Os(VIII)/Ru(III) Catalysed Oxidation of <Emphasis Type="SmallCaps">l</Emphasis>-Valine by Ag(III) Periodate Complex in Aqueous Alkaline Medium: A Comparative Kinetic Study

Abstract  

The kinetics of osmium(VIII) (Os(VIII)) and ruthenium(III) (Ru(III)) catalysed oxidation of l-valine (l-val) by diperiodatoargentate(III) (DPA) in aqueous alkaline medium at 25 °C and a constant ionic strength of 0.006 mol dm⁻³ was studied spectrophotometrically. The stoichiometry is the same in both the catalysed reactions, i.e., [l-val]:[DPA] = 1:1. The reaction is of first order in [Os(VIII)], [Ru(III)], and [DPA] and has less than unit order in [l-val] and negative fractional order in [OH⁻]. Added periodate had no effect on rate of reaction. The products were identified by spot test and characterized by spectral studies. The catalytic constant (K _C) was also calculated for both catalysed reactions at different temperatures. The activation parameters with respect to slow step of the mechanisms were computed and discussed and thermodynamic quantities were also determined. It has been observed that the catalytic efficiency for the present reaction is in the order of Os(VIII) > Ru(III). The probable active species of catalyst and oxidant have been identified.     

Mechanistic studies of ruthenium(III)-catalyzed oxidation of DL-methionine by hexacyanoferrate(III) in an alkaline medium

The kinetics and mechanism of ruthenium(III) catalyzed oxidation of dl-methionine by alkaline hexacyanoferrate(III) (HCF(III)) in an alkaline medium were studied spectrophotometrically at 30±0.1°C. The reaction was first-order-dependent each on [HCF(III)] and [ruthenium(III)] and fractional-order-dependent on [alkali]. The rate of the reaction was found to be decreased with the increase in [methionine]. The main product of oxidation was methionine sulfone nitrile (3-(methylsulfonyl)propanenitrile) and it was identified and confirmed by FT-IR and mass spectral studies. Further, no effect of added reaction product was observed. A plausible mechanism was proposed involving complexation between methionine and ruthenium(III) species, [Ru(H₂O)₅OH]²⁺. Thermodynamic parameters for the reaction, E _a and Δ S ^#, were computed using linear least squares method and are found to be 65.83±1.03 kJ/mol and?249.58±3.35 J/K mol, respectively.

     

Mechanistic Aspects of Os(VIII)/Ru(III) Catalysed Oxidation of L-phenylalanine by Ag(III) Periodate Complex in Aqueous Alkaline Medium

The kinetics of oxidation of ruthenium(III) (Ru(III)) and osmium(VIII) (Os(VIII)) catalysed oxidation of L-phenylalanine (L-Pal) by diperiodatoargentate(III) (DPA) in aqueous alkaline medium at 27 °C and a constant ionic strength of 0.25 mol dm^?3 was studied spectrophotometrically. The involvement of free radicals was observed in the reactions. The reaction between DPA and L-Pal in alkaline medium exhibits stoichiometry as [L-Pal]:[DPA] = 1:1. The reaction is of first order in [Os(VIII)], [Ru(III)] and [DPA] and has negative fractional order in [IO₄ ^?]. It has less than unit order in [L-Pal] and [OH^?]. However, the order in [L-Pal] and [OH^?] changes from first order to zero order as their concentrations increase. The main oxidation products were identified by spot test and spectral studies. The probable mechanisms were proposed and discussed. The catalytic constant (K _c) was also calculated for Os(VIII) and Ru(III) catalysis at different temperatures. The activation parameters with respect to slow step of the mechanisms were computed and discussed and thermodynamic quantities were also calculated. It has been observed that the catalytic efficiency for the present reaction is in the order of Os(VIII) > Ru(III). The active species of catalyst and oxidant have been identified.     

Ru(III)/Os(VIII) Catalysed Oxidation of Gabapentin (Neurotin) Drug by Diperiodatoargentate(III) in Aqueous Alkaline Medium (Stopped Flow Technique): A Comparative Study

The kinetics of ruthenium(III) (Ru(III)) and osmium(VIII) (Os(VIII)) catalysed oxidation of neuroleptic drug, gabapentin (GBP) by diperiodatoargentate(III) (DPA) in alkaline medium at 27 °C and a constant ionic strength of 0.60 mol dm^?3 was studied spectrophotometrically. The oxidation products in both the cases are 1-(hydroxymethyl) cyclohexane acetic acid and Ag(I). The stoichiometry is the same in both the catalysed reactions i.e. [gabapentin]:[DPA] = 1:1. The reaction is of first order in Os(VIII)/Ru(III) and [DPA] and has less than unit order in both [GBP] and [alkali]. The oxidation reaction in alkaline medium has been shown to proceed via a Os(VIII)/Ru(III)-gabapentin complex, which further reacts with one mole of monoperiodatoargentate(III) (MPA) species in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test and spectroscopic studies. The reaction constants involved in the different steps of the mechanism are calculated. The catalytic constant (K _c) was also calculated for both catalysed reactions at different temperatures. From the plots of log K _c versus 1/T, values of activation parameters with respect to the catalyst have been evaluated. The activation parameters with respect to slow step of the mechanism are computed and discussed and thermodynamic quantities are also determined. It has been observed that the catalytic efficiency for the present reaction is in the order of Os(VIII)>Ru(III). The probable active species of catalyst and oxidant have been identified.     

A novel ∈-lysine acylase from <Emphasis Type="Italic">Streptomyces mobaraensis</Emphasis> for synthesis of <Emphasis Type="Italic">N∈</Emphasis>-acyl-<Emphasis Type="SmallCaps">l</Emphasis>-lysines

A novel ∈-lysine acylase (N ₆-acyl-l-lysine amidohydrolase; EC 3.5.1.17) was isolated from Streptomyces mobaraensis and purified to homogeneity by SDS-PAGE from the culture broth. The purified enzyme was monomeric, with a molecular mass of approximately 60 kDa. The enzyme was inactivated by the presence of 1,10-phenanthroline and activated in the presence of Co²⁺ and Zn²⁺. The enzyme showed a pH optimum of 8.0 and was stable at temperatures of up to 50°C for 1 h at pH 8.0. The enzyme specifically catalyzed the hydrolysis of the amide bond of various N∈-acyl-l-lysines. Furthermore, the enzyme efficiently catalyzed the synthesis of N∈-acyl-l-lysines with fatty and aromatic acyl groups in an aqueous buffer. In the syntheses of N∈-decanoyl-l-lysine, N∈-lauroyl-l-lysine, and N∈-myristoyl-l-lysine, the product precipitated and the yield was 90% or higher using 10 mM FA and 0.5 M l-lysine as the substrate.     

Homonuclear tris-dithiocarbamato ruthenium(III) complexes as single-molecule precursors for the synthesis of ruthenium(III) sulfide nanoparticles

Tris(N-phenyldithiocarbamato) ruthenium(III) complexes, [Ru(L¹)₃] (1); tris(N-(4-methylphenyl)dithiocarbamato)) ruthenium(III), [Ru(L²)₃] (2); and tris(N-(4-methoxyphenyl)dithiocarbamato)) ruthenium(III), [Ru(L³)₃] (3) were synthesized and characterized by elemental analysis, thermogravimetric analysis, FTIR, UV–VIS and NMR spectroscopy. TGA analyses show major degradation of all complexes in the range 120–350°C, leading to the formation of residual weight corresponding to ruthenium (III) sulfides. The ¹H-NMR spectra of the ligands and complexes are in agreement with the proposed structures. FTIR studies confirmed that the ligands coordinate the Ru³⁺ ion in a bidentate chelating mode. The complexes were thermolysed at 180°C to prepare hexadecylamine-capped Ru₂S₃ nanoparticles. Powder X-ray diffraction patterns revealed the formation of hexagonal-phase Ru₂S₃ nanoparticles with average crystallite sizes ranging from 8.3 to 9.5?nm. TEM images showed the crystalline clusters with shapes ranging from square to hexagonal, while SEM images elucidated that the particles were agglomerated. Energy-dispersive X-ray spectra confirmed the presents of Ru₂S₃ nanoparticles.     

Osmium(VIII) catalyzed oxidation of a sulfur containing amino acid—a kinetics and mechanistic approach

The kinetics of osmium (VIII) catalyzed oxidation of DL-methionine by hexacyanoferrate(III) (HCF) in aqueous alkaline medium at a constant ionic strength of 0.50 mol dm^?3 was studied spectrophoto-metrically. The reaction between hexacyanoferrate(III) and DL-methionine in alkaline medium exhibits 2:1 stoichiometry (2HCF:DL-methionine). The reaction is of first order each in [HCF] and [Os(VIII)], less than unit order in [alkali] and zero order for [DL-methionine]. The decrease in dielectric constant of the medium increases the rate of the reaction. The added products have no effect on the rate of reaction. The main products were identified by spot test. A free radical mechanism has been proposed. In a prior equilibrium step Os(VIII) binds to OH^? species to form a hydroxide species and reacts with [Fe(CN)₆]^3? in slow step to form an intermediate species(C₁). This reacts with a molecule of DL-methionine in a fast step to give the sulfur radical cation of methionine and yields the sulfoxide product by reacting with another molecule of [Fe(CN)₆]^3?. The rate constant of the slow step of the mechanism is calculated. The activation parameters with respect to slow step of the mechanism are evaluated and discussed.     

Kinetics of graft copolymerization of poly(hexanedioic acid ethylene glycol) and methyl acrylate initiated by potassium diperiodatocuprate(III)

A redox system, potassium diperiodatocuprate(III) [DPC]/poly(hexanedioic acid ethylene glycol) (PEA) system, was employed to initiate graft copolymers of methyl acrylate (MA) and PEA in alkaline medium. The results indicate that the equation of the polymerization rate (R_p) is as follows: R_p = k [MA]^1.62[Cu(III)]^0.69, and that the overall activation energy of graft polymerization is 42.5 kJ/mol. The total conversion at different conditions (concentration of reactants, temperature, concentration of the DPC, and reaction time) was also investigated. The infrared spectra proved that the graft copolymers were synthesized successfully. Some basic properties of the graft copolymer were studied by instrumental analyses, including thermogravimetry and scanning electron microscope. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2376–2381, 2007     

Separation and Spectrophotometric Determination of Osmium(IV) and Ruthenium(III) with O-methoxyphenyl Thiourea as Chromogenic Legand: Sequential Separation of Osmium(IV), Ruthenium(III), and Platinum(IV)

A precise and selective method has been developed for extraction spectrophotometric determination of osmium(IV) and ruthenium(III) using o-methoxyphenyl thiourea (OMePT) as a chromogenic ligand. The basis of the proposed methods are osmium(IV)-OMePT complex was formed in 0.8 mol L^?1 at room temperature while ruthenium(III)-OMePT complex was formed in 3.4 mol L^?1 aqueous hydrochloric acid media after 5.0 min heating in boiling water bath. The osmium(IV)-OMePT and ruthenium(III)-OMePT complex were measured at 518 and 640 nm against the reagent blank, respectively. Complexes were also extracted in 10 mL chloroform and showed comparable absorbance values. Beer’s law was obeyed up to 110.0 μg mL^?1 for osmium(IV)-OMePT complex and up to 50.0 μg mL^?1 for ruthenium(III)-OMePT complex. Molar absorptivity and Sandell’s sensitivity of osmium(IV)-OMePT and ruthenium(III)-OMePT complexes were 2.12 × 10³ L mol^?1 cm^?1, 0.089 μg cm^?2 and 2.34 × 10³ L mol^?1 cm^?1, 0.043 μg cm^?2, respectively. The stoichiometry of osmium(IV)-OMePT and ruthenium(III)-OMePT complex was 1:1 and 1:2, respectively. Stability of osmium(IV)-OMePT complex was > 8 days and that of ruthenium(III)-OMePT complex was > 48 h. The proposed method was successfully applied for determination of osmium(IV) and ruthenium(III) from synthetic mixtures corresponding to platinum-osmium alloy and fissium alloy, respectively. The method was successfully applied for sequential separation of osmium(IV), ruthenium(III), and platinum(IV).     

Biocatalytic synthesis of some chiral drug intermediates by oxidoreductases

Chiral intermediates were prepared by biocatalytic processes with oxidoreductases for the chemical synthesis of some pharmaceutical drug candidates. These include: (i) the microbial reduction of 1-(4-fluorophenyl)-4-[4-(5-fluoro-2-pyrimidinyl)-1-piperazinyl]-1-butanone (1) to R-(+)-1-(4-fluorophenyl)-4-[4-(5-fluoro-2-pyrimidinyl)-1-piperazinyl]-1-butanol (2) [R-(+)-BMY 14802], an antipsychotic agent; (ii) the reduction of N-4-(1-oxo-2-chloroacetyl ethyl) phenyl methane sulfonamide (3) to the corresponding chiral alcohol (4), an intermediate for d-(+)-N-4-{1-hydroxy-2-[(-methylethyl)amino]ethyl}phenyl methanesulfonamide [d-(+) sotalol], a β-blocker with class III antiarrhythmic properties; (iii) biotransformation of Nɛ-carbobenzoxy (CBZ)-l-lysine (7) to Nɛ-CBZ-l-oxylysine (5), an intermediate needed for synthesis of (S)-1-[6-amino-2-{[hydroxy(4-phenylbutyl)phosphinyl]oxy}1-oxohexyl]-l-proline (ceronapril), a new angiotensin converting enzyme inhibitor (6) and (iv) enzymatic synthesis of l-β-hydroxyvaline (9) from α-keto-β-hydroxyisovalerate (16). l-β-Hydroxyvaline (9) is a key chiral intermediate needed for the synthesis of S-(Z)-{[1-(2-amino-4-thiazolyl)-2-{[2,2-dimethyl-4-oxo-1-(sulfooxy)-3-azetidinyl] amino}-2-oxoethylidene]amino}oxyacetic acid (tigemonam) (10), an orally active monobactam.     

Kinetic,Mechanistic and Spectral Investigation of Ruthenium(III) Catalysed Oxidation of Atenolol by Alkaline Diperiodatonickelate(IV) (Stopped Flow Technique)

The kinetics of ruthenium(III) catalysed oxidation of atenolol by diperiodatonickelate(IV) (DPN) in alkaline medium at a constant ionic strength of 1.0 mol dm^–3 has been studied spectrophotometrically using a rapid kinetic accessory. The reaction exhibits 1:1 stoichiometry (DPN:atenolol). The reaction shows first order dependence on [DPN] and [Ruthenium(III)] and apparent less than unit order dependence each in atenolol and alkali concentrations. Addition of periodate has no effect on the rate of reaction. Effect of added products, ionic strength and dielectric constant of the reaction medium have been investigated. The main products were identified by IR, NMR, fluorimetry and mass spectral studies. The results suggest the formation of a complex between the atenolol and ruthenium(III) species which reacts with one mole of diperiodatonickelate(IV) species in a rate determining step, resulting in the formation of a free radical, which in a subsequent fast step yields the products. The reaction constants involved in the mechanism were evaluated. The activation parameters were computed with respect to the slow step of the mechanism and discussed.     

Enzymatic synthesis of N-acyl-l-amino acids in a glycerol-water system using acylase I from pig kidney

N-Medium- and long-chain acyl-l-amino acids were enzymatically synthesized from the corresponding l-amino acids and fatty acids using a reverse hydrolysis. Enzymes that are suitable for the synthetic reaction of N-acyl-l-amino acids were screened on the basis of hydrolytic activity toward N-lauroyl-l-glutamic acid as an indicator. Acylase I from pig kidney (EC 3.5.1.14) showed the highest N-acyl-l-amino acid hydrolytic activity among 57 commercially available enzymes tested. Acylase I effectively catalyzed the synthesis of N-lauroyl-l-amino acids except for N-lauroyl-l-proline and N-lauroyl-l-tyrosine in a glycerol-water system. Under the optimized reaction conditions, N-lauroyl-l-arginine and N-lauroyl-l-glutamic acid were obtained in conversions of 82 and 44%, respectively. The equilibrium constants calculated from the conversion obtained were 5.6, 15.4, 18.0, and 39.4 for the syntheses of N-lauroyl-l-glutamic acid, N_α-lauroyl-l-lysine, N-lauroyl-l-glutamine, and N-lauroyl-l-methionine, respectively. N-Acyl-l-arginines with myristic acid and palmitic acid as the fatty acid were also synthesized using acylase I.     

Investigation of electron-transfer reaction between alkaline hexacyanoferrate(III) and ranitidine hydrochloride – a histamine H2 receptor antagonist,in the presence of homogenous ruthenium(III) catalyst

The ruthenium(III)-catalyzed electron-transfer reaction between hexacyanoferrate(III) and ranitidine hydrochloride is studied in alkaline medium at 25°C and at an ionic strength of 1.10?mol/dm³. The reaction stoichiometry is established and is found to be 1:4, that is, for the oxidation of one mole of ranitidine, four moles of hexacyanoferrate(III) are consumed. The reaction products were characterized by spectral studies such as IR, GC-MS, ¹H-NMR and ¹³C-NMR. The reaction rate shows a less than unit order in substrate and alkali and a first-order dependence in oxidant, [Fe(CN)₆]^3? and the catalyst, ruthenium(III) concentrations. The active species of ruthenium(III), [Ru(H₂O)₅OH]²⁺, forms an intermediate complex with the substrate. The attack of complex by hexacyanoferrate(III) in the rate determining step produces a radical cation, which is further oxidized in the subsequent step to form the oxidation product. The effect of the reaction environment on the rate constant upon adding varying concentrations of KNO₃ and t-butanol was studied. The initially added products did not have any significant effect on the reaction rate. A plausible mechanism is proposed based on the experimental results. The effect of varying temperature on the reaction rate was also studied. The activation parameters for the slow step and the thermodynamic quantities for the equilibrium steps were evaluated.

The mechanism of title reaction has been studied and one mole of ranitidine consumes four moles of [Fe(CN)₆]^3?, as shown in the following equation:     

Novel homogeneous Salen Mn(III) catalysts synthesized from dialdehyde or diketone with o-aminophenol for catalyzing epoxidation of alkenes

A series of novel non-salicylaldehyde based Salen ligands have been synthesized from the condensation of dialdehyde or diketone with o-aminophenol and the corresponding manganese(III) complexes prepared by further coordination of them with . FT-IR, UV–Vis spectra, chemical analysis and the structure optimized by Hartree-Fork/3-21G+ all indicated that the qualities of these novel Mn complexes were relative to their molecular structures. More specifically, glyoxal based Mn complex 2c, which was similar to the traditional Mn(III)-salicylethylenediamine, had a short carbon chain and non geometrical constraint of the aliphatic bridge in the two o-aminophenol, and its quality was the best when compared to glutaraldehyde, 2,4-pentanedione and 1,3-cyclohexanedione based Salen Mn(III) complexes (3c, 4c and 5c). And it was also the excellent catalyst for the epoxidations of several non-functionalized alkenes with molecular oxygen/sacrificial-isobutyaldehyde, PhI(OAc)₂ or H₂O₂ as oxidant.     

Studies on solvent extraction of La(III) using [A336][NO3–] and modeling by statistical analysis and neural network

Solvent extraction of La(III) from acidic nitrate medium has been studied with [A336][NO₃^–] in kerosene. The factors affecting the extraction of La(III) like equilibration time, nitrate ion, extractant and La(III) concentrations, aqueous acidity, O/A ratio variation, nature of diluent, and temperature have been investigated. McCabe-Thiele diagram has been plotted to find out the actual number of theoretical stages needed for complete extraction of lanthanum. The solvent has been successfully regenerated for further use after stripping of the metal. IR studies of [A336][NO₃^–] and La(III) loaded [A336][NO₃^–] have been carried out. Modeling of extraction data has been done using Multiple linear regression analysis and Artificial Neural Network, and the performances have been compared. Error in each case was evaluated in terms of R² and Root mean squared error (RMSE). Maximum extraction of La(III) was 82% when 0.6 M [A336][NO₃^–] was used for extraction. About 98% of the metal has been recovered using 0.2 M HNO₃ as stripping agent. Extractive separation of La(III) and Sm(III) was maximum (β = 65.2) using 0.1 M [A336][NO₃^–]. IR studies revealed formation of lanthanum complex in the extraction process. Artificial Neural Network proved to be better over Multiple linear regression in data prediction.     

Extraction of iridium(III) by ion-pair formation with 2-octylaminopyridine in weak organic acid media

To extract iridium(III), various physicochemical parameters were studied. 2-Octylaminopyridine was used for the extraction of iridium(III) from acetate medium at 8.5 pH. Quantitative extraction of iridium(III) was achieved via ion-pair formation of cation [2-OAPH⁺] and anion [Ir(CH₃COO)₄]^?. The stripping of iridium(III)-laden organic phase was carried out 2 M HCl (3 × 10 mL) . The stoichiometry of the extracted ion–pair complex was found to be 1:4:1 (metal: acetate: extractant). The extracted species [2-OAPH⁺. Ir(CH₃COO)₄^?] is assumed to be an ion association product of [Ir(CH₃COO)₄] ^? and [2-OAPH]⁺. The proposed method was successfully used in the separation of iridium(III) from binary and ternary mixtures. Analysis of various alloy samples was also carried out.     

Synthesis and characterization of biodegradable polylactides and polylactide-block-poly(Z-lysine) copolymers

The reaction of (R,R)-trans-1,2-bis(2,4,6-triisopropylbenzenesulfonamidato)cyclohexane (^RRTBSC-H₂, 1) with MN[Si(CH₃)₃] in tetrahydrofuran (THF) produces [(^RRTBSC)₂M₄(THF)₄] (2: M = Li, 3: M = Na, 4: M = K). Experimental results show that all three complexes 2-4 are active toward the ring-opening polymerization of l-lactide and compound 2 efficiently catalyzes the polymerization of l-lactide in the presence of a variety of alcohols in a controlled fashion with very narrow polydispersity index. In addition, a variety of biodegradable poly(l-lactide)-block-poly(N_ξ-carbobenzyloxy-l-lysine) block copolymers with different ratios have also been synthesized using poly(l-lactide) containing amino chain end (PLLA-NH₂) as a macroinitiator.     

Solvent extraction separation and spectrophotometric determination of ruthenium(III) with p-methylphenyl thiourea: sequential separation of ruthenium,osmium and iron

ABSTRACT

A selective and sensitive solvent extraction and spectrophotometric study of the ruthenium(III)–p-methylphenyl thiourea (PMPT) system is presented. The optimum conditions were determined by a critical study of acid concentration, reagent concentration, equilibration period, heating time and effect of solvent on the equilibrium. Ruthenium(III) forms 1:1 complex with PMPT in 20% ethanol and extracted into chloroform. Conformity to Beer’s law at 600 nm was observed up to 40 µg mL^–1 of ruthenium. Molar absorptivity and Sandell’s sensitivity were found to be 2.31 × 10³ L mol^?1cm^?1 and 0.044 μg cm^?2, respectively. The detection limits were 0.11 μg mL^?1 of ruthenium. The method is free from interferences from large number of cations and anions. Proposed method was successfully applied to the separation and determination of ruthenium from synthetic alloys, catalyst and water samples. Sequential separation and determination method for ruthenium(III), osmium(VIII) and iron(II) has been developed.     

Effect of sulfite on reduction kinetics of Fe(III)NTA chelate

The reduction of Fe(III)NTA (ferric ion coordinated to nitrilotriacetic acid) by sulfite has been found to be first-order with respect to Fe(III)NTA and of order minus one with respect to Fe(II)NTA (one of the reaction products). The order of reaction with respect to HSO^?₃ has been determined to be unity when the molar ratio of Na₂SO₃ to total Fe(III) is less than five. In this paper, the role of sulfite in the reduction scheme is reconsidered, and the reduction rate expression in which the coordination of Fe³⁺ to HSO^?₃ is incorporated, is newly presented. The proposed rate equation covers all reaction data for molar ratios of Na₂SO₃ to total Fe(III) in the range of 1 to 25.     

Photopolymerization of Methyl Methacrylate Sensitized by Tris(2,2′-bipyridine)iron(III)

The photopolymerization of methyl methacrylate (MMA) sensitized by tris(2,2′-bipyridine)iron(III ) complex, [Fe(bpy)₃]³⁺, was studied at 35°C in the presence of an electron donor, triethylamine (TEA) with UV radiation of wavelength 254nm. The initial rate of polymerization, R_p, shows a linear dependence on [MMA] with an exponential value of 1·18±0·04. R_p varies linearly with the square root of the photosensitizer concentration up to 2·00×10^-4moll^-1, and above this concentration, R_p decreases with the increase of photosensitizer concentration. The rate of polymerization is not affected by the concentration of the co-initiator, [TEA]. A suitable mechanism for the reaction is proposed to explain the kinetics of the reaction. © 1997 SCI.