ToF-SIMS Depth Profiling of Trehalose: The Effect of Analysis Beam Dose on the Quality of Depth Profiles

In static secondary ion mass spectrometry (SIMS) experiments, an analysis dose of 10(12) ions/cm(2) typically produces optimum results. However, the same dose used in dual beam depth profiling can significantly degrade the signal. This is because during each analysis cycle a high-energy beam is rastered across the same x-y location on the sample. If a sufficient amount of sample is not removed during each sputter cycle, the subsequent analysis cycle will sample a volume degraded by the previous analysis cycles. The dimensionless parameter R' is used to relate the amount of damage accumulated in the sample to the amount of analysis beam dose used relative to the etching beam. Depth profiles from trehalose films spin-cast onto silicon wafers acquired using Bi(1) (+) and Bi(3) (+) analysis beams were compared. As R' increased, the depth profile and the depth resolution (interface width) both degraded. At R' values below 0.04 for both Bi(1) (+) and Bi(3) (+), the shape of the profile as well as the depth resolution (9 nm) indicated that dual beam analysis can be superior to C(60) single beam depth profiling.     

Meeting Report: Canadian Light Source 8th Annual Users' Meeting Workshops

Four workshops were held on November 18, 2005, prior to the plenary Users' Meeting. The sessions were well attended and featured topics of interest both to veteran synchrotron users and interested workers from a variety of disciplines, ranging from archeology and accelerator physics to plant sciences and “extreme imaging.” A one-day workshop was devoted to future single-bunch operation at the CLS. The workshop's mandate was twofold. One aim was to gauge the interest of the user community for a single bunch mode of operation, including specific requirements such as the bunch current and the bunch purity.     

SYNTHESIS AND X-RAY CRYSTAL STRUCTURE OF THE ASYMMETRIC DITHIADIAZENE BrC6F4NSNSC6H4NO2

The asymmetric dithiadiazene BrC₆F₄NSNSC₆H₄NO₂ crystallizes in the space group P-1 and exhibits a 1D polar chain structure linked via structure-directing Br···O₂N synthons.     

Enantioselective organocatalytic conjugate addition of organoboron nucleophiles

This review covers the use of organoboron nucleophiles in enantioselective conjugate additions catalyzed by organic-based catalysts. It is divided into sections based on the type of nucleophile, with each section arranged in roughly chronological order. The categories of nucleophiles are alkynyl, alkenyl, and aryl boronates or borates. The principle modes of catalysis, iminium formation and boron chelation, are covered.     

Addition of Isocyanides to Tetramesityldigermene: A Comparison of the Reactivity between Surface and Molecular Digermenes

The reaction of benzyl isocyanide, tert‐butyl isocyanide, and 2,6‐dimethylphenyl isocyanide with tetramesityldigermene (Mes₂Ge=GeMes₂) was examined. Whereas the addition of benzyl isocyanide gave the C?NC activation product, Mes₂Ge(CH₂Ph)Ge(CN)Mes₂, tert‐butyl isocyanide, and 2,6‐dimethylphenyl isocyanide did not give stable adducts, rather the rate of conversion of the digermene to the corresponding cyclotrigermane was accelerated. A comparison between the reactivity of the isocyanides with Mes₂Ge=GeMes₂ and the Ge(100)‐2×1 surface was made and some insights into the surface chemistry are offered.     

Ortho-selectivity in the nucleophilic aromatic substitution (SNAr) reactions of 3-substituted, 2,6-dichloropyridines with alkali metal alkoxides

3-Substituted, 2,6-dichloropyridines have featured in the syntheses of small molecule inhibitors of a wide variety of biological targets. Hence, the regioselective displacement of the chlorines is of significant interest. Through conducting an extensive solvent study, we have found that non-polar, aprotic solvents of low hydrogen bond basicities favour substitution of the chlorine ortho to the 3-substituent by alkali metal alkoxides. We present convincing evidence that coordination of the alkali metal counter-ion to the 3-substituent (nitro, ester, amide) is the origin of the ortho-selectivity to give a cyclic, six-membered transition state. Excellent ortho-selectivities (?98:2) for secondary and tertiary alkoxides were realized with the sodium counter-ion, whereas the more reactive primary alkoxides required the harder, more Lewis acidic lithium counter-ion.     

A convenient one-pot synthesis of ethylene blue

We have developed an efficient one-pot, two-step preparation of ethylene blue by eliminating aqueous work-ups and cumbersome purification techniques. Our procedure generates ethylene blue in good overall yields of 45-56% with approximately 95% purity, which is uncommon for the synthesis of a phenothiazinium salt. Due to its unique properties, ethylene blue has great potential for a broad range of biological applications and, as a result, an efficient procedure for the synthesis of ethylene blue is critical.