Nondestructive evaluation of helicopter rotor blades using guided Lamb modes

This paper presents an application for turning and direct modes in a complex composite laminate structure. The propagation and interaction of turning modes and fundamental Lamb modes are investigated in the skin, spar and web sections of a helicopter rotor blade. Finite element models were used to understand the various mode conversions at geometric discontinuities such as web-spar joints. Experimental investigation was carried out with the help of air coupled ultrasonic transducers. The turning and direct modes were confirmed with the help of particle displacements and velocities. Experimental B-Scans were performed on damaged and undamaged samples for qualitative and quantitative assessment of the structure. A strong correlation between the numerical and experimental results was observed and reported.     

Syntheses of 1′,2′-cyclopentyl nucleosides as potential antiviral agents

To discover novel nucleosides as potential antiviral agents, 1′,2′-cyclopentyl nucleosides were designed as hybrids of sofosbuvir and GS-6620. An asymmetric aldol condensation reaction was used as the key transformation to prepare the versatile 1′,2′-cyclopentyl ribose 6, which is useful to explore diverse bases at 1′ and its utility was demonstrated via the syntheses of nucleosides 9 and 11. The 2′-β-methyl-1′,2′-cyclopentyl ribonucleoside scaffold was exemplified via a C-nucleoside which was prepared using a RCM reaction as the key step leading to novel nucleoside 35.     

Use of biotin-streptavidin system for developing a viable, sensitive and specific antigen heterologous assay for hapten

The present study demonstrates improvement in sensitivity and specificity of hapten assay by using antigen heterology in conjunction with low molecular weight biotin label as compared to high molecular weight horseradish peroxidase (HRP) label. For generation of antiserum, cortisol-3-O-carboxylmethyl-oxime-bovine serum albumin (F-3-CMO-BSA) was used as immunogen whereas, for the preparation of primary label, corticosterone-3-carboxymethyl oxime (B-3-CMO) was coupled with biotinylcaproylhydrazide and HRP by employing N-hydroxysuccinimide mediated carbodiimide reaction. The data of the present study revealed that the antigen heterologous assay which employed high molecular weight HRP label showed 100% cross-reaction with corticosterone. On the contrary, when HRP was replaced with low molecular weight biotin label, less than 0.1% cross-reaction was observed with all analogous C₁₈, C₁₉, C₂₁ and C₂₇ steroids including corticosterone (0.2%). Moreover, the sensitivity of the later assay was 0.09 μg/dL, which is appreciable as compared to previously reported enzyme based assays. The recovery of the exogenously spiked serum pools lies in the range of 90.3-104.2%. The intra-assay and inter-assay coefficient of variation (CVs) ranged from 3.3% to 7.8% and 2.3% to 7.7%, respectively. The serum cortisol values obtained by this method correlated well with those obtained by radioimmunoassay; r = 0.9 (n = 50). The use of much stable biotin label in place of HRP has made the antigen heterologous enzyme linked immunosorbent assay (ELISA) of cortisol assay highly specific and sensitive.     

Characterization of a membrane-based gradient generator for use in cell-signaling studies

This paper describes a method to create stable chemical gradients without requiring fluid flow. The absence of fluid flow makes this device amenable to cell signaling applications where soluble factors can impact cell behavior. This device consists of a membrane-covered source region and a large volume sink region connected by a microfluidic channel. The high fluidic resistance of the membrane limits fluid flow caused by pressure differences in the system, but allows diffusive transport of a chemical species through the membrane and into the channel. The large volume sink region at the end of the microfluidic channel helps to maintain spatial and temporal stability of the gradient. The chemical gradient in a 0.5 mm region near the sink region experiences a maximum of 10 percent change between the 6 and 24 h data points. We present the theory, design, and characterization of this device and provide an example of neutrophil chemotaxis as proof of concept for future quantitative cell-signaling applications.     

Use of a diazocoupling reaction for sensitive and selective spectrophotometeric determination of furosemide in spiked human urine and pharmaceuticals

Two simple, sensitive, and selective spectrophotometric methods for the determination of 5-(aminosulfonyl)-4-chloro-2-((2-furanylmethyl)amino)benzoic acid (furosemide, FUR) are described. The methods are based on acid hydrolysis of FUR to free primary aromatic amine and diazotization followed by coupling with N-1-napthylethylene diamine (NEDA) (method A) or 4,5-dihydroxynaphthalene-2,7-disulfonic acid (chromotropic acid, CTA) (method B). The colored reaction product can be measured spectrophotometrically at 520 nm (method A) or 500 nm (method B). Beer’s law is obeyed over the ranges of 1.75–21.0 μg mL⁻¹ and 2.5–30.0 μg mL⁻¹, for method A and method B, respectively. Apparent molar absorptivities and Sandell’s sensitivities (in L mol⁻¹ cm⁻¹ and μg cm⁻² per 0.001 absorbance unit, respectively) were 1.34 × 10⁴ and 0.0253 using NEDA as the coupling agent, and 8.5 × 10³ and 0.0389 using CTA for the same purpose. Analysis of solutions containing seven different concentrations of FUR gave a correlation coefficient of 0.9979 using NEDA and 0.9984 using CTA, while the slope and the correlation coefficient of the regression equation were calculated. The reaction stoichiometry in both methods was evaluated by the limiting logarithmic method and was found to be 1: 1 (diazotized FUR: NEDA or diazotized FUR: CTA). The methods were successfully applied to the determination of FUR in spiked human urine and in pharmaceutical formulations. The recovery of FUR from spiked urine was satisfactory resulting in the values of (109.4 ± 4.37) % using NEDA and (113.0 ± 4.74) % using CTA. Results of the analysis of pharmaceuticals demonstrated that the proposed procedures are at least as accurate and precise as the official method while a statistical analysis indicated that there was no significant difference between the results obtained by the proposed methods and those of the official method.     

Simultaneous determination of 186 fungal and bacterial metabolites in indoor matrices by liquid chromatography/tandem mass spectrometry

This paper describes the application of a previously published multi-mycotoxin method for food and feed matrices based on liquid chromatography/electrospray ionization-tandem mass spectrometry (HPLC/ESI-MS/MS) to the analysis of microbial metabolites in indoor matrices. The range of investigated analytes has been extended by 99 fungal and bacterial metabolites to cover now 186 compounds overall. The method is based on a single extraction step using an acidified acetonitrile/water mixture (which has been determined to be preferable to methanol and ethyl acetate) followed by analysis of the diluted crude extract. The analytical signal of one third of the investigated analytes was reduced by more than 50% due to matrix effects in a spiked extract of house dust, whereas the other investigated materials were less critical in that aspect. For determination of method performance characteristics, a spiked reference material for house dust was chosen as a model sample for an extremely complex matrix. With few exceptions, coefficients of variation of the whole procedure of <10% and limits of detection of <50 μg kg⁻¹ were obtained. The apparent recoveries were below 50% for half of the investigated analytes due to incomplete extraction and/or detection-related matrix effects. The application of the method to 14 samples from damp buildings revealed the presence of 20 different analytes at concentrations of up to 130 mg kg⁻¹. Most of these compounds have never been identified before in real-world samples, although they are known to be produced by indoor-relevant fungi. This underlines the great value of the described method for the on-site determination of microbial metabolites.