Ferricenium complexes: A new type of water-soluble antitumor agent

Summary The antitumor activity of a series of iron complexes, i.e., of ferrocene [Cp₂Fe], of tetrachloroferrates(III) [R₄N]⁺[FeCl₄]^-, and of ferricenium complexes [Cp₂Fe]⁺X^- (X^-=[FeCl₄]^-, 1/2[Cl₃FeOFeCl₃]^2-, [H₅Mo₇O₂₄]^-·2H₂O, [2,4,6-(NO₂)₃C₆H₂O]^-, or [CCl₃COO]^-·2 CCl₃COOH) was investigated against EAT in CF1 mice. Whereas ferrocene and the ammonium tetrachloroferrates(III) did not show recognizable tumor-inhibiting activity, such activity was exhibited by the water-soluble, salt-like ferricenium complexes; the best antineoplastic properties, with optimum cure rates of 100%, were found for ferricenium picrate and ferricenium trichloroacetate.The ferricenium compounds are the first iron complexes for which antineoplastic activity has now been shown. They represent a new type of antitumor agent insofar as they differ fundamentally from known inorganic and organometallic antitumor agents (a) by their ionic, salt-like character, which is responsible for their high water solubility, and (b) by the absence of a cis-dihalometal moiety; this moiety has been recognized as important for the intracellular action of other known inorganic cytostatics.Abbreviations Cp C₅H₅, cyclopentadienyl ring ligand - EAT Ehrlich ascites tumor - IP intraperitoneal(ly) - p.t.t. post transplantationem tumoris Supported by the Fonds der Chemischen Industrie and by Council, University of the Witwatersrand     

Blue copper proteins: Synthesis, spectra, and structures of CuN(3)(SR) and CuN(3)(SR) active site analogues

The reaction of Cu(SR) or [Cu(SR)][ClO₄] derivatives (SR = p-nitrobenzenethiolate or O-ethylcysteinate) with potassium hydrotris(3,5-dimethyl-1-pyrazolyl)borate produces redox pairs of the stoichiometry Cu^IN₃(SR) and Cu^IIN₃(SR). These complexes are well-defined synthetic approximations to the proposed N₃S binding sites of blue (type 1) copper electron transfer proteins. The compounds were investigated by a variety of chemical and spectral (optical, resonance Raman, and electron paramagnetic resonance) techniques; the complex K[Cu(hydrotris(3,5-dimethyl-1-pyrazolyl)borate)(p- NO₂C₆H₄S]-2 acetone was also studied by single-crystal x-ray diffraction methods. The spectrochemical characteristics of the Cu^IIN₃(SR) species are in large part similar to the native system and thus provide some perspective regarding the origin of the unique type 1 spectral parameters and electron transfer properties.     

Mechanism of Catalytic Water Oxidation by the Ruthenium Blue Dimer Catalyst: Comparative Study in D2O versus H2O

Water oxidation is critically important for the development of energy solutions based on the concept of artificial photosynthesis. In order to gain deeper insight into the mechanism of water oxidation, the catalytic cycle for the first designed water oxidation catalyst, cis,cis-[(bpy)₂(H₂O)Ru^IIIORu^III(OH₂)(bpy)₂]⁴⁺ (bpy is 2,2-bipyridine) known as the blue dimer (BD), is monitored in D₂O by combined application of stopped flow UV-Vis, electron paramagnetic resonance (EPR) and resonance Raman spectroscopy on freeze quenched samples. The results of these studies show that the rate of formation of BD[4,5] by Ce(IV) oxidation of BD[3,4] (numbers in square bracket denote oxidation states of the ruthenium (Ru) centers) in 0.1 M HNO₃, as well as further oxidation of BD[4,5] are slower in D₂O by 2.1–2.5. Ce(IV) oxidation of BD[4,5] and reaction with H₂O result in formation of an intermediate, BD[3,4]′, which builds up in reaction mixtures on the minute time scale. Combined results under the conditions of these experiments at pH 1 indicate that oxidation of BD[3,4]′ is a rate limiting step in water oxidation with the BD catalyst.     

An in vitro antibacterial and antifungal effects of cadmium(II) complexes of hexamethyltetraazacyclotetradecadiene and isomers of its saturated analogue

ObjectiveTo evaluate the antibacterial and antifungal effects of cadmium(II) complexes with hexamethyltetraazacyclotetradecadiene ligands.MethodsFive coordinated square pyramidal cadmium(II) complexes and six coordinated square octahedral cadmium(II) complexes have been synthesized by interaction of 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene (denoted by L.2HClO₄) and C-chiral isomers of its saturated analogue (denoted by ‘teta’ and ‘tetb’) with different salts of Cd²⁺ ion [e.g. CdI₂, Cd(NO₃)₂·6H₂O, CdCl₂·2H₂O and Cd(ClO₄)₂·6H₂O] in methanolic solution. Complexes of the ligands were investigated for antibacterial activity by disc diffusion method and antifungal effect by poisoned food technique.ResultsThe newly synthesized cadmium(II) complexes of the ligands were screened as potential antimicrobial agent against a number of medically important bacteria (Staphylococcus aureus, Bacillus cereus, Salmonella typhi, Shigella dysenteriae and Escherichia coli) and against two fungi (Candida albicans and Aspergillus aculeatus). The growth inhibiting activity of the ligands and complexes against bacteria and fungi were compared with the standard antibiotic ampicillin and commercially important antifungal agent, griseofulvin respectively. Among them some of the macrocyclic complexes were found to be more fungitoxic and antibacterial than the reference antifungal drug griseofulvin and antibacterial drug ampicillin respectively.ConclusionsHexamethyltetraazacyclotetradecadiene ligands and its complexes could be considered as very potential antibacterial and antifungal agent with further investigation.     

Spectroscopic evidence for an engineered,catalytically active Trp radical that creates the unique reactivity of lignin peroxidase

The surface oxidation site (Trp-171) in lignin peroxidase (LiP) required for the reaction with veratryl alcohol a high-redox-potential (1.4 V) substrate, was engineered into Coprinus cinereus peroxidase (CiP) by introducing a Trp residue into a heme peroxidase that has similar protein fold but lacks this activity. To create the catalytic activity toward veratryl alcohol in CiP, it was necessary to reproduce the Trp site and its negatively charged microenvironment by means of a triple mutation. The resulting D179W+R258E+R272D variant was characterized by multifrequency EPR spectroscopy. The spectra unequivocally showed that a new Trp radical [g values of g_x = 2.0035(5), g_y = 2.0027(5), and g_z = 2.0022(1)] was formed after the [Fe(IV)=O Por^•+] intermediate, as a result of intramolecular electron transfer between Trp-179 and the porphyrin. Also, the EPR characterization crucially showed that [Fe(IV)=O Trp-179^•] was the reactive intermediate with veratryl alcohol. Accordingly, our work shows that it is necessary to take into account the physicochemical properties of the radical, fine-tuned by the microenvironment, as well as those of the preceding [Fe(IV)=O Por^•+] intermediate to engineer a catalytically competent Trp site for a given substrate. Manipulation of the microenvironment of the Trp-171 site in LiP allowed the detection by EPR spectroscopy of the Trp-171^•, for which direct evidence has been missing so far. Our work also highlights the role of Trp residues as tunable redox-active cofactors for enzyme catalysis in the context of peroxidases with a unique reactivity toward recalcitrant substrates that require oxidation potentials not realized at the heme site.     

Coordination of {Mo142} Ring to La3+ Provides Elliptical {Mo134La10} Ring with a Variety of Coordination Modes

A 28-electron reduced C_2h-Mo-blue 34Ǻ outer ring diameter circular ring, [Mo₁₄₂O₄₂₉H₁₀(H₂O)₄₉(CH₃CO₂)₅(C₂H₅CO₂)]^30- (≡{Mo₁₄₂(CH₃CO₂)₅(C₂H₅CO₂)}) comprising eight carboxylate-coordinated (with disorder) {Mo₂} linkers and six defect pockets in two inner rings (four and three for each, respectively), reacts with La³⁺ in aqueous solutions at pH 3.5 to yield a 28-electron reduced elliptical C_i-Mo-blue ring of formula [Mo₁₃₄O₄₁₆H₂₀(H₂O)₄₆{La(H₂O)₅}₄{La(H₂O)₇}₄{LaCl₂(H₂O)₅}₂]^10- (≡{Mo₁₃₄La₁₀}), isolated as the Na₁₀[Mo₁₃₄O₄₁₆H₂₀(H₂O)₄₆{La(H₂O)₅}₄{La(H₂O)₇}₄{LaCl₂(H₂O)₅}₂]·144 H₂O Na⁺ salt. The elliptical structure of {Mo₁₃₄La₁₀} showing 36 and 31 Å long and short axes for the outer ring diameters is attributed to four (A-D) modes of LaO₉/LaO₇Cl₂ tricapped-trigonal-prismatic coordination (TTP) geometries. Two different LaO₂(H₂O)₇ and one LaO₂(H₂O)₂Cl₂ TTP geometries (as A-C modes) for each of two inner rings result from the coordination of all three defect pockets of the inner ring for {Mo₁₄₂(CH₃CO₂)₅(C₂H₅CO₂)}, and two LaO₄(H₂O)₅ TTP geometries (as D mode) result from the displacement of two (acetate/propionate-coordinated) binuclear {Mo₂} linkers with La³⁺ in each inner ring. The isothermal titration calorimetry (ITC) of the ring modification from circle to ellipsoid, showing the endothermic reaction of [La³⁺]/[{Mo₁₄₂(CH₃CO₂)₅(C₂H₅CO₂)}] = 6/1 with ΔH = 22 kJ⋅mol^-1, ΔS = 172 J⋅K^-1⋅mol^-1, ΔG = −28 kJ⋅mol^-1, and K = 9.9 × 10⁴ M^-1 at 293 K, leads to the conclusion that the coordination of the defect pockets to La³⁺ precedes the replacement of the {Mo₂} linkers with La³⁺. ¹³⁹La- NMR spectrometry of the coordination of {Mo₁₄₂(CH₃CO₂)₅(C₂H₅CO₂)} ring to La³⁺ is also discussed.     

Determination of retinal Schiff base configuration in bacteriorhodopsin

Resonance Raman spectra of the BR₅₆₈, BR₅₄₈, K₆₂₅, and L₅₅₀ intermediates of the bacteriorhodopsin photocycle have been obtained in ¹H₂O and ²H₂O by using native purple membrane as well as purple membrane regenerated with 14,15-¹³C₂ and 12,14-²H₂ isotopic derivatives of retinal. These derivatives were selected to determine the contribution of the C₁₄—C₁₅ stretch to the normal modes in the 1100- to 1400-cm^-1 fingerprint region and to characterize the coupling of the C₁₄—C₁₅ stretch with the NH rock. Normal mode calculations demonstrate that when the retinal Schiff base is in the C[unk]N cis configuration the C₁₄—C₁₅ stretch and the NH rock are strongly coupled, resulting in a large (≈50-cm^-1) upshift of the C₁₄—C₁₅ stretch upon deuteration of the Schiff base nitrogen. In the C[unk]N trans geometry these vibrations are weakly coupled and only a slight (<5-cm^-1) upshift of the C₁₄—C₁₅ stretch is predicted upon N-deuteration. In BR₅₆₈, the insensitivity of the 1201-cm^-1 C₁₄—C₁₅ stretch to N-deuteration demonstrates that its retinal C[unk]N configuration is trans. The C₁₄—C₁₅ stretch in BR₅₄₈, however, shifts up from 1167 cm^-1 in ¹H₂O to 1208 cm^-1 in ²H₂O, indicating that BR₅₄₈ contains a C[unk]N cis chromophore. Thus, the conversion of BR₅₆₈ to BR₅₄₈ (dark adaptation) involves isomerization about the C[unk]N bond in addition to isomerization about the C₁₃[unk]C₁₄ bond. The insensitivity of the native, [14,15-¹³C₂]-, and [12,14-²H₂]K₆₂₅ and L₅₅₀ spectra to N-deuteration argues that these intermediates have a C[unk]N trans configuration. Thus, the primary photochemical step in bacteriorhodopsin (BR₅₆₈ → K₆₂₅) involves isomerization about the C₁₃[unk]C₁₄ bond alone. The significance of these results for the mechanism of proton-pumping by bacteriorhodopsin is discussed.     

Algebraic K-theory of spaces stratified fibered over hyperbolic orbifolds

Among other results, we rationally calculate the algebraic K-theory of any discrete cocompact subgroup of a Lie group G, where G is either O(n, 1), U(n, 1), Sp(n, 1), or F₄, in terms of the homology of the double coset space Γ\G/K, where K is a maximal cocompact subgroup of G. We obtain the formula K_n(ZΓ) [unk] [unk] [unk]_i=0^∞H_i(Γ\G/K; [unk]_n-i), where [unk]_j is a stratified system of Q vector spaces over Γ\G/K and the vector space [unk]_j(ΓgK) corresponding to the double coset ΓgK is isomorphic to K_J(Z(Γ [unk] gKg^-1)) [unk] Q. Note Γ [unk] gKg^-1 is a finite subgroup of Γ. Earlier, a similar formula for discrete cocompact subgroups Γ of the group of rigid motions of Euclidean space was conjectured by F. T. Farrell and W. C. Hsiang and proven by F. Quinn.     

Herbicide resistance in Chlamydomonas reinhardtii results from a mutation in the chloroplast gene for the 32-kilodalton protein of photosystem II

We report the isolation and characterization of a uniparental mutant of Chlamydomonas reinhardtii that is resistant to 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine). Such herbicides inhibit photosynthesis by preventing transfer of electrons in photosystem II from the primary stable electron acceptor Q to the secondary stable electron acceptor complex B, which is thought to contain a protein of 32 kDa and a bound quinone. It has been proposed that herbicide binding to the 32-kDa protein alters the B complex so that electron transfer from Q is prohibited. Both whole and broken-cell preparations of the mutant alga show a resistance to the effects of herbicide on electron transfer from Q to B, as measured by fluorescence-induction kinetics. In the absence of herbicide, mutant cells exhibit a slower rate of Q to B electron transfer than do wild-type cells. The 32-kDa protein from wild-type cells, but not mutant cells, binds azido[¹⁴C]atrazine at 0.1 μM. We have isolated psbA, the chloroplast gene for the 32-kDa protein, from both wild-type and herbicide-resistant algae and sequenced the coding regions of the gene that are contained in five exons. The only difference between the exon nucleotide sequences of the wild-type and mutant psbA is a single T-A to G-C transversion. This mutation results in a predicted amino acid change of serine in the wild-type protein to alanine in the mutant. We suggest that this alteration in the 32-kDa protein is the molecular basis for herbicide resistance in the C. reinhardtii mutant.     

Theoretical study of catalytic mechanism for single-site water oxidation process

Water oxidation is a linchpin in solar fuels formation, and catalysis by single-site ruthenium complexes has generated significant interest in this area. Combining several theoretical tools, we have studied the entire catalytic cycle of water oxidation for a single-site catalyst starting with [Ru^II(tpy)(bpm)(OH₂)]²⁺ (i.e., [Ru^II-OH₂]²⁺; tpy is 2,2^′∶6^′,2^′′-terpyridine and bpm is 2,2′-bypyrimidine) as a representative example of a new class of single-site catalysts. The redox potentials and pK_a calculations for the first two proton-coupled electron transfers (PCETs) from [Ru^II-OH₂]²⁺ to [Ru^IV = O]²⁺ and the following electron-transfer process to [Ru^V = O]³⁺ suggest that these processes can proceed readily in acidic or weakly basic conditions. The subsequent water splitting process involves two water molecules, [Ru^V = O]³⁺ to generate [Ru^III-OOH]²⁺, and H₃O⁺ with a low activation barrier (∼10 kcal/mol). After the key O---O bond forming step in the single-site Ru catalysis, another PECT process oxidizes [Ru^III-OOH]²⁺ to [Ru^IV-OO]²⁺ when the pH is lower than 3.7. Two possible forms of [Ru^IV-OO]²⁺, open and closed, can exist and interconvert with a low activation barrier (< 7 kcal/mol) due to strong spin-orbital coupling effects. In Pathway 1 at pH = 1.0, oxygen release is rate-limiting with an activation barrier ∼12 kcal/mol while the electron-transfer step from [Ru^IV-OO]²⁺ to [Ru^V - OO]³⁺ becomes rate-determining at pH = 0 (Pathway 2) with Ce(IV) as oxidant. The results of these theoretical studies with atomistic details have revealed subtle details of reaction mechanisms at several stages during the catalytic cycle. This understanding is helpful in the design of new catalysts for water oxidation.     

Crystal Structure,Spectroscopic Characterization,Antioxidant and Cytotoxic Activity of New Mg(II) and Mn(II)/Na(I) Complexes of Isoferulic Acid

The Mg(II) and heterometallic Mn(II)/Na(I) complexes of isoferulic acid (3-hydroxy-4-methoxycinnamic acid, IFA) were synthesized and characterized by infrared spectroscopy FT-IR, FT-Raman, electronic absorption spectroscopy UV/VIS, and single-crystal X-ray diffraction. The reaction of MgCl₂ with isoferulic acid in the aqueous solutions of NaOH resulted in synthesis of the complex salt of the general formula of [Mg(H₂O)₆]⋅(C₁₀H₉O₄)₂⋅6H₂O. The crystal structure of this compound consists of discrete octahedral [Mg(H₂O)₆]²⁺ cations, isoferulic acid anions and solvent water molecules. The hydrated metal cations are arranged among the organic layers. The multiple hydrogen-bonding interactions established between the coordinated and lattice water molecules and the functional groups of the ligand stabilize the 3D architecture of the crystal. The use of MnCl₂ instead of MgCl₂ led to the formation of the Mn(II)/Na(I) complex of the general formula [Mn₃Na₂(C₁₀H₇O₄)₈(H₂O)₈]. The compound is a 3D coordination polymer composed of centrosymmetric pentanuclear subunits. The antioxidant activity of these compounds was evaluated by assays based on different antioxidant mechanisms of action, i.e., with ^•OH, DPPH^• and ABTS^•+ radicals as well as CUPRAC (cupric ions reducing power) and lipid peroxidation inhibition assays. The pro-oxidant property of compounds was measured as the rate of oxidation of Trolox. The Mg(II) and Mn(II)/Na(I) complexes with isoferulic acid showed higher antioxidant activity than ligand alone in DPPH (IFA, IC₅₀ = 365.27 μM, Mg(II) IFA IC₅₀ = 153.50 μM, Mn(II)/Na(I) IFA IC₅₀ = 149.00 μM) and CUPRAC assays (IFA 40.92 μM of Trolox, Mg(II) IFA 87.93 μM and Mn(II)/Na(I) IFA 105.85 μM of Trolox; for compounds’ concentration 10 μM). Mg(II) IFA is a better scavenger of ^•OH than IFA and Mn(II)/Na(I) IFA complex. There was no distinct difference in ABTS^•+ and lipid peroxidation assays between isoferulic acid and its Mg(II) complex, while Mn(II)/Na(I) complex showed lower activity than these compounds. The tested complexes displayed only slight antiproliferative activity tested in HaCaT human immortalized keratinocyte cell line within the solubility range. The Mn(II)/Na(I) IFA (16 μM in medium) caused an 87% (±5%) decrease in cell viability, the Mg salt caused a comparable, i.e., 87% (±4%) viability decrease in a concentration of 45 μM, while IFA caused this level of cell activity attenuation (87% ± 5%) at the concentration of 1582 μM (significant at α = 0.05).     

A Theoretical Study of the Binding of [Re6Se8(OH)2(H2O)4] Rhenium Clusters to DNA Purine Base Guanine

Hexanuclear rhenium complexes are promising candidates for use as antitumor drugs. However, to date, there has been no investigation into the nature of their binding to DNA. In this study, density functional theory (DFT) was used to examine the binding of [Re₆Se₈(OH)₂(H₂O)₄] to the DNA purine base guanine. The geometrical structures of cluster-guanine adducts in water were modeled at the zero order regular approximation (ZORA)-PW91 level. Calculating the bond energies allowed us to compare the cis and trans forms of the cluster, and a possible manners of interaction between [Re₆Se₈(OH)₂(H₂O)₃] clusters and DNA was obtained and explained.     

Mechanisms for the activation/electron transfer of neutrophil NADPH-oxidase complex and molecular pathology of chronic granulomatous disease

Summary Professional phagocytes, neutrophils, possess a unique membrane-associated NADPH-oxidase system, dormant in resting cells, which becomes activated upon exposure to the appropriate stimuli and catalyzes the one-electron reduction of molecular oxygen to superoxide, O ₂ ^– . Oxidase activation involves the assembly, in the plasma membrane, of membrane-bound and cytosolic constituents of the oxidase system, which are disassembled in the resting state. The oxidase system consists of two plasma membrane-bound components; low-potential cytochromeb ₅₅₈, which is composed of two subunits of 22-kDa, and 91-kDa, and a possible flavoprotein related to the electron transport between NADPH and cytochromeb ₅₅₈. Recent reports have indicated that FAD-binding sites of the oxidase are contained in cytochromeb ₅₅₈. At least two cytosolic components, 67-kDa protein and a phosphorylated 47-kDa protein, are known to translocate to the plasma membrane, ensuring assembly of an active O ₂ ^– -generating NADPH-oxidase system. It is the purpose of this review to focus on recent data concerning electron transfer mechanisms of the activated neutrophil NADPH-oxidase complex and molecular pathology of chronic granulomatous disease.     

Magnetic and Electrical Behaviors of the Homo- and Heterometallic 1D and 3D Coordination Polymers Based on the Partial Decomposition of the [Cr(C2O4)3]3− Building Block

One-dimensional (1D) oxalate-bridged homometallic {[Mn(bpy)(C₂O₄)]·1.5H₂O}_n (1) (bpy = 2,2’-bipyridine) and heterodimetallic {[CrCu₃(bpy)₃(CH₃OH)(H₂O)(C₂O₄)₄][Cu(bpy)Cr(C₂O₄)₃]·CH₂Cl₂·CH₃OH·H₂O}_n (2) coordination polymers, as well as the three-dimensional (3D) heterotrimetallic {[CaCr₂Cu₂(phen)₄(C₂O₄)₆]·4CH₃CN·2H₂O}_n (3) (1,10-phenanthroline) network, have been synthesized by a building block approach using a layering technique, and characterized by single-crystal X-ray diffraction, infrared (IR) and impedance spectroscopies and magnetization measurements. During the crystallization process partial decomposition of the tris(oxalato)chromate(III) happened and 1D polymers 1 and 2 were formed. The antiferromagnetic interactions between the manganese(II) ions were mediated by oxalate ligands in the chain [Mn(bpy)(C₂O₄)]_n of 1, with intra-chain super-exchange interaction 𝐽 = (−3.134 ± 0.004) K; magnetic interaction between neighbouring chains is negligible making this system closer than other known Mn-chains to the ideal 1D Heisenberg antiferromagnet. Compound 2 comprises a 1D coordination anion [Cu(bpy)Cr(C₂O₄)₃]_nⁿ⁻ (Cr2–Cu4) with alternating [Cr(C₂O₄)₃]³⁻ and [Cu(bpy)]²⁺ units mutually bridged through the oxalate group. Another chain (Cr1–Cu3) is similar, but involves a homodinuclear unit [Cu(bpy)(H₂O)(µ-C₂O₄)Cu(bpy)(CH₃OH)]²⁺ (Cu1–Cu2) coordinated as a pendant group to a terminal oxalate oxygen. Magnetic measurements showed that the Cu1−Cu2 cationic unit is a strongly coupled antiferromagnetic dimer, independent from the other magnetic ions within ferromagnetic chains Cr1–Cu3 and Cr2–Cu4. A 3D polymer {[CaCr₂Cu₂(phen)₄(C₂O₄)₆]·4CH₃CN·2H₂O}_n (3) comprising three different metal centers (Ca²⁺, Cr³⁺ and Cu²⁺) oxalate-bridged, contains Ca²⁺ atoms as nodes connected with four Cr³⁺ atoms through oxalate ligands. The network thus formed can be reduced to an underlying graph of diamondoid (dia) or (6⁶) topology. Magnetization of 3 shows the ferromagnetic oxalate-bridged dimers [Cu^IICr^III], whose mutual interaction could possibly originate through the spin polarization of Ca²⁺ orbitals. Compounds 1 and 3 exhibit lower electrical conductivity at room temperature (RT) in comparison to compound 2.     

Nanocalorimetry in mass spectrometry: a route to understanding ion and electron solvation

A gaseous nanocalorimetry approach is used to investigate effects of hydration and ion identity on the energy resulting from ion–electron recombination. Capture of a thermally generated electron by a hydrated multivalent ion results in either loss of a H atom accompanied by water loss or exclusively loss of water. The energy resulting from electron capture by the precursor is obtained from the extent of water loss. Results for large-size-selected clusters of Co(NH₃)₆(H₂O)_n3⁺ and Cu(H₂O)_n2⁺ indicate that the ion in the cluster is reduced on electron capture. The trend in the data for Co(NH₃)₆(H₂O)_n3⁺ over the largest sizes (n ≥ 50) can be fit to that predicted by the Born solvation model. This agreement indicates that the decrease in water loss for these larger clusters is predominantly due to ion solvation that can be accounted for by using a model with bulk properties. In contrast, results for Ca(H₂O)_n2⁺ indicate that an ion–electron pair is formed when clusters with more than ≈20 water molecules are reduced. For clusters with n = ≈20–47, these results suggest that the electron is located near the surface, but a structural transition to a more highly solvated electron is indicated for n = 47–62 by the constant recombination energy. These results suggest that an estimate of the adiabatic electron affinity of water could be obtained from measurements of even larger clusters in which an electron is fully solvated.     

Novel H-Bonded Synthons in Copper Supramolecular Frameworks with Aminoethylpiperazine-Based Ligands. Synthesis,Structure and Catalytic Activity

New Schiff base complexes [Cu₂(HL¹)(L¹)(N₃)₃]∙2H₂O (1) and [Cu₂L²(N₃)₂]∙H₂O (2) were synthesized. The crystal structures of 1 and 2 were determined by single-crystal X-ray diffraction analysis. The HL¹ ligand results from the condensation of salicylaldehyde and 1-(2-aminoethyl)piperazine, while a new organic ligand, H₂L², was formed by the dimerization of HL¹ via a coupling of two piperazine rings of HL¹ on a carbon atom coming from DMF solvent. The dinuclear building units in 1 and 2 are linked into complex supramolecular networks through hydrogen and coordination bondings, resulting in 2D and 1D architectures, respectively. Single-point and broken-symmetry DFT calculations disclosed negligible singlet–triplet splittings within the dinuclear copper fragments in 1 and 2. Catalytic studies showed a remarkable activity of 1 and 2 towards cyclohexane oxidation with H₂O₂ in the presence of nitric acid and pyridine as promoters and under mild conditions (yield of products up to 21%). Coordination compound 1 also acts as an active catalyst in the intermolecular coupling of cyclohexane with benzamide using di-tert-butyl peroxide (^tBuOO^tBu) as a terminal oxidant. Conversion of benzamide at 55% was observed after 24 h reaction time. By-product patterns and plausible reaction mechanisms are discussed.     

Syntheses and a Solid State Structure of a Dinuclear Molybdenum(V) Complex with Pyridine

A mononuclear complex [MoOCl₄(H₂O)]⁻ readily forms a metal−metal bonded {Mo₂O₄}²⁺ core. A high content of pyridine in the reaction mixture prevents further aggregation of dinuclear cores into larger clusters and a neutral, dinuclear complex with the [Mo₂O₄Cl₂(Py)₄] composition is isolated as a product. Solid state structures of two compounds containing this complex, [Mo₂O₄Cl₂(Py)₄]·2.25Py (1) and [Mo₂O₄Cl₂(Py)₄]·1.5PyHCl (2), were investigated by X-ray crystallography.     

Doppler Flow Velocity and Thermodilution to Assess Coronary Flow Reserve: A Head-to-Head Comparison With [15O]H2O PET

Objectives

This study sought to compare Doppler flow velocity reserve (CFR_Doppl) and thermodilution-derived coronary flow reserve (CFR_thermo) head-to-head with the gold standard for quantification of myocardial perfusion, [¹⁵O]H₂O positron emission tomography (PET).

Conversion of prohistidine decarboxylase to histidine decarboxylase: Peptide chain cleavage by nonhydrolytic serinolysis

Unlabeled prohistidine decarboxylase and prohistidine decarboxylase containing L-[carboxyl-¹⁸O]serine or L-[hydroxyl-¹⁸O]serine were isolated in homogeneous form from mutant 3 of Lactobacillus 30a grown with the appropriately labeled serine. There was no randomization or redistribution of label during growth, isolation of the protein, or enzymatic hydrolysis and reisolation of the labeled amino acids. These proteins were used to show that during proenzyme activation, in which individual π subunits of the proenzyme are converted to α and β subunits of the active enzyme [Formula: see text] (in which π, α, and β subunits have the partial structures shown and Prv designates a pyruvoyl group), no ¹⁸O from H₂¹⁸O is incorporated into the newly formed carboxyl terminus (Ser-81) of the β chain, although no labilization of ¹⁸O from proenzyme labeled with L-[carboxyl-¹⁸O]serine occurred when the proenzyme was activated in H₂¹⁶O by the same procedures. The additional oxygen atom present in the carboxyl group of Ser-81 of the β subunit is transferred from the hydroxyl group of Ser-82 of the proenzyme during the activation reaction. The same result was obtained with wild-type enzyme formed intracellularly. Peptide bond cleavage during activation of the proenzyme thus proceeds by a hitherto unobserved direct or indirect “serinolysis” coupled to α,β-elimination at Ser-82 to yield the pyruvoyl group of the α subunit, rather than by hydrolysis. Possible mechanisms for the reaction are discussed briefly.     

Energies and kinetics of radical pairs involving bacteriochlorophyll and bacteriopheophytin in bacterial reaction centers

Absorbance changes reflecting the formation of a transient radical-pair state, P^F, were measured in reaction centers from Rhodopseudomonas sphaeroides under conditions that blocked electron transfer to a later carrier (a quinone, Q). The temperature dependence of the absorbance changes suggests that P^F is an equilibrium mixture of two states, which appear to be mainly ¹[P^[unk]B^[unk]] and ¹[P^[unk]H^[unk]]. P is a bacteriochlorophyll dimer, B is a bacteriochlorophyll absorbing at 800 nm, and H is a bacteriopheophytin. In the presence of Q^[unk], the energy of ¹[P^[unk]B^[unk]] is about 0.025 eV above that of ¹[P^[unk]H^[unk]], ¹[P^[unk]H^[unk]] can decay to a triplet state, P^R, which also is an equilibrium mixture of two states, separated by about 0.03 eV. The lower of these appears to be mainly a locally excited triplet state of P, ³P; the upper state contains a major contribution from a triplet charge-transfer state, ³[P^[unk]B^[unk]]. The temperature dependence of delayed fluorescence from P^R indicates that ³P lies 0.40 eV below the excited singlet state, P^*, which is about 0.05 eV above ¹[P^[unk]H^[unk]]. The ^1,3[P^[unk]B^[unk]] charge-transfer states thus appear to interact with the locally excited states of P and B to give singlet and triplet states that are separated in energy by about 0.35 eV. This is 10⁶ times larger than the splitting between ¹[P^[unk]H^[unk]] and ³[P^[unk]H^[unk]] and implies strong orbital overlap between P^[unk] and B^[unk]. This is consistent with recent picosecond studies which suggest that electron transfer from P^* to B occurs within 1 ps and is followed in 4 to 10 ps by electron transfer from B^[unk] to H.