Moment analysis method as applied to the 2S --> 2P transition in cryogenic alkali metal/rare gas matrices

The moment analysis method (MA) has been tested for the case of 2S --> 2P ([core]ns1 --> [core]np1) transitions of alkali metal atoms (M) doped into cryogenic rare gas (Rg) matrices using theoretically validated simulations. Theoretical/computational M/Rg system models are constructed with precisely defined parameters that closely mimic known M/Rg systems. Monte Carlo (MC) techniques are then employed to generate simulated absorption and magnetic circular dichroism (MCD) spectra of the 2S --> 2P M/Rg transition to which the MA method can be applied with the goal of seeing how effective the MA method is in re-extracting the M/Rg system parameters from these known simulated systems. The MA method is summarized in general, and an assessment is made of the use of the MA method in the rigid shift approximation typically used to evaluate M/Rg systems. The MC-MCD simulation technique is summarized, and validating evidence is presented. The simulation results and the assumptions used in applying MA to M/Rg systems are evaluated. The simulation results on Na/Ar demonstrate that the MA method does successfully re-extract the 2P spin-orbit coupling constant and Landé g-factor values initially used to build the simulations. However, assigning physical significance to the cubic and noncubic Jahn-Teller (JT) vibrational mode parameters in cryogenic M/Rg systems is not supported.     

Synthesis of (1R,2S)-1-amino-2-vinylcyclopropanecarboxylic acid vinyl-ACCA) derivatives: key intermediates for the preparation of inhibitors of the hepatitis C virus NS3 protease

(1R,2S)-1-Amino-2-vinylcyclopropanecarboxylic acid (vinyl-ACCA) is a key building block in the synthesis of potent inhibitors of the hepatitis C virus NS3 protease such as BILN 2061, which was recently shown to dramatically reduce viral load after administration to patients infected with HCV genotype 1. We have developed a scalable process that delivers derivatives of this unusual amino acid in >99% ee. The strategy was based on the dialkylation of a glycine Schiff base using trans-1,4-dibromo-2-butene as an electrophile to produce racemic vinyl-ACCA, which was subsequently resolved using a readily available, inexpensive esterase enzyme (Alcalase 2.4L). Factors that affect diastereoselection in the initial dialkylation steps were examined and the conditions optimized to deliver the desired diastereomer selectively. Product inhibition, which was encountered during the enzymatic resolution step, initially resulted in prolonged cycle times. Enrichment of racemic vinyl-ACCA through a chemical resolution via diastereomeric salt formation or the use of forcing conditions in the enzymatic reaction both led to improvements in throughput and the development of a viable process. The chemistry described herein was scaled up to produce multikilogram quantities of this building block.     

Synthesis of new o-alkyl substituted arylalkylphosphanes: study of their molecular structure and influence on rhodium-catalyzed propene and 1-hexene hydroformylation

A set of new phosphane ligands designed to increase the branched-to-normal ratio of the hydroformylation reaction were prepared in the same way as the previously reported ortho-alkyl substituted arylphosphanes, which have shown increased i/n ratios in the hydroformylation of propene and 1-hexene. In order to determine the relationship between the catalytic behavior and stereoelectronic properties of the ligands, various functional alkyl groups (methyl, isopropyl, cyclohexyl) were placed on the phosphorus atom directly and in the ortho position of the phenyl ring connected to phosphorus. In the hydroformylation reaction of propene and 1-hexene a higher i/n ratio resulted with nearly all the ligands compared with that of triphenylphosphane. Additionally as the ortho-alkyl-substituent became larger, it had a favorable effect on the i-selectivity. Characterization of the ligands was carried out by NMR spectroscopy (mainly ¹H, ³¹P{¹H}, ¹³C{¹H}, HSQC/HETCOR and COSY-90). Properties of the ligands were also studied by quantum mechanical calculations and by synthesizing three Rh(acac)(CO)(PR₃) derivatives. The o-alkyl-substituent was orientated outside the ligands’ cone angle in the X-ray crystal structures of (2-cyclohexylphenyl)dicyclohexylphosphane and (2,5-dimethylphenyl)bis(4-pyridyl)phosphane, and Rh(acac)(CO)(PR₃) complex of (2-methylphenyl)dicyclohexylphosphane.     

Evaluation of semiquantitative analysis mode in ICP-MS

Semiquantitative analysis mode in inductively coupled plasma mass spectrometry (ICP-MS) has been popularly used for fast screening purposes. Although the benefit of it has been studied by many researchers, its performance of application in real-world routine analyses has not been reported.

In this study, we evaluated the reliability of semiquantitative analysis mode through inter-laboratory comparison using two different ICP-MS systems with one multi-element calibration standard. The suitability of semiquantitative analysis mode in routine analysis laboratory was demonstrated by evaluating its application in different laboratories and in real production laboratory practices. Twenty one elements were measured, namely, Be, B, Al, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, As, Sr, Mo, Ag, Cd, Sn, Sb, Ba, Tl, and Pb in various fresh water reference samples. Good results concerning accuracy (relative percentage error within 10%) and reproducibility (relative standard deviation lower than 5%) were obtained in more than 90% analyzed samples at concentrations equal to or greater than 10 times the detection limit (DL). Semiquantitative analysis mode also enabled the determination of elements that are not present in the calibration standard. The results demonstrated the potential of semiquantitative analysis mode as a reliable approach in routine laboratory determination of simple matrices, where high throughput and cost-effectiveness are desired, as well as in emergency situations where speed of analysis is critical and quite often limited sample information is available.     

Vibrational action spectroscopy of the C-H and C-D stretches in partially deuterated formic acid dimer

Vibrational action spectroscopy of jet-cooled formic acid dimer measures the frequency of the C-H(D) stretching vibration and its coupling to nearby states. The action spectrum of (DCOOH)2 reveals a specific Fermi resonance between the C-D stretch and two antisymmetric combination states formed from the C-O stretch and DCO bend. A three-state deperturbation analysis shows that there is a relatively strong coupling between the fundamental vibration and each of the combination vibrations (mid R:13 cm(-1)mid R:) as well as between the combination states themselves (mid R:7 cm(-1)mid R:). This situation contrasts with that for the action spectrum of (HCOOD)2, where the C-H oscillator is isolated and not strongly coupled to other states.     

Double-quantum filtered 1H MAS NMR spectra

It is shown that straightforward double-quantum filtered (1)H MAS NMR experiments yield spectral lineshapes that permit to estimate the minimum number of (1)H spins in a cluster. The approach may offer an alternative to multiple-quantum experiments for the characterisation of (1)H spin clusters of moderate size. The duration of the double-quantum excitation period has to be chosen suitably, it is necessary to find a practical compromise between optimum double-quantum filtration efficiency and optimum information content of the spectral lineshapes. Some (1)H MAS NMR experiments on partially deuterated maleic acid are reported as well as numerical simulations.     

Preparation of nanocrystalline titania films with different porosity by water-based chemical solution deposition

This study describes the synthesis of nanocrystalline titania layers on silicon and glass substrates by chemical solution deposition, using a water-based citratoperoxo-Ti(IV) precursor solution. The same aqueous solution–gel precursor is used for deposition of, both, thin dense layers by spin-coating and thicker porous layers by tape-casting. In the latter, the precursor solution is modified by the addition of polyvinyl alcohol (PVA), which acts as a thickener and pore-forming agent. Phase composition, film morphology, and the hydrophilic character of the films are studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–VIS transmission measurements, variable angle spectroscopic ellipsometry (VASE), and by contact angle measurements. The thin 180 nm titania film, deposited from the unmodified precursor solution, shows a density of about 96%. Upon ultraviolet illumination, it acquires a highly hydrophilic surface. One hour of illumination is sufficient to obtain a water contact angle of almost 0°. Furthermore, the hydrophilisation process shows to be reversible. Tape-casting and thermal treatment of the modified precursor solution gives rise to the formation of a 500 nm thick, porous, pure anatase film. The nanocrystalline thick film is composed of 20–40 nm particles, and contains clearly defined pores of 20 nm, homogeneously distributed along the surface.     

Batch electrophoretic cells with Eyring fluids: analysis of the hydrodynamics

Mixing and dispersion phenomena caused by the carrier fluid in an electrophoretic cell is the main subject of this study. In particular, the effects of Joule heating on temperature and velocity profiles for Eyring-model fluids (EMF) are studied. The heat transfer is sequentially coupled with momentum transfer to derive an analytical expression for both the temperature and the velocity profiles. These results are then used to show the hydrodynamic behavior of the fluid in a batch electrophoretic cell. Furthermore, the results obtained are useful to compare with the fluid behavior of other carriers of different rheology, such as Newtonian fluids, power-law fluids, and viscoelastic fluids that obey the CEF model. The results show that EMF are potentially good carriers for relatively high Joule heat generation and therefore good candidates to control mixing inside the electrophoretic cell.