Aromatic Π-stacking Interactions Research Articles

Supramolecular assembly in Cu(II) and Zn(II) compounds with pyridine and anthraquinone-1,5-disulfonate: Experimental and theoretical analysis

Two new multi-component coordination compounds of Cu(II) and Zn(II) viz. [Cu(py)2(H2O)4]ADS·2H2O (1) and [Zn(4-CNpy)2(H2O)4]ADS·2H2O (2) (py = pyridine, 4-CNpy = 4-cyanopyridine, ADS = anthraquinone-1,5-disulfonate) have been synthesized in aqueous media at room temperature and characterized using elemental and spectroscopic analyses (FT-IR, electronic), TGA and single crystal X-ray diffraction techniques. Both the compounds crystallize as metal–organic multi-component compounds containing complex cationic moieties along with uncoordinated anionic ADS moieties in the crystal structures. Crystal structure analysis of 1 reveals the stabilisation of the layered assembly of the compound assisted by CH⋯O, OH⋯O hydrogen bonding and π-stacking interactions. Antiparallel CN⋯CN and aromatic π-stacking interactions provide rigidity to the crystal structure of compound 2. In addition, enclathration of lattice water molecules within the supramolecular cavity of 2 provides additional reinforcement to the crystal structure. We have carried out theoretical investigations to analyze π-stacking, H-bonding and antiparallel CN···CN non-covalent interactions observed in the compounds using DFT calculations, quantum theory of atoms in molecules (QTAIM) and non-covalent interaction (NCI) plot index computational tools. The binding energies of the supramolecular assemblies are quite significant due to the ion-pair nature of the interactions which lack directionality; however, the aforementioned weaker non-covalent interactions play crucial roles in the final arrangement of molecules in the solid state due to their directional nature.

Revealing the Role of N Heteroatoms in Noncovalent Aromatic Interactions by Ultrafast Intermolecular Coulombic Decay.

Despite the widely recognized importance of noncovalent interactions involving aromatic rings in many fields, our understanding of the underlying forces and structural patterns, especially the impact of heteroaromaticity, is still incomplete. Here, we investigate the relaxation processes that follow inner-valence ionization in a range of molecular dimers involving various combinations of benzene, pyridine, and pyrimidine, which initiate an ultrafast intermolecular Coulombic decay process. Multiparticle coincidence momentum spectroscopy, combined with ab initio calculations, enables us to explore the principal orientations of these fundamental dimers and, thus, to elucidate the influence of N heteroatoms on the relative preference of the aromatic π-stacking, H-bonding, and CH-π interactions and their dependence on the number of nitrogen atoms in the rings. Our studies reveal a sensitive tool for the structural imaging of molecular complexes and provide a more complete understanding of the effects of N heteroatoms on the noncovalent aromatic interactions at the molecular level.

Cocrystal Approach to Modulate the Photoluminescent Properties of a GFP Chromophore Analogue: Role of Halogen/Hydrogen Bonding in Achieving a Wide Range of Solid-State Fluorescence Emissions

Fine-tuning the photophysical properties of fluorescent organic solids is essential to attain multicolor displays and meet the demand for futuristic light-emitting materials. Here, we report the tunable luminescence of a green fluorescent protein (GFP) chromophore analogue, 3,4,5-TIA (A), based on the formation of two-component molecular cocrystals with six different coformers. Coformers selected to synthesize the binary cocrystals include 1,4-diiodotetrafluorobenzene (B), perfluoronaphthalene (C), 1,4-dibromotetrafluorobenzene (D), 2,3,5,6-tetrafluoroterephthalic acid (E), benzene-1,2,4,5-tetracarbonitrile (F), and benzene-1,2,4,5-tetracarboxylic acid (G). Interestingly, the cocrystals A•C and A•F showed molecular crystal polymorphism with a slight variation in fluorescence, revealing an aggregation-induced emission (AIE). A crystal structure analysis showed the interplay of hydrogen bonding, halogen bonding, and aromatic π-stacking interactions in associating neutral solid components in the cocrystal. All of the novel cocrystals displayed a wide range of photoluminescence ranging from blue to dark orange. The time-dependent density functional theory (TD-DFT) calculations indicate the changes in the energy level structures (HOMO to LUMO) in cocrystals that resulted in variations in fluorescence emission. The study aims to further understand the structure–property relationship between molecular arrangement and photoluminescence.

Synthesis, crystal structure and Hirshfeld surface analysis of (E)-benzo[d][1,3]dioxole-5-carbaldehyde oxime.

The asymmetric unit of the title mol-ecule, C8H7NO3, consists of two mol-ecules differing slightly in conformation and in their inter-molecular inter-actions in the solid. The dihedral angle between the benzene and dioxolane rings is 0.20 (7)° in one mol-ecule and 0.31 (7)° in the other. In the crystal, the two mol-ecules are linked into dimers through pairwise O-H⋯N hydrogen bonds, with these units being formed into stacks by two different sets of aromatic π-stacking inter-actions. The stacks are connected by C-H⋯O hydrogen bonds. A Hirshfeld surface analysis indicates that the most significant contacts in the crystal packing are H⋯O/O⋯H (36.7%), H⋯H (32.2%) and C⋯H/H⋯C (12.7%).

A Tetranuclear Ni(II)-Cubane Cluster Molecule Build by Four µ3-O-Methanolate (MeO) Ligands, Externally Cohesive by Four Unprecedented Bridging µ2-N7,O6-Acyclovirate (acv-H) Anions

Metal ion interactions with nuclei acids and their constituents represent a multi-faceted and growing research field. This contribution deals with molecular recognition between synthetic purine 17 nucleosides and first-row transition metal complexes, with O- and/or N-amino chelators which are able to 18 engage in intra-molecular N-H···(N or O) and O-H···(N or O) interligand interactions. Crystals of these complexes can also display inter-molecular aromatic π-stacking and/or other non-conventional interactions. In this manuscript, we used 2-(2-aminoethoxy)ethanol (2aee) as a potential N,O(e),O(ol)-chelator for nickel(II). However, unexpectedly, the reaction between NiCl2, acyclovir (acv), and 2aee in methanol afforded parallelepiped apple-green crystals of [Ni(acv-H)(MeO)(H2O)]4·8H2O, (1) a tetranuclear molecule with an equimolar Ni(II):µ3-methanolate(1-):µ2-N7,O6-acyclovirate(1-) (acv-H) ratio. The µ2-N7,O6-(acv-H) metal-binding pattern (MBP) is unprecedented in terms of both its anionic and bridging roles. The single-crystal X-ray diffraction structure as well as thermogravimetric analysis and the (FT-IR +Vis-UV) spectra of 1 are reported. Theoretical density functional theory (DFT) calculations are used to analyse the antiparallel π-stacking interactions that govern the formation of self-assembled dimers in the solid state.

1-(Hex-5-en-1-yl)-4-{[3-methyl-2,3-di-hydro-1,3-benzo-thia-zol-2-yl-idene]meth-yl}quinolin-1-ium iodide monohydrate.

The title thia-zole orange derivative, bearing an alkene substituent, crystallized as a monohydrate of its iodide salt, namely, (Z)-1-(hex-5-en-1-yl)-4-{[3-methyl-2,3-di-hydro-1,3-benzo-thia-zol-2-yl-idene]meth-yl}quinolin-1-ium iodide monohydrate, C24H25N2S+·I-·H2O. The packing features aromatic π-stacking and van der Waals inter-actions. The water mol-ecule of crystallization inter-acts with the cation and anion via O-H⋯N and O-H⋯I hydrogen bonds, respectively.

Polyaromatic molecular peanuts

Mimicking biological structures such as fruits and seeds using molecules and molecular assemblies is a great synthetic challenge. Here we report peanut-shaped nanostructures comprising two fullerene molecules fully surrounded by a dumbbell-like polyaromatic shell. The shell derives from a molecular double capsule composed of four W-shaped polyaromatic ligands and three metal ions. Mixing the double capsule with various fullerenes (that is, C60, C70 and Sc3N@C80) gives rise to the artificial peanuts with lengths of ∼3 nm in quantitative yields through the release of the single metal ion. The rational use of both metal–ligand coordination bonds and aromatic–aromatic π-stacking interactions as orthogonal chemical glue is essential for the facile preparation of the multicomponent, biomimetic nanoarchitectures.

Recognition of a Flavin Analogue by Novel Bile Acid-Based Receptors: Effects of Hydrogen Bonding and Aromatic π-Stacking Interactions

Molecular recognition properties are reported for novel bile acid-based receptors that incorporate 2,6-diaminopyridine as a recognition unit. Apart from hydrogen-bonding interactions, the bile acid receptors exhibit significant aromatic π-stacking interactions with the aromatic fused ring of the flavin derivative. These studies provide rationalisation for the differences in binding behaviour of bile acid receptors having differing aromatic arm lengths towards a flavin analogue.

Color-Tunable Amphiphilic Segmented π-Conjugated Polymer Nano-Assemblies and Their Bioimaging in Cancer Cells

We report a unique color tunable amphiphilic segmented π-conjugated polymer design and their π-stack driven diverse self-assembled nanostructures and demonstrate their application as a new classes of aqueous luminescent nanoparticle probes for bioimaging in cervical and breast cancer cells. Oligo-phenylenevinylene (OPV) was employed as rigid luminescent π-core and oligo-ethyleneoxy chains were used as flexible spacers to construct new amphiphilic segmented π-conjugated polymers by Witting–Horner polymerization route. The rigidity of the π-core was varied using tricyclodecanemethyleneoxy, 2-ethylhexyloxy or methoxy pendants and appropriate π-core geometry was optimized to achieve maximum aromatic π-stacking interactions. Solvent-induced chain aggregation of the polymers exhibited a morphological transition from one-dimensional helical nanofibrous to three-dimensional spherical nanoassemblies in good/bad solvent combinations. This morphological transformation was accompanied by the fluorescence color change...

Crystal structures of the pyrazinamide-p-aminobenzoic acid (1/1) cocrystal and the transamidation reaction product 4-(pyrazine-2-carboxamido)benzoic acid in the molten state.

The synthesis of pharmaceutical cocrystals is a strategy to enhance the performance of active pharmaceutical ingredients (APIs) without affecting their therapeutic efficiency. The 1:1 pharmaceutical cocrystal of the antituberculosis drug pyrazinamide (PZA) and the cocrystal former p-aminobenzoic acid (p-ABA), C7H7NO2·C5H5N3O, (1), was synthesized successfully and characterized by relevant solid-state characterization methods. The cocrystal crystallizes in the monoclinic space group P2₁/n containing one molecule of each component. Both molecules associate via intermolecular O-H···O and N-H···O hydrogen bonds [O···O = 2.6102 (15) Å and O-H···O = 168.3 (19)°; N···O = 2.9259 (18) Å and N-H···O = 167.7 (16)°] to generate a dimeric acid-amide synthon. Neighbouring dimers are linked centrosymmetrically through N-H···O interactions [N···O = 3.1201 (18) Å and N-H···O = 136.9 (14)°] to form a tetrameric assembly supplemented by C-H···N interactions [C···N = 3.5277 (19) Å and C-H···N = 147°]. Linking of these tetrameric assemblies through N-H···O [N···O = 3.3026 (19) Å and N-H···O = 143.1 (17)°], N-H···N [N···N = 3.221 (2) Å and N-H···N = 177.9 (17)°] and C-H···O [C···O = 3.5354 (18) Å and C-H···O = 152°] interactions creates the two-dimensional packing. Recrystallization of the cocrystals from the molten state revealed the formation of 4-(pyrazine-2-carboxamido)benzoic acid, C12H9N3O3, (2), through a transamidation reaction between PZA and p-ABA. Carboxamide (2) crystallizes in the triclinic space group P1̅ with one molecule in the asymmetric unit. Molecules of (2) form a centrosymmetric dimeric homosynthon through an acid-acid O-H···O hydrogen bond [O···O = 2.666 (3) Å and O-H···O = 178 (4)°]. Neighbouring assemblies are connected centrosymmetrically via a C-H···N interaction [C···N = 3.365 (3) Å and C-H···N = 142°] engaging the pyrazine groups to generate a linear chain. Adjacent chains are connected loosely via C-H···O interactions [C···O = 3.212 (3) Å and C-H···O = 149°] to generate a two-dimensional sheet structure. Closely associated two-dimensional sheets in both compounds are stacked via aromatic π-stacking interactions engaging the pyrazine and benzene rings to create a three-dimensional multi-stack structure.

Crystallographic and modelling studies suggest that the SKICH domains from different protein families share a common Ig-like fold but harbour substantial structural variations

TAX1BP1 is a pleiotropic multi-domain protein involved in many important biological processes such as signal transduction, cell growth and apoptosis, transcriptional coactivation, membrane trafficking, neurotransmission and autophagy. The N-terminus of TAX1BP1 contains a SKICH domain implicated in autophagy. SKICH domains are also present in four other proteins including NDP52, CALCOCO1, SKIP and PIPP. The SKICH domains of SKIP and PIPP mediate plasma membrane localisation. The functions of the SKICH domains of NDP52 and CALCOCO1 are not known. Here we report the crystal structure of the TAX1BP1 SKICH domain, which has an Ig-like fold similar to the NDP52 SKICH domain. Extensive pairwise and clustered aromatic π-stacking interactions are present in the TAX1BP1 SKICH domain. The aromatic residues mediating these interactions can be classified into four groups with varying degrees of conservation among different protein families. The interactions mediated by highly conserved residues are found in the interior and one outward face of the Ig-like β-barrel, representing common structural features of the SKICH domains. Three TAX1BP1-specific pairwise interactions locate in the loop regions, each augmented by a proline-aromatic interaction. The three proline–aromatic clusters are linked together by more generic hydrophobic interactions, forming a unique hydrophobic surface at one end of the TAX1BP1 SKICH domain. The structures and homologous models of SKICH domains from different proteins reveal substantial differences in electrostatic surface properties of the domains. Together with existing biochemical data, results from the structural study suggest that an intact SKICH domain is required for the autophagy function of TAX1BP1.

Structures and Properties of Molecular Torsion Balances to Decipher the Nature of Substituent Effects on the Aromatic Edge‐to‐Face Interaction

Various recent computational studies initiated this systematic re-investigation of substituent effects on aromatic edge-to-face interactions. Five series of Tröger base derived molecular torsion balances (MTBs), initially introduced by Wilcox and co-workers, showing an aromatic edge-to-face interaction in the folded, but not in the unfolded form, were synthesized. A fluorine atom or a trifluoromethyl group was introduced onto the edge ring in ortho-, meta-, and para-positions to the C-H group interacting with the face component. The substituents on the face component were varied from electron-donating to electron-withdrawing. Extensive X-ray crystallographic data allowed for a discussion on the conformational behavior of the torsional balances in the solid state. While most systems adopt the folded conformation, some were found to form supramolecular intercalative dimers, lacking the intramolecular edge-to-face interaction, which is compensated by the gain of aromatic π-stacking interactions between four aryl rings of the two molecular components. This dimerization does not take place in solution. The folding free enthalpy ΔG(fold) of all torsion balances was determined by (1)H NMR measurements by using 10 mM solutions of samples in CDCl3 and C6D6. Only the ΔG(fold) values of balances bearing an edge-ring substituent in ortho-position to the interacting C-H show a steep linear correlation with the Hammett parameter (σ(meta)) of the face-component substituent. Thermodynamic analysis using van't Hoff plots revealed that the interaction is enthalpy-driven. The ΔG(fold) values of the balances, in addition to partial charge calculations, suggest that increasing the polarization of the interacting C-H group makes a favorable contribution to the edge-to-face interaction. The largest contribution, however, seems to originate from local direct interactions between the substituent in ortho-position to the edge-ring C-H and the substituted face ring.

Side-chain hydrophobicity and the stability of Aβ₁₆₋₂₂ aggregates.

Recent mutagenesis studies using the hydrophobic segment of Aβ suggest that aromatic π-stacking interactions may not be critical for fibril formation. We have tested this conjecture by probing the effect of Leu, Ile, and Ala mutation of the aromatic Phe residues at positions 19 and 20, on the double-layer hexametric chains of Aβ fragment Aβ₁₆₋₂₂ using explicit solvent all-atom molecular dynamics. As these simulations rely on the accuracy of the utilized force fields, we first evaluated the dynamic and stability dependence on various force fields of small amyloid aggregates. These initial investigations led us to choose AMBER99SB-ILDN as force field in multiple long molecular dynamics simulations of 100 ns that probe the stability of the wild-type and mutants oligomers. Single-point and double-point mutants confirm that size and hydrophobicity are key for the aggregation and stability of the hydrophobic core region (Aβ₁₆₋₂₂). This suggests as a venue for designing Aβ aggregation inhibitors the substitution of residues (especially, Phe 19 and 20) in the hydrophobic region (Aβ₁₆₋₂₂) with natural and non-natural amino acids of similar size and hydrophobicity.

Synthesis and reactivity of enediyne–nucleobase hybrids: effect of intramolecular π-stacking

Three distinct classes of nucleobase-containing enediynes 1–9 with varying nature of the linker have been synthesized to explore the effect of π-stacking interaction in accelerating the rate of Bergman cyclization (BC). Chemical reactivity study, both experimental and computations demonstrated the important role that aromatic π-stacking interactions between the appended nucleobases within an enediyne frame play in lowering the activation barrier of Bergman cyclization.

Selective inclusion of PO43− within persistent dimeric capsules of a tris(thiourea) receptor and evidence of cation/solvent sealed unimolecular capsules

A tren-based tris(thiourea) receptor, L with electron-withdrawing p-nitrophenyl terminals has been established as a competent hydrogen-bonding scaffold that can selectively encapsulate PO(4)(3-) within persistent and rigid dimeric capsules, assembled by aromatic π-stacking interactions between the receptor side-arms. A quaternary ammonium salt of PO(4)(3-) capsules (complexes 1 and 1b, 2:1 host-guest) can reproducibly be obtained in quantitative yields by a solution-state deprotonation of [HL](+) moieties and a bound HPO(4)(2-) anion of complex 1a (HPO(4)(2-) complex of protonated L, 2:1 host-guest), induced by the presence of a large excess of anions such as HCO(3)(-), CH(3)CO(2)(-), and F(-). Qualitative as well as quantitative (1)H and (31)P NMR experiments (DMSO-d(6)) have been carried out in detail to demonstrate the selective and preferential inclusion of PO(4)(3-) by L in solution-states. Competitive crystallization experiments performed in the presence of an excess of anions such as HCO(3)(-), HSO(4)(-), CH(3)CO(2)(-), NO(3)(-) and halides (F(-) and Cl(-)) further establish the phenomenon of selective PO(4)(3-) encapsulation as confirmed by (1)H NMR, (31)P NMR, FT-IR and powder X-ray diffraction patterns of the isolated crystals. X-ray structural analyses and (31)P NMR studies of the isolated crystals of phosphate complexes (1, 1a and 1b) provide evidence of the binding discrepancy of inorganic phosphates with protonated and neutral form of L. Furthermore, extensive studies have been carried out with other anions of different sizes and dimensions in solid- and solution-states (complexes 2a, 3, 4 and 5). Crystal structure elucidation revealed the formation of a solvent (DMSO) sealed unimolecular capsule in the F(-) encapsulated complex, 2a (1:1 host-guest), a CO(3)(2-) encapsulated centrosymmetric molecular capsule in 3 (2:1 host-guest) and a cation (tetrabutylammonium) sealed SO(4)(2-) encapsulated unimolecular capsule in 4 (1:1 host-guest). 2D-NOESY NMR experiments carried out on these capsule complexes further confirm the relevant binding stoichiometry of complexes (2a-4) except for the PO(4)(3-)-encapsulated complex (1b) which showed a 1:1 host-guest stoichiometry in solution.

Radical Stabilization Is Crucial in the Mechanism of Action of Lysine 5,6-Aminomutase: Role of Tyrosine-263α As Revealed by Electron Paramagnetic Resonance Spectroscopy

Adenosylcobalamin- and pyridoxal-5'-phosphate-dependent lysine 5,6-aminomutase utilizes free radical intermediates to mediate 1,2-amino group rearrangement, during which an elusive high-energy aziridincarbinyl radical is proposed to be central in the mechanism of action. Understanding how the enzyme participates in stabilizing any of the radical intermediates is fundamentally significant. Y263F mutation abolished the enzymatic activity. With isotope-edited EPR methods, the roles of the Tyr263α residue in the putative active site are revealed. The Tyr263α residue stabilizes a radical intermediate, which most likely is the aziridincarbinyl radical, either by acting as a spin-relay device or serving as an anchor for the pyridine ring of pyridoxal-5'-phosphate through aromatic π-stacking interactions during spin transfer. The Tyr263α residue also protects the radical intermediate from interception by molecular oxygen. This study supports the proposed reaction mechanism, including the aziridincarbinyl radical, which has eluded detection for more than two decades.

Nano structures through self-assembly of protected hydrophobic amino acids: encapsulation of rhodamine B dye by proline-based nanovesicles

The development of novel molecules for the creation of nanometer structures with specific properties has been the current interest of this research. We have developed a set of molecules from hydrophobic ω- and α-amino acids by protecting the –NH2 with Boc (t-butyloxycarbonyl) group and –CO2H with para-nitroanilide such as BocHN–Xx–CONH–(p–NO2)·C6H4, where Xx is γ-aminobutyric acid (γ-Abu), (l)-isoleucine, α-aminoisobutyric acid, proline, etc. These molecules generate various nanometer structures, such as nanofibrils, nanotubes and nanovesicles, in methanol/water through the self-assembly of bilayers in which the nitro benzene moieties are stacked in the middle and the Boc-protected amino acids parts are packed in the outer surface. The bilayers can be further stacked one over the other through hydrophobic interactions to form multilayer structure, which helps to generate different kinds of nanoscopic structures. The formation of the nanostructures has been facilitated through the participation of various noncovalent interactions, such as hydrophobic interactions, hydrogen bonding and aromatic π-stacking interactions. Fluorescence microscopy and UV studies reveal that the nanovesicles generated from pro-based molecule can encapsulate dye molecules which can be released by addition of acid (at pH 2). These single amino acid based molecules are both easy to synthesize and cost-effective and therefore offer novel scaffolds for the future design of nanoscale structures.

Agonist-dependent effects of mutations in the sphingosine-1-phosphate type 1 receptor

The sphingosine-1-phosphate type 1 (S1P 1) receptor is a new target in the treatment of auto-immune diseases as evidenced by the recent approval of FTY720 (Fingolimod). The ligand-binding pocket of the S1P 1 receptor has been generally characterised but detailed insight into ligand-specific differences is still lacking. The aim of the current study is to determine differences in ligand-induced S1P 1 receptor activation using an in silico guided site-directed mutagenesis strategy. S1P 1 mutant receptors (modifications of residues Y98 2.57, R120 3.28, F125 3.33) were probed with a chemically diverse set of S1P 1 agonists (S1P, dihydro-S1P (dhS1P), R-, S- and racemic FTY720-P, VPC24191, SEW2871). Mutation of the R 3.28 residue generally results in a reduction of the potency of all ligands although the synthetic ligands including FTY720-P are less sensitive to these mutations. The Y 2.57F mutation does not affect the potency of any of the ligands tested, but for all ligands except FTY720-P a significant decrease in potency is observed at the Y 2.57A mutant. The F 3.33A mutation significantly decreased the potency of FTY720-P and is detrimental for SEW2871 and VPC24191. The non-aromatic endogenous ligands S1P and dhS1P are less affected by this mutation. Our in silico guided mutagenesis studies identified new molecular determinants of ligand-induced S1P 1 receptor activation: 1) the flexibility of the polar head of the agonist to maintain a tight H-bond network with R 3.28 and 2) the ability of the agonist to make aromatic π-stacking interactions with F 3.33. Interestingly, FTY720-P has both chemical properties and is the only ligand that can efficiently activate the Y 2.57A mutant.

Mutations That Replace Aromatic Side Chains Promote Aggregation of the Alzheimer’s Aβ Peptide

The aggregation of polypeptides into amyloid fibrils is associated with a number of human diseases. Because these fibrils--or intermediates on the aggregation pathway--play important roles in the etiology of disease, considerable effort has been expended to understand which features of the amino acid sequence promote aggregation. One feature suspected to direct aggregation is the π-stacking of aromatic residues. Such π-stacking interactions have also been proposed as the targets for various aromatic compounds that are known to inhibit aggregation. In the case of Alzheimer's disease, the aromatic side chains Phe19 and Phe20 in the wild-type amyloid beta (Aβ) peptide have been implicated. To explicitly test whether the aromaticity of these side chains plays a role in aggregation, we replaced these two phenylalanine side chains with leucines or isoleucines. These residues have similar sizes and hydrophobicities as Phe but are not capable of π-stacking. Thioflavin-T fluorescence and electron microscopy demonstrate that replacement of residues 19 and 20 by Leu or Ile did not prevent aggregation, but rather enhanced amyloid formation. Further experiments showed that aromatic inhibitors of aggregation are as effective against Ile- and Leu-substituted versions of Aβ42 as they are against wild-type Aβ. These results suggest that aromatic π-stacking interactions are not critical for Aβ aggregation or for the inhibition of Aβ aggregation.

Luminescent silver(i) coordination networks based on bis-(3,5-dimethylpyrazolyl)naphthalene ligands

A series of ligands containing two 3,5-dimethylpyrazole units connected to a central fluorescent naphthyl spacer have been used to prepare Ag(I) networks which have been structurally characterised. The ability of Ag(I) ions to tolerate a wide range of coordination environments has resulted in the formation of three different structural types: linear one-dimensional chains, two-dimensional sheets and three-dimensional networks. Upon complexation the ligands arrange so as to maximise inter-ligand aromatic π-stacking interactions, with the consequence that many of the resulting compounds display in the solid-state low-energy exciplex emission features extending well beyond the normal naphthalene emission range.