Fluorescent detection of carbon-carbon bond formation

We have developed a new spectroscopic system for detecting carbon-carbon bond formation by fluorescence to enhance high-throughput catalyst screening and rapid characterization of catalysts on a small scale. Fluorogenic substrates composed of a fluorophore possessing an amino group are readily prepared as amides of alpha,beta-unsaturated carbonyl compounds and generally exhibit low fluorescence, while Michael or Diels-Alder reactions of these fluorogenic substrates provide products of significantly increased fluorescence. The product's fluorescence is approximately 20- to 100-fold higher than that of the substrate. The assay system was validated by screening potential catalysts of the Michael reaction and in solvent optimization experiments. The covalent combination of fluorophores possessing an amino group with alpha,beta-unsaturated carbonyl compounds should provide a diverse range of fluorogenic substrates that may be used to rapidly screen catalysts and to optimize reaction conditions.     

Prediction of anti-HIV activity and cytotoxicity of pyrimidinyl and triazinyl amines: A QSAR study

A QSAR study on a series of pyrimidinyl and triazinyl amines was performed to explore the physico-chemical parameters responsible for their anti-HIV activity and cytotoxicity. Physico-chemical parameters were calculated using WIN CAChe 6.1. Stepwise multiple linear regression analysis was carried out to derive QSAR models which were further evaluated for statistical significance and predictive power by internal and external validation. The selected best QSAR models showed correlation coefficient R of 0.914 and 0.901, and cross-validated squared correlation coefficient Q ² of 0.685 and 0.691 for anti-HIV activity and cytotoxicity, respectively. The developed significant QSAR model indicates that hydrophobicity of the whole molecule plays an important role in the anti-HIV activity and cytotoxicity of pyrimidinyl and triazinyl amine derivatives. When hydrophobicity is increased, anti-HIV activity of the present series of compounds is decreased leading to high cytotoxicity.     

Multi-element substituted hydroxyapatites: synthesis,structural characteristics and evaluation of their bioactivity,cell viability,and antibacterial activity

Synthesis of unsubstituted and multi-element (magnesium, zinc and cobalt) substituted hydroxyapatites (HAP) with varying stoichiometric compositions and evaluation of their morphological and structural characteristics, degree of crystallinity, bioactivity, cytotoxicity and antibacterial activity are addressed. The morphological features are not altered much following the substitution of Mg²⁺, Zn²⁺, and Co²⁺ in the HAP lattice. Nevertheless, their substitution exerts a strong influence on the structural characteristics HAP. Rietveld refinement analysis of the X-ray diffraction patterns indicates a decrease in crystallinity and mineralogical composition of HAP phase, which is accompanied with an increase of β-tricalcium phosphate (β-TCP) phase along with Co₃O₄ phase. Broadening of the PO₄^3? peaks and a decrease in intensity of the OH^? peak are observed by Fourier-transform infrared spectra. A decrease in intensity, broadening and a slight shift in Raman band (at 961?cm^?1 for HAP) towards the lower side suggest the incorporation of Mg, Zn, and Co, disordering of the crystal structure of HAP and formation of β-TCP as additional phase besides HAP. The MgZnCo-HAP’s exhibits a better bioactivity, cell viability and anti-bacterial activity than the unsubstituted HAP. However, a decrease in cell viability and anti-bacterial activity are observed when the stoichiometric ratio of the substituent elements is relatively higher.

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Warum pentose-und nicht hexose-nucleinsäuren? Teil III. Oligo(2′,3′-dideoxy-β-D-glucopyranosyl) nucleotide (‘homo-DNS’): Paarungesigenschaften

Why Pentose-And Not Hexose-Nucleic Acids? Part III. Oligo(2′,3′-dideoxy-β-D -glucopyranosyl)nucleotides. (‘Homo-DNA’): Base-Pairing Properties

1 Summary in collaboration with Prof. Dr. C. E. Wintner, Haverford College, Haverford, PA 19041-1392.

The paper presents results of a comprehensive investigation on the pairing properties of homo-DNA oligonucleotides, the preparation of which has been described in Part II of this series [2]. The investigation was carried out by using established methods described in the literature for the characterization of oligonucleotides in the natural series, such as determination of melting temperatures of oligonucleotide duplexes by temperature-dependent of melting temperatures, determination of pairing stoichiometry by ratio-dependent UV spectroscopy of binary mixtures of pairing partners, temperature-dependent CD spectroscopy, gel electrophoresis under non-denaturing conditions, and – in selected cases – ¹H – and³¹P-NMR spectroscopy. The systematic comparison of the paring properties of homo-DNA oligonucleotides with corresponding DNA nucleotides (up to dodecamers) indicates that homo-DNA is a highly efficient, autonomous, artificial pairing system with a pairing behavior that is in part similar to, but also, in part, strikingly different from, the pairing behavior of DNA. The pairing properties established so far are listed below in a manner that reflects the sequence of subtitles in Chapt.2 of the text; they were determined under the conditions: H²O, 0.15M NaCl, 0.01M Tris-HCl buffer, pH 7, oligonucleotide concentrations in the μM range, 1:1 ratio of single strands in the case of non-selfcompementary sequences.     

Purification and characterization of cysteine protease from germinating cotyledons of horse gram

Background  

Proteolytic enzymes play central role in the biochemical mechanism of germination and intricately involved in many aspects of plant physiology and development. To study the mechanism of protein mobilization, undertaken the task of purifying and characterizing proteases, which occur transiently in germinating seeds of horse gram.     

A Note on the Direct Determination of the Confining Pressure of Cylindrical Specimens

This note presents a simple approach to the direct determination of the confining pressure, q, for a cylindrical specimen encased in a metallic sleeve. The stress analysis of the problem shows that, for a pressure-insensitive material (e.g. metal), q is the quantity by which the stress level of the confined specimen is elevated with respect to the unconfined. As such, q is directly determined by comparing the results of two tests, one with and the second without confinement. For a pressure-sensitive material, q must be determined independently from a plastic stress analysis of the confining sleeve. Then, the same approach can be applied to determine the pressure sensitivity of the material. The present results greatly simplify testing of confined cylindrical specimens for both pressure-insensitive and sensitive materials.     

Role of asymmetries in the chaotic dynamics of the double-well Duffing oscillator

Duffing oscillator driven by a periodic force with three different forms of asymmetrical double-well potentials is considered. Three forms of asymmetry are introduced by varying the depth of the left-well alone, location of the minimum of the left-well alone and above both the potentials. Applying the Melnikov method, the threshold condition for the occurrence of horseshoe chaos is obtained. The parameter space has regions where transverse intersections of stable and unstable parts of left-well homoclinic orbits alone and right-well orbits alone occur which are not found in the symmetrical system. The analytical predictions are verified by numerical simulation. For a certain range of values of the control parameters there is no attractor in the left-well or in the right-well.     

Highly conducting and crystalline doubly doped tin oxide films fabricated using a low-cost and simplified spray technique

Doubly doped (simultaneous doping of antimony and fluorine) tin oxide films (SnO₂:Sb:F) have been fabricated by employing an inexpensive and simplified spray technique using perfume atomizer from aqueous solution of SnCl₂ precursor. The structural studies revealed that the films are highly crystalline in nature with preferential orientation along the (2 0 0) plane. It is found that the size of the crystallites of the doubly doped tin oxide films is larger (69 nm) than that (27 nm) of their undoped counterparts. The dislocation density of the doubly doped film is lesser (2.08×10¹⁴ lines/m²) when compared with that of the undoped film (13.2×10¹⁴ lines/m²), indicating the higher degree of crystallinity of the doubly doped films. The SEM images depict that the films are homogeneous and uniform. The optical transmittance in the visible range and the optical band gap of the doubly doped films are 71% and 3.56 eV respectively. The sheet resistance (4.13 Ω/□) attained for the doubly doped film in this study is lower than the values reported for spray deposited fluorine or antimony doped tin oxide films prepared from aqueous solution of SnCl₂ precursor (without using methanol or ethanol).     

Upstream jetting phenomenon in planar shock wave experiments with ceramic powders

Jetting along upstream impact direction was observed in the experiments that were designed to study the response of ceramic powder materials to planar shock loading generated by impact. The jet formed catastrophically above certain impact stress level at the center of the impacted area and perforated upstream metal cover and flyer plates. Experiments were conducted with different impact stress levels, powder particle sizes, and geometrical parameters. Consistently repeatable results were obtained and effects arising from particle size, initial porosity, impact stress, and reflected wave were assessed. A simple mechanism-based model is used to explain the formation of the jet and estimate the jet velocity.