Efficient Generation of Chemiluminescence during the reduction of manganese(IV) ions with lactic acid

The kinetics and mechanism of chemiluminescence during the reduction of manganese(IV) ions with lactic acid in an H₂SO₄–AcOH medium are studied. Kinetic spectrophotometric measurements are used to determine the profiles of change in the concentrations of Mn(IV) and Mn(III) ions during the reaction. The results from kinetic spectrophotometric measurements are compared to the light yield kinetics. The quantum chemiluminescence and chemiexcitation yields reach record values.     

Kinetics and mechanism of the oxidation of hydroxylamine by a {Mn3O4}4+ core in aqueous acidic media

In this work we report the kinetics of oxidation of hydroxylamine by a trinuclear Mn(IV) oxidant, [Mn(3)(μ-O)(4)(phen)(4)(H(2)O)(2)](4+) (1, phen = 1,10-phenanthroline), in aqueous solution over a pH range 2.0-4.0. The trinuclear Mn(IV) species (1) deprotonates in aqueous solution at physiological pH: 1 ? 2 + H(+); pK(1) = 4.00 (± 0.15) at 25.0 °C, I = 1.0 (M) NaNO(3). Both 1 and 2 are reactive oxidants reacting with the conjugate acid of hydroxylamine, viz. NH(3)OH(+) where the deprotonated oxidant 2 reacts faster. This finding is in contrast to a common observation and belief that protonated oxidants react quicker than their deprotonated analogues. Mn(IV)(3) to Mn(II) transition in the present reaction proceeds through the intervention of a spectrally detected mixed-valent Mn(III)Mn(IV) dimer that quickly collapses to Mn(II). The rate of the reaction was found to be lowered in D(2)O-enriched media in comparison to that in pure H(2)O media. An initial one electron one proton transfer to Mn(IV)(3) (electroprotic; 1e, 1H(+)) could be mechanistically conceived as the rate step. We also demonstrate by means of high level DFT studies that, among the two sets of Mn(IV) atoms in the trinuclear oxidant, the unique one that is coordinated with two phen ligands and two oxo-bridges is reduced to Mn(III) at the rate step. This is explained based on energetic and spin density calculations. Moreover, this result agrees with the charge distribution on the Mn atoms of the trinuclear complex.     

Oxidation of acetanilide by MnO 4 − in the presence of HClO4. A kinetic study

The permanganate ion oxidation of acetanilide was studied spectrophotometrically by measuring the changes in absorbance at 525 nm in perchloric acid solutions. At lower [H⁺], the formation of an intermediate was observed whereas at higher [H⁺], the nature of reaction-time curve was sigmoid. The reaction rate increases with [H⁺] and the kinetics reveals complex order dependence in [H⁺]. The kinetic data for the oxidation of acetanilide indicate that the mechanism involves two steps. The order in [acetanilide] was found to be one. Water soluble Mn(IV) has been identified as an intermediate in the reduction of MnO ₄ ⁻ by acetanilide. The hydrogen ions have been found to decrease the stability of the Mn(IV). Externally added Mn(II) (a product of the reaction) has a composite effect (inhibition and catalysis). The addition of F⁻in the form of NaF has no effect on the reaction rate. The Arrhenius equation was valid for the reaction between 40 and 60 °C. The energy of activation, enthalpy and entropy of activation have been evaluated. Mechanisms consistent with the observed kinetics results have been suggested.     

Reactions of carbonate radical anion with amino-carboxylate complexes of manganese(II) and iron(III)

Abstract

The reaction kinetics of eight amino-carboxylate complexes of Fe(III) and Mn(II) with carbonate radical anion were studied using the pulse radiolysis method and UV-vis spectroscopy. Difference spectra revealed the formation of Fe(IV) and Mn(III) after reaction with CO₃^??. Spectral measurements revealed the first step to be the coordination of carbonate to the metal center. All of these led to the conclusion that the role of coordinated carbonate is essential to the electron transfer process by carbonate radical anion.     

The hexacyanomanganate(IV)-hydrogen peroxide reaction. Kinetic determination of vanadium

The reaction between hexacyanomanganate(IV) and hydrogen peroxide in acidic medium is strongly catalysed by vanadium. The stoichiometry has been proved to be Delta[Mn(IV)]/Delta[H(2)O(2)]=1. S-shaped absorbance-time curves are obtained for a wide range of conditions, which seems to be due to the transient formation of hydroperoxyl radicals, HO(2).; therefore, the reaction is autoinduced. The reaction kinetics is first order on the hexacyanomanganate(IV) concentration. Complex dependence of the initial rate on the H(2)O(2) as well as H(+) concentrations are observed both for the uncatalysed and for the catalysed reactions, but the rate laws are given and reaction mechanisms are proposed. The catalytic effect of vanadium has been used to determine traces of vanadium (the (IV) and (V) oxidation states are determined together). By applying the initial rate method a detection limit of 0.9 ng ml(-1) (18 nM), and a linear range up to 50 ng ml(-1) were found. The relative standard deviations for the 4 and 25.5 ng ml(-1) levels were 5.2 and 2.5% respectively. Positive kinetic interferences from Cr(VI), Hg(I) and Ag(I) have been observed; other interferences are less severe and Cr(IIl), Fe(II) and Fe(III), among many others, do not interfere. The Mn(IV) solution must be prepared daily and its conservation needs some care (0 degrees C) but the proposed method has been applied to the determination of vanadium in a phosphate rock (reference material, BCR No. 32) without previous separations. Recovery experiments have also been performed; excellent results were obtained in both cases.     

Kinetic study of the Ce(III)‐, Mn(II)‐ or Fe(phen)32+‐catalyzed Belousov‐Zhabotinsky reaction with 2‐ketoglutaric acid

The Belousov‐Zhabotinsky (BZ) reaction of bromate ion with 2‐ketoglutaric acid (KGA) in aqueous sulfuric acid catalyzed by Ce(III), Mn(II), or Fe(phen)₃²⁺ ion exhibits sustained barely damped oscillations under aerobic conditions. In general, the reaction oscillates without an induction period. Fe(phen)₃²⁺ ion behaves differently from Ce(III) and Mn(II) ions in catalyzing this oscillating system. The gem‐diol form of KGA exhibits different behavior from that of the keto form of KGA in the BZ reaction. The kinetics and mechanism of the reaction of KGA with Ce(IV), Mn(III), or Fe(phen)₃³⁺ ion was investigated. The order of relative reactivities of metal ions toward reaction with KGA is Mn(III) > Ce(IV) ≫ Fe(phen)₃³⁺. Experimental results are rationalized. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 101–107, 2001     

Preparation and characterization of manganese(IV) in aqueous acetic acid

Mn(IV) acetate was generated in acetic acid solutions and characterized by UV-vis spectroscopy, magnetic susceptibility, and chemical reactivity. All of the data are consistent with a mononuclear manganese(IV) species. Oxidation of several substrates was studied in glacial acetic acid (HOAc) and in 95:5 HOAc-H(2)O. The reaction with excess Mn(OAc)(2) produces Mn(OAc)(3) quantitatively with mixed second-order kinetics, k (25.0 °C) = 110 ± 4 M(-1) s(-1) in glacial acetic acid, and 149 ± 3 M(-1) s(-1) in 95% AcOH, ΔH(?) = 55.0 ± 1.2 kJ mol(-1), ΔS(?) = -18.9 ± 4.1 J mol(-1) K(-1). Sodium bromide is oxidized to bromine with mixed second order kinetics in glacial acetic acid, k = 220 ± 3 M(-1) s(-1) at 25 °C. In 95% HOAc, saturation kinetics were observed.     

Water oxidation catalyzed by the tetranuclear Mn complex [Mn(IV)4O5(terpy)4(H2O)2](ClO4)6

The tetranuclear manganese complex [Mn(IV)(4)O(5)(terpy)(4)(H(2)O)(2)](ClO(4))(6) (1; terpy = 2,2':6',2″-terpyridine) gives catalytic water oxidation in aqueous solution, as determined by electrochemistry and GC-MS. Complex 1 also exhibits catalytic water oxidation when adsorbed on kaolin clay, with Ce(IV) as the primary oxidant. The redox intermediates of complex 1 adsorbed on kaolin clay upon addition of Ce(IV) have been characterized by using diffuse reflectance UV/visible and EPR spectroscopy. One of the products in the reaction on kaolin clay is Mn(III), as determined by parallel-mode EPR spectroscopic studies. When 1 is oxidized in aqueous solution with Ce(IV), the reaction intermediates are unstable and decompose to form Mn(II), detected by EPR spectroscopy, and MnO(2). DFT calculations show that the oxygen in the mono-μ-oxo bridge, rather than Mn(IV), is oxidized after an electron is removed from the Mn(IV,IV,IV,IV) tetramer. On the basis of the calculations, the formation of O(2) is proposed to occur by reaction of water with an electrophilic manganese-bound oxyl radical species, (?)O-Mn(2)(IV/IV), produced during the oxidation of the tetramer. This study demonstrates that [Mn(IV)(4)O(5)(terpy)(4)(H(2)O)(2)](ClO(4))(6) may be relevant for understanding the role of the Mn tetramer in photosystem II.     

Effect of Micelles on kinetics and mechanism of the oxidation of Serine by acid Permanganate

The oxidation of serine (HORCO₂H) by acid permanganate was investigated both in the absence and presence of sodium dodecyl sulfate (SDS). It has been observed that the presence of surfactant enhanced the reaction rate. The reaction is first order with respect to [Serine] and [MnO₄^?]. The reaction is retarded by the hydrogen ion in the absence of SDS but catalyzed in the presence of SDS. The overall rate expression for the reduction of Mn(VII) may be written as In the presence of SDS of the rate law is The reaction appears to involve a parallel consecutive reaction mechanism in which Mn(IV) appears as the reaction intermediate. ??′_4f signifies the rate constant for the reaction path leading to the formation of Mn(IV) from Mn(VII) as reaction intermediate, whereas ??′_2f signifies the rate constant for the reaction path leading to the reduction of Mn(VII) to Mn(II) without prior formation of Mn(IV). A mechanism satisfying the various kinetic parameters has been proposed.     

Laser flash photolysis generation and kinetic studies of corrole-manganese(V)-oxo intermediates

Corrole-manganese(V)-oxo intermediates were produced by laser flash photolysis of the corresponding corrole-manganese(IV) chlorate complexes, and the kinetics of their decay reactions in CH2Cl2 and their reactions with organic reductants were studied. The corrole ligands studied were 5,10,15-tris(pentafluorophenyl)corrole (H3TPFC), 5,10,15-triphenylcorrole (H3TPC), and 5,15-bis(pentafluorophenyl)-10-(p-methoxyphenyl)corrole (H3BPFMC). In self-decay reactions and in reactions with substrates, the order of reactivity of (Cor)Mn(V)(O) was TPC > BPFMC > TPFC, which is inverted from that expected based on the electron-demand of the ligands. The rates of reactions of (Cor)Mn(V)(O) were dependent on the concentration of the oxidant and other manganese species, with increasing concentrations of various manganese species resulting in decreasing rates of reactions, and the apparent rate constant for reaction of (TPFC)Mn(V)(O) with triphenylamine was found to display fractional order with respect to the manganese-oxo species. The kinetic results are consistent in part with a reaction model involving disproportionation of (Cor)Mn(V)(O) to give (Cor)Mn(IV) and (Cor)Mn(VI)(O) species, the latter of which is the active oxidant. Alternatively, the results are consistent with oxidation by (Cor)Mn(V)(O) which is reversibly sequestered in non-reactive complexes by various manganese species.     

Kinetics of polymerization of acrylonitrile initiated by acidic permanganate/thioacetamide redox system

The kinetics of vinyl polymerization of acrylonitrile (AN) initiated by an acidic permanganate/thioacetamide (TAm) redox system have been investigated in aqueous media at 30 ± 0.2°C in nitrogen, and the rate of polymerization measured. The effect of additives like organic solvents, neutral electrolytes, and complexing agents on the rate have been assessed. Based on the experimental results, a suitable reaction scheme involving initiation by organic free radicals generated by the interaction of Mn(IV) with protonated thioacetamide and termination by Mn(III) has been suggested. Various rate and energy parameters have been evaluated.     

Kinetic Study of the Ce(III)‐, Mn(II)‐, or Ferroin‐Catalyzed Belousov‐Zhabotinsky Reaction with Allylmalonic Acid

In a stirred batch experiment and under aerobic conditions, ferroin (Fe(phen)₃²⁺) behaves differently from Ce(III) or Mn(II) ion as a catalyst for the Belousov‐Zhabotinsky (BZ) reaction with allylmalonic acid (AMA). The effects of bromate ion, AMA, metal‐ion catalyst, and sulfuric acid on the oscillating pattern were investigated. The kinetics of the reaction of AMA with Ce(IV), Mn(III), or Fe(phen)₃³⁺ ion was studied under aerobic or anaerobic conditions. The order of reactivity of metal ions toward reaction with AMA is Fe(phen)₃³⁺ > Mn(III) > Ce(IV) under aerobic conditions whereas it is Mn(III) > Ce(IV) > Fe(phen)₃³⁺ under anaerobic conditions. Under aerobic or anaerobic conditions, the order of reactivity of RCH(CO₂H)₂ (R = H (MA), Me (MeMA), Et (EtMA), allyl (AMA), n‐Bu (BuMA), Ph (PhMA), and Br (BrMA)) is PhMA > MA > BrMA > AMA > MeMA > EtMA > BuMA toward reaction with Ce(IV) ion and it is MA > PhMA > BrMA > MeMA > AMA > EtMA > BuMA toward reaction with Mn(III) ion. Under aerobic conditions, the order of reactivity of RCH(CO₂H)₂ toward reaction with Fe(phen)₃³⁺ ion is PhMA > BrMA > (MeMA, AMA) > (BuMA, EtMA) > MA. The experiment results are rationalized.     

Kinetic study of the Ce(III)‐, Mn(II)‐, or ferroin‐catalyzed Belousov‐Zhabotinsky reaction with pyruvic acid

The Ce(III)‐, Mn(II)‐, or ferroin (Fe(phen)₃²⁺)‐catalyzed reaction of bromate ion and pyruvic acid (PA) or its dimer exhibits oscillatory behavior. Both the open‐chain dimer (parapyruvic acid, γ‐methyl‐γ‐hydroxyl‐α‐keto‐glutaric acid, DPA1) and the cyclic‐form dimer (α‐keto‐γ‐valerolactone‐γ‐carboxylic acid, DPA2) show more sustained oscillations than PA monomer. Ferroin behaves differently from Ce(III) or Mn(II) ion in catalyzing these oscillating systems. The kinetics of reactions of PA, 3‐brompyruvic acid (BrPA), DPA1, or DPA2 with Ce(IV), Mn(III), Fe(phen)₃³⁺ ion were investigated. The order of relative reactivity of pyruvic acids toward reaction with Ce(IV), Mn(III), or Fe(phen)₃³⁺ ion is DPA2 > DPA1 > BrPA > PA and that of metal ions toward reaction with pyruvic acids is Mn(III) > Ce(IV) > Fe(phen)₃³⁺. The rates of bromination reactions of pyruvic acids are independent of the concentration of bromine and the order of reactivity toward bromination is (DPA1, DPA2) > BrPA > PA. Experimental results are rationalized. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 408–418, 2000     

Effect of Mn(II) and Ce(IV) Ions on the Oxidation of Lactic Acid by Chromic Acid

The kinetics and mechanism of lactic acid oxidation in the presence of Mn(II) and Ce(IV) ions by chromic acid were studied spectrophotometrically. The oxidation of lactic acid by Cr(VI) was found to proceed in two measurable steps, both of which gave pyruvic acid as the primary product in the absence of Mn(II). 2Cr(VI)+2CH₃CHOHCOOH → 2CH₃COCOOH+Cr(V)+Cr(III) Cr(V)+CH₃CHOHCOOH → Cr(III)+CH₃COCOOHThe observed kinetics was explained due to the catalytic and inhibitory effects of Mn(II) and Ce(IV) on the lactic acid oxidation by Cr(VI). The reactivity of lactic acid depends upon the experimental conditions. It acts as a two-or three-equivalent reducing agent in the absence or presence of Mn(II). It was examined that Cr(III) products resulting from the direct reduction of Cr(VI) by three-equivalent reducing agents. The oxidation of lactic acid follows the complex order kinetics with respect to [lactic acid]. The activation parameters E_a, ΔH^#, and ΔS^# were calculated and discussed.     

A novel carboxylate-free ferromagnetic trinuclear mu(3)-oxo-manganese(III) complex with distorted pentagonal-bipyramidal metal centers

In methanol, the reaction of Mn(ClO(4))(2).6H(2)O and 1,2-bis(biacetylmonoximeimino)ethane (H(2)bamen) in the presence of triethylamine affords a trinuclear complex having the formula [Mn(3)(mu(3)-O)(mu(3)-bamen)(3)]ClO(4).2H(2)O. The structure of this complex shows a symmetric planar central [Mn(III)(3)(mu(3)-O)] unit coordinated to three hexadentate bridging (via oximate groups) ligands. The N(4)O(3) coordination sphere around each metal center is very close to pentagonal-bipyramidal. A cyclic voltammogram of the complex displays two reversible and an irreversible response due to Mn(III)(3) --> Mn(III)(2)Mn(IV), Mn(III)(2)Mn(IV) --> Mn(III)Mn(IV)(2), and Mn(III)Mn(IV)(2) --> Mn(IV)(3) oxidation processes, respectively. Cryomagnetic data reveal that the complex is ferromagnetic.     

Kinetics and mechanism of the reduction of colloidal MnO2 by glycyl-leucine in the absence and presence of surfactants

The kinetics of the reduction of water-soluble colloidal manganese dioxide by glycyl-leucine (Gly-Leu) has been investigated in the presence of perchloric acid both in aqueous as well as micellar media at 35 °C. The study was carried out as functions of [MnO₂], [Gly-Leu] and [HClO₄]. The first-order-rate is observed with respect to [MnO₂], whereas fractional-order-rates are determined in both [Gly-Leu] and [HClO₄]. Addition of sodium pyrophosphate and sodium fluoride enhanced the rate of the reaction. Further, the use of surfactant micelles is highlighted as, in favourable cases, the micelles help the redox reactions by bringing the reactants into a close proximity due to hydrogen bonding. While the ionic surfactants SDS and CTAB have not shown any effect on the reaction rate, the nonionic surfactant TX-100 has catalytic effect which is explained in terms of the mathematical model proposed by Tuncay et al. (1999). The Arrhenius and Eyring equations are valid for the reaction over the range of temperatures used and different activation parameters (E_a, ΔH^#, ΔS^# and ΔG^#) have been evaluated. Kinetic studies show that the redox reaction between MnO₂ and Gly-Leu proceeds through a mechanism combining one- and two-electron pathways: Mn(IV) → Mn(III) → Mn(II) and Mn(IV) → Mn(II). On the basis of the observed results, a possible mechanism has been proposed and discussed.     

Laser flash photolysis generation and kinetic studies of porphyrin-manganese-oxo intermediates. Rate constants for oxidations effected by porphyrin-Mn(V)-oxo species and apparent disproportionation equilibrium constants for porphyrin-Mn(IV)-oxo species

Porphyrin-manganese(V)-oxo and porphyrin-manganese(IV)-oxo species were produced in organic solvents by laser flash photolysis (LFP) of the corresponding porphyrin-manganese(III) perchlorate and chlorate complexes, respectively, permitting direct kinetic studies. The porphyrin systems studied were 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TPFPP), and 5,10,15,20-tetrakis(4-methylpyridinium)porphyrin (TMPyP). The order of reactivity for (porphyrin)Mn(V)(O) derivatives in self-decay reactions in acetonitrile and in oxidations of substrates was (TPFPP) > (TMPyP) > (TPP). Representative rate constants for reaction of (TPFPP)Mn(V)(O) in acetonitrile are k = 6.1 x 10(5) M(-1) s(-1) for cis-stilbene and k = 1.4 x 10(5) M(-1) s(-1) for diphenylmethane, and the kinetic isotope effect in oxidation of ethylbenzene and ethylbenzene-d(10) is k(H)/k(D) = 2.3. Competitive oxidation reactions conducted under catalytic conditions display approximately the same relative rate constants as were found in the LFP studies of (porphyrin)Mn(V)(O) derivatives. The apparent rate constants for reactions of (porphyrin)Mn(IV)(O) species show inverted reactivity order with (TPFPP) < (TMPyP) < (TPP) in reactions with cis-stilbene, triphenylamine, and triphenylphosphine. The inverted reactivity results because (porphyrin)Mn(IV)(O) disproportionates to (porphyrin)Mn(III)X and (porphyrin)Mn(V)(O), which is the primary oxidant, and the equilibrium constants for disproportionation of (porphyrin)Mn(IV)(O) are in the order (TPFPP) < (TMPyP) < (TPP). The fast comproportionation reaction of (TPFPP)Mn(V)(O) with (TPFPP)Mn(III)Cl to give (TPFPP)Mn(IV)(O) (k = 5 x 10(8) M(-1) s(-1)) and disproportionation reaction of (TPP)Mn(IV)(O) to give (TPP)Mn(V)(O) and (TPP)Mn(III)X (k approximately 2.5 x 10(9) M(-1) s(-1)) were observed. The relative populations of (porphyrin)Mn(V)(O) and (porphyrin)Mn(IV)(O) were determined from the ratios of observed rate constants for self-decay reactions in acetonitrile and oxidation reactions of cis-stilbene by the two oxo derivatives, and apparent disproportionation equilibrium constants for the three systems in acetonitrile were estimated. A model for oxidations under catalytic conditions is presented.     

Kinetic study of the Ce(iii)- or Mn(ii)-catalyzed Belousov–Zhabotinsky reactions with mixed organic acid/ketone substrates

In a stirred batch reactor, the Ce(III)- or Mn(II)-catalyzed Belousov–Zhabotinsky reaction with mixed organic acid/ketone substrates exhibits oscillatory behavior. The organic acids studied here are: dl-mandelic acid (MDA), dl-4-bromomandelic acid (BMDA), and dl-4-hydroxymandelic acid (HMDA), and the ketones are: acetone (Me₂CO), methyl ethyl ketone (MeCOEt), diethyl ketone (Et₂CO), acetophenone (MeCOPh), and cyclohexanone ((CH₂)₅CO). The effects of bromate ion, organic acid, ketone, metal-ion catalyst, and sulfuric acid concentrations on the oscillatory patterns are investigated. Both conventional and stopped-flow methods are applied to study the kinetics of the oxidation reactions of the above organic acids by Ce(IV) or Mn(III) ion. The order of relative reactivities of the oxidation reactions of organic acids in 1 M H₂SO₄ is Mn(III)(SINGLEBOND)HMDA reaction>Ce(IV)(SINGLEBOND)HMDA reaction>Mn(III)(SINGLEBOND)BMDA, reaction>Mn(III)(SINGLEBOND)MDA reaction>Ce(IV)(SINGLEBOND)BMDA reaction>Ce(IV)(SINGLEBOND)MDA reaction. Spectrophotometric study of the bromination reactions of the above ketones shows that these reactions are zero-order with respect to bromine and first-order with respect to ketone and that ketone enolization is the rate-determining step. The order of relative rates of bromination or enolization reactions of ketones in 1 M H₂SO₄ is (CH₂)₅CO≫(MeCOEt, Et₂CO, Me₂CO)>MeCOPh. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet:30: 595–604, 1998     

Remarkable CO-catalyst effect of gold nanoclusters on olefin oxidation catalyzed by a manganese-porphyrin complex

The effect of dodecanethiolate-protected metallic nanoclusters of gold (Au:SC12, 1), silver (Ag:SC12), palladium (Pd:SC12), and platinum (Pt:SC12) on the catalytic activity of Mn(TPP)Cl (TPP = tetraphenylporphinato) was investigated in styrene oxidation with iodosylbenzene. Among the four metal clusters, only Au:SC12 led to appreciable acceleration of the catalytic reaction. The major role of the Au cluster was to regenerate the active catalytic path involving Mn(III) and Mn(V) from the deactivated Mn(IV) species. The binary 1/Mn(TPP)Cl catalyst system showed an absorption spectrum characteristic of Mn(III)-porphyrin after reaction, whereas a catalytically ineffective Mn(IV) species was observed as the sole porphyrin species in the absence of the Au cluster or in the presence of Pd, Ag, and Pt clusters. Accordingly, the slow oxidation reaction with Mn(TPP)Cl was accelerated by the addition of Au:SC12, and complete conversion of Mn(IV) into Mn(III) was observed in the absorption spectrum. 1H NMR inspection of the reaction of Au:SC12 and iodosylbenzene revealed that the surface dodecyl groups were partially oxidized into dodecanal and eliminated from the cluster surface, thereby producing unprotected gold sites on the surface. A reactivation mechanism involving the reaction of the Mn-porphyrin and the oxidant activated on the gold surface is proposed.     

Reductive dissolution of microparticulate manganese oxides

Electrochemical dissolution of immobilised microparticulate Mn(III,IV) oxides in slightly acidic solution (pH 4.4) was found to be a very general reaction, which is responsible for well-defined voltammetric peaks. Dissolution of six Mn(III,IV) oxides is initiated by the reduction of Mn(IV) to Mn(III) in the solid phase, which is followed by a massive dissolution via further reduction of Mn(III) to Mn(II), which finally yields soluble Mn²⁺. The reactivity of manganese oxides depends on their structure: the most reactive are amorphous (δ-MnO₂) and layered structures (birnessite); more resistant toward reductive dissolution are α- and λ-MnO₂ and electrochemical manganese dioxide; and least reactive is β-MnO₂. Reductive dissolution of LiMn₂O₄ resembles that of λ-MnO₂, whereas CaMnO₃ dissolves via a different reaction mechanism.