Showing papers in "Supramolecular Chemistry in 2008"
TL;DR: In this article, the interaction of tetrapropoxy-p-tert-butyl-calix[4]arene (1) with H3O+ ions produced by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) and traces of water was studied in nitrobenzene-d 5.
Abstract: Using 1H and 13C NMR spectroscopy, the interaction of tetrapropoxy-p-tert-butyl-calix[4]arene (1) with H3O+ ions produced by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) and traces of water was studied in nitrobenzene-d 5. It was shown that 1 readily forms an equimolecular complex with H3O+. The equilibrium constant K of its formation is 2.6 at 296 K. Exchange between bound and free 1 is fast even under mild excess of HDCC, the correlation time τex being about 0.13 ms. NMR shows that H3O+ is bound to the aryl-oxygen atoms and this binding forces the calixarene cup to adopt a more open and symmetrical conformation. This conclusion is in full accord with high precision quantum DFT calculations which find one structure of the complex corresponding to a global energy minimum, in which the H3O+ ion is bound to three of the oxygen atoms by strong hydrogen bonds and to the remaining oxygen by two weaker hydrogen bonds. The calixarene part is forced into a C4 symmetrical opened form. When stored for weeks, the ...
79 citations
TL;DR: Using 1H and 13C NMR, FT IR spectroscopy together with quantum mechanical DFT calculations, this paper showed that tetraethyl p-tert-butylcalix[4]arene tetraacetate (1) forms a stable equimolecular complex with proton in the form of hydroxonium ion in acetonitrile-d 3.
Abstract: Using 1H and 13C NMR, FT IR spectroscopy together with quantum mechanical DFT calculations, we show that tetraethyl p-tert-butylcalix[4]arene tetraacetate (1) forms a stable equimolecular complex with proton in the form of hydroxonium ion in acetonitrile-d 3. Protons for this complex were offered by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) and converted to hydroxonium ions by traces of water. The complex 1·H3O+ adopts a slightly asymmetric conformation, which is distinctly more cone-like than ligand 1. According to spectral evidence, the hydroxonium ion H3O+ is bound mainly to three of the phenoxy oxygen atoms of 1 by strong hydrogen bonds leaving the ester carbonyl groups, which are the usual coordination site for metal cations, free. Theoretical DFT calculations support the bonding to phenoxy oxygen atoms but slightly prefer a structure with one of the carbonyls being involved in the coordination.
70 citations
TL;DR: The interest in anion coordination chemistry has grown enormously in the last few years as discussed by the authors, and macrocyclic and macro-cyclic-based architectures are at the forefront of the development of new anion receptors.
Abstract: The interest in anion coordination chemistry has grown enormously in the last few years. Macrocyclic and macrocyclic-based architectures are at the forefront of the development of new anion receptors. This mini review is intended to illustrate some of the goals achieved recently in this field highlighting examples that appeared in the literature over the period 2005–2006.
60 citations
TL;DR: In this article, the interaction between cucurbit[n]uril (n = 7, 8) and carboxylate modality of anticancer drug camptothecin (CPT) was studied.
Abstract: The interaction between cucurbit[n]uril (n = 7, 8)(Q[n]) with two forms namely lactone modality and carboxylate modality of anticancer drug camptothecin (CPT) was studied. The results revealed that the combination of Q[n] with the lactone form of CPT was observed by electronic absorption spectroscopy, fluorescence spectroscopy and 1H NMR technique in the acid solution (pH 2) and the total stability constants β were also obtained by Job plot with a host:guest ratio of 2:1; while in the phosphate buffer solution (pH 7.4), only Q[8] bound the carboxylate form of CPT in ratio 1:1, but no obvious interaction between Q[7] and the carboxylate form of CPT was observed. The solubility of CPT was enhanced up to about 70 and 8 times at pH 2 due to the formation of interaction complexes with Q[7] and Q[8], respectively, by using phase solubility method. The cytotoxicity tests revealed that compared with the free CPT, the complexes of Q[n] and CPT had the same cytotoxic activity on the human lung cancer cell line A549...
58 citations
TL;DR: In this article, a water-soluble cavitand was shown to form 1:1 complexes with a series of acyclic and cyclic aliphatic carboxylic acids, and isothermal titration calorimetry was used to determine the standard molar enthalpy change (ΔH°) and binding constant (K a) for the different complexes.
Abstract: A water-soluble cavitand was shown to form 1:1 complexes with a series of acyclic and cyclic aliphatic carboxylic acids. Isothermal titration calorimetry was used to determine the standard molar enthalpy change (ΔH°) and binding constant (K a), and hence the Gibbs free energy (ΔG°) and entropy (ΔS°) change for the different complexes. The thermodynamic determinations were carried out from 288 to 318 K, allowing the standard molar heat capacity changes ( ) also to be derived. Typical of the processes driven by the hydrophobic effect, was observed to be proportional to the accessible (non-polar) surface area of the guest. The cyclic and acyclic guests displayed opposite trends; the heat capacity penalty upon binding increased with longer aliphatic chains, while the opposite was observed with the cyclic guests.
46 citations
TL;DR: In this article, the symmetrical dicyclohexanocucurbit[6]uril, (CyH)2Q[6], was synthesized by the controlled condensation of the diether of cyclohexanol and the dimer of glycoluril.
Abstract: The symmetrical dicyclohexanocucurbit[6]uril has been synthesised by the controlled condensation of the diether of cyclohexanoglycoluril (1) and the dimer of glycoluril (2). The symmetrical dicyclohexanocucurbit[6]uril, (CyH)2Q[6], characterised by the 1H NMR spectroscopy, ESMS and further confirmed by single crystal X-ray diffraction of a cobalt aqua exclusion complex, which demonstrates an ellipsoid cavity. Within a cucurbit[6]uril ellipsoid cavity, an inclusion complex of 5,5′-dimethyl-2,2′-bipyridine adopts a preferred orientation, aligning with the longest axis. The ellipsoid cavity is further supported by semiempirical AM1 gas phase calculations. Preferential orientation of a guest within the ellipsoid cavity of the symmetrical dicyclohexanocucurbit[6]uril
38 citations
TL;DR: In this paper, the design, synthesis and photophysical evaluation of four anthracene based photo-induced electron transfer (PET) sensors (3a-d) for anions is described.
Abstract: The design, synthesis and photophysical evaluation of four anthracene based photoinduced electron transfer (PET) sensors (3a–d) for anions is described. The [4π+4π] photodimerization product, 4, was also obtained from 3b, by slow evaporation from DMSO solution and its X-ray crystal structure determined. The structure of 4 showed the classical dimerization at the 9,10-positions of anthracene. Sensors 3a–d are all based on the use of charge neutral aryl urea receptors, where the recognition of anions such as acetate, phosphate and iodide, was due to the formation of strong hydrogen bonding interactions in DMSO. This anion recognition resulted in enhanced quenching of the anthracene excited state via electron transfer from the receptor; hence the emission was ‘switched on–off’. The sensing of fluoride was, however, found to be a two-step process, which involved initial hydrogen bonding interactions with the receptor, followed by deprotonation and the formation of bifluoride ( ). The changes in the emission s...
35 citations
TL;DR: In this article, 2D NOESY 1H NMR spectroscopy data reveal an unusual head-to-tail packing mode in aqueous solutions, resulting from the cooperative effect of weak hydrophobic interactions.
Abstract: Two amphiphilic water-soluble sulfonatomethylated calix[4]resorcinarene derivatives were studied by various 1H NMR techniques (1H NMR titration, 2D NOESY, NMR diffusion measurements). The derivative with methyl moieties at the lower rim (1) was found to be non-aggregated in the range 0–10 mM in aqueous solutions. Lengthening of the lower rim substituent to pentyl (2) results in self-aggregation of 2 in aqueous solutions with the aggregation number varying from 3 at 1 mM to 20 at 10 mM. The 2D NOESY 1H NMR spectroscopy data reveal an unusual head-to-tail packing mode in aqueous solutions, resulting from the cooperative effect of weak hydrophobic interactions. Binding of guests (tetramethylammonium and N-methylpyridinium) results in additional stabilization of the aggregates whilst the head-to-tail packing mode of the aggregate is retained.
34 citations
TL;DR: In this paper, diffusion NMR was used to evaluate the relative stability of hydrogen-bond molecular capsules and determine the role played by water molecules in the self-assembly of these capsules.
Abstract: Hydrogen-bond molecular capsules have attracted much interest in the last decade. In the present paper, we wish to describe new insights obtained from diffusion NMR when studying the self-assembly of resorcin[4]arenes (2), pyrogallol[4]arenes (3) and octahydroxypyridine[4]arenes (4) in solution. These diffusion NMR studies demonstrate that compounds 2 and 3 self-assemble spontaneously into hexameric capsules in organic solvents. For compound 4, both hexameric capsules and dimeric aggregates were identified. Diffusion NMR was found to be very useful in evaluating the relative stability of these capsules as well as in determining the role played by water molecules in the self-assembly of such systems. Moreover, diffusion NMR enabled us to establish whether the self-assembly of these capsules proceeds with self-sorting. We could demonstrate that the hexamers of 3 are more stable than the hexameric capsules of 2 and that the formation of such hexamers proceeds with self-sorting and no hetero-hexamers are form...
33 citations
TL;DR: How proteins and synthetic compounds bind NO3 −, with an emphasis on crystal structures and calculations, is discussed, which shows synthetic compounds that best mimic proteins in their types of non-covalent interactions are generally the most effective for binding NO3−.
Abstract: Synthetic receptors have been developed for anions such as chloride, phosphate, sulphate and carboxylate. Development of selective receptors for nitrate has, however, been more difficult. Theoretical calculations show that a six-coordinate geometry is the ideal geometry for coordinating NO3 − . Crystallographic data show, however, that NO3 − usually adopts a two- or three-coordinate geometry when interacting with receptors. In this review, we briefly discuss the role of NO3 − in human health and its physical properties. We discuss how proteins and synthetic compounds bind NO3 − , with an emphasis on crystal structures and calculations. Synthetic compounds that best mimic proteins in their types of non-covalent interactions are generally the most effective for binding NO3 − .
32 citations
TL;DR: Two new glucoclusters 2a and 2b, in which the sugar units are connected to the upper rim of methoxycalix and calix[8]arene derivatives via thiourea linkages, were synthesised and their aggregation properties in water studied by 1H NMR, atomic force microscopy and dynamic light scattering to give useful insights into the mode of binding of calixarene-based glycoclusters with lectins.
Abstract: Two new glucoclusters 2a and 2b, in which the sugar units are connected to the upper rim of methoxycalix[6]- and calix[8]arene derivatives via thiourea linkages, were synthesised and their aggregation properties in water studied by 1H NMR, atomic force microscopy and dynamic light scattering. Small size aggregates (2–10 nm diameter) are formed by both macrocycles, which become much larger (200–300 nm) in the presence of a phosphate buffer, whereas other anions have no effect. The glycoclusters 2a and 2b interact with plasmid DNA but do not condense it, while in the presence of a glucose-specific lectin such as Concanavalin A (ConA) agglutination occurs. The data obtained give useful insights into the mode of binding of calixarene-based glycoclusters with lectins. The self-aggregation properties in water solution of glucosylthioureidocalix[6]- and [8]arenes were studied by a combination of different techniques. These glycocalixarenes showed a specific interaction with phosphate ion and ConA evidenced by an...
TL;DR: In this paper, a highly cationic spherical polymeric polysilicon polymer is presented, where the rate of polymerization and the molecular weight of the polymer are controlled by a well-defined nanocavity.
Abstract: Polymerisation within a well-defined nanocavity leads to the precise control of the rate of polymerisation and the molecular weight of the resultant polymer. We prepared a highly cationic spherical...
TL;DR: In this paper, the photophysical behavior and the binding ability of a calix[4]arene derivative with some anions were investigated by fluorescence spectrometry and 1H NMR experiments.
Abstract: A calix[4]arene derivative (1) possessing imidazo[4,5-f]-1,10-phenanthroline groups and its Ru(II) complex (2) have been prepared. The photophysical behavior and the binding ability of 1 and 2 with some anions were investigated by fluorescence spectrometry and 1H NMR experiments. The complex stability constants (K S) for the stoichiometric 1:1 complexation of 1 and 2 with the anions were obtained by the fluorimetric titrations, indicating that the binding abilities of both hosts for F− and AcO− are highest among all anions examined. Interestingly, compound 1 can be used as a colorimetric sensor to F− and AcO− due to anion-induced deprotonation of the NH group of the imidazole ring. In contrast, the addition of Cl− , Br− , I− and to the DMF solution of 2 enhances its relative emission intensity, while the addition of F− and AcO− quenches its fluorescence intensity.
TL;DR: In this paper, a quantitative study of the effects of the number and placement of positive charges on the binding of viologen guests to cucurbit[7]uril and cucurbits[8] was performed.
Abstract: Recent developments in the synthesis and applications of the cucurbit[n]uril family of synthetic hosts has led to an increasing interest in the detailed studies of their interactions with a wide variety of guests. This paper describes a quantitative study of the effects of the number and placement of positive charges on the binding of viologen guests to cucurbit[7]uril and cucurbit[8]uril. A series of viologen derivatives with one to four charges was characterised by isothermal titration calorimetry, 1H NMR spectroscopy and mass spectrometry to determine the stoichiometry, affinity and mode of binding. These data show that stoichiometry can be controlled by the placement of charge, and that affinity can be increased by the addition of positive charges. This study should serve as a guide for the design of supramolecular structures built from viologens and cucurbit[n]urils.
TL;DR: In this article, the authors highlight work on transferring non-covalently bound aggregates to the gas phase by soft ionisation methods, such as electrospray ionisation, and investigate structure and encapsulation properties under solvent-free conditions.
Abstract: Supramolecular capsules composed of two or more self-complementary monomers held together by hydrogen bonds and other weak interactions such as cation–π and C–H–π interactions are able to encapsulate neutral as well as positively charged guests. This mini review will highlight work on transferring such non-covalently bound aggregates to the gas phase by soft ionisation methods, such as electrospray ionisation, and investigating structure and encapsulation properties under solvent-free conditions. These analyses reveal exact information about complex stoichiometry as well as about structure and stability of capsules composed of multiple building blocks. The review is organised such that each type of capsule introduced contributes a new aspect to the overall picture.
TL;DR: In this paper, a redox-responsive inclusion complexation system based on β-CD and poly(NIPAM/FCN) was obtained, where the authors investigated the effect of this complexation on the solution properties of this polymer.
Abstract: Ferrocene-functionalized polymers (poly(NIPAM/FCN)) and their β-CD (β-Cyclodextrin) complex have been prepared. The inclusion complexation between them was investigated by several techniques, including 1H NMR spectra, cyclic voltammetry, UV–vis spectra and dynamic light scattering measurements. The results showed that β-CD could interact with the reduced ferrocene side groups and hardly affect the oxidized form. Thus a redox-responsive inclusion complexation system based on β-CD and poly(NIPAM/FCN) was obtained. In addition, the effect of this inclusion complexation on the solution properties of this polymer was also investigated. LCST (lower critical solution temperature) increased and the viscosity decreased upon addition of β-CD into the reduced polymer solution due to the disruption of the hydrophobic interaction between the ferrocene side groups by the inclusion complexation. Yet LCST and viscosity of the oxidized polymer solution changed slightly, which resulted from the weak interaction exerted by ...
TL;DR: The cone conformer of calix[4]arenes has been evaluated by means of liquid-liquid extraction for a large variety of metal ions and the extraction constants and the stoichiometries of the complexes formed have been determined as discussed by the authors.
Abstract: The binding properties of the cone conformer of O,O,O,O-tetrakis[hydrazinocarbonylmethyl]-4-tert-butylcalix[4]arene, the cone and the 1,3-alternate conformers of the corresponding thia analogue have been evaluated by means of liquid–liquid extraction for a large variety of metal ions. The extraction constants and the stoichiometries of the complexes formed have been determined. Comparison of the extraction properties of calix[4]arenes with their acyclic monomeric analogue clearly demonstrated, that the preorganization of acetylhydrazide groups on the calix[4]arene platform is the cause for a significant improvement of its binding properties. The presence of additional “soft” nitrogen binding sites in acetylhydrazide derivatives of calix[4]arenes compared to their amide derivatives leads to a shift from their classical selectivity for alkali and alkaline earth cations to transition metals. The cone conformer of tetrathiacalix[4]arene shows higher selectivity in a series of d-metal ions compared with its “c...
TL;DR: A neutral 4-amino-1,8-naphthalimide-based anion receptor 1 containing a thiourea binding site was synthesized by simple steps as mentioned in this paper.
Abstract: A neutral 4-amino-1,8-naphthalimide-based anion receptor 1 containing a thiourea binding site was synthesized by simple steps. Its recognition capabilities for various anions were investigated by UV–vis, fluorescence and 1H NMR spectra, which showed that compound 1 could effectively and selectively recognize F− and AcO− over other anions (Cl− , Br− , I− , , , ). In particular, a moderate color change (from greenish yellow to bright yellow) and significant fluorescence quenching were synchronously observed upon addition of F− or AcO− . Nonlinear curve fitting and Job plot method established the formation of 1:1 hydrogen-bonding complex between compound 1 and the bound anions.
TL;DR: In this paper, a series of negatively charges azo-dyes were synthesized and positive charged glass slides were immersed into their aqueous solutions, which revealed the hydrogel as the stable form of this compound under equilibrium conditions.
Abstract: This article highlights the aggregation behaviour of potential low molecular weight hydrogelators on attracting surfaces. Our goal was the development of a method, which enables the finding of new hydrogelators that are not easily recognizable as such because they only form instable or no hydrogels in aqueous solution. To this end, a series of negatively charges azo-dyes was synthesized and positive charged glass slides were immersed into their aqueous solutions. All dyes showed supramolecular organization and significant concentration on the attracting glass surface. Microscopic investigations mostly revealed the formation of crystals. However, one compound, (1-(2-n-octylphenylazo)-2-hydroxy-6-naphthalenesulphonate, selectively formed a hydrogel on the surface whereas it does not gel in aqueous solution. This reveals the hydrogel as the stable form of this compound under equilibrium conditions. This method of surface-induced hydrogelation might facilitate the identification of new hydrogelators. Further ...
TL;DR: A variety of amide-substituted anthracene derivates have been synthesised and their anion complexation properties studied using 1H-NMR titration techniques and have been shown to serve as excellent receptors for oxo-anions and to function as sensors via fluorescence quenching in DMSO-d 6.
Abstract: A variety of amide-substituted anthracene derivates have been synthesised and their anion complexation properties studied using 1H-NMR titration techniques. Additionally, bis-urea functionalised anthracene derivatives have been shown to serve as excellent receptors for oxo-anions and to function as sensors via fluorescence quenching in DMSO-d 6 /0.5% water and MeCN/DMSO (96.5:3.5 v/v).
TL;DR: In this article, a viologen-based thread molecule with a thiol terminus was designed to synthesise a stable cucurbit[8]uril-stabilized charge-transfer (CT) complex on gold, which can be regulated by electrochemical stimuli.
Abstract: The reversible formation of cucurbit[8]uril (CB[8])-stabilized charge-transfer (CT) complex on gold, which can be regulated by electrochemical stimuli, is reported. A viologen-based thread molecule with a thiol terminus was designed to synthesise a stable CB[8]-threaded [2]pseudorotaxane (5 2 + ). A mixed self-assembled monolayer (SAM) of 5 2 + and 3-mercaptopropionic acid (3-MPA) on gold was prepared and characterised by reflectance FT-IR spectroscopy. The formation and disruption of a CT complex on surface was investigated by cyclic voltammetry with the SAM on gold as a working electrode in a supporting electrolyte solution containing 2,6-dihydroxynaphthalene (DHNp). The cathodic peak was shifted to a more negative potential (ΔE∼40 mV) when compared with that measured without DHNp in the electrolyte, which confirmed the formation of a CT complex on gold upon immersion of the SAM of 5 2 + on gold in the supporting electrolyte containing DHNp. When the viologen unit was reduced, the CT complex was destr...
TL;DR: In this article, a mini-review discusses a different type of calixarene inclusion complexes, where the inclusion event occurs due to the coordination of an organic or inorganic ligand to a metal centre attached to the lower rim of the calix[4]arene.
Abstract: Calixarene molecules are often associated with their ability to form inclusion complexes with organic or inorganic guests. These complexes are usually formed due to the guest molecule interactions with the calixarene aromatic cavity and/or substituents attached to it. The present mini-review discusses a different type of calixarene inclusion complexes, where the inclusion event occurs due to the coordination of an organic or inorganic ligand to a metal centre attached to the lower rim of calix[4]arene. Structural and chemical properties of such complexes of ‘uninvited’ guests are discussed.
TL;DR: In this paper, the interaction between apoCopC and Vitamin B6 has been investigated in detail by means of fluorescence spectroscopy, and the authors concluded that a novel supramolecular system is generated.
Abstract: In neutral phosphate buffer solution of pH 7.0, the interaction between apoCopC and Vitamin B6 has been investigated in detail by means of fluorescence spectroscopy. According to the change of Vitamin B6 fluorescence spectra and fluorescence polarization, we can conclude that a novel supramolecular system is generated. ApoCopC can form a 1:5 host-guest inclusion supramolecular complex with Vitamin B6, and the formation constant has been calculated to be (2.24 ± 0.08) × 104 M− 1. It suggests the strong inclusion ability of apoCopC to the guest molecules. In addition, the mechanism of the apoCopC protein fluorescence quenching by Vitamin B6 was also discussed. And based on the Stern-Volmer equation, the apparent quenching constant was estimated to be (2.75 ± 0.05) × 104 M− 1.
TL;DR: In this paper, a series of pyrogallol[4]arenes from ethyl acetate as hydrogen-bonded nanocapsules is crystallized and structural study allows for the determination of the dependence of inter-capsule spacing on the chain length present at the lower rims of these ‘bowl-shaped’ molecules.
Abstract: Upon crystallising a series of pyrogallol[4]arenes from ethyl acetate as hydrogen bonded nanocapsules, structural study allows for the determination of the dependence of inter-capsule spacing on the chain length present at the lower rims of these ‘bowl-shaped’ molecules. Surprisingly, these nanocapsules pack closest together when a hexyl chain length is employed, and reasons for this phenomenon are suggested.
TL;DR: Gold nanorods encapsulated and dispersed into organic solvents by tetrabenzylthiol resorcinarene and by a poly(dithiocarbamate) derived from tetra-N-methyl(aminomethyl)resorcinne (TMAR-DTC) proved to be highly effective at enabling the redispersion of GNRs in various organicsolvents.
Abstract: Gold nanorods (GNRs) were encapsulated and dispersed into organic solvents by tetrabenzylthiol resorcinarene (TBTR) and by a poly(dithiocarbamate) derived from tetra-N-methyl(aminomethyl)resorcinarene (TMAR-DTC), formed by the in situ condensation of TMAR with carbon disulphide. The latter proved to be highly effective at enabling the redispersion of GNRs in various organic solvents. GNRs encapsulated in TMAR-DTC exhibited a strong solvatochromic response, with a refractive index sensitivity of more than 300 nm/RIU. The resorcinarene-encapsulated GNRs could withstand high temperatures for a short period of time, and could be used to nucleate the growth of magnetic nanoshells.
TL;DR: In this paper, brominated calixpyrrole derivatives were prepared using N-bromosuccinimide (NBS) as the brominating agent and anion binding studies carried out by isothermal titration calorimetry (ITC) in 1,2-dichloroethane with Cl−−
Abstract: Calix[4]pyrrole derivatives bearing long n-alkyl ester chains have been synthesized from calix[4]pyrroles containing carboxylic acid functional groups. These systems, which contain ester groups on either the meso- carbon atoms of the calixpyrrole ring or the β-positions of individual pyrrole rings, were prepared from the corresponding carboxylic acids. Esterification was effected using dicyclohexylcarbodiimide/4-dimethylaminopyridine (DCC/DMAP) to obtain long alkyl chain substituted calix[4]pyrroles. In the context of this work, several brominated calixpyrrole derivatives were prepared using N-bromosuccinimide (NBS) as the brominating agent. Anion binding studies carried out by isothermal titration calorimetry (ITC) in 1,2-dichloroethane with Cl− and in the form of their respective tetrabutylammonium salts, revealed that the functionalized ester derivatives have anion binding affinities similar to those of the unsubstituted “parent” systems, octamethylcalix[4]pyrrole (1) and β-octabromocalix[4]pyrrole (2...
TL;DR: It was demonstrated for the 1- ATP and ADP complexes that association strength is increased in the absence of salt (NaCl), and receptor 1 shows a slight preference for the complexation of UMP over nucleotides containing A (adenine), G (guanine), C (cytosine) or T (thymine) as bases.
Abstract: Water soluble dicationic cyclophane-type macrocycles bearing two anthraquinone (1) or two acridine groups (2) have been prepared by chemical modification of S,S-(+)-tetrandrine. Complexation of nucleotide anions (mono- di- and triphosphates) and D/L phenylalanine by tetrandrine derivatives has been studied by UV-Visible and fluorescence titrations in water. Association of nucleotides to semi-synthetic hosts 1 and 2 increases with increasing guest charge in the series AMP2 − < ADP3 − < ATP4 − . It was demonstrated for the 1- ATP and ADP complexes that association strength is increased in the absence of salt (NaCl). Besides, receptor 1 shows a slight preference for the complexation of UMP over nucleotides containing A (adenine), G (guanine), C (cytosine) or T (thymine) as bases. The major forces stabilizing the complexes result from ion pairing between the charged groups of host and guest and from stacking or hydrophobic interactions. Receptor 1 displayed chiral recognition towards D/L phenylalanine.
TL;DR: In this paper, the authors performed NMR titrations with meso-octamethylcalix[4]pyrrole and a variety of organic chloride and bromide salts in dichloromethane-d 2.
Abstract: Proton NMR titrations have been performed with meso-octamethylcalix[4]pyrrole and a variety of organic chloride and bromide salts in dichloromethane-d 2 . The results show apparently increasing chloride stability constants within each set of anion salts (tetrabutylammonium < imidazolium < pyridinium). Addition of 1-ethyl-3-methylimidaolium (EMIM) nitrate to dichloromethane-d 2 solutions of calix[4]pyrrole caused significantly larger downfield shifts of the pyrrole NH protons of calix[4]pyrrole than addition of equimolar quantities of tetrabutylammonium nitrate. The first crystal structure of a nitrate complex of a calix[4]pyrrole is also presented.
TL;DR: In this paper, the bromination/dehydrobromination of stilbenophanes was applied to the synthesis of tolanophanes 1a (n = 2) and 1b (n= 4).
Abstract: The bromination/dehydrobromination of stilbenophanes as a practical, simple and efficient strategy is applied to the synthesis of tolanophanes 1a (n = 2) and 1b (n = 4). The method is significantly superior to the reported methods. A careful conformational study on a novel tolanophane 1b showed that the relative stability of its conformers is directly linked to both twist angle between the two arene rings and the orientation of the alkoxy groups. The strong interaction between 1b and CDCl3 at − 60°C is an unusual feature that is attributed to high restriction in its molecular motion.
TL;DR: A large part of all anticancer drugs contain DNA-binding molecules as mentioned in this paper, emphasising their paramount medicinal significance, and very often, the intensive study of natural products with respect to th...
Abstract: DNA-binding molecules constitute a large part of all anticancer drugs, emphasising their paramount medicinal significance [1]. Very often, the intensive study of natural products with respect to th...