Two modifications of a five‐coordinate silicon complex

TBPY‐5‐34‐(Butane‐1,4‐diyl)(2‐{[1‐(2‐oxidophenyl)ethylidene‐κO]amino‐κN}ethanolato‐κO)silicon, C₁₄H₁₉NO₂Si, crystallizes in two modifications. The monoclinic form, (IIm), was obtained by crystallization over a period of 2 d at room temperature; the orthorhombic form, (IIo), crystallized overnight at 248 K. The main difference between the two molecular structures involves the angles in the equatorial plane of the trigonal bipyramid around silicon. Form (IIm) has an O—Si—O angle of ca 121° and O—Si—C angles of ca 121 and 116°. In form (IIo), the corresponding angles are ∼123, 124 and 111°. There are also significant differences in the packing: (IIm) shows π stacking, whereas (IIo) does not.     

Conductance in homomorphous solvents: Tetrabutylammonium salts and alkali picrates in butyrolactone-sulfolane mixtures

Conductance measurements are reported for LiPi, NaPi, KPi, RbPi, CsPi, Bu₄NPi, Bu₄NBr, Bu₄NClO₄, Bu₄NNO₃, and Bu₄NBBu₄ at 25°C in -butyrolactone-sulfolane mixtures. In these mixtures of solvents that are practically homomorphous, isodielectic and with comparable dipole moments, the ion pair association and ionic mobilities of large ions conform to the expectations of the primitive model. Electrolytes containing lithium or sodium ions show anomalies indicating that other factors besides shape, dipole moment, and polarizability of the solvent molecules are involved in the association and transport processes of these ions.     

New class of potent catalysts of O2.-dismutation. Mn(III) ortho-methoxyethylpyridyl- and di-ortho-methoxyethylimidazolylporphyrins

Three new Mn(III) porphyrin catalysts of O2.-dismutation (superoxide dismutase mimics), bearing ether oxygen atoms within their side chains, were synthesized and characterized: Mn(III) 5,10,15,20-tetrakis[N-(2-methoxyethyl)pyridinium-2-yl]porphyrin (MnTMOE-2-PyP(5+)), Mn(III)5,10,15,20-tetrakis[N-methyl-N'-(2-methoxyethyl)imidazolium-2-yl]porphyrin (MnTM,MOE-2-ImP(5+)) and Mn(III) 5,10,15,20-tetrakis[N,N'-di(2-methoxyethyl)imidazolium-2-yl]porphyrin (MnTDMOE-2-ImP(5+)). Their catalytic rate constants for O2.-dismutation (disproportionation) and the related metal-centered redox potentials vs. NHE are: log k(cat)= 8.04 (E(1/2)=+251 mV) for MnTMOE-2-PyP(5+), log k(cat)= 7.98 (E(1/2)=+356 mV) for MnTM,MOE-2-ImP(5+) and log k(cat)= 7.59 (E(1/2)=+365 mV) for MnTDMOE-2-ImP(5+). The new porphyrins were compared to the previously described SOD mimics Mn(III) 5,10,15,20-tetrakis(N-ethylpyridinium-2-yl)porphyrin (MnTE-2-PyP(5+)), Mn(III) 5,10,15,20-tetrakis(N-n-butylpyridinium-2-yl)porphyrin (MnTnBu-2-PyP(5+)) and Mn(III) 5,10,15,20-tetrakis(N,N'-diethylimidazolium-2-yl)porphyrin (MnTDE-2-ImP(5+)). MnTMOE-2-PyP(5+) has side chains of the same length and the same E(1/2), as MnTnBu-2-PyP(5+)(k(cat)= 7.25, E(1/2)=+ 254 mV), yet it is 6-fold more potent a catalyst of O2.-dismutation , presumably due to the presence of the ether oxygen. The log k(cat)vs. E(1/2) relationship for all Mn porphyrin-based SOD mimics thus far studied is discussed. None of the new compounds were toxic to Escherichia coli in the concentration range studied (up to 30 microM), and protected SOD-deficient E. coli in a concentration-dependent manner. At 3 microM levels, the MnTDMOE-2-ImP(5+), bearing an oxygen atom within each of the eight side chains, was the most effective and offered much higher protection than MnTE-2-PyP(5+), while MnTDE-2-ImP(5+) was of very low efficacy.     

Hair color changes and protein damage caused by ultraviolet radiation

Ultraviolet and visible radiations are known to damage hair. However, quantitative data relating damage to hair type, proteins and color to the radiation wavelength are missing. We studied the effect of UV plus visible, UVA plus visible, visible mercury-vapor lamp radiation and sunlight on (blended) virgin dark-brown, blond and red hair and (one head) virgin black and curly dark-brown hair. All hair types showed a substantial increase in protein loss in water after lamp and sun irradiation. The damaging effect of UVB was about 2-5 times higher than that of UVA plus visible radiation, depending on the hair type. Significant color changes were also observed in every hair type, after lamp and sun irradiation, being more pronounced for the light colored hairs. The luminosity difference parameter was the major contributor to the hair color changes, but significant changes in the red-green and yellow-blue parameters of every hair were observed. In this case, the damaging effect is ascribable mainly to UVA radiation. No significant changes in the mechanical properties or topography were observed in any case. We discuss these results in terms of hair type and composition and melanin types.     

Molecular interactions in 1-pentanol +2-methyl-2-butanol mixtures: Static dielectric constant,viscosity and refractive index investigations at 5, 25 and 45°C

Static dielectric constants, refractive indices and viscosities of 1-pentanol +2-methyl-2-butanol mixtures were measured at 5, 25 and 45°C. The results show that the mixing of the two isomers modifies the polarizability and the resistence of viscous flow of the system depending on the composition and temperature. Short range intermolecular interactions producing hetero-alcohol open dimers are considered.     

On the origin of quasi-racemic aplysinopsin cycloadducts, (bis)indole alkaloids isolated from scleractinian corals of the family Dendrophylliidae. Involvement of enantiodefective Diels-Alderases or asymmetric induction in artifact processes involving adventitious catalysts?

Reported here are two novel quasi-racemic (bis)indole alkaloids, cycloaplysinopsin A (5) and cycloaplysinopsin B (6), isolated from tropical Indo-Pacific (Comoros, Philippines) scleractinian corals of the family Dendrophylliidae. Although their structures suggest a Diels-Alder cycloaddition origin from aplysinopsin-type precursors, neither experiments, nor theory allowed us to clearly distinguish an enzymatic process with scarce enantioselection from the intrusion of an adventitious catalyst in the coral extracts, where the chiral environment caused a slight asymmetric induction.     

Bretonin A and Isobretonin A,Unique Glycerol Derivatives Isolated from a Demosponge of Brittany Waters

It is shown that an unidentified marine demosponge of Brittany contains two unique lipids consisting of glycerol etherified by a C₁₂ trienic linear alcohol and esterified by 4-hydroxybenzoic acid. The latter is attached to the secondary position of glycerol in bretonin A (= 3-[((4E, 6E, 8E)-dodeca-4,6,8-trienyl)oxy]-2-(4-hydroxy-benzoyl)propan-1-ol; 1a ), and to the other primary position of glycerol in isobretonin A ( = (+)-3-[((4E, 6E, 8E)-dodeca-4,6,8-trienyl)oxy]-1-(4-hydroxybenzoyl)propan-2-ol; (+) -2 ). The structures are based on NMR and MS data, including the ones of the acetylation product (?)- 1b of 1a .     

Optical sensors for determination of heavy metal ions

A review is given on optical means for single shot testing (probing) as well as continuous monitoring (sensing) of heavy metal ions (HMs). Following an introduction into indicator based approaches, we discuss the types of indicator dyes and polymeric supports used, as well as existing sensing schemes for HMs. The wealth of information is compiled in the form of tables and critically reviewed. Notwithstanding the tremendous work performed so far, it is obvious that still severe limitations do exist in terms of selectivity, limits of detection, dynamic ranges, applicability to specific problems, and reversibility. On the other hand, such sensors have found — and will find — their application whenever rapid and cost-effective testing is required, where personnel is scarce or unskilled, and in field tests. Despite their limitations, the number of such sensors (and of irreversible probes) for HMs is likely to increase in future.     

Benzene-assisted atmospheric-pressure chemical ionization: a new liquid chromatography/mass spectrometry approach to the analysis of selected hydrophobic compounds

Charge-exchange reactions involving benzene have been successfully exploited to increase the sensitivity of atmospheric-pressure chemical ionization mass spectrometry (APCI-MS) towards hydrophobic compounds of significant environmental relevance which are not detectable with the ordinary APCI techniques. Among them, good sensitivity have been found for (a) highly chlorinated biphenyl derivatives such as dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichloroethane (DDD) and dichlorodiphenyldichloroethene (DDE); (b) cyclopentadienes such as Aldrin and its epoxy derivatives Dieldrin and Endrin; and (c) dibenzofurans and dibenzo-para-dioxins such as 2,3,7,8-tetrachlorodibenzofuran (2,3,7,8-TCDF) and 2,3,7,8-tetrachloro-dibenzo-para-dioxin (2,3,7,8-TCDD). The reactant benzene molecules were introduced into the source either through the nebulizer gas or by direct post-column addition of neat liquid, whereas the targeted compounds were analyzed using a high-performance liquid chromatography (HPLC) RP-18 column using methanol/water solutions as mobile phase. By using benzene as post-column reagent, positive ion mode detection was proven to be significantly enhanced as compared with APCI measurements carried out without benzene assistance.