Synthesis,Structure, and Keto-Enol Tautomerism of 3-R<Superscript>1</Superscript>-5,5-R<Superscript>2</Superscript>,R<Superscript>2</Superscript>-6-R<Superscript>3</Superscript>-2,3,5,6-Tetrahydropyran-2,4-diones

Ethyl esters of 2,4-dibromo-2-R¹-4-R²-3-oxopentanoic and -hexanoic acids react with zinc and aliphatic or aromatic aldehydes under the conditions of the Reformatskii reaction to give 3-R¹-5,5-R², R²-6-R³-2,3,5,6-tetrahydropyran-2,4-diones, which are obtained in three forms: keto, enol with enolization of the keto group, and enol with enolization of the ester group. The keto form is isolated by crystallization from a mixture of CCl₄ and petroleum ether; the first enol form, from MeOH, EtOH, and polar aprotic solvents; and the second enol form, from CHCl₃. The second enol form is oxidized in DMSO to form a keto compound containing a hydroxy group at the 3-position of the heteroring.     

Synthesis of Heterocycles from Arylation Products of Unsaturated Compounds: XIII. 5-R<Superscript>1</Superscript>-Benzyl-2-(R<Superscript>2</Superscript>-2-pyridylimino)thiazolidin-4-ones

Meerwein reactions of arenediazonium bromides with methyl and ethyl acrylates gave 3-aryl-2-bromopropionic acid esters which were subjected to cyclocondensation with N-(2-pyridyl)- and N-(6-methyl-2-pyridyl) thioureas to obtain 5-R¹-benzyl-2-(R²-2-pyridylimino)thiazolidin-4-ones. The latter were shown to exist in solution as E isomers of the imino form.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 7, 2005, pp. 1071–1075.Original Russian Text Copyright © 2005 by Matiichuk, Obushak, Tsyalkovskii.     

Oximation of 2-(R<Superscript>1</Superscript>-Amino)-4-(R<Superscript>2</Superscript>-imino)naphthalen-1(4<Emphasis Type="Italic">H</Emphasis>)-ones

The oximation of 2-(R¹-amino)-4-(R²-imino)naphthalen-1(4H)-ones with hydroxylamine hydrochloride in pyridine afforded 2-(R-amino)-4-(hydroxyimino)naphthalen-1(4H)-ones.     

Synthesis of 3-R<Superscript>1</Superscript>-1-R<Superscript>2</Superscript>-1-R<Superscript>3</Superscript>-4a,10b-dihydro-1<Emphasis Type="Italic">H</Emphasis>-chromeno[3,4-<Emphasis Type="Italic">c</Emphasis>]-pyridine-2,4,5-triones by the Reformatskii reaction

The Reformatskii reagents formed from alkyl esters of -bromoacetic, -bromopropanoic, and -bromoisobutyric acids and zinc react with N-arylamides of 2-oxochromene-3-carboxylic acid, yielding 3-R¹-1-R²-1-R³-4a,10b-dihydro-1H-chromeno[3,4-c]pyridine-2,4,5-triones.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 9, 2004, pp. 1516–1519.Original Russian Text Copyright © 2004 by Shchepin, Fotin, Vakhrin, Shurov.This revised version was published online in April 2005 with a corrected cover date.     

Synthesis of nitro,nitroso, azo,and azido derivatives of (4-R<Superscript>1</Superscript>-5-R<Superscript>2</Superscript>-1,2,3-triazol-1-yl)-1,2,5-oxadiazoles by oxidation and diazotization of the corresponding amines

Nitro-, nitroso-, and azo-1,2,5-oxadiazoles with 4-R¹-5-R²-1,2,3-triazol-1-yl substituents were synthesized by oxidation of amino-(1,2,3-triazol-1-yl)-1,2,5-oxadiazoles (aminotriazolylfurazans). Azido-1,2,5-oxadiazole was prepared by diazotization of amino(triazolyl)furazan followed by treatment of the diazonium salt with sodium azide. Depending on the nature of the substituents and the reagent, triazolylfurazans can undergo destruction to give amino-R-furazans (R = NO₂, N₃, aminofurazanylazo), the amino group being formed from the triazole ring. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1859–1865, August, 2005.     

Cation binding by 2<Superscript>1</Superscript>,3<Superscript>1</Superscript>-diphenyl-l <Superscript>2</Superscript>,4<Superscript>2</Superscript>-dioxo-7,10,13-trioxa-1,4(3,1)-diquinoxalina-2 (2,3),3(3,2)-diindolizinacyclopentadecaphane and its acyclic analog

The binding of cations Li⁺, Na⁺, K⁺, Cs⁺, Ag⁺, Zn²⁺, Ni²⁺, Co²⁺, NH₄ ⁺ (group I), H⁺, Mg²⁺, Al³⁺, Ga³⁺ (group II), and Ca²⁺, Pb²⁺ (group III) by 2¹,3¹-diphenyl-l ²,4²-dioxo- 7,10,13-trioxa-l,4(3,1)-diquinoxalina-2(2,3),3(3,2)-diindolizinacyclopentadecaphane (1), which contains two indolizine and two quinoxaline fragments and 3,6,9-trioxaundecanes spacer, and by its acyclic analog (2) was studied using cyclic voltammetry in MeCN/0.1 M Bu₄NBF₄. It was concluded that the ions of group I are not bound by these compounds, the ions of group II exhibit the reversible redox-switched binding by the carbamoyl groups of the quinoxaline fragments, whereas the ions of group III are bound not only by the initial compounds and radical cations 1 and 2, but also by dication 1. This binding of the Ca²⁺ and Pb²⁺ ions stabilizes dication 1.     

Interaction energies of histidine with cations (H<Superscript>+</Superscript>, Li<Superscript>+</Superscript>, Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>, Mg<Superscript>2+</Superscript>, Ca<Superscript>2+</Superscript>)

The imidazol side group of histidine has two nitrogen atoms capable of being protonated or participating in metal binding. Hence, histidine can take on various metal-bound and protonated forms in proteins. Because of its variable structural state, histidine often functions as a key amino acid residue in enzymatic reactions. Ab initio (HF and MP2) calculations were done in modeling the cation (H⁺, Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺) interaction with side chain of histidine. The region selectivity of metal ion complexation is controlled by the affinity of the side of attack. In the imidazol unite of histidine the ring nitrogen has much higher metal ion (as well as proton) affinity. The complexation energies with the model systems decrease in the following order: Mg²⁺ > Ca²⁺ > Li⁺ > Na⁺ > K⁺. The variation of the bond lengths and the extent of charge transfer upon complexation correlate well with the computed interaction energies.     

Thermodynamics of citrate complexation with Mn<Superscript>2+</Superscript>, Co<Superscript>2+</Superscript>, Ni<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript> ions

Isothermal titration calorimetry has been used to determine the stoichiometry, formation constants and thermodynamic parameters (ΔG ^o, ΔH, ΔS) for the formation of the citrate complexes with the Mn²⁺, Co²⁺, Ni²⁺ and Zn²⁺ ions. The measurements were run in Cacodylate, Pipes and Mes buffer solutions with a pH of 6, at 298.15 K. A constant ionic strength of 100 mM was maintained with NaClO₄. The influence of a metal ion on its interaction energy with the citrate ions and the stability of the resulting complexes have been discussed.     

Synthesis of a <Superscript>14</Superscript>C analogue of N-(3,5-dichlorobenzyl)-4-(fluoromethoxy) benzene carboximidamide-[carboxy-<Superscript>14</Superscript>C] as NR2B-selective NMDA receptor antagonist

N-(3,5-Dichlorobenzyl)-4-(fluoromethoxy) benzenecarboximidamide labeled with carbon-14 was prepared from 4-hydroxy-benzonitrile-[cyano-¹⁴C].     

Extraction of metal ions (Fe<Superscript>3+</Superscript>, Co<Superscript>2+</Superscript>, Ni<Superscript>2+</Superscript>, Cu<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript>) using immobilized-polysiloxane iminobis(n-2-aminophenylacetamide) ligand system

A new insoluble solid functionalized ligand system bearing chelating ligand group of the general formula P-(CH₂)₃-N[CH₂CONH(C₆H₄)NH₂]₂, where P represents [Si–O] _n polysiloxane network, was prepared by the reaction of the immobilized diethyliminodiacetate polysiloxane ligand system, P-(CH₂)₃N(CH₂CO₂Et)₂ with 1,2-diaminobenzene in toluene. ¹³C CP-MAS NMR, XPS and FTIR results showed that most ethylacetate groups (–COOEt) were converted into the amide groups (–N–C=O). The new functionalized ligand system exhibits high capacity for extraction and removal of the metal ions (Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) with efficiency of 95–97% after recovery from its primary metal complexes. This functionalized ligand system formed 1:1 metal to ligand complexes.     

Thermodynamic behavior of complexation of 18-crown-6 with Tl<Superscript>+</Superscript>, Pb<Superscript>2+</Superscript>, Hg<Superscript>2+</Superscript>, and Zn<Superscript>2+</Superscript> metal cations in methanol-water binary media

The equilibrium constants and thermodynamic parameters for complex formation of 18-Crown-6 (18C6) with Tl⁺, Pb²⁺, Hg²⁺, and Zn²⁺ metal cations have been determined by conductivity measurements in methanol (MeOH)-water (H₂O) binary solutions. 18-Crown-6 forms 1:1 complexes with Hg²⁺ and Zn²⁺ cations, but in the case of Tl⁺ and Pb²⁺ cations, in addition to 1:1 stoichiometry, 1:2 (ML₂) complexes are formed in some binary solvents. The thermodynamic parameters (ΔH _c⁰ and ΔS _c⁰), which were obtained from the temperature dependences of equilibrium constants, show that in most cases the complexes are enthalpy destabilized but entropy stabilized. Non-linear behavior is observed between the equilibrium constants (log K _f ) of complexes and the composition of the mixed solvent. The selectivity of the ligand for these metal cations is sensitive to the solvent composition, and, in some cases, the selectivity order is reversed in certain compositions of the mixed solvent. The results also show that the mechanism of complexation reactions and the stoichiometry of complexes of some metal cations change with the nature and even with the composition of the mixed solvent. The article was submitted by the authors in English.     

Quantum-Chemical Investigation of Keto-enol-enethiol Tautomerism in 3-oxo-3-R<Superscript>1</Superscript>-N-R<Superscript>2</Superscript>-propanethioamides

The keto-enol-enethiol tautomerism in 3-oxo-3-R¹-N-R²-propanethioamides under vacuum and in acetone was studied in terms of density functional theory. It was established that the equilibrium depends on the structure of the 3-oxo-3-R¹-N-R²-propanethioamides and on the nature of the solvent, but the most stable form is as a rule the keto form stabilized by an intramolecular hydrogen bond. __________ Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 41, No. 5, pp. 272–277, September–October, 2005.     

Complex formation of maleic acid with the Zn<Superscript>2+</Superscript>, Ni<Superscript>2+</Superscript>, Co<Superscript>2+</Superscript>, Cu<Superscript>2+</Superscript> in aqueous solution

The process of complex formation of maleic acid (H₂L) with the ions Zn²⁺, Ni²⁺, Co²⁺, Cu²⁺ was studied by potentiometric titration in a wide range of concentration ratios at 298 K and I = 0.1 mol/l (NaNO₃). The moieties ZnL, CoL, NiL, NiL ₂ ^2? , CuL, and CuL ₂ ^2? were detected and their stability constants were determined.     

An x-ray diffraction study of the reaction products of copper(II) chloride with N<Superscript>1</Superscript>,N<Superscript>2</Superscript>-bis(5-methylpyridin-2-yl)oxalamide

Polymeric complexes of [Cu₂Cl₂L₂]_∞ copper(I) chloride (1) (L = N¹,N²-bis(5-methylpyridin-2-yl)-oxalamide)) and {[Cu₂(C₂O₄)Cl₂L](L)·2H₂O}_∞ copper(II) chloride (2) are obtained. The complexes are studied by powder and single crystal XRD. It is found that during the reaction of L with copper(II) chloride in the formation of complex 1 copper(II) is reduced to copper(I), while the formation of complex 2 is accompanied by the hydrolysis of the ligand.     

Reaction of 3-oxo-3-R<Superscript>1</Superscript>-<Emphasis Type="Italic">N</Emphasis>-R<Superscript>2</Superscript>-propanethioamides with 2-amino-5-R-pyridines

Direction of a reaction between 3-oxo-3-R¹-N-R²-propanethioamides and 2-amino-5-R-pyridines in acetic acid depends on the structure of initial thioamides: at R¹ = Me, R² = Ar, Et 2-methyl-7-R-4H-pyrido[1,2-a]-pyrimidine-4-thiones are obtained, and at R¹ = Ar, R² = Me form 1-methyl-5-(N-methylaminothiocarbonyl)-4,6-diaryl-1,2-dihydropyridine-2-thiones.     

Synthesis of (2<Emphasis Type="Italic">R</Emphasis>,4<Emphasis Type="Italic">R</Emphasis>)-2-alkyl-3-(2-mercaptobenzoyl)thiazolidine-4-carboxylic acids

Basing on natural amino acid L-cysteine, commercially available aliphatic aldehydes, 2-acetylsulfanylbenzoyl chloride and 2,2′-disulfandiyldibenzoyl dichloride a synthesis was developed of (2R,4R)-2-alkyl-3-(2-mercaptobenzoyl)thiazolidine-4-carboxylic acids, potential antihypertensive compounds, inhibitors of angiotensin transforming enzyme.     

The standard thermodynamic characteristics of resolvation of the K<Superscript>+</Superscript>, Ca<Superscript>2+</Superscript>, Cd<Superscript>2+</Superscript>, and Br<Superscript>−</Superscript> ions in water-acetone mixtures

The standard real and chemical thermodynamic characteristics of transfer of the K⁺, Ca²⁺, Cd²⁺, and Br^? ions from water into water-acetone solvents of various compositions were analyzed to study the rules governing the solvation of these ions in mixed solvents and its special features. All calculations were performed within the framework of the vertical jet method at 298.15 K. The energy of resolvation as a function of ion charges and crystallographic radii was found to increase in the series K⁺ < Ca²⁺ < Cd²⁺ < Al³⁺     

Determination of the stability constant and thermodynamic parameters between Tl<Superscript>+</Superscript>, Ag<Superscript>+</Superscript> and Pb<Superscript>2+</Superscript> cations with 2,6-di(furyl-2yl)-4-(4-methoxy phenyl)pyridine as a new synthesis ligand

The complexation reaction between Tl⁺, Ag⁺ and Pb²⁺ cations with 2,6-di(furyl-2yl)-4-(4-methoxy phenyl)pyridine as a new synthesis ligand in acetonitrile (ACN)–H₂O and methanol (MeOH)–H₂O binary solutions has been studied at different temperatures using conductometric method. The conductometric data show that the stoichiometry of the complexes is 1: 1 [M: L] and the stability constant of complexes changes with the binary solutions identity. Also, the structure of the resulting 1: 1 complexes was optimized using the LanL2dz basis set at the B3LYP level of theory using GAUSSIAN03 software. The results show that the change of logK_f for (DFMP.Pb)²⁺ and (DFMP.Ag)⁺ complexes with the mole ratio of acetonitrile and for (DFMP.Ag)⁺ and (DFMP.Tl)⁺ complexes with the mole ratio of methanol have a linear behavior, while the change of logK_f of (DFMP.Tl)⁺complex in ACN–H₂O binary solutions (with a minimum in X_ACN = 0.5) and (DFMP.Ag)⁺ complex in MeOH–H₂O binary solutions (with a minimum in X_MeOH = 0.75) show a non-linear behavior. The selectivity order of DFMP ligand for these cations in mol % CAN = 25 and 75 obtain Tl⁺ > Pb²⁺ > Ag⁺ but in mol % CAN = 50, the selectivity order observe Pb²⁺ > Tl⁺ > Ag⁺. Also, this selectivity sequence of DFMP in MeOH–H₂O (mol % MeOH = 75 and 100) and (mol % MeOH = 50) is obtained Pb²⁺ > Ag⁺ and Tl⁺ > Ag⁺ > Pb²⁺ respectively. The values of thermodynamic parameters show that these values are influenced by the nature and the composition of binary solution. In all cases, the resulting complexes are enthalpy stabilized and entropy destabilized. The TΔS_C^° versus ΔH_C^° plot of all obtained thermodynamic data shows a fairly good linear correlation which indicates the existence of enthalpy-entropy compensation in the complexation reactions.     

Kinetic aspects of the ion-exchange reactions of Cs<Superscript>+</Superscript>, Na<Superscript>+</Superscript>, Sr<Superscript>2+</Superscript>and Eu<Superscript>2+</Superscript> ions on the H<Superscript>+</Superscript> form of chromium hexacyanoferrate(II)

Summary This paper reports the radiochemical study of the ion-exchange of Cs⁺, Na⁺, Sr²⁺ and Eu³⁺ ions with H⁺ by chromium hexacyanoferrate(II) which was prepared in a granular form using a gel method. The slow steps which determine the rate of exchange of these ions are directly proportional to the particle diameter and this is confirmed from the linearity test of Bt vs. t plots at different particle diameters. Boyed’s equation and Reichenberg’s tables were used for evaluating all the kinetic parameters. The results reveal that the effective particle radii are unchanged for both chromium hexacyanoferrate(II) dried at 60 and 120 °C. The obtained data were analyzed using McKay plots and Arrhenius equation and the kinetic and thermodynamic parameters, e.g., effective diffusion coefficient, activation energies and entropies of activation have been evaluated. The mobility of these ions inside the particles of chromium hexacyanoferrate(II) decrease in the order of Eu³⁺>Sr²⁺>Na⁺⊃Cs⁺.     

Specific features of absorption of Cu<Superscript>2+</Superscript>, Zn<Superscript>2+</Superscript>, Co<Superscript>2+</Superscript>, and Pb<Superscript>2+</Superscript> cations from aqueous solutions by calcium phosphates

Kinetic characteristics of the interaction of trisubstituted calcium phosphate Ca₃(PO₄)₂ · xH₂O with Cu²⁺, Zn²⁺, Co²⁺, and Pb²⁺ ions in aqueous solutions were studied.