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Guest Complexes (guest + complex)
Selected AbstractsDynamic Molecular Tweezers Composed of Dibenzocyclooctatetraene Units: Synthesis, Properties, and Thermochromism in Host,Guest ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2009Tomohiko Nishiuchi Abstract Novel dynamic molecular tweezers (DMTs) 3,a, 3,b, 4,a, 4,b, and 5,b, composed of two tub-shaped dibenzocyclooctatetraene (DBCOT) units, were designed and synthesized. The cyclooctatetraene (COT) rings of these DMTs readily invert in solution, and the molecular structure shows rigid syn and anti forms in an equilibrium mixture in solution. The syn and anti conformers can be observed by NMR. The isomerization barriers of 3,a, 3,b, 4,a, 4,b, and 5,b are in the range of 16.5,21.3,kcal,mol,1, depending on steric repulsion between substituents of the COT rings and protons of the central benzene ring. These DMTs form complexes with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and 1,2,4,5-tetracyano-benzene (TCNB) in solution and in the solid state. The binding abilities of these DMTs increase with electron-donating substituents on COT, which increase the electron densities of the cavity of the syn form, as supported by theoretical calculations. In addition, elongation of the terminal alkoxy chains of the DMTs was found to cause the enhancement of van,der Waals contact with guest molecules. Therefore, 5,b, which has CH2OMe groups on the COT rings and longer ethoxy groups on the terminal benzene rings, showed the highest electron density of the cavity and hence the highest binding ability with the electron-deficient guest molecules. Interestingly, solutions of 3,b, 4,b, and 5,b show thermochromism in the presence of DDQ. A solution of 3,b or 4,b with DDQ in CHCl3 is green due to charge-transfer interaction at room temperature and the color changes from green to yellow upon heating to 60,°C and from green to blue upon cooling to ,40,°C, whereas the high complexation ability of 5,b with DDQ only shows a change in the shade of blue. [source] Selection of a Pentameric Host in the Host,Guest Complexes {[{[P(,-NtBu)]2(,-NH)}5],I},[Li(thf)4]+ and [{[P(,-NtBu)]2(,-NH)}5],HBr,THFCHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2004Felipe García Abstract The structures of the host,guest complexes {[{[P(,-NtBu)]2(,-NH)}5]I},,[Li(thf)4]+ [2,I{Li(thf)4}] and [{[P(,-NtBu)]2(,-NH)}5],HBr,THF (2,HBr,THF) show that increased distortion of the framework of the pentameric macrocycle [{[P(,-NtBu)]2(,-NH)}5] (2) occurs with the larger halide ions. Theoretical studies show that the thermodynamic stabilities of the model host,guest anions [2,X], (X=Cl, Br, I) are in the order Cl,,Br,>I,, that is, the reverse of the templating trend observed experimentally. These studies support the view that the selection of the pentamer 2 over the tetramer [{[P(,-NtBu)]2(,-NH)}4] (1) is kinetically controlled, a conclusion which is also consistent with the previous observation that the frameworks of 1 and 2 are not in dynamic equilibrium with each other. [source] Encapsulation and Stabilization of Reactive Aromatic Diazonium Ions and the Tropylium Ion Within a Supramolecular HostEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 24 2004Julia L. Brumaghim Abstract Supramolecular assemblies with internal cavities are being developed as nanoscale reaction vessels to protect or modify the reactivity of guest species through encapsulation. Diazonium cations and the tropylium cation were examined for their ability to encapsulate in the tetrahedral [Ga4L6]12, supramolecular assembly. The 4-(diethylamino)benzenediazonium cation 1 readily formed a 1:1 host,guest complex with this assembly, and this encapsulation prevented 1 from reacting with 2,4-pentanedione in D2O. The tropylium cation also formed a 1:1 host,guest complex with the [Ga4L6]12, assembly, greatly slowing its decomposition in D2O. Encapsulation in the protected environment of this host cavity alters the reactivity of these guest molecules, giving them greater stability. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] The role of specific interactions in crystalline complex formation.JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 200210-bis(4-bromophenyl)-, 10-dihydroanthracene with dimethyl sulfoxide, 10-dihydroxy-, Structural, thermochemical analysis of inclusion compounds of cis -, trans - Abstract Referring to a crucial problem in crystal engineering and co-crystallization of host,guest complexes, whether the non-covalent supramolecular interactions existing in a pre-crystalline solution state may determine the subsequent crystal structure, the particular inclusion properties of host compounds 1, cis - and 2, trans -9,10-bis(4-bromophenyl)-9,10-dihydroxy-9,10-dihydroanthracene, with dimethyl sulfoxide (DMSO) were studied by using x-ray structure analysis and calorimetric methods. Both hosts form crystalline inclusion complexes with DMSO showing 2:3 (1·DMSO) and 1:4 (2·DMSO) host:guest composition. The crystal structure of 1·DMSO (2:3) is dominated by a strong bifurcated acceptor-type H bond interaction involving 1 and one of the DMSO molecules. Titration calorimetric investigations in solution also confirm the formation of a stable 1·DMSO (1:1) complex unit, suggesting that for crystal nuclei of 1·DMSO (2:3) the pre-formed 1:1 host,guest complex is the relevant building block while the additional molecules of DMSO fill lattice voids. In contrast, compound 2 with a trans configuration of the two hydroxy groups gives much weaker complexation with DMSO in solution, which is in agreement with single H-bond interaction, also realized in the crystal structure of the respective inclusion complex. Thermal decomposition (TG,DSC) measurements of the crystalline complexes supply supporting data for these findings. Copyright © 2002 John Wiley & Sons, Ltd. [source] The host,guest complex between cone-25,26:27,28-bis(methylenedioxy)calix[4]arene and dichloromethaneACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2003Cedric Dielemann The title compound, 25,26:27,28-bis(methylenedioxy)pentacyclo[19.3.1.13,7.19,13.115,19]octacosa-1(25)3,5,7(28),9,11,13(27),15,17,19(26),21,23-dodecaene dichloromethane solvate, C30H24O4·CH2Cl2, possesses crystallographic twofold symmetry in both components. The calixarene shows a pinched cone conformation with an elliptical cavity, in which the guest dichloromethane solvent molecule is accommodated. The contact distance between guest and host (H,ring centroid = 2.44,Å) is extremely short. [source] A host,guest complex of diaquabis[1-hydroxy-2(1H)-pyridinethionato- O,S]magnesium(II) and 2,2,-dithiobis(pyridine N -oxide)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2000Andrew Bond The title compound, [Mg(C5H4NOS)2(H2O)2]·C10H8N2O2S2, is a two-component host,guest material. The 2,2,-dithiobis(pyridine N -oxide) molecule has crystallographic twofold symmetry. The metal complex lies on an inversion centre and associates via C,H,S interactions into chains which thread the 2,2,-dithiobis(pyridine N -oxide) lattice in perpendicular directions. Hydrogen bonds exist between the water molecules of the diaquamagnesium units and the N,O groups of the host lattice. [source] Direct Assignment of Enantiofacial Discrimination on Single Heterocyclic Substrates by Self-induced CDCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2005Carsten Siering Abstract The first direct assignment of highly dynamic enantiofacial discrimination acting on a single heterocyclic substrate has been achieved by a combination of experimental and theoretical CD spectroscopy. The interaction of chirally modified hosts based on triphenylene ketals with appropriate prochiral guests can lead to the preferential formation of one diastereomeric host,guest complex. This reversible stereoselective binding transmits the chiral information from remote chiral groups in the host to the strongly absorbing triphenylene chromophore, which gives rise to self-induced CD. This effect was exploited for the determination of the enantiofacial recognition in various host,guest systems. Inversion of the steric demand either of the chiral substituents at the host or of the prochiral guest leads to almost complete inversion of the resulting CD spectra. For the assignment of the absolute stereochemistry of the complexes, a combined molecular dynamics/quantum-chemical approach was successfully employed. Despite the size and the highly dynamic character of the supramolecular systems, fundamental properties of the systems and details of the spectra were simulated accurately, providing access to fast and reliable assignment of the enantiofacial preference. The results are highly consistent with available X-ray data. [source] Positron Annihilation Lifetimes in Cucurbiturils: Evidence of Internal Inclusion of Gold in CB[7]CHEMPHYSCHEM, Issue 5 2009Pedro Montes-Navajas Abstract Positron lifetime spectroscopy serves to determine the void volumes of cucurbituril (CB) capsules, which are not amenable to standard gas adsorption methods. In the case of the host,guest complex Au§CB[7], it also provides evidence of the inclusion of gold nanoparticles in the CB cavity (see space-filling model; Au golden, C gray, H cyan, N blue, O red). Positron annihilation lifetime (PAL) measurements are carried out to determine the cavity dimensions of hydrated and dehydrated cucurbiturils (CB[n]; n=5,6,7,8). In the case of hydrated samples, the dimensions of the cavity are unrelated to the number of glycoluril units of the CB, whereas for dehydrated samples the cavity dimensions measured by PAL follow the expected order, although the experimental values obtained by PAL are significantly smaller than the dimensions of each CB determined by crystallography. For a host,guest complex in which colloidal gold nanoparticles are assumed to be included inside CB[7], a significant reduction of the cavity size is measured. This represents an experimental evidence of the inclusion of gold inside CB[7], which complements previous high-resolution transmission electron microscopy (TEM) images. [source] Hydrophobic Chemistry in Aqueous Solution: Stabilization and Stereoselective Encapsulation of Phosphonium Guests in a Supramolecular HostEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 22 2004Julia L. Brumaghim Abstract Encapsulation of guest molecules inside supramolecular host assemblies provides a way to stabilize reactive species in aqueous solution. The stabilization of reactive phosphonium/ketone adducts of the general formula [R1MeC(OH)PR3]+ by encapsulation as guest molecules within a [Ga4L6]12, tetrahedral metal,ligand assembly is reported; although these cations decompose in aqueous solution, encapsulation inside the hydrophobic cavity of the assembly lengthens their lifetimes considerably, in some cases up to weeks. By varying the phosphane (PMe3, PEt3, PPhMe2, and PPh2Me) and ketone (acetone, methyl ethyl ketone, 1,1,1-trifluoroacetone, and fluoroacetone) which form these adducts, as well as the pD of the solutions, it was determined that the pH of the solution as well as the size and shape of the guest cations play an important role in the stability of these host,guest complexes. Encapsulation of chiral guests in the chiral [Ga4L6]12, assembly results in the formation of diastereomers, as characterized by 1H, 19F, and 31P NMR spectroscopy. Although the [Ga4L6]12, assembly is formed from non-chiral ligands, the assembly itself has ,,,, or ,,,, chirality around the metal centers. Due to the chirality of this assembly, diastereomeric selectivity is observed upon initial guest encapsulation (typical diastereomeric excesses are 30,50%). This initial diastereomeric selectivity decreases over time to reach an equilibrium but does not become 1:1, indicating both kinetic and thermodynamic processes promote selective guest encapsulation. These experiments demonstrate further the applications of nanoscale reaction vessels, self-assembled by design from non-chiral ligands, in providing a chiral and hydrophobic environment for guest molecules in aqueous solution. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Modified Cyclodextrins as Enantioselective Hosts for Amino AcidsHELVETICA CHIMICA ACTA, Issue 4 2008Pavan Kumar, Vydyula Abstract Two modified , -cyclodextrins, H-2 and H-3, having a flexible appended moiety were studied for the chiral discrimination of the enantiomers of various amino acids by means of fluorescence as signaling option. These hosts quenched the fluorescence intensities of amino acids upon binding. The d- enantiomers were better recognized by these hosts. The association constants (Ks) and enantioselectivity factors (,) of the host,guest complexes were calculated. [source] Inhibition of acid-induced decomposition of diphenyltriazenes by complexation with cyclodextrinsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2010Tingting Xu Acid-promoted NN bond cleavage in 1,3-diphenyltriazenes (X-Ph-N=N-NH-Ph-X; X = H, 4-OCH3), leading to formation of diazonium ions and anilines, is strongly inhibited in aqueous solutions in the presence of cyclodextrins (CDs). The inhibition is ascribed to the formation of inclusion complexes that render the guest diphenyltriazene significantly less basic as a result of the less polar nature of the CD cavity (a microsolvent effect). Association equilibrium constants for 1:1 host,guest complexes increase in the order ,-CD <,-CD , permethyl-,-CD < hydroxypropyl-,-CD, with values for X = 4-OCH3 being larger than those for X = H. In the case of ,-CD, formation of 2:1 host,guest complexes is also involved. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 567,574, 2010 [source] The role of specific interactions in crystalline complex formation.JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 200210-bis(4-bromophenyl)-, 10-dihydroanthracene with dimethyl sulfoxide, 10-dihydroxy-, Structural, thermochemical analysis of inclusion compounds of cis -, trans - Abstract Referring to a crucial problem in crystal engineering and co-crystallization of host,guest complexes, whether the non-covalent supramolecular interactions existing in a pre-crystalline solution state may determine the subsequent crystal structure, the particular inclusion properties of host compounds 1, cis - and 2, trans -9,10-bis(4-bromophenyl)-9,10-dihydroxy-9,10-dihydroanthracene, with dimethyl sulfoxide (DMSO) were studied by using x-ray structure analysis and calorimetric methods. Both hosts form crystalline inclusion complexes with DMSO showing 2:3 (1·DMSO) and 1:4 (2·DMSO) host:guest composition. The crystal structure of 1·DMSO (2:3) is dominated by a strong bifurcated acceptor-type H bond interaction involving 1 and one of the DMSO molecules. Titration calorimetric investigations in solution also confirm the formation of a stable 1·DMSO (1:1) complex unit, suggesting that for crystal nuclei of 1·DMSO (2:3) the pre-formed 1:1 host,guest complex is the relevant building block while the additional molecules of DMSO fill lattice voids. In contrast, compound 2 with a trans configuration of the two hydroxy groups gives much weaker complexation with DMSO in solution, which is in agreement with single H-bond interaction, also realized in the crystal structure of the respective inclusion complex. Thermal decomposition (TG,DSC) measurements of the crystalline complexes supply supporting data for these findings. Copyright © 2002 John Wiley & Sons, Ltd. [source] A Colorimetric Sensor Array for the Detection of the Date-Rape Drug ,-Hydroxybutyric Acid (GHB): A Supramolecular ApproachCHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2010Laurent Abstract ,-Hydroxybutyric acid (GHB), a colourless, odourless and tasteless chemical, has become one of the most dangerous illicit drugs of abuse today. At low doses, this drug is a central nervous system depressant that reduces anxiety and produces euphoria and relaxation, sedating the recipient. There is an urgent need for simple, easy-to-use sensors for GHB in solution. Here, we present a colorimetric sensor array based on supramolecular host,guest complexes of fluorescent dyes with organic capsules (cucurbiturils) for the detection of GHB. [source] The Assembly of Macrocyclic Bis- and Tetra-,-lactams with Embedded Platinum or Palladium Square-Planar CentersCHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2009Daniel Pellico Abstract The synthesis, isolation, and full characterization of different types of stable, metal-assembled macrocyclic ,-lactams are reported. By using adequately functionalized bis-,-lactams with defined stereochemistry as building blocks, a series of mono- and bimetallic Pd and Pt macrocycles has been prepared in good to quantitative yields. These novel structures combine the ,-lactam moiety with transition-metal fragments with cis -square-planar geometry and constitute a new class of metal-assembled cavities involving molecules with biological relevance as building blocks. By combining the adequate ligands, metallic fragments, and tuning the reaction conditions, different mono- and bimetallic macrocyclic ,-lactam cavities can be selectively obtained. Macrocycles with Pt,ethynyl groups are suitable to form host,silver triflate guest complexes in a tweezer fashion. El trabajo describe la síntesis, aislamiento y caracterización completa de una serie de Pd y Pt-metalo-,-lactamas. Estos compuestos se obtienen con excelente rendimiento a partir de bis-,-lactamas adecuadamente funcionalizadas y con estereoquímica definida, y los correspondientes complejos de Pd y Pt. Las bis y tetra-metalo-,-lactamas obtenidas constituyen un nuevo tipo de cavidades macrocíclicas, que combinan en su estructura los fragmentos ,-lactámicos con complejos metálicos de geometría cis-plano cuadrada. Combinando adecuadamente los ligandos precursores (bis-,-lactama y complejo metálico) y las condiciones de reacción, es posible controlar de forma totalmente selectiva, el tamaño del macrociclo obtenido y preparar bis y tetra-,-lactamas mono o bimetálicas. La presencia de fragmentos Pt-etinilo en la estructura permite a las compuestos macrocíclicos obtenidos la formación de complejos pinzados con sales de plata. [source] Expanding Sapphyrin: Towards Selective Phosphate BindingCHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2008Evgeny Abstract The anion-templated syntheses and binding properties of novel macrocyclic oligopyrrole receptors in which pyrrole rings are linked through amide or imine bonds are described. The efficient synthesis was accomplished by anion-templated [1+1] Schiff-base condensation and acylation macrocyclization reactions. Free receptors and their host,guest complexes with hydrochloric acid, acetic acid, tetrabutylammonium chloride, and hydrogen sulfate were analyzed by single-crystal X-ray diffraction analysis. Stability constants with different tetrabutylammonium salts of inorganic acids were determined by standard 1H,NMR and UV/Vis titration techniques in [D6]DMSO/0.5,% water solution. According to the titration data, receptors containing three pyrrole rings (10 and 12) exhibit high affinity (log,Ka=5,7) for bifluoride, acetate, and dihydrogen phosphate, and interact weakly with chloride and hydrogen sulfate. The amido-bipyrrole receptors 11 and 13 with four pyrrole rings exhibit 104 - and 102 -fold selectivity for dihydrogen phosphate, respectively, as inferred from competitive titrations in the presence of tetrabutylammonium acetate. [source] Nanosized Ball Joints Constructed from C60 and Tribenzotriquinacene Sockets: Synthesis, Component Self-Assembly and Structural InvestigationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2007Björn Bredenkötter Dr. Abstract The formation of supramolecular host,guest complexes of fullerene (C60) and two novel tribenzotriquinacene based hosts (5,a and 5,b) was investigated in solution and in the solid state. Stability constants for 1:1 and 2:1 complexes were obtained from spectroscopic (UV/Vis, 1H,NMR) titration experiments. Association constants of K1=(2908±360),L,mol,1 and K2=(2076±300),L,mol,1 for C60/5,a, and K1=(5608±220),L,mol,1 and K2=(673±160),L,mol,1 for C60/5,b were obtained. Single crystal X-ray structural analysis of compound C60,5,b,3,toluene revealed that a molecule of C60 was located at short van der Waals contact distances in the open pre-organised cavity of the rigid host. The supramolecular complex created resembles an engineered nanosized ball joint and represents the first member for a future nanomechanics construction kit. [source] Encapsulation of Cyanometalates by a Tris-macrocyclic Ligand Tricopper(II) Complex: Syntheses, Structural Variation, and Magnetic Exchange Coupling PathwaysCHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2006Mihail Atanasov Prof. Dr. Abstract The reaction of [M(CN)6]3, (M=Cr3+, Mn3+, Fe3+, Co3+) and [M(CN)8]4,/3, (M=Mo4+/5+, W4+/5+) with the trinuclear copper(II) complex of 1,3,5-triazine-2,4,6-triyltris[3-(1,3,5,8,12-pentaazacyclotetradecane)] ([Cu3(L)]6+) leads to partially encapsulated cyanometalates. With hexacyanometalate(III) complexes, [Cu3(L)]6+ forms the isostructural host,guest complexes [{[Cu3(L)(OH2)2][M(CN)6]2}{M(CN)6}],[M(CN)6],30,H2O with one bridging, two partially encapsulated, and one isolated [M(CN)6]3, unit. The octacyanometalates of Mo4+/5+ and W4+/5+ are encapsulated by two tris-macrocyclic host units. Due to the stability of the +IV oxidation state of Mo and W, only assemblies with [M(CN)8]4, were obtained. The Mo4+ and W4+ complexes were crystallized in two different structural forms: [{Cu3(L)(OH2)}2{Mo(CN)8}](NO3)8,15,H2O with a structural motif that involves isolated spherical [{Cu3(L)(OH2)}2{M(CN)8}]8+ ions and a "string-of-pearls" type of structure [{[Cu3(L)]2[M(CN)8]}{M(CN)8}](NO3)4, 20,H2O, with [M(CN)8]4, ions that bridge the encapsulated octacyanometalates in a two-dimensional network. The magnetic exchange coupling between the various paramagnetic centers is characterized by temperature-dependent magnetic susceptibility and field-dependent magnetization data. Exchange between the Cu,,,Cu pairs in the [Cu3(L)]6+ "ligand" is weakly antiferromagnetic. Ferromagnetic interactions are observed in the cyanometalate assemblies with Cr3+, exchange coupling of Mn3+ and Fe3+ is very small, and the octacoordinate Mo4+ and W4+ systems have a closed-shell ground state. [source] Selection of a Pentameric Host in the Host,Guest Complexes {[{[P(,-NtBu)]2(,-NH)}5],I},[Li(thf)4]+ and [{[P(,-NtBu)]2(,-NH)}5],HBr,THFCHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2004Felipe García Abstract The structures of the host,guest complexes {[{[P(,-NtBu)]2(,-NH)}5]I},,[Li(thf)4]+ [2,I{Li(thf)4}] and [{[P(,-NtBu)]2(,-NH)}5],HBr,THF (2,HBr,THF) show that increased distortion of the framework of the pentameric macrocycle [{[P(,-NtBu)]2(,-NH)}5] (2) occurs with the larger halide ions. Theoretical studies show that the thermodynamic stabilities of the model host,guest anions [2,X], (X=Cl, Br, I) are in the order Cl,,Br,>I,, that is, the reverse of the templating trend observed experimentally. These studies support the view that the selection of the pentamer 2 over the tetramer [{[P(,-NtBu)]2(,-NH)}4] (1) is kinetically controlled, a conclusion which is also consistent with the previous observation that the frameworks of 1 and 2 are not in dynamic equilibrium with each other. [source] Use of (S)-BINOL as NMR chiral solvating agent for the enantiodiscrimination of omeprazole and its analogsCHIRALITY, Issue 5 2010Jordi Redondo Abstract The application of (S)-1,1,-binaphthyl-2,2,-diol as NMR chiral solvating agent (CSA) for omeprazole, and three of its analogs (lanso-, panto-, and rabe-prazole) was investigated. The formation of diastereomeric host,guest complexes in solution between the CSA and the racemic substrates produced sufficient NMR signal splitting for the determination of enantiomeric excesses by 1H- or 19F-NMR spectroscopy. Using of hydrophobic deuterated solvents was mandatory for obtaining good enantiodiscrimination, thus suggesting the importance of intermolecular hydrogen bonds in the stabilization of the complexes. The method was applied to the fast quantification of the enantiomeric purity of in-process samples of S -omeprazole. Chirality, 2010. © 2009 Wiley-Liss, Inc. [source] | ||||||||||||||||||||||