| 1. |
- Cider, L., et al.
(författare)
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Cross-Desorption of Differently Adsorbed Carbon-Monoxide on Pd Alpha-Al2o3 by Means of Acetylene
- 1991
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Ingår i: Journal of Molecular Catalysis. - 0304-5102. ; 67:3, s. 323-331
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Tidskriftsartikel (refereegranskat)abstract
- Cross-desorption of carbon monoxide on Pd/alpha-Al2O3 by means of acetylene was studied spectrophotometrically. Both linearly bonded and bridge-bonded carbon monoxide were found to cross-desorb rapidly, and the linearly bonded form was most easily cross-desorbed. It could not be shown whether the cross-desorption of bridge-bonded carbon monoxide proceeded via the linearly bonded form or not. The role played by surface carbonate or some adsorbed species related to carbon monoxide giving absorption bands at 1630, 1510 and 1420 cm-1 is not fully understood at present.
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| 2. |
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| 3. |
- Albinsson, Bo, 1963, et al.
(författare)
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ELECTRONIC-TRANSITION MOMENT DIRECTIONS AND IDENTIFICATION OF LOW-ENERGY N-PI-ASTERISK STATES IN WEAKLY PERTURBED PURINE CHROMOPHORES
- 1993
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 115:1, s. 223-231
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of UV linear dichroism on purine and three methyl derivatives partially oriented in poly(vinyl alcohol) matrix gave direct evidence for the assignment of the first singlet npi* state. Intensity distributions and moment directions for the first three pi --> pi* transitions were also determined. The pi --> pi* transitions in purine were found to be polarized at (angles, relative to the pseudo-symmetry long axis, counted positive in the N7 direction): -31-degrees +/- 5-degrees (II at 265 nm), +38-degrees +/- 5-degrees (III at 244 nm), and +36-degrees +/- 10-degrees (IV at 214 nm). The transition energies and moment directions were not markedly perturbed by methyl substitution at the sixth, seventh, or ninth position. Therefore, these methyl substituents could be used as orientational perturbers to resolve a sign ambiguity problem regarding transition moment directions. The orientation were determined by infrared dichroic measurements using both in-plane and out-of-plane polarized vibrational transitions. In addition, the phosphorescence spectra were studied, including phosphorescence anisotropy, phosphorescence lifetimes, and quantum yields, for the purines in an organic glass at 80 K. Based on these measurements, the lowest triplet state is concluded to have effectively pipi* character, and its emission allowedness appears to originate from spin-orbit interactions primarily with singlet sigmapi* states but also with singlet pipi* states via vibronic mixing. The phosphorescence emission spectra of purine and 6-methylpurine are complex, compared to 7-methylpurine and 9-methylpurine, with emission wavelength-dependent lifetimes and excitation spectra. This is ascribed to a prototropic tautomeric equilibrium between the 7H and 9H forms of purine and 6-methylpurine, a ground-state heterogeneity that we believe has caused confusion in earlier studies and, e.g., led to an assignment of the phosphorescence origin of purine.
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| 4. |
- Albinsson, Bo, 1963
(författare)
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Excitation and Excited State Properties of Heterocyclic Chromophores. Indole and Purine Derivatives of Biological Significance
- 1992
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Proteins and nucleic acids absorb light in the near-UV due to the presence of aromatic heterocyclic chromophores. In this work linear dichroism (LD) in combination with fluorescence polarization anisotropy (FPA) and magnetic circular dichroism (MCD) is used to investigate electronic excitations and excited states of indole derivatives, purine derivatives, the wye base, 2-phenylindole and 4',6-diamidino-2-phenylindole (DAPI). The UV spectrum of indole, which is the chromophoric core of tryptophan, is resolved into contributions from the lowest nearly degenerate 1A1 --> 1La and 1A1 --> 1Lb transitions, and the moment directions for the four lowest transitions in indole and eight selected methyl and methoxy derivatives are determined. Substitution does not generally perturb the transition moment directions, with exception for the 1A1 --> 1Lb and 1A1 --> 1Bb transitions whose moment directions are significantly altered by a methoxy group in 4- or 6-position. The transition moment directions and the resolved UV-spectra were also determined for purine, a model compound for the purine nucleic acid bases, and the tRNA base wye (Y-base). Purine has a clearly resolved n-->p* transition lowest in energy, followed by two nearly degenerate p-->p* transitions with almost perpendicular moment directions. The phosphorescence spectra of purine and three methyl derivatives were investigated and the emitting triplet was found to have effectively pp* character. In addition, the purines with mobile imidazolic protons (purine and 6-methylpurine) are shown to exist, in an organic glass at 80 K, in two tautomeric forms (7H and 9H) as judged from phosphorescence emission and excitation spectra. A DNA-binding probe 4',6-diamidino-2-phenylindole (DAPI) and its parent chromophore 2-phenylindole were finally investigated using the above mentioned experimental techniques as well as quantum mechanical calculations. Five distinct electronic transitions are found above 200 nm and their moment directions are determined. The theoretical results indicate a weak relation of the two lowest transitions in 2-phenylindole to the 1A1 --> 1Lb and 1A1 --> 1La transitions of indole.
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| 5. |
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| 6. |
- Albinsson, Bo, 1963, et al.
(författare)
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EXCITED-STATE PROPERTIES OF THE INDOLE CHROMOPHORE - ELECTRONIC-TRANSITION MOMENT DIRECTIONS FROM LINEAR DICHROISM MEASUREMENTS - EFFECT OF METHYL AND METHOXY SUBSTITUENTS
- 1992
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Ingår i: Journal of Physical Chemistry. - : American Chemical Society (ACS). - 0022-3654 .- 1541-5740. ; 96:15, s. 6204-6212
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Tidskriftsartikel (refereegranskat)abstract
- From measurements of UV and IR linear dichroism on molecules partially oriented in stretched polyethylene host the transition moment directions for the first four pi-pi* transitions of indole and some indole derivatives were determined. Relative to the pseudosymmetry long axis of indole, the transitions were normally found to be polarized at (angles counted away from the ring nitrogen): +42 +/- 50-degrees (1A1 --> 1L(by) at 287 nm), -46 +/- 5-degrees (1A1 --> 1L(a) at 265 nm), 0 +/- 15-degrees (1A1 --> 1B(by) at 220 nm), and for the 1A1 --> 1B(a) transition occurring around 200 nm, at least at +/- 30-degrees away from this axis. In addition, indication for a weak, essentially short axis polarized transition was found at 235 nm, possibly due to the 1A1 --> 1C transition. An ambiguity problem regarding the sign of the angles was resolved by exploiting the change of orientation properties upon introduction of substituents. Orientation parameters (including diagonalizing angle) were determined by consideration of a large number of in-plane as well as out-of-plane polarized vibrational transitions. The question regarding effects on the excited states by the presence of methyl and methoxy substituents, at varied positions in the indole chromophore, was addressed in terms of the perturbations they caused on the transition moments. Whereas none of the four transitions was found to be very sensitive in this respect to methyl or methoxy groups introduced in 2-, 3-, 5-, or 7-position of indole, the directions of the weak 1A1 --> 1L(by) but also the strong 1A1 --> 1B(by) transition were found to become significantly altered by a methoxy group in 4- as well as 6-position. The conclusions are consistent with recent fluorescence anisotropy data and semiempirical calculations.
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| 7. |
- Albinsson, Bo, 1963, et al.
(författare)
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The Electronically Excited-States of 2-Phenylindole
- 1991
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Ingår i: Chemical Physics. - 0301-0104. ; 151:1, s. 149-157
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Tidskriftsartikel (refereegranskat)abstract
- The light absorption of 2-phenylindole (2PI) in the UV region (210-350 nm) is investigated by means of linear dichroism in stretched polyethylene film and fluorescence polarization anisotropy in a propylene glycol glass. Experimentally, 2PI is found to have five distinct electronic transitions located above 200 nm for which the transition moments are determined. The conclusions are supported by quantum chemical calculations and the origin of the so-called composite band is discussed. Comparison with the absorption spectrum of the fluorescent DNA binding probe DAPI is also made and 2PI is found to be an appropriate model system for the electronic transitions of DAPI.
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| 8. |
- Carlsson, Christina, 1968, et al.
(författare)
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OPTICAL AND PHOTOPHYSICAL PROPERTIES OF THE OXAZOLE YELLOW DNA PROBES YO AND YOYO
- 1994
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Ingår i: Journal of Physical Chemistry. - : American Chemical Society (ACS). - 0022-3654 .- 1541-5740. ; 98:40, s. 10313-10321
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Tidskriftsartikel (refereegranskat)abstract
- The photophysical properties of the optical DNA probe YOYO (homodimeric derivative of oxazole yellow) have been characterized in terms of the monomeric part, the YO chromophore. In aqueous solutions YO is virtually nonfluorescent but upon binding to DNA its fluorescence quantum yield is strongly increased. A similar enhancement of the fluorescence is observed for YO in the viscous solvent glycerol. The high fluorescence quantum yield of YO, when bound to DNA or in a viscous solution, is proposed to be a result of decreased rotational mobility around the internuclear bridge between the two aromatic ring systems. This hypothesis is based on similar values of the activation energies for the temperature-dependent nonradiative decay processes (E(A) = 53 kJ/mol) and viscous flow (E(A) = 63 kJ/mol), suggesting related rate-limiting mechanisms. A single electronic transition is found to be responsible for the intense visible absorption band. This conclusion is based on the observation of an essentially wavelength-independent reduced linear dichroism and similarly wavelength independent fluorescence anisotropy, and the fact that the emission spectrum is very nearly a mirror image of the absorption spectrum. The conclusion is further supported by quantum mechanical calculations (CNDO/S). By combination of measurements of fluorescence anisotropy of YO in glycerol and linear dichroism of YO in a stretched poly(vinyl alcohol) film, the transition moment of the strong visible absorption band was found to be nearly long axis polarized, in agreement with the CNDO/S calculations. The low-energy electronic transition and its polarization direction in the YO chromophore remain essentially unperturbed in the YOYO dye, suggesting that the results obtained for the excited state of the YO chromophore are applicable also to YOYO. One difference, though, is that in aqueous solutions the two YO chromophores of YOYO interact with each other, forming an internal dimer, resulting in a distorted absorption spectrum.
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| 9. |
- Doglia, S. M., et al.
(författare)
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QUINACRINE - SPECTROSCOPIC PROPERTIES AND INTERACTIONS WITH POLYNUCLEOTIDES
- 1993
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Ingår i: Biopolymers. - : Wiley. - 0006-3525 .- 1097-0282. ; 33:9, s. 1431-1442
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Tidskriftsartikel (refereegranskat)abstract
- The acridine dye quinacrine and its interactions with calf thymus DNA, poly(dA-dT).poly(dA-dT), and poly(dG-dC).poly(dG-dC) were studied by light absorption, linear dichroism, and fluorescence spectroscopy. The transition moments of quinacrine give rise to absorption bands polarized along the short axis (400-480-nm band), and the long axis (345-nm and 290-nm bands) of the molecule, respectively. Linear dichroism studies show that quinacrine intercalates into calf thymus DNA as well as into the polynucleotides, displaying fairly homogeneous binding to poly (dA-dT).poly(dA-dT), but more than one type of intercalation site for calf thymus DNA and poly(dG-dC).poly(dG-dC). Fluorescence spectroscopy shows that for free quinacrine the pK = 8.1 between the mono- and diprotonated states also remains unchanged in the excited state. Quinacrine bound to calf thymus DNA and polynucleotides exhibits light absorption typical for the intercalated diprotonated form. The fluorescence enhancement of quinacrine bound to poly (dA-dT).poly(dA-dT) may be due to shielding from water interactions involving transient H-bond formation. The fluorescence quenching in poly (dG-dC).poly (dG-dC) may be due to excited state electron transfer from guanine to quinacrine. (C) 1993 John Wiley & Sons, Inc.
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| 10. |
- Holmén, Anders, 1967, et al.
(författare)
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ELECTRONIC-TRANSITION DIPOLE-MOMENTS OF THE 1,N-6-ETHENOADENINE CHROMOPHORE
- 1994
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Ingår i: Journal of Physical Chemistry. - : American Chemical Society (ACS). - 0022-3654 .- 1541-5740. ; 98:51, s. 13460-13469
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Tidskriftsartikel (refereegranskat)abstract
- The electronic spectra of 1,N-6-ethenoadenine (epsilon-adenine, epsilon-A), 3-methyl-epsilon-adenine (3-me-epsilon-A), and epsilon-adenosine (epsilon-Ado) have been examined with respect to the number of electronic transitions, their intensities, and their transition moments, on the basis of measurements of UV and IR linear dichroism (LD) on samples partially oriented in stretched poly(vinyl alcohol) films, fluorescence anisotropy (FA), and magnetic circular dichroism (MCD). The experimental results are compared with semiempirical molecular orbitaI calculations. Four pi-->pi(*) transitions were found to contribute to the UV spectrum of the epsilon-adenine chromophore with the following transition moment directions (relative to the ''adenine'' pseudosymmetry long axis, counted toward N-1): +27 degrees +/- 10 degrees (I at 32 500 cm(-1)), -47 degrees +/- 5 degrees (II at 37 000 cm(-1)), -30 degrees +/- 10 degrees (III at 32 000 cm(-1)), and -11 degrees +/- 10 degrees or -49 degrees +/- 10 degrees (IV at approximate to 46 000 cm(-1)). The orientation parameters in the stretched film experiments were determined from polarized IR measurements combined with UV LD and FA data. In addition, fluorescence emission and excitation spectra and fluorescence lifetimes of E-A in aqueous solutions indicate that epsilon-A does not behave as a single spectroscopic species. In contrast to 3-me-epsilon-A and epsilon-Ado, epsilon-A displays an emission wavelength dependent excitation spectrum and a biexponential fluorescence decay. This observation is attributed to a prototropic tautomeric equilibrium between the 1-H and 3-H forms of epsilon-A.
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