Common Pathway for K562 Cells Endocytosis and Release of Gac-Tf and Ga2-Tf via a Transferrin Receptor

There has been an increasing interest in the use of gallium in anticancer activity. However, whether the uptakes of two species of transferrin, including digallium transferrin (Ga₂‐Tf) and the C‐terminal monogallium transferrin (Ga_C‐Tf) by cells, are different is not well understood. In this work the mechanism of both species passing in and out K562 cells has been established by using ¹²⁵I‐labeled transferrin. There were about (1.5±0.08)×10⁵ binding sites per cell surface. Both Ga₂‐Tf and Ga_C‐Tf were recycled to the cell exterior with a protracted endocytic cycle compared to apotransferrin (apoTf). The cycling time from the internalization to release was calculated about t_1/2= (3.15±0.055) min for apoTf, t_1/2= (4.69±0.09) min for Ga₂‐Tf and t_1/2= (4.78±0.15) min for Ga_C‐Tf. The result implies that metal dissociating from transferrin in acidic endosomes was likely to be the key step. Both Ga₂‐Tf and Ga_C‐Tf into K562 cells are transferrin receptor‐mediated process with a similar rate of endocytosis and release. Our present observations provide useful information for better targeted drugs in specific therapy.     

Electrospray ionization mass spectrometry as a critical tool for revealing new properties of snake venom phospholipase A2

Results from high‐performance liquid chromatography/nano‐electrospray ionization tandem mass spectrometry (HPLC/nESI‐MS/MS) coupled to two‐dimensional sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (2D SDS‐PAGE) indicated that the monomer and dimer of phospholipase A₂ (PLA₂) coexisted in crude Chinese Agkistrodon blomhoffii Ussurensis snake venom (ABUSV). Then, an acidic PLA₂ with the accurate molecular mass of 13979.6 Da was purified from ABUSV (mo‐ABUSV‐aPLA₂). MS/MS‐derived peptides from ABUSV‐aPLA₂ were compared with other homologous snake venom PLA₂s, which in turn showed that ABUSV‐aPLA₂ is a novel snake venom PLA₂. Meanwhile, the ABUSV‐aPLA₂ dimer (di‐ABUSV‐aPLA₂) was also obtained. MS/MS analysis identified the same peptides from di‐ABUSV‐aPLA₂ as from mo‐ABUSV‐aPLA₂, which indicates that di‐ABUSV‐aPLA₂ is a homodimer. One Ca²⁺ ion is contained per ABUSV‐aPLA₂. The Ca²⁺ ion is critical for both the hydrolytic activity and the structure of ABUSV‐aPLA₂. Pro‐Q Emerald and Pro‐Q Diamond specific glycoprotein and phosphoprotein staining combined with MS/MS analysis indicated that the ABUSV‐aPLA₂ is both a glycoprotein and a phosphoprotein, which to our knowledge is the first such report for a snake venom PLA₂ and thus provides new threads for the study of the functions and structures of snake venom PLA₂s. One phosphorylation site and the size of the glycan chain are determined by using HPLC/nESI‐MS/MS and matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) MS. The delicate utilization of ESI‐MS can exert tremendous impact on protein sciences. Copyright © 2009 John Wiley & Sons, Ltd.     

1H‐NMR relaxometric studies of interaction between apoptosis specific MRI paramagnetic contrast agents and micellar models of apoptotic cells

¹H‐NMR was previously used to analyze the interaction between peptides (E3 and R826) selected by phage display to target apoptotic cells and phospholipidic models of these cells. In order to avoid the use of apoptotic cells and to obtain a fast evaluation of the efficiency of the potential MRI contrast agents obtained by grafting these peptides and their scramble analogs on a paramagnetic gadolinium complex, their proton relaxometric behavior was investigated in the presence of micelles mimicking healthy and apoptotic cells. Their preferential interaction with 1,2‐dipalmitoyl‐sn‐glycero‐3‐phospho‐l ‐serine micelles mimicking apoptotic cells as compared with 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine micelles modeling healthy cells was shown by nuclear magnetic relaxation dispersion profiles and the enhancement of the transverse proton relaxation rates at 60 MHz. The association constant values confirm the stronger interaction of the selected conjugated peptides (K_a Gd‐PMN‐E3(gadolinium 2,2′,2′′,2′′′‐[((4‐carboxy)pyridine‐2,6‐diyl)bis(methylenenitrilo)]‐tetrakis acetate) grafted with E3 peptide): 2.43 10⁴ m ^?1; K_a Gd‐DTPA‐R826(gadolinium ((1‐p‐isothiocyanatobenzyl)‐diethylenetriaminepentaacetate) grafted with R826 peptide): 2.91 10⁴ m ^?1) as compared with their conjugated scrambles (K_a Gd‐PMN‐E3sc(gadolinium 2,2′,2′′,2′′′‐[((4‐carboxy)pyridine‐2,6‐diyl)bis(methylenenitrilo)]‐tetrakis acetate) grafted with E3 scramble peptide): 0.18 10⁴ m ^?1; K_a Gd‐DTPA‐R826sc(gadolinium ((1‐p‐isothiocyanatobenzyl)‐diethylenetriaminepentaacetate) grafted with R826 scramble peptide): 0.32 10⁴ m ^?1) even if the conjugation of E3 and R826 seems to decrease their interaction. Copyright © 2015 John Wiley & Sons, Ltd.     

Regularities of silver atom formation in gamma-irradiated aluminium silicates modified by lanthanum oxide(III)

The ESR-method was used to study the regularities of silver atom formation and stabilization in gamma-irradiated aluminium silicates modified by lanthanum oxide. Two types of silver atoms (Ag_I and Ag_II) stabilized at two different sites of the surface, and paramagnetic species Ag⁺₂ have been identified. ESR-spectrum parameters of paramagnetic silver species have been calculated. Under discussion are the nature of silver species Ag_I and Ag_II, and the influence of sample thermal and vacuum treatment prior to γ-irradiation, on the number of paramagnetic silver species observed. The thermal stability of silver species was found to increase with the temperature of sample vacuum pre-treatment. Under study was the dependence of silver species formed on the irradiation dose.     

Probing the Electronic Structure and Photoactivation Process of Nitrogen‐Doped TiO2 Using DRS,PL, and EPR

The electronic structure and photoactivation process in N‐doped TiO₂ is investigated. Diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and electron paramagnetic resonance (EPR) are employed to monitor the change of optical absorption ability and the formation of N species and defects in the heat‐ and photoinduced N‐doped TiO₂ catalyst. Under thermal treatment below 573 K in vacuum, no nitrogen dopant is removed from the doped samples but oxygen vacancies and Ti³⁺ states are formed to enhance the optical absorption in the visible‐light region, especially at wavelengths above 500 nm with increasing temperature. In the photoactivation processes of N‐doped TiO₂, the DRS absorption and PL emission in the visible spectral region of 450–700 nm increase with prolonged irradiation time. The EPR results reveal that paramagnetic nitrogen species (N_s^.), oxygen vacancies with one electron (V_o^.), and Ti³⁺ ions are produced with light irradiation and the intensity of N_s^. species is dependent on the excitation light wavelength and power. The combined characterization results confirm that the energy level of doped N species is localized above the valence band of TiO₂ corresponding to the main absorption band at 410 nm of N‐doped TiO₂, but oxygen vacancies and Ti³⁺ states as defects contribute to the visible‐light absorption above 500 nm in the overall absorption of the doped samples. Thus, a detailed picture of the electronic structure of N‐doped TiO₂ is proposed and discussed. On the other hand, the transfer of charge carriers between nitrogen species and defects is reversible on the catalyst surface. The presence of oxygen‐vacancy‐related defects leads to quenching of paramagnetic N_s^. species but they stabilize the active nitrogen species N_s^?.     

Synthesis and electrochemical sensing behaviour of a new ferrocene functionalized tet ‘a’ macrocyclic receptor towards transition metal ions

A new ferrocene functionalized macrocyclic receptor 1,8‐bis(ferrocenylmethyl)‐5,5,7,12,12,14‐hexamethyl‐1,4,8,11‐tetraazacyclotetradecane (R) has been designed and synthesized to study its potential application as chemosensor. The receptor has been characterized by spectral techniques and X‐ray diffraction. The compound crystallizes in the orthorhombic space group Pcab with four molecules in a unit cell (half‐a‐molecule in the asymmetric unit). The electrochemical studies of the receptor in dioxane–water (7:3 v/v, 25 °C) indicate that the receptor is pH‐dependent with a displacement of E_1/2 to more anodic potentials with a decrease in the pH from 12 to 5. The electrochemical behaviour of R was also studied in the presence of Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ in dioxane–water (7:3 v/v, 25 °C, [Buⁿ₄N][ClO₄]), showing that upon complexation the ferrocene–ferrocenium half‐wave potential shifts anodically in relation to that of the free receptor. The maximum electrochemical shift (ΔE_1/2) of 46 mV was found in the presence of Cu²⁺, followed by Co²⁺ (20 mV), Mn²⁺ (15 mV), Ni²⁺ (13 mV) and Zn²⁺ (9 mV). Moreover, the receptor R is able to electrochemically and selectively sense Cu²⁺ in the presence of the other transition metal cations studied. Copyright © 2007 John Wiley & Sons, Ltd.     

Design and Synthesis of Novel Pyrazole‐based Lp‐PLA2 Inhibitors

A series of novel pyrazole‐based lipoprotein‐associated phospholipase A₂ (Lp‐PLA₂) inhibitors have been designed and synthetized by a variety of acetophenones via a 10‐step convergent approach. The synthetic approach is carefully optimized, and an unsuccessful alternative route is also discussed. The in vitro biological activity reveals that all the synthesized compounds are potent Lp‐PLA₂ inhibitors with compound 13b being the most potent one (Lp‐PLA₂, IC₅₀=1.5 nmol/L).     

UVB Irradiation Enhances TiO2 Nanoparticle‐induced Disruption of Calcium Homeostasis in Human Lens Epithelial Cells

Currently, titanium dioxide nanoparticles (TiO₂ NPs) have been widely used in various applications including cosmetics, food additives and biomedicine. However, there are few reports available using TiO₂ NPs to treat ocular diseases. Posterior capsular opacification (PCO) is the most frequent complication after cataract surgery, which is induced by the proliferation and migration of lens epithelial cells. Thus, inhibiting the proliferation of lens epithelial cells will efficiently reduce the occurrence of PCO. In this study, we investigated the effects of TiO₂ NPs on HLE B‐3 cells with or without ultraviolet B (UVB) irradiation in vitro. We found that TiO₂ NPs can inhibit HLE B‐3 cell growth, cause the elevation of intracellular [Ca²⁺], produce excessive reactive oxygen species (ROS), further reduce Ca²⁺‐ATPase activity and decrease the expression of plasma membrane calcium ATPase 1 (PMCA1), finally disrupt the intracellular calcium homeostasis and induce cell damage. Importantly, UVB irradiation can apparently enhance these effects on HLE B‐3 cells in the presence of TiO₂ NPs. Taken together, the generation of excessive ROS and the disruption of intracellular calcium homeostasis may be both involved in TiO₂ nanoparticle‐induced HLE B‐3 cell damage under UVB irradiation.     

Production of ROS by photosensitized anthracene under sunlight and UV-R at ambient environmental intensities

The aim of this study was to analyze the photostability and phototoxicity mechanism of anthracene (ANT) in a human skin epidermal cell line (HaCaT) at ambient environmental intensities of sunlight/UV‐R (UV‐A and UV‐B). Photomodification of ANT under sunlight/UV‐R exposure produced two photoproducts, anthrone and 9,10 anthracenedione. Generation of ¹O₂, O₂^?? and ^?OH was measured under UV‐R/sunlight exposure. Involvement of reactive oxygen species (ROS) was further substantiated by their quenching with free radical quenchers. Photodegradation of 2‐deoxyguanosine and linoleic acid peroxidation showed that ROS were mainly responsible for ANT phototoxicity. ANT generates significant amount of intracellular ROS in cell line. Maximum cell viability (85%) was reduced under sunlight exposure (30 min). Results of MTT assay accord NRU assay. ANT (0.01 μg mL^?1) induced cell‐cycle arrest at G1 phase. RT‐PCR demonstrated constitutive inducible mRNA expression of CYP 1A1 and 1B1 genes. Photosensitive ANT upregulates CYP 1A1 (2.2‐folds) and 1B1 (4.1‐folds) genes. Thus, the study suggests that ROS and DNA damage were mainly responsible for ANT phototoxicity. ANT exposure may be deleterious to human health at ambient environmental intensities reaching the earth’s surface through sunlight.     

N‐Heterocyclic Carbene Stabilized Boryl Radicals

The reaction of the 2‐(trimethylsilyl)imidazolium triflate 9 with diarylboron halides (4‐R‐C₆H₄)₂BX (R=H, X=Br; R=CH₃, X=Cl; R=CF₃, X=Cl) afforded the NHC‐stabilized borenium cations 10 a – c . Cyclic voltammetry revealed a linear correlation between the Hammett parameter σ _p of the para substituent and the half‐wave potential. Chemical reduction with decamethylcobaltocene, [(C₅Me₅)₂Co], furnished the corresponding radicals 11 a – c ; their characterization by EPR spectroscopy confirmed the paramagnetic character of 11 a – c , with large hyperfine coupling constants to the boron isotopes ¹¹B and ¹⁰B, while delocalization of the unpaired electron into the NHC is negligible. DFT calculations of the percentage of spin density distribution between the carbene (NHC) and the boryl fragments (BR₂) revealed for 11 a – c a spin density ratio (BR₂/NHC) of ca. 9:1, which underlines their distinct boryl radical character. The molecular structure of the most stable species 11 c was established by X‐ray diffraction analysis.     

Three pairs of enantiomers bearing mitochondria‐targeted TPP+ groups as potential anti‐cancer agents

Six complexes with chiral Schiff‐base ligands containing TPP⁺ groups, [VO L ^R,R/^S,S](ClO₄)₂( 1 for RR, 2 for SS), [Ni L ^R,R/S,S](ClO₄)₂·C₂H₅OH ( 3 for RR, 4 for SS) and [CuL^R,R/S,S](ClO₄)₂·CHCl₃·CH₃CH₂OH ( 5 for RR, 6 for SS) ( L ^R,R/S,S = N,N′‐Bis{5‐[(triphenylphosphonium)‐methyl]salicylidine}‐(1R,2R/1S,2S)‐diphenylethane‐1,2‐diamine, were synthesized to serve as mitochondrion‐targeting anticancer drugs. The introduction of TPP⁺ group(s) might markedly influence the properties of complexes. Compounds 3 and 5 were structurally characterized by X‐ray crystallography. Complexes 1–6 could be moderate intercalating agents to CT‐DNA which is determined by several spectroscopy methods. DNA cleavage experiments revealed that all compounds could promote oxidative cleavage of pBR322 plasmid DNA in the presence of H₂O₂. MTT assay indicated 1–6 exhibited effective cytotoxicity on A549 and MCF‐7 cell lines. Notably, the IC₅₀ values of 5 (1.24 ± 0.33 μM) or 6 (1.47 ± 0.52 μM) were approximately 9–11 fold lower than that of cisplatin (IC₅₀ = 13.56 ± 0.88 μM) on A549 cells. 5 and 6 were picked for further study, which indicated that the cytotoxicity seems to result from multiple mechanisms of action, including effectively suppress the growth and proliferation of A549 cells, generation of reactive oxygen species, dissipation of mitochondrial membrane potential, cell cycle perturbation and apoptosis induction. Compounds 1–6 could highly accumulate in the mitochondria by means of ICP‐MS assay. This study demonstrates that 1–6 with mitochondrion‐targeting function could be efficient anticancer drugs.     

Redoxreaktionen an nickelorganokomplexen durch nitrosoverbindungen und aliphatische aldehyde: Möglichkeiten des einsatzes der spintrapmethode

ESR investigations of the reaction between (bipy)Ni(C₂H₅)₂ and aromatic nitroso compounds (RNO) show the formation of paramagnetic, unstable complexes containing the radical RNO^. which is followed by elimination of nitroxide radicals C₂H₅(R)NO^..(bipy)Ni(COD) is oxidized by RNO to give nickel(I) species and several trapped radicals derived from COD. In the presence of aldehydes no paramagnetic nickel species, but ethyl radicals and spin adducts of the aldehydes can be observed. The mechanism of the reaction is discussed.     

Structure and Photochemical Properties of r‐1, c‐2, t‐3, t‐4‐l, 3‐Bis [2‐ (5‐R‐benzoxazolyl) ] −2,4‐di (4‐R' ‐phenyl) cyclobutane

r‐1, c‐2, t‐3, t‐4‐1,3‐Bis[2‐(5‐R‐benzoxazolyl)]‐2,4‐di(4‐R'‐phenyl)cyclobutane (IIa: R=R' = H; IIb: R=Me, R'= H; IIc: R = Me, R' = OMe) was synthesized with high stereo‐selectivity by the photodimerization of trans‐l‐[2‐(5‐R‐benzoxazolyl)]‐2‐(4‐R'‐phenyl) ethene (Ia: R=R' = H; Ib: R = Me, R' = H; Ic: R = Me, R' = OMe) in sulfuric acid. The structures of IIa–IIc were identified by elemental analysis, IR, UV, ¹H NMR, ¹³C NMR and MS. The molecular and crystal structure of IIc has been determined by X‐ray diffraction method. The crystal of IIc (C₃₄H₃₀N₂O₄. 0.5C₂OH) is monoclinic, space group P2₁/n with cell dimensions of a = 1.5416(3), b =0.5625(1), c = 1.7875(4) nm, β = 91.56 (3)°, V= 1.550(1) nm³, Z = 2. The structure shows that the molecule of IIc is centrosymmetric, which indicates that the dimerization process is a head‐to‐tail fashion. The selectivity of the photodimerization of Ia–Ic has been enhanced by using acidic solvent and the reaction speed would be decreased when electron donating group was introduced in the 4‐position of the phenyl group. That the photodimerization is not affected by the presence of oxygen as well as its high stereo‐selectivity demonstrated that the reaction proceeded through an excited singlet state. It was also found that under irradiation of short wavelength UV, these dimers underwent photolysis completely to reproduce its trans‐monomers, and then the new formed species changed into their cis‐isomers through trans‐cis isomerization.     

Mixed alkyl isocyanide-1,4-diaza-1,3-butadiene complexes of chromium: A series of 17-, 18- and 19-electron species of the type [Cr(CO)3(CNR)(R′-DAB)]1+,0,1′

The chromium(0) complexes Cr(CO)₃(CNR)(R′-DAB) (R = Me, CHMe₂, CMe₃, or xylyl; R′ = i-Pr, t-Bu, Cy or p-tol) can be prepared by the reaction of Cr(CO)₃(NCMe)₃ with equimolar quantities of R′-DAB and RNC. These complexes are oxidized to the paramagnetic 17-electron salts [Cr(CO)₃(CNR)(R′-DAB)]PF₆ by [(η⁵-C₅H₅)₂Fe]Pf₆ in ethanol, and can be reduced to the paramagnetic 19-electron radical anions [Cr(CO)₃(CNR)(R′-DAB)]⁻ using NaHg in tetrahydrofuran. The spectroscopic (IR, ¹H NMR, electronic absorption and ESR) and electrochemical properties of the [Cr(CO)₃(CNR)(R′-DAB)]^1+,0,1′ species (where appropriate) have been recorded. The dark red monocationic species [Cr(CO)₃(CNR)(R′-DAB)]PF₆ are subject to disproportionation in solution to give separable mixtures of dark blue Cr(CO)₃(CNR)(R′-DAB) and green [Cr(CNR)₄(R′-DAB)](PF₆)₂.     

Screening of allergic components mediated by H1R in homoharringtonine injection through H1R/CMC‐HPLC/MS

It has been reported that the histamine H₁ receptor (H₁R) gene is up‐regulated in patients with allergic rhinitis and H₁R expression level strongly correlates with the severity of allergy symptoms. Drugs for therapy should avoid allergy symptoms, especially for patients with over‐expressed H₁R. Therefore, screening of the components which could induce H₁R activation is urgently needed for drug safety evaluation. Homoharringtonine injection is a preparation for acute nonlymphocytic leukemia, which is approved by China Food and Drug Administration (CFDA) and US Food and Drug Administration. However, severely adverse reactions often occur with intravenous injection of the preparation. In present study, an H₁R/CMC model was applied for capturing membrane retained components which could induce H₁R activation. Retention components were enriched and analyzed by H₁R/CMC‐HPLC/MS. Homoharringtonine was recognized, separated and identified in homoharringtonine injection. Ca²⁺ flux assay and p‐IP3R expression founded that homoharringtonine retained by the H₁R/CMC model increased phosphorylation of IP3R and promoted cytosolic free Ca²⁺ elevation in a dose‐dependent manner which further verified the activity of homoharringtonine in activating the H₁R. In conclusion, homoharringtonine was screened and identified as a potential allergic factor. This provides an indication that a patient with over‐expressed H₁R should be aware of possible allergic reaction when applying homoharringtonine injection. Copyright © 2014 John Wiley & Sons, Ltd.     

Enhanced Iridium Complex Electrochemiluminescence Cytosensing and Dynamic Evaluation of Cell‐Surface Carbohydrate Expression

A newly prepared [(ppy)₂Ir(dcbpy)]⁺?PF₆^? (ppy: 2‐phenylpyridyl; dcbpy: 4,4′‐dicarboxy‐2,2′‐bipyridyl) and gold nanoparticle functionalized mesoporous silica nanoparticle (Au/Ir‐MSN) is reported. Based on the binding between concanavalin A (Con A) and mannose, the novel nanoparticle was applied to an ultrasensitive electrochemiluminescence (ECL) in situ cytosensing strategy and the dynamic evaluation of cell‐surface carbohydrate expression. The ECL activity of the presented Con A@Au/Ir‐MSN nanoprobe was greatly enhanced by employing a functionalized nanoparticle and graphene nanomaterial with an increased surface area and simultaneously improved electron‐transfer efficiency at the electrode interface. Under optimal conditions, the sandwich‐type ECL cytosensor showed a linear response to K562 cells at concentrations ranging from 1.0×10² to 1.0×10⁶ cells mL^?1 and realized a low detection limit of a single cell. The proposed method could also be successfully used for monitoring the dynamic variation of carbohydrate expression in cancer cells in response to external stimulation by an inhibitor.     

Monitoring H2O2 on the Surface of Single Cells with Liquid Crystal Elastomer Microspheres

Live‐imaging of signaling molecules released from living cells is a fundamental challenge in life sciences. Herein, we synthesized liquid crystal elastomer microspheres functionalized with horse‐radish peroxidase (LCEM‐HRP), which can be immobilized directly on the cell membrane to monitor real‐time release of H₂O₂ at the single‐cell level. LCEM‐HRP could report H₂O₂ through a concentric‐to‐radial (C‐R) transfiguration, which is due to the deprotonation of LCEM‐HRP and the break of inter or intra‐chain hydrogen bonding in LCEM‐HRP caused by HRP‐catalyzed reduction of H₂O₂. The level of transfiguration of LCEM‐HRP revealed the different amounts of H₂O₂ released from cells. The estimated detection sensitivity was ≈2.2×10^?7 μm for 10 min of detection time. The cell lines and cell–cell heterogeneity was explored from different configurations. LCEM‐HRP presents a new approach for in situ real‐time imaging of H₂O₂ release from living cells and can be the basis for seeking more advanced chemical probes for imaging of various signaling molecules in the cellular microenvironment.     

Organometallic Molybdenum(V) Complexes with Primary Phosphine Ligands. Syntheses,Spectroscopic Properties and Molecular Structures of [Cp°MoCl4(PH2R)] (R = But, 1‐Ad,Cy, Ph, 2, 4, 6‐Me3C6H2, 2, 4, 6‐Pri3C6H2, Cp° = C5EtMe4)

[Cp°MoCl₄] (Cp° = C₅EtMe₄) reacts with primary phosphines PH₂R to give the paramagnetic phosphine complexes [Cp°MoCl₄(PH₂R)] [Cp° = C₅EtMe₄, R = Bu^t ( 1 ), 1‐Ad (1‐Ad = 1‐adamantyl; 2 ), Cy ( 3 ), Ph ( 4 ), Mes (Mes = 2, 4, 6‐Me₃C₆H₂; 5 ), Tipp (Tipp = 2, 4, 6‐Prⁱ₃C₆H₂; 6 )]. 1 — 6 were characterized spectroscopically (IR, MS), and X‐ray crystal structures were determined for 1 — 4 and 6 . EPR investigations in liquid and frozen solution confirmed the presence of Mo^V species, and the data were used to analyze the spin‐density distribution in the first coordination sphere. Complexes 3 and 4 react with two equivalents of NEt₃ with formation of [Cp°MoCl₂(η³‐P₄Cy₄H)] ( 7 ) and [Cp°₂Mo₂(μ‐Cl)₂(μ‐P₄Ph₄)] ( 8 ), respectively, in low yield. Complexes 7 and 8 were characterized by X‐ray crystallography.     

Kinetics and mechanism of ligand exchange of coordinated cyanide in hexacyanoferrate(II) by nitroso‐R‐salt in the presence of mercury(II) as a catalyst

The kinetics of Hg(II)‐catalyzed reaction between hexacyanoferrate(II) and nitroso‐R‐salt has been followed spectrophotometrically by monitoring the increase in absorbance at 720 nm, the λ_max of green complex, [Fe(CN)₅ N‐R‐salt]^3? as a function of pH, ionic strength, temperature, concentration of reactants, and the catalyst. In this reaction, the coordinated cyanide ion in hexacyanoferrate(II) gets replaced by incoming N‐R‐salt under the following specified reaction conditions: temperature = 25 ± 0.1°C, pH = 6.5 ± 0.2, and I = 0.1 M (KNO₃). The stoichiometry of the complex has been established as 1:1 by mole ratio method. The rate of catalyzed reaction is slow at low pH values and then increases with pH and attains a maximum value between 6.5 and 6.7. The rate finally falls again at higher pH values due to nonavailability of [H⁺] ions needed to regenerate the catalytic species. The rate of reaction increases initially with [N‐R‐salt] and attains a maximum value and then levels off at higher [N‐R‐salt]. The rate of reaction shows a variable order dependence in [Fe(CN)₆^4?] ranging from unity at lower concentration to 0.1 at higher concentrations. The effect of [Hg²⁺] on the reaction rate shows a complex behavior and the same has been explained in detail. The activation parameters for the catalyzed reactions have been evaluated. A most plausible mechanistic scheme has been proposed based on the experimental observations. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 222–232, 2005     

Formation of Superoxo Species by Interaction of O2 with Na Atoms Deposited on MgO Powders: A Combined Continuous‐Wave EPR (CW‐EPR), Hyperfine Sublevel Correlation (HYSCORE) and DFT Study

The formation of O₂^? radical anions by contact of O₂ molecules with a Na pre‐covered MgO surface is studied by a combined EPR and quantum chemical approach. Na atoms deposited on polycrystalline MgO samples are brought into contact with O₂. The typical EPR signal of isolated Na atoms disappears when the reaction with O₂ takes place and new paramagnetic species are observed, which are attributed to different surface‐stabilised O₂^? radicals. Hyperfine sublevel correlation (HYSCORE) spectroscopy allows the superhyperfine interaction tensor of O₂^?Na⁺ species to be determined, demonstrating the direct coordination of the O₂^? adsorbate to surface Na⁺ cations. DFT calculations enable the structural details of the formed species to be determined. Matrix‐isolated alkali superoxides are used as a standard to enable comparison of the formed species, revealing important and unexpected contributions of the MgO matrix in determining the electronic structure of the surface‐stabilised Na⁺? O₂^? complexes.