John F. Wheeler

Photoredox behavior and chiral discrimination of DNA bound M(diimine)3n+ complexes (M=Ru2+, Cr3+)

Abstract An overview is given of the rapidly developing field of bioinorganic chemistry involving the interaction of Ru(diimine)32+ complexes with double-stranded DNA. This contribution focusses on the photoredox behavior of these DNA bound systems and the presence of chiral discrimination in the binding process. Cr(diimine)33+ complexes are attractive new candidates for such studies in view of their long-lived room temperature luminescence and strong excited state oxidizing power. For these Cr(III) systems we observe strong quenching of the emission signal in the presence of B-DNA, and provide evidence that this quenching is associated with a photoredox process involving guanine base oxidation. We also demonstrate the value of capillary electrophoresis (CE) as a technique for assessing the relative binding constants and the stereoselectivities of transition metal interactions with DNA. In addition, we explore the use of CE as an alternative approach to help resolve literature disagreements between different Ru(phen)32+/DNA binding models.

Phase transitions of reversed-phase stationary phases : cause and effects in the mechanism of retention

We provide a somewhat historical perspective on the work that has been accomplished that supports the suggestion of phase transitions in reversed-phase liquid chromatographic bonded phases. In addition to this general review, we consider from both a practical and theoretical viewpoint the implications of such transitions in the rational design of improved reversed-phase separations. Analytical theory and molecular simulation approaches to chromatographic stationary phases and related systems are reviewed. Initial results are presented on the temperature, density and chain length dependences of stationary phase properties. The role of computer simulation in analyzing transition behavior and retention processes is discussed.

Enhanced selectivity for capillary zone electrophoresis using ion-pair agents

Abstract Capillary zone electrophoresis (CZE) is unique in its simplicity and versatility for liquid separations, yet selectivity for solutes with similar charge and hydrated radius is often lacking. Conventional reversed-phase liquid chromatography (RP-LC) ion-pairing agents, ionic polymers, Group I and II metal cations and dicarboxylic acids have all been effectively used over the past decade to enhance CZE resolution through a combination of complexing effects. This review summarizes the fundamental theory of ion–ion interaction as applied to CZE separations and discusses several of the most important and diverse applications of selectivity enhancement that utilize ion-pair equilibria. In addition, the effect of ion-pair additives on electroosmotic flow and examples where changes in analyte selectivity are unrelated to ion–ion interaction are discussed.

Selectivity enhancement for free zone capillary electrophoresis using conventional ion-pairing agents as complexing additives

Abstract Analyte selectivity in capillary zone electrophoresis may be limited due to similarities in the charge/size ration for related compounds. Conventional cationic and anionic ion-pair agents including alkylsulfonic acids and tetraalkylammonium salts have been investigated as additives to the electrophoretic run buffer to improve both the selectivity and resolution for organosolutes, peptides and proteins. Several different factors are responsible for changes in selectivity and resolution, including ionic interaction and hydrophobic association between solutes and additives as well as the modulation of electroosmotic flow. Selectivity improvements due to ionic interaction can be systematically optimized by varying size and concentration of the ion-pairing agent(s) in the buffer system. Butanesulfonic acid in particular appears to very useful for a diversity of applications including improved neurotransmitter separations, peptide mapping and separations of protein mixtures.

Long‐term and acute effects of zinc contamination of a stream on fish mortality and physiology

A section of the Upper Enoree River in South Carolina, USA, was contaminated with chemical waste in 1985, and high concentrations of zinc persist decades later. In this study, we examined the zinc concentrations in the water, the accumulation of zinc in a variety of fish tissues, the effects of the contaminated water on fish sperm motility in vitro, and the mortality rates of introduced fish. Zinc concentrations in the water samples collected from six sites decreased as distance from the spill site increased, ranging from 7.3 to 0.34 mg/L (p < 0.001). The zinc concentrations of tissues from native fish were highest in liver (mean across sites of 110 ppm/g tissue) and gills (77.4 ppm/g tissue), followed by gonads (30.7 ppm/g tissue) and muscle (6.9 ppm/g tissue) (p < 0.001). The duration of fast motility of Salmo trutta sperm was significantly diminished in sperm activated in samples from the contaminated stream compared with the control stream (p < 0.05). To further evaluate the ability of fish to survive at the sites with different zinc concentrations, groups of Gambusia holbrooki were placed in traps at a reference site (uncontaminated local tributary), and three sites along the contaminated stream. Rapid mortality was observed in the two sites closest to the spill, including one site in which native fish had been found. The introduced G. holbrooki expressed higher zinc concentration in gills than gonads or muscle (p < 0.001), and water zinc concentration significantly affected fish mortality (p < 0.001). The results from these experiments indicate that zinc contamination of streams can have sublethal effects on populations and physiology of fish that are able to survive in the contaminated water.

Chiral separations of transition metal complexes using capillary zone electrophoresis

Several buffer additives that may facilitate chiral separation for optically active transition metal (TM) systems are investigated using capillary zone electrophoresis. The TM complexes evaluated exhibit considerable heterogeneity with respect to total complex charge (0 to 4+), ligand type, and identity of the central metal including Ru2+, Ni2+, Cr3+, and Co3+, threo-D[+]-Isocitrate, potassium antimonyl-d-tartrate and dibenzoyl-L-tartrate are identified as the most efficient chiral selectors. Interestingly, TM complexes exhibiting a (3+) total complex charge exhibit a reversal of enantiomer elution order versus all other complexes when separated using the tartrate additives. Operating parameters including pH, temperature, and capillary length are discussed, and chiral separations of complex mixtures are demonstrated.

Ten-Atom Silver Cluster Signaling and Tempering DNA Hybridization

Silver clusters with ∼10 atoms are molecules, and specific species develop within DNA strands. These molecular metals have sparsely organized electronic states with distinctive visible and near-infrared spectra that vary with cluster size, oxidation, and shape. These small molecules also act as DNA adducts and coordinate with their DNA hosts. We investigated these characteristics using a specific cluster-DNA conjugate with the goal of developing a sensitive and selective biosensor. The silver cluster has a single violet absorption band (λ(max) = 400 nm), and its single-stranded DNA host has two domains that stabilize this cluster and hybridize with target oligonucleotides. These target analytes transform the weakly emissive violet cluster to a new chromophore with blue-green absorption (λ(max) = 490 nm) and strong green emission (λ(max) = 550 nm). Our studies consider the synthesis, cluster size, and DNA structure of the precursor violet cluster-DNA complex. This species preferentially forms with relatively low amounts of Ag(+), high concentrations of the oxidizing agent O2, and DNA strands with ≳20 nucleotides. The resulting aqueous and gaseous forms of this chromophore have 10 silvers that coalesce into a single cluster. This molecule is not only a chromophore but also an adduct that coordinates multiple nucleobases. Large-scale DNA conformational changes are manifested in a 20% smaller hydrodynamic radius and disrupted nucleobase stacking. Multidentate coordination also stabilizes the single-stranded DNA and thereby inhibits hybridization with target complements. These observations suggest that the silver cluster-DNA conjugate acts like a molecular beacon but is distinguished because the cluster chromophore not only sensitively signals target analytes but also stringently discriminates against analogous competing analytes.

GC-MS of ignitable liquids using solvent-desorbed SPME for automated analysis.

Solid-phase microextraction (SPME) is well documented with respect to its convenience and applicability to sampling volatiles. Nonetheless, fire debris analysts have yet to widely adopt SPME as a viable extraction technique, although several fire debris studies have demonstrated the utility of SPME coupled with gas chromatography-mass spectrometry (GC-MS) to identify ignitable liquids. This work considers the expansion of SPME sampling from the customary thermal desorption mode to solvent-based analyte desorption for the analysis of ignitable residues. SPME extraction fibers are desorbed in 30 microL of nonaqueous solvent to yield a solution amenable to conventional GC-MS analysis with standard autosampler apparatus. This approach retains the advantages of convenience and sampling time associated with thermal desorption while simultaneously improving the flexibility and throughput of the method. Based on sampling results for three ignitable liquids (gasoline, kerosene, anddiesel fuel) in direct comparisons with the widely used activated charcoal strip (ACS) method this methodology appears to be a viable alternative to the routinely used ACS method.

Hydrophobic interaction electrokinetic chromatography for the separation of polycyclic aromatic hydrocarbons using non-aqueous matrices.

Capillary electrophoresis methodology is developed to provide a rapid, inexpensive and robust technique for screening polycyclic aromatic hydrocarbons (PAHs) in water using additive complexation. A series of conventional RPLC ion-pairing agents are investigated in three different totally non-aqueous separation solvents, and the relative role of hydrophobic interaction versus electrostatic association is evaluated. Methanol is found to provide optimal selectivity when coupled with the tetrahexylammonium cation providing total analysis times of approximately 15 min for the analysis of thirteen 2-7-ring PAH pollutants. Solid-phase microextraction is demonstrated to be an effective sample preparation technique for extraction/preconcentration of PAHs from water into methanol run buffer prior to injection.

Synthesis of cis-[Cr(diimine)2(1-methylimidazole)2]3+ Complexes and an Investigation of Their Interaction with Mononucleotides and Polynucleotides

A protocol is presented for the synthesis of chromium(III) complexes of the type cis-[Cr(diimine)2(1-methylimidazole)2](3+). These compounds exhibit large excited-state oxidizing powers and strong luminescence in solution. Emission is quenched by added guanine, yielding rate constants that track the driving force for guanine oxidation. The cis-[Cr(TMP)(DPPZ)(1-MeImid)2](3+) species binds strongly to duplex DNA with a preference for AT base sites in the minor groove and may serve as a precursor for photoactivated DNA covalent adduct formation.