Showing papers in "Supramolecular Chemistry in 2007"
TL;DR: The potential of cucurbiturils, water-soluble macrocyclic host molecules composed of glycoluril units, for tuning the properties of fluorescent dyes and advancing new applications is illustrated and original experimental results for the effect of CB7 on the fluorescence properties of three dyes are presented.
Abstract: The potential of cucurbiturils, water-soluble macrocyclic host molecules composed of glycoluril units, for tuning the properties of fluorescent dyes and advancing new applications is illustrated. Cucurbit[7]uril (CB7), which presents a particularly attractive derivative due to its intermediary size and high water solubility, has been shown to display a variety of advantageous effects on fluorescent dyes, which include increased fluorescence intensity and brightness, enhanced photostability, protection towards fluorescence quenchers, solubilization, and deaggregation. Particularly noteworthy is the prolongation of the fluorescence lifetimes of different dyes, which can be traced back to the low polarizability of the host cavity. In addition, the host serves as cation receptor, which causes a considerable shift of protonation equilibria and assists the protonation of fluorescent dyes. The latter effect can be exploited in the design of protolytic fluorophore displacement assays. The perspective of cucurbitu...
229 citations
TL;DR: In this paper, the stability constants (K), reaction enthalpy (H°), and entropy (ΔS°) for complexation of cucurbit[6]uril (CB[6]) with a series of aliphatic alcohols, mono-and diamines, as well as spermidine and spermine, in aqueous solutions of alkali metal chlorides were determined.
Abstract: Using the isothermal calorimetric titration technique, we determined the stability constants (K), reaction enthalpy (ΔH°), and entropy (ΔS°) for complexation of cucurbit[6]uril (CB[6]) with a series of aliphatic alcohols, mono- and diamines, as well as spermidine and spermine, in aqueous solutions of alkali metal chlorides. The K for spermine reached 5.4 × 1010 M− 1 in 0.2 M LiCl, which is the largest amongst the values reported for CB[6]. Propylamine forms the strongest 1:1 complex with CB[6] (K = 21000 M− 1) in 0.1 M Na acetate buffer, which is driven exclusively by entropy. A comparison of K for 1,3-propanediamine versus 1,4-butanediamine reveals an extraordinary >60000-fold enhancement in affinity, which is the largest increment/CH2 ever observed in supramolecular chemistry. The present results in combination with our ESI-MS data reported recently unambiguously demonstrate that CB[6] exists in aqueous solution of alkali metal salts exclusively as a dicationic species, e.g. [CB[6]·2Na]2+.
107 citations
TL;DR: Urea and thiourea inclusion compounds are well known to exhibit a wide range of fundamentally important physico-chemical properties, and through the work of many research groups, these materials have served as model systems for exploring a range of issues of wider relevance to other classes of organic solids.
Abstract: Urea and thiourea inclusion compounds are well known to exhibit a wide range of fundamentally important physico-chemical properties, and through the work of many research groups, these materials have served as model systems for exploring a range of issues of wider relevance to other classes of organic solids. While continuing to investigate these issues, our research in recent years has also focused on issues of a more applied nature, including crystal growth processes, guest exchange processes, the design and development of X-ray dichroic filter materials, and the development of strategies for direct experimental determination of intermolecular interaction energies. This article presents a brief overview of fundamental properties of urea and thiourea inclusion compounds, and reviews some of our recent work in the specific areas identified above.
95 citations
TL;DR: Using 1H and 13C NMR together with density functional theoretical (DFT) calculations, it was shown that p-tert-butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide) (1) forms a stable equimolecular complex with proton in the form of hydroxonium ion in nitrobenzene-d 5.
Abstract: Using 1H and 13C NMR together with density functional theoretical (DFT) calculations, it is shown that p-tert-butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide) (1) forms a stable equimolecular complex with proton in the form of hydroxonium ion in nitrobenzene-d 5. Protons 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 but rapidly motionally averaged conformation, which is distinctly more cone-like than ligand 1. The hydroxonium ion H3O+ is bound partly to thiocarbonyl sulphur atoms and partly to phenoxy oxygen atoms of 1 by strong hydrogen bonds and other electrostatic interactions.
75 citations
TL;DR: In this paper, a mini-review of intermolecular interactions ranging from hydrogen bonding to ionic interactions to aromatic interactions is presented, and the conformational changes between stacked and edge-to-face conformers in benzoquinone-benzene complexes are discussed.
Abstract: In this mini-review we briefly describe intermolecular interactions ranging from hydrogen bonding to ionic interactions to aromatic interactions. Manifestation of these interaction forces is in the design and realization of various ionophores with chemo-sensing capability for biologically important cations and anions. We also explain how the understanding of hydrogen bonding and π-interactions has led to the design of self-assembled organic nanotubes. We further discuss the conformational changes between stacked and edge-to-face conformers in benzoquinone-benzene complexes, which are controlled by alternating electrochemical potential. The resulting flapping motion illustrates a promising pathway toward the design of nanomechanical devices.
69 citations
TL;DR: The recent development of anion selective fluorescent chemosensors reported from the group are covered, which includes urea or thiourea derivatives, imidazolium derivatives, Zn-DPA derivatives and boronic acid modified systems.
Abstract: Sensing anions via fluorescence changes has been an active research target in recent years due to its simplicity and the high detection limits this approach permits. In this mini review, we cover the recent development of anion selective fluorescent chemosensors reported from our group. We classify the anion selective fluorescent chemosensors according to their topology and structure, which includes urea or thiourea derivatives, imidazolium derivatives, Zn-DPA derivatives and boronic acid modified systems.
61 citations
TL;DR: In this paper, the authors investigated the complexation behaviors of acridine red (AR), neutral red (NR) and rhodamine B (RhB) dye guest molecules by three kinds of supramolecular hosts, including β-cyclodextrin (β-CD), calix[4]arene tetrasulfonate (C4AS) and cucurbit[7]uril (CB[7]), in aqueous citrate buffer solution (pH 6.0).
Abstract: The complexation behaviors of acridine red (AR), neutral red (NR) and rhodamine B (RhB) dye guest molecules by three kinds of supramolecular hosts, including β-cyclodextrin (β-CD), calix[4]arene tetrasulfonate (C4AS) and cucurbit[7]uril (CB[7]), have been investigated by means of fluorescence spectra in aqueous citrate buffer solution (pH 6.0). The results obtained show that the three hosts, possessing different types of cavity, lead to various complexation-induced fluorescence of dye guests, and present different binding ability and molecular selectivity. The complexation stability constants decrease in the order of NR > AR > RhB for C4AS and CB[7] hosts, while in the order of RhB > AR > NR for β-CD host. Particularly, CB[7] displays the strongest binding ability with NR (K S = 33300 M− 1), and provides the molecular selectivity of 4.8 for NR/AR pairs. Although the binding ability of C4AS for present dye guests is weaker than CB[7], but the molecular selectivity of the two hosts are nearly equivalent. β-...
57 citations
TL;DR: In this paper, an electron acceptor and a donor of perylene diimide dyes (4a, 4b) were synthesized in an effective way and the π-π interactions between them were discussed in solution and in solid state.
Abstract: An electron acceptor and a donor of perylene diimide dyes (4a, 4b) were synthesized in an effective way. And the π–π interactions between perylene diimide dyes were discussed in solution and in solid state. The existence of weak π–π interactions in 4a, 4b and their mixture was confirmed with UV/vis and fluorescence spectra in dilute solution. Furthermore, the 1H-NMR studies displayed strong π–π interactions in concentrated solution. The packing behavior in solid state was discussed with solid state fluorescence, confocal fluorescence micrograph, scanning electron microscopy and powder X-ray diffraction, indicating stronger intermolecular interactions of 4a–4b than that of 4a–4a or 4b–4b.
50 citations
TL;DR: A concise summary of the advances made over the past four years to produce functional supramolecular devices such as sensors, enzyme assays, and lead candidates for pharmaceutical development is presented.
Abstract: It is 25 years since the first report of a synthetic ion channel transporter. Today, dozens of molecular and supramolecular designs have been developed to facilitate ion and small molecule transport across a bilayer membrane. Presented here is a concise summary of the advances made over the past four years. The transporters are grouped into three mechanistic classes: mobile carrier, monomeric channel, and self-assembled pore. Common building blocks are crown ethers, steroids, cyclodextrins, peptides, curcubiturils, and calixarenes. The eventual goal is to produce functional supramolecular devices such as sensors, enzyme assays, and lead candidates for pharmaceutical development.
47 citations
TL;DR: The properties of dendrimers that make them so applicable to sensing are demonstrated, as well as a review of surface functionalized polyamidoamine, polyamine, and polypeptides that have been employed for biological, chemical and molecular sensing.
Abstract: Dendrimers are three dimensional nanosized synthetic molecules that have internal cavities and numerous surface groups. In recent times they have received increased attention in sensing applications. For dendrimers to be used as sensors, they most commonly require functionalization at their surface. This is because the surface is generally the first point of contact between the dendrimer and the outside world, hence surface functionalization serves to selectively home in on the target analyte. Further, sensor signals may be transmitted through surface functionalities e.g. fluorochromic molecules. It is therefore important to document surface functionalization approaches. Dendrimers with amine surface groups have the advantage of being able to be conjugated to other molecules via an amide linkage, which is one of the most fundamental and widespread chemical bonds in nature. In this paper we demonstrate the properties of dendrimers that make them so applicable to sensing. We review several methods for funct...
45 citations
TL;DR: In this article, the first single-crystal X-ray crystallographic diffraction analysis of a dicationic heterophane showed a non-classic (C−H)+···Cl−" hydrogen bond between the imidazolium rings and halide anions and the formation of unconventional charged assisted hydrogen bonds.
Abstract: The first single-crystal X-ray crystallographic diffraction analysis of a dicationic heterophane showed a non-classic (C–H)+···Cl− hydrogen bond between the imidazolium rings and halide anions and the formation of unconventional charged assisted hydrogen bonds, which were the non-covalent forces driving the anion interactions shown by the dications 4·2X. Here is reported the halide-templated controlled synthesis and chemical response in basic media of 4·2X. Their structural properties were examined at the gas phase by electrospray ionization mass spectrometry in the negative-ion mode and in the solid-state by X-ray crystallography. Thus, the negative-ion ESI-MS response showed that the formation of non-covalent self-aggregates of macrocyclic dications is a consequence of hydrogen-bonded complexes with halide anions. Notably, X-ray diffraction of dication 4a·2Cl·2H2O provides evidence for the H-bonding network, which has a crucial role in crystal packing. The solid-state aggregates showed that chloride an...
TL;DR: The binding of the polyaromatic guest, 3,6-diaminoacridine (Proflavine) to cucurbit[n]uril (CB[n]) where n = 6, 7 and 8 has been studied by fluorescence spectrophotometry and binding constants determined using a least squares fitting method.
Abstract: The binding of the polyaromatic guest, 3,6-diaminoacridine (Proflavine) to cucurbit[n]uril (CB[n]) where n = 6, 7 and 8 has been studied by fluorescence spectrophotometry and binding constants determined using a least squares fitting method. Titration of CB[8] into a solution of Proflavine results in a 95% decrease in fluorescence up to a CB[8] to Proflavine ratio of 2:1. From the induced fluorescence spectra a binding constant of 1.9 × 107 M− 1 was determined. When Proflavine is titrated into a solution of CB[8] a similar binding constant is calculated (1.3 × 107 M− 1). Titration of CB[6] into a solution of Proflavine yields a decrease in fluorescence of 18–20%, but no binding is observed beyond what is seen within experimental error. Finally, titration of CB[7] into a solution of Proflavine results in an increase in fluorescence (32%) and a blue-shift of the emission wavelength from 509 nm to 485 nm. From the induced fluorescence spectra a binding constant of 1.65 × 107 M− 1 was determined. From 1H NMR ...
TL;DR: In this paper, the synthesis and characterization of the head unit building blocks for Schiff-base reactions have been reported, and the crystal structures of the lead-II lead-base macrocyclic complexes are derived.
Abstract: The synthesis and characterization of sodium 3,5-diacetyl-1,2,4-triazolate (4 Me ) and sodium 3,5-dibenzoyl-1,2,4-triazolate (4 Ph ), both of which can be used as head unit building blocks in Schiff-base reactions, are reported. The crystal structures of sodium 3,5-diacetyl-1,2,4-triazolate, as [4 Me (H2O)]∞, and sodium 3,5-dibenzoyl-1,2,4-triazolate, as [4 Ph (CH3OH)2]2, have been determined. The former is a helical polymer whilst the latter is a methanol-bridged dimer. The lead(II) templated cyclization reaction of sodium 3,5-dibenzoyl-1,2,4-triazolate (4 Ph ) with 1,3-diaminopropane or 1,4-diaminobutane, respectively, leads to the formation of two new [2 + 2] Schiff-base macrocycles as their lead(II) complexes, [Pb2 L 3Ph (μ-OH)]ClO4 (5) and [Pb2 L 4Ph (μ-OH)]ClO4 (6), respectively. Transmetallation of 5 with nickel(II) ions yields a novel, structurally characterized, dinickel(II) macrocyclic complex, [Ni2 L 3Ph (NCS)2] (7), which features double triazolate bridging of the two five-coordinate nickel(II...
TL;DR: A new biindolyl scaffold was efficiently synthesized and modified into anion receptors 9 and 10 with extended hydrogen bond donors, which bind oxoanions such as phosphates and carboxylates by multiple hydrogen bonds in DMSO, both of which bind two or three orders of magnitudes higher than does a reference molecule 8.
Abstract: A new biindolyl scaffold, 7,7′-diamino-2,2′-biindolyl, 2 was efficiently synthesized and modified into anion receptors 9 and 10 with extended hydrogen bond donors. The receptor 9 possesses two indole NHs and two amide NHs, while 10 contains two indole NHs and four urea NHs. The receptors 9 and 10 bind oxoanions such as phosphates and carboxylates by multiple hydrogen bonds in DMSO, both of which bind two or three orders of magnitudes higher than does a reference molecule 8 with only two indole NHs. In addition, binding affinities of 10 with a series of dicarboxylates were also investigated, showing the association constants in between 1.6 × 105 M− 1 (malonate) and 8.1 × 105 M− 1 (adipate) in 10% (v/v) MeOH/DMSO at 22 ± 1°C.
TL;DR: The exclusive formation of 1:1 and 2:2 host-guest complexes between cucurbit[8]uril (CB[8]) and electron donor-acceptor (D-A) molecules by host-stabilized charge transfer (CT) interactions is reported in this article.
Abstract: The exclusive formation of 1:1 and 2:2 host–guest complexes between cucurbit[8]uril (CB[8]) and electron donor-acceptor (D–A) molecules by host-stabilized charge-transfer (CT) interactions is reported. Reaction of CB[8] with D–A molecule 1 2 + containing dipyridyliumylethylene as an electron-acceptor unit and 2,6-dihydroxynaphthalene as an electron-donor unit, which are connected by a but-2-enyl linker, resulted in the exclusive formation of 1:1 complex 2 2 + which has been characterized by UV-visible, NMR and mass spectrometry. The 1H-NMR spectrum of 2 2 + revealed that the acceptor and donor units of 1 2 + form an intramolecular CT complex inside the cavity of CB[8], which was also supported by a molecular modeling study. Another D–A molecule (3 2 + ), which contains a rigid 1,4-xylyl linker to connect a dipyridyliumylethylene unit and 2-hydroxynaphthalene unit reacts with CB[8] to form 2:2 complex 4 4 + exclusively. In 4 4 + , two molecules of 3 2 + form a CT complex with each other while the don...
TL;DR: In this paper, a short review presents some compounds that illustrate these features and general approaches to their preparation, as well as general approaches for their preparation and application in the development of porous coordination polymers.
Abstract: A significant challenge in the development of porous coordination polymers (PCP's), beyond control of pore size, is control of the shape and chemical nature of the pores. This short review presents some compounds that illustrate these features and general approaches to their preparation.
TL;DR: In this article, a coordination-driven potential supramolecular host system can be obtained via cyclic linkages of the metal ions and the bridging ligands, N-acylsalicylhydrazides.
Abstract: Metalladiazamacrocycles, coordination driven potential supramolecular host systems, can be obtained via cyclic linkages of the metal ions and the bridging ligands, N-acylsalicylhydrazides. The nuclearity and the shape of the metallamacrocycles could be modulated by controlling the steric interactions caused by N-acyl tails of the ligands. The macrocycles could be utilized for recognition of small organic guest molecules using their hydrophobicity/hydrophilicity, the size and shape/symmetry of the cavities. In addition, these macrocycles can be used as the supramolecular building blocks for the construction of systematically tuned metal-organic frameworks since these clusters have several replaceable solvent sites which could serve as connecting nodes for the formaton of network structures.
TL;DR: Dendrimer photosensitizers, composed of a focal photosensitizing unit surrounded by poly(benzyl ether) dendritic wedges, are introduced for photodynamic therapy (PDT) and show selective accumulation to the ophthalmic neovascular lesion and effective photodynamic effect.
Abstract: Recently, dendrimers are attracting much attention for their development as biomedical nano-devices. In the present paper, we introduce dendrimer photosensitizers, composed of a focal photosensitizing unit surrounded by poly(benzyl ether) dendritic wedges, for photodynamic therapy (PDT). Ionic dendritic porphyrins (DPs) formed supramolecular polyion complex (PIC) micelles through the electrostatic interaction with oppositely charged block copolymers, and showed no self-quenching effect of the focal photosensitizing unit due to the large dendritic wedges. The DP-loaded PIC micelles showed selective accumulation to the ophthalmic neovascular lesion and effective photodynamic effect. For the effective light delivery, dendrimer phthalocyanine (DPc) has also been developed and examined for its photodynamic effect.
TL;DR: In this paper, a short review highlights recent results in the chemistry of nonsymmetrically substituted uranyl-salophen complexes with specific reference to their synthesis and properties, and their use as receptors and catalysts is also emphasized.
Abstract: This short review highlights recent results in the chemistry of nonsymmetrically substituted uranyl-salophen complexes with specific reference to their synthesis and properties. Their use as receptors and catalysts is also emphasized. The possibility of modulating their structure within wide limits by choosing the proper substituted aldehydes and/or ketones as starting materials, coupled with their inherent chirality offers new appealing opportunities for their applications.
TL;DR: In this article, a trifurcated receptor system with three Cu(II)-dipicolylamine ligands was studied for the molecular sensing of phytate, myo-inositol hexakis(phosphate) sodium salt, through an indicator displacement approach.
Abstract: A trifurcated receptor system containing three Cu(II)-dipicolylamine ligands has been studied for the molecular sensing of phytate, myo-inositol hexakis(phosphate) sodium salt, through an indicator displacement approach. From the Cu(II) complex, a molecular sensing ensemble system was best constructed with eosin Y as indicator. The addition of phytate to the chemical ensemble system in an aqueous medium of physiological pH resulted in the restoration of fluorescence of eosin Y as it is displaced from the metal complex by the anion added. The ensemble system shows the maximum fluorescence change in the case of phytate, about 70% change in the cases of myo-inositol 1,4,5-tris(phosphate) and pyrophosphate ions, and negligible changes in the cases of monovalent anions (HPO4 2 − , CH3CO2 − , CO3 2 − , Cl− , Br− , ClO4 − , N3 − , NO3 − ) and inositol. A binding study by isothermal titration calorimetry suggests that the Cu(II) complex tends to recognize phytate preferably in a 2:1 binding mode with K 1 of 7.7 ×...
TL;DR: In this paper, the bridging ligands between metal centers to form metal organic rotaxane frameworks (MORFs) were used to form a 2D "square" net with only one direction comprised of rotaxanes.
Abstract: The [2]pseudorotaxane formed between the dicationic axle 1,2-bis-(4,4′-bipyridinium-mono-N-oxide)ethane and dibenzo-24-crown-8 ether (DB24C8) can act as a bridging ligand between metal centers to form metal organic rotaxane frameworks (MORFs). When cadmium(II) is used as the metal center the resulting structure is a network in which two [2]pseudorotaxanes, two ‘naked’ axles and two triflate anions coordinate to the Cd(II) center in a trans,-trans,-trans-arrangement. The two different linking ligands form a 2D ‘square’ net with only one direction comprised of rotaxanes. These nets layer in an A–B–A–B fashion with the crown ether units of one layer blocking the openings of the next layer to eliminate the formation of channels.
TL;DR: In this paper, a supramolecular self-assembly where a pyridyl-substituted perylene bisimide dye (DPyPBI) axially binds to zinc phthalocyanine (ZnPc), has been designed.
Abstract: A novel supramolecular self-assembly, where a pyridyl-substituted perylene bisimide dye (DPyPBI) axially binds to zinc phthalocyanine (ZnPc), has been designed. Their coordination properties have been studied by UV/vis, fluorescence techniques and 1H NMR spectroscopy, showing that 1:1 and 1:2 double sandwich complexes between DPyPBI and ZnPc are formed.
TL;DR: In this article, the hydrogen-bonding geometries and interaction energies of the different discrete and water-expanded hydrogen bonding patterns formed between the carboxyl and the Carboxylate group have been analyzed systematically by theoretical calculations at the MP2/6-31G(d,p) level of theory.
Abstract: Nine tetraalkylammonium salts, with R = Me, Et, nPr and nBu, of four different carboxylic acids, namely isophthalic acid, 5-nitroisophthalic acid, trimesic acid and pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), have been prepared and their supramolecular structures analyzed by X-ray crystallography The [RCOOH…HOOCR] homodimeric motif characteristic for carboxylic acids has not been detected, but instead, in all compounds a [RCOOH…OOCR]− unit was present The hydrogen-bonding geometries and interaction energies of the different discrete and water-expanded hydrogen-bonding patterns formed between the carboxyl and the carboxylate group have been analyzed systematically by theoretical calculations at the MP2/6-31G(d,p) level of theory Carboxylates are promising candidates for crystal engineering and [O–H…O]− interactions play an important role for the structural organization and chemistry of biomolecules
TL;DR: In this article, Calix[4]pyrrole bearing 5-aryl acridine-derived straps on one side of the tetrapyrrolic core have been synthesized and characterized.
Abstract: Calix[4]pyrrole bearing 5-aryl acridine-derived straps on one side of the tetrapyrrolic core have been synthesized and characterized. The solution state binding studies of the synthesized hosts were investigated by proton NMR spectroscopy and Isothermal Titration Calorimetry (ITC) in acetonitrile. The system displayed enhanced affinities for chloride and bromide anion with high selectivity and the inner aryl C–H of the strap served as a C–H hydrogen bond donor site. The fluorescence measurement indicated that the incorporated acridine moiety has minimal interaction with the anion binding event.
TL;DR: In this article, the supramolecular chirality of noncovalent hydrogen-bonded assemblies formed by multiple cooperative hydrogenbonds between calix[4]arene dimelamines and cyanurates or barbiturates derivatives (rosette assemblies) is described.
Abstract: The control of chirality in synthetic self-assembled systems remains challenging because of their lower stability and their higher susceptibility to racemization when compared to covalent systems. In this review the supramolecular chirality of noncovalent hydrogen-bonded assemblies formed by multiple cooperative hydrogenbonds between calix[4]arene dimelamines and cyanurates or barbiturates derivatives (rosette assemblies) are described. It is shown that the amplification of chirality (a high enantiomeric or diastereomeric excess induced by a small initial amount of chiral bias) of double and tetrarosette assemblies is influenced by bulky substitution on their components and electronic properties of the substituents as well as their proximity to the rosette core. In the absence of chiral centers in their components, the assemblies form as a racemic mixture of both enantiomers (P and M). The synthesis of enantiomerically pure rosette assemblies is conducted via induction of chirality using chiral barbiturates, followed by substitution of the chiral components for achiral cyanurates (chiral memory concept). The addition of an external auxiliary to a racemic mixture of P and M assemblies leading to the formation of one of the two possible diastereomeric assemblies is also described. Moreover, chiral resolution of self-assembled nanostructures on highly oriented pyrolytic graphite (HOPG) surfaces is also discussed.
TL;DR: In this article, a new chromogenic receptor based on 1,2-phenylene derivative containing thiourea moieties was synthesized and examined for its anion binding ability by UV-Vis and 1H NMR studies.
Abstract: A new chromogenic receptor based on 1,2-phenylene derivative containing thiourea moieties is synthesized and examined for its anion binding ability by UV–Vis and 1H NMR studies. The results show that the receptor has selective colorimetric sensing of fluoride over all other anions like chloride, bromide, iodide, nitrate, hydrogen sulphate and acetate.
TL;DR: In this article, a chiral, insulated poly(p-phenylene ethynylene) (PPE) nano-wire can be created by a polymer wrapping method utilizing natural β-1,3-glucan polysaccharide schizophyllan (SPG).
Abstract: It has been demonstrated that a chiral, insulated poly(p-phenylene ethynylene) (PPE) nano-wire can be created by a polymer wrapping method utilizing natural β-1,3-glucan polysaccharide schizophyllan (SPG). Spectroscopic and microscopic measurements have revealed that PPE adopts a rigid conformation and exists as one piece in the helical hollow constructed by two SPG chains. Moreover, the inherent helical structure of SPG can induce the chiral twisting of the insulated PPE backbone. It is believed that the present system is really applicable for designing novel chiral sensors based on PPE.
TL;DR: In this paper, the tautomeric equilibrium between the ketoenamine and enolimine forms for a series of arylimines derived from salicylaldehyde and enaminones (2a-2f) derived from benzoylacetone and substituted anilines has been analyzed in solution by 1H NMR and UV-vis spectroscopy, while IR and X-ray diffraction analyses were used in the solid state.
Abstract: The tautomeric equilibrium between the ketoenamine and enolimine forms for a series of arylimines (1a–1c) derived from salicylaldehyde and enaminones (2a–2f) derived from benzoylacetone and substituted anilines has been analyzed in solution by 1H NMR and UV-vis spectroscopy, while IR and X-ray diffraction analyses were used in the solid state. The X-ray diffraction analysis of 1a, 2a–2c and 2e–2f showed that the most stable tautomer is the ketoenamine and all enaminones present intramolecular NH…O hydrogen bonds forming a six member ring in which the keto form is favored. In addition, the VT-NMR analysis for 2b in solvents of different polarities evidenced the behavior of the tautomeric equilibrium, showing that in DMF and acetone at low temperature, the enolimine tautomer is more stable.
TL;DR: The ability of calix[6]arene triscarboxylic acid derivatives to include ammonium guests has been investigated both in solution and in the solid state as discussed by the authors.
Abstract: The ability of calix[6]arene tris-carboxylic acid derivatives to include ammonium guests has been investigated both in solution and in the solid state. NMR studies and crystallographic data showed that the highly flexible calix[6]arene structures can be shaped in a well defined cone conformation thanks to the formation of an ion-paired cap between the carboxylate groups of the calixarene and their ammonium counter-ions. The resulting supramolecular edifices exhibit remarkable host-guest properties toward ammonium ions even in polar and protic solvents. The recognition process has been rationalized in the solid state by the combination of hydrogen bonding, electrostatic and CH–π interactions, and a remarkable C 3-complementarity between the well-organized binding carboxylates of the host and the ammonium guest. Very interestingly, the endo-cavity complexation of large polycyclic ammonium ions as well as bioactive ammonium ions has been clearly demonstrated through NMR spectroscopy. Finally, the tuning of t...
TL;DR: The binding properties of dibenzo-18crown-6 ether (BTB, 1) and napthobenzo 18crown 6 ether (NTB, 2), containing two thiazole units toward mono, and divalent cations, are outlined in this article.
Abstract: The binding properties of dibenzo-18-crown-6 ether (BTB, 1) and napthobenzo-18-crown-6 ether (NTB, 2), containing two thiazole units toward mono, and divalent cations, are outlined. The ion-selective properties of 1 and 2 were studied by measuring their fluorescent emission responses to alkali, alkaline earth, and transition metal ions. BTB (1) showed the highest binding constant toward Ag+ over Pb2+, Hg2+, and Cu2+. NTB (2) revealed a high selectivity toward Ag+ over Pb2+, Hg2+, and Cu2+.