Coordination Tendency of Some Biologically Important Zwitterionic

Article pubs.acs.org/jced

Coordination Tendency of Some Biologically Important Zwitterionic Buffers toward Metal Ion Nucleotide Complexes at Different Temperatures Hassan A. Azab* and Zeinab M. Anwar Chemistry Department, Faculty of Science, Suez Canal University Ismailia, Egypt ABSTRACT: The formation of binary and ternary complexes of Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Ca(II), Mg(II), and Pd(II) with 4-morpholinoethane sulfonic acid (MES), 2-(cyclohexylamino)ethane sulfonic acid (CHES), and 3-[(N-tris)-(hydroxymethyl)methyl (amino)]-2-hydroxypropanesulfonic acid (TAPSO) as zwitterionic buffers and guanosine 5′-monophosphate (5′-GMP), inosine 5′-monophosphate (5′-IMP), and uridine 5′-monophosphate (5′-UMP) has been studied potentiometrically in the temperature range (288.15 to 318.15) K and at ionic strength I = 0.1 mol·dm−3 (KNO3). Initial estimates of the formation constants of the resulting species and the dissociation constants of the studied ligands have been refined with the SUPERQUAD computer program. The experimental conditions were selected such that self-association of the nucleotides and their complexes was negligibly small; that is, the monomeric and protonated complexes were studied.

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INTRODUCTION Many early buffer systems, for example, phosphate buffers, were not suitable for biological applications. In 1966, Good et al,1 described a set of zwitterionic buffers suitable for biological reactions. Ferguson et al.2 synthesized some zwitterionic buffers as the hydroxyl derivatives of Good’s buffer. Such buffers have better chemical stability and improved solubility over Good’s buffer. Ternary complexes containing nucleotides and zwitterionic buffers have received much attention during the past decade because of their importance in biological systems. They provide useful information in understanding the specific and selective interactions that take place in many biochemical processes. Azab et al.3−13 studied the interaction of metal ions with nucleic acid components and zwitterionic buffers, forming mixed ligand complexes via potentiometric measurements. Herrero and Terron14,15 examined the interaction of some metal ions with nucleotides at different temperatures. In continuation of the previous work on ternary complexes of metal ions with biologically important ligands the mixed ligand complexes of the type M(II) + nucleotides (Nu) + zwitterionic buffers (Z) have been investigated by potentiometric pH titration to determine the formation constants of the normal and protonated mixed ligand complexes formed in solution at different temperatures.

TAPSO to verify/determine the purity; for acidic/basic contaminants the purity averaged 99.5 % for the three compounds, with a standard deviation of 0.05 %. The nucleotides [guanosine 5′-monophosphate (5′-GMP), inosine 5′-monophosphate (5′IMP), and uridine 5′-monophosphate (5′-UMP)] were obtained from Sigma and were used without further purification. The nucleotide solutions were freshly prepared by dissolving the required amount of the solid in deionized water to avoid hydrolysis. The exact concentration of the nucleotides was checked using potentiometric titration. Copper nitrate Cu(NO 3 ) 2 ·6H 2 O, cobalt nitrate Co(NO3)·6H2O, nickel nitrate Ni(NO3)·6H2O, manganese nitrate Mn(NO3)2·6H2O, zinc nitrate Zn(NO3)2·6H2O, magnesium nitrate Mg(NO3)2·6H2O, calcium nitrate Ca(NO3)·6H2O, and palladium nitrate Pd (NO3)2·6H2O, nitric acid, and KOH were from Merck P.a. Stock solutions were prepared using distilled, CO2 free water. The concentration of KOH used for the titrations was determined by titration with a standard solution of potassium hydrogen phthalate (Merck AG). The concentration was found to be 0.0384 ± 0.00004 mol·dm−3 on the basis of three replicate measurements. HNO3 solutions were prepared and standardized potentiometrically with tris(hydroxymethyl) aminomethane on the basis of three replicate measurements; the concentration was found to be 0.0040 ± 0.00005 mol·dm−3. The ESAB2M Computer program was used for this refinement.16 The concentrations of the metal ion stock solution were determined by titration with ethylenediaminetetraacetic

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EXPERIMENTAL SECTION Materials and Solutions. Reagent grade 4-morpholinoethane sulfonic acid (MES), 2-(cyclohexylamino)ethane sulfonic acid (CHES), and 3-[(N-tris)-(hydroxymethyl)methyl(amino)]-2hydroxypropanesulfonic acid (TAPSO) were obtained from Sigma Chemical Co. (St. Louis, MO). Potentiometric pH titration was used to determine the molecular weight of MES, CHES, and © 2012 American Chemical Society

Received: July 25, 2012 Accepted: September 11, 2012 Published: September 24, 2012 2890

dx.doi.org/10.1021/je300830k | J. Chem. Eng. Data 2012, 57, 2890−2895

Journal of Chemical & Engineering Data

Article

acid disodium salt (EDTA).17 The concentration of the metal ions was found to be 0.0010 ± 0.00004 mol·dm−3. Apparatus. Potentiometric pH measurements were performed on the solutions in a double-walled glass vessel at (288.15, 298.15, 308.15, and 318) K with a commercial fisher combined electrode, and a magnetic stirrer was used. A Fisher Accumet pH/ion meter model 325MP was used. The temperature was controlled using a thermostat. Procedure. The test solution was titrated with standard CO2free KOH. The electrodes were calibrated, in both the acidic and the alkaline regions, by titrating 0.01 mol·dm−3 nitric acid with standard potassium hydroxide under the same experimental conditions. The concentration of free hydrogen ion CH+ at each point of the titration is related to the measured electromotive force (emf) E of the cell by the Nernst equation.

E = E° + Q log C H+

Table 2. Dissociation Constants of Nucleotides at Different Temperaturesa,b pKa2

a

308.15 K

318.15 K

5′-GMP 5′-IMP 5′-UMP

9.80 ± 0.02 9.15 ± 0.03 6.18 ± 0.02

9.48 ± 0.02 9.10 ± 0.03 6.36 ± 0.02

9.19 ± 0.02 9.06 ± 0.03 6.52 ± 0.02

8.95 ± 0.02 8.90 ± 0.03 6.68 ± 0.02

I = 0.1 mol·dm−3 KNO3. bRefers to three times standard deviation.

where Eobs and Ecalc refer to the measured potential and that calculated from eq 1. The weighting factor Wi is defined as the reciprocal of the estimated variance of the measurement .

RESULTS AND DISCUSSION The acidity constants of the studied nucleotides 5′-GMP, 5′IMP, and 5′-UMP and the zwittereionic buffers MES, CHES, and TAPSO are determined at four temperatures (288.15, 298.15, 308.15, and 318.15) K in aqueous medium and at constant ionic strength I = 0.1 mol·dm−3 KNO3. The data are collected in Tables 1 and 2. The structures of the studied ligands are shown in Scheme 1.

Wi = 1/σ 2 = 1/[σE2 + (δE /δV )2 σV2]

pKa2 Z

288.15 K

298.15 K

308.15 K

318.15 K

MES CHES TAPSO

6.19 ± 0.02 9.80 ± 0.02 7.69 ± 0.02

6.05 ± 0.02 9.56 ± 0.02 7.60 ± 0.02

5.89 ± 0.02 9.35 ± 0.02 7.45 ± 0.02

5.75 ± 0.02 8.95 ± 0.02 7.35 ± 0.02


Formation constants for the binary and ternary complexes were refined with SUPERQUAD computer program.18 The constants were refined by minimizing U defined by:

∑ Wi (Eobs − Ecalc)2

(3)

where σE and σV are the estimated variances of the potential and volume readings, respectively. The quality of the fit was judged by the values of the sample standard deviation S and the goodness of fit χ2 (Pearson’s test). At σE = 0.1 mV (0.001 pH errors) and σV = 0.005 mL, the values of S in different sets of titrations were between 1.0 and 1.8, and χ2 was between 12.0 and 13.0. The scatter of residuals (Eobs − Ecalc) versus pH was reasonably random, without any significant systematic trends, thus indicating a good fit of experimental data. At the experimental pH values used in the calculations in this work, the interfering effects of hydroxy complexes are negligible. Thus, the secondary ligand Z combines with the binary M(II)− nucleotide complex (1:1) to form the corresponding ternary M(II)−nucleotide−Z (1:1:1) complexes. The initial estimates of the formation constants of normal complexes formed in solutions have been determined using the Irving and Rossotti formula.19,20 The formation constants of the binary M(II)−zwitterionic buffers (Z) are collected in Tables 3, 4, and 5. All of the complexes formed between the divalent metal ions and MES are of the normal type. For all of the temperatures studied the stability constants of Mg complexes are higher than those of Ca.

Table 1. Dissociation Constants of Zwitterionic Buffers at Different Temperaturesa,b

i

298.15 K

(1)

■

U=

288.15 K

Scheme 1. Structure of the Studied Ligands

where E° is a constant which included the standard the potential of the glass electrode and Q is the slope of the glass electrode response. The value of E° for the electrode was determined from a Gran plot derived from a separate titration of nitric acid with standard KOH solution under the same temperature and medium conditions as these for the test solution titration. The results so obtained were analyzed by the nonlinear leastsquares computer program ESAB2M16 to refine E° and the autoprotolysis constant of water KW. During these calculations, KW was refined until the best value for Q was obtained. The results obtained indicated the reversible Nernstian response of the glass electrode used. The solutions titrated can be presented according to the following scheme: HNO3, HNO3 + nucleotide (a); HNO3 + nucleotide + M(II) (b); HNO3 + zwitterionic buffer (c); HNO3 + zwitterionic buffer + M(II) (d), and HNO3 + nucleotide + zwitterionic buffer + M(II) (e). A constant ionic strength was obtained with 0.1 mol·dm−3 KNO3, and the total volume was kept constant at 25.0 cm.3

a

Nu

(2) 2891



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For M(II)−CHES complexes the formation constants of Cu, Ni, and Zn cannot be calculated due to precipitation at nearly low pH values during titration through all of the running experiments in the temperature range (288.15 to 318.15) K. The formation constants of Co complexes are higher than those for Mn, while Ca complexes acquire high stability than Mg for all of the temperatures studied. Pd shows relatively high formation constants, and the value increases with temperature elevation. The formation constants of M(II)−nucleotides binary complexes are calculated and collected in Tables 6, 7, and 8.

Table 3. Formation Constants of M(II)−MES Binary Complexes in a 1:1 Ratio at Different Temperaturesa,b log KM(MES)

a

M(II)

288.15 K

298.15 K

308.15 K

318.15 K

Cu(II) Ni(II) Co(II) Mn(II) Zn(II) Ca(II) Mg(II) Pd(II)

4.71 ± 0.02 3.18 ± 0.02 3.37 ± 0.02 3.20 ± 0.02 3.40 ± 0.03 4.28 ± 0.02 3.80 ± 0.02

4.90 ± 0.02 3.55 ± 0.02 3.45 ± 0.02 3.48 ± 0.02 3.80 ± 0.02 4.21 ± 0.02 3.77 ± 0.02

5.10 ± 0.02 3.94 ± 0.02 3.56 ± 0.02 3.90 ± 0.02 4.28 ± 0.02 4.16 ± 0.02 3.76 ± 0.02 4.07 ± 0.02

5.29 ± 0.02 4.15 ± 0.02 3.66 ± 0.02 4.12 ± 0.02 4.80 ± 0.02 4.12 ± 0.02 3.75 ± 0.02 4.77 ± 0.02

Table 7. Formation Constants of M(II)−5′-IMP Binary Complexes in a 1:1 Ratio at Different Temperaturesa,b


log KM(5′‑IMP)

Table 4. Formation Constants of M(II)−CHES Binary Complexes in a 1:1 Ratio at Different Temperaturesa,b log KM(CHES) M(II) Cu(II) Ni(II) Co(II) Mn(II) Zn(II) Ca(II) Mg(II) Pd(II) a

288.15 K

298.15 K

308.15 K

318.15 K

4.72 ± 0.02 4.52 ± 0.02

4.58 ± 0.02 4.93 ± 0.02

4.47 ± 0.02 4.29 ± 0.02

4.38 ± 0.02 4.20 ± 0.02

4.54 ± 0.02 4.54 ± 0.02 4.63 ± 0.03

4.64 ± 0.02 4.28 ± 0.02 4.78 ± 0.03

4.69 ± 0.02 4.10 ± 0.02 4.94 ± 0.03

4.76 ± 0.02 3.88 ± 0.02 5.09 ± 0.02

a

M(II)

288.15 K

298.15 K


2.90 ± 0.02 1.56 ± 0.02 2.04 ± 0.02 1.80 ± 0.03 2.01 ± 0.02 1.01 ± 0.02 1.20 ± 0.02 3.36 ± 0.02

3.40 ± 0.02 2.95 ± 0.02 2.65 ± 0.02 2.35 ± 0.02 2.57 ± 0.02 1.52 ± 0.02 1.69 ± 0.02 3.27 ± 0.02

308.15 K

318.15 K

3.32 ± 0.02 3.30 ± 0.03 3.32 ± 0.02

3.68 ± 0.02 3.90 ± 0.02 4.20 ± 0.02

2.40 ± 0.02 2.42 ± 0.02 3.16 ± 0.02

3.39 ± 0.02 3.20 ± 0.02 3.06 ± 0.02


Table 8. Formation Constants of M(II)−5′-UMP Binary Complexes in a 1:1 Ratio at Different Temperaturesa,b


log KM(UMP)

Table 5. Formation Constants of M(II)−TAPSO Binary Complexes in a 1:1 Ratio at Different Temperaturesa,b log KM(TAPSO)

a

M(II)

288.15 K

298.15 K

308.15 K

318.15 K


4.71 ± 0.02 3.18 ± 0.02 3.37 ± 0.02 3.20 ± 0.02 3.40 ± 0.03 4.28 ± 0.02 3.80 ± 0.02

4.90 ± 0.02 3.55 ± 0.02 3.45 ± 0.02 3.48 ± 0.02 3.80 ± 0.02 4.21 ± 0.02 3.77 ± 0.02

5.10 ± 0.02 3.94 ± 0.02 3.56 ± 0.02 3.90 ± 0.02 4.28 ± 0.02 4.16 ± 0.02 3.76 ± 0.02 4.07 ± 0.02

5.29 ± 0.02 4.15 ± 0.02 3.66 ± 0.02 4.12 ± 0.02 4.80 ± 0.02 4.12 ± 0.02 3.75 ± 0.02 4.77 ± 0.02

a

288.15 K

298.15 K

308.15 K

318.15 K

3.61 ± 0.02 3.16 ± 0.02 2.75 ± 0.02 2.37 ± 0.02 2.65 ± 0.02 1.54 ± 0.02 1.73 ± 0.03 3.60 ± 0.02

3.90 ± 0.02 3.60 ± 0.02 3.12 ± 0.03 2.74 ± 0.02 3.10 ± 0.02 1.64 ± 0.02 1.78 ± 0.02 3.58 ± 0.02

4.19 ± 0.03 4.01 ± 0.02 3.50 ± 0.02 3.15 ± 0.02 3.51 ± 0.02 1.74 ± 0.02 1.82 ± 0.02 3.56 ± 0.02

308.15 K

318.15 K


3.01 ± 0.02 3.48 ± 0.02 3.35 ± 0.03 3.20 ± 0.02 3.01 ± 0.02 1.20 ± 0.02 1.53 ± 0.02 3.09 ± 0.02

3.50 ± 0.02 3.65 ± 0.02 3.55 ± 0.02 3.76 ± 0.02 3.70 ± 0.02 1.31 ± 0.02 1.65 ± 0.02 3.40 ± 0.02

4.05 ± 0.02 3.80 ± 0.02 3.76 ± 0.03 4.38 ± 0.02 4.44 ± 0.02 1.50 ± 0.02 1.75 ± 0.02 3.61 ± 0.02

4.52 ± 0.02 4.04 ± 0.03 3.97 ± 0.02 4.92 ± 0.02 5.14 ± 0.02 1.61 ± 0.02 1.86 ± 0.02 3.90 ± 0.02

Table 9. Formation Constants of M(II)−5′-GMP−MES Ternary Complexes in a 1:1:1 Ratio at Different Temperaturesa,b,c log KM(GMP)(MES)

log KM(5′‑GMP) 3.30 ± 0.02 2.90 ± 0.02 2.35 ± 0.03 2.01 ± 0.02 2.25 ± 0.02 1.44 ± 0.02 1.69 ± 0.03 3.63 ± 0.03

298.15 K

I = 0.1 mol·dm−3 KNO3. bRefers to three times standard deviation for log KM(UMP) of the following equilibria: M(II) + 5′-UMP ⇌ M(II)−5′-UMP.

Table 6. Formation Constants of M(II)−5′-GMP Binary Complexes in a 1:1 Ratio at Different Temperaturesa,b M(II)

288.15 K

a



M(II)

M(II)

288.15 K

298.15 K

308.15 K

318.15 K


4.68 ± 0.02 4.62 ± 0.02 3.89 ± 0.02 3.86 ± 0.02 7.01 ± 0.02 3.96 ± 0.02 4.22 ± 0.02 4.16 ± 0.03

4.30 ± 0.02 4.20 ± 0.02 3.68 ± 0.02 3.70 ± 0.02 6.85 ± 0.02 3.92 ± 0.02 3.97 ± 0.02 3.90 ± 0.03

3.96 ± 0.02 3.81 ± 0.02 3.50 ± 0.02 3.56 ± 0.02 6.70 ± 0.02 3.86 ± 0.02 3.74 ± 0.02 3.66 ± 0.02

3.62 ± 0.02 3.46 ± 0.02 3.30 ± 0.02 3.41 ± 0.02 6.55 ± 0.02 3.82 ± 0.02 3.53 ± 0.02 3.43 ± 0.03

I = 0.1 mol·dm−3 KNO3. bRefers to three times standard deviation. Refers to the formation constant for monoprotonated complex log KM(GMP)(HMES) according to the equilibria M(II) + GMP−2 + HMES+1 ⇌ [M(II)(GMP)(HMES)]+. a c

I = 0.1 mol·dm−3 KNO3. bRefers to three times standard deviation. 2892



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The formation constants of Mg−5′-GMP binary complexes are higher than Ca−5′-GMP in the entire temperature range (288.15 to 318.15) K. The formation constants of ternary complexes of the type Mn−nucleotide−MES are calculated, and the refined data are collected in Tables 9, 10, and 11. For the ternary complex M(II) + 5′ +GMP + MES at all temperatures studied Pd complexes acquire high stability than Ni complexes.

The calculated formation constants for the ternary system M(II)−nucleotide−CHES are collected in Tables 12 to 14. Table 13. Formation Constants of M(II)−5′-IMP−CHES Ternary Complexes in a 1:1:1 Ratio at Different Temperaturesa,b,c,d log KM(I′MP)(CHES)

Table 10. Formation Constants of M(II)−5′-IMP−MES Ternary Complexes in a 1:1:1 Ratio at Different Temperaturesa,b log KM(IMP)(MES) M(II)

288.15 K

298.15 K

308.15 K

318.15 K


3.59 ± 0.02 3.34 ± 0.02 3.34 ± 0.02 3.36 ± 0.02 3.79 ± 0.02 3.78 ± 0.02 3.54 ± 0.02 3.33 ± 0.02

3.68 ± 0.02 3.41 ± 0.02 3.37 ± 0.02 3.37 ± 0.02 3.88 ± 0.02 3.89 ± 0.02 3.59 ± 0.02 3.42 ± 0.02

3.75 ± 0.02 3.44 ± 0.02 3.38 ± 0.02 3.38 ± 0.02 3.95 ± 0.02 4.00 ± 0.02 3.63 ± 0.02 3.50 ± 0.02

3.83 ± 0.02 3.52 ± 0.02 3.39 ± 0.02 3.39 ± 0.02 4.03 ± 0.02 4.09 ± 0.02 3.66 ± 0.02 3.57 ± 0.02

M(II)

288.15 K

298.15 K

308.15 K

318.15 K


5.61 ± 0.02 5.76 ± 0.02 5.71 ± 0.02 5.50 ± 0.02 5.90d ± 0.02 3.11 ± 0.02 5.06 ± 0.02 5.20 ± 0.03

6.00 ± 0.02 5.46 ± 0.02 5.36 ± 0.02 5.06 ± 0.02 5.25d ± 0.02 3.55 ± 0.02 4.86 ± 0.02 5.00 ± 0.03

6.60 ± 0.02 5.23 ± 0.02 5.02 ± 0.02 4.58 ± 0.02 6.85d ± 0.02 3.94 ± 0.02 4.57 ± 0.02 4.89 ± 0.03

6.80d ± 0.02 5.01 ± 0.02 4.57 ± 0.02 4.11 ± 0.02 7.00d ± 0.02 4.32 ± 0.02 4.83 ± 0.02 4.80 ± 0.03

d

d

d

I = 0.1 mol·dm−3 KNO3. bRefers to three times standard deviation. Refers to the formation constant for monoprotanated complex log KM(IMP)(HCHES) according to the equilibria M(II) + IMP−2 + HCHES+1 ⇌ [M(II)(GMP)(HCHES)]+. dRefers to the formation constant for diprotonated complex log KM(HIMP)(HCHES) according to the equilibria M(II) + HIMP−1 + HCHES+1 ⇌ [M(II)(HIMP)(HCHES)]2+. a c

I = 0.1 mol·dm−3 KNO3. bRefers to three times standard deviation for log KM(IMP)(MES) of the following equilibria: M(II)−5′-IMP + MES ⇌ M(II)−IMP−MES. a

Table 14. Formation Constants of M(II)−5′-UMP−CHES Ternary Complexes in a 1:1:1 Ratio at Different Temperaturesa,b,c

Table 11. Formation Constants of M(II)−5′-UMP−MES Ternary Complexes in a 1:1:1 Ratio at Different Temperaturesa,b

log KM(CHES)

log KM(UMP)(MES) M(II)

288.15 K

298.15 K

308.15 K

318.15 K


5.10 ± 0.02 3.95 ± 0.02 4.04 ± 0.02 4.46 ± 0.02 5.38 ± 0.02 2.56 ± 0.02 4.28 ± 0.02 4.57 ± 0.02

4.50 ± 0.02 3.82 ± 0.02 3.80 ± 0.02 4.20 ± 0.02 4.72 ± 0.02 3.02 ± 0.02 4.01 ± 0.02 4.18 ± 0.02

3.97 ± 0.02 3.72 ± 0.02 3.58 ± 0.02 3.81 ± 0.02 4.08 ± 0.02 3.45 ± 0.02 3.76 ± 0.02 3.80 ± 0.02

3.43 ± 0.02 3.62 ± 0.02 3.40 ± 0.02 3.41 ± 0.02 3.48 ± 0.02 3.92 ± 0.02 3.54 ± 0.02 3.44 ± 0.02

318.15 K


11.60 ± 0.02 6.70 ± 0.02 4.88 ± 0.02 5.00 ± 0.02 11.75 ± 0.02 4.98 ± 0.02 4.11 ± 0.02 5.60 ± 0.02

10.52 ± 0.02 5.66 ± 0.02 4.58 ± 0.02 4.62 ± 0.02 10.70 ± 0.03 4.68 ± 0.02 3.95 ± 0.02 5.30 ± 0.02

9.48 ± 0.02 6.70 ± 0.02 4.29 ± 0.02 4.15 ± 0.02 9.60 ± 0.02 4.36 ± 0.02 3.85 ± 0.02 5.00 ± 0.02

8.35 ± 0.02 7.65 ± 0.02 4.03 ± 0.02 3.84 ± 0.02 8.55 ± 0.02 4.11 ± 0.02 3.72 ± 0.02 4.87 ± 0.02

318.15 K

10.70c ± 0.02 8.65c ± 0.02 5.10 ± 0.02 3.90 ± 0.02 10.85c ± 0.02 3.42 ± 0.02 3.65 ± 0.02 3.10 ± 0.02

9.98c ± 0.02 8.26c ± 0.02 5.86 ± 0.02 5.06 ± 0.02 10.18c ± 0.02 3.60 ± 0.02 3.66 ± 0.02 3.20 ± 0.02

9.20c ± 0.03 7.80c ± 0.02 6.55 ± 0.02 6.50c ± 0.02 9.35c ± 0.02 3.77 ± 0.02 3.77 ± 0.02 3.34 ± 0.02

8.35c ± 0.03 7.45c ± 0.02 7.20 ± 0.02 7.55c ± 0.02 8.50c ± 0.02 3.92 ± 0.02 3.86 ± 0.02 3.47 ± 0.02

For the ternary complex M(II) + 5′-GMP + CHES the formation constants of complexes including Zn are higher than those containing Cu. For the ternary complexes M(II) + 5′-IMP + CHES the formation constants of Zn complexes are higher than those of Cu, and the formation constants of such complexes increase with temperature elevation. In case of the ternary complexes M(II) + 5′-UMP + CHES metal ions Cu, Nim and Zn form monoprotonated complexes where the metal ions react first with the nucleotide molecule forming M(II)−5′-UMP binary complex then the secondary ligand reacts with the binary complex without deprotonation forming a M(II)(5′-UMP)(HCHES) monoprotonated complex. The formation constants of M(II)−nucleotide−TAPSO are calculated and refined according to SUPERQUAD computer program; the data are collected in Tables 15 to 17. The normal complex Mg(5′-GMP)(TAPSO) is slightly more stable than Ca(5′-GMP)(TAPSO). For Pd−5′-GMP, the interaction of CHES with this binary complexes is favored at low temperatures, while the reaction of Pd−5′-GMP with MES is

log KM(G′MP)(CHES) 308.15 K

308.15 K


I = 0.1 mol·dm−3 KNO3. bRefers to three times standard deviation. Refers to the formation constant for monoprotanated complex log KM(UMP)(HCHES) according to the equilibria M(II) + UMP−2 + HCHES+1 ⇌ [M(II)(UMP)(HCHES)]+.

Table 12. Formation Constants of M(II)−5′-GMP−CHES Ternary Complexes in a 1:1:1 Ratio at Different Temperaturesa,b,c 298.15 K

298.15 K

c

I = 0.1 mol·dm−3 KNO3. bRefers to three times standard deviation for log KM(UMP)(MES) of the following equilibria: M(II)−5′-UMP + MES ⇌ M(II)−UMP−MES.

288.15 K

288.15 K

a

a

M(II)

M(II)

I = 0.1 mol·dm−3 KNO3. bRefers to three times standard deviation. Refers to the formation constant for monoprotonated complex log KM(GMP)(HCHES) according to the equilibria M(II) + GMP−2 + HCHES+1 ⇌ [M(II)(GMP)(HCHES)]+. a c

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Table 15. Formation Constants of M(II)−5′-GMP−TAPSO Ternary Complexes in a 1:1:1 Ratio at Different Temperaturesa,b,c,d

Table 17. Formation Constants of M(II)−5′-UMP−TAPSO Ternary Complexes in a 1:1:1 Ratio at Different Temperaturesa,b,c

log KM(GMP)(TAPSO)

log KM(UMP)(TAPSO)

M(II)

288.15 K

298.15 K

308.15 K

318.15 K

M(II)

288.15 K

298.15 K

308.15 K

318.15 K

Cu(II)

7.50d ± 0.03 3.55c ± 0.02 6.20d ± 0.03 3.36c ± 0.01 5.70d ± 0.02 3.31c ± 0.01 6.30d ± 0.03 4.06c ± 0.01 6.23d ± 0.03 ppt 6.80d ± 0.02 3.20c ± 0.02 6.75d ± 0.02 3.20c ± 0.01 6.80d ± 0.03 3.15c ± 0.02

6.74d ± 0.03 3.76c ± 0.03 6.67d ± 0.02 3.65c ± 0.01 6.68d ± 0.02 3.62c ± 0.01 6.71d ± 0.02 3.78c ± 0.02 6.70d ± 0.02 ppt 6.71d ± 0.02 3.39c ± 0.02 6.69d ± 0.02 3.48c ± 0.02 6.56d ± 0.02 3.38c ± 0.02

6.20d ± 0.03 ppt 7.01d ± 0.03 ppt 7.80d ± 0.03 ppt 7.10d ± 0.03 3.60c ± 0.01 7.25d ± 0.03 ppt 3.65 ± 0.02

5.40d ± 0.03 ppt 7.40d ± 0.03 ppt 8.80d ± 0.03 ppt 7.50d ± 0.03 3.35c ± 0.01 7.80d ± 0.03 ppt 3.70d ± 0.02


10.50c ± 0.02 3.60c ± 0.02 1.00c ± 0.02 0.50c ± 0.02 3.50c ± 0.02 7.05 ± 0.02 6.95c ± 0.02 2.82 ± 0.02

8.00c ± 0.02 4.10c ± 0.02 2.50c ± 0.02 2.10c ± 0.02 4.20c ± 0.02 5.10 ± 0.02 5.00 ± 0.02 3.05c ± 0.02

5.95c ± 0.02 4.66c ± 0.02 4.19c ± 0.02 4.01c ± 0.02 4.96c ± 0.03 3.28c ± 0.02 3.27c ± 0.02 3.28c ± 0.02

3.81 ± 0.02 5.15c ± 0.02 5.85c ± 0.03 5.74c ± 0.03 5.55c ± 0.03 4.56c ± 0.02 4.66c ± 0.02 3.49c ± 0.02

3.60c ± 0.02

3.80d ± 0.02

3.47d ± 0.02

3.80d ± 0.02

Ni(II) Co(II) Mn(II) Zn(II) Ca(II) Mg(II) Pd(II)

I = 0.1 mol·dm−3 KNO3. bRefers to three times standard deviation. Refers to the formation constant for monoprotonated complex log KM(UMP)(HTAPSO) according to the equilibria M(II) + UMP−2 + HTAPSO+1 ⇌ [M(II)(UMP)(HTAPSO)]+. a c

temperature. The same behavior is obtained for Ca and Mg− UMP. There is no significant effect of temperature on the rate of attack of CHES toward Pd(II)−5′-UMP.

■

I = 0.1 mol·dm−3 KNO3. bRefers to three times standard deviation. Refers to the formation constant for monoprotonated complex log KM(GMP)(HTAPSO) according to the equilibria M(II) + GMP−2 + HTAPSO+1 ⇌ [M(II)(GMP)(HTAPSO)]+. dRefers to the formation constant for diprotonated complex log KM(HGMP)(HTAPSO) according to the equilibria M(II) + HGMP−1 + HTAPSO+1 ⇌ [M(II)(HGMP)(HTAPSO)]2+. a c

*E-mail address: [email protected]. Notes

The authors declare no competing financial interest.

■

Table 16. Formation Constants of M(II)−5′-IMP−TAPSO Ternary Complexes in a 1:1:1 Ratio at Different Temperaturesa,b,c,d 288.15 K

298.15 K

308.15 K

318.15 K


3.80 ± 0.02 3.65 ± 0.02 3.30 ± 0.02 3.15 ± 0.03 8.80c ± 0.02 3.41 ± 0.02 3.40 ± 0.02 6.94d ± 0.02 2.80c ± 0.02

4.20 ± 0.02 3.95 ± 0.02 3.52 ± 0.02 3.38 ± 0.03 7.05c ± 0.02 3.58 ± 0.02 3.78 ± 0.02 6.71d ± 0.02 3.03c ± 0.02

4.76 ± 0.02 4.28 ± 0.02 3.70 ± 0.02 3.65 ± 0.03 5.30c ± 0.02 3.77 ± 0.02 3.96 ± 0.02 4.01 ± 0.02

5.07d ± 0.02 4.60 ± 0.02 3.88 ± 0.02 3.88 ± 0.03 3.39c ± 0.02 4.00 ± 0.02 4.30 ± 0.02 4.20 ± 0.02

d

REFERENCES

(1) Good, N. E.; Winget, G. D.; Winter, W.; Connolly, T. N.; Izawa, S.; Singh, R. M. M. Hydrogen Ion Buffers for Biological Research. Biochemistry 1966, 5, 467. (2) Ferguson, W. J.; Braunschweiger, K. I.; Braunschweiger, W. R.; Smith, J. R.; McCormick, J. J.; Wasmann, C. C.; Jarvis, N. P.; Bell, D. H.; Good, N. E. Hydrogen Ion Buffers for Biological Research. Anal. Biochem. 1980, 104, 300. (3) Anwar, Z. M.; Azab, H. A. Ternary Complexes in Solution. Comparison of the Coordination Tendency of Some Biologically Important Zwitterionic Buffers Towards the Binary Complexes of Some Transition Metal Ions and Some Amino Acids. J. Chem. Eng. Data 1999, 44, 1151−1154. (4) Anwar, Z. M.; Azab, H. A. Role of Biologically Important Zwitterionic Buffer Secondary ligands in the Stability of the Ternary Complexes Containing Some Metal Ions and Guanosine-5′-Monophosphate, Inosine-5′-Monophosphate and Cytidine-5′-Monophosphate. J. Chem. Eng. Data 2001, 46, 34−40. (5) Anwar, Z. M.; Azab, H. A. Ternary Complexes Formed by Trivalent Lanthanide Ions, Nucleotides and Biological Buffers. J. Chem. Eng. Data 2001, 46, 613−618. (6) Azab, H. A.; Anwar, Z. M.; Sokar, M. Metal Ion Complexes Containing Nucleobases and Some Zwitterionic Buffers. J. Chem. Eng. Data 2004, 49, 62−72. (7) Azab, H. A.; Abo El Nour, K. M.; Sherif, S. Metal Ion Complexes Containing Di, Tripeptides and Biologically Important Zwitterionic Buffers. J. Chem. Eng. Data 2007, 52 (2), 381−390. (8) Azab, H. A.; Orabi, A. S.; El Deghidy, F. S.; Said, H. Ternary Complexes of La(III), Ce(III), Pr(III) or Er(III) with Adenosine 5′mono, 5′-di, and 5′-triphosphate as Primary Ligands and Some Biologically Important Zwitterionic Buffers as Secondary Ligands. J. Solution Chem. 2010, 3, 319−334. (9) Azab, H. A.; Al-Deyab, S. S.; Anwar, Z. M.; Kamel, R. M. Potentiometric, Electrochemical, and Fluorescence Study of the Coordination Properties of the Monomeric and Dimeric Complexes of Eu(III) with Nucleobases and PIPES. J. Chem. Eng. Data 2011, 56 (5), 1960−1969.

log KM(IMP)(TAPSO) M(II)

AUTHOR INFORMATION

Corresponding Author

I = 0.1 mol·dm−3 KNO3. bRefers to three times standard deviation. Refers to the formation constant for monoprotonated complex log KM(IMP)(HTAPSO) according to the equilibria M(II) + IMP−2 + HTAPSO+1 ⇌ [M(II)(IMP)(HTAPSO)]+. dRefers to the formation constant for diprotonated complex log KM(HIMP)(HTAPSO) according to the equilibria M(II) + HIMP−1 + HTAPSO+1 ⇌ [M(II)(HIMP)(HTAPSO)]2+. a c

favored at high temperatures. There is a specific interaction of the TAPSO ate toward the binary Ni−5′-GMP and Ni−5′-IMP forming the corresponding ternary complexes. Generally, for Cu, Ni, Co, Mn, Zn, Mg, and Pd the interaction of MES as a secondary ligand with M(II)−5′-UMP is favored at low temperatures, while upon increasing the temperature the rate of attack is decreased except in the case of Ca(II) where the reverse trend is observed. The reaction of CHES with the binary complexes Co−5′UMP via a stepwise mechanism is favored upon increasing 2894



Article

(10) Azab, H. A.; El-Nady, A. M.; Hassan, A.; Azkal, R. S. A. Ternary Complexes in Solution. Comparison of the Coordination Tendency of Some Polybasic Oxygen Acids Towards the Binary Complexes of Cu(II) and Adenosine 5′- mono-, 5′-di-, and 5′-triphoshate. J. Chem. Eng. Data 1993, 38, 502−505. (11) Azab, H. A.; Hassan, A.; El-Nady, A. M.; Azkal, R. S. A. Ternary Complexes of Nickel(II) with AMP, ADP and ATP as Primary Ligands and Some Biologically Important Polybasic Oxygen Acids as Secondary Ligands. Monatsh. Chem. 1993, 124, 267−271. (12) Azab, H. A.; El-Nady, A. M.; Hassan, A.; Azkal, R. S. A. Potentiometric Studies on the Formation Equilibria of Binary and Ternary Complexes of Cobalt (II) with Adenosine 5′-mono-, 5′-di-, and 5′- triphosphate and some biologically important polybasic oxygen acids. Monatsh. Chem. 1994, 125, 1059−1064. (13) Azab, H. A.; Hassan, A.; El-Nady, A. M.; El-Korashy, S. A.; Hamed, M. M. Ternary Complexes of Co(II) with Adenosine 5′-mono-, 5′-di-, and 5′-Triphosphate as Primary Ligands and Some Biologically Important Zwitterionic Buffers as Secondary Ligands. J. Chem. Eng. Data 1995, 40, 83−87. (14) Herrero, L. A.; Terron, A. Complexation in Solution of Magnesium (II) and Cobalt (II) with Purine 5′-monophosphates and Pyrimidine 5′- monophosphates: a Potentiometeic and Calorimetric Study. Polyhedron 1998, 17 (No. 22), 1825−1835. (15) Herrero, L. A.; Terron, A. Interactions in Solution of Zn(II) and Cd(II) with Nucleoside Monophosphates. A Calorimetric Study. Inorg. Chem. Acta 2002, 339, 233−238. (16) De Stefano, C.; Princi, P.; Rigano, C.; Sammartano, S. Computer Analysis of Equilibrium Data in Solution. ESAB2M: An Improved Version of the ESAB Program. Ann. Chim. (Rome) 1987, 77, 643−675. (17) Schwarzenbach, G.; Flaschra, H. Complexometric Titrations; Methuen and Co. Ltd.: London, 1969. (18) Gans, P.; Sabatini, A.; Vacca, A. Superquad: An Improved General Program for Computation of Formation Constants From Potentiometeic Data. J. Chem. Soc., Dalton Trans. 1985, 1195−1200. (19) Irving, H.; Rossotti, H. S. Methods for Computing Successive Stability Constants From Experimental Formation Curves. J. Chem. Soc. 1953, 3397−3405. (20) Irving, H.; Rossotti, H. S. The Calculation of Formation Curves of Metal Complexes from pH Titration Curves in Mixed Solvents. J. Chem. Soc. 1954, 2904−2910.

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Coordination Tendency of Some Biologically Important Zwitterionic

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