Simple and Equipment-Free Paper-Based Device for Determination of Mercury in Contaminated Soil

This work presents a simple and innovative protocol employing a microfluidic paper-based analytical device (µPAD) for equipment-free determination of mercury. In this method, mercury (II) forms an ionic-association complex of tetraiodomercurate (II) ion (HgI₄²⁻_(aq)) using a known excess amount of iodide. The residual iodide flows by capillary action into a second region of the paper where it is converted to iodine by pre-deposited iodate to liberate I_2(g) under acidic condition. Iodine vapor diffuses across the spacer region of the µPAD to form a purple colored of tri-iodide starch complex in a detection zone located in a separate layer of the µPAD. The digital image of the complex is analyzed using ImageJ software. The method has a linear calibration range of 50–350 mg L⁻¹ Hg with the detection limit of 20 mg L⁻¹. The method was successfully applied to the determination of mercury in contaminated soil and water samples which the results agreed well with the ICP-MS method. Three soil samples were highly contaminated with mercury above the acceptable WHO limits (0.05 mg kg⁻¹). To the best of our knowledge, this is the first colorimetric µPAD method that is applicable for soil samples including mercury contaminated soils from gold mining areas.     

Thermodynamic analysis of DNA binding by a Bacillus single stranded DNA binding protein

Background

Single-stranded DNA binding proteins (SSB) are essential for DNA replication, repair, and recombination in all organisms. SSB works in concert with a variety of DNA metabolizing enzymes such as DNA polymerase.

Results

We have cloned and purified SSB from Bacillus anthracis (SSB_BA). In the absence of DNA, at concentrations ??100 ??g/ml, SSB_BA did not form a stable tetramer and appeared to resemble bacteriophage T4 gene 32 protein. Fluorescence anisotropy studies demonstrated that SSB_BA bound ssDNA with high affinity comparable to other prokaryotic SSBs. Thermodynamic analysis indicated both hydrophobic and ionic contributions to ssDNA binding. FRET analysis of oligo(dT)₇₀ binding suggested that SSB_BA forms a tetrameric assembly upon ssDNA binding. This report provides evidence of a bacterial SSB that utilizes a novel mechanism for DNA binding through the formation of a transient tetrameric structure.

Conclusions

Unlike other prokaryotic SSB proteins, SSB_BA from Bacillus anthracis appeared to be monomeric at concentrations ??100 ??g/ml as determined by SE-HPLC. SSB_BA retained its ability to bind ssDNA with very high affinity, comparable to SSB proteins which are tetrameric. In the presence of a long ssDNA template, SSB_BA appears to form a transient tetrameric structure. Its unique structure appears to be due to the cumulative effect of multiple key amino acid changes in its sequence during evolution, leading to perturbation of stable dimer and tetramer formation. The structural features of SSB_BA could promote facile assembly and disassembly of the protein-DNA complex required in processes such as DNA replication.     

Determination of cefadroxil by sequential injection with spectrophotometric detector.

A sequential injection analysis (SIA) spectrophotometric procedure for cefadroxil determination has been developed. The SIA instrumentation was modified to achieve the desired function and operations by using the software developed to interface the PC with the conventional SIA system. The method is based on the measurement of a red, water-soluble product formed by the reaction between cefadroxil and 4-aminoantipyrine in the presence of alkaline potassium hexacyanoferrate(III) at 510 nm. Optimum conditions for determining the drug were investigated. Beer's law was obeyed over the concentration ranges of 1 - 10 mg L(-1) and 10 - 50 mg L(-1) with a detection limit (3 sigma) of 0.17 mg L(-1) and a limit of quantification (10 sigma) of 0.56 mg L(-1). The relative standard deviations of 1.98% and 1.93% for 5 mg L(-1) and 30 mg L(-1) of the drug, respectively (n = 11) are obtained. The proposed method has been applied satisfactorily to the determination of cefadroxil in commercial pharmaceutical formulations with a sampling rate of 100 h(-1). Results obtained were in good agreement with those obtained by the official HPLC method at the 95% confidence level.     

Chlorinated chromone and diphenyl ether derivatives from the mangrove-derived fungus Pestalotiopsis sp. PSU-MA69

Four new diphenyl ethers, pestalotethers A–D (1–4), three new chromones, pestalochromones A–C (5–7), one new xanthone, pestaloxanthone (8), and one new butenolide, pestalolide (9), together with 11 known compounds were isolated from the mangrove-derived fungus Pestalotiopsis sp. PSU-MA69. Their structures were established by spectroscopic techniques. Compounds 1–3 and 5–7 are the rare chlorinated fungal metabolites of diphenyl ethers and chromones, respectively. Pestalolide (9) displayed weak antifungal activity against Candida albicans and Cryptococcus neoformans.     

Oligonucleotide separation techniques for purification and analysis: What can we learn for today's tasks?

Nucleic acids are the blueprint of life. They are not only the construction plan of the single cell or higher associations of them, but also necessary for function, communication and regulation. Due to the pandemic, the attention shifted in particular to their therapeutic potential as a vaccine. As pharmaceutical oligonucleotides are unique in terms of their stability and application, special delivery systems were also considered. Oligonucleotide production systems can vary and depend on the feasibility, availability, price and intended application. To achieve good purity, reliable results and match the strict specifications in the pharmaceutical industry, the separation of oligonucleotides is always essential. Besides the separation required for production, additional and specifically different separation techniques are needed for analysis to determine if the product complies with the designated specifications. After a short introduction to ribonucleic acids (RNAs), messenger RNA vaccines, and their production and delivery systems, an overview regarding separation techniques will be provided. This not only emphasises electrophoretic separations but also includes spin columns, extractions, precipitations, magnetic nanoparticles and several chromatographic separation principles, such as ion exchange chromatography, ion-pair reversed-phase, size exclusion and affinity.     

A simple flow injection spectrophotometric procedure for the determination of diazepam in pharmaceutical formulation.

A single-channel flow injection (FI) manifold with spectrophotometric detection has been designed and fabricated for diazepam determination. A 100 microl sample and/or standard solution containing diazepam was injected into a flowing stream of 0.1 mol L(-1) hydrochloric acid with the optimum flow rate of 6.8 mL min(-1). As soon as the sample reached the detector, the FI signal as a peak was recorded at 360 nm. The optimum conditions for microg amounts of diazepam were achieved. A linear calibration graph over the range of 2-110 mg L(-1) diazepam was obtained with the regression equation Y = 0.2926X + 0.5896 (r2 = 0.9929). The method was very sensitive, since as little as 0.60 mg L(-1) could be detected; very reproducible with an RSD of 3.3% (n=11); and very rapid with a sampling rate of 100 h(-1). The limit of quantitation (10 sigma) was 2.0 mg L(-1). The proposed FI procedure has been satisfactorily applied to the quantitation of diazepam in commercial pharmaceutical formulations. The obtained results were in excellent agreement with those obtained by the conventional spectrophotometric method, verified by the student t-test at the 95% confidence level.