| 1. |
- 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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| 2. |
- Börjesson, Karl, 1982, et al.
(författare)
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Membrane-Anchored DNA Assembly for Energy and Electron Transfer
- 2009
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 131:8, s. 2831-2839
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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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| 3. |
- Sandin, Peter, 1977, et al.
(författare)
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Highly efficient incorporation of the fluorescent nucleotide analogs tC and tC(O) by Klenow fragment
- 2009
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Ingår i: Nucleic Acids Research. - : Oxford University Press (OUP). - 0305-1048 .- 1362-4962. ; 37:12, s. 3924-3933
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Tidskriftsartikel (refereegranskat)abstract
- Studies of the mechanisms by which DNA polymerases select the correct nucleotide frequently employ fluorescently labeled DNA to monitor conformational rearrangements of the polymerase-DNA complex in response to incoming nucleotides. For this purpose, fluorescent base analogs play an increasingly important role because they interfere less with the DNA-protein interaction than do tethered fluorophores. Here we report the incorporation of the 5'-triphosphates of two exceptionally bright cytosine analogs, 1,3-diaza-2-oxo-phenothiazine (tC) and its oxo-homolog, 1,3-diaza-2-oxo-phenoxazine (tC(O)), into DNA by the Klenow fragment. Both nucleotide analogs are polymerized with slightly higher efficiency opposite guanine than cytosine triphosphate and are shown to bind with nanomolar affinity to the DNA polymerase active site, according to fluorescence anisotropy measurements. Using this method, we perform competitive binding experiments and show that they can be used to determine the dissociation constant of any given natural or unnatural nucleotide. The results demonstrate that the active site of the Klenow fragment is flexible enough to tolerate base pairs that are size-expanded in the major groove. In addition, the possibility to enzymatically polymerize a fluorescent nucleotide with high efficiency complements the tool box of biophysical probes available to study DNA replication.
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| 4. |
- Andreasson, Joakim, 1973, et al.
(författare)
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Photoinduced hole transfer from the triplet state in a porphyrin-based donor-bridge-acceptor system
- 2003
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 107:42, s. 8825-8833
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Tidskriftsartikel (refereegranskat)abstract
- The triplet excited-state deactivation of a gold porphyrin (AuP) in porphyrin-based donor-bridge-acceptor (D-B-A) systems has been studied. The results from room temperature and 80 K measurements are presented. The primary objectives have been to investigate whether electrons/electron holes or excitation energy could be transferred from (AuP)-Au-3 to the appended zinc porphyrin (ZnP) in the dimers. As the bridging chromophores in our D-B-A systems separate the ZnP and AuP moieties by 19 A edge-to-edge, we do not expect a significant contribution to either electron or energy transfer from a direct (through space) exchange mechanism. This gives us the opportunity to scrutinize how the bridging chromophores influence the transfer reactions. The results show that quenching of (AuP)-Au-3 occurs with high efficiency in the dimers that are connected by fully conjugated bridging chromophores, whereas no quenching is observed when the conjugation of the bridge is broken. We also observed that the decay of (AuP)-Au-3 is complex at temperatures below 110 K. In addition to the two previously published lifetimes on the order of some 10-100 mus, we have found a third lifetime on the nanosecond time scale.
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| 5. |
- 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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| 6. |
- Eng, Mattias P, 1977, et al.
(författare)
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Triplet excitation energy transfer in porphyrin-based donor-bridge-acceptor systems with conjugated bridges of varying length: An experimental and DFT study
- 2006
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 110:13, s. 6483-6491
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Tidskriftsartikel (refereegranskat)abstract
- A series of donor-bridge-acceptor (D-B-A) systems with varying donor-acceptor distances have been studied with respect to their triplet energy transfer properties. The donor and acceptor moieties, zinc(II), and free-base porphyrin, respectively, were separated by 2-5 oligo-p-phenyleneethynylene units (OPE) giving rise to edge-to-edge separations ranging between 12.7 and 33.4 angstrom. The study was performed in 2-MTHF at 150 K and it was established that triplet excitation energy transfer occurs with high efficiency in all of the studied D-B-A systems. The distance dependence was exponential with an attenuation factor, beta, equal to 0.45 +/- 0.015 angstrom(-1). The experimental study was also supported by quantum mechanical DFT and TD-DFT calculations on a series of closely related model systems. A thorough analysis of the OPE-bridge conformational dynamics led to an equation that quantitatively models the distance dependence of the electronic coupling found in the experimental study.
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| 7. |
- Eng, Mattias P, 1977, et al.
(författare)
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Triplet photophysics of gold(III) porphyrins
- 2005
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 109:9, s. 1776-1784
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Tidskriftsartikel (refereegranskat)abstract
- Gold porphyrins are often used as electron-accepting chromophores in donor-acceptor complexes for the study of photoinduced electron transfer, and they can also be involved in triplet-triplet energy-transfer interactions with other chromophores. Since the lowest excited singlet state is very short-lived (240 fs), the triplet state is usually the starting point for the transfer reactions, and it is therefore crucial to understand its photophysics. The triplet state of various gold porphyrins has been reported to have a lifetime of around 1.5 ns at room temperature and to have a biexponential decay both in emission and in transient absorption with decay times of around 10 and 100,us at 80 K. In this paper, the triplet photophysics of two gold porphyrins (Au-III 5,15-bis(3,5-di-tert-butylphenyl)-2,8,12,18-tetraethyl-3,7,13,17-tetrame thylporphyrin and Au-III 5,10,15,20-tetra(3,5-di-tert-butylphenyl)porphyrin) are studied by steady-state and time-resolved absorption and emission spectroscopy over a wide temperature range (4-300 K). The study reveals the existence of a dark state with an approximate lifetime of 50 ns, which was not previously observed. This state acts as an intermediate between the short-lived singlet and the triplet state manifold. In addition, we present DFT calculations, in which the core electrons of the central metal were replaced by a pseudopotential to account for the relativistic effects, which suggest that the lowest excited singlet state is an optically forbidden ligand-to-metal charge-transfer (LMCT) state. This LMCT state is an obvious candidate for the experimentally observed dark state, and it is shown to dictate the photophysical properties of gold porphyrins by acting as a gate for triplet state formation versus direct return to the ground state.
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| 8. |
- Ljungdahl, Thomas, 1974, et al.
(författare)
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Geometrically homogeneous series of covalently linked zinc/free-base porphyrin dimers of varying length; design, synthesis and characterization
- 2006
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Ingår i: European Journal of Organic Chemistry. - : Wiley. - 1099-0690 .- 1434-193X. ; :14, s. 3087-3096
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Tidskriftsartikel (refereegranskat)abstract
- Singlet excitation energy transfer, SEET, can be mediated by a bridge, connecting an energy donor and acceptor, via a superexchange mechanism. The mediation efficiency depends on the energy difference between the first excited states of the donor and the bridge, DEDB, as well as the donor-acceptor distance, RDA. We have previously constructed a series of donor-bridge-acceptor, D-B-A, systems that allowed us to study how SEET depends on DEDB. To expand this study into a second dimension, the distance dependence, a new series of D-B-A systems were constructed. This series was based on the same zinc/free-base porphyrin couple as the donor-acceptor pair in the previous series. Their relative orientation was also retained. In contrast to our first series, the bridges in the latter were of varying length. The bridges were oligo(phenyleneethynylene)phenylene (OPE) structures and the length was systematically changed by increasing the no. of phenyleneethynylene units from 1 to 4. To obtain high quality samples, the D-B-A systems were assembled by a building block approach where the zinc and free-base porphyrins were introduced sep. using Heck alkynylations. The performance of the OPE structure as a mediator and scaffold is discussed in terms of singlet excited state energies and flexibility. For the first time, when combining the topical D-B-A systems with our previous subset, a homogeneous series of D-B-A systems has been synthesized that allows for studies of both the distance dependence and the energy difference dependence of SEET.
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| 9. |
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| 10. |
- Ljungdahl, Thomas, 1974, et al.
(författare)
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Positional Scanning Peptide Libraries for Kinase Substrate Specificity Determinations: Straightforward and Reproducible Synthesis Using Pentafluorophenyl Esters.
- 2010
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Ingår i: Journal of combinatorial chemistry. - : American Chemical Society (ACS). - 1520-4774 .- 1520-4766. ; 12:5, s. 733-742
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Tidskriftsartikel (refereegranskat)abstract
- An efficient method to synthesize positional scanning synthetic combinatorial libraries (PS-SCLs) for studying the specificity of protein kinases is presented. Isokinetic ratios for pentafluorophenyl esters were determined iteratively using a new approach incorporating high performance liquid chromatography (HPLC) quantification and statistical experimental design. In the development process a large amount of work was put in to find efficient ways of screening for new isokinetic mixtures and to optimize the process of PS-SCL synthesis. The newly developed methods for the screening of isokinetic mixtures could be used for the screening of other interesting mixtures, but more importantly, the isokinetic ratios determined for the preactivated pentafluorophenyl esters were incorporated into a new efficient protocol. This straightforward protocol allows for a convenient synthesis of high quality PS-SCLs regardless of previous experience in solid phase synthesis.
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