A short proof of finiteness of Murty's principal pivoting algorithm

We give a short proof of the finiteness of Murty's principal pivoting algorithm for solving the linear complementarity problemy = Mz + q, y ^T z = 0,y 0,z 0 withP-matrixM.     

Beitrag zur potentiometrischen Untersuchung von Resorufin und einigen seiner Derivate

Zusammenfassung Durch potentiometrische Untersuchung des Verhaltens von Resorufin, o-Acetylresorufin und Äthoxyresorufin wurde festgelegt, unter welchen Bedingungen es zur Bildung von Semichinon kommt. Ferner wurden die Bedingungen für die titanometrische und stannometrische Bestimmung der angeführten Substanzen ermittelt.

---

Summary Potentiometric investigation of the behavior of resorufin,o-acetylresorufin and ethoxyresorufin revealed the conditions that lead to the formation of semiquinone. The conditions for the titanometric and the stannometric determination of these materials were also established.

---

Résumé On a établi les conditions de formation d'une hémiquinone, par l'étude potentiométrique du comportement de la résorufine, de l'o-acétylrésomfine et de l'éthoxyrésorufine. On en a déduit les conditions du titrage titanométrique et stannométrique de ces substances.

     

Thermoelectric properties of perovskites: Sign change of the Seebeck coefficient and high temperature properties

The possibility to change the Seebeck coefficient sign has been evidenced in the LaCoO₃ perovskites. A small hole doping (Co³⁺/Co⁴⁺) will result in a large positive Seebeck coefficient, while a small electron doping (Co²⁺/Co³⁺) will give a large negative Seebeck coefficient at room temperature. This mechanism is shown to be efficient as well in 1D Ca₃Co₂O₆ deriving from hexagonal perovskites. By doping Ca₃Co₂O₆ with Ti⁴⁺, a mixed valency Co²⁺/Co³⁺ is introduced and the thermopower turns negative.

At high temperature, the Seebeck coefficients of LaCoO₃ and related compounds decrease to small values due to the spin state transition. The values converge towards a positive value, close to +20 μV/K at 800 K. This suggests that at high T, the Seebeck coefficients in the case of localized charges do not depend on the doping, but only on the spin and orbital degeneracies. On the other hand, in the case of metallic-like samples as electron-doped manganites, the properties can be described up to high T in terms of a single-band metal. Due to the linear variation of S as a function of T and the almost constant value of ρ, the ratio S²/ρ which is crucial for high temperature applications increases.     

Steric effects on reaction rates - V. An updated version of the foote-schleyer correlation based on molecular mechanics

The strain changes occurring during solvolysis of secondary tosylates are calculated by a molecular mechanics programme (MM2) using an empirical force-field for carbenium ions. The rate constants for acetolysis of k_C-substrates correlate with these strain changes, defining a straight line representative for k_C behaviour.     

DNA-directed protein immobilization on mixed self-assembled monolayers via a streptavidin bridge

The simultaneous detection of multiple analytes is an important consideration for the advancement of biosensor technology. Currently, few sensor systems possess the capability to accurately and precisely detect multiple antigens. This work presents a simple approach for the functionalization of sensor surfaces suitable for multichannel detection. This approach utilizes self-assembled monolayer (SAM) chemistry to create a nonfouling, functional sensor platform based on biotinylated single-stranded DNA immobilized via a streptavidin bridge to a mixed SAM of biotinylated alkanethiol and oligo(ethylene glycol). Nonspecific binding is minimized with the nonfouling background of the sensor surface. A usable protein chip is generated by applying protein-DNA conjugates which are directed to specific sites on the sensor chip surface by utilizing the specificity of DNA hybridization. The described platform is demonstrated in a custom-built surface plasmon resonance biosensor. The detection capabilities of a sensor using this protein array have been characterized using human chorionic gonadotropin (hCG). The platform shows a higher sensitivity in detection of hCG than that observed using biotinylated antibodies. Results also show excellent specificity in protein immobilization to the proper locations in the array. The vast number of possible DNA sequences combine with the selectivity of base-pairing makes this platform an excellent candidate for a sensor capable of multichannel protein detection.     

NMR relaxation study of crosslinked cis-1,4-polybutadiene

Proton relaxation measurements have been used to investigate the effects of crosslinking on the segmental motion in cis-1,4-polybutadiene samples. The temperature dependence of proton spin–lattice relaxation time T₁ and spin–spin relaxation time T₂ at 60 and 24.3 MHz are reported in cis-1,4-polybutadiene (PB) samples with different crosslink density including uncrosslinked PB and samples with 140, 40, and 14 repeat units between crosslinks. In addition, spin-lattice relaxation times in rotating coordinate frame, T_1p, have also been determined. The relaxation data are interpreted in terms of the effects of crosslinks on segmental chain motions. Because of their sensitivity to low-frequency motion, T₂ data are of major interest. At temperatures well above the T₁ minimum the small T₂ temperature dependence resembles solidlike behavior reflecting the nonzero averaging of dipolar interactions due to anisotropic motion of the chain segments between crosslinks. The magnitude of T₂ at 60°C is found to be proportional to the average mass between crosslinks.     

Investigation of the response of wood-rotting fungi to copper stress by size-exclusion chromatography and capillary zone electrophoresis with ICP MS detection

A method based on the coupling of size-exclusion chromatography (SEC) with inductively coupled plasma mass spectrometry (ICP MS) was developed for screening the changes in the bioligand composition of wood-rotting fungi as a function of their exposure to copper stress. Strains of four different species of wood-rotting fungi: Phanerochaete chrysosporium, Schizophyllum commune, Daedalea quercina and Pleurotus ostreatus were examined. Only one, namely Ph. chrysosporium, showed any significant difference in terms of the fingerprint of Cu-binding ligands between control and exposed cells which suggest trapping of Cu(II) by cell walls as the only resistance mechanisms. In the case of Ph. chrysosporium the bioinduction of a new Cu-binding ligand was demonstrated. The presence of a new compound in the SE chromatographic fraction of interest was confirmed by CZE-ICP MS. Attempts to identify the new compound by electrospray MS/MS failed because of insufficient sensitivity.     

Potential and Limitations of 2D <Superscript>1</Superscript>H–<Superscript>1</Superscript>H Spin-Exchange CRAMPS Experiments to Characterize Structures of Organic Solids

Summary.  A brief overview of our recent results concerning the application of 2D CRAMPS experiments to investigate a wide range of materials is presented. The abilities of the 2D ¹H–¹H spin-exchange technique to characterize the structure of organic solids as well as the limitations resulting from segmental mobility and from undesired coherence transfer are discussed. Basic principles of ¹H NMR line-narrowing and procedures for analysis of the spin-exchange process are introduced. We focused to the qualitative and quantitative analysis of complex spin-exchange process leading to the determination of domain sizes and morphology in heterogeneous multicomponent systems as well as the characterization of clustering of surface hydroxyl groups in polysiloxane networks. Particular attention is devoted to the determination of the ¹H–¹H interatomic distances in the presence of local molecular motion. Finally we discuss limitations of the ¹³C–¹³C correlation mediated by ¹H–¹H spin exchange to obtain structural constraints. The application of Lee-Goldburg cross-polarization to suppress undesired coherence transfer is proposed. Corresponding author. E-mail: brus@imc.cas.cz Received May 28, 2002; accepted (revised) July 1, 2002     

A non-empirical LCAO MO SCF investigation of electronic relaxations accompanying core ionizations in the series X2 and HX (X = F, Cl and Br)

A theoretical analysis has been made of differences in relaxation energies for photoionization from the core levels of the series X₂, HX for X = F, Cl, Br. It is demonstrated that whilst the charge in relaxation energies is largest for F₂ with respect to HF, the contribution to the shifts in core levels is relatively larger for the series X₂ and HX for X = Cl, Br. It is further shown that shifts in binding and relaxation energies show very little dependence on the core levels studied.     

Amide-Bond Syntheses Catalyzed by Penicillin Acylase

The enzymatic synthesis of amide bonds catalyzed by penicillin acylase is investigated both in H₂O solution and in organic solvents containing reverse micelles. The specificity of the reaction is rather high on the side of the acyl component, practically only phenylacetic acid gives sizeable yields. On the contrary, a variety of amino-acid esters, dipeptides, and tripeptides can be used as amino component, e.g., serine methyl ester, methionine ethyl ester, tyrosine ethyl ester, Gly–Asp, Ala–Tyr, Gly–Tyr–Gly etc. However, Many other amino-acid residues do not react, and the possible reasons for this are discussed. Yields varyin rang the 10–80%. A. systematic study to optimize yields by varying the solvent composition is presented for one model reaction. The enzyme is also able to couple certain D-amino-acid residues (e.g. D-methionine ethyl ester or Gly-D -Asp) though at lower rate. Reverse micelles formed by the cationic surfactant cetyltrimethylammonium bromide (CTAB) in CHCl₃/isooctane are used to host penicillin acylase and to perform amide synthesis in which the product is perferentially soluble in the organic solvent mixture. The reaction is studied as a function of pH and certain micellar parameters, e. g. w_o (w_o = [H₂O]/[CTAB]). A new membrane enzyme reactor is utilized to separate the product from the enzyme-containing micelles. The adavantges and the limits of this approach are discussed.