Concise Synthesis of 3D π‐Extended Polyphenylene Cylinders

The synthesis of structurally well‐defined, monodisperse carbon nanotube (CNT) sidewall segments poses a challenge in materials science. The synthesis of polyphenylene cylinders that comprise typical benzene connectivity to resemble precursors of [9,9] and [15,15] CNTs is now reported, and the products were characterized by X‐ray crystallography. To investigate the oxidative cyclodehydrogenation of ring‐strained molecules as a final step towards a bottom‐up synthesis of CNT sidewall segments, phenylene‐extended cyclic p‐hexaphenylbenzene trimers ([3]CHPB) were prepared, and NMR studies revealed a strain‐induced 1,2‐phenyl shift. It was further shown that an increase in ring size leads to selectively dehydrogenated macrocycles. Larger homologues are envisioned to give smooth condensation reactions toward graphenic sidewalls and should be used in the future as seeds for CNT formation.     

π‐Extended Star‐Shaped Polycyclic Aromatic Hydrocarbons based on Fused Truxenes: Synthesis,Self‐Assembly,and Facilely Tunable Emission Properties

A new set of star‐shaped polycyclic aromatic hydrocarbons (PAHs) based on naphthalene‐fused truxenes, TrNaCn (n=1–4), were synthesized and characterized. The synthesis involved a microwave‐assisted six‐fold Suzuki coupling reaction, followed by oxidative cyclodehydrogenation. Multiple dehydrocyclization products could be effectively isolated in a single reaction, thus suggesting that the oxidative cyclodehydrogenation reaction involved a stepwise ring‐closing process. The thermal, optical, and electrochemical properties and the self‐assembly behavior of the resulting oxidized samples were investigated to understand the impact of the ring‐fusing process on the properties of the star‐shaped PAHs. Distinct bathochromic shift of the absorption maxima (λ_max) revealed that the molecular conjugation extended with the stepwise ring‐closing reactions. The optical band‐gap energy of these PAHs varied significantly on increasing the number of fused rings, thereby resulting in readily tunable emissive properties of the resultant star‐shaped PAHs. Interestingly, the generation of rigid “arms” by using perylene analogues caused TrNaC2 and TrNaC3 to show significantly enhanced photoluminescence quantum yields (PLQYs) in solution (η=0.65 and 0.66, respectively) in comparison with those of TrNa and TrNaC1 (η=0.08 and 0.16, respectively). Owing to strong intermolecular interactions, the TrNa precursor was able to self‐assemble into rod‐like microcrystals, which could be facilely identified by the naked eye, whilst TrNaC1 self‐assembled into nanosheets once the naphthalene rings had fused. This study offers a unique platform to gain further insight into—and a better understanding of—the photophysical and self‐assembly properties of π‐extended star‐shaped PAHs.     

Polycyclic Azoniahetarenes: Assessing the Binding Parameters of Complexes between Unsubstituted Ligands and G‐Quadruplex DNA

Polycyclic azoniahetarenes were employed to determine the effect of the structure of unsubstituted polyaromatic ligands on their quadruplex‐DNA binding properties. The interactions of three isomeric diazoniadibenzo[b,k]chrysenes ( 4 a – c ), diazoniapentaphene ( 5 ), diazoniaanthra[1,2‐a]anthracene ( 6 ), and tetraazoniapentapheno[6,7‐h]pentaphene ( 3 ) with quadruplex DNA were examined by DNA melting studies (FRET melting) and fluorimetric titrations. In general, penta‐ and hexacyclic azoniahetarenes bind to quadruplex DNA (K_b≈10⁶ M ^?1) even in the absence of additional functional side chains. The binding modes of 4 a – c and 3 were studied in more detail by ligand displacement experiments, isothermal titration calorimetry, and CD and NMR spectroscopy. All experimental data indicate that terminal π stacking of the diazoniachrysenes to the quadruplex is the major binding mode; however, because of different electron distributions of the π systems of each isomer, these ligands align differently in the binding site to achieve ideal binding interactions. It is proposed that tetraazonia ligand 3 binds to the quadruplex by terminal stacking with a small portion of its π system, whereas a significant part of the bulky ligand most likely points outside the quadruplex structure, and is thus partially placed in the grooves. Notably, 3 and the known tetracationic porphyrin TMPyP4 exhibit almost the same binding properties towards quadruplex DNA, with 3 being more selective for quadruplex than for duplex DNA. Overall, studies on azonia‐type hetarenes enable understanding of some parameters that govern the quadruplex‐binding properties of parent ligand systems. Since unsubstituted ligands were employed in this study, complementary and cooperative effects of additional substituents, which may interfere with the ligand properties, were eliminated.     

Adamantanes, nortricyclenes, and dendrimers with extended silicon backbones

By reaction of the hexabromoheptasilane MeSi(SiMe(2)SiMeBr(2))(3) (1 a) with H(2)O, H(2)S, NH(3), and H(2)NMe the heptasilaadamantanes MeSi(SiMe(2)SiMeO)(3) (4), MeSi(SiMe(2)SiMeS)(3) (5), MeSi(SiMe(2)SiMeNH)(3) (6 a), and MeSi(SiMe(2)SiMeNMe)(3) (6 b), respectively, were prepared in good to moderate yields. Molecular structures of 4, 5, 6 a, and 6 b were determined by X-ray crystallography. The symmetry of the cages is approximately C(3v), and the geometry around the nitrogen atoms is essentially planar. Ab initio SCF/HF calculations with the 6-31G* basis set confirm these results. Reduction of MeSi(SiMe(2)SitBuBr(2))(3) (1 b) with lithium naphthalenide afforded the heptasilanortricyclene MeSi(SiMe(2)SitBu)(3) (7). The (29)Si NMR spectrum of 7 consists of three signals with chemical shifts that agree closely with values predicted by ab initio calculations. (29)Si INADEQUATE spectra also strongly support the nortricyclene structure. Ab initio SCF/HF calculations were performed for the parent molecule Si(7)H(10), and the ring strain of the cage was estimated as 168.8 kJ mol(-1) by using the homodesmic reaction Si(7)H(10) + 3 Si(2)H(6)-->Si(13)H(28). Compound 1 a also served as the starting material for the preparation of first-generation dendrimer 2 a by reaction with six equivalents of Ph(2)MeSiLi. Subsequent protodearylation with HBr and reaction with (Me(2)PhSi)(2)SiMeK afforded second-generation dendrimer 3. All dendrimers were characterized by multinuclear NMR spectroscopy.     

Fluorescent Pyrene‐Based Bis‐azole Compounds: Synthesis and Photophysical Analysis

A rational synthetic procedure for the preparation of a series of pyrene‐based neutral and dicationic bis‐azole compounds is reported. The method allows the tailored design of pyrene‐based azoles with different substituents at the nitrogen atoms of the heterocycles, for which the relative conformation of the resulting bis‐azoles can be easily controlled. The bis‐azoliums were used for the preparation of the related diplatinum complexes by reaction with [{Pt(ppy)(μ‐Cl)₂}₂] (ppy=2‐phenylpyridinate). The X‐ray molecular structure of one of the resulting compounds, a diplatinum(II) bis(N‐heterocyclic carbene) complex, is described. Studies on the photophysical properties of all new species are described. The emission of the bis‐azole‐based compounds seems to be independent of their substitution patterns, which basically indicates that physical properties such as solubility, melting point, and viscosity can be fine‐tuned while maintaining the luminescence properties. Finally, the energies associated with the HOMO and LUMO levels suggest that this family provides versatility to match the energy levels of a wide range of host materials, which is important for the preparation of organic light‐emitting devices.     

Structurally characterized homotrinuclear Salamo‐type nickel(II) complexes: Synthesis,solvent effect and fluorescence properties

Four new solvent‐induced Ni(II) complexes with chemical formulae [{NiL(μ₂‐OAc)(MeOH)}₂Ni]·2MeOH ( 1 ), [{NiL(μ₂‐OAc)}₂(n‐PrOH)(H₂O)Ni]·n‐PrOH ( 2 ), [{NiL(μ₂‐OAc)(DMF)}₂Ni] ( 3 ) and [{NiL(μ₂‐OAc)(DMSO)}₂Ni]·2DMSO ( 4 ), (H₂L = 4‐Nitro‐4′‐chloro‐2,2′‐[(1,3‐propylene)dioxybis(nitrilomethylidyne)]diphenol) have been synthesized and characterized by elemental analyses, FT‐IR, UV–Vis spectra and X‐ray crystallography. X‐ray crystal structure determinations revealed that each of the Ni(II) complexes 1–4 consists of three Ni(II) atoms, two completely deprotonated (L)^2? units, two μ₂‐acetate ions and two coordinated solvent molecules (solvents are methanol, n‐propanol, water, N,N‐dimethylformamide and dimethyl sulphoxide, respectively). Although the four complexes 1–4 were synthesized in different solvents, it is worthwhile that the Ni(II) atoms in the four complexes 1–4 adopt hexa–coordinated with slightly distorted octahedral coordination geometries, and the ratios of the ligand H₂L to Ni(II) atoms are all 2: 3. The complexes 1–4 possess self‐assembled infinite 1D, 3D, 1D and 2D supramolecular structures via the intermolecular hydrogen bonds, respectively. In addition, fluorescence behaviors were investigated in the complexes 1–4 .     

Diverse reactions of 1,4-dilithio-1,3-dienes with nitriles: facile access to tricyclic Delta1-bipyrrolines, multiply substituted pyridines, siloles, and (Z,Z)-dienylsilanes by tuning of substituents on the butadienyl skeleton

Addition cyclization of 1,2,3,4-tetrasubstituted 1,4-dilithio-1,3-dienes (Type I) with four equivalents of various aromatic nitriles in the presence of hexamethylphosphoramide (HMPA) gives exclusively fully substituted pyridines in moderate to good yields. Similarly, trisubstituted pyridines can be prepared by the reaction of 2,3-dialkyl- or diaryl-substituted 1,4-dilithio-1,3-dienes (Type II) with nitriles. However, five- or six-membered-ring fused 2,3-disubstituted 1,4-dilithio-1,3-dienes (Type III) reacted with various aromatic and aliphatic nitriles without alpha-hydrogen atoms to afford tricyclic Delta1-bipyrrolines in high yields. The reaction of six-membered-ring fused 2,3-disubstituted 1,4-dilithio-1,3-diene (Type III) with 2-cyanopyridine afforded the corresponding pyridine, and no tricyclic Delta1-bipyrroline was observed. Seven-membered-ring fused dilithiodienes reacted with PhCN or trimethylacetonitrile to afford the corresponding pyridines in good yield. When 1,2,3,4-tetrasubstituted dilithio reagents (Type I) were treated with Me3SiCN, a tandem silylation/intramolecular substitution process readily occurred to yield siloles, whereas the reaction of 2,3-disubstituted dilithio reagents (Types II and III) with Me3SiCN gave rise to (Z,Z)-dienylsilanes with high stereoselectivity. These results revealed that the formation of tricyclic Delta1-bipyrrolines, pyridines, siloles, and (Z,Z)-dienylsilanes are strongly dependent on the substitution patterns of the dilithio butadienes and the nature of the nitriles employed.     

Anti‐neurotoxic evaluation of synthetic and characterized metal complexes of thiosemicarbazone derivatives

Quinoline‐2‐caboxyaldehyde thiosemicarbazone (HL¹) and quinoline ‐2‐caboxyaldehyde N‐dimethyl thiosemicarbazone (HL²) metal complexes were prepared and characterized using analytical and spectroscopic techniques. The measurements showed that ligands behave as monovalent or neutral tridentate ligands bonding via azomethine, quinoline ring nitrogen atoms and sulfur atoms in thiol or thion forms. The anti‐neurotoxic effect of ligands and their complexes showed that, exposure to aluminum increase oxidative stress in the brain, an effect that could be offset by concomitant thiosemicarbazone complexes. Complexes could be having an effect on absorption or excretion of aluminum, due to their chelating activity. These findings may shed light on the potential clinical importance of thiosemicarbazone complexes in Alzheimer's disease.     

Proteo-dendrimers designed for complementary recognition of cytochrome c: dendrimer architecture toward nanoscale protein complexation

"Proteo-dendrimers" in which polyanionic hepta(glutamic acids), fluorescent zinc porphyrinate cores, hydrophilic polyether surfaces, and nonpeptide hydrophobic dendrons are combined, were developed as a new series of synthetic receptors for protein recognition. They have polyanionic "patch" structures on their surfaces and undergo complementary electrostatic interactions with a positively charged cytochrome c patch, as observed in biological protein-protein recognition systems. Stability constants of the resulting supramolecular complexes were determined in phosphate buffer (pH 7) by monitoring the fluorescence quenching of the zinc porphyrinates. These proteo-dendrimer receptors exhibited higher affinities with cytochrome c proteins in aqueous solutions than with biological cytochrome b5. Furthermore, they effectively blocked complexation of biological cytochrome b5 with cytochrome c, indicating that the proteo-dendrimers and cytochrome b5 similarly occupy the polycationic patch of cytochrome c.     

Functional nanomachines: Recent advances in synthetic molecular machinery

A mini-review: As the top-down approach for miniaturisation of technology reaches its inherent limitations, robust strategies to build nanoscale machinery components, which have the ability to convert an input energy into motion, from the molecular level up, become increasingly important. Nature is certainly the most proficient in the control of molecular level motion; nevertheless, many successes have been enjoyed in the pursuit of mimicking key aspects of nature’s molecular machines, including two state switches, ion pumps, unidirectional rotary motors and molecular robots that can move molecular cargo. This mini-review outlines of some of the most impressive recent examples towards this end.     

Studies toward diazonamide A: initial synthetic forays directed toward the originally proposed structure

A brief introduction into the chemistry of diazonamide A (1) is followed by first-generation sequences to access the originally proposed structure for this unusual marine natural product. These explorations identified a route capable of delivering a model compound possessing the complete heteroaromatic core of the natural product, highlighting in the process several unanticipated synthetic challenges which led both to new methodology as well as an improved synthetic plan that was successfully applied to fully functionalized intermediates.     

Practical Synthesis of Structurally Important Spirodiamine Templates

A general, concise, four‐step synthetic sequence for the preparation of spirodiamine templates is described herein.     

Copper-free monomeric and dendritic palladium catalysts for the Sonogashira reaction: substituent effects, synthetic applications, and the recovery and re-use of the catalysts

A series of bis(tert-butylphosphine)- and bis(cyclohexylphosphine)-functionalized Pd(II) monomers and polyamino (DAB) dendritic catalysts were synthesized and investigated for Sonogashira carbon-carbon coupling reactions in a copper-free procedure. The influence of phosphine substituents (tBu versus Cy) on the reaction kinetics was investigated by a GPC technique to monitor the reactions. The dendritic catalysts containing the cyclohexylphosphine ligands could be recovered and reused without loss of efficiency until the fifth cycle. The dendritic Pd(II) catalysts show a negative dendritic effect, that is, the catalyst efficiency decreases as the dendrimer generation increases.     

A synthetic "tour de force": well-defined multivalent and multimodal dendritic structures for biomedical applications

Dendrimers have several unique properties that make them attractive scaffolds for use in biomedical applications. To date, multivalent and multimodal dendritic structures have been synthesized predominantly by statistical modification of peripheral groups. However, the potential application of such probes in patients demands well-defined and monodisperse materials that have unique structures. Current progress in the field of chemical biology, in particular chemoselective ligation methods, renders this challenge possible. In this Minireview, we outline the different available synthetic strategies, some applications that already make use of this new generation of multivalent and multimodal architectures, and the challenges for future developments.     

Lanthaballs: Chiral,Structurally Layered Polycarbonate Tridecanuclear Lanthanoid Clusters

New balls please! The viability of using carbonate as the primary anion in cluster formation is demonstrated in the synthesis of ‘lanthaballs’, spherical tridecanuclear lanthanoid complexes with a novel [Ln(CO₃)₆] moiety in a [Ln₁₃(CO₃)₁₄] core (see picture). The chirality of the lanthaballs is evidenced in the configuration of extended columns of π‐stacked phenanthroline ligands. The structural and magnetic properties of lanthaballs are investigated.