Elmars Krausz

University of Sydney, Sydney, New South Wales, Australia

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Publications (162)339.33 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Visible/UV absorption in PS II core complexes is dominated by the chl-a absorptions, which extend to ~ 700 nm. A broad 700–730 nm PS II core complex absorption in spinach has been assigned [1] to a charge transfer excitation between ChlD1 and ChlD2. Emission from this state, which peaks at 780 nm, has been seen [2] for both plant and cyanobacterial samples. We show that Thermosynechococcus vulcanus PS II core complexes have parallel absorbance in the 700–730 nm region and similar photochemical behaviour to that seen in spinach. This establishes the low energy charge transfer state as intrinsic to the native PS II reaction centre. High-sensitivity MCD measurements made in the 700–1700 nm region reveal additional electronic excitations at ~ 770 nm and ~ 1550 nm. The temperature and field dependence of MCD spectra establish that the system peaking near 1550 nm is a heme-to-Fe(III) charge transfer excitation. These transitions have not previously been observed for cyt b559 or cyt c550. The distinctive characteristics of the MCD signals seen at 770 nm allow us to assign absorption in this region to a dz2 → dx2 − y2 transition of Mn(III) in the Ca-Mn4O5 cluster of the oxygen evolving centre. Current measurements were performed in the S1 state. Detailed analyses of this spectral region, especially in higher S states, promise to provide a new window on models of water oxidation.
    Biochimica et Biophysica Acta (BBA) - Bioenergetics. 11/2014;
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    ABSTRACT: Oxidation of some manganese complexes containing both carboxylate and water/hydroxo ligands does not result in changes to the carboxylate stretching frequencies. The Water Oxidising Complex of photosystem II is one motivating example. Based on electronic structure theory calculations, we here suggest that the deprotonation of water or hydroxo ligands minimises changes in the vibrational frequencies of co-ligating carboxylates, rendering the carboxylate modes "invisible" in FTIR difference spectroscopy. This deprotonation of water/hydroxo ligands was also found to balance the redox potentials of the Mn(II)/Mn(III) and Mn(III)/Mn(IV) couples, allowing the possibility for successive manganese oxidations at a relatively constant redox potential.
    The Journal of Physical Chemistry B 03/2014; · 3.61 Impact Factor
  • Biochimica et Biophysica Acta (BBA) - Bioenergetics 01/2014; 1837(1):167-177. · 4.62 Impact Factor
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    ABSTRACT: Simultaneously measured absorption (ABS) and magnetic circular dichroism (MCD) spectra of the Q-bands of chlorophyll-a (Chl-a) in ether over 150-186 K reveal that the species that forms at low temperature is a chlorophyll hydrate rather than a diether complex. We have recently proposed a new assignment paradigm for the spectra of chlorophillides which, for the first time, quantitatively accounts for a wide range of observed data. Observations performed at low temperature in ether have historically been very important for the interpretation of the spectra of Chl-a. While our assignment for this system initially anticipated only small spectral changes as the temperature is lowered, significant changes are known to occur. Extensive CAM-B3LYP time-dependent density-functional theory (TD-DFT) calculations verify that the observed spectra of the hydrated species conforms to expectations based on our new assignment, as well as supporting the feasibility of the proposed hydration reactions.
    Physical Chemistry Chemical Physics 12/2013; · 4.20 Impact Factor
  • Jeffrey R Reimers, Elmars Krausz
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    ABSTRACT: A simple procedure is developed enabling the analytical inversion of an (unpolarized) absorption spectrum combined with a Magnetic Circular Dichroism (MCD) spectrum to resolve two overlapping bands of orthogonal polarization. This method is appropriate when (i) the overlapping transitions are well isolated from other bands, and (ii) when their electronic spacing is large enough so that the "A-term" and "C-term" contributions to the MCD spectrum can be ignored and hence only the "B-term" contribution need be considered. We apply this procedure to assign the Q-band system of chlorophylls, though similar challenges also commonly arise throughout both conventional and X-ray MCD (XMCD) spectroscopy. Analytical data inversion has not previously been possible as the inversion process is two-fold underdetermined. We show that the assumptions of isolated spectra and "B-term" dominance yields one generally valid constraint, leaving only one quantity unspecified by the experimental data. For some systems, an approximation leading to equal but opposite sign B-term magnitudes of the two components may be reasonable, but for chlorophyllides we find this constraint to be inappropriate. Instead, we constrain a bounded variable controlling the relative absorption strengths. Derived spectral bandshapes of the individual components are shown to be insensitive to its particular value, allowing weak spectral components of one polarization overlapped by intense components of the other to be immediately exposed. This is demonstrated for the chlorophylls, molecules for which the failure to detect such weak features historically led to incorrect proposals for the Q-band assignments.
    Physical Chemistry Chemical Physics 12/2013; · 4.20 Impact Factor
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    ABSTRACT: Routinely prepared PS II core samples are often contaminated by a significant (~1-5%) fraction of PS I, as well as related proteins. This contamination is of little importance in many experiments, but masks the optical behavior of the deep red state in PS II, which absorbs in the same spectral range (700-730nm) as PS I (Hughes et al. 2006). When contamination levels are less than ~1%, it becomes difficult to quantify the PS I related components by gel-based, chromatographic, circular dichroism or EPR techniques. We have developed a fluorescence-based technique, taking advantage of the distinctively different low-temperature emission characteristics of PS II and PS I when excited near 700nm. The approach has the advantage of providing the relative concentration of the two photosystems in a single spectral measurement. A sensitivity limit of 0.01 % PS I (or better) can be achieved. The procedure is applied to PS II core preparations from Spinach and T. vulcanus. Measurements made of T. vulcanus PS II preparations prepared by re-dissolving crystalized material, indicate a low but measurable PS I related content. The analysis provides strong evidence for a previously unreported fluorescence of PS II cores peaking near 780nm. The excitation dependence of this emission as well as its appearance in both low PS I cyanobacterial and plant based PS II core preparations suggests its association with the deep red state of PS II.
    Biochimica et Biophysica Acta 09/2013; · 4.66 Impact Factor
  • Elmars Krausz
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    ABSTRACT: Photosynthetic pigments are inherently intense optical absorbers and have strong polarisation characteristics. They can also luminesce strongly. These properties have led optical spectroscopies to be, quite naturally, key techniques in photosynthesis. However, there are typically many pigments in a photosynthetic assembly, which when combined with the very significant inhomogeneous and homogeneous linewidths characteristic of optical transitions, leads to spectral congestion. This in turn has made it difficult to provide a definitive and detailed electronic structure for many photosynthetic assemblies. An electronic structure is, however, necessary to provide a foundation for any complete description of fundamental processes in photosynthesis, particularly those in reaction centres. A wide range of selective and differential spectral techniques have been developed to help overcome the problems of spectral complexity and congestion. The techniques can serve to either reduce spectral linewidths and/or extract chromophore specific information from unresolved spectral features. Complementary spectral datasets, generated by a number of techniques, may then be combined in a 'multi-dimensional' theoretical analysis so as to constrain and define effective models of photosynthetic assemblies and their fundamental processes. A key example is the work of Renger and his group (Raszewski, Biophys J 88(2):986-998, 2005) on PS II reaction centre assemblies. This article looks to provide an overview of some of these techniques and indicate where their strengths and weaknesses may lie. It highlights some of our own contributions and indicates areas where progress may be possible.
    Photosynthesis Research 07/2013; · 3.15 Impact Factor
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    ABSTRACT: We provide a new and definitive spectral assignment for the absorption, emission, high-resolution fluorescence excitation, linear dichroism, and/or magnetic circular dichroism spectra of 32 chlorophyllides in various environments. This encompases all data used to justify previous assignments and provides a simple interpretation of unexplained complex decoherence phenomena associated with Qx → Qy relaxation. Whilst most chlorophylls conform to the Gouterman model and display two independent transitions Qx (S2) and Qy (S1), strong vibronic coupling inseparably mixes these states in chlorophyll-a. This spreads x-polarized absorption intensity over the entire Q-band system to influence all exciton-transport, relaxation and coherence properties of chlorophyll-based photosystems. The fraction of the total absorption intensity attributed to Qx ranges between 7% and 33%, depending on chlorophyllide and coordination, and is between 10% and 25% for chlorophyll-a. CAM-B3LYP density-functional-theory calculations of the band origins, relative intensities, vibrational Huang-Rhys factors, and vibronic coupling strengths fully support this new assignment.
    Scientific Reports 01/2013; 3:2761. · 5.08 Impact Factor
  • Joseph L. Hughes, Elmars Krausz
    ChemInform 10/2012; 43(42).
  • M. J. Riley, J. Hall, E. R. Krausz
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    ABSTRACT: Magnetic circular dichroism and magnetic linear dichroism spectroscopy have been used to study the near infrared (3)A(2g) -> T-3(2g) transition of Ni(II) doped MgO. Two sharp electronic origins are observed and it is show that their polarisation behaviour follows that expected from calculations in detail for magnetic dipole allowed transitions in octahedral symmetry. Not all transitions to the spin-orbit components of the T-3(2g) state are observed. We put forward an explanation for why some components are missing, even though they are expected to be of comparable intensity, in terms of the different coupling to the Jahn-Teller active tetragonal distortion in the excited state. The two lower energy spin-orbit split components are nearly independent of this distortion, while the two higher energy components are strongly dependent. We also examine the double quantum transition in the electron paramagnetic resonance spectrum and estimate the magnitude of the random strain of tetragonal symmetry in the MgO lattice.
    Australian Journal of Chemistry 01/2012; 65(9):1298-1304. · 1.87 Impact Factor
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    ABSTRACT: Co(2+)-doped CdSe colloidal nanowires with tunable size and dopant concentration have been prepared by a solution-liquid-solid (SLS) approach for the first time. These doped nanowires exhibit anomalous photoluminescence temperature dependence in comparison with undoped nanowires.
    Chemical Communications 11/2011; 47(43):11894-6. · 6.38 Impact Factor
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  • 01/2011;
  • A. K. Dick, M. J. Riley, E. R. Krausz, G. Schenk
  • 01/2011;
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    ABSTRACT: We re-visit the phenomenon of persistent spectral hole-burning (PSHB) in isolated PS II reaction centers in light of advances in the understanding of the overall electronic structure of PS II. A recent analysis of non-selective photochemical hole-burning and the consequent changes in CD spectra associated with the photo-reduction of PheoD1 (the primary electron acceptor) supports an analysis in which very substantial and non-correlated chlorin site-energy inhomogeneity leads to a range of realizations of the exciton structure of reaction centers. The lowest energy excited state can be described as predominantly involving the dominantly ChlD1 (the primary acceptor) exciton, but in a significant fraction of centers the lowest excited state is a dominantly PheoD2 (the inactive pheophytin) exciton. The narrow linewidth of PSHB reported a decade ago in these systems, with homogeneous holewidths approaching that corresponding to the radiative lifetime, along with our ability to reproduce the published PSHB action spectrum, leads to the suggestion that aspects of hole-burning in these systems can be attributed to centers in which the exciton realizations lead to a predominantly PheoD2 character as the lowest energy exciton. This assignment is discussed in terms of models of the PS II reaction center.
    Physics Procedia 02/2010; 3(4):1601-1605.
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    ABSTRACT: We used non-photochemical persistent spectral hole-burning at 1.4 K to investigate the Qy(1,0) vibrational structure of Chl a in a water-soluble chlorophyll-binding protein (WSCP) which exhibits resolved structure in its broadband optical spectra. FranckCondon vibrational overlap factors were determined from the vibrational hole-burning data and used to simulate the Qy(1,0) spectra. The simulations were not able to accurately reproduce the details of the Qy(1,0) spectrum. This indicates a breakdown of the approximations used for the analysis and demonstrates that vibrationally induced mixing of electronic states (vibronic coupling) is active for Chl a. By considering the inhomogeneous broadening and vibrational hole-burning phenomena in the Qx and Qy(1,0) region of Chl-WSCP in addition to magnetic circular dichroism data, we favor the traditional placement of Qx at λ∼570–590 nm rather than the alternate assignment underneath the Qy(1,0) absorption near λ∼615–630 nm.
    Physics Procedia. 01/2010; 3(4):1591-1599.
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    ABSTRACT: The semiquinone-iron complex of photosystem II was studied using electron spin resonance (ESR) spectroscopy and density functional theory calculations. Two forms of the signal were investigated: 1), the native g approximately 1.9 form; and 2), the g approximately 1.84 form, which is well known in purple bacterial reaction centers and occurs in photosystem II when treated with formate. The g approximately 1.9 form shows low- and high-field edges at g approximately 3.5 and g < 0.8, respectively, and resembles the g approximately 1.84 form in terms of shape and width. Both types of ESR signal were simulated using the theoretical approach used previously for the BRC complex, a spin Hamiltonian formalism in which the semiquinone radical magnetically interacts (J approximately 1 cm(-1)) with the nearby high-spin Fe(2+). The two forms of ESR signal differ mainly by an axis rotation of the exchange coupling tensor (J) relative to the zero-field tensor (D) and a small increase in the zero-field parameter D ( approximately 6 cm(-1)). Density functional theory calculations were conducted on model semiquinone-iron systems to identify the physical nature of these changes. The replacement of formate (or glutamate in the bacterial reaction centers) by bicarbonate did not result in changes in the coupling environment. However, when carbonate (CO(3)(2-)) was used instead of bicarbonate, the exchange and zero-field tensors did show changes that matched those obtained from the spectral simulations. This indicates that 1), the doubly charged carbonate ion is responsible for the g approximately 1.9 form of the semiquinone-iron signal; and 2), carbonate, rather than bicarbonate, is the ligand to the iron.
    Biophysical Journal 10/2009; 97(7):2024-33. · 3.67 Impact Factor
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    ABSTRACT: Low-temperature absorption and CD spectra, measured simultaneously, are reported from Photosystem II (PS II) reduced with sodium dithionite. Spectra were obtained using PS II core complexes before and after photoaccumulation of Pheo(D1)(-), the anion of the primary acceptor. For plant PS II, Pheo(D1)(-) was generated under conditions in which the primary plastoquinone was present as an anion (Q(A)(-)) and as a modified species taken to be the neutral doubly reduced hydroquinone (Q(A)H(2)). The bleaches observed upon Pheo(D1)(-) formation in the presence of Q(A)(-) are shifted to the blue compared those in the presence of Q(A)H(2). This is attributed to the influence of the charge on Q(A)(-), and this effect mirrors the well-known electrochromic effect of Q(A)(-) on the neutral pigments. The absorption bleaches induced by Pheo(D1) reduction are species dependent. Structured changes of the CD in the 680-690 nm spectral region are seen upon photoaccumulation of Pheo(D1)(-) in PS II from plant, Synechocystis and Thermosynechococcus vulcanus. These CD changes are shown to be consistent with the overall electronic assignments of Raszewski et al. [Raszewski et al. Biophys. J. 2008, 95, 105], which place the dominant Pheo(D1) excitation near 672 nm. CD changes associated with Pheo(D1) reduction are modeled to arise from the shift and intensity changes of two CD features: one predominately of Chl(D1) character, the other predominately Pheo(D2) in character. The assignments are also shown to account for the Q(Y) absorption changes in samples where the quinone is its charged (Q(A)(-)) and neutral (Q(A)H(2)) states.
    The Journal of Physical Chemistry B 09/2009; 113(36):12364-74. · 3.61 Impact Factor
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    ABSTRACT: In Photosystem II (PSII) from Thermosynechococcus elongatus, high-light intensity growth conditions induce the preferential expression of the psbA(3) gene over the psbA(1) gene. These genes encode for the D1 protein variants labeled D1:3 and D1:1, respectively. We have compared steady state absorption and photo-induced difference spectra at <10 K of PSII containing either D1:1 or D1:3. The following differences were observed. (i) The pheophytin Q(x) band was red-shifted in D1:3 (547.3 nm) compared to D1:1 (544.3 nm). (ii) The electrochromism on the Pheo(D1) Q(x) band induced by Q(A)(-) (the C550 shift) was more asymmetric in D1:3. (iii) The two variants differed in their responses to excitation with far red (704 nm) light. When green light was used there was little difference between the two variants. With far red light the stable (t(1/2)>50 ms) Q(A)(-) yield was approximately 95% in D1:3, and approximately 60% in D1:1, relative to green light excitation. (iv) For the D1:1 variant, the quantum efficiency of photo-induced oxidation of side-pathway donors was lower. These effects can be correlated with amino acid changes between the two D1 variants. The effects on the pheophytin Q(x) band can be attributed to the hydrogen bond from Glu130 in D1:3 to the 13(1)-keto of Pheo(D1), which is absent for Gln130 in D1:1. The reduced yield with red light in the D1:1 variant could be associated with either the Glu130Gln change, and/or the four changes near the binding site of P(D1), in particular Ser153Ala. Photo-induced Q(A)(-) formation with far red light is assigned to the direct optical excitation of a weakly absorbing charge transfer state of the reaction centre. We suggest that this state is blue-shifted in the D1:1 variant. A reduced efficiency for the oxidation of side-pathway donors in the D1:1 variant could be explained by a variation in the location and/or redox potential of P+.
    Biochimica et Biophysica Acta 07/2009; 1797(1):11-9. · 4.66 Impact Factor

Publication Stats

582 Citations
339.33 Total Impact Points


  • 2013
    • University of Sydney
      • School of Chemistry
      Sydney, New South Wales, Australia
  • 1982–2013
    • Australian National University
      • Research School of Chemistry
      Canberra, Australian Capital Territory, Australia
  • 2001–2009
    • University of Queensland 
      • School of Chemistry and Molecular Biosciences
      Brisbane, Queensland, Australia
  • 2005
    • Deakin University
      • Department of Biological Sciences
      Geelong, Victoria, Australia
  • 2004
    • Lund University
      Lund, Skåne, Sweden
  • 2000
    • Australian Defence Force Academy
      Canberra, Australian Capital Territory, Australia
  • 1993
    • University of Canberra
      Canberra, Australian Capital Territory, Australia
  • 1989–1990
    • Chiba University
      • Department of Physics
      Chiba-shi, Chiba-ken, Japan