Phase transition in Na2SO4: all five polymorphic transformations in DSC

In this investigation, we have characterized the Na₂SO₄ using differential scanning calorimetry (DSC). It is well known that Na₂SO₄ exhibits five polymorphs. However, the experimental evidence for all five polymorphs has never been observed in DSC. In this investigation, the five polymorphic transformations have been observed in heating cycle. Furthermore, the transition I–II is observed, which is not reversible. In addition, phase transition temperature for V→IV and IV→III transition appears to be much closed and may get unnoticed.     

Optical studies of two dimensional gratings in fused silica, GE 124, and Foturan glasses fabricated using femtosecond laser pulses

Herein we present results on the femtosecond laser direct writing and optical characterization studies of two dimensional gratings in fused silica, GE 124, and Foturan^™ glasses. Varieties of structures were achieved with varying input energy and spatial orientation of the samples. Various characterization techniques including fluorescence spectroscopy, micro-Raman spectroscopy, and laser confocal microscopy were employed to analyze the structural and physical modifications at the focal volume resulting in change of refractive index. Diffraction efficiencies of 9–12% were observed from the grating structures. A broad-band emission was observed in the laser-modified region of the Foturan glass. The obtained results are analyzed in the light of recent work in similar glasses and exploring the applications of such structures in the fields of photonics.     

Reliable Technique for the Determination of Sodium Dodecyl Sulphate by Crystal Violet in Relation to the Effluents of Durg‐Bhilai Region

A simple spectrophotometric method applicable to waste water bodies is developed for the determination of anionic surfactant (AS). An ion‐association complex is formed between an anionic surfactant Sodium dodecyl sulphate (SDS) and a cationic dye Crystal Violet (CV). The dark blue colored complex can be easily extracted in organic solvent benzene. The absorbance of the complex in benzene layer is measured spectrophotometrically at maximum wave length (λ max) of 565 nm. Under the optimal experimental conditions, absorbance of the organic extractant obeyed Beer's law over the range of 0.75–10.00 μg mL^?1 of SDS and the LOD was 0.01312 μg L^?1. It is noticed that the present method is much easier, less time consuming and applicable to accelerated urbanization and industrial development found in newly formed Chhattisgarh state in Central India. The validity of the method was tested in regionalized industrial and domestic waste water runoff.     

Structural Basis and Enzymatic Mechanism of the Biosynthesis of C9‐ from C10‐Monoterpenoid Indole Alkaloids

Cutting carbons : The three‐dimensional structure of polyneuridine aldehyde esterase (PNAE) gives insight into the enzymatic mechanism of the biosynthesis of C₉‐ from C₁₀‐monoterpenoid indole alkaloids (see scheme). PNAE is a very substrate‐specific serine esterase. It harbors the catalytic triad S87‐D216‐H244, and is a new member of the α/β‐fold hydrolase superfamily. Its novel function leads to the diversification of alkaloid structures.

     

Quantification of clopidogrel in human plasma by sensitive liquid chromatography/tandem mass spectrometry

A simple, sensitive and rapid high-performance liquid chromatography/positive electrospray ionization tandem mass spectrometry method was developed and validated for the assay of clopidogrel in human plasma. Following liquid-liquid extraction, the analytes were separated using an isocratic mobile phase on a reversed-phase column and analyzed by mass spectrometry in the multiple reaction monitoring mode using the respective [M+H](+) ions, m/z 322/212 for clopidogrel and m/z 264/154 for the internal standard. The assay exhibited a linear dynamic range of 5-6000 pg/mL for clopidogrel in human plasma. The lower limit of quantification was 5 pg/mL with a relative standard deviation of less than 8%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 2.5 min for each sample made it possible to analyze more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.     

Study of electrolyte induced aggregation of gold nanoparticles capped by amino acids

This work reports the electrolyte induced aggregation of gold nanoparticles directly conjugated to amino acid by chemical reduction in aqueous solution. The study was focused on three different classes of amino acids depending on the nature of alpha substituent, viz. l-cysteine, l-leucine, and l-asparagine. The band broadening and the red shift of surface plasmon band with increase in flocculation parameter showed the aggregation of gold nanoparticles with increase in electrolyte concentration and decrease in pH as monitored by UV-visible spectrophotometer. The (1)H NMR spectrum demonstrates that the sulfide bond of cysteine and alpha amino group of leucine and asparagine interact with nanoparticles surface. Furthermore, transmission electron microscope (TEM) and thermogravimetric analysis (TGA) were performed to characterize and to support the fate of stabilization of the gold nanoparticles by amino acid.     

Sensitive and rapid liquid chromatography/tandem mass spectrometry assay for the quantification of amlodipine in human plasma

A simple, sensitive and rapid high-performance liquid chromatography/electrospray ionization tandem mass spectrometry method was developed and validated for the assay of amlodipine in human plasma. Following liquid-liquid extraction, the analytes were separated using an isocratic mobile phase on a reverse-phase C(18) column and analyzed by MS in the multiple reaction monitoring mode using the respective [M+H]+ ions, m/z 409/238 for amlodipine and m/z 409/228 for the IS. The assay exhibited a linear dynamic range of 50-10,000 pg/mL for amlodipine in human plasma. The lower limit of quantification was 50 pg/mL with a relative standard deviation of less than 8%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. The average absolute recoveries of amlodipine and the IS from spiked plasma samples were 74.7 +/- 4.6 and 72.1 +/- 2.0%, respectively. A run time of 1.5 min for each sample made it possible to analyze more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies. The observed maximum plasma concentration (Cmax) of amlodipine (2.5 mg oral dose) was 1425 pg/mL, time to observed maximum plasma concentration (Tmax) was 8.1 h and elimination half-life (T(1/2)) was 50.1 h.     

Simultaneous quantification of atorvastatin and active metabolites in human plasma by liquid chromatography-tandem mass spectrometry using rosuvastatin as internal standard

A simple, sensitive, selective and rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantification of atorvastatin and its active metabolites ortho-hydroxyatorvastatin and para-hydroxyatorvastatin in human plasma using rosuvastatin as internal standard (IS). Following simple liquid-liquid extraction, the analytes were separated using an isocratic mobile phase on a reversed-phase C18 column and analyzed by MS in the multiple reaction monitoring mode using the respective [M+H]+ ions, m/z 559/440 for atorvastatin, m/z 575/466 for ortho-hydroxyatorvastatin, m/z 575/440 for para-hydroxyatorvastatin and m/z 482/258 for the IS. The assay exhibited a linear dynamic range of 0.1-20 ng/mL for atorvastatin and its two metabolites in human plasma. The lower limit of quantification was 100 pg/mL with a relative standard deviation of less than 8%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. The average absolute recoveries of atorvastatin, ortho-hydroxyatorvastatin, para-hydroxyatorvastatin and the IS from spiked plasma samples were 54.2 +/- 3.2, 50.1 +/- 3.8, 65.2 +/- 3.6 and 71.7 +/- 2.7%, respectively. A run time of 2.5 min for each sample made it possible to analyze more than 300 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.