An unequivocal synthesis of some substituted 1,2,4-triazolo[1,5-a]pyrimidines

An unequivocal synthesis of 5-chloro-7-methyl- (8) and 7-methyl-1,2,4-triazolo[1,5-a]pyrimidine (10) from 2-amino-4-chloro-6-methylpyrimidine (5) through the corresponding amidine6 and formamide oxime7 was developed. It was unambigously shown by comparison of the chemical shifts and the magnitude of coupling constants that the compounds obtained by condensation of 3-amino-1,2,4-triazole (12) and ethyl acetoacetate (13) and some further transformations are isomeric 5-methyl substituted 1,2,4-triazolo[1,5-a]pyrimidines1,9, and11.

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Eine eindeutige Synthese einiger substituierter 1,2,4-Triazolo[1,5-a]pyrimidine

Zusammenfassung Es wurde ein eindeutiger Syntheseweg für 5-Chlor-7-methyl- (8) und 7-Methyl-1,2,4-triazolo[1,5-a]pyrimidin (10) ausgehend von 2-Amino-4-chlor-6-methylpyrimidin (5) über das entsprechende Amidin6 und das Formamidoxim7 entwickelt. Durch Vergleich von chemischen Verschiebungen und Kopplungskonstanten konnte eindeutig gezeigt werden, daß die Verbindungen, die bei der Kondensation von 3-Amino-1,2,4-triazol (12) and Ethylacetoacetat (13), sowie einige weitere Transformationsprodukte, isomere 5-Methylsubstituierte 1,2,4-Triazolo[1,5-a]pyrimidine sind (1,9,11).

     

Biocompatible hydrogels based on chitosan,cellulose/starch,PVA and PEDOT:PSS with high flexibility and high mechanical strength

Fabricating mechanically strong hydrogels that can withstand the conditions in internal tissues is a challenging task. We have designed hydrogels based on multicomponent systems by combining chitosan, starch/cellulose, PVA, and PEDOT:PSS via one-pot synthesis. The starch-based hydrogels were homogeneous, while the cellulose-based hydrogels showed the presence of cellulose micro- and nanofibers. The cellulose-based hydrogels demonstrated a swelling ratio between 121 and 156%, while the starch-based hydrogels showed higher values, from 234 to 280%. Tensile tests indicated that the presence of starch in the hydrogels provided high flexibility (strain at break?>?300%), while combination with cellulose led to the formation of stiffer hydrogels (elastic moduli 3.9–6.6 MPa). The ultimate tensile strength for both types of hydrogels was similar (2.8–3.9 MPa). The adhesion and growth of human osteoblast-like SAOS-2 cells was higher on hydrogels with cellulose than on hydrogels with starch, and was higher on hydrogels with PEDOT:PSS than on hydrogels without this polymer. The metabolic activity of cells cultivated for 3 days in the hydrogel infusions indicated that no acutely toxic compounds were released. This is promising for further possible applications of these hydrogels in tissue engineering or in wound dressings.

Graphical abstract

     

Chemie der Seltenerdmetalle, 15. Mitt.: Chlortartratkomplexe der Seltenerdmetalle des Typs LnH2TCl·xH2O

Zusammenfassung Es wurden Komplexe des Typs YH₂ TCl·2H₂O, LaH₂ TCl·3H₂O und CeH₂ TCl·3H₂O isoliert. Die Individualität der Verbindungen wurde mit Hilfe der Thermoanalyse, IR-Absorptionsspektren und Röntgenstreuung geklärt.Complexes of the types YH₂ TCl·2H₂O, LaH₂ TCl·3H₂O and CeH₂ TCl·3H₂O were isolated, and the compounds characterized by thermogravimetric analysis, I. R. spectroscopy and X-ray diffraction.Mit 3 Abbildungen Ln=Y, La, Ce; H₄ T=C₄H₆O₆.     

The radiolysis of bis/1,2-dicarbollyl/cobalt/III/ acid in H2O−CCl4 two-phase system

The radiation-induced oxidation of bis/1,2-dicarbollyl/cobalt/III/ acid to 8-monohydroxy-, and 8,8-dihydroxy-derivatives was observed in two-phase system of 4 to 96 vol. % of CCl₄ and H₂O. Carbon tetrachloride increases the radiation yields of the oxidation of the acid in the investigated dose region, nature of the radiolytic products being the same. The partial radiation yields in the system were ascertained.     

Emulsion liquid membrane extraction of fission products promoted by polyvalent and organic acids

Emulsion liquid membranes (ELM) with di-2-ethylhexylphosphoric acid in n-alkane, and dipicrylamine and cobalt(III) dicarbollide in nitrobenzene stabilized in double emulsions by SPAN 80/85 surfactant were used for preconcentration of radioactive fission products (¹³⁷Cs,⁹⁰Sr,¹³⁹Ce, and¹⁵²Eu) from slightly acidic nitrate solutions. The efficiency of sulfuric, phosphotungstic and silicotungstic acids as stripping agents, and picric acid as the bulky anion additive was investigated. A group separation of the fission products is possible by the ELM technique and can be considered for their removal from waste water solutions.     

The microstructure and optical transmittance thermal analysis of sodium borosilicate bio-glasses

The conditions to fabricate the bulk porous specimens have been studied on account of sodium borosilicate (NBS) glasses. Glass composition, heat treatment at phase separation and TiO₂ addition have been considered in this study. Original glass samples of composition in mol%: sample A: 9.19 Na₂O - 23.58 B₂O₃ - 67.23 SiO₂, sample B: 9.29 Na₂O - 3.17 TiO₂ - 23.82 B₂O₃ - 63.72 SiO₂ were prepared by melting reagent grade chemicals (Na₂CO₃, HBO₃, SiO₂ and AgNO₃) in platinum crucibles at 1480°C for 1 h in air. The melts were poured onto stainless steel plates and were annealed at 500°C for 0.5 h after cooling. Thus, obtained samples were phase separated at 700°C for 2, 15, 25 and 50 h to study their microstructure by scanning electron microscope (SEM). Besides the direct study of the microstructure by SEM, information on glass structural changes of samples are provided by measuring in situ changes by the optical transmittance thermal analysis. The isothermal measurements were carried out at 700, 720 and 740°C. The temperature of phase separation, the leaching and nucleator addition (TiO₂), significantly influence the microstructure of the resulting leached product. TiO₂ additive seems to suppress crystallization of cristobalite: especially at the extended above heat treatment phase separation runs. The phase-separated domains of glasses containing above 80 moles of SiO₂ are so small that it is very hard to observe them by SEM. The glass composition in our case was selected in a way to have relatively large phase separated areas easily observed by SEM at magnification 20 000·. The influence of TiO₂ is not too pronounced. It seems to suppress the cristobalite crystallization, especially of longer heating runs. The image analysis of leached glasses shows the prevailing content of the skeletal phase in a comparison to pores. The TiO₂ content diminishes the content of the skeletal phase. This revised version was published online in July 2006 with corrections to the Cover Date.     

Epoxide networks as model networks

Summary The equilibrium mechanical behaviour of weak diepoxide-monoepoxide-diamine networks, prepared with an excess of diamine and measured in the rubbery state, was compared with theoretical predictions obtained by using the theory of branching processes. The experimental equilibrium moduli fit well the shape of theoretical curves over a broad range of crosslinking density regardless of whether the contribution by trapped entanglements is considered or not. The data fit equally well the theoretical dependence for the front factor A = 1 without entanglement contribution and forA = (f _e - 2)/f _e , (f _e is the average effective functionality of a junction) with an entanglement contribution based on the contact probability between any two units within elastically active network chains (Langley).Dedicated to Prof. Dr.G. Rehage on the occasion of his 60th birthday.With 5 figures     

Synthesis of 5-(4,6-dimethyl-2-pyrimidinyl)-1,3,4-oxadiazole-2-thione and its alkylation,aminomethylation, and acylation

The reaction of the hydrazide of 4,6-dimethyl-2-pyrimidinecarboxylic acid with potassium ethylxnthate gave 5-(4,6-dimethyl-2-pyrimidinyl)-1,3,4-oxadiazole-2-thione. The alkylation of this product in an alkaline medium proceeds at the sulfur atom, while the aminomethylation and acylation proceed at the nitrogen atom. The major criterion for the structure of the S- and N-derivatives is the chemical shift of C₍₂₎ in the 1,3,4-oxadiazole ring in the ¹³C NMR spectra.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 700–705, May, 1993.     

Spectrophotometric method for the determination of demeclocycline using sodium molybdate as analytical reagent

By means of spectroscopic methods it has been found that demeclocycline reacts with molybdate ions forming a complex compound [MoO₃HDMTC]^2–. The relative stability constant of this compound has been determined by applying spectrophotometric methods. Under optimum conditions for complex formation a very sensitive spectrophotometric method for the estimation of demeclocycline in the concentration range 5.0–35.1 g/ml is proposed. The detection limit of the method is 2.5 g/ml of demeclocycline. The relative standard deviation (n=10) varies between 0.76% and 1.46%. The method proved to be accurate and sensitive for the analysis of the demeclocycline content in tablets.     

Chromatic number of Hasse diagrams,eyebrows and dimension

We construct posets of dimension 2 with highly chromatic Hasse diagrams. This solves a previous problem by Nesetril and Trotter.