Competition between Hydrophilic and Argyrophilic Interactions in Surface Enhanced Raman Spectroscopy

The competition for binding and charge‐transfer (CT) from the nitrogen containing heterocycle pyrimidine to either silver or to water in surface enhanced Raman spectroscopy (SERS) is discussed. The correlation between the shifting observed for vibrational normal modes and CT is analyzed both experimentally using Raman spectroscopy and theoretically using electronic structure theory. Discrete features in the Raman spectrum correspond to the binding of either water or silver to each of pyrimidine's nitrogen atoms with comparable frequency shifts. Natural bond orbital (NBO) calculations in each chemical environment reveal that the magnitude of charge transfer from pyrimidine to adjacent silver atoms is only about twice that for water alone. These results suggest that the choice of solvent plays a role in determining the vibrational frequencies of nitrogen containing molecules in SERS experiments.     

Mixer-settler counter-current chromatography with a barricaded spiral disk assembly with glass beads

A novel spiral disk is designed by placing barricades at 6 mm intervals in the middle of the spiral channel to divide the channel into multiple sections. Glass beads are placed in every other section so that the planetary motion produces repetitive mixing and settling of polymer phase systems. Performance of this mixer-settler spiral disk assembly was examined for separation of lysozyme and myoglobin with a polymer phase system. The best results were obtained with a spiral disk equipped with barricades with openings ranging from 1.2 to 0.4 mm on each side at a high revolution speed up to 1200 rpm.     

Mixer-settler counter-current chromatography with multiple spiral disk assembly

A novel system for performing high-speed counter-current chromatography has been developed for separation of biopolymers using polymer phase systems. The spiral disk assembly consisting of eight units, each equipped with over 300 mixer-settler sets, was constructed and performance evaluated in terms of retention of the stationary phase and separation efficiency. A series of experiments was performed with a polymer phase system composed of polyethylene glycol 1000 (12.5%, w/w) and dibasic potassium phosphate (12.5%, w/w) using two stable protein samples of myoglobin and lysozyme at various experimental conditions of flow rates and revolution speeds. The best results were obtained with revolution speeds of 800-1000rpm at flow rates of 0.25-0.5ml/min where the partition efficiency of several 100 theoretical plates was achieved with over 50% stationary phase retention.     

Experimental and numerical comparisons of the break-up of a large bubble

 PIV measurement and numerical simulation of a large scale collapsing gas bubble that results from the burst of a balloon in a deep water pool are presented. There is seen to be excellent qualitative agreement between computation and experiment, and good quantitative agreement to within 8–10% when using a normalised error. This validation allowed subsequent investigation of the bubble flow field in areas not measurable using the PIV technique, such the central jet which generates splash, and in flow areas relevant to an industrial smelting process which can be used to determine a suitable tuyere separation. Received: 14 January 1998/Accepted: 12 August 1998     

The First Bismuth Phosphide Complex: [Li(thf)4]+[{(tBuP)3}2Bi]−

Thermally unstable crystals of the title compound—the first bismuth phosphide complex to be structurally characterized (see picture)—are obtained by the reaction of [Bi(NMe₂)₃] with [tBuPHLi] (1:3) in THF/hexane. Berry pseudorotation of the pseudo-trigonal-bipyramidal [{(tBuP)₃}₂Bi]⁻ ion is prevented for steric reasons.     

A scanning PIV method for fine-scale turbulence measurements

A hybrid technique is presented that combines scanning PIV with tomographic reconstruction to make spatially and temporally resolved measurements of the fine-scale motions in turbulent flows. The technique uses one or two high-speed cameras to record particle images as a laser sheet is rapidly traversed across a measurement volume. This is combined with a fast method for tomographic reconstruction of the particle field for use in conjunction with PIV cross-correlation. The method was tested numerically using DNS data and with experiments in a large mixing tank that produces axisymmetric homogeneous turbulence at \(R_\lambda \simeq 219\) . A parametric investigation identifies the important parameters for a scanning PIV set-up and provides guidance to the interested experimentalist in achieving the best accuracy. Optimal sheet spacings and thicknesses are reported, and it was found that accurate results could be obtained at quite low scanning speeds. The two-camera method is the most robust to noise, permitting accurate measurements of the velocity gradients and direct determination of the dissipation rate.     

Branching pattern and sequence analysis of underivatized oligosaccharides by combined MS/MS of singly and doubly charged molecular ions in negative-ion electrospray mass spectrometry

We previously reported that sequence and partial linkage information, including chain and blood-group types, of reducing oligosaccharides can be obtained from negative-ion electrospray CID MS/MS on a quadrupole-orthogonal time-of-flight instrument with high sensitivity and without derivatization (Chai, W.; Piskarev, V.; Lawson, A. M. Anal. Chem. 2001, 73, 651-657). In contrast to oligonucleotides and peptides, oligosaccharides can form branched structures that result in a greater degree of structural complexity. In the present work we apply negative-ion electrospray CID MS/MS to core-branching pattern analysis using nine 3,6-branched and variously fucosylated oligosaccharides based on hexasaccharide backbones LNH/LNnH as examples. The important features of the method are the combined use of CID MS/MS of singly and doubly charged molecular ions of underivatized oligosaccharides to deduce the branching pattern and to assign the structural details of each of the 3- and 6-branches. These spectra give complimentary structural information. In the spectra of [M - H]-, fragment ions from the 6-linked branch are dominant and those from the 3-linked branch are absent, while fragment ions from both branches occur in the spectra of [M - 2H]2-. This allows the distinction of fragment ions derived from either the 3- or 6-branches. In addition, a unique D2beta-3 ion, arising from double D-type cleavage at the 3-linked glycosidic bond of the branched Gal core residue, provides direct evidence of the branching pattern with sequence and partial linkage information being derived from C- and A-type fragmentations, respectively.     

Fast detection of triacetone triperoxide (TATP) from headspace using planar solid-phase microextraction (PSPME) coupled to an IMS detector

Triacetone triperoxide (TATP) is a high explosive synthesized from easily available reactants making it accessible for illicit uses. In this study, fast detection of TATP is achieved using a novel planar solid-phase microextraction (PSPME) as a preconcentration and sampling device for headspace analysis offering improved sensitivity and reduced sampling time over the conventional fiber-based solid-phase microextraction (SPME) when followed by ion mobility spectrometer (IMS) detection. Quantitation and comparison of the retention capabilities of PSPME as compared to the commercially available SPME were determined using TATP standards and analyzed using gas chromatography–mass spectrometry for SPME analysis and a commercial IMS with no instrumental modification for PSPME. Static and dynamic headspace extractions were used and compared for PSPME extractions, in which low milligram quantities of TATP were detected within 30 s of static mode sampling and less than 5 s in the dynamic mode sampling for PSPME–IMS.     

Catalytic enantioselective protonation of nitronates utilizing an organocatalyst chiral only at sulfur

The highly enantioselective protonation of nitronates formed upon the addition of α-substituted Meldrum's acids to terminally unsubstituted nitroalkenes is described. This work represents the first enantioselective catalytic addition of any type of nucleophile to this class of nitroalkenes. Moreover, for the successful implementation of this method, a new type of N-sulfinyl urea catalyst with chirality residing only at the sulfinyl group was developed, thereby enabling the incorporation of a diverse range of achiral diamine motifs. Finally, the Meldrum's acid addition products were readily converted to pharmaceutically relevant 3,5-disubstituted pyrrolidinones in high yield.