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We have unraveled the effects of an amino substituent in the ortho position on the excited-state dynamics of 4-nitropyridine N-oxide by studying the picosecond fluorescence kinetics and femtosecond transient absorption of a newly synthesized compound, 2-butylamino-6-methyl-4-nitropyridine N-oxide, and by quantum chemical calculations. Similar to the parent compound, the S(1) state of the target molecule has significant charge-transfer character and shows a large (approximately 8000 cm(-1)) static Stokes shift in acetonitrile. Analysis of the experimental and the theoretical results leads, however, to a new scenario in which this intramolecular charge transfer triggers in polar, aprotic solvents an ultrafast (around 100 fs) intramolecular proton transfer between the amino and the N-O group. The electronically excited N-OH tautomer is subsequently subject to solvent relaxation and decays with a lifetime of approximately 150 ps to the ground state.

It has been established by combined absorption and fluorescence measurements that the cationic dye Oxazine 1 (OX) and the polyvalent anionic host calix[8]arenesulfonate (SCA8) form two complexes in simultaneous reactions: OX + SCA8 <--> OX.SCA8 (1), and OX.SCA8 + OX <--> OX(2).SCA8 (2). The equilibrium constants for the two reactions, as functions of the ionic strength (I), and the absorption and fluorescence spectra of the two complex species have been determined by a least-squares fitting method from the experimental data. The variations of the binding constants with the ionic strength could be described on the basis of Debye-Huckel theory. The equilibrium constants are large; their values extrapolated to I = 0 are K(1) = 5.5 x 10(6) M(-1) and K(2) = 4.4 x 10(5) M(-1). The fluorescence of OX undergoes a strong static quenching upon complexation. These results indicate that the complexes are held together by strong electrostatic forces. The addition of non-fluorescent tetramethylammonium chloride to OX-SCA8 mixtures results in a dramatic fluorescent enhancement, which demonstrates the potential applicability of this supramolecular system in fluorescence assays.

The (R)- and (S)-enantiomers of a binaphthyl-appended calix[4]crown-6 ether with two 2,4-dinitrophenylazo chromophore units ((R)-1 and (S)-1) as chiral hosts were tested in their reactions with the enantiomers of alpha-methylbenzylamine ((R)-MBA, (S)-MBA)) and phenylglycinol ((R)-PGL, (S)-PGL) as chiral guests. The visible absorption spectra indicate a two-step process: the first is a nonenantioselective proton transfer from the host to the guest, which is followed by the enantioselective real complexation. In the visible range of the CD spectra a positive/negative band belongs to the absorption of pure (R)-1/(S)-1, and a negative/positive exciton couplet to the absorption of (R)-1-(S)-MBA/(S)-1-(R)-MBA complexes. The latter phenomenon suggests that the complexation of amines is accompanied by a chiral arrangement of the two chromophore units in the hosts. The UV fluorescence of (R)-1/(S)-1 arising from the binaphthyl moiety is quenched by K+ ions, but not by the amine guests, showing that the interaction between the binaphthyl group and the complexed amines is weak., (Copyright 2004 Wiley-Liss, Inc.)

The effects of interference on the photoinduced-absorption signals of thin absorbing films have been studied by recording the picosecond photoinduced-absorption decay curves of an amorphous and a polycrystalline silicon film and applying various probe-beam wavelengths and angles of incidence. The normalized decay curves measured at close to normal incidence have been found to depend strongly on the probe-beam wavelength. By contrast the decay curves obtained at the Brewster angle of incidence have shown a satisfactory coincidence. Theoretical calculations for the photoinduced changes of the transmittance of the film have been performed. These calculations prove that at normal incidence the contributions of the photoinduced changes of the absorption coefficient Δα and of the refractive index Δn to the change in the transmittance Δ T are comparable, whereas when the Brewster angle arrangement is employed, Δ T is proportional to Δα and the effect of the change in the refractive index is negligible.

Infective animal sources and persons in contact with animals were investigated for Yersinia enteroclotica. The 68 isolates from 3115 animals belonged to four serogroups. The most frequent was serogroup O3 (62 strains) found mainly in pigs (41 strains). The same serogroup was isolated from dogs (9 strains), cats (6 strains) and from other animals (6 strains). A total of 556 animals living in the Budapest Zoo were examined. Y. enterocolitica was isolated from the faecal specimens of one chimpanzee and one gibbon. Using the Widal-type agglutination, out of sera of 877 persons in contact with animals, 4.56% were positive with antigens O3 and O9, compared to 0.33% in healthy controls. The study indicates that beside the occasional role of other animal species, pigs should be regarded as the main source of human enteric yersinosis.