| 1. |
- Chen, C. N., et al.
(författare)
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Aggregate manganese Schiff base moieties by terephthalate or acetate : Dinuclear manganese and trinuclear mixed metal Mn-2/Na complexes
- 2003
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 42:11, s. 3540-3548
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Tidskriftsartikel (refereegranskat)abstract
- A reaction system consisting of terephthalic acid, NaOH, inorganic Mn(II) or Mn(III) salt, and salicylidene alkylimine resulted in dinuclear manganese complexes (salpn)(2)Mn-2(mu-phth)(CH3OH)(2) (1, salpn = N,N'-1,3-propylene-bis(salicylideneiminato); phth = terephthalate dianion), (salen)(2)Mn-2(mu-phth)(CH3OH)(2) (2, salen = N,N'-ethylene-bis(salicylideneiminato)), (salen)(2)Mn-2(mu-phth)(CH3OH)(H2O) (3), and (salen)(2)Mn-2(mu-phth) (4), while the absence of NaOH in the reaction led to a mononuclear Mn complex (salph)Mn(CH3OH)(NO3) (5, salph = N,N'-1,2-phenylene-bis(salicylideneiminato)). In addition, a trinuclear mixed metal complex H{Mn2Na(salpn)(2)(mu-OAc)(2)(H2O)(2)}(OAc)(2) (6) was obtained from the reaction system by using maleic acid instead of terephthalic acid. Five-coordinate Mn ions were found in 4 giving rise to an intermolecular interaction and constructing a one-dimensional linear structure. Antiferromagnetic exchange interactions were observed for 1-3, and a total ferromagnetic exchange of 4 was considered to stem from intermolecular magnetic coupling. H-1 NMR signals of phenolate ring and alkylene (or phenylene) backbone of the diamine are similar to those reported in the literature, and the phth protons are at -2.3 to -10.1 ppm. Studies on structure, bond valence sum analysis, and magnetic properties indicate the oxidation states of the Mn ions in 6 to be +3, which are also indicated by ESR spectra in dual mode. Ferromagnetic exchange interaction between the Mn(III) sites was observed with J = 1.74 cm(-1). A quasireversible redox pair at -0.29V/0.12V has been assigned to the redox of Mn-2(III)/Mn(III)Mn(II), implying the intactness of the complex backbone in solution.
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| 2. |
- Zhang, Chunxi, et al.
(författare)
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Formation of Split Electron Paramagnetic Resonance Signals in Photosystem II Suggests That TyrosineZ Can Be Photooxidized at 5 K in the S0 and S1 States of the Oxygen-Evolving Complex
- 2003
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 42:26, s. 8066-8076
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Tidskriftsartikel (refereegranskat)abstract
- The effect of illumination at 5 K of photosystem II in different S-states was investigated with EPR spectroscopy. Two split radical EPR signals around g 2.0 were observed from samples given 0 and 3 flashes, respectively. The signal from the 0-flash sample was narrow, with a width of ~80 G, in which the low-field peak can be distinguished. This signal oscillated with the S1 state in the sample. The signal from the 3-flash sample was broad, with a symmetric shape of ~160 G width from peak to trough. This signal varied with the concentration of the S0 state in the sample. Both signals are assigned to arise from the donor side of PSII. Both signals relaxed fast, were formed within 10 ms after a flash, and decayed with half-times at 5 K of 3-4 min. The signal in the S0 state closely resembles split radical signals, originating from magnetic interaction between YZ and the S2 state, that were first observed in Ca2+-depleted photosystem II samples. Therefore, we assign this signal to YZ in magnetic interaction with the S0 state, YZS0. The other signal is assigned to the magnetic interaction between YZ and the S1 state, YZS1. An important implication is that YZ can be oxidized at 5 K in the S0 and S1 states. Oxidation of YZ involves deprotonation of the tyrosine. This is restricted at 5 K, and we therefore suggest that the phenolic proton of YZ is involved in a low-barrier hydrogen bond. This is an unusually short hydrogen bond in which proton movement at very low temperatures can occur.
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