From dispersed nanodiscs to thin films of layered organic material via reversible swelling

We show that nanodiscs stabilized with polymers order and pile up on a surface upon drying. The resulting surface films with an average thickness of one micron are made of collapsed cohesive layers with smectic long-range order. This occurs with and without plastifying stabilizing polymer and produces crevasses. The stacked discs undergo a two-to-three-dimensional crystallization while bottom layers close to the surface fuse and produce infinite bilayers. Small angle X-ray scattering experiments demonstrate that excess polymer is segregated from the crystalline stack. Water adsorption isotherms show that reversible swelling of the excess polymer does not destroy the compact stack of partially fused nanodiscs collapsed parallel to the surface. In the absence of chemical binding, the stacks of layered nanodiscs can be removed by simple washing with pure water. AFM, TEM and SEM experiments demonstrate that presence of crevasses is quenched by the presence of a plastifying polymer.     

Electrochemical Signal‐triggered Release of Biomolecules Functionalized with His‐tag Units

His‐tagged molecular species, a ferrocene derivative and Protein A, were immobilized on electrode surfaces (Au and graphite) through formation of a chelated complex in the presence of Cu²⁺ cations used as bridging units. The complex was cleaved and the attached molecules were released from the electrode surface by applying reductive potential to the electrodes resulting in Cu²⁺ reduction, thus decomposing the chelate complex. The molecule release process was followed by cyclic voltammetry in case of the ferrocene derivative. His‐tagged Protein A was additionally labeled with a fluorescent tag and its release was followed by fluorescence measurements in the solution and by impedance spectroscopy at the electrode. The studied release of the His‐tagged redox species and biomolecules was considered as a new generic approach to the signal‐controlled molecule release applicable in various biotechnological and biomedical applications.     

TiO2ZrO2 composite: Synthesis,characterization and application as a facile,expeditious and recyclable catalyst for the synthesis of 2-aryl substituted benzoxazole derivatives

The activity of an efficient mesoporous TiO₂ZrO₂ composite catalyst for the synthesis of 2-aryl substituted benzoxazole derivatives using 2-aminophenol and substituted benzaldehydes/heterocyclic aldehydes at moderate temperature was studied. The catalyst was prepared by a co-precipitation method and characterized by X-ray diffraction, BET surface area and scanning electron microscopy. The effect of temperature, solvents and catalyst concentration on the synthesis of benzoxazole derivatives was systematically investigated. Short reaction times, green-reaction profiles, good to excellent yields, reliable cost efficiency, simple workup conditions and reusability of an eco-friendly catalyst are the noteworthy highlights of the reported method. The catalyst could be easily recovered and reused several times without any significant loss in the yield. The use of the present catalytic system to mediate the title chemical synthesis in a synthetic operation is important for the development of new atom-economic strategies and this is efficient in building complex structures from simple starting materials in an environmentally benign fashion.     

Total synthesis and mechanism of action of the antibiotic armeniaspirol A

Emerging antimicrobial resistance urges the discovery of antibiotics with unexplored, resistance-breaking mechanisms. Armeniaspirols represent a novel class of antibiotics with a unique spiro[4.4]non-8-ene scaffold and potent activities against Gram-positive pathogens. We report a concise total synthesis of (±) armeniaspirol A in six steps with a yield of 20.3% that includes the formation of the spirocycle through a copper-catalyzed radical cross-coupling reaction. In mechanistic biological experiments, armeniaspirol A exerted potent membrane depolarization, accounting for the pH-dependent antibiotic activity. Armeniaspirol A also disrupted the membrane potential and decreased oxygen consumption in mitochondria. In planar lipid bilayers and in unilamellar vesicles, armeniaspirol A transported protons across membranes in a protein-independent manner, demonstrating that armeniaspirol A acted as a protonophore. We provide evidence that this mechanism might account for the antibiotic activity of multiple chloropyrrole-containing natural products isolated from various origins that share a 4-acylphenol moiety coupled to chloropyrrole as a joint pharmacophore. We additionally describe an efflux-mediated mechanism of resistance against armeniaspirols.

The antibiotic armeniaspirol A depolarized bacterial and mammalian cell membranes through a protonophore activity, that accounts for its potent antibiotic effects. A total synthesis of (±) armeniaspirol A was achieved in six steps.     

Physicochemical characterization of an Indian traditional medicine, Jasada Bhasma: detection of nanoparticles containing non-stoichiometric zinc oxide

Herbs and minerals are the integral parts of traditional systems of medicine in many countries. Herbo-Mineral medicinal preparations called Bhasma are unique to the Ayurvedic and Siddha systems of Indian Traditional Medicine. These preparations have been used since long and are claimed to be the very effective and potent dosage form. However, there is dearth of scientific analytical studies carried out on these products, and even the existing ones suffer from incomplete analysis. Jasada Bhasma is a unique preparation of zinc belonging to this class. This particular preparation has been successfully used by traditional practitioners for the treatment of diabetes and age-related eye diseases. This work presents a first comprehensive physicochemical characterization of Jasada Bhasma using modern state-of-the-art techniques such as X-ray photoelectron spectroscopy (XPS), inductively coupled plasma (ICP), elemental analysis with energy dispersive X-ray analysis (EDAX), dynamic light scattering (DLS), and transmission electron microscopy (TEM). Our analysis shows that the Jasada Bhasma particles are in oxygen deficient state and a clearly identifiable fraction of particles are in the nanometer size range. These properties like oxygen deficiency and nanosize particles in Jasada Bhasma might impart the therapeutic property of this particular type of medicine. A. C. Joshi: Private Practitioner (Vaidya).     

Investigation of influential factors on the purification of zone‐refined germanium ingot

Zone refining is one of the most important procedures to purify germanium crystals for the fabrication of detectors in our laboratory. In order to properly zone refine high‐purity germanium crystals, it is important to develop perfect cleaning procedures for raw materials, quartz tubes, and the containers holding raw materials. Additionally, vacuum levels, container types, the correct combination of ambient gases, the speed of zone travel, and the ratio of ingot length to molten zone length, all need to be carefully studied in order to obtain the best results possible. In this work, we investigate a number of influential factors in perfecting high‐purity germanium crystal growth, specifically: cleaning procedures, boat composition, vacuum levels in the chamber, zone travel speed, and the ratio of ingot length to molten zone length. Using the van der Pauw Hall technique, we were able to measure the electrical properties of zone‐refined ingots and analyze the origin and distribution of three main impurity elements (boron, aluminum and phosphorus) thereby allowing us to study potential contamination sources. After detailed analysis on the various influential factors, we were able to optimize the zone‐refining procedures.     

Morphology and bilayer integrity of small liposomes during aerosol generation by air-jet nebulisation

Small liposome suspensions (hydrodynamic diameter, 80–130 nm) were nebulised, and the resulting changes in morphology and bilayer integrity were found to be related to surface properties controlled by bilayer composition. Four separate liposome compositions (or liposome types) were investigated using three different phospholipids with unique properties. Morphological changes were studied using light scattering and imaging of liposomes before and after nebulisation, and structural integrity was investigated on the basis of the retention of an encapsulated dye (probe molecule). Nebulisation generated droplets contained liposomes. The liposome particles generated on droplet evaporation had a hollow structure as evidenced by electron imaging, indicating that the lipid bilayer does not collapse on evaporation. The particles of all compositions had mobility diameters between 50 and 90 nm, 1.4–1.6 times smaller than their diameters (hydrodynamic) measured before nebulisation, implying considerable volume shrinkage. Liposomes that had polymer-conjugated lipids covering their external surface underwent aggregation during nebulisation, evidenced by increased diameter after nebulisation. Incorporation of charged lipids reduced nebulisation-induced aggregation, but induced greater membrane rupture during aerosol generation, causing leakage of encapsulated probe molecules. Incorporation of both cholesterol and charged lipids prevented aggregation, but also preserved bilayer integrity, evidenced by the maximum retention of encapsulated dye observed in these conditions (>85%). The findings suggest that liposome bilayer composition can be manipulated to improve the efficiency of liposome aerosol delivery.     

Superposition of Quantum Confinement Energy (SQCE) model for estimating shell thickness in core-shell quantum dots: validation and comparison

A novel theoretical model based on superposition of core and shell band-gaps, termed as SQCE model, is developed and reported here, which enables one to estimate the shell thickness in a core-shell quantum dot (QD), which is critically important in deciding its optical and electronic properties. We apply the model to two experimental core-shell QD systems, CdSe-CdS and CdSe-ZnS, which we synthesize by microemulsion method. We synthesize and study two series of samples, R and S to study the optical properties. The core size is varied in the R-series (by varying water-to-surfactant ratio, R) whereas the shell thickness is varied in the S-series (by varying the shell-to-core precursor molar ratio, S). The core and core-shell QDs from R-series and S-series are characterized for particle size, shape and crystallographic information. The shell thickness for all core-shell QD samples is estimated by SQCE model, and experimentally measured with TEM and SAXS. A close match is observed between experimental values and model predictions, thus validating the model. Further, the optimum shell thickness (corresponding to maximum quantum yield) values for CdS and ZnS over a 4.26 nm CdSe core have been estimated as 0.585 nm and 0.689 nm, respectively, from the SQCE model. The SQCE model developed in this work is applicable to other core-shell quantum dots also, such as CdTe-CdS, CdTe-CdSe and CdS-ZnS, and will serve as a useful complement to experimental measurement.