Cytogenetic effects of singlet oxygen.

Singlet oxygen was generated in the gas phase at atmospheric pressure by the method of heterogeneous photosensitization. In vitro exposure of human lung WI-38 fibroblasts to gas-phase singlet oxygen resulted in sister chromatid exchange.     

The Structure of Tris(3',5'-dimethylpyrazol-1-yl)-s-triazine and Its Use as a Ligand in Coordination Chemistry

The crystal and molecular structure of the title compound (Me₂-TPzT) has been determined by X-ray analysis. The observed molecular conformation presents the nitrogen atoms of three pyrazole rings in the same relative positions. The molecules are joined through intermolecular contacts forming chains that are arranged in a distorted hexagonal symmetry. Two complexes containing this ligand have been prepared: [{Pd(en)}₃(Me₂-TPzT)](PF₆)₆ and [{Ag(PPh₃)}3(Me₂-TPzT)](ClO₄)₃, which, due to their insolubility, have been characterized only by microanalysis, IR, ¹H NMR and, in the latter case, by mass spectrometry.     

Multivariate characterization of wine vinegars from the south of Spain according to their metallic content

Forty wine vinegar samples from the south of Spain were analyzed for mineral content. Nine metals (As, Ca, Cu, Fe, K, Mg, Mn, Na and Zn) were chosen as chemical features that may account for the rate of the vinegar fermentation process. Pattern recognition techniques were applied for distinguishing quick and slow processed vinegars. The results obtained indicated an excellent performance in both recalling and prediction ability.     

Group-Theoretic analysis of the mixing angle in the electroweak gauge group

In this paper we provide strong mathematical support for the idea that the experimentally measured magnitude 1 –M _W ² /M _Z ² associated with sin² _W in the standard model of electroweak interactions cannot be simultaneously identified with the squared quotient of the electric charge by theSU(2) charge,e ²/g ². In fact, the natural, mathematical requirement that the Weinberg rotation between the gauge fields associated with the third component of the weak isospin (T ₃) and the hypercharge (Y) proceeds from aglobal Lie-group homomorphism of theSU(2) U(l) _Y gauge group in some locally isomorphic Lie group [which then proves to beU(2)], and not from alocal (Lie algebra)isomorphism, imposes strong restrictions so as to fix the single valuee ²/g ²=1/2. The two definitions of sin² _W can only be identified in the asymptotic limit corresponding to an earlier stage of the universe before the spontaneous symmetry breaking had taken place.     

Synthesis and electronic properties of poly (E,E)-[6.2]-(2,5) thiophenophane-1,5-diene)

Cationic cyclopolymerization of (E, E)-[6.2]-(2,5) thiophenophane-1,5-diene ( 2 ) gave polymer 3 which has bridged thiophene rings pendant to the polymer backbone. The structural, thermal, and electronic properties of polymer 3 were compared to those of its benzene analogue ( 1 ) and its nonbridged analogue poly (2-vinylthiophene) ( 5 ). The onsets of thermal degradation for polymers 3 and 5 under helium were 425 and 382°C, respectively. Polymer 3 exhibited conductivity in the 10^?3?10^?4 S/cm range when exposed to iodine vapor, four orders of magnitude higher than for 5 treated in the same manner. Apparent energies of activation for conductivity in iodine saturated polymers 3 (0.57 eV) and 5 (0.61 eV) were calculated from conductivity temperature dependence measurements. Conductivity parameters for iodine saturated 3 show both a higher level of conductivity and weaker temperature dependence than for the corresponding cyclopolymer 1 which has benzene rather than thiophene moieties, suggesting that greater charge generation occurs in 3 , due to the lower oxidation potential of the thiophenophane repeat units. Differences in conductivity behavior for iodine saturated polymers 1, 3 , and 5 are discussed in terms of both charge generation and mobility. © 1994 John Wiley & Sons, Inc.     

Efficient synthesis of porphyrin-containing,benzoquinone-terminated,rigid polyphenylene dendrimers

A series of rigid polyphenylene, free-base porphyrin-containing dendrimers terminated with either dimethoxybenzene or benzoquinone end-groups were prepared by a combined divergent and convergent synthesis. Unlike previous routes for preparing polyphenylene dendrimers that are incompatible with end-groups bearing certain functional moieties, the synthetic methodology chosen for this work enables incorporation of functional groups on the dendrimer end-groups during preparation of the dendrimer wedges and during synthesis of the final dendrimer. The basic strategy utilized a convergent preparation of dendrimer wedges using Suzuki coupling conditions, which were then either attached to a porphyrin core in a divergent coupling step or cyclized to form the porphyrin dendrimer in a convergent step. The latter approach was found to be more general and resulted in higher yields and more readily separated products. Steady-state absorption measurements for these dendrimers showed Soret and Q-band absorptions typical of free-base porphyrins. Preliminary steady-state fluorescence measurements of these dendrimers indicate quenching of the S1 state of the free-base porphyrin in all benzoquinone-containing dendrimers that is attributed to efficient electron-transfer from the excited porphyrin to the benzoquinone end-groups. The amount of fluorescence quenching was in good agreement with the number of benzoquinone groups at the dendrimer periphery and the distance between the porphyrin and benzoquinone groups as calculated by semiempirical (AM1) molecular orbital calculations.     

Temperature dependence of viscosity for sucrose laurate/water micellar systems

The viscous behavior of sucrose laurate aqueous systems of high hydrophilic-lipophilic balance up to a 50% (wt) surfactant concentration at temperatures between 5°C and 60°C has been studied. Systems up to a 45% (wt) surfactant concentration show Newtonian behavior. The influence of temperature was studied using the activated diffusive relaxation model described by Goodwin. A maximum specific viscosity that appears at lower temperature as sucrose laurate concentration increases can be observed. These results are related to the micellar growth of the sucrose laurate aggregates as temperature rises. More concentrated systems show complex viscous response. Thus, a limit viscosity at low shear rates and a shear-thinning behavior after a critical shear rate are observed. Limit viscosity decreases and critical shear rate increases as temperature rises. This behavior is related to the threshold micelle concentration for entanglement of rod-like micelles.Nomenclature A Parameter of the equation that relatesE and temperature - B Pre-exponential factor of the Arrhenius equation - C Sucrose ester concentration (kg · m^–3) - CMC Critical micelle concentration - E Activation energy for long-range diffusive motion (Goodwin model) - E _a Activation energy of the viscous flow (Arrhenius equation) - E ₀ Parameter of the equation that relatesE and temperature - HLB Hydrophilic/lipophilic balance of the sucrose ester - J Constant that depends on the aqueous phase viscosity and mean micellar radius - k Boltzmann's constant - k ₁ Parameter of the Goodwin equation - k ₂ Parameter of the Goodwin equation - q _rel Contribution of the hydrodynamic interactions - R _e External radius of the sensor system - R _i Inner radius of the sensor system - T Temperature - T _max Temperature at the maximum viscosity - Newtonian viscosity - _i Intrinsic viscosity - _rel Relative viscosity = _solution/_water - _red Reduced viscosity = _sp/C - _sp Specific viscosity = _rel – 1 - ₀ Zero-shear-rate viscosity     

Structure of (1αH,6βH,7αH,8αH)-1α,10α-epoxy-8β-hydroxy-germacr-2,11(13)-dien-6,12-olide (Incomptine B): A sesquiterpenoid lactone

C₁₅H₁₈O₄ is monoclinic,P2₁. Unit-cell dimensions at 293 K area=15.048(5),b=9.756(3),c=15.815(5)Å,=114.18(2)°,V=2118(1)ų,D _x=1.23 g cm^–3, andZ=6. The structure has been determined from single-crystal data collected with a four-circle diffractometer and refined from 2816 observed reflections toR=0.054. The structural features determined from chemical and spectroscopic studies are confirmed and extended. The incomptine B occurs as three independent molecules with different conformations. The stereochemistry at C(6), C(7), and C(8) is 6S, 7R, and 8R. The 10-membered ring has an approximate C₂ symmetry for the A, B, and C molecules. The -methylene -lactone ring adopts a half-chair conformation for molecule A, and a conformation intermediate between-envelope and half-chair for the B and C molecules, respectively. The structures are stabilized by a three-dimensional network of O-HO hydrogen bonds and several C-HO interactions.