Base dependent pyrrolidine ring pucker in aep-PNA monomers: NMR and PSEUROT analysis

The aep-PNA is a chiral and cyclic PNA analogue, which has a stronger and base dependent binding affinity with complementary DNA. To understand the base dependent properties at monomer level, the structural studies of aep-PNA-(T/C/A) monomers have been carried out focussing on the conformational analysis of pyrrolidine ring pucker in aep-PNA by ¹H NMR and the coupling constant data fitted into PSEUROT software. The results indicate that the type of pyrrolidine pucker depends on the electronic nature of substituent, implying the effect of pyrimidine or purine substituents in determining the ring pucker in monomers. This may consequently influence the aep-PNA oligomer conformation. Since pyrrolidine nucleic acids have emerged as an important class of PNA analogues, present results may have importance for their future development.     

Sensitivity enhancement and matrix effect evaluation during summation of multiple transition pairs—case studies of clopidogrel and ramiprilat

Sensitivity enhancement via summation of multiple MRM transition pairs is gaining popularity in tandem mass spectrometric assays. Numerous validation experiments describing the assays for two model substrates, clopidogrel and ramiprilat, were performed. The quantitation of clopidogrel was achieved by the summation of transition pairs m/z 322.2 to m/z 212.0 and m/z 322.2 to m/z 184.0, while that of ramiprilat was achieved by the summation of transition pairs m/z 389.2 to m/z 206.1 and m/z 389.2 to m/z156.1. The use of summation approach achieved sensitivities of >2 fold for both compounds as compared with the reported single MRM transition pair assays. The validation experiments addressed some important assay development issues, such as: (a) lack of impact of matrix effect; (b) unequivocal verification of the percentage contribution of each MRM transition pair towards sensitivity; (c) sensitivity enhancement factor achieved by summation approach of MRM transition pairs; and (d) accurate prediction of quality control samples using summation approach vs a single MRM transition pair. In summary, the appropriateness of using two MRM transition pairs for quantitation was demonstrated for both clopidogrel and ramiprilat. Additionally, pharmacokinetic application of the MRM transition pair assays using a summation approach was established for the two compounds. Copyright © 2009 John Wiley & Sons, Ltd.     

Global gyrokinetic stability of pressure-gradient-driven electromagnetic modes in tokamaks with regions of low shear

Tokamaks with large pressure gradients (alpha(max)) formed in regions of weak magnetic shear are shown to be susceptible to novel, low-n, global, kinetic, electromagnetic modes with a toroidal mode number n in the range 21 on the magnetic axis and alpha(max) near q(min), new, global kinetic infernal modes with a strong mode rotation omega(r) and a finite growth rate gamma<|omega(r)| are found. For equilibria with reverse shear where q(min) is off axis and alpha(max) near q(min), the existence of an unstable low-n global branch of Alfve n ion temperature gradient modes is revealed with an oscillatory gamma as a function of n. The addition of trapped electron dynamics is shown to be further destabilizing.     

Determining the adsorptive and catalytic properties of strained metal surfaces using adsorption-induced stress

We demonstrate a model for determining the adsorptive and catalytic properties of strained metal surfaces based on linear elastic theory, using first-principles calculations of CO adsorption on Au and K surfaces and CO dissociation on Ru surface. The model involves a single calculation of the adsorption-induced surface stress on the unstrained metal surface, which determines quantitatively how adsorption energy changes with external strain. The model is generally applicable to both transition- and non-transition-metal surfaces, as well as to different adsorption sites on the same surface. Extending the model to both the reactant and transition state of surface reactions should allow determination of the effect of strain on surface reactivity.     

Nano Fe3O4 as magnetically recyclable catalyst for the synthesis of α-aminophosphonates in solvent-free conditions

The three component, one-pot synthesis of α-aminophosphonates has been achieved using super magnetic nano iron oxide at 50 °C under solvent-free conditions in excellent yields. The major advantages of the present method are high yields, short reaction times, magnetically recyclable catalyst, and solvent-free reaction conditions.     

Triflic acid-promoted aza-Prins-Ritter reaction sequence: a novel synthesis of 4-amidopiperidine derivatives

4-Amidopiperidine derivatives have been prepared for the first time in good yields and with high selectivity by means of aza-Prins-Ritter reaction sequence using 1.2 equiv of triflic acid under mild reaction conditions.     

Determination of PuO2% in power reactor mixed oxide fuel blends (0.4–44% PuO2) by neutron well co-incidence counting technique

Neutron Well Coincidence Counting has been explored as a non destructive assay technique for determining the percentage of PuO₂ in blended mixture of UO₂ and PuO₂ powders. The method has been applied to MOX blends having PuO₂ content varying from 0.4 to 44% for both thermal and fast reactors. The use of Neutron Well Coincidence Counting technique is validated as a process control step for determining PuO₂ content in the fabrication of MOX fuel by comparing it with chemical analysis of sintered pellets. It has been used at Advanced Fuel fabrication Facility, Bhabha Atomic Research Centre, Tarapur during the manufacture of MOX fuel of various types for thermal and fast reactors.