Selective and sensitive voltammetric sensor based on modified multiwall carbon nanotubes paste electrode for simultaneous determination of l-cysteine and folic acid

This paper reports the selective and sensitive voltammetric determination of l-cysteine in the presence of folic acid using ethynylferrocene modified carbon nanotubes paste electrode in 0.1 M phosphate buffer solution (pH 7.0). Using square wave voltammetry, we could measure l-cysteine and folic acid in one mixture independently from each other by a potential difference of about 410 mV for the first time. Square wave voltammetric peak current of l-cysteine and folic acid increased linearly with their concentrations in the ranges of 0.2–250.0 and 1.0–500.0 μmol?L^?1, respectively. The detection limits of 0.07 and 0.6 μmol?L^?1 were achieved for l-cysteine and folic acid, respectively. The proposed voltammetric sensor was successfully applied to the determination of l-cysteine and folic acid in real samples.     

Manipulation of the Conformation and Enzymatic Properties of T1 Lipase by Site-Directed Mutagenesis of the Protein Core

In silico and experimental investigations were conducted to explore the effects of substituting hydrophobic residues, Val, Met, Leu, Ile, Trp, and Phe into Gln 114 of T1 lipase. The in silico investigations accurately predicted the enzymatic characteristics of the mutants in the experimental studies and provided rationalization for some of the experimental observations. Substitution with Leu successfully improved the conformational stability and enzymatic characteristics of T1 lipase. However, replacement of Gln114 with Trp negatively affected T1 lipase and resulted in the largest disruption of protein stability, diminished lipase activity and inferior enzymatic characteristics. These results suggested that the substitution of a larger residue in a densely packed area of the protein core can have considerable effects on the structure and function of an enzyme. This is especially true when the residue is next to the catalytic serine as demonstrated with the Phe and Trp mutation.     

Practical syntheses of proposed and revised manzacidin B and their congeners

A concise and highly stereoselective total synthesis of manzacidin B and its congeners has been developed following chelation-controlled syn-epoxidation and Lewis acid catalyzed intramolecular regioselective epoxide ring opening to generate the quarternary amine center. Elaboration of the triol moiety to the target molecule was achieved in good overall yield, representing practical total syntheses of manzacidin B and its congeners. From the XRD, NMR, and analytical data, the correct structure of natural manzacidin B, (4R,5R,6R)-6, was confirmed.     

Simultaneous determination of two major snow crab aeroallergens in processing plants by use of isotopic dilution tandem mass spectrometry

Snow crab is a major fishery in the North Atlantic region. During crab processing the proteins are aerosolized and some are responsible for development of occupational asthma. Tropomyosin and arginine kinase have recently been reported as major snow crab allergens. A liquid chromatographic tandem mass spectrometric method has been developed for simultaneous analysis of these two proteins in air samples collected from processing plants. These proteins were initially isolated then characterized by use of mass spectrometry to determine their primary structure and signature peptides. The signature peptides were chemically synthesized in light and heavy forms and used as standards for developing the multiple-reaction monitoring transitions to monitor allergen levels. A validation study was performed; precision and accuracy were 1.8–8% and 91–104%, respectively. Replicate air samples were collected on air filters from two crab-processing plants in Newfoundland and Labrador (NL) and four located in Quebec. In NL, measured levels of both tropomyosin and arginine kinase were between 1 and 20 ng m⁻³. In Quebec plants, however, levels were found to be much higher at 2–2400 ng m⁻³. Significant differences were also observed among the plants and individual processing workstations. For the first time arginine kinase has been detected in its aerosolized form in processing plants. In general, levels of the allergens were highest in the butchering and cooking areas; plant design can, however, have a significant effect on levels of the allergens.     

The prenylated dioxopiperazine alkaloid Cristatin A has selective telomeric DNA G-quadruplex stabilising properties

Cristatin A (1a/b), a prenylated dioxopiperazine alkaloid, has been shown to bind selectively to telomeric quadruplex DNA using a FRET-based DNA melting assay. Crucially, the molecule is more drug-like than most previously identified quadruplex-binding agents, and provides a unique chemical scaffold for future chemical biology and drug discovery studies.     

Bubble dynamics in microchannel: An overview of the state-of-the-art

The inception of the boiling, in a pool or flow boiling, is the formation of the vapor bubble at an active nucleation site that plays a crucial role in the boiling process and it becomes critical and unfolds many facets when channel size reduces to submicron. The detailed knowledge of the bubble dynamics is helpful in establishing the thermal and hydraulic flow behavior in the microchannel. In the current paper, bubble dynamics that include bubble nucleation at the nucleation site, its growth, departure, and motion along the flow in a microchannel(s) are discussed in detail. Different models developed for critical cavity radius favorable for bubble nucleation are compiled and observe that models exhibit large deviation. The bubble growth models are compiled and concluded that the development of a more generalize bubble growth model is necessary that would be capable of accounting for inertia controlled and thermal diffusion controlled regions. Bubbles at nucleation sites in a microchannel grow under the influence of various forces such as surface tension, inertia, shear, gravitational and evaporation momentum. Parametric analysis of these forces reckoned that the threshold between macro- to microchannel could be identify through critical analysis of such forces. Eventually, the possible impact of the various factors such as operating conditions, geometrical parameters, thermophysical properties of fluid on bubble dynamics in microchannel has been reported.

     

Thermal characteristics of gelatin extracted from shaari fish skin

Gelatin extraction yield increased with the increase of acetic acid concentration and temperature. Gelatin extracted from shaari skin using 0.1 N acid solutions and temperatures of 323 and 353 K gave highest protein content comparable to that of commercial bovine and porcine gelatins. In general, gelatin extracted from shaari gelatin showed lower onset of glass transition temperature than mammalian gelatins. For shaari skin gelatin, the onset of glass transition temperature decreased with the increase of extraction temperature up to 323 K and then remained nearly constant. The decrease in glass transition was more pronounced for gelatin extracted at 0.01 N compared to the 0.1 and 1.0 N samples. Unfolding temperature decreased exponentially with the increase of extraction temperature. The unfolding temperature shifted to lower temperature, and the decrease was more pronounced in the case of higher (1.0 N) concentrated samples. The extraction concentration and temperature did not show significant effect on the onset solids-melting temperature.     

A modified,economical and efficient synthesis of variably substituted pyrazolo[4,3‐d]pyrimidin‐7‐ones

1‐Methyl‐3‐propyl‐1H‐pyrazole‐5‐carboxylic acid ( 3 ) was exclusively brominated at the 4‐position by bromine in the dark. Brominated product 8 was then converted into 1‐methyl‐3‐propyl‐1H‐pyrazole‐5‐car‐boxamide 9 by successive treatment with thionyl chloride and ammonium hydroxide. Carboxamide 9 was treated with various aroyl amides under microwave (MW) irradiation to afford 4‐aroylamino‐1‐methyl‐3‐propyl‐1H‐pyrazole‐5‐carboxamides 10‐22 and 5‐aryl‐1‐methyl‐3‐propyl‐1,6‐dihydro‐1H‐pyrazolo[4,3‐d]pyrimidin‐7‐ones 23‐35. The 1H‐pyrazole‐5‐carboxamides 10‐22 were also converted to pyrimidinones 23‐35 either by conventional heating or by MW irradiation. However, MW irradiation method gives excellent yields in very short time.