Universally catenarian and going-down pairs of rings

For a ring extension is called a universally catenarian pair if every domain , is universally catenarian. When R is a field it is shown that the only universally catenarian pairs are those satisfying . For several satisfactory results are given. The second purpose of this paper is to study going-down pairs (Definition 5.1). We characterize these pairs of rings and we establish a relationship between universally catenarian, going-down and residually algebraic pairs. Received: 1 July 1999; in final form: 5 June 2000 / Published online: 17 May 2001     

Crystal Structure, (31P, 13C) MAS-NMR,IR Spectroscopy and Thermal Investigations of 2,6-Dimethylanilinium Dihydrogenmonophosphate Monohydrate

Chemical preparation, crystal structure, thermal analysis, IR absorption, and NMR studies are given for a new hybrid organic-inorganic compound, the (2,6-dimethyanilinium) dihydrogenophosphate monohydrate [C ₈ H ₁₂ N]H ₂ PO ₄ ·H ₂ O. This compound crystallizes in a triclinic P=1 unit-cell, with a = 7.392(5) Å, b = 8.323(3) Å, c = 10.306(5) Å, α = 95.769 (4)°, β = 102.642 (3)°, γ = 113.498(2)°, V = 554.88(5) Å ³ , and Z = 2. Its crystal structure is determined and refined to R = 0.040 with 1942 independent reflections. The atomic arrangement can be described by inorganic layers built by H ₂ PO ₄ ^? anions, and H ₂ O molecules with which the organic molecules perform different interactions to form a stable 3D network. Solid state ³¹ P and ¹³ C CP-MAS-NMR spectroscopies are in agreement with the X-ray structure.     

Mathematical Modeling of the Response of Polymer Gel Dosimeters to HDR and LDR Brachytherapy Radiation

A model is developed to simulate the response of polyacrylamide gel (PAG) dosimeters to single spherical brachytherapy seeds. The model predicts the amount of polymer formed and crosslink density as a function of radial distance and time, using either a HDR Ir¹⁹² seed or a LDR I¹²⁵ seed. Results indicate that PAG dosimeters should provide accurate dosimetry when used for HDR brachytherapy at distances larger than 4 mm from the center of the seed and that PAG dosimeters will give poor results for LDR dosimetry because of the long time available for the monomer and crosslinker to diffuse toward the seed during polymerization.

     

Synthesis and antiviral evaluation of new 2,5-disubstituted 1,3,4-oxadiazole derivatives and their acyclic nucleoside analogues

Abstract  

A number of new 5-[(naphthalen-1-yloxy)-methyl]-1,3,4-oxadiazole derivatives were synthesized. Sugar 2-[5-[(naphthalen-1-yloxy)methyl]-1,3,4-oxadiazol-2-ylthio]acetohydrazones were prepared by condensation of the hydrazide with the corresponding monosaccharides. Cyclization of the sugar hydrazones with acetic anhydride afforded the substituted oxadiazoline derivatives. The synthesized compounds displayed different degrees of antiviral activities or inhibitory actions against HCV and HIV viruses.     

Optimization and validation of an RP-HPLC method for direct determination of metformin hydrochloride in human urine and in a dosage form

A simple, selective, sensitive, accurate, and precise method was developed for determination of metformin hydrochloride (MF) in human urine using RP-HPLC. The method depends upon using an octylsilyl (C8) 5 microm particle size column at ambient temperature with mobile phase consisting of 33 mM sodium dihydrogen phosphate containing 6.38 mM hexanesulfonic acid sodium salt and adjusted to apparent pH 3.0 with phosphoric acid-acetonitrile (93 + 7, v/v) at a flow rate of 1.5 mL/min. Quantitation was achieved with UV detection at 231 nm based on peak area with a linear calibration curve over the concentration range of 0.01-50 microg/mL. The proposed method was applied to the determination of the urinary excretion pattern of MF (the cumulative amounts excreted were calculated without pretreatment of the urine sample) and for determination of the dissolution pattern of MF tablets. The proposed method was completely validated according to the U.S. Food and Drug Administration guidelines.     

Systems membranes--combining the supramolecular and dynamic covalent polymers for gas-selective dynameric membranes

The adequate selection of components makes possible the generation of double dynameric membranes, allowing the fine constitutional modulation of the gas transport performances.     

Structural and Magnetic Properties of NiFe2−2xSnxCuxO4

The substituted nickel ferrite (NiFe_2−2xSn_xCu_xO₄, x=0, 0.1, 0.2, 0.3) was prepared by the conventional ceramic method. The effect of substitution of Fe³⁺ ions by Sn⁴⁺ and Cu²⁺ cations on the structural and magnetic properties of the ferrite was studied by means of ⁵⁷Fe Mössbauer spectroscopy, alternating gradient force magnetometry (AGFM) and Faraday balance. Whereas undoped NiFe₂O₄ adopts a fully inverse spinel structure of the type (Fe)[NiFe]O₄, Sn⁴⁺ and Cu²⁺ cations tend to occupy octahedral positions in the structure of the substituted ferrite. Based on the results of Mössbauer spectroscopic measurements, the crystal-chemical formula of the substituted ferrite may be written as (Fe)[NiFe_1−2xSn_xCu_x]O₄, where parentheses and square brackets enclose cations in tetrahedral (A) and octahedral [B] coordination, respectively. The Néel temperature and the saturation magnetization values of the NiFe_2−2xSn_xCu_xO₄ samples were found to decrease with increasing degree of substitution (x). The variation of the saturation magnetization with x measured using the AGFM method and that calculated on the basis of the Mössbauer spectroscopic measurements are in qualitative agreement.     

Heat transfer enhancement by application of nano-powder

In this investigation, laminar flow heat transfer enhancement in circular tube utilizing different nanofluids including Al₂O₃ (20 nm), CuO (50 nm), and Cu (25 nm) nanoparticles in water was studied. Constant wall temperature was used as thermal boundary condition. The results indicate enhancement of heat transfer with increasing nanoparticle concentrations, but an optimum concentration for each nanofluid suspension can be found. Based on the experimental results, metallic nanoparticles show better enhancement of heat transfer coefficient in comparison with oxide particles. The promotions of heat transfer due to utilizing nanoparticles are higher than the theoretical correlation prediction.     

Isatin Imines in the Reaction with Iminophosphine: X-Ray Structure of Phospholane Derivatives

3-Imino-1-methyl-indolin-2-one (2a) reacts with phosphorus hexamethyltriamide 1(1:1 mol) in dry toluene at room temperature to give the dimeric spirophospholane 4a. On the other hand, the reaction of 3-(4-arylimino)-1-methylindoline-2-ones 2b–2c with trisdimethylaminophosphine 1 in boiling toluene gave phosphoramides 4b and 4c. Furthermore, 1-benzyl-3-(4-arylimino)indolin-2-ones 3a–3c react with aminophosphine 1 in excess as solvent at 110 °C for 6–8 h to give phosphonamides 5a–5c. Possible reaction mechanism are considered and the structural assignments are based on spectroscopic data and x-ray analysis.     

Utilization of Dipotassium Salt of Galactaric Acid Bis(Hydrazidocarbodithioic Acid) As a Synthone for Double-Headed 1,3,4-Thiadiazoline, 1,3,4-Oxadiazoline and 1,2,4-Triazoline Acyclo C-Nucleosides

Condensation of galactaric acid bis hydrazide (1) with carbon disulfide in the presence of ethanolic potassium hydroxide gave the dipotassium salt of galactaric acid bis (hydrazidocarbodithioic acid) (2). Heterocyclization of the key compound 2 produced three different types of double headed acyclo C-nucleosides: acid-catalyzed dehydrative cyclization afforded the 5-thioxo-1,3,4-thiadiazoline 3, base-catalyzed dehydrosulfurative cyclization gave the 5-thioxo-1,3,4-oxadiazoline 5, and condensative cyclization with concomitant dehydrosulfuration and dehydration with different nitrogen nucleophiles yielded the 5-thioxo-1,2,4-triazolines 7 and 9a, b. Acetylation of the prepared acyclo C-nucleosides 3, 5, 7 and 9a, b with acetic anhydride in the presence of pyridine at ambient temperature caused acetylation of the sugar hydroxyls as well as heterocyclo imino protons to give the tetra-O-acetates 4, 6, and 10a, b, respectively. Representative members of the prepared compounds were tested for antimicrobial activity.