Muttiphoton Ionization of Benzene-Ammonia Clusters: Intracluster Reaction and Cluster Ion Stability

Neutral benzene-ammonia clusters, prepared in a supersonic expansion, were ionized using multiphoton ionization. The cluster ions were investigated with a time-of-flight mass spectrometer. The observed major cluster ions, under 355-nm laser irradiation, resulting from prompt intracluster ion-molecule reaction and fragmentation following ionization are (C₆H₆)_m(NH₃)_nH⁺, m = 1–6, n = 1–4 and (C₆H₆)_m⁺, m = 1–3. The results of isotopic labeling experiments clearly indicate that C₆H₆ does not participate in intracluster ion-molecule reactions to form (C₆H₆)_m(NH₃)_nH⁺. A local maximum appears at n = 2 in the intensity distribution of (C₆H₆)_m(NH₃) _nH⁺ for each value of m under all experimental conditions. This finding indicates that (C₆H₆)_m(NH₃)₂H⁺ is more stable than any other (C₆H₅)_m(NH₃)_mH⁺ (n = 1,3,4) for m = 1–6.     

Mass analyzed threshold ionization spectroscopy of 5-methylindole and 3-methylindole cations and the methyl substitution effect

The vibrationally resolved mass analyzed threshold ionization spectra of jetcooled 5-methylindole (5MI) and 3-methylindole (3MI) have been recorded by ionizing via various vibronic levels of each species. The adiabatic ionization energies (IEs) of 5MI and 3MI are determined to be 61,696+/-5 and 60,679+/-5 cm(-1), which are less than that of indole by 895 and 1912 cm(-1), respectively. Comparing these data with those of 1-methylindole and indole suggests that the methyl substitution on the pyrrole part leads to a greater redshift in the IE than on the benzene part. These experimental findings are well supported by the theoretical calculations. Analysis on these new data shows that many active vibrations of the 5MI cation are related to the CH(3) torsion and in-plane ring bending vibrations. In contrast, the observed vibrational bands of the 3MI cation are very weak due to unfavorable Franck-Condon transition.     

Camphor containing organocatalysts in asymmetric aldol reaction on water

A new class of bifunctional organocatalysts were synthesized and proved to be effective in catalyzing aldol reaction on water with high to excellent diastereo- and enantioselectivities.     

A complete Raman mapping of phase transitions in Si under indentation

Crystalline Si substrates are studied for pressure‐induced phase transformation under indentation at room temperature (RT) using a Berkovich tip. Raman spectroscopy, as a nondestructive tool, is used for the identification of the transformed phases. Raman lines as well as area mapping are used for locating the phases in the indented region. Calculation of pressure contours in the indented region is used for understanding the phase distribution. We report here a comprehensive study of all the phases of Si, reported so far, leading to possible understanding of material properties useful for possible electromechanical applications. As a major finding, distribution of the amorphous phase in the indented region deviates from the conventional wisdom of being in the central region alone. We present phase mapping results for both Si(100) and Si(111) substrates. Copyright © 2009 John Wiley & Sons, Ltd.     

Metal Trifluoromethanesulfonate‐Catalyzed Regioselective Reductive Ring Opening of Benzylidene Acetals

A systematic study of various metal trifluoromethanesulfonates as efficient catalysts in the regioselective reductive ring opening of benzylidene acetals is described, including the effects of solvents, reducing agents, and temperature. These catalysts are found to be effective in cleaving the 4,6‐O‐acetal rings of hexopyranosides at either O4 or O6, respectively. When used in conjunction with a 1 M solution of BH₃·THF in THF without extra addition of any solvent, it affects the ring fission at the O6 position to generate the corresponding primary alcohols, whereas O4‐opening takes place in acetonitrile in the presence of dimethylethylsilane as the reductant leading to the secondary hydroxyl derivatives in high selectivity and yields. These methodologies can be applied to a wide range of substrates containing various functional groups.     

Supramolecular assembly of gold(I) complexes of diphosphines and N,N'-bis-4-methylpyridyl oxalamide

We report herein the supramolecular assembly and spectroscopic and luminescent properties of gold(I) complexes of diphosphines (dppm [bis(diphenylphosphino)methane], dppp [1,3-bis(diphenylphosphino)propane], and dpppn [1,5-bis(diphenylphosphino)pentane]) and N,N'-bis-4-methylpyridyl oxalamide (L). The dppm and dppp cases form the rectangular structures, [dppm(Au(2))L](2)(ClO(4))(4) and [dppp(Au(2))L](2)(ClO(4))(4), with four gold(I) ions at the corners, as well as two L and two dppm or dppp ligands as edges, featuring 38- and 42-membered rings for the former and the latter, respectively. Remarkably, the packing of the dppp complexes shows interesting one-dimensional rectangular channels in the solid state, most likely due to intermolecular pi...pi interactions. The dpppn complex has been structurally characterized as a one-dimensional coordination polymer, {[(dpppn)(3.5)(Au(7))L(3.5)](PF(6))(7)}. The absorptions and emissions of the compounds are in general due to intraligand transitions, but aurophilic or pi...pi interactions could also make partial contributions. The dipyridyl amide system with the amides incorporated into the bridging ligands as well as the one-dimensional rectangular channels in the solid state for the dppp-based rectangle make this a promising family of metal-containing cyclic peptides in crystal engineering and molecular-recognition studies.     

Using FSBT technique with Rough Set Theory for personal investment portfolio analysis

This study proposes a novel Forward Search and Backward Trace (FSBT) technique based on Rough Set Theory to improve data analysis and extend the scope of observations made from sample data to solve personal investment portfolio problems. Rough Set Theory mathematically classifies data into class sets. The class set with the most objects may generate one decision rule. The rules generated from RST are rough and fragmented, that are very difficult to interpret the information. An empirical case is used to generate more than 85 rules by the RST method in comparison with FSBT method which only generated 14 rules. This result can show our proposed method is better than traditional RST method based on class sets that contain the most objects. Much of human knowledge is described in natural language. It is a very important thing to convert information from computer databases into normal human language. Sample data taken from features with the same backgrounds are used to compile different portfolios that investment companies and investment advisors can employ to satisfy the investor’ needs. The method not only can provide decision-making rules, but also can offer alternative strategies for better data analysis. We believe that the FSBT technique can be fully applied in research on investment marketing.     

A New Approach for Visual Cryptography

Visual cryptography is to encrypt a secret image into some shares (transparencies) such that any qualified subset of the shares can recover the secret visually. The conventional definition requires that the revealed secret images are always darker than the backgrounds. We observed that this is not necessary, in particular, for the textual images.In this paper, we proposed an improved definition for visual cryptography based on our observation, in which the revealed images may be darker or lighter than the backgrounds. We studied properties and obtained bounds for visual cryptography schemes based on the new definition. We proposed methods to construct visual cryptography schemes based on the new definition. The experiments showed that visual cryptography schemes based on our definition indeed have better pixel expansion in average.