Automatic analysis of mixed spectra : Generalised spectral subtraction applied to electron spin resonance spectroscopy

A new technique is described for estimating the pure component spectra from a set of linearly independent spectra. The process is one of generalised spectral subtraction in which an iterative combination of multivariate linear least-squares analysis and matrix transformation is applied to the input data to give estimates of the number of independent components in the original mixed spectra. This technique is applicable to bipolar data (e.g. from e.p.r. spectra) as well as absorption spectra determined by any spectroscopic technique, provided that the spectra may be reasonably assumed to be an additive mixture of unknown pure components. Numerical model examples are given together with an experimental application to electron spin resonance.     

Toward the molecular flashlight: preparation,properties, and photophysics of a hypericin-luciferin tethered molecule

The synthesis of a molecule containing hypericin and luciferin moieties joined by a tether is reported. The light-induced (in vitro) antiviral activity as well as the photophysical properties of this new compound are measured and compared with those of the parent compounds, hypericin and pseudohypericin. This tethered molecule exhibits excited-state behavior that is very similar to that of its parent compounds and antiviral activity that is identical, within experimental error, to that of its more closely related parent compound, pseudohypericin. The implications for a photodynamic therapy that is independent of external light sources are discussed.     

The electronic structure of small lithium clusters

Ab initio molecular orbital calculations using the STO-6G and STO6-21G basis sets have been performed for the cluster series Li _n ⁺ , Li _n , and Li _n ^– (wheren=2–7). Thirty-two optimized structures are discussed and reported, many of which (especially for the anionic structures) have not yet been considered. The calculations suggest that for all three species the optimum geometries are planar. Of the two levels of theories that were investigated, STO-6G//STO-6G and STO6-21G//STO-6G, the latter hybrid theory was found to be less reliable. In particular, for the anionic structures these calculations should provide a platform from which more sophisticated, i.e., configuration interaction, geometry optimization can be performed.     

Critical micelle concentrations for alkyltrimethylammonium bromides in water from 25 to 160°C

Critical micelle concentrations were determined by conductance measurements for decyl-, dodecyl-, tetradecyl- and hexadecyltrimethylammonium bromide in water at 25, 60, 95, 130, and 160°C. The results are discussed in terms of the equilibrium model and the nonlinear Poisson-Boltzmann model for micelle formation. The free energies of transferring a methylene group from water to the oil-like interior of the micelle are found to be –781 at 25°C, –796 at 60°C, –819 at 95°C, –815 at 130°C, and –787 at 160°C cal-mol^–1.     

Dual analyte flow injection fluorescence immunoassays using thiophilic gel reactors and synchronous scanning detection

Heterogeneous fluorescence immunoassays have been automated using flow injection manifolds incorporating thiophilic gel solid phase reactors to separate antibody-bound and unbound analyte molecules. Antibody elution is achieved by changes in ionic strength, thus allowing the use of pH sensitive fluorescent labels. This facilitates the development of dual analyte systems, in which two competitive immunoassays with separate labels are monitored in parallel. Detection of the fluorophores by high speed synchronous fluorescence scanning while the flow is briefly stopped utilises either one synchronous interval which detects both fluorophores, or two separate scans at different wavelength intervals, one for each fluorophore. Simultaneous analyses of serum albumin and transferrin exemplify these novel approaches. Spectroscopic interferences are very small, analyte recoveries are close to 100%, with a relative standard deviation of 5-6% and a sampling rate of 20 h-1.     

Naphthalene Complexation by β-Cyclodextrin: Influence of Added Short Chain Branched and Linear Alcohols

Naphthalene forms 1 : 1 complexes with -cyclodextrin (-CD)in water. The binding constant is 377 ± 35 M^-1. Addition of linear or branched alcohols causes a reduction in the apparent strength of naphthalene binding (K_app) compared to the value in the absence of additives. For example, 1% 1-pentanol reduces K_app to 184 ± 31 M^-1. Branching does not alter K_app much for a given number of carbon atoms, e.g., it is 113 ± 9 M^-1for 2-pentanol and 116 ± 8 M^-1for 3-pentanol. The exception to this is tert-butanol for which K_app is 577 ± 40 M^-1. The variation in K_app as a function of [1-pentanol] yields values for the individual equilibrium constants contributing to K_app. This reveals that a ternary complex forms involving naphthalene, the CD and 1-pentanol. The constant for formation of the ternary complex is 99 ± 29 M^-2. NaI quenching of naphthalene fluorescence indicates that the CD cavity partially protects the naphthalene excited state fromthis water phase quencher. Interestingly, the Stern–Volmer constant is lower in the presence of 1-pentanol than in its absence, although there should be more unbound (and therefore more NaI accessible) naphthalene in the former system than in the latter. These apparently contradictory results are discussed in terms of ternary complex formation.     

Studies in qualitative inorganic analysis. Part XXVI

Summary The preliminary tests for organic radicals, which are based on charring by strong heating or by hot concentrated sulphuric acid are examined. Even when both these tests are applied some organic acids escape identification. Two alternative procedures based upon oxidation of organic matter with potassium dichromate in dilute sulphuric have been examined. The first procedure involves a reduction of the dichromate ion to the distinctive green chromium(III) ion. This occurs with all organic radicals commonly encountered in qualitative inorganic analysis, except acetate and salicylate. Interference due to inorganic reducing agents is overcome by a preliminary oxidation with hydrogen peroxide. The second procedure involves decomposition of carbonates, bicarbonates, and cyanates with dilute sulphuric acid, followed by oxidation of organic matter with potassium dichromate in sulphuric acid to carbon dioxide, which is detected with lime water. Of the radicals commonly encountered in qualitative inorganic analysis only acetate gives a negative result.

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Zusammenfassung Die Vorprobe auf organische Anionen auf Grund ihrer Verkohlung durch kräftiges Erhitzen oder durch Einwirkung konz. Schwefelsäure wurde überprüft. Auch bei Anwendung beider Arbeitsweisen entziehen sich einige organische Säuren dem Nachweis. Zwei andere Verfahren auf der Grundlage der Oxydation des organischen Materials mit Kaliumbichromat in verd. Schwefelsäure wurden untersucht. Das erste führt zur Reduktion des Bichromats zu deutlich grün gefärbtem Cr(III) mit allen bei der anorganischen Analyse üblicherweise auftretenden organischen Anionen, ausgenommen Acetat und Salicylat. Störungen durch reduzierende anorganische Substanzen werden durch deren vorherige Oxydation mit Wasserstoffperoxid umgangen. Das zweite Verfahren sieht die vorherige Zersetzung anwesender Carbonate, Bicarbonate oder Cyanate mit verd. Schwefelsäure vor, wonach das organische Material mit Kaliumbichromat-Schwefelsäure zu Kohlendioxid oxydiert wird, das mit Kalklösung nachgewiesen wird. Von den in der anorganischen Analyse üblichen organischen Anionen gibt nur Acetat ein negatives Resultat.

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Résumé On examine les essais préliminaires pour radicaux organiques, fondés sur la carbonisation par chauffage à température élevée ou sur l'action de l'acide sulfurique concentré chaud. Même en appliquant ces deux modes de recherche, certains des acides organiques échappent à l'identification. On a étudié deux autres procédés susceptibles d'être utilisés. Ils reposent sur l'oxydation de la matière organique par le bichromate de potassium en milieu sulfurique dilué. Le premier met en jeu la réduction de l'ion bichromate en ion chrome-III vert caractéristique. Cette réaction se produit avec tous les radicaux organiques habituellement rencontrés en analyse minérale qualitative, sauf avec les acétates et les salicylates. On élimine l'interférence due aux agents réducteurs minéraux par oxydation préliminaire par l'eau oxygénée. Le second procédé met en jeu la décomposition des carbonates, hydrogénocarbonates et cyanates par l'acide sulfurique dilué, suivie d'une oxydation de la matière organique par le bichromate de potassium dans l'acide sulfurique, en gaz carbonique que l'on met en évidence par l'eau de chaux. Seul l'ion acétate donne un résultat négatif parmi tous les radicaux rencontrés habituellement en analyse minérale qualitative.