Cobalt(III)-promoted hydrolysis of atp

The rate of phosphate hydrolysis of ATP in the substitution-inert complex Co(NH₃)₄ATP-has been examined in the presence and absence of [Co(cyclen)(H₂O)₂]³⁺. The rate of hydrolysis of Co(NH₃)₄ATP- in the absence of [Co(cyclen)(H₂O)₂]³⁺ is essentially independent of pH in the range 6.0 to 9.0, and the rate constant is 2.6 × 10^?5 sec ^?1 at pH 9.0, 40°C, and 1.0 M ionic strength Rate constants for the hydrolysis of Co(NH₃)₄ATP- in the presence of [Co(cyclen)(H₂O)₂]³⁺ are sharply dependent upon pH in the same range. The rate constants at pH 8.0, 8.6, and 9.0 are 8, 63, and 95 times larger than the rate constant at pH 7.0. At pH 9 the rate constant is 1.2 × 10^?3 sec^?1 for 16 mM Co(NH₃)₄ATP- in the presence of 10 mM [Co(cyclen)(H₂O)₂]³⁺. The proposed mechanism for hydrolysis involves the coordination of a phosphate group of Co(NH₃)₄ATP- by [Co(cyclen)(H₂O)₂]³⁺ to form a dinuclear species, followed by internal attack of coordinated hydroxide on the phosphate chain.     

Equilibria in N-heterocyclic complexes. Part 45. Ligand electron densities in coordinated pyridine

Results of INDO calculations on the species pyridine (py), (pyH)⁺, [py-CH₃]⁺, [Fe(NH₃)_x(py)_6−x]²⁺, [Fe(NH₃)₅(py)]³⁺, [Fe(CN)₅(py)]³⁻, and [Co(CN)₅(py)]²⁻ are presented and discussed, comparing quaternization and coordination.     

Interaction of Purine Nucleotides with Cobalt-Hexammine,Cobalt-Pentammine and Cobalt- Tetrammine Cations. Evidence for the Rigidity of Adenosine and Flexibility of Guanosine and Deoxyguanosine Sugar Conformations

Abstract

The interaction of adenosine-5′-monophosphate (5′-AMP), guanosine-5′-monophosphate (5′-GMP) and 2′-deoxyguanosine-5′-monophosphate (5′-dGMP) with the [Co(NH₃)₆]³⁺, [CO(NH₃)₅C1]²⁺ and [CO(NH₃)₄C1₂]⁺ cations has been investigated in aqueous solution with metal/nucleotide ratios (r) of 1/2, 1 and 2 at neutral pH. The solid complexes have been isolated and characterized by FT-IR and ¹H-NMR spectroscopy.

The complexes are polymeric in nature both in the crystalline solid and aqueous solution. The binding of the cobalt-hexammine cation is indirectly (via NH₃) through the N-7 and the PO₃ ^2- groups of the AMP and via O-6, N-7 and the PO₃ ^2- of the GMP and dGMP anions (outer-sphere). The cobalt-pentammine and cobalt-tetrammine bindings are through the phosphate groups (inner-sphere) and the N-7 site (outer-sphere) of these nucleotide anions. The ribose moiety shows C2′-endo/anti conformation, in the free AMP and GMP anions as well as in the cobalt-ammine - AMP complexes, whereas a mixture of the C2′-endo/anti and C3′-endo/anti sugar puckers were observed for the Co(NH₃)₆-GMP, Co(NH₃)₅-GMP and a C3′-endo/anti conformer for the Co(NH₃)₄-GMP complexes. The deoxyribose showed an O4′-endo/anti conformation for the free dGMP anion and a C3′-endo/anti for the Co(NH₃)₆-dGMP, Co(NH₃)₅-dGMP and Co(NH₃)₄-dGMP complexes.     

Three Co(III)-Fe(II) complexes based on hexacyanoferrates: Syntheses, spectroscopic and structural characterizations

Red or orange crystals of [Co(NH₃)₆]₂Cl₂[Fe(CN)₆] · 4H₂O (1), [Co(en)₃]₂Cl₂[Fe(CN)₆] · 2H₂O (2) and [Co(en)₃]₄[Fe(CN)₆]₃ · 21.6H₂O (3) were isolated from the aqueous systems Co³⁺-L_N-[Fe(CN)₆]⁴⁻ (L_N = NH₃, en = 1,2-diaminoethane). In all isolated samples the combination of Mössbauer (δ values were from the range −0.07 to −0.08 mm/s) and IR spectra (ν(CN) stretching vibrations in the range 2015-2047 cm⁻¹) confirms the presence of low spin Fe(II) in [Fe(CN)₆]⁴⁻ anions. X-ray structure analyses corroborate the ionic character of all studied compounds. These contain diamagnetic [Co(NH₃)₆]³⁺ (1) or [Co(en)₃]³⁺ (2 and 3) complex cations and diamagnetic [Fe(CN)₆]⁴⁻ complex anions. In compounds 1 and 2 chloride anions are present, too. All three compounds contain water of crystallization, in compound 3 as many as 21.6 molecules per formula unit.     

Dinuclear complexes with a μ-cyano ligand. Part X. Synthesis and characterization of several derivatives of cis-diaquaamminecobalt(III) complexes. Influence of pH

Six new dinuclear complexes, derived from cis-[Co(H₂O)₂(NH₃)₄]³⁺, cis-[Co(H₂O)₂(en)₂]³⁺ and [M(CN)₄^2? (M = Ni, Pd, Pt) were prepared and characterized by means of chemical analysis, electronic and IR measurements. The influence of the pH on the rate of the reaction was studied for the two derivatives of [Pd(CN)₄]^2?, showing that the best conditions to obtain the dinuclear compounds are at pH near 6, where the predominant species are cis-[Co(OH)(H₂O)(amine)₂]²⁺. The [Pt(CN)₄]^2? derivatives show PtPt interactions both in the solid state and in solution.     

Shape selectivity in outer-sphere electron transfer reactions

Chiral induction has been examined in the four diastereomeric products formed in a series of outer-sphere electron transfer reactions between the oxidants [Co(ox)₃]³⁻, [Co(edta)]⁻, [Co(gly)(ox)₂]²⁻, C₁-cis(N)-[Co(gly)₂(ox)]⁻, [Co(en)(ox)₂]⁻, C₂-cis(N)-[Co(gly)₂(ox)]⁻ and trans(N)-[Co(gly)₂(ox)]⁻ with [Co((RR,SS)-chxn)₃]²⁺ and [Co((R, S)-pn)₃]²⁺ as reductants. The products; [Co((RR,SS)-chxn)₃-lel₃]³⁺, [Co((RR,SS)-chxn)₃-lel₂ob]³⁺, [Co((RR,SS)-chxn)₃-lelob₂]³⁺, [Co((RR,SS)-chxn)₃-ob₃]³⁺ and corresponding species for [Co((R, S)-pn)₃]³⁺ show patterns of selectivity which are analyzed in terms of the size and structure of the reactants. The presence of a pseudo-C₃ carboxylate face on the oxidant enhances selectivity but the pattern is quite different for those oxidants that contain oxalate as one of their ligands compared with non-oxalate containing species such as [Co(edta)]⁻. A very simple model is developed in which the reductant employs a limited set of interactions corresponding to the major symmetry axes. The unrestricted reductant has very low aggregate selectvity. Steric and hydrogen bonding patterns in both oxidant and reductant enhance individual interactions resulting in the observed selectivities.     

Catalytic effect of cis-diammineplatinum α-pyrrolidone tan adsorbed on a platinum electrode in electrochemical oxidation of water into molecular oxygen

Cyclic voltammograms of cis-diammineplatinum α-pyrrolidone-blue and -tan, [Pt₄(NH₃)₈(C₄H₆NO)₄]ⁿ⁺ (n = 5 and 6, respectively) show for either complex only one redox peak at 0.53 V (average potential of the anodic and cathodic peak potentials). Coulometry and UVVis spectra of bulk- electrolyzed solution indicated that the redox peak corresponds to the reaction [Pt₄(NH₃)₈(C₄H₆NO)₄]⁸⁺ + 4e ⇄ 2[Pt₂(NH₃)₄(C₄H₆NO)₂]²⁺. When cyclic voltammetry is carried out in a solution of [Pt₄(NH₃)₈(C₄H₆NO)₄]⁶⁺ or a platinum electrode adsorbed with [Pt₄(NH₃)₈(C₄H₆NO)₄]⁶⁺ is used in the presence of oxidizing agent in the solution, O₂ gas generates from the electrode surface with large catalytic cathodic current at potentials below ca. 0.8 V. The O₂ gas was confirmed to generate from water by GC-MS analysis. This abnormal O₂ generation phenomenon is explained with cyclic reactions of chemical surface oxide formation on the electrode by the oxidizing agent and electrochemical reduction of the surface oxide. Oxygen gas generates from the reaction of [Pt₄(NH₃)₈(C₄H₆NO)₄]⁸⁺ or [Pt₄(NH₃)₈(C₄H₆NO)₄]⁶⁺ with OH⁻ produced in the course of the electrochemical reduction of the electrode surface oxide. The ability of [Pt₄(NH₃)₈(C₄H₆NO)₄]⁸⁺ and [Pt₄(NH₃)₈(C₄H₆NO)₄]⁶⁺ to oxidize OH⁻ into O₂ has been reported previously.     

Change of RNase P RNA function by single base mutation correlates with perturbation of metal ion binding in P4 as determined by NMR spectroscopy

The solution structures of two 27 nt RNA hairpins and their complexes with cobalt(III)-hexammine [Co(NH₃)₆³⁺] were determined by NMR spectroscopy. The RNA hairpins are variants of the P4 region from Escherichia coli RNase P RNA: a U-to-A mutant changing the identity of the bulged nucleotide, and a U-to-C, C-to-U double mutant changing only the bulge position. Structures calculated from NMR constraints show that the RNA hairpins adopt different conformations. In the U-to-C, C-to-U double mutant, the conserved bulged uridine in the P4 wild-type stem is found to be shifted in the 3′-direction by one nucleotide when compared with the wild-type structure. Co(NH₃)₆³⁺ is used as a spectroscopic probe for Mg(H₂O)₆²⁺ binding sites because both complexes have octahedral symmetry and have similar radii. Intermolecular NOE crosspeaks between Co(NH₃)₆³⁺ and RNA protons were used to locate the site of Co(NH₃)₆³⁺ binding to both RNA hairpins. The metal ion binds in the major groove near a bulge loop in both mutants, but is shifted 3′ by about one base pair in the double mutant. The change of the metal ion binding site is compared with results obtained on corresponding mutant RNase P RNA molecules as reported by Harris and co-workers (RNA, 1, 210–218).     

Action of hexaamminecobalt on the activity of Serratia marcescens nuclease

Using CD spectroscopic and kinetic analysis, a refined mechanism of Co(NH₃) ₆ ³⁺ action on activity of Serratia marcescens nuclease was elucidated. The mechanism was identical with previously found mechanisms of Mg²⁺ and C₇H₅O₂Hg⁺. Similarly to Mg²⁺ and C₇H₅O₂Hg⁺, Co(NH₃) ₆ ³⁺ binding to the DNA substrate induced changes in the secondary structure which resulted in changes of the enzymatic activity of the S. marcescens nuclease. Upon binding of 0.03 Co(NH₃) ₆ ³⁺ per DNA phosphate, highly polymerized DNA displayed A-form characteristics. The DNA transition from B-form to A-form intermediate was followed by a decrease of the nuclease activity. The diminishing nuclease activity was consistent with diminishing values of Km and Kcat. Co(NH₃)₆ ³⁺ binding to the highly polymerized DNA caused a 1.7–2.8-fold decrease in Km, and 13.3–19.9 decrease in Vmax compared with Mg-DNA complex. A vast excess of Co(NH₃)₆ ³⁺ did not affect the activity of S. marcescens nuclease if the DNA in the assay mixture remained in its B-form conformation. Preincubation of S. marcescens nuclease with Co(NH₃)₆ ³⁺ did not influence the tertiary structure of the enzyme.     

Reduction of pentaamminenitrocobalt(III) by hexaaquachromium(II) ion. Reinvestigation of the mechanism

Products of the reduction of [CoNO₂(NH₃)₅]²⁺ by Cr²⁺ were separated and identified under the conditions of [Cr²⁺]₀/[Co(IlI)]₀⩽3 and 0.02 M ⩽[H⁺] ⩽ 0.75 M. The product distribution was dependent on both [Cr²⁺]_o and [H⁺]. The following mechanism is proposed: [CoNO₂(NH₃)₅]²⁺ + Cr²⁺→Co²⁺ + [CrONO(H₂O)₅]²⁺ (i) [CrONO(H₂O)₅]²⁺ + H⁺→[Cr(H₂O)₆]³⁺ + HNO₂ (ii) [CrONO(H₂O)₅]²⁺ + Cr²⁺→Cr(IV) + [CrNO(H₂O)₅]²⁺ (iii) Cr(IV) + Cr²⁺→[(H₂O)₄Cr(OH)₂Cr(H₂O)₄]⁴⁺ (iv) HNO₂ + 2Cr²⁺→[Cr(H₂O)₆]³⁺ + [CrNO(H₂O)₅]²⁺ (v)     

Synthesis, characterisation and substitution kinetics of unusually labile trans-[Co(tmen)(diamine)Cl2] complexes

The mixed diamine complexes trans-[Co(tmen)(diamine)Cl₂]⁺ have been synthesised (tmen = NH₂C(Me)₂C(Me)₂NH₂; diamine = en = NH₂(CH₂)₂NH₂, and ibn = NH₂C(Me)₂CH₂NH₂). Replacement of one en ligand in trans-[Co(en)₂Cl₂]⁺ by one tmen ligand engenders an enormous rate enhancement (2000-fold) for acid hydrolysis. Solvolysis rates have been measured in Me₂SO and DMF for these complexes and also trans-[Co(tmen)₂Cl₂]⁺ which is more reactive again (10⁴-fold). The measured reactivities in DMF at 2 °C establish that the kinetic effect of replacing each en by tmen is incremental, and the extreme base catalysed racemisation rate for (+)-[Co(tmen)₃]³⁺ can now be explained on this basis.     

The kinetics and mechanism of the reaction of 2′-deoxy-5′-guanosinemonophosphoric acid and the diaqua form of cis-platin

2′-Deoxy-5′-guanosinemonosphoric acid (B) reacts with cis-[Pt(NH₃)₂(OH₂)₂]²⁺ in two steps to form the cis-[Pt(NH₃)₂B₂]^y+ ion. In the first step 2′-d-5′- GMPH₂ reacts some ten times faster than 5′-GMPH₂ does. Rate constants, ΔH^#, ΔS^# and ΔV^# are very similar for the two bases in the second reaction. It is proposed that the product in the first step contains no water and is cis-[Pt(NH₃)₂B]^x+ in which the nucleobase is bidentate bonding through both N(7) of guanine and an oxygen atom of the phosphate group.     

A >22 Å long metal-complex anion and a 1D cationic coordination polymer, both based on 4,4′-bipyridine-N,N′-dioxide, yielding a 3D and 2-fold interpenetrated fsc net of the hydrogen-bonded metal-organic 1D polymer

The cationic one-dimensional (1D) coordination polymer chain ¹_∞{[Co(μ-bpdo)(H₂O)₄]²⁺} and the metal-complex anion trans-[Co(SO₄)₂(bpdo)₂(H₂O)₂]²⁻, both based on the 4,4′-bipyridine-N,N′-dioxide (bpdo) ligand, form a complementary supramolecular pair ¹_∞{[Co(μ-bpdo)(H₂O)₄]²⁺}_nn[Co(SO₄)₂(bpdo)₂(H₂O)₂]²⁻ (1) with respect to charge balance and hydrogen bonding. With a length of >22.14 ? along the bpdo-Co-bpdo axis the metal-complex trans-[Co(SO₄)₂(bpdo)₂(H₂O)₂]²⁻ is one of the longest and anisotropic counter anions (aspect ratio 22.14:8.11:4.17) observed so far in coordination polymers. Hydrogen-bonding of the anion links the cationic metal-organic 1D polymer into a 2-fold interpenetrated three-dimensional (3D) fsc (or sqc11) 4,6-c 2-nodal net of stoichiometry (4-c)(6-c) with square-planar, 4-connected (Co in anion) and octahedral, 6-connected (Co in cation) nodes in a 1:1 ratio. The 4-c point symbol is (4⁴.6²), the 6-c one (4⁴.6¹⁰.8) yielding a point symbol for the fsc net of (4⁴.6²)(4⁴.6¹⁰.8). The synthesis of 1 requires the presence of a Schiff base. Synthesis under the same conditions in the absence of the Schiff base yields the molecular complex and cocrystal [Co(bpdo)(H₂O)₅]SO₄·1/2bpdo (2) which is related (as pseudo-polymorph) to the known solvate [Co(bpdo)(H₂O)₅]SO₄·2H₂O (3) (CSD Refcodes RAXMUZ and RAXMUZ01).     

Mechanism of metal-promoted catalysis of nucleic acid hydrolysis by Escherichia coli ribonuclease H

 Catalytic activation of Escherichia coli ribonuclease H by a series of inert chromium complexes [Cr(NH₃)_6-x(H₂O)_x]³⁺ (x = 0–6) that bear water and ammine ligands in well-defined geometries in the inner coordination shell has been examined. Such complexes are observed to function by transition state stabilization. The importance of hydrogen bonding and electrostatics to catalytic activation of this reaction were quantitatively evaluated. The availability of [Cr(NH₃)_6-x(H₂O)_x]³⁺ complexes of varying coordination geometry also affords a probe of the preferred structural arrangement for hydrogen-bonding interactions. Under the solution conditions employed, a facial array of bound water molecules is required to promote catalysis, as expected from comparison with the ligation of the enzyme-bound Mg²⁺–cofactor. These results exclude a structural role for the essential metal cofactor. Hydrogen bonding appears to be the dominant stabilizing interaction. In the absence of bound water ligands (for example, in the specific cases of Cr(NH₃)₆ ³⁺ and Co(NH₃)₆ ³⁺), hydrogen bond stabilization is precluded: however, catalysis is observed as a result of the increased positive charge on the complex. Apparently the trivalent charge offsets the poorer hydrogen bonding abilities of the ammine ligands. Received: 11 June 1996 / Accepted: 31 July 1996     

Biochemical effects of binding [(H2O)(NH3)5RuII]2+ to DNA and oxidation to[(NH3)5RuIII]n—DNA.

The reaction of [(H₂O)(NH₃)₅Ru^II]²⁺ with calf thymus and salmon sperm DNA has been studied over a wide fange of transition metal ion concentrations. Kinetic studies revealcd a biphasic reaction with an initial fairly rapid coordination of the metal ion being followed by slower reactions. Binding studies were done under pseudo-equilibrium conditions following completion of the initial rapid reaction. Spectra and HPLC of acid-hydrolyzed samples of [(NH3)₅Ru^II]n-DNA prepared by incubation of [(H₂O)(NH₃)₅Ru^II]²⁺ with DNA (where [P_DNA] = 1.5 mM and reactant [Ru^II]/[P_DNA] ratios were in the fange 0.1 to 0.3) followed by air oxidation showed the predominant binding site on helical DNA to be in the major groove at the N-7 of guanine. The equilibrium constant for [(H₂O)(NH₃)₅Ru^II]²⁺ binding to the G⁷ site in helical CT DNA is 5.1 x 103. Differential pulse voltammetry exhibited a single peak at 48 mV, which is attributed to the reduction of Rum on the G⁷ sites.At [Run]/[P_DNA] <0.5, Tm values for the DNA decreased linearly with increasing ruthenium concentration and an increase in the intensity of the 565 nm dG→ Ru(III) charge transfer band was noted upon melting. The UV and CD spectra of these samples indicated no extensive destacking or alteration in geometry (B family) compared to unsubstituted DNA. At [Run]/[P_DNA]〉 0.5 or when single-stranded DNA was used, increased absorbance at 530 nm and 480 nm suggested additional binding to the exocyclic amine sites of adenine and cytosine residues. HPLC and individual spectrophotometric identification of the products derived from hydrolysis of these spec~es yielded both [(Gua)(NH₃)₅Ru^III] and [(Ade)(NH₃)₅Ru^III]. Earlier studies have established the cytidine and adenosine binding sites of [(NH₃)₅Ru^III] to be at their exocyclic amines (C4 and A6). Coordination to these positions indicates disruption of the double helix since these amines are involved in hydrogen bonding on the interior of B-DNA.Agrose gel electrophoresis of superhelical pBR322 plasmid DNA after exposure to various complexes of [(nh₃)₅Ruⁱⁱⁱ] in the presence of a reductant and air generally revealed moderately efficient cleavage of the DNA, presumably due to the generation of hydroxyl radical via Fenton's chemistry. However, similar studies involving [(NH₃)₅Ru^III] directly coordinated to the DNA showed no strand cutting above background. Polyacrylamide gel electrophoresis of a 381 bp, 3′-³²P-labeled fragment of pBR322 plasmid DNA containing low levels of bound [(NH₃)₅ Ru^III] further indicated negligible DNA cutting by the coordinated metal ion.     

Assisted self-association of dicyanoaurate, [Au(CN)2], and dicyanoargentate, [Ag(CN)2], through hydrogen bonding to metal ammonia complexes

The salts - yellow [Cr(NH₃)₆][Ag(CN)₂]₃ · 2H₂O, red [Co(NH₃)₆][Ag(CN)₂]₃ · 2H₂O, red [Co(NH₃)₆][Au(CN)₂]₃ · 2H₂O, pale yellow [Ru(NH₃)₆][Ag(CN)₂]₃ · 2H₂O, yellow K[Cr(NH₃)₆]₂[Au(CN)₂]₇ · 4H₂O, and colorless [(μ²-NH₂)₂Pt₂(NH₃)₁₀][Au(CN)₂]₆ · 5.5{OS(CH₃)₂} · 0.5H₂O - have been prepared by evaporation of aqueous solutions of potassium dicyanoargenate or potassium dicyanoaurate and salts of the appropriate cations. Hydrogen bonding between the cations and the cyano groups of the anions facilitates the formation of structures with strong metallophilic interactions between the anions. Thus, the [Au(CN)₂]⁻ or [Ag(CN)₂]⁻ ions self-associate into linear trimers in the isostructural set of crystals, [Cr(NH₃)₆][Ag(CN)₂]₃ · 2H₂O (Ag?Ag distance; 3.1610(4) Å), [Co(NH₃)₆][Ag(CN)₂]₃ · 2H₂O (Ag?Ag distance; 3.1557(2) Å), [Co(NH₃)₆][Au(CN)₂]₃ · 2H₂O (Au?Au distance; 3.0939(4) Å), and [Ru(NH₃)₆][Ag(CN)₂]₃ · 2H₂O (Ag?Ag distance; 3.1584(5) Å). Crystalline [(μ²-NH₂)₂Pt₂(NH₃)₁₀][Au(CN)₂]₆ · 5.5{OS(CH₃)₂} · 0.5H₂O also contains nearly linear trimers of the dicyanoaurate ion. Yellow crystals of K[Cr(NH₃)₆]₂[Au(CN)₂]₇ · 4H₂O contain a centrosymmetric, bent chain of seven dicyanoaurate ions with Au?Au separations of 3.1806(3), 3.2584(4), and 3.1294(4) Å.     

Age-dependent changes in diastolic Ca and Na concentrations in dystrophic cardiomyopathy: Role of Ca entry and IP3

Duchenne muscular dystrophy (DMD) is a lethal X-inherited disease caused by dystrophin deficiency. Besides the relatively well characterized skeletal muscle degenerative processes, DMD is also associated with a dilated cardiomyopathy that leads to progressive heart failure at the end of the second decade. The aim of the present study was to characterize the diastolic Ca²⁺ concentration ([Ca²⁺]_d) and diastolic Na⁺ concentration ([Na⁺]_d) abnormalities in cardiomyocytes isolated from 3-, 6-, 9-, and 12-month old mdx mice using ion-selective microelectrodes. In addition, the contributions of gadolinium (Gd³⁺)-sensitive Ca²⁺ entry and inositol triphosphate (IP₃) signaling pathways in abnormal [Ca²⁺]_d and [Na⁺]_d were investigated. Our results showed an age-dependent increase in both [Ca²⁺]_d and [Na⁺]_d in dystrophic cardiomyocytes compared to those isolated from age-matched wt mice. Gd³⁺ treatment significantly reduced both [Ca²⁺]_d and [Na⁺]_d at all ages. In addition, blockade of the IP₃-pathway with either U-73122 or xestospongin C significantly reduced ion concentrations in dystrophic cardiomyocytes. Co-treatment with U-73122 and Gd³⁺ normalized both [Ca²⁺]_d and [Na⁺]_d at all ages in dystrophic cardiomyocytes. These data showed that loss of dystrophin in mdx cardiomyocytes produced an age-dependent intracellular Ca²⁺ and Na⁺ overload mediated at least in part by enhanced Ca²⁺ entry through Gd³⁺ sensitive transient receptor potential channels (TRPC), and by IP₃ receptors.     

Reactions of pentaammineruthenium complexes with 1,2- and 1,4-dicyanobenzene and cyanobenzamides: evidences of neighboring group participation

The spectral (UV-Vis and IR) and electrochemical behavior of the nitrile bonded complexes [Ru(NH₃)₅L]²⁺ (L = 1,4-dicyanobenzene (1,4-dcb), 1,2-dicyanobenzene (1,2-dcb)), [Ru(NH₃)₅(NHC(OH)-bz-4-CN)]³⁺, [Ru(NH₃)₅(NHC(O)-bz-2-CN)]²⁺ and [Ru(NH₃)₅(NH(C)NHC(O)bz)]³⁺ (NH(C)NHC(O)-bz = 3-imino-1-oxo-isoindoline) are described. Oxidation of [Ru(NH₃)₅L]²⁺, at 0 ? pH ? 6, is followed by hydrolysis of the coordinated nitrile to give amide complexes in which the amide is through the nitrogen, with pH-dependent rate constants. The estimated values of the rate constant of hydrolysis (k_obs) at 25 °C are 2.9 × 10⁻³ s⁻¹ for [Ru(NH₃)₅(1,4-dcb)]³⁺ and 5.6 × 10⁻³ s⁻¹ for [Ru(NH₃)₅(1,2-dcb)]³⁺ at pH 4.65. Reduction of [Ru(NH₃)₅(NHC(O)-bz-4-CN)]²⁺ and [Ru(NH₃)₅(NHC(O)-bz-2-CN)]²⁺ is followed by two reactions, one is an aquation forming [Ru(NH₃)₅(OH₂)]²⁺ and free ligand, and the other an intramolecular linkage isomerization forming [Ru(NH₃)₅(NC-bz-4-NH₂C(O))]²⁺ and [Ru(NH₃)₅(NC-bz-2-NH₂C(O))]²⁺. The oxidized1,2-cyanobenzamide complex [Ru(NH₃)₅(NHC(OH)-bz-2-CN)]³⁺ undergoes an amide to nitrile intramolecular linkage isomerization, followed by a cyclization reaction resulting in [Ru(NH₃)₅(NH-(C)(HN-C(O)-2-bz))]³⁺ ((NH-(C)(HN-C(O)-2-bz)) = 3-imino-1-oxo-isoindoline bonded through the exocyclic nitrogen) (pK_a = 4.3). The rates of these reactions, which occur with neighboring group participation, increase with acidity. The reduced form, [Ru(NH₃)₅(NH-(C)(HN-C(O)-2-bz))]²⁺, is relatively substitution inert.     

Fabrication of chronocoulometric DNA sensor based on gold nanoparticles/poly(l-lysine) modified glassy carbon electrode

In this work, we fabricated a sensitivity chronocoulometric DNA sensor (CDS) based on gold nanoparticles (AuNPs)/poly(l-lysine) complex film modified glassy carbon electrode. Hexaammineruthenium(III) chloride ([Ru(NH₃)₆]³⁺) was used as the electroactive indicator. The assembled process was investigated by cyclic voltammetry (CV) and chronocoulometry (CC). CC is used to monitor the DNA hybridization event by measurement of electrostatic binding [Ru(NH₃)₆]³⁺. Under the optimal conditions, the signal of [Ru(NH₃)₆]³⁺ was linear with the logarithm of the concentration of the complementary oligonucleotides from 1.0 × 10⁻¹³ to 1.0 × 10⁻¹¹ M, and the detection limit is 3.5 × 10⁻¹⁴ M.     

Flexibility of DNA and RNA upon Binding to Different Metal Cations. An Investigation of the B to A to Z Conformational Transition by Fourier Transform Infrared Spectroscopy

Abstract

The interaction of DNA and RNA with Cu(II), Mg(II), [Co(NH₃)₆]³⁺ [Co(NH₃)₅Cl]²⁺ chlorides and, cis- and trans-Pt(NH₃)₂Cl₂ (CIS-DDP, trans-DDP) has been studied by Fourier Transform Infrared (FT-IR) spectroscopy and a correlation between metal-base binding and conformational transitions in the sugar pucker has been established. It has been found that RNA did not change from A-form on complexation with metals, whereas DNA exhibited a B to Z transition. The marker bands for the A-form (C′₃-endo-anti conformation) were found to be near 810–816 cm^?1, while the bands at 825 and 690 cm^?1 are marker bands for the B- conformation (C′₂-endo, anti), The B to Z (C₃′-endo, syn conformation) transition is characterized by the shift of the band at 825 cm^?1 to 810–816 cm^?1 and the shift of the guanine band at 690 cm^?1 to about 600–624 cm^?1.