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Kenneth D Karlin

Publications and source records attributed to Kenneth D Karlin.

At least 37 records · Page 2Linked to original sources
PubMed2005

Carbon-halogen bond activation mechanism by copper(I) complexes of (2-pyridyl)alkylamine ligands.

The reaction of p-substituted benzyl halides ((Y)BnX; X = Cl, Br, and I; Y = p-substituent, OMe, t-Bu, Me, H, F, Cl, and NO(2)) and copper(I) complexes supported by a series of (2-pyridyl)alkylamine ligands has been investigated to shed light on the mechanism of copper(I) complex mediated carbon-halogen bond activation, including ligand effects on the redox reactivity of copper(I) complexes which are relevant to the chemistry. For both the tridentate ligand (Phe)L(Pym2) [N,N-bis(2-pyridylmethyl)-2-phenylethylamine] and tetradentate ligand TMPA [tris(2-pyridylmethyl)amine] complexes, the C-C coupling reaction of benzyl halides proceeded smoothly to give corresponding 1,2-diphenylethane derivatives and copper(II)-halide complex products. Kinetic analysis revealed that the reaction obeys second-order kinetics both on the copper complex and the substrate; rate = k[Cu](2)[(Y)BnX](2). A reaction mechanism involving a dinuclear copper(III)-halide organometallic intermediate is proposed, on the basis of the kinetic results, including observed electronic effects of p-substituents (Hammett plot) and the rate dependence on the BDE (bond dissociation energy) of the C-X bond, as well as the ligand effects.

Journal Article↗
PubMed2005

Changing selectivity of DNA oxidation from deoxyribose to Guanine by ligand design and a new binuclear copper complex.

A dinuclear copper complex [CuII2(PD'O)(H2O)2]3+ (1) (where PD'OH is a pyridylalkylamine containing binucleating ligand) promotes guanine oxidation in single-stranded DNA in the presence of 3-mercaptopropionic acid and dioxygen. This reaction is detected after subsequent piperidine treatment. Little spontaneous strand scission indicative of deoxyribose oxidation is observed in contrast to the results known for other copper complexes. Chemical characterization and nanospray ionization mass spectrometry analysis of oligodeoxynucleotides treated with 1 suggest conversion of guanine residues to their 2,6-diamino-5-formamidino-4-hydroxypyrimidine (+18 amu) and possibly 5,8-dihydroxy-7,8-dihydroguanine (+34 amu) derivatives. The selectivity toward nucleobase rather than deoxyribose oxidation is discussed in terms of the specific nature of the dicopper (hydro)peroxo species formed with the PD'OH ligand versus the intermediates formed in the presence of other binucleating ligands.

Copper↗
PubMed2004

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).

Copper↗
PubMed2004

Photochemical organic oxidations and dechlorinations with a mu-oxo bridged heme/non-heme diiron complex.

Steady state and laser flash photolysis studies of the heme/non-heme mu-oxo diiron complex [((6)L)Fe(III)-O-Fe(III)-Cl](+) (1) have been undertaken. The anaerobic photolysis of benzene solutions of 1 did not result in the buildup of any photoproduct. However, the addition of excess triphenylphosphine resulted in the quantitative photoreduction of 1 to [((6)L)Fe(II)...Fe(II)-Cl](+) (2), with concomitant production by oxo-transfer of 1 equiv of triphenylphosphine oxide. Under aerobic conditions and excess triphenylphosphine, the reaction produces multiple turnovers (approximately 28) before the diiron complex is degraded. The anaerobic photolysis of tetrahydrofuran (THF) or toluene solutions of 1 likewise results in the buildup of 2. The oxidation products from these reactions included gamma-butyrolactone (approximately 15%) for the reaction in THF and benzaldehyde (approximately 23%) from the reaction in toluene. In either case, the O-atom which is incorporated into the carbonyl product is derived from dioxygen present under workup or under aerobic photolysis conditions. Transient absorption measurements of low-temperature THF solutions of 1 revealed the presence of an (P)Fe(II)-like [P = tetraaryl porphyrinate dianion] species suggesting that the reactive species is a formal (heme)Fe(II)/Fe(IV)=O(non-heme) pair. The non-heme Fe(IV)=O is thus most likely responsible for C-H bond cleavage and subsequent radical chemistry. The photolysis of 1 in chlorobenzene or 1,2-dichlorobenzene resulted in C-Cl cleavage reactions and the formation of [[((6)L)Fe(III)-Cl...Fe(III)-Cl](2)O](2+) (3), with chloride ligands that are derived from solvent dehalogenation chemistry. The resulting organic products are biphenyl trichlorides or biphenyl monochlorides, derived from dichlorobenzene and chlorobenzene, respectively. Similarly, product 3 is obtained by the photolysis of benzene-benzyl chloride solutions of 1; the organic product is benzaldehyde (approximately 70%). A brief discussion of the dehalogenation chemistry, along with relevant environmental perspectives, is included.

Electron Spin Resonance Spectroscopy↗
PubMed2004

Heme-copper/dioxygen adduct formation relevant to cytochrome c oxidase: spectroscopic characterization of [(6L)FeIII-(O2(2-))-CuII]+.

In the further development and understanding of heme-copper dioxygen reactivity relevant to cytochrome c oxidase O(2)-reduction chemistry, we describe a high-spin, five-coordinate dioxygen (peroxo) adduct of an iron(II)-copper(I) complex, [((6)L)Fe(II)Cu(I)](BArF(20)) (1), where (6)L is a tetraarylporphyrinate with a tethered tris(2-pyridylmethyl)amine chelate for copper. Reaction of 1 with O(2) in MeCN affords a remarkably stable [t(1/2) (rt; MeCN) approximately 60 min] adduct, [((6)L)Fe(III)-(O(2) (2-))-Cu(II)](+) (2) [EPR silent; lambda(max)=418 (Soret), 561 nm], formulated as a peroxo complex based on manometry (1:O(2)=1:1; spectrophotometric titration, -40 degrees C, MeCN), mass spectrometry {MALDI-TOF-MS: (16)O(2), m/z 1191 ([((6)L)Fe(III)-((16)O(2) (2-))-Cu(II)](+)); (18)O(2), m/z 1195}, and resonance Raman spectroscopy (nu((O-O))=788 cm(-1); Delta(16)O(2)/(18)O(2)=44 cm(-1); Delta(16)O(2)/(16/18)O(2)=22 cm(-1)). (1)H and (2)H NMR spectroscopy (-40 degrees C, MeCN) reveals that 2 is the first heme-copper peroxo complex which is high-spin, with downfield-shifted pyrrole resonances (delta(pyrrole)=75 ppm, s, br) and upfield shifted peaks at delta= -22, -35, and -40 ppm, similar to the pattern observed for the mu-oxo complex [((6)L)Fe(III)-O-Cu(II)](BAr(F)) (3) (known S=2 system, antiferromagnetically coupled high-spin Fe(III) and Cu(II)). The corresponding magnetic moment measurement (Evans method, CD(3)CN, -40 degrees C) also confirms the S=2 spin state, with mu(B)=4.9. Structural insights were obtained from X-ray absorption spectroscopy, showing Fe-O (1.83 A) and Cu-O (1.882 A) bonds, and an Fe...Cu distance of 3.35(2) A, suggestive of a mu-1,2-peroxo ligand present in 2. The reaction of 2 with cobaltocene gives 3, differing from the observed full reduction seen with other heme-Cu peroxo complexes. Finally, thermal decomposition of 2 yields 3, with concomitant release of 0.5 mol O(2) per mol 2, as confirmed quantitatively by an alkaline pyrogallol dioxygen scavenging solution.

Binding Sites↗
PubMed2004

Heme/Cu/O2 reactivity: change in FeIII-(O2 2-)-CuII unit peroxo binding geometry effected by tridentate copper chelation.

A new heme-peroxo-copper complex structural type with mu-eta2:eta2 peroxo ligation has been generated utilizing a heterobinucleating ligand with bis(2-(2-pyridyl)ethyl)amine tridentate chelate for copper. Oxygenation of [(2L)FeIICuI]+ (1) at -80 degrees C in CH2Cl2/6%EtCN, 1 (lambdamax, 426, 530 nm) produces [(2L)FeIII-(O22-)-CuII)]+ (3) (lambdamax, 419, 488, 544, 575 nm). Stopped-flow kinetic/spectroscopic probing reveals that a superoxo complex, [(2L)FeIII-(O2-)...CuI(NCEt)]+ (2) (lambdamax = 544 nm), initially forms, k1 = 5.23 +/- 0.09 x 104 M-1 s-1 (-105 degrees C). Subsequent intramolecular reaction of the copper(I) ion in 2 occurs with k2 = 2.74 +/- 0.04 x 101 s-1 (-105 degrees C), producing 3. Resonance Raman spectroscopy (rR) confirms the peroxo assignment for 3; nu(O-O) = 747 cm-1 (Delta(18O2) = -40 cm-1). In an 16O-18O mixed isotope experiment a single band is observed at 730 cm-1. The low nu(O-O) value and the absence of a splitting of the 730 cm-1 band are indicative of a symmetrical binding of the peroxide group in a side-on mu-eta2:eta2 geometry. This conclusion is supported by X-ray absorption spectroscopy on 3. Copper K-edge EXAFS indicates a five-coordinate metal center: 2 N, 2.028(7) A; 2 O, 1.898(7) A; 1 N, 2.171(12) A. An outer-sphere Fe scatterer is found at 3.62(1) A. The iron center K-edge EXAFS fits to either a five- or six-coordinate metal center: 4 N(pyrrole), approximately 2.1 A; 1,2 O, approximately 1.9 A. A preedge feature (Fe(1s) --> Fe(3d) transition) at 7113.2(2) eV resembles that obtained for a eta2-peroxo ferric heme complex, being weaker and at approximately 1.5 eV lower energy than those found in five-coordinate (P)FeIII-X (in C4v symmetry) complexes. Arguments based on rR properties of relevant peroxo compounds also effectively point to the copper(II) ion in 3 as being side-on bound, leading to the very low O-O stretching frequency observed in comparison to those of heme-peroxo species or heme-peroxo-copper complexes with a tetradentate copper chelate. These investigations derive from interest in establishing relevant and/or fundamental O2 chemistry at heme-copper centers, in relation to heme-copper oxidase active-site chemistry.

Chelating Agents↗
PubMed2004

Mono-, bi-, and trinuclear CuII-Cl containing products based on the tris(2-pyridylmethyl)amine chelate derived from copper(I) complex dechlorination reactions of chloroform.

The ligand TMPA (tris(2-pyridylmethyl)amine) and its copper complexes have played a prominent role in recent (bio)inorganic chemistry studies; the copper(I) complex [CuI(TMPA)(CH3CN)]+ possesses an extensive dioxygen reactivity, and it is also known to effect the reductive dechlorination of substrates such as dichloromethane and benzyl and allyl chlorides. In this report, we describe a set of new analogues of TMPA, ligand 6TMPAOH, binucleating Iso-DO, and trinucleating SYMM. Copper(I) complexes with these ligands and a previously described binucleating ligand DO react with chloroform, resulting in reductive dechlorination and production of [CuIIx(L)Clx]x+ (x = 1, 2, or 3). X-ray crystal structures of [CuII(6TMPAOH)Cl]PF6, [CuII2(Iso-DO)Cl2](PF6)2, [CuII2(DO)Cl2](PF6)2, and [Cu3(SYMM)Cl3](PF6)3 are presented, and the compounds are also characterized by UV-vis and EPR spectroscopies as well as cyclic voltammetry. The steric influence of a pyridyl 6-substituent (in the complexes with 6TMPAOH, Iso-DO, and SYMM) on the solid state and solution structures and redox potentials are compared and contrasted to those chlorocopper(II) complexes with a pyridyl 5'-substituent (in [CuII2(DO)Cl2](PF6)2 and in [CuII(TMPA)Cl]+). Some insights into the reductive dechlorination process have been obtained by using 2H NMR spectroscopy in following the reaction of [Cu2(Iso-DO)(CH3CN)2](PF6)2 with CDCl3, in the presence or absence of a radical trap, 2,4-di-tert-butylphenol.

Chelating Agents↗
PubMed2004

Oxidant types in copper-dioxygen chemistry: the ligand coordination defines the Cu(n)-O2 structure and subsequent reactivity.

The considerable recent advances in copper-dioxygen coordination chemistry demonstrate the existence of a variety of dioxygen-derived Cu(n)-O(2) complexes, forming a basis for discussion of alternate oxidant types in copper chemistry and biochemistry. Peroxo complexes may react as nucleophilic reagents, and several types of electrophilic mono- or dicopper (hydro)peroxides exist. Side-on peroxo-dicopper(II) species effect aromatic hydroxylations, including phenolic substrates, in model systems and in the enzyme tyrosinase. Bis-micro-oxo-dicopper(III) entities are capable of hydrogen-atom abstraction reactions, or atom transfer to phosphines and sulfides. The scope and mechanisms of mononuclear Cu(II) superoxides or peroxides are yet to be established, but may be relevant to monooxygenases like peptidylglycine alpha-hydroxylating monooxygenase.

Copper↗
PubMed2004

Solvent effects on the conversion of dicopper(II) micro-eta(2):eta(2)-peroxo to bis-micro-oxo dicopper(III) complexes: direct probing of the solvent interaction.

A new tridentate ligand, PYAN, is employed to investigate solvent influences for dioxygen reactivity with [Cu(PYAN)(MeCN)]B(C(6)F(5))(4) (1). Stopped-flow kinetic studies confirm that the adducts [[u(II)(PYAN)]2)(O(2))][B(C(6)F(5))(4)](2) (2(Peroxo)) and [[u(III)(PYAN)]2)(O)(2)][B(C(6)F(5))(4)](2) (2(Oxo)) are in rapid equilibrium. Thermodynamic parameters for the equilibrium between 2(Peroxo) and 2(Oxo) re as follows: THF, deltaH degrees approximately -15.7 kJ/mol, deltaS degrees approximately -83 J/K.mol; acetone, deltaH degrees approximately -15.8 kJ/mol, deltaS degrees approximately -76 J/K.mol. UV-visible absorption and resonance Raman spectroscopic signatures demonstrate that the equilibrium is highly solvent dependent; the mixture is mostly 2(Peroxo) in CH(2)Cl(2), but there are significantly increasing quantities of 2(Oxo) along the series methylene chloride --> diethyl ether --> acetone --> tetrahydrofuran (THF). Copper(II)-N(eq) stretches (239, 243, 244, and 246 cm(-)(1) in CH(2)Cl(2), Et(2)O, acetone, and THF, respectively) are identified for 2(Peroxo), but they are not seen in 2(Oxo), revealing for the first time direct evidence for solvent coordination in the more open 2(Peroxo) structure.

Copper↗
PubMed2004

Synthesis and spectroscopy of micro-oxo (O(2)(-))-bridged heme/non-heme diiron complexes: models for the active site of nitric oxide reductase.

In this paper, we describe the synthesis and study of a series of heme/non-heme Fe-O-Fe' complexes supported by a porphyrin and the tripodal nitrogen ligand TMPA [TMPA = tris(2-pyridylmethyl)amine]. The complete synthesis of [((6)L)Fe-O-Fe(X)](+) (1) (X = OMe(-) or Cl(-), 69:31 ratio), where (6)L is the dianion of 5-(o-O-[(N,N-bis(2-pyridylmethyl)-2-(6-methoxyl)pyridinemethanamine)phenyl]-10,15,20-tris(2,6-difluorophenyl)porphine, is reported. The crystal structure for 1.PF(6) reveals an intramolecular heme/non-heme diferric complex bridged by an Fe-O-Fe' moiety; 90 degree angle (Fe-O-Fe') = 166.7(3) degrees, and d(Fe.Fe') = 3.556 A. Crystal data for C(70)H(57)ClF(12)Fe(2)N(8)O(3)P (1.PF(6)): triclinic, Ponemacr;, a = 13.185(3) A, b = 14.590 (3) A, c = 16.885(4) A, alpha = 104.219(4) degrees, beta = 91.572(4) degrees, gamma = 107.907(4) degrees, V = 2977.3(11) A(3), Z = 2, T = 150(2) K. Complex 1 (where X = Cl(-)) is further characterized by UV-vis (lambda(max) = 328, 416 (Soret), 569 nm), (1)H NMR (delta 27-24 [TMPA -CH(2)-], 16.1 [pyrrole-H], 15.2-10.5 [PY-3H, PY-5H], 7.9-7.2 [m- and p-phenyl-H], 6.9-5.8 [PY-4H] ppm), resonance Raman (nu(as)(Fe-O-Fe') 844 cm(-)(1)), and Mössbauer (delta(Fe) = 0.47, 0.41 mm/s; deltaE(A) = 1.59, 0.55 mm/s; 80 K) spectroscopies, MALDI-TOF mass spectrometry (m/z 1202), and SQUID susceptometry (J = - 114.82 cm(-)(1), S = 0). We have also synthesized a series of 3-, 4-, and 5-methyl-substituted as well as selectively deuterated TMPA(Fe') complexes and condensed these with the hydroxo complex (F(8))FeOH or (F(8)-d(8))FeOH to yield "untethered" Fe-O-Fe' analogues. Along with selective deuteration of the methylene hydrogens in TMPA, complete (1)H NMR spectroscopic assignments for 1 have been accomplished. The magnetic properties of several of the untethered complexes and a comparison to those of 1 are also presented. Complex 1 and related species represent good structural and spectroscopic models for the heme/non-heme diiron active site in the enzyme nitric oxide reductase.

Binding Sites↗
PubMed2003

An iron-peroxo porphyrin complex: new synthesis and reactivity toward a Cu(II) complex giving a heme-peroxo-copper adduct.

Side-on eta2-peroxo-iron porphyrins are strong nucleophiles. In cytochrome P450-like aromatase and other enzymes, such species are postulated as the active oxidants. In cytochrome c oxidase, hemea3-peroxo, hemea3-hydroperoxo, or hemea3-(mu-peroxo)-copper species are proposed as transient intermediates forming prior to O-O bond cleavage. In this report, we describe (1) a facile method for reduction of a heme-O2 species [(F8TPP)FeIII(O2-)(S)] (2), generating the ferric peroxo porphyrin complex [(F8TPP)FeIII(O22-)]- (3) (UV-vis, THF: lambdamax = 435 (Soret), 540(sh), 561; EPR: g = 8.7, 4.2), and (2) that this can be subsequently reacted with a ligand-copper(II) complex, [CuII(TMPA)-(CH3CN)](ClO4)2 (4), affording a heme-peroxo-copper heterobinuclear compound, [(F8TPP)FeII(O22-)-CuII(TMPA)](ClO4) (5). Generation of [(F8TPP)FeIII(O22-)]- (3) using cobaltocene as a one-electron reductant was monitored by UV-vis, EPR, and 1H NMR spectroscopies. Reaction between 3 and 4 was followed by UV-vis spectroscopy, and the product 5 could be precipitated and characterized. Coordination by copper(II) in 5 makes possible further reduction of the mu-peroxo complex by cobaltocene yielding the mu-oxo analogue, [(F8TPP)FeIII(O2-)-CuII(TMPA)](ClO4) (6).

Copper↗
PubMed2003

Distinguishing rate-limiting electron versus H-atom transfers in Cu2O2-mediated oxidative N-dealkylations: application of inter- versus intramolecular kinetic isotope effects.

Copper-dioxygen adducts are important biological oxidants. To gain a better understanding of the underlying chemistries of such species, we report on a series of Cu2II-O2 complexes, [{CuII(MePY2)R'}2(O2)](B(C6F5)4)2 (1R') (where (MePY2)R' is a 4-pyridyl substituted bis[2-(2-(4-R'-pyridyl)ethyl]methylamine; R' = H, MeO, Me2N; Zhang, C. X.; et al. J. Am. Chem. Soc. 2003, 125, 634-635), which readily oxidize exogenous substrates. In this study, we explore the mechanism by which 1R' facilitates the oxidative N-dealkylation of para-substituted N,N-dimethylanilines (R-DMA; R = MeO, Me, H, CN). In the case of 1H, the linear free-energy correlation plot (rho = -2.1) and intramolecular deuterium kinetic isotope effect (KIEintra, using p-R-(C6H4)-N(CH3)(CD3)) profile suggest that R-DMA oxidation occurs through rate-limiting electron transfer (ET). This mechanism was further enforced by comparison of KIEintra versus the intermolecular KIE (KIEinter, using p-R-(C6H4)-N(CH3)2 versus p-R-(C6H4)-N(CD3)2). It was found that KIEinter < KIEintra, suggesting an ET process. In the case of both 1MeO and 1Me2N, the KIEintra profile and linear free-energy correlation plots (rho = -0.49 and -0.99 for 1Me2N and 1MeO with especially poor fitting for the latter) are inconclusive in distinguishing between a rate-limiting ET or hydrogen atom transfer (HAT) pathway. Comparisons of KIEinter versus KIEintra demonstrate a switch in mechanism from ET to HAT for 1Me2N and 1MeO oxidation of R-DMA as R-DMA is made less reducing. In the case of 1Me2N, MeO-DMA and Me-DMA are oxidized via a rate-limiting ET (KIEinter < KIEintra), while H-DMA and CN-DMA are oxidized through a HAT pathway (KIEinter approximately KIEintra). For 1MeO, oxidation occurs through an ET pathway for MeO-, Me-, and H-DMA (KIEinter < KIEintra), while CN-DMA is oxidized though a HAT process (KIEinter approximately KIEintra). Copper complex attributes, which may contribute to the mechanistic observations, are suggested.

Alkylation↗
PubMed2003

The rate of O2 and CO binding to a copper complex, determined by a "flash-and-trap" technique, exceeds that for hemes.

The observation and fast time-scale kinetic determination of a primary dioxygen-copper interaction have been studied. The ability to photorelease carbon monoxide from [Cu(I)(tmpa)(CO)](+) in mixtures of CO and O(2) in tetrahydrofuran (THF) between 188 and 218 K results in the observable formation of a copper-superoxide species, [Cu(II)(tmpa)(O(2)(-))](+) lambda(max) = 425 nm. Via this "flash-and-trap" technique, temperature-dependent kinetic studies on the forward reaction between dioxygen and [Cu(I)(tmpa)(thf)](+) afford activation parameters DeltaH = 7.62 kJ/mol and DeltaS = -45.1 J/mol K. The corresponding reverse reaction proceeds with DeltaH = 58.0 kJ/mol and DeltaS = 105 J/mol K. Overall thermodynamic parameters are DeltaH degrees = -48.5 kJ/mol and DeltaS degrees = -140 J/mol K. The temperature-dependent data allowed us to determine the room-temperature second-order rate constant, k(O2) = 1.3 x 10(9) M(-1) s(-1). Comparisons to copper and heme proteins and synthetic complexes are discussed.

Carbon Monoxide↗
PubMed2003

Synthesis, characterization, and laser flash photolysis reactivity of a carbonmonoxy heme complex.

We present here the synthesis, characterization, and flash photolysis study of [(F(8)TPP)Fe(II)(CO)(THF)] (1) [F(8)TPP = tetrakis(2,6-difluorophenyl)porphyrinate(2-)]. Complex 1 crystallizes from THF/heptane solvent system as a tris-THF solvate, [(F(8)TPP)Fe(II)(CO)(THF)].3THF (1.3THF), with ferrous ion in the porphyrin plane (C(61)H(52)F(8)FeN(4)O(5); a = 11.7908(2) A, b = 20.4453(2) A, c = 39.9423(3), alpha = 90 degrees, beta = 90 degrees, gamma = 90 degrees; orthorhombic, P2(1)2(1)2(1), Z = 8; Fe-N(4)(av) = 2.00 A; N-Fe-N (all) = 90.0 degrees ). This complex (as 1.THF) has also been characterized by (1)H NMR [six-coordinate, low-spin heme; CD(3)CN, RT, delta 8.82 (s, pyrrole-H, 8H), 7.89 (s, para-phenyl-H, 8H), 7.46 (s, meta-phenyl-H, 4H), 3.58 (s, THF, 8H), 1.73 (s, THF, 8H)], (2)H NMR (pyrrole-deuterated analogue) [(F(8)TPP-d(8))Fe(II)(CO)(THF)] [THF, RT, delta 8.78 ppm (s, pyrrole-D)], (13)C NMR (on (13)CO-enriched adduct) [THF-d(8), RT, delta 206.5 ppm; CD(2)Cl(2), RT, delta 206.1 ppm], UV-vis [THF, RT, lambda(max), 411 (Soret), 525 nm], and IR [293 K, solution, nu(CO) 1979 cm(-)(1) (THF), 1976 cm(-)(1) (acetone), 1982 cm(-)(1) (CH(3)CN)] spectroscopies. In order to more fully understand the intricacies of solvent-ligand binding (as compared to CO rebinding to the photolyzed heme), we have also synthesized the bis-THF adduct [(F(8)TPP)Fe(II)(THF)(2)]. Complex 2 also crystallizes from THF/heptane solvent system as a bis-THF solvate, [(F(8)TPP)Fe(II)(THF)(2)].2THF (2.2THF), with ferrous iron in the porphyrin plane (C(60)H(52)F(8)FeN(4)O(4); a = 21.3216(3) A, b = 12.1191(2) A, c = 21.0125(2) A, alpha = 90 degrees, beta = 105.3658(5) degrees, gamma = 90 degrees; monoclinic, C2/c, Z = 4; Fe-N(4)(av) = 2.07 A; N-Fe-N (all) = 90.0 degrees ). Further characterization of 2 includes UV-vis [THF, lambda(max), 421 (Soret), 542 nm] and (1)H NMR [six-coordinate, high spin heme; THF-d(8), RT, delta 56.7 (s, pyrrole-H, 8H), 8.38 (s, para-phenyl-H, 8H), 7.15 (s, meta-phenyl-H, 4H)] spectroscopies. Flash photolysis studies employing 1 were able to resolve the CO rebinding kinetics in both THF and cyclohexane solvents. In CO saturated THF [[CO] approximately 5 mM] and at [1] congruent with 5 microM, the conversion of [(F(8)TPP)Fe(II)(THF)(2)] (produced after photolytic displacement of CO) to [(F(8)TPP)Fe(II)(CO)(THF)] was monoexponential, with k(obs) = 1.6 (+/-0.2) x 10(4) s(-)(1). Reduction in [CO] by vigorous Ar purging gave k(obs) congruent with 10(3) s(-)(1) in cyclohexane. The study presented in this report lays the foundation for applying fast-time scale studies based on CO flash photolysis to the more complicated heterobimetallic heme/Cu systems.

Carbon Monoxide↗
PubMed2003

Spectroscopy and bonding in side-on and end-on Cu2(S2) cores: comparison to peroxide analogues.

Spectroscopic methods combined with density functional calculations were used to study the disulfide-Cu(II) bonding interactions in the side-on micro -eta(2):eta(2)-bridged Cu(2)(S(2)) complex, [[Cu(II)[HB(3,5-Pr(i)(2)pz)(3)]](2)(S(2))], and the end-on trans- micro -1,2-bridged Cu(2)(S(2)) complex, [[Cu(II)(TMPA)](2)(S(2))](2+), in correlation to their peroxide structural analogues. Resonance Raman shows weaker S-S bonds and stronger Cu-S bonds in the disulfide complexes relative to the O-O and Cu-O bonds in the peroxide analogues. The weaker S-S bonds come from the more limited interaction between the S 3p orbitals relative to that of the O 2s/p hybrid orbitals. The stronger Cu-S bonds result from the more covalent Cu-disulfide interactions relative to the Cu-peroxide interactions. This is consistent with the higher energy of the disulfide valence level relative to that of the peroxide. The ground states of the side-on Cu(2)(S(2))/Cu(2)(O(2)) complexes are more covalent than those of the end-on Cu(2)(S(2))/Cu(2)(O(2)) complexes. This derives from the larger sigma-donor interactions in the side-on micro -eta(2):eta(2) structure, which has four Cu-disulfide/peroxide bonds, relative to the end-on trans- micro -1,2 structure, which forms two bonds to the Cu. The larger disulfide/peroxide sigma-donor interactions in the side-on complexes are reflected in their more intense higher energy disulfide/peroxide to Cu charge transfer transitions in the absorption spectra. The large ground-state covalencies of the side-on complexes result in significant nuclear distortions in the ligand-to-metal charge transfer excited states, which give rise to the strong resonance Raman enhancements of the metal-ligand and intraligand vibrations. Particularly, the large covalency of the Cu-disulfide interaction in the side-on Cu(2)(S(2)) complex leads to a different rR enhancement profile, relative to the peroxide analogues, reflecting a S-S bond distortion in the opposite directions in the disulfide/peroxide pi(sigma) to Cu charge transfer excited states. A ligand sigma back-bonding interaction exists only in the side-on complexes, and there is more sigma mixing in the side-on Cu(2)(S(2)) complex than in the side-on Cu(2)(O(2)) complex. This sigma back-bonding is shown to significantly weaken the S-S/O-O bond relative to that of the analogous end-on complex, leading to the low nu(S)(-)(S)/nu(O)(-)(O) vibrational frequencies observed in the resonance Raman spectra of the side-on complexes.

Copper↗
PubMed2003

Copper(I) and copper(II) complexes possessing cross-linked imidazole-phenol ligands: structures and dioxygen reactivity.

Catalytic reduction of O2 to H2O, and coupling to membrane proton translocation, occurs at the heterobinuclear heme a3-CuB active site of cytochrome c oxidase. One of the CuB ligated histidines is cross-linked to a neighboring tyrosine (C-N bond; tyrosine C6 and histidine epsilon-nitrogen), and the protic residue of this cross-linked His-Tyr moiety is proposed to participate as both an electron and a proton donor in the catalytic dioxygen reduction event. To provide insight into the chemistry of such a moiety, we have synthesized and characterized tetra- and tridentate pyridylalkylamine chelate ligands {LN4OR and LN3OR (R = H or Me)}, which include an imidazole-phenol (or anisole) cross-link and their copper(I/II) complexes. [CuI(LN4OH)]B(C6F5)4 (1) reacts with dioxygen at -80 degrees C in THF, forming an unstable trans-mu-1,2-peroxodicopper(II)complex, which subsequently converts to a dimeric copper(II)-phenolate complex [{Cu(LN4O-)}2](B(C6F5)4)2 (5a). The close analogue [CuI(LN4OMe)]B(C6F5)4 (3) binds dioxygen reversibly at -80 degrees C in tetrahydrofuran. Stopped-flow kinetics of the reaction [CuI(LN3OH)]ClO4 (2) with O2 in CH2Cl2 indicate a steady formation of the purple dimeric product [{Cu(LN3O-)}2](ClO4)2 (5b), which has been analyzed in the temperature range from -40 to +20 degrees C, DeltaH = -9.6 (6) kJ mol-1, DeltaS = -168 (2) J mol-1 K-1 (k(-40 degrees C) = 1.05(4) x 106 and k(+20 degrees C) = 4.6(2) x 105 M-2 s-1). The X-ray crystal structures of 1, [CuII(LN3OH)(MeOH)(OClO3-)](ClO4) (4), 5a, and 5b are reported.

Copper↗
PubMed2003

Synthesis and characterization of reduced heme and heme/copper carbonmonoxy species.

Carbon monoxide readily binds to heme and copper proteins, acting as a competitive inhibitor of dioxygen. As such, CO serves as a probe of protein metal active sites. In our ongoing efforts to mimic the active site of cytochrome c oxidase, reactivity toward carbon monoxide offers a unique opportunity to gain insight into the binding and spectroscopic characteristics of synthetic model compounds. In this paper, we report the synthesis and characterization of CO-adducts of ((5/6)L)Fe(II), [((5/6)L)Fe(II)...Cu(I)](B(C(6)F(5))(4)), and [(TMPA)Cu(I)(CH(3)CN)](B(C(6)F(5))(4)), where TMPA = tris(2-pyridylmethyl)amine and (5/6)L = a tetraarylporphyrinate tethered in either the 5-position ((5)L) or 6-position ((6)L) to a TMPA copper binding moiety. Reaction of ((5/6)L)Fe(II) [in THF (293 K): UV-vis 424 (Soret), 543-544 nm; (1)H NMR delta(pyrrole) 52-59 ppm (4 peaks); (2)H NMR (from ((5)L-d(8))Fe(II)) delta(pyrrole) 53.3, 54.5, 55.8, 56.4 ppm] with CO in solution at RT yielded ((5/6)L)Fe(II)-CO [in THF (293 K): UV-vis 413-414 (Soret), 532-533 nm; IR nu(CO)(Fe) 1976-1978 cm(-1); (1)H NMR delta(pyrrole) 8.8 ppm; (2)H NMR (from ((5)L-d(8))Fe(II)-CO) delta(pyrrole) 8.9 ppm; (13)C NMR delta((CO)Fe) 206.8-207.1 ppm (2 peaks)]. Experiments repeated in acetonitrile, acetone, toluene, and dichloromethane showed similar spectroscopic data. Binding of CO resulted in a change from five-coordinate, high-spin Fe(II) to six-coordinate, low-spin Fe(II), as evidenced by the upfield shift of the pyrrole resonances to the diamagnetic region ((1)H and (2)H NMR spectra). Addition of CO to [((5/6)L)Fe(II)...Cu(I)](B(C(6)F(5))(4)) [in THF (293 K): UV-vis ((6)L only) 424 (Soret), 546 nm; (1)H NMR delta(pyrrole) 54-59 ppm (multiple peaks); (2)H NMR (from [((5)L-d(8))Fe(II).Cu(I)](B(C(6)F(5))(4))) delta(pyrrole) 53.4 ppm (br)] gave the bis-carbonyl adduct [((5/6)L)Fe(II)-CO...Cu(I)-CO](B(C(6)F(5))(4)) [in THF (293 K): UV-vis ((6)L only) 413 (Soret), 532 nm; IR nu(CO)(Fe) 1971-1973 cm(-1), nu(CO)(Cu) 2091-2093 cm(-1), approximately 2070(sh) cm(-1); (1)H NMR delta(pyrrole) 8.7-8.9 ppm; (2)H NMR (from [((5)L-d(8))Fe(II)-CO...Cu(I)-CO](B(C(6)F(5))(4))) delta(pyrrole) 8.9 ppm; (13)C NMR delta((CO)Fe) 206.8-208.1 ppm (2 peaks), delta((CO)Cu) 172.4 ((5)L), 178.2 ((6)L) ppm]. Experiments in acetonitrile, acetone, and toluene exhibited spectral features similar to those reported. The [((5/6)L)Fe(II)-CO.Cu(I)-CO](B(C(6)F(5))(4)) compounds yielded (CO)(Fe) spectra analogous to those seen for ((5/6)L)Fe(II)-CO and (CO)(Cu) spectra similar to those seen for [(TMPA)Cu(I)-CO](B(C(6)F(5))(4)) [in THF (293 K): IR nu(CO)(Cu) 2091 cm(-1), approximately 2070(sh) cm(-1); (13)C NMR delta((CO)Cu) 180.3 ppm]. Additional IR studies were performed in which the [((5)L)Fe(II)-CO...Cu(I)-CO](B(C(6)F(5))(4)) in solution was bubbled with argon in an attempt to generate the iron-only mono-carbonyl [((5)L)Fe(II)-CO.Cu(I)](B(C(6)F(5))(4)) species; in coordinating solvent or with axial base present, decreases in characteristic IR-band intensities revealed complete loss of CO from copper and variable loss of CO from the heme.

Copper↗