Synthesis of novel macrocyclic crown ethers from D-glucose

A simple and efficient synthetic protocol for an easy access of carbohydrate-linked crown ethers from cheap and readily available D-glucose in good yields has been devised. The base-mediated cyclization of sugar-linked bis-iodo podands in CH₃CN with amines, including ethylamine and furfurylamine afforded the novel chiral monoaza-15-crown-5-type macrocyclic crown ethers anellated to 3-O-benzyl-1,2-O-isopropylidene-α-D-glucofuranose and 3-O-benzyl-1,2-O-isopropylidene-α-D-allofuranose. The glucose-based crown ethers have been characterized by spectroscopy techniques including IR, ¹H NMR, and ¹³C NMR.     

8-hydroxyquinoline based neutral tripodal ionophore as a copper (II) selective electrode and the effect of remote substitutents on electrode properties

New PVC membrane ion selective electrodes based on 1,3,5-Tris(8-quinolinoxymethyl)-2,4,6-trimethylbenzene (MO8HQ) are reported. The basic sensing material belongs to the group of tripodal ionophores. Also their derivatives prepared by placing suitable substitutents at fifth position of 8-oxine moiety, i.e, 1,3,5-Tris(5-chloro-8-quinolinoxymethyl)-2,4,6-trimethylbenzene (5CHQ), 1,3,5-Tris(5-benzoyl-8-quinolinoxymethyl)-2,4,6-trimethylbenzene (5BHQ) and 1,3,5-Tris[(5-phenylhydroxymethylene)-8-quinolinoxymethyl]-2,4,6-trimethylbenzene (HYD-8HQ) ionophores have also been used to make copper-selective membrane electrodes. Among all the four electrodes, MO8HQ and HYD-8HQ ionophores based electrodes show excellent response towards Cu (II) ions. The electrodes having composition 33% PVC, 4% MO8HQ and 63% dibutyl phthalate (DBP) and 33% PVC, 6% HYD-8HQ, 63% dibutyl phthalate (DBP) exhibit a good Nernstian response to Cu (II) ions in the range of 1.0 × 10⁻⁶ to 1 × 10⁻¹ M. The electrode shows a reasonably fast response time of 15 s. The effect of pH and electrode response is also reported. It shows good selectivity for Cu (II) ions in comparison to heavy metal ions, transition metal ions and for alkali and alkaline earth metal ions. The electrode response and selectivity remains unchanged for at least 5 months. The electrode can be used as an indicator electrode in the potentiometric titration of Cu (II) ions with EDTA.     

Optimum ramp-stress accelerated life test for m identical repairable systems

This paper proposes optimum ramp accelerated life test (ALT) of m identical repairable systems using non-homogeneous power law process (PLP) under failure truncated case. An ALT with linearly increasing stress is a ramp test. In particular, a ramp test with two different linearly increasing stresses is a simple ramp test. The optimum ramp test with different stress rates is formulated by determining the proportions of test systems allocated to each stress rate using D-optimality criterion. D-optimality criterion minimizes the reciprocal of the determinant of the Fisher information matrix of the model parameters. The method developed is illustrated using two stress rates and three stress rates. It has been found that it takes much longer to obtain same estimated expected no. of failures at baseline condition than at stress levels.     

Synthesis and structural characterization of pincer type bicyclic diacyloxy- and diazaselenuranes

Synthesis and structural characterization of a new class of pincer type bicyclic diacyloxy- and diazaselenuranes is reported. The reaction of dimethyl 2-bromo-5-tert-butylisophthalate (28) with sodium benzeneselenolate affords the corresponding monoselenide, dimethyl 5-tert-butyl-2-(phenylselanyl)isophthalate (29). Reduction of 29 with LiAlH(4) provides 5-tert-butyl-2-(phenylselanyl)-1,3-phenylene)dimethanol 31. Oxidation of 29 or its hydrolyzed derivative, 5-tert-butyl-2-(phenylselanyl)isophthalic acid (30), with H(2)O(2) results in the formation of bicyclic diacyloxyselenurane (25). The reaction of 30 with aniline using the DCC coupling reaction gives 5-tert-butyl-N(1),N(3)-diphenyl-2-(phenylselanyl)isophthalamide (38). Reaction of 38 with H(2)O(2) leads to the formation of the corresponding bicyclic diazaselenurane (27) via selenoxide intermediate 39. Compounds 25, 27, 29 and 31 were characterized by single crystal X-ray crystallography. The structural aspects of the pincer type bicyclic chalcogenuranes are investigated using experimental and computational studies and compared with the related systems.     

Effect of gold electrode crystallographic orientations on charge transport through aromatic molecular junctions

ABSTRACT

We examined the electrical conduction through single-molecular junctions comprising of anthracenedithiol molecule coupled to two gold electrodes having ?1,0,1?, ?1,1,0? and ?1,1,1? crystallographic orientations. Owing to this jellium model, we evaluated the values of current and conductance using non-equilibrium Green's functions combined with extended Huckel theory. This data was further interpreted in terms of transmission spectra, density of states and their molecular orbital analysis for zero bias. We evinced the oscillating conductance in all three cases, due to the oscillation of orbital energy relative to Fermi level. Our detailed analysis suggested that electrode orientation can tune the molecule–electrode coupling and hence conduction. Anthracene molecular junction with ?1,1,0? orientation displayed favourable conduction, when compared to the other two orientations, thus can provide us an insight while designing futuristic molecular electronic devices.     

Surface‐enhanced Raman measurements and DFT calculations for l‐tryptophan of varying pH in silver sol

The interaction of l ‐tryptophan (Trp) with silver colloids was investigated at between pH values of 6.11 and 10.6 of the sol. The measurements of surface‐enhanced Raman bands of Trp in the colloidal solution indicate the evolution of interaction between the metal particles and the molecules with increasing pH values for the sol. The experimental observations were explained using the estimated atomic charge distribution in the zwitterionic and anionic forms of the residue, obtained by density functional theory calculations. The variation in the ratio of the spectral intensities of the Fermi resonance bands with the pH reflects the effect of the colloidal environment on Trp. The results obtained can be used as a marker for describing the nature of the interaction of silver colloids with the specific terminus of the residue, at varying pH environments. Copyright © 2012 John Wiley & Sons, Ltd.     

Nanocrystalline SnO2–TiO2 thin film deposited on base of equilateral prism as an opto-electronic humidity sensor

Present paper reports the synthesis of SnO₂–TiO₂ nanocomposite, its characterization and performance as opto-electronic humidity sensor. Nanocrystalline SnO₂–TiO₂ film was deposited on the base of an equilateral prism using a photo resist spinner and the as prepared film was annealed at 200 °C for 2 h. The crystal structure of the prepared film was investigated using X-ray diffraction (XRD). Minimum crystallite size of the material was found 7 nm. Surface morphology of the film was investigated by Scanning electron microscope (SEM LEO-0430, Cambridge). SEM image shows that the film is porous. Differential scanning calorimetry (DSC) of as synthesized material shows two exothermic peaks at about 40 and 110 °C, respectively which are due to the evaporation of chemical impurities and water. Further the prepared film was investigated through the exposure of humidity and relative humidity (%RH) was measured directly in terms of modulation in the intensity of light recorded on a digital power meter. The maximum sensitivity of sensor was found 4.14 μW/%RH, which is quite significant for sensor fabrication purposes.     

“Doubly Selective” Antimicrobial Polymers: How Do They Differentiate between Bacteria?

We have investigated how doubly selective synthetic mimics of antimicrobial peptides (SMAMPs), which can differentiate not only between bacteria and mammalian cells, but also between Gram‐negative and Gram‐positive bacteria, make the latter distinction. By dye‐leakage experiments on model vesicles and complementary experiments on bacteria, we were able to relate the Gram selectivity to structural differences of these bacteria types. We showed that the double membrane of E. coli rather than the difference in lipid composition between E. coli and S. aureus was responsible for Gram selectivity. The molecular‐weight‐dependent antimicrobial activity of the SMAMPs was shown to be a sieving effect: while the 3000 g mol^?1 SMAMP was able to penetrate the peptidoglycan layer of the Gram‐positive S. aureus bacteria, the 50000 g mol^?1 SMAMP got stuck and consequently did not have antimicrobial activity.     

Antimicrobial Polymers Prepared by Ring‐Opening Metathesis Polymerization: Manipulating Antimicrobial Properties by Organic Counterion and Charge Density Variation

The synthesis and characterization of a series of poly(oxanorbornene)‐based synthetic mimics of antimicrobial peptides (SMAMPs) is presented. In the first part, the effect of different organic counterions on the antimicrobial properties of the SMAMPs was investigated. Unexpectedly, adding hydrophobicity by complete anion exchange did not increase the SMAMPs’ antimicrobial activity. It was found by dye‐leakage studies that this was due to the loss of membrane activity of these polymers caused by the formation of tight ion pairs between the organic counterions and the polymer backbone. In the second part, the effect of molecular charge density on the biological properties of a SMAMP was investigated. The results suggest that, above a certain charge threshold, neither minimum inhibitory concentration (MIC₉₀) nor hemolytic activity (HC₅₀) is greatly affected by adding more cationic groups to the molecule. A SMAMP with an MIC₉₀ of 4 μg mL^?1 against Staphylococcus aureus and a selectivity (=HC₅₀/MIC₉₀) of 650 was discovered, the most selective SMAMP to date.