Synthesis of a Helical Bilayer Nanographene

A rigid, inherently chiral bilayer nanographene has been synthesized as both the racemate and enantioenriched M isomer (with 93 % ee) in three steps from established helicenes. This folded nanographene is composed of two hexa‐peri‐hexabenzocoronene layers fused to a [10]helicene, with an interlayer distance of 3.6 Å as determined by X‐ray crystallography. The rigidity of the helicene linker forces the layers to adopt a nearly aligned AA‐stacked conformation, rarely observed in few‐layer graphene. By combining the advantages of nanographenes and helicenes, we have constructed a bilayer system of 30 fused benzene rings that is also chiral, rigid, and remains soluble in common organic solvents. We present this as a molecular model system of bilayer graphene, with properties of interest in a variety of potential applications.     

Structural characterization of a lariat ether based on 4,10-diaza-2,3,11,12-dibenzo-18-crown-6 and of a coordination Pb(II) complex using picrate as co-ligand

A new lariat ether, N,N′-di(methylenecarboxyethoxy)-4,10-diaza-2,3,11,12-dibenzo-18-crown-6, C₂₈H₃₈N₂O₈, has been characterized and tested for Pb²⁺ extraction in a picrate medium. The isolated complex, [(picrato-O,O′)-(N,N′-di-methylenecarboxyethoxy-4,10-diaza-2,3,11,12-dibenzo-18-crown-6)]-lead(II) picrate, [C₃₄H₄₀N₅O₁₅Pb]⁺[C₆H₂N₃O₇]⁻, includes a 7-coordinated Pb²⁺ cation complex where sidearms of the macrocycle are involved in complexation, with Pb‐O bond lengths of 2.587(4) and 2.617(4) ?. Picrate ions serve both as co-ligand and as anion for charge balance. Both free ligand and Pb²⁺ complex have been X-ray characterized: a = 18.4723(16), b = 24.0057(19), c = 14.4309(14) ?, β = 112.962(7)°, P2₁/c, for the ligand; a = 12.7591(15), b = 21.951(2), c = 16.4389(15) ?, β = 97.144(8)°, P2₁/n, for the complex.     

Inside Back Cover: Electronic Control of the Scholl Reaction: Selective Synthesis of Spiro vs Helical Nanographenes (Angew. Chem. Int. Ed. 7/2023)

Scholl oxidation has become an essential reaction in the bottom-up synthesis of molecular nanographenes. Herein, we describe a Scholl reaction controlled by the electronic effects on the starting substrate ( 1 a , b ). Anthracene-based polyphenylenes lead to spironanographenes under Scholl conditions. In contrast, an electron-deficient anthracene substrate affords a helically arranged molecular nanographene formed by two orthogonal dibenzo[fg,ij]phenanthro-[9,10,1,2,3-pqrst]pentaphene (DBPP) moieties linked through an octafluoroanthracene core. Density Functional Theory (DFT) calculations predict that electronic effects control either the first formation of spirocycles and subsequent Scholl reaction to form spironanographene 2 , or the expected dehydrogenation reaction leading solely to the helical nanographene 3 . The crystal structures of four of the new spiro compounds (syn 2 , syn 9 , anti 9 and syn 10 ) were solved by single crystal X-ray diffraction. The photophysical properties of the new molecular nanographene 3 reveal a remarkable dual fluorescent emission.     

Preparation,NMR studies and crystal structure of mononuclear and dinuclear Pd(II) and Pt(II) complexes that contain 1,2-bis[3-(3,5-dimethyl-1-pyrazolyl)-2-thiapropyl]benzene

The reaction between 1,2-bis[3-(3,5-dimethyl-1-pyrazolyl)-2-thiapropyl]benzene (bddf) and [MCl₂(CH₃CN)₂] (M = Pd(II), Pt(II)) in a 1:1 M/L ratio in CH₂Cl₂ or acetonitrile solution, respectively, gave the complexes trans-[MCl₂(bddf)] (M = Pd(II) (1), Pt(II) (4)), and in a 2:1 M/L ratio led to [M₂Cl₄(bddf)] (M = Pd(II) (2), Pt(II) (5)). Treatment of 1 and 4 with AgBF₄ and NaBPh₄, respectively, gave the compounds [Pd(bddf)](BF₄)₂ (3) and [Pt(bddf)](BPh₄)₂ (6). When complexes 3 and 6 were heated under reflux in a solution of Et₄NBr in CH₂Cl₂/CH₃OH (1:1) for 24 h, analogous complexes to 1 and 4 with bromides instead of chlorides bonded to the metallic centre were obtained. These complexes were characterised by elemental analyses, conductivity measurements, infrared, ¹H, ¹H{¹⁹⁵Pt}, ¹³C{¹H}, ¹⁹⁵Pt{¹H} NMR, HSQC and NOESY spectroscopies. The X-ray crystal structure of the complex [Pd(bddf)](BF₄)₂ · H₂O has been determined. The metal atom is tetracoordinated by the two azine nitrogen atoms of the pyrazole rings and two thioether groups.     

Combinatorial approach to N-substituted aminocyclitol libraries by solution-phase parallel synthesis and preliminary evaluation as glucocerebrosidase inhibitors

Libraries of N-substituted aminocyclitol derivatives of the scyllo and racemic chiro series by means of parallel solution-phase methodology with the help of robotic technology are described. Chemical diversity has been introduced by reaction of selected scaffolds with a set of aldehydes, acyl chlorides, sulfonyl chlorides, chloroformates, and amines to afford the corresponding amines, amides, sulfonamides, carbamates and ureas, respectively. The optimized methodology has proven excellent, in terms of overall purities of the resulting libraries, for the production of amides. Sulfonamides and carbamates have been obtained in slightly lower purities, while amines afforded modest results. Selected library members have been evaluated as inhibitors of recombinant glucocerebrosidase with K(i) values ranging in the low micromolar scale for the most active members.     

Reaction mechanism in the photochemistry of the antileukaemic agents 2-chloro- and 2-bromo-2'-deoxyadenosine, studied by nanosecond laser flash photolysis.

The reaction mechanism in the UV photochemistry of 2-chloro-2'-deoxyadenosine (Cladibrine) and 2-bromo-2'-deoxyadenosine in aqueous solution has been studied by laser photolysis at nanosecond time resolution. It is found that excitation at 266 nm wavelength produces heterolytic cleavage of the halogen-carbon bond by one-photon absorption and formation of the unstable 2-hydroxy tautomer of 2'-deoxyisoguanosine as predominant 'primary' product. The 2-hydroxy tautomer then transforms in 10(-6)-10(-5) s into the stable 2-oxo tautomer in an acid-base-catalysed reaction. A reaction mechanism is proposed and discussed in relation to previous UV low-intensity studies of these halogenodeoxyadenosines.     

Speciation of volatile mercury species present in digester and deposit gases

Volatile mercury compounds have been speciated in gases evolved from fermentation of sewage sludge as well as municipal waste. The species were trapped by sequential sampling, using a noble‐metal trap in series with an activated‐carbon trap. Thermally desorbed Hg⁰ and (CH₃)₂Hg were separated by GC at 70 °C and detected by cold vapour atomic fluorescence spectroscopy after thermal reduction. The amounts of mercury detected in the sewage gas correspond to concentrations in the range 50–110 ng m⁻³ for both species whereas the deposit gases were found to contain only elemental mercury. Monomethylmercury species could not be positively identified in any of the gas samples. Copyright © 1999 John Wiley & Sons, Ltd.     

Light scattering by coated Gaussian and aggregate particles

Light scattering by nonspherical and inhomogeneous small particles is studied by varying particle shapes, sizes, and compositions. We introduce an efficient tool for deforming particle shape and composition by adding a coating on an initial particle. This concave-hull transformation is applied to wavelength-scale Gaussian and aggregate particles, and the differences in the optical properties of the coated particles are compared to those of the uncoated geometries. The light-scattering computations are performed using the discrete-dipole approximation method which allows for internal inhomogeneity and irregular particle shapes. The results are analyzed concentrating on the intensity of the scattered light, the degree of linear polarization for unpolarized incident light, and the depolarization ratio. Polarization results yield the most significant differences and, moreover, coated aggregates are observed to produce net positive polarization, whereas it is negative for the Gaussian particles, also resembling the polarization of a spherical particle. As for the depolarization ratio, an intriguing double-lobe feature is observed near the backscattering direction for both particle geometries regardless of size, shape, and composition. The double-lobe maxima and minima generally coincide with those of the intensity and polarization.