EXPRESS: Landmark Publications in Analytical Atomic Spectrometry: Fundamentals and Instrumentation Development.

The almost-two-centuries history of spectrochemical analysis has generated a body of literature so vast that it has become nearly intractable for experts, much less for those wishing to enter the field. Authoritative, focused reviews help to address this problem but become so granular that the overall directions of the field are lost. This broader perspective can be provided partially by general overviews but then the thinking, experimental details, theoretical underpinnings and instrumental innovations of the original work must be sacrificed. In the present compilation, this dilemma is overcome by assembling the most impactful publications in the area of analytical atomic spectrometry. Each entry was proposed by at least one current expert in the field and supported by a narrative that justifies its inclusion. The entries were then assembled into a coherent sequence and returned to contributors for a round-robin review.

Acetaldehyde reactions during wine bottle storage.

Acetaldehyde is a major wine oxidation product. Here, three Cabernet Sauvignon wines, containing different levels of acetaldehyde from different micro-oxygenation (mOx) regimes, including yeast-mediated treatments, were aged under closures differing in oxygen ingress. Oxygen, phenolics, carbonyls and heterocyclic acetals were measured. Acetaldehyde levels at bottling was a significant factor in the phenolic compound profile after one year, with anthocyanins most affected, then flavonols, flavonoids and hydroxycinnamic acids, but there were negligible effects on benzoic acids. The effect of bottle closures with increased oxygen ingress had a similar trend. Increased acetaldehyde levels and oxygen ingress also yielded higher levels of the heterocyclic acetals from glycerol. These changes reflect aging, and suggest that managing mOx during production could be used to reduce the time needed to achieve some aged wine characteristics.

Yeast alter micro-oxygenation of wine: oxygen consumption and aldehyde production.

BACKGROUND: Micro-oxygenation (MOx) is a common winemaking treatment used to improve red wine color development and diminish vegetal aroma, amongst other effects. It is commonly applied to wine immediately after yeast fermentation (phase 1) or later, during aging (phase 2). Although most winemakers avoid MOx during malolactic (ML) fermentation, it is often not possible to avoid because ML bacteria are often present during phase 1 MOx treatment. We investigated the effect of common yeast and bacteria on the outcome of micro-oxygenation. RESULTS: Compared to sterile filtered wine, Saccharomyces cerevisiae inoculation significantly increased oxygen consumption, keeping dissolved oxygen in wine below 30 µg L-1 during micro-oxygenation, whereas Oenococcus oeni inoculation was not associated with a significant impact on the concentration of dissolved oxygen. The unfiltered baseline wine also had both present, although with much higher populations of bacteria and consumed oxygen. The yeast-treated wine yielded much higher levels of acetaldehyde, rising from 4.3 to 29 mg L-1 during micro-oxygenation, whereas no significant difference was found between the bacteria-treated wine and the filtered control. The unfiltered wine exhibited rapid oxygen consumption but no additional acetaldehyde, as well as reduced pyruvate. Analysis of the acetaldehyde-glycerol acetal levels showed a good correlation with acetaldehyde concentrations. CONCLUSION: The production of acetaldehyde is a key outcome of MOx and it is dramatically increased in the presence of yeast, although it is possibly counteracted by the metabolism of O. oeni bacteria. Additional controlled experiments are necessary to clarify the interaction of yeast and bacteria during MOx treatments. Analysis of the glycerol acetals may be useful as a proxy for acetaldehyde levels. © 2017 Society of Chemical Industry.

Improvements to a Grating-Based Spectral Imaging Microscope and Its Application to Reflectance Analysis of Blue Pen Inks.

A modified design of a chromatically resolved optical microscope (CROMoscope), a grating-based spectral imaging microscope, is described. By altering the geometry and adding a beam splitter, a twisting aberration that was present in the first version of the CROMoscope has been removed. Wavelength adjustment has been automated to decrease analysis time. Performance of the new design in transmission-absorption spectroscopy has been evaluated and found to be generally similar to the performance of the previous design. Spectral bandpass was found to be dependent on the sizes of apertures, and the smallest measured spectral bandpass was 1.8 nm with 1.0 mm diameter apertures. Wavelength was found to be very linear with the sine of the grating angle (R(2) = 0.9999995), and wavelength repeatability was found to be much better than the spectral bandpass. Reflectance spectral imaging with a CROMoscope is reported for the first time, and this reflectance spectral imaging was applied to blue ink samples on white paper. As a proof of concept, linear discriminant analysis was used to classify the inks by brand. In a leave-one-out cross-validation, 97.6% of samples were correctly classified.

A rapid, one step preparation for measuring selected free plus SO2-bound wine carbonyls by HPLC-DAD/MS.

Carbonyl compounds are produced during fermentation and chemical oxidation during wine making and aging, and they are important to wine flavor and color stability. Since wine also contains these compounds as α-hydroxysulfonates as a result of their reaction with sulfur dioxide, an alkaline pre-treatment requiring oxygen exclusion has been used to release these bound carbonyls for analysis. By modifying the method to hydrolyze the hydroxysulfonates with heating and acid in the presence of 2,4-dinitrophenylhydrazine (DNPH), the carbonyl compounds are simultaneously and quickly released and derivatized, resulting in a simpler and more rapid method. In addition, the method avoids air exclusion complications during hydrolysis by the addition of sulfur dioxide. The method was optimized for temperature, reaction time, and the concentrations of DNPH, sulfur dioxide and acid. The hydrazones were shown to be stable for 10 h, adequate time for chromatographic analysis by HPLC-DAD/MS. This method is demonstrated for 2-ketoglutaric acid, pyruvic acid, acetoin and acetaldehyde, wine carbonyls of very different reactivities, and it offers good specificity, high recovery and low limits of detection. This new rapid, simple method is demonstrated for the measurement of carbonyl compounds in a range of wines of different ages and grape varieties.

SmI2-H2O-mediated 5-exo/6-exo lactone radical cyclisation cascades.

The SmI2-H2O reagent system mediates challenging 5-exo/6-exo lactone radical cascade cyclisations that deliver carbo[5.4.0]bicyclic motifs in a diastereoselective, one-pot process that establish two new carbocyclic rings and four stereocentres.

Radical cyclization cascades of unsaturated Meldrum's acid derivatives.

Unsaturated, differentially substituted Meldrum's acid derivatives undergo cascade cyclizations upon ester reduction with SmI(2)-H(2)O. The cascade cyclizations proceed in good yield and with high diastereocontrol and convert simple, achiral starting materials to complex molecular architectures, bearing up to four stereocenters, in a single operation. The cascades are triggered by the generation and trapping of unusual radical-anions formed by electron transfer to the ester carbonyl.

Total synthesis of the marine metabolite (±)-polysiphenol via highly regioselective intramolecular oxidative coupling.

(±)-Polysiphenol (1), an atropisomerically stable 4,5-dibrominated 9,10-dihydrophenanthrene from Polysiphonia ferulacea, was prepared by a biomimetically inspired highly regioselective intramolecular oxidative coupling of a dibrominated dihydrostilbene. The installation of the two bromine atoms prior to oxidative coupling prevents further oxidation to a planar aromatized phenanthrene. By this strategy, the synthesis of (±)-polysiphenol was achieved in four steps in 70% overall yield. Synthesis of the naturally occurring 5,5'-(ethane-1,2-diyl)bis(3-bromobenzene-1,2-diol) (2) (the likely biogenetic precursor of polysiphenol) and 5,5'-(ethane-1,2-diyl)bis(3,4,6-tribromobenzene-1,2-diol) (9) are also reported. The origins of the regioselectivity in the oxidative coupling are explored.

Crystal structure of the phage T4 recombinase UvsX and its functional interaction with the T4 SF2 helicase UvsW.

Bacteriophage T4 provides an important model system for studying the mechanism of homologous recombination. We have determined the crystal structure of the T4 UvsX recombinase, and the overall architecture and fold closely resemble those of RecA, including a highly conserved ATP binding site. Based on this new structure, we reanalyzed electron microscopy reconstructions of UvsX-DNA filaments and docked the UvsX crystal structure into two different filament forms: a compressed filament generated in the presence of ADP and an elongated filament generated in the presence of ATP and aluminum fluoride. In these reconstructions, the ATP binding site sits at the protomer interface, as in the RecA filament crystal structure. However, the environment of the ATP binding site is altered in the two filament reconstructions, suggesting that nucleotide cannot be as easily accommodated at the protomer interface of the compressed filament. Finally, we show that the phage helicase UvsW completes the UvsX-promoted strand-exchange reaction, allowing the generation of a simple nicked circular product rather than complex networks of partially exchanged substrates.

Note: Toward multiple addressable optical trapping.

We describe a setup for addressable optical trapping in which a laser source is focused on a digital micromirror device and generates an optical trap in a microfluidic cell. In this paper, we report a proof-of-principle single beam/single micromirror/single three-dimensional trap arrangement that should serve as the basis for a multiple-trap instrument.

Chromatically resolved optical microscope (CROMoscope): a grating-based instrument for spectral imaging.

The chromatically resolved optical microscope (CROMoscope) is capable of spectral imaging with tunable spectral and spatial resolutions. Because of its remarkably simple design, the CROMoscope can be easily assembled and aligned. Spectral resolution as low as 2.5 nm full width at half maximum (fwhm) was measured using an atomic emission line of Hg. Absorption spectra of different parts of a micrograph can readily be compiled using white-light illumination. Chloroplast absorption from an Elodea plant leaf was used to demonstrate this capability. Spectral imaging is widely applicable to many areas of science, and the CROMoscope is particularly simple to adapt to conventional microscopes and should enable detailed spectroscopic information to be obtained from microscopy.

Infochemistry and infofuses for the chemical storage and transmission of coded information.

This article describes a self-powered system that uses chemical reactions--the thermal excitation of alkali metals--to transmit coded alphanumeric information. The transmitter (an "infofuse") is a strip of the flammable polymer nitrocellulose patterned with alkali metal ions; this pattern encodes the information. The wavelengths of 2 consecutive pulses of light represent each alphanumeric character. While burning, infofuses transmit a sequence of pulses (at 5-20 Hz) of atomic emission that correspond to the sequence of metallic salts (and therefore to the encoded information). This system combines information technology and chemical reactions into a new area--"infochemistry"--that is the first step toward systems that combine sensing and transduction of chemical signals with multicolor transmission of alphanumeric information.

Atmospheric pressure chemical ionization source. 1. Ionization of compounds in the gas phase.

A novel chemical ionization source for organic mass spectrometry is introduced. This new source uses a glow discharge in the flowing afterglow mode for the generation of excited species and ions. The direct-current gas discharge is operated in helium at atmospheric pressure; typical operating voltages and currents are around 500 V and 25 mA, respectively. The species generated by this atmospheric pressure glow discharge are mixed with ambient air to generate reagent ions (mostly ionized water clusters and NO+), which are then used for the ionization of gaseous organic compounds. A wide variety of substances, both polar and nonpolar, can be ionized. The resulting mass spectra generally show the parent molecular ion (M+ or MH+) with little or no fragmentation. Proton transfer from ionized water clusters has been identified as the main ionization pathway. However, the presence of radical molecular ions (M+) for some compounds indicates that other ionization mechanisms are also involved. The analytical capabilities of this source were evaluated with a time-of-flight mass spectrometer, and preliminary characterization shows very good stability, linearity, and sensitivity. Limits of detection in the single to tens of femtomole range are reported for selected compounds.

Atmospheric pressure chemical ionization source. 2. Desorption-ionization for the direct analysis of solid compounds.

The flowing afterglow-atmospheric pressure glow discharge (APGD) ionization source described in part 1 of this study (in this issue) is applied to the direct analysis of condensed-phase samples. When either liquids or solids are exposed to the ionizing beam of the APGD, strong signals for the molecular ions of substances present on their surfaces can be detected without compromising the integrity of the solid sample structure or sample substrate. As was observed for gas-phase compounds in part 1 of this study, both polar and nonpolar substances can be ionized and detected by mass spectrometry. The parent molecular ion (or its protonated counterpart) is usually the main spectral feature, with little or no fragmentation in evidence. Preliminary quantitative results show that this approach offers very good sensitivity (detection limits in the picogram regime are reported for several test compounds in part 1 of this study) and linear response to the analyte concentration. Examples of the application of this strategy to the analysis of real-world samples, such as the direct analysis of pharmaceutical compounds or foods is provided. The ability of this source to perform spatially resolved analysis is also demonstrated. Preliminary studies of the mechanisms of the reactions involved are described.

Anthocyanin Interactions with DNA: Intercalation, Topoisomerase I Inhibition and Oxidative Reactions.

Anthocyanins and their aglycone anthocyanidins are pigmented flavonoids found in significant amounts in many commonly consumed foods. They exhibit a complex chemistry in aqueous solution, which makes it difficult to study their chemistry under physiological conditions. Here we used a gel electrophoresis assay employing supercoiled DNA plasmid to examine the ability of these compounds (1) to intercalate DNA, (2) to inhibit human topoisomerase I through both inhibition of plasmid relaxation activity (catalytic inhibition) and stabilization of the cleavable DNA-topoisomerase complex (poisoning), and (3) to inhibit or enhance oxidative single-strand DNA nicking. We found no evidence of DNA intercalation by anthocyan(id)ins in the physiological pH range for any of the compounds used in this study-cyanidin chloride, cyanidin 3-O-glucoside, cyanidin 3,5-O-diglucoside, malvidin 3-O-glucoside and luteolinidin chloride. The anthocyanins inhibited topoisomerase relaxation activity only at high concentrations (> 50 muM) and we could find no evidence of topoisomerase I cleavable complex stabilization by these compounds. However, we observed that all of the anthocyan(id)ins used in this study were capable of inducing significant oxidative DNA strand cleavage (nicking) in the presence of 1 mM DTT (dithiothreitol), while the free radical scavenger, DMSO, at concentrations typically used in similar studies, completely inhibited DNA nicking. Finally, we propose a mechanism to explain the anthocyan(id)in induced oxidative DNA cleavage observed under our experimental conditions.

High-throughput elemental analysis of small aqueous samples by emission spectrometry with a compact, atmospheric-pressure solution-cathode glow discharge.

A miniaturized version of an atmospheric-pressure glow discharge using a solution as the cathode was recently evaluated for elemental analysis of continuously sampled aqueous solutions. Although continuous sampling is useful, transient analysis is required for certain applications, including chromatographic or similar separations, small-volume sampling, high-throughput sampling, and on-line preconcentration. The miniaturized solution-cathode glow discharge seems particularly well suited to transient analysis by virtue of its low dead volume and high sensitivity. Two benefits of transient analysis were exploited here: high throughput and small sample volume. Sampling 25-microL volumes at 1000 samples/h, the discharge achieved detection limits ranging from 5 pg (0.2 ppb) for Li to 6 ng (270 ppb) for Hg.

Compact glow discharge for the elemental analysis of aqueous samples.

Glow discharge sources have shown impressive analytical performance, cost effectiveness, and versatility but have traditionally been ill-suited for the analysis of liquids or solutions. However, in recent years, glow discharges operated at atmospheric pressure have shown progress in this direction. In particular, glow discharges have been operated with the solution to be analyzed acting as one of the electrodes (most typically, and most successfully, the cathode). These sources exhibit many of the traditional advantages of glow discharges (such as low power requirements) and possess the additional benefit of not requiring vacuum equipment. In the present study, a modified design is introduced and its analytical performance is evaluated. The modification from the most similar source is primarily a reduction in discharge volume (nearly 5-fold, to 2 mm(3)) and a corresponding increase in power density. With the new design, detection limits for a range of metals are greatly improved, with most now in the single and sub-part per billion range.

The phage T4 protein UvsW drives Holliday junction branch migration.

The phage T4 UvsW protein has been shown to play a crucial role in the switch from origin-dependent to recombination-dependent replication in T4 infections through the unwinding of origin R-loop initiation intermediates. UvsW also functions with UvsX and UvsY to repair damaged DNA through homologous recombination, and, based on genetic evidence, has been proposed to act as a Holliday junction branch migration enzyme. Here we report the purification and characterization of UvsW. Using oligonucleotide-based substrates, we confirm that UvsW unwinds branched DNA substrates, including X and Y structures, but shows little activity in unwinding linear duplex substrates with blunt or single-strand ends. Using a novel Holliday junction-containing substrate, we also demonstrate that UvsW promotes the branch migration of Holliday junctions efficiently through more than 1000 bp of DNA. The ATP hydrolysis-deficient mutant protein, UvsW-K141R, is unable to promote Holliday junction branch migration. However, both UvsW and UvsW-K141R are capable of stabilizing Holliday junctions against spontaneous branch migration when ATP is not present. Using two-dimensional agarose gel electrophoresis we also show that UvsW acts on T4-generated replication intermediates, including Holliday junction-containing X-shaped intermediates and replication fork-shaped intermediates. Taken together, these results strongly support a role for UvsW in the branch migration of Holliday junctions that form during T4 recombination, replication, and repair.