Spectral-luminescence and acid-base properties of 4,7-diaminocoumarins

The absorption and luminescence spectra of a series of 4,7-diaminocoumarins have been investigated in ethanol and acetonitrile solution. The pk_a ^I and pk_a ^II values for several of the compounds have been measured. It has been found that the site of primary protonation is the nitrogen atom in the 7-position, and that the second protonation reaction occurs at the lactone oxygen atom. The effects of steric and electronic factors on the spectral-luminescence and acid-base characteristics of these compounds are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1610–1618, December, 1990.     

Reactions of 3-iodo-7-dialkylaminocoumarins with secondary amines

The reaction of 3-iodo-7-diethylaminocoumarin and 2,3,6,7-tetrahydro-10-iodo-1H,5H-quinolizino[9,9a,1-gh]coumarin with secondary amines (diethylamine, piperidine, morpholine, imidazole, and benzimidazole) leads to 4,7-diaminocoumarins. The corresponding 3-iodo-4-chloro-7-dialkylaminocoumarins under similar conditions give 3-iodo-4,7-diaminocoumarins. 4-Aminomethyl derivatives of coumarins are formed in the reactions of 3-iodo-4-methyl-7-diethylaminocoumarin and 2,3,6,7-tetrahydro-9-methyl-10-iodo-1H,5H-quinolizino[9,9a,1-gh]coumarin with these secondary amines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 609–618, May, 1991.     

Basicity of 3-formyl-4,7-diaminocoumarins and their azomethine derivatives

The basicity of a series of 3-formyl-4,7-diaminocoumarins and their azomethine derivatives was studied. By using PMR data, it was determined that primary protonation of most aldehydes affects the nitrogen atom in the 7 position and, in the case of azomethines, the nitrogen atom of the azomethine group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 349–352, March, 1993.     

Electronic structure and reactivity of guanylthiourea: A quantum chemical study

Electronic structure analysis of guanylthiourea (GTU) and its isomers has been carried out using quantum chemical methods. Two major tautomeric classes (thione and thiol) have been identified on the potential energy (PE) surface. In both the cases conjugation of pi‐electrons and intramolecular H‐bonds have been found to play a stabilizing role. Various isomers of GTU on its PE surface have been analyzed in two different groups (thione and thiol). The interconversion from the most stable thione conformer ( GTU‐1 ) to the most stable thiol conformer ( GTU‐t1 ) was found to take place via bimolecular process which involves protonation at sulfur atom of GTU‐1 followed by subsequent C? N bond rotation and deprotonation. The detailed analysis of the protonation has been carried out in gas phase and aqueous phase (using CPMC model). Sulfur atom (S1) was found to be the preferred protonation site (over N4) in GTU‐1 in gas phase whereas N4 was found to be the preferred site of protonation in aqueous medium. The mechanism of S‐alkylation reaction in GTU has also been studied. The formation of alkylated analogs of thiol isomers (alkylated guanylthiourea) is believed to take place via bimolecular process which involves alkyl cation attack at S atom followed by C? N bond rotation and deprotonation. The reactive intermediate RS(NH₂)C? N? C(NH₂)₂⁺ belongs to the newly identified ^⊕N(←L)₂ class of species and provides the necessary dynamism for easy conversion of thione to thiol. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Synthesis of 4,7-diamino-3-formylcoumarins and azomethines derived from them

A series of 4,7-diamino-3-formylcoumarins has been synthesized by the reaction of 7-dialkylamino-4-chloro-3-formylcoumarins with primary and secondary amines and by the formylation of 4,7-diaminocoumarins by the Vilsmeier reaction. The corresponding Schiff's bases are formed by reaction with primary amines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 338–348, March, 1993.     

Diazanaphthalenes: A 13C NMR investigation on the site of protonation and pKa values

The pH dependence of the ¹³C chemical shifts (δ) of the diazanaphthalenes has been recorded. From this dependence the pK_a values have been determined using the Henderson-Hasselbach equation. The change in ¹³C chemical shifts under the influence of nitrogen protonation (Δδ) has been predicted using the Δδ values of quinoline and isoquinoline. The correlation between observed and expected Δδ values of the symmetric diazanaphthalenes is very good. Assuming these changes in chemical shifts to be of general validity, the site of protonation in the asymmetric diazanaphthalenes has been determined by comparison of the expected Δδ values for α- and β-nitrogen protonation with the observed ones. The site of protonation for 1,6- and 1,7-naphthyridine is the β-nitrogen atom, whereas for cinnoline both monoprotonated species are present in a significant amount.     

Ion-neutral complexes resulting from dissociative protonation: Fragmentation of <Emphasis Type="Italic">α</Emphasis>-furanylmethyl benzyl ethers and 4-<Emphasis Type="Italic">N,N</Emphasis>-dimethylbenzyl benzyl ethers

The loss of CH₂O during mass spectrometry in two series of α-aromaticmethyl benzyl ether compounds, namely, α-furanylmethyl p-substituted-benzyl ethers and 4-N,N-dimethylbenzyl p-substituted-benzyl ethers, is particularly interesting. The fragmentation mechanism is proposed to involve an ion-neutral complex-mediated pathway. Specifically, before the formation of an ion-neutral intermediate, the proton is transferred from the thermodynamically favored site at either the ether oxygen atom or the nitrogen atom to the dissociative protonation site at C_α position in either the furyl group or the 4-N,N-dimethylphenyl group. This transfer has been clarified via computational studies and isotopically labeled experiments. In addition, the decomposition of the intermediate may be affected by the substituent groups on the phenyl ring. This conclusion is indicated by the reasonably good correlation between ln[([M + H − CH₂O]⁺)/([M + H − CH₂O − C₆H₅R]⁺)] and the substituent constants.     

Structure of the cationic forms of pyrimido [4,5-b][1,4]thiazines — A new type of folic acid antagonist

The protonation of 4-methoxy-, 4-amino-, and 4-dimethylamino-6-aminopyrimido[4,5-b][1,4]thiazines and N-(4-methoxy-5-pyrimidinyl)acetamidine was studied by ¹H and ¹³C NMR spectroscopy. It is shown that the addition of a proton in the first three compounds takes place at the N₅ atom of the thiazine ring, whereas in the case of N-(4-methoxy-5-pyrimidinyl) acetamidine primary protonation is observed at the nitrogen atom of the amidine group, and the second proton adds to the N₁ atom of the pyrimidine ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 49–54, January, 1979.     

1H n.m.r. investigation on the site of hydration in the asymmetric diazanaphthalenes

The site of hydration for 1,6- and 1,7-naphthyridine has been determined by specific line broadening in the ¹H n.m.r. spectra on the addition of water. The site of hydration appears to be the same as the site of protonation (β-nitrogen atom). The site of hydration in quinazoline has been shown to be the α-nitrogen atom. This strongly indicates that the site of protonation in this compound will also be at that nitrogen.     

A theoretical study of protonated N2O

Ab initio MO calculations predict the preferred site of protonation of N₂O to be at the oxygen atom, and yield a structure of N₂OH⁺ and protonation energies in excellent accord with experiment.     

Spectral-luminescence properties and acid-base properties of luminophores obtained from 3-iodo-7-dialkylaminocoumarins

The absorption and fluorescence spectra of the conjugate acids of 7-dialkylaminocoumarins were studied, and their pK_a ^I, pK_a ^II, and pK_a ^* values were determined. It was established with the aid of PMR data that the primary protonation generally involves the nitrogen-containing substituent in the 3 or 4 position, while the secondary protonation involves the nitrogen atom in the 7 position.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1170–1175, September, 1991.     

Cobalt(III), copper(II), and nickel(II) complexes of 1-thia-4,7-diazacyclononane-S-oxide

Summary The title complexes [ML₂]ⁿ⁺=Co^III, Cu^II, Ni^II; L=1-thia-4,7-diazacyclononane-S-oxide) have been prepared and characterized spectroscopically. The sulphoxide group is coordinated through the oxygen atom and the complexes have atrans-O,O geometry. The nickel(II) complex of bis(2-amino-ethyl)sulphoxide has also been studied.     

13C NMR spectra of the bases and conjugate acids of 3- and 5-formyl-,acetyl-, and carbethoxypyrroles

The effect of protonation of the oxygen atom of the carbonyl group and the carbon atom of the pyrrole ring on the ¹³C chemical shifts in a series of 3- and 5-formyl-, 3-acetyl-, and 3-carbethoxypyrroles was studied. The structures of the conjugate acids of the 5-carbethoxypyrroles was established on the basis of measurement of the ¹H and ¹³C NMR spectra. It is shown that protonation of the 5-carbethoxypyr roles occurs at the ring 5-C atom in 28–35 N H₂SO₄. The effect of structural factors and the acidity of the medium on the relative stabilities of the CH conjugate acids of the investigated compounds is examined.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 485–492, April, 1979.     

A zinc–lithium complex of 4,7‐bis(2‐aminoethyl)‐1,4,7‐triazacyclononane‐1‐acetate

The asymmetric unit of {[4,7‐bis(2‐amino­ethyl)‐1,4,7‐tri­aza­cyclo­nonan‐1‐yl]acetato}zinc(II) triaqua{μ‐[4,7‐bis(2‐amino­ethyl)‐1,4,7‐tri­aza­cyclo­nonan‐1‐yl]acetato}lithium(I)zinc(II) chloride diperchlorate, [Zn(C₁₂H₂₆N₅O₂)][LiZn(C₁₂H₂₆N₅O₂)(H₂O)₃]Cl(ClO₄)₂, obtained from the reaction between the lithium salt of 4,7‐bis(2‐amino­ethyl)‐1,4,7‐tri­aza­cyclo­nonane‐1‐acetate and Zn(ClO₄)₂, contains two Zn^II complexes in which each Zn^II ion is six‐coordinated by five N‐atom donors and one O‐­atom donor from the ligand. One carboxyl­ate O‐atom donor is not involved in coordination to a Zn^II atom, but coordinates to an Li⁺ ion, the tetrahedral geometry of Li⁺ being completed by three water mol­ecules. The two complexes are linked via a hydrogen bond between a primary amine N—H group and the carboxyl­ate‐O atom not involved in coordination to a metal.     

Reactions of 4-chloro-7-dialkylamino- and 3-alkyl-4-chloro-7-dialkylaminocoumarins with primary and secondary alkylamines

Reaction of series of 4-chloro-7-dialkylaminocoumarins and 3-alkyl-4-chloro-7-dialkylaminocoumarins with primary and secondary amines, namely tert-butylamine, benzylamine, cyclohexylamine, monoethanolamine, diethylamine, piperidine, and morpholine, has yielded novel substituted 4,7-diaminocoumarins. The PMR spectra of these newly synthesized compounds are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 836–841, June, 1990.     

Kinetics of Acid‐Catalyzed Dissociation of Copper(II) N‐Alkyl‐Substituted Diamino Diamide Complexes

The dissociation kinetics of the copper(II) complexes of 4‐methyl‐4,7‐diazadecanediamide (4‐Me‐L‐2,2,2), 4,7‐dimethyl‐4,7‐diazadecanediamide (4,7‐N,N′‐Me₂‐L‐2,2,2), 4‐ethyl‐4,7‐diazadecanediamide (4‐Et‐L‐2,2,2), and 4‐methyl‐4,8‐diazaundecanediamide (4‐Me‐L‐2,3,2) have been studied at 25.0 °C and μ = 4.0 M (NaClO₄ + HClO₄) by the stopped‐flow method. These reactions are specific‐acid catalyzed; however, the rate constants of these reactions do not depend on the concentrations of acetic, chloroacetic, and dichloroacetic acids. At pH values below 1.4, both the proton‐assisted and the direct protonation pathways make contributions to the rates. The ratios of the rate constant of dissociation by the direct protonation pathway to the rate constant by the proton‐assisted pathway for the complexes in aqueous solution were measured and discussed.     

Cadmium Iodide Complex with 4-Aminomethylbenzoic Acid: Synthesis,Crystal Structure,and Luminescent Properties

[СdI₂(4-АmbaH)₂] · H₂O has been synthesized by the reaction between CdI₂ and 4-aminomethylbenzoic acid (4-AmbaH) in an aqueous solution. According to X-ray diffraction data, a 4-AmbaH aromatic molecule crystallizes in the form of a zwitterion with protonation of the NH ₃ ⁺ amino group and deprotonation of the carboxylate group, which is chelately coordinated to the Cd²⁺ ion. In addition to two iodine atoms, the Cd²⁺ atom located on the double crystallographic axis is coordinated to the chelate carboxylate O(1) and O(2) atoms of two crystallographically equivalent ligands 4-AmbaH. The octahedral geometry of the Cd²⁺ ion is strongly distorted due to the chelate addition of 4-AmbaH. The chelate coordination of COO–groups is confirmed by IR spectroscopy data. The complex has luminescent properties.     

Kinetics of Acid‐Catalyzed Dissociation of Nickel (II) N‐Alkyl‐Substituted Diamino Diamide Complexes

The dissociation kinetics of the nickel (II) complexes of 4‐methyl‐4,7‐diazadecanediamide (4‐Me‐L‐2,2,2), 4,7‐dimethyl‐4,7‐diazadecanediamide (4,7‐N, N′‐Me2‐L‐2,2,2), 4‐ethyl‐4,7‐diazadecanediamide (4‐Et‐ L‐2,2,2), and 4‐methyl‐4,8‐diazaundecanediamide (4‐Me‐L‐2,3,2) have been studied at 25.0 °C and μ = 4.0 M (NaClO₄ + HClO₄) by the stopped‐flow method. These reactions are specific‐acid catalyzed; however, the rate constants of these reactions do not depend on the concentrations of acetic, chloro acetic, and dichloroacetic acids. At pH values be low 1.0, both the proton‐assisted and the direct protonation path ways make contributions to the rates. The ratios of the rate constant of dissociation by the direct protonation path way to the rate constant by the proton‐assisted path way for the complexes in aqueous solution were measured and discussed.     

Chemistry of strained polycyclic compounds—V : The stereospecific cationic cage expansion reaction of 4-homocubane carbinols to 1,3-bishomocubane bridgehead alcohols

The cationic rearrangement of four homocubane bridgehead carbinols viz dimethyl 4-(1-bromopentacyclo[4.3.0.0^2,5.0^3,8.0^4,7]nonyl-9-one ethylene ketal) carbinol 2, diphenyl 4-(1-bromopentacyclo[4.3.0.0^2,5.0^3,8.0^4,7]nonyl-9-one ethylene ketal) carbinol 3, 4-(1-bromopentacyclo[4.3.0.0^2,5.0^3,8.0^4,7] nonyl-9-one ethylene ketal) carbinol 4 and 4-(1-bromopentacyclo[4.3.0.0^2,5.0^3,8.0^4,7]nonyl) carbinol 16, has been studied undervarious conditions.Exclusive migration of the C₄C₇ (or the equivalent C₃C₄ bond) in the homocubane skeleton was observed leading to 1,3-bishomocubane bridgehead alcohols. Relief of cage constraint governs the selective course of these cage expansions.     

DFT studies on key intermediates in thiamin catalysis

The diphosphate ester (ThDP) of thiamin (vitamin B₁) is an important cofactor of enzymes within the carbohydrate metabolism. From experiments of site‐specific variants and nuclear magnetic resonance (NMR) studies, it is known that the protonation of the N1′ atom is a significant step in the coenzyme activation by the enzymatic environment. Therefore, we have performed density functional theory (DFT) calculations on the B3LYP/6‐31G* level of N1′H and N1′CH₃ thiamin as model systems to study the protonation and methylation effect on the structure and the electronic properties of the 4′‐amino group. The relaxed rotational barriers related to the C4′‐4′N bond are correlated with findings of ¹H NMR studies and proton/deuterium exchange experiments. Moreover, the effect of N1′ protonation was studied in more detail on the hydroxyethyl‐thiamin carbanion (HETh^?), a key intermediate during catalysis of some ThDP‐dependent enzymes. The relaxed rotational barriers related to the C2? C2α bond and the reaction coordinates of the proton transfer 4′N? H→C2α of HETh^? and N1′H‐HETh^? show that they are significantly determined by the protonation at N1′ of HETh^?. The influence of the apoenzyme environment on the active coenzyme conformation is modeled in a very simple way. The characteristic torsion angles Φ_T and Φ_P are considered to be restricted in terms of their values in the corresponding enzyme as well as free optimization parameters. Frequency calculations were performed to characterize the minima and transition state structures, respectively. The applicability of the DFT method was checked by comparing calculations on the MP2‐HF‐SCF/6‐31G* level. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004