The complexation of rhodium(III) with acyclic diaminedithioether (DADTE) ligands

(103)Rhodium(III) complexes derived from seven acyclic tetradentate N(2)S(2) ligands (one diaminedithiol and six diaminedithioether ligands) have been synthesized and characterized. Structural variations in the ligand include the length of carbon backbone between the coordinating atoms (222; 232; 323; 333), the presence or absence of gem-dimethyl groups α to sulfur, and the nature of the organic moiety on the sulfurs (hydrogen, p-methoxybenzyl and methyl). For each ligand, the formation of cis and/or trans dichloro isomeric complexes was assessed. Two complexes have been further characterized by single crystal X-ray diffraction. Preparation of the (103)Rhodium(III) complexes was conducted and overall radiochemical yields, in vitro stability and log D(7.4) values were measured. From these studies, the ligand with the 232 chain length, gem-dimethyl groups and the methyl thioether (L4) emerged as a preferred ligand for formation of rhodium complexes with trans geometry and highest radiochemical yields.     

Thermal and field emission effects of laser radiation on metal whisker diodes: Application to infrared detection devices

In a series of recent experiments, research groups have made absolute frequency measurements with laser beams in the infrared region of the spectrum (λ ? 10 μm) using a metal point contact diode for generation, frequency mixing and detection. It has been postulated that the mechanism for the nonlinear current-voltage characteristic of the diode is tunnelling of electrons through an intermediate oxide film from the whisker into the metal base, i.e., the configuration is considered to be a metal-oxide-metal (MOM) tunnelling junction. Several features of the diode's operation create considerable doubt concerning the applicability of the MOM tunnelling mechanism. Analysis of the available experimental data led us to postulate an alternate solid state mechanism, namely a thermally enhanced field emission process. Such emission would be a consequence of the immersion of the whisker tip in the laser radiation resulting in (1) conduction heating which induces thermionic emission and (2) generation of an electric field at the tip necessary for electron tunnelling by field emission. In this paper we calculate rigorously the power absorbed in the metal whisker from the incident radiation. From the power absorbed, the heat conduction equation is solved for model geometries to obtain the laser induced temperature distribution at the whisker surface. Estimates of the electric field are obtained and combined with temperature calculations to obtain the nonlinear I–V characteristics of the thermally enhanced field emission model. Finally some simple experiments are proposed to test the thermal field emission hypothesis as a possible mechanism to explain the nonlinear characteristics of the metal whisker point contact diode.     

A parametric study of the surface potential and band bending in silicon

A unified approach to band bending is described, and the macroscopic electronic potential through the silicon surface is calculated as a function of temperature in the ranges 300–500°K and 100–1600°K, externally applied electric field, for zero field and for 10³ to 10⁵ V/cm, and donor and acceptor concentrations, from 10¹² to 10¹⁸ cm^?3. The results, presented in graphical and tabular forms, are intended to serve the convenience of researchers in a wide area of surface and high temperature silicon physics such as in thermionic, field, and photoelectric emission work and in high temperature, and field modulated transport studies. The calculations are based on an essentially classical approach to the solution of the electrostatic band bending problem, using the surface state density for silicon proposed by Allen and Gobeli on the basis of their photoelectric investigations. The cases considered were limited to nondegenerate, intrinsic, and n- and p-doped silicon in which all impurity states are fully ionized.     

Influence of the boundary conditions on the fermi energy and density of states in a free-electron solid of sub-micron dimensions

Asymptotic expressions for the distribution of the eigenvalues of the Helmholtz-Schrödinger equation are used to anlyze the dependence of the Fermi energy, E_F, and the density of states, ρ(E), on sample size, shape, and electron density, in a free-electron model with Dirichlet boundary conditions. It is found that for very small samples E_F is increased relative to its asymptotic (i.e., bulk) value and ρ(E) is decreased relative to its bulk value. These effects are more pronounced for samples with low electron density and with a large surface-to-volume ratio. In general E_F and ρ(E_F) deviate significantly from their bulk values only for systems with fewer than 50,000 electrons and/or with linear dimensions of 100 Å or less. The use of smoothing functions to represent the density of states obtained from the exact eigenvalue distribution is also discussed. It is shown that an oscillating density of states leads to small cusps in the plot of E_F as a function of sample size. This is in qualitative agreement with the results of experiments on size-dependent oscillations in field emission from thin metallic films. Comparison is also made between photoemission experiments from thin films and other results obtained in this study.     

Synthesis of 1-(β-D-ribofuranosyl)indol-3-acetic acid

By condensation of ethyl indolin-3-acetate ( 4 ) and 2,3,5-tri-O-benzoylribofuranosyl-1-acetate ( 5 ), ethyl 1-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)indolin-3-acetate ( 6 ) was obtained in good yield. The indoline nucleoside 6 was aromatized to ethyl 1-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)indol-3-acetate ( 7 ) with DDQ. The treatment of the indole nucleoside with barium hydroxide and methanol gave the methyl ester 8 , which was further treated in water to give the desired 1-(β-D-ribofuranosyl)indol-3-acetic acid ( 9 ).     

MALDI-TOF mass signatures for differentiation of yeast species,strain grouping and monitoring of morphogenesis markers

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) is demonstrated to be a potentially useful tool for the rapid identification of yeasts, the grouping of Candida albicans strains, and the monitoring of germ tube-specific markers. Co-crystallized with sinapinic acid as the MALDI matrix, intact yeast cells yielded a sufficient number of medium-sized ions (4–15 kDa) in MALDI mass spectra to provide “mass signatures” that were diagnostic of strain type. For most isolates, the mass signatures were affected by the growth medium, length of incubation and the cell preparation method. While the overall past success of this methodology for fungal cells has been relatively low compared to its application to bacteria, fixing the yeast cells in 50% methanol inactivated the cells, reduced cell aggregation in aqueous suspension solution, and more importantly, it significantly improved the mass signature quality. This simple but critical advance in sample treatment improved mass spectrometric signal-to-noise ratios and allowed the identification of yeasts by a mass signature approach. Under optimized conditions, Candida species (C. albicans, C. glabrata, C. krusei, C. kefyr), Aspergillus species (A. terreus, A. fumigatus, A. syndowii) and other yeast genera (Cryptococcus neoformans, Saccharomyces cerevisiae and a Rhodotorula sp.) could be distinguished. Within the C. albicans species, several common ions in the m/z 5,000–10,000 range were apparent in the mass spectra of all tested strains. In addition to shared ions, the mass spectra of individual C. albicans strains permitted grouping of the strains. Principal component analysis (PCA) was employed to confirm spectral reproducibility and C. albicans strain grouping by mass signatures. Finally, C. albicans germ tubes produced MALDI-TOF mass signatures that differed from yeast forms of this species. This is a rapid, sensitive and simple method for identifying yeasts, grouping strains and following the morphogenesis of C. albicans. Figure       

Efficient synthesis of 4-oxo-4,5-dihydrothieno[3,2-c]quinoline-2-carboxylic acid derivatives from aniline

The first reported synthesis of potential kinase inhibitors, 4-oxo-4,5-dihydrothieno[3,2- $c$ ]quinoline-2-carboxylic acid derivatives starting from aniline is described. This efficient high yielding sequence was carried out in six steps without any chromatographic purification. A tandem nucleophilic aromatic substitution/cyclization reaction was used as a key step in the sequence. The versatile intermediate 2-carboxylic acid was used as a suitable precursor to access the functionalization of the C-ring, by convergent analog synthesis of several novel derivatives.     

Phonologically determined asymmetries in vocabulary structure across languages

Studies of spoken-word recognition have revealed that competition from embedded words differs in strength as a function of where in the carrier word the embedded word is found and have further shown embedding patterns to be skewed such that embeddings in initial position in carriers outnumber embeddings in final position. Lexico-statistical analyses show that this skew is highly attenuated in Japanese, a noninflectional language. Comparison of the extent of the asymmetry in the three Germanic languages English, Dutch, and German allows the source to be traced to a combination of suffixal morphology and vowel reduction in unstressed syllables.     

Pure drug nanoparticles in tablets: what are the dissolution limitations?

There has been increasing interests for drug companies to incorporate drug nanoparticles into their existing formulations. However, technical knowledge in this area is still in its infancy and more study needs to be done to stimulate growth in this fledging field. There is a need to scrutinize the performance of pure drug nanoparticles in tablets, particularly relating formulation variables to their dissolution performance. Application of the pure form, synthesized without the use of surfactants or stabilizers, is often preferred to maximize drug loading and also to minimize toxicity. Cefuroxime axetil, a poorly water-soluble cephalosporin antibiotic, was used as the model drug in the formulation development. Drug release rate, tablet disintegration time, tensile strength and energy of failure were predominantly influenced by the amount of super-disintegrant, amount of surfactant, compression force and diluent species, respectively. The compression rate had minimal impact on the responses. The main hurdle confronting the effective use of pure drug nanoparticles in tablets is the difficulty in controlling aggregation in solution, which could potentially be aggravated by the tabletting process. Through the use of elevated levels of surfactants (8 w/w% sodium dodecyl sulphate), drug release from the nanoparticle preparation was enhanced from 58.0 ± 2.7% to 72.3 ± 0.7% in 10 min. Hence, it is recommended that physical formulations for pure drug nanoparticles be focused on the particle de-aggregation step in solution, if much higher rates are to be desired. In conclusion, even though pure drug nanoparticles could be easily synthesized, limitations from aggregation may need to be overcome, before successful application in tablets can be fully realized.