| 1. |
- Höök, Fredrik, 1966, et al.
(författare)
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Characterization of PNA and DNA Immobilization and Subsequent Hybridization with DNA Using Acoustic-Shear-Wave Attenuation Measurements
- 2001
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 17:26, s. 8305-8312
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Tidskriftsartikel (refereegranskat)abstract
- We report here how the quartz crystal microbalance with dissipation monitoring (QCM-D) technique, simultaneously measuring changes in the induced energy dissipation, D (cf. viscoelastic properties), and the frequency, f (cf. coupled mass), can be used to characterize the bound state of single-stranded peptide nucleic acid (PNA) and deoxyribose nucleic acid (DNA) in relation to their ability to function as selective probe(s) for fully complementary and single-mismatch DNA. The possibility to use the QCM-D technique for detection of binding kinetics and structural differences in the formed duplexes is also presented. We found that thiol-PNA and thiol-DNA attached via a sulfur group directly on a bare-gold surface are less efficient as probes for DNA than are biotin-PNA and biotin-DNA, coupled on top of a two-dimensional (2-D) arrangement of streptavidin, formed on a biotinylated phospholipid bilayer on a SiO2 surface. The fully complementary and singly mismatched DNA oligomers hybridize with the immobilized PNA and DNA. A single mismatch is discriminated via a significant difference in the binding and dissociation kinetics, demonstrating a high selectivity and thus successful immobilization of functional single strands. The observed ratios between hybridization-induced energy dissipation (DeltaD) and the frequency shift (Deltaf) made it possible to discriminate thiol-PNA directly attached to a gold surface from biotin-PNA coupled to the streptavidin 2-D arrangement, where the former were shown to be inefficient for detecting subsequent hybridization. Structural differences of the immobilized layers composed of biotin-PNA-DNA and biotin-DNA-DNA were clearly reflected by the DeltaD and Deltaf response.
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| 2. |
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| 3. |
- Tjerneld, F., et al.
(författare)
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Linear Dichroism of Chloroplasts and Subchloroplast Fractions Oriented by Flow
- 1977
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Ingår i: Spectroscopy Letters. - : Informa UK Limited. - 1532-2289 .- 0038-7010. ; 10:6, s. 489-493
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Tidskriftsartikel (refereegranskat)abstract
- Chloroplasts as well as subchloroplast vesicles show linear dichroism (LD) when subjected to a hydrodynamic gradient. LD is positive for the ππ in-plane polarized bands indicating that the chlorophyll porphyrin ring is in average oriented parallel1 to the elongated membrane surfaces. The vesicle fraction enriched inphotosystem I1 shows lower LD/A at 660 nm indicating lower average orientation of chlorophyll and the fraction enriched in photosystem I shows higher LD/A at 700 nm indicating that P700 is more oriented than the bulk chlorophyll.
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| 4. |
- Wittung Stafshede, Pernilla, 1968, et al.
(författare)
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Detection of point mutations in DNA by PNA-based quartz-crystal biosensor
- 2000
-
Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 1873-4359 .- 0927-7757. ; 174:1-2, s. 269-273
-
Tidskriftsartikel (refereegranskat)abstract
- Currently there is an extensive search for biosensors for detecting genetic defects by hybridisation to immobilised oligonucleotides. A concept able to detect a single mismatch in a 15mer single-strand target of the p53 tumor suppresser gene is presented (a mutation found in many types of cancer cells). In this method, the unique hybridisation properties of the DNA mimic peptide nucleic acid (PNA) are combined with electronically detected mass and shear dissipation at the surface of a quartz crystal. Cysteine-labeled PNA efficiently immobilises on crystal-gold surface at 20 degrees C. At 60 degrees C, addition of complementary DNA results in a signal response corresponding to hybridisation between DNA and the PNA-covered surface, whereas addition of DNA differing in only one of the 15 bases gives no response at all.
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| 5. |
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| 6. |
- 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
-
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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| 7. |
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| 8. |
- 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
-
Ingår i: Journal of Physical Chemistry. - : American Chemical Society (ACS). - 0022-3654 .- 1541-5740. ; 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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| 9. |
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| 10. |
- Albinsson, Bo, 1963, et al.
(författare)
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Polarized Spectroscopy with Fluorescent Biomolecular Building Blocks
- 2016
-
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
-
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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| 11. |
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| 12. |
- 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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| 13. |
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| 14. |
- 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.). - 0471330035 ; , s. 741-768 (Chapter 26)
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 15. |
- Ardhammar, Malin, 1970, et al.
(författare)
-
In vitro membrane penetration of modified peptide nucleic acid (PNA)
- 1999
-
Ingår i: Journal of Biomolecular Structure and Dynamics. - : Informa UK Limited. - 0739-1102 .- 1538-0254. ; 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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| 16. |
- Banchelli, M., et al.
(författare)
-
Phospholipid membranes decorated by cholesterol-based oligonucleotides as soft hybrid nanostructures
- 2008
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 112:35, s. 10942-10952
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Tidskriftsartikel (refereegranskat)abstract
- DNA monomers and oligomers are currently showing great promise as building blocks for supramolecular arrays that can self-assemble in a fashion preprogrammed by the base pairing code. The design and build-up of hybrid DNA/amphiphilic self-assemblies can expand the range of possible architectures and enhance the selectivity toward a well-specified geometry. We report on the self-assembly properties in aqueous solution of a cholesteryl-tetraethylenglycol single stranded 18-mer oligonucleotide (ON(1)TEG-Chol) and on its spontaneous insertion in fluid phospholipid membranes. Up to 500 units of these lipophilic ss-oligonucleotides can be incorporated in the outer leaflet of 350 A radius POPC vesicle. The insertion and hybridization with the complementary oligonucleotide are monitored through light scattering as an increase of hydrodynamic thickness, which is interpreted in terms of average distance between anchoring sites. The conformation of the ss-oligonucleotidic portion is strongly dependent on surface coverage, passing from a quasi-random coil to a more rigid configuration, as concentration increases. Interestingly, conformational details affect in a straightforward fashion the hybridization kinetics. Liposomes with single- and double-strand decorations remain stable within the experimental time window (about one week). The structure represents an example of successful and stable amphiphile/DNA supramolecular hybrid, where a DNA guest is held in a membrane by hydrophobic interactions. The lipophilic oligonucleotide under investigation is therefore a suitable building block that can effectively serve as a hydrophobic anchor in the fluid bilayer to assemble supramolecular constructs based on the DNA digital code.
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| 17. |
- Becker, Hans-Christian, 1971, et al.
(författare)
-
DNA Binding mode and sequence specificity of piperazinylcarbonyloxyethyl derivatives of anthracene and pyrene
- 1999
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 121:51, s. 11947-11952
-
Tidskriftsartikel (refereegranskat)abstract
- Four novel piperazinylcarbonyloxyethyl derivatives of anthracene and pyrene have been prepared and investigated with respect to sequence specificity and synergism between hydrophobic and electrostatic effects upon binding to DNA. Linear and circular dichroism spectroscopy was used to assess the orientation of the aromatic chromophores relative to the nucleobases. Anthracene and pyrene derivatives 2a and 3 are both concluded to bind to homo-polynucleotide poly(dA-dT)(2) by intercalation of their aromatic moieties between base pairs, with a binding constant K-AT of 4 x 10(5) M-1 and 2 x 10(6) M-1, respectively. Significantly reduced affinities (K-GC = 3 x 10(4) M-1 and 10(5) M-1, respectively) are observed with poly(dG-dC)(2), due to less favorable interactions of the piperazinium tail in the minor groove. Base pair specificity is reflected in the binding thermodynamics, with the binding to AT being more enthalpically driven than the binding to GC. Phenyl substitution at the quaternary piperazinium site of the anthracene derivative 2b, does not affect the ratio K-AT/K-GC, but reduces the affinity for both AT End GC slightly. Moreover, the phenyl group in the 10-position of 4 prevents intercalation, and apparently, this compound binds externally to both AT and GC duplex polynucleotides. The results are discussed in terms of general features of the interactions of the intercalating and minor-groove binding molecular moieties, and their interplay with each other, with potentials for tuning specificity.
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| 18. |
- Becker, Hans-Christian, 1971, et al.
(författare)
-
DNA Binding Properties of 2,7-Diazapyrene and its N-methylated Cations Studied by Linear and Circular Dichroism Spectroscopy and Calorimetry
- 1997
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 119:25, s. 5798-5803
-
Tidskriftsartikel (refereegranskat)abstract
- The binding of 2,7-diazapyrene (DAP), N-methyl-2,7-diazapyrenium monocation (MDAP), and N,N'-dimethyl-2,7-diazapyrenium dication (DMDAP) to calf thymus DNA has been studied with respect to molecular geometry and thermodynamics. It is concluded from flow linear dichroism (LD) and induced circular dichroism (CD) spectra that the three diazapyrenes bind by intercalation to alternating AT as well as GC polynucleotide duplexes, as indicated by strong interactions with the transitions of the nucleobases in conjunction with approximately perpendicular orientations of the in-plane symmetry axes relative to the DNA helix axis. The reduced LD (LDt = LD/A(iso)) of the DNA complexes is characterized by marked fine structure, decreasing in the order DAP > MDAP > DMDAP. This finding is interpreted in terms of a microscopic heterogeneity associated with rotational mobility of the ligand in a tilted intercalation pocket, with the dication DMDAP having less rotational freedom than the neutral DAP has. Other distinct differences between the three diazapyrenes are revealed in their thermodynamic parameters of binding. DAP binds with a negative Delta H degrees (-9 kcal/mol) and a negative Delta S degrees (-7 cal/(mol K)), whereas the binding of the dication DMDAP is entropically driven (+43 cay(mol K)) but enthalpically disfavored (+5.2 kcal/mol), the monocation MDAP having an intermediate position (Delta H degrees = -3 kcal/mol, Delta S degrees = +12 cal/(mol K)).
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| 19. |
- Becker, Hans-Christian, 1971, et al.
(författare)
-
DNA binding thermodynamics and sequence specificity of chiral piperazinecarbonyloxyalkyl derivatives of anthracene and pyrene
- 2000
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 122:35, s. 8344-8349
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we report the DNA binding proper ties of piperazinecarbonyloxy-2-propyl derivatives of anthracene (2), pyrene (3), and phenylanthracene (4). An intercalative binding mode is found for 2 and 3, while the phenyl group of 4 prevents intercalation and leads to external binding. Preferential binding of the (S)-enantiomers is found for both anthracene 2 and pyrene 3. However, the enantiomeric preference is small, with K-(R)/K-(S) being around 0.5 for both the anthracene and the pyrene compounds. This is interpreted in terms of orientation polarity in the binding, by which any intrinsic enantioselectivity is canceled by averaging of opposite binding orientations. The affinities for poly(dA-dT)(2) (AT) are 10(4) M-1 for anthracene derivative 2, and 5 x 10(5) M-1 for pyrene derivative 2. The affinities for poly(dG-dC)(2) (GC) are I order of magnitude lower than those for AT. This is explained by steric interference of the piperazinium tail with the exocyclic amino groups of guanine in the minor groove of GC, leading to a more shallow intercalation in GC than in AT, as also indicated by significantly less negative reduced linear dichroism of the intercalator absorption bands in the GC complexes. This behavior is consistent with that observed for the previously studied achiral analogues.(1) Binding thermodynamics support the difference in binding mode between AT and GC. The binding enthalpy of the AT complexes is significantly more negative than that of the corresponding GC complexes. This indicates a larger overlap of intercalating moiety and nucleobases in the AT complexes, consistent with the linear dichroism results.
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| 20. |
- Becker, Hans-Christian, 1971, et al.
(författare)
-
Ground- and excited-state properties of molecular complexes between adenine and 2,7-diazapyrene and its N-methylated cations
- 1997
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 101:47, s. 8853-8860
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Tidskriftsartikel (refereegranskat)abstract
- It has recently been found that 2,7-diazapyrenes upon interaction with nucleic acids form stacked (''intercalation'') complexes, which for the methylated derivatives exhibit new absorption features assigned as charge-transfer (CT) transitions.' To better understand the basis of these interactions and associated optical properties, the geometries and electronic spectra of complexes of adenine (A) with 2,7-diazapyrene (DAP), N-methyl-2,7-diazapyrenium (MDAP(+)), and N,N-dimethyl-2,7-diazapyrenium (DMDAP(2+)) have been modeled using semiempirical AM1 and PM3 geometry optimizations, ab initio (vacuum and Onsager model) energy calculations, and ZINDO/S calculations. In addition, absorption spectra, fluorescence quenching, and H-1 NMR spectra for the complexes in aqueous solution have been measured. For the A-DAP complex, a coplanar, hydrogen-bonded complex is predicted by the calculations, while A-MDAP(+) and A-DMDAP(2+) complexes should have edge-to-face geometry. The association is predicted to be of electrostatic nature, mainly between the pyridinium nitrogen (MDAP(+), DMDAP(2+)) and N-1/NH2 of adenine. There seems to be a preference (6 kcal/mol) for the hydrogen-bonded A-DAP complex, and the energetic difference between face-to-face and edge-to-face A-MDAP(+) and A-DMDAP(2+) complexes is 3 and 8 kcal/mol, respectively (Onsager ab initio, epsilon = 79.5). By contrast, the H-1 NMR data and experimental absorption spectra in conjunction with calculated spectra instead indicate that all three adenine-diazapyrene complexes assume face-to-face arrangement in water because of hydrophobic effects. In agreement with the putative CT absorption of diazapyrenium-DNA complexes, absorption tails are also observed for A-DMDAP(2+) and A-MDAP(+), however not for the A-DAP complex. Most satisfactorily, charge-transfer transitions are predicted by the calculations to occur in the correct wavelength region for A-DMDAP(2+) (strongest) and A-MDAP(+), while A-DAP is predicted not to have any CT transitions. Correspondingly, the observation of quenching of fluorescence of MDAP(+) and DMDAP(2+) (but not DAP) by adenine can explained by charge transfer from adenine to the diazapyrenium.
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| 21. |
- Behravan, G., et al.
(författare)
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THE INTERACTION OF ELLIPTICINE DERIVATIVES WITH NUCLEIC-ACIDS STUDIED BY OPTICAL AND H-1-NMR SPECTROSCOPY - EFFECT OF SIZE OF THE HETEROCYCLIC RING
- 1994
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Ingår i: Biopolymers. - : Wiley. - 0006-3525 .- 1097-0282. ; 34:5, s. 599-609
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Tidskriftsartikel (refereegranskat)abstract
- The DNA interaction of derivatives of ellipticine with heterocyclic ring systems with three, four, or five rings and a dimethylaminoethyl side chain was studied. Optical spectroscopy of drug complexes with calf thymus DNA, poly [(dA-dT).(dA-dT)], or poly [(dG-dC).(dG-dC)] showed a 10 nm bathochromic shift of the light absorption bands of the pentacyclic and tetracyclic compounds upon binding to the nucleic acids, which indicates binding by intercalation. For the tricyclic compound a smaller shift of 1-3 nm was observed upon binding to the nucleic acids. Flow linear dichroism studies show that the geometry of all complexes is consistent with intercalation of the ring system, except for the DNA and poly [(dG-dC).(dG-dC)] complexes of the tricyclic compound, where the average angle between the drug molecular plane and the DNA helix axis was found to be 65 degrees. One-dimensional H-1-nmr spectroscopy was used to study complexes between d(CGCGATCGCG)(2) and the tricyclic and pentacyclic compounds. The results on the pentacyclic compound show nonselective broadening due to intermediate chemical exchange of most oligonucleotide resonances upon drug binding. The imino proton resonances are in slow chemical exchange, and new resonances with upheld shifts approaching 1 ppm appear upon drug binding, which supports intercalative binding of the pentacyclic compound. The results on the tricyclic compound show more rapid binding kinetics and very selective broadening of resonances. The data suggest that the tricyclic compound is in an equilibrium between intercalation and minor groove binding, with a preference to bind close to the AT base pairs with the side chain residing in the minor groove. (C) 1994 John Wiley and Sons, Inc.
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| 22. |
- Beke-Somfai, Tamas, 1977, et al.
(författare)
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Double-lock ratchet mechanism revealing the role of alpha SER-344 in FoF1 ATP synthase
- 2011
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 108:12, s. 4828-4833
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Tidskriftsartikel (refereegranskat)abstract
- In a majority of living organisms, FoF1 ATP synthase performs the fundamental process of ATP synthesis. Despite the simple net reaction formula, ADP + Pi. ATP + H2O, the detailed step-by-step mechanism of the reaction yet remains to be resolved owing to the complexity of this multisubunit enzyme. Based on quantum mechanical computations using recent high resolution X-ray structures, we propose that during ATP synthesis the enzyme first prepares the inorganic phosphate for the gamma P-O-ADP bond-forming step via a double-proton transfer. At this step, the highly conserved alpha S344 side chain plays a catalytic role. The reaction thereafter progresses through another transition state (TS) having a planar PO3- ion configuration to finally form ATP. These two TSs are concluded crucial for ATP synthesis. Using stepwise scans and several models of the nucleotide-bound active site, some of the most important conformational changes were traced toward direction of synthesis. Interestingly, as the active site geometry progresses toward the ATP-favoring tight binding site, at both of these TSs, a dramatic increase in barrier heights is observed for the reverse direction, i.e., hydrolysis of ATP. This change could indicate a "ratchet" mechanism for the enzyme to ensure efficacy of ATP synthesis by shifting residue conformation and thus locking access to the crucial TSs.
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| 23. |
- Beke-Somfai, Tamas, 1977, et al.
(författare)
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Energy phase shift as mechanism for catalysis
- 2012
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 535, s. 169-172
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Tidskriftsartikel (refereegranskat)abstract
- Catalysts are agents that by binding reactant molecules lower the energy barriers to chemical reaction. After reaction the catalyst is regenerated, its unbinding energy recruited from the environment, which is associated with an inevitable loss of energy. We show that combining several catalytic sites to become energetically and temporally phase-shifted relative to each other provides a possibility to sustain the overall reaction by internal 'energy recycling', bypassing the need for thermal activation, and in principle allowing the system to work adiabatically. Using an analytical model for superimposed, phase-shifted potentials of F-1-ATP synthase provides a description integrating main characteristics of this rotary enzyme complex.
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| 24. |
- Beke-Somfai, Tamas, 1977, et al.
(författare)
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Mechanical Control of ATP Synthase Function: Activation Energy Difference between Tight and Loose Binding Sites
- 2010
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 1520-4995 .- 0006-2960. ; 49:3, s. 401-403
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Tidskriftsartikel (refereegranskat)abstract
- Despite exhaustive chemical and crystal structure studies, the mechanistic details of how F o F 1 -ATP synthase can convert mechanical energy to chemical, producing ATP, are still not fully understood. On the basis of quantum mechanical calculations using a recent highresolution X-ray structure, we conclude that formation of the P-O bond may be achieved through a transition state (TS) with a planar PO 3 - ion. Surprisingly, there is a more than 40 kJ/mol difference between barrier heights of the loose and tight binding sites of the enzyme. This indicates that even a relatively small change in active site conformation, induced by the γ-subunit rotation, may effectively block the back reaction in β TP and, thus, promote ATP. © 2009 American Chemical Society.
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| 25. |
- Beke-Somfai, Tamas, 1977, et al.
(författare)
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Rate of hydrolysis in ATP synthase is fine-tuned by alpha-subunit motif controlling active site conformation
- 2013
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 110:6, s. 2117-2122
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Tidskriftsartikel (refereegranskat)abstract
- Computer-designed artificial enzymes will require precise understanding of how conformation of active sites may control barrier heights of key transition states, including dependence on structure and dynamics at larger molecular scale. FoF1 ATP synthase is interesting as a model system: a delicate molecular machine synthesizing or hydrolyzing ATP using a rotary motor. Isolated F-1 performs hydrolysis with a rate very sensitive to ATP concentration. Experimental and theoretical results show that, at low ATP concentrations, ATP is slowly hydrolyzed in the so-called tight binding site, whereas at higher concentrations, the binding of additional ATP molecules induces rotation of the central gamma-subunit, thereby forcing the site to transform through subtle conformational changes into a loose binding site in which hydrolysis occurs faster. How the 1-angstrom-scale rearrangements are controlled is not yet fully understood. By a combination of theoretical approaches, we address how large macromolecular rearrangements may manipulate the active site and how the reaction rate changes with active site conformation. Simulations reveal that, in response to.-subunit position, the active site conformation is fine-tuned mainly by small alpha-subunit changes. Quantum mechanics-based results confirm that the sub-Angstrom gradual changes between tight and loose binding site structures dramatically alter the hydrolysis rate.
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| 26. |
- Bergqvist, Björn, 1965, et al.
(författare)
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Effect of microwave radiation on permeability of liposomes. Evidence against non-thermal leakage
- 1994
-
Ingår i: Biochimica et Biophysica Acta - General Subjects. - : Elsevier BV. - 1872-8006 .- 0304-4165. ; 1201:1, s. 51-54
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Tidskriftsartikel (refereegranskat)abstract
- The effect of 2.45 GHz microwave radiation on the permeability of unilamellar phosphatidylcholine liposomes has been studied. Leakage of 5(6)-calboxyfluorescein from the liposomes was measured using spectrofluorimetry after exposure to either microwaves or thermal heating for 5-20 min intervals. The exposure temperature, 37.6 +/- 0.5 degrees C, was well above the phase transition temperature of the lipid membrane. The microwave exposure did not result in any non-thermal increase in permeability above that produced by thermal heating. This study refutes the results reported by Saalman et al. [1] in which an increased liposome permeability due to microwave exposure was reported. The refined analysis in the present study shows that this increased liposome permeability was not a non-thermal microwave effect.
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| 27. |
- Blaszczak, Z., et al.
(författare)
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Electrooptical Kerr Effect Studies of Hemoglobin
- 1985
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Ingår i: Physical Optics of Dynamic Phenomena & Processes in Macromolecular Systems: Proceedings of the 27th Microsymposium on Macromolecules, Prague; ed. by Blahoslav Sedlacek. - 311010234X ; , s. 325-328
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 28. |
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| 29. |
- Bombelli, F. B., et al.
(författare)
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DNA Closed Nanostructures: A Structural and Monte Carlo Simulation Study
- 2008
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 112:48, s. 15283-15294
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Tidskriftsartikel (refereegranskat)abstract
- DNA nanoconstructs are obtained in solution by using six unique 42-mer DNA oligonucleotides, whose sequences have been designed to form a pseudohexagonal structure. The required flexibility is provided by the insertion of two non-base-paired thymines in the middle of each sequence that work as flexible hinges and constitute the corners of the nanostructure when formed. We show that hexagonally shaped nanostructures of about 7 nm diameter and their corresponding linear open constructs are formed by self-assembly of the specifically designed linear oligonucleotides. The structural and dynamical characterization of the nanostructure is obtained in situ for the first time by using dynamic light scattering (DLS), a noninvasive method that provides a fast dynamic and structural analysis and allows the characterization of the different synthetic DNA nanoconstructs in solution. A validation of the LS results is obtained through Monte Carlo (MC) simulations and atomic force microscopy (AFM). In particular, a mesoscale molecular model for DNA, developed by Knotts et al., is exploited to perform MC simulations and to obtain information about the conformations as well as the conformational flexibilities of these nanostructures, while AFM provides a very detailed particle analysis that yields an estimation of the particle size and size distribution. The structural features obtained by MC and AFM are in good agreement with DLS, showing that DLS is a fast and reliable tool for characterization of DNA nanostructures in solution. © 2008 American Chemical Society.
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| 30. |
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| 31. |
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| 32. |
- Bosaeus, Niklas, 1982, et al.
(författare)
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A stretched conformation of DNA with a biological role?
- 2017
-
Ingår i: Quarterly Reviews of Biophysics. - 1469-8994 .- 0033-5835. ; 50, s. UNSP e11-e11
-
Tidskriftsartikel (refereegranskat)abstract
- We have discovered a well-defined extended conformation of double-stranded DNA, which we call Sigma-DNA, using laser-tweezers force-spectroscopy experiments. At a transition force corresponding to free energy change Delta G = 1.57 +/- 0.12 kcal (mol base pair)(-1) 60 or 122 base-pair long synthetic GC-rich sequences, when pulled by the 3'-3' strands, undergo a sharp transition to the 1.52 +/- 0.04 times longer Sigma-DNA. Intriguingly, the same degree of extension is also found in DNA complexes with recombinase proteins, such as bacterial RecA and eukaryotic Rad51. Despite vital importance to all biological organisms for survival, genome maintenance and evolution, the recombination reaction is not yet understood at atomic level. We here propose that the structural distortion represented by Sigma-DNA, which is thus physically inherent to the nucleic acid, is related to how recombination proteins mediate recognition of sequence homology and execute strand exchange. Our hypothesis is that a homogeneously stretched DNA undergoes a 'disproportionation' into an inhomogeneous Sigma-form consisting of triplets of locally B-like perpendicularly stacked bases. This structure may ensure improved fidelity of base-pair recognition and promote rejection in case of mismatch during homologous recombination reaction. Because a triplet is the length of a gene codon, we speculate that the structural physics of nucleic acids may have biased the evolution of recombinase proteins to exploit triplet base stacks and also the genetic code.
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| 33. |
- Bosaeus, Niklas, 1982, et al.
(författare)
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Force-induced melting of DNA-evidence for peeling and internal melting from force spectra on short synthetic duplex sequences
- 2014
-
Ingår i: Nucleic Acids Research. - : Oxford University Press (OUP). - 0305-1048 .- 1362-4962. ; 42:12, s. 8083-8091
-
Tidskriftsartikel (refereegranskat)abstract
- Overstretching of DNA occurs at about 60-70 pN when a torsionally unconstrained double-stranded DNA molecule is stretched by its ends. During the transition, the contour length increases by up to 70% without complete strand dissociation. Three mechanisms are thought to be involved: force-induced melting into single-stranded DNA where either one or both strands carry the tension, or a B-to-S transition into a longer, still base-paired conformation. We stretch sequence-designed oligonucleotides in an effort to isolate the three processes, focusing on force-induced melting. By introducing site-specific inter-strand cross-links in one or both ends of a 64 bp AT-rich duplex we could repeatedly follow the two melting processes at 5 mM and 1 M monovalent salt. We find that when one end is sealed the AT-rich sequence undergoes peeling exhibiting hysteresis at low and high salt. When both ends are sealed the AT sequence instead undergoes internal melting. Thirdly, the peeling melting is studied in a composite oligonucleotide where the same AT-rich sequence is concatenated to a GC-rich sequence known to undergo a B-to-S transition rather than melting. The construct then first melts in the AT-rich part followed at higher forces by a B-to-S transition in the GC-part, indicating that DNA overstretching modes are additive.
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| 34. |
- Bosaeus, Niklas, 1982, et al.
(författare)
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Tension induces a base-paired overstretched DNA conformation
- 2012
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 109:38, s. 15179-15184
-
Tidskriftsartikel (refereegranskat)abstract
- Mixed-sequence DNA molecules undergo mechanical overstretching by approximately 70% at 60-70 pN. Since its initial discovery 15 y ago, a debate has arisen as to whether the molecule adopts a new form [Cluzel P, et al. (1996) Science 271: 792-794; Smith SB, Cui Y, Bustamante C (1996) Science 271: 795-799], or simply denatures under tension [van Mameren J, et al. (2009) Proc Natl Acad Sci USA 106: 18231-18236]. Here, we resolve this controversy by using optical tweezers to extend small 60-64 bp single DNA duplex molecules whose base content can be designed at will. We show that when AT content is high (70%), a force-induced denaturation of the DNA helix ensues at 62 pN that is accompanied by an extension of the molecule of approximately 70%. By contrast, GC-rich sequences (60% GC) are found to undergo a reversible overstretching transition into a distinct form that is characterized by a 51% extension and that remains base-paired. For the first time, results proving the existence of a stretched basepaired form of DNA can be presented. The extension observed in the reversible transition coincides with that produced on DNA by binding of bacterial RecA and human Rad51, pointing to its possible relevance in homologous recombination.
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| 35. |
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| 36. |
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| 37. |
- Börjesson, Karl, 1982, et al.
(författare)
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A membrane anchored DNA-based energy/electron transfer assembly
- 2008
-
Ingår i: Nucleic acids symposium series (2004). - 1746-8272. ; :52, s. 691-691
-
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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| 38. |
- Börjesson, Karl, 1982, et al.
(författare)
-
Functionalized Nanostructures: Redox-Active Porphyrin Anchors for Supramolecular DNA Assemblies
- 2010
-
Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 4:9, s. 5037-5046
-
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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| 39. |
- Börjesson, Karl, 1982, et al.
(författare)
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Membrane-Anchored DNA Assembly for Energy and Electron Transfer
- 2009
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 131:8, s. 2831-2839
-
Tidskriftsartikel (refereegranskat)abstract
- In this work we examine the trapping and conversion of visible light energy into chemical energy using a supramolecular assembly. The assembly consists of a light-absorbing antenna and a porphyrin redox center, which are covalently attached to two complementary 14-mer DNA strands, hybridized to form a double helix and anchored to a lipid membrane. The excitation energy Is finally trapped In the lipid phase of the membrane as a benzoquinone radical anion that could potentially be used In subsequent chemical reactions. In addition, In this model complex, the hydrophobic porphyrin moiety acts as an anchor into the liposome positioning the DNA construct on the lipid membrane surface. The results show the suitability of our system as a prototype for DNA-based light-harvesting devices, In which energy transfer from the aqueous phase to the interior of the lipid membrane Is followed by charge separation. © 2009 American Chemical Society.
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| 40. |
- Börjesson, Karl, 1982, et al.
(författare)
-
Soft-Surface DNA Nanotechnology: DNA Constructs Anchored and Aligned to Lipid Membrane
- 2011
-
Ingår i: Angewandte Chemie - International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 50:36, s. 8312-8315
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Tidskriftsartikel (refereegranskat)abstract
- No strings attached: At least three attachment points are needed to align a two-dimensional DNA nanoconstruct to a soft lipid membrane surface with a porphyrin nucleoside as membrane anchor (see picture). The resulting freely diffusing DNA constructs can be reversibly assembled on the surface thus enabling the possibility of a self-repairing system. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
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| 41. |
- Carlsson, Christina, 1968, et al.
(författare)
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Dancing DNA in Capillary Solution Electrophoresis
- 1995
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 117:13, s. 3871-3872
-
Tidskriftsartikel (refereegranskat)
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| 42. |
- Carlsson, Christina, 1968, et al.
(författare)
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OPTICAL AND PHOTOPHYSICAL PROPERTIES OF THE OXAZOLE YELLOW DNA PROBES YO AND YOYO
- 1994
-
Ingår i: Journal of Physical Chemistry. - : American Chemical Society (ACS). - 0022-3654 .- 1541-5740. ; 98:40, s. 10313-10321
-
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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| 43. |
- Carlsson, Christina, 1968, et al.
(författare)
-
Screening for genetic mutations
- 1996
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 380:6571, s. 207-
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 44. |
- Carlsson, Nils, 1978, et al.
(författare)
-
DNA hosted and aligned in aqueous interstitia of a lamellar liquid crystal - a membrane-biomacromolecule interaction model system
- 2013
-
Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 9:33, s. 7951-7959
-
Tidskriftsartikel (refereegranskat)abstract
- We report that DNA molecules can be intercalated and macroscopically oriented in the aqueous interstitia of a lyotropic lamellar liquid crystal. Using UV-vis linear dichroism and fluorescence spectroscopy we show that double-stranded oligonucleotides (25 base pairs) in the water-octanoate-decanol system remain base-paired in the B conformation and are confined in two dimensions, with the helix axis preferentially parallel to the lipid bilayer surfaces but free to rotate within this plane. The degree of helix confinement and the corresponding 2-D orientation can be improved by decreasing the thickness of the water interstitia via the fraction of water in the ternary mixture. Not surprisingly, the corresponding single-stranded oligonucleotides are not aligned, with their persistence length being short in comparison to the lamellar interstitium thickness. We propose this as a model system for studying interactions of DNA-ligand complexes near a lipid bilayer membrane which we demonstrate by using dye probes that are either covalently attached to one end of the oligonucleotide or reversibly bound by intercalation between the base pairs. Three cationic dyes, all strongly bound by intercalation to DNA when free in solution, are found to not bind to DNA but to prefer the membrane surface. The covalently attached Cy5 also binds to the bilayer while Cy3 tends to end-stack to the oligonucleotide duplex. The orientation of Cy5 parallel to the membrane indicates that electrostatic surface binding predominates over insertion into the hydrophobic interior of the membrane. Anionic and zwitterionic dyes (FAM and ROX) are found to remain randomly oriented in the water between the lipid bilayer surfaces. This journal is © The Royal Society of Chemistry.
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| 45. |
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| 46. |
- Chiragwandi, Zackary, 1968, et al.
(författare)
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Properties of a bio-photovoltaic nano-device
- 2008
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:48, s. 18717-18721
-
Tidskriftsartikel (refereegranskat)abstract
- Properties of an on-chip photovoltaic nanodevice are demonstrated. The dyes comprise green florescent proteins(GFP). Dependence of recently reported zero external potential bias (ZEPB) photocurrent (I) on temperature,power, and wavelength (λ) is shown. Correlation between UV-vis spectrum of the GFP and the ZEPB I(λ)of the device is reported. The temperature dependence suggests the ZEPB photocurrent to reflect a liquidcrystal type ordering where the current declines monotonically with increasing temperature. The influence ofan external bias on the photocurrent is demonstrated. The resulting light-induced current is analyzed in termsof resistive and quantum mechanical contributions.
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| 47. |
- Choi, S. D., et al.
(författare)
-
Binding Mode of [Ruthenium(II) (1,10-Phenanthroline)2L]2+ with Poly(dT*dA-dT) Triplex. Ligand Size Effect on Third-Strand Stabilization
- 1997
-
Ingår i: Biochemistry. - : American Chemical Society (ACS). - 1520-4995 .- 0006-2960. ; 36:1, s. 214-223
-
Tidskriftsartikel (refereegranskat)abstract
- The binding of homochiral [Ru(II)(1,10-phenanthroline)(2)L](2+) complexes {where L = 1,10-phenanthroline (phen), dipyrido[3,2-a:2',3'-c]phenazine (DPPZ) or benzodipyrido[3,2-a:2',3'-c]phenazine (BDPPZ)} to poly(dT*dA-dT) triplex has been investigated by linear and circular dichroism and thermal denaturation. Analysis of the linear dichroism spectra indicates that the extended DPPZ and BDPPZ ligands lie approximately parallel to the base-pair and base-tripler planes consistent with intercalation which is also supported by strong hypochromism in the interligand absorption bands with either duplex or tripler. The spectral properties of any of the metal complex enantiomers were similar for binding to either duplex or tripler DNA, indicating that the third strand, which occupies the major groove of the template duplex, has little effect on the binding geometries and hence supports the hypothesis that the metal complexes all bind from the minor groove with the DPPZ and BDPPZ ligands intercalated but without intercalation in the case of [Ru(phen)(3)](2+). Third-strand stabilization depended on the nature of the third substituted phenanthroline chelate ligand but was not directly related to its size, with stabilizing power increasing in the order phen
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| 48. |
- Coates, C. G., et al.
(författare)
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Picosecond time-resolved resonance Raman probing of the light-switch states of Ru(Phen)(2)dppz (2+)
- 2001
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 105:50, s. 12653-12664
-
Tidskriftsartikel (refereegranskat)abstract
- Picosecond time-resolved resonance Raman (picosecond-TR3) spectroscopy has been used to conduct an extensive photophysical characterization of the light- switch complex [Ru(phen)(2)dppz](2+) as a function of environment, in which studies have been carried out in aqueous and nonaqueous media and in DNA. The results are considered in rotation to a previous report describing environment-sensitive lowest triplet MLCT states. Vibrational marker features and enhancement patterns were used to determine the rapid progression (< 20 ps) between two triplet MLCT states in aqueous environment, followed by subnanosecond, nonradiative deactivation to the ground state. In nonaqueous environment, the long-lived, emissive triplet MLCT state is spectrally identified as the short-lived first triplet MLCT state observed in water, in agreement with the earlier proposed mechanism. The present data are shown to correlate well with previous nanosecond RR findings for the complex in each environment. Interestingly, a precursor state has been identified upon excitation in both nonaqueous solvent and in DNA, which precedes the triplet MLCT state, and the lifetime of which appears to be environment dependent. Observation of this state is discussed in relation to other recent femtosecond spectroscopic studies on this complex.
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| 49. |
- Colmenarejo, G., et al.
(författare)
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Electronic Spectra and Transition Moments of 6-(2’-Pyridiniumyl)phenanthridinium Photoactive DNA Intercalators
- 1997
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Ingår i: Journal of Physical Chemistry B Materials. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 101:26, s. 5196-5204
-
Tidskriftsartikel (refereegranskat)abstract
- The electronic transitions giving rise to the UV-visible absorption spectra of two pyridinium-phenanthridinium viologens, 6,7-dihydropyridol[2',1':3,4]pyrazinol[1,2-f]phenanthridinediium dication (1) and 7,8-dihydro-6H-pyrido[2',1':3,4]diazepino[1,2-f]phenanthridinediium dication (2), have been investigated with respect to energies, intensities, and transition moment directions. A combination of methods has been applied: UV-visible absorption, circular dichroism, magnetic circular dichroism, fluorescence anisotropy, Linear dichroism In stretched poly(vinyl alcohol) films, and semiempirical molecular orbital calculations. For both drugs, the lowest energy absorption band, occurring around 400 nm, results from two separate transitions. The corresponding electric transition dipole moments lie in the phenanthridine plane and are polarized, respectively, in the direction of the pyridine moiety (the lower energy transition) and parallel to the phenanthridine long axis (the higher energy transition). Up to four additional different pi --> pi* transitions account for a second band that peaks at 250 nm; they show different polarizations within the phenanthridine plane. The lowest energy transition of the whole spectrum of both drugs corresponds to the promotion of an electron from the HOMO to the LUMO, which are molecular orbitals mainly localized in the phenanthridine and pyridine rings, respectively, thereby implying a charge transfer, upon excitation, from the phenanthridine toward the pyridine ring. The experimental and theoretical results are discussed in relation to the spectroscopic, redox, and photochemical properties of these drugs.
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| 50. |
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