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Interaction of 2-aminopyrimidine with dichloro-[I-alkyl-2-(naphthylazo) imidazole]palladium(II) complexes: kinetic and mechanistic studies.

Ghosh PK, Saha S, Mahapatra A - Chem Cent J (2007)

Bottom Line: Heterocyclic compounds are found widely in nature and are essential to many biochemical processes.Addition of LiCl to the reaction does not influence its rate.The activation parameters, Delta(double dagger)H degrees and Delta(double dagger)S degrees, were determined and support the kinetic rate data.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemistry, Jadavpur University, Kolkata, India. jupradip@yahoo.com

ABSTRACT

Background: The anticancer properties of cisplatin and palladium(II) complexes stem from the ability of the cis-MCl2 fragment to bind to DNA bases. However, cisplatin also interacts with non-cancer cells, mainly through bonding molecules containing -SH groups, resulting in nephrotoxicity. This has aroused interest in the design of palladium(II) complexes of improved activity and lower toxicity. The reaction of DNA bases with palladium(II) complexes with chelating N,N'donors of the cis-MCl2 configuration constitutes a model system that may help explore the mechanism of cisplatin's anticancer activity. Heterocyclic compounds are found widely in nature and are essential to many biochemical processes. Amongst these naturally occurring compounds, the most thoroughly studied is that of pyrimidine. This was one of the factors that encouraged this study into the kinetics and mechanism of the interaction of 2-aminopyrimidine (2-NH2-Pym) with dichloro-[1-alkyl-2-(alpha-naphthylazo)imidazole]palladium(II) [Pd(alpha-NaiR)Cl2, 1] and dichloro-[1-alkyl-2-(beta-naphthylazo)imidazole]palladium(II) [Pd(beta-NaiR)Cl2, 2] complexes where the alkyl R = Me (a), Et (b), or Bz (c).

Results: 2-NH2-Pym reacts with 1a, 1b, and 1c to yield [[1-alkyl-2-(alpha-naphthylazo)imidazole]bis(2-aminopyrimidine)]palladium(II) (3a, 3b, 3c) dichloride and with 2a, 2b, and 2c to yield [[1-alkyl-2-(beta-naphthylazo)imidazole]bis(2-aminopyrimidine)]palladium(II) (4a, 4b, 4c) dichloride in an acetonitrile (MeCN) medium. The products were characterized using spectroscopic techniques (FT-IR, UV-Vis, NMR). The ligand substitution reactions follow second order kinetics - first order dependence on the concentration of the Pd(II) complex and 2-NH2-Pym. Addition of LiCl to the reaction does not influence its rate. The thermodynamic parameters (standard enthalpy of activation, Delta(double dagger)H degrees and standard entropy of activation, Delta(double dagger)S degrees) were determined from variable temperature kinetic studies. The magnitude of the second order rate constant, k2, at 298 K, was shown to increase thus: b

Conclusion: The kinetics of the reaction between Pd(II) complexes (1 and 2) and 2-NH2-Pym were examined spectrophotometrically at 530 nm in MeCN under pseudo-first-order conditions. The reaction rate is largely influenced by the pi-acidity of the chelating ligand, with substitution in the naphthyl azoimidazole backbone influencing the rate of the substitution process. The activation parameters, Delta(double dagger)H degrees and Delta(double dagger)S degrees, were determined and support the kinetic rate data.

No MeSH data available.


Plot of Δ‡H0 versus Δ‡S0, i.e., iso-kinetic plot for the reactions: Pd(R/aiR)Cl2 + 2-NH2-Pym in MeCN.
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Figure 6: Plot of Δ‡H0 versus Δ‡S0, i.e., iso-kinetic plot for the reactions: Pd(R/aiR)Cl2 + 2-NH2-Pym in MeCN.

Mentions: The reaction rate increases with temperature as expected from the Eyring equation. Activation parameters, standard enthalpy of activation (Δ‡H°) and standard entropy of activation (Δ‡S°) was calculated using Eyring plots (Figures 4 and 5), which are recorded in Table 2. The activation parameter values support the experimental k2-values. The order for the Δ‡H° and Δ‡S° values is : b > a > c and 1 > 2. The iso-kinetic plot (Figure 6) suggests an identical mechanism as that for the reaction of Pd(N,N/)Cl2 with 2-NH2-Pym. Kinetic studies in the presence of externally added Cl- ions (LiCl) reveal that the rate as well as kobs almost remain unchanged with variation of [Cl-]0 when all other variants are constant, thus supporting the mechanism outline (see Scheme 2). The dissociation of the first Pd-Cl bond is the rate-determining step, and is therefore not affected by externally Cl- ion as LiCl. The reaction product was isolated and characterized as [Pd(N,N/)(2-NH2-Pym)2](ClO4)2.


Interaction of 2-aminopyrimidine with dichloro-[I-alkyl-2-(naphthylazo) imidazole]palladium(II) complexes: kinetic and mechanistic studies.

Ghosh PK, Saha S, Mahapatra A - Chem Cent J (2007)

Plot of Δ‡H0 versus Δ‡S0, i.e., iso-kinetic plot for the reactions: Pd(R/aiR)Cl2 + 2-NH2-Pym in MeCN.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2194761&req=5

Figure 6: Plot of Δ‡H0 versus Δ‡S0, i.e., iso-kinetic plot for the reactions: Pd(R/aiR)Cl2 + 2-NH2-Pym in MeCN.
Mentions: The reaction rate increases with temperature as expected from the Eyring equation. Activation parameters, standard enthalpy of activation (Δ‡H°) and standard entropy of activation (Δ‡S°) was calculated using Eyring plots (Figures 4 and 5), which are recorded in Table 2. The activation parameter values support the experimental k2-values. The order for the Δ‡H° and Δ‡S° values is : b > a > c and 1 > 2. The iso-kinetic plot (Figure 6) suggests an identical mechanism as that for the reaction of Pd(N,N/)Cl2 with 2-NH2-Pym. Kinetic studies in the presence of externally added Cl- ions (LiCl) reveal that the rate as well as kobs almost remain unchanged with variation of [Cl-]0 when all other variants are constant, thus supporting the mechanism outline (see Scheme 2). The dissociation of the first Pd-Cl bond is the rate-determining step, and is therefore not affected by externally Cl- ion as LiCl. The reaction product was isolated and characterized as [Pd(N,N/)(2-NH2-Pym)2](ClO4)2.

Bottom Line: Heterocyclic compounds are found widely in nature and are essential to many biochemical processes.Addition of LiCl to the reaction does not influence its rate.The activation parameters, Delta(double dagger)H degrees and Delta(double dagger)S degrees, were determined and support the kinetic rate data.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemistry, Jadavpur University, Kolkata, India. jupradip@yahoo.com

ABSTRACT

Background: The anticancer properties of cisplatin and palladium(II) complexes stem from the ability of the cis-MCl2 fragment to bind to DNA bases. However, cisplatin also interacts with non-cancer cells, mainly through bonding molecules containing -SH groups, resulting in nephrotoxicity. This has aroused interest in the design of palladium(II) complexes of improved activity and lower toxicity. The reaction of DNA bases with palladium(II) complexes with chelating N,N'donors of the cis-MCl2 configuration constitutes a model system that may help explore the mechanism of cisplatin's anticancer activity. Heterocyclic compounds are found widely in nature and are essential to many biochemical processes. Amongst these naturally occurring compounds, the most thoroughly studied is that of pyrimidine. This was one of the factors that encouraged this study into the kinetics and mechanism of the interaction of 2-aminopyrimidine (2-NH2-Pym) with dichloro-[1-alkyl-2-(alpha-naphthylazo)imidazole]palladium(II) [Pd(alpha-NaiR)Cl2, 1] and dichloro-[1-alkyl-2-(beta-naphthylazo)imidazole]palladium(II) [Pd(beta-NaiR)Cl2, 2] complexes where the alkyl R = Me (a), Et (b), or Bz (c).

Results: 2-NH2-Pym reacts with 1a, 1b, and 1c to yield [[1-alkyl-2-(alpha-naphthylazo)imidazole]bis(2-aminopyrimidine)]palladium(II) (3a, 3b, 3c) dichloride and with 2a, 2b, and 2c to yield [[1-alkyl-2-(beta-naphthylazo)imidazole]bis(2-aminopyrimidine)]palladium(II) (4a, 4b, 4c) dichloride in an acetonitrile (MeCN) medium. The products were characterized using spectroscopic techniques (FT-IR, UV-Vis, NMR). The ligand substitution reactions follow second order kinetics - first order dependence on the concentration of the Pd(II) complex and 2-NH2-Pym. Addition of LiCl to the reaction does not influence its rate. The thermodynamic parameters (standard enthalpy of activation, Delta(double dagger)H degrees and standard entropy of activation, Delta(double dagger)S degrees) were determined from variable temperature kinetic studies. The magnitude of the second order rate constant, k2, at 298 K, was shown to increase thus: b

Conclusion: The kinetics of the reaction between Pd(II) complexes (1 and 2) and 2-NH2-Pym were examined spectrophotometrically at 530 nm in MeCN under pseudo-first-order conditions. The reaction rate is largely influenced by the pi-acidity of the chelating ligand, with substitution in the naphthyl azoimidazole backbone influencing the rate of the substitution process. The activation parameters, Delta(double dagger)H degrees and Delta(double dagger)S degrees, were determined and support the kinetic rate data.

No MeSH data available.


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