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1.
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2.
  • Albinsson, Bo, 1963-, et al. (författare)
  • ELECTRONIC-TRANSITION MOMENT DIRECTIONS AND IDENTIFICATION OF LOW-ENERGY N-PI-ASTERISK STATES IN WEAKLY PERTURBED PURINE CHROMOPHORES
  • 1993
  • Ingår i: Journal of the American Chemical Society. - 0002-7863. ; 115:1, s. 223-231
  • 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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3.
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4.
  • Albinsson, Bo, 1963-, et al. (författare)
  • EXCITED-STATE PROPERTIES OF THE INDOLE CHROMOPHORE - ELECTRONIC-TRANSITION MOMENT DIRECTIONS FROM LINEAR DICHROISM MEASUREMENTS - EFFECT OF METHYL AND METHOXY SUBSTITUENTS
  • 1992
  • Ingår i: Journal of Physical Chemistry. - 0022-3654. ; 96:15, s. 6204-6212
  • 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.
  • Ardhammar, Malin, 1970-, et al. (författare)
  • Absolute configuration and electronic state properties of light-switch complex [Ru(phen)2dppz]2+ deduced from oriented circular dichroism in a lamellar liquid crystal host
  • 2002
  • Ingår i: Chemical Physics Letters. - 0009-2614. ; 354:1-2, s. 44-50
  • Tidskriftsartikel (refereegranskat)abstract
    • Circular dichroism (CD) of enantiomers of [Ru(phen)(2)dppz](2+) oriented in a octanoate-decanol-water lamellar liquid crystal has been measured parallel to the orientation axis. where the sample does not exhibit linear dichroism (LD). At an inclined incidence, the emerging LD shows that the chromophores have an along-chain orientation in the liquid crystal. The changes in the CD spectrum compared to an isotropic sample, in conjunction with CD calculations, allow us to assess the absolute configuration of the enantiomers and assign the CD bands to specific electronic transitions.
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9.
  • Ardhammar, Malin, 1970-, et al. (författare)
  • DNA-Drug Interactions
  • 2000
  • Ingår i: Circular dichroism: principles and applications (Eds. Berova, N., Nakanishi, K. and Woody, R.W.). - 0-471-33003-5 ; s. 741-76826
  • Bokkapitel (övrigt vetenskapligt)
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10.
  • Ardhammar, Malin, 1970-, et al. (författare)
  • In vitro membrane penetration of modified peptide nucleic acid (PNA)
  • 1999
  • Ingår i: Journal of Biomolecular Structure & Dynamics. - 0739-1102. ; 17:1, s. 33-40
  • Tidskriftsartikel (refereegranskat)abstract
    • Efficient cellular uptake is crucial for the success of any drug directed towards targets inside cells. Peptide nucleic acid (PNA), a DNA analog with a promising potential as a gene-directed drug, has been shown to display slow membrane penetration in cell cultures. We here used liposomes as an in vitro model of cell membranes to investigate the effect on penetration of a PNA molecule colvalently modified with a lipophilic group, an adamantyl moiety. The adamantyl attachment was found to increase the membrane-penetration rate of PNA three-fold, as compared to corresponding unmodified PNA. From the penetration behaviour of a number of small and large molecules we could conclude that passive diffusion is the mechanism for liposome-membrane passage. Flow linear dichroism (LD) of the modified PNA in presence of rod-shaped micelles, together with octanol-water distribution experiments. showed that the adamantyl-modified PNA is amphiphilic; the driving force behind the observed increased membrane-penetration rate appears to be an accumulation of the PNA in the lipid double layer.
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