Thermal analysis of some metal n-benzoyl-n-phenylhydroxylamine chelates

The preparation and thermal analysis of the metal chelates of N-benzoyl-N-phenylhydroxylamine (BPHA) with Al(III), Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Mn(II), Ni(II) and Zn(II) is discussed. The differential thermal analysis apparatus is described in detail. DTA and TGA curves of BPHA arid the chelates from 25 to 700° in oxygen and in nitrogen are presented.     

Redox chemistry of morpholine-based Os(VI)-hydrazido complexes: trans-[Os(VI)(tpy)(Cl)2(NN(CH2)4O)](2+)

The oxidations of benzyl alcohol, PPh3, and the sulfides (SEt2 and SPh2) (Ph = phenyl and Et = ethyl) by the Os(VI)-hydrazido complex trans-[Os(VI)(tpy)(Cl)2(NN(CH2)4O)](2+) (tpy = 2,2':6',2' '-terpyridine and O(CH2)4N(-) = morpholide) have been investigated in CH3CN solution by UV-visible monitoring and product analysis by gas chromatography-mass spectrometry. For benzyl alcohol and the sulfides, the rate law for the formation of the Os(V)-hydrazido complex, trans-[Os(V)(tpy)(Cl)2(NN(CH2)4O)](+), is first order in both trans-[Os(VI)(tpy)(Cl)2(NN(CH2)4O)](2+) and reductant, with k(benzyl) (25.0 +/- 0.1 degrees C, CH3CN) = (1.80 +/- 0.07) x 10(-4) M(-1) s(-1), k(SEt2) = (1.33 +/- 0.02) x 10(-1) M(-1) s(-1), and k(SPh2) = (1.12 +/- 0.05) x 10(-1) M(-1) s(-1). Reduction of trans-[Os(VI)(tpy)(Cl)2(NN(CH2)4O)](2+) by PPh3 is rapid and accompanied by isomerization and solvolysis to give the Os(IV)-hydrazido product, cis-[Os(IV)(tpy)(NCCH3)2(NN(CH2)4O)](2+), and OPPh3. This reaction presumably occurs by net double Cl-atom transfer to PPh3 to give Cl2PPh3 that subsequently undergoes hydrolysis by trace H2O to give the final product, OPPh3. In the X-ray crystal structure of the Os(IV)-hydrazido complex, the Os-N-N angle of 130.9(5) degrees and the Os-N bond length of 1.971(7) A are consistent with an Os-N double bond.     

Aspects of the mechanism of catalysis of glucose oxidase: A docking, molecular mechanics and quantum chemical study

The complex structure of glucose oxidase (GOX) with the substrate glucose was determined using a docking algorithm and subsequent molecular dynamics simulations. Semiempirical quantum chemical calculations were used to investigate the role of the enzyme and FAD co-enzyme in the catalytic oxidation of glucose. On the basis of a small active site model, substrate binding residues were determined and heats of formation were computed for the enzyme substrate complex and different potential products of the reductive half reaction. The influence of the protein environment on the active site model was estimated with a point charge model using a mixed QM/MM method. Solvent effects were estimated with a continuum model. Possible modes of action are presented in relation to experimental data and discussed with respect to related enzymes. The calculations indicate that the redox reaction of GOX differs from the corresponding reaction of free flavins as a consequence of the protein environment. One of the active site histidines is involved in substrate binding and stabilization of potential intermediates, whereas the second histidine is a proton acceptor. The former one, being conserved in a series of oxidoreductases, is also involved in the stabilization of a C4a-hydroperoxy dihydroflavin in the course of the oxidative half reaction.     

Separation of positional isomers of oxidation catalyst precursors

A series of polypyridyl ruthenium complexes of the general formula [Ru(tpy)(bpy')Cl]+ where tpy is 2,2':6',2"-terpyridine and bpy' is 4-carboxy-4'-methyl-2,2'-bipyridine (4-CO2H-4'-Mebpy), a proline derviative (4-CO-Pra-(Boc)(OMe)-4'-Mebpy), or 4-((diethoxyphosphinyl)methyl)-4'-methyl-2,2'-bipyridine (4-CH2PO3Et2-4'-Mebpy) are prepared. For each complex, two isomers exist, and these are separated chromatographically. The structure of the hexafluorophosphate salt of cis-[Ru(tpy)(4-CO2H-4'-Mebpy)Cl]+, cis-1, is determined by X-ray crystallography. The salt crystallizes in the monoclinic space group Cc with a = 12.4778(6) A, b = 12.6086(6) A, c = 20.1215(9) A, beta = 107.08200(1) degrees, Z = 4, R = 0.058, and Rw = 0.072. The structures of the remaining complexes are assigned by 1H NMR comparisons with cis-1. The complexes are potentially important precursors for the incorporation of RuIV=O2+ oxidants into polymers or peptides or for their adsorption onto oxide surfaces. Preliminary electrochemical results for the isomers of [Ru(tpy)(4-CH2PO3H2-4'-Mebpy)(H2O)]2+, 4, adsorbed on ITO (In2O3:Sn) surfaces add support to a recently proposed electron-transfer mechanism involving cross-surface proton-coupled electron transfer.     

Photoinduced carbon monoxide migration in a synthetic heme-copper complex

Time-resolved infrared (TRIR) flash photolytic techniques have been employed to initiate and observe the efficient dissociation of CO from a synthetic heme-CO/copper complex, [((6)L)Fe(II)(CO)..Cu(I)](+) (2), in CH(3)CN and acetone at room temperature. In CH(3)CN, a significant fraction of the photodissociated CO molecules transiently bind to copper (nu(CO)(Cu) = 2091 cm(-)(1)) giving [((6)L)Fe(II)..Cu(I)(CO)](+) (4), with an observed rate constant, k(1) = 1.5 x 10(5) s(-)(1). That is followed by a slower direct transfer of CO from the copper moiety back to the heme (nu(CO)(Fe) = 1975 cm(-)(1)) with k(2) = 1600 s(-)(1). Additional transient absorption (TA) UV-vis spectroscopic experiments have been performed monitoring the CO-transfer reaction by following the Soret band. Eyring analysis of the temperature-dependent data yields DeltaH(double dagger) = 43.9 kJ mol(-)(1) for the 4-to-2 transformation, similar to that for CO dissociation from [Cu(I)(tmpa)(CO)](+) in CH(3)CN (DeltaH(double dagger) = 43.6 kJ mol(-)(1)), suggesting CO dissociation from copper regulates the binding of small molecules to the heme within [((6)L)Fe(II)..Cu(I)](+)(3). Our observations are analagous to those observed for the heme(a3)/Cu(B) active site of cytochrome c oxidase, where photodissociated CO from the heme(a3) site immediately (ps) transfers to Cu(B) followed by millisecond transfer back to the heme.     

Crystal Structure,Electronic Structure,and Luminescence of Cs2KYF6:Pr3+

The crystal structure, electronic states and VUV spectroscopic behaviour of Cs₂KYF₆ doped with Pr³⁺ ions have been investigated both by experimental and theoretical methods. Cs₂KYF₆ ( , Z = 4, a = 945.5(3) pm, R1_all = 0.0297) crystallizes with the cubic elpasolite type of structure. The local relaxation of the activator ions in the host lattices has been calculated by the projector augmented wave method (computer code VASP). The electronic states have been calculated using a spin density functional procedure based on the atomic sphere approximation (computer code ASW). VUV spectroscopic measurements show fast 4f¹5d¹ → 4f² emission of nanosecond duration as well as slow 4f² → 4f² emission depending on the excitation energy which indicates the occupation of different sites in the host lattice. This assumption was verified by a recently developed quantum mechanical method. The combination of the experimental and the theoretical results show that the Pr³⁺ ions are occupying three different sites, namely the Y³⁺ and the Cs⁺ site as well as the K⁺ site.     

Mechanistic implications of proton transfer coupled to electron transfer.

The kinetics of electron transfer for the reactions cis-[Ru(IV)(bpy)2(py)(O)]2+ + H+ + [Os(II)(bpy)3]2+ <==> cis-[Ru(III)(bpy)2(py)(OH)]2+ + [Os(III)(bpy)3]3+ and cis-[Ru(III)(bpy)2(py)(OH)]2+ + H+ + [Os(II)(bpy)3]2+ <==> cis-[Ru(II)(bpy)2(py)(H2O)]2+ + [Os(III)(bpy)3]3+ have been studied in both directions by varying the pH from 1 to 8. The kinetics are complex but can be fit to a double "square scheme" involving stepwise electron and proton transfer by including the disproportionation equilibrium, 2cis-[Ru(III)(bpy)2(py)(OH)]2+ <==> (3 x 10(3) M(-1) x s(-1) forward, 2.1 x 10(5) M(-1) x s(-1) reverse) cis-[Ru(IV)(bpy)2(py)(O)]2+ + cis-[Ru(II)(bpy)2(py)(H2O)]2+. Electron transfer is outer-sphere and uncoupled from proton transfer. The kinetic study has revealed (1) pH-dependent reactions where the pH dependence arises from the distribution between acid and base forms and not from variations in the driving force; (2) competing pathways involving initial electron transfer or initial proton transfer whose relative importance depends on pH; (3) a significant inhibition to outer-sphere electron transfer for the Ru(IV)=O2+/Ru(III)-OH2+ couple because of the large difference in pK(a) values between Ru(IV)=OH3+ (pK(a) < 0) and Ru(III)-OH2+ (pK(a) > 14); and (4) regions where proton loss from cis-[Ru(II)(bpy)2(py)(H2O)]2+ or cis-[Ru(III)(bpy)2(py)(OH)]2+ is rate limiting. The difference in pK(a) values favors more complex pathways such as proton-coupled electron transfer.     

Oxidation of ammonia in osmium polypyridyl complexes

The oxidations of cis- and trans-[OsIII(tpy)(Cl)2(NH3)](PF6), cis-[OsII(bpy)2(Cl)(NH3)](PF6), and [OsII(typ)(bpy)(NH3)](PF6)2 have been studied by cyclic voltammetry and by controlled-potential electrolysis. In acetonitrile or in acidic, aqueous solution, oxidation is metal-based and reversible, but as the pH is increased, oxidation and proton loss from coordinated ammonia occurs. cis- and trans-[OsIII(tpy)(Cl)2(NH3)](PF6) are oxidized by four electrons to give the corresponding OsVI nitrido complexes, [OSVI(typ)(Cl)2(N)]+. Oxidation of [Os(typ)(bpy)(NH3)](PF6)2 occurs by six electrons to give [Os(tpy)(bpy)(NO)](PF6)3. Oxidation of cis-[OsII(bpy)2(Cl)(NH3)](PF6) at pH 9.0 gives cis-[OsII(bpy)2(Cl)(NO)](PF6)2 and the mixed-valence form of the mu-N2 dimer [cis-[Os(bpy)2(Cl)2[mu-N2)](PF6)3. With NH4+ added to the electrolyte, cis-[OsII(bpy)2(Cl)(N2)](PF6) is a coproduct. The results of pH-dependent cyclic voltammetry measurements suggest OsIV as a common intermediate in the oxidation of coordinated ammonia. For cis- and trans-[OsIII(tpy)(Cl)2(NH3)]+, OsIV is a discernible intermediate. It undergoes further pH-dependent oxidation to [OsVI(tpy)(Cl)2(N)]+. For [OsII(tpy)(bpy)(NH3)]2+, oxidation to OsIV is followed by hydration at the nitrogen atom and further oxidation to nitrosyl. For cis-[OsII(bpy)2(Cl)-(NH3)]+, oxidation to OsIV is followed by N-N coupling and further oxidation to [cis-[Os(bpy)2(Cl)2(mu-N2)]3+. At pH 9, N-N coupling is competitive with capture of OsIV by OH- and further oxidation, yielding cis-[OsII(bpy)2(Cl)(NO)]2+.     

Efficient photodissociation of O2 from synthetic heme and heme/M (M = Fe, Cu) complexes

Single wavelength excitation (lambdaex = 355 or 532 nm) of low-temperature stabilized (198 K) synthetic heme-dioxygen and heme-dioxygen/M complexes, where M = copper or iron in a non-heme environment, results in the dissociation of dioxygen as indicated by the generation of the ferrous heme (Soret band, 427 nm) and the bleaching of the ferric-superoxide (FeIII(O2-)) 410-nm Soret band in the transient absorption difference spectrum. Dioxygen rebinds to the four heme complexes studied with comparable rate constants ( approximately 6-9 x 105 M-1 s-1). However, the quantum yield for complete dissociation of O2 from our simplest heme-O2 complex (F8)FeIII(O2-) (phi = 0.60) is higher than the other complexes measured (phi = approximately 0.2-0.3) as well as that for oxy-myoglobin (phi = 0.3).     

The coherent K L 0 C → K S 0 C regeneration at high energies

New experimental results on the coherentK _L ⁰ C K _S ⁰ C regeneration in the momentum range 10p30 GeV/c are presented. For the quantity (f ₀–¯f ₀/k (where f₀ and¯f ₀ are theKC and¯K ⁰C forward scattering amplitudes andk is the wave number) we have obtained: arg (f ₀–¯f ₀)/k=–126±14 and ¦(f ₀–¯f ₀/k¦ p ^{–0.62±0.14} These results are well described by a simple Regge pole model including only the (-trajectory exchange in thet-channel with the intercept (0) close to 0.4.Presented at the IV International Symposium on High Energy and Elementary Particle Physics, Warszaw, September 1975.