Prakash Mohanty

Kinetics and mechanism of reaction of trans‐(diaqua)(N,N′‐ethylene‐bis‐salicylidenimine) chromium(iii) with sulfur(iv): The labilizing effect of coordinated sulfite

The reaction of trans-[Cr(Salen)(OH2)2]+ with aqueous sulfite yields trans-[Cr(Salen)(OH2)(OSO2(SINGLEBOND)O)]− (O-bonded isomer). The rate and activation parameter data for the formation of the sulfito complex are consistent with a mechanism involving rate-limiting addition of SO2 to the CrIII(SINGLEBOND)OH bond. The complex ions, trans-[(OH2)Cr(Salen)(OSO2(SINGLEBOND)O)]−, and trans-[(OH)Cr(Salen)(OSO2(SINGLEBOND)O)]2−, undergo reversible anation by NCS−, N3−, imidazole, and pyridine resulting in the formation of trans-[XCr(Salen)(OSO2(SINGLEBOND)O)](N+1)−(n=1 for X=N3−,NCS−, and 0 for X=imidazole and pyridine) predominantly via dissociative interchange mechanism. The labilizing action of the coordinated sulfite on the trans-CrIII-X bond in trans-[XCr(Salen)(OSO2)](n+1)− follows the sequence: NCS−pyridine ca. N3− ca. imidazole. Data analysis indicated that the coordinated sulfite has little trans activating influence.

Kinetics and mechanism of the reaction of aquachromium(III) with l-ascorbic acid in aqueous media

The kinetics of the reaction of l-ascorbic acid (H2A) with aquachromium(III) has been studied over the range 0.04 ≤ [H2A]T ≤ 0.16 mol dm−3, 3.5 ≤ pH ≤ 6.0, 25.0 ≤ t ≤ 50.0∘C, 0.03 ≤ I ≤ 1.0 mol dm−3 (KNO3) and 0% ≤ [MeOH] ≤ 20% (v/v). The reaction takes place via an outer-sphere association between Cr3+/CrOH2+ and H2A, followed by transformation of the outer- into an inner-sphere complex by slow interchange. The anation rate constants for Cr3+ and CrOH2+ species (k1 and k2) at 25∘C and I=1.0moldm−3 (KNO3) are 1.68×10−4 and 2.14×10−4s−1, respectively. ΔH‡ and ΔS‡ for the k1 and k2 paths are 27.0±2kJmol−1, −227±5J K−1mol−1 and 57.2± 4kJmol−1, −123±14JK−1mol−1, respectively. Anation of Cr(H2O)3+6 and Cr(H2O)5OH2+ follow an Ia path.

Synthesis and Characterization of a Product of a Reaction Between Trans-dichlorido-bis-(ethylenediamine)cobalt(III) with L-cystine

Substitution reaction of complex, trans-[CoCl2(en)2]Cl, with sulfur containing agent L-cystine, has been studied 1.0 × 10−1 mol dm−3 aqueous perchlorate medium at various temperatures (30°C to 50°C) and pH (4.45 to 3.30) using Uv-vis spectrophotometer. The products are characterized by physico-chemical and spectroscopic methods datasets at various pH and temperatures. From this method, cis-[CoCl(en)2(H2O)]2+, hydrolysis of trans-[CoCl2(en)2]+, has formed complex to L-cystine, acts as bidentate ligand, through one Co–S and Co–N bonds at low pH (3.30). At high pH (3.75 to 4.45), this complex has formed product through Co–N and Co–O bonds. The activation parameters Ea, ΔH# and ΔS# have been determined. The products, SNi, and reversible rate constants have been evaluated.

Reactivity of disulfide peptide l-cystine with iodido (diethylenetriamine)platinum(II) and synthesis of products in the presence of an iodide ion

Substitution reactions of complex [PtI(dien)]+ (where, dien=diethylenetriamine ) with sulfur-containing peptide l-cystine has been studied in 1.0×10−1 M aqueous perchlorate or acetate medium between 298≤T (K)≤323 and 2.30≤pH≤4.45 using a UV–visible spectrophotometer. Products obtained have characterized from their physico-chemical and spectroscopic methods at various pH and temperatures. From this characterization, products have indicated that [PtI(dien)]+ has formed a complex with l-cystine and acts as a bidentate ligand, through Pt–S bond at 2.30≤pH≤3.30 and through Pt–N and Pt–S bond of cystine in 3.95≤pH≤4.45. At 2.30≤pH≤3.30, ring opening and closing of dien have occurred at 308 and 323 K, respectively, and the same has happened at pH≥3.95. All reactions have followed the rate law – d[mixture]/dt=(k 1+k 2 [cystine]) [Pt(II)], where k 2 denotes the second-order rate constant. Activation parameters E a , Δ H # and Δ S # have been determined. Product formation and reversible and forward reaction rate constants have also been evaluated.

Kinetics and mechanism of the complex formation between oxalatopentaamminecobalt(III) and aluminium(III) and gallium(III); a comparative study

SummaryThe reversible complex formation between oxalatopentaammine cobalt(III), aluminium(III) and gallium(III) was investigated by the stopped flow technique at 30 ± 0.1 °C and I = 1.0 mol dm−3. The reactivity sequence: GaIII > AlIII is observed, however, the major path for gallium(III) was (NH3)5CoC2O4H2+ + GaOH2+ →(NH3)5CoC2O4-Ga4+ + H2O. The formation and dissociation rate constants of the binuclear species have been compared with the analogous data for iron(III) and nickel(II) reported earlier. The results reflect the fact that the half-bonded exalato moiety of (NH3)5CoC2Oinf4p+ acts as a chelating agent for the metal ions.

Study of Nickel (II) Catalysed Oxidation of Glycylglycine by Heptavalent Manganese: A Kinetic Study

Kinetics of the Ni(II) catalysed oxidation of glycylglycine by alkaline KMnO4 has been studied spectrophotometrically over the range 2.0 ≤ 10 3 (Gly-Gly) ≤ 6.0 mol dm -3 ; 1.25 ≤ 10 7 (OH - ) ≤ 10.0mol dm -3 ; 293 ≤ T ≤ 313 K and I = 0.5 mol dm -3 (KNO3). The reaction exhibits first order in (MnO4 - )T and (Ni(II))T but fractional order in both (Gly-Gly)T and (OH - )Trespectively. The rate of reaction is found to increase with increase in (Gly-Gly)T and (OH - )T.For uncatalysed reactionΔH # (kJmol -1 ) and ΔS # (JK -1 mol -1 ) are found to be44.4 ± 1.8 and -182 ± 6.0respectively but for Ni(II) catalysed reaction, the parameters ΔH # (kJ mol -1 ) and ΔS # (JK -1 mol -1 ) are found to be 23.46 ± 2.53 and -159.1 ± 8.43 respectively. The Ni(II) catalysed reaction passes through a new reaction path with less activation energy. The ΔH o (kJ mol -1 )and ΔS o (JK -1 mol -1 ) values for logK1 and logK2 are found to be 42.2& -30.6 and280.1&-37.9. The negative activation entropy is indicative of ordered transition state for electron transfer reaction. The product of the reaction is found to be glyoxalwhich is supported by FTIR data.

Kinetics and Mechanism of Electron Transfer to Heptavalent Manganese by DL-Aspartic Acid in Alkaline Aqueous and Micellar Media

The kinetics and mechanism of the electron transfer of DL-Aspartic acid (Asp) by Mn (VII) in alkaline medium has been studied spectrophotometrically over the range [Asp] mol dm−3; mol dm−3; K and mol dm−3 (KNO3). The reaction exhibits first-order dependence in but shows fractional-order dependence in both and . The reaction was studied in the presence of sodium dodecyl sulfate (SDS); an increase in the rate with the increase in the micellar concentration was observed. The products were characterized by spectral analysis. A mechanism involving free radicals is proposed. Asp binds to form a complex that subsequently decomposes to products. Activation parameters ° (kJ mol−1) and ° (JK−1 mol−1) for the reaction are and , respectively. The negative value of ° indicates that oxidation occurs via inner sphere mechanism.

Reactivity of Aquadiethylenetriamineplatinum(II) Ion with Disulfide Moiety Cystine: A Kinetic and Mechanistic Approach

Abstract Substitution reactions of the complex [Pt(dien)H2O]2+ (where dien = diethylentriamine or 1,5-diamino-3-azapentane) with sulfur-containing L-cystine have been studied in a 1.0 × 10−1 mol dm−3 aqueous perchlorate medium at various temperatures (298–323 K) and 4.45 ≤ pH ≤ 2.15 using UV-vis spectroscopy. The products obtained have been characterized by their infrared and 1H NMR datasets at various pH levels and temperatures. From infrared and 1H NMR data, products have indicated that [Pt(dien)H2O]2+ reacted with L-cystine forming a Pt–S bond at low pH. At high pH, a product complex through the Pt–N bond has been formed. All rate constants have been evaluated from nonlinear double exponential plots. The activation parameters ΔH# and ΔS# have been determined using the Eyring equation. The products, SNi, and reversible rate constants have been evaluated. Supplemental materials are available for this article. Go to the publishers online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. GRAPHICAL ABSTRACT

Synthesis, characterization, and mechanism of trans-dichlorido-bis-(ethylenediamine)cobalt(III) with L-cystine in the presence of chloride

Substitution reactions of trans-[CoCl2(en)2]Cl (where en = ethylenediamine) with L-cystine has been studied in 1.0 × 10−1 mol dm−3 aqueous perchlorate at various temperatures (303–323 K) and pH (4.45–3.30) using UV-Vis spectrophotometer on various [Cl−] from 0.05 to 0.01 mol L−1. The products have been characterized by their physico-chemical and spectroscopic data. Trans-[CoCl(en)2(H2O)]2+, from the hydrolysis of trans-[CoCl2(en)2]+ in the presence of Cl−, formed a complex with L-cystine at all temperatures in 1 : 1 molar ratio. L-cystine is bidentate to Co(III) through Co–N and Co–S bonds. Product formation and reversible reaction rate constants have been evaluated. The rate constants for SNi mechanism have been evaluated and activation parameters E a, ΔH #, and ΔS # are determined.

Nonenzymatic NADH-Dependent Reduction of Keggin-Type 12-Tungstocobaltate(III) in Aqueous Medium

The kinetics of the electron transfer reaction of NADH with 12-tungstocobaltate(III) has been studied over the range 5.07 ≤ 104 [NADH] ≤ 15.22 mol dm-3, 7.0 ≤ pH ≤ 8.0 and 20 ≤ t ≤ 35 oC in aqueous medium. The electron transfer reaction showed first-order dependence each in [NADH]T and [12-tungstocobaltate(III)]T. The products of the reaction were found to be NAD+ and 12-tungstocobaltate(II). The activation parameters ΔH# (kJ mol-1) and ΔS# (JK-1mol-1) of the electron transfer reactions were found to be 64.4±1.8 and -48.86±6.0. Negative value of ΔS# is an indicative of an ordered transition state for the electron transfer reaction.