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| 2. |
- 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, 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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| 6. |
- Albinsson, Bo, 1963, et al.
(författare)
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Polarized Spectroscopy with Fluorescent Biomolecular Building Blocks
- 2016
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Ingår i: Fluorescent Analogues of Biomolecular Building Blocks: Design and Applications: Design and Applications (eds M. Wilhelmsson and Y. Tor). - Hoboken, NJ, USA : John Wiley & Sons, Inc. - 9781118175866 ; , s. 40-54
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- © 2016 by John Wiley & Sons, Inc. All rights reserved. This chapter considers linear dichroism (LD), magnetic circular dichroism (MCD), and Forster resonance energy transfer (FRET) and how these phenomena are related to and may report on transition moment orientations and on molecular structure. MCD is an asset in combination with LD and fluorescence anisotropy for the deciphering of transition moment directions in biophysically important chromophores, and many examples of applications are found among nucleobases. A property corresponding to the absorption anisotropy (linear dichroism) for emission is the fluorescence anisotropy. The amino acid tryptophan, with indole as its photoactive aromatic chromophore, is the most frequently used natural fluorescent probe in biophysical contexts, due to its relatively high fluorescence quantum yield and well-resolved absorption profile in the near-UV. The single-molecule fluorescence-detected linear dichroism (smFLD) method is a useful complement to smFRET since it can help to avoid misinterpretation of false smFRET signals.
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| 7. |
- Ardhammar, Malin, 1970, et al.
(författare)
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In vitro membrane penetration of modified peptide nucleic acid (PNA)
- 1999
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Ingår i: Journal of Biomolecular Structure and Dynamics. - : Informa UK Limited. - 0739-1102 .- 1538-0254. ; 17:1, s. 33-40
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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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| 8. |
- Austeng, Dordi, et al.
(författare)
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Incidence of and risk factors for neonatal morbidity after active perinatal care : extremely preterm infants study in Sweden (EXPRESS)
- 2010
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Ingår i: Acta Paediatrica. - : Wiley. - 0803-5253 .- 1651-2227. ; 99:7, s. 978-992
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Tidskriftsartikel (refereegranskat)abstract
- Aims: The aim of this study was to determine the incidence of neonatal morbidity in extremely preterm infants and to identify associated risk factors. Methods: Population based study of infants born before 27 gestational weeks and admitted for neonatal intensive care in Sweden during 2004-2007. Results: Of 638 admitted infants, 141 died. Among these, life support was withdrawn in 55 infants because of anticipation of poor long-term outcome. Of 497 surviving infants, 10% developed severe intraventricular haemorrhage (IVH), 5.7% cystic periventricular leucomalacia (cPVL), 41% septicaemia and 5.8% necrotizing enterocolitis (NEC); 61% had patent ductus arteriosus (PDA) and 34% developed retinopathy of prematurity (ROP) stage >= 3. Eighty-five per cent needed mechanical ventilation and 25% developed severe bronchopulmonary dysplasia (BPD). Forty-seven per cent survived to one year of age without any severe IVH, cPVL, severe ROP, severe BPD or NEC. Tocolysis increased and prolonged mechanical ventilation decreased the chances of survival without these morbidities. Maternal smoking and higher gestational duration were associated with lower risk of severe ROP, whereas PDA and poor growth increased this risk. Conclusion: Half of the infants surviving extremely preterm birth suffered from severe neonatal morbidities. Studies on how to reduce these morbidities and on the long-term health of survivors are warranted.
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| 9. |
- Börjesson, Karl, 1982, et al.
(författare)
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A membrane anchored DNA-based energy/electron transfer assembly
- 2008
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Ingår i: Nucleic acids symposium series (2004). - 1746-8272. ; :52, s. 691-691
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Tidskriftsartikel (refereegranskat)abstract
- In this work the trapping and conversion of visible light energy into chemical energy is examined using a supramolecular assembly. This consists of a light absorbing antenna and a porphyrin redox centre both covalently attached to a DNA strand, which in turn is bound to a lipid membrane. The excitation energy is finally trapped as a benzoquinone radical anion that could potentially be used in subsequent chemical reactions.
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| 10. |
- Börjesson, Karl, 1982, et al.
(författare)
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Functionalized Nanostructures: Redox-Active Porphyrin Anchors for Supramolecular DNA Assemblies
- 2010
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 4:9, s. 5037-5046
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Tidskriftsartikel (refereegranskat)abstract
- We have synthesized and studied a supramolecular system comprising a 39-mer DNA with porphyrin-modified thymidine nucleosides anchored to the surface of large unilamellar vesicles (liposomes). Liposome porphyrin binding characteristics, such as orientation, strength, homogeneity, and binding site size, was determined, suggesting that the porphyrin is well suited as a photophysical and redox-active lipid anchor, in comparison to the inert cholesterol anchor commonly used today. Furthermore, the binding characteristics and hybridization capabilities were studied as a function of anchor size and number of anchoring points, properties that are of importance for our future plans to use the addressability of these redox-active nodes in larger DNA-based nanoconstructs. Electron transfer from photoexcited porphyrin to a lipophilic benzoquinone residing in the lipid membrane was characterized by steady-state and time-resolved fluorescence and verified by femtosecond transient absorption.
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