Azo‐Coupling Reactions Used in Analytical Chemistry: The Role of Reactants, Intermediates, and Aqueous Medium

Pankratov, A. N.

doi:10.1002/hlca.200490143

Cited by 9 publications

(4 citation statements)

References 37 publications

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“…The results presented in Table 4 show that as in the case considered in [23][24][25][26][27], the density distribution of water molecules in the cell approaches that of water in the liquid state, even if we neglect the fact that part of the cell volume is occupied by the molecular system I -IV . Table 1.…”

Section: Resultsmentioning

confidence: 84%

Tautomerism and Regioselectivity of the Protonation of 2-Pyrrolidone. Stereoselectivity of Complexation between Palladium(II), Chloride Ion, and 2-Pyrrolidone

2005

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Palladium(II) complexes with organic ligands are promising as medicines [1] that interact with functional groups of biological systems to give the corresponding coordination entities [2]. In the study of reactions of the palladium ion with bioligands, its interactions with inorganic compounds contained in an organism's fluids should also be considered. It is not improbable that inorganic ligands (H 2 O , Cl -, etc.) competing with biologically active substances for the metal ion can reduce its toxicity. On the other hand, coordination of inorganic ligands by the metal cation can diminish the efficiency of palladium-based medicines; for this reason, mixed-ligand complexes of palladium(II), in which the opposite trends are more or less counterbalanced, are acceptable as medicines.It is expedient to use the chloride ion as an inorganic ligand since it is contained in biological fluids. For instance, blood plasma is simulated by 0.86% (0.147 mol/l) NaCl, while the gastric juice is simulated by 0.1 M HCl [3].2-Pyrrolidone (2-pyrrolidinone, pyrrolidine-2-one, 2-oxopyrrolidine, and γ -butyrolactam) is a promising ligand for the formation of biologically active complexes with platinum metal cations [4]; 2-pyrrolidone can exhibit lactam-lactim tautomerism [5,6]. In sufficiently acidic media, protonation of 2-pyrrolidone (which is possible both at the N and O atoms) can compete with its coordination by metal cations. In[7], dichlorobis(pyrrolin-2-ol)palladium [Pd ( C 4 H 7 NO ) 4 Cl 2 ] was synthesized by the reaction of palladium(II) chloride with 2-pyrrolidone in aqueous acetone and its crystal and molecular structures were determined by X-ray diffraction analysis [8]. The structure consists of an electrically neutral complex and two 2-pyrrolidone molecules attached to it by intermolecular éç ··· é hydrogen bonds [8]. The most important features of the complexation is the lactim (pyrroline-2-ol) structure of the organic ligand, N-coordination, and the cis -structure of dichlorobis(pyrroline-2-ol)palladium [8].Usually, complexation reactions yield trans -isomeric products [9, 10]. However, it is cis -isomers that are of interest as potential antitumor preparations. For this reason, it is important to explain the stereoselectivity of complexation.The goal of this study was to calculate, by quantumchemical methods, the tautomerism and regioselectivity of the protonation of 2-pyrrolidone in the gas phase and an aqueous solution and to justify the stereoselectivity of the complexation between palladium(II), chloride ion, and pyrroline-2-ol. EXPERIMENTALQuantum-chemical calculations for the gas phase were performed by the AM1 [11] and PM3 methods Abstract -According to the AM1, PM3, HF/6-31G(d,p), and MP2/6-31G(d,p)//HF/6-31G(d,p) calculations, it is the lactam tautomer of 2-pyrrolidone that is thermodynamically most stable in both the gas phase and an aqueous solution. Analysis of the PM3 data with consideration of the medium showed that the tautomeric equilibrium of 2-pyrrolidone (pyrroline-2-ol) in aqueous solution is shift...

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Section: Resultsmentioning

confidence: 84%

Tautomerism and Regioselectivity of the Protonation of 2-Pyrrolidone. Stereoselectivity of Complexation between Palladium(II), Chloride Ion, and 2-Pyrrolidone

2005

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“…In this case, the entropy is frequently identical in the series of isomers of compounds with similar structures while its change is almost constant in analogous reactions involving related compounds with close molecular geometries [20,[26][27][28][29][30][31][32][33].…”

Section: The Symmetrical Hydrogen Bond In [Pd(h 2 O) 3 (H 3 O)] 3+mentioning

confidence: 99%

Ligand Exchange in Pd(II)-NaCl-H2O and Pd(II)-HCl-H2O Systems: Quantum-Chemical Consideration

2005

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The Pd-containing compounds exhibit the biological activity. The variety of the biological properties of the Pd ions and of another platinum-group metals is determined by the chemical and stereochemical properties of coordination compounds of these metals with the biologically active ligands (DNA, amino acids, peptides, etc.) and, in particular, by the structure of the metal-ligand coordination site (fragment or functional group of a biological system) [1]. The Pd(II) complexes with organic ligands are considered to be promising in the production of medicines [2].While studying reactions of the Pd 2+ ion with bioligands, one should take into consideration its interaction with inorganic compounds contained in liquid media of a living organism. It is not improbable that inorganic ligands (H 2 O , Cl -, etc.) can compete with the biologically active ligands for the metal ion and thus reduce toxicity of the latter ion. On the other hand, binding of the metal cation with inorganic ligands can decrease the efficiency of medicines prepared from compounds of this metal. The Pd(II) complexes are known to be bonded by the DNA molecules and to violate ordinary course of the replication process (transcription and translation) [1]. The Pd ( II )-NaCl -H 2 O and Pd ( II )-HCl -H 2 O systems can be used to model the behavior of the Pd(II) compounds in biological liquids. For instance, a 0.86% (0.147 M) solution of NaCl can be used as a model of blood plasma, while a 0.1 M solution of HCl, as that of a gastric juice [3]. The aim of this work was to study the reactions of exchange of the H 2 O and H 3 O + ligands for Cl -in the chloride and hydrogen chloride solutions of Pd(II). EXPERIMENTAL Potassium tetrachloropalladate(II) was synthesized as described in [4] from metallic Pd and Pd ë l 2 . The K 2 [ PdCl 4 ] (0.03067 M) and NaCl (0.1 M) solutions were prepared from the precisely weighed samples; a 0.1 M solution of HCl was prepared from a reagent with fixed concentration.The kinetic studies were carried out using spectrophotometric method. The electronic absorption spectra of the reaction mixtures were recorded on a UV VIS SPECORD spectrophotometer. The working solution of K 2 [ PdCl 4 ] with a concentration of 8.496 × 10 -5 mol/l was prepared by dilution. The initial solution of K 2 [ PdCl 4 ] (3.610 ml) and the solution of 0.1 M NaCl or HCl (20 µ l) were pored into a cell (1 cm) with the aid of a dispenser.The quantum-chemical calculations were performed by ZINDO/1 [5], PM3 [6], and RHF/STO-6G(d) [7] methods with the HyperChem 1 program package and full optimization using the Polak-Ribiere algorithm [8]. The gradient rate did not exceed 0.02 kcal/(mol Å).Abstract -The behavior of potassium tetrachloropalladate(II) in media simulating biological liquids is studied. The rate of aquation in aqueous NaCl solutions is shown to be higher than the rate at which the Cl -ligand enters the inner coordination sphere of the Pd atom. In HCl solutions, the formation of the Pd chloro complexes predominates due to protonation of water molec...

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“…The precise interpretation of the results requires methods appropriate to the calculations of open layers species. Pankratov (2004;2005;2012) reported scientific bases of the analytical characteristics prediction for azo coupling reactions.…”

Section: Introductionmentioning

confidence: 99%

Study of the vibronic coupling in the ground state of Methylthio radical

Int¹

2019

Preprint

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Using a methodology based on the crude adiabatic approximation, we study the complete linear and quadratic vibronic coupling in the ground state of SCH3 radical. In order to build the representation of the hamiltonian, we evaluated 30 integrals intervening in the formulation of the vibronic coupling. Diagonalization of this representation gives the vibronic levels. For the lowest vibronic states, the implied modes are Q1 (symmetric C-S stretching) and Q4 (CH3 rocking). Energy gaps A1-A2 and A2-ε resulting from the splitting due to the Jahn-Teller coupling E e = A1 + A2+ ε are evaluated to 250 and 169 cm-1, respectively. Essential coupling parameters are surrounded to simplify the study of highly vibronic states.

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Azo‐Coupling Reactions Used in Analytical Chemistry: The Role of Reactants, Intermediates, and Aqueous Medium

Cited by 9 publications

References 37 publications

Tautomerism and Regioselectivity of the Protonation of 2-Pyrrolidone. Stereoselectivity of Complexation between Palladium(II), Chloride Ion, and 2-Pyrrolidone

Tautomerism and Regioselectivity of the Protonation of 2-Pyrrolidone. Stereoselectivity of Complexation between Palladium(II), Chloride Ion, and 2-Pyrrolidone

Ligand Exchange in Pd(II)-NaCl-H2O and Pd(II)-HCl-H2O Systems: Quantum-Chemical Consideration

Study of the vibronic coupling in the ground state of Methylthio radical

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