THERMODYNAMIC AND PARTICLE-DYNAMIC STUDIES ON SYNTHESIS OF SILICA NANOPARTICLES USING MICROWAVE-INDUCED PLASMA CVD

1. Introduction1.1 Silica nanoparticles and synthesis methods Silica (SiO2) nanoparticles are widely used in industry asan active filler for polymer reinforcement, a rheologicaladditive in fluids, a free flow agent in powders, and anagent for chemical mechanical polishing during IC (inte-grated circuit) fabrication (Sniegowski & de Boer, 2000).Silica powder is also used for producing silicon carbide(Koc & Cattamanchi, 1998) or opaque silica aerosols (Leeet al., 1995). Many methods can …     

Selective capturing and detection of Salmonella typhi on polycarbonate membrane using bioconjugated quantum dots

Present work demonstrates the utilization of surface modified polycarbonate (PC) membrane as solid phase and antibody conjugated CdSe/ZnS quantum dots (QDs) as fluorescent label for the sensitive and selective detection of Salmonella typhi (S. typhi) in water in a period of 2.5 h. PC membrane was surface modified with glycine and activated by EDC/NHS for immobilization of S. typhi specific IgG. Antibody immobilized porous PC membrane was incubated with bacteria contaminated water for immunocapturing of S. typhi. Antibody conjugated QDs were also prepared by using carbodiimide chemistry. Both modified PC membrane and quantum dots were characterized by using various modern analytical tools. It was estimated that 1.95 molecules of QDs were successfully bio-conjugated per unit of IgG. PC membrane with captured bacteria was incubated with prepared IgG conjugated QDs for the formation of sandwich complex. Analysis of the regions of interest (ROI) in fluorescent micrographs showed that newly developed method based on PC and fluorescent QDs has 100 times higher detection sensitivity (100 cells/mL) as compared with detection using conventional dye (FITC) based methods.     

Mass-transport models with multiple-chipping processes

We study mass-transport models with multiple-chipping processes. The rates of these processes are dependent on the chip size and mass of the fragmenting site. In this context, we consider k-chip moves (where k = 1, 2, 3, ...); and combinations of 1-chip, 2-chip and 3-chip moves. The corresponding mean-field (MF) equations are solved to obtain the steady-state probability distributions, P(m) vs. m. We also undertake Monte Carlo (MC) simulations of these models. The MC results are in excellent agreement with the corresponding MF results, demonstrating that MF theory is exact for these models.     

Temporal order discrimination of tonal sequences by younger and older adults: the role of duration and rate

The effect of tone duration and presentation rate on the discrimination of the temporal order of the middle two tones of a four-tone sequence was investigated in young normal-hearing (YNH) and older hearing-impaired (OHI) listeners. The frequencies and presentation level of the tone sequences were selected to minimize the effect of hearing loss on the performance of the OHI listeners. Tone durations varied from 20 to 400 ms and presentation rates from 2.5 to 25 toness. Two experiments were conducted with anisochronous (nonuniform duration and rate across entire sequence) and isochronous (uniform rate and duration) sequences, respectively. For the YNH listeners, performance for both isochronous and anisochronous sequences was determined primarily by presentation rate such that performance decreased at rates faster than 5 toness. For anisochronous tone sequences alone, the effects of rate were more pronounced at short tone durations. For the OHI listeners, both presentation rate and tone duration had an impact on performance for both isochronous and anisochronous sequences such that performance decreased as rate increased above 5 toness or duration decreased below 40 ms. Temporal masking was offered as an explanation for the interaction of short durations and fast rates on temporal order discrimination for the anisochronous sequences.     

Quantification of fenoprofen in human plasma using UHPLC–tandem mass spectrometry for pharmacokinetic study in healthy subjects

A rapid, simple and sensitive ultra-performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) method has been developed to quantify fenoprofen, a nonsteroidal anti-inflammatory drug in human plasma for a pharmacokinetic study in healthy subjects. Owing to high levels of protein binding, protein precipitation followed by solid-phase extraction was employed for the extraction of fenoprofen and fenoprofen-d3 (used as internal standard) from 200 μL human plasma. Separation was performed on a BEH C₁₈ (50 × 2.1 mm, 1.7 μm) column using methanol−0.2% acetic acid in water (75:25, v/v) under isocratic elution. Electrospray ionization was operated in the negative mode for sample ionization. Ion transitions used for quantification in the selected reaction monitoring mode were m/z 241/197 and m/z 244/200 for fenoprofen and fenoprofen-d3, respectively. Under the optimized conditions, fenoprofen showed excellent linearity in the concentration range 0.02–20 μg/mL (r² ≥ 0.9996), adequate sensitivity, favorable accuracy (96.4–103.7%) and precision (percentage coefficient of variation ≤4.3) with negligible matrix effect. The validated method was successfully applied to a pharmacokinetic study of fenoprofen in healthy subjects. The significant features of the method include higher sensitivity, small plasma volume for processing and a short analysis time.     

Sensitive,selective and rapid determination of lafutidine in human plasma by solid phase extraction-liquid chromatography-tandem mass spectrometry

A simple, sensitive and high throughput liquid chromatography-tandem mass spectrometry method has been developed for the determination of lafutidine in human plasma. Sample clean-up involved solid phase extraction of lafutidine along with ranitidine as the internal standard from 100 μL of human plasma. The chromatographic separation is achieved within 2.5 min on a Grace Denali C18 (50 × 4.6 mm, 5 μ) column using 2 mM ammonium acetate, pH 3.0 adjusted with acetic acid and acetonitrile (20: 80, v/v) as the mobile phase. The precursor → product ion transitions for lafutidine (m/z 432.2 → 351.4) and IS (m/z 315.3 → 176.3) were monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring and positive ion mode. The method is validated over a wide dynamic concentration range of 0.25–1000 ng/mL. The mean relative recovery for lafutidine across quality controls is 97.9%. The relative matrix effect between eight different plasma lots, expressed as coefficient of variation of the slopes of the calibration lines is 1.94. The method is applied to a bioequivalence study of 10 mg lafutidine tablet formulation in 26 healthy Indian male subjects under fasting condition. The reproducibility of study data is demonstrated by analysis of 93 incurred samples.     

Quantitation of donepezil and its active metabolite 6-O-desmethyl donepezil in human plasma by a selective and sensitive liquid chromatography-tandem mass spectrometric method

A sensitive and selective liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for the simultaneous determination of donepezil (D) and its pharmacologically active metabolite, 6-O-desmethyl donepezil (6-ODD) in human plasma is developed using galantamine as internal standard (IS). The analytes and IS were extracted from 500 microL aliquots of human plasma via solid-phase extraction (SPE) on Waters Oasis HLB cartridges. Chromatographic separation was achieved in a run time of 6.0 min on a Waters Novapak C18 (150 mm x 3.9 mm, 4 microm) column under isocratic conditions. Detection of analytes and IS was done by tandem mass spectrometry, operating in positive ion and multiple reaction monitoring (MRM) acquisition mode. The protonated precursor to product ion transitions monitored for D, 6-ODD and IS were at m/z 380.1-->91.2, 366.3-->91.3 and 288.2-->213.2, respectively. The method was fully validated for its selectivity, interference check, sensitivity, linearity, precision and accuracy, recovery, matrix effect, ion suppression/enhancement, cross-specificity, stability and dilution integrity. A linear dynamic range of 0.10-50.0 ng mL(-1) for D and 0.02-10.0 ng mL(-1) for 6-ODD was evaluated with mean correlation coefficient (r) of 0.9975 and 0.9985, respectively. The intra-batch and inter-batch precision (%CV, coefficient of variation) across five quality control levels was less than 7.5% for both the analytes. The method was successfully applied to a bioequivalence study of 10mg donepezil tablet formulation in 24 healthy Indian male subjects under fasting condition.     

Thiacalixarene Appended Azo-based Supramolecular Systems: Self-assembly and Photo Tuning Reversible Liquid Crystalline Properties

Four new azo-based supramolecular materials containing thiacalixarene core substituted by variable alkoxy groups ( TFA₁ – TFA₄ ) have been designed and synthesized for the mesomorphic and photoswitching properties. The liquid crystalline behavior were accomplished by using DSC, POM, and XRD studies. All azo-based thiacalixarene based materials with short and higher chain length display columnar hexagonal mesophase with broad temperature range. The thermal behavior of all the materials was investigated by DSC and TGA study. The structural and conformational study of the lower rim functionalized materials was confirmed by using different techniques. These thiacalixarene moulded liquid crystalline compounds shows columnar self-assembly type behavior and higher thermal stability. The introduction of bi-substituted azo-ester network towards the lower rim of thiacalixarene core has impact on the electron delocalization and liquid crystalline properties. The photoswitching properties suggested cis and trans azo-isomerization under radiation of UV light and higher thermal back relaxation time. The mesogenic behaviour of compound TFA₂ and TFA₄ were demolished by the influence of cis and trans isomerization. The structure-property correlation is studied to understand the variation in mesogenic properties with the substitution of variable alkoxy side chain.     

Colorimetric sensor for ATP in aqueous solution

A new chromogenic complex 1.Zn has been synthesized, and its interactions with different biologically important phosphates have been investigated in aqueous solution (pH approximately 7.2). A visual color change can be detected on binding of ATP to 1.Zn, whereas no such change is observed when other biologically related anions (AMP, ADP, PPi, or Phosphate) are used. Complex 1.Zn can also be used as a staining agent for yeast cells allowing detection under normal light microscopy.