STM/TERS observation of (M)-type diphenyl[7]thiaheterohelicene on Ag(111).

The chiral recognition of a self-assembled structure of enantiopure (M)-type 2,13-diphenyl[7]thiaheterohelicene ((M)-Ph-[7]TH) was investigated on a Ag(111) substrate by scanning tunnelling microscopy (STM) and tip-enhanced Raman spectroscopy (TERS). In contrast to previous research of thiaheterohelicene and its derivatives showing zigzag row formation on the Ag(111) substrate, the hexagonal ordered structure was observed by STM. The obtained TERS spectra of (M)-Ph-[7]TH were consistent with the Raman spectra calculated on the basis of density functional theory (DFT), which suggests that (M)-Ph-[7]TH was adsorbed on the substrate without decomposition. The sample bias voltage dependence of STM images combined with the calculated molecular orbitals of (M)-Ph-[7]TH indicates that a phenyl ring was observed as a protrusion at +3.0 V, whereas the helicene backbone was observed at +0.5 V. From these results, a possible model of the hexagonal structure was proposed. Owing to the phenyl ring, the van der Waals interaction between (M)-Ph-[7]TH and the substrate becomes strong. This leads to the formation of the hexagonal structure with the same symmetry as the substrate.

Light Emission from M-Type Enantiomer of 2,13-bis(hydroxymethyl)[7]-thiaheterohelicene Molecules Adsorbed on Au(111) and C60/Au(111) Surfaces Investigated by STM-LE.

Light emission from the M-type enantiomer of a helicene derivative (2,13-bis(hydroxymethyl)[7]-thiaheterohelicene) adsorbed on the clean Au(111) and the C60-covered Au(111) surfaces were investigated by tunneling-current-induced light-emission technique. Plasmon-originated light emission was observed on the helicence/Au(111) surface and it was strongly suppressed on the area where the helicene molecules were adsorbed at the edges of the Au(111) terraces. To avoid luminescence quenching of excited helicene molecules and to suppress strong plasmon light emission from the Au(111) surface, C60 layers were used as decoupling buffer layers between helicene molecules and the Au(111) surface. Helicene molecules were adsorbed preferentially on the Au(111) surface rather than on the C60 buffer layers due to the small interaction of the molecules and C60 islands. This fact motivated us to deposit a multilayer of helicene molecules onto the C60 layers grown on the Au(111) surface, leading to the fact that the helicene/C60 multilayer showed strong luminescence with the molecules character. We consider that such strong light emission from the multilayer of helicene molecules has a plasmon origin strongly modulated by the molecular electronic states of (M)-[7]TH-diol molecules.

A chiral wedge molecule inhibits telomerase activity.

In addition to the Watson-Crick double helix, secondary DNA structures are thought to play important roles in a variety of biological processes. One important example is the G-quadruplex structure that is formed at the chromosome ends, which inhibits telomerase activity by blocking its access to telomeres. G-quadruplex structures represent a new class of molecular targets for DNA-interactive compounds that may be useful to target telomeres. Here, we reported the first example of enantioselective recognition of quadruplex DNA by a chiral cyclic helicene. We propose a new ligand-binding cleft between two telomeric human G-quadruplexes linked by a TTA linker. We found that the cyclic helicene M1 exhibited potent inhibitory activity against telomerase.

Highly silver ion selective fluorescence ionophore: fluorescent properties of polythiazaalkane derivatives bearing 8-(7-hydroxy-4-methyl)coumarinyl moiety in aqueous solution and in liquid-liquid extraction systems.

Two novel fluoroionophores, N-(7-hydroxy-4-methylcoumarin-8-ylmethyl)-3,9-dithia-6-azaundecane (1) and N-(7-hydroxy-4-methylcoumarin-8-ylmethyl)-3,9-dithia-6-azaundecane (2), were synthesized as fluorescence extractants for selective silver determination. The absorption and fluorescence spectra were measured in aqueous 1,4-dioxane solution (28 v/v%) in the absence and presence of silver ion, and their acid dissociation constants were determined from the pH-dependent spectral changes. In the liquid-liquid extraction of some metal ions from neutral aqueous solution into dichloromethane phase, compounds 1 and 2 exhibited excellent silver ion selectivity, and dramatic fluorescence spectral changes were observed in the dichloromethane solutions containing these compounds. The determination limit of 2 for silver ion was 2.0 x 10(-8) mol dm(-3) in the liquid-liquid extraction.

Synthesis and properties of a series of well-defined and polydisperse benzo[1,2-b:4,3-b']dithiophene oligomers.

Monodisperse and polydisperse oligomers of benzo[1,2-b:4,3-b']dithiophene (BDT) (1-14), including three types of oligomers with different spacers combining BDT units (direct linkage, vinylene spacers, and ethynylene spacers), were synthesized, and their thermal, optical, and electrochemical properties were investigated. The oligomers were synthesized using Suzuki, Stille, Wittig, and Sonogashira coupling reactions. All of the monodisperse oligomers showed high melting points and 5% weight loss temperatures (T(d) > 400 degrees C). The fluorescence maxima of all oligomers were red-shifted, and the emission colors varied from blue to yellow as the chain lengths-and thus the conjugation lengths-increased. The vinylene-bridged oligomers emitted at longer wavelengths than the direct-linked and ethynylene-bridged oligomers. UV-vis absorption spectra in toluene solution indicated an effective conjugation length of about six BDT units for polydisperse oligomer 5. Cyclic voltammetry measurement indicated that tetramer 3 had high electrochemical stability. Although tetramer 3 and vinylene-bridged tetramer 8 exhibited reversible oxidation waves, ethynylene-bridged tetramer 13 showed an irreversible oxidation process. Each type of monodisperse oligomer exhibited higher HOMO levels with increasing chain length.

The recognition of higher-order G-quadruplex by chiral cyclic-helicene molecules.

The G-quadruplex structures represent a new class of molecular targets for DNA-interactive compounds that might be useful for targeting telomeres. Here we describe a study on the structure-based design of cyclic helicenes displaying chiral and steric selection in binding to higher-order G-quadruplexes. We propose a new ligand-binding site for G-quadruplex-binding compounds. These results provide proof of concept for small molecule inhibitors of telomerase associated with higher-order G-quadruplex structures.

(P)-helicene displays chiral selection in binding to Z-DNA.

Enantiomeric helicenes of (P)-A and (M)-A were synthesized. The binding of the helicenes to B- and Z-DNA was studied quantitatively by CD, equilibrium dialysis, and fluorescence spectroscopy. Enantiomeric (P)-A not only bound selectively to Z-DNA but also effectively converted the B-DNA conformation to Z-DNA. The enantioselectivity of the helicenes offers a new route for the rational design of inhibitors of biological functions that may depend on Z-DNA.

The recognition of Z-DNA by chiral helicene.

Enantiomeric helicenes of (P)-A and (M)-A were synthesized. The binding of the helicenes to B- and Z-DNA was studied quantitatively by CD, equilibrium dialysis, and fluorescence spectroscopy. Enantiomeric (P)-A not only bound selectively to Z-DNA, but also effectively converted the B-DNA conformation to Z-DNA. The enantio-selectivity of the helicenes offers a new route for the rational design of inhibitors of biological functions that may depend on Z-DNA.

Elongation and contraction of molecular springs. Synthesis, structures, and properties of bridged [7]thiaheterohelicenes.

A series of bridged [7]thiaheterohelicenes 3a-c and 4 with a variety of helical pitches have been prepared from racemic and optical pure 2,13-bis(hydroxymethyl)dithieno[3,2-e:3',2'-e']benzo[1,2-b:4,3-b']bis[1]benzothiophene (1) in order to investigate the helical structures in solution. Recrystallizations of (PM)-3a, (PM)-3b, (PM)-3c, and (P)-4 from hexane-dichloromethane gave crystals suitable for X-ray crystallography, while recrystallization of (PM)-4 with benzene gave an inclusion complex with a stoichiometry of (PM-4)(4).(C(6)H(6)). X-ray analyses of (PM)-3a-c, (PM-4)(4).(C(6)H(6)), and (P)-4 indicate that the dihedral angles between terminal thiophene rings of the helical framework significantly vary from 22 degrees for 4 to 59 degrees for 3c. This represents as increase of 37 degrees or 168%. Although the (13)C NMR and UV absorption spectra of bridged helicenes 3a-c and unbridged helicene 5 are essentially the same, the molar rotation of 5 is very large compared with those of 3a-c and 4. A red shift (15 nm) in the circular dichroism (CD) spectrum is observed for 4, suggesting that this compound is more planar than 3a-c in solution. In the series of [7]thiaheterohelicenes studied, the minimum helical pitch is 2.70 A for 4.

Non-Photochemical Route to Chiral Disubstituted [7]Thiaheterohelicenes via Biaryl- and Carbonyl-Coupling Reactions.

Non-photochemical syntheses of optically active dimethyl[7]thiaheterohelicenes (P)-(+)-14 and (M)-(-)-14 are described. The key transformations in the syntheses are the metal-mediated biaryl coupling reactions between two benzodithiophene units having oxazoline moieties and the intramolecular McMurry coupling reaction of the biaryl dialdehydes (S)-13 and (R)-13. The configuration of the atropisomer 10a obtained from the biaryl coupling reaction was shown to be S by X-ray analysis.