A new convolution theorem for the Stieltjes transform and its application to a class of singular integral equations

Dedicated to the memory of Professor David Vernon Widder (1898–1990)     

Isomerisation of butene in isobutene on ferrierite catalyst: A mono- or a bimolecular process?

The isomerisation of n-butene into isobutene has been studied over a ferrierite catalyst being in a selective state (aged catalyst) or non-selective state (fresh catalyst). It is observed, by using ¹³C=C---C---C, that a bimolecular process operates on the non-selective catalyst whereas a monomolecular process exists on the selective catalyst.     

Simultaneous time- and wavelength-resolved fluorescence microscopy of single molecules

Single fluorophores and single-pair fluorescence resonance energy transfer were studied with a new confocal fluorescence microscope that allows, for the first time, the wavelength and emission time of each detected photon to be simultaneously measured with single molecule sensitivity. In this apparatus, the photons collected from the sample are imaged through a dispersive optical system onto a time and position sensitive photon detector. For each detected photon the detection system records its wavelength, its emission time relative to the excitation pulse, and its absolute emission time. A histogram over many photons can generate a full fluorescence spectrum and correlated decay plot for a single molecule for any time interval. At the single molecule level, this approach makes possible entirely new types of temporal and spectral correlation spectroscopies. This paper presents our initial results on simultaneous time- and wavelength-resolved fluorescence measurements of single rhodamine 6G (R6G), tetramethylrhodamine (TMR), and Cy3 molecules embedded in thin films of poly(methyl methacrylate) (PMMA), and of single-pair fluorescence resonance energy transfer between two Alexa fluorophores spaced apart by a short polyproline peptide.     

Partial thermal analysis of kerogen oxidation products

A method is proposed which, in principle, permits resolution of complex TG curves into elementary curves. The method is based on appropriate preheating of the substrate. In fact, the method represents partial differential thermogravimetric analysis (PDTG). In this paper it was used, together with IR spectroscopy, for analysis of the precipitated acids obtained by partial oxidation of the kerogen from an oil shale. The precipitated acids were found to consist of five components, characterized by similar thermal properties. General qualitative and quantitative characteristics of the individual components are suggested.

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Zusammenfassung Es wird eine Methode beschrieben, mit der es prinzipiell möglich ist, komplexe TG-Kurven in Elementarkurven zu zerlegen. Diese Methode beruht auf einem geeigneten Vorerhitzen des Substrates und stellt eigentlich ein partielles differentialthermogravimetrisches Verfahren (PDTG) dar, das in dieser Arbeit zusammen mit der IR-Spektroskopie angewendet wurde, um durch teilweise Oxydation von aus Kerogen eines Schieferöles gefällte Säuren zu untersuchen. Fünf Säuren, deren thermische Charakteristika einander ähnlich sind, konnten festgestellt werden. Es wurde eine allgemeine Charakteristik qualitativer and quantitativer Art der einzelnen Komponenten gegeben.

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Influence of CdS-filler on the thermal properties of polystyrene

Influence of CdS-filler particles in the micrometer size range on the properties of the polystyrene (PS) matrix was studied using structural and thermal techniques. Improvement of the thermal stability of the PS matrix for about 50 K was found in the presence of the CdS-filler. Infrared measurements revealed that interaction between the surface of CdS-filler particles and the PS chain is weak. Non-significant changes in the glass transition temperature of the PS matrix upon the incorporation of CdS-filler particles also suggest weak interaction between filler and polymer.     

Effect of the eluent composition in gel chromatography of99mTc (Sn)-methylene diphosphonate

Gel chromatography of^99mTc(Sn)-MDP on Sephadex has been performed by using the eluents of different composition and pH. Samples with constant ligand/reductant ratio were eluted by pure physiological saline as well as by saline which contained either the ligand only or both the ligand and the reductant. Their concentrations in the eluent were the same as those used in the preparation of the labeled complex.     

Statistical Evaluation of the Quality Control Results of 99mTc(Sn)-DPD

The results of the quality control of ^99mTc-DPD produced during five consequtive years are statistically evaluated. Radiochemical purity of the kit determined in 75 batches was 98.3±1.3%. TLC on silica gel with the mixture of acetone and methanole (1:1, v/v) was used to determine the content of free pertechnetate. The labeled complex and ^99mTc-hydrolyzate was separated by using ascending paper (Schleicher & Schull) chromatography and lN NaCl as the mobile phase. Reliable results were obtained showing that the content of the impurities ^99mTc-pertechnetate and ^99mTc-hydrolyzate is 1.7±1.3% and 3.4±2.1%, respectively. The biodistribution depends on the quantity of DPD. For the animal experiments its content should be 70–80 g/kg b.w. The experiments revealed that the mean value of bone distribution was 8.8±1.9%/g and in muscles 0.043± 0.42%/g. The uptake in liver and kidneys was below 3%, i.e., 0.65±0.29 and 1.71±0.68%/organ, respectively. The bone/muscle ratio should be at least 160. The analysis shows that the obtained values are arranged around their, statistically allowed, mean values.     

Solid Phase Extraction of Cesium from Aqueous Solution Using Sol-Gel Encapsulated Cobalt Hexacyanoferrate

The synthesis and evaluation of silica sol-gels doped with cobalt hexacyanoferrate (CoHCF) for solid phase extraction of Cs⁺ from aqueous solution is described. The CoHCF is formed by first introducing K₄Fe(CN)₆ (HCF) into the sol-gel and subsequently contacting the porous solid to a solution containing Co²⁺. Generally, sols contain alcohol as a co-solvent, which limits the solubility of HCF. Inclusion of generation-4 polyamidoamine (G4-PAMAM) dendrimer in the sol-gel increases the level of HCF and, in turn, the CoHCF. The uptake capacity of this composite was 0.43±0.01mmolCs⁺g^–1. A second approach to increasing the level of HCF silica is to exclude alcohol from the sol and use ultrasound to obtain a homogeneous suspension; HCF concentrations up to 0.17M in the sol were thereby achieved. After gelation and reaction with Co²⁺, the resulting composite had a capacity of 0.61±0.01mmolCs⁺g^–1. With 0.5mMCs⁺ as the sample, the presence of either 0.5–100mM Na⁺ or 10mMCa²⁺ did not change that value at the 95% confidence level.     

Experimental resolution of early steps in protein folding: testing molecular dynamics simulations

Time-resolved Tyr fluorescence spectroscopy coupled with a laser-induced temperature-jump (T-jump) was employed to follow the folding relaxation dynamics of the B-domain of Staphylococcal protein A. The single Tyr is located in helix 1 (H1) and is a sensitive probe of the structure of this helix and the overall helical bundle structure. The results from this study were compared to those from a complementary infrared T-jump study on this protein [Vu, D. M.; Myers, J. K.; Oas, T. G.; Dyer, R. B. Biochemistry 2004, 43, 3582]. Both methods detect a microsecond process that follows the cooperative relaxation of the helical bundle core. However, a fast process (10-7 s) that follows the relaxation of the individual helices was observed only with the infrared probe. Thus, fast formation of H1 is not observed, but rather H1 forms in the microsecond phase, concomitantly with the docking to (and stabilization by) the other two helices to form the helical bundle structure. This observation validates the results of several previous molecular dynamics simulations that predict H1 formation only in the final assembly of the helix bundle.     

Highly diastereoselective synthesis and NMR characterization of natural indolizidine alkaloids

A diastereoselective, general and versatile access to disubstituted indolizidines is described. The nmr conformational analysis permits us to establish preferred conformations.