A novel self-healing supramolecular polymer system

Utilising supramolecular pi-pi stacking interactions to drive miscibility in two-component polymer blends offers a novel approach to producing materials with unique properties. We report in this paper the preparation of a supramolecular polymer network that exploits this principle. A low molecular weight polydiimide which contains multiple pi-electron-poor receptor sites along its backbone forms homogeneous films with a siloxane polymer that features pi-electron-rich pyrenyl end-groups. Compatibility results from a complexation process that involves chain-folding of the polydiimide to create an optimum binding site for the pi-electron-rich chain ends of the polysiloxane. These complementary pi-electron-rich and -poor receptors exhibit rapid and reversible complexation behaviour in solution, and healable characteristics in the solid state in response to temperature. A mechanism is proposed for this thermoreversible healing behaviour that involves disruption of the intermolecular pi-pi stacking cross-links as the temperature of the supramolecular film is increased. The low T-g siloxane component can then flow and as the temperature of the blend is decreased, pi-pi stacking interactions drive formation of a new network and so lead to good damage-recovery characteristics of the two-component blend.

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.

Helices, chirality and interpenetration: the versatility and remarkable interconversion of silver-copper cyanide frameworks

The structural transformations between cesium silver-copper cyanides under modest conditions, both in solution and in the solid state, are described. Three new cesium silver(I) copper(I) cyanides with three-dimensional (3-D) framework structures were prepared as single crystals from a one-pot reaction initially heated under hydrothermal conditions. The first product to appear, Cs3Ag2Cu3(CN)(8) (I), when left in contact with the supernatant produced CsAgCu(CN)(3) (II) and CsAgCu(CN)(3)center dot 1/3H(2)O (III) over a few months via a series of thermodynamically controlled cascade reactions. Crystals of the hydrate (III) can be dehydrated to polycrystalline CsAgCu(CN)(3) (II) on heating at 100 degrees C in a remarkable solid-state transformation involving substantial breaking and reconnection of metal-cyanide linkages. Astonishingly, the conversion between the two known polymorphs of CsAg2Cu(CN)(4), which also involves a major change in connectivity and topology, occurs at 180 degrees C as a single-crystal to single-crystal transformation. Structural features of note in these materials include the presence of helical copper-cyanide chains in (I) and (II), which in the latter compound produce a chiral material. In (II) and (III), the silver-copper cyanide networks are both self- and interpenetrating, features also seen in the known polymorphs of CsAg2Cu(CN)(4).

Mono- and binuclear bipyridyl derivatives of the Mo(eta(3)-C3H5)(CO)(2) fragment: structural studies and fluxionality in solution

New mono- and binuclear complexes of the Mo(eta(3)-C3H5)(CO)(2) fragment, containing bipyridyl ligands (2,2'-bpy, 4,4'-Me-2-2,2'-bpy) as chelates, and mono- (4-CNpy, 4-Mepy, NCMe, Br) or bidentate nitrogen ligands (4,4'-bpy, bipyridylethylene, pyrazine) as terminal or bridging ligands, respectively, were prepared. The binuclear complex [{Mo(eta(3)-C3H5)(CO)(2)(2,2'-bpy)}(2)(mu-4,4'-bpy)][PF6](2) (2) was shown by X-ray diffraction to assemble in the crystal forming large channels with a rectangular section. A longer bridge, such as bipyridylethylene, led to a different structure (3). 4-CNpy behaved as monodentate ligand (4), coordinating through the pyridine nitrogen as a terminal ligand. NMR spectroscopy studies showed that the complexes exhibited a fluxional behavior in solution, the endo and exo forms of the more symmetrical equatorial isomers being usually present and interconverting in solution. The solid state structures of the complexes revealed a preference for the more symmetrical equatorial isomer, with the two chelate ligands in trans positions in the binuclear species. The rings tended to become parallel in the organized crystal. (C) 2003 Elsevier B.V. All rights reserved.

Liquid ultraviolet matrix-assisted laser desorption/ionization mass spectrometry for automated proteomic analysis

We have combined several key sample preparation steps for the use of a liquid matrix system to provide high analytical sensitivity in automated ultraviolet - matrix-assisted laser desorption/ ionisation - mass spectrometry (UV-MALDI-MS). This new sample preparation protocol employs a matrix-mixture which is based on the glycerol matrix-mixture described by Sze et al. U. Am. Soc. Mass Spectrom. 1998, 9, 166-174). The low-ferntomole sensitivity that is achievable with this new preparation protocol enables proteomic analysis of protein digests comparable to solid-state matrix systems. For automated data acquisition and analysis, the MALDI performance of this liquid matrix surpasses the conventional solid-state MALDI matrices. Besides the inherent general advantages of liquid samples for automated sample preparation and data acquisition the use of the presented liquid matrix significantly reduces the extent of unspecific ion signals in peptide mass fingerprints compared to typically used solid matrices, such as 2,5-dihydrox-ybenzoic acid (DHB) or alpha-cyano-hydroxycinnamic acid (CHCA). In particular, matrix and lowmass ion signals and ion signals resulting from cation adduct formation are dramatically reduced. Consequently, the confidence level of protein identification by peptide mass mapping of in-solution and in-gel digests is generally higher.

Evaluation of the binding ability of a novel dioxatetraazamacrocyclic receptor that contains two phenanthroline units: selective uptake of carboxylate anions

The novel dioxatetraaza macrocycle [26]phen(2)N(4)O(2), which incorporates two phenanthroline units, has been synthesized, and its acid-base behavior has been evaluated by potentiometric and H-1 NMR methods. Six protonation constants were determined, and the protonation sequence was established by NMR. The location of the fifth proton on the phen nitrogen was confirmed by X-ray determinations of the crystal structures of the receptor as bromide and chloride salts. The two compounds have the general molecular formula {(H-5[26]phen(2)N(4)O(2))X-n(H2O)(5-n)}X(n-1)(.)mH(2)O, where X = Cl, n = 3, and m = 6 or X = Br, n = 4, and m = 5.5. In the solid state, the (H-5[26]phen(2)N(4)O(2))(5+) cation adopts a "horseshoe" topology with sufficient room to encapsulate three or four halogen anions through the several N-(HX)-X-... hydrogen-bonding interactions. Two supermolecules {(H-5[26]phen(2)N(4)O(2))X-n(H2O)(5-n)}((5-n)+) form an interpenetrating dimeric species, which was also found by ESI mass spectrum. Binding studies of the protonated macrocycle with aliphatic (ox(2-), mal(2-), suc(2-), cit(3-), cta(3-)) and aromatic (bzc(-), naphc(-), anthc(-), pyrc(-), ph(2-), iph(2-), tph(2-), btc(3-)) anions were determined in water by potentiometric methods. These studies were complemented by H-1 NMR titrations in D2O of the receptor with selected anions. The H-i[26]phen(2)N(4)O(2)(i+) receptor can selectively uptake highly charged or extended aromatic carboxylate anions, such as btc(3-) and pyrc(-), in the pH ranges of 4.0-8.5 and < 4.0, respectively, from aqueous solution that contain the remaining anions as pollutants or contaminants. To obtain further insight into these structural and experimental findings, molecular dynamics (MD) simulations were carried out in water solution.