Simplifying the complex 1H NMR spectra of fluorine-substituted benzamides by spin system filtering and spin-state selection: multiple-quantum-single-quantum correlation

The proton NMR spectra of fluorine-substituted benzamides are very complex (Figure 1) due to severe overlap of (1)H resonances from the two aromatic rings, in addition to several short and long-range scalar couplings experienced by each proton. With no detectable scalar couplings between the inter-ring spins, the (1)H NMR spectra can be construed as an overlap of spectra from two independent phenyl rings. In the present study we demonstrate that it is possible to separate the individual spectrum for each aromatic ring by spin system filtering employing the multiple-quantum-single-quantum correlation methodology. Furthermore, the two spin states of fluorine are utilized to simplify the spectrum corresponding to each phenyl ring by the spin-state selection. The demonstrated technique reduces spectral complexity by a factor of 4, in addition to permitting the determination of long-range couplings of less than 0.2 Hz and the relative signs of heteronuclear couplings. The technique also aids the judicious choice of the spin-selective double-quantum-single-quantum J-resolved experiment to determine the long-range homonuclear couplings of smaller magnitudes.     

A Defined α‐Helix in the Bifunctional O‐Glycosylated Natriuretic Peptide TcNPa from the Venom of Tropidechis carinatus

Natriuretic peptides (NP) play important roles in human cardiac physiology through their guanylyl cyclase receptors NPR‐A and NPR‐B. Described herein is a bifunctional O‐glycosylated natriuretic peptide, TcNPa, from Tropidechis carinatus venom and it unusually targets both NPR‐A and NPR‐B. Characterization using specific glycosidases and ETD‐MS identified the glycan as galactosyl‐β(1‐3)‐N‐acetylgalactosamine (Gal‐GalNAc) and was α‐linked to the C‐terminal threonine residue. TcNPa contains the characteristic NP 17‐membered disulfide ring with conserved phenylalanine and arginine residues. Both glycosylated and nonglycosylated forms were synthesized by Fmoc solid‐phase peptide synthesis and NMR analysis identified an α‐helix within the disulfide ring containing the putative pharmacophore for NPR‐A. Surprisingly, both forms activated NPR‐A and NPR‐B and were relatively resistant towards proteolytic degradation in plasma. This work will underpin the future development of bifunctional NP peptide mimetics.     

Titrimetric and Spectrophotometric Determination of Some Phenothiazine Psychotropics in Pure Form and in Pharmaceutical Formulations with Metavanadate

 Two simple, fast, accurate and precise methods for the determination of six phenothiazines and a number of their pharmaceutical formulations are described. The titrimetric method involves the oxidation of the drugs by metavanadate in sulphuric acid medium and titration of vanadium(IV) formed, with cerium(IV) using ferroin indicator and acetone as catalyst. In spectrophotometry, vanadium(IV) formed was reacted with ferriin and the resulting ferroin measured at 510 nm. Phenothiazines in the ranges 5–100 mg and 2.5–25.0 μg mL⁻¹ can be determined by titrimetry and spectrophotometry, respectively, with detection limits of 0.96–2.05 mg and 0.0359–0.0565 μg mL⁻¹, respectively. Both methods were applied successfully to the determination of the studied drugs in pharmaceutical preparations. The reliability of the assays was established by parallel determination by the official methods of British Pharmacopoeia and the results being statistically evaluated. Received September 26, 2000. Revision March 25, 2001.     

Magnetite tethered mesoionic carbene‐palladium (II): An efficient and reusable nanomagnetic catalyst for Suzuki‐Miyaura and Mizoroki‐Heck cross‐coupling reactions in aqueous medium

In this paper, a highly active, air‐ and moisture‐stable and easily recoverable magnetic nanoparticles tethered mesoionic carbene palladium (II) complex (MNPs‐MIC‐Pd) as nanomagnetic catalyst was successfully synthesized by a simplistic multistep synthesis under aerobic conditions using commercially available inexpensive chemicals for the first time. The synthesized MNPs‐MIC‐Pd nanomagnetic catalyst was in‐depth characterized by numerous physicochemical techniques such as FT‐IR, ICP‐AES, FESEM, EDS, TEM, p‐XRD, XPS, TGA and BET surface area analysis. The prepared MNPs‐MIC‐Pd nanomagnetic catalyst was used to catalyze the Suzuki–Miyaura and Mizoroki–Heck cross‐coupling reactions and exhibited excellent catalytic activity for various substrates under mild reaction conditions. Moreover, MNPs‐MIC‐Pd nanomagnetic catalyst could be easily and rapidly recovered by applying an external magnet. The recovered MNPs‐MIC‐Pd nanomagnetic catalyst exhibited very good catalytic activity up to ten times in Suzuki–Miyaura and five times in Mizoroki–Heck cross‐coupling reactions without considerable loss of its catalytic activity. However, MNPs‐MIC‐Pd nanomagnetic catalyst shows notable advantages such as heterogeneous nature, efficient catalytic activity, mild reaction conditions, easy magnetic work up and recyclability.     

Discerning the degenerate transitions of scalar coupled H NMR spectra: Correlation and resolved techniques at higher quantum

The blend of spin topological filtering and the spin state selective detection of single quantum transitions by the two dimensional multiple quantum-single quantum correlation and higher quantum resolved techniques have been employed for simplifying the complexity of scalar coupled ¹H NMR spectra. The conventional two dimensional COSY and TOCSY experiments, though identify the coupled spin networks, fail to differentiate them due to severe overlap of transitions. Non-selective excitation of homonuclear higher quantum of protons results in filtering of spin systems irrespective of their spin topologies. The spin state selection by passive ¹⁹F spins provides fewer transitions in each cross section of the single quantum dimension simplifying the analyses of the complex spectra. The degenerate single quantum transitions are further discerned by spin selective double and/or triple quantum resolved experiments that mimic simultaneous heteronuclear and selective homonuclear decoupling in the higher quantum dimension. The techniques aided the determination of precise values of spectral parameters and relative signs of the couplings.     

Electrode materials for aqueous rechargeable lithium batteries

In this review, we describe briefly the historical development of aqueous rechargeable lithium batteries, the advantages and challenges associated with the use of aqueous electrolytes in lithium rechargeable battery with an emphasis on the electrochemical performance of various electrode materials. The following materials have been studied as cathode materials: LiMn₂O₄, MnO₂, LiNiO₂, LiCoO₂, LiMnPO₄, LiFePO₄, and anatase TiO₂. Addition of certain additives like TiS₂, TiB₂, CeO₂, etc. is found to increase the performance of MnO₂ cathode. The following materials have been studied as anode materials: VO₂ (B), LiV₃O₈, LiV₂O₅, LiTi₂(PO4)₃, TiP₂O₃, and very recently conducting polymer, polypyrrole (PPy). The cell PPy/LiCoO₂, constructed using polypyrrole as anode delivers an average voltage of 0.86?V with a discharge capacity of 47.7?mA?h?g^?1. It retains the capacity for first 120 cycles. The cell, LiTi₂(PO₄)₃/1?M Li₂SO₄/LiMn₂O₄, delivers a capacity of 40?mA?h?g^?1 and specific energy of 60?mW?h?g^?1 with an output voltage of 1.5?V over 200 charge?Cdischarge cycles. An aqueous lithium cell constructed using MWCNTs/LiMn₂O₄ as cathode material is found to exhibit more than 1,000 cycles with good rate capability.     

A novel synthetic approach to 4-acetamido-1-arylindazoles via Semmler–Wolff rearrangement of 1-aryl-6,7-dihydro-5H-indazol-4-one oxime

A simple and efficient procedure for the syntheses of 4-acetamido-1-arylindazoles from corresponding 1-aryl-6,7-dihydro-5H-indazol-4-one oximes by Semmler–Wolff aromatization using acetic anhydride and sodium iodide is reported.     

Semmler–Wolff aromatisation: a concise route for the synthesis of 5-amino-quinazolines and 4-amino-indoles

A simple and efficient methodology for the synthesis of 5-amino-quinazolines and 4-amino-indoles via Semmler–Wolff aromatisation reaction has been carried out. The oximation of keto intermediates followed by Semmler–Wolff aromatisation using acetic anhydride and a catalytic amount of sodium iodide in xylene provided the desired quinazolines and indoles.     

Beta-induced bremsstrahlung shielding parameters in various types of steels

ABSTRACT

Present work studies the bremsstrahlung efficiency, bremsstrahlung dose rate, probability of energy loss by beta during bremsstrahlung emission and specific bremsstrahlung constant of the beta radionuclide for various steels such as XM-5, 317LM, XM-17216, AL-6XN, JS700, NIROSTA 4565S and stainless steel. We have compared the shielding properties among the studied different steels. From the detailed study, the steel type 317LM is having the highest bremsstrahlung dose rate and specific bremsstrahlung constant values than the other studied steels. This means the steel type 317LM is a good absorber of bremsstrahlung radiation than the other studied steels. Hence it is better to use the steel type 317LM in the nuclear power plants than stainless steels and other steels to avoid the secondary radiation such as bremsstrahlung.