Hydrogen peroxide promoted hydroxylation of haloarenes and heteroarenes

Addition of aqueous hydrogen peroxide significantly accelerates the substitution reactions of hydroxide salts with haloarenes bearing electron withdrawing substituents. A similar effect is observed in the reactions of hydroxide salts with halogenated heteroarenes. Reactions are carried out in water or water-THF at ambient temperature or at 50-60 °C.     

Temperature dependence of europium carbonate complexation

The temperature dependencies of europium carbonate stability constants were examined at 15, 25, and 35°C in 0.68 molal Na⁺(ClO ₄ ^? , HCO ₃ ^? ) using a tributyl phosphate solvent extration technique. Our distribution data can be explained by the equilibria $$\begin{gathered} Eu^{3 + } + H_2 O + CO_2 (g)_ \leftarrow ^ \to EuCO_3^ + + 2H^ + \hfill \\ - log\beta _{12} = 9.607 + 496(t + 273.16)^{ - 1} \hfill \\ Eu^{3 + } + 2H_2 O + 2CO_2 (g)_ \leftarrow ^ \to Eu(CO_3 )_2^ - + 4H^ + \hfill \\ - log\beta _{24} = 21.951 + 670(t + 273.16)^{ - 1} \hfill \\ Eu^{3 + } + H_2 O + CO_2 (g)_ \leftarrow ^ \to EuHCO_3^{2 + } + H^ + \hfill \\ - log\beta _{11} = 1.688 + 1397(t + 273.16)^{ - 1} \hfill \\ \end{gathered}$$      

New tetranorlabdanoic acid from aerial parts of Salvia aethiopis

Salvia aethiopis is a perennial plant native to Eurasia and known by the common names Mediterranean sage or African sage. This plant has been used in Iranian medicine as a carminative and tonic. The ethanolic extract of aerial part of S. aethiopis exhibited moderate to weak activity towards delta and kappa opioid receptors (46.3 and 45.3% displacement, respectively). Chromatographic purification of the ethanolic extract on silica gel column led to isolation of one new: 3α-hydroxy-8α-acetoxy-13,14,15,16-tetranorlabdan-12-oic acid (I) and three known compounds: sesquiterpene spathulenol (II), β-sitosterol (III) and β-sitosterol-3-O-glucoside (IV). The structures of all isolated compounds were elucidated by their NMR (1D and 2D) and MS spectral data. All the fractions and isolated compounds were tested for cannabinoid and opioid receptor binding assays.     

Laser Flash Photolysis Studies of the UVA Sunscreen Mexoryl SX

Abstract The results of a nanosecond laser flash photolysis investigation of the UVA sunscreen Mexoryl* SX in various solvent environments and within a commercial sunscreen formulation are reported. To the best of our knowledge this is the first laser flash photolysis study of a commercial suncare formulation. In each of these environments kinetic UV-visible absorption measurements following nanosecond 355 nm laser excitation reveals a short-lived species with a solvent-dependent absorption maximum around 470–500 nm and a solvent-dependent lifetime of 50–120 ns. This transient absorption is attributed to the triplet state of Mexoryl* SX on the basis that it is quenched by molecular oxygen leading to the formation of singlet oxygen in acetonitrile. The singlet oxygen quantum yield (φ_Δ), determined by comparative time-resolved near-infrared luminescence measurements and extrapolated to the limit of complete triplet state quenching, is estimated as 0.09 ± 0.03 in acetonitrile. In aqueous solution the shorter triplet state lifetime combined with lower ambient oxygen concentrations precludes significant triplet state quenching. For the commercial sunscreen formulation there was no observable difference in the measured triplet lifetime between samples exposed to oxygen or argon, suggesting that the singlet oxygen quantum yield in such environments is likely to be orders of magnitude lower than that measured in acetonitrile.     

The influence of annealing on thermal transitions in a nematic copolyester

Thermal transitions of a glassy, main chain, liquid crystalline, random copolyester, HIQ‐40, have been characterized. HIQ‐40 is made from 40 mol percent p‐hydroxybenzoic acid (HBA) and 30 mol % each of p‐hydroquinone (HQ) and isophthalic acid (IA). This polymer is soluble in organic solvents, permitting the preparation of thin, solution‐cast films that are in a glassy, metastable, optically isotropic state. On first heating of an isotropic HIQ‐40 film in a calorimeter, one glass transition is observed at low temperature (approximately 42°C), and is ascribed to the glass/rubber transition of the isotropic polymer. A cold crystallization exotherm centered near 150°C is observed. This is associated with the development of low levels of crystalline order. A broad melting endotherm is centered at about 310°C; this endotherm marks the melting of crystallites and the transformation to a nematic fluid. A nematic to isotropic transition was not observed by calorimetry. After quenching from the nematic melt, a T_g is observed in the range of 110–115°C and is associated with the glass/rubber transition of the nematically ordered polymer. Annealing optically isotropic films at temperatures above the isotropic glass transition results in the systematic development of axial order. In these annealed samples, T_g increases rapidly until it is near the annealing temperature, then T_g increases more slowly at longer annealing times. In as‐cast films annealed at 120–135°C, the light intensity transmitted through a sample held between crossed polarizers in an optical microscope (a qualitative measure of birefringence and, in turn, axial order) initially increases rapidly and uniformly throughout the sample and, at longer annealing times, approaches asymptotic values that are higher at higher annealing temperatures. The increase in transmitted intensity is ascribed to the development of axial order. The uniform increase in transmitted intensity suggests that ordering occurs by a rather global process and not via a nucleation and growth mechanism. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 505–522, 1999     

Photochemical studies of A2-E.

Lipofuscin is thought to be involved in age-related macular degeneration as is one of its proposed components, an amphiphillic pyridinium-based bis-retinoid with a quaternary nitrogen atom, known as A2-E. We report the triplet state spectra obtained from photosensitisation using anthracene and 1-nitronaphthalene in benzene and methanol. The triplet state of A2-E has lambda(max) at 550 nm and a lifetime of approximately 30 micros, it is efficiently quenched by molecular oxygen with a second-order quenching rate constant of approximately 1 x 10(9) dm(3) mol(-1) s(-1). There is no significant triplet state formation from direct laser excitation of A2-E and hence its quantum yield of triplet state formation must be <0.01.