Influence of Proline Chirality on Neighbouring Azaproline Residue Stereodynamic Nitrogen Preorganization

We report herein the first systematic crystal structural investigation of azaproline incorporated in homo- and heterochiral diprolyl peptides. The X-ray crystallography data of peptides 1 – 5 illustrates that stereodynamic nitrogen in azaproline adopted the stereochemistry of neighbouring proline residue without depending on its position in the peptide sequence. Natural bond orbital analysis of crystal structures indicates O_azPro−C′_Pro of peptides 4 and 5 participating in n→π* interaction with stabilization energy about 1.21–1.33 kcal/mol. Density functional theory calculations suggested that the endo-proline ring puckering favoured over exo-conformation by 6.72–7.64 kcal/mol. NBO and DFT data reveals that the n→π* interactions and proline ring puckering stabilize azaproline chirality with the neighbouring proline stereochemistry. The CD, solvent titration, variable-temperature and 2D NMR experimental results further supported the crystal structures conformation.     

Unexpected deviation from diene behaviour of uracil amidine: towards synthesis of some pyrido[2,3-<Emphasis Type="Italic">d</Emphasis>]pyrimidine derivatives

Condensation products obtained from the treatment of uracil amidine with preformed or in situ generated suitably substituted olefins unexpectedly undergo intramolecular cyclisation during silica gel chromatography to generate pyrido[2,3-d]pyrimidines. Various reaction conditions are studied and the altered nature of the uracil amidine molecule is further explored by reacting it with different suitably substituted alkenes.     

Analytical solution of the scalar wave equation for slightly deformed optical Bragg waveguide

Using a simple analytical method, we study the electromagnetic-wave propagation in an optical Bragg waveguide which is slightly deformed at one side. We show the results of computations in the form of dispersion curves and provide a comparison with standard circular Bragg waveguides and step-index circular waveguides. We show that the correspondence between the cutoff V values for the standard step-index fiber and the new Bragg waveguide, which is slightly flattened on one side, is quite close for the lowest mode under the weak guidance condition.     

Effect of magnetic field and radiative condensation on the Jeans instability of dusty plasma with polarization force

The Jeans instability of self-gravitating dusty plasma with polarization force is investigated considering the effects of magnetic field, dust temperature and radiative condensation. The condition of Jeans instability and expression of critical Jeans wave number are obtained which depend upon polarization force and dust temperature but these are unaffected by the presence of magnetic field. The radiative heat-loss functions also modify the Jeans condition of instability and expression of critical Jeans wave number. It is observed that the polarization force and ratio of radiative heat-loss functions have destabilizing while magnetic field and dust temperature have stabilizing influence on the growth rate of Jeans instability.     

Studies on 6-[(dimethylamino)methylene]aminouracil: a facile one-pot synthesis of novel pyrimido[4,5-d]pyrimidine derivatives

The reactions of 6-[(dimethylamino)methylene]aminouracil 1, with various heterocumulenes such as aryl isocyanates and isothiocyanates give rise to novel pyrimido[4,5-d]pyrimidines in excellent yields, after elimination of dimethylamine from the (1:1) cycloadducts and tautomerisation. This procedure provides a convenient method for direct synthesis of pyrimido[4,5-d]pyrimidine derivatives under thermal conditions.     

Synthesis and study of mesomorphic properties of unsymmetrical cyclohexanone-derived bis-chalcones

A series of (2E,6E)-2-(4-n-alkoxybenzylidene)-6-((benzo[d][1,3]dioxol-6-yl)methylene)cyclohexanones were synthesised by stepwise condensation reactions from cyclohexanone. The optical and thermal analysis of the series indicated the mesomorphic properties of some derivatives. The compounds with C7–C16 substituents showed the nematic phases in the range of 90–73°C. The single crystal X-ray analysis confirms the head to tail packing arrangement.     

Correction: Effects of novel intake manifold design and investigation of diesel engine operating on different alternative fuels

Journal of Thermal Analysis and Calorimetry -