Ab initio study of the tautomeric forms of some quinolinediones

7,8-dihydroquinoline-4,5 (1H,6H)-dione (1) and 7,8-dihydroquinoline-2,5-(1H,6H)-dione (2) in their tautomeric oxo and hydroxy forms have been studied by ab initio Hartree-Fock calculations; tautomerization energies predict a more stable hydroxy structure having an intramolecular hydrogen bond for compound 1, whereas the oxo form is slightly-preferred for compound 2. Fourier Transform-Infra Red (FT-IR) spectra in CHCl₃ solution indicate that the predicted most stable tautomers in the vapour phase remain as such.     

Role of micro-crystalline parameters in the physical properties of cotton fibers

Karnataka state in India is very well known for its cotton cultivation and there are innumerable varieties of these cotton fibers. Although, the yield and other types of characterization have been carried out on these fibers, the structure-property relation is not well studied till today. We have examined four different raw cotton fibers using Wide Angle X-ray Scattering (WAXS) technique and also we have computed micro-crystalline parameters. This study brings out the structure-property relation in cotton fibers.     

An unusual, mild and convenient one-pot two-step access to (E)-stilbenes from hydroxy-substituted benzaldehydes and phenylacetic acids under microwave activation: a new facet of the classical Perkin reaction

A mild and convenient one-pot two-step synthesis of hydroxystilbenes with trans selectivity has been developed through a modified Perkin reaction between benzaldehydes and phenylacetic acids bearing 4- or 2-hydroxy substitution at the aromatic ring, in the presence of piperidine-methylimidazole and polyethylene glycol under microwave irradiation. The observation of a simultaneous condensation-decarboxylation leading to the unusual formation of hydroxystilbenes in lieu of α-phenylcinnamic acid reveals an interesting facet to the classical Perkin reaction. The developed protocol provides a green alternative to the prevalent methods employing a toxic decarboxylating agent in the form of quinoline/Cu salt, and the requirement for harsh protection-deprotection steps for the synthesis of hydroxylated stilbenes.     

Thermal analysis of a drug-polymeric excipient solid system

Differential scanning calorimetry has been applied to the study of the solid system cross-linked polyvinylpyrrolidone/trimethoprim.Different results have been systematically obtained on co-ground and not co-ground mixtures, suggesting some type of interaction to take place between components as a consequence of co-grinding.A simple phenomenological model of the interaction is proposed, which quite satisfactorily agrees with thermal data.

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Zusammenfassung Das feste System von vernetztem Polyvinyl-pyrolidin/Trimethoprim wurde mittels DSC untersucht. Unterschiedliche Ergebnisse wurden systematisch für zusammen und nicht zusammen verriebene Mischungen gefunden, was auf eine Wechselwirkung zwischen Komponenten beim Verreiben hindeutet. Ein einfaches phänomenologisches Modell dieser Wechselwirkung wird vorgeschlagen, das mit thermischen Daten befriedigend übereinstimmt.

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This work has been partially supported by Ministero Pubblica Istruzione (Fondi 60%).     

Validated Chiral LC Method for the Enantiomeric Separation of β-Amino-β-(3-Methoxyphenyl) Propionic Acid

A chiral liquid chromatographic method for enantiomeric resolution of β-amino-β-(3-methoxyphenyl) propionic acid was developed and validated. The “hybrid” π-electron donor–acceptor based stationary phase (R,R) Whelk-01 was found to be enantiomerically selective for (R) and (S) enantiomers of β-amino-β-(3-methoxyphenyl) propionic acid with a resolution greater than 2.0. The effects of isopropyl alcohol and ethanol on enantioselectivity and resolution of enantiomers were evaluated. Calibration curves were linear over the range of 0.10–1.00, with a regression coefficient (r) of 0.999. The limit of detection (LOD) and limit of quantification (LOQ) were 300 and 1,000 ng mL⁻¹ respectively for 10 μL injection volume. The percentage RSD of the peak area of six replicate injections of (S) enantiomer at LOQ concentration was 2.8. The percentage recovery of (S) enantiomer from (R) enantiomer samples ranged from 92 to 102. The test solution was observed to be stable up to 24 h after the preparation. The developed normal phase chiral LC method can be used for the enantiomeric purity evaluation of R-β-amino-β-(3-methoxyphenyl) propionic acid.     

Sulfur K-edge XAS and DFT calculations on [Fe4S4]2+ clusters: effects of H-bonding and structural distortion on covalency and spin topology

Sulfur K-edge X-ray absorption spectroscopy of a hydrogen-bonded elongated [Fe4S4]2+ cube is reported. The data show that this synthetic cube is less covalent than a normal compressed cube with no hydrogen bonding. DFT calculations reveal that the observed difference in electronic structure has significant contributions from both the cluster distortion and from hydrogen bonding. The elongated and compressed Fe4S4 structures are found to have different spin topologies (i.e., orientation of the delocalized Fe2S2 subclusters which are antiferromagnetically coupled to each other). It is suggested that the H-bonding interaction with the counterion does not contribute to the cluster elongation. A magneto-structural correlation is developed for the Fe4S4 cube that is used to identify the redox-active Fe2S2 subclusters in active sites of HiPIP and ferredoxin proteins involving these clusters.