Unusual effects in single molecule tautomerization: hemiporphycene.

Parent hemiporphycene, a recently obtained constitutional isomer of porphyrin, exists in room temperature solutions and polymer matrices in the form of two trans tautomers interconverting via double hydrogen transfer. Using confocal fluorescence microscopy, it was possible to monitor tautomerization in single hemiporphycene molecules embedded in a PMMA film by monitoring the spectral and temporal evolution of their fluorescence spectra. The emission spectra of the two tautomeric forms are similar to those obtained from ensemble studies.

Supersonic jet spectroscopy of parent hemiporphycene: Structural assignment and vibrational analysis for S and S electronic states.

Hemiporphycene (HPc), a constitutional isomer of porphyrin, is studied under supersonic expansion conditions by means of laser-induced fluorescence, visible-visible hole-burning experiments, single vibronic level fluorescence techniques, and quantum chemical calculations. Only one form of jet-cooled HPc is observed, in contrast to solution studies that evidence a mixture of two tautomeric forms separated in energy by ∼1 kcal/mol. Reliable structural assignment is provided by simulating absorption and emission patterns at the density functional theory and time-dependent density functional theory levels of theory.

Spectroscopic and microscopic investigations of tautomerization in porphycenes: condensed phases, supersonic jets, and single molecule studies.

We describe various experimental approaches that have been used to obtain a detailed understanding of double hydrogen transfer in porphycene, a model system for intramolecular hydrogen bonding and tautomerism. The emerging picture is that of a multidimensional tautomerization coordinate, with several vibrational modes acting as reaction-promoters or inhibitors through anharmonic intermode coupling. Tunnelling processes, coherent in the case of isolated molecules and incoherent in condensed phases, are found to play a major role even at elevated temperatures.

Supersonic Jet Spectroscopy and Density Functional Theory Study of Isomeric Diazines: 1,4- and 1,8-Diazatriphenylene. Why Do They Differ So Deeply?

We report on laser-induced fluorescence excitation and dispersed fluorescence spectra of two isomeric compounds: 1,4- and 1,8-diazatriphenylene (1,4- and 1,8-DAT) isolated in supersonic molecular jets, and their 1:1 complexes with protic solvents. We found that the ground and excited state vibronic patterns of bare 1,4-DAT differ significantly from those of 1,8-DAT, and those of the complexes of both isomers. A marked activity of several out-of-plane vibrations in 1,4-DAT and the symptoms of the distortion of the S excited molecule were diagnosed from the vibronic spectra, whereas planar structures were predicted for 1,8-DAT in S and S states.

Spectroscopic study of jet-cooled deuterated porphycenes: unusual isotopic effects on proton tunneling.

Porphycene (Pc) is a well-known model for studying double hydrogen transfer, which shows vibrational-mode-specific tunneling splitting when isolated in supersonic jets or helium nanodroplets. The effect of deuteration on tunneling splitting is reported for jet-cooled heterogeneous, deuterated Pc samples (Pc-d(mix)) with the prevailing contribution of Pc-d12 isotopologue. The sample introduced into the gas phase using laser desorption is studied by means of laser-induced fluorescence (LIF) and single vibronic level fluorescence (SVLF) measurements, in combination with quantum chemical calculations.

From ultrafast events to equilibrium--uncovering the unusual dynamics of ESIPT reaction: the case of dually fluorescent diethyl-2,5-(dibenzoxazolyl)-hydroquinone.

The excited state intramolecular proton transfer (ESIPT) reaction of the dually fluorescent 2,5-diethyl-(dibenzoxazolyl)-hydroquinone (DE-BBHQ) was studied with several time resolved techniques. The complementary character of up-conversion and time correlated single photon counting methods was demonstrated. According to the up-conversion experiments, the primary excited dienol form transforms into the monoketo tautomer in a very efficient ultrafast (∼100 fs) proton transfer reaction.

Spectroscopy and photophysics of bifunctional proton donor-acceptor indole derivatives.

We report spectroscopic and photophysical studies of a series of selected indole derivatives in solutions and under supersonic jet isolation conditions. All the compounds can assume two rotameric forms, syn and anti. The bifunctional molecules containing both the hydrogen bond donor (indole NH group) and acceptor centers (oxygen, nitrogen, or sulfur atoms) located in separate moieties covalently linked by a single bond are compared with the compound that does not have any acceptor center, 2-(1H-pyrrol-2'-yl)-1H-indole.

Vibrations of porphycene in the S0 and S1 electronic states: single vibronic level dispersed fluorescence study in a supersonic jet.

Supersonic jet-isolated porphycene has been studied using the techniques of laser-induced fluorescence excitation, single vibronic level fluorescence, and spectral hole burning, combined with quantum mechanical calculations of geometry and vibrational structure of the ground and lowest electronically excited singlet states. Porphycene is a model for coherent double hydrogen tunneling in a symmetrical double well potential, as evidenced by tunneling splittings observed in electronic absorption and emission. The results led to reliable assignment of low frequency modes in S0 and S1 electronic states.

Excited-state intramolecular proton transfer reaction modulated by low-frequency vibrations: an effect of an electron-donating substituent on the dually fluorescent bis-benzoxazole.

Excited-state intramolecular proton transfer (ESIPT) reaction has been studied in a molecule showing dual fluorescence, the 2,5-bis(2-benzoxazolyl)-4-methoxyphenol (BBMP), and its isotopomers, where the methoxy, and alternatively, the OH group has been deuterated. Attention is focused on the influence of electron donating OCH(3) substituent on fast excited state reaction. Comparison between the resonance-enhanced multiphoton ionization spectrum and the laser-induced excitation of the primary and phototautomeric emissions has been done.

Effect of alkyl substituents on excited state intramolecular proton transfer dynamics of jet-cooled bis(benzoxazolyl)phenoles.

Structural factors affecting the dynamics of the excited state intramolecular proton transfer (ESIPT) are studied for alkyl derivatives of 2,5-bis(2-benzoxazolyl)phenol. Two fluorescence bands with equal decay times are observed in solution, while only one--emitted by the phototautomer--in supersonic jet. All evidence indicates the existence of a potential barrier in the S(1) state.

Fluorescence studies of terrylene in a supersonic jet: indication of a dark electronic state below the allowed transition.

Jet-cooled terrylene has been studied in helium buffer gas using a pulsed nozzle by means of laser-induced fluorescence. Fluorescence excitation and two-color depletion experiments (resulting in hole burning spectra) are presented. Analysis of the spectra leads to the conclusion that another excited electronic state is present in the vicinity of the allowed 1B1u state.

Evidence for two forms, double hydrogen tunneling, and proximity of excited states in bridge-substituted porphycenes: supersonic jet studies.

Laser-induced fluorescence and dispersed fluorescence spectra measured in supersonic jets for 9,10,19,20-tetra-n-methylporphycene and 9,10,19,20-tetra-n-propylporphycene reveal, for both compounds, the presence of two different species which are assigned to trans and cis tautomeric forms. Doublet splitting of lines is observed, disappearing upon deuteration of the inner nitrogen atoms. This finding is interpreted as an indication of double hydrogen tunneling.

Imaging of tautomerism in a single molecule.

Fluorescence imaging is used to visualize directly the transfer of two inner hydrogen atoms in single porphycene molecules. This reaction leads to a chemically equivalent but differently oriented structure and hence results in a rotation of the transition dipole moments. By probing single immobilized molecules with an azimuthally polarized laser beam in the focal spot of a confocal microscope we observe ring-like emission patterns, possible only for a chromophore with two nearly orthogonal transition dipole moments.

Inactivation of jack bean urease by allicin.

Allicin--diallyl thiosulfinate--is the main biologically active component of freshly crushed garlic. Allicin was synthesized as described elsewhere and was tested for its inhibitory ability against jack bean urease in 20 mM phosphate buffer, pH 7.0 at 22 degrees C.

Synthesis and in vitro antifungal activity of 1-amino-3,4-dialkylnaphthalene-2-carbonitriles and their analogues.

Twenty-four 3- and/or 4-alkyl-substituted 1-aminonaphthalene-2-carbonitriles and their analogues were prepared and evaluated for growth-inhibiting activity against four phytopathogenic fungi: Fusarium culmorum, Alternaria brassicicola, Botrytis cinerea and Penicillium expansum. The results obtained were compared with the activity of a commercial fungicide. The highest fungistatic activity was revealed by amino nitriles having hydrogen atoms or only one short alkyl group (CH3, C2H5) at the 3- or 4-position of the naphthalene system.

Mutagenicity of bay-region amino-substituted cyclopenta[a]phenanthrenes and 2- and 5-aminochrysene.

The relative mutagenic potentials of 11-amino-16,17-dihydro-15H-cyclopenta[a]phenanthrene, its 17-keto derivative, and 2- and 5-aminochrysene have been compared in Salmonella typhimurium TA98 and TA100 in the presence of a postmitochondrial liver preparation from Aroclor 1254 induced rats. The 11-amino hydrocarbon is a very weak mutagen (0.27 revertants/nmol), whereas the 11-amino-17-ketone is much more active (129 revertants/nmol).

Use of the Role Checklist with the patient with multiple personality disorder.

A paucity of occupational therapy evaluation tools exists for use with patients with multiple personality disorder. The Model of Human Occupation (Kielhofner & Burke, 1980), particularly the volition and habituation subsystems within this model, proved useful for the identification of the many facets of patients with multiple personality disorder on a short-term treatment unit. The Role Checklist (Oakley, Kielhofner, Barris, & Richler, 1986), a tool derived from the Model of Human Occupation, was adapted for use with this population and was found to be beneficial in the identification of common goals held by most of the personalities of each patient with multiple personality disorder.

Tautomerism of isoguanosine and solvent-induced keto-enol equilibrium.

Ultraviolet and infrared absorption spectroscopy, in aqueous and non-aqueous media, have been employed to study the tautomerism of 9-substituted isoguanines, including the nucleoside isoguanosine. With the aid of a series of model compounds, it was shown that 9-substituted isoguanines, and isoguanosine, in aqueous medium are predominantly in the form N (1) H, 2-keto-6-amino. In dioxane solution the tautomeric equilibrium is shifted in the direction of the enol form.