Spectrophotometric study of melting of double stranded Poly[A]·Poly[U] in the aqueous solution

Experimentally observed changes in the electronic absorption spectrum of sodium salt of synthetic polyadenyl–polyuridyl acid (Poly[A]·Poly[U]) in the aqueous solution (pH = 7.0, I = 0.15 mol/L) with the change in temperature were explained in terms of co-existence of two different forms of the Poly[A]·Poly[U] strands. Chemometrics analysis of full set of melting curves measured at 120 wavelengths in the UV spectral range has been performed using evolving factor analysis (EFA) and KALS designed for the calculation of equilibrium constants from spectrometry data without a priori set model of the system. Using the Van’t Hoff equation, we have determined thermodynamic constants of the biopolymer transition from the double stranded helix into the random coil conformation (helix–coil transition), they can be further used to quantify the possibility of these structures to be involved in biochemical processes. Molecular model of partially denatured Poly[A]′·Poly[U]′ complex has been biult by means of molecular mechanics.     

Novel Method for the Synthesis of [1,2,4]Triazino[4,3‐c]quinazoline System

4‐Hydrazinoquinazoline was found to form new 2‐(3,4‐dihydro‐3oxo‐2H‐[1,2,4]triazino[4,3‐c]quinazolin‐4‐yl)acetic acid with maleic anhydride in on‐step sequence. Proposed heterocyclization includes, probably, acylation reaction followed by intramolecular uncleophilic addition.     

Synthesis of 2-substituted 6,8-dinitro[1,2,4]triazolo[1,5-a]pyridines and the formation of the related zwitterionic σ-adducts

A method for the synthesis of 2-substituted 6,8-dinitro[1,2,4]triazolo[1,5-a]pyridines is proposed. The method includes the reaction of 2-chloro-3,5-dinitropyridine with the corresponding 5-substituted tetrazoles. The resulting compounds react with anhydro bases of α- and γ-methylazinium salts to give zwitterionic σ-adducts. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1405–1407, July, 1999.     

Cyclopenta[b]thienyl ligand in organometallic chemistry. Studies of the regioselectivity of the synthesis of new σ-element-substituted cyclopenta[b]thiophene derivatives

Reactions of 2-ethyl-5-methylcyclopenta[b]thienyllithium (thiopentalenyllithium) (2) with various electrophilic reagents afford σ-element-substituted thiopentalenes. However, the reaction with Ph₃SnCl yields only one of two possible isomers,viz, triphenyl(4H-cyclopenta[b] thiophen-4-yl)stannane (4c), whereas the reactions with Me₃SiCl, Me₃SiCl, or Ph₂PCl give both possible isomers,viz., trimethyl(6H-cyclopenta[b]thiophen-6-yl)silane (3a) and trimethyl(4H-cyclopental[b]thiophen-4-yl)silane (4a), trimethyl(6H-cyclopenta[b]thiophen-6-yl)stannane (3b) and trimethyl(4H-cyclopental[b]thiophen-4-yl)stannane (4b), or diphenyl(6H-cyclopenta[b]thiophen-6-yl)phosphine (3d) and diphenyl(4H-cyclopenta[b]thiophen-4-yl)phosphine (4d) in ratios of 1∶2, 1∶2, or 1∶1, respectively. The structure of compound4c was established by X-ray diffraction analysis. The observed regioselectivity of formation of compound4c is attributed to the specific precoordination of the tin atom by the sulfur atom of the thiopentalenyl ligand and to the steric overcrowding of the Sn atom in organotin electrophiles. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1285–1289, July, 2000.     

Tetraviologen calix[4]resorcine as a mediator of the electrochemical reduction of [PdCl4]2– for the production of Pd0 nanoparticles

1. Download : Download full-size image

     

Theoretical Study of the Photochemical Reaction Mechanism of Bicyclo [4.1.0 ] heptane

IntroductionPhotochemical reactions, which involve a three-membered ring, have been of great interest to experi-mental photochemists[1—10]. A main reason for thisphenomenon is that the cyclopropane ring exhibits somereaction characteristics of double bon…     

Modification of the σ-framework of [60]fullerene for bulk-heterojunction solar cells

Modification of the σ-framework of [60]fullerene has been shown to be a new avenue toward n-type materials for bulk-heterojunction solar cells. This approach allowed distinct control of the LUMO level of the C(60)π-system and resulted in a clear improvement of an open-circuit voltage.     

Intramolecular Ullmann-type C−N coupling for the synthesis of substituted benzo[4,5]imidazo[1,2-a]pyrrolo[3,4-c]pyridines

An efficient CuI catalyzed intramolecular Ullmann-type C−N coupling reaction is described here. Newly substituted 1H-benzo[4,5]imidazo[1,2-a]pyrrolo[3,4-c]pyridine-1,3,5(2H, 11H)-trione has been easily synthesized from ortho halogenated N-substituted pyrrolo[3,4-c]pyridine-1,3,6(5H)-triones in presence of CuI catalyst and K₂CO₃ base without any ligand. This procedure is based on intramolecular Ullmann-type reaction and provides a proficient method of making fused tetracyclic heterocycles.     

Synthesis of bridgehead-substituted azabicyclo[2.2.1]heptane and -[3.3.1]nonane derivatives for the elaboration of α7 nicotinic ligands

Azabicyclo[2.2.1]heptane and -[3.3.1]nonane scaffolds (X = Cl, Br) containing a pyridinyl substituent at the bridgehead position were prepared via two complementary chemical pathways, either by the transformation of a methoxy group into a synthetically valuable chlorine atom at the C-6 position of the pyridine moiety or by means of a regioselective C-6 deprotonation/halogenation process of the pyridine moiety exemplified by chlorination or bromination. These newly generated scaffolds were then engaged in Suzuki-Miyaura coupling reactions to provide α7 nicotinic ligands. Both chemical series were evaluated in vitro for their affinity at α7 nicotinic receptors, revealing nanomolar potency with significant selectivity over the α4β2 nicotinic subtype. These approaches offer a general access to these α7 nicotinic scaffolds and ligands.     

Synthesis of derivatives of the new heterocyclic system pyrimido[4′,5′:4,5]pyrimido[1,2-a]benzimidazole

3-Phenyl-5-methyl(phenyl)-1H,3H-pyrimido[4,5:4,5]pyrimido[1,2-a]benzimi-dazole-2,4-diones were obtained by the cyclization of N-phenyl-N-[3-ethoxycar-bonyl-4-methyl(phenyl)pyrimido [1,2-a]benzimidazol-2-yl]ureas by the action of potassium carbonate. 2-Methyl-5-phenyl-1H-pyrimido[4,5:4,5]pyrimido[1,2-a]benzimidazol-4-one was obtained by the reaction of N-3-ethoxycarbonyl-4-phenylpyrimido[1,2-a]benzimidazol-2-yl]-N,N-dimethylacetamidine with ammonium acetate in ethanol. The synthesized compounds are members of a new heterocyclic system. The molecular and crystal structure of the solvate of 3-phenyl-5-methyl-1H,3H-pyrimido[4,5:4,5] pyrimido[1,2-a]benzimidazole-2,4-dione with two molecules of DMF was studied by x-ray crystallographic analysis.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2587–2592, November, 1991.     

Synthesis of Spiro[benzo[h]chromene-4,3′-indoles] and Spiro[benzo[f]chromene-1,3′-indoles]

Russian Journal of Organic Chemistry - New spiro heterocycles, spiro[benzo[h]chromene-4,3′-indoles] and spiro[benzo[f]chromene-1,3′-indoles], have been synthesized in 50–60% yield...     

Synthesis of Benzo[4,5]furo[3,2-b]thieno[2,3-d]pyridines —Derivatives of a New Heterocyclic System

Russian Journal of Organic Chemistry - Methyl 2-(bromomethyl)thiophene-3-carboxylates reacted with substituted 2-hydroxybenzonitriles to give methyl...     

Investigation of regioselectivity in the synthesis of spiro [pyrrolidine-2,3′-oxindoles] by use of the Huisgen reaction

The Huisgen reaction has been used to synthesize five-membered heterocyclic compounds in high yield and with high regio and stereoselectivity. In the synthesis of spiro [pyrrolidine-2,3′-oxindole] derivatives from isatin, α-amino acids, and (E)-β-phenyl nitroolefins, two regioisomers were obtained in each reaction. The regioselectivity of the major product was found to be different from that in reported work, and was investigated at the B3LYP/6-311G* level of theory. On the basis of this new finding, several conditions, for example molar ratio, solvent, and temperature, which affect the regioselectivity of this reaction were investigated; the results obtained are discussed. It was found that the regioselectivity of this reaction was affected by solvent and temperature, irrespective of the ratio of the reactants. Low temperature and high solvent polarity leads to high regioselectivity, and protic solvents result in higher yield and regioselectivity. These results are of benefit for regioselective synthesis of some compounds.     

Effect of Water–Ethanol Solvents on the Protonation Constants of Cryptand[2.2.2]

The protonation constants of cryptand[2.2.2] are determined potentiometrically at 298 K in water–ethanol solvents of variable composition. An increase in the concentration of a solution’s nonaqueous component reduces the equilibrium constants of the reactions of mono- and biprotonated cryptand[2.2.2] formation. The contribution from the resolvation of reagents to the change in the Gibbs energy of the studied reactions is estimated. The reduction in the protonation constants of cryptand[2.2.2] in water–ethanol solvents is mainly due to enhancement of the solvation of protons in water–ethanol mixtures.     

Theophylline as a new and green catalyst for the one-pot synthesis of spiro[benzo[α]pyrano[2,3-c]phenazine]and benzo[α]pyrano[2,3-c]phenazine derivatives under solvent-free conditions

A green,convenient,high yielding and one-pot procedure for the synthesis of novel spiro[benzo[α]pyrano[2,3-c]phenazine]derivatives by domino multi-component condensation reaction between 2-hydroxynaphthalene-l,4-dione,benzene-l,2-diamines,ninhydrine,and malononitrile in the presence of a catalytic amount of 1,3-dimethyl-7H-purine-2,6-dione(theophylline) as an expedient,eco-friendly and reusable solid base catalyst under thermal,microwave irradiation and solvent-free conditions.This procedure has also been applied successfully for the synthesis of benzo[α]pyrano[2,3-c]phenazines.     

Synthesis of selenium-containing biindolyls and their Diels–Alder reaction toward the synthesis of heteroannulated [a]- and [c]-carbazoles

We reported the first syntheses of 2- and 3-(2-(benzo[b]selenophen-2-yl)-indoles and their Diels–Alder reactions to furnish six unique annulated benzoselenphene carbazoles. This facile route can be used to synthesize selenium-containing biindolyl derivatives that possessed potential pharmaceutical activities.     

Self－assembly of Novel Hetero[3]rotaxane, [2]Rotaxanes and [2]Catenane

One linear template 13 and one cyclophane template 15, both incorporating two electron rich 1,4‐dialkoxybenzene units and one diamide unit, have been synthesized. By utilizing donor‐acceptor interaction and/or intermolecular hydrogen bonding assembling principles, one novel hetero[3]rotazane 22·4Cl, possessing one neutral and one tetracationic ring components, has been synthesized from 13, through neutral [2]rotaxane 21 as intermediate. With 15 as template, tetracationic [2]catenane 23·4PF₆ was assembled by using donor‐acceptor interaction, but no neutral [2]rotaxane could be obtained under the typical conditions of hydrogen bonding assembling principle. The interlocked supramolecular compounds have been characterized and their spectral properties are investigated.     

Enhancement of the power factor of [Bi1.68Ca2O4]RS[CoO2]1.69 – Ag composites prepared by the spray-drying method

[Bi_1.68Ca₂O₄]^RS[CoO₂]_1.69 (BCCO) sample and Ag-BCCO composites (with 10, 20 or 30 wt% Ag) have been prepared by the spray-drying technique and uniaxially/isostatically packed. Scanning electron microscopy reveals that the Ag particles are well distributed in the BCCO cobaltite matrix at low Ag contents. The Ag particles have an important effect on densification and grain orientation of the samples, with a direct impact on their electrical conductivity. The electrical conductivity is higher for the uniaxial samples and increases with the Ag content up to 20% in weight, while the Seebeck coefficient is hardly affected. These features induce an improvement of the power factor, reaching a maximum value of 2.2 μW K^?2 cm^?1 at ～1050 K for the uniaxial sample with 20 wt% Ag. Our results suggest that the spray-drying technique is a promising method to obtain composites with a well-dispersed secondary phase.     

New Approach to Synthesis of Tetrahydroisoquino[2,1-c] [1,3]benzodiazepine

A concise and efficient synthesis of the new compounds tetrahydroisoquino [2,1-c] [1,3]benzodiazepine 5 and 7 is reported.