Regioselective one-pot synthesis of 9-alkyl-6-chloropyrido[3,2-e][1,2,4]triazolo[4,3-a]pyrazines. Reactivity of aliphatic and aromatic hydrazides

[reaction: see text] The one-pot synthesis of new 9-alkyl-6-chloropyrido[3,2-e][1,2,4]triazolo[4,3-a]pyrazines has been achieved. Hydrazides regioselectively reacted as nucleophiles with the 3-chloro substituent of 2,3-dichloropyrido[2,3-b]pyrazine. An intramolecular cyclization afforded the tricycle nonxanthine adenosine receptor antagonists.     

Comparison of UV derivative-spectrophotometry and partial least-squares (PLS-1) calibration for determination of methotrexate and leucovorin in biological fluids

Binary mixtures of methotrexate (MTX) and leucovorin (LV) have been resolved by application of first-derivative spectrophotometry and partial least squares calibration (PLS-1). By measuring the first-derivative signals of MTX and LV at 354 and 300 nm, respectively, simultaneous determination was possible. The mean recoveries for urine samples were 91 and 96% for MTX and LV, respectively. Partial least squares (PLS-1) multivariate calibration has been applied to the determination of these compounds in serum and in urine without pretreatment of the samples. The absorption spectra of serum or urine samples spiked with methotrexate and/or leucovorin, were used to optimize the calibration matrixes by the PLS-1 method. The sensitivity and selectivity of the proposed procedures were calculated. Mean recoveries were 101 and 97% for MTX and LV, respectively, for serum samples, and 101 and 98% for MTX and LV, respectively, for urine samples.     

Synthesis of biologically active compounds based on 2-ferrocenylmethylene-3-quinuclidone

Biologically active nitrogen heterocycles (1–7) containing ferrocene and quinuclidine fragments were synthesized. 3-Methylene-2-ferrocenylmethylenequinuiclidine forms adducts withN-phenylimides of azodicarboxylic (the structure was established by X-ray structural analysis) and malefic acids. 3-Methylene-2-fer-rocenylmethylenequinticlidine also undergoes [4+2]-cyclodimerization when heated and adds salts of the 3-methyl-2-ferrocenylmethyleneI-azoniabicyclo[2.2.2]oct-3-yl cation at the terminal methylene group to form a linear addition product.Instituto de Quimica, Universidad Nacional Autonoma de Mexico (UNAM), Circuito Exterior, Ciudad Universitaria, Coyoacan.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp 2743–2750, November, 1996.     

Er as marker for order–disorder determination in the PbTiO3 system

Er³⁺ ions were added to the PbTiO₃ network using the polymeric precursor method to characterize the order–disorder transformation found in this material by means of experimental and theoretical approach. The disordered and ordered material structures were studied by photoluminescence measurements, X-ray diffraction (XRD) and UV–visible spectroscopy. The Er³⁺ ions served as a marker to identify the structural short-range order beginning in the PbTiO₃ matrix. From photoluminescence results it was concluded that disordered PbTiO₃ powders have a certain short range order in the network that are undetected by XRD measurements. The electronic structures were calculated by the ab initio periodic method in DFT level with the non-local B3LYP hybrid approximation for the Ti atom site interpretation using density of states (DOS) results. This analysis enabled understanding that Ti atom sphere coordination can create possible states for radioactive return and trap of electron–holes pair.     

An Experimental Investigation of Deformation and Fracture of Nacre–Mother of Pearl

Nacre, also known as mother-of-pearl, is a hard biological composite found in the inside layer of many shells such as oyster or abalone. It is composed of microscopic ceramic tablets arranged in layers and tightly stacked to form a three-dimensional brick wall structure, where the mortar is a thin layer of biopolymers (20–30 nm). Although mostly made of a brittle ceramic, the structure of nacre is so well designed that its toughness is several order of magnitudes larger that the ceramic it is made of. How the microstructure of nacre controls its mechanical performance has been the focus of numerous studies over the past two decades, because such understanding may inspire novel composite designs though biomimetics. This paper presents in detail uniaxial tension experiment performed on miniature nacre specimens. Large inelastic deformations were observed in hydrated condition, which were explained by sliding of the tablets on one another and progressive locking generated by their microscopic waviness. Fracture experiments were also performed, and for the first time the full crack resistance curve was established for nacre. A rising resistance curve is an indication of the robustness and damage tolerance of that material. These measurements are then discussed and correlated with toughening extrinsic mechanisms operating at the microscale. Moreover, specific features of the microstructure and their relevance to associated toughening mechanisms were identified. These features and mechanisms, critical to the robustness of the shell, were finely tuned over millions of years of evolution. Hence, they are expected to serve as a basis to establish guidelines for the design of novel man-made composites.     

Regioselective N-functionalization of tetraazacycloalkanes

[reaction: see text] Bisaminal type compounds obtained by condensation of pyruvic aldehyde with the suitable open-chain tetraamine followed by cyclization with either dibromoethane or dibromopropane can be regioselectively quaternized by a wide range of alkylating agents. Removal of the bisaminal bridge yields the monosubstituted tetraazamacrocycle or bismacrocycle. Further functionalization allows the preparation of bifunctional ligands or trisubstituted macrocycles. The structure of six compounds was solved by X-ray diffraction, and the unexpected results are rationalized according to the molecular modeling calculations.