Fluorogenic Probes with Substitutions at the 2 and 7 Positions of Cephalosporin are Highly BlaC‐Specific for Rapid Mycobacterium tuberculosis Detection

Current methods for the detection of Mycobacterium tuberculosis (Mtb) are either time consuming or require expensive instruments and are thus are not suitable for point‐of‐care diagnosis. The design, synthesis, and evaluation of fluorogenic probes with high specificity for BlaC, a biomarker expressed by Mtb, are described. The fluorogenic probe CDG‐3 is based on cephalosporin with substitutions at the 2 and 7 positions and it demonstrates over 120 000‐fold selectivity for BlaC over TEM‐1 Bla, the most common β‐lactamase. CDG‐3 can detect 10 colony‐forming units of the attenuated Mycobacterium bovis strain BCG in human sputum in the presence of high levels of contaminating β‐lactamases expressed by other clinically prevalent bacterial strains. In a trial with 50 clinical samples, CDG‐3 detected tuberculosis with 90 % sensitivity and 73 % specificity relative to Mtb culture within one hour, thus demonstrating its potential as a low‐cost point‐of‐care test for use in resource‐limited areas.     

Microkinetic model for NO–CO reaction: Model reduction

The objective of this work is to elucidate controlling mechanisms in NO_x reduction, develop reduced‐order reaction models, and analyze the reactor performance using the reduced‐order reaction model for the NO–CO reaction. We start with the microkinetic model on platinum, which describes the mechanism of catalytic reduction of NO by CO. The formation of the main product N₂O and the competitive formation of the side product N₂ are accounted for in the microkinetic model. Sensitivity and reaction path analysis have been carried out to determine the rate‐limiting steps as well as the most abundant reactive intermediates in the system. Owing to the differences between system performance at high and low temperatures, the model has been analyzed in detail in these temperature regimes. Two closed‐form expressions, corresponding to the two global reactions involved, have been derived. The characteristic features of the microkinetic model such as the sharp increase in NO conversion and the selectivity to N₂O are captured well by the reduced model. The reduced‐order model has been extended to the rhodium catalyst as well. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 577–585, 2012     

Development and validation of an ultra high performance liquid chromatography electrospray ionization tandem mass spectrometry method for the simultaneous determination of selected flavonoids in Ginkgo biloba

A rapid and sensitive ultra high performance liquid chromatography electrospray ionization tandem mass spectrometry method was developed and validated for the simultaneous determination of 13 flavonoids in leaf, stem, and fruit extracts of male and female trees of Ginkgo biloba to investigate gender‐ and age‐related variations of flavonoids content. Chromatographic separation was accomplished on an Acquity UPLC BEH C₁₈ column (50 mm × 2.1 mm id, 1.7 μm) in 5 min. Quantitation was performed using negative electrospray ionization mass spectrometry in multiple reaction monitoring mode. The calibration curves of all analytes showed a good linear relationship (r² ≥ 0.9977) over the concentration range of 1–1000 ng/mL. The precision evaluated by an intra‐ and interday study showed RSD ≤ 1.98% and good accuracy with overall recovery in the range from 97.90 to 101.09% (RSD ≤ 1.67%) for all analytes. The method sensitivity expressed as the limit of quantitation was typically 0.25–3.57 ng/mL. The results showed that the total content of 13 flavonoids was higher in the leaf extract of an old male Ginkgo tree compared to young female Ginkgo trees.     

Intensity based algorithms for biospeckle analysis

In this paper, two algorithms, one is an Alternative Fujii method and other is parameterized form of temporal difference (PTD) method are presented. Experimental results for both the methods using sequential biospeckle images of fresh apple have been presented and compared with the results obtained using that of Generalized Difference (GD) and Parameterized Fujii. Good agreements are seen for particular values of parameters.     

A biocompatible surfactant with folded hydrophilic head group: enhancing the stability of self-inclusion complexes of ferrocenyl in a beta-cyclodextrin unit by bond rigidity

This work reports a new biocompatible surfactant structure, of which the hydrophilic head group is composed of a folded, stable self-inclusion complex of a ferrocenyl substituted beta-cyclodextrin (betaCD). While multiple intra- or intermolecular complexes can exist for this amphiphile, the molecule folds into a unique intramolecular complex with well-defined conformation, in which part of the aliphatic chain and the ferrocene group are both included in the annular cavity of betaCD. Study of different isosteric covalent linkages indicates that this folded structure is stable against displacement by the presence of other small guest molecules. Furthermore, in contrast to ferrocene-CD conjugates that are without the aliphatic chain, the presence of small guest molecules in solution does not influence at all the induced circular dichroism signal of this amphiphile, indicating a sterically congested, but stable, folded conformation of the inclusion complex. This new amphiphile is surface active and, more importantly, does not denature the membrane protein bacteriorhodopsin. Finally, because this surfactant forms self-assembled aggregates, this work introduces a folded structure into soft matters formed by amphiphiles in water.     

Pd gate MOS sensor for hydrogen detection

The performance of Pd gate MOS hydrogen sensor was studied using C–V and G–V characteristics. The device was fabricated on p-type <100> (1–6Ω cm.) silicon with thermal oxide layer of about 100 Å. The C–V and G–V responses of sensor were measured at different frequencies (1 kHz, 10 kHz, and 100 kHz) upon exposure to hydrogen (conc. 1–8%) at room temperature. It was observed that value of zero bias capacitance decreases with increase in frequency as well as hydrogen concentration. The inversion potential (V_inv.) and flat band voltage (V_FB) of the device approach higher values as frequency is reduced. Interface trap density (N_it) was also determined corresponding to the peak in the conductance curve, using a bias scan conductance method at fixed frequency. N_it was found to be decreasing with increasing concentrations of hydrogen. The sensor showed better sensitivity at lower frequency.     

Sensing mechanism of Pd-doped SnO2 sensor for LPG detection

In the present work, studies have been made to analyze the sensitivity, response, recovery time and sensing mechanism of Pd-doped thick film SnO₂ sensor for detection of LPG. To achieve this, thick film Pd-doped (0.25 and 1% by weight in available Indium doped SnO₂ thick film paste supplied by ESL, USA) along with an undoped (Indium doped) SnO₂ sensors were fabricated on a 1″ × 1″ alumina substrate. It consists of a gas sensitive layer (doped SnO₂), a pair of electrodes underneath the gas sensing layer serving as a contact pad for sensor. Also, a heater element on the backside of the substrate was printed for generating appropriate operating temperature at the substrate necessary for acquiring gas sensing properties. The sensor doped with 1% palladium showed the maximum sensitivity of 72% at 350 °C for 0.5% concentration of LPG. Possible detailed sensing mechanism of Pd-doped SnO₂ sensor for LPG detection has been proposed.     

Photoluminescence and electroluminescence studies of polyvinyl carbazole films

Polyvinyl carbazole (PVK) film has been prepared by solution method. Its absorption, photoluminescence (PL) and electroluminescence (EL) have been studied. For PL and absorption studies, film of PVK was prepared by spreading PVK solution on clean glass plate. The dried film was taken out of the glass plate and used for absorption, thickness measurement and PL studies. The film is transparent in the visible region and absorption starts at 340 nm wavelength. The absorption peaks are obtained at 280, 250 and 220 nm, indicating that optical gap of film is 3.65 eV and molecular orbitals exist at 4.43, 4.96 and 5.64 eV. PL studies reveal that excitation by violet light gives luminescence at 430, 480 and 690 nm. For EL studies, cell is prepared by depositing PVK film on a portion of conducting glass plate and taking aluminum foil as second electrode. It is observed from the characteristics that the current varies linearly, where as EL intensity varies non-linearly with increasing voltage. Higher brightness has been observed at higher frequencies. EL spectrum shows a sharp peak at 400 nm and a broad and less intense peak at 700 nm, which are attributed to radiative decay of singlet exciton and defect centers, respectively.     

Multivalent Sialosides: A Tool to Explore the Role of Sialic Acids in Biological Processes

Sialic acids (Sias) are fascinating nine‐carbon monosaccharides that are primarily found on the terminus of the oligosaccharide chains of glycoproteins and glycolipids on cell surfaces. These Sias undergo a variety of structural modifications at their hydroxy and amine positions, thereby resulting in structural diversity and, hence, coordinating a variety of biological processes. However, deciphering the structural functions of such interactions is highly challenging, because the monovalent binding of Sias is extremely weak. Over the last decade, several multivalent Sia ligands have been synthesized to modulate their binding affinity with proteins/lectins. In this Minireview, we highlight recent developments in the synthesis of multivalent Sia probes and their potential applications. We will discuss four key multivalent families, that is, polymers, dendrimers, liposomes, and nanoparticles, and will emphasize the major parameters that are essential for the specific interactions of these molecules with proteins in biological systems.     

Carbonyl Sulfide (COS) Donor Induced Protein Persulfidation Protects against Oxidative Stress

The emergence of hydrogen sulfide (H₂S) as an important signalling molecule in redox biology with therapeutic potential has triggered interest in generating this molecule within cells. One strategy that has been proposed is to use carbonyl sulfide (COS) as a surrogate for hydrogen sulfide. Small molecules that generate COS have been shown to produce hydrogen sulfide in the presence of carbonic anhydrase, a widely prevalent enzyme. However, other studies have indicated that COS may have biological effects which are distinct from H₂S. Thus, it would be useful to develop tools to compare (and contrast) effects of COS and H₂S. Here we report enzyme‐activated COS donors that are capable of inducing protein persulfidation, which is symptomatic of generation of hydrogen sulfide. The COS donors are also capable of mitigating stress induced by elevated reactive oxygen species. Together, our data suggests that the effects of COS parallel that of hydrogen sulfide, laying the foundation for further development of these donors as possible therapeutic agents.