Four novel cobalt(III) and ruthenium(II) complexes [Ru(en)(2) (pyip)](2+) (1), [Ru(en)(2)(aip)](2+) (2), [Co(en)(2)(pyip)](3+) (3) and [Co(en)(2)(aip)](3+) (4), (en = ethylenediamine, pyip =(pyip = 2-(1-pyrenyl)-1H-imidazo[4,5-f]1,10]phenanthroline), (aip = 2-(9-anthryl)-1H-imidazo[4,5,-fl[1,10] phenanthroline) have been synthesized and characterized. The interaction of these complexes with calf thymus DNA was investigated using absorption (UV/vis) and emission spectroscopy, viscosity measurements as well as DNA melting and plasmid DNA cleavage studies. The experimental results show that the four complexes can bind to DNA in an intercalation mode. The DNA-binding affinity of complex 1 (K-b = 2.6 +/- 0.3 x 10(5) M-1) is greater than that of complexes 2, 3 and 4. Moreover, these four complexes have been found to promote the cleavage of plasmid DNA pBR322.
Reactions of aqueous solution of silicate with hydroxocomplexes of Al(III), Sn(IV), Zn(II) and Ga(III) have been experimentally studied. All studied reactions have produced gel in the whole volume of reaction mixture, and according to our hypothesis the essence of these reactions is polycondensation between silicate anions and anions of hydroxocomplex of the given amphoteric element, with formation of crosslinked inorganic polymer. Criterion for studying the course of the tested reactions has been the gel-point time of the reaction mixture. Dependences of the gel-point time on temperature, on KOH concentration and on molar ratios of silicate/amphoteric element in reaction Mixture have been recorded. Products of the studied reactions have been analyzed by means of X-ray fluorescent spectrometry. All obtained results are in accord with the hypothesis of polycondensation reaction between silicate and hydroxocomplexes, and indicate that the reaction between silicate and hydroxoaluminate is merely one case of a more general chemical reaction.
The kinetics of the reactions of L-cysteine and N-acetylcysteine with cis[Pt(en)(OH2)(2)](2+) have been studied spectrophotometrically as a function of [Pt(en) (OH2)(2)](2+)(T) [L-cysteine](T)/[N-acetylcysteine](T) and temperature at pH (4.0) where the Pt(II) complex exists predominantly as a diaqua species and L-cysteine and N-acetylcysteine as zwitterions. The substitution reaction shows two consecutive processes; the first step is the ligand assisted anation and the second one is the chelation step. The anation rate constants for N-acetylcysteine were found to be greater than that for L-cysteine. Delta H-1(#)(61.6 +/- 1.8 kJ mol(-1)) Delta H-2(#) (47.5 +/- 2.0 kJ mol(-1)), Delta S-1(#) (-54.4 +/- 5.3 J.K-1 mol(-1)) and Delta S-2(#) (-164.8 +/- 6.5 J.K-1 mol(-1)) for 1 2 L-cysteine and Delta H-1(#) (23.2 +/- 0.8 kJ mol(-1)), Delta H-2(#) (61.5 +/- 0.6 kJ mol(-1)) and Delta S-1(#) 1 2 1 (-178.6 +/- 2.6 J.K-1 mol(-1)) Delta S-2(#) (-115.6 +/- 2.0 J.K-1 mol(-1)) for N-acetylcysteine indicate an associative mode of activation for both the ligand Substitution processes in the two consecutive steps.
The kinetics of exchange of cyanide in hexacyanoferrate(II) by N-methylpyrazinium cation (Mpz(+)) has been investigated spectrophotometrically in the aqueous medium by measuring the increase in absorbance of the intense blue complex [Fe(CN)(5) MPz](2-) at its lambda(max) 655 nm, 25.0 +/- 0.1 degrees C and I = 0.1 M (KNO(3)) in potassium hydrogen phthalate buffer. The reaction rate is the maximum at pH 6.0. Increase in the rates with increasing [Fe(CN)(6)(4-)] and [Mpz(+)] have been observed. The reaction exhibits second order kinetics; first order in each of the reactants: [Fe(CN)(6)(4-)] and [Mpz(+)]. The first order kinetics with respect to [Mpz(+)] at low concentrations shifts to zero order at higher concentrations. The temperature dependence Study has resulted in energy of activation, enthalpy of activation and entropy of activation as 85.9 +/- 4.4 kJ mol(-1), 83.5 +/- 4.4 kJ mol(-1) and -15.7 +/- 1.7 JK(-1) mol(-1), respectively, which are indicative of interchange dissociative mechanism. The reaction rate has been found to decrease with decreasing dielectric constant of the medium, which supports that the intermediate complex formed is more polar than reactants. The data suggests that the substitution proceeds via formation the complex between [Fe(CN)(6)](4-) and Mpz(+) and a plausible mechanism has been proposed.
The kinetics of interaction between L-asparagine and cis-[Ru(bipy)(2)(H2O)(2)](2+) have been studied spectrophotometrically as a function of [Ru(bipy)(2)(H2O)(2)(2+1)], [L- asparaginel and temperature at a particular pH 4.8 where the Substrate complex exists predominantly as a diaqua species and L-asparagine] as a zwitterion. The reaction has been found to proceed through two consecutive steps. The first step involves the ligand assisted anation while the second step involves chelation when the second aqua ligand is displaced. Rate constants have been evaluated and activation parameters are calculated. The low enthalpy of activation and large negative value of entropy of activation indicate an associative mode of activation for both the steps.
The kinetics of oxidation of 3-amino-1-propanol (3-AP) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium have been studied by spectrophotometry in the temperature range 298.2 K-313.2 K. The reaction was found to be pseudo-first order with respect to DPC and 1 < n(ap) < 2 to 3-AP. It was found that under pseudo-first order conditions ([3-AP](0) >> [DPC](0)), the observed rate constant k(obs), changed differently under different concentration of [OH(-)]. At low [OH(-)], k(obs) decreased with increase in [OH(-)], but at higher [OH(-)], k(obs) increase with increase in [OH(-)], and periodate had a retarding effect on the reaction rate. There is a weak negative salt effect. The main products were identified by spot tests. Based on the experimental results, a probable reaction mechanism of oxidation is proposed. The rate equation derived from the mechanism can explain all the experimental phenomena. The activation parameters, along with the rate constants of the rate-determining step, were determined.
The chemical status and kinetics of the reaction between silicate ions and hydroxoaluminate ions (at Si/Al molar ratio 2: 1) in KOH aqueous solution has been experimentally studied. It is assumed that condensation of OH groups bonded to silicon and aluminum occurs in this reaction forming a cross-linked polymer; and that the reaction represents the essence of synthesis of so-called geopolymer from alumino-silicate minerals. Time required for the change of the Solution to a gel was measured as the reaction rate criterion. Measured dependences of the gel-point time oil KOH concentration in the reaction solution exhibit a linear trend. The gel-point time decreases with increasing temperature. A measurable increase in pH value of the solution appears during the reaction. Measurement of the gel-point time for different Si/Al molar ratios has confirmed that the selected ratio 2:1 has been optimal. For a quantitative description of the reaction course and for explanation of the observed phenomena, the theories of polycondensation reactions and protolytic equilibria have been applied. Theoretically calculated dependences of the gel-point time on KOH concentration are in accord with experimentally determined values, which confirms anticipated polycondensation mechanism of the reaction under Study.
Irradiation at 254 or 313 nm of solutions of (Bu 4 N) 2 [ReBr 6 ] in ethyl bromide exposed to air causes complete conversion of the hexabromorhenate(IV) to perrhenate ion.The rate of the reaction is linearly dependent on the incident light intensity and on a combination of the fraction of light absorbed by the rhenium complex and the fraction absorbed by the ethyl bromide.The experimental results are consistent with a mechanism in which the peroxy radical CH 3 CH(Br)OO, produced in both the solvent-initiated and metal-initiated pathways, oxidizes [ReBr 6 ] 2-by electron transfer.
Vanadium(V) oxidation of lactic acid shows first order dependency on lactic acid, vanadium(V), H+ and HSO4 . These observations remain unaltered in the presence of externally added surfactants. The effect of adding a cationic surfactant (CPC), anionic surfactant (SDS) and neutral surfactant (TX-100) has been studied. CPC inhibits the reactions while SDS and TX-100 accelerate the reaction to different extents. Observed effects have been explained by considering the hydrophobic and electrostatic interaction between the surfactants and reactants
The kinetics and mechanism of 2, 2 '-bipyridyl (bpy) catalysis of the chromium(VI) oxidation of 1, 2-propanediol in aqueous acidic medium has been studied spectrophotometrically. The reaction shows pseudo-first order with respect to Cr(VI) and fractional order with respect to 1, 2-propanediol. The observed rate constant (k(obs)) increases with the increase in [H(+)] and [bpy]. Change in ionic strength does not influence the rate obviously and no free radicals are detected. Thus, HCrO(4)(-) is assumed the main existing species of Cr(VI). Based on the experimental results, a probable reaction mechanism of oxidation is proposed. The rate equation derived from the mechanism can explain all the experimental phenomena. The activation parameters along with rate constants of the rate-determining step have been calculated.
The oxidation of E-aminocaproic acid by the Ag(III) complex, bis(dihydrogen tellurato)argentite(III) was studied by the stopped-flow method. It was both first order with respect to Ag(III) complex and epsilon-aminocaproic acid. A plausible mechanism involving a pre-equilibrium adduct formation between the Ag(III) complex and e-aminocaproic acid was proposed from the kinetics study. The rate law derived from the mechanism can explain all experimental phenomena. The activation parameters along with rate constants were calculated.
The substitution reaction of cyanocobalamin with pentaaquarhodium (III) has been studied spectrophotometrically as a function of pH, [Rh(III)](T) and [cyanocobalamin]T. The rate of the reaction increases with increase in [Rh(III)](T) but decreases with increase in [H+] ion. The activation parameters Delta H-#(55.8 +/- 3.4) kJ mol(-1) and Delta S-#(-136 +/- 10) J K(-1)mol(-1) have been calculated from the Eyring plots and anation rate constant k(s), was compared with the aqua exchange and anation rate constants of analogous substitution reactions. Delta G degrees, Delta H degrees, Delta S degrees for the outer sphere association process have been calculated from kinetic measurement. The mechanistic pathway for the substitution reaction within the outer sphere complex is consistent with an association interchange (I-a) type of phenomenon.
The kinetics and mechanism of the adduct formation of two Co(II) tetraaza complexes, [Co(ampen)] {[(N,N′-ethylenebis-(o-amino-α-phenylbenzylideneiminato)cobalt(II)]} and [Co(campen)] {[(N,N′-ethylenebis-(5-chloro-o-amino-α-phenylbenzylideneiminato)cobalt(II)]}, with four organic bases, 4-nitro imidazole (4-NO2Imid), 4-methyl imidazole (4-MeImid), imidazole (Imid), and 1-methyl imidazole (1-MeImid), in DMF were studied spectrophotometrically. The kinetic parameters and the second-order k2 rate constants show the following nucleophilicity trend of the bases toward the given substrate: 4-NO2Imid > 4-MeImid > Imid > 1-MeImid. The linear plots of kobs vs. the molar concentration of the base, the high span of k2 values, and the large negative values of ΔS≠ suggest an associative (A) mechanism. © 2007 Wiley Periodicals, Inc. 39: 137–144, 2007
The oxidation of the binary complex chromium(III)-uridine, [Cr-III(Urd)(H2O)(5)](3+) and the ternary one chromium(III) uridine aspartic complex, [Cr-III(Urd)(Asp) (H2O)(3)](2+), by periodate have been studied kinetically in aqueous solution to yield Cr-VI, over 20-40 degrees C and the 2.62-3.68 pH range. The oxidation of [Cr-III (Urd)(H2O)(5)](3+) by periodate, obeys the rate law, rate = [Cr(III)urd(H2O)(5)](3+) [H5IO(6)]{k(4)K(5) + (k(5)K(6)K(2)/[H+)}, while the reaction of [Cr-III (Urd) (Asp)(H2O)(3)](2+) with periodate following the rate equation d[Cr-VI]/dt = (k(6)K(8)[Cr-III](T) [IO4-])/ {1 + K-8[IO4-]+ ([H+]/K-7)}. Thermodynamic activation parameters have been calculated.
The kinetics and mechanism of oxidation of [Co(II)TTHA](4-) (where TTHA =Triehylenetetraaminehexaaceticacid) by periodate ion has been studied in aqueous acidic medium. The reaction has been investigated spectrophotometrically at lambda(max) = 550 nm under pseudo-first-order condition by taking large excess of oxidant, [IO4-] at pH = 4.0+/-0.02, I = 0.1 M (CH3COONa + NaNO3) and at three different temperatures viz. 15 degrees C, 20 degrees C and 25 degrees C. The electron transfer reaction between [Co(II)TTHA](4-) and [104] obeys inner-sphere reaction pathway through the formation of long-lived intermediate complex which eventually get converted into a corresponding [Co(III)TTHA](3-) complex as final reaction product.The experimental observations have shown that the reaction exhibit first-order dependence in [Co(II)TTHA](4-). The variation of pseudo-first-order rate constant (k(obs)) with [IO4-] keeping other reaction variables fixed at constant value is found to obey the following emperical equation.k(obs) = a[IO4-](2)/b + c[IO4-]This rate law is consistent with a three step mechanistic scheme. The values of k(obs), are almost invariant with increasing pH and attributed due to the reaction of deprotonated form of [Co(II)TTHA](4-) complex and [IO4-] in the whole pH region. Eyring's equations has been used to calculate the activation parameters and found to be Delta H-# = 16.63 kJ mole(-1); Delta S-# = - 214.00 JK(-1)mole(-1). These values are consistent with three step mechanistic scheme as proposed.
Iridium(III) chloride further catalyses the oxidation of iodide ions by K3Fe(CN)(6), catalyzed by hydrogen ions obtained from perchloric acid. Rate when the reaction is catalyzed only by the hydrogen ions was separated from the rate when iridium(III) and H(+)ions both catalyze the reaction. Separate reactions, studied in the presence as well as in the absence of IrCl3 under similar conditions were found to follow second order kinetics in [I-] with direct proportionality in [Fe(CN)(6)](3-) and [IrCl3]. Rate was found to follow first order kinetics with respect to [H+] at low concentrations, tending to become second order at higher concentrations of [H+]. Externally added [Fe(CN)(6)](4-) ions in the beginning strongly retard the rate effect, but further addition affects the rate to a little extent. Change in ionic strength has no effect on the rate. Arrhenius parameters were calculated and probable mechanisms were proposed.
The kinetics and mechanisms of uncatalysed substitution of coordinated cyanide in hexacyanoferrate(H) by phenylhydrazine (PhNHNH2) has been studied spectrophotometrically at lambda = 488 nm (lambda(max) of cherry red complex [Fe(CN)(5) PhNHNH2](3-)) as a function of [Fe(CN)(6)(4-)], [PhNHNH2] at pH = 2.8 +/- 0.02, temperature = 30 +/- 0.1 degrees C and I =0.02 M 6 dm(-3) (KNO3). The reaction obeys first-order kinetics each in [Fe(CN)(6)(4-)] and [PhNHNH2]6 The initial rate determined by the plane mirror method has been used to find out the dependences in each reactant throughout the present investigation. The initial rate varies linearly with increasing concentration of hexacyanoferrate(II) while keeping other variables fixed at an optimum value. The initial rate is also found to increase in the beginning with increasing concentration of phenylhydrazine up to [PhNHNH2] <= 1.0 X 10(-2) M, passes through a maximum and then finally falls. The effects of pH and temperature on initial rate have also been studied and explained. The activation parameters have also been evaluated and support the proposed mechanism. A plausible mechanistic scheme has been proposed based on the experimental findings. The composition of the complex formed during the course of reaction has been established to be 1:1 by the mole ratio method. A repetitive spectral scan is also provided in support of exchange of cyanide ions by phenylhydrazine in hexacyanoferrate(II).
The kinetics of reaction between copper(H) and thiosulfate ions and formation of an intermediate complex, Cu(S2O3)aq, are investigated. The kinetics of fading of the color of this complex has been traced spectrophotometrically using a stopped-flow apparatus. The experimental reaction order (between 2 and 2.5) shows that the mechanism involves, in the first step, fast formation of the complex and, in the second, the reaction between two complex molecules. The influence of temperature on the reaction kinetics has been studied and the reaction's activation entropy (-214 JK(-1) mol(-1)) suggests an associative nature for the transition state.
