| 1. |
- Holm, Anne Ivalu Sander, et al.
(författare)
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Vacuum-ultraviolet circular dichroism spectroscopy of DNA : a valuable tool to elucidate topology and electronic coupling in DNA
- 2010
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 12:33, s. 9581-9596
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Tidskriftsartikel (refereegranskat)abstract
- Circular dichroism (CD) is a powerful technique to obtain information on electronic transitions and has been used extensively for studies on DNA. Most experiments are done in the UV region but new information is often revealed from extending the wavelength region down into the vacuum ultraviolet (VUV) region. Such experiments are most easily carried out with synchrotron radiation (SR) light sources that provide large photon fluxes. Here we provide a summary of the SRCD data taken on different DNA strands with emphasis on results from our own laboratory within the last five years.(1-3) Signal intensities in the VUV are often significantly larger than those in the UV, and the electronic coupling between bases may increase with excitation energy. CD spectroscopy is particularly useful for investigating the extent of electronic coupling within a strand, i.e., the degree of delocalisation of the excited-state electronic wavefunction. The spatial extent of the wavefunction may be limited to just one base or it extends over two or more bases in a stack or between bases on different strands.(4,5) The actual character of the electronically excited state is linked to base composition and sequence as well as DNA folding motif (A-, B-, Z-DNA, triplexes, quadruplexes, etc.). The latter depends on experimental conditions such as solution acidity, temperature, ionic strength, and solvent.
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| 2. |
- Nielsen, Lisbeth Munksgaard, et al.
(författare)
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Effect of introducing thymine spacers into an adenine strand : Electronic decoupling?
- 2011
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Ingår i: Journal of Photochemistry and Photobiology A. - : Elsevier BV. - 1010-6030 .- 1873-2666. ; 220:1, s. 1-3
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Tidskriftsartikel (refereegranskat)abstract
- Electronic coupling between DNA bases governs the deexcitation pathways after light absorption as well as the ability of the DNA strand to conduct charge. UV excitation of single strands of adenine bases involves two adjacent bases while the spatial extent of the excited state wavefunction following VUV excitation is over eight bases. In this work, we have recorded synchrotron radiation circular dichroism spectra for a series of DNA strands on the form A(n)T(m)A(n), n = 1-5 and m = 1-3, in aqueous solution to study the effect of introducing thymine spacers on the electronic coupling between the adenines. We find that a single thymine spacer is enough to eliminate the strong coupling between the adenine bases for all excitation wavelengths between 175 nm and 330 nm.
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| 3. |
- Kjaer, Christina, et al.
(författare)
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Circular dichroism, anisotropy and absorption spectroscopy of chlorophyll b in methanol and mixed methanol-water solutions
- 2020
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 22:46, s. 26961-26966
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Tidskriftsartikel (refereegranskat)abstract
- The spectroscopic properties of chlorophyll (Chl) strongly depend on interactions with other Chl molecules, a fact that nature exploits in light harvesting by photosynthetic proteins. In solution, complex Chl aggregates are formed that depend not only on the solvent, but also on the detailed preparation procedure. Here we report synchrotron radiation circular dichroism (SRCD) spectra of Chlb in methanol (MeOH) and MeOH/H2O mixtures; in the latter, water molecules assist in the formation of Chl aggregates as Chlb is too hydrophobic to dissolve in water. The magnitude of the most prominent CD signal increases up to 100-fold over time (2-15 hours) when the water content is increased from 0 to 50% in volume, the signal is non-conservative (almost exclusively negative), and sensitive to sample preparation. Three different types of signature CD spectra (Types A to C) are identified depending on preparation, and the change in CD signal over time and with temperature is further analyzed with anisotropy spectroscopy (ratio of simultaneously recorded CD to absorption) and principal component analysis (PCA). We show that CD is clearly superior to pure absorption spectroscopy in identifying structural changes, and anisotropy spectroscopy further increases the sensitivity towards smaller structural changes. PCA on temperature dependent CD data show that depending on preparation, and thus the type of aggregate as revealed by the CD signature, either one (Type A) or two chiral species (Type B) are identified in the spectra, further evidencing the complex nature of Chlb aggregates. Furthermore, the CD signal decreases linearly with volume when a sample of Chlb in MeOH/H2O (i.e., a sample of Chlb aggregates) is diluted, which implies that the aggregation process is irreversible: once aggregates are formed, they largely do not revert back to monomers. However, anisotropy spectroscopy reveals that there are small changes in the aggregates, not directly noticeable in CD and absorption. The work presented here demonstrates, compared to absorption spectroscopy, a clear advantage of CD and anisotropy spectroscopy in studying the complex evolution of Chl samples with time and temperature.
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| 4. |
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| 5. |
- Wierup, Per, et al.
(författare)
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Moderate mitral regurgitation in patients undergoing CABG--the MoMIC trial.
- 2009
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Ingår i: Scandinavian cardiovascular journal. - : Informa UK Limited. - 1651-2006 .- 1401-7431. ; 43:1, s. 50-6
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The presence of mild to moderate ischemic mitral regurgitation (IMR) marks a significantly reduced long-term survival and increased hospitalizations due to heart-failure. However, it is common practice in many institutions to refrain from repairing the mitral valve in these patients. There are no available conclusive data to support this practice, and thus there is a need for an adequately powered randomized trial. STUDY DESIGN: The Moderate Mitral Regurgitation In Patients Undergoing CABG (MoMIC) trial is the first international multi-center, large-scale study to clarify whether moderate IMR in CABG patients should be corrected. A total of 550 CABG patients with moderate IMR are to be randomized to treatment of either CABG alone or CABG plus mitral valve correction. The primary end point is a composite end point of mortality and rehospitalization for heart failure at five years. The inclusion and randomization of patients started in February 2008. IMPLICATION: If correction of moderate IMR in CABG patients proves to be the superior strategy, most patients should be treated accordingly.
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