A combined optical and EPR spectroscopy study: azobenzene-based biradicals as reversible molecular photoswitches.

Azobenzene compounds are known as versatile examples for photoswitchable systems because of their isomeric cis- and trans-configurations. The switching between these isomers can be reversibly controlled by light excitation. In this study we characterize two members of this class by joining the azobenzene moiety with each two paramagnetic nitroxide spin labels.

Modular Two-Step Approach for the Stereodivergent Synthesis of 1,3-Diamines with Three Continuous Stereocenters.

A two-step reaction sequence for the highly stereodivergent construction of 1,3-diamines with three continuous stereocenters is reported. This novel method enables the controlled synthesis of any given diastereomer of the 1,3-diamine scaffold from a simple set of starting materials in a highly modular manner. The disclosed approach is based on the reaction of an enamide with an in situ generated N-acylimine followed by a subsequent trapping of the generated intermediate with a suitable nucleophile.

A chiral analog of the bicyclic guanidine TBD: synthesis, structure and Brønsted base catalysis.

Starting from ()-β-phenylalanine, easily accessible by lipase-catalyzed kinetic resolution, a chiral triamine was assembled by a reductive amination and finally cyclized to form the title compound . In the crystals of the guanidinium benzoate salt the six membered rings of adopt conformations close to an envelope with the phenyl substituents in pseudo-axial positions. The unprotonated guanidine catalyzes Diels-Alder reactions of anthrones and maleimides (25-30% ee).

Self-Assembled Monolayers of Pseudo-C-Symmetric, Low-Band-Gap Areneoxazolethiolates on Gold Surfaces.

A series of three homologous arene[2,3-d]-oxazole-2-thiols (benzoxazole-2-thiol (BOxSH), naphthaleneoxazole-2-thiol (NOxSH), and anthraceneoxazole-2-thiol (AOxSH)) were deposited onto Au(111) to obtain surfaces suitable as injection layers for organic electronics. The guiding idea was that the increasingly extended conjugated system would lower the band gap of the films while the introduction of the annulated heteroaromatic ring would provide the opportunity for pseudosymmetric attachment of the sulfur anchor, what should lower the conformational freedom of the system. In fact, the annulation of the oxazole ring lowers the optical band gaps of the parent compounds to 3.

A one-pot multistep cyclization yielding thiadiazoloimidazole derivatives.

A versatile synthetic procedure is described to prepare the benzimidazole-fused 1,2,4-thiadiazoles 2a-c via a methanesulfonyl chloride initiated multistep cyclization involving the intramolecular reaction of an in-situ generated carbodiimide with a thiourea unit. The structure of the intricate heterocycle 2a was confirmed by single-crystal X-ray analysis and its mechanism of formation supported by DFT computations.

Four (2,2'-bipyridyl)(ferrocenyl)boronium derivatives.

Crystal structures are reported for four (2,2'-bipyridyl)(ferrocenyl)boronium derivatives, namely (2,2'-bipyridyl)(ethenyl)(ferrocenyl)boronium hexafluoridophosphate, [Fe(C5H5)(C17H15BN2)]PF6, (Ib), (2,2'-bipyridyl)(tert-butylamino)(ferrocenyl)boronium bromide, [Fe(C5H5)(C19H22BN3)]Br, (IIa), (2,2'-bipyridyl)(ferrocenyl)(4-methoxyphenylamino)boronium hexafluoridophosphate acetonitrile hemisolvate, [Fe(C5H5)(C22H20BN3O)]PF6·0.5CH3CN, (IIIb), and 1,1'-bis[(2,2'-bipyridyl)(cyanomethyl)boronium]ferrocene bis(hexafluoridophosphate), [Fe(C17H14BN3)2](PF6)2, (IVb). The asymmetric unit of (IIIb) contains two independent cations with very similar conformations.

A six-component metallosupramolecular pentagon via self-sorting.

The six-component pentagon P1 with its five dynamic vertices was conceived on the basis of three different orthogonal metal complex units in a 1-fold completive self-sorting of four linear ligands and two metal ions without using directional bonding.

A low-temperature modification of hexa-tert-butyldisilane and a new polymorph of 1,1,2,2-tetra-tert-butyl-1,2-diphenyldisilane.

Crystals of hexa-tert-butyldisilane, C24H54Si2, undergo a reversible phase transition at 179 (2) K. The space group changes from Ibca (high temperature) to Pbca (low temperature), but the lattice constants a, b and c do not change significantly during the phase transition. The crystallographic twofold axis of the molecule in the high-temperature phase is replaced by a noncrystallographic twofold axis in the low-temperature phase.

Three different fluoro- or chloro-substituted 1'-deoxy-1'-phenyl-β-D-ribofuranoses.

Crystal structures are reported for three fluoro- or chloro-substituted 1'-deoxy-1'-phenyl-β-D-ribofuranoses, namely 1'-deoxy-1'-(2,4,5-trifluorophenyl)-β-D-ribofuranose, C11H11F3O4, (I), 1'-deoxy-1'-(2,4,6-trifluorophenyl)-β-D-ribofuranose, C11H11F3O4, (II), and 1'-(4-chlorophenyl)-1'-deoxy-β-D-ribofuranose, C11H13ClO4, (III). The five-membered furanose ring of the three compounds has a conformation between a C2'-endo,C3'-exo twist and a C2'-endo envelope. The ribofuranose groups of (I) and (III) are connected by intermolecular O-H···O hydrogen bonds to six symmetry-related molecules to form double layers, while the ribofuranose group of (II) is connected by O-H···O hydrogen bonds to four symmetry-related molecules to form single layers.

1-(Bromo-mercurio)ferrocene.

The asymmetric unit of the title compound, [Fe(C5H5)(C5H4BrHg)], contains two independent mol-ecules, A and B, in which the Hg-C bond lengths are 2.045 (6) and 2.046 (6) Å, the Hg-Br bond lengths are 2.

A five-component nanorotor with speed regulation.

A five-component supramolecular nanorotor with reversibly acting brakes has been prepared from a four-component nanorotor by adding the photo- and heat-responsive 2,2'-diazastilbene as a signal transducer. The rotational speed was reversibly switched between 86 and 38 kHz.

Design, synthesis, and biological testing of novel naphthoquinones as substrate-based inhibitors of the quinol/fumarate reductase from Wolinella succinogenes.

Novel naphthoquinones were designed, synthesized, and tested as substrate-based inhibitors against the membrane-embedded protein quinol/fumarate reductase (QFR) from Wolinella succinogenes, a target closely related to QFRs from the human pathogens Helicobacter pylori and Campylobacter jejuni. For a better understanding of the hitherto structurally unexplored substrate binding pocket, a structure-activity relationship (SAR) study was carried out. Analogues of lawsone (2-hydroxy-1,4-naphthoquinone 3a) were synthesized that vary in length and size of the alkyl side chains (3b-k).

Iridium-based lab-on-a-molecule for Hg2+ and ClO- with two distinct light-up emissions.

The nonemissive iridium complex 2 is a lab-on-a-molecule for the highly selective detection of Hg(2+) and ClO(-) among 33 analytes using its oxime residues as reactive units. At pH 5, chemodosimeter 2 responds to Hg(2+) by dehydration, whereas at pH 8, it is oxidized by ClO(-), resulting in 450- and 235-fold emission increases, respectively, at two distinct wavelengths.

Four related diethyl [(arylamino)(4-ethynylphenyl)methyl]phosphonates.

Crystal structures are reported for four related diethyl [(arylamino)(4-ethynylphenyl)lmethyl]phosphonate derivatives, namely diethyl [(4-bromoanilino)(4-ethynylphenyl)methyl]phosphonate, C19H21BrNO3P, (I), diethyl ((4-chloro-2-methylanilino){4-[2-(trimethylsilyl)ethynyl]phenyl}methyl)phosphonate, C23H31ClNO3PSi, (II), diethyl ((4-fluoroanilino){4-[2-(trimethylsilyl)ethynyl]phenyl}methyl)phosphonate, C22H29FNO3PSi, (III), and diethyl [(4-ethynylphenyl)(naphthalen-2-ylamino)methyl]phosphonate, C23H24NO3P, (IV). The conformation of the anilinobenzyl group is very similar in all four compounds. The P-C bond has an approximately staggered conformation, with the aniline and ethynylphenyl groups in gauche positions with respect to the P=O double bond.

5-[(1R,2R,4R)-2-Meth-oxy-1,7,7-tri-methylbi-cyclo-[2.2.1]hept-2-yl]-1H-tetra-zole.

The title compound, C12H20N4O, undergoes a phase transition on cooling. The room-temperature structure is tetra-gonal (P43212, Z' = 1), with the meth-oxy-bornyl group being extremely disordered. Below 213 K the structure is ortho-rhom-bic (P212121, Z' = 2), with ordered mol-ecules.

A phenanthroline-terpyridine hybrid as a chameleon-type ligand in a reversible metallosupramolecular rearrangement.

Phenanthroline-terpyridine hybrid 1 was designed as a chameleon-type ligand to satisfy both HETPHEN and HETTAP coordination modes. In the presence of Cu(+), 1 exclusively self-assembled to triangle T1, whereas Zn(2+) addition produced a 2:1 mixture of triangle T2 and square S2. Interconversion between T1 and (T2 + S2) states was triggered by the addition of Zn(2+) and reversed by selectively removing Zn(2+) with ligand 7.

Merging strong and weak coordination motifs in the integrative self-sorting of a 5-component trapezoid and scalene triangle.

In a dynamic six-component library, the formation of the rather weak HETPYP-I complexation can be enforced by exploiting the orthogonality and high stability of its counterpart in the sorting process, a HETTAP complex. The concept was used in a follow-up integrative self-sorting, enabling the formation of two five-component supramolecular structures: a trapezoid and a scalene triangle.

Biphenyl- and phenylnaphthalenyl-substituted 1H-imidazole-4,5-dicarbonitrile catalysts for the coupling reaction of nucleoside methyl phosphonamidites.

Crystal structures are reported for three substituted 1H-imidazole-4,5-dicarbonitrile compounds used as catalysts for the coupling reaction of nucleoside methyl phosphonamidites, namely 2-(3',5'-dimethylbiphenyl-2-yl)-1H-imidazole-4,5-dicarbonitrile, C19H14N4, (I), 2-(2',4',6'-trimethylbiphenyl-2-yl)-1H-imidazole-4,5-dicarbonitrile, C20H16N4, (II), and 2-[8-(3,5-dimethylphenyl)naphthalen-1-yl]-1H-imidazole-4,5-dicarbonitrile, C23H16N4, (III). The asymmetric unit of (I) contains two independent molecules with similar conformations. There is steric repulsion between the imidazole group and the terminal phenyl group in all three compounds, resulting in the nonplanarity of the molecules.

Studies of the solvatochromic emission properties of N-aroylurea derivatives II: influence of hydrogen-bonding interactions.

The solvatochromic emission properties of five naphthoylurea derivatives with different substitution patterns at the naphthoylurea functionality were investigated, with a particular focus on the influence of inter- and intramolecular H-bonding interactions. The bathochromic shifts of the emission maxima correlate well with the acceptor number or Catalán's acidity of the solvent (Δλ = 47-86 nm), indicating an excited species with a pronounced negative charge that is stabilized by H-bond donating (HBD) solvents. In media with restricted free volume the formation of the charged species is not favored, because the required conformational change to establish an intramolecular charge transfer (ICT) between the fluorophore and the acylurea substituent is hindered, and the emission mainly originates from the locally excited state.

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) ≈10(6) M(-1)) even in the absence of additional functional side chains.

2-({4-[4-(1H-Benzimidazol-2-yl)phen-yl]-1H-1,2,3-triazol-1-yl}meth-oxy)ethanol.

In the title molecule, C(18)H(17)N(5)O(2), the dihedral angle between the benzene plane and the benzimidazole plane is 19.8 (1)° and the angle between the benzene plane and the triazole plane is 16.7 (1)°.

N-(2,6-Diisopropyl-phen-yl)formamide toluene 0.33-solvate.

The crystal packing of the title compound, C(13)H(19)NO·0.33C(7)H(8), shows a channel at [001], which contains grossly disordered toluene solvent mol-ecules. The angle between the benzene ring and the mean plane of the formamide group is 71.

Rapid and highly sensitive dual-channel detection of cyanide by bis-heteroleptic ruthenium(II) complexes.

Two new ruthenium complexes [Ru(bipy)(2)(PDA)](2+) (1) and [Ru(phen)(2)(PDA)](2+) (2) (PDA = 1,10-phenanthroline-4,7-dicarboxaldehyde) have been synthesized to detect cyanide based on the well-known formation of cyanohydrins. Both 1[PF(6)](2) and 2[PF(6)](2) were fully characterized by various spectroscopic techniques and their solid state structures determined by single-crystal X-ray diffraction. Their anion binding properties in pure and aqueous acetonitrile were thoroughly examined using two different channels, i.

Erythromycin A dimethyl sulfoxide disolvate 1.43-hydrate.

The title compound, C(37)H(67)NO(13)·2C(2)H(6)OS·1.43H(2)O, is a macrolide anti-biotic with better solubility and better dermal penetration abilities than erythromycin A itself. The asymmetric unit of this form contains one erythromycin A mol-ecule, two dimethyl sulfoxide (DMSO) solvent mol-ecules, a fully occupied water mol-ecule and a partially occupied water mol-ecule with an occupancy factor of 0.