1-Azathioxanthone Appended Lanthanide(III) DO3A Complexes That Luminesce Following Excitation at 405 nm**

Since the pioneering report by Selvin, we have been fascinated by the potential of using lanthanide luminescence in bioimaging. The uniquely narrow emission lines and long luminescence lifetimes both provide the potential for background free images together with full certainty of probe localization. General use of lanthanide based bioimaging was first challenged by low brightness, and later by the need of UV (<405 nm) excitation sources not present in commercial microscopes. Here, we designed three lanthanide-based imaging probes based on a known motif to investigate the limitations of 405 nm excitation. These were synthesized, characterized, investigated on dedicated as well as commercial microscopes, and the photophysics was explored in detail. It was proven without doubt that the lanthanide complexes enter the cells and luminesce internally. Even so, no lanthanide luminescence were recovered on the commercial microscopes. Thus, we returned to the photophysical properties that afforded the conclusion that – despite the advances in light sources and photodetectors – we need new designs that can give us brighter lanthanide complexes before bioimaging with lanthanide luminescence becomes something that is readily done.     

A new mechanism for ozonolysis of unsaturated organics on solids: phosphocholines on NaCl as a model for sea salt particles

The ozonolysis of an approximately one monolayer film of 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine (OPPC) on NaCl was followed in real time using diffuse reflection infrared Fourier transform spectrometry (DRIFTS) at 23 degrees C. Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry and Auger electron spectroscopy were used to confirm the identification of the products. Ozone concentrations ranged from 1.7 x 10(12) to 7.0 x 10(13) molecules cm(-3) (70 ppb to 2.8 ppm). Upon exposure to O3, there was a loss of C[double bond, length as m-dash]C accompanied by the formation of a strong band at approximately 1110 cm(-1) due to the formation of a stable secondary ozonide (1,2,4-trioxolane, SOZ). The yield of the SOZ was smaller when the reaction was carried out in the presence of water vapor at concentrations corresponding to relative humidities between 2 and 25%. The dependencies of the rate of SOZ formation on the concentrations of ozone and water vapor are consistent with the initial formation of a primary ozonide (1,2,3-trioxolane, POZ) that can react with O3 or H2O in competition with its thermal decomposition to a Criegee intermediate and aldehyde. Estimates were obtained for the rate constants for the POZ thermal decomposition and for its reactions with O3 and H2O, as well as for the initial reaction of O3 with OPPC. The SOZ decomposed upon photolysis in the actinic region generating aldehydes, carboxylic acids and anhydrides. These studies show that the primary ozonide has a sufficiently long lifetime when formed on a solid substrate that direct reactions with O3 and H2O can compete with its thermal decomposition. In dry polluted atmospheres, ozone-alkene reactions may lead in part to the formation of stable secondary ozonides whose chemistry, photochemistry and toxicity should be taken into account in models of such regions.     

GC/MS of terpenes in walnut-tree leaves after accelerated solvent extraction

Terpenes, e. g. (+)-alpha-pinene, (-)-camphene, (-)-(-pinene, myrcene, R-(+)-limonene, eucalyptol, (+/-)-linalool, (-)-bornyl acetate, (-)-trans-caryophyllene, and alpha-humulene were determined in leaves of walnut trees from the Juglandaceae family (walnut tree, royal (J. regia L.), black (J. nigra L.), and Siebold (J. sieboldiana, var. Cordiformis Lam.) using gas chromatography with mass spectrometric detection. Terpenes were repeatedly (3 cycles, 5 min each) extracted from leaves of walnut trees by accelerated (pressurized) solvent extraction (ASE) 150 bar and 120 degrees C. The efficiency of ASE extraction was superior to that of steam distillation, solvent extraction according to Soxhlet, sonication, and extraction by agitation. Differences in relative concentrations and distribution of terpenes were studied in dependence on the species of walnut tree and on different locations.     

Acylation of N-p-toluenesulfonylpyrrole under Friedel-Crafts conditions: evidence for organoaluminum intermediates

The Friedel-Crafts acylation of N-p-toluenesulfonylpyrrole under Friedel-Crafts conditions has been reinvestigated. Evidence is presented in support of the hypothesis that when AlCl₃ is used as the Lewis acid, acylation proceeds via reaction of an organoaluminum intermediate with the acyl halide. This leads to the production of the 3-acyl derivative as the major product. With weaker Lewis acids (EtAlCl₂, Et₂AlCl) or less than 1 equiv of AlCl₃ the relative amount of 2-acyl product is increased. A mechanistic rationalization is presented to explain these data.     

Resolution enhancement in solid-state NMR of oriented membrane proteins by anisotropic differential linebroadening

We demonstrate that a significant improvement in the spectral resolution may be achieved in solid-state NMR experiments of proteins in inhomogeneously disordered oriented lipid bilayers. Using 1H homonuclear decoupling instead of standard 1H heteronuclear decoupling, the 15N line widths may be reduced by up to seven times for such samples. For large oriented membrane proteins, such resolution enhancements may be crucial for assignment and structural interpretation.     

A small methanoato ligand in the structural differentiation of copper(II) complexes

Several copper(II) methanoato complexes, namely mononuclear [Cu(O₂CH)₂(2-mpy)₂] (1) (2-mpy = 2-methylpyridine), binuclear [Cu₂(μ-O₂CH)₄(2-mpy)₂] (2), and the polynuclear {[Cu(μ-O₂CH)₂(2-mpy)₂][Cu₂(μ-O₂CH)₄]}_n (3) and {Na₂[Cu(μ-O₂CH)₂(O₂CH)₂][Cu₂(μ-O₂CH)₄]}_n (4), have been synthesized. The mononuclear complex 1 is formed by two asymmetric chelate methanoate anions and two 2-methylpyridine molecules, giving a highly distorted ‘elongated octahedral’ coordination sphere. Complex 1 decomposes outside the mother-liquid, transforming into a regular isolated binuclear paddle-wheel complex 2 with four intra-binuclear bridging methanoates and two axial 2-mpy ligands. The polynuclear complex 3 is formed of alternate mononuclear and binuclear building blocks resembling the central cores of 1 and 2, but with significant differences, especially for the methanoates of the mononuclear units. The oxygen atom of the mononuclear unit in the octahedral axial position in 3 is simultaneously coordinated to the axial position of the binuclear paddle-wheel central core, thus enabling a chain type of structure. A chain of alternate mononuclear and binuclear building blocks, as in the neutral compound 3, are found as well in the ionic polymeric compound 4, though two types of bridges are found in 4, while there is only one type in 3. Namely, the axial position of the octahedral mononuclear unit in 4 is occupied by the methanoate oxygen atom that is already a part of the binuclear paddle-wheel unit, while one equatorial methanoate from the mononuclear unit serves as a triatomic bridge to the axial position of the binuclear building block. A very strong antiferromagnetic interaction is found for all the complexes with the paddle-wheel building blocks [Cu₂(μ-O₂CH)₄] 2–4 (−2J = 444–482 cm⁻¹), attributed to the methanoate intra-binuclear bridges. On the other hand, this strong antiferromagnetism, found already at room temperature, reduces the intensity of the EPR S = 1 spin signals reported for the isolated paddle-wheel complex 2. For the polymeric 3, only the spin S = ½ signals are found in the EPR spectra, and they are assigned to the mononuclear building blocks. No signals with a clear origin are however seen in the room temperature EPR spectrum of the polymeric analogue 4, only the S = ½ signals in the low temperature spectra. This feature is suggested to be due to a specific influence between the adjacent S = 1 (binuclear) and S = ½ (mononuclear) species via their bridges.