Synthesis, relaxometric and photophysical properties of a new pH-responsive MRI contrast agent: the effect of other ligating groups on dissociation of a p-nitrophenolic pendant arm

Two gadolinium(III) chelates, GdNP-DO3A (1-methlyene-(p-NitroPhenol)-1,4,7,10-tetraazacycloDOdecane-4,7,10-triAcetate) and GdNP-DO3AM (1-methlyene(p-NitroPhenol)-1,4,7,10-tetraazacycloDOdecane-4,7,10-triacetAMide), containing a single nitrophenolic pendant arm plus either three acetate or three amide pendant arms were synthesized and characterized. The properties of the gadolinium, terbium, and dysprosium complexes of these ligands were examined as a function of pH. The extent and mechanism of the changes in water relaxivity with pH of each gadolinium complex was found to differ substantially for the two complexes. The water relaxivity of Gd(NP-DO3A) increases from 4.1 mM(-1) s(-1) at pH 9 to 7.0 mM(-1) s(-1) at pH 5 as a result of acid-catalyzed dissociation of the nitrophenol from the lanthanide. The nitrophenol group in Gd(NP-DO3AM) does not dissociate from the metal center even at pH 5; therefore, the very modest increase in relaxivity in this complex must be ascribed to an increase in prototropic exchange rate of the bound water and/or phenolic protons.     

Acetone chemical ionization studies III–displacement reactions in alkyl acetates

Acetone chemical ionization mass spectra of acyclic, cyclic and bicyclic alkyl acetates were studied. In addition to the formation of [M + H]⁺, [M + 43]⁺ and [M + 59]⁺ ions, ions corresponding to displacement by acetone were also observed. The results suggest that the displacement by acetone follows an S_N1-like mechanism in the source of the mass spectrometer. Similarity between solution-phase solvolysis reactions and gas-phase displacement reactions was observed with bicyclic alkyl acetates, 2-phenylethyl acetate and cyclooctyl acetate.     

Mass spectral study of derivatives of 2-aryloxy-2-methylpropanoicacids

Electron impact mass spectra are reported for series of 2-aryloxy-2-methylpropanoic acids, 2-aryloxy-2-methylpropanamides and N-phenyl-2-aryloxy-2-methylpropanamides. Fragmentation mechanisms are discussed on the basis of deuterium labelling, meastable ions and accurate mass measurements.     

Synthesis and Spectroscopic Investigation of Diketopyrrolopyrrole - Spiropyran Dyad for Fluorescent Switch Application

We report the synthesis and characterization of a new fluorescent dyad SP-DPP-SP(9) via efficient palladium-catalyzed Sonogashira coupling of prop-2-yn-1-yl 3-(3′,3’dimethyl-6-nitrospiro[chromene-2,2′-indolin]-1′-yl)propanoatespiropyran, SP(8), a well known photochromic accepter, with 3,6-bis(5-bromothiophen-2-yl)-2,5-bis((R)-2-ethylhexyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione, DPP(4), a highly fluorescent donor. Under visible light exposure the SP unit is in a closed hydrophobic form, whereas under UV irradiation it converts to a polar, hydrophilic open form named Merocyanine (MC), which is responsible for functioning of photo-switch application. The photochemistry pertaining to fluorescence switch, ‘on/off’ behaviour, of model dyad SP-DPP-SP(9) is experimentally analyzed in solution as well as in solid state in polymer matrices by photoluminescence(PL) and absorption spectroscopy. After absorption of UV light the spiropyran unit of the dyad under goes the rupture of the spiro C-O bond leading to the formation of MC. The absorption band of MC fairly overlaps to the fluorescence of DPP unit resulting quenching of fluorescence via fluorescence resonance energy transfer from exited DPP unit to ground state MC. In contrary, the fluorescence of DPP is fully regained upon transformation of MC to SP by exposure to visible light or thermal stimuli. Hence, the fluorescence intensity of dyad 9 is regulated by reversible conversion among the two states of the photochromic spiropyran units and the fluorescence resonance energy transfer (FRET) between the MC form of SP and the DPP unit. Conversely, these scrutiny of the experiment express that the design of dyad 9 is viable as efficient fluorescent switch molecule in many probable commercial applications, such as, logic gates and photonic and optical communications.     

On Modeling Change Points in Non-Homogeneous Poisson Processes

Failures in repairable systems are often described by means of non-homogeneous Poisson processes, identified by their intensity and mean value functions. Intervention on the systems are likely to modify their reliability, and changes in intensities and mean value functions are therefore induced. We consider different scenarios in which interventions take places and propose models describing each of them. Bayesian analyses, relying on Markov-chain Monte Carlo methods, are illustrated along with applications to simulated and real, widely-known, data.     

Warping stresses in circular concrete slabs on hetényi foundation

Summary Non-dimensional deflection, moment and pressure coefficients have been evaluated for circular concrete slabs on Hetényi foundation. The slab is subjected to temperature which either increases or decreases linearly with depth of slab. The results are compared with the results of Leonards and Harr, to study the effect of continuity. The results are also compared with the results for strip slabs on Hetényi foundation. The results indicate that stresses at the centre of slabs are, in general, higher for slabs on Winkler foundation when compared to those of the slabs on Hetényi foundation.

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Übersicht Es werden dimensionslose Beiwerte für Verschiebung, Moment und Druck an kreisförmigen Betonplatten auf einem Hetényi-Grund abgeschätzt. Dabei wird angenommen, daß die Plattentemperatur mit der Plattentiefe entweder linear ansteigt oder linear abfällt. Die Ergebnisse werden mit denen von Leonards und Harr, sowie mit den an Streifenplatten auf Hetényi-Grund erhaltenen verglichen. Es zeigt sich, daß die Beanspruchung in der Plattenmitte im allgemeinen größer ist bei Lagerung auf einem Winkler-Grund, verglichen mit einem Hetényi-Grund.

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The authors are very much thankful to Prof. K. Seetharamiah, Head of the Department of Civil and Hydraulic Engineering, Indian Institute of Science, Bangalore.     

Orchids as Sources of Novel Nanoinsecticides? Efficacy of <Emphasis Type="Italic">Bacillus sphaericus</Emphasis> and <Emphasis Type="Italic">Zeuxine gracilis</Emphasis>-Fabricated Silver Nanoparticles Against Dengue,Malaria and Filariasis Mosquito Vectors

Mosquitoes are the most critical group of insects in the context of public health, since they transmit key parasites and pathogens, causing millions of deaths annually. Insecticides from natural products may boost the effectiveness of vector control programs. In this study, we tested silver nanoparticles (AgNPs) fabricated using the leaf extract of the orchid Zeuxine gracilis as reducing agent, and the microbial pesticide Bacillus sphaericus, against the mosquitoes Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus. The synthesis of AgNP was confirmed analyzing the excitation of surface Plasmon resonance using ultraviolet–visible (UV–Vis) spectrophotometry. SEM and TEM showed the irregular shapes of AgNPs. EDX spectroscopy, FTIR spectroscopy, X-ray diffraction and dynamic light scattering analysis were carried out. AgNPs were highly effective against the larvae of An. stephensi (LC₅₀ = 8.48 µg/mL), Ae. aegypti (LC₅₀ = 10.39 µg/mL) and Cx. quinquefasciatus (LC₅₀ = 13.21 µg/mL), respectively. Combined treatments testing B. sphaericus with AgNPs were also effective against An. stephensi (LC₅₀ = 12.32 µg/mL), Ae. aegypti (LC₅₀ = 14.78 µg/mL) and Cx. quinquefasciatus (LC₅₀ = 19.19 µg/mL). Overall, this study suggests that the orchid-synthesized AgNPs can be a rapid, environmentally safer bio-pesticide to be used in synergy with B. sphaericus to control mosquito vectors.     

Advances in chemoselective and/or stereoselective semihydrogenation of alkynes

The chemoselective semihydrogenation of alkynes is one of the most important reactions in synthetic organic chemistry. During the last decade or so, a multitude of innovative catalytic methods have been developed to address the selective hydrogenation of alkynes. This digest focuses on the recent developments in chemoselective semihydrogenation of alkynes to alkenes.     

Self-Assembled Superstructure of Xanthene Derivatives

Various multi carbon homologations of 9-phenyl-9H-xanthen-9-ol (1) were obtained through a C-C bond formation by reacting it with various enolisable ketones in the presence of 1,1′-(ethane-1,2-diyl)dipyridinium bistribromide (EDPBT). All the ten derivatives along with the starting xanthen-9-ol have been characterized by single crystal X-ray diffraction. They all form self-assembled superstructure in the solid state. The self-assembling patterns in these supramolecular architectures were explained based on steric and electronic nature of the pendant arm. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A load balancing system in the many-server heavy-traffic asymptotics

Queueing Systems - We study a load balancing system in the many-server heavy-traffic regime. We consider a system with N servers, where jobs arrive to the system according to a Poisson process and...