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Chelation of lanthanide and actinide cations within a suitable macrocyclic ligand often results in a rigid, kinetically inert, and thermodynamically stable complex. A benchmark for such cation-ligand suitability are cyclen-derived macrocyclic ligands, frequently used as large cation hosts for various applications. Herein, a comprehensive study of the 1,4,7,10-tetrakis(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane ligand (DOTAM) chelates of U IV and Ce III and their properties in aqueous solutions is presented. By employing multiple analysis techniques, including X-ray crystallography, UV-vis absorbance, 1 H NMR, UPLC-MS, cyclic voltammetry, and differential pulse voltammetry, the study has revealed that the two aqueous complexes undergo a spontaneous, gradual, and stepwise hydrolysis of each of the coordinated amides toward carboxylates. The coordination of U IV in the studied reaction has been shown to significantly enhance the reaction rate, leading to an acceleration of up to 6 orders of magnitude compared to the natural process of simple aqueous amides at room temperature. An attempt to describe the unusual chelated metal cation amide-activation feature, based on the relatively lower rigidity of the complex structure, is presented. Additionally, the electrochemical properties of the complex series are discussed in detail, along with the limitations of the analytical methods employed.

Conjugated arrays composed of corrole macrocycles are increasingly more common, but their chemistry still lags behind that of their porphyrin counterparts. Here, we report on the insertion of iron(III) into a β,β-fused corrole dimer and on the electronic effects that this redox active metal center has on the already rich coordination chemistry of [H 3 tpfc] COT, where COT = cyclo-octatetraene and tpfc = tris(pentafluorophenyl)corrole. Synthetic manipulations were performed for the isolation and full characterization of both the 5-coordinate [Fe III tpfc(py)] 2 COT and 6-coordinate [Fe III tpfc(py) 2 ] 2 COT, with one and two axial pyridine ligands per metal, respectively. X-Ray crystallography reveals a dome-shaped structure for [Fe III tpfc(py)] 2 COT and a perfectly planar geometry which (surprisingly at first) is also characterized by shorter Fe-N (corrole) and Fe-N (pyridine) distances. Computational investigations clarify that the structural phenomena are due to a change in the iron(III) spin state from intermediate ( S = 3/2) to low ( S = 1/2), and that both the 5- and 6-coordinated complexes are enthalpically favored. Yet, in contrast to iron(III) porphyrins, the formation enthalpy for the coordination of the first pyridine to Fe(III) corrole is more negative than that of the second pyridine coordination. Possible interactions between the two corrole subunits and the chelated iron ions were examined by UV-Vis spectroscopy, electrochemical techniques, and density functional theory (DFT). The large differences in the electronic spectra of the dimer relative to the monomer are concluded to be due to a reduced electronic gap, owing to the extensive electron delocalization through the fusing bridge. A cathodic sweep for the dimer discloses two redox processes, separated by 230 mV. The DFT self-consistent charge density for the neutral and cationic states (1- and 2-electron oxidized) reveals that the holes are localized on the macrocycle. A different picture emerges from the reduction process, where both the electrochemistry and the calculated charge density point toward two consecutive electron transfers with similar energetics, indicative of very weak electron communication between the two redox active iron(III) sites. The binuclear complex was determined to be a much better catalyst for the electrochemical hydrogen evolution reaction (HER) than the analogous mononuclear corrole.

The coordination and redox chemistry of aqueous Ce IV/III macrocyclic compounds were studied by using the ligands DOTA and DOTP (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetra(methylene phosphonic acid), respectively). The hydrolysis tendency of the tetravalent cation in the presence of DOTA is shown to result in the formation of a highly ordered, fluorite-like [Ce IV 6 (O) 4 (OH) 4 (H 2 O) 8 (DOTAH) 4 ] oxo-hydroxo structure both in solution and in the solid state. The lifetime of the analogous species formed in the presence of DOTP was found to be much shorter. Spectroscopic measurements of the latter suggest its similarity to the former. Its gradual decomposition in solution leads to the accumulation of the in-cage complexes [Ce IV DOTP] and [Ce III DOTP(H 2 O)], which were crystallographically characterized in this study. The redox energetics and spectroscopic characteristics for the transition between these two in-cage complexes in aqueous solutions were studied as well. Together with the crystallographic structures of the above-mentioned species, the in-cage [Ce IV DOTA(H 2 O)] complex structure is presented herein for the first time. An elaborative analysis of the X-ray crystallographic structural data obtained for the in-cage complexes studied herein and similar structures published previously suggests that hard-bonding cyclen-derived ligands are, counter-intuitively, better suited for encapsulating, and perhaps kinetically stabilize softer cations than harder ones with DOTP, marked as a possible adequate chelator for the study of the aqueous properties of Ln II and Ac III cations., (© 2022 Wiley-VCH GmbH.)

The Cu I/II ATP react with methyl radicals to form methane and methanol, where Cu I ATP reacts with • CH 3 in a process that is surprisingly slow. The low-rate constant of this process is attributed to the significant rearrangement of the chelating ligand required for the transient's formation. These results were corroborated by DFT calculations of the relevant compounds., (Copyright © 2022. Published by Elsevier Inc.)

The mechanism of reaction of DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) with ·CH 3 , CH 3 O 2 · and ·OH radicals were studied. The radicals were formed in situ radiolytically. The methyl radicals react orders of magnitude slower with DOTA and with M III (DOTA) - than the hydroxyl radicals. The various final products were identified and mechanisms for their formation are proposed. CH 3 O 2 · radicals do not react, or react too slowly to be observed, with DOTA and with M III (DOTA) - as long as the central cation is not oxidized by the peroxyl radical. The results imply that synthesis of the M III (DOTA) - (M III  = radioisotope) complexes in a water-organic solvent (ethanol or 2-propanol or acetonitrile) mixture is not only kinetically desired but the so formed complex also decreases the radiolytic decomposition of DOTA., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Two new aqueous U IV complexes were synthesized by the interaction between the tetravalent uranium cation and the (1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetra(methylene phosphonic acid) (DOTP) macrocyclic ligand. Two distinct homonuclear complexes were identified; the first was characterized by X-ray crystallography as a unique "out-of-cage", [U(DOTPH 6 ) 2 ] complex, in which the U IV cation is octa-coordinated to 4 phosphonic arms from each ligand in a square anti-prism geometry, with a C 4 symmetry. The second is the "in-cage" [U(DOTPH 4 )] complex, in which the tetravalent cation is located between the macrocycle O 4 and N 4 planes. With the help of UV-Vis absorption, 1 H/ 31 P NMR, ATR-IR, and MALDI-TOFMS analytical techniques, the chemical interchange between both species is presented. It is shown that the one-way transition is governed by the formation of a multiple number of soluble oligomeric species consisting of varied stoichiometric ratios of both characterized homonuclear complexes., (© 2021 Wiley-VCH GmbH.)

The redox chemistry of Ce III DOTA in cage in carbonate solutions was studied using electrochemistry and radiolysis techniques (continuous radiolysis and pulse radiolysis). Spectroscopic measurements point out that the species present in the solutions at high bicarbonate concentrations are [Ce III DOTA(CO 3 )] 3- (or less plausible [Ce III DOTA(HCO 3 )] 2- ) with the carbonate (bicarbonate) anion as the ninth ligand versus [Ce III DOTA(H 2 O)] - present in the absence of bicarbonate. Electrochemical results show a relatively low increase in the thermodynamic stabilization of the redox couple Ce IV/III in the presence of carbonate versus its aqueous analogue. [Ce IV DOTA(CO 3 )] 2- and [Ce IV DOTA(H 2 O)], prepared electrochemically, decompose photolytically. However, kept in the dark, both are relatively long lived; [Ce IV DOTA(H 2 O)], though, is orders of magnitude kinetically more stable (a considerably longer half-life). Thus, one concludes that the carbonate species have a different mechanism of decomposition depending also on the presence of dioxygen after its preparation (in deaerated/aerated solutions). The [Ce IV DOTA(CO 3 )] 2- species is produced radiolytically by oxidation of the trivalent species by CO 3 •- with a rate constant, measured using pulse radiolysis, of 3.3 × 10 5 M -1 s -1 . This rate constant is at least 1 order of magnitude smaller than most of the rate constants so far reported for the reaction of CO 3 •- with transition metal/lanthanide (cerium)/actinide complexes. This result together with the bulkiness of the reactants might suggest an outer-sphere electron transfer rather than the inner-sphere one so far proposed. The lifetime of the tetravalent cerium species obtained radiolytically in the presence of carbonate is shorter than the electrochemical one, suggesting a different conformer involved.

Methyl radicals play key roles in various chemical and biological processes. Mechanistic studies of methyl radicals with their precursor, Dimethyl Sulfoxide (DMSO), were extensively studied. Though the involved mechanisms seemed to be clarified, essentially none of the studies have been performed at conditions relevant to both biological and catalytic systems, i.e. low steady state radical concentrations. A chain-like reaction, as an inverse function of the radicals concentrations ([ • CH 3 ] ss ), increases the methyl radical yields. The nature of the additional products obtained differs from those commonly observed. Furthermore it is shown that methyl radicals abstract a methyl group from DMSO to yield ethane. Herein we report a novel mechanism relevant mainly at low steady state radical concentrations, which may change the understanding of certain reaction routes present in both biological systems and catalytic chemical systems. Thus the results point out that mechanistic studies have to be carried out at dose rates forming radicals at analogous concentrations to those present in the process of interest., (Copyright © 2020 Elsevier Inc. All rights reserved.)

A combined experimental and density functional theory (DFT) investigation was employed in order to examine the mechanism of electrochemical CO 2 reduction and H 2 formation from water reduction in neutral aqueous solutions. A water soluble cobalt porphyrin, cobalt [5,10,15,20-(tetra-N-methyl-4-pyridyl)porphyrin], (CoTMPyP), was used as catalyst. The possible attachment of different axial ligands as well as their effect on the electrocatalytic cycles were examined. A cobalt porphyrin hydride is a key intermediate which is generated after the initial reduction of the catalyst. The hydride is involved in the formation of H 2 and formate and acts as an indirect proton source for the formation of CO in these H + -starving conditions. The experimental results are in agreement with the computations and give new insights into electrocatalytic mechanisms involving water soluble metalloporphyrins. We conclude that in addition to the porphyrin's structure and metal ion center, the electrolyte surroundings play a key role in dictating the products of CO 2 /H 2 O reduction., (© 2020 Wiley-VCH GmbH.)

The 1,4,7,10-tetrazacyclodecane-1,4,7,10-tetraacetic acid (DOTA) aqueous complex of U IV with H 2 O, OH - , and F - as axial ligands was studied by using UV/Vis spectrophotometry, ESI-MS, NMR spectroscopy, X-ray crystallography, and electrochemistry. The U IV -DOTA complex with either water or fluoride as axial ligands was found to be inert to oxidation by molecular oxygen, whereas the complex with hydroxide as an axial ligand slowly hydrolyzed and was oxidized by dioxygen to a diuranate precipitate. The combined data set acquired shows that, although axial substitution of fluoride and hydroxide ligands instead of water does not seem to significantly change the aqueous DOTA complex structure, it has an important effect on the electronic configuration of the complex. The U IV /U III redox couple was found to be quasi-reversible for the complex with both axially bonded H 2 O and hydroxide, but irreversible for the complex with axially bonded fluoride. Intriguingly, binding of the axial fluoride renders the irreversible one-electron U V /U IV oxidation of the [U IV (DOTA)(H 2 O)] complex quasi-reversible, which suggests the formation of the short-lived pentavalent form of the complex, an aqueous non-uranyl chelated U V cation., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Recently it was reported that copper bicarbonate/carbonate complexes are good electro-catalysts for water oxidation. However, the results did not enable a decision whether the active oxidant is a Cu III or a Cu IV complex. Kinetic analysis of pulse radiolysis measurements coupled with DFT calculations point out that Cu III (CO 3 ) n 3-2n complexes are the active intermediates in the electrolysis of Cu II (CO 3 ) n 2-2n solution. The results enable the evaluation of E°[(Cu III/II (CO 3 ) n ) aq ]≈1.42 V versus NHE at pH 8.4. This redox potential is in accord with the electrochemical report. As opposed to literature suggestions for water oxidation, the present results rule out single-electron transfer from Cu III (CO 3 ) n 3-2n to yield hydroxyl radicals. Significant charge transfer from the coordinated carbonate to Cu III results in the formation of C 2 O 6 2- by means of a second-order reaction of Cu III (CO 3 ) n 3-2n . The results point out that carbonate stabilizes transition-metal cations at high oxidation states, not only as a good sigma donor, but also as a non-innocent ligand., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The complexation of 1,4,7,10-tetrazacyclodecane-1,4,7,10-tetraacetic acid (DOTA) ligand with two trivalent actinides (Am 3+ and Pu 3+ ) was investigated by UV-visible spectrophotometry, NMR spectroscopy, and extended X-ray absorption fine structure in conjunction with computational methods. The complexation process of these two cations is similar to what has been previously observed with lanthanides(III) of similar ionic radius. The complexation takes place in different steps and ends with the formation of a (1:1) complex [(An(III)DOTA)(H 2 O)] - , where the cation is bonded to the nitrogen atoms of the ring, the four carboxylate arms, and a water molecule to complete the coordination sphere. The formation of An(III)-DOTA complexes is faster than the Ln(III)-DOTA systems of equivalent ionic radius. Furthermore, it is found that An-N distances are slightly shorter than Ln-N distances. Theoretical calculations showed that the slightly higher affinity of DOTA toward Am over Nd is correlated with slightly enhanced ligand-to-metal charge donation arising from oxygen and nitrogen atoms.

Objectives: The aim of the study was to investigate whether lycopene from natural sources (tomato extract) is able to protect newborns milk formula, against oxidative damage caused by exposure to hydroxyl radicals, and is there a difference between milk substitutes from various sources., Methods: Four commercial brands of infant milk formula: two of the formulas were dairy milk (A-d and B-d) and two were based on soy bean vegan milk (A-s and B-s), were exposed to ionizing radiation radical (·OH). Lipid peroxidation was determined by measuring malondialdehyde (MDA) using thiobarbituric acid reactive substance test (TBARS)., Results: When suspensions containing the four brands of formula were subjected to oxidizing media produced by ionizing radiation (hydroxyl radicals), lipid peroxidation increased linearly as a function of the irradiation dose (R = 0.99). It was found that lycopene in a concentration of 0.6 mM, reduced the radiation damage only in the soy-based formula; decrease of ∼40% of the damage achieved in B-s, and ∼20% reduction in the damage caused to A-s, significantly p < 0.01., Conclusions: Lycopene in dairy milk did not protect against hydroxyl radicals; however, lycopene found to protect against hydroxyl radicals in soy milk. This result suggests different mechanisms of radical production that arises from high iron levels present in the soy milk and involving the high-valent iron peroxo species.

A self-assembled supramolecular dimeric entity via an exceptionally short (2.404 Å) and strong (22.9 kcal mol(-1)) [O-H-O](-) hydrogen bond is the key to the special reactivity of vasarenes with fluoride salts. Vasarene is a self-assembled, vase-shaped compound, obtained by the reaction between ninhydrin and phloroglucinol. Analogous compounds are prepared by replacing the phloroglucinol with other polyhydroxy aromatics. Vasarenes show special affinity towards compounds of the type M(+)F(-), where M being a large monovalent cation, producing ion-pair-vasarene adducts. The first step in the proposed mechanism is the dissociation of the M(+)F(-) salt releasing F(-) to the solution, which may provide an explanation as to why only MF salts, which include large monovalent cations, undergo this reaction. From a practical point of view, the ease of their preparation and their special affinity towards fluoride salts make vasarenes potential means for salt separation. The readily formed dimeric structure with the very short [O-H-O](-) negative charge-assisted H-bond (-CAHB) can also be further used as a model in theoretical studies of such systems and understanding their role in biological processes.

The title compound, [Cs(CH3COO)(C28H16O8)(C2H5OH)]·C2H5OH, is the product of the complexation between one vasarene analogue [1], bis ninhydrin naphthalene-1,3-diol and CsF, where the F(-) ion has reacted with residual acetic acid (AcOH), to form a [1]·CsOAc complex. The inter-molecular inter-actions with the multiple oxygen-containing functional groups of the ligand, as well as O-H⋯O hydrogen bonds involving the ethanol solvent mol-ecules, stabilize the complex, forming a chain along [100]. Additional parallel-displaced π-π stacking, with an inter-planar distance of 3.669 (1) Å, connect several unit cells in a three-dimensional supra-molecular structure, though, the larger size of AcO(-) (1.60 Å) compared to F(-) (1.33 Å) prevents the tight packing that was once achieved with other vasarene complexes of CsF.

It was recently reported that the reaction of methyl radicals with Pt(0) nanoparticles (NPs), prepared by the reduction of Pt(SO4)2 with NaBH4, is fast and yields as the major product stable (Pt(0)-NPs)-(CH3)n and as side products, in low yields, C2H6, C2H4, and some oligomers. We decided to study the effect of this coating on the properties of the Pt(0)-NPs. The results show that the coating can cover up to 75% of the surface Pt(0) atoms. The rate constant of the reaction, k((.)CH3+Pt(0)-NPs), decreases with the increase in the surface coverage, leading to competing reaction paths in the solution, which gradually become dominant, affecting the composition of the products. The methyl coating also affects the zeta potential, the UV spectra, and the electrocatalytic reduction of water in the presence of the NPs. Thus, the results suggest that binding alkyl radicals to Pt(0) surfaces might poison the NPs catalytic activity. When the Pt(0)-NPs are prepared by the reduction of a different precursor salt, PtCl6(2-), nearly no C2 H4 and oligomers are formed and the methyl coating covers a larger percentage of the surface Pt(0) atoms. The difference is attributed to the morphology of the Pt(0)-NPs: those prepared from Pt(SO4)2 are twinned nanocrystals, whereas those prepared from PtCl6(2-) consist mostly of single crystals. Thus, the results indicate that the side products, or most of them at least, are formed on the twinned Pt(0) nanocrystal edges created between (111) facets. In addition, the results show that Pt(0)-NPs react very differently compared with other noble metals, for example, Au(0) and Ag(0); this difference is attributed in part to the difference in the bond strength, (M(0)-NP)-CH3, and should be considered in heterogeneous catalytic processes involving alkyl radicals as intermediates., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Ni(II)L(2), L(2) = 1-propyl-1,3,5,8,12-pentaazacyclotetradecane, was covalently bound to a silica support. This complex can be reversibly oxidized to the corresponding Ni(III) complex. The latter complex is relatively long lived. Therefore electron exchange columns based on this material can be prepared.

Surprisingly the oxidation of MoO4(3-) by H2O2 involves two H2O2 molecules. It is proposed that generally when the reaction of a reducing agent with H2O2, to form a single electron oxidized product and a hydroxyl radical, is endothermic the reaction involves more than one H2O2 molecule.

The H/D kinetic isotope effect (KIE) for the reaction of methyl radicals with glycine in aqueous solutions at pH 10.6 equals 16 ± 3. This result proves that the methyl radical abstracts a hydrogen atom from the methylene group of glycine and not an electron from the unpaired couple on the nitrogen atom. The rate constant of the reaction of methyl radicals with glycine at pH 7.0 is orders of magnitude smaller than that at pH 10.6.

Methyl radicals react in fast reactions, with rate constants k>1×10(8)  M(-1)  s(-1), with Au(0), Ag(0) and TiO(2) nanoparticles (NPs) dispersed in aqueous solutions to form intermediates, (NP)-(CH(3))(n), in which the methyl groups are covalently bound to the NPs. These intermediates decompose to form ethane. As n≥2 is required for the formation of C(2)H(6), the minimal lifetime (τ) of the methyls bound to the NPs, (NP)-CH(3), can be estimated from the rate of production of the CH(3)(·) radicals and the NPs concentration. The results obtained in this study, using a very low dose rate γ-source for NP = Ag(0), Au(0), and TiO(2) point out that τ of these intermediates is surprisingly long, for example, ≥8 and ≥188 sec for silver and gold, respectively. These data point out that the NP-C bond dissociation energies are ≥70 kJ  mol(-1). Under low rates of production of CH(3)(·), that is, when the rate of formation of ethane is very low, other reactions may occur, consequently the mechanism proposed is "broken". This is observed in the present study only for TiO(2) NPs. These results have to be considered whenever alkyl radicals are formed near surfaces. Furthermore, the results point out that the rate of reaction of methyl radicals with (NP)-(CH(3))(n) depends on n, that is, the number of methyl radicals bound to the NPs affect the properties of the NPs., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Methyl radicals react with TiO(2) nanoparticles (NPs) immersed in aqueous solutions to form transients in which the methyls are covalently bound to the particles. The rate constant for this reaction approaches the diffusion-controlled limit and increases somewhat with the number of methyls bound to the particle. The transients decompose to yield ethane. Thus, formally the particles "catalyse" the dimerization of the radicals, a reaction that is diffusion-controlled. Rutile powders behave similarly to the TiO(2) NPs whereas the mechanism for the decomposition of the transients formed in the analogous reaction of the radicals with anatase powders differs. These results are of importance as alkyl radicals are formed near the surface of TiO(2) in a variety of important photocatalytic processes. The results imply that the reactions of alkyl radicals with TiO(2) have to be considered in these processes., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Four commercial brands of infant milk formula were investigated, and the amount of shelf lipid peroxidation was determined by measuring malondialdehyde (MDA) or, more exactly, thiobarbituric acid reactive substance (TBARS) levels, which are the end products of lipid peroxidation. TBARS level, indicated by MDA concentration, was higher in the vegetarian brands. The vegetarian brands are, as expected, more prone to oxidation than dairy brands, as they contain more unsaturated fats. The introduction of formate anion diminishes the peroxide amounts initially present in the milk samples as well as those induced by radiation-induced oxidation.

Ni(I)(1,4,8,11-tetraazacyclotetradecane)(+), Ni(I)L(+), was produced in neutral aqueous solutions by radiolytic techniques. The mechanism and kinetics of the reaction of Ni(I)L(+) with maleate and fumarate were studied applying pulse-radiolysis and analysis of the final products. Surprisingly the mechanisms of reduction of maleate and fumarate differ considerably. Based on the results it was also shown that Ni(II)L(2+) is an electrocatalyst for the reduction of alkenes in aqueous solutions.

The first report regarding SOD activity of metallocorroles, investigated via the combination of the cytochrome C assay, pulse radiolysis, and electrochemistry, is used for identifying the main criteria needed for achieving good performance, as well as for elucidating mechanistic aspects of their action.

The effects of 10 paramagnetic metal complexes (Fe(III)EDTA(H2O)-, Fe(III)EDTA(OH)2-, Fe(III)PDTA-, Fe(III)DTPA2-, Fe(III)2O(TTHA)2-, Fe(III)(CN)6(3-), Mn(II)EDTA(H2O)2-, Mn(II)PDTA2-, Mn(II)beta-EDDADP2-, and Mn(II)PO4(-)) on F- ion 19F NMR transverse relaxation rates (R2 = 1/T2) were studied in aqueous solutions as a function of temperature. Consistent with efficient relaxation requiring formation of a metal/F- bond, only the substitution inert complexes Fe(III)(CN)6(3-) and Fe(III)EDTA(OH)2- had no measured effect on T2 relaxation of the F- 19F resonance. For the remaining eight complexes, kinetic parameters (apparent second-order rate constants and activation enthalpies) for metal/F- association were determined from the dependence of the observed relaxation enhancements on complex concentration and temperature. Apparent metal/F- association rate constants for these complexes (k(app,F-)) spanned 5 orders of magnitude. In addition, we measured the rates at which O2*- reacts with Fe(III)PDTA-, Mn(II)EDTA(H2O)2-, Mn(II)PDTA2-, and Mn(II)beta-EDDADP2- by pulse radiolysis. Although no intermediate is observed during the reduction of Fe(III)PDTA- by O2*-, each of the Mn(II) complexes reacts with formation of a transient intermediate presumed to form via ligand exchange. These reactivity patterns are consistent with literature precedents for similar complexes. With these data, both k(app,O2-) and k(app,F-) are available for each of the eight reactive complexes. A plot of log(k(app,O2-)) versus log(k(app,F-)) for these eight showed a linear correlation with a slope approximately 1. This correlation suggests that rapid metal/O2*- reactions of these complexes occur via an inner-sphere mechanism whereas formation of an intermediate coordination complex limits the overall rate. This hypothesis is also supported by the very low rates at which the substitution inert complexes (Fe(III)(CN)6(3-) and Fe(III)EDTA(OH)2-) are reduced by O2*-. These results suggest that F- 19F NMR relaxation can be used to predict the reactivities of other Fe(III) complexes toward reduction by O2*-, a key step in the biological production of reactive oxygen species.

Thin films consisting of a fulleropyrrolidine derivative 1 and a novel water-soluble porphyrin 2 were prepared by the Langmuir-Shäfer (LS, horizontal lifting) method. In particular, a solution of 1 in chloroform and dimethyl sulfoxide was spread on the water surface, while porphyrin 2 (bearing peripheral anionic groups) was dissolved into the aqueous subphase. To the best of our knowledge, such a versatile method of film fabrication for fullerene/porphyrin mixed composite films has never been used before. Evidence of the effective interactions between the two moieties at the air-water interface was obtained from the analysis of the floating layers by means of surface pressure versus area per molecule Langmuir curves, Brewster angle microscopy and UV-visible reflection spectroscopy. The characterisation of the LS films by UV-visible spectroscopy reveals that the two constituents behave as discrete and weakly interacting pi systems. The use of polarised light suggests the existence of a preferential direction of the macrocyclic rings with an edge-on arrangement with respect to the substrate surface. Finally, photoaction spectra were recorded from films deposited by only one horizontal lifting onto indium-tin-oxide (ITO) electrodes and the observed photocurrent increased notably with increasing transfer surface pressure.

Novel organic (positively charged fullerene)-inorganic (negatively charged CdTe nanoparticle) nanoensembles were devised through electrostatic interactions and probed as versatile donor-acceptor hybrids. Photoirradiation of their homogeneous solutions, containing the electrostatically packed components, let to very long-lived (1.3 ms) charge separated states.

A new class of pi-extended TTF-type electron donors (11 a-c) has been synthesized by Wittig-Horner olefination of bianthrone (9) with 1,3-dithiole phosphonate esters (10 a-c). In cyclic voltammetry experiments, donors 11 a-c reveal a single, electrochemically irreversible oxidation-yielding the corresponding dicationic products-at relatively low oxidation potentials (approximately 0.7-0.8 V). Theoretical calculations, performed at the DFT level (B3 P86/6-31 G*), predict a highly-folded C(2h) structure for 11 a. In the ground state, the molecule adopts a double saddle-like conformation to compensate the steric hindrance. The calculations suggest that the intramolecular charge transfer associated with the HOMO-->LUMO transition is responsible for an absorption band observed above 400 nm. While the radical cation 11 a*+ retains the folded C(2h) structure predicted for the neutral molecule as the most stable conformation, the dication 11 a(2+) has a fully aromatic D(2) structure, formed by an orthogonal 9,9'-bianthryl central unit to which two singly-charged dithiole rings are attached. The drastic conformational changes that compounds 11 undergo upon oxidation account for their electrochemical properties. By means of pulse radiolysis measurements, radical-induced one-electron oxidation of 11 a-c was shown to lead to the radical cation species (11 a-c*+), which were found to disproportionate with generation of the respective dication species (11 a-c(2+)) and the neutral molecules (11 a-c).

Redox gradients have been used to tailor the arrangement of photoactive ITO-electrodes at the molecular level.

We have developed a molecular-level switch-a C(60)/cytochrome c modified ITO electrode-that reversibly transmits and processes solar energy.