| Summary: | 博士 === 東海大學 === 化學系 === 97 === Part I. Kinetic studies of the reactions of pentacyanonitrosylferrate(2-) with ligands containing acidic methylene groups
The kinetic studies of the addition reactions of pentacyanonitrosyl- ferrate(2-) (NP) with acidic methylene ligands of the form CH2LL’ (L = L’ = –CN; L = –CN, L’ = –CONH2; L = L’ = –COCH3) have been carried out in basic solutions. The increase in the second order rate constants for the formation of Fe(CN)5N(O)CLL’4– complexes with the increase of OH– concentration indicated that ӨCHLL’ is the reactive species of the reactions. In addition to the pKa, the lability of the methylene protons of the ligands in aqueous solution also governs the reactivity of the reactions. The nitrosation products were rather unstable with respect to the dissociation into Fe(CN)5OH23– and oxime compounds. The kinetic measurements showed that the rates of dissociation were first order and were rather insensitive to the hydroxide concentration for the ligands under study.
Part II. Kinetic studies of the oxidation of catechin and rutin by pentaammineruthenium(III) complexes
The reaction of catechin and rutin with Ru(NH3)5L3+ (L = N-methylpyrazinium (pzCH3+), pyrazine (pz) and isonicotinamide (isn)) complexes underwent a two electron oxidation on the catechol ring (B ring) with the formation of quinone products. The kinetics of the oxidation, carried out at [H+] = 0.01 – 1.0 M and pH = 4.0 – 7.6, suggested that the reaction process involves the rate determining one-electron oxidation of the flavonoids in the form of H2X (k0), HX– (k1) and X2– (k2) by Ru(NH3)5L3+ complexes to form the corresponding semiquinone radicals, followed by the rapid scavenge of the radicals by the Ru(III) complexes. The specific rate constants (k0, k1 and k2) were measured and the results together with the application of the Marcus theory were used to estimate the self-exchange parameters for the one-electron couples of the flavonoids, H2X/H2X+•, HX–/HX• and X2–/X–•.
Part III. Stabilities and reactivities of the cyano-bridged binuclear complexes of trans-isonicotinamidetetraammineruthenium and hexacyanoferrate
The binuclear complexes, trans-(isn)(NH3)4RuNCFe(CN)5n (n = 2-, 1-, 0), were prepared both in aqueous solutions and as isolated salts. Their properties, particularly that of the mixed-valence species (M), were characterized by UV-vis, infrared, electrochemical and kinetic studies. The results suggested that Ru(III)-Fe(II) was both thermodynamically and kinetically stable oxidation states of M. The extent of delocalization of M was estimated by the analysis of intervalence band on the basis of Hush’s theory. The stabilization of M with respect to its oxidation state isomer (M’) was investigated and it was found that the electrostatic effect associated with the net charges of metal moieties constituted the dominate factor governing the stability of M.
Part IV. Kinetic studies of the substitution reactions of
trans-Os(en)2(η2-H2)(H2O)2+
The substitution reactions of trans-Os(en)2(η2-H2)(H2O)2+ with a series of nucleotides (5’-AMP, 5’-GMP, 5’-CMP, 5’-TMP, 5’-UMP) have been carried out in aqueous solution. The stabilization of η2-H2 complexes is attributed to the formation of Os(II) to σ*(H2) backbonding. The formation of η2-H2 complexes is characterized by 1H-NMR spectra which shows a signal in the range of δ = 0 to -20 ppm, away from all signals of en and other organic ligands. The actual chemical shift depends on the ligand used. This unique property allows the potential for the use of trans-Os(en)2(η2-H2)(H2O)2+ complex as a probe of 1H-NMR spectroscopy. The spectroscopic (electronic and 1H-NMR) and the kinetic studies suggested that Os(II) first underwent a fast pre-equilibrium reaction with the phosphate of the nucleotides to form phosphate-bound complexes, which was followed by linkage-isomerization to form nucleobase complexes. The bind sites of nucleobases are N7, N1, N3, N3, and N3 for 5’-GMP, 5’-AMP, 5’-CMP, 5’-TMP, and 5’-UMP, respectively. The kinetic studies of the formation reaction further suggested that the reaction underwent a dissociative mechanism by loss of the H2O ligand to form a 16e five-coordinate intermediate which is further stabilized by rearrangement to an 18e dihydride complex of Os(IV), Os(en)2(H)22+.
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