Rapid, uncatalyzed ring-opening polymerization of individual macrocyclic poly(arylene thioether ketone)s under dynamic heating conditions

Uncatalyzed, ring-opening polymerization of individual macrocyclic poly(arylene thioether ketone)s (1-4) and mixtures (5) under dynamic heating conditions has been demonstrated for the first time. High-molecular-weight, film-forming products were obtained after heating of the macrocycles up to 480 degreesC, with a heating rate of 10-20 degreesC /min. Depending on the macrocyclic structure and heat treatment conditions, the polymers obtained were amorphous or semicrystalline, soluble or slightly crosslinked. NMR analyses of the soluble polymers revealed their linear, highly regular structure. According to NMR, DSC, and TGA studies, the polymers obtained do not contain any residual macrocycles. The polymers with thio-p-arylene moieties in the main chain were thermally stabile. The catalyzed ring opening polymerization of 5 carried out in diphenyl sulfone solution is also reported for comparison. Using quantum mechanical calculations of the ring opening of macrocycles, a reaction mechanism is suggested. Preparation of nanosized poly(thioether ketone) fibrils by a replication method is described.

Induced-fit binding of π-electron donor substrates to macrocyclic aromatic ether-imide-sulfones: a versatile approach to molecular assembly

Novel macrocyclic receptors which bind electron-donor aromatic substrates via π-stacking donor- acceptor interactions are obtained by cyclo-imidization of an amine-functionalized arylether-sulfone with pyromellitic- and 1,4,5,8-naphthalene-tetracarboxylic dianhydrides. These macrocycles complex with a wide variety of π-donor substrates including tetrathiafulvalene, naphthalene, anthracene, pyrene, perylene, and functional derivatives of these polycyclic hydrocarbons. The resulting supramolecular assemblies range from simple 1:1 complexes, to [2]- and [3]-pseudorotaxanes, and even (as a result of crystallographic disorder) an apparent polyrotaxane. Direct, five-component self-assembly of a metal-centred [3]pseudorotaxane is also observed, on complexation of a macrocyclic ether-imide with 8-hydroxyquinoline in the presence of palladium(II) ions. Binding studies in solution were carried out by 1H NMR and UV-visible spectroscopy, and the stoichiometries of binding were confirmed by Job plots based on charge-transfer absorption bands. The highest association constants are found for strong π-donor guests with large surface-areas, notably perylene and 1-hydroxypyrene, for which Ka values of 1.4 x 103 and 2.3 x 103 M-1 respectively are found. Single crystal X-ray analyses of the receptors and their derived complexes reveal large, induced-fit distortions of the macrocyclic frameworks as a result of complexation. These structures provide compelling evidence for the existence of strong, attractive forces between the electronically-complementary aromatic π-systems of host and guest.

Metal-directed assembly of large dinuclear copper(II) dithiocarbamate macrocyclic complexes

The synthesis of a range of dinuclear Cu(II) dithiocarbamate (dtc)-based macrocycles and their characterisation are described. By carefully tuning the size of the aromatic spacer, cavities of different dimensions can be designed. The length and flexibility of the chosen spacer group dictates the intermetallic distance and hence the degree of communication between the two metal centres as evidenced by electrochemical and EPR experiments. This is illustrated by crystallographic evidence that show the macrocycles can host guests (such as CH2Cl2) or can fold and form unexpected Cu(I) dtc clusters.

Two macrocyclic pentaaza compounds containing pyridine evaluated as novel chelating agents in copper(II) and nickel(II) overload

Two pentaaza macrocycles containing pyridine in the backbone, namely 3,6,9,12,18-pentaazabicyclo[12.3.1] octadeca-1(18),14,16-triene ([15]pyN(5)), and 3,6,10,13,19-pentaazabicyclo[13.3.1]nonadeca-1(19),15,17-triene ([16]pyN(5)), were synthesized in good yields. The acid-base behaviour of these compounds was studied by potentiometry at 298.2 K in aqueous solution and ionic strength 0.10 M in KNO3. The protonation sequence of [15]pyN(5) was investigated by H-1 NMR titration that also allowed the determination of protonation constants in D2O. Binding studies of the two ligands with Ca2+, Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+ metal ions were performed under the same experimental conditions. The results showed that all the complexes formed with the 15-membered ligand, particularly those of Cu2+ and especially Ni2+, are thermodynamically more stable than with the larger macrocycle. Cyclic voltammetric data showed that the copper(II) complexes of the two macrocycles exhibited analogous behaviour, with a single quasi-reversible one-electron transfer reduction process assigned to the Cu(II)/Cu(I) couple. The UV-visible-near IR spectroscopic and magnetic moment data of the nickel(II) complexes in solution indicated a tetragonal distorted coordination geometry for the metal centre. X-band EPR spectra of the copper(II) complexes are consistent with distorted square pyramidal geometries. The crystal structure of [Cu([15]pyN(5))](2+) determined by X-ray diffraction showed the copper(II) centre coordinated to all five macrocyclic nitrogen donors in a distorted square pyramidal environment.

Sesquiterpenoids lactones: benefits to plants and people

Sesquiterpenoids, and specifically sesquiterpene lactones from Asteraceae, may play a highly significant role in human health, both as part of a balanced diet and as pharmaceutical agents, due to their potential for the treatment of cardiovascular disease and cancer. This review highlights the role of sesquiterpene lactones endogenously in the plants that produce them, and explores mechanisms by which they interact in animal and human consumers of these plants. Several mechanisms are proposed for the reduction of inflammation and tumorigenesis at potentially achievable levels in humans. Plants can be classified by their specific array of produced sesquiterpene lactones, showing high levels of translational control. Studies of folk medicines implicate sesquiterpene lactones as the active ingredient in many treatments for other ailments such as diarrhea, burns, influenza, and neurodegradation. In addition to the anti-inflammatory response, sesquiterpene lactones have been found to sensitize tumor cells to conventional drug treatments. This review explores the varied ecological roles of sesquiterpenes in the plant producer, depending upon the plant and the compound. These include allelopathy with other plants, insects, and microbes, thereby causing behavioural or developmental modification to these secondary organisms to the benefit of the sesquiterpenoid producer. Some sesquiterpenoid lactones are antimicrobial, disrupting the cell wall of fungi and invasive bacteria, whereas others protect the plant from environmental stresses that would otherwise cause oxidative damage. Many of the compounds are effective due to their bitter flavor, which has obvious implications for human consumers. The implications of sesquiterpenoid lactone qualitiesfor future crop production are discussed.

Ring-opening polymerization in molten PEEK: transient reduction of melt-viscosity by macrocyclic aromatic thioetherketones

Blends of PEEK with macrocyclic thioether-ketones show initial melt-viscosities reduced by more than an order of magnitude relative to the polymer itself, enabling more facile processing and fabrication. On raising the temperature of the melt, however, the macrocycle undergoes spontaneous, entropically-driven ring-opening polymerization (ED-ROP), so that the properties of the final polymer should not, in principle, be compromised by the presence of low-MW macrocyclic material.

Diastereoselective and enantioselective preparation of nor-mevaldic acid surrogates through desymmetrisation methodology. Enantioselective synthesis of (+) and (-) nor-mevalonic lactones

Solvent-free desymmetrisation of a meso-dialdehyde with chiral alcohols, led to preparation of 4-silyloxy-6-alkyloxytetrahydro-2H-pyran-2-one derivatives with a 96% de. This methodology, which yields the corresponding methyl nor-mevaldates with 99% ee, has been applied to the enantioselective synthesis of the (-)-(R) and (+)-(S) nor-mevalonic acid lactones.

Sequence-selective assembly of tweezer-molecules on linear templates enables frameshift-reading of sequence information

Monomer-sequence information in synthetic copolyimides can be recognised by tweezer-type molecules binding to adjacent triplet-sequences on the polymer chains. In the present paper different tweezer-molecules are found to have different sequence-selectivities, as demonstrated in solution by 1H NMR spectroscopy and in the solid state by single crystal X-ray analyses of tweezer-complexes with linear and macrocyclic oligo-imides. This work provides clear-cut confirmation of polyimide chain-folding and adjacent-tweezer-binding. It also reveals a new and entirely unexpected mechanism for sequence-recognition which, by analogy with a related process in biomolecular information processing, may be termed "frameshift-reading". The ability of one particular tweezer-molecule to detect, with exceptionally high sensitivity, long-range sequence-information in chain-folding aromatic copolyimides, is readily explained by this novel process.

Bis(hydroxy-isoindolinone)s: synthesis, stereochemistry, polymer chemistry, and supramolecular assembly

Pseudoacid chlorides of 2,5-bis(4-fluorobenzoyl) terephthalic acid and 4,6-bis(4-fluorobenzoyl) isophthalic acid condense with primary amines to afford diastereomeric bis(hydroxyindolinone)s in good isolated yields and with diamines to give high molecular weight poly(hydroxyindolinone)s. Bis-N-pyrenemethyl bis(hydroxyindolinone)s assemble, even in dipolar solvents such as DMSO, with macrocyclic diimide-sulfones to give [3]pseudorotaxanes stabilized by electronically complementary aromatic π−π-stacking and shape-complementary van der Waals interactions.

Metal complexes of a tetraazacyclophane: solution and molecular modelling studies

An alternative synthetic approach to yield the compound 2,3,5,6,8,9,11,14-octahydrobenzo[1][ 1,4,7,10]tetraazacyclotetradecine (bz[14]N-4) is presented. The protonation constants of bz[14]N-4 and the stability constants of its complexes with Ni2+, Cu2+, Zn2+, Cd2+, Pb2+ were determined in H2O at 25degreesC with ionic strength 0.10 mol dm(-3) in KNO3 and they were compared with structurally related macrocycles cyclam (1,4,8,11-tetraazacyclotetradecane) and cyclen (1,4,7,10-tetraazacyclododecane). These studies indicate that only 1 : 1 ( M : L) species are formed in solution, and the ligand exhibits a high affinity for larger ions such as Cd2+ and Pb2+. The X-ray study of [bz[14]N4H3](3+) shows that an inclusion compound with a chloride counter-anion is formed through NH...Cl hydrogen bonds. Spectroscopic data in solution ( electronic and NMR spectra) showed that the macrocycle adopts a planar arrangement upon metal complexation. Molecular mechanics calculations reveal that in spite of the presence of the benzene ring in the macrocyclic framework this ligand can encapsulate metal ions with different stereo-electronic sizes in square planar arrangements. Our results indicate that the presence of the benzene ring in the backbone of the bz[14]N-4 confers a coordination behaviour intermediate between that of cyclam and cyclen.

A novel approach to processing high-performance polymers that exploits entropically driven ring-opening polymerization

Blends of the poly(ether sulfone) derived from 4,4'-biphenol and 4,4'-dichlorodiphenylsulfone (Radel-R(TM)) with its homologous macrocyclic oligomers show greatly lowered melt viscosities relative to that of the parent polymer, potentially enabling more facile production and fabrication of fiber-reinforced composite materials. The macrocycles can then undergo entropically driven ring-opening polymerization in situ. The required blends can be obtained easily in one step, by carrying out polycondensations at concentrations lower than those usually used for polymer synthesis.

Binding studies of a protonated dioxatetraazamacrocycle with carboxylate substrates

The tetraprotonated form of the dioxatetraazamacrocycle, 6,19-dioxa-3,9,16,22-tetraaza[22.2.2.2(11,14)]-triaconta-1(26),11,13,24, 27,29-hexaene, (H4L1)(4+), was used as the receptor for binding studies with carboxylate anionic substrates of different shapes, sizes, and charges [succinate (suc(2-)), cyclo- hexanetricarboxylate (cta(3-)), phthalate (ph(2-)), isophthalate (iph(2-)), terephthalate (tph(2-)), and benezenetricarboxylate (btc(3-))]. Association constants were determined by potentiometry in aqueous solution at 298.2 K and 0.10 M KCl and by H-1 NMR titration in D2O. The strongest association was found for the btc3- anion at 5-7 pH region. From both techniques it was possible to establish the binding preference trend of the receptor for the different substrates, and the H-1 NMR spectroscopy gave important suggestions about the type of interactions between partners and the location of the substrates in the supramolecular entities formed. The effective binding constants at pH 6 follow the order: btc(3-)>iph(2-)>cta(3-) =ph(2-)>tph(2-)>suc(2-). All the studies suggest that the anionic substrates bind to the receptor via N-H center dot center dot center dot O = C hydrogen bonds and electrostatic interactions, and the aromatic substrates can also establish pi-pi stacking interactions. The crystal structures of (H4L1)(4+) and its supramolecular assemblies with ph(2-) and tph(2-) were determined by X-ray diffraction. The last two structures showed that the association process in solid state occurs via multiple N-H center dot center dot center dot O = C hydrogen bonds with the anionic substrate located outside the macrocyclic cavity of the receptor. Molecular dynamics simulations carried out for the association of (H4L1)(4+) with tph(2-) and btC(3-) in water solution established at atomic level the existence of all interactions suggested by the experimental studies, which act cooperatively in the binding process. Furthermore, the binding free energies were estimated and the values are in agreement with the experimental ones, indicating that the binding of these two anionic substrates occurs into the receptor cavity. However, the tph(2-) has also propensity to leave the macrocyclic cavity and its molecular recognition can also happen at the top of the receptor. (C) 2008 Elsevier Ltd. All rights reserved.

Cascade dicopper architectures of a dibenzodioxatetraazamacrocycle

The dibenzodioxatetraazamacrocycle [26]pbz(2)N(4)O(2) was characterised by single crystal X-ray diffraction and the protonation constants of this compound and the stability constants of its copper(II) and lead(II) complexes were determined by potentiometry in water at 298.2 K in 0.10 mol dm(-3) in KNO3. Mono- and dinuclear complexes were found for both metal ions, the dinuclear complexes being the main species in the 5-7.5 pH range for copper(II) and 7.5-8.5 for lead(II). As expected the values of the stability constants for the copper(II) complexes are lower than those for related macrocycles containing only nitrogen atoms. The presence of mono- and dinuclear copper complexes was also confirmed by electrospray ionization mass spectrometry. These results suggest that the symmetric macrocyclic cavity of [26]pbZ(2)N(4)O(2) has enough space for the coordination of two metal ions. Additionally, NMR spectroscopy showed that the dinuclear complex of lead(II) has high symmetry. The equilibrium constants of the dinuclear copper(II) complexes and dicarboxylate anions (oxalate, malonate and succinate) were also determined in 0.10 mol dm-3 aqueous KNO3 solution. Only species containing one anion, Cu(2)H(h)LA((2+h)), were found, strongly suggesting that the anion bridges the two copper(II) ions. The binding constants of the cascade species formed by [Cu-2[26]pbZ(2)N(4)O(2)(H2O)(4+) with dicarboxylate anions decrease with the increase in length of the alkyl chain of the anion, a fact which was attributed to a higher conformational energy necessary for the rearrangement of the macrocycle to accommodate the larger anions bridging the two copper(II) centres. The variation of the magnetic susceptibility with temperature Of [Cu-2(H-2[26]pbz(2)N(4)O(2))(oxa)(3)]-4H(2)O and [Cu-2([26]pbz(2)N(4)O(2))(suc)Cl-2] were measured and the two complexes showed different behaviour. (c) 2007 Elsevier Ltd. All rights reserved.

Extreme complementarity in a macrocycle-tweezer complex

Interaction of a novel pyrene-based tweezer molecule with a macrocyclic ether-imide-sulfone results in formation of a strongly bound complex (K-a = 24 000 M-1) in which binding results not only from pi-pi stacking interactions involving pyrene units as donors and macrocyclic naphthalene-tetracarboximide and biphenylenedisulfone groups as acceptors but also from N-(HO)-O-... and C-(HO)-O-... hydrogen bonds and from "reverse" pi-stacking of the electron-poor isophthaloyl residue of the tweezer with an electron-rich 3-aminophenoxy residue of the macrocyclic imide.

Carboxylate anions binding and sensing by a novel tetraazamacrocycle containing ferrocene as receptor

A tetraazamacrocycle containing ferrocene moieties has been synthesized and characterized. The tetraprotonated form of this compound was evaluated as a receptor (R) for anion recognition of several substrates (S), Cl-, PF6-, HSO4-, H2PO4- and carboxylates, such as p-nitrobenzoate (p-nbz(-)), phthalate (ph(2-)), isophthalate (iph(2-)) and dipicolinate (dipic(2-)). H-1 NMR titrations in CD3OD indicated that this receptor is not suitable for recognizing HSO4- and H2PO4-, but weakly binds p-nbz(-), and strongly interacts with ph(2-), dipic(2-), and iph(2-) anions forming 1 : 2 assembled species. The largest beta(2) binding constant was determined for ph(2-), followed by dipic(2-) and finally iph(2-). The effect of the anionic substrates on the electron-transfer process of the ferrocene units of R was evaluated using cyclic voltammetry (CV) and square wave voltammetry (SWV) in methanol solution and 0.1 mol dm(-3) (CH3)(4)NCl as the supporting electrolyte. Titrations of the receptor were undertaken by addition of anion solutions in their tetrabutylammonium or tetramethylammonium forms. The protonated ligand exhibits a reversible voltammogram, which shifts cathodically in the presence of the substrates. The data revealed kinetic constraints in the formation of the receptor/substrate entity for dipic(2-), ph(2-) and iph(2-) anions, but not for p-nbz(-). In spite of the slow kinetics of assembled species formation with the ph(2-) substrate, this anion provides the largest redox-response when the supramolecular entity is formed, followed by dipic(2-), iph(2-) and finally p-nbz(-) anions. This trend is in agreement with the H-1 NMR results and the values of the binding constants. Single crystal X-ray structures of the receptor with PF6-, ph(2-), iph(2-) and p-nbz(-) were carried out and showed that supermolecules with a RS2 stoichiometry are formed with the first three anions, but RS4 with p-nbz(-). In all cases the binding occurs outside the macrocyclic cavity via N-H center dot center dot center dot O=C hydrogen bonds for carboxylate anions and N - H center dot center dot center dot F hydrogen bonds for the PF6- anion, which is in agreement with the solution results. The macrocyclic framework adopts different conformations in order to interact with each substrate having Fe center dot center dot center dot Fe intramolecular distances ranging from 10.125(14) to 12.783(15) angstrom.