Reduced band gap dithieno[3,2-b:2',3'-d]pyrroles: new n-type organic materials via unexpected reactivity

Direct addition of tetracyanoethylene to N-(p-hexylphenyl)dithieno[3,2-b:2',3'-d]pyrrole yields not only the aromatic mono- and bis-tricyanovinyl-substituted products but also a quinoidal product with dicyanomethylene groups. The analogous reaction with dithieno[3,2-b:2',3'-d]thiophene yields exclusively the aromatic mono-tricyanovinyl product. The aromatic and quinoidal products possess red-shifted absorptions, increased electron affinities, and favorable pi-stacking motifs in comparison to the unsubstituted oligomers.     

Effective Solubilization Procedure for Analysis of Silkworm Hemolymph Proteins by Two-Dimensional Gel Electrophoresis

The outstanding capability of two-dimensional gel electrophoresis in separating all types of proteins basically depends on the efficiency of sample preparation. Sample preparation is one of the most critical steps in two-dimensional gel electrophoresis. Unfortunately, due to severe solubility, resolution of protein on gel is usually hampered, and thus, analysis remains a difficult task. However, technically several problems are generally encountered during protein extraction and isoelectric focusing. In the present investigation, we emphasized on evaluation and comparison of six different protein solubilization methods intended for resolving and analyzing silkworm hemolymph proteins by two-dimensional gel electrophoresis. Our findings revealed that the buffer composition of 8 M urea, 4 % 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate, 40 mM Tris base, 65 mM dithiothreitol, and 0.2 % ampholyte can effectively solubilize and yields maximum protein spots.     

Shedding Light on the Interactions of Hydrocarbon Ester Substituents upon Formation of Dimeric Titanium(IV) Triscatecholates in DMSO Solution

The dissociation of hierarchically formed dimeric triple lithium bridged triscatecholate titanium(IV) helicates with hydrocarbyl esters as side groups is systematically investigated in DMSO. Primary alkyl, alkenyl, alkynyl as well as benzyl esters are studied in order to minimize steric effects close to the helicate core. The ¹H NMR dimerization constants for the monomer–dimer equilibrium show some solvent dependent influence of the side chains on the dimer stability. In the dimer, the ability of the hydrocarbyl ester groups to aggregate minimizes their contacts with the solvent molecules. Due to this, most solvophobic alkyl groups show the highest dimerization tendency followed by alkenyls, alkynyls and finally benzyls. Furthermore, trends within the different groups of compounds can be observed. For example, the dimer is destabilized by internal double or triple bonds due to π–π repulsion. A strong indication for solvent supported London dispersion interaction between the ester side groups is found by observation of an even/odd alternation of dimerization constants within the series of n-alkyls, n-Ω-alkenyls or n-Ω-alkynyls. This corresponds to the interaction of the parent hydrocarbons, as documented by an even/odd melting point alternation.     

Electronic properties of single-walled carbon nanotubes inside cyclic supermolecules

Possible ways for manipulating carbon nanotubes (CNTs) with cyclic supermolecules are studied using density functional theory. Electronic structure calculations with structure optimizations have been performed for the (4,4) and (8,0) single-walled carbon nanotubes (SWNTs) complexed with crown ethers as well as for the (4,0) SWNT with beta-cyclodextrin. A slight polarization of charge in both the nanotube and the supermolecule is observed upon rotaxane complexation, but the interaction is mainly repulsive, and the systems stay 2.8-3.5 A apart. The supermolecule does not affect the electronic band structure of the nanotube significantly within such a configuration. The situation differs noticeably for chemically cross-linked SWNTs and crown ethers, where a peak arises at the Fermi energy in the density of states. As a result, the band gap of semiconducting CNT(8,0) (0.5 eV) vanishes, and a new conduction channel opens for the metallic CNT(4,4).     

Structure and matrix isolation infrared spectrum of formyl fluoride dimer: blue-shift of the C-H stretching frequency

Infrared spectroscopy (IR) of formyl fluoride (HCOF) dimer is studied in low-temperature argon and krypton matrixes. New IR absorptions, ca. 17 cm(-1) blue shifted from the monomer C-H stretching fundamental, are assigned to the HCOF dimer. The MP2/6-311++G calculations were utilized to define structures and harmonic frequencies of various HCOF dimers. Among the four optimized structures, the dimer having two C-H...O hydrogen bonds possesses strongest intermolecular bonding. The calculated harmonic frequencies of this dimer structure are shifted from the monomer similarly as observed in the experiment. Thus, we suggest that the experimentally observed blue shifted C-H bands belong to the dimer with two C-H...O hydrogen bonds. This observation includes the HCOF dimer to the class of hydrogen bonded complexes showing blue shift in their vibrational energies.     

A linear Fe–O–Fe unit in bis­(dibenzyl­dimethyl­ammonium) μ‐oxo‐bis­[tribromo­ferrate(III)]

The title compound, (C₁₆H₂₀N)₂[Fe₂Br₆O], crystallizes with one dibenzyl­dimethylammonium cation and one half of a μ‐oxo‐bis­[tribromo­ferrate(III)] anion in the asymmetric unit. The bridging oxo group is situated on an inversion centre, resulting in a linear conformation for the Fe—O—Fe unit. The iron(III) cations have tetra­hedral geometry, with bond angles in the range 106.8 (1)–112.2 (1)°. The ion pairs are held together by Coulombic forces and C—H⋯Br hydrogen bonds. Each Br⁻ anion forms one hydrogen bond. No C—H⋯O hydrogen bonds are found between the O atom in the Fe—O—Fe unit and surrounding counter‐cations, consistent with the linear configuration of the Fe—O—Fe unit.     

Reactions of 9-substituted guanines with bromomalondialdehyde in aqueous solution predominantly yield glyoxal-derived adducts

Reactions of 9-ethylguanine, 2'-deoxyguanosine and guanosine with bromomalondialdehyde in aqueous buffers over a wide pH-range were studied. The main products were isolated and characterized by (1)H and (13)C NMR and mass spectroscopy. The final products formed under acidic and basic conditions were different, but they shared the common feature of being derived from glyoxal. Among the 1 : 1 adducts, 1,N(2)-(trans-1,2-dihydroxyethano)guanine adduct (6) predominated at pH < 6 and N(2)-carboxymethylguanine adduct (10a,b) at pH > 7. In addition to these, an N(2)-(4,5-dihydroxy-1,3-dioxolan-2-yl)methylene adduct (11a,b) and an N(2)-carboxymethyl-1,N(2)-(trans-1,2-dihydroxyethano)guanine adduct (12) were obtained at pH 10. The results of kinetic experiments suggest that bromomalondialdehyde is significantly decomposed to formic acid and glycolaldehyde under the conditions required to obtain guanine adducts. Glycolaldehyde is oxidized to glyoxal, which then modifies the guanine base more readily than bromomalondialdehyde. Besides the glyoxal-derived adducts, 1,N(2)-ethenoguanine (5a-c) and N(2),3-ethenoguanine adducts (4a-c) were formed as minor products, and a transient accumulation of two unstable intermediates, tentatively identified as 1,N(2)-(1,2,2,3-tetrahydroxypropano)(8) and 1,N(2)-(2-formyl-1,2,3-trihydroxypropano)(9) adducts, was observed.     

CH‐Directed Anion–π Interactions in the Crystals of Pentafluorobenzyl‐Substituted Ammonium and Pyridinium Salts

Simple pentafluorobenzyl‐substituted ammonium and pyridinium salts with different anions can be easily obtained by treatment of the parent amine or pyridine with the respective pentafluorobenzyl halide. Hexafluorophosphate is introduced as the anion by salt metathesis. In the case of the ammonium salt 4 , water co‐crystallisation seems to suppress effective anion–π interactions of bromide with the electron‐deficient aromatic system, whereas with salts 5 and 6 such interactions are observed despite the presence of water. However, due to asymmetric hydrogen‐bonding interactions with ammonium side chains, the anion of 5 is located close to the rim of the pentafluorophenyl group (η¹ interaction). In 6 the CH–anion hydrogen bonding is more symmetric and fixes the anion on top of the ring (η⁶). A similar structure‐controlling effect is observed in case of the 1,4‐diazabicyclo[2.2.2]octane derivatives 7 . Here the position of the anion (Cl, Br, I) is shifted according to the length of the weak CH–halide interaction. The hexafluorophosphate 7 d reveals that this “non‐coordinating” anion can be located on top of an aromatic π system. In the methyl‐substituted pyridinium salts 9 and 10 different locations of the bromide anions with respect to the π system are observed. This is due to different conformations of the mono‐ versus disubstituted pyridine, which leads to different directions of the weak, but structurally important, H_Me? Br bonds.     

p-(1H-phenanthro[9,10-d]imidazol-2-yl)- substituted calix[4]arene, a deep cavity for guest inclusion

The reaction of tetra-p-formyltetra-O-propylcalix[4]arene with phenanthrenequinone in the presence of NH(4)OAc affords compound 2, a new class of calixarene with an expanded aromatic cavity, that could be stabilized by hydrogen-bonded bridges and/or ion pairing, thus preventing collapse into fully stacked pinched cone conformations as depicted. Two partially protonated calixarenes interdigitate in the solid state to give rise to a self-assembled face-to-face dimer, stabilized by pi-pi stacking interactions.