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Despite the ease of preparing di-ferric [2Fe-2S] clusters, preparing stable mixed-valence analogues remains a challenge, as these clusters have limited thermal stability. Herein we identify two decomposition products of the mixed-valence thiosalicylate-ligated [2Fe-2S] cluster, [Fe 2 S 2 (SArCOO) 2 ] 3- ((SArCOO) 2- = thiosalicylate).

An enantioselective Pd-catalyzed vicinal diamination of unactivated alkenes using N-fluorobenzenesulfonimide as both an oxidant and a source of nitrogen is reported. The use of Ph-pybox and Ph-quinox ligands afforded differentially protected vicinal diamines in good yields with high enantioselectivities. Mechanistic experiments revealed that the high enantioselectivity arises from selective formation of only one of four possible diastereomeric aminopalladation products of the chiral Pd complex. The aminopalladation complex was characterized by X-ray crystallography.

The role of proton transfer in the photoluminescence intermittency (PI) of single molecules of violamine R (VR) overgrown in potassium acid phthalate (KAP) crystals is evaluated in comparisons of protonated (KAP) and deuterated (DKAP) mixed crystals between 23 and 60 °C. The PI is analyzed by the construction of cumulative distribution functions that are statistically compared. We find that the on- and off-interval duration distributions change with isotopic substitution consistent with proton transfer contributing to the PI of VR. The on- and off-interval duration distributions have distinct temperature dependencies consistent with different mechanisms for dark state production and decay. Additional evidence for proton-transfer is provided by distributions of single molecule emission-energy maxima that reflect emission from protonated and deprotonated VR. A mechanism for the PI of KAP is presented, where the dark state is assigned to formation of the colorless, leuco form of VR, formed by proton transfer from VR to the KAP lattice, and decay of the dark state involves ring-opening promoted by proton transfer from KAP to VR. The distributed kinetics for dark-state production and decay are modeled using a log-normal distribution for the PI data in preference to a power-law previously assumed. A discussion of the log-normal distribution with regards to PI and proton transfer is presented.

Separated concerted proton-electron transfer (sCPET) reactions of two series of phenols with pendent substituted pyridyl moieties are described. The pyridine is either attached directly to the phenol (HOAr-pyX) or connected through a methylene linker (HOArCH(2)pyX) (X = 4-NO(2), 5-CF(3), 4-CH(3), and 4-NMe(2)). Electron-donating and -withdrawing substituents have a substantial effect on the chemical environment of the transferring proton, as indicated by IR and (1)H NMR spectra, X-ray structures, and computational studies. One-electron oxidation of the phenols occurs concomitantly with proton transfer from the phenolic oxygen to the pyridyl nitrogen. The oxidation potentials vary linearly with the pK(a) of the free pyridine (pyX), with slopes slightly below the Nerstian value of 59 mV/pK(a). For the HOArCH(2)pyX series, the rate constants k(sCPET) for oxidation by NAr(3)(•+) or [Fe(diimine)(3)](3+) vary primarily with the thermodynamic driving force (ΔG°(sCPET)), whether ΔG° is changed by varying the potential of the oxidant or the substituent on the pyridine, indicating a constant intrinsic barrier λ. In contrast, the substituents in the HOAr-pyX series affect λ as well as ΔG°(sCPET), and compounds with electron-withdrawing substituents have significantly lower reactivity. The relationship between the structural and spectroscopic properties of the phenols and their CPET reactivity is discussed.

Hydrogen activation by nickel: A tBuPCP pincer ligand facilitates formation of cationic Ni(II) dihydrogen and terminal dinitrogen complexes. The compounds have been characterized by X-ray crystallography and NMR spectroscopy. Addition of base promotes heterolytic cleavage of H(2) to form the corresponding neutral hydride complex., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Cyclopentadienyl and pentamethylcyclopentadienyl ruthenium(II) complexes have been synthesized with cyclic (RPCH(2)NR'CH(2))(2) ligands, with the goal of using these [Cp(R'')Ru(P(R)(2)N(R')(2))](+) complexes for catalytic O(2) reduction to H(2)O (R = t-butyl, phenyl; R' = benzyl, phenyl; R" = methyl, H). In each compound, the Ru is coordinated to the two phosphines, positioning the amines of the ligand in the second coordination sphere where they may act as proton relays to a bound dioxygen ligand. The phosphine, amine, and cyclopentadienyl substituents have been systematically varied in order to understand the effects of each of these parameters on the properties of the complexes. These Cp(R")Ru(P(R)(2)N(R')(2))(+) complexes react with O(2) to form η(2)-peroxo complexes, which have been characterized by NMR, IR, and X-ray crystallography. The peak reduction potentials of the O(2) ligated complexes have been shown by cyclic voltammetry to vary as much as 0.1 V upon varying the phosphine and amine. In the presence of acid, protonation of these complexes occurs at the pendent amine, forming a hydrogen bond between the protonated amine and the bound O(2). The ruthenium-peroxo complexes decompose upon reduction, precluding catalytic O(2) reduction. The irreversible reduction potentials of the protonated O(2) complexes depend on the basicity of the pendent amine, giving insight into the role of the proton relay in facilitating reduction.

A synthetic cycle for the CO(2)-to-CO conversion (with subsequent release of CO) based on iron(II), a redox-active pydridinediimine ligand (PDI), and an O-atom acceptor is reported. This conversion is a passive-type ligand-based reduction, where the electrons for the CO(2) conversion are supplied by the reduced PDI ligand and the ferrous state of the iron is conserved.

The AIE properties of two trifluoromethyl substituted distyrylbenzene model compounds were compared. The fluorescence quantum efficiency of these molecules can be modulated by tuning their subtle solid-state intermolecular interactions.

Sodium terephthalate (TA) produced from a PET pyrolysis product and waste glycerol (WG) from biodiesel manufacture were supplied to Pseudomonas putida GO16 in a fed-batch bioreactor. Six feeding strategies were employed by altering the sequence of TA and WG feeding. P. putida GO16 reached 8.70 g/l cell dry weight (CDW) and 2.61 g/l PHA in 48 h when grown on TA alone. When TA and WG were supplied in combination, biomass productivity (g/l/h) was increased between 1.3- and 1.7-fold and PHA productivity (g/l/h) was increased 1.8- to 2.2-fold compared to TA supplied alone. The monomer composition of the PHA accumulated from TA or WG was predominantly composed of 3-hydroxydecanoic acid. PHA monomers 3-hydroxytetradeeanoic acid and 3-hydroxytetradecenoic acid were not present in PHA accumulated from TA alone but were present when WG was supplied to the fermentation. When WG was either the sole carbon source or the predominant carbon source supplied to the fermentation the molecular weight of PHA accumulated was lower compared to PHA accumulated when TA was supplied as the sole substrate. Despite similarities in data for the properties of the polymers, PHAs produced with WG present in the PHA accumulation phase were tacky while PHA produced where TA was the sole carbon substrate in the polymer accumulation phase exhibited little or no tackiness at room temperature. The co-feeding of WG to fermentations allows for increased utilisation of TA. The order of feeding of WG and TA has an effect on TA utilisation and polymer properties.

The synthesis, structural, and spectroscopic characterization of four new coordinatively unsaturated mononuclear thiolate-ligated manganese(II) complexes ([Mn(II)(S(Me2)N(4)(6-Me-DPEN))](BF(4)) (1), [Mn(II)(S(Me2)N(4)(6-Me-DPPN))](BPh(4))·MeCN (3), [Mn(II)(S(Me2)N(4)(2-QuinoPN))](PF(6))·MeCN·Et(2)O (4), and [Mn(II)(S(Me2)N(4)(6-H-DPEN)(MeOH)](BPh(4)) (5)) is described, along with their magnetic, redox, and reactivity properties. These complexes are structurally related to recently reported [Mn(II)(S(Me2)N(4)(2-QuinoEN))](PF(6)) (2) (Coggins, M. K.; Kovacs, J. A. J. Am. Chem. Soc.2011, 133, 12470). Dioxygen addition to complexes 1-5 is shown to result in the formation of five new rare examples of Mn(III) dimers containing a single, unsupported oxo bridge: [Mn(III)(S(Me2)N(4)(6-Me-DPEN)](2)-(μ-O)(BF(4))(2)·2MeOH (6), [Mn(III)(S(Me2)N(4)(QuinoEN)](2)-(μ-O)(PF(6))(2)·Et(2)O (7), [Mn(III)(S(Me2)N(4)(6-Me-DPPN)](2)-(μ-O)(BPh(4))(2) (8), [Mn(III)(S(Me2)N(4)(QuinoPN)](2)-(μ-O)(BPh(4))(2) (9), and [Mn(III)(S(Me2)N(4)(6-H-DPEN)](2)-(μ-O)(PF(6))(2)·2MeCN (10). Labeling studies show that the oxo atom is derived from (18)O(2). Ligand modifications, involving either the insertion of a methylene into the backbone or the placement of an ortho substituent on the N-heterocyclic amine, are shown to noticeably modulate the magnetic and reactivity properties. Fits to solid-state magnetic susceptibility data show that the Mn(III) ions of μ-oxo dimers 6-10 are moderately antiferromagnetically coupled, with coupling constants (2J) that fall within the expected range. Metastable intermediates, which ultimately convert to μ-oxo bridged 6 and 7, are observed in low-temperature reactions between 1 and 2 and dioxygen. Complexes 3-5, on the other hand, do not form observable intermediates, thus illustrating the effect that relatively minor ligand modifications have upon the stability of metastable dioxygen-derived species.

A model system for biological Rieske clusters that incorporates bis-benzimidazolate ligands ((Pr)bbim)(2-) has been developed ((Pr)bbimH(2) = 4,4-bis(benzimidazol-2-yl)heptane). The diferric and mixed-valence clusters have been prepared and characterized in both their protonated and deprotonated states. The thermochemistry of interconversions of these species has been measured, and the effect of protonation on the reduction potential is in good agreement to that observed in the biological systems. The mixed-valence and protonated congener [Fe(2)S(2)((Pr)bbim)((Pr)bbimH)](Et(4)N)(2) (4) reacts rapidly with TEMPO or p-benzoquinones to generate diferric and deprotonated [Fe(2)S(2)((Pr)bbim)(2)](Et(4)N)(2) (1) and 1 equiv of TEMPOH or 0.5 equiv of p-benzohydroquinones, respectively. The reaction with TEMPO is the first well-defined example of concerted proton-electron transfer (CPET) at a synthetic ferric/ferrous [Fe-S] cluster., (© 2012 American Chemical Society)

Pyrolysis of plastic waste is an alternative way of plastic recovery and could be a potential solution for the increasing stream of solid waste. The objective of this work was to increase the yield the gaseous olefins (monomers) as feedstock for polymerization process and to test the applicability of a commercial Ziegler-Natta (Z-N): TiCl(4)/MgCl(2) for cracking a mixture of polyolefins consisted of 46%wt. of low density polyethylene (LDPE), 30%wt. of high density polyethylene (HDPE) and 24%wt. of polypropylene (PP). Two sets of experiments have been carried out at 500 and 650°C via catalytic pyrolysis (1% of Z-N catalyst) and at 650 and 730°C via only-thermal pyrolysis. These experiments have been conducted in a lab-scale, fluidized quartz-bed reactor of a capacity of 1-3kg/h at Hamburg University. The results revealed a strong influence of temperature and presence of catalyst on the product distribution. The ratios of gas/liquid/solid mass fractions via thermal pyrolysis were: 36.9/48.4/15.7%wt. and 42.4/44.7/13.9%wt. at 650 and 730°C while via catalytic pyrolysis were: 6.5/89.0/4.5%wt. and 54.3/41.9/3.8%wt. at 500 and 650°C, respectively. At 650°C the monomer generation increased by 55% up to 23.6%wt. of total pyrolysis products distribution while the catalyst was added. Obtained yields of olefins were compared with the naphtha steam cracking process and other potentially attractive processes for feedstock generation. The concept of closed cycle material flow for polyolefins has been discussed, showing the potential benefits of feedstock recycling in a plastic waste management., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Even though mechanical properties depend strongly on the arrangement of collagen fibers in mineralized tissues, it is not yet well resolved. Only a few semi-quantitative evaluations of the fiber arrangement in bone, like spectroscopic techniques or circularly polarized light microscopy methods are available. In this study the out-of-plane collagen arrangement angle was calibrated to the linear birefringence of a longitudinally fibered mineralized turkey leg tendon cut at variety of angles to the main axis. The calibration curve was applied to human cortical bone osteons to quantify the out-of-plane collagen fibers arrangement. The proposed calibration curve is normalized to sample thickness and wavelength of the probing light to enable a universally applicable quantitative assessment. This approach may improve our understanding of the fibrillar structure of bone and its implications on mechanical properties., (Copyright © 2011 Elsevier Inc. All rights reserved.)

A series of pincer ((tBu)PCP)Pd(II)-OR complexes ((tBu)PCP = 2,6-bis(CH(2)P(t)Bu(2))C(6)H(3), R = H, CH(3), C(6)H(5), CH(2)C(CH(3))(3), CH(2)CH(2)F, CH(2)CHF(2), CH(2)CF(3)) were synthesized to explore the generality of hydrogenolysis reactions of palladium-oxygen bonds. Hydrogenolysis of the Pd hydroxide complex to generate the Pd hydride complex and water was shown to be inhibited by formation of a water-bridged, hydrogen-bonded Pd(II) hydroxide dimer. The Pd alkoxide and aryloxide complexes exhibited more diverse reactivity. Depending on the characteristics of the -OR ligand (steric bulk, electron-donating ability, and/or the presence of β-hydrogen atoms), hydrogenolysis was complicated by hydrolysis by adventitious water, a lack of reactivity with hydrogen, or a competing dissociative β-hydride abstraction reaction pathway. Full selectivity for hydrogenolysis was observed with the partially fluorinated Pd(II) 2-fluoroethoxide complex. The wide range of Pd-OR substrates examined helps to clarify the variety of reaction pathways available to late-transition-metal alkoxides as well as the conditions necessary to tune the reactivity to hydrogenolysis, hydrolysis, or dissociative β-hydride abstraction.

Ethyl acetate extract of the sponge Ircinia sp., collected by SCUBA divers off the coast of southern India, contained a cholest-based sterol of insignificant antimicrobial activity, with one carboxylic acid side chain (3alpha, 7beta-dihydroxy-5beta-cholan-24-oic acid, DCA). The structure of the compound was determined by spectroscopic data and single crystal X-ray diffraction studies. DCA crystallizes in the tetragonal space group P4(1)2(1)2, chirality documented by solution optical rotation [alpha]D = +67.4 degrees (c 0.16, CHCl3).

Nitrile hydratases (NHases) are thiolate-ligated Fe(III)- or Co(III)-containing enzymes, which convert nitriles to the corresponding amide under mild conditions. Proposed NHase mechanisms involve M(III)-NCR, M(III)-OH, M(III)-iminol, and M(III)-amide intermediates. There have been no reported crystallographically characterized examples of these key intermediates. Spectroscopic and kinetic data support the involvement of a M(III)-NCR intermediate. A H-bonding network facilitates this enzymatic reaction. Herein we describe two biomimetic Co(III)-NHase analogues that hydrate MeCN, and four crystallographically characterized NHase intermediate analogues, [Co(III)(S(Me2)N(4)(tren))(MeCN)](2+) (1), [Co(III)(S(Me2)N(4)(tren))(OH)](+) (3), [Co(III)(S(Me2)N(4)(tren))(NHC(O)CH(3))](+) (2), and [Co(III)(O(Me2)N(4)(tren))(NHC(OH)CH(3))](2+) (5). Iminol-bound 5 represents the first example of a Co(III)-iminol compound in any ligand environment. Kinetic parameters (k(1)(298 K) = 2.98(5) M(-1) s(-1), ΔH(‡) = 12.65(3) kcal/mol, ΔS(‡) = -14(7) e.u.) for nitrile hydration by 1 are reported, and the activation energy E(a) = 13.2 kcal/mol is compared with that (E(a) = 5.5 kcal/mol) of the NHase enzyme. A mechanism involving initial exchange of the bound MeCN for OH- is ruled out by the fact that nitrile exchange from 1 (k(ex)(300 K) = 7.3(1) × 10(-3) s(-1)) is 2 orders of magnitude slower than nitrile hydration, and that hydroxide bound 3 does not promote nitrile hydration. Reactivity of an analogue that incorporates an alkoxide as a mimic of the highly conserved NHase serine residue shows that this moiety facilitates nitrile hydration under milder conditions. Hydrogen-bonding to the alkoxide stabilizes a Co(III)-iminol intermediate. Comparison of the thiolate versus alkoxide intermediate structures shows that C≡N bond activation and C═O bond formation proceed further along the reaction coordinate when a thiolate is incorporated into the coordination sphere.

Nitric oxide (NO) is frequently used to probe the substrate-binding site of "spectroscopically silent" non-heme Fe(2+) sites of metalloenzymes, such as superoxide reductase (SOR). Herein we use NO to probe the superoxide binding site of our thiolate-ligated biomimetic SOR model [Fe(II)(S(Me(2))N(4)(tren))](+) (1). Like NO-bound trans-cysteinate-ligated SOR (SOR-NO), the rhombic S = 3/2 EPR signal of NO-bound cis-thiolate-ligated [Fe(S(Me(2))N(4)(tren)(NO)](+) (2; g = 4.44, 3.54, 1.97), the isotopically sensitive ν(NO)(ν((15)NO)) stretching frequency (1685(1640) cm(-1)), and the 0.05 Å decrease in Fe-S bond length are shown to be consistent with the oxidative addition of NO to Fe(II) to afford an Fe(III)-NO(-) {FeNO}(7) species containing high-spin (S = 5/2) Fe(III) antiferromagnetically coupled to NO(-) (S = 1). The cis versus trans positioning of the thiolate does not appear to influence these properties. Although it has yet to be crystallographically characterized, SOR-NO is presumed to possess a bent Fe-NO similar to that of 2 (Fe-N-O = 151.7(4)°). The N-O bond is shown to be more activated in 2 relative to N- and O-ligated {FeNO}(7) complexes, and this is attributed to the electron-donating properties of the thiolate ligand. Hydrogen-bonding to the cysteinate sulfur attenuates N-O bond activation in SOR, as shown by its higher ν(NO) frequency (1721 cm(-1)). In contrast, the ν(O-O) frequency of the SOR peroxo intermediate and its analogues is not affected by H-bonds to the cysteinate sulfur or other factors influencing the Fe-SR bond strength; these only influence the ν(Fe-O) frequency. Reactions between 1 and NO(2)(-) are shown to result in the proton-dependent heterolytic cleavage of an N-O bond. The mechanism of this reaction is proposed to involve both Fe(II)-NO(2)(-) and {FeNO}(6) intermediates similar to those implicated in the mechanism of NiR-promoted NO(2)(-) reduction.

The effects of solution-state dielectric and intermolecular interactions on the degree of charge separation in metastable spirooxazine photomerocyanines (PMCs) is investigated. We report the first X-ray diffraction (XRD) analyses of an open form, a metastable photomerocyanine, of the spirooxazine class of photochromic molecules in two derivatives: spiro[azahomoadamantane-isoquinolinoxazine] (1) and spiro[azahomoadamantane-phenanthrolinoxazine] (2). Using the results of XRD analysis of the open photomerocyanine forms, in conjunction with computation, solvatochromism, and solution NMR studies, we have investigated the effect of the medium on the ground-state structure of these photomerocyanines. Solvatochromism and NMR chemical shift studies of 1 and 2 support the assignment of a quinoidal structure in nonpolar solvents and a zwitterionic structure in high-polarity solvents. The effect of azahomoadamantyl substitution is explored by comparing 1 and 2 with the analogous indolyl derivatives, spiro[indoline-isoquinolinoxazine] (3) and spiro[indoline-phenanthrolinoxazine] (4) through XRD analysis of the closed spirooxazine (SO) forms, solution-state kinetic experiments, solvatochromism, and NMR studies. Longer C(spiro)-O bond lengths in the SO form and slower rates of thermal PMC --> SO isomerization for the azahomoadamantyl derivatives are associated with greater zwitterionic character in the PMC form, as found in the solvatochromism studies. XRD analysis of photomerocyanines 1 and 2 indicate a greater contribution from the canonical zwitterionic resonance form relative to the quinoidal form in the solid state. Structural differences observed in two pseudopolymorphs of 2-PMC suggest that the degree of charge-separated character is influenced by the crystal packing environment. These results provide direct structural evidence for the effects of the medium polarity on charge-separated states of photomerocyanines.

In 1919, Perucca reported anomalous optical rotatory dispersion from chiral NaClO(3) crystals that were colored by having been grown from a solution containing an equilibrium racemic mixture of a triarylmethane dye (Perucca, E. Nuovo Cimento 1919, 18, 112-154). Perucca's chiroptical observations are apparently consistent with a resolution of the propeller-shaped dye molecules by NaClO(3) crystals. This implies that Perucca achieved the first enantioselective adsorption of a racemic mixture on an inorganic crystal, providing evidence of the resolution of a triarylmethyl propeller compound lacking bulky ortho substituents. Following the earlier report, NaClO(3) crystals dyed with aniline blue are described herein. The rich linear optical properties of (001), (110), and (111) sections of these mixed crystals are described via their absorbance spectra in polarized light as well as images related to linear dichroism, linear birefringence, circular dichroism, and anomalous circular extinction. The linear dichroism fixes the transition electric dipole moments in the aromatic plane with respect to the growth faces of the NaClO(3) cubes. Likewise, circular dichroism measurements of four orientations of aniline blue in NaClO(3) fix a bisignate tensor with respect to the crystal growth faces. Electronic transition moments and circular dichroism tensors were computed ab initio for aniline blue. These calculations, in conjunction with the crystal-optical properties, establish a consistent mixed-crystal model. The nature of the circular extinction depends upon the crystallographic direction along which the crystals are examined. Along 100, the crystals evidence circular dichroism. Along 110, the crystals evidence mainly anomalous circular extinction. These two properties, while measured by the differential transmission of left and right circularly polarized light, are easily distinguished in their transformation properties with respect to reorientations of the sample plates. Circular dichroism is symmetric with respect to the wave vector, whereas anomalous circular extinction is antisymmetric. Analysis of Perucca's raw data reveals that he was observing a convolution of linear and circular optical properties. The relatively large circular dichroism should in principle establish the absolute configuration of the propeller-shaped molecules associated with d- or l-NaClO(3) crystals. However, this determination was not as straightforward as it appeared at the outset. In the solid state, unlike in solution, a strong chiroptical response is not in and of itself evidence of enantiomeric resolution. It is shown how it is possible to have a poor resolution-even an equal population of P and M propellers-within a given chiral NaClO(3) crystal and still have a large circular dichroism.

The anomalous birefringence and circular differential reflection of NH(4)H(2)PO(4) (point group ̅42m), cut on the optic axis, have been found to cause an additional signal in measurements of the optical rotation employing polarized light technology, with the sample between crossed and slightly modulated linear polarizers (tilting high accuracy universal polarimetry). The azimuthal rotation of the linearly polarized light, up to 100 times larger than expected, is described in terms of a circularly polarized light mode along the optic axis of varying amplitude. Experimental evidence leading to our conclusion is given and a qualitative model for the effect is presented., (© 2010 IOP Publishing Ltd)

Three new enantiopure aryl-thioureas have been synthesized, N-(4-X-phenyl)-N-[1(S)-1-phenylethyl]thiourea, X= Cl, Br, and NO2 (compounds 1-3, respectively). Large single crystals of up to 0.5 cm(3) were grown from methanol/ethanol solutions. Molecular structures were derived from X-ray diffraction studies and the crystal morphology was compared to calculations employing the Bravais-Friedel, Donnay-Harker model. Molecular packing was further studied with Hirshfeld surface calculations. Semi-empirical classical model calculations of refractive indices, optical rotation and the electro-optic effect were performed with OPTACT on the basis of experimentally determined refractive indices. Compound 3 (space group P 1 (No. 1)) was estimated to possess a large electro-optic coefficient r(333) of approximately 30 pm/V, whereas 1 and 2 (space Group P 2(1) (No. 4) exhibit much smaller effects.

Metallocenes and other transition metal complexes, activated by methylaluminoxane allow the synthesis of polyolefins with a highly defined microstructure, tacticity, and stereoregularity. New copolymers, long chain branched polymers, and polyolefin nanocomposites are produced by these highly active catalysts. A better understanding of the structure of active sites for the olefin polymerization will lead to findings of new and simpler co-catalysts. Ethene or propene can be copolymerized with 1-olefin macromers with chain lengths up to 12,000 g mol(-1) as well as with cyclic olefins. Polypropenes of high molecular weight and filled with multi-walled carbon nanotubes show exciting new physical and mechanical properties and are prepared by in situ polymerization. These, and other polyolefin specialities, will be new future materials in a wide range of applications.

This communication describes studies of oxidatively induced C-C bond-forming reductive elimination from ((t)Bu(2)bpy)Pd(II)(Me)(2). With the outer-sphere oxidant ferrocenium, the data are consistent with a mechanism involving Pd(III) and Pd(IV) intermediates, with C-C bond formation occurring from the latter. The reaction with Ag(+) appears to proceed via a Pd-Ag(+) adduct, which then undergoes inner sphere electron transfer to generate Pd(III). In contrast, the slower benzoquinone reaction forms ethane by a different pathway that does not involve methyl group scrambling and generates Pd(0) products.

Malaria remains a major global health burden and current drug therapies are compromised by resistance. Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH) was validated as a new drug target through the identification of potent and selective triazolopyrimidine-based DHODH inhibitors with anti-malarial activity in vivo. Here we report x-ray structure determination of PfDHODH bound to three inhibitors from this series, representing the first of the enzyme bound to malaria specific inhibitors. We demonstrate that conformational flexibility results in an unexpected binding mode identifying a new hydrophobic pocket on the enzyme. Importantly this plasticity allows PfDHODH to bind inhibitors from different chemical classes and to accommodate inhibitor modifications during lead optimization, increasing the value of PfDHODH as a drug target. A second discovery, based on small molecule crystallography, is that the triazolopyrimidines populate a resonance form that promotes charge separation. These intrinsic dipoles allow formation of energetically favorable H-bond interactions with the enzyme. The importance of delocalization to binding affinity was supported by site-directed mutagenesis and the demonstration that triazolopyrimidine analogs that lack this intrinsic dipole are inactive. Finally, the PfDHODH-triazolopyrimidine bound structures provide considerable new insight into species-selective inhibitor binding in this enzyme family. Together, these studies will directly impact efforts to exploit PfDHODH for the development of anti-malarial chemotherapy.

Single-molecule dark states are often attributed to photoexcited triplets with scant evidence of the participation of paramagnetic molecules. The photodynamics of blinking single molecules of 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM) in crystals of potassium hydrogen phthalate (KAP) were compared with the lifetimes of DCM triplet states, likewise in KAP, whose zero-field splitting (ZFS) tensors were fully characterized by time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy. Luminescent mixed crystals of KAP were grown from solutions containing 10(-4) -10(-9) M DCM, a model optically nonlinear chromophore. The luminescent dye was localized in the {111} crystalline growth sectors. The photoexcited triplets states of DCM in the heavily dyed (10(-4) M) crystals were analyzed by TR-EPR spectroscopy. The photoexcited singlet states of DCM in lightly dyed crystals (10(-9) M) were analyzed by single-molecule microscopy. Large blue shifts in the absorption and emission spectra of DCM in KAP were interpreted as a consequence of protonation at the dimethylamino nitrogen atom, an assignment supported by calculations of the zero-field splitting (ZFS) tensors of molecules in their triplet states. Experimental ZFS tensors with eigenvalues comparable to those of the computed tensors were determined from the angular dependence of the EPR spectra of DCMH(+) triplets within KAP single crystals with respect to the applied magnetic field. Data from individual growth sectors failed to show magnetically equivalent site occupancies, evidence of the kinetic ordering during growth. The intermittent fluorescence of individual chromophores was analyzed. The distributions of on(off) times were characterized by distributed rates fit to power laws. The lifetime of the triplet states was analyzed from the time decay of the EPR signals between 100 and 165 K. The data were well fit with a single time constant for the signal decay, a result wholly inconsistent with the blinking of single molecules with off times commonly of tens of seconds. Triplet decay was extrapolated to approximately 25 micros at room temperature. Therefore, the assumption that single-molecule dark states originate with triplet excited states is not sustainable for single DCM molecules in KAP.

Herapathite crystals were first prepared when an assistant to the toxicologist Herapath mixed iodine with the urine of a quinine-fed dog. Herapath was shocked when his transparent crystals sitting one atop the other at right angles were "black as midnight" and predicted that they would replace costly mineral polarizers. Such a change in practice in optics had to await Land, who oriented fragile herapathite microcrystals in extruded polymers, a process that produced the first large-aperture light polarizers and, in turn, the Polaroid empire. Curiously, the crystal structure of herapathite has never been established, and thus its chromophore and mechanism of action remain a mystery. The single crystal structure of herapathite is herein established, and its complete dichroism can be attributed to delocalized excitations along ...I3-...I3-... chains. The workings of herapathite, one of the most successful serendipitously engineered crystals, is only now understood.

Reactions are described that interconvert vanadium(IV) oxo-hydroxo complexes [V(IV)O(OH)(R(2)bpy)(2)]BF(4) (1a-c) and vanadium(V) dioxo complexes [V(V)O(2)(R(2)bpy)(2)]BF(4) (2a-c) [R(2)bpy = 4,4'-di-tert-butyl-2,2'-bipyridine ((t)Bu(2)bpy), a; 4,4'-dimethyl-2,2'-bipyridine (Me(2)bpy), b; 2,2'-bipyridine (bpy), c]. These are rare examples of pairs of isolated, sterically unencumbered, first-row metal-oxo/hydroxo complexes that differ by a hydrogen atom (H(+) + e(-)). The V(IV)-(t)Bu(2)bpy derivative 1a has a useful (1)H NMR spectrum, despite being paramagnetic. Complex 2a abstracts H(*) from organic substrates with weak O-H and C-H bonds, converting 2,6-(t)Bu(2)-4-MeO-C(6)H(2)OH (ArOH) and 2,2,6,6-tetramethyl-N-hydroxypiperidine (TEMPOH) to their corresponding radicals ArO(*) and TEMPO, hydroquinone to benzoquinone, and dihydroanthracene to anthracene. The equilibrium constant for 2a + ArOH <==> 1a + ArO(*) is (4 +/- 2) x 10(-3), implying that the VO-H bond dissociation free energy (BDFE) is 70.6 +/- 1.2 kcal mol(-1). Consistent with this value, 1a is oxidized by 2,4,6-(t)Bu(3)C(6)H(2)O(*). All of these reactions are surprisingly slow, typically occurring over hours at ambient temperatures. The net hydrogen-atom pseudo-self-exchange 1a + 2b <==> 2a + 1b, using the (t)Bu- and Me-bpy substituents as labels, also occurs slowly, with k(se) = 1.3 x 10(-2) M(-1) s(-1) at 298 K, DeltaH(double dagger) = 15 +/- 2 kcal mol(-1), and DeltaS(double dagger) = 16 +/- 5 cal mol(-1) K. Using this k(se) and the BDFE, the vanadium reactions are shown to follow the Marcus cross relation moderately well, with calculated rate constants within 10(2) of the observed values. The vanadium self-exchange reaction is ca. 10(6) slower than that for the related Ru(IV)O(py)(bpy)(2)(2+)/Ru(III)OH(py)(bpy)(2)(2+) self-exchange. The origin of this dramatic difference has been probed with DFT calculations on the self-exchange reactions of 1c + 2c and on monocationic ruthenium complexes with pyrrolate or fluoride in place of the py ligands. The calculations reproduce the difference in barrier heights and show that transfer of a hydrogen atom involves more structural reorganization for vanadium than the Ru analogues. The vanadium complexes have larger changes in the metal-oxo and metal-hydroxo bond lengths, which is traced to the difference in d-orbital occupancy in the two systems. This study thus highlights the importance of intrinsic barriers in the transfer of a hydrogen atom, in addition to the thermochemical (bond strength) factors that have been previously emphasized.

[CpIrCl(2)](2) () and new CpIr(III)(L-L)X complexes (L-L = N-O or C-N chelating ligands; X = Cl, I, Me) have been prepared and their reactivity with two-electron chemical oxidants explored. Reaction of with PhI(OAc)(2) in wet solvents yields a new chloro-bridged dimer in which each of the Cp ligands has been singly acetoxylated to form [Cp(OAc)Ir(III)Cl(2)](2) () (Cp(OAc) = eta(5)-C(5)Me(4)CH(2)OAc). Complex and related carboxy- and alkoxy-functionalized Cp(OR) complexes can also be prepared from plus (PhIO)(n) and ROH. [Cp(OAc)Ir(III)Cl(2)](2) () and the methoxy analogue [Cp(OMe)Ir(III)Cl(2)](2) () have been structurally characterized. Treatment of [CpIrCl(2)](2) () with 2-phenylpyridine yields CpIr(III)(ppy)Cl () (ppy = cyclometallated 2-phenylpyridyl) which is readily converted to its iodide and methyl analogues CpIr(III)(ppy)I and CpIr(III)(ppy)Me (). CpIr(III) complexes were also prepared with N-O chelating ligands derived from anthranilic acid (2-aminobenzoic acid) and alpha-aminoisobutyric acid (H(2)NCMe(2)COOH), ligands chosen to be relatively oxidation resistant. These complexes and were reacted with potential two-electron oxidants including PhI(OAc)(2), hexachlorocyclohexadienone (C(6)Cl(6)O), N-fluoro-2,4,6-trimethylpyridinium (Me(3)pyF(+)), [Me(3)O]BF(4) and MeOTf (OTf = triflate, CF(3)SO(3)). Iridium(V) complexes were not observed or implicated in these reactions, despite the similarity of the potential products to known CpIr(V) species. The carbon electrophiles [Me(3)O]BF(4) and MeOTf appear to react preferentially at the N-O ligands, to give methyl esters in some cases. Overall, the results indicate that Cp is not inert under oxidizing conditions and is therefore not a good supporting ligand for oxidizing organometallic complexes.

A reputation restored: Eligio Perucca (see photo) first observed the enantioselective adsorption of a racemic mixture to a chiral crystal (NaClO(3)) in Turin in 1919. However, this milestone in enantioselective chemistry and chiroptics went unnoticed. Identified previously as a coward who refused in 1941 to supervise the research of the budding stereochemist Primo Levi because of the race laws, Perucca was opposed to the fascist regime.

The syntheses and structures of three new coordinatively unsaturated, monomeric, square-pyramidal thiolate-ligated Fe(III) complexes are described, [Fe(III)((tame-N(3))S(2)(Me2))](+) (1), [Fe(III)(Et-N(2)S(2)(Me2))(py)](1-) (3), and [Fe(III)((tame-N(2)S)S(2)(Me2))](2-) (15). The anionic bis-carboxamide, tris-thiolate N(2)S(3) coordination sphere of 15 is potentially similar to that of the yet-to-be characterized unmodified form of NHase. Comparison of the magnetic and reactivity properties of these reveals how anionic charge build up (from cationic 1 to anionic 3 and dianionic 15) and spin-state influence apical ligand affinity. For all of the ligand-field combinations examined, an intermediate S = 3/2 spin state was shown to be favored by a strong N(2)S(2) basal plane ligand field, and this was found to reduce the affinity for apical ligands, even when they are built in. This is in contrast to the post-translationally modified NHase active site, which is low spin and displays a higher affinity for apical ligands. Cationic 1 and its reduced Fe(II) precursor are shown to bind NO and CO, respectively, to afford [Fe(III)((tame-N(3))S(2)(Me))(NO)](+) (18, nu(NuO) = 1865 cm(-1)), an analogue of NO-inactivated NHase, and [Fe(II)((tame-N(3))S(2)(Me))(CO)] (16; nu(CO) stretch (1895 cm(-1)). Anions (N(3)(-), CN(-)) are shown to be unreactive toward 1, 3, and 15 and neutral ligands unreactive toward 3 and 15, even when present in 100-fold excess and at low temperatures. The curtailed reactivity of 15, an analogue of the unmodified form of NHase, and its apical-oxygenated S = 3/2 derivative [Fe(III)((tame-N(2)SO(2))S(2)(Me2))](2-) (20) suggests that regioselective post-translational oxygenation of the basal plane NHase cysteinate sulfurs plays an important role in promoting substrate binding. This is supported by previously reported theoretical (DFT) calculations.

The conversion of the petrochemical polymer polyethylene terephthalate (PET) to a biodegradable plastic polyhydroxyal-kanoate (PHA) is described here. PET was pyrolised at 450 degrees C resulting in the production of a solid, liquid, and gaseous fraction. The liquid and gaseous fractions were burnt for energy recovery, whereas the solid fraction terephthalic acid (TA) was used as the feedstock for bacterial production of PHA. Strains previously reported to grow on TA were unable to accumulate PHA. We therefore isolated bacteria from soil exposed to PET granules at a PET bottle processing plant From the 32 strains isolated, three strains capable of accumulation of medium chain length PHA (mclPHA) from TA as a sole source of carbon and energy were selected for further study. These isolates were identified using 16S rDNA techniques as P. putida (GO16), P. putida (GO19), and P. frederiksbergensis (GO23). P. putida GO16 and GO19 accumulate PHA composed predominantly of a 3-hydroxydecanoic acid monomer while P. frederiksbergensis GO23 accumulates 3-hydroxydecanoic acid as the predominant monomer with increased amounts of 3-hydroxydodecanoic acid and 3-hydroxydodecenoic acid compared to the other two strains. PHA was detected in all three strains when nitrogen depleted below detectable levels in the growth medium. Strains GO16 and GO19 accumulate PHA at a maximal rate of approximately 8.4 mg PHA/l/h for 12 h before the rate of PHA accumulation decreased dramatically. Strain GO23 accumulates PHA at a lower maximal rate of 4.4 mg PHA/l/h but there was no slow down in the rate of PHA accumulation over time. Each of the PHA polymers is a thermoplastic with the onset of thermal degradation occurring around 308 degrees C with the complete degradation occurring by 370 degrees C. The molecular weight ranged from 74 to 123 kDa. X-ray diffraction indicated crystallinity of the order of 18-31%. Thermal analysis shows a low glass transition (-53 degrees C) with a broad melting endotherm between 0 and 45 degrees C.

The reaction of molecular oxygen with iridium pincer hydride complexes, ((tBu)PCP)Ir(H)(X) [(tBu)PCP = kappa(3)-C(6)H(3)(CH(2)P(t)Bu(2))(2), X = Ph, H, CCPh], results in O(2) induced reductive elimination and formation of the novel dioxygen complexes ((tBu)PCP)Ir(O(2))(n) [n = 1 (), 2 ()].

Reaction of NaBH4 with (tBuPOCOP)IrHCl affords the previously reported complex (tBuPOCOP)IrH2(BH3) (1) (tBuPOCOP = kappa(3)-C6H3-1,3-[OP(tBu)2]2). The structure of 1 determined from neutron diffraction data contains a B-H sigma-bond to iridium with an elongated B-H bond distance of 1.45(5) A. Compound 1 crystallizes in the space group P1 (Z = 2) with a = 8.262 (5) A, b = 12.264 (5) A, c = 13.394 (4) A, and V = 1256.2 (1) A(3) (30 K). Complex 1 can also be prepared by reaction of BH3 x THF with (tBuPOCOP)IrH2. Reaction of (tBuPOCOP)IrH2 with pinacol borane gave initially complex 2, which is assigned a structure analogous to that of 1 based on spectroscopic measurements. Complex 2 evolves H2 at room temperature leading to the borane complex 3, which is formed cleanly when 2 is subjected to dynamic vacuum. The structure of 3 has been determined by X-ray diffraction and consists of the (tBuPOCOP)Ir core with a sigma-bound pinacol borane ligand in an approximately square planar complex. Compound 3 crystallizes in the space group C2/c (Z = 4) with a = 41.2238 (2) A, b = 11.1233 (2) A, c = 14.6122 (3) A, and V = 6700.21 (19) A(3) (130 K). Reaction of (tBuPOCOP)IrH2 with 9-borobicyclononane (9-BBN) affords complex 4. Complex 4 displays (1)H NMR resonances analogous to 1 and exists in equilibrium with (tBuPOCOP)IrH2 in THF solutions.

Mechanistic pathways of metalloenzymes are controlled by the metal ion's electronic and magnetic properties, which are tuned by the coordinated ligands. The functional advantage gained by incorporating cysteinates into the active site of non-heme iron enzymes such as superoxide reductase (SOR) is not entirely understood. Herein we compare the structural and redox properties of a series of structurally-related thiolate, alkoxide, and amine-ligated Fe(II) complexes in order to determine how the thiolate influences properties critical to function. Thiolates are shown to reduce metal ion Lewis acidity relative to alkoxides and amines, and have a strong trans influence thereby helping to maintain an open coordination site. Comparison of the redox potentials of the structurally analogous compounds described herein indicates that alkoxide ligands favor the higher-valent Fe(3+) oxidation state, amine ligands favor the reduced Fe(2+) oxidation state, and thiolates fall somewhere in between. These properties provide a functional advantange for substrate reducing enzymes in that they provide a site at the metal ion for substrate to bind, and a moderate potential that facilitates both substrate reduction, and regeneration of the catalytically active reduced state. Redox potentials for structurally-related Co(II) complexes are shown to be cathodically-shifted relative to their Fe(II) analogues, making them ineffective reducing agents for substrates such as superoxide.

Oriented achiral molecules and crystals with D(2d) symmetry or one of its non-enantiomorphous subgroups, S(4), C(2v), or C(s), can rotate the plane of transmitted polarized light incident in a general direction. This well-established fact of crystal optics is contrary to the teaching of optical activity to students of organic chemistry. This Minireview gives an overview of the measurement and calculation of the chiroptical properties of some achiral compounds and crystals. Methane derivatives with four identical ligands related by reflection symmetry are quintessential optically inactive compounds according to the logic of van't Hoff. Analysis of the optical activity of simple achiral compounds such as H(2)O and NH(3) provides general aspects of chiroptics that are not readily broached when considering chiral compounds exclusively. We show here, through the use of group theoretical arguments, the transformation properties of tensors, and diagrams, why some achiral, acentric compounds are optically active while others are not.

Ruthenium bis(beta-diketonato) complexes have been prepared at both the RuII and RuIII oxidation levels and with protonated and deprotonated pyridine-imidazole ligands. RuII(acac)2(py-imH) (1), [RuIII(acac)2(py-imH)]OTf (2), RuIII(acac)2(py-im) (3), RuII(hfac)2(py-imH) (4), and [DBU-H][RuII(hfac)2(py-im)] (5) have been fully characterized, including X-ray crystal structures (acac = 2,4-pentanedionato, hfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionato, py-imH = 2-(2'-pyridyl)imidazole, DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene). For the acac-imidazole complexes 1 and 2, cyclic voltammetry in MeCN shows the RuIII/II reduction potential (E1/2) to be -0.64 V versus Cp2Fe+/0. E1/2 for the deprotonated imidazolate complex 3 (-1.00 V) is 0.36 V more negative. The RuII bis-hfac analogues 4 and 5 show the same DeltaE1/2 = 0.36 V but are 0.93 V harder to oxidize than the acac derivatives (0.29 and -0.07 V). The difference in acidity between the acac and hfac derivatives is much smaller, with pKa values of 22.1 and 19.3 in MeCN for 1 and 4, respectively. From the E1/2 and pKa values, the bond dissociation free energies (BDFEs) of the N-H bonds in 1 and 4 are calculated to be 62.0 and 79.6 kcal mol(-1) in MeCN - a remarkable difference of 17.6 kcal mol(-1) for such structurally similar compounds. Consistent with these values, there is a facile net hydrogen atom transfer from 1 to TEMPO* (2,2,6,6-tetramethylpiperidine-1-oxyl radical) to give 3 and TEMPO-H. The DeltaG degrees for this reaction is -4.5 kcal mol(-1). 4 is not oxidized by TEMPO* (DeltaG degrees = +13.1 kcal mol(-1)), but in the reverse direction TEMPO-H readily reduces in situ generated RuIII(hfac)2(py-im) (6). A RuII-imidazoline analogue of 1, RuII(acac)2(py-imnH) (7), reacts with 3 equiv of TEMPO* to give the imidazolate 3 and TEMPO-H, with dehydrogenation of the imidazoline ring.

A polarized light imaging technique is introduced that simultaneously captures and unfolds transmittance, fast/slow axes directions and birefringence or linear dichroism from single camera exposures. The technique, based on the rotating polarizer method, is capable of sampling an object through polarizers at four different angles in a single image with the use of an image multiplexer. The range of possible applications is demonstrated with examples from the fields of biology, medicine, forensics and material sciences.

A series of five-coordinate thiolate-ligated complexes [M(II)(tren)N4S(Me2)]+ (M = Mn, Fe, Co, Ni, Cu, Zn; tren = tris(2-aminoethyl)amine) are reported, and their structural, electronic, and magnetic properties are compared. Isolation of dimeric [Ni(II)(SN4(tren)-RS(dang))]2 ("dang"= dangling, uncoordinated thiolate supported by H bonds), using the less bulky [(tren)N4S](1-) ligand, pointed to the need for gem-dimethyls adjacent to the sulfur to sterically prevent dimerization. All of the gem-dimethyl derivatized complexes are monomeric and, with the exception of [Ni(II)(S(Me2)N4(tren)]+, are isostructural and adopt a tetragonally distorted trigonal bipyramidal geometry favored by ligand constraints. The nickel complex uniquely adopts an approximately ideal square pyramidal geometry and resembles the active site of Ni-superoxide dismutase (Ni-SOD). Even in coordinating solvents such as MeCN, only five-coordinate structures are observed. The MII-S thiolate bonds systematically decrease in length across the series (Mn-S > Fe-S > Co-S > Ni-S approximately Cu-S < Zn-S) with exceptions occurring upon the occupation of sigma* orbitals. The copper complex, [Cu(II)(S(Me2)N4(tren)]+, represents a rare example of a stable CuII-thiolate, and models the perturbed "green" copper site of nitrite reductase. In contrast to the intensely colored, low-spin Fe(III)-thiolates, the M(II)-thiolates described herein are colorless to moderately colored and high-spin (in cases where more than one spin-state is possible), reflecting the poorer energy match between the metal d- and sulfur orbitals upon reduction of the metal ion. As the d-orbitals drop in energy proceeding across the across the series M(2+) (M= Mn, Fe, Co, Ni, Cu), the sulfur-to-metal charge-transfer transition moves into the visible region, and the redox potentials cathodically shift. The reduced M(+1) oxidation state is only accessible with copper, and the more oxidized M(+4) oxidation state is only accessible for manganese.

The optical rotatory power of achiral crystals of achiral pentaerythritol molecules was measured. The maximum rotations were found to be +/-6 degrees /mm. The quantum mechanically computed rotation of pentaerythritol molecules using linear response theory was 6 times larger although the experimental and theoretical tensors were similarly oriented to within 5 degrees .

Superoxide reductases (SORs) are cysteine-ligated, non-heme iron enzymes that reduce toxic superoxide radicals (O2-). The functional role of the trans cysteinate, as well as the mechanism by which SOR reduces O2-, is unknown. Herein is described a rare example of a functional metalloenzyme analogue, which catalytically reduces superoxide in a proton-dependent mechanism, via a trans thiolate-ligated iron-peroxo intermediate, the first example of its type. Acetic-acid-promoted H2O2 release, followed by Cp2Co reduction, regenerates the active Fe(II) catalyst. The thiolate ligand and its trans positioning relative to the substrate are shown to contribute significantly to the catalyst's function, by lowering the redox potential, changing the spin state, and dramatically lowering the nuFe-O stretching frequency well-below that of any other reported iron-peroxo, while leaving nuO-O high, so as to favor superoxide reduction and Fe-O, as opposed to O-O, bond cleavage. Thus we provide critical insight into the relationship between the SOR structure and its function, as well as important benchmark parameters for characterizing highly unstable thiolate-ligated iron-peroxo intermediates.

Rhythmic precipitates of centrosymmetric phthalic acid were analyzed by a square-wave mechanically modulated circular extinction imaging microscope. Spherulites were bisected into square-millimeter sized heterochiral domains that are a consequence of circular intensity differential scattering of left and right circularly polarized light. The dissymmetry and chiral amplification indicated optically was confirmed in the microtexture established by atomic force and scanning electron microscopies.

Nitrile hydratase (NHase) is one of a growing number of enzymes shown to contain post-translationally modified cysteine sulfenic acids (Cys-SOH). Cysteine sulfenic acids have been shown to play diverse roles in cellular processes, including transcriptional regulation, signal transduction, and the regulation of oxygen metabolism and oxidative stress responses. The function of the cysteine sulfenic acid coordinated to the iron active site of NHase is unknown. Herein we report the first example of a sulfenate-ligated iron complex, [Fe(III)(ADIT)(ADIT-O)](+) (5), and compare its electronic and magnetic properties with those of structurally related complexes in which the sulfur oxidation state and protonation state have been systematically altered. Oxygen atom addition was found to decrease the unmodified thiolate Fe-S bond length and blue-shift the ligand-to-metal charge-transfer band (without loss of intensity). S K-edge X-ray absorption spectroscopy and density functional theory calculations show that, although the modified RS-O(-) fragment is incapable of forming a pi bond with the Fe(III) center, the unmodified thiolate compensates for this loss of pi bonding by increasing its covalent bond strength. The redox potential shifts only slightly (75 mV), and the magnetic properties are not affected (the S = (1)/(2) spin state is maintained). The coordinated sulfenate S-O bond is activated and fairly polarized (S(+)-O(-)). Addition of strong acids at low temperatures results in the reversible protonation of sulfenate-ligated 5. An X-ray structure demonstrates that Zn(2+) binds to the sulfenate oxygen to afford [Fe(III)(ADIT)(ADIT-O-ZnCl(3))] (6). The coordination of ZnCl(3)(-) to the RS-O(-) unit causes the covalent overlap with the unmodified thiolate to increase further. A possible catalytic role for the unmodified NHase thiolate, involving its ability to "tune" the electronics in response to protonation of the sulfenate (RS-O(-)) oxygen and/or substrate binding, is discussed.

A novel approach to the recycling of polystyrene is reported here; polystyrene is converted to a biodegradable plastic, namely polyhydroxyalkanoate (PHA). This unique combinatorial approach involves the pyrolysis of polystyrene to styrene oil, followed by the bacterial conversion of the styrene oil to PHA by Pseudomonas putida CA-3 (NCIMB 41162). The pyrolysis (520 degrees C) of polystyrene in a fluidized bed reactor (Quartz sand (0.3-0.5 mm)) resulted in the generation of an oil composed of styrene (82.8% w/w) and low levels of other aromatic compounds. This styrene oil, when supplied as the sole source of carbon and energy allowed for the growth of P. putida CA-3 and PHA accumulation in shake flask experiments. Styrene oil (1 g) was converted to 62.5 mg of PHA and 250 mg of bacterial biomass in shake flasks. A 1.6-fold improvement in the yield of PHA from styrene oil was achieved by growing P. putida CA-3 in a 7.5 liter stirred tank reactor. The medium chain length PHA accumulated was comprised of monomers 6, 8, and 10 carbons in length in a molar ratio of 0.046:0.436:1.126, respectively. A single pyrolysis run and four fermentation runs resulted in the conversion of 64 g of polystyrene to 6.4 g of PHA.

A series of novel nonlinear optical (NLO) chromophores 1-4 incorporating the ferrocenyl (Fc) group as an electron donor and 2-dicyanomethylene-3-cyano-4-methyl-2,5-dihydrofuran (TCF) derivatives as electron acceptors are presented. The use of a constant Fc donor and varied acceptors and bridges makes it possible to systematically determine the contribution of the conjugated bridge and the acceptor strength to chromophore nonlinear optical activity. The X-ray crystal structures of all four chromophores allow for the systematic investigation of the structure-property relationship for this class of molecules. For example, the crystal structures reveal that both cyclopentadienyl groups in the ferrocenyl donor contribute to the electron donating ability. The first-order hyperpolarizabilities beta of these chromophores, measured by hyper-Rayleigh scattering (HRS) relative to p-nitroaniline are reported. These beta values are compared to those calculated by density functional theory (DFT). The excellent agreement between the theoretical and experimental beta values demonstrates that a linear relation exists between the hyperpolarizability and the bond length alternation. An electrooptic coefficient, r(33), of approximately 25 pm/V at 1300 nm, for compound 4, incorporated into a polymer matrix, is competitive with organic chromophores. Moreover, this r(33) is more than 30 times larger than the previously reported value for an organometallic chromophore in a poled polymer matrix. This work not only underscores the potential for Fc donor moieties, which have been underutilized, but also demonstrates that experimental characterization and theoretical simulations are now congruent, viable methods for assessing potential performance of NLO materials.

The reactivity between a thiolate-ligated five-coordinate complex [FeII(SMe2N4(tren))]+ (1) and dioxygen is examined in order to determine if O2 activation, resembling that of the metalloenzyme cytochrome P450, can be promoted even when O2 binds cis, as opposed to trans, to a thiolate. Previous work in our group showed that [FeII(SMe2N4(tren))]+ (1) reacts readily with superoxide (O2-) in the presence of a proton source to afford H2O2 via an Fe(III)-OOH intermediate, thus providing a biomimetic model for the metalloenzyme superoxide reductase (SOR). Addition of O2 to 1 affords binuclear mu-oxo-bridged [FeIII(SMe2N4(tren))]2(mu2-O)(PF6)2.3MeCN (3). At low temperatures, in protic solvents, an intermediate is detected, the details of which will be the subject of a separate paper. Although the thiolate ligand does not appear to perturb the metrical parameters of the unsupported mu-oxo bridge (Fe-O= 1.807(8) A, and Fe-O-Fe= 155.3(5) degrees fall in the usual range), it decreases the magnetic coupling between the irons (J=-28 cm(-1)) and creates a rather basic oxo site. Protonation of this oxo using strong (HBF4, HCl) or weak (HOAc, NH4PF6, LutNHCl) acids results in bridge cleavage to cleanly afford the corresponding monomeric anion-ligated (OAc- (6), or Cl- (7)) or solvent-ligated (MeCN (4)) derivatives. Addition of OH- converts [FeIII(SMe2N4(tren))(MeCN2+ (4) back to mu-oxo 3. Thus, mu-oxo bridge cleavage is reversible. The protonated mu-hydroxo-bridged intermediate is not observed. In an attempt to prevent mu-oxo dimer formation, and facilitate the observation of O2-bound intermediates, a bulkier tertiary amine ligand, tren-Et4= N-(2-amino-ethyl)-N-(2-diethylamino-ethyl)-N',N'-diethyl-ethane-1,2-diamine, and the corresponding [FeII(SMe2N4(tren-Et4))]+ (5) complex was synthesized and structurally characterized. Steric repulsive interactions create unusually long FeII-N(3,4) amine bonds in 5 (mean distance=2.219(1) A). The [(tren-Et4)N4SMe2]1- ligand is unable to accommodate iron in the +3 oxidation state, and consequently, in contrast to most thiolate-ligated Fe(II) complexes, [FeII(SMe2N4(tren-Et4))]+ (5) does not readily react with O2. Oxidation of 5 is irreversible, and the potential (Epa=+410 mV (vs SCE)) is anodically shifted relative to 1 (E1/2=-100 mV (vs SCE)).

The title compound, K(+).[(C(8)H(5)O(4))(2)H](-).2H(2)O or K(+).C(16)H(11)O(8)(-).2H(2)O, was prepared by slow evaporation of an aqueous solution of potassium hydrogen phthalate. The molecular complex consists of a potassium cation coordinated to a proton-bound hydrogen phthalate dimer and two water molecules. The potassium cation resides on a twofold axis in a distorted square-antiprism coordination geometry. The compound is isomorphous with the ammonium analogue, previously misidentified. As potassium hydrogen phthalate is frequently used in the manufacture of buffers, organic carbon standards, acidimetric standards and various other products, the crystallization of a compound with a different stoichiometery from a solution containing the acidimetric standard has important practical implications.