The separation of overlapping peaks in cyclic voltammetry by means of semi-differential transformation

A method for extracting single peaks from complex linear sweep and cyclic voltamperograms is presented. Voltamperograms are transformed by means of semidifferentiation, then all undesired peaks are removed from the semiderivative curve and replaced by calculated baselines. The resulting curve is semiintegrated back, giving a voltamperogram with one peak only. Baselines in the semiderivative domain are determined by the least-squares curve-fitting of datapoints from peak border regions, using the equation that describes the semiderivative peak of a reversible electrode process. With this procedure peaks can be removed without assumptions about the mechanism of the underlying electrode reaction. Due to its design, the algorithm presented is suitable for the fully automatic processing of cyclic and linear sweep voltamperograms. Performance of the procedure was checked with generated reversible voltamperograms as well as in real experiments with both reversible and irreversible systems. The smallest distance between two peaks of equal height, for which the described method can yield correct results, has been found to be 110 mV for a reversible one-electron process at 298 K. This procedure can also be applied to the elimination of the cathodic current from the cyclic voltamperogram of a single component in order to get a pure anodic current value, free from cathodic contribution, or vice versa.     

The learning machine in quantitative chemical analysis: Part I. Anodic Stripping Voltammetry of Cadmium,Lead and Thallium

The linear learning machine method was applied to the determination of cadmium, lead and thallium down to 10^-8M by anodic stripping voltammetry at a hanging mercury drop electrode. With a total of three trained multicategory classifiers, concentrations of Cd, Pb and Tl could be predicted with an accuracy of ±10%. The classifiers were trained with the use of least-squares minimization. Numerical problems in the data matrix inversion were overcome by using singular value decomposition.     

Surface Aggregation of Candida albicans on Glass in the Absence and Presence of Adhering Streptococcus gordonii in a Parallel-Plate Flow Chamber: A Surface Thermodynamical Analysis Based on Acid-Base Interactions

Adhesive interactions between yeasts and bacteria are important in the maintenance of infectious mixed biofilms on natural and biomaterial surfaces in the human body. In this study, the extended DLVO (Derjaguin-Landau-Verwey-Overbeek) approach has been applied to explain adhesive interactions between C. albicans ATCC 10261 and S. gordonii NCTC 7869 adhering on glass. Contact angles with different liquids and the zeta potentials of both the yeasts and bacteria were determined and their adhesive interactions were measured in a parallel-plate flow chamber.Streptococci were first allowed to adhere to the bottom glass plate of the flow chamber to different seeding densities, and subsequently deposition of yeasts was monitored with an image analysis system, yielding the degree of initial surface aggregation of the adhering yeasts and their spatial arrangement in a stationary end point. Irrespective of growth temperature, the yeast cells appeared uncharged in TNMC buffer, but yeasts grown at 37 degrees C were intrinsically more hydrophilic and had an increased electron-donating character than cells grown at 30 degrees C. All yeasts showed surface aggregation due to attractive Lifshitz-van der Waals forces. In addition, acid-base interactions between yeasts, yeasts and the glass substratum, and yeasts and the streptococci were attractive for yeasts grown at 30 degrees C, but yeasts grown at 37 degrees C only had favorable acid-base interactions with the bacteria, explaining the positive relationship between the surface coverage of the glass by streptococci and the surface aggregation of the yeasts. Copyright 1999 Academic Press.     

Thermal addition of xathenethione to allenes: “A Concerted Two Step” (π2s+π2s+π2s)-cycloaddition

(2+2)- and (4+2)-cycloadducts are formed by thermal reaction of xanthenethione with allenes. Activation parameters for ths “concerted two step” (_π2_s+_π2_s+_π2_s) reaction are presented.     

Photocycloaddition of N-methylthiophthalimide with alkynes

$\text{N}$-Methylthiophthalimide undergoes photochemical cycloaddition reactions with diphenylacetylene, hex-3-yne and bis(methylthio)acetylene to form spiro-thietes; in solution the spiro-thiete from the bis(methylthio)alkyne is in equilibrium with its ring-opened isomer.     

Kritische Sehnen auf Riemannschen Elementarraumstücken

Ohne Zusammenfassung     

A synthetic study towards the PSA1 tetrasaccharide repeating unit

A synthetic study to the protected tetrasaccharide repeating unit of zwitterionic polysaccharide PSA1 using 1-thio, 1-seleno and 1-hydroxyl functionalized donor glycosides is presented. The ABC trisaccharide part was successfully assembled using an iterative dehydrative glycosylation protocol.     

High-performance liquid chromatographic determination of some anthraquinone and naphthoquinone dyes occurring in historical textiles

A reversed-phase HPLC method has been developed for identification and quantitation of nine natural quinone dyes and applied to historical textile fibres. A Purospher RP18e column was used with a convex gradient of methanol in a mobile phase of 0.1 M aqueous citrate buffer (pH 2.5) and spectrophotometric diode-array detection at 270 nm. For identification of alizarin, purpurin and xanthopurpurin, occurring together in the madder plant, an isocratic method was used with a methanol-0.2 M acetate buffer (pH 4.3) (75:25) as the mobile phase. After an acid extraction of textile fibres and the analysis of the extracts, alizarin and purpurin were identified and quantitated in three fibres.