Microwave-induced clay-catalyzed ring opening of N-tosylaziridines: a green approach to achiral and chiral diamines

N-Tosylaziridines react efficiently with amines in the presence of Montmorillonite K-10 as catalyst under microwave irradiation in solvent-free conditions to yield the corresponding achiral and chiral diamines regio- and stereoselectively, in a few minutes and in high yields.     

Vibrational, EPR and optical spectroscopy of the Cu doped glasses with (90-x)TeO2-10GeO2-xWO3 (7.5 ≤ x ≤ 30) composition

Infrared, EPR and optical absorption studies on (90-x)TeO₂-10GeO₂-xWO₃ (7.5 ≤ x ≤ 30) glasses containing Cu²⁺ spin probe have been carried out. The Infrared spectral studies show that the structure of glass network consists of [TeO₄], [TeO₃]/[TeO_3 + 1], [WO₄], [WO₆] and [GeO₆] units in the disordered manner. Physical parameters such as density (ρ), molar volume (V_m), oxygen packing density (OPD), oxygen molar volume (V_o), optical basicity (Λ), oxide ion polarizability (α_O²⁻), inter ionic distances and the concentration of ions per unit volume of Te, Ge, W, Cu and O have been determined. The spin-Hamiltonian parameters (g_||, g_⊥ and A_||) of Cu²⁺ ions in the present glasses have been estimated from EPR spectra at 300 K. Bonding parameters such as α², β₁², β², Γ_σ, and Γ_π have been calculated from both optical absorption and EPR data. The observed variations in spin-Hamiltonian parameters and bonding parameters have been correlated to the structural modifications due to the WO₃ incorporation into the TeO₂ glass network at constant 10 mol% GeO₂ content.     

Synthesis and conformational studies of peptides from new C-linked carbo-beta-amino acids (beta-Caas) with anomeric methylamino- and difluorophenyl moieties

New C-linked carbo-beta-amino acids (beta-Caas), Cbz-(S)-beta-Caa-(NHBoc)-OMe (1) and Cbz-(R)-beta-Caa-(NHBoc)-OMe (2), with an additional amine group (methylamino group of NHBoc) at the C-1 position of the lyxofuranoside side chain and Boc-(S)-beta-Caa-(diFP)-OMe (3) and Boc-(R)-beta-Caa-(diFP)-OMe (4), with a C-difluorophenyl (diFP) moiety at the anomeric position of the lyxofuranoside side chain were prepared from D-mannose. Beta-peptides [tetra- and hexapeptides] were synthesized from these beta-Caas, 'epimeric' [at the amine stereocentre (C(beta))], using the concept of 'alternating chirality' to carry out their conformational studies [NMR (CDCl(3)), CD and MD]. In the monomer design, it was envisaged that the presence of an additional amine group in 1 or 2 would help in solubilizing the peptides in water, while, the C-difluorophenyl (diFP) moiety of 3 and 4 is expected to enhance the biological activity. The peptides having 1 and 2, though could not retain their 12-10-mixed helices in water, have shown moderate activity against gram positive and gram negative bacterial strains. The peptides prepared from 3 and 4, much against our expectations, did not display any biological activity.     

12/10- and 11/13-mixed helices in alpha/gamma- and beta/gamma-hybrid peptides containing C-linked carbo-gamma-amino acids with alternating alpha- and beta-amino acids

New classes of alpha/gamma- and beta/gamma-hybrid peptides have been synthesized with novel 12/10- and 11/13-mixed helical patterns, respectively. The alpha/gamma-peptides were derived from the dipeptide repeats with alternating arrays of l-Ala and gamma-Caa((l)) (C-linked carbo-gamma-amino acid from d-mannose), which generated a new 12/10-mixed helix, for the first time, without a beta-amino acid. The beta/gamma-peptides made from an alternating arrangement of beta-Caa((x)) (C-linked carbo-beta-amino acid) and gamma-Caa((x)) (C-linked carbo-gamma-amino acid from d-xylose), on the other hand, resulted in an unprecedented 11/13-helix. The secondary structures in these peptides have been ascertained from detailed NMR studies, and CD spectroscopy and molecular dynamics investigations provided additional support for the structures derived.     

Synthesis of 2-Benzoyl-3-aryl-N-arylsulphonylaziridines from the Reaction of N-Arylsulphonylimines with Dimethylsulphonium Phenacylide - The First Example of A Functionalized-Methylene Transfer to Azomethines

The first example of phenacyl group transfer from dimethylsulphonium phenacylide to N-arylsulphonylimines to yield 2-benzoyl-1-arylsulphonylaziridines is described.     

A new and facile route for the synthesis of chiral 1,2-diamines and 2,3-diamino acids

The synthesis of chiral diamines and diamino acids has been achieved from the corresponding N-arylsulfonyl aziridines through reaction with a chiral isocyanate and subsequent hydrolysis of 2-imidazolidinones. The method appears to be general and of wide applicability.     

Arylation of Rhodium(II) Azavinyl Carbenes with Boronic Acids

A highly efficient and stereoselective arylation of in situ-generated azavinyl carbenes affording 2,2-diaryl enamines at ambient temperatures has been developed. These transition-metal carbenes are directly produced from readily available and stable 1-sulfonyl-1,2,3-triazoles in the presence of a rhodium carboxylate catalyst. In several cases, the enamines generated in this reaction can be cyclized into substituted indoles employing copper catalysis.     

Three-dimensional elliptic grid generation with fully automatic boundary constraints

A new procedure for generating smooth uniformly clustered three-dimensional structured elliptic grids is presented here which formulates three-dimensional boundary constraints by extending the two-dimensional counterpart¹ presented by the author earlier. This fully automatic procedure obviates the need for manual specification of decay parameters over the six bounding surfaces of a given volume grid. The procedure has been demonstrated here for the Mars Science Laboratory (MSL) geometries such as aeroshell and canopy, as well as the Inflatable Aerodynamic Decelerator (IAD) geometry and a 3D analytically defined geometry. The new procedure also enables generation of single-block grids for such geometries because the automatic boundary constraints permit the decay parameters to evolve as part of the solution to the elliptic grid system of equations. These decay parameters are no longer just constants, as specified in the conventional approach, but functions of generalized coordinate variables over a given bounding surface. Since these decay functions vary over a given boundary, orthogonal grids around any arbitrary simply-connected boundary can be clustered automatically without having to break up the boundaries and the corresponding interior or exterior domains into various blocks for grid generation. The new boundary constraints are not limited to the simply-connected regions only, but can also be formulated around multiply-connected and isolated regions in the interior. The proposed method is superior to other methods of grid generation such as algebraic and hyperbolic techniques in that the grids obtained here are C² continuous, whereas simple elliptic smoothing of algebraic or hyperbolic grids to enforce C² continuity destroys the grid clustering near the boundaries.     

Computation of internal turbulent flow with a large separated flow region

An implicit two-equation turbulence solver, KEM. in generalized co-ordinates, is used in conjunction with the three-dimensional incompressible Navier–Stokes solver, INS3D, to calculate the internal flow in a channel and a channel with a sudden 2:3 expansion. A new and consistent boundary procedure for a low Reynolds number form of the κ-ε turbulence model is chosen to integrate the equations up to the wall. The high Reynolds number form of the equations is integrated using wall functions. The latter approach yields a faster convergence to the steady-state solution than the former. For the case of channel flow, both the wall-function and wall-boundary-condition approaches yield results in good agreement with the experimental data. The back-step (sudden expansion) flow is calculated using the wall-function approach. The predictions are in reasonable agreement with the experimental data.