Exclusive Detection of Sub-Nanomolar Levels of Palladium(II) in Water: An Excellent Probe for Multiple Applications

A new colorimetric probe has been developed for the detection and estimation of Pd-II at sub-nanomolar concentrations. The probe consisted of rhodamine (signaling unit), which was linked with a bis-picolyl moiety (binding site) through a phenyl ring. Pd-II induced opening of the spirolactam ring of the probe with the generation of a prominent pink color. The excellent selectivity of the probe towards Pd-II over Pd-0 or Rh-II ensured its potential utility for the detection of residual palladium contamination in pharma-ceutical drugs and in Pd-catalyzed reactions. The probe showed a ``turn-on'' (bright yellow) fluorescence upon the addition of Pd-II, which made it suitable for the detection of Pd contaminants in mammalian cells.

IR spectroscopy as a probe for C-H center dot center dot center dot X hydrogen bonded supramolecular synthons

Weak hydrogen bonds of the type C-H center dot center dot center dot X (X: N, O, S and halogens) have evoked considerable interest over the years, especially in the context of crystal engineering. However, association patterns of weak hydrogen bonds are generally difficult to characterize, and yet the identification of such patterns is of interest, especially in high throughput work or where single crystal X-ray analysis is difficult or impossible. To obtain structural information on such assemblies, we describe here a five step IR spectroscopic method that identifies supramolecular synthons in weak hydrogen bonded dimer assemblies, bifurcated systems, and p-electron mediated synthons. The synthons studied here contain C-H groups as hydrogen bond donors. The method involves: (i) identifying simple compounds/cocrystals/salts that contain the hydrogen bonded dimer synthon of interest or linear hydrogen bonded assemblies between the same functionalities; (ii) scanning infrared (IR) spectra of the compounds; (iii) identifying characteristic spectral differences between dimer and linear; (iv) assigning identified bands as marker bands for identification of the supramolecular synthon, and finally (v) identifying synthons in compounds whose crystal structures are not known. The method has been effectively implemented for assemblies involving dimer/linear weak hydrogen bonds in nitrobenzenes (C-H center dot center dot center dot O-NO), nitro-dimethylamino compounds (NMe2 center dot center dot center dot O2N), chalcones (C-H center dot center dot center dot O=C), benzonitriles (C-H center dot center dot center dot N C) and fluorobenzoic acids (C-H center dot center dot center dot F-C). Two other special cases of C-H center dot center dot center dot pi and N-H center dot center dot center dot pi synthons were studied in which the band shape of the C-H stretch in hydrocarbons and the N-H deformation in aminobenzenes was examined.

The phenanthroimidazole-based dizinc(II) complex as a fluorescent probe for the pyrophosphate ion as generated in polymerase chain reactions and pyrosequencing

A highly selective and sensitive phenanthroimidazole tagged Mannich base type dizinc(II) fluorescent probe (R-Zn2+) has been developed for the pyrophosphate ion (PPi) with a very low limit of detection (LOD) of 0.25 ppm; this also assesses PPi from DNA polymerization chain reaction (PCR).

Enantio-differentiation of molecules with diverse functionalities using a single probe

This study reports (1S,2S)-N,N'-dihydroxy-N,N'-bis(diphenylacetyl)-1,2-cyclohexanediamine, a C-2 symmetric chiral hydroxamic acid ((S)-CBHA-DPA), as a unique probe for discrimination of molecules with diverse functionalities. The proposed CSA is also utilized for the accurate measurement of enantiomeric excess.

A low-power, low-cost soil-moisture sensor using dual-probe heat-pulse technique

This paper presents the development and testing of an integrated low-power and low-cost dual-probe heat-pulse (DPHP) soil-moisture sensor in view of the electrical power consumed and affordability in developing countries. A DPHP sensor has two probes: a heater and a temperature sensor probe spaced 3 mm apart from the heater probe. Supply voltage of 3.3V is given to the heater-coil having resistance of 33 Omega power consumption of 330 mW, which is among the lowest in this category of sensors. The heater probe is 40 mm long with 2 mm diameter and hence is stiff enough to be inserted into the soil. The parametric finite element simulation study was performed to ensure that the maximum temperature rise is between 1 degrees C and 5 degrees C for wet and dry soils, respectively. The discrepancy between the simulation and experiment is less than 3.2%. The sensor was validated with white clay and tested with red soil samples to detect volumetric water-content ranging from 0% to 30%. The sensor element is integrated with low-power electronics for amplifying the output from thermocouple sensor and TelosB mote for wireless communication. A 3.7V lithium ion battery with capacity of 1150 mAh is used to power the system. The battery is charged by a 6V and 300 mA solar cell array. Readings were taken in 30 min intervals. The life-time of DPHP sensor node is around 3.6 days. The sensor, encased in 30 mm x 20 mm x 10 mm sized box, and integrated with electronics was tested independently in two separate laboratories for validating as well as investigating the dependence of the measurement of soil-moisture on the density of the soil. The difference in the readings while repeating the experiments was found out to be less than 0.01%. Furthermore, the effect of ambient temperature on the measurement of soil-moisture is studied experimentally and computationally. (C) 2015 Elsevier B.V. All rights reserved.

Dispersible crystalline nanobundles of YPO4 and Ln (Eu, Tb)-doped YPO4: rapid synthesis, optical properties and bio-probe applications

Undoped and Ln(3+) (Eu and Tb)-doped crystalline nanobundles of YPO4 were prepared by a facile microwave-assisted route with water as a solvent and without using any surfactant. TEM investigations reveal that the as-prepared powder consists of lenticular-shaped nanobundles (similar to 100 nm in diameter) made of very small nanorods with diameter less than 10 nm and length varying from 20 to 50 nm. Each nanorod in turn is single crystalline, as revealed by HRTEM imaging. The as-prepared nanobundles are easily dispersible in various solvents, especially water, without any surface functionalization, which is critical for various bio-probe applications like cell and tissue imaging. The Eu- and Tb-doped YPO4 nanobundles show good photoluminescence properties and were further evaluated for their use as fluorescent biolabels. Our results show that HeLa cells labelled with Eu- and Tb-doped YPO4 nanobundles show bright red (Eu) and green (Tb) intracellular luminescence under a confocal microscope. Concentration-and time-dependent MTT cell viability assays show that the nanobundles show low toxicity towards cells which makes them promising in bioimaging field.

Neutron powder diffraction study of Ba3ZnRu2-xIrxO9 (x=0, 1, 2) with 6H-type perovskite structure

The triple perovskites Ba3ZnRu2-xIrxO9 with x = 0, 1, and 2 are insulating compounds in which Ru(Ir) cations form a dimer state. Polycrystalline samples of these materials were studied using neutron powder diffraction (NPD) at 10 and 295 K. No structural transition nor evidence of long range magnetic order was observed within the investigated temperature range. The results from structural refinements of the NPD data and its polyhedral analysis are presented, and discussed as a function of Ru/Ir content. (C) 2015 Elsevier Masson SAS. All rights reserved.

Neutron diffraction, Mossbauer effect and Electron Paramagnetic Resonance studies on multiferroic Pb(Fe2/3W1/3)O-3

Multiferroic Pb(Fe2/3W1/3)O-3 ceramics were synthesized via a modified two-stage Columbite method. Single phase formation was confirmed from the analysis of x-ray and neutron diffraction patterns recorded at room temperature. Structural analysis of the diffraction data reveals cubic phase (space group Pm-3m) for the title compound. Magnetic structure of the title compound at room temperature exhibits G-type antiferromagnetic structure. The Mossbauer spectroscopy and Electron Paramagnetic Resonance (EPR) studies were carried out at 300 K. The isomer shift and quadrupole splitting of the Mossbauer spectra confirms the trivalent state of iron (Fe3+). The Mossbauer spectra also suggest that the iron and tungsten are randomly distributed at the octahedral, B site. EPR spectra show a single broad line associated with Fe3+ ions. Both spectra clearly exhibit weak ferromagnetic behaviour of Pb(Fe2/3W1/3)O-3 ceramic at 300 K. Considering neutron diffraction, Mossbauer and EPR results together, it may be stated here that Pb(Fe2/3W1/3)O-3 exhibits antiferromagnetic behavior along with weak ferromagnetism at room temperature.

Probing Photoexcited Carriers in a Few-Layer MoS2 Laminate by Time-Resolved Optical Pump-Terahertz Probe Spectroscopy

We report the dynamics of photoinduced carriers in a free-standing MoS2 laminate consisting of a few layers (1-6 layers) using time-resolved optical pump-terahertz probe spectroscopy. Upon photoexcitation with the 800 nm pump pulse, the terahertz conductivity increases due to absorption by the photoinduced charge carriers. The relaxation of the non-equilibrium carriers shows fast as well as slow decay channels, analyzed using a rate equation model incorporating defect-assisted Auger scattering of photoexcited electrons, holes, and excitons. The fast relaxation time occurs due to the capture of electrons and holes by defects via Auger processes, resulting in nonradiative recombination. The slower relaxation arises since the excitons are bound to the defects, preventing the defect-assisted Auger recombination of the electrons and the holes. Our results provide a comprehensive understanding of the non-equilibrium carrier kinetics in a system of unscreened Coulomb interactions, where defect-assisted Auger processes dominate and should be applicable to other 2D systems.

Gauge invariance in the theoretical description of time-resolved angle-resolved pump/probe photoemission spectroscopy

Nonequilibrium calculations in the presence of an electric field are usually performed in a gauge, and need to be transformed to reveal the gauge-invariant observables. In this work, we discuss the issue of gauge invariance in the context of time-resolved angle-resolved pump/probe photoemission. If the probe is applied while the pump is still on, one must ensure that the calculations of the observed photocurrent are gauge invariant. We also discuss the requirement of the photoemission signal to be positive and the relationship of this constraint to gauge invariance. We end by discussing some technical details related to the perturbative derivation of the photoemission spectra, which involve processes where the pump pulse photoemits electrons due to nonequilibrium effects.

Magnetic structures and magnetic phase transitions in the Mn-doped orthoferrite TbFeO3 studied by neutron powder diffraction

The magnetic structures and the magnetic phase transitions in the Mn-doped orthoferrite TbFeO3 studied using neutron powder diffraction are reported. Magnetic phase transitions are identified at T-N(Fe/Mn) approximate to 295K where a paramagnetic-to-antiferromagnetic transition occurs in the Fe/Mn sublattice, T-SR(Fe/Mn) approximate to 26K where a spin-reorientation transition occurs in the Fe/Mn sublattice and T-N(R) approximate to 2K where Tb-ordering starts to manifest. At 295 K, the magnetic structure of the Fe/Mn sublattice in TbFe0.5Mn0.5O3 belongs to the irreducible representation Gamma(4) (G(x)A(y)F(z) or Pb'n'm). A mixed-domain structure of (Gamma(1) + Gamma(4)) is found at 250K which remains stable down to the spin re-orientation transition at T-SR(Fe/Mn) approximate to 26K. Below 26K and above 250 K, the majority phase (>80%) is that of Gamma(4). Below 10K the high-temperature phase Gamma(4) remains stable till 2K. At 2 K, Tb develops a magnetic moment value of 0.6(2) mu(B)/f.u. and orders long-range in F-z compatible with the Gamma(4) representation. Our study confirms the magnetic phase transitions reported already in a single crystal of TbFe0.5Mn0.5O3 and, in addition, reveals the presence of mixed magnetic domains. The ratio of these magnetic domains as a function of temperature is estimated from Rietveld refinement of neutron diffraction data. Indications of short-range magnetic correlations are present in the low-Q region of the neutron diffraction patterns at T < T-SR(Fe/Mn). These results should motivate further experimental work devoted to measure electric polarization and magnetocapacitance of TbFe0.5Mn0.5O3. (C) 2016 AIP Publishing LLC.

Magnetic structures and magnetic phase transitions in the Mn-doped orthoferrite TbFeO3 studied by neutron powder diffraction

The magnetic structures and the magnetic phase transitions in the Mn-doped orthoferrite TbFeO3 studied using neutron powder diffraction are reported. Magnetic phase transitions are identified at T-N(Fe/Mn) approximate to 295K where a paramagnetic-to-antiferromagnetic transition occurs in the Fe/Mn sublattice, T-SR(Fe/Mn) approximate to 26K where a spin-reorientation transition occurs in the Fe/Mn sublattice and T-N(R) approximate to 2K where Tb-ordering starts to manifest. At 295 K, the magnetic structure of the Fe/Mn sublattice in TbFe0.5Mn0.5O3 belongs to the irreducible representation Gamma(4) (G(x)A(y)F(z) or Pb'n'm). A mixed-domain structure of (Gamma(1) + Gamma(4)) is found at 250K which remains stable down to the spin re-orientation transition at T-SR(Fe/Mn) approximate to 26K. Below 26K and above 250 K, the majority phase (>80%) is that of Gamma(4). Below 10K the high-temperature phase Gamma(4) remains stable till 2K. At 2 K, Tb develops a magnetic moment value of 0.6(2) mu(B)/f.u. and orders long-range in F-z compatible with the Gamma(4) representation. Our study confirms the magnetic phase transitions reported already in a single crystal of TbFe0.5Mn0.5O3 and, in addition, reveals the presence of mixed magnetic domains. The ratio of these magnetic domains as a function of temperature is estimated from Rietveld refinement of neutron diffraction data. Indications of short-range magnetic correlations are present in the low-Q region of the neutron diffraction patterns at T < T-SR(Fe/Mn). These results should motivate further experimental work devoted to measure electric polarization and magnetocapacitance of TbFe0.5Mn0.5O3. (C) 2016 AIP Publishing LLC.

Stimuli-responsive colorimetric and NIR fluorescence combination probe for selective reporting of cellular hydrogen peroxide

Hydrogen peroxide (H2O2) is a key reactive oxygen species and a messenger in cellular signal transduction apart from playing a vital role in many biological processes in living organisms. In this article, we present phenyl boronic acid-functionalized quinone-cyanine (QCy-BA) in combination with AT-rich DNA (exogenous or endogenous cellular DNA), i.e., QCy-BA subset of DNA as a stimuli-responsive NIR fluorescence probe for measuring in vitro levels of H2O2. In response to cellular H2O2 stimulus, QCy-BA converts into QCy-DT, a one-donor-two-acceptor (D2A) system that exhibits switch-on NIR fluorescence upon binding to the DNA minor groove. Fluorescence studies on the combination probe QCy-BA subset of DNA showed strong NIR fluorescence selectively in the presence of H2O2. Furthermore, glucose oxidase (GOx) assay confirmed the high efficiency of the combination probe QCy-BA subset of DNA for probing H2O2 generated in situ through GOx-mediated glucose oxidation. Quantitative analysis through fluorescence plate reader, flow cytometry and live imaging approaches showed that QCy-BA is a promising probe to detect the normal as well as elevated levels of H2O2 produced by EGF/Nox pathways and post-genotoxic stress in both primary and senescent cells. Overall, QCy-BA, in combination with exogenous or cellular DNA, is a versatile probe to quantify and image H2O2 in normal and disease-associated cells.

Tetraphenylethene-Based Conjugated Fluoranthene: A Potential Fluorescent Probe for Detection of Nitroaromatic Compounds

This study reports the synthesis and photophysical properties of a star-shaped, novel, fluoranthene-tetraphenylethene (TFPE) conjugated luminogen, which exhibits aggregation-induced blue-shifted emission (AIBSE). The bulky fluoranthene units at the periphery prevent intramolecular rotation (IMR) of phenyl rings and induces a blueshift with enhanced emission. The AIBSE phenomenon was investigated by solvatochromic and temperature-dependent emission studies. Nanoaggregates of TFPE, formed by varying the water/THF ratio, were investigated by SEM and TEM and correlated with optical properties. The TFPE conjugate was found to be a promising fluorescent probe towards the detection of nitroaromatic compounds (NACs), especially for 2,4,6-trinitrophenol (PA) with high sensitivity and a high Stern-Volmer quenching constant. The study reveals that nanoaggregates of TFPE formed at 30 and 70% water in THF showed unprecedented sensitivity with detection limits of 0.8 and 0.5ppb, respectively. The nanoaggregates formed at water fractions of 30 and 70% exhibit high Stern-Volmer constants (K-sv=79998 and 51120m(-1), respectively) towards PA. Fluorescence quenching is ascribed to photoinduced electron transfer between TFPE and NACs with a static quenching mechanism. Test strips coated with TFPE luminogen demonstrate fast and ultra-low-level detection of PA for real-time field analysis.