FOURIER TRANSFORM INFRARED SPECTROELECTROCHEMISTRY OF THE BACTERIOCHLOROPHYLL a ANION RADICAL

Abstract— Fourier transform infrared (FTIR) difference spectroscopy of the electrochemically generated anion radical of bacteriochlorophyll a was used to follow the molecular changes upon one-electron reduction. An IR spectroelectrochemical cell was constructed, allowing in situ electrolysis in connection with spectroscopic investigations from 200 to 10 000 nm. FTIR difference spectra of the BChl a anion formation in THF d₈ at U =+0.9 V (as determined by ferrocene calibration) were obtained. After complete formation of the radical, the reverse process was followed. Comparison of visible and IR spectra of the reduction and re-oxidation processes indicates that more than 90% of the BChl a anion could be formed with 90% of it being reversible. The main IR absorbance changes are observed for the conjugated and even for the non-conjugated C=O groups of BChl a . These results demonstrate the use of the combination of FTIR spectroscopy and electrochemistry for the characterization of radicals of the isolated pigments and of their in vivo bonding to the protein environment.     

Effect of mobile phase density gradients on efficiency in packed column supercritical fluid chromatography

Summary The efficiency of packed columns was measured as a function of flow rate, temperature, outlet density, and the density differential across the column, unsing pure carbon dioxide as the mobile phase. Although density differentials are often blamed for a serious loss in efficiency in packed column supercritical fluid chromatography, the results show that efficiency was not a function of the density differential. Peak shapes suggest that apparent loss in efficiency is actually due to inadequate solubility of the solute in carbon dioxide.     

Upper limit for thermal direct photon production in heavy-ion collisions at 60 and 200A·GeV

The production of direct photons has been investigated in reactions ofp and¹⁶O projectiles at 60 and 200A·GeV with C and Au nuclei. Photon and ⁰ spectra have been measured in the pseudorapidity range 1.52.1 for the transverse momentum region 0.4 GeV/cp _T 2.8 GeV/c employing the lead-glass spectrometer SAPHIR. An upper limit of 15% at the 90% confidence level for the direct photon signal relative to the neutral pion production is obtained from the comparison of measured photon spectra with Monte Carlo simulations of the hadronic background based on the reconstructed yield of ⁰ and mesons. Consequences for a possible phase transition to a quark-gluon plasma are discussed.     

Chemistry of polybutadiene—iron carbonyl systems

The treatment of polybutadienes with iron carbonyls results in formation of polymers containing tricarbonyl(conjugated diene)iron units [C₈H₁₂Fe(CO)₃] and also results in geometrical isomerization of free double bonds. Heating of the iron carbonyl-containing polymers gives ferromagnetic products with enhanced thermal stability. The incorporation of iron carbonyl groups into the polymer is favored by basic solvents and high temperatures, the geometrical isomerization by acidic solvents and low temperatures. Steric factors are powerful in determining the rate of isomerization.     

Continuous sample deposition from reversed-phase liquid chromatography to tracks on a matrix-assisted laser desorption/ionization precoated target for the analysis of protein digests

Peptide mass fingerprinting by matrix-assisted laser desorption/ionization (MALDI)-mass spectrometry (MS) is one of the standard high-throughput methods for protein identification today. Traditionally this method has been based on spotting peptide mixtures onto MALDI targets. While this method works well for more abundant proteins, low-abundance proteins mixed with high-abundance proteins tend to go undetected due to ion suppression effects, instrumental dynamic range limitations and chemical noise interference. We present an alternative approach where liquid chromatography (LC) effluent is continuously collected as linear tracks on a MALDI target. In this manner the chromatographic separation is spatially preserved on the target, which enables generation of off-line LC-MS and LC-MS/MS data by MALDI. LC-MALDI sample collection provides improved sensitivity and dynamic range, spatial resolution of peptides along the sample track, and permits peptide mass mapping of low-abundance proteins in mixtures containing high-abundance proteins. In this work, standard and ribosomal protein digests are resolved and captured using LC-MALDI sample collection and analyzed by MALDI-TOF-MS.     

Separation of Natural Food Pigments in Saponified and Un-Saponified Paprika Oleoresin by Ultra High Performance Supercritical Fluid Chromatography (UHPSFC)

The natural pigments in paprika were rapidly and efficiently separated by ultra high performance supercritical fluid chromatography. The separation of both un-saponified and saponified mixtures of paprika oleoresin were optimized, with run times of 10.6 min. Three different C18 columns, a cyano, silica and diol column, all 3 × 100 mm, with 1.8 μm particles were compared. The best separation for the un-saponified sample was found with an SB-C18 column, while the saponified samples were best separated on a bare silica, RX-Sil column. A SB-CN column allowed near optimum separation of both the unsaponified, and saponified samples, with similar run times. The best mobile phase was carbon dioxide (CO₂) modified with isopropyl alcohol (IPA), with a composition gradient. Fingerprints of several commercial pepper products indicated that one appeared to be colored with artificial dyes, while the color of a chili powder may have been enhanced with a paprika extract. Spectra, using CO₂ with IPA as modifier, produced a single maximum at 453 nm, which appears to represent up to a 30 nm solvatochromic shift from the maxima in most organic solvents. Acetonitrile (ACN) as modifier produced spectra with two maxima and a similar solvatochromic shift. These results appear to be the first on saponified paprika oleoresin samples using SFC. It is also the first detailed report on the separation of un-saponified samples. The results are up to six times faster than comparable results by HPLC. It appears that SFC is a viable, superior alternative to HPLC for the analysis of this important commercial product, without using ACN, or chlorinated solvents.

     

Rapid, Direct Quantitation of the Preservatives Benzoic and Sorbic Acid (and Salts) Plus Caffeine in Foods and Aqueous Beverages Using Supercritical Fluid Chromatography

The preservatives benzoate and sorbate, plus caffeine were rapidly separated and quantified, in just over 2 min, in a wide range of beverages and foods, using supercritical fluid chromatography (SFC). Fifteen beverages and 10 semi-liquid foods were evaluated. The benzoate and sorbate were originally present in the samples as the acid, or the sodium, or potassium salt. The aqueous samples were diluted 3:1 with acidified methanol, to insure the acids were protonated, then directly injected. The solutes were isocratically eluted from a 4 × 250 mm, 5 μm Diol column with 3.5 mL min^?1 of 8.5 % methanol containing 0.3 % acetic acid at 50 °C and a column outlet pressure of 150 bar. The real samples exhibited remarkably little interference. All the beverages were accurately labeled. However, many of the foods, such as salad dressings, mustard, etc., were mislabeled. The method was linear over a wide range with correlation coefficients for all three solutes >0.999. RSD’s were generally less than 1 %. The results agreed with the caffeine content on the labels within a few percent. Surprisingly, this appears to be the first published separation of benzoic and sorbic acid preservatives in food, and beverages using SFC, and one of a very few SFC applications where aqueous samples were simply diluted and injected. Compared to published references, the SFC method was found to be up to 7 times faster than HPLC, and eliminated the use of acetonitrile.