Lower rim substituted tert-butylcalix[4]arenes. Part 8: Calix[4]arenes with dialkoxyphosphoryl functions. Synthesis and complexing properties

New compounds: 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(3-diisopropoxyphosphorylpropoxy)calix[4]arene (1) and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(3-methoxyethoxyphosphorylpropoxy)calix[4]arene (2) were synthesized and their ionophoric properties in ion-selective membrane electrodes were studied in comparison with already described by us 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(3-diethoxyphophorylpropoxy)calix[4]arene (3). Complexes of 1 with calcium(II), lanthanum(III), europium(III) and gadolinium(III) nitrates were prepared in direct reaction of the ligand and appropriate metal salts. They were characterized by spectral data (IR, UV/Vis, luminescence, NMR, ESI-MS) and elemental analysis. The similarity in complexing behavior of the (dialkoxyphosphoryl)propoxy-calix[4]arenes toward calcium and some lanthanides was observed.     

Spectroscopic and photochemical properties of the lichen compound lobaric acid

Lichens synthesize and accumulate photoprotective compounds against possible damage induced by UV radiation in the photobiont. A biological model has been recently formulated that allows the use of lichens to evaluate changes at different UV radiation levels. The thermodynamics, photophysical and photochemical properties of lobaric acid were studied in acetonitrile, ethanol and Brij 35(3%) micelles at different pH values. Also the sun protector factor (SPF) was determined by in vitro methods. Lobaric acid was extracted from Stereoculon alpinum Laur. and characterized by means of standard procedures. Solutions were irradiated in oxygen and under nitrogen conditions with a UV medium pressure lamp. Lobaric acid absorbs at 287, 303 nm, and no fluorescence emission was observed. The maximum value of the molar extinction coefficient (5479.6 M(-1) cm(-1)) was obtained in Brij 35 at pH 12. Solubility is pH dependant and is highest in Brij 35 at pH 12 (4.45 x 10(-4) M). Photoconsumption quantum yields ranged between 10(-4) and 10(-5) in aerobic and anaerobic experimental conditions. Lobaric acid SPF was very low (0.5) compared with homosalate (4.0), (reference solar filter). Two pKa values, 5.05 (carboxylic acid group deprotonation) and 9.75 (phenolic OH deprotonation), were determined.     

Insight into the mechanism of three component condensation leading to aminomethylenebisphosphonates

Three-component reaction of a primary amine, diethyl phosphite and triethyl orthoformate followed by acid hydrolysis of the adduct provides N-substituted aminomethylenebisphosphonic acids in good yields. Being extremely versatile, it is commonly utilized for preparation of compounds possessing potential antiosteoporotic, antibacterial, anticancer, antiparasitic or herbicidal activity. However, the mechanism of the reaction remains unknown. p-Nitroaniline has been found an interesting tool to shed light on this matter. Its use allowed to separate and identify four intermediates, both non-phosphorus and phosphorus containing, and subsequently suggest the mechanism of the whole process. The acquired knowledge was helpful in explanation the route and the final product structure obtained for more complex reaction proceeding with the use of 4-aminopyridine. Additional alkylation of the pyridine nitrogen atom, leading to unexpected N-(1-alkylpyridinium-4-amino)methylenebisphosphonic acids was unambiguously proved.     

Large-scale simulations of a-Si:H: the origin of midgap states revisited

Large-scale classical and quantum simulations are used to generate a-Si:H structures. The bond-resolved density of the occupied electron states discloses the nature of microscopic defects responsible for levels in the gap. Highly strained bonds give rise to band tails and midgap states. The latter originate mainly from stretched bonds, in addition to dangling bonds, and can act as hole traps. This study provides strong evidence for photoinduced degradation (Staebler-Wronski effect) driven by strain, thus supporting recent work on a-Si, and sheds light on the role of hydrogen.     

Mercury(II) dibromo-bis-(3-amino-5-mercapto-1,2,4-triazole): synthesis,crystal structure,and infrared characterization

The title compound C₄H₈N₈S₂HgBr₂ was prepared and characterized by means of X-ray crystallography, and i.r. measurements. The crystals are orthorhombic, space group Pbcn (no. 60) witha=9.707(2),b=8.609(1),c=16.128(2) Å, andZ=4. The compound exhibits discrete monometallic units with the 1,2,4-triazole molecule acting as a monodentate ligand. The structure consists of units in which the mercury atom is coordinated in a distorted tetrahedral geometry by two sulfur and two bromine atoms. The NH and NH₂ group of the 3-amino-5-mercapto-1,2,4-triazole unit are involved in intermolecular hydrogen bonds. Infrared bands are diagnostic of the coordination environment around the metal atoms.     

Effects of Multi Global Bifurcations on Basin Organization,Catastrophes and Final Outcomes in a Driven Nonlinear Oscillator at the 2T-Subharmonic Resonance

The behavior of the escape driven oscillator at the 2T-periodic subharmonic resonance is considered, and the mechanism of generating different fractal patterns of the basins of attraction of coexisting attractors, as well as its effects on the unpredictable asymptotic system behaviors, are the main points of interest. The analysis is based on the numerical study of the sudden qualitative changes of the structure of basin-phase portraits, the changes implied by multi global bifurcations. Attention is focused on two qualitatively different regions of control space: the region prior to the subcritical flip bifurcation, where all three attractors (2T-periodic, T-periodic and the attractor at infinity) coexist, and the region after the bifurcation, where only two attractors (2T-periodic and the attractor at infinity) coexist. In particular, the concept of the global (homoclinic and heteroclinic) bifurcations is extended to the latter region, where the arising flip saddle (instead of the direct saddle) is involved in the events. The possible forms of unpredictable outcomes, which arise in both regions of control parameters, are pointed out.     

Cyclization reactions of quaternary salts of azaaromatics

Cyclization reactions of quaternary salts of azaaromatics including inter- and intramolecular condensation as well as radical processes are described.Institute of Chemistry, Pedagogical University, Czestochowa, Poland. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 23–40, January, 1997.     

Atomic number dependent non-local pseudopotentials

A new ab initio method is introduced for constructing accurate pseudopotentials. A new model is obtained with a simple and realistic analytical expression. This contains explicitly both important characteristics of the atomic observables, namely the regular dependence on the atomic number and the non-locality. The application to the Li-like ions of the first row is presented. The whole spectrum of energy eigenvalues is reproduced within 0.3% and HF wavefunctions within 0.5%.     

Refinement of the crystal and molecular structure of 3,5-diamino-1,2,4-dithiazolium bromide. Comparative investigation on the thiouret hydrohalides

The crystal and molecular structure of 3,5-diamino-1,2,4-dithiazolium bromide has been refined from three-dimensional counter data (856 reflections) by least-squares methods, anisotropically for the nonhydrogen and isotropically for the hydrogen atoms, to a finalR=0.036:a=9.948(1),b=12.731(1),c=5.098(1) Å, B=98.70(1)° at 18°C,Z=4,P2₁/n. The S-S (2.075 Å) distance is intermediate between those of the thiouret hydrochloride and hydroiodide. The C-N(terminal) and C-N(bridging) distances are close to their average value (1.322 Å) within their standard deviations. Thev(NH₂) and (NH₂) frequencies of the thiouret hydrohalides are close to those of dithiobiuret while thev(NH) and (NH) bands are, as expected, absent. Thev(CN) andv(CS) bands are shifted to higher and lower frequencies, respectively, while a newv(SS) broad band is observed in the 430–410 cm^–1 region.