Conformational Control of a Polyether-Linked Porphyrin Dimer Induced by Complexation with a Sodium Cation

Abstract

A porphyrin dimer with a polyether linkage was newly synthesized and its conformational change triggered by complexation with an sodium cation was examined. It was confirmed by ¹H NMR titration experiments that the dimer bearing a pentaoxyehtylene linkage (1b) was effectively formed a 1:1 complex with a sodium perchlorate. A detailed investigation of the CIS values for the protons confirmed that the complex of 1b?Na⁺ adopts a slipped face-to-face conformation.     

Triplet–Triplet Energy Transfer from a UV‐A Absorber Butylmethoxydibenzoylmethane to UV‐B Absorbers

The phosphorescence decay of a UV‐A absorber, 4‐tert‐butyl‐4′‐methoxydibenzolymethane (BMDBM) has been observed following a 355 nm laser excitation in the absence and presence of UV‐B absorbers, 2‐ethylhexyl 4‐methoxycinnamate (octyl methoxycinnamate, OMC) and octocrylene (OCR) in ethanol at 77 K. The lifetime of the lowest excited triplet (T₁) state of BMDBM is significantly reduced in the presence of OMC and OCR. The observed quenching of BMDBM triplet by OMC and OCR suggests that the intermolecular triplet–triplet energy transfer occurs from BMDBM to OMC and OCR. The T₁ state of OCR is nonphosphorescent or very weakly phosphorescent. However, we have shown that the energy level of the T₁ state of OCR is lower than that of the enol form of BMDBM. Our methodology of energy‐donor phosphorescence decay measurements can be applied to the study of the triplet–triplet energy transfer between UV absorbers even if the energy acceptor is nonphosphorescent. In addition, the delayed fluorescence of BMDBM due to triplet–triplet annihilation was observed in the BMDBM–OMC and BMDBM–OCR mixtures in ethanol at 77 K. Delayed fluorescence is one of the deactivation processes of the excited states of BMDBM under our experimental conditions.     

Stoichiometric photoisomerization of mononuclear ruthenium(II) monoaquo complexes controlling redox properties and water oxidation catalysis

Although various reactions involved in photoexcited states of polypyridyl ruthenium(II) complexes have been extensively studied, photoisomerization of the complexes is very rare. We report the first illustration of stoichiometric photoisomerization of trans-[Ru(tpy)(pynp)OH(2)](2+) (1a) [tpy = 2,2':6',2'-terpyridine; pynp = 2-(2-pyridyl)-1,8-naphthyridine] to cis-[Ru(tpy)(pynp)OH(2)](2+) (1a') and the isolation of 1a and 1a' for X-ray crystallographic analysis. Polypyridyl ruthenium(II) aquo complexes are attracting much attention related to proton-coupled electron transfer and water oxidation catalysis. We demonstrate that the photoisomerization significantly controls the redox reactions and water oxidation catalyses involving the ruthenium(II) aquo complexes 1a and 1a'.     

Gadolinium tagging for high-precision measurements of 6 nm distances in protein assemblies by EPR

Double electron-electron resonance (DEER) distance measurements of a protein complex tagged with two Gd(3+) chelates developed for rigid positioning of the metal ion are shown to deliver outstandingly accurate distance measurements in the 6 nm range. The accuracy was assessed by comparison with modeled distance distributions based on the three-dimensional molecular structures of the protein and the tag and further comparison with paramagnetic NMR data. The close agreement between the predicted and experimentally measured distances opens new possibilities for investigating the structure of biomolecular assemblies. As an example, we show that the dimer interface of rat ERp29 in solution is the same as that determined previously for human ERp29 in the single crystal.     

Photostability of the laser dye DCM in various inorganic-organic host matrices

The laser dye, 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM) was incorporated in various inorganic-organic host matrices by the sol-gel technique. The photostability of the DCM-doped materials under CW argon laser irradiation was investigated. The absorption of DCM monomer ar 480 nm decreased with increasing irradiation time and was accompanied by an increase in the absorption at 352 nm by inactive photoproducts. Photostability was estimated by measuring the decay rates of DCM fluorescences in different host matrices. The rates exhibited two components; a rapid decay within the first several tens of seconds followed by a slower luminescence decay. The rapid decay depended upon the DCM content in the matrix while the slow decay component was related to the mobility of the DCM in the different matrices. The silica host matrix containing phenyl and a small amount of epoxy groups exhibited the best photostability of the materials examined.     

ACCESSORY CELL ABILITY OF LANGERHANS CELLS FOR SUPERANTIGEN IS RESISTANT TO ULTRAVIOLET-B LIGHT

Abstract We examined the effects of ultraviolet-B (UVB) irradiation on the accessory cell ability of Langerhans cells (LC) to induce a T-cell response to a superantigen, staphylococcal enterotoxin B (SEB). The ability of LC-enriched epidermal cells (LC-EC) to evoke a T-cell response to SEB was retained at the doses of UVB (up to 40 mJ/ cm²) that profoundly affected the antigen-presenting function of LC-EC for a hapten, trinitrophenyl (TNP), and a protein antigen, conalbumin. Thus, the LC accessory function for superantigens is more resistant to UVB irradiation than that for ordinary antigens. This UVB resistance is presumably due to no requirement of antigen processing for superantigens as chemically fixed or chloroquine-treated LC-EC still retained their ability to induce T-cell responses to SEB. Higher doses of UVB (more than 60 mJ/cm²) reduced the accessory cell ability of LC-EC for SEB up to 50% of control. The addition of monoclonal antibodies against adhesion molecules between LC and T cells to the culture resulted in substantial suppression of the T-cell response to SEB induced by nonirradiated LC-EC, while the U VB-irradiated LC-EC-induced T-cell response was not significantly blocked with these monoclonal antibodies. This suggested that the reduction of LC ability for superantigen by high doses of UVB is at least partly due to impairment of adhesion molecules on LC by UVB irradiation.     

Photohaptenic Properties of Fluoroquinolones

Abstract— Although quinolone antibacterial agents have both phototoxicity and photoallergenicity, the latter's potency has been poorly investigated compared with the former's. Some of the photoallergic chemicals serve as photohap-tens, which lead to T-cell-mediated immune reactions after photobinding to protein by UVA radiation. We examined the photohaptenic potential of fluoroquinolones, including lomefloxacin (LFLX), ciplofloxacin, norfloxacin, ofloxacin, levofloxacin, fleroxacin, enoxacin and spar-floxacin (SPFX). The absorption spectra of the quinolo-nes were altered by UVA irradiation, with an exception of SPFX that seems to be photostable toward UVA. Bovine serum albumin and murine epidermal cells were coupled with these fluoroquinolones other than SPFX by exposure to UVA. Subcutaneous inoculation of fluoro-quinolone-photomodified epidermal cells induced and elicited a delayed-type hypersensitivity reaction in mice. However, epidermal cells incubated with LFLX without UVA exposure also induced and elicited a significant hypersensitivity reaction to a lesser degree than LFLX-pho-tomodified epidermal cells. Furthermore, there was cross-reactivity between LFLX-photomodified epidermal cells and simply LFLX-incubated cells. This suggests that cells can be weakly modified with LFLX even in the dark and that UVA irradiation promotes this modification. Our study demonstrated that fluoroquinolones have photohaptenic properties to which their photoallergenicity is probably ascribed.     

Spin alignment in the charge transfer phosphorescent state of the tetracyanobenzene-biphenyl complex in crystalline state

Intermolecular charge-transfer phosphorescence and fluorescence were observed for a biphenyl single crystal containing 1,2,4,5-tetracyanobenzene as a guest at various temperatures between 29 and 1.47°K. The non-exponential phosphorescence decay due to the spin alignment in the charge-transfer, triplet state was first observed and the phosphorescence lifetimes of the three sublevels were determined to be 0.9, 2.5, and 7.9 see at 1.47°K.     

Cathodic characteristics of amorphous manganese oxides as lithium secondary battery

The amorphous manganese dioxides were prepared by reduction method using various reagents. The particle size and morphology depended on reducing agents, some of which were aggregated round particles of sub micron order, and the others were small fine fibers like of a few nm in width and several tens nm in length. The former showed low Li-insertion capacity of around 200 mAhg⁻¹, while the latter material showed high capacity of 500 mAhg⁻¹ in the OCV measurements until 1 V vs. Li. The as-prepared MnO₂ contains some amount of water in the structure. The H₂O-free MnO₂ obtained by heat-treatment under high oxygen pressure was inferior in electrode property to MnO₂ containing water in the structure. The H₂O content related to the electrode performance. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

115Cd photonuclear production for115Cd−115mIn generator

Production of¹¹⁵Cd by means of photonuclear reaction and preparation of a^115mIn generator, based on the genetic sequence of¹¹⁵Cd^115mIn, were studied. The production rates of¹¹⁵Cd by the¹¹⁶Cd(γ, n)¹¹⁵Cd reaction were determined as a function of the maximum bremsstrahlung energies between 35 and 60 MeV. Then the parent,¹¹⁵Cd, was produced by irradiating about 0.15g of CdO with the bremsstrahlung from a 60 MeV-150 μA electron beam. After the parent in the Cd ₄ ²⁻ form was adsorbed on the Dowex 1x8 resin column, the daughter was eluted with a physiologic saline adjusted to pH 1. The generator was milked over a period of 3 days, during which time about 900 ml of eluent were allowed to flow through the column. Even after the milkings were repeated 15 times with 60 ml of the eluent, no¹¹⁵Cd was found in the^115mIn fractions (the detection limit of inactive cadmium: 0.02 μg).