Synthesis,IR Spectra,and Steric Structure of Macrocycles Derived from Pyrimidine Compounds

A new macrocycle including pyrimidine fragments, 12,23,36-trimethyl-24,40-dioxo-15,33-dithia-2,9,13,22,26,35,38,39-octaazatetracyclo[32.3.1.110,14.122,26]tetraconta-1(38),10(39),11,13,23,34,36-heptaene, was synthesized. According to the data of IR and UV spectroscopy and HF/6-31G** quantum-chemical calculations, macrocyclic compounds of this series in crystal exist in the amino form, one NH group of which is likely to be involved in intramolecular hydrogen bond, and the other, in intermolacular hydrogen bond. The strength of the latter depends on the macroring size. In solution, the above structures are supplemented by conformers containing both intramolecularly H-bonded and free amino groups, predominantly with trans structure of the HÄNÄCÍN fragment. The imino form of the aminopyrimidine moieties is hardly probable.     

Thermal-vacuum tests of hollow composite rods intended for structures in space

A procedure for thermal-vacuum tests for elements of real rod structure in spaces is presented. The procedure makes it possible to determine the heat conductivity of polymer-composite materials in a wide range of temperatures. According to the procedure, the tested samples are cooled by liquid nitrogen and heated by a contact method. The experimental data are processed by solving the coefficient inverse problem of heat conductivity.     

Condensation of thiourea with uracyl derivatives containing ketone and ketoester fragments,alkylation and macrocyclization of the condensation products

By condensation of thiourea with 6-methyluracyl derivatives containing ketone and ketoester fragmenst in the alkyl chains attached to the nitrogen atoms of the pyrimidine ring the products containing 6-methyl- or 3,6-dimethyluracyl fragment and one or two 6-methyl-4-oxo-2-thio-1,2,3,4-tetrahydropyrimidin-5-yl fragments were synthesized. These compounds can be alkylated with alkyl bromides.     

Study of the protonation (methylation) position and tautomeric structure of thiopyrimidine derivatives by 2D <Superscript>1</Superscript>H—<Superscript>15</Superscript>H NMR HSQC/HMBC. Experimental approach and theoretical modeling

Two-dimensional ₁H—₁₅N NMR HSQC/HMBC experiments enable the unambiguous determination of the protonation (methylation) position and tautomeric structure of nitrogen-containing heterocycles. In investigated thiopyrimidines protonation (or methylation) occurs at the N(1) atom of the pyrimidine ring. The tautomeric structures of these compounds were established based on the analysis of ₁H—₁₅N NMR spectra. Ab initio calculations of chemical shifts (GIAO B3LYP/6-31G(d)//HF/6-31G) are in full agreement with experimental values. The stability of various protonated (methylated) and tautomeric species is explained in terms of a thermodynamic approach.     

Numerical Studies of the Influence of the Porosity on Macroscopic Elastic Properties of Carbon/Carbon Composites

Material parameter identification of the carbon/carbon composites was provided using numerical implementation of semi-analytical methods and FE-calculations. The distribution of the fibers and pores obtained from microstructural studies is used as input for homogenization schemes for the determination of the effective elastic constants. The predictions are compared to experimental results. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Regulation of the rate of hydrolysis of phosphorus acid esters in organized systems based on amphiphilic pyrimidinophanes

The aggregation and catalytic activity of supramolecular systems based on new macrocyclic dimeric surfactants (pyrimidinophanes) was studied both in the absence and in the presence of polyethyleneimine (PEI). It was found that the critical micelle concentrations measured by tensiometry were independent of the structure of surfactants. The morphology of aggregates was responsible for various characters of the catalytic effects of pyrimidinophanes in the hydrolysis of phosphonic acid esters. A less hydrophobic pyrimidinophane exhibited a typical effect of cationic surfactants to accelerate the reaction both in the absence and in the presence of PEI. Unlike cationic micelles, a heminal-type pyrimidinophane exhibited an anomalous behavior: it had no effect on the rates of hydrolysis of the substrates and did not inhibit the hydrolysis. Upon the addition of lanthanum ions, the catalytic activity of dimeric surfactants increased. The overall catalytic effect due to the action of supramolecular systems based on pyrimidinophanes, PEI, and lanthanum ions can increase the rates of hydrolysis of the substrates by three orders of magnitude, as compared with that of alkaline hydrolysis.     

Heterocyclophanes with 6-methyluracyl and hydantoin fragments. Ring contraction in 1,3-bis(5-bromopentyl)-5-nitrouracyl

Russian Journal of Organic Chemistry -