Synthesis,stability, and spectroscopic and electronic properties of three benzocyclohepta[alpha]azulenylium ions

Novel pi-systems, three benzocyclohepta[alpha]azulenylium ions, 7a-c, are synthesized, and their stability and properties have been characterized in terms of the position of the benzo-annulation and compared with those of the parent cyclohepta[alpha]azulenylium ion 4. Benzocyclohepta[6,7-alpha]azulenylium ion (7a) (p K R+ = 7.3, E red = -0.567 V vs Ag/Ag+) and benzocyclohepta[6,5-alpha]azulenylium ion (7b) (p K R+ = 5.1, E red = -0.482 V vs Ag/Ag+), which are annulated with benzene on the position having a high bond order of 4, are not appreciably destabilized compared with cyclohepta[alpha]azulenylium ion (4) (p K R+ = 7.3, E red = -0.458 V vs Ag/Ag+). On the other hand, benzocyclohepta[7,6-alpha]azulenylium ion (7c) (p K R+ = 1.6, Ered = -0.197 V vs Ag/Ag+) is considerably destabilized, probably due to enhanced contribution of the quinoid structure of the benzene ring, which is annulated on the position having a low bond order of the cyclohepta[alpha]azulenylium ion moiety. Furthermore, the cations 7a and 7b are more stable than 12,13-dihydrobenzocyclohepta[7,6-alpha]azulenylium ion (25) (p K R+ = 4.8, E red = -0.513 V vs Ag/Ag+), which is a dihydrogenated compound of 7a, while 7c is less stable than 25. These features are reflected in the considerable red shift of the longest absorption maximum of the electronic spectrum of 7c, as compared with those of 4, 7a, and 7b, and in the chemical shifts of the protons and their coupling constants of the (1)H NMR spectra. Furthermore, the (1)H NMR spectra and electronic spectra of 5H-benzocyclohepta[6,7-alpha]azulen-5-one (8a) and 7H-benzocyclohepta[6,5-alpha]azulen-7-one (8b) in acidic media have also been studied to clarify the spectral characteristics similar to those of 7a and 7b.     

Control of photoinduced energy- and electron-transfer steps in zinc porphyrin-oligothiophene-fullerene linked triads with solvent polarity

The dramatic changes of the lifetimes of the charge-separated (CS) states were confirmed in zinc porphyrin (ZnP)-oligothiophene (nT)-fullerene (C(60)) linked triads (ZnP-nT-C(60)) with the solvent polarity. After the selective excitation of the ZnP moiety of ZnP-nT-C(60), an energy transfer took place from the (1)ZnP moiety to the C(60) moiety, generating ZnP-nT-(1)C(60). In polar solvents, the CS process also took place directly via the (1)ZnP moiety, generating ZnP(*+)-nT-C(60)(*-), as well as the energy transfer to the C(60) moiety. After this energy transfer, an indirect CS process took place from the (1)C(60) moiety. In the less polar solvent anisole, the radical cation (hole) of ZnP(*+)-nT-C(60)(*-) shifted to the nT moiety; thus, the nT moiety behaves as a cation trapper, and the rates of the hole shift were evaluated to be in the order of 10(8) s(-1); then, the final CS states ZnP-nT(*+)-C(60)(*-) were lasting for 6-7 mus. In the medium polar solvent o-dichlorobenzene (o-DCB), ZnP-nT(*+)-C(60)(*-) and ZnP(*+)-nT-C(60)(*-) were present as an equilibrium, because both states have almost the same thermodynamic stability. This equilibrium resulted in quite long lifetimes of the CS states (450-910 mus) in o-DCB. In the more polar benzonitrile, the generation of ZnP-nT(*+)-C(60)(*-) was confirmed with apparent short lifetimes (0.6-0.8 mus), which can be explained by the fast hole shift to more stable ZnP(*+)-nT-C(60)(*-) followed by the faster charge recombination. It was revealed that the relation between the energy levels of two CS states, which strongly depend on the solvent polarity, causes dramatic changes of the lifetimes of the CS states in ZnP-nT-C(60); that is, the most appropriate solvents for the long-lived CS state are intermediately polar solvents such as o-DCB. Compared with our previous data for H(2)P-nT-C(60), in which H(2)P is free-base porphyrin, the lifetimes of the CS states of ZnP-nT-C(60) are approximately 30 times longer than those in o-DCB.     

Simultaneous determination of bromide and iodide ions by capillary isotachophoresis using quaternary ammonium salts

Bromide and iodide ions were determined simultaneously by capillary isotachophoresis using an aqueous electrolyte system; the separation principle was based on the ion-pairing equilibria between tetradecyldimethylbenzylammonium ion and these anions in the leading electrolyte. The interaction between iodide ion and tetradecyldimethylbenzylammonium ion was stronger than that for bromide ion. Thus complete separation of bromide and iodide ions could be obtained by using a leading electrolyte containing 1.5 mM tetradecyldimethylbenzylammonium ion. The pH of the leading electrolyte was adjusted to 5.0. The relative standard deviations of the zone length for bromide and iodide ions were 1.1 and 1.2%, respectively, when mixture of 3.0 mM of these ions was analysed. A 150-μl volume could be injected for the simultaneous determination of low concentrations of bromide and iodide ions.     

Alternate stranded triplex formation of chimeric DNA composed of tandem alpha- and beta-anomeric strands

A chimeric oligoDNA composed of a natural beta-anomeric oligonucleotide portion and an unnatural alpha-anomeric oligonucleotide portion forms an alternate stranded triplex possessing enhanced thermal stability compared to the triplexes composed of the parental oligomers.     

Finding of remarkable synergistic effect on the aroxyl-radical-scavenging rates under the coexistence of α-tocopherol and catechins

Measurements of aroxyl radical (ArO^•)-scavenging rate constants () of antioxidants (AOHs) (α-tocopherol (α-TocH) and three catechins (CatHs) (ie, epicatechin (EC), epigallocatechin (EGC), and epigallocatechin gallate (EGCG)) were performed in ethanol solution, using stopped-flow spectrophotometry. values were measured not only for each AOH, but also for the mixtures of two AOHs (α-TocH and CatH). A notable synergistic effect that the value of α-TocH increases 1.29, 1.84, and 1.65 times under the coexistence of constant concentrations of EC, EGC, and EGCG, respectively, was observed for the solutions including α-TocH and CatH. Similarly, values of CatHs (EC, EGC, and EGCG) increased 1.72, 2.25, and 2.34 times under the coexistence of constant concentrations of α-TocH, respectively. UV-Vis absorption of α-tocopheroxyl radical (α-Toc^•) (λ_max = 428 nm), which had been produced by reaction of α-TocH with ArO^•, decreased remarkably under the coexistence of α-TocH and CatHs due to the fast α-TocH-regeneration reaction by CatHs. The result suggests that the prooxidant reaction due to α-Toc^• is suppressed by the coexistence of CatHs. By analyzing the formation and decay curves of α-Toc^•, it has been ascertained that one molecule of EGCG having three OH groups at B-ring may rapidly regenerate three molecules of α-Toc^• to α-TocH.     

Synthesis of amidocrownophanes with 27‐ and 28‐membered rings and their molecular recognition toward urea and its derivatives

Novel crownophanes with 27‐ and 28‐membered rings having two hydroxyl groups, two amide groups, and aromatic moieties such as naphthalene, pyridine, and phenyl rings were successfully synthesized by a one‐step reaction from the corresponding macrocyclic polyethers via “tandem Claisen rearrengement” in moderate yields. They can solubilize urea and its derivatives into chloroform solution, while the corresponding macrocyclic polyethers do not solubilize them. According to NMR studies, crownophanes 1 and 2 interact with urea and its derivatives forming 1:1 complexes.     

Beta-1,3-glucan polysaccharides as novel one-dimensional hosts for DNA/RNA, conjugated polymers and nanoparticles

Beta-1,3-glucan polysaccharides have triple-stranded helical structures whose sense and pitch are comparable to those of polynucleotides. We recently revealed that the beta-1,3-glucans could interact with certain polynucleotides to form triple-stranded and helical macromolecular complexes consisting of two polysaccharide-strands and one polynucleotide-strand. This unique property of the beta-1,3-glucans has made it possible to utilize these polysaccharides as potential carriers for various functional polynucleotides. In particular, cell-uptake efficiency of the resultant polysaccharide/polynucleotide complexes was remarkably enhanced when functional groups recognized in a biological system were introduced as pendent groups. The beta-1,3-glucans can also interact with various one-dimensional architectures, such as single-walled carbon nanotubes, to produce unique nanocomposites, in which the single-walled carbon nanotubes are entrapped within the helical superstructure of beta-1,3-glucans. Various conductive polymers and gold nanoparticles are also entrapped within the helical superstructure in a similar manner. In addition, diacetylene monomers entrapped within the helical superstructure can be photo-polymerized to afford the corresponding poly(diacetylene)-nanofibers with a uniform diameter. These findings indicate that the beta-1,3-glucans are very attractive and useful materials not only in biotechnology but also in nanotechnology. These unique properties of the beta-1,3-glucans undoubtedly originate from their inherent, very strong helix-forming character which has never been observed for other polysaccharides.     

Synthesis and functionalities of poly(N-vinylalkylamide). V. Control of a lower critical solution temperature of poly(N-vinylalkylamide)

N-vinyl-n-butyramide (NVBA), N-vinylisovaleramide (NVIVA), and N-vinyl-n-valeramide (NVVA), which are N-vinylalkylamides with different alkyl groups were synthesized and their solution behavior in a polymeric form was examined. Copolymers of N-vinylisobutyramide (NVIBA) with N-vinylacetamide (NVA), NVIBA with NVVA, and NVVA with NVA were prepared by the solution polymerization to control the LCSTs. The resultant polyNVBA showed a lower critical solution temperature (LCST) sharply at 32°C, but polyN-vinylisovaleramide (polyNVIVA) and polyN-vinyl-n-valeramide(polyNVVA) that have n-butyl and isobutyl groups, respectively, on their side chains were insoluble even in cold water. The water solubility of the resulting polymers was found to vary, depending on the molecular shapes as well as the side chain length of the alkyl groups in question. The copolymers consisting of NVVA, NVIBA, and NVA in water showed LCSTs sharply between 10 and 90°C, depending on changes in their comonomer content. It was found that the changes in LCST that are caused by the incorporation of comonomers are due to changes in the overall hydrophilicity of the polymer. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3087–3094, 1997