cis- and trans-N-nitroso-2,4-diphenylazetidines

The synthesis of cis- and trans-2,4-diphenylazetidines as well as that of their N-nitroso derivatives is described. The “abnormal” reduction of the N-nitrosamines gives a cis-trans mixture of the expected 1,2-diphenylcyclopropanes. However, no stereochemical correlations could be made owing to the base-induced isomerization of the starting N-nitrosamines during the course of the reaction.     

Characterization of etched electrochemical detection for electrophoresis in micron inner diameter capillaries

An enhanced etched electrochemical (EC) detection technique has been developed for CE in micron inner diameter capillaries. The design improvements allow for better alignment between the capillary bore and the electrode. This new method involves utilizing a carbon fiber microelectrode and etching both the carbon fiber and the detection end of a micrometer-sized inner diameter capillary to limit dead volume and analyte diffusion at the amperometric EC detector. To understand the factors affecting enhanced detector efficiency, a detailed examination of the relationship between detector design and performance has been completed by exploring the effects of varying electrode diameter, tip shape, and size, in addition to the etch length of the capillary outlet. The enhanced detection provides peak efficiencies as high as 75000 theoretical plates and estimated detection limits as low as 40 nM for dopamine. This etched detection method should further facilitate volume-limited sample analysis by CE.     

A general mass spectrometry-based assay for the quantitation of protein-ligand binding interactions in solution

A new method that utilizes matrix-assisted laser desorption/ionization (MALDI) mass spectrometry and exploits the hydrogen/deuterium (H/D) exchange properties of proteins was developed for measuring the thermodynamic properties of protein-ligand complexes in solution. Dissociation constants (Kd values) determined by the method for five model protein-ligand complexes that included those with small molecules, nucleic acids, peptides, and other proteins were generally in good agreement with Kd values measured by conventional methods. Important experimental advantages of the described method over existing methods include: the ability to make measurements in a high-throughput and automated fashion, the ability to make measurements using only picomole quantitities of protein, and the ability to analyze either purified or unpurified protein-ligand complexes.     

Amide interactions in chlorinated solvents

Enthalpies of solution and of transfer of amides for the solvents chloroform (CHCl₃), methylenechloride (CH₂Cl₂), carbontetrachloride (CCl₄), cyclohexane (C₆H₁₂), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), and ethylacetate (EtOAc) have been used to isolate and quantify the solvation interactions of amides in chlorinated solvents. Specific interactions at the aminde carbonyl and N–H groups have been identified. An analysis of the transfer enthalpies of pyrrole and methylpyrrole from cyclohexane to the chlorinated solvents shows that specific interactions between the pyrroles and these solvents are similar in nature. A means of calculating differences in the transfers of different solutes between the same solvent pair is given.Work done at Lebanon Valley College.     

Penta­chloro‐1,3,6‐tris­(diethyl­phenyl­phosphino)­dirhenium(II,III)

The title complex [systematic name: penta­chloro‐1κ³Cl,2κ²Cl‐tris(diethylphenylphosphino)‐1κP,2κ²P‐dirhenium(II,III)(Re—Re)], 1,3,6‐Re₂Cl₅(PEt₂Ph)₃ or [Re₂Cl₅(C₁₀H₁₅P)₃], consists of dirhenium mol­ecules with eclipsed structures similar to those of previously characterized 1,3,6‐Re₂Cl₅(PR₃)₃ compounds. The Re—Re bond distance is 2.2262 (3) Å and the metal–metal bond order is 3.5.     

Instrumental barriers in biological Fourier transform infrared spectroscopy

Biological applications of infrared spectroscopy have pressed for ever greater instrumental capabilities in terms of spectral sensitivity and quantitative exactness. Improved instrumentation has provided measurement of many vibrational modes in biological samples that previously were lost in noise. With highly optimized sampling conditions, useful measurements have been made with a peak-to-peak noise level less than 5 microabsorbance (5×10^–6 absorbance), at 0.5 cm^–1 resolution. However, optical and instrumental instabilities often result in sine waves that are not totally removed by the ratio of sample to reference. These often limit effective spectral sensitivity to 50 or 100 microabsorbance, peak-to-peak, and constitute a non-random noise. Non-atmospheric absorptions, especially one at 1959 cm^–1 with 0.8 cm^–1 band width (FWHM) are reported. The latter is due to a trace impurity in the KBr beam splitter substrate and compensator plate. Improvements in instrumentation and sampling conditions are expected to yield measurements of absorption bands as small as 50 microabsorbance with excellent signal/noise.     

Increased throughput in quantitative bioanalysis using parallel-column liquid chromatography with mass spectrometric detection

The feasibility of quantitative bioanalysis by parallel-column liquid chromatography in conjunction with a conventional single-source electrospray mass spectrometer has been investigated using plasma samples containing a drug and its three metabolites. Within a single chromatographic run time, sample injections were made alternately onto each of two analytical columns in parallel at specified intervals, with a mass spectrometer data file opened at every injection. Thus, the mass spectrometer collected data from two sample injections into separate data files within a single chromatographic run time. Therefore, without sacrificing the chromatographic separation or the selected reaction monitoring (SRM) dwell time, the sample throughput was increased by a factor of two. Comparing the method validation results obtained using the two-column system with those obtained using the corresponding conventional single-column approach, the methods on the two systems were found to be equivalent in terms of accuracy and precision. The parallel-column system is simple and can be implemented using existing laboratory equipment with no additional capital outlays. A parallel-column system configured in this manner can be used not only for the within-a-run analysis of two samples containing two different sets of chemical entities, but also for the within-a-run analysis of two samples containing the same set of chemical entities.