David E. Henderson

Low temperature high-performance liquid chromatography of cis-trans proline dipeptides

Isomeric dipeptides which contain proline at the C-terminus and undergo on-column cis-trans isomerization were separated by reversed-phase chromatography at subambient column temperature. Chromatography at low temperatures offers a convenient method for measuring the relative concentrations of the isomers and, thus, the calculation of the equilibrium constants for such cis-trans isomerization at various conditions of solvent, pH, and temperature. Pure fractions of the cis and trans isomers were collected and used in kinetic studies of the isomerization. High-performance liquid chromatography at temperatures near the freezing point of the eluent is a potentially useful tool for the study of a wide range of biochemical molecules.

Physicochemical studies of biologically active peptides by low-temperature reversed-phase high-performance liquid chromatography

The high-performance liquid chromatographic separation of biologically active peptides containing 1-prolyl residues is demonstrated. Rapid isomer interconversion between cis- and trans-isomeric forms at the prolyl peptide bond is shown to produce classical secondary equilibrium effects in the peak shapes. By operating the column at temperatures in the range -15 degrees C to 5 degrees C it is possible to obtain normal separations of the various isomeric forms. The use of low column temperatures makes physicochemical studies possible, e.g., the effect of pH on isomer composition in free solution as reported here for morphiceptin.

Developments in the high-performance liquid chromatography of metallo-organic compounds

Abstract A number of developments in the high-performance liquid chromatography of metallo-organic complexes are described. Micellar chromatography of cobalt(III)—iminodiacetate isomer anions has been carried out with hexadecyltrimethylammonium bromide surfactant, with full resolution of cis and facial trans isomers. A dynamic ion-exchange micellar mechanism is proposed. Neutral N,N′-ethylenebis(acetylacetoneimine) chelates of copper(II) and nicker(II) are separated using sodium dodecyl sulfate in methanol—water as the mobile phase, which constrains the copper complex to be eluted before the nickel chelate. The separation of thermally labile isomers of aluminium trifluoroacetylacetonates is described, isomerization being precluded at O°C. Direct-current argon plasma emission spectral detection is used to confirm elution of cobalt, chromium at aluminum complexes.

Physicochemical studies of fac-mer isomerism of aluminium beta-diketonates by high performance liquid chromatography at low temperature

Abstract The kinetics of interconversion of fac and mer isomers of Al(III) beta-diketonates both in free solution and during chromatographic elution are reported using low temperature high performance liquid chromatography to prepare and analyse pure isomeric complexes. Studies of retention and separation mechanisms of these complexes are also conducted using variation in column temperature to elucidate the contributions of enthalpy and entropy effects.

Comparative Computer Simulation of Several Signal to Noise Enhancement Techniques

Abstract Techniques for signal to noise ratio enhancement (filtering) of noisy experimental data are compared by comprehensive computer simulation using synthetic data. The four important descriptors: signal to noise ratio enhancement, peak width increase, peak maximum displacement, and computation time on a laboratory minicomputer are determined for each filter type studied. Comparative results indicate important trends and considerations of signal processing as well as providing a foundation for the selection of filter designs for a given instrumental situation.

Acidity of machine-made snow and its effect on pH and aluminum speciation in New England streams during spring thaw

The pH of machine-made snow and its effect on an acid-sensitive watershed in Vermont were studied. Spring runoff from snowmaking was found to be less acidic and to contain less dissolved inorganic aluminum. Dissolved inorganic aluminum has been associated with damage to aquatic life. The extensive use of machine-made snow by the ski industry in most of the northeast region of the US may be beneficial to aquatic life.