HYDRATED ELECTRON FORMATION IN NANOSECOND and PICOSECOND LASER FLASH PHOTOLYSIS OF HEMATOPORPHYRIN IN AQUEOUS SOLUTION

Nanosecond (lambda exc = 266, 355 and 532 nm) and picosecond (lambda exc = 355 nm) laser flash photolysis of hematoporphyrin (Hp) was performed in neutral (pH 7.4) and alkaline (pH 12) aqueous solution, as well as in the presence of 0.1% Triton X-100. The dependence of the yield of photoproduced hydrated electrons (e-aq) on laser pulse energy was studied over a wide range of energies (0.2 to greater than 1000 mJ cm-2). The results show that e-aq are predominantly formed in a two-photon process at lambda exc = 266 and 355 nm. One-photon quantum yields are higher at lambda exc = 266 nm than at lambda exc = 355 nm. Both one-photon and two-photon pathways are less efficient at higher Hp concentration, reflecting the influence of Hp self-aggregation. Two-photon e-aq formation is more efficient when 30 ps pulses are used for excitation, as compared to 10 ns pulses. No e-aq could be detected at lambda exc = 532 nm. Nanosecond pulse-induced transient spectra obtained at pH 7.4 are also discussed.     

The chemistry of pyridine thiols and related ligands,Part 6. The crystal and molecular structure of [1,3–bis(diphenylphosphino)-propane][bis(pyridine-2–thiolato)]ruthenium(II). A comparison with solution phase behaviour

Reaction of cis-RuCl2(dppp)2 with pyridine-2–thiol (HpyS) in the presence of Et3N in dry benzene replaces both the chloro groups and a diphosphine molecule to form Ru(dppp)(pyS)2 (1) [dppp=Ph2P(CH2)3PPh2], whose crystal and molecular structure has been determined with the help of single crystal X-ray crystallography. The discrete molecules of (1) adopt a distorted octahedral structure containing chelating pyridine-2–thiolato and dppp ligands with trans-S, cis-N and cis-P atom dispositions. The important interatomic parameters are: Ru-S, 2.443(2), 2.339(2); Ru-N, 2.133(5), 2.129(5); Ru-P, 2.274(2), 2.279(2)Å; trans-bond angles, S-Ru-S, 153.89(6); N-Ru-P, 172.76(13), 163.51(14)°; bite angles: P-Ru-P, 90.71(6); N-Ru-S, 67.18(14), 67.72(14)°. The n.m.r. spectra (1H, 13C, 31P) of (1) are also reported in order to compare solution phase behaviour with the solid state structure. The 13C-n.m.r. spectrum of the complex shows the presence of non-equivalent phenyls in the Ph2P-moiety.     

Synthesis,spectroscopy and structures of halogen and sulfur-bridged dinuclear silver(I) complexes with N1-substituted thiophene-2-carbaldehyde thiosemicarbazone

The reactions of silver(I) halides (Cl or Br) with thiophene-2-carbaldehyde N¹-methyl thiosemicarbazone (HttscMe) in the presence of Ph₃P (1:1:1 molar ratio) yield halogen-bridged dimers, [Ag₂(μ-X)₂(η¹-S-HttsMe)₂(PPh₃)₂] (X = Cl, 1; Br, 2). The use of 2,2′-bipyridine in lieu of Ph₃P in the reaction of silver(I) chloride with HttscMe yields the sulfur-bridged dimer, [Ag₂(μ-S-HttscMe)₂(η¹-HttsMe)₂] · 2CHCl₃ 3. The substituents have altered the nature of bridge between the two silver atoms. The Ag···Ag separation (3.4867(5) Å) in complex 3 is less than that in the halogen-bridged dimers (3.734(4) Å 1; 3.746(5) Å 2). Unlike PPh₃ the co-ligand 2,2′-bipyridine did not coordinate to the silver center, but was necessary for crystallization in the reaction with the thio-ligand. NMR spectroscopy revealed that the complexes remained unchanged in the solution state (CDCl₃).     

Synthesis of 1D {Cu6(mu3-SC3H6N2)4(mu-SC3H6N2)2(mu-I)2I4}n and 3D {Cu2(mu-SC3H6N2)2(mu-SCN)2}n polymers with 1,3-imidazolidine-2-thione: bond isomerism in polymers

The reaction of copper(I) iodide with 1, 3-imidazolidine-2-thione (SC3H6N2) in a 1:2 molar ratio (M/L) has formed unusual 1D polymers, {Cu6(mu3-SC3H6N2)4(mu-SC3H6N2)2(mu-I)2I4}n (1) and {Cu6(mu3-SC3H6N2)2(mu-SC3H6N2)4(mu-I)4I2}n (1a). A similar reaction with copper(I) bromide has formed a polymer {Cu6(mu3-SC3H6N2)2(mu-SC3H6N2)4(mu-Br)4Br2}n (3a), similar to 1a, along with a dimer, {Cu2(mu-SC3H6N2)2(eta1-SC3H6N2)2Br2} (3). Copper(I) chloride behaved differently, and only an unsymmetrical dimer, {Cu2(mu-SC3H6N2)(eta1-SC3H6N2)3Cl2} (4), was formed. Finally, reactions of copper(I) thiocyanate in 1:1 or 1:2 molar ratios yielded a 3D polymer, {Cu2(mu-SC3H6N2)2(mu-SCN)2}n (2). Crystal data: 1, C9H18Cu3I3N6S3, triclinic, P, a = 9.6646(11) A, b = 10.5520(13) A, c = 12.6177(15) A, alpha = 107.239(2) degrees , beta = 99.844(2) degrees , gamma = 113.682(2) degrees , V = 1061.8(2) A(3), Z = 2, R = 0.0333; 2, C(4)H(6)CuN(3)S(2), monoclinic, P2(1)/c, a = 7.864(3) A, b = 14.328(6) A, c = 6.737(2) A, beta = 100.07(3) degrees , V = 747.4(5), Z = 4, R = 0.0363; 3, C12H24Br2Cu2N8S4, monoclinic, C2/c, a = 19.420(7) A, b = 7.686(3) A, c = 16.706(6) A, beta = 115.844(6) degrees , V = 2244.1(14) A(3), Z = 4, R = 0.0228; 4, C12H24Cl2Cu2N8S4, monoclinic, P2(1)/c, a = 7.4500(6) A, b = 18.4965(15) A, c = 16.2131(14) A, beta = 95.036(2) degrees , V = 2225.5(3) A(3), Z = 4, R = 0.0392. The 3D polymer 2 exhibits 20-membered metallacyclic rings in its structure, while synthesis of linear polymers, 1 and 1a, represents an unusual example of I (1a)-S (1) bond isomerism.     

Paraquat induces oxidative stress, neuronal loss in substantia nigra region and Parkinsonism in adult rats: Neuroprotection and amelioration of symptoms by water-soluble formulation of Coenzyme Q10

Background  

Parkinson's disease, for which currently there is no cure, develops as a result of progressive loss of dopamine neurons in the brain; thus, identification of any potential therapeutic intervention for disease management is of a great importance.     

Chemistry of iron complexes—IX. I.r. and e.s.r. studies of triisothiocyanatobis(triarylphosphine/arsine oxide) iron(III) and their polynuclear metal complexes with mercury(II) chloride

Summary X-band e.s.r. and i.r. spectra of [Fe(NCS)₃(Ph₃PO)₂](1) and [Fe(NCS)₃(p-Tol₃AsO)₂](2), before and after heating to 100, 150 and 200° C (±2°C), were studied at room temperature. Reactions of (1) and (2) with HgCl₂ in Me₂CO form heteropolymetallic 13 (Fe:hg) complexes: [Fe(NCS)₃(Ph₃PO)₂(HgCl₂)₃]·2Me₂CO (3) and [Fe(NCS)₃(p-Tol₃AsO)₂(HgCl₂)₃]·H₂O (4). Room temperature i.r. and e.s.r. spectra of (3) and (4) have been studied.     

Ligating properties oftert-phosphine/arsine sulphides or selenides,Part IX. Preparation and spectroscopic studies of copper(I)/copper(II) complexes with bis(—phosphine chalcogenides)

Summary The analytical, molar conductance and spectroscopic studies of new complexes of copper(I) and copper(II) with bis(—phosphine chalcogenides), Ph₂P(E)(CH₂)_n-P(E)Ph₂(L-L) are reported. The complexes are of the types: (a) [CuX(L-L)](X, n, E: Cl, 2–4, Br, 2, S; Cl, Br, 1, Se); (b) [Cu₂X₂(L-L)] (X, n, E: Cl, Br, 2, 3, Se) and (c) [CuCl₂(L-L)] (n, E: 2, 3, S). Possible structures have been derived.     

Synthesis and structures of monomeric [chloro(isatin-3-thiosemicarbazone)bis(triphenylphosphine)]copper(I) and dimeric [dichlorobis(thiophene-2-carbaldehyde thiosemicarbazone)bis(triphenylphosphine)]dicopper(I)] complexes

Reaction of copper(I) chloride with thiophene-2-carbaldehyde thiosemicarbazone (Httsc) in acetonitrile in the presence of Ph₃P yielded a sulfur-bridged dimer [Cu₂Cl₂(μ₂-S-Httsc)₂(PPh₃)₂] · 2CH₃CN (1), while a similar reaction with isatin-3-thiosemicarbazone (H₂itsc) formed a monomer, [CuCl(H₂itsc)(Ph₃P)₂] · 2CH₃CN (3). Furan-2-carbaldehyde thiosemicarbazone (Hftsc) also formed a compound of the composition [Cu₂Cl₂(Hftsc)₂(PPh₃)₂] · 2H₂O (2). Complexes 1–3 have been characterized using elemental analysis, IR, ¹H and ³¹P NMR spectroscopy and single crystal X-ray crystallography (1 and 3). Acetonitrile is engaged in hydrogen bonding with the chlorine atom {NCCH₂–H?Cl)}, which is necessary for the stabilization of the bridging sulfur in 1. In compound 3, however, acetonitrile is strongly hydrogen bonded to the NH hydrogen of the isatin ring {CH₃CN?NH(isatin)} and not to the chlorine atom. The Cu?Cu contact of 2.7719(5) Å in dimer 1 is close to twice the van der Waals radius of the Cu atom (2.80 Å).     

Investigation of Silver(I) Ion Sensing Property of Ruthenium(II) Thiosemicarbazone Complex Using Coated Graphite and Polymeric Membrane Electrodes

A ruthenium(II) complex [Ru(PPh₃)₂(pytsc)₂] {Hpytsc = pyridine‐2‐carbaldehydethiosemicarbazone, (C₅H₅N)C²(H)=N³‐N²(H)‐C¹(=S)N¹H} has been used as an ion carrier for the selective determination of silver(I) ions in solution. Silver(I) ion‐selective coated graphite based (CGE) and PVC polymeric membrane based (PME) electrodes exhibit Nernstian slope for silver(I) ions over a wide concentration range from 1.0 × 10⁻¹ M to 5.0 × 10⁻⁶ M (with CGE) and 1.0 × 10⁻¹ M to 2.0 × 10⁻⁵ M (with PME). The working pH range of these electrodes has been found to be from 1.2 to 7.2 for CGE and 2.2 to 6.5 for PME. The proposed CGE sensor exhibits better analytical features like sensitivity and selectivity towards different secondary ions in comparison to the corresponding PME with no interference from mercury(II) ions . These electrodes also act as indicator electrodes in potentiometric titration and have been successfully used for the determination of silver content in solution of real samples (1 gm dissolved in 100 mL of dilute nitric acid) such as silver ornaments and thin silver foils. Silver content determined by the use of ion selective electrode was found to vary in the concentration range from 1.20 x 10⁻² M to 7.45 x 10⁻² M and results were found to be comparable with those obtained from the traditional volumetric method of analysis. It is the first report of a metal‐ligand complex used as an ion carrier in ion selective electrode, which is selective for a metal ion other than the one used in the complex.