Transport of Cu(II) from an albumin mimic peptide, GlyGlyHisGly, to histidine and penicillamine

Cu in blood has been believed to transport into cell via albumin and some amino acids. To shed light on the Cu transport process we studied the reaction of the Cu(II)-peptide with the amino acid by absorption and CD spectra. Albumin mimic peptides GlyGly-L-HisGly (GGHG) and penta-Gly(G5) formed stable 4N coordinated Cu(II) complexes, but in the reaction with histidine (His) and penicillamine (Pes) the ternary Cu(II) complex formations were observed different by the kinetic study. Cu(II)-G5 complexes reacted with Pes to form the ternary complex Cu(H(-1)G5)(Pes(-)) which was subsequently transformed to the binary complex Cu(Pes(-))(2). In the system with GGHG the Cu(II) was also transported from GGHG to Pes, but the ternary Cu(H(-1)GGHG)(Pes(-)) complex as the intermediate was detected a trace. The ternary complex would be spontaneously transformed to Cu(Pes(-))(2) upon forming, because the rate constant of the ternary complex formation k(1+)= approximately 2M(-1)s(-1) was less than k(2+)= approximately 5 x 10(2)M(-1)s(-1) for the Cu(Pes(-))(2) formation at physiological pH. In the Cu(II)-GGHG-His system the ternary Cu(H(-1)GGHG)(His) complex was also hardly identified because the formation constant K(1) and k(1+) were very small and the equilibrium existed between Cu(H(-2)GGHG) and Cu(His)(2) and its overall equilibrium constant beta(2) for Cu(His)(2) was very small to be 1.00+/-0.05 M(-1) at pH 9.0. These results indicated that the ternary complex is formed in the Cu transport process from the albumin to the amino acid, but His imidazole nitrogen in the fourth-binding site of Cu(II) strongly resists the replacement by the incoming ligand.     

Preparation, structures and electrochemical property of phosphine substituted diiron azadithiolates relevant to the active site of Fe-only hydrogenases

Mono- and di-phosphine diiron azadithiolate complexes [{(mu-SCH(2))(2)N(4-NO(2)C(6)H(4))}Fe(2)(CO)(5)(PMe(3))] (2), [{(mu-SCH(2))(2)N(4-NO(2)C(6)H(4))}{Fe(CO)(2)L}(2)] (3, L=PMe(3); 4, PMe(2)Ph) and the mu-hydride diiron complex [3(FeHFe)](+)[PF(6)](-) were prepared as biomimetic models of the active site of Fe-only hydrogenases. The complexes 2-4 and [3(FeHFe)](+)[PF(6)](-) were characterized by IR, (31)P, (1)H and (13)C NMR spectra and their molecular structures were determined by single crystal X-ray analyses. The PMe(3) ligand in complex 2 lies on the basal position. The PMe(3)-disubstituted complex 3 exists as two configuration isomers, transoid basal/basal and apical/basal, in the crystalline state, while two PMe(2)Ph ligands of 4 are in an apical/basal orientation. The variable temperature (31)P NMR spectra of 2 and 3 were made to have an insight into the existence of the possible conformation isomers of 2 and 3 in solution. The [3(FeHFe)](+) cation possesses the sole transoid ba/ba geometry as other reported mu-hydride diiron analogues. The electrocatalytic property of {(mu-SCH(2))(2)NC(6)H(5)}[Fe(CO)(2)PMe(3)](2) (5) was studied for proton reduction in the presence of HOAc.     

Synthesis, DNA-binding and photocleavage studies of cobalt(III) mixed-polypyridyl complexes: [Co(phen)(2)(dpta)](3+) and [Co(phen)(2)(amtp)](3+)

Two novel cobalt(III) mixed-polypyridyl complexes [Co(phen)(2)(dpta)](3+) and [Co(phen)(2)(amtp)](3+) (phen=1,10-phenanthroline, dpta=dipyrido-[3,2-a;2',3'-c]- thien-[3,4-c]azine, amtp=3-amino-1,2,4-triazino[5,6-f]1,10-phenanthroline) have been synthesized and characterized. The interaction of these complexes with calf thymus DNA was investigated by spectroscopic, cyclic voltammetry, and viscosity measurements. Results suggest that the two complexes bind to DNA via an intercalative mode. Moreover, these Co(III) complexes have been found to promote the photocleavage of plasmid DNA pBR322 under irradiation at 365nm. The mechanism studies reveal that hydroxyl radical (OH()) is likely to be the reactive species responsible for the cleavage of plasmid DNA by [Co(phen)(2)(dpta)](3+) and superoxide anion radical (O(2)(-)) acts as the key role in the cleavage reaction of plasmid DNA by [Co(phen)(2)(amtp)](3+).     

Synthesis, spectroscopic and X-ray characterization of a copper(II) complex with the Schiff base derived from pyridoxal and aminoguanidine: NMR spectral studies of the ligand

A copper(II) complex with the pyridoxal-aminoguanidine (PL-AG) Schiff base adduct, as an organic compound of the very potent biological activity and promising pharmacological importance in the treatment of diabetic complications, has been prepared and characterized. The X-ray structural analysis of the [CuCl2(PL-AG)] complex showed that it has a distorted pseudo-square-pyramidal (4+1) structure with the tridentate ONN Schiff base in the equatorial plane, with the Cu-O(1), Cu-N(1) and Cu-N(3) bond lengths of 1.917(2)A, 1.930(2)A and 1.984(2)A, respectively. The bond length of the equatorial Cu-Cl(1) is 2.279(1)A, while that of the apical Cu-Cl(2) is 2.792(1)A. Pyridoxal fragment is coordinated in its zwitterionic form. In addition to the X-ray structural analysis, the complex was characterized by IR spectrometric, conductometric and magnetic techniques, and the ligand itself by IR, 1H and 13C NMR spectra.     

Manganese(II) tri-tert-butoxysilanethiolate complexes with imidazole-based coligands: a neutral complex with four independent ligands and MNOS2 core (M=Mn) related to the liver alcohol dehydrogenase catalytic center (M=Zn)

The reaction of [Mn{SSi(OBu(t))3}2(MeOH)4] with imidazole and its two methyl substituted derivatives leads to different types of heteroleptic manganese(II) thiolate complexes. Reaction with 1-methylimidazole gives the silanethiolate devoid of methanol but with two nitrogen ligands and thus central MnN(2)S(2) core. The reaction with imidazole leads to the methanol solvated complex with only one nitrogen ligand but manganese coordination sphere enlarged to MnO(2)NS(2) due to an O,S-chelation by tri-tert-butoxysilanethiolate ligand. Molecules of this compound interact through a set of N-H...(Me)O-H...S hydrogen bonds with methanol hydroxyl group being simultaneously acceptor and donor. With 2-methylimidazole the product is an assembly of two different neutral complexes joined again by hydrogen bonds, however, this time of N-H...S type. One of these complexes has the previously mentioned MnO(2)NS(2) core. The second neutral complex exhibits four donor atoms (MnNOS(2)core) derived from four independent ligands, i.e., two silanethiolate rests, one N-heterocyclic base and one alcohol. This structure presents similarities with a zinc-based alcohol dehydrogenase active site that have never been obtained before, including with other metals (Zn, Co). It may, therefore, be considered the first neutral structural model of liver alcohol dehydrogenase (LADH).     

Near edge X-ray absorption fine structure spectroscopy (NEXAFS) of pigment-protein complexes: peridinin-chlorophyll a protein (PCP) of Amphidinium carterae

Peridinin-chlorophyll a protein (PCP) is a unique water soluble antenna complex that employs the carotenoid peridinin as the main light-harvesting pigment. In the present study the near edge X-ray absorption fine structure (NEXAFS) spectrum of PCP was recorded at the carbon K-edge. Additionally, the NEXAFS spectra of the constituent pigments, chlorophyll a and peridinin, were measured. The energies of the lowest unoccupied molecular levels of these pigments appearing in the carbon NEXAFS spectrum were resolved. Individual contributions of the pigments and the protein to the measured NEXAFS spectrum of PCP were determined using a “building block” approach combining NEXAFS spectra of the pigments and the amino acids constituting the PCP apoprotein. The results suggest that absorption changes of the pigments in the carbon near K-edge region can be resolved following excitation using a suitable visible pump laser pulse. Consequently, it may be possible to study excitation energy transfer processes involving “optically dark” states of carotenoids in pigment-protein complexes by soft X-ray probe optical pump double resonance spectroscopy (XODR).     

Spectroscopic, viscositic and electrochemical studies of DNA interaction with a novel mixed-ligand complex of nickel (II) that incorporates 1-methylimidazole and thiocyanate groups

A novel mixed-ligand nickel(II) complex that contains 1-methylimidazole and thiocyanate, Ni(NCS)(2)(Mim)(4) (Mim=1-methylimidazole), was synthesized and its structure was determined by X-ray crystallography, IR spectrum and elemental analysis, etc. Its DNA-binding properties were studied by electronic absorption spectral, viscositive and electrochemical measurements. The absorption spectral and viscositive results suggest that the nickel(II) complex binds to DNA via partial intercalation. The addition of DNA results in the decrease of the peak current of the nickel(II) complex proved their interaction. The slight differences of peak profiles and electrochemical parameters between free and DNA-bound Ni(NCS)(2)(Mim)(4) showed the formation of an electrochemical inactive complex between Ni(NCS)(2)(Mim)(4) and DNA. The binding site and binding constant of the complex to DNA were determined by electrochemical titration method.     

EPR spectroscopy of the manganese cluster of photosystem II

Electron paramagnetic resonance (EPR) spectroscopy is a valuable tool for understanding the oxidation state and chemical environment of the Mn₄Ca cluster of photosystem II. Since the discovery of the multiline signal from the S₂ state, EPR spectroscopy has continued to reveal details about the catalytic center of oxygen evolution. At present EPR signals from nearly all of the S-states of the Mn₄Ca cluster, as well as from modified and intermediate states, have been observed. This review article describes the various EPR signals obtained from the Mn₄Ca cluster, including the metalloradical signals due to interaction of the cluster with a nearby organic radical.     

Expression, assembly and auxiliary functions of photosystem II oxygen-evolving proteins in higher plants

The oxygen-evolving complex (OEC) of higher plant photosystem II (PSII) consists of an inorganic Mn₄Ca cluster and three nuclear-encoded proteins, PsbO, PsbP and PsbQ. In this review, we focus on the assembly of these OEC proteins, and especially on the role of the small intrinsic PSII proteins and recently found “novel” PSII proteins in the assembly process. The numerous auxiliary functions suggested during the past few years for the OEC proteins will likewise be discussed. For example, besides being a manganese-stabilizing protein, PsbO has been found to bind calcium and GTP and possess a carbonic anhydrase activity. In addition, specific roles have been suggested for the two isoforms of the PsbO protein in Arabidopsis thaliana. PsbP and PsbQ seem to play an additional role in the formation of PSII supercomplexes and in grana stacking, besides their originally recognized role in providing a proper calcium and chloride ion concentration for water splitting.