformation with the protein binding site as those mediated by the water molecule in the complex of 1 with Con A. Isothermal titration microcalorimetry (ITC) measurements showed that 2 has a more favorable entropy of binding compared to 1. This term, which was expected, arises from the return of the highly ordered water molecule to bulk solution. The favorable entropy term was, however, offset by a relatively large unfavorable enthalpy term. This observation was rationalized by comparing the extent of hydrogen bond and solvation changes during binding. It is proposed that an indirect interaction through a water molecule will provide a larger number of hydrogen bonds in the complex that have higher occupancies than in bulk solution, thereby stabilizing the complex. 相似文献
64.
A practical approach for the stereoselective introduction of beta-arabinofuranosides has been developed on the basis of locking an arabinosyl donor in a conformation in which nucleophilic attack from the beta face is favored. The new glycosyl donor was designed by analyzing optimized geometries of low-energy conformers of the arabinofuranosyl oxacarbenium ion. The Newman projection of the E(3) conformer indicated that nucleophilic attack from the alpha face is disfavored because an eclipsed H-2 will be encountered. On the other hand, an approach from the beta face was expected to be more favorable, because it will experience only staggered substituents. The arabinofuranosyl oxacarbenium ion could be locked in the E(3) conformation by employing a 3,5-O-di-tert-butylsilane protecting group, which places C-5 and O-3 in a pseudoequatorial orientation, resulting in a perfect chair conformation of the protecting group. The new glycosyl donor gave excellent beta selectivities in a range of glycosylations with glycosyl acceptors having primary and secondary alcohols. The attractiveness of the new methodology was demonstrated by the chemical synthesis of a fragment of arabinogalactan, which is an important constituent of the primary plant cell wall. 相似文献
65.
Dr. Frédéric Friscourt Prof. Dr. Christoph J. Fahrni Prof. Dr. Geert‐Jan Boons 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(40):13996-14001
Fluorogenic reactions, in which non‐ or weakly fluorescent reagents produce highly fluorescent products, are attractive for detecting a broad range of compounds in the fields of bioconjugation and material sciences. Herein, we report that a dibenzocyclooctyne derivative modified with a cyclopropenone moiety (Fl‐DIBO) can undergo fast strain‐promoted cycloaddition reactions under catalyst‐free conditions with azides, nitrones, nitrile oxides, as well as mono‐ and disubstituted diazo‐derivatives. Although the reaction with nitrile oxides, nitrones, and disubstituted diazo compounds gave cycloadducts with low quantum yield, monosubstituted diazo reagents produced 1H‐pyrazole derivatives that exhibited an approximately 160‐fold fluorescence enhancement over Fl‐DIBO combined with a greater than 10 000‐fold increase in brightness. Concluding from quantum chemical calculations, fluorescence quenching of 3H‐pyrazoles, which are formed by reaction with disubstituted diazo‐derivatives, is likely due to the presence of energetically low‐lying (n,π*) states. The fluorogenic probe Fl‐DIBO was successfully employed for the labeling of diazo‐tagged proteins without detectable background signal. Diazo‐derivatives are emerging as attractive reporters for the labeling of biomolecules, and the studies presented herein demonstrate that Fl‐DIBO can be employed for visualizing such biomolecules without the need for probe washout. 相似文献
66.
Li X Guo J Asong J Wolfert MA Boons GJ 《Journal of the American Chemical Society》2011,133(29):11147-11153
Nanocarriers that combine multiple properties in an all-in-one system hold great promise for drug delivery. The absence of technology to assemble highly functionalized devices has, however, hindered progress in nanomedicine. To address this deficiency, we have chemically synthesized poly(ethylene oxide)-β-poly(ε-caprolactone) (PEO-b-PCL) block polymers modified at the apolar PCL terminus with thioctic acid and at the polar PEO terminus with an acylhydrazide, amine, or azide moiety. The resulting block polymers were employed to prepare nanoparticles that have a gold core, an apolar polyester layer for drug loading, a polar PEO corona to provide biocompatibility, and three different types of surface reactive groups for surface functionalization. The acylhydrazide, amine, or azide moieties of the resulting nanoparticles could be reacted with high efficiencies with modules having a ketone, isocyanate, or active ester and alkyne function, respectively. To demonstrate proof of principle of the potential of multisurface functionalization, we prepared nanoparticles that have various combinations of an oligo-arginine peptide to facilitate cellular uptake, a histidine-rich peptide to escape from lysosomes, and an Alexa Fluor 488 tag for imaging purposes. It has been shown that uptake and subcellular localization of the nanoparticles can be controlled by multisurface modification. It is to be expected that the modular synthetic methodology provides unique opportunities to establish optimal configurations of nanocarriers for disease-specific drug delivery. 相似文献
67.
Bonfanti M Díaz C Somers MF Kroes GJ 《Physical chemistry chemical physics : PCCP》2011,13(10):4552-4561
We have studied the effect of lattice displacement on the interaction of H(2) with the Cu(111) surface using the Specific Reaction Parameter (SRP) approach to Density Functional Theory (DFT). We have systematically investigated how the motion of the surface atoms affects some features of the Potential Energy Surface (PES), such as the dissociation barrier height and the barrier geometry corresponding to some representative reaction pathways, and the anisotropy of the potential at these geometries. This analysis has allowed us to identify the surface degrees of freedom that are likely to be most relevant for H(2) dissociation. In particular, we have found that the lattice coordinate displacements that have the largest effect on the H(2)/Cu(111) DFT-SRP barrier heights and locations concern the motion of the 1st layer and 2nd layer Cu atoms in the Z direction, and motion of the 1st layer atoms in the directions parallel to the surface. Whereas the first degree of freedom mostly affects the barrier geometry, the second and third motions can lower or raise the barrier height. The latter effect cannot be described with the usual surface oscillator dynamical models employed in the past to include surface motion, and its dynamical influence on the dissociative adsorption needs to be further investigated. 相似文献
68.
Yann Ferrand Dr. Emmanuel Klein Dr. Nicholas P. Barwell Matthew P. Crump Dr. Jesus Jiménez‐Barbero Prof. Cristina Vicent Dr. Geert‐Jan Boons Prof. Sampat Ingale Anthony P. Davis Prof. 《Angewandte Chemie (International ed. in English)》2009,48(10):1775-1779
Changing employment : Receptor 1 binds β‐N‐acetylglucosaminyl (β‐GlcNAc) up to 100 times more strongly than it does glucose. This synthetic lectin shows affinities similar to wheat germ agglutinin (WGA), a natural lectin used to bind GlcNAc. Remarkably, 1 is more selective than WGA. It favors especially the glycoside unit in glycopeptide 2 , a model of the serine‐O‐GlcNAc posttranslational protein modification.
69.
Valdés Á Brillet J Grätzel M Gudmundsdóttir H Hansen HA Jónsson H Klüpfel P Kroes GJ Le Formal F Man IC Martins RS Nørskov JK Rossmeisl J Sivula K Vojvodic A Zäch M 《Physical chemistry chemical physics : PCCP》2012,14(1):49-70
An overview of a collaborative experimental and theoretical effort toward efficient hydrogen production via photoelectrochemical splitting of water into di-hydrogen and di-oxygen is presented here. We present state-of-the-art experimental studies using hematite and TiO(2) functionalized with gold nanoparticles as photoanode materials, and theoretical studies on electro and photo-catalysis of water on a range of metal oxide semiconductor materials, including recently developed implementation of self-interaction corrected energy functionals. 相似文献
70.
A microwave-assisted, one-pot, three-step Sonogashira cross-coupling-desilylation-cycloaddition sequence was developed for the convenient preparation of 1,4-disubstituted 1,2,3-triazoles starting from a range of halides, acyl chlorides, ethynyltrimethylsilane, and azides. 相似文献