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1.
Chemistry ; 26(33): 7374-7383, 2020 Jun 10.
Artigo em Inglês | MEDLINE | ID: mdl-32083359

RESUMO

The synthesis of tetramethoxyresorcinarene podands bearing p-toluene arms connected by -SO3 - (1) and -CH2 O- (2) linkers is presented herein. In the solid state, the resorcinarene podand 1 forms an intramolecular self-inclusion complex with the pendant p-toluene group of a podand arm, whereas the resorcinarene podand 2 does not show self-inclusion. The conformations of the flexible resorcinarene podands in solution were investigated by variable-temperature experiments using 1D and 2D NMR spectroscopic techniques as well as by computational methods, including a conformational search and subsequent DFT optimisation of representative structures. The 1 H NMR spectra of 1 and 2 at room temperature show a single set of proton signals that are in agreement with C4v symmetry. At low temperatures, the molecules exist as a mixture of boat conformations featuring slow exchange on the NMR timescale. Energy barriers (ΔG≠ 298 ) of 55.5 and 52.0 kJ mol-1 were calculated for the boat-to-boat exchange of 1 and 2, respectively. The results of the ROESY experiments performed at 193 K and computational modelling suggest that in solution the resorcinarene podand 1 adopts a similar conformation to that present in its crystal structure, whereas podand 2 populates a more versatile range of conformations in solution.

2.
Chem Asian J ; 14(5): 647-654, 2019 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-30644629

RESUMO

The anion-binding properties of three closely related oligoamide foldamers were studied using NMR spectroscopy, isothermal titration calorimetry and mass spectrometry, as well as DFT calculations. The 1 H NMR spectra of the foldamers in [D6 ]acetone solution revealed partial preorganization by intramolecular hydrogen bonding, which creates a suitable cavity for anion binding. The limited size of the cavity, however, enabled efficient binding by the inner amide protons only for the chloride anion resulting in the formation of a thermodynamically stable 1:1 complex. All 1:1 chloride complexes displayed a significant favourable contribution of the entropy term. Most likely, this is due to the release of ordered solvent molecules solvating the free foldamer and the anion to the bulk solution upon complex formation. The introduction of electron-withdrawing substituents in foldamers 2 and 3 had only a slight effect on the thermodynamic constants for chloride binding compared to the parent receptor. Remarkably, the binding of chloride to foldamer 3 not only produced the expected 1:1 complex but also open aggregates with 1:2 (host:anion) stoichiometry.

3.
Chemistry ; 23(65): 16671-16680, 2017 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-29105164

RESUMO

A series of aromatic oligoamide foldamers with two or three pyridine-2,6-dicarboxamide units as their main folding motifs and varying aromatic building blocks as linkers have been synthetized to study the effects of the structural variation on the folding properties and conformational stability. Crystallographic studies showed that in the solid state the central linker unit either elongates the helices and more open S-shaped conformations, compresses the helices to more compact conformations, or acts as a rigid spacer separating the pyridine-2,6-dicarboxamide units, which for their part add the predictability of the conformational properties. Multidimensional NMR studies showed that, even in solution, foldamers show conformational stability and folded conformations comparable to the solid-state structures.

4.
J Colloid Interface Sci ; 464: 59-65, 2016 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-26609923

RESUMO

HYPOTHESIS: Macrocyclic amphiphiles form interesting self-assembling structures, including solid lipid nanoparticles, which have potential applications in drug encapsulation. Aryl-extended calixpyrroles, which act as anion binding hosts, are expected to form solid lipid nanoparticles, even though the alkyl chains have unusual perpendicular geometry with respect to the hydrophilic head group. The preparation conditions and the alkyl chain length should affect the size and stability of the particles. EXPERIMENTS: Solid lipid nanoparticles of two aryl-extended calixpyrroles with resorcinol walls and either meso-dodecyl or meso-methyl alkyl chains were compared. Ethanolic solutions of the calixpyrroles were mixed with water and the resulting nanoparticle dispersions were studied with dynamic light scattering and nanoparticle tracking analysis. The effect of different calixpyrrole/ethanol/water ratios on particle size was tested. The surface charge of the particles at different pH and NaCl concentration was determined by zeta potential measurements. FINDINGS: The meso-dodecyl calixpyrrole produced small nanoparticles with mean hydrodynamic diameters between 40 and 70nm in 0.86-4.28M ethanol. The particles were stable in solution for several months. Particles prepared from meso-methyl calixpyrrole were larger and less stable. The smallest particles were obtained with low calixpyrrole concentration and calixpyrrole/ethanol ratio. Larger ethanol/water ratio induced broader particle size distributions. Increasing pH aided the stability of the particles due to increased negative surface charge.

5.
Chemistry ; 21(26): 9493-504, 2015 Jun 22.
Artigo em Inglês | MEDLINE | ID: mdl-25965104

RESUMO

A series of small, unsymmetrical pyridine-2,6-dicarboxylamide oligoamide foldamers with varying lengths and substituents at the end groups were synthetized to study their conformational properties and folding patterns. The @-type folding pattern resembled the oxyanion-hole motifs of enzymes, but several alternative folding patterns could also be characterized. Computational studies revealed several alternative conformers of nearly equal stability. These folding patterns differed from each other in their intramolecular hydrogen-bonding patterns and aryl-aryl interactions. In the solid state, the foldamers adopted either the globular @-type fold or the more extended S-type conformers, which were very similar to those foldamers obtained computationally. In some cases, the same foldamer molecule could even crystallize into two different folding patterns, thus confirming that the different folding patterns are very close in energy in spite of their completely different shapes. Finally, the best match for the observed NOE interactions in the liquid state was a conformation that matched the computationally characterized helix-type fold.

6.
Chem Asian J ; 9(7): 1860-7, 2014 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-24782080

RESUMO

An unexpected and previously unknown resorcinarene mono-crown with a fused benzofuran moiety in its macrocyclic core was obtained as a byproduct from a bridging reaction of tetramethoxy resorcinarene with tetraethylene glycol ditosylate. The formation of the fused benzofuran moiety in the resorcinarene macrocycle resulted in a unique rigid and puckered boat conformation, as shown by XRD studies in the solid state. Modification of the macrocycle was also observed to affect the photophysical properties in solution by enhancing the fluorescence brightness compared with a conventional resorcinarene macrocycle. The fluorescent properties enabled unique detection of structural features, that is, the rigid boat conformation with the conjugated benzofuran system and the more flexible crown bridge part, in solution.


Assuntos
Benzofuranos/química , Calixarenos/química , Fenilalanina/análogos & derivados , Benzofuranos/síntese química , Técnicas de Química Sintética , Cristalografia por Raios X , Fluorescência , Conformação Molecular , Estrutura Molecular , Fenilalanina/química , Espectrometria de Fluorescência , Relação Estrutura-Atividade
7.
Anal Chem ; 85(7): 3489-92, 2013 Apr 02.
Artigo em Inglês | MEDLINE | ID: mdl-23506040

RESUMO

Diffusion ordered NMR spectroscopy (DOSY) was used as an analytical tool to estimate the size of thiol-stabilized gold nanoclusters in solution, namely, phenylethanethiol (PET) stabilized Au25(PET)18, Au38(PET)24, and Au144(PET)60. This was achieved by determining the diffusion coefficient and hydrodynamic radius from solution samples that were confirmed to be monodispersed by electrospray ionization mass spectrometry. The average cluster diameters obtained by this technique were estimated to be 1.7, 2.2, and 3.1 nm for the Au25(PET)18, Au38(PET)24, and Au144(PET)60 nanoclusters, respectively, which were shown to agree well with the average diameters of the corresponding single crystal or theoretical structures reported in the literature. Consequently, the DOSY technique is demonstrated to be a potentially valuable nondestructive tool for characterization of nanoparticle mixtures and verifying the purity of product solutions.


Assuntos
Ouro/química , Espectroscopia de Ressonância Magnética/métodos , Nanoestruturas/química , Compostos de Sulfidrila/química , Difusão , Modelos Moleculares , Tamanho da Partícula
8.
Org Lett ; 15(5): 1096-9, 2013 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-23418984

RESUMO

An improved Lewis acid catalyzed synthesis method for methyl tetramethoxy resorcinarene is described, which produced the missing lower rim methyl derivative of this partially O-alkylated resorcinarene family. Structural characterization by means of variable temperature NMR experiments and single crystal X-ray diffraction studies furthermore revealed that the resorcinarene core adopts different conformations in the solid state and in solution.

9.
Nanoscale ; 4(14): 4095-8, 2012 Jul 21.
Artigo em Inglês | MEDLINE | ID: mdl-22532448

RESUMO

A simple one-pot method for the preparation of subnanometre-size benzotriazolate (BTA) protected copper clusters, Cu(n)BTA(m), is reported. The clusters were analyzed by optical and infrared spectroscopy, mass spectrometry and transmission electron microscopy together with computational methods. We suggest a structural motif where the copper core of the Cu(n)BTA(m) clusters is protected by BTA-Cu(i)-BTA units.


Assuntos
Cobre/química , Triazóis/química , Complexos de Coordenação/síntese química , Complexos de Coordenação/química , Teoria Quântica , Espectrofotometria Ultravioleta
10.
Org Biomol Chem ; 10(10): 2019-25, 2012 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-22290247

RESUMO

Silver complexes of a cation binding supramolecular host, resorcinarene bis-crown (CNBC5) with propyl, nonyl, decyl and undecyl alkyl chains were investigated by NMR titration, picrate extraction and single crystal X-ray diffraction. Binding studies showed that both 1 : 1 and 1 : 2 (host-Ag(+)) complexes are present in solution with only a slight effect of the lower rim alkyl chain length on the binding constants (log K 4.0-4.2 for 1 : 2 complexes). Solid state complexes of the resorcinarene bis-crowns bearing either C(3) or C(11) chains were obtained. Single crystal X-ray analyses showed that both derivatives bind silver ions by metal-arene and Ag···O coordination from the crown ether bridges and from the solvent, and pack in layered or bilayered fashion. Furthermore, the amphiphilic nature of C11BC5 was demonstrated using the Langmuir balance technique. Langmuir-Blodgett films of the amphiphilic C11BC5-Ag complex were transferred onto a substrate and shown to possess antibacterial activity against E. coli.


Assuntos
Antibacterianos/química , Calixarenos/química , Complexos de Coordenação/química , Fenilalanina/análogos & derivados , Prata/química , Antibacterianos/farmacologia , Calixarenos/farmacologia , Complexos de Coordenação/farmacologia , Cristalografia por Raios X , Escherichia coli/efeitos dos fármacos , Infecções por Escherichia coli/tratamento farmacológico , Estrutura Molecular , Fenilalanina/química , Fenilalanina/farmacologia , Prata/farmacologia
11.
Chem Asian J ; 7(4): 809-17, 2012 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-22311655

RESUMO

Mixed-donor atom tetramethoxy resorcinarene bis-thiacrown hosts, in which the crown unit contains both hard oxygen and soft sulfur donor atoms, were synthesized for soft metal cation binding. The binding properties were investigated both in solution and in the solid state by NMR spectroscopy and X-ray crystallography. It was found that the resorcinarene bis-thiacrowns were able to complex silver cations with remarkable affinity forming readily 1:2 host-guest complexes in solution. The solid state structures also revealed that the bis-thiacrowns form silver complexes in an unanticipated endo- and exo-cavity fashion within the same host molecule. Both the solution and solid state studies indicated the sulfur atoms to be the major contributing donor atoms in forming the binding interactions with silver cations.

12.
Org Biomol Chem ; 9(3): 906-14, 2011 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-21132217

RESUMO

o-Nitroaniline functionalized resorcinarene octapodands 1-5 with pendant methyl, ethyl, pentyl, nonyl or 1-decenyl groups, respectively, were synthesized and their structural properties investigated using X-ray crystallography and NMR spectroscopy. The upper rim of each podand is identical containing flexible side arms, in which rotation around the -OCH(2)CH(2)N- linkers create excellent possibilities for polymorphism. Two conformational polymorphs of acetone solvate of 2 were identified containing different side arm orientation and crystal packing. Compound 1 crystallized from acetone and nitromethane yielding two pseudopolymorphs with different packing motifs. The longer alkyl chains of 3-5 lead to differences in solubility and induce amphiphilic properties, which were studied at the air-water interface using the Langmuir-film technique. Crystals of amphiphilic compound 5, which has hydrophobic alkyl tails at the lower rim and hydrophilic nitroaniline groups at the upper rim, showed an interesting packing motif with alternating aromatic and aliphatic layers. Versatile structures of the octapodands in solid state and in solution serve as an example of how conformational flexibility can be utilized in crystal engineering and creating self-assembling monolayer structures.

13.
Inorg Chem ; 49(24): 11473-84, 2010 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-21090769

RESUMO

Ditopic salophen-UO(2) receptors 1-4 and 7 co-crystallize with tetramethylammonium (TMA) chloride and fluoride salts producing good quality crystals amenable for X-ray diffraction characterization. The arrangement of the receptor and salt units in the crystal lattice is such that tetrameric ball-shaped assemblies are formed, where an inner cluster of four TMA cations are surrounded by an outer shell of four UO(2)-bound anions. These elaborate architectures, which occur in all cases, regardless of a certain degree of structural modification on the receptors, lead to lattices that belong to non-centrosymmetric (NCS) space groups. Interestingly, the tetragonal symmetry of the tetrameric ball-shaped assemblies is either retained (I4̅) or lost (R3c and I4̅3d) at the lattice level, without compromising the NCS nature of the crystal lattices. The principal X-ray investigation on TMAX (X = Cl/F) co-crystals, that is, 1-(TMA)Cl, 2-(TMA)Cl, 3-(TMA)Cl, 4-(TMA)Cl, 7-(TMA)Cl, and 7-(TMA)F, is accompanied by NMR and electrospray ionization (ESI) mass spectrometry studies to gather additional insight on the modality of formation of the solid state structures observed. The important role of cation-π interactions in the receptor-salt recognition process is renewed and strengthened by comparison with NMR titration data with a novel reference compound, the salophen-UO(2) complex 8. Given the importance of NCS and polar crystalline solids in the development of functional materials, this study shows that this property can be introduced into elaborate host-guest systems, as those which assemble in the architectures described here, thus expanding its field of applicability.

14.
Org Biomol Chem ; 7(20): 4211-7, 2009 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-19795059

RESUMO

The synthesis and structural properties of tetramethoxy resorcinarene mono-crown-5 (1) are described. The binding characteristics of 1 toward acetylcholine and tetramethylammonium salts were investigated by 1H NMR titration. It was observed that the cavity of 1 provides a better fit to acetylcholine compared to the smaller tetramethylammonium cation, as acetylcholine is able to interact with both the crown ether moiety and the free hydroxyl groups of receptor 1 simultaneously.


Assuntos
Calixarenos/química , Calixarenos/síntese química , Fenilalanina/análogos & derivados , Compostos de Amônio Quaternário/química , Sítios de Ligação , Coronantes/química , Hidróxidos/química , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Conformação Molecular , Fenilalanina/síntese química , Fenilalanina/química
15.
J Am Chem Soc ; 129(12): 3641-8, 2007 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-17338524

RESUMO

Efficient ditopic receptors for quaternary ammonium and iminium salts have been obtained upon functionalization of the uranyl-salophen unit with conformationally flexible side arms bearing phenyl or beta-naphthyl substituents. Binding affinities in chloroform solution have been measured for a large number of quaternary salts comprising tetramethylammonium (TMA), tetrabutylammonium (TBA), acetylcholine (ACh), N-methylpyridinium (NMP), and N-methylisoquinolinium (NmiQ) cations. Recognition of the anion partner is ensured by coordination to the hard Lewis acidic uranyl center, whereas cation-pi/CH-pi interactions of the quaternary ions are established with the aromatic pendants. The role of the cation-anion interactions on the dynamics of exchange between the free and complexed species is discussed. Solid-state structures have been obtained for a few salt-receptor combinations. In the solid state, side-armed receptor molecules form assemblies that enclose ion pair aggregates of varying composition and structure, including AChCl dimers, two different kinds of tetrameric (TMA)Cl clusters, and unidimentional salt strips of (NMP)Br. The lack of side arms as preferential binding sites for the polar quaternary cations prevents association patterns of the kinds formed with the side-armed receptors, as shown by the crystal structure of the complex of (TMA)Cl with the parent uranyl-salophen receptor.

16.
Org Lett ; 8(24): 5473-6, 2006 Nov 23.
Artigo em Inglês | MEDLINE | ID: mdl-17107050

RESUMO

The synthesis and characterization of new tetramethoxy resorcinarene bis-crown ethers BC4 and BC5 are described. The complexation properties of the compounds toward alkali metal cations were studied by 1H NMR spectroscopy and X-ray crystallography, which revealed that BC5 can accommodate two cations simultaneously inside the crown pockets formed by the crown ether bridges and the resorcinarene skeleton. [reaction: see text].

17.
Inorg Chem ; 45(16): 6099-101, 2006 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-16878909

RESUMO

Complexation of CsF with the ditopic uranyl-salen receptor results in a solid-state structure, in which the coordination sphere of cesium is filled by ligation to one of the chlorine atoms of the solvent chloroform. This X-ray structure is the first example of chloroform ligation to an alkali-metal ion.

18.
Chem Commun (Camb) ; (11): 1209-11, 2006 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-16518493

RESUMO

Crystallization studies of C-methyl pyrogallarene with potassium, rubidium and caesium bromides or chlorides resulted in a hydrogen bonded molecular cage in which the alkali metal cations are eta6 coordinated to aromatic rings via strong cation-pi interactions.

19.
Chemistry ; 12(16): 4289-96, 2006 May 24.
Artigo em Inglês | MEDLINE | ID: mdl-16568487

RESUMO

The assembly of C-methyl resorcinarene into a tubular supramolecular solid-state structure, its thermal stability, and its hosting properties are reported. Careful control of the crystallisation conditions of C-methyl resorcinarene and 1,4-dimethyl-1,4-diazoniabicyclo[2.2.2]octane (1,4-dimethyl DABCO) dibromide leads to a formation of two crystallographically different, but structurally very similar, solid-state nanotube structures. These structures undergo a remarkable variety of supramolecular interactions, which lead to the formation of 0.5 nm diameter nonpolar tubes through the crystal lattice. The formation of these tubes is templated by suitably sized small alcohols, namely, n-propanol, 2-propanol, or n-butanol. The self-assembly involves close pi...pi interactions between the adjacent resorcinarenes, and C--H...pi and cation...pi interactions between the resorcinarenes and the guest 1,4-dimethyl DABCO dications. The crystals of these supramolecular tube structures are thermally very stable and the included solvent alcohol can be removed from the tubes without breaking the single-crystalline structure of the assembly. After removal of the solvent molecules the tubes can be filled with other small, less polar solvent molecules such as dichloromethane.


Assuntos
Temperatura Alta , Nanotubos/química , Fenilalanina/análogos & derivados , Calixarenos , Cristalização , Conformação Molecular , Fenilalanina/química , Piperazinas/química , Solventes/química
20.
J Am Chem Soc ; 127(11): 3831-7, 2005 Mar 23.
Artigo em Inglês | MEDLINE | ID: mdl-15771518

RESUMO

Hard anions have long been known to bind strongly to the uranium of uranyl-salophen complexes. Upon functionalization of the salophen framework with one or two benzyloxy substituents, efficient ditopic receptors for alkali metal ions are obtained. The solid-state structures of complexes formed by the two-armed receptor 1 with CsF and with the chlorides of K+, Rb+, and Cs+ reported here reveal the existence of dimeric supramolecular assemblies in which two receptor units assemble into capsules fully enclosing (MX)2 ion quartets. In addition to the strong coordinative binding of the anion to the uranyl center and to electrostatic cation-anion interactions, stabilizing interactions arise from coordination of each cation to six oxygens, three from each receptor, and most importantly, to two aromatic sidearms belonging to different receptors. There are marked differences in organization at the supramolecular level in the CsCl complex of the one-armed receptor 3, in that four uranyl-salophen units instead of two are assembled in a capsule-like arrangement housing a (CsCl)2 ion quartet. However, both receptors achieve the common goal of having each metal cation in close contact with carbon atoms of two aromatic rings. 1H NMR data provide strong evidence that cation-pi(arene) interactions with the sidearms participate in binding also in solution.

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