Kania A.,Jagiellonian University |
Pilch M.,Jagiellonian University |
Rutkowska-Zbik D.,Polish Academy of Sciences |
Susz A.,Jagiellonian University |
And 4 more authors.
High pressure in combination with optical spectroscopy was used to gain insights into the interactions between Mg2+, Zn2+, and Ni2+ ions and macrocyclic ligands of porphyrinoid type. In parallel, the central metal ion-macrocycle bonding was investigated using theoretical approaches. The symmetry properties of the orbitals participating in this bonding were analyzed, and pigment geometries and pressure/ligation effects were computed within DFT. Bacteriopheophytin a was applied as both a model chelator and a highly specific spectroscopic probe. The analysis of solvent and pressure effects on the spectral properties of the model Mg2+, Zn 2+, and Ni2+ complexes with bacteriopheophytin a shows that various chemical bonds are formed in the central pocket, depending on the valence configuration of the central metal ion. In addition, the character of this bonding depends on symmetry of the macrocyclic system. Since in most cases it is not coordinative bonding, these results challenge the conventional view of metal ion bonding in such complexes. In (labile) complexes with the main group metals, the metal ion-macrocycle interaction is mostly electrostatic. Significantly, water molecules are not preferred as a second axial ligand in such complexes, mainly due to the entropic constraints. The metal ions with a closed d shell may form (stable) complexes with the macrocycle via classical coordination bonds, engaging their p and s orbitals. Transition metals, due to the unfilled d shell, do form much more stable complexes, because of strong bonding via both coordination and covalent interactions. These conclusions are confirmed by DFT computations and theoretical considerations, which altogether provide the basis to propose a consistent and general mechanism of how the central metal ion and its interactions with the core nitrogens govern the physicochemical properties of metalloporphyrinoids. © 2014 American Chemical Society. Source
Bujak L.,Nicolaus Copernicus University |
Czechowski N.,Nicolaus Copernicus University |
Piatkowski D.,Nicolaus Copernicus University |
Litvin R.,Nicolaus Copernicus University |
And 5 more authors.
Applied Physics Letters
The influence of plasmon excitations in spherical gold nanoparticles on the optical properties of a light-harvesting complex 2 (LH2) from the purple bacteria Rhodopseudomonas palustris has been studied. Systematic analysis is facilitated by controlling the thickness of a silica layer between Au nanoparticles and LH2 complexes. Fluorescence of LH2 complexes features substantial increase when these complexes are separated by 12 nm from the gold nanoparticles. At shorter distances, non-radiative quenching leads to a decrease of fluorescence emission. The enhancement of fluorescence originates predominantly from an increase of absorption of pigments comprising the LH2 complex. © 2011 American Institute of Physics. Source
Brotosudarmo T.H.P.,University of Glasgow |
Brotosudarmo T.H.P.,Ma Chung University |
Collins A.M.,Washington University in St. Louis |
Collins A.M.,Sandia National Laboratories |
And 5 more authors.
The differing composition of LH2 (peripheral light-harvesting) complexes present in Rhodopseudomonas palustris 2.1.6 have been investigated when cells are grown under progressively decreasing light intensity. Detailed analysis of their absorption spectra reveals that there must be more than two types of LH2 complexes present. Purified HL (high-light) and LL (low-light) LH2 complexes have mixed apoprotein compositions. The HL complexes contain PucAB a and PucAB b apoproteins. The LL complexes contain PucAB a, PucAB dand PucB b-only apoproteins. This mixed apoprotein composition can explain their resonance Raman spectra. Crystallographic studies and molecular sieve chromatography suggest that both the HL and the LL complexes are nonameric. Furthermore, the electron-density maps do not support the existence of an additional Bchl (bacteriochlorophyll) molecule; rather the density is attributed to the N-termini of the α-polypeptide. © The Authors Journal compilation © 2011 Biochemical Society. Source
Fiedor L.,Jagiellonian University |
Heriyanto,Jagiellonian University |
Heriyanto,Ma Chung University |
Fiedor J.,Jagiellonian University |
And 2 more authors.
Journal of Physical Chemistry Letters
The aim of this work is the verification of symmetry effects on the electronic absorption spectra of carotenoids. The symmetry breaking in cis-β-carotenes and in carotenoids with nonlinear π-electron system is of virtually no effect on the dark transitions in these pigments, in spite of the loss of the inversion center and evident changes in their electronic structure. In the cis isomers, the S2 state couples with the higher excited states and the extent of this coupling depends on the position of the cis bend. A confrontation of symmetry properties of carotenoids with their electronic absorption and IR and Raman spectra shows that they belong to the C1 or C2 but not the C2h symmetry group, as commonly assumed. In these realistic symmetries all the electronic transitions are symmetry-allowed and the absence of some transitions, such as the dark S0 → S1 transition, must have another physical origin. Most likely it is a severe deformation of the carotenoid molecule in the S1 state, unachievable directly from the ground state, which means that the Franck-Condon factors for a vertical S0 → S1 transition are negligible because the final state is massively displaced along the vibrational coordinates. The implications of our findings have an impact on the understanding of the photophysics and functioning of carotenoids. © 2016 American Chemical Society. Source
Swastika W.,Ma Chung University |
Haneishi H.,Chiba University
The use of circulant matrix as the sensing matrix in compressed sensing (CS) scheme has recently been proposed to overcome the limitation of random or partial Fourier matrices. Aside from reducing computational complexity, the use of circulant matrix for magnetic resonance (MR) image offers the feasibility in hardware implementations. This paper presents the simulation of compressed sensing for thoracic MR imaging with circulant matrix as the sensing matrix. The comparisons of reconstruction of three different type MR images using circulant matrix are investigated in term of number of samples, number of iteration and signal to noise ratio (SNR). The simulation results showed that circulant matrix works efficiently for encoding the MR image of respiratory organ, especially for smooth and sparse image in spatial domain. © 2012 Universitas Ahmad Dahlan. Source