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Enediynes are anti-cancer agents that are highly cytotoxic due to their propensity for low thermal activation of radical generation. The diradical intermediate produced from Bergman cyclization of the enediyne moiety may induce DNA damage and cell lethality. The cytotoxicity of enediynes and difficulties in controlling their thermal cyclization has limited their clinical use. We recently showed that enediyne toxicity at 37 °C can be mitigated by metallation, but cytotoxic effects of 'metalloenediynes' on cultured tumor cells are potentiated by hyperthermia. Reduction of cytotoxicity at normothermia suggests metalloenediynes will have a large therapeutic margin, with cell death occurring primarily in the heated tumor. Based on our previousClonogenic survival, apopotosis and DNA binding assays were used to determine mechanisms of enhancement of FeSOFeSOBy leveraging the unique thermal activation properties of metalloenediynes, we propose that localized moderate hyperthermia can be used to confine the cytotoxicity of these compounds to tumors, while sparing normal tissue.

Multimetallic architectures that combine chemically diverse materials to affect tandem reactions within a single scaffold drive future nanocatalyst development. Here, we show the unique, interlatti...

Fibrin plays a critical role in wound healing and hemostasis, yet it is also the main case of cardiovascular diseases and thrombosis. Here, we show the unique design of Au-Cu@PANI alloy core-shell rods for fibrin clot degradation. Microscopic (transmission electron microscopy (TEM), scanning transmission electron microscopy-energy-dispersive X-ray (STEM-EDX)) and structural characterizations (powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS)) of the Au-Cu@PANI hybrid material reveal the formation of Au-Cu heterogeneous alloy core rods (aspect ratio = 3.7) with thin Cu

Multi-metallic hybrid nancatalysts consisting of a porous metal oxide host and metal satellite guests serve as a scaffold for multi-step transformations of divergent and energy-challenging substrates. Here we have developed a 3D porous MgO framework (Lewis basic host) with Ag(0) nanoparticles (noble metal guest) for ambient pressure activation and insertion of CO(2) into unsaturated alkyne substrates. The hybrid MgO@Ag-x (x = 2, 5, 7, 8 at % Ag) catalysts are synthesized by impregnating Ag(+) ions in porous MgO cubes followed by reduction using NaBH(4). Morphological (SEM, TEM, EDX mapping) and structural (PXRD, XPS) characterization reveal that the micron-sized hybrid cubes derive from self-assembly of ~100 nm (edge length) MgO cubes decorated with ~ 5 to 25 nm Ag(0) NPs. Detailed XPS analysis illustrates Ag(0) is present in two forms

Environmental impacts of continued CO2 production have led to an increased need for new methods of CO2 removal and energy development. Nanomaterials are of special interest for these applications, because of their unique chemical and physical properties that allow for highly active surfaces. Here, we successfully synthesize AgPd nanodendrite-modified Au nanoprisms in various shapes (nanoprisms, hexagonal nanoplates, and octahedral nanoparticles) by selective metal deposition. This strategy involves coupling galvanic replacement between Ag layers in Au@Ag core–shell nanoprisms and H2PdCl4 with a coreduction process of silver and palladium ions. Synthesis of AgPd nanodendrite-tipped (4.14–11.47 wt % Pd) and -edged (25.25–31.01 wt % Pd) Au nanoparticles can be controlled simply by tuning the concentration of H2PdCl4. More importantly, these multicomponent AgPd nanodendrite-modified Au nanoparticles show exceptional electrocatalytic performance for CO2 reduction. AgPd nanodendrite-edged Au nanoprisms show mor...

A suite of lanthanoenediyne complexes of the form Ln(macrocycle)X(3) (Ln = La(3+), Ce(3+), Eu(3+), Gd(3+), Tb(3+), Lu(3+); X = NO(3)(−), Cl(−), OTf(−)) was prepared by utilizing an enediyne-containing [2 + 2] hexaaza-macrocycle (2). The solid-state Bergman cyclization temperatures, measured via DSC, decrease with the denticity of X (bidentate NO(3)(−), T = 267−292 °C; monodentate Cl(−), T = 238–262 °C; noncoordinating OTf(−), T = 170–183 °C). (13)C NMR characterization shows that the chemical shifts of the acetylenic carbon atoms also rely on the anion identity. The alkyne carbon closest to the metal binding site, C(A), exhibits a Δδ > 3 ppm downfield shift, while the more distal alkyne carbon, C(B), displays a concomitant Δδ ≤ 2.5 ppm upfield shift, reflecting a depolarization of the alkyne on metal inclusion. For all metals studied, the degree of perturbation follows the trend 2 < NO(3)(−) < Cl(−) < OTf(−). This belies a greater degree of electronic rearrangement in the coordinated macrocycle as the denticity of X and its accompanying shielding of the metal’s Lewis acidity decrease. Computationally modeled structures of LnX(3) show a systematic increase in the lanthanide–2 coordination number (CN(La-mc) = 2 (NO(3)(−)), 4 (Cl(−)), 5 (H(2)O, model for OTf(−))) and a decrease in the mean Ln−N bond length (La−N(average) = 2.91 Å (NO(3)(−)), 2.78 Å (Cl(−)), 2.68 Å (H(2)O)), further suggesting that a decrease in the anion coordination number correlates with an increase in the metal–macrocycle interaction. Taken together, these data illustrate a Bergman cyclization landscape that is influenced by the bonding of metal to an enediyne ligand but whose reaction barrier is ultimately dominated by the coordinating ability of the accompanying anion.

Developing facile synthetic routes to multifunctional nanoparticles combining the magnetic properties of iron oxides with the optical and catalytic utility of noble metal particles remains an important goal in realizing the potential of hybrid nanomaterials. To this end, we have developed a single route to noble metal-decorated magnetic nanoparticles (Fe3O4@SiO2-M; M = Au, Pd, Ag, and PtAg) and characterized them by HRTEM and STEM/EDX imaging to reveal their nanometer size (16 nm Fe3O4 and 1-5 nm M seeds) and uniformity. This represents one of the few examples of genuine multifunctional particles on the nanoscale. We show that these hybrid structures have excellent catalytic activity for the reduction of 4-nitrophenol (knorm = 2 × 10(7) s(-1) mol(Pd)(-1); 5 × 10(6) s(-1) mol(Au)(-1); 5 × 10(5) s(-1) mol(PtAg)(-1); 7 × 10(5) s(-1) mol(Ag)(-1)). These rates are the highest reported for nano-sized comparables, and are competitive with mesoparticles of similar composition. Due to their magnetic response, the particles are also suitable for magnetic recovery and maintain99% conversion for at least four cycles. Using this synthetic route, Fe3O4@SiO2-M particles show great promise for further development as a precursor to complicated anisotropic materials or for applications ranging from nanocatalysis to biomedical sensing.

Halting cancer progression by altering the tumor microenvironment is an exciting new frontier in oncology. One target for new therapies is the structural support provided by the extracellular matrix, which for cancer cells is often abnormal and undergoes drastic modification during angiogenesis, tumor proliferation, and metastasis. We have developed a new magnetic nanoparticle-based agent, Fe3O4–PEG–EDDA (EDDA: (Z)-octa-4-en-2,6-diyne-1,8-diamine), that is capable of generating radicals via Bergman cyclization of the pendant enediyne during mild hyperthermia treatment using an alternating magnetic field. We observe formation of a cyclized aromatic product in the Raman spectra of the thermally excited material and can detect polymeric product after periods of induction. When mixed with the basement membrane extract Matrigel, the nanoparticles do not interfere with normal biopolymer network formation. Applying the same hyperthermia conditions as in solution samples, Fe3O4–PEG–EDDA causes structural collapse...

Enediyne natural products are a class of compounds that were recognized for their potential as chemotherapeutic agents many years ago, but found to be highly cytotoxic due to their propensity for low thermal activation. Bergman cyclization of the enediyne moiety produces a diradical intermediate, and may subsequently induce DNA damage and account for the extreme cytotoxicity. While difficulties in controlling the thermal cyclization reaction have limited the clinical use of cyclic enediynes, we have previously shown that enediyne activity, and thus toxicity at physiological temperatures can be modulated by metallation of acyclic enediynes. Furthermore, the cytotoxicity of “metalloenediynes” can be potentiated by hyperthermia. In this study, we characterized a suite of novel metallated enediyne motifs that usually induced little or no cytotoxicity when two different human cancer cell lines were treated with the compounds at 37°C, but showed a significant enhancement of cytotoxicity after cells were exposed to moderate hyperthermia during drug treatment. Cultured U-1 melanoma or MDA-231 breast cancer cells were treated with various concentrations of Cu, Fe and Zn complexes of the enediyne (Z)-N,N′-bis[1-pyridyl-2-yl-meth-(E)-ylidene]octa-4-ene-2,6-diyne-1,8-diamine (PyED) and clonogenic survival was assessed to determine the effects of the drugs at 37°C and 42.5°C. Toxicity at 37°C varied for each compound, but hyperthermia potentiated the cytotoxicity of each compound in both cell lines. Cytotoxicity was concentration-, time- and temperature-dependent. Heating cells during drug treatment resulted in enhanced apoptosis, but the role of cell cycle perturbation in the response of the cells to the drugs was less clear. Lastly, we showed that hyperthermia enhanced the number of DNA double-strand breaks (DSBs) induced by the compounds, and inhibited their repair after drug treatment. Thus, thermal enhancement of cytotoxicity may be due, at least in part, to the propensity of the enediyne moiety to induce DSBs, and/or a reduction in DSB repair efficiency. We propose that “tuning” of metalloenediyne toxicity through better-controlled reactivity could have potential clinical utility, since we envision that such compounds could be administered systemically as relatively non-toxic agents, but cytotoxicity could be enhanced in, and confined to a tumor volume when subjected to localized heating.

A series of M(PyED)·X (X = 2Cl−, SO42−) pyridine–metalloenediyne complexes [M = Cu(II), Fe(II), or Zn(II)] and their independently synthesized, cyclized analogs have been prepared to investigate their potential as radical-generating DNA-damaging agents. All complexes possess a 1:1 metal-to-ligand stoichiometry as determined by electronic absorption spectroscopy and X-ray diffraction. Solution structural analysis reveals a pπ Cl → Cu(II) LMCT (22,026 cm−1) for Cu(PyED)·2Cl, indicating three nitrogens and a chloride in the psuedo-equatorial plane with the remaining pyridine nitrogen and solvent in axial positions. EPR spectra of the Cu(II) complexes exhibit an axially elongated octahedron. This spectroscopic evidence, together with density functional theory computed geometries, suggest six-coordinate structures for Cu(II) and Fe(II) complexes and a five-coordinate environment for Zn(II) analogs. Bergman cyclization via thermal activation of these constructs yields benzannulated product indicative of diradical generation in all complexes within 3 h at 37 °C. A significant metal dependence on the rate of the reaction is observed [Cu(II) > Fe(II) > Zn(II)], which is mirrored in in vitro DNA-damaging outcomes. Whereas in situ chelation of PyED leads to considerable degradation in the presence of all metals within 1 h under hyperthermia conditions, Cu(II) activation produces >50% compromised DNA within 5 min. Additionally, Cu(II) chelated PyED outcompetes DNA polymerase I to successfully inhibit template strand extension. Exposure of HeLa cells to Cu(PyBD)·SO4 (IC50 = 10 μM) results in a G2/M arrest compared with untreated samples, indicating significant DNA damage. These results demonstrate metal-controlled radical generation for degradation of biopolymers under physiologically relevant temperatures on short timescales.

Thrombosis is a hallmark of several chronic diseases leading to potentially fatal heart attacks and strokes. Frontline interventions include intravenous delivery of potent, enzymatic fibrinolytics that possess a high risk for inducing systemic bleeding. As a conceptual countermeasure, we have developed a water-soluble PEGylated gold nanoparticle appended with the enediyne diamine (Z)-octa-4-en-2,6-diyne-1,8-diamine that is capable of photothermally generating 1,4-diradical species under visible excitation (λ = 514 nm, 100 mW, 2–6 h). In the absence of biopolymer substrate, photothermal excitation of these particles leads to self-quenching polymer coating formation in water. When these radical-generating nanoparticles are intrinsically applied toward the blood clot structural protein assembly fibrin, as well as its nonpolymerized precursor protein fibrinogen, scanning electron microscopy images reveal significantly modified fibrin clot morphology, as evidenced by larger void spaces and collapsed fiber regi...

Reaction of 2 equiv of 1,2-bis((diphenylphosphino)ethynyl)benzene (dppeb, 1) with Pt(cod)Cl2 followed by treatment with N2H4 yields the reduced Pt(0) metalloenediyne, Pt(dppeb)2, 2. This complex is stable to both air oxidation and metal-mediated Bergman cyclization under ambient conditions due to the nearly idealized tetrahedral geometry. Reaction of 2 with 1 equiv of I2 in the presence of excess 1,4-cyclohexadiene (1,4-CHD) radical trap rapidly and near-quantitatively generates the cis-Bergman-cyclized, diiodo product 3 ((31)P: δ = 41 ppm, J(Pt-P) = 3346 Hz) with concomitant loss of 1 equiv of uncyclized phosphine chelate ((31)P: δ = -33 ppm). In contrast, addition of 2 equiv of I2 in the absence of additional radical trap instantaneously forms a metastable Pt(dppeb)2(2+) intermediate species, 4, that is characterized by δ = 51 ppm in the (31)P NMR (J(Pt-P) = 3171 Hz) and ν(C≡C) = 2169 cm(-1) in the Raman profile, indicating that it is an uncyclized, bis-ligated complex. Over 24 h, 4 undergoes ligand exchange to form a neutral, square planar complex that spontaneously Bergman cyclizes at ambient temperature to give the crystalline product Pt(dppnap-I2)I2 (dppnap-I2 = (1,4-diiodonaphthalene-2,3-diyl)bis(diphenylphosphine)), 5, in 52% isolated yield. Computational analysis of the oxidation reaction proposes two plausible flattened tetrahedral structures for intermediate 4: one where the phosphine core has migrated to a trans-spanning chelate geometry, and a second, higher energy structure (3.3 kcal/mol) with two cis-chelating phosphine ligands (41° dihedral angle) via a restricted alkyne-terminal starting point. While the energies are disparate, the common theme in both structures is the elongated Pt-P bond lengths (>2.4 A), indicating that nucleophilic ligand substitution by I(-) is on the reaction trajectory to the cyclized product 5. The efficiency of the redox-mediated Bergman cyclization reaction of this stable Pt(0) metalloenediyne prodrug and resulting cisplatin-like byproduct represents an intriguing new strategy for potential dual-threat metalloenediyne therapeutics.

Porphyrins have remarkable utility in optical and materials applications due to their extensive π-network and the corresponding electronic properties associated with this delocalization. Recent strategies have focused on methods to modulate these properties by chemically extending the conjugation. Our approach to periphery modification has centered on the application of diradicals generated through unique diyne-ene and diazo-keto functionalization at the β,β′-position of the macrocycle. In the former case, Bergman cyclization of the enediyne motif generates a new aromatic ring via a 1,4-phenyl diradical intermediate. In the absence of bimolecular quenchers in very high concentrations, the diradical adds across the adjacent phenyl rings of the meso -positions to extend the aromaticity across three rings. In the second case, dione or diazo-keto functionalization and subsequent reaction with nucleophiles in the presence of Ag + generates acetals that lead to modified chemical properties and potentially, additional reactivity at the periphery. Diazoketochlorin photolysis on the other hand, leads to rapid N 2 extrusion and initial carbene formation. The carbene is short lived and cannot be trapped even at extremely low temperatures (2 K). The subsequent Wolff ring-contracted ketene, however, is detectable, demonstrating that the out-of-plane electronic configuration is initially generated and reacts to give the nucleophile-quenched species, as well as relaxing to form exocyclic ring addition and other radical-based products. In addition to generating unique infrared and electronic spectral properties, together these strategies offer unusual synthetic opportunities, to markedly modulate macrocycle electronic structure in a highly asymmetric manner to form truly distinct porphyrinoid constructs.

Reaction of Ni(II) 2,3-dibromo-5,10,15,20-tetraphenylporphyrin with substituted stannyl alkynes generates substituted 2,3-dialkynylporphyrins in good yields. Thermolysis of these motifs with stoichiometric or even catalytic equivalents of PtCl2 yields unusual phenanthroporphyrins with only small amounts of the established picenoporphyrin or other side products.

The synthesis of a new series of free-base, Ni(II) and Zn(II) 2,3,12,13-tetra(ethynyl)-5,10,15,20-tetraphenyl porphyrins is described. Upon heating, two of the four ethynyl moieties undergo Bergman cyclization to afford the monocyclized 2,3-diethynyl-5,20-diphenylpiceno[10,11,12,13,14,15-jklmn]porphyrin in 30 %, 10 %, and trace yields, respectively. The structures of all products were investigated by using quantum chemical calculations and the free-base analogue was isolated and crystallized; all compounds show significant deviation from the idealized planar structure. No fully-cyclized bispiceno[20,1,2,3,4,5,10,11,12,13,14,15-fghij]porphyrin was isolated from the reaction mixture. To understand why only two of the four enthynyl groups undergo Bergman cyclization, the reaction coordinates were examined by using DFT at the PWPW91/cc-pVTZ(-f) level coupled to a continuum solvation model. The barrier to cyclization of the second pair of ethynyl groups was found to be 5.5 kcal mol(-1) higher than the first, suggesting a negative cooperative effect and significantly slower rate for the second cyclization. Cyclization reactions for model porphyrin-enediynes with ethene- and H-functionality substitutions at the meso-phenyl rings were also examined, and found to have a similar barrier to diradical formation for the second cyclization event as for the first in these highly planar molecules. By enforcing an artificial 30° cant in two of the pyrrole rings of the porphyrin, the second barrier was increased by 2 kcal mol(-1) in the ethene model system; this suggests that the disruption of the π conjugation of the extended porphyrin structure is the cause of the increased barrier to the second cyclization event.

Gold nanoparticle theranostic agents have dramatic potential in the fight against disease, particularly cancer, as multifunctional platforms combining biocompatibility, unique optical properties for detection/activation, and heat generation. In this vein, a new thiol-functionalized enediyne surfactant ligand was synthesized and coordinated to gold nanoparticles, as confirmed by the red-shift in the optical spectrum from λ = 520 to 529 nm upon ligand exchange. Raman spectra of the nanoparticle conjugate material show characteristic vibrations at 2192 (alkyne), 1582 (alkene), and 670 cm–1 (C–S). The photoreactivity of the material is explored under two sets of photolysis conditions: solution, λexc = 514 nm, RT, t = 8 h; solid aggregate, λexc = 785 nm, T = −190 °C, t = 4 h. Under these conditions, exciting into the surface plasmon of the Au nanoparticle substrate transfers heat to the organic ligand layer, initiating enediyne cyclization and generating surface radicals that lead to subsequent polymerization....

Photolysis of metalated (Cu and Ni) and free base 2-diazo-3-oxochlorins within a frozen matrix (λ = 457.9 nm, toluene, 80 K) generates a single photointermediate with a hypsochromically shifted electronic absorption spectrum relative to the starting diazochlorins. The appearance of ketene (~2131 cm(-1)) and azete (~1670 cm(-1)) vibrations in infrared absorption and Raman spectra, respectively, identifies this intermediate as resulting from the Wolff rearrangement of the diazochlorins upon N(2) loss. Computational modeling of the vibrational spectra and TDDFT simulation of the electronic transitions of potential photointermediates corroborate this assignment. Isolation and analysis of photoproducts of these diazochlorins formed within n-butanol-doped frozen toluene matrices indicate near exclusive formation of azeteoporphyrins. In sharp contrast, room temperature laser photolysis of these materials yields a mixture of photoproducts deriving from the presence of both carbene and ketene intermediates. Computational modeling of the intramolecular reactivity of the proposed sp(2) carbene intermediate shows exclusive bond insertion to the adjacent phenyl group, and no evidence of Wolff rearrangement. Computational reaction profile analyses reveal that the barrierless Wolff rearrangement proceeds via an out-of-plane carbene electronic configuration that is generated directly during the loss of N(2). The formation of out-of-plane carbene, resulting in the exclusive formation of the observed ketene photointermediate at low temperatures, is consistent with orbital symmetry considerations and by the geometric constraints imposed by the frozen matrix. Combined, this leads to a model showing that azeteoporphyrin formation via the Wolff rearrangement is dependent upon the structural disposition of the adjacent framework, and the specific reaction intermediate formed is very sensitive to this feature.

Water-soluble ZnS quantum dots (QDs) were synthesized using a co-precipitation method. Both undoped and Eu3+-doped ZnS QDs showed emission bands peaking at around 420 nm. The highest photoluminescence (PL) quantum yield (QY) was measured to be 17% for undoped ZnS QDs capped with SiO2. Thermal neutron induced pulse height and pulse shape spectra were measured for composites composed of 6LiF nanoparticles, undoped ZnS QDs, and poly(vinyl alcohol) (PVA) matrix. The pulse height spectra from the nanocomposites were analyzed with a track-structure model. The pulse decay time of scintillation photons is 10–30 ns. The fast decay rates and clear pulse height peaks induced by thermal neutrons indicate that ZnS QD based nanocomposites are promising scintillators for detecting high-flux thermal neutrons.

A new route for adding self-healing properties to soluble polymers is presented briefly. Self-healing block copolymers (polystyrene-block-polybutadiene block-polystyrene from Sigma-Aldrich) were obtained by dissolving the polymer in a solvent that neither dissolves the microbubbles nor deactivate the Grubbs catalyst. The self-healing block copolymer has been obtained by mixing the polymer, the solvent, the microbubbles filled with monomer (dicyclopentadiene), and the Grubbs' catalyst followed by the evaporation of the solvent. The structure of self-healed high elasticity block copolymer has been investigated by optical and Scanning Electron Microscopy. Raman spectroscopy and mechanical data suggested that the block copolymer exhibits self-healing features. Copyright © 2008 John Wiley & Sons, Ltd.

Irradiation of 2-diazo-3-oxochlorins (200 W, lambdaor = 345 nm, 10 degrees C) in the presence of nucleophilic and biomimetic substrates 1-butanol, tosylhydrazine, or tetrahydrofurfuryl alcohol generates Wolff-rearranged, pyrrole ring-contracted azeteoporphyrinoids in 11-34% yield, with the corresponding hydroxyporphyrins in up to 55% yield. For metalated diazo-oxochlorins, these products compete with intramolecular exocyclic ring formation by meso-phenyl ring addition, which occurs in up to 76% yield in the absence of substrate. The dependence of product distribution on substrate is established by photolysis in neat dichlorometane. Under these conditions, formation of the Wolff-rearranged product is inhibited and the phenyl addition product dominates (76%) due to the absence of a good nucleophile. A conceptually analogous dependence is also observed for the free-base derivative, with the exocyclic ring-containing dimerization product isolated in 42% yield. The third reaction pathway, formation of the hydroxyporphyrin, is enhanced by the presence of non-nucleophilic, oxidizable substrates such as 1,4-cyclohexadiene (M = Cu; 55%); however, in the presence of the bulky and oxidatively more stable tert-butyl alcohol, intramolecular exocyclic ring-quenching is observed in 51% yield with no detection of the hydroxyporphyrin. X-ray structure characterization of the azeteoporphyrinoids reveals a planar macrocycle, illustrating the strong influence of periphery contraction. Specifically, the copper-containing azeteoporphyrinoids show remarkably short Cu-N(azete) distances of 1.88-1.90 A. All porphyrinoid photoproducts possess intense absorption bands throughout the visible spectral region, indicating that ring-contracted substrate adducts, as well as phenyl ring addition products, maintain porphyrinoid aromaticity. Overall, the ability of these chromophores to photochemically react under substrate control may make unimolecular porphyrinoid photoreagents such as these useful for applications in photobiology or O2-independent photodynamic therapy.

We present a novel synthetic strategy to 2,2-dialkoxy-3-oxochlorins [M = 2H, Ni(II), Cu(II)] (i.e., acetaloxochlorins). Reaction of the corresponding 2,3-dioxochlorin with stoichiometric amounts of silver triflate (AgOTf) in the presence of excess alcohol yields the desired acetaloxochlorins within several hours of reflux in up to 90% yield for n-alcohols, and in 25-89% yields for functionalized alcohol substrates. Similar reaction conditions applied to 2-diazo-3-oxochlorins generates the 2,2-dialkoxy-3-oxochlorins (12-60% yields) accompanied by alkoxyporphyrins (10-27% yields). Electronic spectroscopy reveals for the acetaloxochlorins characteristic π-π* absorption features throughout the visible region and their X-ray crystal structures exhibit marked distortion from planarity of the n-conjugated macrocycle due in part to the steric bulk at the periphery.

The electronic and vibrational Raman spectra of octa-substituted (R = –SC 10 H 21 ) Co- and Cu-porphyrazines are reported in their solid-state, mesophase, and isotropic liquid forms, as well as in THF solution. Their electronic spectra are composed of traditional Soret (CuS10 = 355 nm, CoS10 = 347 nm) and lower energy Q-bands (CuS10 = 669 nm, CoS10 = 639 nm), as well as a weaker, functionality-specific sulfur n → porphyrin π ∗ feature (CuS10 = 500 nm; CoS10 = 447 nm). In contrast to the broad Q-band for CoS10 in all three neat phases, the lower energy analogue for CuS10 is markedly sharper in the microcrystalline state, but similarly broadens in the mesophase, indicative of long range macrocycle π–π interactions that persist even into the liquid state. The resonance ( λ = 647 nm) and off-resonance ( λ = 785 nm) Raman spectra of these materials in each phase exhibit four diagnostic vibrations; the C α –N m stretch (∼1540–1553) cm −1 , C β –C β stretch (∼1450 cm −1 ), C α –C β –N p stretch (∼1300–1315 cm −1 ), and C α –C β stretch (∼1070 cm −1 ). For CoS10, these vibrations systematically shift to lower energy upon melting, while those for CuS10 collapse to degenerate sets. The differences in the electronic and vibrational profiles as a function of temperature suggest that the mesophase structure is governed by strong axial Co–S interactions for CoS10 which template macrocycle π–π stacking, while for CuS10 the same contacts exist, but they are phase dependent and markedly weaker. These inter-porphyrazine interactions are, therefore, responsible for the distinct differences in the melting and clearing temperatures of their respective mesophases. Finally, based on these diagnostic spectroscopic signatures, a photo-thermal, phase-switching mechanism is demonstrated with λ = 785 nm excitation at reduced temperatures, leading to the ability to spectrally monitor and phase change with a single photon source.

The rapid, microwave-assisted aerobic synthesis of silver nanowires based on the polyol method is described. Benchtop dissolution of NaCl and AgNO3 (ratio 1:6 to 1:3) in ethylene glycol and subsequent heating using microwave irradiation (300 W) in the presence of polyvinylpyrrolidone generates Ag nanowires in ∼80% yield in 3.5 min. Upon purification, microscopy (TEM, SEM) and powder X-ray diffraction reveal a uniform set of crystalline Ag nanowires with dimensions of 45 nm × 4−12 μm. Wire formation is highly dependent upon the microwave heating power, time, and NaCl:AgNO3 ratio because of the rapid heating process and the presence of O2 as an etching coreagent. Extended microwave heating causes the wires to fuse if in proximity or degrade to shorter wires presumably via the etching reaction. In the absence of O2/Cl-, the wires melt upon extended microwave heating (>4 min), suggesting that nanowire melting may contribute to the observed morphology under etching conditions. Compared to existing wet-chemical...

We report a new and direct synthesis of 2-diazo-3-oxochlorins [M = 2 H, Ni(II), Cu(ll), Zn(II)]. Reaction of the corresponding 2,3-dioxochlorin with p-toluenesulfonylhydrazine yields the desired 2-diazo-3-oxochlorins in 59-74% yield after a reaction time of three to nine hours. Addition of a stoichiometric amount of Zn(II) acetate leads to coordination of the dione and increases the electrophilicity of the carbonyl groups. This promotes nucleophilic attack by the hydrazine derivative, leading to a six-fold enhancement of the reaction rate and product formation in very good yields.

Two novel, thioether containing benzannulated enediyne ligands, 1,2-bis(3-(quinolin-8-ylsulfanyl)prop-1-ynyl)benzene (1), and 1,2-bis(3-(pyridin-2-ylmethylsulfanyl)prop-1-ynyl)benzene (2) have been synthesized and characterized along with their corresponding Cu(I), Ag(I), Cu(II), and Pd(II) metalloenediyne complexes (3–10). Single crystal X-ray structures of the d10 and d8 N2S2 complexes show thioether coordination leading to distorted tetrahedral and trans square planar geometries about the metal centers, respectively. Based on their X-ray structures, all complexes are expected to exhibit high Bergman cyclization temperatures (>200 °C), and indeed this is the case for the Cu(I) and Ag(I) complexes (211–218 °C). In contrast, the corresponding divalent, tetragonal and trans square planar complexes of Cu(II) and Pd(II) exhibit more facile reactivity and lower solid state Bergman cyclization temperatures (186–190 °C) which more closely resemble values expected for cis-complexes. The unusual order in the thermal reactivities of these constructs can be attributed to a previously evaluated mechanism by which weak thioether coordination permits an elevated temperature trans-to-cis geometric rearrangement prior to Bergman cyclization.

Electron spin resonance investigations on styrene-polyisoprene-polystyr- ene block copolymer loaded with various amounts of multiwalled carbon nanotubes are reported. The temperature dependence of resonance line parameters in the range 290-425 K was analyzed. It was proved that the main resonance line represents a bottleneck of localized and delocalized electrons residing on carbon nanotubes. The temperature dependence of the g-factor and double integral of resonance spectra con- firmed this interpretation. The temperature dependence of the resonance linewidth of composites containing various concentrations of nanotubes was explained by the ther

The preparation and characterization of titanium-doped iron oxides–styrene isoprene styrene block copolymer composites is reported. The precursor, as-synthesized nanoparticles, contains akaganeite, maghemite, and titanium-doped maghemite. Hysteresis loops obtained by SQUID measurements revealed an exchange biased field assigned to the presence of akaganeite nanoparticles. It was found that the coercive field and the exchange bias field decreases as the temperature of the sample is increased. The temperature dependence of the magnetization revealed a blocking temperature of about 220 K. The ESR spectra in the temperature range 150 K to about 300 K are single broad resonance lines. It was observed that the resonance line position is strongly temperature dependent due to the combined action of the external and molecular magnetic fields. The decrease of the resonance line width as the temperature is increased is governed by the reorientation of the magnetization. Thermally activated movements of magnetic nanoparticles within the soft phase (polyisoprene) of the matrix may also contribute to resonance line narrowing. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3432–3437, 2005

All living organisms alter their physiology in response to changes in oxygen tension. The photosynthetic bacterium uses the RegB-RegA signal transduction cascade to control a wide variety of oxygen-responding processes such as respiration, photosynthesis, carbon fixation and nitrogen fixation. We demonstrate that a highly conserved cysteine has a role in controlling the activity of the sensor kinase, RegB. In vitro studies indicate that exposure of RegB to oxidizing conditions results in the formation of an intermolecular disulfide bond and that disulfide bond formation is metal-dependent, with the metal fulfilling a structural role. Formation of a disulfide bond in vitro is also shown to convert the kinase from an active dimer into an inactive tetramer state. Mutational analysis indicates that a cysteine residue flanked by cationic amino acids is involved in redox sensing in vitro and in vivo. These residues appear to constitute a novel 'redox-box' that is present in sensor kinases from diverse species of bacteria.

We present combined results of optical, scattering, and spectroscopic studies of (K2O)15(Nb2O5)15(TeO2)70 glass and glass ceramic and comment on possible mechanisms of the optical behavior in terms of existing theory. The glass ceramic is confirmed to generate second-harmonic light. Combined neutron and X-ray diffraction data have been indexed to an orthorhombic unit cell (a = 3.39 A, b = 4.78 A, c = 6.38 A). Additionally, we show that the previously proposed fluorite-based model is insufficient for the crystal phase using real-space analysis. The orthorhombic unit cell allows the possibility of a conventional explanation for the second-harmonic generation (SHG). Peak broadening and scattering length difference analyses are combined to formulate a model of anion disorder in the crystal phase. TEM and SAXS reveal domains of ≈15 nm in both the glass and glass ceramic. The role of liquid−liquid phase separation in the crystallization behavior of this material is discussed. Solid-state 93Nb MAS NMR and Raman ...

The compounds [(tBuCO2)3M2(μ-O2CC6F4CO2)M2(O2CtBu)3], M4PFT, where M = Mo or W, are shown by model fitting of the powder X-ray diffraction data to have an infinite “twisted” structure involving M···O intermolecular interactions in the solid state. The dihedral angle between the M2 units of each molecule is 54°. Electronic structure calculations employing density functional theory (Gaussian 98 and ADF2000.01, gradient corrected and time dependent) on the model compounds (HCO2)3M2(μ-O2CC6F4CO2)M2(O2CH)3, where M = Mo or W, reveal that in the gas phase the model compounds adopt planar D2h ground-state structures wherein M2 δ to bridge π* back-bonding is maximized. The calculations predict relatively small HOMO−LUMO gaps of 1.53 eV for M = Mo and 1.22 eV for M = W for this planar structure and that, when the “conjugation” is removed by rotation of the plane of the C6F4 ring to become orthogonal to the M4 plane, this energy gap is nearly doubled to 2.57 eV for M = Mo and 2.18 eV for M = W. The Raman and resona...

The response of a series of metalloporphyrazine liquid crystals to external magnetic fields has been investigated. Small-angle neutron scattering (SANS) data of the octa(n-decylthio)porphyrazine complexes of the diamagnetic late first-row transition elements (Ni, Zn) reveal a perpendicular orientation of the columnar directors with respect to applied magnetic fields as low as 0.50 T when the samples are cooled from their isotropic phases. The threshold aligning field for the analogous cobalt derivative is half that of the diamagnetic complexes, while the copper porphyrazine exhibits no preferred alignment at fields as high as 1.02 T. We account for these observations on the basis of the competing diamagnetic and paramagnetic moments of the complexes. Correlated solid state and mesophase 13C NMR studies on the nickel and zinc complexes indicate time-averaged disk tilt angles of 27° with respect to the columnar directors in the liquid-crystalline phase.

The compounds ((t)BuCO(2))(3)M(2)(mu-O(2)CCO(2))M(2)(O(2)C(t)Bu)(3) (M(4)OXA), where M = Mo or W, are shown by analysis of powder X-ray diffraction data to have extended lattice structures wherein oxygen atoms from the oxalate and pivalate ligands of one M(4)OXA molecule are linked to metal atoms of neighboring molecules. Raman, resonance Raman, electronic absorption (2-325 K in 2-MeTHF), and emission spectra are reported, together with corresponding spectra of the mu-O(2)(13)C(13)CO(2) isotopomers. To aid in the assignment, the Raman spectra of K(2)C(2)O(4).H(2)O and K(2)(13)C(2)O(4).H(2)O have also been recorded. The visible region of the electronic spectra is dominated by intense, fully allowed MLCT transitions, M(2) delta to oxalate pi*, which show pronounced thermochromism and extensive vibronic progressions associated with the oxalate ligand at low temperatures. With excitation into these charge-transfer bands, strong resonance enhancement is seen for Raman bands assigned to the oxalate nu(1)(a(g)) and, to a lesser extent, nu(2)(a(g)) modes. Electronic structure calculations for the model compounds (HCO(2))(3)M(2)(mu-O(2)CCO(2))M(2)(O(2)CH)(3), employing density functional theory (gradient corrected and time-dependent) with the Gaussian 98 and ADF 2000 packages, predict the planar oxalate D(2h) configuration to be favored, which maximizes M(2) delta to oxalate pi* back-bonding, and indicate low barriers (

A convenient and rapid synthesis of the title compound is described. The key step in the procedure is the Stephens Castro coupling of 3-prop-2-ynyloxy-pyridine with cis-1,2-dichloroethylene and subsequent column purification in the final stage.

The syntheses of tetradentate enediyne macrocycles with 24 (tact1:1)-, 26 (tact1:2)-, and 28 (tact2:2)-membered rings are described, along with their thermal reactivities and those of the corresponding Cu(II) (Cu(tact1:1), Cu(tact1:2)) and Zn(II) (Zn(tact1:1), Zn(tact1:2)) complexes. These enediyne macrocyclic ligands are not benzannulated and thus exhibit thermal Bergman cyclization temperatures near 200 degrees C by differential scanning calorimetry (DSC). Moreover, the synthetic route allows incorporation of additional carbon atoms into the macrocycles which increases their conformational flexibilities and lowers their Bergman cyclization temperatures. Specifically, as the size of the macrocycle increases, the temperatures at which these compounds undergo Bergman cyclization decrease by approximately 5 degrees C per additional carbon atom, leading to an overall decrease across the series of 19 degrees C. Incorporation of Cu(II) and Zn(II) into these macrocycles further reduces their cyclization temperatures relative to those of the free ligands. More uniquely, for Cu(tact1:1) and Zn(tact1:1), the observed cyclization temperatures vary by 27 degrees C with the Zn(II) complex lying to higher temperature (Cu(tact1:1) = 121 degrees C, (Zn(tact1:1) = 148 degrees C). As the macrocycle size is increased, the decrease in the Bergman cyclization temperatures observed for the free ligands does not systematically hold for the Cu(II) and Zn(II) derivatives. Rather, the Cu(II) complex exhibits the expected 9 degrees C decrease in the cyclization temperature (Cu(tact1:2) = 112 degrees C), whereas the temperature for the Zn(II) analogue increases by 15 degrees C (Zn(tact1:2) = 163 degrees C). From the X-ray crystal structure of the free ligand and the geometric structural preferences of the electronic configurations of Cu(II) and Zn(II), the higher cyclization temperatures for the Zn(II) complex with the larger ring size can be explained by a distortion of the macrocycle toward a more tetrahedral metal center geometry.

We report the syntheses, reactivities, and structure evaluations of a series of Cu(I) and Cu(II) metalloenediynes of conjugated 1,6-bis(pyridine-3)hex-3-ene-1,5-diyne (PyED, 7) and 1,6-bis(quinoline-3)hex-3-ene-1,5-diyne (QnED, 8) enediyne ligands, as well as their benzoenediyne analogues. Differential scanning calorimetry demonstrates that the [Cu(PyED)(2)](NO(3))(2) (11) exhibits a Bergman cyclization temperature (156 degrees C) which is dramatically reduced from that of the corresponding [Cu(PyED)(2)](PF(6)) (19) analogue (326 degrees C), indicating that large differences in the reactivities of these metalloenediynes can be accessed by variations in metal oxidation state. The distorted, 4-coordinate dichloride compound Cu(PyED)(Cl)(2) (15) exhibits a cyclization temperature (265 degrees C) between those of 11 and 19, suggesting that variation in geometry of the copper center is responsible for the wide range of reactivities. Similar results are obtained for the benzoenediyne and quinoline analogues. The structures of the Cu(II) systems have also been evaluated by a combination of electronic absorption and EPR spectroscopies which reveal tetragonal, 6-coordinate structures for the bis(enediyne) complexes, and tetrahedrally distorted 4-coordinate Cu(enediyne)Cl(2) species. For the bis(quinoline) enediyne derivatives 12 and 14 the larger g-anisotropy (g( parallel) = 2.27-2.28; g( perpendicular) = 2.06-2.07) indicates strong oxygen coordination from counterion. Molecular mechanics/dynamics calculations reveal that the geometries of these metal centers force the alkyne termini to a wide range of distances (3.85-4.20 A), thereby accounting for the variability in Bergman cyclization temperatures. Overall, the results show that ligand rigidity plays a prominent role in the conformational response of the enediyne to metal center geometry, which results in enhanced variations in the Bergman cyclization temperatures between complexes of different geometries.

Several singlet and triplet potential energy surfaces (PES) for the Bergman cyclization of cis-1,5-hexadiyne-3-ene (1a) have been computed by UDFT, CI, CASCI, CASSCF, and CASMP2 methods. It is found that the first six excited states of 1a can be qualitatively described as linear combinations of the configurations of weakly interacting ethylene and acetylene units. Although the symmetry relaxation from C2nu to C2 makes cyclization of the 13B state Woodward-Hoffmann allowed, it also increases the probability of competing cis-trans isomerization. Hydrogen atom abstraction is another plausible pathway because the terminal alkyne carbons possess a large radical character. In view of the competing processes, we conclude that the Bergman cyclization along the 13B path is unlikely despite its exothermicity (Delta = -42 kcal/mol). Calculations on cyclic analogues of 1a lead to similar conclusions. A less exothermic, but more plausible pathway for photochemical cyclization lies on the 2(1)A PES (Delta = -18 kcal/mol). Compared to the 1(1)A(1) and 1(3)B states, the 2(1)A state has less in-plane electron repulsion which may facilitate cyclization. The resulting p-benzyne intermediate has an unusual electronic structure combining singlet carbene and open-shell diradical features. Deactivation of the 2(1)A state of 1a is a competing pathway.

The photochemical reactivities of 3-hydroxy-1,2,3-benzotriazine-4(3H)-one (1a) and tris[3-hydroxy-1,2,3-benzotriazine-4(3H)-one]iron(III) (1b) have been studied in solution and low temperature (5–77 K) glasses. Photoexcitation (λ345 nm) of 1a and 1b ultimately results in population of a ligand-centered excited state that releases N2. Electron paramagnetic resonance reveals the presence of S = 1 and S = 0 diradical intermediates upon photolysis of 1a and 1b, respectively, at 4 K. These species convert to an S = 1/2, nitrogen-centered monoradical species (aN = 23 G) upon warming to 77 K ia H-atom abstraction from the matrix. In solution, the first intermediates observed upon photolyses (λ = 355 nm) of 1a and 1b are oxime ketenes (5: λ = 385, 440 nm; 9: λ = 390, 430, 740 nm) that are formed from collapse of the diradical to generate a 4-membered β-lactam ring. The decay kinetics for the oxime ketene 5 decay can be fitted to a biexponential expression representing a parallel reaction mechanism with an element of reversibility. Thus, the data proposes the existence of an equilibrium between the oxime ketene and the spectroscopically silent β-lactam intermediate, as well as a first or pseudo first-order solvent-dependent pathway for the oxime ketene. The kinetics for formation and decay of the ketene are strongly influenced by the presence of the Fe(III) center, which leads to an increase in the lifetime of the diradical in solution, and a retarded rate of formation for the oxime ketene 9. The solution lifetimes suggest that the diradical intermediates only persist sufficiently long to react with bound solution substrates, whereas the ketene intermediates have suitable kinetic viabilities to react bimolecularly in solution.

Bleomycin (BLM) is a glycopeptide antibiotic produced by the fungus Streptomyces verticillus which is used clinically for anticancer therapy. It is most active as an iron complex. A detailed spectroscopic and theoretical study of the ferric form of the drug, Fe(III)BLM, and its activated form, ABLM, is reported. ABLM, which has been shown to be a ferric hydroperoxide complex, is the last detectable intermediate in the reaction cycle of BLM that leads to a DNA radical and subsequent cleavage. Both forms of the drug are low-spin Fe(III) complexes and were studied with electron paramagnetic resonance (EPR), magnetic circular dichroism (MCD), and absorption (ABS) spectroscopy. In addition, resonance Raman (rR) and circular dichroism (CD) spectra are reported for Fe(III)BLM. The g matrix was analyzed in detail, and Griffith's model for low-spin d5 complexes was experimentally evaluated. A ligand field analysis of the d−d region of the optical spectra resulted in a complete determination of the ligand field par...

We report the preparation and thermal reactivities of unique Cu(I) and Cu(II) metalloenediyne complexes of the flexible 1,8-bis(pyridine-3-oxy)oct-4-ene-2,6-diyne ligand (bpod, 1). The thermal reactivities of these metalloenediynes are intimately modulated by metal oxidation state. Using differential scanning calorimetry (DSC), we demonstrate that the [Cu(bpod)2]+ complex (2) undergoes Bergman cyclization at 203 °C, whereas the Cu(II) analogue (3) is substantially more reactive and cyclizes at 121 °C. Similar results are also observed for mixed ligand [Cu(bpod)(pyridine)2]+/2+ analogues 4 (194 °C) and 5 (116 °C), suggesting that both complexes of a given oxidation state have comparable structures. The Cu(bpod)Cl2 compound (6) exhibits a cyclization temperature (152 °C) midway between the those of Cu(I) and Cu(II) complexes, which can be explained by the propensity for cis-CuN2Cl2 structures to exhibit dihedral angle distortion. The oxidation-state-dependent thermal reactivity is unprecedented and reflects...

We report the X-ray diffraction structure and thermal reactivity of the metalloenediyne compound bis(1,2-bis(diphenylphosphinoethynyl)benzene)palladium(0) (Pd(dppeb)2, 1). The structure of 1 features a tetrahedral Pd(0) center with four phosphorus atoms from two chelating ligands. The PPdP bond angles nearly match the idealized 109.5° geometry expected for a d10 metal center in a tetrahedral ligand field. The tetrahedral geometry of the metal center forces the alkyne termini separation of the enediyne ligand to a distance of 3.47 A, which results in a thermally stable compound at room temperature. However, at 115 °C 1 exhibits solvent-dependent reactivity. In o-fluorotoluene, 1 decomposes via ligand dissociation, while in o-dichlorobenzene, carbon−halide bond activation of solvent occurs leading to the oxidative addition product trans-Pd((2-chlorophenyl)diphenylphosphine)2Cl2 and free (2-chlorophenyl)diphenylphosphine. The thermal reactivity of 1 is markedly more endothermic (44 kcal/mol) than that of the...

The geometric and electronic structures of high-spin ferrous complexes of bleomycin (FeIIBLM) and a series of systematically perturbed BLM derivatives have been investigated by optical absorption, circular dichroism (CD), and magnetic circular dichroism (MCD) spectroscopies. The active site of the unmodified drug complex is six-coordinate with the coordination sphere completed by at least five endogenous ligands including the pyrimidine, imidazole, deprotonated amide, and secondary and primary amine functionalities with either the 3-O-carbamoyl substituent of the mannose sugar or solvent bound at the sixth site. This weak sixth ligand is the exchangeable site of exogenous small molecule binding. Perturbing the carbamoyl substituent alters the coordination environment of the metal and decreases the azide binding affinities of the perturbed complexes. This is correlated with altered DNA cleaving capabilities. Additionally, altering the binding of the axial primary amine significantly affects the iron coordi...

Several benzoxazole and benzothiazole compounds have been prepared and their extended configurations characterized by optical absorption and emission spectroscopy. In general, solutions of these compounds fluoresce strongly and exhibit emission spectral profiles which mirror their respective excitation spectra. One exception to this correlation results from a chromophore with a nonplanar ground state configuration which disrupts the extended π-network, promoting a strong hypsochromic shift of the absorption spectrum. The absorption, excitation, and emission spectra of these compounds also show a strong vibronic progression of ∼1300 cm-1 in accordance with the energy of ring-stretching modes for aromatic frameworks. This excited state molecular distortion is consistent with the ππ* nature of the optical excitation. Also, the energy gap between excitation and emission 0−0 bands of these benzoxazole and benzothiazole compounds and their polymeric forms are strongly influenced by the minimum allowed intermole...

The rates for the photoinduced bimolecular reactions of a homologous series of RuII diimines with cytochrome (cyt) c in its oxidized and reduced forms have been measured. The electronic coupling and reorganization energy of the system have been adjusted such that the inverted region may be accessed at reasonable driving forces. The electron transfer (ET) rate constants for *RuII diimine/FeIIcyt c reaction increase monotonically and approach the diffusion limit of 8.8 × 108 M-1 s-1 at ΔG° = −0.7 V. At a higher driving force, which may be accessed with the powerfully oxidizing *Ru(diCF3-bpy)32+, the rate for ET is observed to drop off. Similarly, the high driving forces achieved with *RuII diimine/FeIIIcyt c (−ΔG ≥ 1.12 V) are manifested in a decrease of the ET rate constant with increasing exergonicity. The observed ET rates for both systems are well described by a bimolecular model for ET occurring over an equilibrium distribution of reactant separation distances, each having a different formation probabi...

The geometric and electronic structure of high-spin ferrous complexes of bleomycin (Fe{sup II}BLM) and the structural analog PMAH ([Fe{sup II}PMA]{sup +}, where PMAH is a macrocyclic ligand with pyrimidine, imidazole, deprotonated amide, and secondary and primary amine functionalities) have been investigated by optical (Abs) and X-ray (XAS) absorption, magnetic circular dichroism (MCD), and resonance Raman (rR) spectroscopies. The lability of high-spin iron combined with steric constraints of the BLM ligand framework and its weaker axial interaction with solvent support a dissociative mechanism for O{sub 2} reactivity. Our spectroscopic studies of solid [Fe{sup II}PMA]{sup +} have defined the nature of such a five-coordinate intermediate as square pyramidal which provides an open coordination position for reaction with O{sub 2}. A major electronic structure difference between Fe{sup II}BLM (and [Fe{sup II}PMA]{sup +}) and other non-heme ferrous sites is the presence of low-energy CT transitions which reflect strong iron(II) {yields} pyrimidine backbonding. Despite generally being considered a non-heme iron system due to the absence of an extensive delocalized {pi} network, the existence of low-energy MLCT transitions with reasonable intensity, hence the presence of some backbonding, identifies BLM as an important link bridging the chemistry of non-heme and heme active sites. 113 refs., 17 figs.,more » 4 tabs.« less

Activated Bleomycin (BLM) is the first mononuclear non-heme iron oxygen intermediate stable enough for detailed spectroscopic study. DNA degradation by activated BLM involves C-H bond cleavage at the C4[prime] position of deoxyribose moieties and results in the production of base propenals. It has been postulated that activated BLM is an oxo-ferryl intermediate on the basis of its reactivity and analogy with cytochrome P-450 chemistry. Alternatively, spectroscopic and model studies have indicated activated BLM to have an iron(III)-peroxide site. In this study, X-ray absorption spectroscopy (XAS) has been used to directly probe the oxidation and spin states of the iron in activated BLM and to determine if a short iron-oxo bond is present, which would be characteristic of the oxo-ferryl species of heme iron. Both the pre-edge and edge regions of the Fe K-edge spectra indicate that activated BLM is a low spin ferric complex. The pre-edge intensity of activated BLM is also similar to that of low spin ferric BLM and does not show the intensity enhancement which would be present if there were a short Fe-O bond. Furthermore, bond distances obtained from EXAFS are similar to those in low spin Fe[sup III]BLM and show no evidence for a shortmore » iron-oxo bond. 33 refs., 4 figs., 1 tab.« less

Two electrons in two weakly coupled orbitals give rise to two states (diradical) with electrons residing in separate orbitals and two states (zwitterionic) with both electrons paired in one orbital or the other. This two-electron, two-orbital state manifold has eluded experimental confirmation because the zwitterionic states have been difficult to locate. Two-photon excitation of fluorescence from Mo(2)CI(4)(PMe(3))(4) (D2d) has been measured with linearly and circularly polarized light. From the polarization ratio and the energy of the observed transition, the 2(1)A(1) (delta*delta*) excited state has been located and characterized. In conjunction with the one-photon allowed (1)B(2) (deltadelta*) excited state, the zwitterionic state manifold for the quadruply bonded metal-metal class of compounds is thus established.