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Comparative study of kinetics of catalysed oxidation of glucose and galactose by hexacyanoferrate (III) ion and copper sulphate in alkaline medium.

Introduction

Carbohydrates are one of three basic macronutrients needed to sustain life (the other two are proteins and fats). Carbohydrates serve as energy stores, fuels, and metabolic intermediate in biosynthesis. They also involve in the transport of energy and their derivatives include many important bimolecular that play key roles in the immune system, fertilization, pathogenesis, blood clotting, and development. [1] The kinetics of oxidation of sugars has been subject of extensive research in recent years. This is due to the increasing economic and biological importance of carbohydrate to living organisms. The oxidation of reducing sugar have been carried out in acidic and alkaline medium using such oxidants as transition metals ions, inorganic acids, organometallic complexes and enzymes [2].

Oxidation occurs under different conditions of pH, temperature and ionic strength giving products that depend on the reaction conditions used [3] The Kinetics and thermodynamics of glucose oxidase catalyzed oxidation reaction of glucose was studied over different reaction conditions. [4] kinetics and mechanism of Mn(ii) catalyzed oxidation of DArabinose and D-xylose by chromium(vi) ions in perchloric acid medium was also reported. [5] Oxidation of reducing sugars (aldo and keto hexoses) by alkaline potassium ferricyanide was carried out to study kinectics and transformation. [6]

The objective of this project work is to compare the kinetics of catalytic oxidation of two monosaccharides (glucose and galactose) with two oxidants (hexacyanoferrate (III) and copper sulphate) in alkaline medium under the different condition of substrate concentration, oxidant concentration, ionic strength, pH and temperature on the rate of oxidation of glucose and galactose.

Experimental:

Chemical reagents of analytical grade, obtained from Merck and BDH. They were used as received and where necessary, some chemical reagents were subjected to further purification.

Stock solutions of the sugars as well as the oxidant were prepared using distilled water. Also fresh solutions of buffer were prepared for use when needed.

Instrumentation

The instrument used for this experiment includes a UV-visible spectrophotometer (Camspec M106), a thermostat, and pH-meter (Crison micropH 2000). The weighing balance (Mettler P165) was also used to measure the entire chemical reagent used and thermometer (0-120[degrees]C) was used to check the temperature.

Kinetic Measurement:

The reaction rates was measure with different flasks containing each solution of the oxidants, substrates, catalysts, KN[O.sub.3] and buffer solution were arranged in a water bath. The water bath was allowed to attain a constant temperature of 40[degrees]C. The oxidation reaction was initiated by mixing requisite quantities of the sugar solution and a mixture containing the oxidant, potassium nitrate, buffer solution and the catalyst. The kinectics of oxidation reaction were followed spectrophotometrially reported The absorbance which changes with time was recorded at at 600nm and 420nm for copper sulphate and hexacyannoferrate(III). All kinetic measurement was made under pseudo first order condition with the concentration of subsrate in large excess relative to the oxidant concentration for each of the reaction. [7]

Results and Discussion

The general kinetics features observed with the sugars (glucose and galactose) used are similar.The values of [k.sub.obs] were determined from the slopes of the plot of log absorbance against time, Figure 1a-b shows such plot for glucose / hexacyannoferrate(III) and galactose/ hexacyannoferrate(III) reactions respectively. The values of [k.sub.obs] in each sugar-xidant reaction as shown in table 1 increases with increase in sugar concentration .This agree with literature reports.[8] The second order rate constant ([k.sub.2]) was obtained from the slope of linear plot of pseudo- first order rate constant, [k.sub.obs] against substrate concentration table 2. The order of the reactivity of the sugars are glucose > galactose for copper sulphate as oxidant and galactose > glucose for hexacyannoferrate(III) as oxidant Similar result where [k.sub.2] relative result of two substrate was affected by different oxidant. [3] The results in table 3 also show that the rates of the reaction are enhanced by the increase in pH of the reaction medium. This is in agreement with literature report [9]. The salt effect of KN[O.sub.3] as shown in table 4, increase the rate of the reaction as the salt increases suggesting that the reaction takes place between ions of similar charges. [10]

For the catalysed oxidation of sugars, the positive effect of catalysis was observed with [Cu.sup.2+] as catalyst in the reaction of galactose,but not in glucose with hexacyannoferrate(III) as oxidant table 5a. This positive effect of [Cu.sup.2+] on sugar oxidation was reported. [11] On the other hand [Cr.sup.3+] inhibit reaction of both substrate with copper sulphate as the oxidant as shown in table 5b.The different in the catalytic ability of [Cu.sup.2+] and [Cr.sup.3+] has also being reported [12].

[FIGURE 1a OMITTED]

The oxidation of sugars was carried out at different temperatures from 40 - 50[degrees]C. The pseudo first order rate constants increased with increased with increase in temperature The thermodynamic parameters are given in table 7a-b. show that that the reactions of glucose with each of the oxidants give a higher Ea than that of galactose. This indicate that much energy has to be surmounted for the reaction of glucose for both oxidant used. In reaction involves glucose higher value of [DELTA][H.sup.#] was observed. The [DELTA][S.sup.#] is negative in all the reactions,. [4,9]

References

[1.] Matthews, C.E., K.E. Van Holde and K.G. Ahern, 1999. Biochemistry. 3rd edition. Benjamin Cummings.

[2.] Singh, H.S., A. Gupta and A.K. Singh, 1998. "Oxidation of reducing sugars by osmium tetroxide in alkaline medium''. Transition metal chemistry journal, 23: 277-281.

[3.] Odebunmi, E.O. and H. Marufu, 1999. "Kinetics and mechanism of oxidation of D- glucose and D-sorbitol by KMn[O.sub.4] and Hexachloroirridate (iv)", Nigerian journal of Science, 33: 134-143.

[4.] Odebunmi, E.O. and S.O. Owalude, 2005. "Kinetics and mechanism of oxidation of sugars by chromium in perchloric acid medium" J, Chem. Soc. Nigeria, 30(2): 187-191.

[5.] Ogunlaja, A.S., E.O. Odebunmi and S.O. Owalude, 2009. "Kinetics and mechanism of Mn (II) catalyzed oxidation of D-Arabinose and D-xylose by chromium (vi) ions in perchloric acid medium". The pacific journal of Science and Technology, 10(1): 451-461.

[6.] Krinshna, K.V. and P.J.P. Rao, 1995. "Oxidation of reducing sugars by hexacyanoferate(III) in alkaline medium and Lobry de Bruyn transformation". Transition Metals Chemistry, 20: 344-346.

[7.] Odebunmi, E.O. and S.O. Owalude, 2005. "Kinetics and Mechanism Of Oxidation of Sugar by Chromium(VI) in Perchloric Acid Medium", J. Chemistry Society, Nigeria, 30(2): 187-191.

[8.] Mahmood, T., Q. Haque, I. Mahmood, Asghar S. Ali and Z.T. Maqsood, 2009. "Study of the non-catalyzed molecular reaction of reducing sugars". Journal of Scientia Iranica of chemistry and Chemical Engineering, 16(1): 22-28.

[9.] Okoro, H.K. and E.O. Odebunmi, 2009. "Kinetics and Mechanism of Oxidation of Sugar and Sugar Alcohols by KMn[O.sub.4]". Int.J. of physical chem., 4(9): 471-479.

[10.] Shashikala, V. and K.S. Rangappa, 2002. "A novel mechanism for the oxidation of erythroseries pentoses and hexoses by n-arylbromosulphona-mides in alkaline medium" Journal of Carbohydrate Chemistry, 21(3): 219-234.

[11.] Renata, T.I., M.P. Elonice, F.M. Marina and A.M. Ferreira, 1999. ''Kinetics of the degradative Oxidation of Sugar- type ligands Catalysed by copper(II) ions. Departmento de Quimica Fundemental, Brazil.

[12.] Fasanya, S.O., 2009. "Kinectics of Catalysed Oxidation of Maltose and Xylose by Hexacyanoferrate(III) ion in alkaline buffer solution'' Unpublished M.Sc. thesis, Depertiment of ChemistryUniversity of Ilorin, Ilorin, Nigeria, pp: 44-60.

Okeola F.O., Odebunmi E.O. and Olagoke O.A. Chemistry Department University of Ilorin Ilorin,nigeria

Okeola F.O., Odebunmi E.O. and Olagoke O.A.: Comparative Study of Kinetics of Catalysed Oxidation of Glucose and Galactose by Hexacyanoferrate (III) Ion and Copper Sulphate in Alkaline

Corresponding Author

Okeola F.O., Chemistry Department University of Ilorin Ilorin,nigeria Email: okeolaf@yahoo.com; okeola.of@unilorin.edu.ng Phone Number: +2348058749768, +2348038626501
Table 1: Effect of Variation of Substrate Concentration on the rate
of oxidation by Fe[(CN).sub.6.sup.-3] anCuS[O.sub.4] at 40[degrees]C,
pH=9.3

Concentration of substrate x   [K.sub.obs] x
[10.sup.-2] (M)                [10.sup.-3][s.sup.-1]

                               Glucose

                               Fe[(CN).sub.6.sup.3-]    CuS[O.sub.4]

2                              2.39                     2.94
4                              2.41                     3.92
6                              2.54                     5.10
8                              2.92                     6.50
10                             3.30                     10.62

Concentration of substrate x   [K.sub.obs] x
[10.sup.-2] (M)                [10.sup.-3][s.sup.-1]

                               Galactose

                               Fe[(CN).sub.6.sup.3-]    CuS[O.sub.4]

2                              1.40                     1.83
4                              4.31                     3.32
6                              4.64                     4.20
8                              5.32                     5.14
10                             7.40                     8.13

Table 2: Second Order Rate Constant of Sugar at 40[degrees]C,
pH==9.3,

Oxidant                 Sugar        [k.sub.2][dm.sup.3]
                                     [mol.sup.-1][s.sup.-1]

CuS[O.sub.4]            Glucose      89.72
                        Galactose    72.10
Fe[(CN).sub.6.sup.3-]   Glucose      11.65
                        Galactose    65.05

Table 3: Effect of pH on its Rate of Oxidation at 40[degrees]C

        CuS[O.sub.4]

pH      Glucose                Galactose

        [k.sub.obs] x          [k.sub.obs] x
        [10.sup.-3]            [10.sup.-3]
        [S.sup.-1]             [S.sup.-1]

9.60    3.84                   3.23
10.0    4.42                   3.91
10.6    5.85                   4.70
11.0    7.93                   7.39
11.2    9.34                   8.20

        Fe[(CN).sub.6.sup.-3]

pH      Glucose                Galactose

        [k.sub.obs] x          [k.sub.obs] x
        [10.sup.-3]            [10.sup.-3]
        [S.sup.-1]             [S.sup.-1]

9.60    2.38                   1.60
10.0    2.40                   1.71
10.6    2.45                   1.82
11.0    2.64                   1.86
11.2    3.54                   1.92

Table 4: Effect of Ionic Strenght on Rate of its Oxidation of
Substrate at 40[degrees]C sugar conc. 0.02M pH 9.3

                    CuS[O.sub.4]

[KN[O.sub.3]] (M)   Glucose                 Galactose
                    [K.sub.obs] x           [K.sub.obs] x
                    [10.sup.-][3s.sup.-1]   [10.sup.-][3s.sup.-1]

0.03                3.41                    2.53
0.06                3.64                    3.45
0.09                5.23                    5.01
0.12                7.24                    6.30
0.15                9.81                    7.98

                    Fe[(CN).sub.6.sup.-3]

[KN[O.sub.3]] (M)   Glucose                 Galactose
                    [K.sub.obs] x           [K.sub.obs] x
                    [10.sup.-][3s.sup.-1]   [10.sup.-][3s.sup.-1]

0.03                3.90                    3.82
0.06                4.42                    4.33
0.09                5.20                    5.12
0.12                5.29                    5.20
0.15                5.40                    5.71

Table 5a: Result of sugar oxidation by Fe[(CN).sub.6.sup.-3]
with Cu(II) ion catalyst at 40[degrees]C

Concentration (M)      [K.sub.obs] [10.sup.-3][S.sup.-1]

                       Catalysed Glucose      Uncatalysed Glucose

0.02                   1.83                   2.20
0.04                   1.90                   2.34
0.06                   2.15                   2.71
0.08                   2.43                   3.10
0.10                   2.64                   3.18

Concentration (M)      [K.sub.obs] [10.sup.-3][S.sup.-1]

                       Catalysed Galactose    Uncatalysed Galactose

0.02                   1.49                   1.40
0.04                   5.00                   4.31
0.06                   5.13                   4.64
0.08                   7.51                   5.32
0.10                   7.74                   7.40

Table 5b: Result of sugar oxidation by CuS[O.sub.4]
with Cr(III) ion catalyst at 40[degrees]C

Concentration (M)      [K.sub.obs] x ]10.sup.-3] [S.sup.-1]

                       Catalysed Glucose      Uncatalysed Glucose

0.02                   2.30                   2.94
0.04                   2.74                   3.92
0.06                   3.00                   5.10
0.08                   3.42                   6.50
0.10                   3.93                   10.6

Concentration (M)      [K.sub.obs] x ]10.sup.-3] [S.sup.-1]

                       Catalysed Galactose    Uncatalysed Galactose

0.02                   1.80                   1.83
0.04                   1.92                   3.32
0.06                   2.10                   4.20
0.08                   2.28                   5.14
0.10                   2.44                   8.13

Table 6a: Effect of Temperature on Rate of its Oxidation by
CuS[O.sub.4] sugar conc. 0.02M pH = 9.3 [KN[O.sub.3]] = 0.2M

Temperature    [Glucose]                   [Galactose]
([degrees]C)   [k.sub.obs] x               [K.sub.obs] x
               [10.sup.-3][S.sup.-1]       [10.sup.-3][S.sup.-1]

40             2.71                        2.00
50             3.54                        2.02
60             4.23                        2.08
70             6.50                        2.20
80             7.81                        2.39

Table 6b: Effect of Temperature on Rate of its Oxidation by
Fe[(CN).sub.6.sup.-3] sugar conc. 0.02M pH = 9.3 [KN[O.sub.3]] = 0.2M

Temperature    [Glucose]                   [Galactose]
([degrees]C)   [k.sub.obs] x [10.sup.-3]   [K.sub.obs] x [10.sup.-3]
               [S.sup.-1]                  [S.sup.-1]

40             1.83                        1.00
50             2.41                        1.11
60             2.62                        1.24
70             3.50                        1.38
80             4.29                        1.51

Table 7a: Arrhenius And Thermodynamic Activation Parameter For The
Oxidation Of Sugars By CuS[O.sub.4] at 40[degrees]C sugar conc. 0.02M
pH = 9.3 [KN[O.sub.3]] = 0.2M

Substrate    Ea KJ[mol.sup.-1]   A [dm.sup.3]      [DELTA]
                                 [mol.sup.-1]      [H.sup.#]
                                 [s.sup.-1]        KJ[mol.sup.-1]

Glucose      124.5               0.68              -2477
Galactose    13.40               0.07              -2588

Substrate    [DELTA]             [DELTA]
             [S.sup.#]           [G.sup.#]
             KJ[mol.sup.-1]      KJ[mol.sup.-1]

Glucose      -248.3              75.24
Galactose    -267.2              81.04

Table 7b: Arrhenius And Thermodynamic Activation Parameter For The
Oxidation Of Sugars By Hexacyannoferrate (III) at 40[degrees]C sugar
conc. 0.02M pH = 9.3 [KN[O.sub.3]] = 0.2M

Substrate    Ea KJ[mol.sup.-1]    A [dm.sup.3]     [DELTA]
                                  [mol.sup.-1]     [H.sup.#]
                                  [s.sup.-1]       KJ[mol.sup.-1]

Glucose      63.18                0.10             -2539
Galactose    12.30                0.10             -2589

Substrate    [DELTA]              [DELTA]
             [S.sup.#]            [G.sup.#]
             KJ[mol.sup.-1]       KJ[mol.sup.-1]

Glucose      -243.32              73.62
Galactose    -243.16              73.52
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Title Annotation:Original Article
Author:Okeola, F.O.; Odebunmi, E.O.; Olagoke, O.A.
Publication:Advances in Environmental Biology
Article Type:Report
Geographic Code:6NIGR
Date:Sep 1, 2010
Words:2371
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